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diff --git a/18779-tei.tei b/18779-tei.tei new file mode 100644 index 0000000..37919c7 --- /dev/null +++ b/18779-tei.tei @@ -0,0 +1,18202 @@ +<?xml version="1.0" encoding="utf-8" ?> + +<!-- +The Project Gutenberg EBook of Physiology and Hygiene for Secondary +Schools by Francis M. Walters, A.M. + + + +This eBook is for the use of anyone anywhere at no cost and with almost no +restrictions whatsoever. You may copy it, give it away or re-use it under +the terms of the Project Gutenberg License included with this eBook or +online at http://www.gutenberg.org/license + + + +Title: Physiology and Hygiene for Secondary Schools + +Author: Francis M. Walters, A.M. + +Release Date: November 15, 2005 [Ebook #18779] + +Language: English + +Character set encoding: UTF-8 +--> + +<!DOCTYPE TEI.2 SYSTEM "http://www.gutenberg.org/tei/marcello/0.4/dtd/pgtei.dtd"> + +<TEI.2 lang="en-us"> +<teiHeader> + <fileDesc> + <titleStmt> + <title>Physiology and Hygiene for Secondary Schools</title> + <author><name reg="Walters, Francis M., A.M.">Francis M. Walters, A.M.</name></author> + </titleStmt> + <editionStmt> + <edition n="1">Edition 1</edition> + </editionStmt> + <publicationStmt> + <publisher>Project Gutenberg</publisher> + <date value="2005-11-15">November 15, 2005</date> + <idno type="etext-no">18779</idno> + <idno type="DPid">projectID40b648ffb51b8</idno> + <availability> + <p>This eBook is for the use of anyone anywhere at no cost and + with almost no restrictions whatsoever. You may copy it, give it + away or re-use it under the terms of the Project Gutenberg + License online at www.gutenberg.org/license</p> + </availability> + </publicationStmt> + + <sourceDesc> + <bibl> + <title>Physiology and Hygiene for Secondary Schools</title> + <author><name reg="Walters, Francis M., A.M.">Francis M. Walters, A.M.</name></author> + <imprint> + <pubPlace>Boston</pubPlace> + <pubPlace>New York</pubPlace> + <pubPlace>Chicago</pubPlace> + <publisher>D.C. Heath and Co.</publisher> + <date>1909</date> + </imprint> + </bibl> + </sourceDesc> + </fileDesc> + + <encodingDesc> + <classDecl> + <taxonomy id="lc"> + <bibl> + <title>Library of Congress Classification</title> + </bibl> + </taxonomy> + </classDecl> + </encodingDesc> + <profileDesc> + <langUsage> + <language id="en-us">United States English</language> + </langUsage> + <textClass> + <classCode scheme="lc"> + *** <!-- LoC Class (PR, PQ, ...) --> + </classCode> + <keywords> + <list> + <!-- <item></item> any keywords for PG search engine --> + </list> + </keywords> + </textClass> + </profileDesc> + <revisionDesc> + <change> + <date value="2005-11">November 2005</date> + <respStmt> + <name>Joshua Hutchinson, </name> + <name>Kevin Handy, </name> + <name>John Hagerson, </name> + <name>Online Distributed Proofreading Team</name> + </respStmt> + <item>Project Gutenberg Edition</item> + </change> + </revisionDesc> +</teiHeader> + +<pgExtensions> + <pgStyleSheet> + .w95 { } + .w75 { } + .w55 { } + .w45 { } + .w40 { } + .w35 { } + .w30 { } + .w25 { } + @media pdf { + .w95 { width: 95% } + .w75 { width: 75% } + .w55 { width: 55% } + .w45 { width: 45% } + .w40 { width: 40% } + .w35 { width: 35% } + .w30 { width: 30% } + .w25 { width: 25% } + } + </pgStyleSheet> +</pgExtensions> + +<text> +<front> + +<div> +<divGen type="pgheader" /> +</div> + +<div> +<divGen type="encodingDesc" /> +</div> + +<div rend="page-break-before: always"> +<divGen type="titlepage" /> +</div> + +<div rend="page-break-before: always"> +<p rend="text-align: center">D.C. Heath and Co. - Publishers</p> +<p rend="text-align: center">Original copyright 1909</p> + +<p rend="display">"It is quite possible to give instruction in this subject in +such a manner as not only to confer knowledge which is +useful in itself, but to serve the purpose of a training in +accurate observation, and in the methods of reasoning of +physical science."—<hi rend="font-style: italic">Huxley.</hi></p> + +</div> + +<div rend="page-break-before: always"> + +<index index="toc" /><index index="pdf" /> + +<head>Preface</head> + +<p>The aim in the preparation of this treatise on the human body has +been, first, to set forth in a <hi rend="font-style: +italic">teachable</hi> manner the actual science of physiology; and +second, to present the facts of hygiene largely as <hi rend="font-style: +italic">applied physiology</hi>. The view is held that "right living" +consists in the harmonious adjustment of one's habits to the nature and +plan of the body, and that the best preparation for such living is a +correct understanding of the physical self. It is further held that the +emphasizing of physiology augments in no small degree the educative +value of the subject, greater opportunity being thus afforded for +exercise of the reasoning powers and for drill in the <hi +rend="font-style: italic">modus operandi</hi> of natural forces. In the +study of physiology the facts of anatomy have a place, but in an +elementary course these should be restricted to such as are necessary +for revealing the general structure of the body.</p> + +<p>Although no effort has been spared to bring this work within the +comprehension of the pupil, its success in the classroom will depend +largely upon the method of handling the subject by the teacher. It is +recommended, therefore, that the <hi rend="font-style: +italic">relations</hi> which the different organs and processes sustain +to each other, and to the body as a whole, be given special prominence. +The pupil should be impressed with the essential unity of the body and +should see in the diversity of its activities the serving of a common +purpose. In creating such an impression the introductory paragraphs at +the beginning of many of the chapters and the summaries throughout the +book, as well as the general arrangement of the subject-matter, will be +found helpful.</p> + +<p>Since the custom largely prevails of teaching physiology in advance +of the sciences upon which it rests—biology, physics, and chemistry—care +should be exercised to develop correct ideas of the principles and +processes derived from these sciences. Too much latitude has been taken +in the past in the use of comparisons and illustrations drawn from +"everyday life." To teach that the body is a "house," "machine," or +"city"; that the nerves carry "messages"; that the purpose of oxygen is +to "burn up waste"; that breathing is to "purify the blood," etc., may +give the pupil phrases which he can readily repeat, but teaching of this +kind does not give him correct ideas of his body.</p> + +<p>The method of teaching, however, that uses the pupil's experience as +a basis upon which to build has a value not to be overlooked. The fact +that such expressions as those quoted above are so easily remembered +proves the value of connecting new knowledge with the pupil's +experience. But <hi rend="font-style: italic">the inadequacy of this +experience must be recognized</hi> and taken into account. The concepts +of the average pupil are entirely too indefinite and limited to supply +the necessary <hi rend="font-style: italic">foundation for a +science</hi> such as physiology. Herein lies the great value of +experiments and observations. They supplement the pupil's experience, +and increase both the number and definiteness of his concepts. No degree +of success can be attained if this phase of the study is omitted.</p> + +<p>The best results in physiology teaching are of course attained where +laboratory work is carried on by the pupils, but where this cannot be +arranged, class experiments and observations must suffice. The Practical +Work described at the close of most of the chapters is mainly for class +purposes. While these serve a necessary part in the development of the +subject, it is not essential that all of the experiments and +observations be made, the intention being to provide for some choice on +the part of the teacher. A note-book should be kept by the pupil.</p> + +<p>To adapt the book to as wide a range of usefulness as possible, more +subject-matter is introduced than is usually included in an elementary +course. Such portions, however, as are unessential to a proper +understanding of the body by the pupil are set in small type, to be used +at the discretion of the teacher.</p> + +<p>The use of books of reference is earnestly recommended. For this +purpose the usual high school texts may be employed to good advantage. A +few more advanced works should, however, be frequently consulted. For +this purpose Martin's <hi rend="font-style: italic">Human Body</hi> +(Advanced Course), Rettger's <hi rend="font-style: italic">Advanced +Lessons in Physiology</hi>, Thornton's <hi rend="font-style: +italic">Human Physiology</hi>, Huxley's <hi rend="font-style: +italic">Lessons in Elementary Physiology</hi>, Howell's <hi +rend="font-style: italic">A Text-book of Physiology</hi>, Hough and +Sedgwick's <hi rend="font-style: italic">Hygiene and Sanitation</hi>, +and Pyle's <hi rend="font-style: italic">Personal Hygiene</hi> will be +found serviceable.</p> + +<p>In the preparation of this work valuable assistance has been rendered +by Dr. C.N. McAllister, Department of Psychology, and by Professor B.M. +Stigall, Department of Biology, along the lines of their respective +specialties, and in a more general way by President W.J. Hawkins and +others of the Warrensburg, Missouri, State Normal School. Expert advice +from Professor S.D. Magers, Instructor in Physiology and Bacteriology, +State Normal School, Ypsilanti, Michigan, has been especially helpful, +and many practical suggestions from the high school teachers of +physiology of Kansas City, Missouri, Professor C.H. Nowlin, Central +High School, Dr. John W. Scott, Westport High +School, and Professor A.E. Shirling, Manual Training High School, all of +whom read both manuscript and proofs, have been incorporated. +Considerable material for the Practical Work, including the respiration +experiment (page 101) and the reaction time experiment (page 323), were +contributed by Dr. Scott. Professor Nowlin's suggestions on +subject-matter and methods of presentation deserve special mention. To +these and many others the author makes grateful acknowledgment.</p> + +<p rend="text-align: right">F.M.W.</p> + +<p><hi rend="font-variant: small-caps">Missouri State Normal +School</hi>,<lb /> + +<hi rend="font-variant: small-caps">Second District</hi>, May 1, +1909.</p> + +</div> + +<div rend="page-break-before: always"> + +<index index="toc" /><index index="pdf" /> + +<head>Contents</head> + +<divGen type="toc" /> + +</div> + +</front> + +<body rend="page-break-before: right"> + +<div> + +<pb n="001" /><anchor id="Pg001" /> + +<head>PHYSIOLOGY AND HYGIENE</head> + +<p></p> + +</div> + +<div> + +<index index="toc" /><index index="pdf" /> + +<head>PART I: THE VITAL PROCESSES</head> + +<p></p> + +<div> + +<index index="toc" /><index index="pdf" /> + +<head>CHAPTER I - INTRODUCTION</head> + +<p>To derive strength equal to the daily task; to experience the +advantages of health and avoid the pain, inconvenience, and danger of +disease; to live out contentedly and usefully the natural span of life: +these are problems that concern all people. They are, however, but +different phases of one great problem—the problem of properly managing +or caring for the body. To supply knowledge necessary to the solution of +this problem is the chief reason why the body is studied in our public +schools.</p> + +<p><hi rend="font-weight: bold">Divisions of the Subject.</hi>—The body +is studied from three standpoints: structure, use of parts, and care or +management. This causes the main subject to be considered under three +heads, known as anatomy, physiology, and hygiene.</p> + +<p><hi rend="font-style: italic">Anatomy</hi> treats of the construction +of the body—the parts which compose it, what they are like, and where +located. Its main divisions are known as gross anatomy and histology. +<hi rend="font-style: italic">Gross anatomy</hi> treats of the larger +structures of the body, while <hi rend="font-style: +italic">histology</hi> treats of the minute structures of which these +are composed—parts too small to be seen with the naked eye and which +have to be studied with the aid of the microscope.</p> + +<p><pb n="002" /><anchor id="Pg002" /><hi rend="font-style: +italic">Physiology</hi> treats of the function, or use, of the different +parts of the body—the work which the parts do and how they do it—and of +their relations to one another and to the body as a whole.</p> + +<p><hi rend="font-style: italic">Hygiene</hi> treats of the proper care +or management of the body. In a somewhat narrower sense it treats of the +"laws of health." Hygiene is said to be <hi rend="font-style: +italic">personal</hi>, when applied by the individual to his own body; +<hi rend="font-style: italic">domestic</hi>, when applied to a small +group of people, as the family; and public, or <hi rend="font-style: +italic">general</hi>, when applied to the community as a whole or to the +race.</p> + +<p><hi rend="font-weight: bold">The General Aim of Hygiene.</hi>—There +are many so-called laws of health, and for these laws it is essential in +the management of the body to find a common basis. This basic law, +suggested by the nature of the body and conditions that affect its +well-being, may be termed the <hi rend="font-style: italic">Law of +Harmony: The mode of living must harmonize with the plan of the +body</hi>. To live properly one must supply the conditions which his +body, on account of its nature and plan, requires. On the other hand, he +must avoid those things and conditions which are injurious, <hi +rend="font-style: italic">i.e.</hi>, out of harmony with the body plan. +To secure these results, it is necessary to determine what is and what +is not in harmony with the plan of the body, and to find the means of +applying this knowledge to the everyday problems of living. Such is the +general aim of hygiene. Stated in other words: Hygiene has for its +general aim the bringing about of an essential harmony between the body +and the things and conditions that affect it.<note place="foot"><p>The +body is affected by what it does (exercise, work, sleep), by things +taken into it (food, air, drugs), and by things outside of it (the house +in which one lives, climate, etc.). That phase of hygiene which has for +its object the making of the surroundings of the body healthful is known +as <hi rend="font-style: italic">sanitation</hi>.</p></note></p> + +<p><pb n="003" /><anchor id="Pg003" /><hi rend="font-weight: +bold">Relation of Anatomy and Physiology to the Study of +Hygiene.</hi>—If the chief object in studying the body is that of +learning how to manage or care for it, and hygiene supplies this +information, why must we also study anatomy and physiology? The answer +to this question has already been in part suggested. In order to +determine what things and conditions are in harmony with the plan of the +body, we must know what that plan is. This knowledge is obtained through +a study of anatomy and physiology. The knowledge gained through these +subjects also renders the study of hygiene more interesting and +valuable. One is enabled to see <hi rend="font-style: italic">why</hi> +and <hi rend="font-style: italic">how</hi> obedience to hygienic laws +benefits, and disobedience to them injures, the body. This causes the +teachings of hygiene to be taken more seriously and renders them more +practical. In short, anatomy and physiology supply a necessary basis for +the study of hygiene.</p> + +<p><hi rend="font-weight: bold">Advantages of Properly Managing the +Body.</hi>—One result following the mismanagement of the body is loss of +health. But attending the loss of health are other results which are +equally serious and far-reaching. Without good health, people fail to +accomplish their aims and ambitions in life; they miss the joy of +living; they lose their ability to work and become burdens on their +friends or society. The proper management of the body means health, and +it also means the capacity for work and for enjoyment. Not only should +one seek to preserve his health from day to day, but he should so manage +his body as to use his powers to the best advantage and prolong as far +as possible the period during which he may be a capable and useful +citizen.</p> </div> + +<div rend="page-break-before: always"> + +<index index="toc" /><index index="pdf" /> + +<pb n="004" /><anchor id="Pg004" /> + +<head>CHAPTER II - GENERAL VIEW OF THE BODY</head> + +<p><hi rend="font-weight: bold">External Divisions.</hi>—Examined from +the outside, the body presents certain parts, or divisions, familiar to +all. The main, or central, portion is known as the <hi rend="font-style: +italic">trunk</hi>, and to this are attached the <hi rend="font-style: +italic">head</hi>, the <hi rend="font-style: italic">upper +extremities</hi>, and the <hi rend="font-style: italic">lower +extremities</hi>. These in turn present smaller divisions which are also +familiar. The upper part of the trunk is known as the <hi +rend="font-style: italic">thorax</hi>, or chest, and the lower part as +the <hi rend="font-style: italic">abdomen</hi>. The portions of the +trunk to which the arms are attached are the <hi rend="font-style: +italic">shoulders</hi>, and those to which the legs are joined are the +<hi rend="font-style: italic">hips</hi>, while the central rear portion +between the neck and the hips is the <hi rend="font-style: +italic">back</hi>. The fingers, the hand, the wrist, the forearm, the +elbow, and the upper arm are the main divisions of each of the upper +extremities. The toes, the foot, the ankle, the lower leg, the knee, and +the thigh are the chief divisions of each of the lower extremities. The +head, which is joined to the trunk by the neck, has such interesting +parts as the eyes, the ears, the nose, the jaws, the cheeks, and the +mouth. The entire body is inclosed in a double covering, called the <hi +rend="font-style: italic">skin</hi>, which protects it in various +ways.</p> + +<p><hi rend="font-weight: bold">The Tissues.</hi>—After examining the +external features of the body, we naturally inquire about its internal +structures. These are not so easily investigated, and much which is of +interest to advanced students must be omitted from an elementary course. +We may, however, as a first step in this study, determine what kinds of +materials enter into <pb n="005" /><anchor id="Pg005" />the +construction of the body. For this purpose the body of some small animal +should be dissected and studied. (See observation at close of chapter.) +The different materials found by such a dissection correspond closely to +the substances, called <hi rend="font-style: italic">tissues</hi>, which +make up the human body. The main tissues of the body, as ordinarily +named, are the <hi rend="font-style: italic">muscular</hi> tissue, the +<hi rend="font-style: italic">osseous</hi> tissue, the <hi +rend="font-style: italic">connective</hi> tissue, the <hi +rend="font-style: italic">nervous</hi> tissue, the <hi rend="font-style: +italic">adipose</hi> tissue, the <hi rend="font-style: +italic">cartilaginous</hi> tissue, and the <hi rend="font-style: +italic">epithelial</hi> and <hi rend="font-style: italic">glandular</hi> +tissue. Most of these present different varieties, making all together +some fifteen different kinds of tissues that enter into the construction +of the body.<note place="foot"><p>When classified according to their essential structure, +the tissues fall into four main groups: epithelial and glandular tissue, +muscular tissue, nervous tissue, and connective tissue. According to +this system the osseous, cartilaginous, and adipose tissues are classed +as varieties of connective tissue. See page <ref target="Pg018">18</ref>.</p></note></p> + +<p><hi rend="font-weight: bold">General Purposes of the +Tissues.</hi>—The tissues, first of all, <hi rend="font-style: +italic">form the body</hi>. As a house is constructed of wood, stone, +plaster, iron, and other building materials, so is the body made up of +its various tissues. For this reason the tissues have been called the +<hi rend="font-style: italic">building materials</hi> of the body.</p> + +<p>In addition to forming the body, the tissues supply the means through +which its work is carried on. They are thus the <hi rend="font-style: +italic">working materials</hi> of the body. In serving this purpose the +tissues play an active rôle. All of them must perform the activities of +growth and repair, and certain ones (the so-called active tissues) must +do work which benefits the body as a whole.</p> + +<p><hi rend="font-weight: bold">Purposes of the Different +Tissues.</hi>—In the construction of the body and also in the work which +it carries on, the different tissues are made to serve different +purposes. The osseous tissue is the chief substance in the bony +framework, or skeleton, while the muscular tissue produces the different +movements of the body. The connective<pb n="006" /><anchor id="Pg006" /> tissue, which is everywhere abundant, serves the general +purpose of connecting the different parts together. Cartilaginous tissue +forms smooth coverings over the ends of the bones and, in addition to +this, supplies the necessary stiffness in organs like the larynx and the +ear. The nervous tissue controls the body and brings it into proper +relations with its surroundings, while the epithelial tissue (found upon +the body surfaces and in the glands) supplies it with protective +coverings and secretes liquids. The adipose tissue (fat) prevents the +too rapid escape of heat from the body, supplies it with nourishment in +time of need, and forms soft pads for delicate organs like the +eyeball.</p> + +<p><hi rend="font-weight: bold">Properties of the Tissues.</hi>—If we +inquire how the tissues are able to serve such widely different +purposes, we find this answer. The tissues differ from one another both +in composition and in structure and, on this account, differ in their +properties.<note place="foot"><p>The properties of substances are the +qualities or characteristics (color, weight, etc.) by means of which +they are recognized.</p></note> Their different properties enable them +to serve different purposes in the body. Somewhat as glass is adapted by +its transparency, hardness, and toughness to the use made of it in +windows, the special properties of the tissues adapt them to the kinds +of service which they perform. Properties that adapt tissues to their +work in the body are called <hi rend="font-style: italic">essential</hi> +properties. The most important of these essential properties are as +follows:</p> + +<p>1. Of osseous tissue, hardness, stiffness, and toughness. 2. Of +muscular tissue, contractility and irritability. 3. Of nervous tissue, +irritability and conductivity. 4. Of cartilaginous tissue, stiffness and +elasticity. 5. Of connective tissue, toughness and pliability. 6. Of +epithelial tissue, ability to resist the action of external forces and +power to secrete.</p> + +<pb n="007" /><anchor id="Pg007" /> +<figure url="images/image01.png" + rend="page-float: 'hp'; text-align: center; w25"> +<head><lb />Fig. 1—Hand and forearm, showing the grouping of muscular and +connective tissues in the organ for grasping.</head> +<figDesc>Fig. 1</figDesc> +</figure> + +<p><hi rend="font-weight: bold">Tissue Groups.</hi>—In the construction +of the body the tissues are grouped together to form its various +divisions or parts. A group of tissues which serves some special purpose +is known as an <hi rend="font-style: italic">organ</hi>. The hand, for +example, is an organ for grasping (Fig. 1). While the different organs +of the body do not always contain the same tissues, and never contain +them in the same proportions, they do contain such tissues as their work +requires and these have a special arrangement—one adapted to the work +which the organs perform.</p> + +<p>In addition to forming the organs, the tissues are also grouped in +such a manner as to provide supports for organs and to form cavities in +which organs are placed. The various cavities of the body are of +particular interest and importance. The three largest ones are the <hi +rend="font-style: italic">cranial</hi> cavity, containing the brain; the +<hi rend="font-style: italic">thoracic</hi> cavity, containing the heart +and the lungs; and the <hi rend="font-style: italic">abdominal</hi> +cavity, containing the stomach, the liver, the intestines, and other +important organs (Fig. 2). Smaller cavities serving different purposes +are also found.</p> + +<p rend="text-align: center"><pb n="008" /><anchor id="Pg008" /> +<figure url="images/image02.png" rend="page-float: 'hp'; text-align: center; w75"> +<head><lb />Fig. 2—Diagram of a lengthwise section of the body to show its +large cavities and the organs which they contain.</head> +<figDesc>Fig. 2</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Organs and Systems.</hi>—The work of the +body is carried on by its various organs. Many, in fact the majority, of +these organs serve more than one purpose. The tongue<pb n="009" /><anchor id="Pg009" /> +is used in talking, in +masticating the food, and in swallowing. The nose serves at least three +distinct purposes. The mouth, the arms, the hands, the feet, the legs, +the liver, the lungs, and the stomach are also organs that serve more +than one purpose. This introduces the principle of economy into the +construction of the body and diminishes the number of organs that would +otherwise be required.</p> + +<p>The various organs also <hi rend="font-style: italic">combine</hi> +with one another in carrying on the work of the body. An illustration of +this is seen in the digestion of the food—a process which requires the +combined action of the mouth, stomach, liver, intestines, and other +organs. A number of organs working together for the same purpose form a +<hi rend="font-style: italic">system</hi>. The chief systems of the body +are the digestive system, the circulatory system, the respiratory +system, the muscular system, and the nervous system.</p> + +<p><hi rend="font-weight: bold">The Organ and its Work.</hi>—A most +interesting question relating to the work of the organ is this: Does the +organ work for its own benefit or for the benefit of the body as a +whole? Does the hand, for example, grasp for itself or in order that the +entire body may come into possession? Only slight study is sufficient to +reveal the fact that each organ performs a work which benefits the body +as a whole. In other words, just as the organ itself is a part of the +body, the work which it does is a part of the necessary work which the +body has to do.</p> + +<p>But in working for the general good, or for the body as a whole, each +organ becomes a sharer in the benefits of the work done by every other +organ. While the hand receives only a little of the nourishment +contained in the food which it places in the mouth or of the heat from, +fuel which it places on the fire, it is aided and supported by the work +of all the other organs of the body—eyes, <pb n="010" /><anchor +id="Pg010" /> feet, brain, heart, etc. The hand does not and cannot work +independently of the other organs. It is one of the partners in a very +close combination where, by doing a particular work, it, shares in the +profits of all. What is true of the hand is true of every other organ of +the body.</p> + +<p><hi rend="font-weight: bold">An Organization.</hi>—The relations +which the different organs sustain to each other and to the body as a +whole suggest the possibility of classifying the body as an +organization. This term is broadly applied to a variety of combinations. +An organization is properly defined as <hi rend="font-style: italic">any +group of individuals which, in working together for a common purpose, +practices the division of labor</hi>. This definition will be better +understood by considering a few familiar examples.</p> + +<p>A baseball team is an organization. The team is made up of individual +players. These work together for the common purpose of winning games. +They practice the division of labor in that the different players do +different things—one catching, another pitching, and so on. A +manufacturing establishment which employs several workmen may also be an +organization. The article manufactured provides the common purpose +toward which all strive; and, in the assignment of different kinds of +work to the individual workmen, the principle of division of labor is +carried out. For the same reason a school, a railway system, an army, +and a political party are organizations.</p> + +<p>An organization of a lower order of individuals than these human +organizations is to be found in a hive of bees. This is made up of the +individual bees, and these, in carrying on the general work of the hive, +are known to practice the division of labor.</p> + +<p><hi rend="font-weight: bold">Is the Body an Organization</hi>?—If the +body is an organization, it must fulfill the conditions of the +definition. It<pb n="011" /><anchor id="Pg011" /> must be made up of +separate or individual parts. These must work together for the same +general purpose, and, in the accomplishment of this purpose, must +practice the division of labor. That the body practices the division of +labor is seen in the related work of the different organs. That it is +made up of minute, but individual, parts will be shown in the chapter +following. That it carries on a <hi rend="font-style: italic">general +work</hi> which is accomplished through the combined action of its +individual parts is revealed through an extended study of its various +activities. <hi rend="font-style: italic">The body is an +organization.</hi> Moreover, it is one of the most complex and, at the +same time, most perfect of the organizations of which we have +knowledge.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—Viewed from the outside, +the body is seen to be made up of divisions which are more or less +familiar. Viewed internally, it is found to consist of different kinds +of materials, called tissues. The tissues are adapted, by their +properties, to different purposes both in the construction of the body +and in carrying on its work. The working parts of the body are called +organs and these in their work combine to form systems. The entire body, +on account of the method of its construction and the character of its +work, may be classed as an organization.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. Name and locate the +chief external divisions of the body.</p> + +<p>2. What tissues may be found by dissecting the leg of a chicken?</p> + +<p>3. Name the most important properties and the most important uses of +muscular tissue, osseous tissue, and connective tissue.</p> + +<p>4. Define an organ. Define a system. Name examples of each.</p> + +<p>5. Name the chief cavities of the body and the organs which they +contain.</p> + +<p>6. What tissues are present in the hand? How does each of these aid +in the work of the hand?</p> + +<p><pb n="012" /><anchor id="Pg012" />7. Define an organization. Show +that a railway system, an army, and a school are organizations.</p> + +<p>8. What is meant by the phrase "division of labor"? In what manner is +the division of labor practiced in a shoe or watch factory? What are the +advantages?</p> + +<p>9. What are the proofs that the body is an organization?</p> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">Observation on the Tissues.</hi>—Examine +with care the structures in the entire leg of a chicken, squirrel, +rabbit, or other small animal used for food. Observe, first of all, the +external covering, consisting of cuticle and hair, claws, scales, or +feathers, according to the specimen. These are similar in structure, and +they form the epidermis, which is one kind of <hi rend="font-style: +italic">epithelial</hi> tissue. With a sharp knife lay open the skin and +observe that it is attached to the parts underneath by thin, but tough, +threads and sheaths. These represent a variety of <hi rend="font-style: +italic">connective</hi> tissue. The reddish material which forms the +greater portion of the specimen is a variety of <hi rend="font-style: +italic">muscular</hi> tissue, and its divisions are called muscles. With +a blunt instrument, separate the muscles, by tearing apart the +connective tissue binding them together, and find the glistening white +strips of connective tissue (tendons) which attach them to the bones. +Find near the central part of the leg a soft, white cord (a nerve) which +represents one variety of <hi rend="font-style: italic">nervous</hi> +tissue. The bones, which may now be examined, form the <hi +rend="font-style: italic">osseous</hi> tissue. At the ends of the bones +will be found a layer of smooth, white material which represents one +kind of <hi rend="font-style: italic">cartilaginous</hi> tissue. The <hi +rend="font-style: italic">adipose</hi>, or fatty, tissue, which is found +under the skin and between the other tissues, is easily recognized.</p> + +<p><hi rend="font-weight: bold">Relation of the Tissues to the +Organs.</hi>—Observe in the specimen just studied the relation of the +different tissues to the organ as a whole (regarding the leg as an +organ), <hi rend="font-style: italic">i.e.</hi>, show how each of the +tissues aids in the work which the organ accomplishes. Show in +particular how the muscles supply the foot with motion, by tracing out +the tendons that connect them with the toes. Pull on the different +tendons, noting the effect upon the different parts of the foot.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="013" /><anchor id="Pg013" /> + +<head>CHAPTER III - THE BODY ORGANIZATION</head> + +<p>What is the nature of the body organization? What are the individual +parts, or units, that make it up? What general work do these carry on +and upon what basis do they practice the division of labor? The answers +to these questions will suggest the main problems in the study of the +body.</p> + +<p rend="text-align: center"> <figure +url="images/image03.png" rend="page-float: 'hp'; text-align: center; w95"> <head><lb />Fig. 3—Diagram +showing the relation of the cells and the intercellular material. <hi +rend="font-style: italic">C.</hi> Cells. <hi rend="font-style: +italic">I.</hi> Intercellular material.</head> <figDesc>Fig. 3</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Complex Nature of the Tissues.</hi>—To +the unaided eye the tissues have the appearance of simple structures. +The microscope, however, shows just the reverse to be true. When any one +of the tissues is suitably prepared and carefully examined with this +instrument, at least two classes of materials can be made out. One of +these consists of minute particles, called <hi rend="font-style: +italic">cells</hi>; the other is a substance lying between the cells, +known as the <hi rend="font-style: italic">intercellular material</hi> +(Fig. 3). The cells and the intercellular material, though varying in +their relative proportions, are present in all the tissues.</p> + +<p><hi rend="font-weight: bold">The Body a Cell Group.</hi>—The +biologist has found that the bodies of all living things, plants as well +as animals, consist either of single cells or of groups of cells. The +single cells live independently of one another, but the cells that form +groups are attached to, and are more or less dependent upon, one +another. In the first condition are <pb n="014" /><anchor id="Pg014" /> +found the very lowest forms of life. In the second, life reaches its +greatest development. The body of man, which represents the highest type +of life, is recognized as a group of cells. In this group each cell is +usually separate and distinct from the others, but is attached to them, +and is held in place by the intercellular material.</p> + +<p><hi rend="font-weight: bold">Protoplasm, the Cell Substance.</hi>—The +cell is properly regarded as an <hi rend="font-style: +italic">organized</hi> bit of a peculiar material, called <hi +rend="font-style: italic">protoplasm</hi>. This is a semi-liquid and +somewhat granular substance which resembles in appearance the white of a +raw egg. Its true nature and composition are unknown, because any +attempt to analyze it kills it, and dead protoplasm is essentially +different from living protoplasm. It is known, however, to be a highly +complex substance and to undergo chemical change readily. It appears to +be the only kind of matter with which life is ever associated, and for +this reason protoplasm is called the <hi rend="font-style: +italic">physical basis of life</hi>. Its organization into separate +bits, or cells, is necessary to the life activities that take place +within it.</p> + +<p><hi rend="font-weight: bold">Structure of the Cell.</hi>—Though all +portions of the cell are formed from the protoplasm, this essential +substance differs both in structure and in function at different places +in the cell. For this reason the cell is looked upon as a complex body +having several distinct parts. At or near the center is a clear, rounded +body, called the <hi rend="font-style: italic">nucleus</hi>. This plays +some part in the nourishment of the cell and also in the formation of +new cells. If it be absent, as is sometimes the case, the cell is +short-lived and unable to reproduce itself. The variety of protoplasm +contained in the nucleus is called the <hi rend="font-style: +italic">nucleoplasm</hi>.</p> + +<p rend="text-align: center"> +<figure url="images/image04.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 4—Diagram of a +typical cell (after Wilson). 1. Main body. 2. Nucleus. 3. +Attraction sphere. 4. Food particles and waste. 5. Cell-wall. 6. Masses +of active material found in certain cells, called plastids.</head> +<figDesc>Fig. 4</figDesc> +</figure></p> + +<p>Surrounding the nucleus is the <hi rend="font-style: italic">main +body</hi> of the cell, sometimes referred to as the "protoplasm." Since +the<pb n="015" /><anchor id="Pg015" /> protoplasm forms all parts of +the cell, this substance is more properly called the <hi +rend="font-style: italic">cytoplasm</hi>, or cell plasm. Surrounding and +inclosing the cytoplasm, in many cells, is a thin outer layer, or +membrane, which affords more or less protection to the contents of the +cell. This is usually referred to as the <hi rend="font-style: +italic">cell-wall</hi>. A fourth part of the cell is also described, +being called the <hi rend="font-style: italic">attraction sphere</hi>. +This is a small body lying near the nucleus and coöperating with that +body in the formation of new cells. Food particles, wastes, and other +substances may also be present in the cytoplasm. The parts of a typical +cell are shown in Fig. 4.</p> + +<p><hi rend="font-weight: bold">Importance of the Cells.</hi>—The cells +must be regarded as the living, working parts of the body. They are the +active agents in all of the tissues, enabling them to serve their +various purposes. Working through the tissues, they build up the body +and carry on its different activities. They are recognized on this +account as <hi rend="font-style: italic">the units of structure and of +function</hi>, and are the "individuals" in the body organization. Among +the most important and interesting of the activities of the cells are +those by which they build up the body, or cause it to grow.</p> + +<p><pb n="016" /><anchor id="Pg016" /><hi rend="font-weight: bold">How the Cells enable the Body to +Grow.</hi>—Every cell is able to take new material into itself and to +add this to the protoplasm. This tends to increase the amount of the +protoplasm, thereby causing the cells to increase in size. A general +increase in the size of the cells has the effect of increasing the size +of the entire body, and this is one way by which they cause it to grow. +There is, however, a fixed limit, varying with different cells, to the +size which they attain, and this is quite low. (The largest cells are +scarcely visible to the naked eye.) Any marked increase in the size of +the body must, therefore, be brought about by other means. Such a means +is found in the formation of new cells, or <hi rend="font-style: +italic">cell reproduction</hi>. The new cells are always formed <hi +rend="font-style: italic">by</hi> and <hi rend="font-style: +italic">from</hi> the old cells, the essential process being known as +<hi rend="font-style: italic">cell-division</hi>.</p> + +<p rend="text-align: center"> +<figure url="images/image05.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 5—Steps in +cell-division (after Wilson). Note that the process begins with the +division of the attraction sphere, then involves the nucleus, and +finally separates the main body.</head> +<figDesc>Fig. 5</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Cell-Division.</hi>—By dividing, a +single cell will, on attaining its growth, separate into two or more new +cells. The process is quite complex and is imperfectly understood. It is +known, however, that the act of separation is preceded by a series of +changes in which the attraction sphere<pb n="017" /><anchor id="Pg017" /> and the nucleus actively +participate, and that, as a result of these changes, the contents of the +old cell are rearranged to form the new cells. Some of the different +stages in the process, as they have been studied under the microscope, +are indicated in Fig. 5.</p> + +<p>Gradually, through the formation of new cells and by the growth of +these cells after they have been formed, the body attains its full size. +When growth is complete, cell reproduction is supposed to cease except +where the tissues are injured, as in the breaking of a bone, or where +cells, like those at the surface of the skin, are subject to wear. Then +new material continues to be added to the protoplasm throughout life, +but in amount only sufficient to replace that lost from the protoplasm +as waste.</p> + +<p rend="text-align: center"> +<figure url="images/image06.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 6—A tumbler partly filled with marbles covered +with water, suggesting the relations of the cells to the lymph.</head> +<figDesc>Fig. 6</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Cell Surroundings.</hi>—All cells are +said to be <hi rend="font-style: italic">aquatic</hi>. This means simply +that they require water for carrying on their various activities. The +cells, in order to live, must take in and give out materials, and water +is necessary to both processes. It is also an essential part of the +protoplasm. Deprived of water, cells become inactive and usually die. +Aquatic surroundings are provided for the cells of the body through a +liquid known as the <hi rend="font-style: italic">lymph</hi>, which is +distributed throughout the intercellular material (Fig. 6). This +consists of water containing oxygen and food substances in solution. +Besides supplying these to the cells, the lymph also receives their +wastes. Through the lymph the necessary conditions for cell life are +provided in the body.</p> + +<p><hi rend="font-weight: bold">The General Work of Cells.</hi>—In +handling the materials<pb n="018" /><anchor id="Pg018" /> derived from the lymph, the cells carry +on three well-defined processes, known as absorption, assimilation, and +excretion.</p> + +<p><hi rend="font-style: italic">Absorption</hi> is the process of +taking water, food, and oxygen into the cells.</p> + +<p><hi rend="font-style: italic">Assimilation</hi> is a complex process +which results in the addition of the absorbed materials to the +protoplasm. Through assimilation the protoplasm is built up or +renewed.</p> + +<p><hi rend="font-style: italic">Excretion</hi> is the throwing off of +such waste materials as have been formed in the cells. These are passed +into the lymph and thence to the surface of the body.</p> + +<p>Absorption, assimilation, excretion, and also reproduction are +performed by all classes of cells. They are, on this account, referred +to as the <hi rend="font-style: italic">general work of cells</hi>.</p> + +<p><hi rend="font-weight: bold">The Special Work of Cells.</hi>—In +addition to the general work which all cells do in common, each class of +cells in the body is able to do some particular kind of work—a work +which the others cannot do or which they can do only to a limited +extent. This is spoken of as the <hi rend="font-style: italic">special +work of cells</hi>. Examples of the special work of cells are found in +the production of motion by muscle cells and in the secretion of liquids +by gland cells. It may be noted that while the general work of cells +benefits them individually, their special work benefits the body as a +whole. Another example of the special work of cells is found in the</p> + +<p rend="text-align: center"> +<figure url="images/image07.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 7—Cartilage cells, surrounded by the intercellular material +which they have deposited.</head> +<figDesc>Fig. 7</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Production of the Intercellular +Material.</hi>—Though most of the cells of the body deposit to a slight +extent this material, the greater part of it is produced by a single +class of cells found in bone, cartilage, and connective tissue. +Cartilage, bone, and connective tissue differ greatly from the other +tissues in the amount of intercellular material which they contain, the +difference being due to these cells.<pb n="019" /><anchor id="Pg019" /> +In the connective tissue they deposit the fibrous material so +important in holding the different parts of the body together. In the +cartilage they produce the gristly substance which forms by far its +larger portion (Fig. 7). In the bones they deposit a material similar to +that in the cartilage, except that with it is mixed a mineral substance +which gives the bones their hardness and stiffness.<note place="foot"><p>Certain of these cells also form deposits of fat, giving +rise to the adipose, or fatty, tissue.</p></note> The intercellular +material, in addition to connecting the cells, supplies to certain +tissues important properties, such as the elasticity of cartilage and +the stiffness of the bones.</p> + +<p><hi rend="font-weight: bold">Nature of the Body +Organization.</hi>—The division of labor carried on by the different +organs, as shown in the preceding chapter, is in reality carried on by +the cells that form the organs. To see that this is true we have only to +observe the relation of cells to tissues and of tissues to organs. The +cells form the tissues and the tissues form the organs. This arrangement +enables the special work of different kinds of cells to be combined in +the work of the organ as a whole. This is seen in the hand which, in +grasping, uses motion supplied by the muscle cells, a controlling +influence supplied by the nerve cells, a framework supplied by the bone +cells, and so on. The cells supply the basis for the body organization +and, properly speaking, the body is <hi rend="font-style: italic">an +organization of cells</hi><note place="foot"><p>Any organized structure, such as the body, whose parts +are pervaded by a common life, is known as an <hi rend="font-style: +italic">organism</hi>. The term "organism" is frequently applied to the +body.</p></note> (Recall the definition<pb n="020" /><anchor id="Pg020" /> of an organization, page 10.) In +this organization there are to be observed:</p> + +<p>1. A definite arrangement of the cells to form the tissues. A tissue +is a group of like cells.</p> + +<p>2. A definite arrangement of the tissues in the organ. Each organ +contains the tissues needed for its work.</p> + +<p>3. In several instances there is a definite arrangement of organs to +form systems.</p> + +<p>4. The body as a whole is made up of organs and systems, together +with the structures necessary for their support and protection.</p> + +<p>There now remains a further question for consideration. What is the +one supreme end, or purpose, toward which all the activities of the body +organization are directed? This purpose will naturally have some +relation to the maintenance, or preservation, of the cell group which we +call the body.</p> + +<p><hi rend="font-weight: bold">The Maintenance of Life.</hi>—The +preservation of any cell group in its natural condition, whether it be +plant or animal, is accomplished through keeping it alive. If life +ceases, the group quickly disintegrates and its elements become +scattered, a fact which is verified through everyday observation. Though +the nature of life is unknown, it may be looked upon as the organizer +and preserver of the protoplasm. But in preserving the protoplasm it +also preserves the entire cell group, or body. Life is thus the most +essential condition of the body. <hi rend="font-style: italic">With life +all portions of the body are concerned, and toward its maintenance all +the activities of the body organization are directed</hi>.</p> + +<p><hi rend="font-weight: bold">The Nutrient Fluid in its Relations to +the Cells.</hi>—The maintenance of life within the cells requires, as we +have seen, that they be supplied with water, food, and oxygen, and that +they be relieved of such wastes as they form.<pb n="021" /><anchor +id="Pg021" /> This double purpose is accomplished through the agency of +an internal nutrient fluid, a portion of which has already been referred +to as the lymph. Not only does this fluid supply the means for keeping +the cells alive, but, through the cells, it is also the means of +preserving the life of the body as a whole.</p> + +<p>The cells, however, rapidly exhaust the nutrient fluid. They take +from it food and oxygen and they put into it their wastes. To prevent +its becoming unfit for supplying their needs, food and oxygen must be +continually added to this fluid, and waste materials must be continually +removed. This is not an easy task. As a matter of fact, the preparation, +distribution, and purification of the nutrient fluid requires the direct +or indirect aid of practically all parts of the body. It supplies for +this reason a broad basis for the division of labor on the part of the +cells.</p> + +<p><hi rend="font-weight: bold">Relation of the Body to its +Environment.</hi>—While life is directly dependent upon the internal +nutrient fluid, it is indirectly dependent upon the physical +surroundings of the body. Herein lies the need of the <hi +rend="font-style: italic">external</hi> organs—the feet and legs for +moving about, the hands for handling things, the eyes for directing +movements, etc. That the great needs of the body are supplied from its +surroundings are facts of common experience. Food, shelter, air, +clothing, water, and the means of protection are external to the body +and form a part of its environment. In making the things about him +contribute to his needs, man encounters a problem which taxes all his +powers. Only by toil and hardship, "by the sweat of his brow," has he +been able to wrest from his surroundings the means of his +sustenance.</p> + +<p><hi rend="font-weight: bold">The Main Physiological +Problems.</hi>—The study of the body is thus seen to resolve itself +naturally into the consideration of two main problems:</p> + +<p><pb n="022" /><anchor id="Pg022" />1. <hi rend="font-style: +italic">That of maintaining in the body a nutrient fluid for the +cells.</hi></p> + +<p>2. <hi rend="font-style: italic">That of bringing the body into such +relations with its surroundings as will enable it to secure materials +for the nutrient fluid and satisfy its other needs.</hi></p> + +<p>The first problem is <hi rend="font-style: italic">internal</hi> and +includes the so-called vital processes, known as digestion, circulation, +respiration, and excretion. The second problem is <hi rend="font-style: +italic">external</hi>, as it were, and includes the work of the external +organs—the organs of motion and of locomotion and the organs of special +sense. These problems are closely related, since they are the two +divisions of the one problem of maintaining life. Neither can be +considered independently of the other. In the chapter following is taken +up the first of these problems.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The individual parts, or +units, that form the body organization are known as cells. These consist +of minute but definitely arranged portions of protoplasm and are held +together by the intercellular material. They build up the body and carry +on its different activities. The tissues are groups of like cells. By +certain general activities the cells maintain their existence in the +tissues and by the exercise of certain special activities they adapt the +tissues to their purposes in the body. The body, as a cell organization, +has its activities directed under normal conditions toward a single +purpose—that of maintaining life. In the accomplishment of this purpose +a nutrient fluid is provided for the cells and proper relations between +the body and its surroundings are established.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. If a tissue be +compared to a brick wall, to what do the separate bricks correspond? To +what the mortar between the bricks?</p> + +<p>2. Draw an outline of a typical cell, locating and naming the main +divisions.</p> + +<p>3. How do the cells enable the body to grow? Describe the process of +cell-division.</p> + +<p><pb n="023" /><anchor id="Pg023" />4. How does the +general work of cells differ from their special work? Define absorption, +excretion, and assimilation as applied to the cells.</p> + +<p>5. Compare the conditions surrounding a one-celled animal, living in +water, to the conditions surrounding the cells in the body.</p> + +<p>6. What is meant by the term "environment"? How does man's +environment differ from that of a fish?</p> + +<p>7. What is the necessity for a nutrient fluid in the body?</p> + +<p>8. Why is the maintenance of life necessarily the chief aim of all +the activities of the body?</p> + +<p>9. State the two main problems in the study of the body.</p> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">Observations.</hi>—1. Make some +scrapings from the inside of the cheek with a dull knife and mix these +with a little water on a glass slide. Place a cover-glass on the same +and examine with a compound microscope. The large pale cells that can be +seen in this way are a variety of epithelial cells.</p> + +<p>2. Mount in water on a glass slide some thin slices of cartilage and +examine first with a low and then with a high power of microscope. +(Suitable slices may be cut, with a sharp razor, from the cartilage +found at the end of the rib of a young animal.) Note the small groups of +cells surrounded by, and imbedded in, the intercellular material.</p> + +<p>3. Mount and examine with the microscope thin slices of elder pith, +potato, and the stems of growing plants. Make drawings of the cells thus +observed.</p> + +<p>4. Examine with the microscope a small piece of the freshly sloughed +off epidermis of a frog's skin. Examine it first in its natural +condition, and then after soaking for an hour or two in a solution of +carmine. Make drawings.</p> + +<p>5. Mount on a glass slide some of the scum found on stagnant water +and examine it with a compound microscope. Note the variety and relative +size of the different things moving about. The forms most frequently +seen by such an examination are one-celled plants. Many of these have +the power of motion.</p> + +<p>6. Examine tissues of the body, such as nervous, muscular, and +glandular tissues, which have been suitably prepared and mounted for +microscopic study, using low and high powers of the microscope. Make +drawings of the cells in the different tissues thus observed.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="024" /><anchor id="Pg024" /> + +<head>CHAPTER IV - THE BLOOD</head> + +<p>Two liquids of similar nature are found in the body, known as the +blood and the lymph. These are closely related in function and together +they form the nutrient fluid referred to in the preceding chapter. The +blood is the more familiar of the two liquids, and the one which can +best be considered at this time.</p> + +<p><hi rend="font-weight: bold">The Blood: where Found.</hi>—The blood +occupies and moves through a system of closed tubes, known as the blood +vessels. By means of these vessels the blood is made to circulate +through all parts of the body, but from them it does not escape under +normal conditions. Though provisions exist whereby liquid materials may +both enter and leave the blood stream, it is only when the blood vessels +are cut or broken that the blood, as blood, is able to escape from its +inclosures.</p> + +<p><hi rend="font-weight: bold">Physical Properties of the +Blood.</hi>—Experiments such as those described at the close of this +chapter reveal the more important physical properties of the blood. It +may be shown to be heavier and denser than water; to have a faint odor +and a slightly salty taste; to have a bright red color when it contains +oxygen and a dark red color when oxygen is absent; and to undergo, when +exposed to certain conditions, a change called coagulation. These +properties are all accounted for through the different materials that +enter into the formation of the blood.</p> + +<p rend="text-align: center"> +<figure url="images/image08.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 8—Blood corpuscles, highly magnified. <hi rend="font-style: italic">A.</hi> +Red corpuscles as they appear in diluted blood. <hi rend="font-style: +italic">B.</hi> Arrangement of red corpuscles in rows between which are +white corpuscles, as may be seen in undiluted blood. <hi +rend="font-style: italic">C.</hi> Red corpuscles much enlarged to show +the form.</head> +<figDesc>Fig. 8</figDesc> +</figure></p> + +<p><pb n="025" /><anchor id="Pg025" /><hi rend="font-weight: bold">Composition of the Blood.</hi>—To the +naked eye the blood appears as a thick but simple liquid; but when +examined with a compound microscope, it is seen to be complex in nature, +consisting of at least two distinct portions. One of these is a clear, +transparent liquid; while the other is made up of many small, round +bodies that float in the liquid. The liquid portion of the blood is +called the <hi rend="font-style: italic">plasma</hi>; the small bodies +are known as <hi rend="font-style: italic">corpuscles</hi>. Two +varieties of corpuscles are described—the <hi rend="font-style: +italic">red</hi> corpuscles and the <hi rend="font-style: +italic">white</hi> corpuscles (Fig. 8). Other round particles, smaller +than the corpuscles, may also be seen under favorable conditions. These +latter are known as <hi rend="font-style: italic">blood +platelets</hi>.</p> + +<p><hi rend="font-weight: bold">Red Corpuscles.</hi>—The red corpuscles +are classed as cells, although, as found in the blood of man and the +other mammals (Fig. 9), they have no nuclei.<note place="foot"><p>In +birds, reptiles, amphibians, and fishes the red corpuscles have nuclei +(Fig. 9).</p></note> Each one consists of a little mass of protoplasm, +called the <hi rend="font-style: italic">stroma</hi>, which contains a +substance having a red color, known as <hi rend="font-style: +italic">hemoglobin</hi>. The shape of the red corpuscle is that of a +circular disk with concave sides. It has a width of about 1/3200 of an +inch (7.9 microns<note place="foot"><p>The micron is the unit of +microscopical measurements. It is equal to 1/1000 of a millimeter and is +indicated by the symbol μ.</p></note>) and a thickness of<pb n="026" +/><anchor id="Pg026" /> about 1/13000 of an inch (1.9 microns). The red +corpuscles are exceedingly numerous, there being as many as five +millions in a small drop (one cubic millimeter) of healthy blood. But +the number varies somewhat and is greatly diminished during certain +forms of disease.</p> + +<p rend="text-align: center"> +<figure url="images/image09.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 9—Red corpuscles +from various animals. Those from mammals are without nuclei, while +those from birds and cold-blooded animals have nuclei.</head> +<figDesc>Fig. 9</figDesc> +</figure></p> + +<p>It is the <hi rend="font-style: italic">function</hi> of the red +corpuscles to serve as <hi rend="font-style: italic">oxygen +carriers</hi> for the cells. They take up oxygen at the lungs and +release it at the cells in the different tissues.<note +place="foot"><p>The peculiar shape of the red corpuscle has no doubt +some relation to its work. Its circular form is of advantage in getting +through the small blood vessels, while its extreme thinness brings all +of its contents very near the surface—a condition which aids the +hemoglobin in taking up oxygen. If the corpuscles were spherical in +shape, some of the hemoglobin could not, on account of the distance from +the surface, so readily unite with the oxygen.</p></note> The +performance of this function depends upon the hemoglobin.</p> + +<p><hi rend="font-weight: bold">Hemoglobin.</hi>—This substance has the +remarkable property of forming, under certain conditions, a weak +chemical union with oxygen and, when the conditions are reversed, of +separating from it. It forms<pb n="027" /><anchor id="Pg027" /> about nine tenths of the solid +matter of the red corpuscles and to it is due the colors of the blood. +When united with the oxygen it forms a compound, called <hi +rend="font-style: italic">oxyhemoglobin</hi>, which has a bright red +color; the hemoglobin alone has a dark red color. These colors are the +same as those of the blood as it takes on and gives off oxygen. The +stroma, which forms only about one tenth of the solid matter of the +corpuscles, serves as a contrivance for holding the hemoglobin. The +conditions which cause the hemoglobin to unite with oxygen in the lungs +and to separate from it in the tissues, will be considered later +(Chapter VIII).</p> + +<p><hi rend="font-weight: bold">Disappearance and Origin of Red +Corpuscles.</hi>—The red corpuscles, being cells without nuclei, are +necessarily short-lived. It has been estimated that during a period of +one to two months, all the red corpuscles in the body at a given time +will have disappeared and their places taken by new ones. The origin of +new corpuscles, however, and the manner of ridding the blood of old ones +are problems that are not as yet fully solved. The removal of the +products of broken down corpuscles is supposed to take place both in the +liver and in the spleen.<note place="foot"><p>The coloring matter of the bile consists of compounds +formed by the breaking down of the hemoglobin; the spleen contains many +large cells that seem to have the power first of "engulfing" and later +of decomposing red corpuscles. A further evidence that the spleen aids +in the removal of worn-out corpuscles is found in the fact that during +diseases that cause a destruction of the red corpuscles, such as the +different forms of malaria, the spleen becomes enlarged.</p></note></p> + +<p>Regarding the origin of the red corpuscles, the evidence now seems +conclusive that large numbers of them are formed in the red marrow of +the bones. The red marrow is located in what is known as the spongy +substance of the bones (Chapter XIV) and consists, to a large extent, of +cells somewhat like the red corpuscles, but differing from them in +having nuclei. These appear to be constantly in a state of reproduction. +The blood, flowing through the minute cavities containing these cells, +carries those that have been loosened out into the blood stream. Nuclei +appear in the red corpuscles at the time of their formation, but these +quickly separate and, according to some authorities, form the blood +platelets.</p> + +<p><hi rend="font-weight: bold">White Corpuscles.</hi>—The white +corpuscles, or <hi rend="font-style: italic">leucocytes</hi>, are cells +of a general spherical shape, each containing one, two, or more nuclei. +They are much less numerous than the red, there being on the average +only one white <pb n="028" /><anchor id="Pg028" />corpuscle to about +every five hundred of the red ones. On the other hand, the white +corpuscles are larger than the red, one of the former being equal in +volume to about three of the latter.</p> + +<p rend="text-align: center"> +<figure url="images/image10.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 10—<hi rend="font-weight: bold">Escape of white +corpuscles from a small blood vessel</hi> (Hall). At <hi +rend="font-style: italic">A</hi> the conditions are normal, but at <hi +rend="font-style: italic">B</hi> some excitation in the surrounding +tissue leads to a migration of corpuscles. 1, 2, and 3 show different +stages of the passage.</head> +<figDesc>Fig. 10</figDesc> +</figure></p> + +<p>The white corpuscles are found, when studied under favorable +conditions, to possess the power of changing their shape and, by this +means, of moving from place to place. This property enables them to +penetrate the walls of capillaries and to pass with the lymph in between +the cells of the tissues. The white corpuscles are, therefore, not +confined to the blood vessels, as are the red corpuscles, but migrate +through the intercellular spaces (Fig. 10). If any part of the body +becomes inflamed, the white corpuscles collect there in large numbers; +and, on breaking down, they form most of the white portion of the sore, +called the <hi rend="font-style: italic">pus</hi>.</p> + +<p><pb n="029" /><anchor id="Pg029" />New white corpuscles are formed +from old ones, by cell-division. Their production may occur in almost +any part of the body, but usually takes place in the lymphatic glands +(Chapter VI) and in the spleen, where conditions for their development +are especially favorable. In these places they are found in great +abundance and in various stages of development.</p> + +<p><hi rend="font-weight: bold">Functions of White Corpuscles.</hi>—The +main use of the white corpuscles appears to be that of a destroyer of +disease germs. These consist of minute organisms that find their way +into the body and, by living upon the tissues and fluids and by +depositing toxins (poisons) in them, cause different forms of disease. +Besides destroying germs that may be present in the blood, the white +corpuscles also leave the blood and attack germs that have invaded the +cells. By forming a kind of wall around any foreign substance, such as a +splinter, that has penetrated the skin, they are able to prevent the +spread of germs through the body. In a similar manner they also prevent +the germs from boils, abscesses, and sore places in general from getting +to and infecting other parts of the body.<note place="foot"><p>An infected part of the body, such as a boil or abscess, +should never be bruised or squeezed until the time of opening. Pressure +tends to break down the wall of white corpuscles and to spread the +infection. Pus from a sore contains germs and should not, on this +account, come in contact with any part of the skin. (See treatment of +skin wounds, Chapter XVI.)</p></note> +Another function ascribed +to the white corpuscles is that of aiding in the coagulation of the +blood (page 31); and still another, of aiding in the healing of +wounds.</p> + +<p><hi rend="font-weight: bold">Plasma.</hi>—The plasma is a complex +liquid, being made up of water and of substances dissolved in the water. +The dissolved substances consist mainly of foods for the cells and +wastes from the cells.</p> + +<p>1. <hi rend="font-style: italic">The foods</hi> represent the same +classes of materials as are taken in the daily fare, <hi +rend="font-style: italic">i.e.</hi>, proteids, carbohydrates,<pb n="030" /><anchor id="Pg030" /> +fats, and salts (Chapter IX). +Three kinds of proteids are found in the plasma, called <hi +rend="font-style: italic">serum albumin</hi>, <hi rend="font-style: +italic">serum globulin</hi>, and <hi rend="font-style: +italic">fibrinogen</hi>. These resemble, in a general way, the white of +raw egg, but differ from each other in the readiness with which they +coagulate. Fibrinogen coagulates more readily than the others and is the +only one that changes in the ordinary coagulation of the blood. The +others remain dissolved during this process, but are coagulated by +chemical agents and by heat. While all of the proteids probably serve as +food for the cells, the fibrinogen, in addition, is a necessary factor +in the coagulation of the blood (page 31).</p> + +<p>The only representative of the carbohydrates in the plasma is <hi +rend="font-style: italic">dextrose</hi>. This is a variety of sugar, +being derived from starch and the different sugars that are eaten. The +<hi rend="font-style: italic">fat</hi> in the plasma is in minute +quantities and appears as fine droplets—the form in which it is found in +milk. While several mineral salts are present in small quantities in the +plasma, <hi rend="font-style: italic">sodium chloride</hi>, or common +salt, is the only one found in any considerable amount. The mineral +salts serve various purposes, one of which is to cause the proteids to +dissolve in the plasma.</p> + +<p>2. <hi rend="font-style: italic">The wastes</hi> are formed at the +cells, whence they are passed by the lymph into the blood plasma. They +are carried by the blood until removed by the organs of excretion. The +two waste products found in greatest abundance in the plasma are carbon +dioxide and urea.</p> + +<p>The substances dissolved in the plasma form about 10 per cent of the +whole amount. The remaining 90 per cent is water. Practically all the +constituents of the plasma, except the wastes, enter the blood from the +digestive organs.</p> + +<p><hi rend="font-weight: bold">Purposes of Water in the Blood.</hi>—Not +only is water the<pb n="031" /><anchor id="Pg031" /> most abundant constituent of the +blood; it is, in some respects, the most important. It is the liquefying +portion of the blood, holding in solution the constituents of the plasma +and floating the corpuscles. Deprived of its water, the blood becomes a +solid substance. Through the movements of the blood the water also +serves the purpose of a transporting agent in the body. The cells in all +parts of the body require water and this is supplied to them from the +blood. Water is present in the corpuscles as well as in the plasma and +forms about 80 per cent of the entire volume of the blood.</p> + +<p><hi rend="font-weight: bold">Coagulation of the Blood.</hi>—If the +blood is exposed to some unnatural condition, such as occurs when it +escapes from the blood vessels, it undergoes a peculiar change known as +<hi rend="font-style: italic">coagulation</hi>.<note place="foot"><p>Coagulation is not confined to the blood. The white of +an egg coagulates when heated and when acted upon by certain chemicals, +and the clabbering of milk also is a coagulation.</p></note> +In this change the +corpuscles are collected into a solid mass, known as the <hi +rend="font-style: italic">clot</hi>, thereby separating from a liquid +called the <hi rend="font-style: italic">serum</hi>. The serum, which is +similar in appearance to the blood plasma, differs from that liquid in +one important respect as explained below.</p> + +<p><hi rend="font-weight: bold">Causes of Coagulation.</hi>—Although +coagulation affects all parts of the blood, only one of its constituents +is found in reality to coagulate. This is the fibrinogen. The formation +of the clot and the separation of the serum is due almost entirely to +the action of this substance. Fibrinogen is for this reason called the +<hi rend="font-style: italic">coagulable constituent of the blood</hi>. +In the plasma the fibrinogen is in a liquid form; but during coagulation +it changes into a white, stringy solid, called <hi rend="font-style: +italic">fibrin</hi>. This appears in the clot and is the cause of its +formation. Forming as a network of <pb n="032" /><anchor id="Pg032" />exceedingly fine and very delicate +threads (Fig. 11) <hi rend="font-style: italic">throughout the mass of +blood</hi> that is coagulating, the fibrin first entangles the +corpuscles and then, by contracting, draws them into the solid mass or +clot.<note place="foot"><p>If the blood be stirred or "whipped" while it is +coagulating, the clot may be broken up and the fibrin separated as fast +as it forms. The blood which then remains consists of serum and +corpuscles and will not coagulate. It is known as "defibrinated" +blood.</p></note> The contracting of the fibrin also squeezes out the serum. This +liquid contains all the constituents of the plasma except the +fibrinogen.</p> + +<p rend="text-align: center"> +<figure url="images/image11.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 11—<hi rend="font-weight: bold">Fibrin +threads</hi> (after Ranvier). These by contracting draw the corpuscles +together and form the clot.</head> +<figDesc>Fig. 11</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Fibrin Ferment and Calcium.</hi>—Most +difficult of all to answer have been the questions: What causes the +blood to coagulate outside of the blood vessels and what prevents its +coagulation inside of these vessels? The best explanation offered as yet +upon this point is as follows: Fibrinogen does not of itself change into +fibrin, but is made to undergo this change by the presence of another +substance, called <hi rend="font-style: italic">fibrin ferment</hi>. +This substance is not a regular constituent of the blood, but is formed +as occasion requires. It is supposed to result from the breaking down of +the white corpuscles, and perhaps also from the blood platelets, when +the blood is exposed to unnatural conditions. The formation of the +ferment leads in turn to the changing of the fibrinogen into fibrin.</p> + +<p>Another substance which is necessary to the process of coagulation is +the element calcium. If compounds of calcium are absent from the blood, +coagulation does not take place. These are, however, regular +constituents of healthy blood. Whether the presence of the calcium is +necessary to the formation of the ferment or to the action of the +ferment upon the fibrinogen is unknown.</p> + +<p><hi rend="font-weight: bold">Purpose of Coagulation.</hi>—The purpose +of coagulation is to check the flow of blood from wounds. The fact that +the blood is contained in and kept flowing continuously<pb n="033" /><anchor id="Pg033" /> through a system of <hi +rend="font-style: italic">connected</hi> vessels causes it to escape +rapidly from the body whenever openings in these vessels are made. Clots +form at such openings and close them up, stopping in this way the flow +that would otherwise go on indefinitely. Coagulation, however, does not +stop the flow of blood from the large vessels. From these the blood runs +with too great force for the clot to form within the wound.</p> + +<p><hi rend="font-weight: bold">Time Required for Coagulation.</hi>—The +rate at which coagulation takes place varies greatly under different +conditions. It is influenced strongly by temperature; heat hastens and +cold retards the process. It may be prevented entirely by lowering the +temperature of the blood to near the freezing point. The presence of a +foreign substance increases the rapidity of coagulation, and it has been +observed that bleeding from small wounds is more quickly checked by +covering them with linen or cotton fibers. The fibers in this case +hasten the process of coagulation.</p> + +<p><hi rend="font-weight: bold">Quantity of Blood.</hi>—The quantity of +blood is estimated to be about one thirteenth of the entire weight of +the body. This for the average individual is an amount weighing nearly +twelve pounds and having a volume of nearly one and one half gallons. +About 46 per cent by volume of this amount is made up of corpuscles and +54 per cent of plasma. Of the plasma about 10 per cent consists of +solids and 90 per cent of water, as already stated.</p> + +<p><hi rend="font-weight: bold">Functions of the Blood.</hi>—The blood +is the great carrying, or distributing, agent in the body. Through its +movements (considered in the next chapter) it carries food and oxygen to +the cells and waste materials from the cells. Much of the blood may, +therefore, be regarded as <hi rend="font-style: italic">freight</hi> in +the process of transportation. The blood also carries, or distributes, +heat. Taking up heat in the warm parts of the body, it gives it off at +places having a lower temperature. This enables all parts of the body to +keep at about the same temperature.</p> + +<p>In addition to serving as a carrier, the blood has antiseptic +properties, i.e., it destroys disease germs. While <pb n="034" /><anchor +id="Pg034" /> this function is mainly due to the white corpuscles, it is +due in part to the plasma.<note place="foot"><p>Certain substances, called <hi rend="font-style: +italic">opsonins</hi>, have recently been shown to exist in the plasma, +that aid the white corpuscles in their work of destroying germs. The +opsonins appear to act in such a manner as to weaken the germs and make +them more susceptible to the attacks of the white corpuscles.</p></note> Through its coagulation, the blood also +closes leaks in the small blood vessels. The blood is thus seen to be a +liquid of several functions.</p> + +<p rend="text-align: center"> +<figure url="images/image12.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 12—<hi rend="font-weight: bold">A balanced +change</hi> in water. The level remains constant although the water is +continually changing; suggestive of the changes in the blood.</head> +<figDesc>Fig. 12</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Changes in the Blood.</hi>—In performing +its functions in the body the blood must of necessity undergo rapid and +continuous change. The red corpuscles, whose changes have already been +noted, appear to be the most enduring constituents of the blood. The +plasma is the portion that changes most rapidly. Yet in spite of these +changes the quantity and character of the blood remain practically +constant.<note place="foot"><p>Some of the changes in the blood are very closely +related to our everyday habits and inclinations. For example, a lack of +nourishment in the blood causes hunger and this leads to the taking of +food. If the fluids of the body become too dense, a feeling of thirst is +aroused which prompts one to drink water.</p></note> This is because there is a <hi rend="font-style: +italic">balancing</hi> of the forces that bring about the changes. The +addition of various materials to the blood just equals the withdrawal of +the same materials from the blood. Somewhat as a vessel of water (Fig. +12) having an inflow and an outflow which are equal in amount may keep +always at the same level, the balancing of the intake and outgo of the +blood keeps its composition about the same from time to time.</p> + +<p><hi rend="font-weight: bold">Hygiene of the Blood.</hi>—The blood, +being a changeable liquid, is easily affected through our habits of +living. Since it may be affected for ill as well as for good, one<pb n="035" /><anchor +id="Pg035" /> should cultivate those habits that are beneficial and +avoid those that are harmful in their effects. Most of the hygiene of +the blood, however, is properly included in the hygiene of the organs +that act upon the blood—a fact which makes it unnecessary to treat this +subject fully at this time.</p> + +<p>From a health standpoint, the most important constituents of the +blood are, perhaps, the corpuscles. These are usually sufficient in +number and vigor in the blood of those who take plenty of physical +exercise, accustom themselves to outdoor air and sunlight, sleep +sufficiently, and avoid the use of injurious drugs. On the other hand, +they are deficient in quantity and inferior in quality in the bodies of +those who pursue an opposite course. Impurities not infrequently find +their way into the blood through the digestive organs. One should eat +wholesome, well-cooked food, drink freely of <hi rend="font-style: +italic">pure</hi> water, and limit the quantity of food <hi +rend="font-style: italic">to what can be properly digested</hi>. The +natural purifiers of the blood are the organs of excretion. The skin is +one of these and its power to throw off impurities depends upon its +being clean and active.</p> + +<p><hi rend="font-weight: bold">Effect of Drugs.</hi>—Certain drugs and +medicines, including alcohol and quinine,<note place="foot"><p>Metchnikoff, <hi rend="font-style: italic">The New +Hygiene</hi>.</p></note> have recently been shown to +destroy the white corpuscles. The effect of such substances, if +introduced in considerable amount in the body, is to render one less +able to withstand attacks of disease. Many patent medicines are widely +advertised for purifying the blood. While these may possibly do good in +particular cases, the habit of doctoring one's self with them is open to +serious objection. Instead of taking drugs and patent medicines for +purifying the blood, one should study to live more hygienically. We may +safely rely upon<pb n="036" /><anchor id="Pg036" /> wholesome food, pure water, +outdoor exercise and sunlight, plenty of sleep, and a clean skin for +keeping the blood in good condition. If these natural remedies fail, a +physician should be consulted.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The blood is the carrying +or transporting agent of the body. It consists in part of constituents, +such as the red corpuscles, that enable it to carry different +substances; and in part of the materials that are being carried. The +latter, which include food and oxygen for the cells and wastes from the +cells, may be classed as freight. Certain constituents in the blood +destroy disease germs, and other constituents, by coagulating, close +small leaks in the blood vessels. Although subject to rapid and +continuous change, the blood is able—by reason of the balancing of +materials added to and withdrawn from it—to remain about the same in +quantity and composition.</p> + +<p>Exercises.—1. Compare blood and water with reference to weight, +density, color, odor, and complexity of composition.</p> + +<p>2. Show by an outline the different constituents of the blood.</p> + +<p>3. Compare the red and white corpuscles with reference to size, +shape, number, origin, and function.</p> + +<p>4. Name some use or purpose for each constituent of the blood.</p> + +<p>5. What constituents of the blood may be regarded as freight and what +as agents for carrying this freight?</p> + +<p>6. After coagulation, what portions of the blood are found in the +clot? What portions are found in the serum?</p> + +<p>7. What purposes are served by water in the blood?</p> + +<p>8. Show how the blood, though constantly changing, is kept about the +same in quantity, density, and composition.</p> + +<p>9. In the lungs the blood changes from a dark to a bright red color +and in the tissues it changes back to dark red. What is the cause of +these changes?</p> + +<p>10. If the oxygen and hemoglobin formed a strong instead of a weak +chemical union, could the hemoglobin then act as an oxygen carrier? Why?</p> + +<p><pb n="037" /><anchor id="Pg037" />11. What habits of living favor the +development of corpuscles in the blood?</p> + +<p>12. Why will keeping the skin clean and active improve the quality of +one's blood?</p> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">To demonstrate the Physical Properties +of Blood</hi> (Optional).—Since blood is needed in considerable quantity +in the following experiments, it is best obtained from the butcher. To +be sure of securing the blood in the manner desired, take to the butcher +three good-sized bottles bearing labels as follows:</p> + +<p><hi rend="font-weight: bold">1</hi> Fill two thirds full. While the +blood is cooling, stir rapidly with the hand or a bunch of switches to +remove the clot.</p> + +<p><hi rend="font-weight: bold">2</hi> Fill two thirds full and set +aside without shaking or stirring.</p> + +<p><hi rend="font-weight: bold">3</hi> Fill two thirds full and +thoroughly mix with the liquid in the bottle.</p> + +<p>Label 3 must be pasted on a bottle, having a tight-fitting stopper, +which is filled one fifth full of a saturated solution of Epsom salts. +The purpose of the salts is to prevent coagulation until the blood is +diluted with water as in the experiments which follow.</p> + +<p><hi rend="font-weight: bold">Experiments.</hi>—1. Let some of the +defibrinated blood (bottle 1) flow (not fall) on the surface of water in +a glass vessel. Does it remain on the surface or sink to the bottom? +What does the experiment show with reference to the relative weight of +blood and water?</p> + +<p>2. Fill a large test tube or a small bottle one fourth full of the +defibrinated blood and thin it by adding an equal amount of water. Then +place the hand over the mouth and shake until the blood is thoroughly +mixed with the air. Compare with a portion of the blood not mixed with +the air, noting any difference in color. What substance in the air has +acted on the blood to change its color?</p> + +<p>3. Fill three tumblers each two thirds full of water and set them in +a warm place. Pour into one of the tumblers, and thoroughly mix with the +water, two tablespoonfuls of the blood containing the Epsom salts. After +an interval of half an hour add blood to the second tumbler in the<pb +n="038" /><anchor id="Pg038" /> same manner, and after another half hour +add blood to the third. The water dilutes the salts so that coagulation +is no longer prevented. Jar the vessel occasionally as coagulation +proceeds; and if the clot is slow in forming, add a trace of some salt +of calcium (calcium chloride). After the blood has been added to the +last tumbler make a comparative study of all. Note that coagulation +begins in all parts of the liquid at the same time and that, as the +process goes on, the clot shrinks and is drawn toward the center.</p> + +<p>4. Place a clot from one of the tumblers in experiment 3 in a large +vessel of water. Thoroughly wash, adding fresh water, until a white, +stringy solid remains. This substance is fibrin.</p> + +<p>5. Examine the coagulated blood obtained from the butcher (bottle 2). +Observe the dark central mass (the clot) surrounded by a clear liquid +(the serum). Sketch the vessel and its contents, showing and naming the +parts into which the blood separates by coagulation.</p> + +<p><hi rend="font-weight: bold">To examine the Red +Corpuscles.</hi>—Blood for this purpose is easily obtained from the +finger. With a handkerchief, wrap one of the fingers of the left hand +from the knuckle down to the first joint. Bend this joint and give it a +sharp prick with the point of a sterilized 'needle just above the root +of the nail. Pressure applied to the under side of the finger will force +plenty of blood through a very small opening. (To prevent any +possibility of blood poisoning the needle should be sterilized. This may +be done by dipping it in alcohol or by holding it for an instant in a +hot flame. It is well also to wash the finger with soap and water, or +with alcohol, before the operation.) Place a small drop of the blood in +the middle of a glass slide, protect the same with a cover glass, and +examine with a compound microscope. At least two specimens should be +examined, one of which should be diluted with a little saliva or a +physiological salt solution.<note place="foot"><p>A physiological salt solution is prepared by dissolving +.6 of a gram of common salt in 100 cc. of distilled water or pure +cistern water. This solution, having the same density as the plasma of +the blood, does not act injuriously upon the corpuscles.</p></note> In the diluted specimen the red +corpuscles appear as amber-colored, circular, disk-shaped bodies. In the +undiluted specimen they show a decided tendency to arrange themselves in +rows, resembling rows of coins. (Singly, the corpuscles do not appear +red when highly magnified.)</p> + +<p>A few white corpuscles may generally be found among the red ones in +the undiluted specimen. These become separated by the formation<pb +n="039" /><anchor id="Pg039" /> of the red corpuscles into rows. They +are easily recognized by their larger size and by their silvery +appearance, due to the light shining through them.</p> + +<p><hi rend="font-weight: bold">To examine White Corpuscles.</hi>—Obtain +from the butcher a small piece of the neck sweetbread of a calf. Press +it between the fingers to squeeze out a whitish, semi-liquid substance. +Dilute with physiological salt solution on a glass slide and examine +with a compound microscope. Numerous white corpuscles of different kinds +and sizes will be found. Make sketches.</p> + +<p><hi rend="font-weight: bold">To prepare Models of Red +Corpuscles.</hi>—Several models of red corpuscles should be prepared for +the use of the class. Clay and putty may be pressed into the form of red +corpuscles and allowed to harden, and small models may be cut out of +blackboard crayon. Excellent models can be molded from plaster of Paris +as follows: Coat the inside of the lid of a baking powder can with oil +or vaseline and fill it even full of a thick mixture of plaster of Paris +and water. After the plaster has set, remove it from the lid and with a +pocket-knife round off the edges and hollow out the sides until the +general form of the corpuscle is obtained. The models may be colored red +if it is desired to match the color as well as the form of the +corpuscle.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="040" /><anchor id="Pg040" /> +<head>CHAPTER V - THE CIRCULATION</head> + +<p>A Carrier must move. To enable the blood to carry food and oxygen <hi +rend="font-style: italic">to</hi> the cells and waste materials <hi +rend="font-style: italic">from</hi> the cells, and also to distribute +heat, it is necessary to keep it moving, or circulating, in all parts of +the body. So closely related to the welfare of the body is the +circulation<note place="foot"><p>The term "circulation" literally means moving in a +circle. While the blood does not move through the body in a circle, the +term is justified by the fact that the blood flows out continually from +a single point, the heart, and to this point is continually +returning.</p></note> of the blood, that its stoppage for only a brief interval +of time results in death.</p> + +<p><hi rend="font-weight: bold">Discovery of the Circulation.</hi>—The +discovery of the circulation of the blood was made about 1616 by an +English physician named Harvey. In 1619 he announced it in his public +lectures and in 1628 he published a treatise in Latin on the +circulation. The chief arguments advanced in support of his views were +the presence of valves in the heart and veins, the continuous movement +of the blood in the same direction through the blood vessels, and the +fact that the blood comes from a cut artery in jets, or spurts, that +correspond to the contractions of the heart.</p> + +<p>No other single discovery with reference to the human body has proved +of such great importance. A knowledge of the nature and purpose of the +circulation was the necessary first step in understanding the plan of +the body and the method of maintaining life, and physiology as a science +dates from the time of Harvey's discovery.</p> + +<p><hi rend="font-weight: bold">Organs of Circulation.</hi>—The organs +of circulation, or blood vessels, are of four kinds, named the heart, +the arteries, the capillaries, and the veins. They serve as <pb n="041" /><anchor id="Pg041" />contrivances +both for holding the +blood and for keeping it in motion through the body. The heart, which is +the chief organ for propelling the blood, acts as a force pump, while +the arteries and veins serve as tubes for conveying the blood from place +to place. Moreover, the blood vessels are so connected that the blood +moves through them in a regular order, performing two well-defined +circuits.</p> + +<p rend="text-align: center"> +<figure url="images/image13.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 13—<hi rend="font-weight: bold">Heart</hi> in +position in thoracic cavity. Dotted lines show positin of diaphragm and +of margins of lungs.</head> +<figDesc>Fig. 13</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Heart.</hi>—The human heart, roughly +speaking, is about the size of the clenched fist of the individual +owner. It is situated very near the center of the thoracic cavity and is +almost completely surrounded by the lungs. It is cone-shaped and is so +suspended that the small end hangs downward, forward, and a little to +the left. When from excitement, or other cause, one becomes conscious of +the movements of the heart, these appear to be in the left portion of +the chest, a fact which accounts for the erroneous impression that the +heart is on the left side. The position of the heart in the cavity of +the chest is shown in Fig. 13.</p> + +<p><hi rend="font-weight: bold">The Pericardium.</hi>—Surrounding the +heart is a protective covering, called the pericardium. This consists of +a closed membranous sac so arranged as to form a double covering around +the heart. The heart does not lie inside<pb n="042" /><anchor id="Pg042" /> of the pericardial sac, as seems +at first glance to be the case, but its relation to this space is like +that of the hand to the inside of an empty sack which is laid around it +(Fig. 14). The inner layer of the pericardium is closely attached to the +heart muscle, forming for it an outside covering. The outer layer hangs +loosely around the heart and is continuous with the inner layer at the +top. The outer layer also connects at certain places with the membranes +surrounding the lungs and is attached below to the diaphragm. Between +the two layers of the pericardium is secreted a liquid which prevents +friction from the movements of the heart.</p> + +<p rend="text-align: center"> +<figure url="images/image14.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 14—<hi rend="font-weight: bold">Diagram of +section of the pericardial sac</hi>, heart removed. <hi +rend="font-style: italic">A.</hi> Place occupied by the heart. <hi +rend="font-style: italic">B.</hi> Space inside of pericardial sac. <hi +rend="font-style: italic">a.</hi> Inner layer of pericardium and outer +lining of heart. <hi rend="font-style: italic">b.</hi> Outer layer of +pericardium. <hi rend="font-style: italic">C.</hi> Covering of lung. <hi +rend="font-style: italic">D.</hi> Diaphragm.</head> +<figDesc>Fig. 14</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Cavities of the Heart.</hi>—The heart is +a hollow, muscular organ which has its interior divided by partitions +into four distinct cavities. The main partition extends from top to +bottom and divides the heart into two similar portions, named from their +positions the right side and the left side. On each side are two +cavities, the one being directly above the other. The upper cavities are +called <hi rend="font-style: italic">auricles</hi> and the lower ones +<hi rend="font-style: italic">ventricles</hi>. To distinguish these +cavities further, they are named from their positions the right auricle +and the left auricle, and the right ventricle and the left ventricle +(Fig. 15). The auricles on each side communicate with the ventricles +below; but after birth there is no communication between the cavities on +the opposite sides of the heart. All the cavities of the heart are lined +with a smooth, delicate membrane, called the <hi rend="font-style: +italic">endocardium</hi>.</p> + +<p rend="text-align: center"> +<figure url="images/image15.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 15—<hi rend="font-weight: bold">Diagram showing +plan of the heart.</hi> 1. Semilunar valves. 2. Tricuspid valve. 3. +Mitral valve. 4. Right auricle. 5. Left auricle. 6. Right ventricle. 7. +Left ventricle. 8. Chordæ tendineæ. 9. Inferior vena cava. 10. Superior +vena cava. 11. Pulmonary artery. 12. Aorta. 13. Pulmonary veins.</head> +<figDesc>Fig. 15</figDesc> +</figure></p> + +<p><pb n="043" /><anchor id="Pg043" /><hi rend="font-weight: bold">Valves of the Heart.</hi>—Located at +suitable places in the heart are four gate-like contrivances, called +valves. The purpose of these is <hi rend="font-style: italic">to give +the blood a definite direction</hi> in its movements. They consist of +tough, inelastic sheets of connective tissue, and are so placed that +pressure on one side causes them to come together and shut up the +passageway, while pressure on the opposite side causes them to open. A +valve is found at the opening of each auricle into the ventricle, and at +the opening of each ventricle into the artery with which it is +connected.</p> + +<p>The valve between the right auricle and the right ventricle is called +the <hi rend="font-style: italic">tricuspid</hi> valve. It is suspended +from a thin ring of connective tissue which surrounds the opening, and +its free margins extend into the ventricle (Fig. 16). It consists of +three parts, as its name implies, which are thrown together in closing +the opening. Joined to the free edges of this valve are many small, +tendinous cords which connect at their lower ends with muscular pillars +in the walls of the ventricle. These are known as the <hi +rend="font-style: italic">chordæ tendineæ</hi>, or heart tendons. Their +purpose is to serve as <hi rend="font-style: italic">valve stops</hi>, +to prevent the valve from being thrown, by the force of the blood +stream, back into the auricle.</p> + +<p>The <hi rend="font-style: italic">mitral</hi>, or bicuspid, valve is +suspended around the opening between the left auricle and the left +ventricle,<pb n="044" /><anchor id="Pg044" /> with the free margins +extending into the ventricle. It is exactly similar in structure and +arrangement to the tricuspid valve, except that it is stronger and is +composed of two parts instead of three.</p> + +<p rend="text-align: center"> +<figure url="images/image16.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 16—<hi rend="font-weight: bold">Right side of +heart</hi> dissected to show cavities and valves. <hi rend="font-style: +italic">B.</hi> Right semilunar valve. The tricuspid valve and the +chordæ tendineæ shown in the ventricle.</head> +<figDesc>Fig. 16</figDesc> +</figure></p> + +<p>The <hi rend="font-style: italic">right semilunar</hi> valve is +situated around the opening of the right ventricle into the pulmonary +artery. It consists of three pocket-shaped strips of connective tissue +which hang loosely from the walls when there is no pressure from above; +but upon receiving pressure, the pockets fill and project into the +opening, closing it completely (Fig. 16). The <hi rend="font-style: +italic">left semilunar</hi> valve is around the opening of the left +ventricle into the aorta, and is similar in all respects to the right +semilunar valve.</p> + +<p><hi rend="font-weight: bold">Differences in the Parts of the +Heart.</hi>—Marked differences are found in the walls surrounding the +different cavities of the heart. The walls of the ventricles are much +thicker and stronger than those of the auricles, while the walls of the +left ventricle are two or three times thicker than those of the right. A +less marked but similar difference exists between the auricles and also +between the valves on the two sides of the heart. These differences in +structure are all accounted for by the work done by the different +portions of the heart. The greater the work, the heavier the structures +that perform the work.</p> + +<p rend="text-align: center"> +<figure url="images/image17.png" rend="page-float: 'hp'; text-align: center; w35"> +<head><lb />Fig. 17—<hi rend="font-weight: bold">Diagram of the circulation</hi>, showing in +general the work done by each part of the heart. The right ventricle +forces the blood through the lungs and into the left auricle. The left +ventricle forces blood through all parts of the body and back to the +auricle. The auricles force blood into the ventricles.</head> +<figDesc>Fig. 17</figDesc> +</figure></p> + +<p><pb n="045" /><anchor id="Pg045" /><hi rend="font-weight: bold">Connection with Arteries and +Veins.</hi>—Though the heart is in communication with all parts of the +circulatory system, it makes actual connection with only a few of the +blood tubes. These enter the heart at its upper portion (Fig. 15), but +connect with its different cavities as follows:</p> + +<p>1. <hi rend="font-style: italic">With the right auricle</hi>, the +superior and the inferior venæ cavæ and the coronary veins. The superior +vena cava receives blood from the head and the upper extremities; the +inferior vena cava, from the trunk and the lower extremities; and the +coronary veins, from the heart itself.</p> + +<p>2. <hi rend="font-style: italic">With the left auricle</hi>, the four +pulmonary veins. These receive blood from the lungs and empty it into +the left auricle.</p> + +<p>3. <hi rend="font-style: italic">With the right ventricle</hi>, the +pulmonary artery. This receives blood from the heart and by its branches +distributes it to all parts of the lungs.</p> + +<p>4. <hi rend="font-style: italic">With the left ventricle</hi>, the +aorta. The aorta receives blood from the heart and through its branches +delivers it to all parts of the body.</p> + +<p><hi rend="font-weight: bold">How the Heart does its Work.</hi>—The +heart is a muscular pump<note place="foot"><p>The heart at first glance seems to bear little +resemblance to the pumps in common use. When it is remembered, however, +that any contrivance which moves a fluid by varying the size of a cavity is a pump, +it is seen that not only the heart, but the chest in breathing and also +the mouth in sucking a liquid through a tube, are pumps in principle. +The ordinary syringe bulb illustrates the class of pumps to which the +heart belongs. (See Practical Work.)</p></note> and does its work through the contracting +and<pb n="046" /><anchor id="Pg046" /> relaxing of its walls. During +contraction the cavities are closed and the blood is forced out of them. +During relaxation the cavities open and are refilled. The valves direct +the flow of the blood, being so arranged as to keep it moving always in +the same direction (Fig. 17).</p> + +<p>The heart, however, is not a single or a simple pump, but consists in +reality of <hi rend="font-style: italic">four</hi> pumps which +correspond to its different cavities. These connect with each other and +with the blood vessels over the body in such a manner that each aids in +the general movement of the blood.</p> + +<p rend="text-align: center"> +<figure url="images/image18.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 18—Diagram illustrating the "cardiac +cycle."</head> +<figDesc>Fig. 18</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Work of Auricles and Ventricles +Compared.</hi>—In the work of the heart the two auricles contract at the +same time—their contraction being followed immediately by the +contraction of both ventricles. After the contraction of the ventricles +comes a period of rest, or relaxation, about equal in time to the period +of contraction of both the auricles and the ventricles.<note place="foot"><p>The contraction of the heart is known as the <hi +rend="font-style: italic">systole</hi> and its relaxation as the <hi +rend="font-style: italic">diastole</hi>. The systole plus the diastole +forms the so-called "cardiac cycle" (Fig. 18). This consists of (1) the +contraction of the auricles, (2) the contraction of the ventricles, and +(3) the period of rest. The heart systole includes the contraction of +both the auricles and the ventricles.</p></note> On account of +the work which they perform, the auricles have been called the "feed +pumps" of the heart; and the ventricles, the "force pumps."<note place="foot"><p>Martin, <hi rend="font-style: italic">The Human +Body</hi>.</p></note> It is the +function of the auricles to collect the blood from the veins, to let +this run slowly into the ventricles when both the<pb n="047" /><anchor id="Pg047" /> auricles and ventricles are +relaxed, and finally, by contracting, <hi rend="font-style: italic">to +force an excess of blood into the ventricles</hi>, thereby distending +their walls. The ventricles, having in this way been fully charged by +the auricles, now contract and force their contents into the large +arteries.</p> + +<p><hi rend="font-weight: bold">Sounds of the Heart.</hi>—Two distinct +sounds are given out by the heart as it pumps the blood. One of them is +a dull and rather heavy sound, while the other is a short, sharp sound. +The short sound follows quickly after the dull sound and the two are +fairly imitated by the words "lūbb, dŭp." While the cause of the +first sound is not fully understood, most authorities believe it to be +due to the contraction of the heart muscle and the sudden tension on the +valve flaps. The second sound is due to the closing of the semilunar +valves. These sounds are easily heard by placing an ear against the +chest wall. They are of great value to the physician in determining the +condition of the heart.</p> + +<p><hi rend="font-weight: bold">Arteries and Veins.</hi>—These form two +systems of tubes which reach from the heart to all parts of the body. +The arteries receive blood from the heart and distribute it to the +capillaries. The veins receive the blood from the capillaries and return +it to the heart. The arteries and veins are similar in structure, both +having the form of tubes and both having three distinct layers, or +coats, in their walls. The corresponding coats in the arteries and veins +are made up of similar materials, as follows:</p> + +<p>1. <hi rend="font-style: italic">The inner coat</hi> consists of a +delicate lining of flat cells resting upon a thin layer of connective +tissue. The inner coat is continuous with the lining of the heart and +provides a smooth surface over which the blood glides with little +friction.</p> + +<p>2. <hi rend="font-style: italic">The middle coat</hi> consists mainly +of non-striated, or involuntary, muscular fibers. This coat is quite +thin in the veins, but in the arteries it is rather thick and +strong.</p> + +<p>3. <hi rend="font-style: italic">The outer coat</hi> is made up of a +variety of connective<pb n="048" /><anchor id="Pg048" /> tissue and is also much thicker +and stronger in the arteries than in the veins.</p> + +<p rend="text-align: center"> +<figure url="images/image19.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 19—Artery dissected to show the coats.</head> +<figDesc>Fig. 19</figDesc> +</figure></p> + +<p>Marked differences exist between the arteries and the veins, and +these vessels are readily distinguished from each other. The walls of +the arteries are much thicker and heavier than those of the veins (Fig. +19). As a result these tubes stand open when empty, whereas the veins +collapse. The arteries also are highly elastic, while the veins are but +slightly elastic. On the other hand, many of the veins contain valves, +formed by folds in the inner coat (Fig. 20), while the arteries have no +valves. The blood flows more rapidly through the arteries than through +the veins, the difference being due to the fact that the system of veins +has a greater capacity than the system of arteries.</p> + +<p rend="text-align: center"> +<figure url="images/image20.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 20—Vein split open to show the valves.</head> +<figDesc>Fig. 20</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Why the Arteries are Elastic.</hi>—The +elasticity of the arteries serves a twofold purpose. It keeps the +arteries from bursting when the blood is forced into them from the +ventricles, and it is a means of <hi rend="font-style: italic">supplying +pressure to the blood while the ventricles are in a condition of +relaxation.</hi> The latter purpose is accomplished as follows:</p> + +<p>Contraction of the ventricles fills the arteries overfull, causing +them to swell out and make room for the excess of blood. Then while the +ventricles are resting and filling, the stretched arteries press upon +the blood to keep it<pb n="049" /><anchor id="Pg049" /> flowing into +the capillaries. In this way <hi rend="font-style: italic">they cause +the intermittent flow from, the heart to become a steady stream in the +capillaries</hi>.</p> + +<p>The swelling of the arteries at each contraction of the ventricle is +easily felt at certain places in the body, such as the wrist. This +expansion, known as the "pulse," is the chief means employed by the +physician in determining the force and rapidity of the heart's +action.</p> + +<p><hi rend="font-weight: bold">Purpose of the Valves in the +Veins.</hi>—The valves in the veins are not used for directing the <hi +rend="font-style: italic">general</hi> flow of the blood, the valves of +the heart being sufficient for this purpose. Their presence is necessary +because of the pressure to which the veins are subjected in different +parts of the body. The contraction of a muscle will, for example, close +the small veins in its vicinity and diminish the capacity of the larger +ones. The natural tendency of such pressure is to empty the veins in two +directions—one in the same direction as the regular movement of the +blood, but the other in the opposite direction. The valves by closing +cause the contracting muscle to push the blood in one direction +only—toward the heart. The valves in the veins are, therefore, an +economical device for <hi rend="font-style: italic">enabling variable +pressure</hi> in different parts of the body <hi rend="font-style: +italic">to assist in the circulation</hi>. Veins like the inferior vena +cava and the veins of the brain, which are not compressed by movements +of the body, do not have valves.</p> + +<p><hi rend="font-weight: bold">Purposes of the Muscular Coat.</hi>—The +muscular coat, which is thicker in the arteries than in the veins and is +more marked in small arteries than in large ones, serves two important +purposes. In the first place it, together with the elastic tissue, keeps +the capacity of the blood vessels <hi rend="font-style: italic">equal to +the volume of the blood</hi>. Since the blood vessels are capable of +holding more blood than may be<pb n="050" /><anchor id="Pg050" /> present at a given time in the +body, there is a liability of empty spaces occurring in these tubes. +Such spaces would seriously interfere with the circulation, since the +heart pressure could not then reach all parts of the blood stream. This +is prevented by the contracted state, or "tone," of the blood vessels, +due to the muscular coat.</p> + +<p>In the second place, the muscular coat serves the purpose of <hi +rend="font-style: italic">regulating</hi> the amount of blood which any +given organ or part of the body receives. This it does by varying the +caliber of the arteries going to the organ in question. To increase the +blood supply, the muscular coat relaxes. The arteries are then dilated +by the blood pressure from within so as to let through a larger quantity +of blood. To diminish the supply, the muscle contracts, making the +caliber of the arteries less, so that less blood can flow to this part +of the body. Since the need of organs for blood varies with their +activity, the muscular coat serves in this way a very necessary +purpose.</p> + +<p rend="text-align: center"> +<figure url="images/image21.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 21—Diagram of network of capillaries between a +very small artery and a very small vein. Shading indicates the change of +color of the blood as it passes through the capillaries. <hi +rend="font-style: italic">S.</hi> Places between capillaries occupied by +the cells.</head> +<figDesc>Fig. 21</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Capillaries.</hi>—The capillaries +consist of a network of minute blood vessels which connect the +terminations of the smallest arteries with the beginnings of the +smallest veins (Fig. 21). They have an average diameter of less than one +two-thousandth of an inch (12 µ) and an average length of less than one +twenty-fifth of an inch (1 millimeter). Their walls consist of a single +<pb n="051" /><anchor id="Pg051" /> coat which is continuous with the +lining of the arteries and veins. This coat is formed of a single layer +of thin, flat cells placed edge to edge (Fig. 22). With a few +exceptions, the capillaries are found in great abundance in all parts of +the body.</p> + +<p rend="text-align: center"> +<figure url="images/image22.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 22—<hi rend="font-weight: bold">Surface of +capillary</hi> highly magnified, showing its coat of thin cells placed +edge to edge.</head> +<figDesc>Fig. 22</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Functions of the Capillaries.</hi>—On +account of the thinness of their walls, the capillaries are able to +serve a twofold purpose in the body:</p> + +<p>1. They admit materials into the blood vessels.</p> + +<p>2. They allow materials to pass from the blood vessels to the +surrounding tissues.</p> + +<p>When it is remembered that the blood, as blood, does not escape from +the blood vessels under normal conditions, the importance of the work of +the capillaries is apparent. To serve its purpose as a carrier, there +must be places where the blood can load up with the materials which it +is to carry, and places also where these can be unloaded. Such places +are supplied by the capillaries.</p> + +<p>The capillaries also serve the purpose of spreading the blood out and +of bringing it very near the individual cells in all parts of the body +(Fig. 21).</p> + +<p><hi rend="font-weight: bold">Functions of Arteries and +Veins.</hi>—While the capillaries provide the means whereby materials +may both enter and leave the blood, the arteries and veins serve the +general purpose of passing the blood from one set of capillaries to +another. Since pressure is necessary for moving the blood, these tubes +must connect with the source of the pressure, which is the heart. In the +arteries and veins the blood neither receives nor gives up material, but +having received or given up material at one set of capillaries, it is +then pushed through these tubes to where it can serve a similar purpose +in another set of capillaries (Fig. 23).</p> + +<p><hi rend="font-weight: bold">Divisions of the Circulation.</hi>—Man, +in common with all warm-blooded animals, has a double circulation, a +fact<pb n="052" /><anchor id="Pg052" /> which explains the double +structure of his heart. The two divisions are known as the <hi +rend="font-style: italic">pulmonary</hi> and the <hi rend="font-style: +italic">systemic</hi> circulations. By the former the blood passes from +the right ventricle through the lungs, and is then returned to the left +auricle; by the latter it passes from the left ventricle through all +parts of the body, returning to the right auricle.</p> + +<p>The general plan of the circulation is indicated in Fig. 23. All the +blood flows continuously through both circulations and passes the +various parts in the following order: right auricle, tricuspid valve, +right ventricle, right semilunar valve, pulmonary artery and its +branches, capillaries of the lungs, pulmonary veins, left auricle, +mitral valve, left ventricle, left semilunar valve, aorta and its +branches, systemic capillaries, the smaller veins, superior and inferior +venæ cavæ, and then again into the right auricle.</p> + +<p>In the pulmonary capillaries the blood gives up carbon dioxide and +receives oxygen, changing from a dark red to a bright red color. In the +systemic capillaries it gives up oxygen, receives carbon dioxide and +other impurities, and changes back to a dark red color.</p> + +<p>In addition to the two main divisions of the circulation, special +circuits are found in various places. Such a circuit in the liver is +called the <hi rend="font-style: italic">portal</hi> circulation, and +another in the kidneys is termed the <hi rend="font-style: +italic">renal</hi> circulation. To some extent the blood supply to the +walls of the heart is also outside of the general movement; it is called +the <hi rend="font-style: italic">coronary</hi> circulation.</p> + +<p rend="text-align: center"> +<figure url="images/image23.png" rend="page-float: 'hp'; text-align: center; w75"> +<head><lb />Fig. 23—<hi rend="font-weight: bold">General scheme of the +circulation</hi>, showing places where the blood takes on and gives off +materials. 1. Body in general. 2. Lungs. 3. Kidneys. 4. Liver. 5. Organs +of digestion. 6. Lymph ducts. 7. Pulmonary artery. 8. Aorta.</head> +<figDesc>Fig. 23</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Blood Pressure and Velocity.</hi>—The +blood, in obedience to physical laws, passes continuously through the +blood vessels, moving always from a place of greater to one of less +pressure. Through the contraction of the ventricles, a relatively high +pressure is maintained in the arteries nearest the heart.<note +place="foot"><p>The pressure maintained by the left ventricle has been +estimated to be nearly three and one half pounds to the square inch—a +pressure sufficient to sustain a column of water eight feet high. The +pressure maintained by the right ventricle is about one third as great. +In maintaining this pressure the heart does a work equal to about one +two-hundredth of a horse power.</p></note> This pressure diminishes +rapidly in the<pb n="054" /><anchor id="Pg054" /> small arteries, +becomes comparatively slight in the capillaries, and falls practically +to nothing in the veins. Near the heart in the superior and inferior +venæ cavæ, the pressure at intervals is said to be <hi rend="font-style: +italic">negative</hi>. This means that the blood from these veins is +actually drawn into the right auricle by the expansion of the chest +walls in breathing.<note place="foot"><p>The location of the heart in +the thoracic cavity causes movements of the chest walls to draw blood +into the right auricle for the same reason that they "draw" air into the +lungs.</p></note></p> + +<p>The velocity of the blood is greatest in the arteries, less in the +veins, and <hi rend="font-style: italic">much</hi> less in the +capillaries than in either the arteries or the veins. The slower flow of +the blood through the capillaries is accounted for by the fact that +their united area is many times greater than that of the arteries which +supply, or the veins which relieve, them. This allows the same quantity +of blood, flowing through them in a given time, a wider channel and +causes it to move more slowly. The time required for a complete +circulation is less than one minute.</p> + +<p><hi rend="font-weight: bold">Summary of Causes of Circulation.</hi>—The +chief factor in the circulation of the blood is, of course, the +heart. The ventricles keep a pressure on the blood which is sufficient +to force it through all the blood tubes and back to the auricles. The +heart is aided in its work by the elasticity of the arteries, which +keeps the blood under pressure while the ventricles are in a state of +relaxation. It is also aided by the muscles and elastic tissue in all of +the blood vessels. These, by keeping the blood vessels in a state of +"tone," or so contracted that their capacity just equals the volume of +the blood, enable pressure from the heart to be transmitted to all parts +of the blood stream. A further aid to the circulation is found in the +valves in the veins, which enable muscular contraction within the body, +and variable pressure upon its surface, to drive the blood toward the +heart. The heart is also aided to some extent by the movements of the +chest walls in breathing. The organs Of circulation are under the +control of the nervous system (Chapter XVIII).</p> + +<div> +<pb n="055" /><anchor id="Pg055" /> +<head>HYGIENE OF THE CIRCULATION</head> + +<p><hi rend="font-weight: bold">Care of the Heart.</hi>—The heart, +consisting largely of muscle, is subject to the laws of muscular +exercise. It may be injured by over-exertion, but is strengthened by a +moderate increase in its usual work.<note place="foot"><p>Active +exercise through short intervals, followed by periods of rest, such as +the exercise furnished by climbing stairs, or by short runs, is +considered the best means of strengthening the heart.</p></note> It may +even be subjected to great exertion without danger, if it be trained by +gradually increasing its work. Such training, by giving the heart time +to gain in size and strength, prepares it for tasks that could not at +first be accomplished.</p> + +<p>In taking up a new exercise requiring considerable exertion, +precautions should be observed to prevent an overstrain of the heart. +The heart of the amateur athlete, bicyclist, or mountain climber is +frequently injured by attempting more than the previous training +warrants. The new work should be taken up gradually, and feats requiring +a large outlay of physical energy should be attempted only after long +periods of training.</p> + +<p>Since the heart is controlled by the nervous system, it frequently +becomes irregular in its action through conditions that exhaust the +nervous energy. Palpitations of the heart, the missing of beats, and +pains in the heart region frequently arise from this cause. It is +through their effect upon the nervous system that worry, overstudy, +undue excitement, and dissipation cause disturbances of the heart. In +all such cases the remedy lies in the removal of the cause. The nervous +system should also be "toned up" through rest, plenty of sleep, and +moderate exercise in the open air.</p> + +<p><hi rend="font-weight: bold">Effect of Drugs.</hi>—A number of +substances classed as drugs, mainly by their action on the nervous +system, <pb n="056" /><anchor id="Pg056" />produce undesirable effects upon +the organs of circulation. Unfortunately some of these are extensively +used, alcohol being one of them. If taken in any but small quantities, +alcohol is a disturbing factor in the circulation. It increases the rate +of the heart beat and dilates the capillaries. Its effect upon the +capillaries is shown by the "bloodshot" eye and the "red nose" of the +hard drinker. Another bad effect from the use of much alcohol is the +weakening of the heart through the accumulation of fat around this organ +and within the heart muscle. The use of alcohol also leads in many cases +to a hardening of the walls of the arteries, such as occurs in old age. +This effect makes the use of alcohol especially dangerous for those in +advanced years.</p> + +<p>Tobacco contains a drug, called nicotine, which has a bad effect upon +the heart in at least two ways: 1. When the use of tobacco is begun in +early life, it interferes with the growth of the heart, leading to its +weakness in the adult. 2. When used in considerable quantity, by young +or old, it causes a nervous condition both distressing and dangerous, +known as "tobacco heart."</p> + +<p>Tea and coffee contain a drug, called caffeine, which acts upon the +nervous system and which may, on this account, interfere with the proper +control of the heart. In some individuals the taking of a very small +amount of either tea or coffee is sufficient to cause irregularities in +the action of the heart. Tea is considered the milder of the two liquids +and the one less liable to injure.</p> + +<p><hi rend="font-weight: bold">Effect of Rheumatism.</hi>—The disease +which affects the heart more frequently than any other is rheumatism. +This attacks the lining membrane, or endocardium, and causes, not +infrequently, a shrinkage of the heart valves. The heart is thus +rendered defective and, to perform its<pb n="057" /><anchor id="Pg057" /> +function in the body, must work +harder than if it were in a normal condition. Rheumatic attacks of the +heart do most harm when they occur in early life—the period when the +valves are the most easily affected. Any tendency toward rheumatism in +children has, therefore, a serious significance and should receive the +attention of the physician. Any one having a defective heart should +avoid all forms of exercise that demand great exertion.</p> + +<p><hi rend="font-weight: bold">Strengthening of the Blood Vessels.</hi>—Disturbances +of the circulation, causing too much blood to be sent to +certain parts of the body and an insufficient amount to others, when +resulting from slight causes, are usually due to weakness of the walls +of the blood vessels, particularly of the muscular coat. Such weakness +is frequently indicated by extreme sensitiveness to heat or cold and by +a tendency to "catch cold." From a health standpoint the preservation of +the normal muscular "tone" of the blood vessels is a problem of great +importance. Though the muscles of the blood vessels cannot be exercised +in the same manner as the voluntary muscles, they may be called actively +into play through all the conditions that induce changes in the blood +supply to different parts of the body. The usual forms of physical +exercise necessitate such changes and indirectly exercise the muscular +coat. The exposure of the body to cold for short intervals, because of +the changes in the circulation which this induces, also serves the same +purpose. A cold bath taken with proper precautions is beneficial to the +circulation of many and so also is a brisk walk on a frosty morning. +Both indirectly exercise and strengthen the muscular coat of the blood +vessels. On the other hand, too much time spent indoors, especially in +overheated rooms, leads to a weakening of the muscular coat and should +be avoided.</p> + +<p><pb n="058" /><anchor id="Pg058" /><hi rend="font-weight: +bold">Checking of Flow of Blood from Wounds.</hi>—The loss of any +considerable quantity of blood is such a serious matter that every one +should know the simpler methods of checking its flow from wounds. In +small wounds the flow is easily checked by binding cotton or linen fiber +over the place. The absorbent cotton, sold in small packages at drug +stores, is excellent for this purpose and should be kept in every home. +A simple method of checking "nosebleed" is that of drawing air through +the bleeding nostril, while the other nostril is compressed with the +finger.<note place="foot"><p>Nosebleed in connection with any kind of severe sickness +should receive prompt attention, since a considerable loss of blood when +the body is already weak may seriously delay recovery.</p></note> Another method is to "press with the finger (or insert a +small roll of paper) under the lip against the base of the nose." <note place="foot"><p>Newton, <hi rend="font-style: italic">Practical +Hygiene</hi>.</p></note> +Where the bleeding is persistent, the nostril should be plugged with a +small roll of clean cotton or paper. When this is done, the plug should +not be removed too soon because of the likelihood of starting the flow +afresh.</p> + +<p>In dealing with large wounds the services of a physician are +indispensable. But in waiting for the physician to arrive temporary aid +must be rendered. The one who gives such aid should first decide whether +an artery or a vein has been injured. This is easily determined by the +nature of the blood stream, which is in jets, or spurts, from an artery, +but flows steadily from a vein. If an artery is injured, the limb should +be tightly bandaged on the side of the wound nearest the heart; if a +vein, on the side farthest from the heart. In addition to this, the +edges of the wound should be closed and covered with cotton fiber and +the limb should be placed on a support above the level of the rest of +the body. A large handkerchief makes a convenient bandage if properly +applied. This should be folded <pb n="059" /><anchor id="Pg059" />diagonally and a knot tied in the +middle. Opposite ends are then tied, making a loose-fitting loop around +the limb. The knot is placed directly over the blood vessel to be +compressed and a short stick inserted in the loop. The necessary +pressure is then applied by twisting the handkerchief with the stick. +Time must not be lost, however, in the preparation of a suitable +bandage. The blood vessel should be compressed with the fingers while +the bandage is being prepared.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The blood, to serve as a +transporting agent, must be kept continually moving through all parts of +the body. The blood vessels hold the blood, supply the channels and +force necessary for its circulation, and provide conditions which enable +materials both to enter and to leave the blood stream. The heart is the +chief factor in propelling the blood, although the muscles and the +elastic tissue in the walls of the arteries and the valves in the veins +are necessary aids in the process. In the capillaries the blood takes on +and gives off materials, while the arteries and veins serve chiefly as +tubes for conveying the blood from one system of capillaries to +another.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. Of what special value +in the study of the body was the discovery of the circulation of the +blood?</p> + +<p>2. State the necessity for a circulating liquid in the body.</p> + +<p>3. Show by a drawing the general plan of the heart, locating and +naming the essential parts. Show also the connection of the large blood +vessels with the cavities of the heart.</p> + +<p>4. Compare the purpose served by the chordæ tendineæ to that served +by doorstops (the strips against which the door strikes in closing).</p> + +<p>5. Explain how the heart propels the blood. To what class of pumps +does it belong? What special work is performed by each of its +divisions?</p> + +<p>6. Define a valve. Of what use are the valves in the heart? In the +veins?</p> + +<p><pb n="060" /><anchor id="Pg060" />7. By what means is pressure from +contracting muscles in different parts of the body made to assist in the +circulation?</p> + +<p>8. Of what advantage is the elasticity of the arteries?</p> + +<p>9. How is blood forced from the capillaries back to the heart?</p> + +<p>10. Why should there be a difference in structure between the two +sides of the heart?</p> + +<p>11. Following Fig. 23, trace the blood through a complete +circulation, naming all the divisions of the system in the order of the +flow of the blood.</p> + +<p>12. If the period of rest following the period of contraction of the +heart be as long as the period of contraction, how many hours is the +heart able to rest out of every twenty-four?</p> + +<p>13. State the functions of the capillaries. Show how their structure +adapts them to their work.</p> + +<p>14. What kind of physical exercise tends to strengthen the heart? +What forms of exercise tend to injure it? State the effects of alcohol +and tobacco on the heart.</p> + +<p>15. How may rheumatism injure the heart?</p> + +<p>16. Give directions for checking the flow of blood from small and +from large blood vessels.</p> +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p>In showing the relations of the different parts of the heart, a large +dissectible model is of great service (Fig. 24). Indeed, where the time +of the class is limited, the practical work may be confined to the study +of the heart model, diagrams of the heart and the circulation, and a few +simple experiments. However, where the course is more extended, the +dissection of the heart of some animal as described below is strongly +advised.</p> + +<p><hi rend="font-weight: bold">Observations on the Heart.</hi>—Procure, +by the assistance of a butcher, the heart of a sheep, calf, or hog. To +insure the specimen against mutilation, the lungs and the diaphragm must +be left attached to the heart. In studying the different parts, good +results will be obtained by observing the following order:</p> + +<p>1. Observe the connection of the heart to the lungs, diaphragm, and +large blood vessels. Inflate the lungs and observe the position of the +heart with reference to them.</p> + +<p>2. Examine the sac surrounding the heart, called the <hi +rend="font-style: italic">pericardium</hi>. Pierce its lower portion and +collect the pericardial fluid. Increase the <pb n="061" /><anchor +id="Pg061" />opening thus made until it is large enough to slip the +heart out through it. Then slide back the pericardium until its +connection with the large blood vessels above the heart is found. +Observe that a thin layer of it continues down from this attachment, +forming the outer covering of the heart.</p> + +<p>3. Trace out for a short distance and study the veins and arteries +connected with the heart. The arteries are to be distinguished by their +thick walls. The heart may now be severed from the lungs by cutting the +large blood vessels, care being taken to leave a considerable length of +each one attached to the heart.</p> + +<p rend="text-align: center"> +<figure url="images/image24.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 24—Model for demonstrating the heart.</head> +<figDesc>Fig. 24</figDesc> +</figure></p> + +<p>4. Observe the outside of the heart. The thick, lower portion +contains the cavities called <hi rend="font-style: +italic">ventricles</hi>; the thin, upper, ear-shaped portions are the +<hi rend="font-style: italic">auricles</hi>. The thicker and denser side +lies toward the left of the animal's body and is called the <hi +rend="font-style: italic">left</hi> side of the heart; the other is the +<hi rend="font-style: italic">right</hi> side. Locate the right auricle +and the right ventricle; the left auricle and the left ventricle.</p> + +<p>5. Lay the heart on the table with the front side up and the apex +pointing from the operator. This places the left side of the heart to +his left and the right side to his right. Notice the groove between the +ventricles, called the inter-ventricular groove. Make an incision half +an inch to the right of this groove and cut toward the base of the heart +until the pulmonary artery is laid open. Then, following within half an +inch of the groove, cut down and around the right side of the heart. The +wall of the right ventricle may now be raised and the cavity exposed. +Observe the extent of the cavity, its shape, its lining, its columns of +muscles, its half columns of muscles, its tendons (chordæ tendineæ), the +tricuspid valve from the under side, etc. Also notice the valve at the +beginning of the pulmonary artery (the right semilunar) and the sinuses, +or depressions, in the artery immediately behind its divisions.</p> + +<p>6. Now cut through the middle of the loosened ventricular wall from +the apex to the middle of the right auricle, laying it open for +<pb n="062" /><anchor id="Pg062" />observation. Observe the +openings into the auricle, there being one each for the vena cava +superior, the vena cava inferior, and the coronary vein. Compare the +walls, lining, shape, size, etc., with the ventricle below.</p> + +<p>7. Cut off the end of the left ventricle about an inch above the +apex. This will show the extension of the cavity to the apex; it will +also show the thickness of the walls and the shape of the cavity. Split +up the ventricular wall far enough to examine the mitral valve and the +chordæ tendineæ from the lower side.</p> + +<p>8. Make an incision in the left auricle. Examine its inner surface +and find the places of entrance of the pulmonary veins. Examine the +mitral valve from above. Compare the two sides of the heart, part for +part.</p> + +<p>9. Separate the aorta from the other blood vessels and cut it +entirely free from the heart, care being taken to leave enough of the +heart attached to the artery to insure the semilunar valve's being left +in good condition. After tying or plugging up the holes in the sides of +the artery, pour water into the small end and observe the closing of the +semilunar valve. Repeat the experiment until the action of the valve is +understood. Sketch the artery, showing the valve in a closed +condition.</p> + +<p><hi rend="font-weight: bold">To illustrate the Action of a +Ventricle.</hi>—Procure a syringe bulb with an opening at each end. +Connect a rubber tube with each opening, letting the tubes reach into +two tumblers containing water. By alternately compressing and releasing +the bulb, water is pumped from one vessel into the other. The bulb may +be taken to represent one of the ventricles. What action of the +ventricle is represented by compressing the bulb? By releasing the +pressure? Show by a sectional drawing the arrangement of the valves in +the syringe bulb.</p> + +<p rend="text-align: center"> +<figure url="images/image25.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 25—Illustrating elasticity of arteries.</head> +<figDesc>Fig. 25</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">To show the Advantage of the Elasticity +of Arteries.</hi>—Connect the syringe bulb used in the last experiment +with a rubber tube three or four feet in length and having rather thin +walls. In the opposite end of the rubber tube insert a short glass tube +which has been drawn (by heating) to a fine point (Fig. 25). Pump water +into the rubber tube, observing:</p> + +<p>1. The swelling of the tube (pulse) as the water is forced into it. +(This is best observed by placing the fingers on the tube.)</p> + +<p><pb n="063" /><anchor id="Pg063" />2. The forcing of water from the +pointed tubs during the interval when no pressure is being applied from +the bulb. Compare with the action of the arteries when blood is forced +into them from the ventricles.</p> + +<p>Repeat the experiment, using a long glass tube terminating in a point +instead of the rubber tube. (In fitting the glass tube to the bulb use a +very short rubber tube.) Observe and account for the differences in the +flow of water through the inelastic tube.</p> + +<p><hi rend="font-weight: bold">To show the Advantage of Valves in the +Veins.</hi>—Attach an open glass tube one foot in length to each end of +the rubber tube used in the preceding experiment and fill with water (by +sucking) to within about six inches of the end. Lay on the table with +the glass tubes secured in an upright position (Fig. 26). Now compress +the tube with the hand, noting that the water rises in both tubes, being +pushed in both directions. This effect is similar to that produced on +the blood when a vein having no valves is compressed.</p> + +<p rend="text-align: center"> +<figure url="images/image26.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 26.—<hi rend="font-weight: bold">Simple +apparatus</hi> for showing advantage of valves in veins.</head> +<figDesc>Fig. 26</figDesc> +</figure></p> + +<p>Now imitate the action of a valve by clamping the tube at one point, +or by closing it by pressure from the finger, and then compressing with +the hand some portion of the tube on the table. Observe in this instance +that the water is <hi rend="font-weight: bold">all</hi> pushed in the +same direction. The movement of the water is now like the effect +produced on the blood in veins having valves when the veins are +compressed.</p> + +<p><hi rend="font-weight: bold">To show the Position of the Valves in +the Veins.</hi>—Exercise the arm and hand for a moment to increase the +blood supply. Expose the forearm and examine the veins on its surface. +With a finger, stroke one of the veins toward the heart, noting that, as +the blood is pushed along on one side of the finger the blood follows on +the other side. Now stroke the vein toward the hand. Places are found +beyond which the blood does not follow the finger. These mark the +positions of valves.</p> + +<p><hi rend="font-weight: bold">To show Effect of Exercise upon the +Circulation.</hi>—1. With a finger on the "pulse" at the wrist or +temple, count the number of heart beats during a period of one minute +under the following conditions: (<hi rend="font-style: italic">a</hi>) +when sitting; (<hi rend="font-style: italic">b</hi>) when standing; (<hi +rend="font-style: italic">c</hi>) after active exercise, as running. +What relation, if any, do these observations indicate between the +general activity of the body and the work of the heart?</p> + +<p>2. Compare the size of the veins on the backs of the hands when they +are placed side by side on a table. Then exercise briskly the <pb +n="064" /><anchor id="Pg064" />right hand and arm, clenching and +unclenching the fist and flexing the arm at the elbow. Place the hands +again side by side and, after waiting a minute, observe the increase in +the size of the veins in the hand exercised. How is this accounted +for?</p> + +<p><hi rend="font-weight: bold">To Show the Effect of Gravity on the +Circulation.</hi>—Hold one hand high above the head, at the same time +letting the other hand hang loosely by the side. Observe the difference +in the color of the hands and the degree to which the large veins are +filled. Repeat the experiment, reversing the position of the hands. What +results are observed? In what parts of the body does gravity aid in the +return of the blood to the heart? In what parts does it hinder? Where +fainting is caused by lack of blood in the brain (the usual cause), is +it better to let the patient lie down flat or to force him into a +sitting posture?</p> + +<p><hi rend="font-weight: bold">To study the Circulation in a Frog's +Foot</hi> (Optional).—A compound microscope is needed in this study and +for extended examination it is best to destroy the frog's brain. This is +done by inserting some blunt-pointed instrument into the skull cavity +from the neck and moving it about. A small frog, on account of the +thinness of its webs, gives the best results. It should be attached to a +thin board which has an opening in one end over which the web of the +foot may be stretched. Threads should extend from two of the toes to +pins driven into the board to secure the necessary tension of the web, +and the foot and lower leg should be kept moist. Using a two-thirds-inch +objective, observe the branching of the small arteries into the +capillaries and the union of the capillaries to form the small veins. +The appearance is truly wonderful, but allowance must be made for the +fact that the <hi rend="font-style: italic">motion</hi> of the blood is +magnified, as well as the different structures, and that it appears to +move much faster than it really does. With a still higher power, the +movements of the corpuscles through the capillaries may be studied.</p> + +<p><hi rend="font-variant: small-caps">Note.</hi>—To perform this experiment without destroying the brain, the +frog is first carefully wrapped with strips of wet cloth and securely +tied to the board. The wrapping, while preventing movements of the frog, +must not interfere with the circulation.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="065" /><anchor id="Pg065" /> + +<head>CHAPTER VI - THE LYMPH AND ITS MOVEMENT THROUGH THE BODY</head> + +<p rend="text-align: center"> +<figure url="images/image27.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 27—<hi rend="font-weight: bold">Diagram showing +position of the lymph</hi> with reference to the blood and the cells. +The central tube is a capillary. The arrows indicate the direction of +slight movements in the lymph.</head> +<figDesc>Fig. 27</figDesc> +</figure></p> + +<p>The blood, it will be remembered, moves everywhere through the body +in a system of <hi rend="font-style: italic">closed</hi> tubes. These +keep it from coming in contact with any of the cells of the body except +those lining the tubes themselves. The capillaries, to be sure, bring +the blood very near the cells of the different tissues; still, there is +need of a liquid to fill the space between the capillaries and the cells +and to transfer materials from one to the other. The lymph occupies this +position and does this work. The position of the lymph with reference to +the capillaries and the cells is shown in Fig. 27.</p> + +<p><hi rend="font-weight: bold">Origin of the Lymph.</hi>—The chief +source of the lymph is the plasma of the blood. As before described, the +walls of the capillaries consist of a single layer of flat cells placed +edge to edge. Partly on account of the pressure upon the blood and +partly on account of the natural tendency of liquids to pass through +animal membranes, a considerable portion of the plasma penetrates the +thin walls and enters the spaces occupied by the lymph.</p> + +<p><pb n="066" /><anchor id="Pg066" />The cells themselves also help to form the lymph, since the water and +wastes leaving the cells add to its bulk. These mix with the plasma from +the blood, forming the resultant liquid which is the lymph. A +considerable amount of the material absorbed from the food canal also +enters the lymph tubes, but this passes into the blood before reaching +the cells.</p> + +<p><hi rend="font-weight: bold">Composition and Physical Properties of +the Lymph.</hi><note place="foot"><p>On account of its position in the body, the lymph is not +easily collected for examination. Still, nearly every one will recall +some experience that has enabled him to see lymph. The liquid in a water +blister is lymph, and so also is the liquid which oozes from the skin +when it is scraped or slightly scratched. Swelling in any part of the +body is due to the accumulation of lymph at that place.</p></note>—As would naturally be expected, the composition of +the lymph is similar to that of the blood. In fact, nearly all the +important constituents of the blood are found in the lymph, but in +different proportions. Food materials for the cells are present in +smaller amounts than in the blood, while impurities from the cells are +in larger amounts. As a rule the red corpuscles are absent from the +lymph, but the white corpuscles are present and in about the same +numbers as in the blood.</p> + +<p>The physical properties of the lymph are also similar to those of the +blood. Like the blood, the lymph is denser than water and also +coagulates, but it coagulates more slowly than does the blood. The most +noticeable difference between these liquids is that of color, the lymph +being colorless. This is due to the absence of red corpuscles. The +quantity of lymph is estimated to be considerably greater than that of +the blood.</p> + +<p><hi rend="font-weight: bold">Lymph Vessels.</hi>—Most of the lymph +lies in minute cavities surrounding the cells and in close relations +with the capillaries (Figs. 27 and 30). These are called <hi +rend="font-style: italic">lymph spaces</hi>. Connecting with the lymph +spaces on the one<pb n="067" /><anchor id="Pg067" /> hand, and with certain blood +vessels on the other, is a system of tubes that return the lymph to the +blood stream. The smallest of these, and the ones in greatest abundance, +are called <hi rend="font-style: italic">lymphatics</hi>. They consist +of slender, thin-walled tubes, which resemble veins in structure, and, +like the veins, have valves. They differ from veins, however, in being +more uniform in size and in having thinner walls.</p> + +<p rend="text-align: center"> +<figure url="images/image28.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 28—<hi rend="font-weight: bold">Diagram of +drainage system for the lymph.</hi> 1. Thoracic duct. 2. Right +lymphatic duct. 3. Left subclavian vein. 4. Right subclavian vein. 5. +Superior vena cava. 6. Lacteals. 7. Lymphatic glands. The small tubes +connecting with the lymph spaces in all parts of the body are the +lymphatics.</head> +<figDesc>Fig. 28</figDesc> +</figure></p> + +<p>The lymphatics in different places gradually converge toward, and +empty into, the two main lymph tubes of the body. The smaller of these +tubes, called the <hi rend="font-style: italic">right lymphatic +duct</hi>, receives the lymph from the lymphatics in the right arm, the +right side of the head, and the region of the right shoulder. It +connects with, and empties its contents into, the right subclavian vein +at the place where it is joined by the right jugular vein (Fig. 28).</p> + +<p>The larger of the lymph tubes is called the <hi rend="font-style: +italic">thoracic duct</hi>. This receives lymph from all parts of the +body<pb n="068" /><anchor id="Pg068" /> not drained by the right +lymphatic duct, and empties it into the left subclavian vein. Connection +is made with the subclavian vein on the upper side at the place where it +is joined by the left jugular vein. The thoracic duct has a length of +from sixteen to eighteen inches, and is about as large around as a goose +quill. The lower end terminates in an enlargement in the abdominal +cavity, called the <hi rend="font-style: italic">receptacle of the +chyle</hi>. It is provided with valves throughout its course, in +addition to one of considerable size which guards the opening into the +blood vessel.</p> + +<p>The lymphatics which join the thoracic duct from the small intestine +are called the <hi rend="font-style: italic">lacteals</hi> (Fig. 28). +These do not differ in structure from the lymphatics in other parts of +the body, but they perform a special work in absorbing the digested fat +(Chapter XI).</p> + +<p><hi rend="font-weight: bold">Lymphatic Glands.</hi>—The lymphatic +glands, sometimes called lymph nodes, are small and somewhat rounded +bodies situated along the course of the lymphatic tubes. They vary in +size, some of them being an inch or more in length. The lymph vessels +generally open into them on one side and leave them on the other (Figs. +28 and 30). They are not glands in function, but are so called because +of their having the general form of glands. They provide favorable +conditions for the development of white corpuscles (page 29). They also +separate harmful germs and poisonous wastes from the lymph, thereby +preventing their entrance into the blood.</p> + +<p><hi rend="font-weight: bold">Relations of the Lymph, the Blood, and +the Cells.</hi>—While the blood is necessary as a carrying, or +transporting, agent in the body, the lymph is necessary for transferring +materials from the blood to the cells and <hi rend="font-style: +italic">vice versa</hi>. Serving as a physiological "go between," or +medium of exchange, the lymph enables the blood to minister to the<pb n="069" /><anchor id="Pg069" /> needs of the cells. But the lymph +and the blood, everything considered, can hardly be looked upon as two +separate and distinct liquids. Not only do they supplement each other in +their work and possess striking similarities, but each is made in its +movements to pass into the vessels occupied by the other, so that they +are constantly mixing and mingling. For these and other reasons, they +are more properly regarded as two divisions of a single liquid—one +which, by adapting itself to different purposes,<note place="foot"><p>In certain small animals of the lowest types a single +liquid, serving as a medium of exchange between the cells and the body +surface, supplies all the needs of the organism. In larger animals, +however, where materials have to be moved from one part of the cell +group to another, a portion of the nutrient fluid is used for purposes +of transportation. This is confined in channels where it is set in +motion by suitable organs. The portion which remains outside of the +channels then transfers material between the cells, on the one hand, and +the moving liquid, on the other.</p></note> supplies all the +conditions of a nutrient fluid for the cells.</p> + +<p><hi rend="font-weight: bold">Movements of the Lymph.</hi>—As compared +with the blood, the lymph must be classed as a quiet liquid. But, as +already suggested, it has certain movements which are necessary to the +purposes which it serves. A careful study shows it to have three +well-defined movements as follows:</p> + +<p>1. A movement from the capillaries toward the cells.</p> + +<p>2. A movement from the cells toward the capillaries.</p> + +<p>3. A movement of the entire body of lymph from the lymph spaces into +the lymphatics and along these channels to the ducts through which it +enters the blood.</p> + +<p>By the first movement the cells receive their nourishment. By the +second and third movements the lymph, more or less laden with +impurities, is returned to the blood stream. (See Figs. 28 and 30.)</p> + +<p><hi rend="font-weight: bold">Causes of the Lymph Movements.</hi>—Let +us consider first the movement through the lymph tubes. No pump, like +the heart, is known to be connected with these tubes and<pb n="070" /><anchor id="Pg070" /> to supply the pressure necessary +for moving the lymph. There are, however, several forces that indirectly +aid in its flow. The most important of these are as follows:</p> + +<p>1. <hi rend="font-style: italic">Blood Pressure at the +Capillaries.</hi>—The plasma which is forced through the capillary walls +by pressure from the heart makes room for itself by pushing a portion of +the lymph out of the lymph spaces. This in turn presses upon the lymph +in the tubes which it enters. In this way pressure from the heart is +transmitted to the lymph, forcing it to move.</p> + +<p>2. <hi rend="font-style: italic">Variable Pressure on the Walls of +the Lymph Vessels.</hi>—Pressure exerted on the sides of the lymph tubes +by contracting muscles tends to close them up and to push the lymph past +the valves, which, by closing, prevent its return (Fig. 29). Pressure at +the surface of the body, provided that it is variable, also forces the +lymph along. The valves in the lymph vessels serve the same purpose as +those in the veins.</p> + +<p rend="text-align: center"> +<figure url="images/image29.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 29—<hi rend="font-weight: bold">Diagram</hi> to +show how the muscles pump lymph. <hi rend="font-style: italic">A.</hi> +Relaxed muscle beside which is a lymphatic tube. <hi rend="font-style: +italic">B.</hi> Same muscle in state of contraction.</head> +<figDesc>Fig. 29</figDesc> +</figure></p> + +<p>3. <hi rend="font-style: italic">The Inspiratory Force.</hi>—When the +thoracic cavity is enlarged in breathing, the unbalanced atmospheric +pressure is exerted from all directions towards the thoracic space. This +not only causes the air to flow into the lungs (Chapter VII), but also +causes a movement of the blood and lymph in such of their tubes as enter +this cavity. It will be noted that both of the large lymph ducts +terminate where their contents may be influenced by the respiratory +movements. (See Practical Work.)</p> + +<p><hi rend="font-weight: bold">Where the Lymph enters the +Blood.</hi>—The fact that the lymph is poured into the blood at but two +places, and these very close to each<pb n="071" /><anchor id="Pg071" /> +other, requires a word of explanation. As a matter of fact, it is +impossible for the lymph to flow into blood vessels at most places on +account of the blood pressure. This would force the blood into the lymph +vessels, instead of allowing the lymph to enter the blood. The lymph can +enter only at some place where the blood pressure is less than the +pressure that moves the lymph. Such a place is found in the thoracic +cavity. As already pointed out (page 54), the blood pressure in the +veins entering this cavity becomes, with each expansion of the chest, +negative, i.e., less than the pressure of the atmosphere on the outside +of the body. This, as we have seen, aids in the flow of the blood into +the right auricle. It also aids in the passage of lymph into the blood +vessels. The lymph is said to be "sucked in," which means that it is +forced in by the unbalanced pressure of the atmosphere.<note place="foot"><p>Surgeons in opening veins near the thoracic cavity have +to be on their guard to prevent air from being sucked into them, thereby +causing death.</p></note> Some +advantage is also gained by the lymph duct's entering the subclavian +vein on the upper side and at its union with the jugular vein. +Everything considered, it is found that the lymph flows into the blood +vessels where it can be "drawn in" by the movements of breathing and +where it meets with no opposition from the blood stream itself (Fig. +30).</p> + +<p rend="text-align: center"> +<figure url="images/image30.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 30—<hi rend="font-weight: bold">Diagram</hi> +showing general movement of lymph from the place of relatively high +pressure at the lymph spaces to the place of relatively low pressure in +the thoracic cavity.</head> +<figDesc>Fig. 30</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Lymph Movements at the Cells.</hi>—The +double movement of the lymph from the capillaries toward the cells<pb n="072" /><anchor id="Pg072" /> and from the cells +toward the capillaries is not entirely understood. Blood pressure in the +capillaries undoubtedly has much to do in forcing the plasma through the +capillary walls, but this tends to prevent the movement of the lymph in +the opposite direction. Movements between the blood and the lymph are +known to take place in part according to a general principle, known as +<hi rend="font-style: italic">osmosis</hi>, or dialysis.</p> + +<p rend="text-align: center"> +<figure url="images/image31.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 31—<hi rend="font-weight: bold">Vessel</hi> with +an upright membranous partition for illustrating osmosis.</head> +<figDesc>Fig. 31</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Osmosis.</hi>—The term "osmosis" is used +to designate the passage of liquids through some partition which +separates them. Thus, if a vessel with an upright membranous partition +be filled on the one side with pure water and on the other with water +containing salt, an exchange of materials will take place through the +membrane until the same proportion of salt exists on the two sides (Fig. +31). The cause of osmosis is the motion of the molecules, or minute +particles, that make up the liquid substance. If the partition were not +present, this motion would simply cause a mixing of the liquids.</p> + +<p><hi rend="font-weight: bold">Conditions under which Osmosis +occurs.</hi>—Osmosis may be shown by suitable experiments (see Practical +Work) to take place under the following conditions:</p> + +<p>1. The liquids on the two sides of the partition must be <hi +rend="font-style: italic">unlike</hi> either in density or in +composition. Since the effect of the movement is to reduce the liquids +to the same condition, <hi rend="font-style: italic">a difference in +density causes the flow to be greater from the less dense toward the +denser liquid</hi>, than in the opposite direction; while <hi +rend="font-style: italic">a difference in composition causes the +substances in solution to move from the place of greater abundance +toward places of less abundance</hi>.</p> + +<p>2. The liquids must be capable of wetting, or penetrating, the +partition. If but one of the liquids penetrates the partition, the flow +will be in but one direction.</p> + +<p>3. The liquids on the two sides of the partition must readily mix +with each other.</p> + +<p><hi rend="font-weight: bold">Osmosis at the Cells.</hi>—In the body +osmosis takes place between the<pb n="073" /><anchor id="Pg073" /> +blood and the lymph and between the lymph and the cells, the movements +being through the capillary walls and the membranes inclosing the cells +(Fig. 27). Oxygen and food materials, which are found in great abundance +in the blood, are less abundant in the lymph and still less abundant in +the cells. According to the principle of osmosis, the main flow of +oxygen and food is from the capillaries toward the cells. On the other +hand, the wastes are most abundant in the cells where they are formed, +less abundant in the lymph, and least abundant in the blood. Hence the +wastes flow from the cells toward the capillaries.</p> + +<p><hi rend="font-weight: bold">Solutions.</hi>—Neither the blood plasma +nor the lymph, as already shown, are simple liquids; but they consist of +water and different substances dissolved in the water. They belong to a +class of substances called <hi rend="font-style: italic">solutions</hi>. +The chief point of interest about substances in solution is that they +are very finely divided and that their little particles are free to move +about in the liquid that contains them. Both the motion and the finely +divided condition of the dissolved substances are necessary to the +process of osmosis. All substances, however, that appear to be in +solution are not able to penetrate membranes, or take part in +osmosis.</p> + +<p><hi rend="font-weight: bold">Kinds of Solutions in the Body.</hi>—The +substances in solution in the body liquids are of two general kinds +known as <hi rend="font-style: italic">colloids</hi> and <hi +rend="font-style: italic">crystalloids</hi>. The crystalloids are able +to pass through membranous partitions, while the colloids are not. An +example of a colloid is found in the albumin of an egg, which is unable +to penetrate the membrane which surrounds it. Examples of crystalloids +are found in solutions of salt and sugar in water. The inability of a +colloid to penetrate a membrane is due to the fact that it does not form +a true solution. Its particles (molecules), instead of being completely +separated, still cling together, forming little masses that are too +large to penetrate the membrane. Since, however, it has the appearance, +on being mixed with water, of being dissolved, it is called a <hi +rend="font-style: italic">colloidal solution</hi>. The crystalloid +substance, on the other hand, completely separates in the water and +forms a <hi rend="font-style: italic">true solution</hi>—one which is +able to penetrate the partition or membrane.</p> + +<p><hi rend="font-weight: bold">Osmosis not a Sufficient Cause.</hi>—The +passage of materials through animal membranes, according to the +principle of osmosis, is limited to crystalloid substances. But colloid +substances are also known to pass through the various partitions of the +body. An example of such is found in the proteids of the blood which, as +a colloidal solution, pass through the capillary walls to become a part +of the lymph. Perhaps<pb n="074" /><anchor id="Pg074" /> the best explanation offered as +yet for this passage is that the colloidal substances are changed by the +cells lining the capillaries into substances that form true solutions +and that after the passage they are changed back again to the colloidal +condition.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—Between the cells and the +capillaries is a liquid, known as the lymph, which is similar in +composition and physical properties to the blood. It consists chiefly of +escaped plasma. The vessels that contain it are connected with the +system for the circulation of the blood. By adding new material to the +lymph and withdrawing waste material from it, the blood keeps this +liquid in a suitable condition for supplying the needs of the cells. +Supplementing each other in all respects, the blood and the lymph +together form the nutrient cell fluid of the body. The interchange of +material between the blood and the lymph, and the lymph and the cells, +takes place in part according to the principle of osmosis.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. Explain the necessity +for the lymph in the body.</p> + +<p>2. Compare lymph and water with reference to density, color, and +complexity of composition.</p> + +<p>3. Compare lymph and blood with reference to color, composition, and +movement through the body.</p> + +<p>4. Show how blood pressure in the capillaries causes a flow of the +lymph.</p> + +<p>5. Show how contracting muscles cause the lymph to move. Compare with +the effect of muscular contraction upon the blood in the veins.</p> + +<p>6. Trace the lymph in its flow from the right hand to where it enters +the blood; from the feet to where it enters the blood.</p> + +<p>7. What conditions prevail at the cells to cause a movement of food +and oxygen in one direction and of waste materials in the opposite +direction?</p> + +<p>8. What part does water play in the exchanges at the cells?</p> + +<p>9. Show that the blood and the lymph together fulfill all the +requirements of a nutrient cell fluid in the body.</p> + +<div> +<pb n="075" /><anchor id="Pg075" /> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">To illustrate the Effect of Breathing +upon the Flow of Lymph.</hi>—Tightly holding one end of a glass tube +between the lips, let the other end extend into water in a tumbler on a +table. In this position quickly inhale air through the nostrils, noting +that with each inhalation there is a slight movement of the water up the +tube. (No sucking action should be exerted by the mouth.) Apply to the +movements in the large blood and lymph vessels entering the thoracic +cavity.</p> + +<p><hi rend="font-weight: bold">To illustrate Osmosis.</hi>—1. Separate +the shell from the lining membrane at one end of an egg, over an area +about one inch in diameter. To do this without injuring the membrane, +the shell must first be broken into small pieces and then picked off +with a pair of forceps, or a small knife blade. Fit a small glass tube, +eight or ten inches long, into the other end so that it will penetrate +the membrane and pass down into the yolk. Securely fasten the tube to +the shell by melting beeswax around it, and set the egg in a small +tumbler partly filled with water. Examine in the course of half an hour. +What evidence now exists that the water has passed through the +membrane?</p> + +<p>2. Tie over the large end of a "thistle tube" (used by chemists) a +thin animal membrane, such as a piece of the pericardium or a strip of +the membrane from around a sausage. Then fill the bulb and the lower end +of the tube with a concentrated solution of some solid, such as sugar, +salt, or copper sulphate. Suspend in a vessel of water so that the +liquid which it contains is just on a level with the water in the +vessel. Examine from time to time, looking for evidence of a movement in +each direction through the membrane. Why should the movement of the +water into the tube be greater than the movement in the opposite +direction? (If the thistle tube has a very slender stem, it is better to +fill the bulb before tying on the membrane. The opening in the stem may +be plugged during the process of filling.)</p> + +<p rend="text-align: center"> +<figure url="images/image32.png" rend="page-float: 'hp'; text-align: center; w45"> +<head><lb />Fig. 32—An osmosometer.</head> +<figDesc>Fig. 32</figDesc> +</figure></p> + +<p><hi rend="font-variant: small-caps">Note.</hi>—With a special piece of apparatus, known as an <hi +rend="font-style: italic">osmosometer</hi>, the principle of osmosis may +be more easily illustrated than by the method in either of the above +experiments (Fig. 32). This apparatus may be obtained from supply +houses.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="076" /><anchor id="Pg076" /> + +<head>CHAPTER VII - RESPIRATION</head> + +<p>Through the movements of the blood and the lymph, materials entering +the body are transported to the cells, and wastes formed at the cells +are carried to the organs which remove them from the body. We are now to +consider the passage of materials from outside the body to the cells and +<hi rend="font-style: italic">vice versa</hi>. One substance which the +body constantly needs is oxygen, and one which it is constantly throwing +off is carbon dioxide. Both of these are constituents of</p> + +<p><hi rend="font-weight: bold">The Atmosphere.</hi>—The atmosphere, or +air, completely surrounds the earth as a kind of envelope, and comes in +contact with everything upon its surface. It is composed chiefly of +oxygen and nitrogen,<note place="foot"><p>Oxygen forms about 21 per cent of the atmosphere, +nitrogen about 78 per cent, carbon dioxide about .03 per cent, and the +recently discovered element argon about 1 per cent. The oxygen is in a +<hi rend="font-style: italic">free</hi>, or uncombined, condition—the +form in which it can be used in the body.</p></note> but it also contains a small per cent of other +substances, such as water-vapor, carbon dioxide, and argon. All of the +regular constituents of the atmosphere are gases, and these, as compared +with liquids and solids, are very light. Nevertheless the atmosphere has +weight and, on this account, exerts pressure upon everything on the +earth. At the sea level, its pressure is nearly fifteen pounds to the +square inch. The atmosphere forms an essential part of one's physical +environment and serves various purposes. The process<pb n="077" /><anchor id="Pg077" /> by which gaseous materials are +made to pass between the body and the atmosphere is known as</p> + +<p><hi rend="font-weight: bold">Respiration.</hi>—As usually defined, +respiration, or breathing, consists of two simple processes—that of +taking air into special contrivances in the body, called the lungs, and +that of expelling air from the lungs. The first process is known as <hi +rend="font-style: italic">inspiration</hi>; the second as <hi +rend="font-style: italic">expiration</hi>. We must, however, distinguish +between respiration by the lungs, called <hi rend="font-style: +italic">external respiration</hi>, and respiration by the cells, called +<hi rend="font-style: italic">internal respiration</hi>.</p> + +<p><hi rend="font-style: italic">The purpose of respiration</hi> is +indicated by the changes that take place in the air while it is in the +lungs. Air entering the lungs in ordinary breathing parts with about +five per cent of itself in the form of oxygen and receives about four +and one half per cent of carbon dioxide, considerable water-vapor, and a +small amount of other impurities. These changes suggest a twofold +purpose for respiration:</p> + +<p>1. To obtain from the atmosphere the supply of oxygen needed by the +body.</p> + +<p>2. To transfer to the atmosphere certain materials (wastes) which +must be removed from the body.</p> + +<p>The chief organs concerned in the work of respiration are</p> + +<p><hi rend="font-weight: bold">The Lungs.</hi>—The lungs consist of two +sac-like bodies suspended in the thoracic cavity, and occupying all the +space not taken up by the heart. They are not simple sacs, however, but +are separated into numerous divisions, as follows:</p> + +<p>1. The lung on the right side of the thorax, called the right lung, +is made up of three divisions, or <hi rend="font-style: +italic">lobes</hi>, and the left lung is made up of two lobes.</p> + +<p>2. The lobes on either side are separated into smaller<pb n="078" /><anchor id="Pg078" /> divisions, called <hi +rend="font-style: italic">lobules</hi> (Fig. 33). Each lobule receives a +distinct division of an air tube and has in itself the structure of a +miniature lung.</p> + +<p rend="text-align: center"> +<figure url="images/image33.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 33—<hi rend="font-weight: bold">Lungs and air +passages</hi> seen from the front. The right lung shows the lobes and +their divisions, the lobules. The tissue of the left lung has been +dissected away to show the air tubes.</head> +<figDesc>Fig. 33</figDesc> +</figure></p> + +<p>3. In the lobule the air tube divides into a number of smaller tubes, +each ending in a thin-walled sac, called an <hi rend="font-style: +italic">infundibulum</hi>. The interior of the infundibulum is separated +into many small spaces, known as the <hi rend="font-style: +italic">alveoli</hi>, or air cells.</p> + +<p>The lungs are remarkable for their lightness and delicacy of +structure.<note place="foot"><p>The peculiar work devolving upon the organs of +respiration necessitates a special plan of construction—one adapted to +the properties of the atmosphere. Being concerned in the movement of +air, a gaseous substance, they will naturally have a structure different +from the organs of circulation which move a liquid (the blood). All the +organs of the body are adapted by their structure to the work which they +perform.</p></note> They consist chiefly of the tissues that form their sacs, +air tubes, and blood vessels; the membranes that line their inner and +outer surfaces; and the connective tissue that binds these parts +together. All these tissues are more or less elastic. The relation of +the different parts of the lungs to<pb n="079" /><anchor id="Pg079" /> each other and to the outside +atmosphere will be seen through a study of the</p> + +<p><hi rend="font-weight: bold">Air Passages.</hi>—The air passages +consist of a system of tubes which form a continuous passageway between +the outside atmosphere and the different divisions of the lungs. The air +passes through them as it enters and leaves the lungs, a fact which +accounts for the name.</p> + +<p rend="text-align: center"> +<figure url="images/image34.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 34—<hi rend="font-weight: bold">Model of section +through the head</hi>, showing upper air passages and other parts. 1. +Left nostril. 2. Pharynx. 3. Tongue and cavity of mouth. 4. Larynx. 5. +Trachea. 6. Esophagus.</head> +<figDesc>Fig. 34</figDesc> +</figure></p> + +<p>The incoming air first enters the <hi rend="font-style: +italic">nostrils</hi>. These consist of two narrow passages lying side +by side in the nose, and connecting with the pharynx behind. The lining +of the nostrils, called <hi rend="font-style: italic">mucous +membrane</hi> is quite thick, and has its surface much extended by +reason of being spread over some thin, scroll-shaped bones that project +into the passage. This membrane is well supplied with blood vessels and +secretes a considerable quantity of liquid. Because of the nature and +arrangement of the membrane, the nostrils are able to <hi +rend="font-style: italic">warm</hi> and <hi rend="font-style: +italic">moisten</hi> the incoming air, and to <hi rend="font-style: +italic">free it from dust particles</hi>, preparing it, in this way, for +entrance into the lungs (Fig. 34).</p> + +<p>The nostrils are separated from the mouth by a thin layer of bone, +and back of both the mouth and the nostrils is the pharynx. The <hi +rend="font-style: italic">pharynx</hi> and the <hi rend="font-style: +italic">mouth</hi> serve as parts of the food canal, as well as air +passages, and are<pb n="080" /><anchor id="Pg080" /> described in connection with the +organs of digestion (Chapter X). Air entering the pharynx, either by the +nostrils or by the mouth, passes through it into the <hi +rend="font-style: italic">larynx</hi>. The larynx, being the special +organ for the production of the voice, is described later (Chapter XXI). +The entrance into the larynx is guarded by a movable lid of cartilage, +called the <hi rend="font-style: italic">epiglottis</hi>, which prevents +food particles and liquids, on being swallowed, from passing into the +lower air tubes. The relations of the nostrils, mouth, pharynx, and +larynx are shown in Fig. 34.</p> + +<p>From the larynx the air enters the <hi rend="font-style: +italic">trachea</hi>, or windpipe. This is a straight and nearly round +tube, slightly less than an inch in diameter and about four and one half +inches in length. Its walls contain from sixteen to twenty C-shaped, +cartilaginous rings, one above the other and encircling the tube. These +incomplete rings, with their openings directed backward, are held in +place by thin layers of connective and muscular tissue. At the lower end +the trachea divides into two branches, called the bronchi, each of which +closely resembles it in structure. Each <hi rend="font-style: +italic">bronchus</hi> separates into a number of smaller divisions, +called the <hi rend="font-style: italic">bronchial tubes</hi>, and these +in turn divide into still smaller branches, known as the <hi +rend="font-style: italic">lesser bronchial tubes</hi> (Fig. 33). The +lesser bronchial tubes, and the branches into which they separate, are +the smallest of the air tubes. One of these joins, or expands into, each +of the minute lung sacs, or infundibula. Mucous membrane lines all of +the air passages.</p> + +<p><hi rend="font-weight: bold">General Condition of the Air +Passages.</hi>—One necessary condition for the movement of the air into +and from the lungs is an unobstructed passageway.<note place="foot"><p>In ordinary inspirations the force that causes the air +to move through the passages is scarcely an ounce to the square inch, +while in forced inspirations it does not exceed half a pound. On this +account the closing of any of the air passages by pressure, or by the +presence of foreign substances, would keep the air from reaching some +part of the lungs.</p></note> The air +passages<pb n="081" /><anchor id="Pg081" /> must be kept open and free from +obstructions. They are <hi rend="font-style: italic">kept open</hi> by +special contrivances found in their walls, which, by supplying a degree +of stiffness, cause the tubes to keep their form. In the trachea, +bronchi, and larger bronchial tubes, the stiffness is supplied by rings +of cartilage, while in the smaller tubes this is replaced by connective +and muscular tissue. The walls of the larynx contain strips and plates +of cartilage; while the nostrils and the pharynx are kept open by their +bony surroundings.</p> + +<p rend="text-align: center"> +<figure url="images/image35.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 35—<hi rend="font-weight: bold">Ciliated +epithelial cells.</hi> <hi rend="font-style: italic">A.</hi> Two cells +highly magnified. <hi rend="font-style: italic">c.</hi> Cilia, <hi +rend="font-style: italic">n.</hi> Nucleus. <hi rend="font-style: +italic">B.</hi> Diagram of a small air tube showing the lining of +cilia.</head> +<figDesc>Fig. 35</figDesc> +</figure></p> + +<p>The air passages are <hi rend="font-style: italic">kept clean</hi> by +cells especially adapted to this purpose, known as the <hi +rend="font-style: italic">ciliated epithelial cells</hi>. These are +slender, wedge-shaped cells which have projecting from a free end many +small, hair-like bodies, called <hi rend="font-style: italic">cilia</hi> +(Fig. 35). They line the mucous membrane in most of the air passages, +and are so placed that the cilia project into the tubes. Here they keep +up an inward and outward wave-like movement, which is quicker and has +greater force in the <hi rend="font-style: italic">outward</hi> +direction. By this means the cilia are able to move small pieces of +foreign matter, such as dust particles and bits of partly dried mucus, +called phlegm, to places where they can be easily expelled from the +lungs.<note place="foot"><p>Coughing, which is a forceful expulsion of air, has for +its purpose the ejection of foreign substances from the throat and +lungs. Sneezing, on the other hand, has for its purpose the cleansing of +the nostrils. In coughing, the air is expelled through the mouth, while +in sneezing it is expelled through the nostrils.</p></note></p> + +<p rend="text-align: center"> +<figure url="images/image36.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 36—<hi rend="font-weight: bold">Terminal air +sacs.</hi> The two large sacs are infundibula; the small divisions are +alveoli. (Enlarged.)</head> +<figDesc>Fig. 36</figDesc> +</figure></p> + +<p><pb n="082" /><anchor id="Pg082" /><hi rend="font-weight: bold">The +Alveoli.</hi>—The alveoli, or air cells, are the small divisions of the +infundibula (Fig. 36). They are each about one one-hundredth of an inch +(1/4 mm.) in diameter, being formed by the infolding of the infundibular +wall. This wall, which has for its framework a thin layer of elastic +connective tissue, supports a dense network of capillaries (Fig. 37), +and is lined by a single layer of cells placed edge to edge. By this +arrangement the air within the alveoli is brought very near a large +surface of blood, and the exchange of gases between the air and the +blood is made possible. It is at the alveoli that the oxygen passes from +the air into the blood, and the carbon dioxide passes from the blood +into the air. At no place in the lungs, however, do the air and the +blood come in direct contact. Their exchanges must in all cases take +place through the capillary walls and the layer of cells lining the +alveoli.</p> + +<p rend="text-align: center"> +<figure url="images/image37.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 37—<hi rend="font-weight: bold">Inner lung +surface (magnified)</hi>, the blood vessels injected with coloring +matter. The small pits are alveoli, and the vessels in their walls are +chiefly capillaries.</head> +<figDesc>Fig. 37</figDesc> +</figure></p> + +<p rend="text-align: center"> +<figure url="images/image38.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 38.—<hi rend="font-weight: bold">Diagram to show the double movement of air and +blood through the lungs.</hi> The blood leaves the heart by the +pulmonary artery and returns by the pulmonary veins. The air enters and +leaves the lungs by the same system of tubes.</head> +<figDesc>Fig. 38</figDesc> +</figure></p> + +<p rend="text-align: center"> +<figure url="images/image39.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 39—<hi rend="font-weight: bold">Diagram to show +air and blood movements in a terminal air sac.</hi> While the air moves +into and from the space within the sac, the blood circulates through the +sac walls.</head> +<figDesc>Fig. 39</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Blood Supply to the Lungs.</hi>—To +accomplish the purposes of respiration, not only the air, but the blood +also, must be passed into and from the lungs. The chief<pb n="084" /><anchor id="Pg084" /> artery conveying blood to the +lungs is the <hi rend="font-style: italic">pulmonary artery</hi>. This +starts at the right ventricle and by its branches conveys blood to the +capillaries surrounding the alveoli in all parts of the lungs. The +branches of the pulmonary artery lie alongside of, and divide similarly +to, the bronchial tubes. At the places where the finest divisions of the +air tubes enter the infundibula, the little arteries branch into the +capillaries that penetrate the infundibular walls (Figs. 38 and 39). +From these capillaries the blood is conveyed by the pulmonary veins to +the left auricle.</p> + +<p>The lungs also receive blood from two (in some individuals three) +small arteries branching from the aorta, known as the <hi +rend="font-style: italic">bronchial arteries</hi>. These convey to the +lungs blood that has already been supplied with oxygen, passing it into +the capillaries in the walls of the bronchi, bronchial tubes, and large +blood vessels, as well as the connective tissue between the lobes of the +lungs. This blood leaves the lungs partly by the bronchial veins and +partly by the pulmonary veins. No part of the body is so well supplied +with blood as the lungs.</p> + +<p rend="text-align: center"> +<figure url="images/image40.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 40—<hi rend="font-weight: bold">The pleuræ.</hi> +Diagram showing the general form of the pleural sacs as they surround +the lungs and line the inner surfaces of the chest (other parts +removed). <hi rend="font-style: italic">A, A'.</hi> Places occupied by +the lungs. <hi rend="font-style: italic">B, B'.</hi> Slight space within +the pleural sacs containing the pleural secretion, <hi rend="font-style: +italic">a, a'.</hi> Outer layer of pleura and lining of chest walls and +upper surface of diaphragm. <hi rend="font-style: italic">b, b'.</hi> +Inner layer of pleura and outer lining of lungs. <hi rend="font-style: +italic">C.</hi> Space occupied by the heart. <hi rend="font-style: +italic">D.</hi> Diaphragm.</head> +<figDesc>Fig. 40</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Pleura.</hi>—The pleura is a thin, +smooth, elastic, and tough membrane which covers the outside of the +lungs and lines the inside of the chest walls. The covering of each lung +is continuous with the lining of the chest wall on its respective side +and forms with it a closed sac by<pb n="085" /><anchor id="Pg085" /> which the lung is surrounded, the +arrangement being similar to that of the pericardium. Properly speaking, +there are two pleuræ, one for each lung, and these, besides inclosing +the lungs, partition off a middle space which is occupied by the heart +(Fig. 40). They also cover the upper surface of the diaphragm, from +which they deflect upward, blending with the pericardium. A small amount +of liquid is secreted by the pleura, which prevents friction as the +surfaces glide over each other in breathing.</p> + +<p><hi rend="font-weight: bold">The Thorax.</hi>—The force required for +breathing is supplied by the box-like portion of the body in which the +lungs are placed. This is known as the thorax, or chest, and includes +that part of the trunk between the neck and the abdomen. The space which +it incloses, known as the thoracic cavity, is a <hi rend="font-style: +italic">variable</hi> space and the walls surrounding this space are <hi +rend="font-style: italic">air-tight.</hi> A framework for the thorax is +supplied by the ribs which connect with the spinal column behind and +with the sternum, or breast-bone, in front. They form joints with the +spinal column, but connect with the sternum by strips of cartilage. The +ribs do not encircle the cavity in a horizontal direction, but slope +downward from the spinal column both toward the front and toward the +sides, this being necessary to the service which they render in +breathing.</p> + +<p><hi rend="font-weight: bold">How Air is Brought into and Expelled +from the Lungs.</hi>—The principle involved in breathing is that air +flows from a place of <hi rend="font-style: italic">greater</hi> to a +place of <hi rend="font-style: italic">less</hi> pressure. The +construction of the thorax and the arrangement of the lungs within it +provide for the application of this principle in a most practical +manner. The lungs are suspended from the upper portion of the thoracic +cavity, and the trachea and the upper air passages provide the only +opening to the outside atmosphere. Air entering the thorax must on<pb n="086" /><anchor id="Pg086" /> this account pass into the lungs. +As the thorax is enlarged the air in the lungs expands, and there is +produced within them a place of <hi rend="font-style: italic">slightly +less</hi> air pressure than that of the atmosphere on the outside of the +body. This difference causes the air to flow into the lungs.</p> + +<p rend="text-align: center"> +<figure url="images/image41.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 41—<hi rend="font-weight: bold">Diagram illustrating the bellows principle in +breathing.</hi> <hi rend="font-style: italic">A.</hi> The human bellows. +<hi rend="font-style: italic">B.</hi> The hand bellows. Compare part for +part.</head> +<figDesc>Fig. 41</figDesc> +</figure></p> + +<p>When the thorax is diminished in size, the air within the lungs is +slightly compressed. This causes it to become denser and to exert on +this account a pressure <hi rend="font-style: italic">slightly +greater</hi> than that of the atmosphere on the outside. The air now +flows out until the equality of the pressure is again restored. Thus the +thorax, by making the pressure within the lungs first slightly less and +then slightly greater than the atmospheric pressure, causes the air to +move into and out of the lungs.</p> + +<p>Breathing is well illustrated by means of the common hand bellows, +its action being similar to that of the thorax. It will be observed that +when the sides are spread apart air flows into the bellows. When they +are pressed together the air flows out. If an air-tight sack were hung +in the bellows with its mouth attached to the projecting tube, the +arrangement would resemble closely the general plan of the breathing +organs (Fig. 41). One respect, however, in which the bellows differs +from the thorax should be noted. The thorax is never sufficiently +compressed to drive out all the air. Air is always present in the lungs. +This keeps them more or less distended and pressed against the thoracic +walls.</p> + +<p><hi rend="font-weight: bold">How the Thoracic Space is +Varied.</hi>—One means of varying the size of the thoracic cavity is +through the movements of the ribs and their resultant effect upon the +walls<pb n="087" /><anchor id="Pg087" /> of the thorax. In bringing about +these movements the following muscles are employed:</p> + +<p>1. The <hi rend="font-style: italic">scaleni</hi> muscles, three in +number on each side, which connect at one end with the vertebræ of the +neck and at the other with the first and second ribs. Their contraction +slightly raises the upper portion of the thorax.</p> + +<p>2. The <hi rend="font-style: italic">elevators of the ribs</hi>, +twelve in number on each side, which are so distributed that each single +muscle is attached, at one end, to the back portion of a rib and, at the +other, to a projection of the vertebra a few inches above. The effect of +their contraction is to' elevate the middle portion of the ribs and to +turn them outward or spread them apart.</p> + +<p>3. The <hi rend="font-style: italic">intercostal</hi> muscles, which +form two thin layers between the ribs, known as the <hi +rend="font-style: italic">internal</hi> and the <hi rend="font-style: +italic">external</hi> intercostal muscles. The external intercostals are +attached between the outer lower margin of the rib above and the outer +upper margin of the rib below, and extend obliquely downward and +forward. The internal intercostals are attached between the inner +margins of adjacent ribs, and they extend obliquely downward and +backward from the front. The contraction of the external intercostal +muscles raises the ribs, and the contraction of the internal +intercostals tends to lower them.</p> + +<p rend="text-align: center"> +<figure url="images/image42.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 42—<hi rend="font-weight: bold">Simple +apparatus</hi> for illustrating effect of movements of the ribs upon the +thoracic space; strips of cardboard held together by pins, the front +part being raised or lowered by threads moving through attachments at 1 +and 2. As the front is raised the space between the uprights is +increased. The front upright corresponds to the breastbone, the back one +to the spinal column, the connecting strips to the ribs, and the threads +to the intercostal muscles.</head> +<figDesc>Fig. 42</figDesc> +</figure></p> + +<p>By slightly raising and spreading apart the ribs the thoracic space +is increased in two directions—from front to back and from side to side. +Lowering and converging the ribs has, of course, the opposite effect +(Fig. 42). Except in forced expirations the ribs are lowered and +converged by their own weight and by the elastic reaction of the +surrounding parts.</p> + +<p><pb n="088" /><anchor id="Pg088" /><hi rend="font-weight: bold">The Diaphragm.</hi>—Another means of +varying the thoracic space is found in an organ known as the diaphragm. +This is the dome-shaped, <hi rend="font-style: italic">movable +partition</hi> which separates the thoracic cavity from the cavity of +the abdomen. The edges of the diaphragm are firmly attached to the walls +of the trunk, and the center is supported by the pericardium and the +pleura. The outer margin is muscular, but the central portion consists +of a strong sheet of connective tissue. By the contraction of its +muscles the diaphragm is pulled down, thereby increasing the thoracic +cavity. By raising the diaphragm the thoracic cavity is diminished.</p> + +<p>The diaphragm, however, is not raised by the contraction of its own +muscles, but <hi rend="font-style: italic">is pushed up</hi> by the +organs beneath. By the elastic reaction of the abdominal walls (after +their having been pushed out by the lowering of the diaphragm), pressure +is exerted on the organs of the abdomen and these in turn press against +the diaphragm. This crowds it into the thoracic space. In forced +expirations the muscles in the abdominal walls contract to push up the +diaphragm.</p> + +<p><hi rend="font-weight: bold">Interchange of Gases in the +Lungs.</hi>—During each inspiration the air from the outside fills the +entire system of bronchial tubes, but the alveoli are largely filled, at +the same time, by the air which the last expiratory effort has left in +the passages. By the action of currents and eddies and by the rapid +diffusion of gas particles, the air from the outside mixes with that in +the alveoli and comes in contact with the membranous walls. Here the +oxygen, after being dissolved by the moisture in the membrane, diffuses +into the blood. The carbon dioxide, on the other hand, being in excess +in the blood, diffuses toward the air in the alveoli. The interchange of +gases at the lungs, however, is not fully understood, and it is possible +that other forces than osmosis play a part.</p> + +<p rend="text-align: center"> +<figure url="images/image43.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 43—<hi rend="font-weight: bold">Diagram</hi> +illustrating lung capacity.</head> +<figDesc>Fig. 43</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Capacity of the Lungs.</hi>—The air +which passes into and from the lungs in ordinary breathing, called the +<hi rend="font-style: italic">tidal</hi> air, is but a small part of<pb n="089" /><anchor id="Pg089" /> the whole amount of air which the +lungs contain. Even after a forced expiration the lungs are almost half +full; the air which remains is called the <hi rend="font-style: +italic">residual</hi> air. The air which is expelled from the lungs by a +forced expiration, less the tidal air, is called the <hi +rend="font-style: italic">reserve</hi>, or supplemental, air. These +several quantities are easily estimated. (See Practical Work.) In the +average individual the total capacity of the lungs (with the chest in +repose) is about one gallon. In forced inspirations this capacity may be +increased about one third, the excess being known as the <hi +rend="font-style: italic">complemental</hi> air (Fig. 43).</p> + +<p rend="text-align: center"> +<figure url="images/image44.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 44—<hi rend="font-weight: bold">Diagram</hi> +illustrating internal respiration and its dependence on external +respiration. (Modified from Hall.) (See text.)</head> +<figDesc>Fig. 44</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Internal, or Cell, Respiration.</hi>—The +oxygen which enters the blood in the lungs leaves it in the tissues, +passing through the lymph into the cells (Fig. 44). At the same time the +carbon dioxide which is being formed at the cells passes into the blood. +An exchange of gases is thus taking place between the cells and the +blood, similar to<pb n="090" /><anchor id="Pg090" /> that taking place between the +blood and the air. This exchange is known as <hi rend="font-style: +italic">internal</hi>, or cell, respiration. By internal respiration the +oxygen reaches the place where it is to serve its purpose, and the +carbon dioxide begins its movement toward the exterior of the body. This +"breathing by the cells" is, therefore, <hi rend="font-style: +italic">the final and essential act of respiration</hi>. Breathing by +the lungs is simply the means by which the taking up of oxygen and <hi +rend="font-weight: bold">the</hi> giving off of carbon dioxide by the +cells is made possible.</p> + +<div> +<head>HYGIENE OF RESPIRATORY ORGANS</head> + +<p>The liability of the lungs to attacks from such dread diseases as +consumption and pneumonia makes questions touching their hygiene of +first importance. Consumption does not as a rule attack sound lung +tissue, but usually has its beginning in some weak or enfeebled spot in +the lungs which has lost its "power of resistance." Though consumption +is not inherited, as some suppose, lung weaknesses may be transmitted +from parents to children. This, together with the fact, now generally +recognized, that consumption is contagious, accounts for the frequent +appearance of this disease in the same family. Consumption as well as +other respiratory affections can in the majority of cases be <hi +rend="font-style: italic">prevented</hi>, and in many cases cured, by an +intelligent observation of well-known laws of health.</p> + +<p><hi rend="font-weight: bold">Breathe through the Nostrils.</hi>—Pure +air and plenty of it is the main condition in the hygiene of the lungs. +One necessary provision for obtaining <hi rend="font-style: italic">pure +air</hi> is that of breathing through the nostrils. Air is the carrier +of dust particles and not infrequently of disease germs.<note place="foot"><p>The amount of dust suspended in what we ordinarily think +of as pure air is shown when a beam of direct sunlight enters an +otherwise darkened room.</p></note> Partly +through<pb n="091" /><anchor id="Pg091" /> the small hairs in the nose, but +mainly through the moist membrane that lines the passages, the nostrils +serve as filters for removing the minute solid particles (Fig. 45). +While it is important that nose breathing be observed at all times, it +is especially important when one is surrounded by a dusty or smoky +atmosphere. Otherwise the small particles that are breathed in through +the mouth may find a lodging place in the lungs.</p> + +<p rend="text-align: center"> +<figure url="images/image45.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 45—<hi rend="font-weight: bold">Human air +filter.</hi> Diagram of a section through the nostrils; shows projecting +bones covered with moist membrane against which the air is made to +strike by the narrow passages. 1. Air passages. 2. Cavities in the +bones. 3. Front lower portion of the cranial cavity.</head> +<figDesc>Fig. 45</figDesc> +</figure></p> + +<p>In addition to removing dust particles and germs, other purposes are +served by breathing through the nostrils. The warmth and moisture which +the air receives in this way, prepare it for entering the lungs. Mouth +breathing, on the other hand, looks bad and during sleep causes snoring. +The habit of nose breathing should be established early in life.<note place="foot"><p>Some children find it difficult to breathe through the +nostrils on account of growths (called adenoids) in the upper pharynx. +Such children should have medical attention. The removal of these +growths not only improves the method of breathing, but in many instances +causes a marked improvement in the general health and personal +appearance.</p></note></p> + +<p><hi rend="font-weight: bold">Cultivate Full Breathing.</hi>—Many +people, while apparently taking in sufficient air to supply their need +for oxygen, do not breathe deeply enough to "freely ventilate the +lungs." "Shallow breathing," as this is called,<pb n="092" /><anchor id="Pg092" /> is objectionable because it fails +to keep up a healthy condition of the entire lung surface. Portions of +the lungs to which air does not easily penetrate fail to get the fresh +air and exercise which they need. As a consequence, they become weak +and, by losing their "power of resistance," become points of attack in +diseases of the lungs.<note place="foot"><p>The weakest portions of the lungs appear to be the tiny +lobes at the top. As they occupy the part of the thorax most difficult +to expand, air penetrates them much less freely than it does the lobes +below. In most cases of consumption (some authorities give as high as +eighty per cent), the upper lobes are the first to be affected. Flat +chests and round shoulders, by increasing this natural difficulty in +breathing, have long been recognized as causes which predispose to +consumption.</p></note> The breathing of each individual should +receive attention, and where from some cause it is not sufficiently full +and deep, the means should be found for remedying the defect.</p> + +<p><hi rend="font-weight: bold">Causes of Shallow +Breathing.</hi>—Anything that impedes the free movement of air into the +lungs tends to cause shallow breathing A drooping of the back or +shoulders and a curved condition of the spinal column, such as is caused +by an improper position in sitting, interfere with the free movements of +the ribs and are recognized causes. Clothing also may impede the +respiratory movements and lead to shallow breathing. If too tight around +the chest, clothing interferes with the elevation of the ribs; and if +too tight around the waist, it prevents the depression of the diaphragm. +Other causes of shallow breathing are found in the absence of vigorous +exercise, in the leading of an indoor and inactive life, in obstructions +in the nostrils and upper pharynx, and in the lack of attention to +proper methods of breathing.</p> + +<p>To prevent shallow breathing one should have the habit of sitting and +standing erect. The clothing must not be allowed to interfere with the +respiratory movements. The taking of exercise sufficiently vigorous to +cause deep and<pb n="093" /><anchor id="Pg093" /> rapid breathing should be a +common practice and one should spend considerable time out of doors. If +one has a flat chest or round shoulders, he should strive by suitable +exercises to overcome these defects. Obstructions in the nostrils or +pharynx should be removed.</p> + +<p><hi rend="font-weight: bold">Breathing Exercises.</hi>—In overcoming +the habit of shallow breathing and in strengthening the lungs generally, +the practicing of occasional deep breathing has been found most valuable +and is widely recommended. With the hands on the hips, the shoulders +drawn back and <hi rend="font-style: italic">down</hi>, the chest pushed +upward and forward, and the chin slightly depressed, draw the air slowly +through the nostrils until the lungs are <hi rend="font-style: +italic">completely</hi> full. After holding this long enough to count +three slowly, expel it quickly from the lungs. Avoid straining. To get +the benefit of pure air, it is generally better to practice deep +breathing out of doors or before an open window.</p> + +<p>By combining deep breathing with simple exercises of the arms, +shoulders, and trunk much may be done towards straightening the spine, +squaring the shoulders, and overcoming flatness of the chest. Though +such movements are best carried on by the aid of a physical director, +one can do much to help himself. One may safely proceed on the principle +that slight deformities of the chest, spine, and shoulders are corrected +by gaining and keeping the natural positions, and may employ any +movements which will loosen up the parts and bring them where they +naturally belong.<note place="foot"><p>The following exercise, from Dudley A. Sargent's <hi +rend="font-style: italic">Health, Strength, and Power</hi>, will be +found most beneficial: "Stand with the feet together, face downward, +arms extended downward, and backs of the hands touching. Raise the +hands, arms, and elbows, keeping the backs of the hands together until +they pass the chest and face. Then continue the movement upward, until +the hands separate above the head with the face turned upward, when they +should be brought downward and outward in a large +circle to the starting point. Begin to inhale as the arms are raised and +take in as much air as possible by the time the hands are above the +head, then allow the breath to go out slowly as the arms descend."</p></note></p> + +<p><pb n="094" /><anchor id="Pg094" /> <hi rend="font-weight: +bold">Serious Nature of Colds.</hi>—That many cases of consumption have +their beginning in severe colds (on the lungs) is not only a matter of +popular belief, but the judgment also of physicians. Though the cold is +a different affection from that of consumption, it may so lower the +vitality of the body and weaken the lung surfaces that the germs of +consumption find it easy to get a start. On this account a cold on the +chest which does not disappear in a few days, but which persists, +causing more or less coughing and pain in the lungs, must be given +serious consideration.<note place="foot"><p>Colds may frequently be broken up at their beginning by +taking a prolonged <hi rend="font-style: italic">hot</hi> bath and going +to bed. After getting a start, however, they run a course of a few days, +a week, or longer, depending upon the natural vigor of the individual +and the care which he gives his body during the time. In throwing off a +cold, the following suggestions will be found helpful:</p> + +<p>1. Dress warmly (without overdoing it) and avoid getting chilled. 2. +Diminish the usual amount of work and increase the period for sleep. If +very weak, stay in bed. Save the energy for throwing off the cold. 3. If +able to be about, spend considerable time in light exercise out of +doors, but avoid getting chilled. 4. Keep the bowels active, taking a +cathartic if necessary. 5. To relieve pain in the chest, apply a mustard +plaster or a flannel cloth moistened with some irritating substance, +such as turpentine or a mixture of equal parts of kerosene and lard. +Keep up a mild irritation until the pain is relieved, but avoid +blistering.</p></note> The usual home remedies failing to give +relief, a physician should be consulted. It should also be noted that +certain diseases of a serious nature (pneumonia, diphtheria, measles, +etc.) have in their beginning the appearance of colds. On this account +it is wise not only to call a physician, but to call him early, in +severe attacks of the lungs. Especially if the attack be attended by +difficult breathing, fever, and a rapid pulse is the case serious and +medical advice necessary.</p> + +<p><hi rend="font-weight: bold">Ventilation.</hi>—The process by which +the air in a room is kept fresh and pure is known as ventilation. It is +a<pb n="095" /><anchor id="Pg095" /> double process—that of bringing +fresh air into the room and that of getting rid of air that has been +rendered impure by breathing <note place="foot"><p>Not only do the lungs remove oxygen from the air and add +carbon dioxide to it, but they separate from the body considerable +moisture and, according to some authorities, a small amount of an +impurity referred to as "animal matter." Odors also arise from the +skin, teeth, and clothing which, if not dangerous to the health, are +offensive to the nostrils. If on going into a room such odors are +detected, the ventilation is not sufficient. This is said to be a +reliable test.</p></note> or by lamps. Outdoor air is usually of +a different temperature (colder in winter, warmer in summer) from that +indoors, and as a consequence differs from it slightly in weight. On +account of this difference, suitable openings in the walls of buildings +induce currents which pass between the rooms and the outside atmosphere +even when there is no wind. In winter care must be taken to prevent +drafts and to avoid too great a loss of heat from the room. A cold draft +may even cause more harm to one in delicate health than the breathing of +air which is impure. To ventilate a room successfully the problem of +preventing drafts must be considered along with that of admitting the +fresh air.</p> + +<p rend="text-align: center"> +<figure url="images/image46.png" rend="page-float: 'hp'; text-align: center; w40"> +<head><lb />Fig. 46—Window adjusted for ventilation without +drafts.</head> +<figDesc>Fig. 46</figDesc> +</figure></p> + +<p>The method of ventilation must also be adapted to the construction of +the building, the plan of heating, and the condition of the weather. +Specific directions cannot be given, but the following suggestions will +be found helpful in ventilating rooms where the air is not warmed before +being admitted:</p> + +<p>1. <hi rend="font-style: italic">Introduce, the air through many +small openings</hi> rather than a few large ones. If the windows are +used for this purpose, raise the lower sash and drop the upper one <hi +rend="font-style: italic">slightly</hi> for <hi rend="font-style: +italic">several</hi> windows, varying the width to suit the conditions +(Fig. 46). By this means sufficient air may be introduced without +causing drafts.</p> + +<p>2. <hi rend="font-style: italic">Introduce the air at the warmest +portions of the room.</hi><pb n="096" /><anchor id="Pg096" /> The air should, if possible, be +warmed before reaching the occupants.</p> + +<p>3. If the wind is blowing, <hi rend="font-style: italic">ventilate +principally on the sheltered side of the house</hi>.</p> + +<p>Ample provision should be made for fresh air in sleeping rooms, and +here again drafts must be avoided. Especially should the bed be so +placed that strong air currents do not pass over the sleeper. In +schoolhouses and halls for public gatherings the means for efficient +ventilation should, if possible, be provided in the general plan of +construction and method of heating.</p> + +<p rend="text-align: center"> +<figure url="images/image47.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 47—<hi rend="font-weight: bold">Artificial respiration</hi> as a laboratory +experiment. Expiration. Prone-posture method of Schaffer.</head> +<figDesc>Fig. 47</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Artificial Respiration.</hi>—When +natural breathing is temporarily suspended, as in partial drowning, or +when one has been overcome by breathing some poisonous gas, the saving +of life often depends upon the prompt application of artificial +respiration. This is accomplished by alternately compressing and +enlarging the thorax by means of variable pressure on the outside, +imitating the natural process as nearly as possible. Following is the +method proposed by Professor E.A. Schaffer of England, and called by +him "the <hi rend="font-style: italic">prone-posture</hi> method of +artificial respiration":</p> + +<p><pb n="097" /><anchor id="Pg097" />The patient is laid +face downward with an arm bent under the head, and <hi rend="font-style: +italic">intermittent</hi> pressure applied vertically over the shortest +ribs. The pressure drives the air from the lungs, both by compressing +the lower portions of the chest and by forcing the abdominal contents +against the diaphragm, while the elastic reaction of the parts causes +fresh air to enter (Figs. 47 and 48). "The operator kneels or squats by +the side of, or across the patient, places his hands over the lowest +ribs and swings his body backward and forward so as to allow his weight +to fall vertically on the wrists and then to be removed; in this way +hardly any muscular exertion is required.... The pressure is applied +gradually and slowly, occupying some three seconds; it is then withdrawn +during two seconds and again applied; and so on some twelve times per +minute."<note place="foot"><p>E.A. Schaffer, "Artificial Respiration in its +Physiologic Aspects," <hi rend="font-style: italic">The Journal of the +American Medical Association</hi>, September, 1908.</p></note></p> + +<p rend="text-align: center"> +<figure url="images/image48.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 48—Artificial respiration. Inspiration.</head> +<figDesc>Fig. 48</figDesc> +</figure></p> + +<p>The special advantages of the prone-posture method over others that +have been employed are: I. It may be applied by a single individual and +fora long period of time without exhaustion. 2. It allows the mucus and +water (in case of drowning) to run out of the mouth, and causes the +tongue to fall forward so as not to obstruct the passageway. 3. It +brings a sufficient amount of air into the lungs.<note place="foot"><p>Testing the prone-posture method by suitable apparatus, Professor +Schaffer has found it capable of introducing more air per minute into +the lungs than any of the other methods of artificial respiration, and +more even than is introduced by ordinary breathing.</p></note></p> + +<p><pb n="098" /><anchor id="Pg098" />While applying artificial +respiration, the heat of the body should not be allowed to escape any +more than can possibly be helped. In case of drowning, the patient +should be wrapped in dry blankets or clothing, while bottles of hot +water may be placed in contact with the body. The circulation should be +stimulated, as may be done by rubbing the hands, feet, or limbs in the +direction of the flow of the blood in the veins.</p> + +<p><hi rend="font-weight: bold">Tobacco Smoke and the Air</hi> +Passages.—Smoke consists of minute particles of unburnt carbon, or soot, +such as collect in the chimneys of fireplaces and furnaces. If much +smoke is taken into the lungs, it irritates the delicate linings and +tends to clog them up. Tobacco smoke also contains the poison nicotine, +which is absorbed into the blood. For these reasons the cigarette user +who inhales the smoke does himself great harm, injuring his nervous +system and laying the foundation for diseases of the air passages. The +practice of smoking indoors is likewise objectionable, since every one +in a room containing the smoke is compelled to breathe it.</p> + +<p><hi rend="font-weight: bold">Alcohol and Diseases of the +Lungs.</hi>—Pneumonia is a serious disease of the lungs caused by germs. +The attacks occur as a result of exposure, especially when the body is +in a weakened condition. A noted authority states that "alcoholism is +perhaps the most potent predisposing cause" of pneumonia.<note place="foot"><p>Osier, <hi rend="font-style: italic">The Principles and +Practice of Medicine</hi>.</p></note> A person +addicted to the use of alcohol is also less likely to recover from the +disease than one who has avoided its use, a result due in part to the +weakening effect of alcohol upon the heart. The congestion of the lungs +in pneumonia makes it very difficult for the heart to force the blood +through them. The weakened heart of the drunkard gives way under the +task.</p> + +<p>The statement sometimes made that alcohol is beneficial<pb n="099" /><anchor id="Pg099" /> in pulmonary tuberculosis is +without foundation in fact. On the other hand, alcoholism is a +recognized cause of consumption. Some authorities claim that this +disease is more frequent in heavy drinkers than in those of temperate +habits, in the proportion of about three to one, and that possibly half +of the cases of tuberculosis are traceable to alcoholism.<note place="foot"><p>Huber, <hi rend="font-style: italic">Consumption and +Civilization</hi>.</p></note></p> + +<p><hi rend="font-weight: bold">The Outdoor Cure for Lung +Diseases</hi>—Among the many remedies proposed for consumption and +kindred diseases, none have proved more beneficial, according to +reports, than the so-called "outdoor" cure. The person having +consumption is fed plentifully upon the most nourishing food, and is +made to spend practically his entire time, including the sleeping hours, +<hi rend="font-style: italic">out of doors</hi>. Not only is this done +during the pleasant months of summer, but also during the winter when +the temperature is below freezing. Severe exposure is prevented by +overhead protection at night and by sufficient clothing to keep the body +warm. The abundant supply of pure, cold air toughens the lungs and +invigorates the entire body, thereby enabling it to throw off the +disease.</p> + +<p>The success attending this method of treating consumptives suggests +the proper mode of strengthening lungs that are not diseased, but simply +weak. The person having weak lungs should spend as much time as he +conveniently can out of doors. He should provide the most ample +ventilation at night and have a sleeping room to himself. He should +practice deep breathing exercises and partake of a nourishing diet. +While avoiding prolonged chilling and other conditions liable to induce +colds, he should take advantage of every opportunity of exposing himself +fully and freely to the outside atmosphere.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The purpose of respiration +is to bring about an exchange of gases between the body and the +atmosphere. The organs employed for this purpose, called the respiratory +organs, are adapted to handling materials in the <hi rend="font-style: +italic">gaseous</hi> state, and are operated in accordance with +principles governing the movements of the atmosphere. By alternately +increasing and diminishing<pb n="100" /><anchor id="Pg100" /> the thoracic space, air is made +to pass between the outside atmosphere and the interior of the lungs. +Finding its way into the smallest divisions of the lungs, called the +alveoli, the air comes very near a large surface of blood. By this means +the carbon dioxide diffuses out of the blood, and the free oxygen +enters. Through the combined action of the organs of respiration and the +organs that move the blood and the lymph, the cells in all parts of the +body are enabled to exchange certain gaseous materials with the outside +atmosphere.</p> + +<p rend="text-align: center"> +<figure url="images/image49.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 49—Model for demonstrating the lungs.</head> +<figDesc>Fig. 49</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Exercises.—</hi>1. How does air entering +the lungs differ in composition from air leaving the lungs? What +purposes of respiration are indicated by these differences?</p> + +<p>2. Name the divisions of the lungs.</p> + +<p>3. Trace air from the outside atmosphere into the alveoli. Trace the +blood from the right ventricle to the alveoli and back again to the left +auricle.</p> + +<p>4. How does the movement of air into and from the lungs differ from +that of the blood through the lungs with respect to (<hi +rend="font-style: italic">a</hi>) the direction of the motion. (<hi +rend="font-style: italic">b</hi>) the causes of the motion, and (<hi +rend="font-style: italic">c</hi>) the tubes through which the motion +takes place?</p> + +<p>5. How are the air passages kept clean and open?</p> + +<p>6. Describe the pleura. Into what divisions does it separate the +thoracic cavity?</p> + +<p>7. Describe and name uses of the diaphragm.</p> + +<p>8. If 30 cubic inches of air are passed into the lungs at each +inspiration and .05 of this is retained as oxygen, calculate the number +of cubic feet of oxygen consumed each day, if the number of inspirations +be 18 per minute.</p> + +<p>9. Find the <hi rend="font-style: italic">weight</hi> of a day's +supply of oxygen, as found in the above problem, allowing 1.3 ounces as +the weight of a cubic foot.</p> + +<p>10. Make a study of the hygienic ventilation of the schoolroom.</p> + +<p><pb n="101" /><anchor id="Pg101" />11. Give advantages of full breathing over shallow breathing.</p> + +<p>12. How may a flat chest and round shoulders be a cause of +consumption? How may these deformities be corrected?</p> + +<p>13. Give general directions for applying artificial respiration.</p> +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p>Examine a dissectible model of the chest and its contents (Fig. 49). +Note the relative size of the two lungs and their position with +reference to the heart and diaphragm. Compare the side to side and +vertical diameters of the cavity. Trace the air tubes from the trachea +to their smallest divisions.</p> + +<p><hi rend="font-weight: bold">Observation of Lungs</hi> +(Optional).—Secure from a butcher the lungs of a sheep, calf, or hog. +The windpipe and heart should be left attached and the specimen kept in +a moist condition until used. Demonstrate the trachea, bronchi, and the +bronchial tubes, and the general arrangement of pulmonary arteries and +veins. Examine the pleura and show lightness of lung tissue by floating +a piece on water.</p> + +<p><hi rend="font-weight: bold">To show the Changes that Air undergoes +in the Lungs.</hi>—1. Fill a quart jar even full of water. Place a piece +of cardboard over its mouth and invert, without spilling, in a pan of +water. Inserting a tube under the jar, blow into it air that has been +held as long as possible in the lungs. When filled with air, remove the +jar from the pan, keeping the top well covered. Slipping the cover +slightly to one side, insert a burning splinter and observe that the +flame is extinguished. This proves the absence of sufficient oxygen to +support combustion. Pour in a little limewater<note place="foot"><p>To prepare limewater some small lumps of <hi +rend="font-style: italic">fresh</hi> lime (either slacked or unslacked) +are added to a large bottle of water and thoroughly shaken. This is put +aside until the lime all settles to the bottom and the water above is +perfectly clear. This is now ready for use and may be poured off as +needed. When the supply is exhausted add more water and shake +again.</p></note> and shake to mix with +the air. The change of the limewater to a milky white color proves the +presence of carbon dioxide.</p> + +<p rend="text-align: center"> +<figure url="images/image50.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 50—<hi rend="font-weight: bold">Apparatus</hi> +for showing changes which air undergoes while in the lungs.</head> +<figDesc>Fig. 50</figDesc> +</figure></p> + +<p>2. The effects illustrated in experiment 1 may be shown in a somewhat +more striking manner as follows: Fill two bottles of the same<pb n="102" /><anchor id="Pg102" /> size each one fourth full of +limewater and fit each with a two-holed rubber stopper (Fig. 50). Fit +into each stopper one short and one long glass tube, the long tube +extending below the limewater. Connect the short tube of one bottle and +the long tube of the other bottle with a Y-tube. Now breathe slowly +three or four times through the Y-tube. It will be found that the +inspired air passes through one bottle and the expired air through the +other. Compare the effect upon the limewater in the two bottles. Insert +a small burning splinter into the top of each bottle and note result. +What differences between inspired and expired air are thus shown?</p> + +<p>3. Blow the breath against a cold window pane. Note and account for +the collection of moisture.</p> + +<p>4. Note the temperature of the room as shown by a thermometer. Now +breathe several times upon the bulb, noting the rise in the mercury. +What does this experiment show the body to be losing through the +breath?</p> + +<p><hi rend="font-weight: bold">To show Changes in the Thoracic +Cavity.</hi>—1. To a yard- or meter-stick, attach two vertical strips, +each about eight inches long, as shown in Fig. 51. The piece at the end +should be secured firmly in place by screws or nails. The other should +be movable. With this contrivance measure the sideward and forward +expansion of a boy's thorax. Take the diameter first during a complete +inspiration and then during a complete expiration, reading the +difference. Compare the forward with the sideward expansion.</p> + +<p rend="text-align: center"> +<figure url="images/image51.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 51—<hi rend="font-weight: bold">Apparatus</hi> +for measuring chest expansion.</head> +<figDesc>Fig. 51</figDesc> +</figure></p> + +<p>2. With a tape-line take the circumference of the chest when all the +air possible has been expelled from the lungs. Take it again when the +lungs have been fully inflated. The difference is now read as the chest +expansion.</p> + +<p rend="text-align: center"> +<figure url="images/image52.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 52—<hi rend="font-weight: bold">Simple +apparatus</hi> for illustrating the action of the diaphragm.</head> +<figDesc>Fig. 52</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">To illustrate the Action of the +Diaphragm.</hi>—Remove the bottom from a large bottle having a small +neck. (Scratch a deep mark with a<pb n="103" /><anchor id="Pg103" /> file and hold on the end of this +mark a hot poker. When the glass cracks, lead the crack around the +bottle by heating about one half inch in advance of it.) Place the +bottle in a large glass jar filled two thirds full of water (Fig. 52). +Let the space above the water represent the chest cavity and the water +surface represent the diaphragm. Raise the bottle, noting that the water +falls, thereby increasing the space and causing air to enter. Then lower +the bottle, noting the opposite effect. To show the movement of the air +in and out of the bottle, hold with the hand (or arrange a support for) +a burning splinter over the mouth of the bottle.</p> + +<p><hi rend="font-weight: bold">To estimate the Capacity of the +Lungs.</hi>—Breathing as naturally as possible, expel the air into a +spirometer (lung tester) during a period, say of ten respirations (Fig. +53). Note the total amount of air exhaled and the number of "breaths" +and calculate the amount of air exhaled at each breath. This is called +the <hi rend="font-style: italic">tidal</hi> air.</p> + +<p rend="text-align: center"> +<figure url="images/image53.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 53—<hi rend="font-weight: bold">Apparatus</hi> +(spirometer) for measuring the capacity of the lungs.</head> +<figDesc>Fig. 53</figDesc> +</figure></p> + +<p>2. After an ordinary inspiration empty the lungs as completely as +possible into the spirometer, noting the quantity exhaled. This amount, +less the tidal air, is known as the <hi rend="font-style: +italic">reserve</hi> air. The air which is now left in the lungs is +called the <hi rend="font-style: italic">residual</hi> air. On the +theory that this is equal in amount to the reserve air, calculate the +capacity of the lungs in an ordinary inspiration.</p> + +<p>3. Now fill the lungs to the full expansion of the chest and empty +them as completely as possible into the spirometer, noting the amount +expelled. This, less the tidal air and the reserve air, is called the +<hi rend="font-style: italic">complemental</hi> air. Now calculate the +total capacity of the lungs.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="104" /><anchor id="Pg104" /> + +<head>CHAPTER VIII - PASSAGE OF OXYGEN THROUGH THE BODY</head> + +<p>What is the nature of oxygen? What is its purpose in the body and how +does it serve this purpose? How is the blood able to take it up at the +lungs and give it off at the cells? What becomes of it after being used? +These are questions touching the maintenance of life and they deserve +careful consideration.</p> + +<p><hi rend="font-weight: bold">Nature of Oxygen.</hi>—To understand the +relation which oxygen sustains to the body we must acquaint ourselves +with certain of its chemical properties. It is an element<note place="foot"><p>An <hi rend="font-style: italic">element</hi> is a +single kind of matter. Those substances are classed as elements which +cannot be separated into different kinds of matter. Two or more elements +combined in definite proportions by weight form a <hi rend="font-style: +italic">compound</hi>. The elements are few in number, only about eighty +being known. Compounds, on the other hand, are exceedingly numerous.</p></note> of intense +affinity, or combining power, and is one of the most active of all +chemical agents. It is able to combine with most of the other elements +to form chemical compounds. A familiar example of its combining action +is found in ordinary combustion, or burning. On account of the part it +plays in this process, oxygen is called the <hi rend="font-style: +italic">supporter of combustion</hi>; but it supports combustion by the +simple method of uniting. The ashes that are left and the invisible +gases that escape into the atmosphere are the compounds formed by the +uniting process. It thus appears that oxygen, in common with the other +elements, may exist in either of two forms:</p> + +<p><pb n="105" /><anchor id="Pg105" />1. That in which it is in a <hi rend="font-style: italic">free</hi>, +or uncombined, condition—the form in which it exists in the +atmosphere.</p> + +<p>2. That in which it is a part of compounds, such as the compounds +formed in combustion.</p> + +<p>Oxygen manifests its activity to the best advantage when it is in a +free state, or, more accurately speaking, when it is passing from the +free state into one of combination. It is separated from its compounds +and brought again into a free state by overcoming with heat, or some +other force, the affinity which causes it to unite.</p> + +<p><hi rend="font-weight: bold">How Oxygen unites.</hi>—The chemist +believes oxygen, as well as all other substances, to be made up of +exceedingly small particles, called <hi rend="font-style: +italic">atoms</hi>. The atoms do not exist singly in either elements or +compounds, but are united with each other to form groups of atoms that +are called <hi rend="font-style: italic">molecules</hi>. In an element +the molecules are made up of one kind of atoms, but in a compound the +molecules are made up of as many kinds of atoms as there are elements in +the compound. Changes in the composition of substances (called chemical +changes) are due to rearrangements of the atoms and the formation of new +molecules. The atoms, therefore, are the units of chemical combination. +In the formation of new compounds they unite, and in the breaking up of +existing compounds they separate.</p> + +<p>The uniting of oxygen is no exception to this general law. All of its +combinations are brought about by the uniting of its atoms. In the +burning of carbon, for example, the atoms of oxygen and the atoms of +carbon unite, forming molecules of the compound known as carbon dioxide. +The chemical formula of this compound, which is CO_<hi rend="vertical-align: sub">2</hi>, shows the +proportion in which the atoms unite—one atom of carbon uniting with two +atoms of oxygen in each of the molecules. The affinity of oxygen for +other<pb n="106" /><anchor id="Pg106" /> elements, and the affinity of +other elements for oxygen, and for each other, resides in their +atoms.</p> + +<p><hi rend="font-weight: bold">Oxidation.</hi>—The uniting of oxygen +with other elements is termed <hi rend="font-style: +italic">oxidation</hi>. This may take place slowly or rapidly, the two +rates being designated as <hi rend="font-style: italic">slow</hi> +oxidation and <hi rend="font-style: italic">rapid</hi> oxidation. +Examples of slow oxidation are found in certain kinds of decay and in +the rusting of iron. Combustion is an example of rapid oxidation. Slow +and rapid oxidation, while differing widely in their effects upon +surrounding objects, are alike in that both produce heat and form +compounds of oxygen. In slow oxidation, however, the heat may come off +so gradually that it is not observed.</p> + +<p><hi rend="font-weight: bold">Movement of Oxygen through the +Body.</hi>—Oxygen has been shown in the preceding chapters to pass from +the lungs into the blood and later to leave the blood and, passing +through the lymph, to enter the cells. That oxygen does not become a +permanent constituent of the cells is shown by the constancy of the body +weight. Nearly two pounds of oxygen per day are known to enter the cells +of the average-sized person. If this became a permanent part of the +cells, the body would increase in weight from day to day. Since the body +weight remains constant, or nearly so, we must conclude that oxygen +leaves the body about as fast as it enters. Oxygen enters the body as a +<hi rend="font-style: italic">free</hi> element. The form in which it +leaves the body will be understood when we realize the purpose which it +serves and the method by which it serves this purpose.</p> + +<p><hi rend="font-weight: bold">Purpose of Oxygen in the Body.</hi>—The +question may be raised: Is it possible for oxygen to serve a purpose in +the body without remaining in it? This, of course, depends upon what the +purpose is. That it is possible for oxygen to serve a purpose and at the +same time pass on through<pb n="107" /><anchor id="Pg107" /> the place where it serves that +purpose, is seen by studying the combustion in an ordinary stove (Fig. +54). Oxygen enters at the draft and for the most part passes out at the +flue, but in passing through the stove it unites with, or oxidizes, the +fuel, causing the combustion which produces the heat.</p> + +<p rend="text-align: center"> +<figure url="images/image54.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 54—<hi rend="font-weight: bold">Coal stove</hi> +illustrating rapid oxidation.</head> +<figDesc>Fig. 54</figDesc> +</figure></p> + +<p>Now it is found that certain chemical processes, mainly oxidations, +are taking place in the body. These produce the heat for keeping it warm +and also supply other forms of energy,<note place="foot"><p>The term <hi rend="font-style: italic">energy</hi>, as +used here, has the same general meaning as the word <hi +rend="font-style: italic">power</hi>. See Chapter XII.</p></note> including motion. It is the +purpose of oxygen to keep up these oxidations and, by so doing, to aid +in supplying the body with energy. It serves this purpose in much the +same way that it supports combustion, <hi rend="font-style: +italic">i.e.</hi>, by uniting with, or oxidizing, materials derived from +foods that are present in the cells.</p> + +<p><hi rend="font-weight: bold">Does Oxygen serve Other +Purposes?</hi>—It has been suggested that oxygen may serve the purpose +of oxidizing, or destroying, substances that are injurious and of +acting, in this way, as a purifying agent in the body. In support of +this view is the natural tendency of oxygen to unite with substances and +the well-known fact that oxygen is an important natural agent in +purifying water. It seems probable, therefore, that it may to a slight +extent serve this purpose in the body. It is probable also that oxygen +aids through its chemical activity in the formation of compounds<pb n="108" /><anchor id="Pg108" /> which are to become a part of the +cells. Both of these uses, however, are of minor importance when +compared with <hi rend="font-style: italic">the main use of oxygen</hi>, +which <hi rend="font-style: italic">is that of an aid in supplying +energy to the body</hi>.</p> + +<p><hi rend="font-weight: bold">Oxygen and the Maintenance of +Life.</hi>—In the supplying of energy to the body, one of the conditions +necessary to the maintenance of life is provided. Because oxygen is +necessary to this process, and because death quickly results when the +supply of it is cut off, oxygen is frequently called the supporter of +life. This idea is misleading, for oxygen has no more to do with the +maintenance of life than have the food materials with which it unites. +Life appears to be more dependent upon oxygen than upon food, simply +because the supply of it in the body at any time is exceedingly small. +Being continually surrounded by an atmosphere containing free oxygen, +the body depends upon this as a constant source of supply, and does not +store it up. Food, on the other hand, is taken in excess of the body's +needs and stored in the various tissues, the supply being sufficient to +last for several days. When the supply of either oxygen or food is +exhausted in the body, life must cease.</p> + +<p><hi rend="font-weight: bold">The Oxygen Movement a +Necessity.</hi>—Since <hi rend="font-style: italic">free</hi> oxygen is +required for keeping up the chemical changes in the cells, and since it +ceases to be free as soon as it goes into combination, its continuous +movement through the body is a necessity. The oxygen compounds must be +removed as fast as formed in order to make room for more free oxygen. +This movement has already been studied in connection with the blood and +the organs of respiration, but the consideration of certain details has +been deferred till now. By what means and in what form is the oxygen +passed <hi rend="font-style: italic">to</hi> and <hi rend="font-style: +italic">from</hi> the cells?</p> + +<p><pb n="109" /><anchor id="Pg109" /><hi rend="font-weight: bold">Passage of Oxygen through the +Blood.</hi>—In serving its purpose at the cells, the oxygen passes twice +through the blood—once as it goes toward the cells and again as it +passes from the cells to the exterior of the body:</p> + +<p><hi rend="font-style: italic">Passage toward the Cells.</hi>—This is +effected mainly through the hemoglobin of the red corpuscles. At the +lungs the oxygen and the hemoglobin form a weak chemical compound that +breaks up and liberates the oxygen when it reaches the capillaries in +the tissues. The separation of the oxygen from the hemoglobin at the +tissues appears to be due to two causes: first, to the weakness of the +chemical attraction between the atoms of oxygen and the atoms that make +up the hemoglobin molecule; and second, to a difference in the so-called +<hi rend="font-style: italic">oxygen pressure</hi> at the lungs and at +the tissues.<note place="foot"><p>The oxygen pressure of the atmosphere is that portion of +the total atmospheric pressure which is due to the weight of the oxygen. +Since oxygen comprises about one fifth of the atmosphere, the pressure +which it exerts is about one fifth of the total atmospheric pressure, +or, at the sea level, about three pounds to the square inch (15 x 1/5 = +3). This is the oxygen pressure of the atmosphere. The low oxygen +pressure in the tissues is due to its scarcity, and this scarcity is due +to its entering into combination at the cells.</p></note></p> + +<p>The attraction of the oxygen and the hemoglobin is sufficient to +cause them to unite where the oxygen pressure is more than one half +pound to the square inch, but it is not sufficiently strong to cause +them to unite or to prevent their separation, if already united, where +the oxygen pressure is less than one half pound to the square inch. The +oxygen pressure at the lungs, which amounts to nearly three pounds to +the square inch, easily causes the oxygen and the hemoglobin to unite, +while the almost complete absence of any oxygen pressure at the tissues, +permits their separation. The blood in its circulation constantly flows +from the place of high oxygen pressure at the lungs<pb n="110" /><anchor id="Pg110" /> to the place of low oxygen +pressure at the tissues and, in so doing, loads up with oxygen at one +place and unloads it at the other (Fig. 55).</p> + +<p><hi rend="font-style: italic">Passage from the Cells.</hi>—Since +oxygen leaves the free state at the cells and becomes a part of +compounds, we are able to trace it from the body only by following the +course of these compounds. Three waste compounds of importance are +formed at the cells—carbon dioxide (CO<hi rend="vertical-align: sub">2</hi>), water (H<hi rend="vertical-align: sub">2</hi>O), and urea +(N<hi rend="vertical-align: sub">2</hi>H<hi rend="vertical-align: sub">4</hi>CO). The first is formed by the union of oxygen with carbon, +the second by its union with hydrogen, and the third by its union with +nitrogen, hydrogen, and carbon. These compounds are carried by the blood +to the organs of excretion, where they are removed from the body. The +water leaves the body chiefly as a liquid, the urea as a solid dissolved +in water, and the carbon dioxide as a gas. The passage of carbon dioxide +through the blood requires special consideration.</p> + +<p rend="text-align: center"> +<figure url="images/image55.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 55—<hi rend="font-weight: bold">Diagram +illustrating movement, of oxygen and carbon dioxide through the +body</hi> (S.D. Magers). Each moves from a place of relatively high to a +place of relatively low pressure. (See text.)</head> +<figDesc>Fig. 55</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Passage of Carbon Dioxide through the +Blood.</hi>—Part of the carbon dioxide is dissolved in the plasma of the +blood, and part of it is in weak chemical combination with substances +found in the plasma and in the corpuscles. Its passage through the blood +is accounted for in the same<pb n="111" /><anchor id="Pg111" /> way as the passage of the oxygen. +Its ability to dissolve in liquids and to enter into chemical +combination varies as the <hi rend="font-style: italic">carbon dioxide +pressure</hi><note place="foot"><p>See footnote on oxygen pressure, page 109.</p></note> This in turn varies with the amount of the carbon +dioxide, which is greatest at the cells (where it is formed), less in +the blood, and still less in the lungs. Because of these differences, +the blood is able to take it up at the cells and release it at the lungs +(Fig. 55).</p> + +<p rend="text-align: center"> +<figure url="images/image56.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 56—<hi rend="font-weight: bold">Soap bubble</hi> +floating in a vessel of carbon dioxide, illustrating the difference in +weight between air and carbon dioxide gas.</head> +<figDesc>Fig. 56</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Properties of Carbon +Dioxide.</hi>—Carbon dioxide is a colorless gas with little or no odor. +It is classed as a heavy gas, being about one third heavier than air<note place="foot"><p>The impression prevails to some extent that carbon +dioxide, on account of its weight, settles out of the atmosphere, +collecting in old wells and at the floor in crowded rooms. Any such +settling of the carbon dioxide is prevented by the rapid motion of its +molecules. This motion not only prevents a separation of carbon dioxide +and air after they are mixed, but causes them to mix rapidly when they +are separated, if they still have surface contact. The carbon dioxide +found in old wells is formed there by decaying vegetable or animal +matter. In rooms it is no more abundant at the floor than in other +parts.</p></note> +(Fig. 56). It does not support combustion, but on the contrary is used +to some extent to extinguish fires. It is formed by the oxidation of +carbon in the body, and by the combustion of carbon outside of the body. +It is also formed by the decay of animal and vegetable matter. From +these sources it is continually finding its way into the atmosphere. +Although not a poisonous gas, carbon dioxide may, if it surround the +body, shut out the supply of oxygen and cause death.<note place="foot"><p>On account of the formation of carbon dioxide in places +containing decaying material, the descent into an old well or other +opening into the earth is often a hazardous undertaking. Before making +such a descent the air should always be tested by lowering a lighted +lantern or candle. Artificial respiration is the only means of restoring +one who has been overcome by this gas (page 97).</p></note></p> + +<p><pb n="112" /><anchor id="Pg112" /><hi rend="font-weight: bold">Final Disposition of Carbon +Dioxide.</hi>—It is readily seen that the union of carbon and oxygen, +which is continually removing oxygen from the air and replacing it with +carbon dioxide, tends to make the whole atmosphere deficient in the one +and to have an excess of the other. This tendency is counteracted +through the agency of vegetation. Green plants absorb the carbon dioxide +from the air, decompose it, build the carbon into compounds (starch, +etc.) that become a part of the plant, and return the free oxygen to the +air (Fig. 57). In doing this, they not only preserve the necessary +proportion of oxygen and carbon dioxide in the atmosphere, but also put +the carbon and oxygen in such a condition that they can again unite. The +force which enables the plant cells to decompose the carbon dioxide is +supplied by the sunlight (Chapter XII).</p> + +<p rend="text-align: center"> +<figure url="images/image57.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 57—<hi rend="font-weight: bold">Under +surface</hi> of a geranium leaf showing breathing pores, highly +magnified (O.H.).</head> +<figDesc>Fig. 57</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Summary.</hi>—Oxygen, by uniting with +materials at the cells, keeps up a condition of chemical activity +(oxidation) in the body. This supplies heat and the other forms of +bodily energy. Entering as a free element, oxygen leaves the body as a +part of the waste compounds which it helps to form. The free oxygen is +transported from the lungs to the cells by means of the hemoglobin of +the red corpuscles, while the combined oxygen in carbon dioxide and +other compounds from the cells is carried mainly by the plasma. The +limited supply of free oxygen in the body at any time makes necessary +its continuous introduction into the body.</p> + +<p><pb n="113" /><anchor id="Pg113" /><hi rend="font-weight: bold">Exercises.</hi>—1. Describe the +properties of oxygen. How does it unite with other elements? How does it +support combustion?</p> + +<p>2. State the purpose of oxygen in the body. What properties enable it +to fulfill this purpose?</p> + +<p>3. What is the proof that oxygen does not remain permanently in the +body? How does the oxygen entering the body differ from the same oxygen +as it leaves the body?</p> + +<p>4. What is the necessity for the <hi rend="font-style: +italic">continuous</hi> introduction of oxygen into the body, while food +is introduced only at intervals?</p> + +<p>5. How are the red corpuscles able to take up and give off oxygen? +How is the plasma able to take up and give off carbon dioxide?</p> + +<p>6. If thirty cubic inches of air pass from the lungs at each +expiration and 4.5 per cent of this is carbon dioxide, calculate the +number of cubic feet of the gas expelled in twenty-four hours, +estimating the number of respirations at eighteen per minute.</p> + +<p>7. What is the weight of this volume of carbon dioxide, if one cubic +foot weigh 1.79 ounces?</p> + +<p>8. What portion of this weight is oxygen and what carbon, the ratio +by weight of carbon to oxygen in carbon dioxide being twelve to +thirty-two?</p> + +<p>9. What is the final disposition of carbon dioxide in the +atmosphere?</p> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">To show the Difference between Free +Oxygen and Oxygen in Combination.</hi>—Examine some crystals of +potassium chlorate (KC<hi rend="vertical-align: sub">l</hi>O<hi rend="vertical-align: sub">3</hi>). They contain oxygen <hi rend="font-style: +italic">in combination</hi> with potassium and chlorine. Place a few of +these in a small test tube and heat strongly in a gas or alcohol flame. +The crystals first melt, and the liquid which they form soon appears to +boil. If a splinter, having a spark on the end, is now inserted in the +tube, it is kindled into a flame. This shows the presence of <hi +rend="font-style: italic">free</hi> oxygen, the heat having caused the +potassium chlorate to decompose. The difference between free and +combined oxygen may also be shown by decomposing other compounds of +oxygen, such as water and mercuric oxide.</p> + +<p><hi rend="font-weight: bold">Preparation and Properties of +Oxygen.</hi>—Intimately mix 3 grams (1/2 teaspoonful) of potassium +chlorate with half its bulk of manganese dioxide, and place the mixture +in a large test tube. Close the test tube with a tight-fitting stopper +which bears a glass tube of sufficient<pb n="114" /><anchor id="Pg114" +/> length and of the right shape to convey the escaping gas to a small +trough or pan partly filled with water, on the table. Fill four +large-mouthed bottles with water and, by covering with cardboard, invert +each in the trough of water. Arrange the test tube conveniently for +heating, letting the end of the glass tube terminate under the mouth of +one of the bottles (Fig. 58). Using an alcohol lamp or a Bunsen burner, +heat over the greater portion of the tube at first, but gradually +concentrate the flame upon the mixture. Do not heat too strongly, and +when the gas is coming off rapidly, remove the flame entirely, putting +it back as the action slows down. After all the bottles have been +filled, remove the end of the glass tube from the water, but leave the +bottles of oxygen inverted in the trough until they are to be used. On +removing the bottles from the trough, keep the tops covered with wet +cardboard.</p> + +<p rend="text-align: center"> +<figure url="images/image58.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 58—<hi rend="font-weight: bold">Apparatus</hi> +for generating oxygen.</head> +<figDesc>Fig. 58</figDesc> +</figure></p> + +<p>1. Examine a bottle of oxygen, noting its lack of color. Insert a +small burning splinter in the upper part of the bottle and observe the +change in the rate of burning. The air contains free oxygen, but it is +diluted with nitrogen. Compare this with the undiluted oxygen in the +bottle as to effect in causing the splinter to burn.</p> + +<p>2. In a second bottle of oxygen insert a splinter without the flame, +but having a small spark on the end. As soon as the oxygen kindles the +spark into a flame, withdraw from the bottle and blow out the flame, but +again insert the spark. Repeat the experiment as long as the spark is +kindled by the oxygen into a flame. This experiment is usually performed +as a test for undiluted oxygen.</p> + +<p>3. Make a hollow cavity in the end of a short piece of crayon. Fasten +a wire to the crayon, and fill the cavity with powdered sulphur.<pb n="115" /><anchor id="Pg115" /> Ignite the sulphur in the flame +of an alcohol lamp or Bunsen burner, and lower it into a bottle of +oxygen. Observe the change in the rate of burning, the color of the +flame, and the material formed in the bottle by the burning. The gas +remaining in the bottle is sulphur dioxide (SO<hi rend="vertical-align: sub">2</hi>), formed by the <hi +rend="font-style: italic">uniting</hi> of the sulphur and the +oxygen.</p> + +<p>4. Bend a small loop on the end of a piece of picture wire. Heat the +loop in a flame and insert it in some powdered sulphur. Ignite the +melted sulphur which adheres, and insert it quickly in a bottle of +oxygen. Observe the dark, brittle material which is formed by the +burning of the iron. It is a compound of the iron with oxygen, similar +to iron rust, and formed by their uniting.</p> + +<p><hi rend="font-weight: bold">Preparation and Properties of Carbon +Dioxide.</hi>—1. (<hi rend="font-style: italic">a</hi>) Attach a piece +of carbon (charcoal) no larger than the end of the thumb to a piece of +wire. Ignite the charcoal in a hot flame and lower it into a vessel of +oxygen. Observe its combustion, letting it remain in the bottle until it +ceases to burn. Note that the burning has consumed a part of the carbon +and has used up the free oxygen. Has anything been formed in their +stead?</p> + +<p>(<hi rend="font-style: italic">b</hi>) Remove the charcoal and add a +little limewater. Cover the bottle with a piece of cardboard, and bring +the gas and the limewater in contact by shaking. Note any change in the +color of the limewater. If it turns white, the presence of carbon +dioxide is proved.</p> + +<p>2. Burn a splinter in a large vessel of air, keeping the top covered. +Add limewater and shake. Note and account for the result.</p> + +<p>3. Place several pieces of marble (limestone) in a jar holding at +least half a gallon. Barely cover the marble with water, and then add +hydrochloric acid until a gas is rapidly evolved. This gas is carbon +dioxide.</p> + +<p>(<hi rend="font-style: italic">a</hi>) Does it possess color?</p> + +<p>(<hi rend="font-style: italic">b</hi>) Insert a burning splinter to +see if it supports combustion.</p> + +<p>(<hi rend="font-style: italic">c</hi>) Place a bottle of oxygen by +the side of the vessel of carbon dioxide. Light a splinter and +extinguish the flame by lowering it into the vessel of carbon dioxide. +Withdraw immediately, and if a spark remains on the splinter, thrust it +into the bottle of oxygen. Then insert the relighted splinter into the +carbon dioxide. Repeat several times, kindling the flame in one gas and +extinguishing it in the other. Finally show that the spark also may be +extinguished by holding the splinter a little longer in the carbon +dioxide.</p> + +<p>(<hi rend="font-style: italic">d</hi>) Tip the jar containing the +carbon dioxide over the mouth of a tumbler, as in pouring water, though +not far enough to spill the acid, and<pb n="116" /><anchor id="Pg116" /> then insert a burning splinter in +the tumbler. Account for the result. Inference as to the weight of +carbon dioxide.</p> + +<p rend="text-align: center"> +<figure url="images/image59.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 59—<hi rend="font-weight: bold">Simple +apparatus</hi> for illustrating passage of oxygen through the body.</head> +<figDesc>Fig. 59</figDesc> +</figure></p> + +<p>(<hi rend="font-style: italic">e</hi>) Review experiments (page 101) +showing the presence of carbon dioxide in the breath.</p> + +<p><hi rend="font-weight: bold">To illustrate the General Movement of +Oxygen through the Body.</hi>—Into a glass tube, six inches in length +and open at both ends, place several small lumps of charcoal (Fig. 59). +Fit into one end of this tube, by means of a stopper, a smaller glass +tube which is bent at right angles and which is made to pass through a +close-fitting stopper to the bottom of a small bottle. Another small +tube is fitted into a second hole in this stopper, but terminating near +the top of the bottle, and to this is connected a rubber tube about +eighteen inches in length. The arrangement is now such that by sucking +air from the top of the bottle, it is made to enter at the distant end +of the tube containing the charcoal. After filling the bottle one third +full of limewater, heat the tube containing the charcoal until it begins +to glow. Then suck the air through the apparatus (as in smoking, without +drawing it into the lungs), observing what happens both in the tube and +in the bottle. What are the proofs that the oxygen, in passing through +the tube, unites with the carbon, forms carbon dioxide, and liberates +energy? Compare the changes which the oxygen undergoes while passing +through the tube with the changes which it undergoes in passing through +the body.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="117" /><anchor id="Pg117" /> + +<head>CHAPTER IX - FOODS AND THE THEORY OF DIGESTION</head> + +<p>The body is constantly in need of new material. Oxidation, as shown +in the preceding chapter, rapidly destroys substances at the cells, and +these have to be replaced. Upon this renewal depends the supply of +energy. Moreover, there is found to be an actual breaking down of the +living material, or protoplasm, in the body. While this does not destroy +the cells, as is sometimes erroneously stated, it reduces the quantity +of the protoplasm and makes necessary a process of repair, or +rebuilding, of the tissues. This also requires new material. Finally, +substances, such as water and common salt, are required for the aid +which they render in the general work of the body. Since these are +constantly being lost in one way or another, they also must be replaced. +These different needs of the body for new materials are supplied +through</p> + +<p><hi rend="font-weight: bold">The Foods.</hi>—Foods are substances +that, on being taken into the healthy body, are of assistance in +carrying on its work. This definition properly includes oxygen, but the +term is usually limited to substances introduced through the digestive +organs. As suggested above, foods serve at least three purposes:</p> + +<p>1. They, with oxygen, supply the body with energy.</p> + +<p>2. They provide materials for rebuilding the tissues.</p> + +<p>3. They supply materials that aid directly or indirectly in the +general work of the body.</p> + +<p><pb n="118" /><anchor id="Pg118" /><hi rend="font-weight: bold">The +Simple Foods, or Nutrients.</hi>—From the great variety of things that +are eaten, it might appear that many different kinds of substances are +suitable for food. When our various animal and vegetable foods are +analyzed, however, they are found to be similar in composition and to +contain only some five or six kinds of materials that are essentially +different. While certain foods may contain only a single one of these, +most of the foods are mixtures of two or more. These few common +materials which, in different proportions, form the different things +that are eaten, are variously referred to as simple foods, food-stuffs, +and <hi rend="font-style: italic">nutrients</hi>, the last name being +the one generally preferred. The different classes of nutrients are as +follows:</p> + +<p rend="text-align: center"> +<table> +<row> +<cell>Nutrients:</cell> +</row> +<row> +<cell>Proteids</cell> +</row> +<row> +<cell>(Albuminoids)</cell> +</row> +<row> +<cell>Carbohydrates</cell> +</row> +<row> +<cell>Fats</cell> +</row> +<row> +<cell>Mineral salts</cell> +</row> +<row> +<cell>Water</cell> +</row> +</table> +</p> + +<p>It is now necessary to become somewhat familiar with the different +nutrients and the purposes which they serve in the body.</p> + +<p><hi rend="font-weight: bold">Proteids.</hi>—The proteids are obtained +in part from the animal and in part from the plant kingdom, there being +several varieties. A well-known variety, called <hi rend="font-style: +italic">albumin</hi>, is found in the white of eggs and in the plasma of +the blood, while the muscles contain an abundance of another variety, +known as <hi rend="font-style: italic">myosin</hi>. Cheese consists +largely of a kind of proteid, called <hi rend="font-style: +italic">casein</hi>, which is also present in milk, but in a more +diluted form. If a mouthful of wheat is chewed for some time, most of it +is dissolved and swallowed, but there remains in the mouth a sticky, +gum-like substance. This is <hi rend="font-style: italic">gluten</hi>, a +form of proteid which occurs<pb n="119" /><anchor id="Pg119" /> in different grains. Again, +certain vegetables, as beans, peas, and peanuts, are rich in a kind of +proteid which is called <hi rend="font-style: italic">legumen</hi>.</p> + +<p>Proteids are compounds of carbon, hydrogen, oxygen, nitrogen, and a +small per cent of sulphur. Certain ones (the nucleo-proteids from +grains) also contain phosphorus. All of the proteids are highly complex +compounds and form a most important class of nutrients.</p> + +<p><hi rend="font-weight: bold">Purposes of Proteids.</hi>—The chief +purpose of proteids in the body is to rebuild the tissues. Not only do +they supply all of the main elements in the tissues, but they are of +such a nature chemically that they are readily built into the +protoplasm. They are absolutely essential to life, no other nutrients +being able to take their place. An animal deprived of them exhausts the +proteids in its body and then dies. In addition to rebuilding the +tissues, proteids may also be oxidized to supply the body with +energy.</p> + +<p><hi rend="font-weight: bold">Albuminoids</hi> form a small class of +foods, of minor importance, which are similar to proteids in +composition, but differ from them in being unable to rebuild the +tissues. Gelatin, a constituent of soup and obtained from bones and +connective tissue by boiling, is the best known of the albuminoid foods. +On account of the nitrogen which they contain, proteids and albuminoids +are often classed together as <hi rend="font-style: italic">nitrogenous +foods</hi>.</p> + +<p><hi rend="font-weight: bold">Carbohydrates.</hi>—While the +carbohydrates are not so essential to life as are the proteids, they are +of very great value in the body. They are composed of carbon, hydrogen, +and oxygen, and are obtained mainly from plants. There are several +varieties of carbohydrates, but they are similar in composition. All of +those used as food to any great extent are starch and certain kinds of +sugar.</p> + +<p><pb n="120" /><anchor id="Pg120" /><hi rend="font-weight: +bold">Starch</hi> is the carbohydrate of greatest importance as a food, +and it is also the one found in the greatest abundance. All green plants +form more or less starch, and many of them store it in their leaves, +seeds, or roots (Fig. 60). From these sources it is obtained as food. +<hi rend="font-style: italic">Glycogen</hi>, a substance closely +resembling starch, is found in the body of the oyster. It is also formed +in the liver and muscles of the higher animals, being prepared from the +sugar of the blood, and is stored by them as reserve food (Chapter XI). +Glycogen is, on this account, called <hi rend="font-style: +italic">animal starch</hi>. Starch on being eaten is first changed to +sugar, after which it may be converted into glycogen in the liver and in +the muscles.</p> + +<p rend="text-align: center"> +<figure url="images/image60.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 60—<hi rend="font-weight: bold">Starch +grains</hi> in cells of potato as they appear under the microscope. (See +practical work.)</head> +<figDesc>Fig. 60</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Sugars.</hi>—There are several varieties +of sugar, but the important ones used as foods fall into one or the +other of two classes, known as <hi rend="font-style: italic">double +sugars</hi> (disaccharides) and <hi rend="font-style: italic">single +sugars</hi> (monosaccharides). To the first class belong <hi +rend="font-style: italic">cane sugar</hi>, found in sugar cane and +beets, <hi rend="font-style: italic">milk sugar</hi>, found in sweet +milk, and <hi rend="font-style: italic">maltose</hi>, a kind of sugar +which is made from starch by the action of malt. The important members +of the second class are <hi rend="font-style: italic">grape sugar</hi>, +or dextrose, and <hi rend="font-style: italic">fruit sugar</hi>, or +levulose, both of which are found in fruits and in honey.</p> + +<p>The most important of all sugars, so far as its use in the body is +concerned, is <hi rend="font-style: italic">dextrose</hi>. To this form +all the other sugars, and starch also, are converted before they are +finally used in the body. The close chemical relation<pb n="121" /><anchor id="Pg121" /> between the different +carbohydrates makes such a conversion easily possible.</p> + +<p><hi rend="font-weight: bold">Fats.</hi>—The fats used as foods belong +to one or the other of two classes, known as solid fats and oils. The +solid fats are derived chiefly from animals, and the oils are obtained +mostly from plants. Butter, the fat of meats, olive oil, and the oil of +nuts are the fats of greatest importance as foods. Fats, like the +carbohydrates, are composed of carbon, hydrogen, and oxygen. They are +rather complex chemical compounds, though not so complex as proteids. +Since neither fats nor carbohydrates contain nitrogen, they are +frequently classed together as <hi rend="font-style: +italic">non-nitrogenous</hi> foods.</p> + +<p><hi rend="font-weight: bold">Purpose Served by Carbohydrates, Fats, +and Albuminoids.</hi>—These classes of nutrients all serve the common +purpose of supplying energy. By uniting with oxygen at the cells, they +supply heat and the other forms of bodily force. This is perhaps their +only purpose.<note place="foot"><p>While awaiting oxidation at the cells, the carbohydrates +and fats are stored up by the body, the carbohydrates as glycogen and +the fats as some form of fat. In this sense they are sometimes looked +upon as serving to build up certain of the tissues.</p></note> Proteids also serve this purpose, but they are not so +well adapted to supplying energy as are the carbohydrates and the fats. +In the first place they do not completely oxidize and therefore do not +supply so much energy; and, in the second place, they form waste +products that are removed with difficulty from the body.</p> + +<p><hi rend="font-weight: bold">Mineral Salts and their +Uses.</hi>—Mineral salts are found in small quantities in all of the +more common food materials, and, as a rule, find their way into the body +unnoticed. They supply the elements which are found in the body in small +quantities and serve a variety of <pb n="122" /><anchor id="Pg122" +/>purposes.<note place="foot"><p>The following table shows the main +elements in the body and their relation to the different nutrients:</p> + +<p rend="text-align: center"> +<figure url="images/image61.png" rend="page-float: 'hp'; text-align: center; w95"> +<head></head> +<figDesc>Nutrient Table</figDesc> +</figure></p></note> +Calcium phosphate and +calcium carbonate are important constituents of the bones and teeth; and +the salts containing iron renew the hemoglobin of the blood. Others +perform important functions in the vital processes. The mineral compound +of greatest importance perhaps is sodium chloride, or common salt.<note place="foot"><p>The recently advanced theory that the molecules of the +mineral salts, by dissolving in water, separate into smaller divisions, +part of which are charged with positive electricity and part with +negative electricity, has suggested several possible uses for sodium +chloride and other mineral salts in the body. The sodium chloride in the +tissues is in such concentration as to be practically all separated into +its sodium and chlorine particles, or ions. It has recently been shown +that the sodium ions are necessary for the contraction of the muscles, +including the muscles of the heart. There is also reason for believing +that the different ions may enter into temporary combination with food +particles, and in this way assist in the processes of nutrition.</p></note> +This is a natural constituent of most of our foods, and is also added to +food in its preparation for the table. When it is withheld from animals +for a considerable length of time, they suffer intensely and finally +die. It is necessary in the blood and lymph to keep their constituents +in solution, and is thought to play an important rôle in the chemical +changes of the cells. It is constantly leaving the body as a waste +product and must be constantly supplied in small quantities in the +foods.</p> + +<p><pb n="123" /><anchor id="Pg123" /><hi rend="font-weight: bold">Importance of Water.</hi>—Water finds +its way into the body as a pure liquid, as a part of such mixtures as +coffee, chocolate, and milk, and as a constituent of all our solid +foods. (See table of foods, page 126.) It is also formed in the body by +the oxidation of hydrogen. It passes through the body unchanged, and is +constantly being removed by all the organs of excretion. Though water +does not liberate energy in the body nor build up the tissues in the +sense that other foods do, it is as necessary to the maintenance of life +as oxygen or proteids. It occurs in all the tissues, and forms about 70 +per cent of the entire weight of the body. Its presence is necessary for +the interchange of materials at the cells and for keeping the tissues +soft and pliable. As it enters the body, it carries digested food +substances with it, and as it leaves it is loaded with wastes. Its chief +physiological work, which is that of a <hi rend="font-style: +italic">transporter of material</hi>, depends upon its ability to +dissolve substances and to flow readily from place to place.</p> + +<p><hi rend="font-weight: bold">Relative Quantity of Nutrients +Needed.</hi>—Proteids, carbohydrates, and fats are the nutrients that +supply most of the body's nourishment. The most hygienic diet is the one +which supplies the proteids in sufficient quantity to rebuild the +tissues and the carbohydrates and fats in the right amounts to supply +the body with energy. Much experimenting has been done with a view to +determining these proportions, but the results so far are not entirely +satisfactory. According to some of the older estimates, a person of +average size requires for his daily use five ounces of proteid, two and +one half ounces of fat, and fifteen ounces of carbohydrate. Recent +investigations of this problem seem to show that the body is as well, if +not better, nourished by a much smaller amount of proteid—not more than +two and one half ounces (60 grams) daily.<note place="foot"><p>Chittenden, <hi rend="font-style: italic">The Nutrition +of Man</hi>.</p></note></p> + +<p><pb n="124" /><anchor id="Pg124" /> While there is probably no +necessity for the healthy individual's taking his proteid, fat, and +carbohydrate in <hi rend="font-style: italic">exact</hi> proportions (if +the proportions best suited to his body were known), the fact needs to +be emphasized that proteids, although absolutely necessary, should form +but a small part (not over one fifth) of the daily bill of fare. In +recognition of this fact is involved a principle of health and also one +of economy. The proteids, especially those in meats, are the most +expensive of the nutrients, whereas the carbohydrates, which should form +the greater bulk of one's food, are the least expensive.</p> + +<p><hi rend="font-weight: bold">Effects of a One-sided Diet.</hi>—The +plan of the body is such as to require a <hi rend="font-style: +italic">mixed diet</hi>, and all of the great classes of nutrients are +necessary. If one could subsist on any single class, it would be +proteids, for proteids are able both to rebuild tissue and to supply +energy. But if proteids are eaten much in excess of the body's need for +rebuilding the tissues, and this excess is oxidized for supplying +energy, a strain is thrown upon the organs of excretion, because of the +increase in the wastes. Not only is there danger of overworking certain +of these organs (the liver and kidneys), but the wastes may linger too +long in the body, causing disorder and laying the foundation for +disease. On the other hand, if an insufficient amount of proteid is +taken, the tissues are improperly nourished, and one is unable to exert +his usual strength. What is true of the proteids is true, though in a +different way, of the other great classes of foods. A diet which is +lacking in proteid, carbohydrate, or fat, or which has any one of them +in excess, is not adapted to the requirements of the body.</p> + +<p><hi rend="font-weight: bold">Composition of the Food Materials.</hi>—One +who intelligently provides the daily bill of fare must have some +knowledge of the nature and quantity of the nutrients<pb n="125" /><anchor id="Pg125" /> present in the different +materials used as food. This information is supplied by the chemist, who +has made extensive analyses for this purpose. Results of such analyses +are shown in Table 1 (page 126), which gives the percentage of proteids, +fats, carbohydrates, water, and mineral salts in the edible portions of +the more common of our foods.</p> + +<p rend="text-align: center"> +<figure url="images/image61a.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 61—Relative proportions of different nutrients in well-known foods.</head> +<figDesc>Fig. 61</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Food Supply to the Table.</hi>—The main +problem in supplying the daily bill of fare is that of securing through +the different food materials the requisite amounts of proteids, +carbohydrates, and fats. In this matter a table showing the composition +of foods can be used to great advantage. Consulting the table on page +126, it is seen that large per cents of proteids are supplied by lean +meat, eggs, cheese, beans, peas, peanuts, and oatmeal, while fat is in +excess in fat meat, butter, and nuts (Fig. 61). Carbohydrates are +supplied in abundance by potatoes, rice, corn, sugar, and molasses. The +different cereals also contain a large percentage of carbohydrates in +the form of starch.</p> + +<pb n="126" /><anchor id="Pg126" /> + +<table rend="latexcolumns: '|p{0.75cm}|p{0.75cm}|p{0.75cm}|p{0.75cm}|p{0.75cm}|p{0.75cm}|p{0.75cm}|p{0.75cm}|'"> +<head>TABLE I. <hi rend="font-variant: small-caps">The Composition of +Food Materials</hi><note place="foot"><p>Compiled from different +sources, but mainly from Atwater's <hi rend="font-style: italic">Foods: +Nutritive Value and Cost</hi>, published by the U.S. Department of +Agriculture.</p></note></head> + +<row> +<cell rend="font-size: 50%">Food Materials</cell> +<cell rend="font-size: 50%">Water</cell> +<cell rend="font-size: 50%">Solids</cell> +<cell rend="font-size: 50%">Proteid</cell> +<cell rend="font-size: 50%">Fat</cell> +<cell rend="font-size: 50%">Carbohydrates</cell> +<cell rend="font-size: 50%">Mineral Matter</cell> +<cell rend="font-size: 50%">Heat Value of One Pound</cell> +</row> + +<row> +<cell rend="font-size: 50%">Animal foods, edible portion</cell> +<cell rend="font-size: 50%">Per cent</cell> +<cell rend="font-size: 50%">Per cent</cell> +<cell rend="font-size: 50%">Per cent</cell> +<cell rend="font-size: 50%">Per cent</cell> +<cell rend="font-size: 50%">Per cent</cell> +<cell rend="font-size: 50%">Per cent</cell> +<cell rend="font-size: 50%">Calories<note place="foot"><p>The calorie is the adopted heat unit. As used in this +table it may be defined as the quantity of heat required to raise 1 +kilogram (2.2 pounds) of water, 1 degree centigrade. The calories also +show the relative amount of energy supplied by the different foods.</p></note></cell> +</row> + +<row> +<cell rend="font-size: 50%">Beef: Shoulder</cell> +<cell rend="font-size: 50%">63.9</cell> +<cell rend="font-size: 50%">36.1</cell> +<cell rend="font-size: 50%">19.5</cell> +<cell rend="font-size: 50%">15.6</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">1</cell> +<cell rend="font-size: 50%">1020</cell> +</row> + +<row> +<cell rend="text-align: right; font-size: 50%">Rib</cell> +<cell rend="font-size: 50%">48.1</cell> +<cell rend="font-size: 50%">51.9</cell> +<cell rend="font-size: 50%">15.4</cell> +<cell rend="font-size: 50%">35.6</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">.9</cell> +<cell rend="font-size: 50%">1790</cell> +</row> + +<row> +<cell rend="text-align: right; font-size: 50%">Sirloin</cell> +<cell rend="font-size: 50%">60</cell> +<cell rend="font-size: 50%">40</cell> +<cell rend="font-size: 50%">18.5</cell> +<cell rend="font-size: 50%">20.5</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">1</cell> +<cell rend="font-size: 50%">1210</cell> +</row> + +<row> +<cell rend="text-align: right; font-size: 50%">Round</cell> +<cell rend="font-size: 50%">68.2</cell> +<cell rend="font-size: 50%">31.8</cell> +<cell rend="font-size: 50%">20.5</cell> +<cell rend="font-size: 50%">10.1</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">1.2</cell> +<cell rend="font-size: 50%">805</cell> +</row> + +<row> +<cell rend="font-size: 50%">Veal: Shoulder</cell> +<cell rend="font-size: 50%">68.8</cell> +<cell rend="font-size: 50%">31.2</cell> +<cell rend="font-size: 50%">20.2</cell> +<cell rend="font-size: 50%">9.8</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">790</cell> +</row> + +<row> +<cell rend="font-size: 50%">Mutton: Leg</cell> +<cell rend="font-size: 50%">61.8</cell> +<cell rend="font-size: 50%">38.2</cell> +<cell rend="font-size: 50%">18.3</cell> +<cell rend="font-size: 50%">19</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">.9</cell> +<cell rend="font-size: 50%">1140</cell> +</row> + +<row> +<cell rend="text-align: right; font-size: 50%">Loin</cell> +<cell rend="font-size: 50%">49.3</cell> +<cell rend="font-size: 50%">50.7</cell> +<cell rend="font-size: 50%">15</cell> +<cell rend="font-size: 50%">35</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">.7</cell> +<cell rend="font-size: 50%">1755</cell> +</row> + +<row> +<cell rend="font-size: 50%">Pork: Shoulder</cell> +<cell rend="font-size: 50%">50.3</cell> +<cell rend="font-size: 50%">49.7</cell> +<cell rend="font-size: 50%">16</cell> +<cell rend="font-size: 50%">32.8</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">.9</cell> +<cell rend="font-size: 50%">1680</cell> +</row> + +<row> +<cell rend="text-align: right; font-size: 50%">Ham, salted, smoked</cell> +<cell rend="font-size: 50%">41.5</cell> +<cell rend="font-size: 50%">58.5</cell> +<cell rend="font-size: 50%">16.7</cell> +<cell rend="font-size: 50%">39.1</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">2.7</cell> +<cell rend="font-size: 50%">1960</cell> +</row> + +<row> +<cell rend="text-align: right; font-size: 50%">Fat, salted</cell> +<cell rend="font-size: 50%">12.1</cell> +<cell rend="font-size: 50%">87.9</cell> +<cell rend="font-size: 50%">.9</cell> +<cell rend="font-size: 50%">82.8</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">4.2</cell> +<cell rend="font-size: 50%">3510</cell> +</row> + +<row> +<cell rend="font-size: 50%">Sausage: Pork</cell> +<cell rend="font-size: 50%">41.5</cell> +<cell rend="font-size: 50%">58.8</cell> +<cell rend="font-size: 50%">13.8</cell> +<cell rend="font-size: 50%">42.8</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">2.2</cell> +<cell rend="font-size: 50%">2065</cell> +</row> + +<row> +<cell rend="font-align: right; font-size: 50%">Bologna</cell> +<cell rend="font-size: 50%">62.4</cell> +<cell rend="font-size: 50%">37.6</cell> +<cell rend="font-size: 50%">18.8</cell> +<cell rend="font-size: 50%">42.8</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">3</cell> +<cell rend="font-size: 50%">1015</cell> +</row> + +<row> +<cell rend="font-size: 50%">Chicken</cell> +<cell rend="font-size: 50%">72.2</cell> +<cell rend="font-size: 50%">27.8</cell> +<cell rend="font-size: 50%">24.4</cell> +<cell rend="font-size: 50%">1</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">1.4</cell> +<cell rend="font-size: 50%">540</cell> +</row> + +<row> +<cell rend="font-size: 50%">Eggs</cell> +<cell rend="font-size: 50%">73.8</cell> +<cell rend="font-size: 50%">26.2</cell> +<cell rend="font-size: 50%">14.9</cell> +<cell rend="font-size: 50%">10.5</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">.8</cell> +<cell rend="font-size: 50%">721</cell> +</row> + +<row> +<cell rend="font-size: 50%">Milk</cell> +<cell rend="font-size: 50%">87</cell> +<cell rend="font-size: 50%">13</cell> +<cell rend="font-size: 50%">3.6</cell> +<cell rend="font-size: 50%">4</cell> +<cell rend="font-size: 50%">4.7</cell> +<cell rend="font-size: 50%">.7</cell> +<cell rend="font-size: 50%">325</cell> +</row> + +<row> +<cell rend="font-size: 50%">Butter</cell> +<cell rend="font-size: 50%">10.5</cell> +<cell rend="font-size: 50%">89</cell> +<cell rend="font-size: 50%">.6</cell> +<cell rend="font-size: 50%">85</cell> +<cell rend="font-size: 50%">.5</cell> +<cell rend="font-size: 50%">.3</cell> +<cell rend="font-size: 50%">3515</cell> +</row> + +<row> +<cell rend="font-size: 50%">Cheese: Full cream</cell> +<cell rend="font-size: 50%">30.2</cell> +<cell rend="font-size: 50%">69.8</cell> +<cell rend="font-size: 50%">28.3</cell> +<cell rend="font-size: 50%">35.5</cell> +<cell rend="font-size: 50%">1.8</cell> +<cell rend="font-size: 50%">4.2</cell> +<cell rend="font-size: 50%">2070</cell> +</row> + +<row> +<cell rend="text-align: right; font-size: 50%">Skim milk</cell> +<cell rend="font-size: 50%">41.3</cell> +<cell rend="font-size: 50%">58.7</cell> +<cell rend="font-size: 50%">38.4</cell> +<cell rend="font-size: 50%">6.8</cell> +<cell rend="font-size: 50%">6.9</cell> +<cell rend="font-size: 50%">4.6</cell> +<cell rend="font-size: 50%">1165</cell> +</row> + +<row> +<cell rend="font-size: 50%">Fish: Codfish</cell> +<cell rend="font-size: 50%">82.6</cell> +<cell rend="font-size: 50%">17.4</cell> +<cell rend="font-size: 50%">15.8</cell> +<cell rend="font-size: 50%">.5</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">1.2</cell> +<cell rend="font-size: 50%">310</cell> +</row> + +<row> +<cell rend="text-align: right; font-size: 50%">Salmon</cell> +<cell rend="font-size: 50%">63.6</cell> +<cell rend="font-size: 50%">36.4</cell> +<cell rend="font-size: 50%">21.6</cell> +<cell rend="font-size: 50%">13.4</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">1.4</cell> +<cell rend="font-size: 50%">965</cell> +</row> + +<row> +<cell rend="text-align: right; font-size: 50%">Oysters</cell> +<cell rend="font-size: 50%">87.1</cell> +<cell rend="font-size: 50%">12.9</cell> +<cell rend="font-size: 50%">6</cell> +<cell rend="font-size: 50%">1.2</cell> +<cell rend="font-size: 50%">3.7</cell> +<cell rend="font-size: 50%">2</cell> +<cell rend="font-size: 50%">230</cell> +</row> + +<row> +<cell rend="font-size: 50%">Vegetable foods</cell> +<cell rend="font-size: 50%"></cell> +<cell rend="font-size: 50%"></cell> +<cell rend="font-size: 50%"></cell> +<cell rend="font-size: 50%"></cell> +<cell rend="font-size: 50%"></cell> +<cell rend="font-size: 50%"></cell> +<cell rend="font-size: 50%"></cell> +</row> + +<row> +<cell rend="font-size: 50%">Wheat flour</cell> +<cell rend="font-size: 50%">12.5</cell> +<cell rend="font-size: 50%">87.5</cell> +<cell rend="font-size: 50%">11</cell> +<cell rend="font-size: 50%">1.1</cell> +<cell rend="font-size: 50%">74.9</cell> +<cell rend="font-size: 50%">.5</cell> +<cell rend="font-size: 50%">1645</cell> +</row> + +<row> +<cell rend="font-size: 50%">Graham flour (wheat)</cell> +<cell rend="font-size: 50%">13.1</cell> +<cell rend="font-size: 50%">86.9</cell> +<cell rend="font-size: 50%">11.7</cell> +<cell rend="font-size: 50%">1.7</cell> +<cell rend="font-size: 50%">71.7</cell> +<cell rend="font-size: 50%">1.8</cell> +<cell rend="font-size: 50%">1635</cell> +</row> + +<row> +<cell rend="font-size: 50%">Rye flour</cell> +<cell rend="font-size: 50%">13.1</cell> +<cell rend="font-size: 50%">86.9</cell> +<cell rend="font-size: 50%">6.7</cell> +<cell rend="font-size: 50%">.8</cell> +<cell rend="font-size: 50%">78.7</cell> +<cell rend="font-size: 50%">.7</cell> +<cell rend="font-size: 50%">1625</cell> +</row> + +<row> +<cell rend="font-size: 50%">Buckwheat flour</cell> +<cell rend="font-size: 50%">14.6</cell> +<cell rend="font-size: 50%">85.4</cell> +<cell rend="font-size: 50%">6.9</cell> +<cell rend="font-size: 50%">1.4</cell> +<cell rend="font-size: 50%">76.1</cell> +<cell rend="font-size: 50%">1</cell> +<cell rend="font-size: 50%">1605</cell> +</row> + +<row> +<cell rend="font-size: 50%">Oatmeal</cell> +<cell rend="font-size: 50%">7.6</cell> +<cell rend="font-size: 50%">92.4</cell> +<cell rend="font-size: 50%">15.1</cell> +<cell rend="font-size: 50%">7.1</cell> +<cell rend="font-size: 50%">68.2</cell> +<cell rend="font-size: 50%">2</cell> +<cell rend="font-size: 50%">1850</cell> +</row> + +<row> +<cell rend="font-size: 50%">Cornmeal</cell> +<cell rend="font-size: 50%">15</cell> +<cell rend="font-size: 50%">85</cell> +<cell rend="font-size: 50%">9.2</cell> +<cell rend="font-size: 50%">3.8 +</cell> +<cell rend="font-size: 50%">70.6</cell> +<cell rend="font-size: 50%">1.4</cell> +<cell rend="font-size: 50%">1645</cell> +</row> + +<row> +<cell rend="font-size: 50%">Rice</cell> +<cell rend="font-size: 50%">12.4</cell> +<cell rend="font-size: 50%">87.6</cell> +<cell rend="font-size: 50%">7.4</cell> +<cell rend="font-size: 50%">.4</cell> +<cell rend="font-size: 50%">79.4</cell> +<cell rend="font-size: 50%">.4</cell> +<cell rend="font-size: 50%">1630</cell> +</row> + +<row> +<cell rend="font-size: 50%">Peas</cell> +<cell rend="font-size: 50%">12.3</cell> +<cell rend="font-size: 50%">87.7</cell> +<cell rend="font-size: 50%">26.7</cell> +<cell rend="font-size: 50%">1.7</cell> +<cell rend="font-size: 50%">56.4</cell> +<cell rend="font-size: 50%">2.9</cell> +<cell rend="font-size: 50%">1565</cell> +</row> + +<row> +<cell rend="font-size: 50%">Beans</cell> +<cell rend="font-size: 50%">12.6</cell> +<cell rend="font-size: 50%">87.4 +</cell> +<cell rend="font-size: 50%">23.1</cell> +<cell rend="font-size: 50%">2</cell> +<cell rend="font-size: 50%">59.2</cell> +<cell rend="font-size: 50%">3.1</cell> +<cell rend="font-size: 50%">1615</cell> +</row> + +<row> +<cell rend="font-size: 50%">Potatoes</cell> +<cell rend="font-size: 50%">78.9</cell> +<cell rend="font-size: 50%">21.1</cell> +<cell rend="font-size: 50%">2.1</cell> +<cell rend="font-size: 50%">.1</cell> +<cell rend="font-size: 50%">17.9 +</cell> +<cell rend="font-size: 50%">1</cell> +<cell rend="font-size: 50%">375</cell> +</row> + +<row> +<cell rend="font-size: 50%">Tomatoes</cell> +<cell rend="font-size: 50%">95.3</cell> +<cell rend="font-size: 50%">4.7</cell> +<cell rend="font-size: 50%">.8</cell> +<cell rend="font-size: 50%">.4</cell> +<cell rend="font-size: 50%">3.2</cell> +<cell rend="font-size: 50%">.3</cell> +<cell rend="font-size: 50%">80</cell> +</row> + +<row> +<cell rend="font-size: 50%">Apples</cell> +<cell rend="font-size: 50%">83.2 +</cell> +<cell rend="font-size: 50%">16.8</cell> +<cell rend="font-size: 50%">.2</cell> +<cell rend="font-size: 50%">.4</cell> +<cell rend="font-size: 50%">15.9</cell> +<cell rend="font-size: 50%">.3</cell> +<cell rend="font-size: 50%">315</cell> +</row> + +<row> +<cell rend="font-size: 50%">Sugar, granulated</cell> +<cell rend="font-size: 50%">2</cell> +<cell rend="font-size: 50%">98</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">...</cell> +<cell rend="font-size: 50%">97.8</cell> +<cell rend="font-size: 50%">.3</cell> +<cell rend="font-size: 50%">1820</cell> +</row> + +<row> +<cell rend="font-size: 50%">White bread (wheat)</cell> +<cell rend="font-size: 50%">32.3</cell> +<cell rend="font-size: 50%">67.7</cell> +<cell rend="font-size: 50%">8.2</cell> +<cell rend="font-size: 50%">1.7</cell> +<cell rend="font-size: 50%">56.3</cell> +<cell rend="font-size: 50%">.0</cell> +<cell rend="font-size: 50%">1280</cell> +</row> + +<row> +<cell rend="font-size: 50%">Peanuts</cell> +<cell rend="font-size: 50%">9.2</cell> +<cell rend="font-size: 50%">90.8</cell> +<cell rend="font-size: 50%">25.8</cell> +<cell rend="font-size: 50%">24.4</cell> +<cell rend="font-size: 50%">38.6</cell> +<cell rend="font-size: 50%">2</cell> +<cell rend="font-size: 50%">2560</cell> +</row> + +<row> +<cell rend="font-size: 50%">Almonds</cell> +<cell rend="font-size: 50%">4.8</cell> +<cell rend="font-size: 50%">95.2</cell> +<cell rend="font-size: 50%">21</cell> +<cell rend="font-size: 50%">17.3</cell> +<cell rend="font-size: 50%">54.9</cell> +<cell rend="font-size: 50%">2</cell> +<cell rend="font-size: 50%">3030</cell> +</row> + +<row> +<cell rend="font-size: 50%">Walnuts (English)</cell> +<cell rend="font-size: 50%">2.5</cell> +<cell rend="font-size: 50%">97.5</cell> +<cell rend="font-size: 50%">16.6</cell> +<cell rend="font-size: 50%">16.1</cell> +<cell rend="font-size: 50%">63.4</cell> +<cell rend="font-size: 50%">1.4</cell> +<cell rend="font-size: 50%">3285</cell> +</row> +</table> + +<p><pb n="128" /><anchor id="Pg128" /><hi rend="font-style: +italic">Variety</hi> in the selection of foods for the table is an +essential feature, but this should not increase either the work or the +expense of supplying the meals. Each single meal can, and should, be +simple in itself and, at the same time, differ sufficiently from the +meal preceding and the one following to give the necessary variety in +the course of the day. The bill of fare should, of course, include +fruits (for their tonic effects) and very small amounts perhaps of +substances which stimulate the appetite, such as pepper, mustard, etc., +known as condiments.</p> + +<p><hi rend="font-weight: bold">Purity of Food.</hi>—The fact that many +of the food substances are perishable makes it possible for them to be +eaten in a slightly decayed condition. Such substances are decidedly +unwholesome (some containing poisons) and should be promptly rejected. +Not only do fresh meats, fruits, and vegetables need careful inspection, +but canned and preserved goods as well. If canned foods are imperfectly +sealed or if not thoroughly cooked in the canning process, they decay +and the acids which they generate act on the metals lining the cans, +forming poisonous compounds. The contents of "tin" cans should for this +reason be transferred to other vessels as soon as opened.</p> + +<p>Foods are also rendered impure or weakened through adulteration, the +watering of milk being a familiar example. The manufacture of jellies, +preserves, sirups, and various kinds of pickles and condiments has +perhaps afforded the largest field for adulterations, although it is +possible to adulterate nearly all of the leading articles of food. A +long step in the prevention of food and drug adulteration was taken in +this country by the passage of the <hi rend="font-style: italic">Pure +Food Law</hi>. By forcing manufacturers of foods and medicines to state +on printed labels the composition of their products, this law has made +it possible for the consumer to know what he is purchasing and putting +into his body.</p> + +<p><hi rend="font-weight: bold">Alcohol not a Food.</hi>—Many people in +this and other countries drink in different beverages, such as whisky, +beer, wine, etc., a varying amount of alcohol. This substance has a +temporary stimulating or exciting effect, and the claim has been made +that it serves as a food. Recently<pb n="129" /><anchor id="Pg129" /> it has been shown that alcohol +when introduced into the body in small quantities and in a greatly +diluted form, is nearly all oxidized, yielding energy as does fat or +sugar. If no harmful effects attended the use of alcohol, it might on +this account be classed as a food. But alcohol is known to be harmful to +the body. When used in large quantities, it injures nearly all of the +tissues, and when taken habitually, even in small doses, it leads to the +formation of the alcohol habit which is now recognized and treated as a +disease. This and other facts show that alcohol is not adapted to the +body plan of taking on and using new material (Chapter XI), and no +substance lacking in this respect can properly be classed as a food.<note place="foot"><p>While alcohol cannot be classed as a food, it is +believed by some authorities to contain <hi rend="font-style: +italic">food value</hi> and, in the hands of the physician, to be a +substance capable of rendering an actual service in the treatment of +certain diseases. It might, for example, be used where one's power of +digestion is greatly impaired, since alcohol requires no digestion. But +upon this point there is a decided difference of opinion. Certain it is +that no one should attempt to use alcohol as food or medicine except +under the advice and direction of his physician.</p></note> +Instead of classing alcohol as a food, it should be placed in that long +list of substances which are introduced into the body for special +purposes and which are known by the general name of</p> + +<p><hi rend="font-weight: bold">Drugs.</hi>—Drugs act strongly upon the +body and tend to bring about unusual and unnatural results. Their use +should in no way be confused with that of foods. If taken in health, +they tend to disturb the physiological balance of the body by unduly +increasing or diminishing the action of the different organs. In disease +where this balance is already disturbed, they may be administered for +their counteractive effects, but always under the advice and direction +of a physician. Knowing the nature of the disturbance which the drug +produces, the physician can administer it to advantage, should the body +be out of physiological<pb n="130" /><anchor id="Pg130" /> balance, or diseased. Not only are drugs of no value in +health, but their use is liable to do much harm.</p> + +<div> +<head>NATURE OF DIGESTION</head> + +<p>Before the nutrients can be oxidized at the cells, or built into the +protoplasm, they undergo a number of changes. These are necessary for +their entrance into the body, for their distribution by the blood and +the lymph, and for the purposes which they finally serve. The first of +these changes is preparatory to the entrance of the nutrients and is +known as <hi rend="font-style: italic">digestion</hi>. The organs which +bring about this change, called digestive organs, have a special +construction which adapts them to their work. It will assist materially +in understanding these organs if we first learn something of the nature +of the work which they have to perform.</p> + +<p><hi rend="font-weight: bold">How the Nutrients get into the +Body.</hi>—The nature of digestion is determined by the conditions +affecting the entrance of nutrients into the body. Food in the stomach +and air in the lungs, although surrounded by the body, are still outside +of what is called the <hi rend="font-style: italic">body proper</hi>. To +gain entrance into the body proper, a substance must pass through the +body wall. This consists of the skin on the outside and of the mucous +linings of the air passages and other tubes and cavities which are +connected with the external surface.</p> + +<p>To get from the digestive organs into the blood, the nutrients must +pass through the mucous membrane lining these organs and also the walls +of blood or lymph vessels. Only <hi rend="font-style: italic">liquid +materials</hi> can make this passage. It is necessary, therefore, to +reduce to the liquid state all nutrients not already in that condition. +<hi rend="font-style: italic">This reduction to the liquid state +constitutes the digestive process</hi>.</p> + +<p><pb n="131" /><anchor id="Pg131" /><hi rend="font-weight: bold">How Substances are Liquefied.</hi>—While +the reduction of solids to the liquid state is accomplished in some +instances by heating them until they melt, they are more frequently +reduced to this state by subjecting them to the action of certain +liquids, called <hi rend="font-style: italic">solvents</hi>. Through the +action of the solvent the minute particles of the solid separate from +each other and disappear from view. (Shown in dropping salt in water.) +At the same time they mix with the solvent, forming a <hi +rend="font-style: italic">solution</hi>, from which they separate only +with great difficulty. For this reason solids in solution can diffuse +through porous partitions along with the solvents in which they are +dissolved (page 73).</p> + +<p>By digestion the nutrients are reduced to the form of a solution. <hi +rend="font-style: italic">The process is</hi>, simply speaking, <hi +rend="font-style: italic">one of dissolving</hi>. The liquid employed as +<hi rend="font-style: italic">the digestive solvent is water</hi>. The +different nutrients dissolve in water, mixing with it to form a solution +which is then passed into the body proper.</p> + +<p><hi rend="font-weight: bold">Digestion not a Simple +Process.</hi>—Digestion is by no means a simple process, such, for +instance, as the dissolving of salt or sugar in water. These, being +soluble in water, dissolve at once on being mixed with a sufficient +amount of this liquid. The majority of the nutrients, however, are +insoluble in water and are unaffected by it when acting alone. Fats, +starch, and most of the proteids do not dissolve in water. Before these +can be dissolved they have to be changed chemically and converted into +substances that are <hi rend="font-style: italic">soluble in water</hi>. +This complicates the process and <hi rend="font-style: italic">prevents +the use of water alone</hi> as the digestive solvent.</p> + +<p><hi rend="font-weight: bold">A Similar Case.</hi>—If a piece of +limestone be placed in water, it does not dissolve, because it is +insoluble in water. If hydrochloric acid is now added to the water, the +limestone<pb n="132" /><anchor id="Pg132" /> is soon dissolved (Fig. +62). (See Practical Work.) It seems at first thought that the acid +dissolves the limestone, but this is not the case. The acid produces a +chemical change in the limestone (calcium carbonate) and converts it +into a compound (calcium chloride) that is soluble in water. As fast as +this is formed it is dissolved by the water, which is the real solvent +in the case. The acid simply plays the part of a chemical converter.</p> + +<p rend="text-align: center"> +<figure url="images/image62.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 62—The dissolving of limestone in water +containing acid, suggesting the double action in the digestion of most +foods.</head> +<figDesc>Fig. 62</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Digestive Fluids.</hi>—Several +fluids—saliva, gastric juice, pancreatic juice, bile, and intestinal +juice—are employed in the digestion of the food. The composition of +these fluids is in keeping with the nature of the digestive process. +While all of them have water for their most abundant constituent, there +are dissolved in the water small amounts of active chemical agents. It +is the work of these agents to convert the insoluble nutrients into +substances that are soluble in water. The digestive fluids are thus able +to act in a <hi rend="font-style: italic">double</hi> manner on the +nutrients—to change them chemically and to dissolve them. The chemical +agents which bring about the changes in the nutrients are called <hi +rend="font-style: italic">enzymes</hi>, or digestive ferments.</p> + +<p><hi rend="font-weight: bold">Foods Classed with Reference to +Digestive Changes.</hi>—With reference to the changes which they undergo +during digestion, foods may be divided into three classes as +follows:</p> + +<p>1. Substances already in the liquid state and requiring no digestive +action. Water and solutions of simple foods in water belong to this +class. Milk and liquid fats, or oils, do not belong to this class.</p> + +<p>2. Solid foods soluble in water. This class includes<pb n="133" /><anchor id="Pg133" /> common salt and sugar. These +require no digestive action other than dissolving in water.</p> + +<p>3. Foods that are insoluble in water. These have first to be changed +into soluble substances, after which they are dissolved.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—Materials called foods +are introduced into the body for rebuilding the tissues, supplying +energy, and aiding in its general work. Only a few classes of +substances, viz., proteids, carbohydrates, fats, water, and some mineral +compounds have all the qualities of foods and are suitable for +introduction into the body. Substances known as drugs, which may be used +as medicines in disease, should be avoided in health. Before foods can +be passed into the body proper, they must be converted into the liquid +form, or dissolved. In this process, known as digestion, water is the +solvent; and certain chemical agents, called enzymes, convert the +insoluble nutrients into substances that are soluble in water.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. How does oxidation at +the cells make necessary the introduction of new materials into the +body?</p> + +<p>2. What different purposes are served by the foods?</p> + +<p>3. What is a nutrient? Name the important classes.</p> + +<p>4. What are food materials? From what sources are they obtained?</p> + +<p>5. Name the different kinds of proteids; the different kinds of +carbohydrates. Why are proteids called nitrogenous foods and fats and +carbohydrates non-nitrogenous foods?</p> + +<p>6. Show why life cannot be carried on without proteids; without +water.</p> + +<p>7. What per cents of proteid, fat, and carbohydrate are found in +wheat flour, oatmeal, rice, butter, potatoes, round beef, eggs, and +peanuts?</p> + +<p>8. State the objection to a meal consisting of beef, eggs, beans, +bread, and butter; to one consisting of potatoes, rice, bread, and +butter. Which is the more objectionable of these meals and why?</p> + +<p>9. State the general plan of digestion.</p> + +<p><pb n="134" /><anchor id="Pg134" />10. Show that digestion is not a +simple process like that of dissolving salt in water.</p> +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">Elements supplied by the Foods.</hi>—The +following brief study will enable the pupil to identify most of the +elements present in the body and which have, therefore, to be supplied +by the foods.</p> + +<p><hi rend="font-style: italic">Carbon.</hi>—Examine pieces of charred +wood, coke, or coal, and also the "lead" in lead pencils. Show that the +charred wood and the coal will burn. Recall experiment (page 114) +showing that carbon in burning forms carbon dioxide.</p> + +<p><hi rend="font-style: italic">Hydrogen.</hi>—Fill a test tube one +third full of strong hydrochloric acid and drop into it several small +scraps of zinc. The gas which is evolved is hydrogen. When the hydrogen +is coming off rapidly, bring a lighted splinter to the mouth of the +tube. The gas should burn. Hold a cold piece of glass over the flame and +observe the deposit of moisture. Hydrogen in burning forms water. +Extinguish the flame by covering the top of the tube with a piece of +cardboard. Now let the escaping gas collect in a tumbler inverted over +the tube. After holding the tumbler in this position for two or three +minutes, remove and, keeping inverted, thrust a lighted splinter into +it. (The gas should either burn or explode.) What does this experiment +show relative to the weight of hydrogen as compared with that of +air?</p> + +<p><hi rend="font-style: italic">Nitrogen.</hi>—Nitrogen forms about +four fifths of the atmosphere, where, like oxygen, it exists in a free +state. It may be separated from the oxygen of an inclosed portion of air +by causing that gas to unite with phosphorus. Place a piece of +phosphorus the size of a pea in a depression in a flat piece of cork. +(Handle phosphorus with wet fingers or with forceps.) Place the cork on +water and have ready a glass fruit jar holding not more than a quart. +Ignite the phosphorus with a hot wire and invert the jar over it, +pushing the mouth below the surface of the water. The phosphorus uniting +with the oxygen fills the jar with white fumes of phosphoric oxide. +These soon dissolve in the water, leaving a clear gas above. This is +nitrogen. Place a cardboard under the mouth of the jar and turn it right +side up, leaving in the water and keeping the top covered. Light a +splinter and, slipping the cover to one side, thrust the flame into the +jar of nitrogen, noting the effect. (Flame is extinguished.) Compare +nitrogen with oxygen in its relation to combustion. What purpose is +served by each in the atmosphere?</p> + +<p><pb n="135" /><anchor id="Pg135" /><hi rend="font-style: italic">Oxygen.</hi>—Review experiments (page +114) showing the properties of oxygen.</p> + +<p><hi rend="font-style: italic">Phosphorus.</hi>—Examine a small piece +of phosphorus, noting that it has to be kept under water. Lay a small +piece on the table and observe the tiny stream of white smoke rising +from it, formed by slow oxidation. Dissolve a piece as large as a pea in +a teaspoonful of carbon disulphide in a test tube, pour this on a piece +of porous paper, and lay the paper on an iron support. When the carbon +disulphide evaporates the phosphorus takes fire spontaneously. (The heat +from the slow oxidation is sufficient to ignite the phosphorus in the +finely divided condition.) What is the most striking property of +phosphorus? What purpose does it serve in the match?</p> + +<p><hi rend="font-style: italic">Sulphur.</hi>—Examine some sulphur, +noting its color and the absence of odor or taste. (Impure sulphur may +have an odor and a taste.) Burn a little sulphur in an iron spoon, +noting that the compound which it forms with oxygen by burning has a +decided odor.</p> + +<p><hi rend="font-style: italic">Other Elements.</hi>—<hi +rend="font-style: italic">Magnesium.</hi> Examine and burn a piece of +magnesium ribbon, noting the white compound of magnesium oxide which is +formed. <hi rend="font-style: italic">Iron.</hi> Examine pieces of the +metal and also some of its compounds, as ferrous sulphate, ferric +chloride, and ferric oxide or iron rust. <hi rend="font-style: +italic">Sodium.</hi> Drop a piece of the metal on water and observe +results. Sodium decomposes water. It has to be kept under some liquid, +such as kerosene, which contains no oxygen. (It should not be touched +except with the fingers wet with kerosene.) <hi rend="font-style: +italic">Chlorine.</hi> Pour strong hydrochloric acid on a little +manganese dioxide in a test tube, and warm gently over a low flame. The +escaping gas is chlorine. Avoid breathing much of it.</p> + +<p><hi rend="font-weight: bold">Composition of the Nutrients.</hi>—The +simplest way of determining what elements make up the different +nutrients is by heating them and studying the products of decomposition, +as follows:</p> + +<p><hi rend="font-style: italic">To show that Carbohydrates contain +Carbon, Hydrogen, and Oxygen.</hi>—Place one half teaspoonful of +powdered starch in a test tube and heat strongly. Observe that <hi +rend="font-style: italic">water</hi> condenses on the sides of the tube +and that a black, charred mass remains behind. The black mass consists +mainly of <hi rend="font-style: italic">carbon</hi>. The water is +composed of hydrogen and oxygen. These three elements are thus shown to +be present in the starch. The experiment may be repeated, using sugar +instead of starch.</p> + +<p><hi rend="font-style: italic">To show that Proteids contain Carbon, +Hydrogen, Oxygen, Nitrogen, and Sulphur.</hi>—Place in a test tube some +finely divided proteid<pb n="136" /><anchor id="Pg136" /> which has +been thoroughly dried (dried beef or the lean of hard cured bacon). Heat +strongly in the hood of a chemical laboratory or some other place where +the odors do not get into the room. First hold in the escaping gases a +wet strip of red litmus paper. This will be turned blue, showing <hi +rend="font-style: italic">ammonia</hi> (NH<hi rend="vertical-align: sub">3</hi>) to be escaping. Next +hold in the mouth of the tube a strip of a paper wet with a solution of +lead nitrate. This is turned black or brown on account of <hi +rend="font-style: italic">hydrogen sulphide</hi>(H<hi rend="vertical-align: sub">2</hi>S) which is being +driven off. Observe also that <hi rend="font-style: italic">water</hi> +condenses in the upper part of the tube and that a black, charred mass +remains behind. Since the products of decomposition (H<hi rend="vertical-align: sub">2</hi>O, NH<hi rend="vertical-align: sub">3</hi>, +H<hi rend="vertical-align: sub">2</hi>S, and the charred mass) contain hydrogen, oxygen, nitrogen, +sulphur, and carbon, these elements are of course present in the proteid +tested.</p> + +<p><hi rend="font-style: italic">To show the Presence of Mineral +Matter.</hi>—Burn a piece of dry bread by holding it in a clear, hot +flame, and observe the ash that is left behind. This is the mineral +matter present in the bread.</p> + +<p><hi rend="font-weight: bold">Tests for Nutrients.</hi> <hi +rend="font-style: italic">Proteids.</hi>—Cover the substance to be +tested with strong nitric acid and heat gradually to boiling. If proteid +is present it turns yellow and partly dissolves in the acid, forming a +yellow solution. Let cool and then add ammonia. The yellow solid and the +solution are turned a deep orange color. Apply this test to foods +containing proteid such as white of egg, cheese, lean meat, etc.</p> + +<p><hi rend="font-style: italic">Starch.</hi>—<hi rend="font-style: +italic">(a)</hi> Place a small lump of starch in one fourth of a pint of +water and heat gradually to boiling, stirring well. Then add enough +water to form a thin liquid and fill a test tube half full. Add to this +a few drops of a solution of iodine. (Prepare by dissolving a crystal of +iodine in 25 cubic centimeters (1/20 pint) of a solution of potassium +iodide in water and add water to this until it is a light amber color.) +The starch solution is turned blue, <hi rend="font-style: +italic">(b)</hi> Cut with a razor a thin slice from a potato. Place this +in a weak solution of iodine for a few minutes and then examine with the +microscope, using first a low and then a high power. Numerous starch +grains inclosed in cellulose walls will be seen (Fig. 60).</p> + +<p><hi rend="font-style: italic">Dextrose, or Grape Sugar.</hi>—Place a +solution of the substance supposed to contain grape sugar in a test tube +and add a few drops of a dilute solution of copper sulphate. Then add +sodium hydroxide solution until the precipitate which first forms is +redissolved and a clear blue liquid obtained. Heat the upper portion of +the liquid slowly to near the boiling point. A little below the boiling +point the blue color disappears and a yellow-red precipitate is formed. +If the upper layer of<pb n="137" /><anchor id="Pg137" /> the liquid is now boiled, the +color deepens and this may be contrasted with the blue color below. +Apply this test to the sugar in raisins and in honey.</p> + +<p><hi rend="font-style: italic">Fat.</hi>—Fat is recognized by its +effect on paper, making a greasy stain which does not disappear on +heating and which renders the paper translucent. Try butter, lard, or +olive oil. Also show the presence of fat in peanuts by crushing them in +a mortar and rubbing the powder on thin paper. If the substance to be +tested contains but little fat, this may be dissolved out with ether. If +a drop of ether containing the fat is placed on paper, it evaporates, +leaving the fat, which then forms the stain.</p> + +<p><hi rend="font-weight: bold">To show the Effect of Alcohol upon +Proteid.</hi>—Place some of the white of a raw egg in a glass vessel and +cover it with a small amount of alcohol. As the albumin (proteid) +hardens, or coagulates, observe that the quantity of clear liquid +increases. This is due to the <hi rend="font-style: +italic">withdrawal</hi> of water from the albumin by the alcohol. Since +the tissues are made up chiefly of proteids, a piece of muscle or of +liver may be used in the experiment, instead of the egg, with similar +results.</p> + +<p><hi rend="font-weight: bold">To illustrate the Digestive +Process.</hi>—To a tumbler two thirds full of water add a little salt. +Stir and observe that the salt is dissolved. Taste the solution to see +that the salt has not been changed chemically. Now add a little powdered +limestone to the water and stir as before. Observe that the limestone +does not dissolve. Then add some hydrochloric acid and observe the +result. State the part played by the acid and by the water in dissolving +the limestone. Apply to the digestion of the different classes of +foods.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="138" /><anchor id="Pg138" /> +<head>CHAPTER X - ORGANS AND PROCESSES OF DIGESTION</head> + +<p>The organs of digestion are adapted to the work of dissolving the +foods by both their structure and arrangement. Most of them consist +either of tubes or cavities and these are so connected, one with the +other, as to form a continuous passageway entirely through the body. +This passageway is known as</p> + +<p><hi rend="font-weight: bold">The Alimentary Canal. </hi>—The +alimentary canal has a length of about thirty feet and, while it begins +at the mouth, all but about eighteen inches of it is found in the +abdominal cavity. On account of its length it lies for the most part in +coils, the two largest ones being known as the small intestine and the +large intestine. Connected with the alimentary canal are the glands that +supply the liquids for acting on the food. The divisions of the canal +and most of the glands that empty liquids into it are shown in Fig. 63 +and named in the table below:</p> + +<p rend="text-align: center"> +<figure url="images/image62a.png" rend="page-float: 'hp'; text-align: center; w95"> +<figDesc>Table</figDesc> +</figure></p> + +<p><pb n="139" /><anchor id="Pg139" /><hi rend="font-weight: +bold">Coats of the Alimentary Canal.</hi>—The walls of the alimentary +canal, except at the mouth, are distinct from the surrounding tissues +and consist in most places of at least three layers, or coats, as +follows:</p> + +<p rend="text-align: center"> +<figure url="images/image63.png" rend="page-float: 'hp'; text-align: center; w40"> +<head><lb />Fig. 63—<hi rend="font-weight: bold">Diagram of the +digestive system.</hi> 1. Mouth. 2. Soft palate. 3. Pharynx. 4. Parotid +gland. 5. Sublingual gland. 6. Submaxillary gland. 7. Esophagus. 8. +Stomach. 9. Pancreas. 10. Vermiform appendix. 11. Cæcum. 12. Ascending +colon. 13. Transverse colon. 14. Descending colon. 15. Sigmoid flexure. +16. Rectum. 17. Ileo-cæcal valve. 18. Duct from liver and pancreas. 19. +Liver.<lb /><lb /> +Diagram does not show comparative length of the small intestine.</head> +<figDesc>Fig. 63</figDesc> +</figure></p> + +<p>1. An <hi rend="font-style: italic">inner coat</hi>, or lining, known +as the mucous membrane. This membrane is not confined to the alimentary +canal, but lines, as we have seen, the different air passages. It +covers, in fact, all those internal surfaces of the body that connect +with the external surface. It derives its name from the substance which +it secretes, called <hi rend="font-style: italic">mucus</hi>. In +structure it resembles the skin, being continuous with the skin where +cavities open to the surface. It is made up of two layers—a thick +underlayer which contains blood vessels, nerves, and glands, and a thin +surface layer, called the <hi rend="font-style: italic">epithelium.</hi> +The epithelium, like the cuticle, is without blood vessels, nerves, or +glands.</p> + +<p>2. A <hi rend="font-style: italic">middle coat</hi>, which is +muscular and which forms a continuous layer throughout the canal, except +at the mouth. (Here its place is taken by the strong muscles of +mastication which are separate and distinct from each other.) As a<pb +n="140" /><anchor id="Pg140" /> rule the muscles of this coat are +involuntary. They surround the canal as thin sheets and at most places +form two distinct layers. In the inner layer the fibers encircle the +canal, but in the outer layer they run longitudinally, or lengthwise, +along the canal.<note place="foot"><p>A layer of connective tissue between the mucous membrane +and the muscular coat is usually referred to as the <hi +rend="font-style: italic">submucous</hi> coat. This contains numerous +blood vessels and nerves and binds the muscular coat to the mucous +membrane.</p></note></p> + +<p>3. An <hi rend="font-style: italic">outer</hi> or <hi +rend="font-style: italic">serous coat</hi>, which is limited to those +portions of the canal that occupy the abdominal cavity. This coat is not +found above the diaphragm. It is a part of the lining membrane of the +cavity of the abdomen, called</p> + +<p rend="text-align: center"> +<figure url="images/image64.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 64—<hi rend="font-weight: bold">Diagram of the +peritoneum.</hi> 1. Transverse colon. 2. Duodenum. 3. Small intestine. +4. Pancreas.</head> +<figDesc>Fig. 64</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Peritoneum.</hi>—The peritoneum is +to the abdominal cavity what the pleura is to the thoracic cavity. It +forms the outer covering for the alimentary canal and other abdominal +organs and supplies the inner lining of the cavity itself. It is also +the means of holding these organs in place, some of them being suspended +by it from the abdominal walls (Fig. 64). By the secretion of a small +amount of liquid, it prevents friction of the parts upon one +another.</p> + +<p><hi rend="font-weight: bold">Digestive Glands.</hi>—The glands which +provide the different fluids for acting on the foods derive their +constituents from the blood. They are situated either in the mucous +membrane or at convenient places outside of the<pb n="141" /><anchor id="Pg141" /> canal and pass their liquids into +it by means of small tubes, called ducts. In the canal the food and the +digestive fluids come in direct contact—a condition which the dissolving +processes require. Each kind of fluid is secreted by a special kind of +gland and is emptied into the canal at the place where it is needed.</p> + +<p><hi rend="font-weight: bold">The Digestive Processes.</hi>—Digestion +is accomplished by acting upon the food in different ways, as it is +passed along the canal, with the final result of reducing it to the form +of a solution. Several distinct processes are necessary and they occur +in such an order that those preceding are preparatory to those that +follow. These processes are known as <hi rend="font-style: +italic">mastication, insalivation, deglutition, stomach digestion</hi>, +and <hi rend="font-style: italic">intestinal</hi> digestion. As the +different materials become liquefied they are transferred to the blood, +and substances not reduced to the liquid state are passed on through the +canal as waste. The first two of the digestive processes occur in</p> + +<p><hi rend="font-weight: bold">The Mouth.</hi>—This is an oval-shaped +cavity situated at the very beginning of the canal. It is surrounded by +the lips in front, by the cheeks on the sides, by the hard palate above +and the soft palate behind, and by the tissues of the lower jaw below. +The mucous membrane lining the mouth is, soft and smooth, being covered +with flat epithelial cells. The external opening of the mouth is guarded +by the lips, and the soft palate forms a <hi rend="font-style: +italic">movable</hi> partition between the mouth and the pharynx. In a +condition of repose the mouth space is practically filled by the teeth +and the tongue, but the cavity may be enlarged and room provided for +food by depressing the lower jaw.</p> + +<p>The mouth by its construction is well adapted to carrying on the +processes of mastication and insalivation. By the first process the +solid food is reduced, by the cutting<pb n="142" /><anchor id="Pg142" /> and grinding action of the teeth, +to a finely divided condition. By the second, the saliva becomes mixed +with the food and is made to act upon it.</p> + +<p rend="text-align: center"> +<figure url="images/image65.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 65—<hi rend="font-weight: bold">The teeth.</hi> +<hi rend="font-style: italic">A.</hi> Section of a single molar. 1. +Pulp. 2. Dentine. 3. Enamel. 4. Crown. 5. Neck. 6. Root. <hi +rend="font-style: italic">B.</hi> Teeth in position in lower jaw. 1. +Incisors. 2. Canine. 3. Biscuspids. 4. Molars. <hi rend="font-style: +italic">C.</hi> Upper and lower teeth on one side. 1. Incisors. 2. +Canines. 3. Biscuspids. 4. Molars. 5. Wisdom. <hi rend="font-style: +italic">D.</hi> Upper and lower incisor, to show gliding contact.</head> +<figDesc>Fig. 65</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Accessory Organs of the Mouth.</hi>—The +work of mastication and insalivation is accomplished through organs +situated in and around the mouth cavity. These comprise:</p> + +<p>1. <hi rend="font-style: italic">The Teeth.</hi>—The teeth are set in +the upper and lower jaws, one row directly over the other, with their +hardened surfaces facing. In reducing the food, the teeth of the lower +jaw move against those of the upper, while the food is held by the +tongue and cheeks between the grinding surfaces. The front teeth are +thin and chisel-shaped. They do not meet so squarely as do the back +ones, but their edges glide over each other, like the blades of +scissors—a condition that adapts them to cutting off and separating the +food (<hi rend="font-style: italic">D</hi>, Fig. 65). The back teeth are +broad and irregular, having surfaces that are adapted to crushing and +grinding.</p> + +<p>Each tooth is composed mainly of a bone-like substance, called <hi +rend="font-style: italic">dentine</hi>, which surrounds a central space, +containing blood vessels and<pb n="143" /><anchor id="Pg143" /> nerves, +known as the <hi rend="font-style: italic">pulp cavity</hi>. It is set +in a depression in the jaw where it is held firmly in place by a bony +substance, known as <hi rend="font-style: italic">cement</hi>. The part +of the tooth exposed above the gum is the <hi rend="font-style: +italic">crown</hi>, the part surrounded by the gum is the <hi +rend="font-style: italic">neck</hi>, and the part which penetrates into +the jaw is the <hi rend="font-style: italic">root</hi> (<hi +rend="font-style: italic">A</hi>, Fig. 65). A hard, protective material, +called <hi rend="font-style: italic">enamel</hi>, covers the exposed +surface of the tooth.</p> + +<p>The teeth which first appear are known as the <hi rend="font-style: +italic">temporary</hi>, or milk, teeth and are twenty in number, ten in +each jaw. They usually begin to appear about the sixth month, and they +disappear from the mouth at intervals from the sixth to the thirteenth +year. As they leave, teeth of the second, or <hi rend="font-style: +italic">permanent</hi>, set take their place. This set has thirty-two +teeth of four different kinds arranged in the two jaws as follows:</p> + +<p>In front, above and below, are four chisel-shaped teeth, known as the +<hi rend="font-style: italic">incisors</hi>. Next to these on either +side is a tooth longer and thicker than the incisors, called the <hi +rend="font-style: italic">canine</hi>. Back of these are two short, +rounded and double pointed teeth, the <hi rend="font-style: +italic">bicuspids</hi>, and back of the bicuspids are three heavy teeth +with irregular grinding surfaces, called the <hi rend="font-style: +italic">molars</hi> (<hi rend="font-style: italic">B</hi> and <hi +rend="font-style: italic">C</hi>, Fig. 65). Since the molar farthest +back in each jaw is usually not cut until maturity, it is called a <hi +rend="font-style: italic">wisdom</hi> tooth. The molars are known as the +superadded permanent teeth because they do not take the place of milk +teeth, but form farther back as the jaw grows in length.</p> + +<p rend="text-align: center"> +<figure url="images/image66.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 66—<hi rend="font-weight: bold">Diagram</hi> +showing directions of muscular fibers in tongue.</head> +<figDesc>Fig. 66</figDesc> +</figure></p> + +<p>2. <hi rend="font-style: italic">The Tongue.</hi>—The tongue is a +muscular organ whose fibers extend through it in several directions +(Fig. 66). Its structure adapts it to a variety of movements. During +mastication the tongue transfers the food from one part of the mouth to +another, and, with the aid of the cheeks, holds the food between the +rows of teeth. (By an outward pressure from the tongue and an inward +pressure from the cheek the food is kept between the grinding surfaces.) +The tongue has functions in addition to these and is a most useful +organ.</p> + +<p><pb n="144" /><anchor id="Pg144" />3. <hi rend="font-style: +italic">The Muscles of Mastication.</hi>—These are attached to the lower +jaw and bring about its different movements. The <hi rend="font-style: +italic">masseter</hi> muscles, which are the heavy muscles in the +cheeks, and the <hi rend="font-style: italic">temporal</hi> muscles, +located in the region of the temples, raise the lower jaw and supply the +force for grinding the food. Small muscles situated below the chin +depress the jaw and open the mouth.</p> + +<p rend="text-align: center"> +<figure url="images/image67.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 67—<hi rend="font-weight: bold">Salivary +glands</hi> and the ducts connecting them with the mouth.</head> +<figDesc>Fig. 67</figDesc> +</figure></p> + +<p>4. <hi rend="font-style: italic">The Salivary Glands.</hi>—These +glands are situated in the tissues surrounding the mouth, and +communicate with it by means of ducts (Fig. 67). They secrete the +saliva. The salivary glands are six in number and are arranged in three +pairs. The largest, called the <hi rend="font-style: +italic">parotid</hi> glands, lie, one on either side, in front of and +below the ears. A duct from each gland passes forward along the cheek +until it opens in the interior of the mouth, opposite the second molar +tooth in the upper jaw. Next in size to the parotids are the <hi +rend="font-style: italic">submaxillary</hi> glands. These are located, +one on either side, just below and in front of the triangular bend in +the lower jaw. The smallest of the salivary glands are the <hi +rend="font-style: italic">sublingual</hi>. They are situated in the +floor of the mouth, on either side, at the front and base of the tongue. +Ducts from the submaxillary and sublingual glands open into the mouth +below the tip of the tongue.</p> + +<p><hi rend="font-weight: bold">The Saliva and its Uses.</hi>—The saliva +is a transparent and somewhat slimy liquid which is slightly alkaline. +It<pb n="145" /><anchor id="Pg145" /> consists chiefly of water (about +99 per cent), but in this are dissolved certain salts and an active +chemical agent, or enzyme, called <hi rend="font-style: +italic">ptyalin</hi>, which acts on the starch. The ptyalin changes +starch into a form of sugar (maltose), while the water in the saliva +dissolves the soluble portions of the food. In addition to this the +saliva moistens and lubricates the food which it does not dissolve, and +prepares it in this way for its passage to the stomach. The last is +considered the most important use of the saliva, and dry substances, +such as crackers, which require a considerable amount of this liquid, +cannot be eaten rapidly without choking. Slow mastication favors the +secretion and action of the saliva.</p> + +<p><hi rend="font-weight: bold">Deglutition.</hi>—Deglutition, or +swallowing, is the process by which food is transferred from the mouth +to the stomach. Though this is not, strictly speaking, a digestive +process, it is, nevertheless, necessary for the further digestion of the +food. Mastication and insalivation, which are largely mechanical, +prepare the food for certain chemical processes by which it is +dissolved. The first of these occurs in the stomach and to this organ +the food is transferred from the mouth. The chief organs concerned in +deglutition are the tongue, the pharynx, and the esophagus.</p> + +<p><hi rend="font-weight: bold">The Pharynx</hi> is a round and somewhat +cone-shaped cavity, about four and one half inches in length, which lies +just back of the nostrils, mouth, and larynx. It is remarkable for its +openings, seven in number, by means of which it communicates with other +cavities and tubes of the body. One of these openings is into the mouth, +one into the esophagus, one into the larynx, and one into each of the +nostrils, while two small tubes (the eustachian) pass from the upper +part of the pharynx to the middle ears.</p> + +<p>The pharynx is the part of the food canal that is crossed<pb n="146" /><anchor id="Pg146" /> by the passageway for the air. To +keep the food from passing out of its natural channel, the openings into +the air passages have to be carefully guarded. This is accomplished +through the soft palate and epiglottis, which are operated somewhat as +valves. The muscular coat of the pharynx is made up of a series of +overlapping muscles which, by their contractions, draw the sides +together and diminish the cavity. The mucous membrane lining the pharynx +is smooth, like that of the mouth, being covered with a layer of flat +epithelial cells.</p> + +<p><hi rend="font-weight: bold">The Esophagus</hi>, or gullet, is a tube +eight or nine inches long, connecting the pharynx with the stomach. It +lies for the most part in the thoracic cavity and consists chiefly of a +thick mucous lining surrounded by a heavy coat of muscle. The muscular +coat is composed of two layers—an inner layer whose fibers encircle the +tube and an outer layer whose fibers run lengthwise.</p> + +<p><hi rend="font-weight: bold">Steps in Deglutition.</hi>—The process +of deglutition varies with the kind of food. With bulky food it consists +of three steps, or stages, as follows: 1. By the contraction of the +muscles of the cheeks, the food ball, or bolus, is pressed into the +center of the mouth and upon the upper surface of the tongue. Then the +tongue, by an upward and backward movement, pushes the food under the +soft palate and into the pharynx.</p> + +<p>2. As the food passes from the mouth, the pharynx is drawn up to +receive it. At the same time the soft palate is pushed upward and +backward, closing the opening into the upper pharynx, while the +epiglottis is made to close the opening into the larynx. By this means +all communication between the food canal and the air passages is +temporarily closed. The upper muscles of the pharynx now contract upon +the food, forcing it downward and into the esophagus.</p> + +<p>3. In the esophagus the food is forced along by the successive +contractions of muscles, starting at the upper end of the tube, until +the stomach is reached.</p> + +<p>Swallowing is doubtless aided to some extent by the force of +gravity. <pb n="147" /><anchor id="Pg147" />That it is independent of this +force, however, is shown by the fact that one may swallow with the +esophagus in a horizontal position, as in lying down.</p> + +<p rend="text-align: center"> +<figure url="images/image68.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 68—<hi rend="font-weight: bold">Gastric +Glands.</hi> <hi rend="font-style: italic">A.</hi> Single gland showing +the two kinds of secreting cells and the duct where the gland opens on +to the surface. <hi rend="font-style: italic">B.</hi> Inner surface of +stomach magnified. The small pits are the openings from the glands.</head> +<figDesc>Fig. 68</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Stomach.</hi>—The stomach is the +largest dilatation of the alimentary canal. It is situated in the +abdominal cavity, immediately below the diaphragm, with the larger +portion toward the left side. Its connection with the esophagus is known +as the <hi rend="font-style: italic">cardiac orifice</hi> and its +opening into the small intestine is called the <hi rend="font-style: +italic">pyloric orifice</hi>. It varies greatly in size in different +individuals, being on the average from ten to twelve inches at its +greatest length, from four to five inches at its greatest width, and +holding from three to five pints. It has the coats common to the canal, +but these are modified somewhat to adapt them to its work.</p> + +<p><hi rend="font-style: italic">The mucous membrane</hi> of the stomach +is thick and highly developed. It contains great numbers of minute +tube-shaped bodies, known as the <hi rend="font-style: italic">gastric +glands</hi> (Fig. 68). These are of two general kinds and secrete large +quantities of a liquid called the gastric juice. When the stomach is +empty, the mucous membrane is thrown into folds which run lengthwise +over the inner surface. These disappear, however, when the walls of the +stomach are distended with food.</p> + +<p><pb n="148" /><anchor id="Pg148" /><hi rend="font-style: italic">The muscular coat</hi> consists of <hi +rend="font-style: italic">three</hi> separate layers which are named, +from the direction of the fibers, the circular layer, the longitudinal +layer, and the oblique layer (Fig. 69). +The circular layer becomes quite thick at the pyloric orifice, +forming a distinct band which serves as a valve.</p> + +<p rend="text-align: center"> +<figure url="images/image69.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 69—<hi rend="font-weight: bold">Muscles of the +stomach</hi> (from Morris' <hi rend="font-style: italic">Human +Anatomy</hi>). The layer of Longitudinal fibers removed.</head> +<figDesc>Fig. 69</figDesc> +</figure></p> + +<p>The outer coat of the stomach, called the <hi rend="font-style: +italic">serous coat</hi>, is a continuation of the peritoneum, the +membrane lining the abdominal cavity.</p> + +<p><hi rend="font-weight: bold">Stomach Digestion.</hi>—In the stomach +begins the definite work of dissolving those foods which are insoluble +in water. This, as already stated, is a double process. There is first a +chemical action in which the insoluble are changed into soluble +substances, and this is followed immediately by the dissolving action of +water. The chief substances digested in the stomach are the proteids. +These, in dissolving, are changed into two soluble substances, known +as<pb n="149" /><anchor id="Pg149" /> <hi rend="font-style: +italic">peptones</hi> and <hi rend="font-style: italic">proteoses</hi>. +The digestion of the proteids is, of course, due to the</p> + +<p><hi rend="font-weight: bold">Gastric Juice.</hi>—The gastric juice is +a thin, colorless liquid composed of about 99 per cent of water and +about 1 per cent of other substances. The latter are dissolved in the +water and include, besides several salts, three active chemical +agents—hydrochloric acid, pepsin, and rennin. <hi rend="font-style: +italic">Pepsin</hi> is the enzyme which acts upon proteids, but it is +able to act only in an acid medium—a condition which is supplied by the +<hi rend="font-style: italic">hydrochloric acid</hi>. Mixed with the +hydrochloric acid it converts the proteids into peptones and +proteoses.</p> + +<p><hi rend="font-weight: bold">Other Effects of the Gastric +Juice.</hi>—In addition to digesting proteids, the gastric juice brings +about several minor effects, as follows:</p> + +<p>1. It checks, after a time, the digestion of the starch which was +begun in the mouth by the saliva.<note place="foot"><p>The saliva may continue to act for a considerable time +after the food enters the stomach. "Careful examination of the contents +of the fundus (large end of the stomach) by Cannon and Day has shown +that no inconsiderable amount of salivary digestion occurs in the +stomach."—FISCHER, <hi rend="font-style: italic">The Physiology of +Alimentation</hi>.</p></note> This is due to the presence of the +hydrochloric acid, the ptyalin being unable to act in an acid +medium.</p> + +<p>2. While there is no appreciable action on the fat itself, the +proteid layers that inclose the fat particles are dissolved away (Fig. +79), and the fat is set free. By this means the fat is broken up and +prepared for a special digestive action in the small intestine.</p> + +<p>3. Dissolved albumin, like that in milk, is curded, or coagulated, in +the stomach. This action is due to the <hi rend="font-style: +italic">rennin</hi>. The curded mass is then acted upon by the pepsin +and hydrochloric acid in the same manner as the other proteids.</p> + +<p><pb n="150" /><anchor id="Pg150" />4. The hydrochloric acid acts on certain of the insoluble mineral +salts found in the foods and reduces them to a soluble condition.</p> + +<p>5. It is also the opinion of certain physiologists that cane sugar +and maltose (double sugars) are converted by the hydrochloric acid into +dextrose and levulose (single sugars).</p> + +<p>After a variable length of time, the contents of the stomach is +reduced to a rather uniform and pulpy mass which is called <hi +rend="font-style: italic">chyme</hi>. Portions of this are now passed at +intervals into the small intestine.</p> + +<p><hi rend="font-weight: bold">Muscular Action of the Stomach.</hi>—The +muscles in the walls of the stomach have for one of their functions the +mixing of the food with the gastric juice. By <hi rend="font-style: +italic">alternately</hi> contracting and relaxing, the different layers +of muscle keep the form of the stomach changing—a result which agitates +and mixes its contents. This action varies in different parts of the +organ, being slight or entirely absent at the cardiac end, but quite +marked at the pyloric end.</p> + +<p>Another purpose of the muscular coat is to empty the stomach into the +small intestine. During the greater part of the digestive period the +muscular band at the pyloric orifice is contracted. At intervals, +however, this band relaxes, permitting a part of the contents of the +stomach to be forced into the small intestine. After the discharge the +pyloric muscle again contracts, and so remains until the time arrives +for another discharge.</p> + +<p>In addition to emptying the stomach into the small intestine, these +muscles also aid in emptying the organ upward and through the esophagus +and mouth, should occasion require. Vomiting in case of poisoning, or if +the food for some reason fails to digest, is a necessary though +unpleasant operation. It is accomplished by the<pb n="151" /><anchor id="Pg151" /> contraction of all the muscles of +the stomach, together with the contraction of the walls of the abdomen. +During these contractions the pyloric valve is closed, and the muscles +of the esophagus and pharynx are in a relaxed condition.<note place="foot"><p>Perhaps the simplest method of inducing vomiting is that +of thrusting a finger down the throat. To make this method effective the +finger should be held in the throat until the vomiting begins. An +emetic, such as a glass of lukewarm salt water containing a teaspoonful +of mustard, should also be taken, and, in the case of having swallowed +poison, the vomiting should be repeated several times. It may even be +advantageous to drink water and then vomit it up in order to wash out +the stomach.</p></note></p> + +<p rend="text-align: center"> +<figure url="images/image70.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 70—<hi rend="font-weight: bold">Passage from +stomach</hi> into small intestine. Illustration also shows arrangement +of mucous membrane in the two organs. <hi rend="font-style: +italic">D.</hi> Bile duct.</head> +<figDesc>Fig. 70</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Small Intestine.</hi>—This division +of the alimentary canal consists of a coiled tube, about twenty-two feet +in length, which occupies the central, lower portion of the abdominal +cavity (Fig. 71). At its upper extremity it connects with the pyloric +end of the stomach (Fig. 70), and at its lower end it joins the large +intestine. It averages a little over an inch in diameter, and gradually +diminishes in size from the stomach to the large intestine. The first +eight or ten inches form a short curve, known as the <hi +rend="font-style: italic">duodenum</hi>. The upper two fifths of the +remainder is called the <hi rend="font-style: italic">jejunum</hi>, and +the lower three fifths is known as the <hi rend="font-style: +italic">ileum</hi>. The ileum joins that part of the large intestine +known as the cæcum, and at their place of union is a marked constriction +which prevents material from passing from the large into the small +intestine (Fig. 73). This is known as the <hi rend="font-style: +italic">ileo-cæcal valve</hi>.</p> + +<p><hi rend="font-style: italic">The mucous membrane</hi> of the small +intestine is richly supplied with blood vessels and contains glands that +secrete<pb n="152" /><anchor id="Pg152" /> a digestive fluid known as the +<hi rend="font-style: italic">intestinal juice</hi>. The membrane is +thrown into many transverse, or circular, folds which increase its +surface and also prevent materials from passing too rapidly through the +intestine. One important respect in which the small intestine differs +from all other portions of the food canal is that its surface is covered +with great numbers of minute elevations known as the villi. The purpose +of these is to aid in the absorption of the nutrients as they become +dissolved (Chapter XI).</p> + +<p><hi rend="font-style: italic">The muscular coat</hi> of the small +intestine is made up of two distinct layers—the inner layer consisting +of circular fibers and the outer of longitudinal fibers. These muscles +keep the food materials mixed with the juices of the small intestine, +but their main purpose is to force the materials undergoing digestion +through this long and much-coiled tube.</p> + +<p>The outer, or <hi rend="font-style: italic">serous</hi>, coat of the +small intestine, like that of the stomach, is an extension from the +general lining of the abdominal cavity, or peritoneum. In fact, the +intestine lies in a fold of the peritoneum, somewhat as an arm in a +sling, while the peritoneum, by connecting with the back wall of the +abdominal cavity, holds this great coil of digestive tubing in place +(Fig. 64). The portion of the peritoneum which attaches the intestine to +the wall of the abdomen is called the <hi rend="font-style: +italic">mesentery</hi>.</p> + +<p>Most of the liquid acting on the food in the small intestine is +supplied by two large glands, the liver and the pancreas, that connect +with it by ducts.</p> + +<p rend="text-align: center"> +<figure url="images/image71.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 71—<hi +rend="font-weight: bold">Abdominal cavity</hi> with organs of digestion +in position.</head> +<figDesc>Fig. 71</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Liver</hi> is situated immediately +below the diaphragm, on the right side (Figs. 71 and 72), and is the +largest gland in the body. It weighs about four pounds and is separated +into two main divisions, or lobes. It is complex in structure and +differs from the other glands in several particulars. It receives blood +from two distinct sources—the portal vein<pb n="154" /><anchor id="Pg154" /> and the hepatic artery. <hi +rend="font-style: italic">The portal vein</hi> collects the blood from +the stomach, intestines, and spleen, and passes it to the liver. This +blood is loaded with food materials, but contains little or no oxygen. +The <hi rend="font-style: italic">hepatic artery</hi>, which branches +from the aorta, carries to the liver blood rich in oxygen. In the liver +the portal vein and the hepatic artery divide and subdivide, and finally +empty their blood into a single system of capillaries surrounding the +liver cells. These capillaries in turn empty into a single system of +veins which, uniting to form the <hi rend="font-style: italic">hepatic +veins</hi> (two or three in number), pass the blood into the inferior +vena cava (Fig. 72).</p> + +<p rend="text-align: center"> +<figure url="images/image72.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 72—<hi rend="font-weight: bold">Relations of the +liver.</hi> Diagram showing the connection of the liver with the large +blood vessels and the food canal.</head> +<figDesc>Fig. 72</figDesc> +</figure></p> + +<p>The liver secretes daily from one to two pounds of a liquid called +<hi rend="font-style: italic">bile</hi>. A reservoir for the bile is +provided by a small, membranous sack, called the <hi rend="font-style: +italic">gall bladder</hi>, located on the underside of the liver. The +bile passes from the gall bladder, and from the right and left lobes of +the liver, by three separate ducts. These unite to form a common tube +which, uniting with the duct from the pancreas, empties into the +duodenum. Though usually described as a digestive gland, the liver has +other functions of equal or greater importance (Chapter XIII).</p> + +<p><pb n="155" /><anchor id="Pg155" /><hi rend="font-weight: bold">The +Bile</hi> is a golden yellow liquid, having a slightly alkaline reaction +and a very bitter taste. It consists, on the average, of about 97 per +cent of water and 3 per cent of solids.<note place="foot"><p>Hammerstein, <hi rend="font-style: italic">Text-book of +Physiological Chemistry.</hi></p></note> The solids include bile +pigments, bile salts, a substance called cholesterine, and mineral +salts. The pigments (coloring matter) of the bile are derived from the +hemoglobin of broken-down red corpuscles (page 27).</p> + +<p>Much about the composition of the bile is not understood. It is +known, however, to be necessary to digestion, its chief use being to aid +in the digestion and absorption of fats. It is claimed also that the +bile aids the digestive processes in some general ways—counteracting the +acid of the gastric juice, preventing the decomposition of food in the +intestines, and stimulating muscular action in the intestinal walls. No +enzymes have been discovered in the bile.</p> + +<p><hi rend="font-weight: bold">The Pancreas</hi> is a tapering and +somewhat wedge-shaped gland, and is so situated that its larger +extremity, or head, is encircled by the duodenum. From here the more +slender portion extends across the abdominal cavity nearly parallel to +and behind the lower part of the stomach. It has a length of six or +eight inches and weighs from two to three and one half ounces. Its +secretion, the pancreatic juice, is emptied into the duodenum by a duct +which, as a rule, unites with the duct from the liver.</p> + +<p><hi rend="font-weight: bold">The Pancreatic Juice</hi> is a colorless +and rather viscid liquid, having an alkaline reaction. It consists of +about 97.6 per cent of water and 2.4 per cent of solids. The solids +include mineral salts (the chief of which is sodium carbonate) and four +different chemical agents, or enzymes,—trypsin, amylopsin, steapsin, and +a milk-curding enzyme. These active constituents make of the pancreatic +juice the<pb n="156" /><anchor id="Pg156" /> most important of the digestive +fluids. It acts with vigor on all of the nutrients insoluble in water, +producing the following changes:</p> + +<p>1. It converts the starch into maltose, completing the work begun by +the saliva. This action is due to the <hi rend="font-style: +italic">amylopsin</hi>,<note place="foot"><p>Amylopsin is absent from the pancreatic juice of +infants, a condition which shows that milk and not starch is their +natural food.</p></note> which is similar to ptyalin but is more +vigorous.</p> + +<p>2. It changes proteids into peptones and proteoses, completing the +work begun by the gastric juice. This is accomplished by the <hi +rend="font-style: italic">trypsin</hi>, which is similar to, but more +active than, the pepsin.</p> + +<p>3. It digests fat. In this work the active agent is the <hi +rend="font-style: italic">steapsin</hi>.</p> + +<p>The necessity of a milk-curding enzyme, somewhat similar to the +rennin of the gastric juice, is not understood.</p> + +<p><hi rend="font-weight: bold">Digestion of Fat.</hi>—Several theories +have been proposed at different times regarding the digestion and +absorption of fat. Among these, what is known as the "solution theory" +seems to have the greatest amount of evidence in its favor. According to +this theory, the fat, under the influence of the steapsin, absorbs water +and splits into two substances, recognized as glycerine and fatty acid. +This finishes the process so far as the glycerine is concerned, as this +is soluble in water; but the fatty acid, which (from certain fats) is +insoluble in water,<note place="foot"><p>The fact that butter is more easily digested than other +fatty substances is probably due to its consisting largely of a kind of +fat which, on splitting, forms a fatty acid (butyric) which is soluble +in water.</p></note> requires further treatment. The fatty acid is now +supposed to be acted on in one, or both, of the following ways: 1. To be +dissolved as fatty acid by the action of the bile (since bile is +capable<pb n="157" /><anchor id="Pg157" /> of dissolving it under certain +conditions). 2. To be converted by the sodium carbonate into a form of +soap which is soluble in water.</p> + +<p>The emulsification of fat is known to occur in the small intestine. +By this process the fat is separated into minute particles which are +suspended in water, but not changed chemically, the mixture being known +as an <hi rend="font-style: italic">emulsion</hi>. While this is +believed by some to be an actual process of digestion, the advocates of +the solution theory claim that it is a process accompanying and aiding +the conversion of fat into fatty acid and glycerine.<note place="foot"><p>Fischer, <hi rend="font-style: italic">Physiology of +Alimentation.</hi></p></note></p> + +<p><hi rend="font-weight: bold">The Intestinal Juice</hi> is a clear +liquid with an alkaline reaction, containing water, mineral salts, and +certain proteid substances that may act as enzymes. It assists in +bringing about an alkaline condition in the small intestine and aids in +the reduction of cane sugar and maltose to the simple sugars, dextrose +and levulose. Since it is difficult to obtain this liquid in sufficient +quantities for experimenting, its uses have not been fully determined. +Recent investigators, however, assign to it an important place in the +work of digestion.</p> + +<p><hi rend="font-weight: bold">Work of the Small Intestine.</hi>—The +small intestine is the most important division of the alimentary canal. +It serves as a receptacle for holding the food while it is being acted +upon; it secretes the intestinal juice and mixes the food with the +digestive fluids; it propels the food toward the large intestine; and, +in addition to all this, serves as an organ of absorption.</p> + +<p>Digestion is practically finished in the small intestine, and a large +portion of the reduced food is here absorbed. There is always present, +however, a variable amount of material that is not digested. This, +together with a considerable volume of liquid, is passed into</p> + +<p><pb n="158" /><anchor id="Pg158" /><hi rend="font-weight: bold">The +Large Intestine.</hi>—The large intestine is a tube from five to six +feet in length and averaging about one and one half inches in diameter. +It begins at the lower right side of the abdominal cavity, forms a coil +which almost completely surrounds the coil of small intestine, and +finally terminates at the surface of the body (Figs. 2, 71 and 73). It +has three divisions, known as the cæcum, the colon, and the rectum.</p> + +<p rend="text-align: center"> +<figure url="images/image73.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 73—<hi rend="font-weight: bold">Passage from +small into large intestine.</hi> At the ileo-cæcal valve is the narrowest +constriction of the food canal.</head> +<figDesc>Fig. 73</figDesc> +</figure></p> + +<p><hi rend="font-style: italic">The cæcum</hi> is the pouch-like +dilatation of the large intestine which receives the lower end of the +small intestine. It measures about two and one half inches in diameter +and has extending from one side a short, slender, and blind tube, called +the <hi rend="font-style: italic">vermiform appendix</hi>. This +structure serves no purpose in digestion, but appears to be the rudiment +of an organ which may have served a purpose at some remote period in the +history of the human race. The cæcum gradually blends into the second +division of the large intestine, called the colon.</p> + +<p><hi rend="font-style: italic">The colon</hi> consists of four parts, +described as the ascending colon, the transverse colon, the descending +colon, and the sigmoid flexure, or sigmoid colon. The first three +divisions are named from the direction of the movement of materials +through them and the last from its shape, which is similar to that of +the Greek letter sigma (Σ).</p> + +<p><hi rend="font-style: italic">The rectum</hi> is the last division of +the large intestine<pb n="159" /><anchor id="Pg159" /> It is a nearly straight tube, +from six to eight inches in length, and connects with the external +surface of the body.</p> + +<p>The general structure of the large intestine is similar to that of +the small intestine, and, like the small intestine, it is held in place +by the peritoneum. It differs from the small intestine, however, in its +lining of mucous membrane and in the arrangement of the muscular coat. +The mucous membrane presents a smooth appearance and has no villi, while +the longitudinal layer of the muscular coat is limited to three narrow +bands that extend along the greater length of the tube (Fig. 74). These +bands are shorter than the coats, and draw the large intestine into a +number of shallow pouches, by which it is readily distinguished from the +small intestine (Fig. 71).</p> + +<p rend="text-align: center"> +<figure url="images/image74.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 74—<hi rend="font-weight: bold">Section of large +intestine</hi>, showing the coats. 1. Serous coat. 2. Circular layer of +muscle. 3. Submucous coat. 4. Mucous membrane. 5. Muscular bands +extending lengthwise over the intestine.</head> +<figDesc>Fig. 74</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Work of the Large Intestine.</hi>—The +large intestine serves as a receptacle for the materials from the small +intestine. The digestive fluids from the small intestine continue their +action here, and the dissolved materials also continue to be absorbed. +In these respects the work of the large intestine is similar to that of +the small intestine. It does, however, a work peculiar to itself in that +it collects and retains undigested food particles, together with other +wastes, and ejects them periodically from the canal.</p> + +<p><hi rend="font-weight: bold">Work of the Alimentary Muscles.</hi>—The +mechanical part of digestion is performed by the muscles that encircle +the food canal. Their uses, which have already been mentioned in +connection with the different organs of<pb n="160" /><anchor id="Pg160" /> digestion, may be here +summarized: They supply the necessary force for masticating the food. +They propel the food through the canal. They mix the food with the +different juices. At certain places they partly or completely close the +passage until a digestive process is completed. They may even cause a +reverse movement of the food, as in vomiting. All of the alimentary +muscles, except those around the mouth, are involuntary. Their work is +of the greatest importance.</p> + +<p><hi rend="font-weight: bold">Other Purposes of the Digestive +Organs.</hi>—The digestive organs serve other important purposes besides +that of dissolving the foods. They provide favorable conditions for +passing the dissolved material into the blood. They dispose of such +portions of the foods as fail, in the digestive processes, to be reduced +to a liquid state. A considerable amount of waste material is also +separated from the blood by the glands of digestion (especially the +liver), and this is passed from the body with the undigested portions of +food. Then the food canal (stomach in particular) is a means of holding, +or storing, food which is awaiting the processes of digestion. +Considering the number of these purposes, the digestive organs are +remarkably simple, both in structure and in method of operation.</p> + +<div> +<head>HYGIENE OF DIGESTION</head> + +<p>Many of the ills to which flesh is heir are due to improper methods +of taking food and are cured by observing the simple rules of eating. +Habit plays a large part in the process and children should, for this +reason, be taught early to eat properly. Since the majority of the +digestive processes are involuntary and the food, after being swallowed, +is practically beyond control, careful attention must be given to the +proper mastication of the food and to such other phases of digestion as +are under control.</p> + +<p><hi rend="font-weight: bold">Necessity for Thorough +Mastication.</hi>—Mastication prepares the food for the digestive +processes which follow. Unless the food has been properly masticated, +the digestive<pb n="161" /><anchor id="Pg161" /> fluids in the stomach +and intestines cannot act upon it to the best advantage. When the food +is carefully chewed, a larger per cent of it is actually digested—a +point of importance where economy in the use of food needs to be +practiced.</p> + +<p>A fact not to be overlooked is that one cannot eat hurriedly and +practice thorough mastication. The food must not be swallowed in lumps, +but reduced to a finely divided and pulpy mass. This requires time. The +one who hurries through the meal is necessarily compelled to bolt his +food. Thirty minutes is not too long to give to a meal, and a longer +period is even better.</p> + +<p>Perhaps the most important result of giving plenty of time to the +taking of food is that of <hi rend="font-style: italic">stimulating the +digestive glands to a proper degree of activity</hi>. That both the +salivary and gastric glands are excited by the sight, smell, and thought +of food and, through taste, by the presence of food in the mouth, has +been fully demonstrated. Food that is thoroughly masticated and relished +will receive more saliva and gastric juice, and probably more of other +juices, than if hastily chewed and swallowed. This has a most important +bearing upon the efficiency of the digestive processes.</p> + +<p><hi rend="font-weight: bold">Order of Taking Food.</hi>—There has +been evolved through experience a rather definite order of taking food, +which our knowledge of the process of digestion seems to justify. The +heavy foods (proteids for the most part) are eaten first; after which +are taken starchy foods and fats; and the meal is finished off with +sweetmeats and pastry.<note place="foot"><p>Beginning the meal with a little soup, as is frequently +done, may be of slight advantage in stimulating the digestive glands. To +serve this purpose, however, and not interfere with the meal proper, it +should contain little greasy or starchy material and should be taken in +small amount.</p></note> The scientific arguments for this order are +the following:</p> + +<p>1. By receiving the first of the gastric flow the proteids can +begin<pb n="162" /><anchor id="Pg162" /> digesting without delay. Since +these are the main substances acted on in the stomach, the time required +for their digestion is shortened by eating them first.</p> + +<p>2. Sugar, being of the nature of predigested starch, quickly gets +into the blood and <hi rend="font-style: italic">satisfies the +relish</hi> for food. The result of taking sugar first may be to cause +one to eat less than he needs and to diminish the activity of the +glands.</p> + +<p>3. Fat or grease, if taken first, tends to form a coating over the +walls of the stomach and around the material to be digested. This +prevents the juices from getting to and mixing with the foods upon which +they are to act.</p> + +<p>4. Starch following the proteids, for the most part, does not so +quickly come in contact with the gastric juice. This enables the ptyalin +of the saliva to continue its action for a longer time than if the +starch were eaten first.</p> + +<p><hi rend="font-weight: bold">Liquids during the Meal.</hi>—Liquids as +ordinarily taken during the meal are objectionable. They tend to +diminish the secretion of the saliva and to cause rapid eating. Instead +of eating slowly and swallowing the food only so fast as the glands can +supply the necessary saliva, the liquid is used to wash the food down. +Water or other drinks should be taken after the completion of the meal +or when the mouth is completely free from food. Even then it should be +taken in small sips. While the taking of a small amount of water in this +way does no harm, a large volume has the effect of weakening the gastric +juice. Most of the water needed by the body should be taken between +meals.</p> + +<p><hi rend="font-weight: bold">The State of Mind</hi> has much to do +with the proper digestion of the food. Worry, anger, fear, and other +disturbed mental states are known to check the secretion of fluids and +to interfere with the digestive processes. While the cultivation of +cheerfulness is important for its general hygienic effects, it is of +especial value in relation to digestion. Intense emotions, either during +or following the<pb n="163" /><anchor id="Pg163" /> meal, should if possible be +avoided. The table is no place for settling difficulties or +administering rebuke. The conversation, on the other hand, should be +elevating and joy giving, thereby inducing a desirable reactionary +influence upon the digestive processes.</p> + +<p><hi rend="font-weight: bold">Care of the Teeth.</hi>—The natural +teeth are indispensable for the proper mastication of the food. Of +especial value are the molars—the teeth that grind the food. The +development of the profession of dentistry has made possible the +preservation of the teeth, even when naturally poor, as long as one has +need of them. To preserve the teeth they must be kept clean. They should +be washed at least once a day with a soft-bristled brush, and small +particles of food, lodged between them, should be removed with a wooden +pick. The biting of hard substances, such as nuts, should be avoided, on +account of the danger of breaking the enamel, although the chewing of +tough substances is considered beneficial.</p> + +<p>Decayed places in the teeth should be promptly filled by the dentist. +It is well, even when decayed places are not known to exist, to have the +teeth examined occasionally in order to detect such places before they +become large. On account of the expense, pain, and inconvenience there +is a tendency to put off dental work which one knows ought to be done. +Perhaps in no other instance is procrastination so surely punished. The +decayed places become larger and new points of decay are started; and +the pain, inconvenience, and expense are increased proportionately.</p> + +<p><hi rend="font-weight: bold">The Natural Appetite</hi> should be +followed with reference to both the kind and the amount of food eaten. +No system of knowledge will ever be devised which can replace the +appetite as an aid in the taking of food. <hi rend="font-style: +italic">It is</hi><pb n="164" /><anchor id="Pg164" /> <hi rend="font-style: +italic">nature's means of indicating the needs of the body</hi>. The +natural appetite may be spoiled, however, by overeating and by the use +of highly seasoned foods, or by indulging in stimulants during the meal. +It is spoiled in children by too free indulgence in sweetmeats. By +cultivating the natural appetite and heeding its suggestions, one has at +his command an almost infallible guide in the taking of food.</p> + +<p><hi rend="font-weight: bold">Preparation of Meals.</hi>—The cooking +of food serves three important purposes. It renders the food more +digestible, relieving the organs of unnecessary work; it destroys +bacteria that may be present in the food, diminishing the likelihood of +introducing disease germs into the body; and it makes the food more +palatable, thereby supplying a necessary stimulus to the digestive +glands. While the methods employed in the preparation of the different +foods have much to do with the ease with which they are digested and +with their nourishing qualities, the scope of our subject does not +permit of a consideration of these methods.</p> + +<p><hi rend="font-weight: bold">Quantity of Food.</hi>—Overeating and +undereating are both objectionable from a hygienic standpoint. +Overeating, by introducing an unnecessary amount of food into the body, +overworks the organs of digestion and also the organs of excretion. It +may also lead to the accumulation of burdensome fat and of harmful +wastes. On the other hand, the taking of too little food impoverishes +the blood and weakens the entire body. As a rule, however, more people +eat too much than too little, and to quit eating before the appetite is +fully satisfied is with many persons a necessary precaution. The power +of self-control, valuable in all phases of life, is indispensable in the +avoidance of overeating.</p> + +<pb n="165" /><anchor id="Pg165" /> + +<p><hi rend="font-weight: bold">Frequency of Taking Food.</hi>—Eating between +meals is manifestly an unhealthful practice. The question has also been +raised as to whether the common habit of eating three times a day is +best suited to all classes of people. Many people of weak digestive +organs have been benefited by the plan of two meals a day, while others +adopt the plan of eating one heavy meal and two light ones. Either plan +gives the organs of digestion more time to rest and diminishes the +liability of overeating. On the other hand, those doing heavy muscular +work can hardly derive the energy which they need from less than three +good meals a day. Though no definite rule can be laid down, there is +involved a hygienic principle which all should follow: <hi +rend="font-style: italic">Meals should not overlap</hi>. The stomach +should be free from food taken at a previous meal before more is +introduced into it. When this principle is not observed, material +ferments in the stomach, causing indigestion and other disorders. It +should be noted, however, that the overlapping may be due to overeating +as well as to eating too frequently.</p> + +<p><hi rend="font-weight: bold">Dangers from Impure Food.</hi>—Food is +frequently the carrier of disease germs and for this reason requires +close inspection (page 128). Typhoid fever, a most dangerous disease, is +usually contracted through either impure food or impure water (Chapter +XXIII). One safeguard against disease germs, as stated above, is +thorough cooking. Too much care cannot be exercised with reference to +the water for drinking purposes. Water which is not perfectly clear, +which smells of decaying material, or which forms a sediment on standing +is usually not fit to drink. It can, however, be rendered comparatively +harmless by boiling. The objections which many people have to drinking +boiled water are removed when it is boiled the day before it is<pb n="166" /><anchor id="Pg166" /> used, so as to give it time to +cool, settle, and replace the air driven off by the boiling.</p> + +<p><hi rend="font-weight: bold">Care of the Bowels.</hi>—In considering +the hygiene of the alimentary canal, the fact that it is used as a means +of separating the impurities from the body must not be overlooked. +Frequently, through lack of exercise, negligence in evacuating the +bowels, or other causes, a weakened condition of the canal is induced +which results in the retention of impurities beyond the time when they +should be discharged. This is a great annoyance and at the same time a +menace to the health.</p> + +<p>In most cases this condition can be relieved, and prevented from +recurring, by observing the following habits: 1. Have a regular time +each day for evacuating the bowels. This is a most important factor in +securing the necessary movements. 2. Drink a cup of cold water on rising +in the morning and on retiring at night. 3. Eat generously of fruits and +other coarse foods, such as corn bread, oatmeal, hominy, cabbage, etc. +4. Practice persistently such exercises as bring the abdominal muscles +into play. These exercises strengthen indirectly the muscles of the +canal. 5. Avoid overwork, especially of the nervous system.</p> + +<p><hi rend="font-weight: bold">Alcohol and Digestion.</hi>—Though +exciting temporarily a greater flow of the digestive fluids, alcoholic +drinks taken in any but very small quantities are considered detrimental +to the work of digestion. Large doses retard the action of enzymes, +inflame the mucous lining of the stomach,<note place="foot"><p>Dr. William Beaumont, an American surgeon of the last +century, made a series of observations upon a human stomach (that of +Alexis St. Martin) having an artificial opening, the result of a gunshot +wound. Much of our knowledge of the digestion of different foods was +obtained through these observations. In spite of the protests of his +physician, St. Martin would occasionally indulge in strong drink and +always with the same result—the lining of the stomach became much +inflamed and very sensitive, and the natural processes of digestion were +temporarily suspended.</p></note> and<pb n="167" /><anchor id="Pg167" /> bring about a diseased condition +of the liver. It may be noted, however, that the bad effects of +alcoholic beverages upon the stomach, the liver, and the body in general +are less pronounced when these are taken as a part of the regular +meals.</p> + +<p><hi rend="font-weight: bold">Effects of Tea and Coffee.</hi>—In +addition to the stimulating agent caffeine, tea and coffee contain a +bitter, astringent substance, known as tannin. On account of the tannin +these beverages tend to retard digestion and to irritate the lining of +the stomach—effects that may be largely obviated by methods of +preparing tea and coffee which dissolve little of the tannin. (They +should be made without continued boiling or steeping.) The +caffeine may do harm through its stimulating effect upon the +nervous system (page 56) and through the introduction of a special +waste into the body. In chemical composition caffeine closely resembles +a waste, called uric acid, and in the body is converted into this +substance. If one is in a weakened condition, the uric acid may fail to +be oxidized to urea, as occurs normally, or to be thrown off as uric +acid. In this case it accumulates in the body, causing rheumatism and +related diseases. It thus happens that while some people may use tea and +coffee without detriment, others are injured by them.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The main structure in the +digestive system is the alimentary canal. This provides cavities where +important dissolving processes take place, and tubes for joining these +cavities, while glands connecting with the canal supply the necessary +liquids for changing and dissolving the foods. The general plan of +digestion is that of passing the food through the canal, beginning with +the mouth, and of acting on it at various places, with the final result +of reducing most of it to the liquid state. The digestive fluids<pb +n="168" /><anchor id="Pg168" /> supply water which acts as a solvent and +carries the active chemical agents, or enzymes, that convert the +insoluble foods into substances that are soluble. The muscles in the +walls of the canal perform the mechanical work of digestion, while the +nervous system controls and regulates the activity of the various organs +concerned in this work.</p> + +<p>Exercises.—1. State the general purpose of digestion. How does +digested food differ from that not digested?</p> + +<p>2. Name all the divisions of the alimentary canal in the order in +which the food passes through them.</p> + +<p>3. What other work besides digestion is carried on by the alimentary +canal?</p> + +<p>4. What is gained by the mastication of the food? Why should +mastication precede the other processes of digestion?</p> + +<p>5. What is the work of the tongue in digestion?</p> + +<p>6. State the purposes served by the gastric juice.</p> + +<p>7. Give reasons for regarding the small intestine as the most +important division of the food canal.</p> + +<p>8. At what places, and by the action of what liquids, are fats, +proteids, and starch digested?</p> + +<p>9. What enzymes are found in the pancreatic juice? What is the +digestive action of each?</p> + +<p>10. Describe the work performed by the muscles of the stomach, the +mouth, the esophagus, and the small intestine.</p> + +<p>11. What advantages are derived from the use of cooked food?</p> + +<p>12. State the advantages of drinking pure water.</p> + +<p>13. If all the food that one needs to take at a single meal can be +thoroughly masticated in fifteen minutes, why is it better to spend a +longer time at the table?</p> + +<p>14. What is meant by the overlapping of meals? What bad results +follow? How avoided?</p> +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p>Examine a dissectible model of the human abdomen (Fig. 75), noting +the form, location, and connection of the different organs. Find the +connection of the esophagus with the stomach, of the stomach with the +small intestine, and of the small intestine with the large +intestine.<pb n="169" /><anchor id="Pg169" /> Sketch a general outline of the +cavity, and locate in this outline its chief organs.</p> + +<p>Where it is desirable to learn something of the actual structure of +the digestive organs, the dissection of the abdomen of some small animal +is necessary. On account of unpleasant features likely to be associated +with such a dissection, however, this work is not recommended for +immature pupils.</p> + +<p rend="text-align: center"> +<figure url="images/image75.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 75—Model for demonstrating the abdomen and its +contents.</head> +<figDesc>Fig. 75</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Dissection of the Abdomen.</hi> +(Optional)—For individual study, or for a small class, a half-grown cat +is perhaps the best available material. It should be killed with +chloroform, and then stretched, back downward, on a board, the feet +being secured to hold it in place.</p> + +<p>The teacher should make a preliminary examination of the abdomen to +see that it is in a fit condition for class study. If the bladder is +unnaturally distended, its contents may be forced out by slight +pressure. The following materials will be needed during the dissection, +and should be kept near at hand: a sharp knife with a good point, a pair +of heavy scissors, a vessel of water, some cotton or a damp sponge, and +some fine cord. During the dissection the specimen should be kept as +clean as possible, and any escaping blood should be mopped up with the +cotton or the sponge. The dissection is best carried out by observing +the following order:</p> + +<p>1. Cut through the abdominal wall in the center of the triangular +space where the ribs converge. From here cut a slit downward to the +lower portion of the abdomen, and sideward as far as convenient. Tack +the loosened abdominal walls to the board, and proceed to study the +exposed parts. Observe the muscles in the abdominal walls, and the fold +of the <hi rend="font-style: italic">peritoneum</hi> which forms an +apron-like covering over the intestines.</p> + +<p>2. Observe the position of the stomach, liver, spleen, and +intestines, and then, by pushing the intestines to one side, find the +kidneys and the bladder.</p> + +<p>3. Study the liver with reference to its location, size, shape, and +color. On the under side, find the gall bladder, from which a small tube +leads to the small intestine. Observe the portal vein as it passes into +<pb n="170" /><anchor id="Pg170" /> the liver. As the liver is filled +with blood, neither it nor its connecting blood vessels should be cut at +this time.</p> + +<p>4. Trace out the continuity of the canal. Find the esophagus where it +penetrates the diaphragm and joins the stomach. Find next the union of +the stomach with the small intestine. Then, by carefully following the +coils of the small intestine, discover its union with the large +intestine.</p> + +<p>5. Within the first coil of the small intestine, as it leaves the +stomach, find the <hi rend="font-style: italic">pancreas</hi>. Note its +color, size, and branches. Find its connection with the small +intestine.</p> + +<p>6. Beginning at the cut portion of the abdominal wall, lift the thin +lining of the peritoneum and carefully follow it toward the back and +central portion of the abdomen. Observe whether it extends back of or in +front of the kidneys, the aorta, and the inferior vena cava. Find where +it leaves the wall as a <hi rend="font-style: italic">double</hi> +membrane, the <hi rend="font-style: italic">mesentery</hi>, which +surrounds and holds in place the large and small intestines. Sketch a +coil of the intestine, showing the mesentery.</p> + +<p>7. Find in the center of the coils of small intestine a long, slender +body having the appearance of a gland. This is the beginning of the <hi +rend="font-style: italic">thoracic duct</hi> and is called the <hi +rend="font-style: italic">receptacle of the chyle</hi>. From this the +thoracic duct rapidly narrows until it forms a tiny tube difficult to +trace in a small animal.</p> + +<p>8. Cut away about two inches of the small intestine from the +remainder, having first tied the tube on the two sides of the section +removed. Split it open for a part of its length, and wash out its +contents. Observe its coats. Place it in a shallow vessel containing +water, and examine the mucous membrane with a lens to find the <hi +rend="font-style: italic">villi</hi>. Make a drawing of this section, +showing the coats.</p> + +<p>9. Study the connection of the small intestine with the large. Split +them open at the place of union, wash out the contents, and examine the +ileo-cæcal valve.</p> + +<p>10. Observe the size, shape, and position of the kidneys. Do they lie +in front of or back of the peritoneum? Do they lie exactly opposite each +other? Note the connection of each kidney with the aorta and the +inferior vena cava by the renal artery and the renal vein. Find a +slender tube, the <hi rend="font-style: italic">ureter</hi>, running +from each kidney to the bladder. Do the ureters connect with the top or +with the base of the bladder? Show by a sketch the connection of the +kidneys with the large blood vessels and the bladder.</p> + +<p><pb n="171" /><anchor id="Pg171" /><hi rend="font-weight: bold">To +demonstrate the Teeth.</hi>—Procure from the dentist a collection of +different kinds of teeth, both sound and decayed.</p> + +<p>(<hi rend="font-style: italic">a</hi>) Examine external surfaces of +different kinds of teeth, noting general shape, cutting or grinding +surfaces, etc. Make a drawing of an incisor and also of a molar.</p> + +<p>(<hi rend="font-style: italic">b</hi>) After soaking some of the +teeth for a couple of days in warm water saw one of them in two +lengthwise, and another in two crosswise, and smooth the cut surfaces +with fine emery or sand paper. Examine both kinds of sections, noting +arrangement and extent of dentine, enamel, and pulp. Make drawings.</p> + +<p>(<hi rend="font-style: italic">c</hi>) Examine a decayed tooth. Which +substance of the tooth appears to decay most readily? Why is it +necessary to cut away a part of the tooth before filling?</p> + +<p>(<hi rend="font-style: italic">d</hi>) Test the effect of acids upon +the teeth by leaving a tooth over night in a mixture of one part +hydrochloric acid to four parts water, and by leaving a second tooth for +a couple of days in strong vinegar. Examine the teeth exposed to the +action of acids, noting results.</p> + +<p><hi rend="font-weight: bold">To show the Importance of +Mastication.</hi>—Fill two tumblers each half full of water. Into one +put a lump of rock salt. Into the other place an equal amount of salt +that has been finely pulverized. Which dissolves first and why?</p> + +<p><hi rend="font-weight: bold">To illustrate Acid and Alkaline +Reactions.</hi>—To a tumbler half full of water add a teaspoonful of +hydrochloric or other acid, as vinegar. To a second tumbler half full of +water add an equal amount of cooking soda. Taste each liquid, noting the +sour taste of the acid, and the alkaline taste of the soda. Hold a piece +of red litmus paper in the soda solution, noting that it is turned blue. +Then hold a piece of blue litmus paper in the acid solution, noting that +it is turned red. Add acid to the soda solution, and soda to the acid +solution, until the conditions are reversed, testing with the red and +blue litmus papers.</p> + +<p>Hold, for a minute or longer, a narrow strip of red litmus paper in +the mouth, noting any change in the color of the paper. Repeat, using +blue litmus paper. What effect, if any, has the saliva upon the color of +the papers? Has the mouth an acid or an alkaline reaction?</p> + +<p><hi rend="font-weight: bold">To show the Action of Saliva on +Starch.</hi>—1 (Optional). Prepare starch paste by mixing half a +teaspoonful of starch in half a pint of water and heating the mixture to +boiling. Place some of this in a test tube and thin it by adding more +water. Then add a small drop of<pb n="172" /><anchor id="Pg172" /> iodine solution (page 136) to the +solution of starch. It should turn a deep blue color. This is the test +for starch.</p> + +<p>Now collect from the mouth, in a clean test tube, two or three +teaspoonfuls of saliva. Add portions of this to small amounts of fresh +starch solution in two test tubes. Let the tubes stand for five or ten +minutes surrounded by water having about the temperature of the body. +Test for changes that have occurred as follows:</p> + +<p>(<hi rend="font-style: italic">a</hi>) To one tube add a little of +the iodine solution. If it does not turn blue, it shows that the starch +has been converted into some other substance by the saliva, (<hi +rend="font-style: italic">b</hi>) To the other tube add a few drops of a +very dilute solution of copper sulphate. Then add sodium (or potassium) +hydroxide, a few drops at a time, until the precipitate which first +forms dissolves and turns a deep blue. Then gradually heat the upper +portion of the liquid to boiling. If it turns an orange or yellowish red +color, the presence of a form of sugar (maltose or dextrose) is proved. +See page 136.</p> + +<p>2. Hold some powdered starch in the mouth until it completely +dissolves and observe that it gradually acquires a sweetish taste. This +shows the change of starch into sugar.</p> + +<p><hi rend="font-weight: bold">To illustrate the Action of the Gastric +Juice.</hi>—Add to a tumbler two thirds full of water as much scale +pepsin (obtained from a drug store) as will stay on the end of the large +blade of a penknife. Then add enough hydrochloric acid to give a +slightly sour taste. Place in the artificial gastric juice thus prepared +some boiled white of egg which has been finely divided by pressing it +through a piece of wire gauze. Also drop in a single large lump. Keep in +a warm place (about the temperature of the body) for several hours or a +day, examining from time to time. What is the general effect of the +artificial gastric juice upon the egg?</p> + +<p><hi rend="font-weight: bold">To illustrate Effect of Alcohol upon +Gastric Digestion.</hi>—Prepare a tumbler half full of artificial +gastric juice as in the above experiment, and add 10 cubic centimeters +of this to each of six clean test tubes bearing labels. To five of the +tubes add alcohol from a burette as follows: (1) .5 c.c., (2) 1 c.c., +(3) 1.5 c.c., (4) 2 c.c., and (5) 3 c.c., leaving one tube without +alcohol. Now add to each tube about 1/4 gram of finely divided white of +egg from the experiment above, and place all of the tubes in a beaker +half full of water. Keep the water a little above the temperature of the +body for several hours, examining the tubes at intervals to note the +progress of digestion. Inferences.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="173" /><anchor id="Pg173" /> +<head>CHAPTER XI - ABSORPTION, STORAGE, AND ASSIMILATION</head> + +<p>The dissolved nutrients, to reach the cells, must be transferred from +the alimentary canal to the blood stream. This process is known as <hi +rend="font-style: italic">absorption</hi>. In general, absorption means +the penetration of a liquid into the pores of a solid, and takes place +according to the simple laws of molecular movements. The absorption of +food is, however, not a simple process, and the passage takes place +through an <hi rend="font-style: italic">active</hi> (living) membrane. +Another difference is that certain foods undergo chemical change while +being absorbed.</p> + +<p><hi rend="font-weight: bold">Small Intestine as an Organ of +Absorption.</hi>—While absorption may occur to a greater or less extent +along the entire length of the alimentary canal, most of it takes place +at the small intestine. Its great length, its small diameter, and its +numerous blood vessels all adapt the small intestine to the work of +absorption. The transverse folds in the mucous membrane, by retarding +the food in its passage and by increasing the absorbing surface, also +aid in the process. But of greatest importance are the minute elevations +that cover the surface of the mucous membrane, known as</p> + +<p><hi rend="font-weight: bold">The Villi.</hi>—Each single elevation, +or villus, has a length of about one fiftieth of an inch and a diameter +about half as great (<hi rend="font-style: italic">A</hi>, Fig. 76), and +contains the following essential parts:</p> + +<p>1. An outer layer of epithelial cells, resting upon a connective +tissue support.</p> + +<p><pb n="174" /><anchor id="Pg174" />2. A small lymph tube, called a +<hi rend="font-style: italic">lacteal</hi>, which occupies the center of +the villus and connects at the base with other lymph tubes, also called +lacteals (<hi rend="font-style: italic">B</hi>, Fig. <hi +rend="font-style: italic">76</hi>).</p> + +<p>3. A network of capillaries.</p> + +<p>The villi are structures especially adapted to the work of +absorption, and they are found only in the small intestine. +The mucous membrane in all parts of the canal, however, is capable of +taking up some of the digested materials.</p> + + +<p rend="text-align: center"> +<figure url="images/image76.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 76—<hi rend="font-weight: bold">The villi.</hi> +<hi rend="font-style: italic">A.</hi> Diagram of a small section of +mucous membrane of small intestine. 1. Villi. 2. Small glands, called +<hi rend="font-style: italic">crypts</hi>.<lb /><lb /> +<hi rend="font-style: italic">B.</hi> Diagram showing structure of +villi. 1. Small artery. 2. Lacteal. 3. Villus showing termination of the +lacteal. 4. Villus showing capillaries. 5. Villus showing both the +lacteal and the capillaries. 6. Small vein. 7. Layer of epithelial +cells.</head> +<figDesc>Fig. 76</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Work of Capillaries and Lacteals.</hi>—The +capillaries and lacteals act as receivers of material as it passes +through the layer of epithelial cells covering the mucous membrane. The +lacteals take up the digested fats,<note place="foot"><p>The lacteals (from the Latin <hi rend="font-style: +italic">lacteus</hi>, milky) are so called on account of their +appearance, which is white, or milk-like, due to the fat droplets.</p></note> and the capillaries receive all +the other kinds of nutrients. These vessels do not, of course, retain +the absorbed materials, but pass them on. Their final destination is the +general circulation, which they reach by two well-defined channels, or +routes.</p> + +<p><hi rend="font-weight: bold">Routes to the Circulation.</hi>—The two +routes from the<pb n="175" /><anchor id="Pg175" /> place of absorption to the +general circulation are as follows:</p> + +<p>1. <hi rend="font-style: italic">Route taken by the Fat.</hi>—The fat +is conveyed by the lacteals from the villi to the receptacle of the +chyle. At this place it mingles with the lymph from the lower parts of +the body, and with it passes through the thoracic duct to the left +subclavian vein. Here it enters the general circulation. Thus, to reach +the general circulation, the fat has to pass through the villi, the +lacteals, the receptacle of the chyle, and the thoracic duct (Fig. 77). +Its passage through these places, like the movements in all lymph +vessels, is slow, and it is only gradually admitted to the blood +stream.</p> + +<p rend="text-align: center"> +<figure url="images/image77.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 77—<hi rend="font-weight: bold">Diagram of +routes</hi> from food canal to general circulation. See text.</head> +<figDesc>Fig. 77</figDesc> +</figure></p> + +<p>2. <hi rend="font-style: italic">Route of All the Nutrients except +Fat.</hi>—Water and salts and the digested proteids and carbohydrates, +in passing into the capillaries, mix there with the blood. But this +blood, instead of flowing directly to the heart, is passed through the +portal vein to the liver, where it enters a <hi rend="font-style: +italic">second set of capillaries</hi> and is brought very near the +liver cells. From the liver it is passed through the hepatic veins into +the inferior vena cava, and<pb n="176" /><anchor id="Pg176" /> by these it is emptied into the +right auricle. This route then includes the capillaries in the mucous +membrane of the stomach and intestines, the branches of the portal vein, +the portal vein proper, the liver, and the hepatic veins (Fig. 77). In +passing through the liver, a large portion of the food material is +temporarily retained for a purpose and in a manner to be described later +(page 177).</p> + +<p><hi rend="font-weight: bold">Absorption Changes.</hi>—During +digestion the insoluble foods are converted into certain soluble +materials, such as peptones, maltose, and glycerine,—the conversion +being necessary to their solution. A natural supposition is that these +materials enter and become a part of the blood, but examination shows +them to be absent from this liquid. (See Composition of the Blood, page +30.) There are present in the blood, however, substances closely related +to the peptones, maltose, glycerine, etc.; substances which have in fact +been formed from them. During their transfer from the food canal, the +dissolved nutrients undergo changes, giving rise to the materials in the +blood. Thus are the serum albumin and serum globulin of the blood +derived from the peptones and proteoses; the dextrose, from the maltose +and other forms of sugar; and the fat droplets, from the glycerine, +fatty acid, and soluble soap.</p> + +<p>While considerable doubt exists as to the cause of these changes and +as to the places also where some of them occur, their purpose is quite +apparent. The materials forming the dissolved foods, although adapted to +absorption, are not suited to the needs of the body, and if introduced +in this form are likely to interfere with its work.<note place="foot"><p>Peptones and proteoses, when injected directly into the +blood, are found to act as poisons.</p></note> They are changed, +therefore, into the forms which the body can use.</p> + +<p><pb n="177" /><anchor id="Pg177" /><hi rend="font-weight: bold">A +Second Purpose of Digestion.</hi>—Comparing the digestive changes with +those of absorption, it is found that they are of a directly opposite +nature; that while digestion is a process of tearing down, or +separating,—one which reduces the food to a more finely divided +condition—there is in absorption a process of building up. From the +comparatively simple compounds formed by digestion, there are formed +during absorption the more complex compounds of the blood. The one +exception is dextrose, which is a simple sugar; but even this is +combined in the liver and the muscles to form the more complex compound +known as glycogen. (See Methods of Storage, below.) These facts have +suggested a second purpose of digestion—that of reducing foods to forms +sufficiently simple to enable the body to construct out of them the more +complex materials that it needs. Evidence that digestion serves such a +purpose is found in the fact that both proteids and carbohydrates are +reduced to a simpler form than is necessary for dissolving them.<note place="foot"><p>The soluble double sugars (maltose, milk sugar, and cane +sugar) are reduced to the simple sugars (dextrose and levulose). +Furthermore the action on the proteids does not stop with the production +of peptones and proteoses, but these in turn are still further +reduced.</p></note></p> + +<p><hi rend="font-weight: bold">The Storage of Nutriment.</hi>—For some +time after the taking of a meal, food materials are being absorbed more +rapidly than they can be used by the cells. Following this is an +interval when the body is taking no food, but during which the cells +must be supplied with nourishment. It also happens that the total amount +of food absorbed during a long interval may be in excess of the needs of +the cells during that time; and it is always possible, as in disease, +that the quantity absorbed is not equal to that consumed. To provide +against emergencies, and to keep up a uniform supply of food to the +cells, it is necessary that the body store up nutrients in excess of its +needs.</p> + +<p><hi rend="font-weight: bold">Methods of Storage.</hi>—The general +plan of storage varies with the different nutrients as follows:</p> + +<p>1. <hi rend="font-style: italic">The carbohydrates</hi> are stored in +the form of <hi rend="font-style: italic">glycogen</hi>. This, as +already stated (page 120), is a substance closely resembling starch. It +is stored in the cells of both the<pb n="178" /><anchor id="Pg178" /> liver and the muscles, but mainly +in the liver (Fig. 78). It is a chief function of the liver to collect +the excess of dextrose from the blood passing through it, and to convert +it into glycogen, which it then stores within its cells. It does not, +however, separate all of the dextrose from the blood, a small amount +being left for supplying the immediate needs of the tissues. As this is +used, the glycogen in the liver is changed back to dextrose and, +dissolving, again finds its way into the blood. In this way, the amount +of dextrose in the blood is kept practically constant. The carbohydrates +are stored also by converting them into fat.</p> + +<p rend="text-align: center"> +<figure url="images/image78.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 78—<hi rend="font-weight: bold">Liver cells</hi> +where is stored the glycogen. <hi rend="font-style: italic">C.</hi> +Capillaries.</head> +<figDesc>Fig. 78</figDesc> +</figure></p> + +<p rend="text-align: center"> +<figure url="images/image79.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 79—<hi rend="font-weight: bold">Stored-up +fat.</hi> The figure shows four connective tissue cells containing small +particles of fat. 1. Nucleus. 2. Protoplasm. 3. Fat. 4. Connective +tissue fibers.</head> +<figDesc>Fig. 79</figDesc> +</figure></p> + +<p>2. <hi rend="font-style: italic">The fat</hi> is stored for the most +part in the connective tissue. Certain of the connective tissue cells +have the property of taking fat from the blood and of depositing it +within their inclosing membranes (Fig. 79). When this is done to excess, +and the cells become filled with fat, they form the so-called <hi +rend="font-style: italic">adipose tissue</hi>. Most of this tissue is +found under the skin, between the muscles, and among the organs +occupying the abdominal cavity. If one readily takes on fat, it may also +collect in the<pb n="179" /><anchor id="Pg179" /> connective tissue +around the heart. The stored-up fat is redissolved as needed, and enters +the blood, where it again becomes available to the active cells.</p> + +<p>3. <hi rend="font-style: italic">The proteids</hi> form a part of all +the tissues, and for this reason are stored in larger quantities than +any of the other food substances. The large amount of proteid found in +the blood may also be looked upon as storage material. The proteids in +the various tissues are spoken of as <hi rend="font-style: +italic">tissue proteids</hi>, and those in the blood as <hi +rend="font-style: italic">circulating proteids</hi>. The proteids of the +tissues serve the double purpose of forming a working part of the cell +protoplasm, and of supplying reserve food material. That they are +available for supplying energy, and are properly regarded as <hi +rend="font-style: italic">storage material</hi>, is shown by the rapid +loss of proteid in starving animals. When the proteids are eaten in +excess of the body's need for rebuilding the tissues, they are supposed +to be broken up in such a manner as to form glycogen and fat, which may +then be stored in ways already described.</p> + +<p><hi rend="font-weight: bold">General Facts Relating to +Storage.</hi>—The form into which the food is converted for storage in +the body is that of <hi rend="font-style: italic">solids</hi>—the form +that takes up the least amount of space. These solids are of such a +nature that they can be changed back into their former condition and, by +dissolving, reënter the blood.</p> + +<p>Only energy-yielding foods are stored. Water and salts, though they +may be absorbed in excess of the needs of the body, are not converted +into other substances and stored away. Oxygen, as already stated (page +108), is not stored. The interval of storage may be long or short, +depending upon the needs of the body. In the consumption of stored +material the glycogen is used first, then as a rule the fat, and last of +all the proteids.</p> + +<p><hi rend="font-weight: bold">Storage in the Food Canal.</hi>—Not +until three or four hours have elapsed are all the nutrients, eaten at a +single meal, digested and passed into the body proper. The undigested +food is held in reserve, awaiting digestion, and <pb n="180" /><anchor +id="Pg180" />is only gradually absorbed as this process takes place. It +may properly, on this account, be regarded as <hi rend="font-style: +italic">stored material</hi>. That such storage is of advantage is shown +by the observed fact that substances which digest quickly (sugar, +dextrin, "predigested foods," etc.) do not supply the needs of the body +so well as do substances which, like starch and proteids, digest slowly. +Even substances digesting quite slowly (greasy foods and pastry), since +they can be stored longer in the food canal, may be of real advantage +where, from hard work or exposure, the body requires a large supply of +energy for some time. These "stay by" the laborer, giving him strength +after the more easily digested foods have been used up. Storage by the +food canal is limited chiefly to the stomach.</p> + +<p><hi rend="font-weight: bold">Regulation of the Food Supply to the +Cells.</hi>—The storage of food materials is made to serve a second +purpose in the plan of the body which is even more important than that +of supplying nourishment to the cells during the intervals when no food +is being taken. It is largely the means whereby the rate of supply of +materials to the cells is regulated. The cells obtain their materials +from the lymph, and the lymph is supplied from the blood. Should food +substances, such as sugar, increase in the blood beyond a low per cent, +they are converted into a form, like glycogen, in which they are held in +reserve, or, for the time being, placed beyond the reach of the cells. +When, however, the supply is reduced, the stored-up materials reënter +the blood and again become available to the cells. By this means their +rate of supply to the cells is practically constant.</p> + +<p>We are now in a position to understand why carbohydrates, fats, and +proteids are so well adapted to the needs of the body, while other +substances, like alcohol, which<pb n="181" /><anchor id="Pg181" /> may also liberate energy, prove +injurious. It is because foods are of such a chemical nature that they +are adapted in all respects to the body plan of taking up and using +materials, while the other substances are lacking in some +particular.</p> + +<p rend="text-align: center"> +<figure url="images/image80.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 80—<hi rend="font-weight: bold">Diagrams +illustrating the relation of nutrients</hi> and the non-relation of +these to alcohol. <hi rend="font-style: italic">A.</hi> Inter-relation +and convertibility of proteids, fats, and carbohydrates (after +Hall).<lb /><lb /> +<hi rend="font-style: italic">B.</hi> Diagram showing disposition of +alcohol if this substance is taken in quantity corresponding to that of +the nutrients (F.M.W.). The alcohol thrown off as waste is unoxidized +and yields no energy.</head> +<figDesc>Fig. 80</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Why Alcohol is not a Food.</hi>—If the +passage of alcohol through the body is followed, it is seen, in the +first place, that it is a simple liquid and undergoes no digestive +change; and in the second place, that it is rapidly absorbed from the +stomach in both weak and concentrated solutions. This introduces it +quickly into the blood, and once there, it diffuses rapidly into the +lymph and then into the cells. Since the body cannot store alcohol or +convert it into some nutrient that can be stored (Fig. 80), <hi +rend="font-style: italic">there is no way of</hi><pb n="182" /><anchor id="Pg182" /> <hi rend="font-style: +italic">regulating the amount that shall be present in the blood, or of +supplying it to the cells as their needs require</hi>. They must take it +in excess of their needs, regardless of the effect, at least until the +organs of excretion can throw off the surplus as waste. Compared with +proteid, carbohydrates, or fats, alcohol is an <hi rend="font-style: +italic">unmanageable</hi> substance in the body. Attempting to use it as +a food is as foolish as trying to burn gasolene or kerosene in an +ordinary wood stove. It may be done to a limited extent, but is an +exceedingly hazardous experiment. Not being adapted to the body method +of using materials, alcohol cannot be classed as a food.</p> + +<p><hi rend="font-weight: bold">Assimilation.</hi>—Digestion, +absorption, circulation, and storage of foods are the processes that +finally make them available to the cells in the different parts of the +body. There still remains another process for these materials to undergo +before they serve their final purposes. This last process, known as <hi +rend="font-style: italic">assimilation</hi>, is the appropriation of the +food material by the cell protoplasm. In a sense the storage of fat by +connective tissue cells and of glycogen by the liver cells is +assimilation. The term is limited, however, to the disposition of +material with reference to its final use. Whether all the materials used +by the cells actually become a part of the protoplasm is not known. It +is known, however, that the cells are the places where most of the +oxidations of the body occur and that materials taking part in these +oxidations must, at least, come in close contact with the protoplasm. +Assimilation, then, is the last event in a series of processes by which +oxygen, food materials, and cell protoplasm are brought into close and +<hi rend="font-style: italic">active</hi> relations. The steps leading +up to assimilation are shown in Table II.</p> + +<pb n="183" /><anchor id="Pg183" /> + +<table rend="latexcolumns: 'p{1.25cm}|p{1.25cm}|p{1.25cm}|p{1.25cm}|p{1.25cm}|p{1.25cm}'"> +<head>TABLE II. THE PASSAGE OF MATERIALS TO THE CELLS</head> + +<row> +<cell rend="font-size: 50%">MATERIALS</cell> +<cell rend="font-size: 50%">DIGESTION</cell> +<cell rend="font-size: 50%">ABSORPTION</cell> +<cell rend="font-size: 50%">ROUTE TO THE GENERAL CIRCULATION</cell> +<cell rend="font-size: 50%">STORAGE</cell> +<cell rend="font-size: 50%">CONDITION IN THE BLOOD</cell> +</row> + +<row> +<cell rend="font-size: 50%">Proteids</cell> +<cell rend="font-size: 50%">Changed into proteoses and peptones by the action of the gastric and pancreatic juices.</cell> +<cell rend="font-size: 50%">In passing into the capillaries, the proteoses and peptones change into the proteids of the blood.</cell> +<cell rend="font-size: 50%">Through the portal vein to the liver and from there through the hepatic veins into the inferior vena cava.</cell> +<cell rend="font-size: 50%">Become a part of the protoplasm of all the cells.</cell> +<cell rend="font-size: 50%">As proteids in colloidal solution.</cell> +</row> + +<row> +<cell rend="font-size: 50%">Fat</cell> +<cell rend="font-size: 50%">Changed into fatty acid, glycerine, and soluable soap by the bile and pancreatic juice.</cell> +<cell rend="font-size: 50%">In passing into the lacteals, the glycerine unites with the soluable soap and fatty acid to form the oil droplets of the blood.</cell> +<cell rend="font-size: 50%">Through the lacteals to the thoracic duct, by which it is emptied into the left subclavian vein.</cell> +<cell rend="font-size: 50%">As fat in the cells of collective tissue.</cell> +<cell rend="font-size: 50%">Chiefly as minute oil droplets.</cell> +</row> + +<row> +<cell rend="font-size: 50%">Starch</cell> +<cell rend="font-size: 50%">Reduced to some of the different forms of sugar, as maltose, dextrose, etc.</cell> +<cell rend="font-size: 50%">Enters the capillaries as dextrose.</cell> +<cell rend="font-size: 50%">Through the portal vein, liver, hepatic veins, into inferior vena cava.</cell> +<cell rend="font-size: 50%">As glycogen chiefly by the liver, but to some extent by muscle cells.</cell> +<cell rend="font-size: 50%">As dextrose in solution.</cell> +</row> + +<row> +<cell rend="font-size: 50%">Water</cell> +<cell rend="font-size: 50%">Undergoes no change.</cell> +<cell rend="font-size: 50%">Taken up by both the lacteals and capillaries, but to the greater extent by the capilaries.</cell> +<cell rend="font-size: 50%">Both routes, but mostly by way of the liver.</cell> +<cell rend="font-size: 50%">Is not stored in the sense that energy foods are.</cell> +<cell rend="font-size: 50%">As the water which serves as a carrier of all the other constituents of the blood.</cell> +</row> + +<row> +<cell rend="font-size: 50%">Common salt</cell> +<cell rend="font-size: 50%">Undergoes no change.</cell> +<cell rend="font-size: 50%">Taken up by the capillaries without undergoing apparent change.</cell> +<cell rend="font-size: 50%">By way of portal vein, liver, and hepatic veins into inferior vena cava.</cell> +<cell rend="font-size: 50%">Not stored.</cell> +<cell rend="font-size: 50%">In solution.</cell> +</row> + +<row> +<cell rend="font-size: 50%">Oxygen</cell> +<cell rend="font-size: 50%"></cell> +<cell rend="font-size: 50%">Taken up by the capillaries at the lungs.</cell> +<cell rend="font-size: 50%">Already in the general circulation.</cell> +<cell rend="font-size: 50%">Is not stored.</cell> +<cell rend="font-size: 50%">United with the hemoglobin and to a small extent in solution in the plasma.</cell> +</row> +</table> + + +<p><pb n="184" /><anchor id="Pg184" /><hi rend="font-weight: bold">Tissue Enzymes.</hi>—The important part +played by enzymes in the digestion of the food has suggested other uses +for them in the body. It has been recently shown that many of the +chemical changes in the tissues are in all probability due to the +presence of enzymes. An illustration of what a tissue enzyme may do is +seen in the changes which fat undergoes. In order for the body to use up +its reserve fat, it must be transferred from the connective tissue +cells, where it is stored, to the cells of the active tissues where it +is to be used. This requires that it be reduced to the form of a +solution and that it reënter the blood. In other words, it must be <hi +rend="font-style: italic">redigested</hi>. For bringing about these +changes a substance identical in function with the steapsin of the +pancreatic juice has been shown to exist in several of the tissues.</p> + +<p>Although this subject is still under investigation, it may be stated +with certainty that there are present in the tissues, enzymes that +change dextrose to glycogen and <hi rend="font-style: italic">vice +versa</hi>, that break down and build up the proteids, and that aid in +the oxidations at the cells. The necessity for such enzymes is quite +apparent.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The digested nutrients are +taken up by the capillaries and the lymph vessels and transferred by two +routes to the circulation. In passing from the alimentary canal into the +circulation the more important of the foods undergo changes which adapt +them to the needs of the body. Since materials are absorbed more rapidly +than they are used, means are provided for storing them and for +supplying them to the cells as their needs require. <hi +rend="font-style: italic">Capability of storage is an essential quality +of energy-yielding foods</hi>; and substances, such as alcohol, which +lack this quality are not adapted to the needs of the body. For causing +the chemical changes that occur in the storage of foods, as well as the +oxidations at the cells, the presence of active agents, or enzymes, is +necessary.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. In what respects does +the absorption of food materials from the alimentary canal differ from +the absorption of a simple liquid by a solid?</p> + +<p><pb n="185" /><anchor id="Pg185" />2. In what different ways is the small intestine especially adapted +to the work of absorption?</p> + +<p>3. What are the parts of a villus? What are the lacteals? Account for +the name.</p> + +<p>4. What part is played by the capillaries and the lacteals in the +work of absorption? How does their work differ?</p> + +<p>5. What changes, if any, take place in water, common salt, fat, +proteids, and carbohydrates during absorption?</p> + +<p>6. What double purpose is served by the processes of digestion?</p> + +<p>7. Trace the passage of proteids, fats, and carbohydrates from the +small intestine into the general circulation.</p> + +<p>8. What is the necessity for storing nutrients in the body? Why is it +not also necessary to store up oxygen?</p> + +<p>9. In what form and at what places is each of the principal nutrients +stored?</p> + +<p>10. How is the rate of supply of food to the cells regulated? Why is +the body unable to regulate the supply of alcohol to the cells when this +substance is taken?</p> + +<p>11. Explain Fig. 80, page 181. What becomes of the alcohol if this is +taken in any but very small quantities?</p> + +<p>12. State the general purpose of enzymes in the body. Name the +enzymes found in each of the digestive fluids. What ones are found in +the tissues?</p> + +<div> +<head>PRACTICAL WORK</head> + +<p>Illustrate the ordinary meaning of the term "absorption" by bringing +the end of a piece of crayon in contact with water, or a piece of +blotting paper in contact with ink, noting the passage of the liquid +into the crayon or the paper. Show how absorption from the food canal +differs from this kind of absorption.</p> + +<p>Show by a diagram similar to Fig. 77 the two routes by which the +foods pass from the alimentary canal into the blood stream.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="186" /><anchor id="Pg186" /> +<head>CHAPTER XII - ENERGY SUPPLY OF THE BODY</head> + +<p>If one stops taking food, it becomes difficult after a time for him +to move about and to keep warm. These results show that food has some +relation to the energy of the body, for motion and heat are forms of +energy. The relation of oxygen to the supply of energy has already been +discussed (Chapter VIII). We are now to inquire more fully into the +energy supply of the body, and to consider those conditions which make +necessary the introduction of both food and oxygen for this purpose.</p> + +<p><hi rend="font-weight: bold">Kinds of Bodily Energy.</hi>—The healthy +body has at any time a considerable amount of <hi rend="font-style: +italic">potential</hi>, or reserve, energy,—energy which it is not using +at the time, but which it is able to use as its needs require. When put +to use, this energy is converted into such forms of <hi +rend="font-style: italic">kinetic</hi> energy<note place="foot"><p>Energy, which is defined as <hi rend="font-style: +italic">the ability to do work</hi>, or <hi rend="font-style: italic">to +cause motion</hi>, exists in two general types, or forms, known as +kinetic energy and as potential energy. <hi rend="font-style: +italic">Kinetic</hi> energy is energy at work, or energy in the act of +producing motion; while <hi rend="font-style: italic">potential</hi> +energy is reserve, or stored, energy. All moving bodies have kinetic +energy, and all stationary bodies which have within them the <hi +rend="font-style: italic">capability</hi> of causing motion possess +potential energy. A bent bow, a piece of stretched rubber, a suspended +weight, the water above a mill dam, all have the capability of causing +motion and all have potential energy. Examples of kinetic energy are +found in the movements of machinery, in steam and electricity, in winds, +and in currents of water. Kinetic is the active, and potential the +inactive, form of energy.</p></note> as are indicated by the +different kinds of bodily power. These are as follows:</p> + +<p>1. <hi rend="font-style: italic">Power of Motion.</hi>—The body can +move itself from place to place and it can give motion to things about +it.</p> + +<p><pb n="187" /><anchor id="Pg187" />2. <hi rend="font-style: italic">Heat Power.</hi>—The body keeps +itself warm and is able to communicate warmth to its surroundings.</p> + +<p>3. <hi rend="font-style: italic">Nervous Power.</hi>—Through the +nervous system the body exercises the power of control over its +different parts.</p> + +<p>As motion, heat, and nervous power the body uses most of its +energy.</p> + +<p><hi rend="font-weight: bold">The Source of Bodily Energy.</hi>—As +already indicated, the energy of the body is supplied through the food +and the oxygen. These contain energy in the potential form, which +becomes kinetic (active) through their uniting with each other in the +body. Somewhat as the power of the steam engine is derived from the +combustion of fuel in the furnaces, the energy of the body is supplied +through the oxidations at the cells. How the food and oxygen come to +possess energy is seen by a study of the general methods by which energy +is stored up and used.</p> + +<p rend="text-align: center"> +<figure url="images/image81.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 81—<hi rend="font-weight: bold">Simple +device</hi> for storing energy through gravity.</head> +<figDesc>Fig. 81</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Simple Methods of Storing +Energy.</hi>—Energy is stored by converting the kinetic into the +potential form. Two of the simplest ways of doing this are the +following:</p> + +<p>1. <hi rend="font-style: italic">Storing of Energy through +Gravity.</hi>—On account of the attraction between the earth and all +bodies upon the earth, the mere lifting of a weight puts it in a +position where gravity can cause it to move (Fig. 81). As a consequence +<hi rend="font-style: italic">the raising of bodies above the earth's +surface is a means of storing energy</hi>—the energy remaining stored +until the<pb n="188" /><anchor id="Pg188" /> bodies fall. As they fall, the +stored-up (potential) energy becomes kinetic and can be made to do +work.</p> + +<p>2. <hi rend="font-style: italic">Storing of Energy through +Elasticity.</hi>—Energy is stored also by doing work in opposition to +elasticity, as in bending a bow or in winding a clock spring. The +bending, twisting, stretching, or compressing of elastic substances puts +them in a condition of <hi rend="font-style: italic">strain</hi> which +causes them to exert a pressure (called elastic force) that tends to +restore them to their former condition. Energy stored by this means +becomes active as the distorted or compressed substance returns to its +former shape or volume.</p> + +<p>These simple methods of storing energy will serve to illustrate the +general principles upon which such storage depends:</p> + +<p>1. To store energy, energy must be expended, or work done.</p> + +<p>2. The work must be against some force, such as gravity or +elasticity, which can undo the work, i.e., bring about an effect +opposite to that of the work.</p> + +<p>3. The stored energy becomes active (kinetic) as the force through +which the energy was stored undoes the work, or puts the substance upon +which the work was done into its former condition (gravity causing +bodies to fall, etc.).</p> + +<p>These principles are further illustrated by the</p> + +<p><hi rend="font-weight: bold">Storing of Energy through Chemical +Means.</hi>—A good example of storing energy by chemical means is that +of decomposing water with electricity. If a current of electricity is +passed through acidulated water in a suitable apparatus (Fig. 82), the +water separates into its component gases, oxygen and hydrogen. These +gases now have power (energy) which they did not possess before they +were separated. The hydrogen will burn in the oxygen,<pb n="189" /><anchor id="Pg189" /> giving heat; and if the two gases +are mixed in the right proportions and then ignited, they explode with +violence. This energy was derived from the electricity. It was stored by +<hi rend="font-style: italic">decomposing</hi> the water.</p> + +<p rend="text-align: center"> +<figure url="images/image82.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 82—<hi rend="font-weight: bold">Storing energy +by chemical means.</hi> Apparatus for decomposing water with +electricity.</head> +<figDesc>Fig. 82</figDesc> +</figure></p> + +<p>Energy is stored by chemical means by causing it to do work in +opposition to the force of chemism, or chemical affinity. Instead of +changing the form of bodies or moving them against gravity, it overcomes +the force that causes atoms to unite and to hold together after they +have united. Since in most cases the atoms on separating from any given +combination unite at once to form other combinations, we may say that +<hi rend="font-style: italic">energy is stored when strong chemical +combinations are broken up and weak ones formed</hi>. Energy stored by +this means becomes active when the atoms of weak combinations unite to +form combinations that are strong.<note place="foot"><p>As the atoms of hydrogen and oxygen that make up the +molecules of water separate, they unite with atoms of their own kind—the +hydrogen with hydrogen and the oxygen with oxygen atoms. Since these +combinations are weaker than those of the water molecules, energy is +required to bring about the change. But when hydrogen burns in the +oxygen, the change is from a weaker to a stronger combination. The +stored-up energy is then given up or becomes active.</p></note></p> + +<p><hi rend="font-weight: bold">How Plants store the Sun's +Energy.</hi>—The earth's supply of energy comes from the sun. While much +of this, after warming and lighting the earth's surface, is lost by +radiation, a portion of it is stored up and retained. The sun's energy +is stored both through the force of gravity<note place="foot"><p>In the evaporation of water, the energy of the sun is +stored with reference to the force of gravity. In evaporating, water +rises as a gas, or vapor, above the earth's surface, but on condensing into a liquid, it falls as +rain. It then finds its way through streams back to the ocean. All water +above the sea level is in such a position that gravity can act on it to +cause motion, and it possesses, on this account, potential or stored-up +energy. It is because of this energy that rapids and waterfalls are such +important sources of power.</p></note><pb n="190" /><anchor id="Pg190" /> and by chemical means, the latter +being the more important of the two methods. Plants supply the means for +storing it chemically (Fig. 83). Attention has already been called to +the fact (page 112) that growing plants are continually taking carbon +dioxide into their leaves from the air. This they decompose, adding the +carbon to compounds in their tissues and returning the oxygen to the +air. It is found, however, that this process does not occur unless the +plants are exposed to sunlight. The sunlight supplies the energy for +overcoming the attraction between the atoms of oxygen and the atoms of +carbon, while the plant itself serves as the instrument through which +the sunlight acts. The energy for decomposing the carbon dioxide then +comes from the sun, and through the decomposition of the carbon dioxide +the sun's energy is stored—becomes potential. It remains stored until +the carbon of the plant again unites with the oxygen of the air, as in +combustion.</p> + +<p rend="text-align: center"> +<figure url="images/image83.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 83—<hi rend="font-weight: bold">Nature's +device</hi> for storing energy from the sun. See text.</head> +<figDesc>Fig. 83</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Sun's Energy in Food and +Oxygen.</hi>—Food is derived directly or indirectly from plants and +sustains the same relation to the oxygen of the air as do the plants +themselves. (The elements in the food have an attraction for<pb n="191" /><anchor id="Pg191" /> the oxygen, but are separated +chemically from it.) On account of this relation they have potential +energy—the energy derived through the plant from the sun. When a person +eats the food and breathes the oxygen, this energy becomes the +possession of the body. It is then converted into kinetic energy as the +needs of the body require.</p> + +<p rend="text-align: center"> +<figure url="images/image84.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 84—<hi rend="font-weight: bold">Simple +apparatus</hi> for illustrating transformation of energy. Potential +energy is converted into heat and heat into motion.</head> +<figDesc>Fig. 84</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">From the Sun to the Cells.</hi>—It thus +appears that the body comes into possession of energy, and is able to +use it, through a series of transferences and transformations that can +be traced back to the sun.<note place="foot"><p>Energy, like matter, can neither be created nor +destroyed. It can, however, be transferred from one body to another and +transformed from one form to another form. Whenever work is done, energy +is transferred from the body doing the work, to the body upon which the +work is done. During this process there may, or may not, be a +transformation of energy. In turning a grindstone, kinetic energy is +passed to the stone and used without transformation, but in winding a +clock, the kinetic energy from the hand is transformed into potential +energy in the clock spring. Then as the clock runs down this is +retransformed into kinetic energy, causing the movements of the +wheels.</p> + +<p>Not only is kinetic transformed into potential energy and <hi +rend="font-style: italic">vice versa</hi>, but the different forms of +kinetic energy (heat, light, electricity, sound, and mechanical motion) +are readily transformed the one into the other. With suitable devices, +mechanical motion can be changed into heat, sound, or electricity; heat +into motion and light; and electricity into all the other forms of +energy. These transformations are readily explained by the fact that the +different varieties of kinetic energy are but different forms of motion +(Fig. 84).</p></note> Coming to the earth as kinetic energy, it +is transformed into potential energy and stored in the compounds of +plants and in the oxygen of the air. Through the food and the oxygen the +potential energy is transferred to the cells of the body. Then by the +uniting of the food and the oxygen at the cells (oxidation), the +potential becomes kinetic energy and is<pb n="192" /><anchor id="Pg192" /> used by the body in doing its +work. The phrase "Child of the Sun" has sometimes been applied to man to +express his dependence upon the sun for his supply of energy.</p> + +<p><hi rend="font-weight: bold">Why Oxygen and Food are Both +Necessary.</hi>—The necessity for introducing both oxygen and food into +the body for the purpose of supplying energy is now apparent. The energy +which is used in the body is not the energy of food alone. Nor is it the +energy of oxygen alone. It belongs to both. It is due to their +attraction for each other and their condition of separation. It cannot, +therefore, become kinetic except through their union. To introduce one +of these substances into the body without the other, would neither +introduce the energy nor set it free. They must both be introduced into +the body and there caused to unite.</p> + +<p><hi rend="font-weight: bold">Bodily Control of Energy.</hi>—A fact of +importance in the supply of energy to the body is that the rate of +transformation (changing of potential to kinetic) is just sufficient for +its needs. It is easily seen that too rapid or too slow a rate would +prove injurious. The oxidations at the cells are, therefore, under such +control that the quantity of kinetic energy supplied to the body as a +whole, and to the different organs, is proportional to the work that is +done. This is attained, in part at least, through the ability of the +body to store up the food materials and hold them in reserve until they +are to be oxidized (page 180).</p> + +<p><hi rend="font-weight: bold">Animal Heat and Motion.</hi>—Most of the +body's energy is expended as heat in keeping warm. It is estimated that +as much as five sixths of the whole amount is used in this way. The +proportion, however, varies with different persons and is not constant +in the same individual during different seasons of the year. This heat +is used in keeping the body at that temperature which is best suited to +<pb n="193" /><anchor id="Pg193" />carrying on the vital processes. All +parts of the body, through oxidation, furnish heat. Active organs, +however, such as the muscles, the brain, and the glands (especially the +liver), furnish the larger share. The blood in its circulation serves as +a <hi rend="font-style: italic">heat distributer</hi> for the body and +keeps the temperature about the same in all its parts (page 33).</p> + +<p>Next to the production of heat, in the consumption of the body's +energy, is the production of motion. This topic will be considered in +the study of the muscular system (Chapter XV).</p> + +<p><hi rend="font-weight: bold">Some Questions of Hygiene.</hi>—The +heat-producing capacity of the body sustains a very important relation +to the general health. A sudden chill may result in a number of +derangements and is supposed to be a predisposing cause of <hi +rend="font-style: italic">colds</hi>. One's capacity for producing heat +may be so low that he is unable to respond to a sudden demand for heat, +as in going from a warm room into a cold one. As a consequence, the body +is unable to protect itself against unavoidable exposures.</p> + +<p><hi rend="font-style: italic">Impairment of the heat-producing +capacity</hi> is brought about in many ways. Several diseases do this +directly, or indirectly, to quite an extent. In health too great care in +protecting the body from cold is the most potent cause of its +impairment. Staying in rooms heated above a temperature of 70° F., +wearing clothing unnecessarily heavy, and sleeping under an excess of +bed clothes, all diminish the power of the body to produce heat. They +accustom it to producing only a small amount, so that it does not +receive sufficient of what might be called <hi rend="font-style: +italic">heat-producing exercise</hi>. Lack of physical exercise in the +open air, as well as too much time spent in poorly lighted and +ventilated rooms, tends also to reduce one's ability to produce heat. +Moreover, since most of the heat of the body comes<pb n="194" /><anchor id="Pg194" /> from the union of oxygen and food +materials at the cells, a lack of either of these will interfere with +the production of heat.</p> + +<p><hi rend="font-weight: bold">Results of Exhaustion.</hi>—Through +overwork, or excesses in pleasurable pursuits, one may make greater +demands upon the energy of his body than it can properly supply. The +resulting condition, known as <hi rend="font-style: +italic">exhaustion</hi>, is not only a matter of temporary +inconvenience, but may through repetition lead to a serious impairment +of the health. It should be noted, in this connection, that the energy +of the body is spent in two general ways: first, in carrying on the +vital processes; and second, in the performance of voluntary activities. +Since, in all cases, there is a limit to one's energy, it is easily +possible to expend so much in the voluntary activities that the amount +left is not sufficient for the vital processes. This leads to various +disturbances and, among other things, renders the body less able to +supply itself with energy.</p> + +<p><hi rend="font-weight: bold">The Problem of Increasing One's +Energy.</hi>—Since the energy supply is kept up through the food and the +oxygen, it might be inferred that the introduction of these substances +into the body in larger amounts would increase the energy at one's +disposal. This does not necessarily follow. Oxidation at the cells is +preceded by digestion, absorption, circulation, and assimilation. It is +followed and influenced by the removal of wastes from the body. A +careful study of the problem leads to the conclusion that while the +energy supply to the body does depend upon the introduction of the +proper amounts of food and oxygen, it also depends upon the efficiency +of the vital processes. The maximum amount of energy may, therefore, be +expected when the body is in a condition of perfect health. Hence, one +desiring to increase the amount of his energy must<pb n="195" /><anchor id="Pg195" /> give attention to all those +conditions that improve the health.</p> + +<p><hi rend="font-weight: bold">Effect of Stimulants on the Energy +Supply.</hi>—In the effort to get out of the body as much as possible of +work or of pleasure, various stimulants, such as alcohol, tobacco, and +strong tea and coffee, have been used. Though these have the effect of +giving a temporary feeling of strength and of enabling the individual in +some instances to accomplish results which he could not otherwise have +brought about, the general effect of their use is to lessen, rather than +to increase, the sum total of bodily power. The student, for example, +who drinks strong coffee in order to study late at night is able to +command less energy on the day following. While enabling him to draw +upon his reserve of nervous power for the time being, the coffee +deprives him of sleep and needed rest.</p> + +<p>The danger of stimulants, so far as energy is concerned, is this: +they tend to exhaust the bodily reserve so that there is not sufficient +left for properly running the vital processes. Evidences of their +weakening effect are found in the feeling of discomfort and lassitude +which result when stimulants to which the body has become accustomed are +withdrawn. Not until one gets back his bodily reserve is he able to work +normally and effectively. Increase in bodily energy comes through health +and not through the use of stimulants.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The body requires a +continuous supply of energy. To obtain this supply, materials possessing +potential, or stored-up, energy are introduced into it. The free oxygen +of the air and the substances known as foods, on account of the chemical +relations which they sustain to each other, contain potential energy and +are utilized for supplying the body. So long as the foods are not +oxidized, the energy remains in the potential form, but in the process +of oxidation the potential energy is changed to kinetic energy and made +to do the work of the body.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. In what different +ways does the body use energy?</p> + +<p>2. Show that a stone lying against the earth has no energy, while the +same stone above the earth has energy.</p> + +<p><pb n="196" /><anchor id="Pg196" />3. How does potential energy +differ from kinetic energy?</p> + +<p>4. What kind of energy is possessed by a bent bow? By a revolving +wheel? By a coiled spring? By the wind? By gunpowder?</p> + +<p>5. How does decomposing water with electricity store energy?</p> + +<p>6. Account for the energy possessed by the oxygen of the air and food +substances.</p> + +<p>7. Trace the energy supply of the body back to the sun.</p> + +<p>8. Why must both oxygen and food be introduced into the body in order +to supply it with energy?</p> + +<p>9. How may overwork and overexercise diminish the energy supply of +the body?</p> + +<p>10. How may one increase the amount of his energy?</p> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">Suggested Experiments.</hi>—1. The +change of kinetic into potential energy may be shown by stretching a +piece of rubber, by lifting a weight, and by separating the armature +from a magnet.</p> + +<p>2. The change of potential into kinetic energy may be shown by +letting weights fall to the ground, by releasing the end of a piece of +stretched rubber, and by burning substances.</p> + +<p>3. The change of one form of kinetic energy to another may be +illustrated by rubbing together two pieces of wood until they are +heated, by ringing a bell, and by causing motion in air or in water by +heating them. If suitable apparatus is at hand, the transformation of +electrical energy into heat, light, sound, and mechanical motion can +easily be shown.</p> + +<p>4. A weight connected by a cord with some small machine and made to +run it, will help the pupil to grasp the general principles in the +storage of energy through gravity. A vessel of water on a high support +from which the water is siphoned on to a small water wheel will serve +the same purpose.</p> + +<p>5. The storing of energy by chemical means may be illustrated by +decomposing potassium chlorate with heat or by decomposing water by +means of a current of electricity.</p> + +<p>6. Study the transfer of energy from the body to surrounding objects, +as in moving substances and lifting weights.</p> + +<p>Fill a half gallon jar two thirds full of water and carefully take +the temperature with a chemical thermometer. Hold the hand in the water +for four or five minutes and take the temperature again. Inference.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="197" /><anchor id="Pg197" /> +<head>CHAPTER XIII - GLANDS AND THE WORK OF EXCRETION</head> + +<p>In our study so far we have been concerned mainly with the +introduction of materials into the body. We are now to consider the +removal of materials from the body. The structures most directly +concerned in this work are known as</p> + +<p><hi rend="font-weight: bold">Glands.</hi>—As generally understood, +glands are organs that prepare special liquids in the body and pour them +out upon free surfaces. These liquids, known as <hi rend="font-style: +italic">secretions</hi>, are used for protecting exposed parts, +lubricating surfaces that rub against each other, digesting food, and +for other purposes. They differ widely in properties as well as in +function, but are all alike in being composed chiefly of water. The +water, in addition to being necessary to the work of particular fluids, +serves in all cases as a carrier of solid substances which are dissolved +in it.</p> + +<p><hi rend="font-weight: bold">General Structure of Glands.</hi>—While +the various glands differ greatly in size, form, and purpose, they +present striking similarities in structure. All glands contain the +following parts:</p> + +<p>1. Gland, or secreting, cells. These are <hi rend="font-style: +italic">specialized</hi> cells for the work of secretion and are the +active agents in the work of the gland. They are usually cubical in +shape.</p> + +<p>2. A basement membrane. This is a thin, connective tissue support +upon which the secreting cells rest.</p> + +<p>3. A network of capillary and lymph vessels. These<pb n="198" /><anchor id="Pg198" /> penetrate the tissues immediately +beneath the secreting cells.</p> + +<p>4. A system of nerve fibers which terminate in the secreting cells +and in the walls of the blood vessels passing to the glands.</p> + +<p>These structures—secreting cells, basement membrane, capillary and +lymph vessels, and nerve fibers—form the essential parts of all glands. +The capillaries and the lymph vessels supply the secreting cells with +fluid, and the nerves control their activities.</p> + +<p><hi rend="font-weight: bold">Kinds of Glands.</hi>—Glands differ from +one another chiefly in the arrangement of their essential parts.<note place="foot"><p>The simplest arrangement of the parts of a gland is that +where they are spread over a plain surface. This arrangement is found in +serous membranes, such as the pleura and peritoneum. These membranes, +however, are not called glands, but secreting surfaces.</p></note> The +most common plan is that of arranging the parts around a central cavity +formed by the folding or pitting of an exposed surface. Many such glands +are found in the mucous membrane, especially that lining the alimentary +canal, and are most numerous in the stomach, where they supply the +gastric juice. If these glands have the general form of tubes, they are +called <hi rend="font-style: italic">tubular</hi> glands; if sac-like in +shape, they are called <hi rend="font-style: italic">saccular</hi> +glands. Both the tubular and the saccular glands may, by branching, form +a great number of similar divisions which are connected with one +another, and which communicate by a common opening with the place where +the secretion is used. This forms a <hi rend="font-style: +italic">compound</hi> gland which, depending on the structure of the +minute parts, may be either a <hi rend="font-style: italic">compound +tubular</hi> or a <hi rend="font-style: italic">compound saccular</hi> +gland. The larger of the compound saccular glands are also called <hi +rend="font-style: italic">racemose</hi> glands, on account of their +having the general form of a cluster, or raceme, similar<pb n="199" /><anchor id="Pg199" /> to that of a bunch of +grapes. The general structure of the different kinds of glands is shown +in Fig. 85.</p> + +<p rend="text-align: center"> +<figure url="images/image85.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 85—<hi rend="font-weight: bold">Diagram +illustrating evolution of glands.</hi> <hi rend="font-style: +italic">A.</hi> Simple secreting surface. 1. Gland cells. 2. Basement +membrane. 3. Blood vessel. 4. Nerve. <hi rend="font-style: +italic">B.</hi> Simple tubular gland. <hi rend="font-style: +italic">C.</hi> Simple saccular gland. <hi rend="font-style: +italic">D.</hi> Compound tubular gland. <hi rend="font-style: +italic">E.</hi> Compound saccular gland. <hi rend="font-style: +italic">F.</hi> A compound racemose gland with duct passing to a free +surface. <hi rend="font-style: italic">G.</hi> Relation of food canal to +different forms of glands. The serous coat has a secreting surface.</head> +<figDesc>Fig. 85</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Nature of the Secretory Process.</hi>—At +one time the gland was regarded merely as a kind of filter which +separated from the blood the ingredients found in its secretions. Recent +study, however, of several facts relating to secretion has led to +important modifications of this view. The secretions of many glands are +known to contain substances that are not found in the blood, or, if +present, are there in exceedingly small amounts. Then again the cells of +certain glands have been found to undergo marked changes during the +process of secretion. If, for example, the<pb n="200" /><anchor id="Pg200" /> cells of the pancreas be examined +after a period of rest, they are found to contain small granular bodies. +On the other hand, if they are examined after a period of activity, the +granules have disappeared and the cells themselves have become smaller +(Fig. 86). The granules have no doubt been used up in forming the +secretion. These and other facts have led to the conclusion that +secretion is, in part, the separation of materials without change from +the blood, and, in part, a process by which special substances are +prepared and added to the secretion. According to this view the gland +plays the double rôle of a <hi rend="font-style: italic">filtering +apparatus</hi> and of a <hi rend="font-style: italic">manufacturing +organ</hi>.</p> + +<p rend="text-align: center"> +<figure url="images/image86.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 86—<hi rend="font-weight: bold">Secreting cells +from the pancreas</hi> (after Langley). <hi rend="font-style: +italic">A.</hi> After a period of rest. <hi rend="font-style: +italic">B.</hi> After a short period of activity. C. After a period of +prolonged activity. In <hi rend="font-style: italic">A</hi> and <hi +rend="font-style: italic">B</hi> the nuclei are concealed by the +granules that accumulate during the resting period.</head> +<figDesc>Fig. 86</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Kinds of Secretion.</hi>—In a general +way all the liquids produced by glands may be considered as belonging to +one or the other of two classes, known as the <hi rend="font-style: +italic">useful</hi> and the <hi rend="font-style: italic">useless</hi> +secretions. To the first class belong all the secretions that serve some +purpose in the body, while the second includes all those liquids that +are separated as waste from the blood. The first are usually called <hi +rend="font-style: italic">true secretions</hi>, or secretions proper, +while the second are called <hi rend="font-style: +italic">excretions</hi>. The most important glands producing liquids of +the first class are those of digestion (Chapter X).</p> + +<p><pb n="201" /><anchor id="Pg201" /><hi rend="font-weight: +bold">Excretory Work of Glands.</hi>—The process of removing wastes from +the body is called <hi rend="font-style: italic">excretion</hi>. While +in theory excretion may be regarded as a distinct physiological act, it +is, in fact, leaving out the work of the lungs, but a phase of the work +of glands. From the cells where they are formed, the waste materials +pass into the lymph and from the lymph they find their way into the +blood. They are removed from the blood by glands and then passed to the +exterior of the body.</p> + +<p><hi rend="font-weight: bold">The Necessity for Excretion</hi> is +found in the results attending oxidation and other chemical changes at +the cells (page 107). Through these changes large quantities of +materials are produced that can no longer take any part in the vital +processes. They correspond to the ashes and gases of ordinary combustion +and form wastes that must be removed. The most important of these +substances, as already noted (page 110), are carbon dioxide, water, and +urea.<note place="foot"><p>In the oxidations that occur in the body it is not +supposed that the nutrients are immediately converted to carbon dioxide, +water, and urea. On the other hand, it is held that their reduction +takes place gradually, as the reduction of sugar by fermentation, and +that the wastes leaving the body are but the "end products" and show +only the final results.</p></note> A number of mineral salts are also to be included with the +waste materials. Some of these are formed in the body, while others, +like common salt, enter as a part of the food. They are solids, but, +like the urea, leave the body dissolved in water.</p> + +<p>Waste products, if left in the body, interfere with its work (some +of, them being poisons), and if allowed to accumulate, cause death. +Their removal, therefore, is as important as the introduction of food +and oxygen into the body. The most important of the excretory glands +are</p> + +<p><hi rend="font-weight: bold">The Kidneys.</hi>—The kidneys are two +bean-shaped glands, situated in the back and upper portion of the +abdominal<pb n="202" /><anchor id="Pg202" /> cavity, one on each side of the +spinal column. They weigh from four to six ounces each, and lie between +the abdominal wall and the peritoneum. Two large arteries from the +aorta, called the <hi rend="font-style: italic">renal arteries</hi>, +supply them with blood, and they are connected with the inferior vena +cava by the <hi rend="font-style: italic">renal veins</hi>. They remove +from the blood an exceedingly complex liquid, called the <hi +rend="font-style: italic">urine</hi>, the principal constituents of +which are water, salts of different kinds, coloring matter, and urea. +The kidneys pass their secretion by two slender tubes, the <hi +rend="font-style: italic">ureters</hi>, to a reservoir called the <hi +rend="font-style: italic">bladder</hi> (Fig. 87).</p> + +<p rend="text-align: center"> +<figure url="images/image87.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 87—<hi rend="font-weight: bold">Relations of the +kidneys.</hi> (Back view.) 1. The kidneys. 2. Ureters. 3. Bladder. 4. +Aorta. 5. Inferior vena cava. 6. Renal arteries. 7. Renal veins.</head> +<figDesc>Fig. 87</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Structure of the Kidneys.</hi>—Each +kidney is a compound tubular gland and is composed chiefly of the parts +concerned in secretion. The ureter serves as a duct for removing the +secretion, while the blood supplies the materials from which the +secretion is formed. On making a longitudinal section of the kidney, the +upper end of the ureter is found to expand into a basin-like enlargement +which is embedded in the concave side of the kidney. The cavity within +this enlargement is called the <hi rend="font-style: italic">pelvis of +the kidney</hi>, and into it project a number of cone-shaped elevations +from the kidney substance, called the <hi rend="font-style: +italic">pyramids</hi> (Fig. 88).</p> + +<p>From the summits of the pyramids extend great numbers of very small +tubes which, by branching, penetrate to<pb n="203" /><anchor id="Pg203" /> all parts of the kidneys. These +are the <hi rend="font-style: italic">uriniferous tubules</hi>, and they +have their beginnings at the outer margin of the kidney in many small, +rounded bodies called the <hi rend="font-style: italic">Malpighian +capsules</hi> (<hi rend="font-style: italic">A</hi>, Fig. 88). Each +capsule incloses a cluster of looped capillaries and connects with a +single tubule (Fig. 89). From the capsule the tubule extends toward the +concave side of the kidney and, after uniting with similar tubules from +other parts, finally terminates at the pyramid. Between its origin and +termination, however, are several convolutions and one or more loops or +turns. After passing a distance many times greater than from the surface +to the center of the kidney, the tubule empties its contents into the +expanded portion of the ureter.</p> + +<p rend="text-align: center"> +<figure url="images/image88.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 88—<hi rend="font-weight: bold">Sectional view +of kidney.</hi> 1. Outer portion or cortex. 2. Medullary portion. 3. +Pyramids. 4. Pelvis. 5. Ureter. <hi rend="font-style: italic">A.</hi> +Small section enlarged to show the tubules and their connection with the +capsules.</head> +<figDesc>Fig. 88</figDesc> +</figure></p> + +<p rend="text-align: center"> +<figure url="images/image89.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 89—<hi rend="font-weight: bold">Malpighian +capsule</hi> highly magnified (Landois). <hi rend="font-style: +italic">a.</hi> Small artery entering capsule and forming cluster of +capillaries within. <hi rend="font-style: italic">e.</hi> Small vein +leaving capsule and branching into <hi rend="font-style: italic">c</hi>, +a second set of capillaries, <hi rend="font-style: italic">h.</hi> +Beginning of uriniferous tubule.</head> +<figDesc>Fig. 89</figDesc> +</figure></p> + +<p><pb n="204" /><anchor id="Pg204" />The uriniferous tubules are lined +with secreting cells. These differ greatly at different places, but they +all rest upon a basement membrane and are well supplied with +capillaries. These cells provide one means of separating wastes from the +blood (Fig. 90).</p> + +<p rend="text-align: center"> +<figure url="images/image90.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 90—<hi rend="font-weight: bold">Diagram +illustrating renal circulation.</hi> 1. Branch from renal artery. 2. +Branch from renal vein. 3. Small artery branches, one of which enters a +Malpighian capsule (5). 6. Small vein leaving the capsule and branching +into the capillaries (7) which surround the uriniferous tubules. 4. +Small veins which receive blood from the second set of capillaries. 8. +Tubule showing lining of secreting cells.</head> +<figDesc>Fig. 90</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Blood Supply to the Kidneys.</hi>—The +method by which the kidneys do their work is suggested by the way in +which the blood circulates through them. The renal artery entering each +kidney divides into four branches and these send smaller divisions to +all parts of the kidney. At the outer margin of the kidney, called the +<hi rend="font-style: italic">cortex</hi>, the blood is passed through +<hi rend="font-style: italic">two sets of capillaries</hi>. The first +forms the clusters in the Malpighian capsules and receives the blood +directly from the smallest arteries. The second forms a network around +the uriniferous tubules and receives the blood which has passed from the +capillary clusters into a system of small veins (Fig. 90). From the last +set of capillaries the blood is passed into veins which leave the +kidneys where the artery branches enter, uniting there to form the main +renal veins.</p> + +<p><pb n="205" /><anchor id="Pg205" /><hi rend="font-weight: bold">Work +of the Kidneys.</hi>—Why should the blood pass through two systems of +capillaries in the kidneys? This is because the separation of waste is +done in part by the Malpighian capsules and in part by the uriniferous +tubules. Water and salts are removed chiefly at the capsules, while the +remaining solid constituents of the urine pass through the secreting +cells that line the tubules. It was formerly believed that the kidneys +obtained their secretion by a process of filtration from the blood, but +this belief has been gradually modified. The prevailing view now is that +the processes of filtration and secretion are both carried on by the +kidneys,—that the capillary clusters in the Malpighian bodies serve as +delicate filters for the separation of water and salts, while the +secreting cells of the tubules separate substances by the process of +secretion.</p> + +<p>On account of the large volume of blood passing through the kidneys +this liquid is still a bright red color as it flows into the renal veins +(Fig. 90). The kidney cells require oxygen, but the amount which they +remove from the blood is not sufficient to affect its color noticeably. +The blood in the renal veins, having given up most of its impurities and +still retaining its oxygen, is considered the purest blood in the +body.</p> + +<p><hi rend="font-weight: bold">Urea</hi> is the most abundant solid +constituent of the urine and is the chief waste product arising from the +oxidation of nitrogenous substances in the body. Although secreted by +the cells lining the uriniferous tubules, it is not formed in the +kidneys. The secreting cells simply separate it from the blood where it +already exists. The muscles also have been suggested as a likely source +of urea, for here the proteids are broken down in largest quantities; +but the muscles produce little if any urea. Its production has been +found to be the <hi rend="font-style: italic">work of the liver</hi>. In +the muscular tissue, and in the other tissues as well, the proteids are +reduced to a lower order of compounds, such as the compounds of<pb n="206" /><anchor id="Pg206" /> ammonia, which pass into the +blood and are then taken up by the liver. By the action of the liver +cells these are converted into urea and this is turned back into the +blood. From the blood the urea is separated by the secreting cells of +the kidneys.</p> + +<p><hi rend="font-weight: bold">Work of the Liver.</hi>—The liver, +already described as an organ of digestion (page 152), assists in the +work of excretion both by changing waste nitrogenous compounds into urea +and by removing from the blood the wastes found in the bile. While the +chief work of the liver is perhaps not that of excretion, its functions +may here be summarized. The liver is, first of all, a <hi +rend="font-style: italic">manufacturing organ</hi>, producing, as we +have seen, three distinct products—bile, glycogen, and urea. On account +of the nature of the urea and the bile, the liver is properly classed as +an <hi rend="font-style: italic">excretory organ</hi>; but in the +formation of the glycogen it plays the part of a <hi rend="font-style: +italic">storage organ</hi>. Then, on account of the use made of the bile +after it is passed into the food canal, the liver is also classed as a +<hi rend="font-style: italic">digestive organ</hi>. These different +functions make of the liver an organ of the first importance.</p> + +<p><hi rend="font-weight: bold">Excretory Work of the Food +Canal.</hi>—The glands connected with the food canal, other than the +liver, while secreting liquids that aid in digestion, also separate +waste materials from the blood. These are passed into the canal, whence +they leave the body with the undigested portions of the food and the +waste from the liver. Though the nature and quantity of the materials +removed by these glands have not been fully determined, recent +investigations have tended to enhance the importance attached to this +mode of excretion.</p> + +<p><hi rend="font-weight: bold">The Perspiratory Glands.</hi>—The +perspiratory, or sweat, glands are located in the skin. They belong to +the type of simple tubular glands and are very numerous over the<pb +n="207" /><anchor id="Pg207" /> entire surface of the body. A typical +sweat gland consists of a tube which, starting at the surface of the +cuticle, penetrates to the under portion of the true skin and there +forms a ball-shaped coil. The coiled extremity, which forms the +secreting portion, is lined with secreting cells and surrounded by a +network of capillaries. The portion of the tube passing from the coil to +the surface serves as a duct (Figs. 91 and 121).</p> + +<p rend="text-align: center"> +<figure url="images/image91.png" rend="page-float: 'hp'; text-align: center; w40"> +<head><lb />Fig. 91—<hi rend="font-weight: bold">Diagram of +section through a sweat gland.</hi> <hi rend="font-style: +italic">a.</hi> Outer layer of skin or cuticle. <hi rend="font-style: +italic">b.</hi> Dermis or true skin. <hi rend="font-style: italic">d, +e.</hi> Sections of the tube forming the coiled portion of the gland. +<hi rend="font-style: italic">c.</hi> Duct passing to the surface. The +other structures of the skin not shown.</head> +<figDesc>Fig. 91</figDesc> +</figure></p> + +<p>The sweat glands secrete a thin, colorless fluid, called <hi +rend="font-style: italic">perspiration</hi>, or sweat. This consists +chiefly of water, but contains a small per cent of salts and of urea. +The excretory work of these glands seems not to be so great as was +formerly supposed, but they supplement in a practical way the work of +the kidneys and, during diseases of these organs, show an increase in +excretory function to a marked degree. The perspiration also aids in the +regulation of the temperature of the body (Chapter XVI).</p> + +<p><hi rend="font-weight: bold">Excretory Work of the Lungs.</hi>—While +the lungs cannot be regarded as glands, they do a work in the removal of +waste from the body which must be considered in the general process of +excretion. They are especially adapted to the removal of gaseous +substances from the blood, and it is through them that most of the +carbon dioxide leaves the body. The lungs<pb n="208" /><anchor id="Pg208" /> remove also a considerable +quantity of water. This is of course in the gaseous form, being known as +water vapor.</p> + +<p><hi rend="font-weight: bold">Ductless Glands and Internal +Secretion.</hi>—Midway in function between the glands that secrete +useful liquids and those that remove waste materials from the blood is a +class of bodies, found at various places, known as the <hi +rend="font-style: italic">ductless glands.</hi> They are so named from +their having the general form of glands and from the fact that they have +no external openings or ducts. They prepare special materials which are +passed into the blood and which are supposed to exert some beneficial +effect either upon the blood or upon the tissues through which the blood +circulates. The most important of the ductless glands are the thyroid +gland, located in the neck; the suprarenal bodies, situated one just +over each kidney; and the thymus gland, a temporary gland in the upper +part of the chest. The spleen and the lymphatic glands (page 68) are +also classed with the ductless glands. The liver, the pancreas, and +(according to some authorities) the kidneys, in addition to their +external secretions, produce materials that pass into the blood. They +perform in this way a function like that of the ductless glands. The +work of glands in preparing substances that enter the blood is known as +<hi rend="font-style: italic">internal secretion.</hi></p> + +<p><hi rend="font-weight: bold">Quantity of Excretory Products.</hi>—If +the weight of the normal body be taken at intervals, after growth has +been attained, there will be found to be practically no gain or loss +from time to time. This shows that materials are leaving the body as +fast as they enter and that the tissues are being torn down as fast as +they are built up. It also shows that substances do not remain in the +body <hi rend="font-style: italic">permanently</hi>, but only so long +perhaps as is necessary for them to give up their energy, or serve some +additional purpose in the ever changing protoplasm. The excretory organs +then remove from the body a quantity of material that is equal in weight +to the materials absorbed by the organs of digestion and respiration. +This is estimated for the average individual to be about five pounds +daily. The passage of waste from the body is summarized in Table +III.</p> + +<table rend="latexcolumns: 'p{1.5cm}|p{1.5cm}|p{1.5cm}|p{1.5cm}|p{1.5cm}'"> +<head>TABLE III. THE PASSAGE OF WASTE MATERIALS FROM THE BODY</head> + +<row> +<cell rend="font-size: 50%">Materials</cell> +<cell rend="font-size: 50%">State</cell> +<cell rend="font-size: 50%">How Formed in the Body</cell> +<cell rend="font-size: 50%">Condition in the Blood</cell> +<cell rend="font-size: 50%">How Removed from the Blood</cell> +</row> + +<row> +<cell rend="font-size: 50%">Carbon dioxide</cell> +<cell rend="font-size: 50%">Gas</cell> +<cell rend="font-size: 50%">By the oxidation of the carbon of proteids, +carbohydrates, and fats.</cell> +<cell rend="font-size: 50%">Dissolved in the plasma and in loose +combination with salts in the blood.</cell> +<cell rend="font-size: 50%">Separated from the blood at the +alveoli of the lungs and then forced through the air passages into the +atmosphere.</cell> +</row> + +<row> +<cell rend="font-size: 50%">Urea</cell> +<cell rend="font-size: 50%">Solid</cell> +<cell rend="font-size: 50%">By the oxidation in the liver of nitrogenous compounds.</cell> +<cell rend="font-size: 50%">Dissolved in the plasma.</cell> +<cell rend="font-size: 50%">Removed by the uriniferous tubules of the +kidneys and to a small extent by the perspiratory glands.</cell> +</row> + +<row> +<cell rend="font-size: 50%">Water</cell> +<cell rend="font-size: 50%">Liquid</cell> +<cell rend="font-size: 50%">By the oxidation of the hydrogen of proteids, +carbohydrates, and fats. Amount formed in the body is small.</cell> +<cell rend="font-size: 50%">As water.</cell> +<cell rend="font-size: 50%">Removed by all the organs of excretion, but in the largest quantities by +the kidneys and the skin.</cell> +</row> + +<row> +<cell rend="font-size: 50%">Salts</cell> +<cell rend="font-size: 50%">Solid</cell> +<cell rend="font-size: 50%"></cell> +<cell rend="font-size: 50%">Dissolved in the plasma.</cell> +<cell rend="font-size: 50%">By the kidneys, liver, +and skin.</cell> +</row> +</table> + +<div> +<pb n="210" /><anchor id="Pg210" /> +<head>HYGIENE</head> + +<p>The separation of wastes from the body has such a close relation to +the health that all conditions affecting it should receive the most +careful attention. Their retention beyond the time when they should be +discharged undoubtedly does harm and is the cause of many bodily +disorders.</p> + +<p><hi rend="font-weight: bold">Value of Water.</hi>—As a rule the +work of excretion is aided by drinking <hi rend="font-style: +italic">freely</hi> of pure water. As water is the natural dissolver and +transporter of materials in the body, it is generally conceded by +hygienists and physicians that the taking of plenty of water is a +healthful practice. People do not as a rule drink a sufficient amount of +water, about three pints per day being required by the average adult, in +addition to that contained in the food. Most of the water should, of +course, be taken between meals, although the sipping of a small amount +during meals does not interfere with digestion. As stated elsewhere, the +taking of a cup of water on retiring at night and again on rising in the +morning is very generally recommended.</p> + +<p><hi rend="font-weight: bold">Protection of Kidneys and Liver.</hi>—The +kidneys and liver are closely related in their work and in many +instances are injured or benefited by the same causes. Both, as already +stated (page 124), are liable to injury from an <hi rend="font-style: +italic">excess of proteid food</hi>, especially meats, and also by a +condition of inactivity of the bowels (page 166). The free use of +alcohol also has an injurious effect on both of these organs.<note place="foot"><p>Alcohol, if used in considerable quantity, leads to +cirrhosis of the liver and Bright's disease of the kidneys, both very +dangerous diseases. Dr. William Osler in his treatise, <hi +rend="font-style: italic">The Practice of Medicine</hi>, states that +alcohol is the chief cause of cirrhosis of the liver. Dr. T.N. Bogart, +specialist in kidney diseases, asserts that one third of all the cases +of Bright's disease coming under his observation are caused by +alcohol.</p></note> On the +other hand, increasing the activity of the skin has a beneficial effect +upon them, especially<pb n="211" /><anchor id="Pg211" /> the kidneys. Exercise and +bathing, which tend to make the skin more active, are valuable aids both +in ridding the body of impurities and in lessening the work of the other +excretory organs. One having a disease of the kidneys, however, needs to +exercise great care in bathing on account of the bad results which +follow getting chilled.</p> + +<p><hi rend="font-weight: bold">Special Care after Certain +Diseases.</hi>—Certain diseases, as measles, diphtheria, scarlet fever, +and typhoid fever, sometimes have the effect of weakening the kidneys +(and other vital organs) and of starting disease in them. When this +occurs it is usually the result of exposure or of over-exertion while the +body is in a weakened condition. Severe chilling at such a time, by +driving blood from the surface to the parts within, often causes +inflammation of the kidneys. On recovering from any wasting disease one +should exercise great caution both in resuming his regular work and in +exposing his body to wet or cold.</p> + +<p><hi rend="font-weight: bold">Misunderstood Symptoms.</hi>—Pains in +the small of the back, an increase in the secretions of the kidneys, and +a sediment in the urine very naturally suggest some disorder of the +kidneys. It is a fact, however, that these symptoms have little or no +relation to the state of the kidneys and may occur when the kidneys are +in a perfectly healthy condition. The kidneys are not located in the +small of the back, but above this place, so that pains in this region +are evidently not from the kidneys, while the increase in the flow of +the urine may arise from a number of causes, one of which is an increase +of certain waste products passed into the blood. The symptoms referred +to are frequently the results of nervous exhaustion, resulting from +overstudy, worry, eye strain, or some other condition that overtaxes the +nervous system. When this is the case, relief is obtained through +resting the nerves. Actual<pb n="212" /><anchor id="Pg212" /> disease of the kidneys can only +be determined through a chemical and microscopic examination of the +urine. To resort to some patent medicine for kidney trouble without +knowing that such trouble exists, as is sometimes done, is both foolish +and unhygienic.</p> + +<p><hi rend="font-weight: bold">Alcoholic Beverages and the Elimination +of Waste.</hi>—Causing as it does such serious diseases as cirrhosis of +the liver and Bright's disease of the kidneys (footnote, page 210), +alcohol will greatly interfere in this way with the elimination of +waste. There is also evidence to the effect that it interferes with +waste elimination before the stage is reached of causing disease of +these organs. Researches have shown that alcohol increases the amount of +uric acid in the body and decreases the amount of urea found in the +urine. The conclusion to be drawn is that alcohol interferes in some way +with the change of the harmful uric acid into the comparatively harmless +urea—an interference which in some instances results in great harm. It +has also been shown that malted liquors, such as beer and ale, contain +substances which, like the caffein of tea and coffee (page 167), are +readily converted into uric acid.<note place="foot"><p>Hall, <hi rend="font-style: italic">The Purin +Bodies</hi>.</p></note> Wines contain acids which may also +act injuriously. The harm which such substances do is, of course, +additional to that caused by the alcohol.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—As a result of the +oxidations and other changes at the cells, substances are produced that +can no longer serve a purpose in the body. They are of the nature of +waste, and their continuous removal from the body is as necessary to the +maintenance of life as the introduction of food and oxygen. The organs +whose work it is to remove the waste, excepting the lungs, are glands; +and the material which they remove are of the nature of secretions. From +the cells, the waste passes through the lymph in the blood. From the +blood it is separated by the excretory organs and passed to the exterior +of the body.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. What general purposes +are served by the glands in the body?</p> + +<p><pb n="213" /><anchor id="Pg213" />2. What are the parts common to +all glands? What purpose is served by each of these parts?</p> + +<p>3. How do tubular glands differ in structure from saccular glands? +What is a racemose gland? Why so called?</p> + +<p>4. Describe the nature of the secretory process.</p> + +<p>5. What conditions render necessary the formation of waste materials +in the body? Why must these be removed?</p> + +<p>6. How do the waste materials get from the cells to the organs of +excretion?</p> + +<p>7. Show by a drawing the connections of the kidneys with the large +blood vessels and the bladder. Name parts of drawing.</p> + +<p>8. In what do the uriniferous tubes have their beginning? In what do +they terminate? With what are they lined?</p> + +<p>9. Why should the blood pass through two sets of capillaries in the +kidneys?</p> + +<p>10. Bright's disease of the kidneys affects the uriniferous tubes and +interferes with their work. What impurity is then left in the blood?</p> + +<p>11. Trace water and salts from the Malpighian capsules to the +bladder, naming parts through which they pass.</p> + +<p>12. Trace carbon dioxide from the cells to the outside +atmosphere.</p> + +<p>13. How does the quantity of material introduced into the body +compare with that which is removed by the organs of excretion?</p> + +<p>14. Name two ways of lessening the work of the kidneys.</p> + +<p>15. Why is the drinking of plenty of pure water a healthful +practice?</p> +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">To suggest the Double Work of +Glands.</hi>—Prepare a simple filter by fitting a piece of porous paper +into a glass funnel. Through this pass pure water and also water having +salt dissolved in it and containing some sediment, as sand. The water +and the dissolved salt pass through, while the sediment remains on the +filter. Now substitute a fresh piece of paper in the funnel and drop on +its surface a little solid coloring matter, such as cochineal. Again +pass the liquid through the funnel. This time it comes through colored, +the color being added by the filter. Compare the filter and materials +filtered to the gland and the materials concerned in secretion (blood, +the liquid secreted, substances added by the gland, etc.).</p> + +<p rend="text-align: center"> +<figure url="images/image92.png" rend="page-float: 'hp'; text-align: center; w40"> +<head><lb />Fig. 92—<hi rend="font-weight: bold">The physiological scheme.</hi> Diagram +suggesting the essential relation of the bodily activities. See Summary +of Part I, page 215, and Summary of Part II, page 413.</head> +<figDesc>Fig. 92</figDesc> +</figure></p> +</div> + +<div> +<pb n="215" /><anchor id="Pg215" /> +<head>SUMMARY OF PART I</head> + +<p>The body is an organization of different kinds of cells; it grows +through the growth and reproduction of these cells; and its life as a +whole is maintained by providing such conditions as will enable the +cells to keep alive. Of chief importance in the work of the body is a +nutrient fluid which supplies the cells with food and oxygen and +relieves them of waste. A moving portion of this fluid, called the +blood, serves as a transporting agent, while another portion, called the +lymph, passes the materials between the blood and the cells. Through +their effects upon the blood and the lymph, the organs of circulation, +respiration, digestion, and excretion minister in different ways to the +cells, and aid in the maintenance of life. By their combined action two +distinct movements are kept up in the body, as follows:</p> + +<p>1. An <hi rend="font-style: italic">inward</hi> movement which +carries materials from the outside of the body toward the cells.</p> + +<p>2. An <hi rend="font-style: italic">outward</hi> movement which +carries materials from the cells to the outside of the body.</p> + +<p>Passing <hi rend="font-style: italic">inward</hi> are the oxygen and +food materials <hi rend="font-style: italic">in a condition to unite +with each other</hi> and thereby change their potential into kinetic +energy. Passing <hi rend="font-style: italic">outward</hi> are the +oxygen and the elements that formed the food materials <hi +rend="font-style: italic">after having united</hi> at the cells and +liberated their energy.</p> + +<p>As a final and all-important result, there is kept up a <hi +rend="font-style: italic">continuous series of chemical changes</hi> in +the cells. These liberate the energy, provide special substances needed +by the cells, and preserve the life of the body (Fig. 92).</p> + +<p>In the chapters which follow, we are to consider the problem of +adjusting the body to and of bringing it into proper relations with its +surroundings.</p> +</div> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="216" /><anchor id="Pg216" /> +<head>PART II: MOTION, COORDINATION, AND SENSATION</head> +<p></p> + +<div> +<index index="toc" /><index index="pdf" /> +<head>CHAPTER XIV - THE SKELETON</head> + +<p>One necessary means of establishing proper relations between the body +and its surroundings is <hi rend="font-style: italic">motion</hi>.<note place="foot"><p>Review "Main Physiological Problems," page 21.</p></note> +Not only can the body move itself from place to place, but it is able to +move surrounding objects as well. In the production of motion three +important systems are employed—the muscular system, the nervous system, +and a system of mechanical devices which are found mainly in the +skeleton. The muscular system supplies the energy for operating the +mechanical devices, while the nervous system controls the movements.<note place="foot"><p>In the production of motion in the body, as well as in +the production of any kind of <hi rend="font-style: +italic">purposeful</hi> motion outside of the body, three conditions +must be fulfilled. There is required, in the first place, a mechanical +device or machine which is so constructed as to produce a certain kind +of motion. In the second place, energy is needed to operate this device. +And, finally, there must be some controlling force, by means of which +the motion is made to accomplish definite results. The driving of a +horse hitched to a wagon will illustrate these conditions. The wagon is +the mechanical device, the horse furnishes the energy, and the driver +supplies the controlling force. In this, as in most cases, the +machinery, the source of energy, and the controlling force are +disconnected except when at work; but in the body all three occur +together in the same structure.</p></note> +Although the skeleton serves other purposes, such as giving shape to the +body and protecting certain organs, its main use is that of an aid in +the production of motion.</p> + +<p><pb n="217" /><anchor id="Pg217" /><hi rend="font-weight: bold">Skeleton Tissues.</hi>—The tissues +employed in the construction of the skeleton are the osseous, the +cartilaginous, and the connective tissues. These are known as the +supporting tissues of the body. They form the bones, supply the elastic +pads at the ends of the bones, and furnish strong bands, called +ligaments, for fastening the bones together. The skeleton forms about 16 +per cent of the weight of the body. Its tissues, being of a more durable +nature than the rest of the body, do not so readily decay. Especially is +this true of the osseous tissue, which may be preserved indefinitely, +after removal from the body, by simply keeping it dry.</p> + +<p><hi rend="font-weight: bold">The Bones.</hi>—The separate units, or +parts, of which the skeleton is constructed are called bones. They are +the hard structures that can be felt in all parts of the body, and they +comprise nearly the entire amount of material found in the prepared +skeleton. As usually estimated, the bones are 208 in number. They vary +greatly in size and shape in different parts of the body.</p> + +<p><hi rend="font-weight: bold">Composition and Properties of +Bones.</hi>—The most noticeable and important properties of the bones +are those of hardness, stiffness, and toughness. Upon these properties +the uses of the bones depend. These properties may, in turn, be shown to +depend upon the presence in osseous tissue of two essentially different +kinds of substance, known as the <hi rend="font-style: italic">animal +matter</hi> and the <hi rend="font-style: italic">mineral matter</hi>. +If a bone is soaked in an acid, the mineral matter is dissolved out, and +as a result it loses its properties of hardness and stiffness. (See +Practical Work.) This is because the mineral matter supplies these +properties, being composed of substances which are hard and closely +resemble certain kinds of rock. The chief materials forming the mineral +matter are calcium phosphate and calcium carbonate.</p> + +<p><pb n="218" /><anchor id="Pg218" />On the other hand, burning a bone destroys the animal matter. When +this is done the bone loses its toughness, and becomes quite brittle. +The property of toughness is, therefore, supplied by the animal matter. +This consists mainly of a substance called <hi rend="font-style: +italic">ossein</hi>, which may be dissolved out of the bones by boiling +them. Separated from the bones it is known as <hi rend="font-style: +italic">gelatine</hi>. The blood vessels and nerves in the bones, and +the protoplasm of the bone cells, are also counted in with the animal +matter.</p> + +<p rend="text-align: center"> +<figure url="images/image93.png" rend="page-float: 'hp'; text-align: center; w40"> +<head><lb />Fig. 93—<hi rend="font-weight: bold">Section of a +long bone</hi> (<hi rend="font-style: italic">tibia</hi>), showing the +gross structure.</head> +<figDesc>Fig. 93</figDesc> +</figure></p> + +<p>If a dry bone from a full-grown, but not old, animal be weighed +before and after being burned, it is found to lose about one third of +its weight. From this we may conclude that about one third of the bone +by weight is animal matter and two thirds is mineral matter. This +proportion, however, varies with age, the mineral matter increasing with +advance of years.</p> + +<p><hi rend="font-weight: bold">Gross Structure of Bones.</hi>—The gross +structure of the bones is best learned by studying both dry and fresh +specimens. (See Practical Work.) The ends of the bones are capped by a +layer of smooth, elastic cartilage, while all the remaining surface is +covered by a rather dense sheath of connective tissue, called the <hi +rend="font-style: italic">periosteum</hi>. Usually the central part<pb n="219" /><anchor id="Pg219" /> of the long bones is hollow, +being filled with a fatty substance known as the <hi rend="font-style: +italic">yellow marrow</hi>. Around the marrow cavity the bone is very +dense and compact, but most of the material forming the ends is porous +and spongy. These materials are usually referred to as the <hi +rend="font-style: italic">compact substance</hi> and the <hi +rend="font-style: italic">cancellous</hi>, or <hi rend="font-style: +italic">spongy, substance</hi> of the bones (Fig. 93).</p> + +<p>The arrangement of the compact and spongy substance varies with the +different bones. In the short bones (wrist and ankle bones, vertebræ, +etc.) and also in the flat bones (skull bones, ribs, shoulder blades, +etc.) there is no cavity for the yellow marrow, all of the interior +space being filled with the spongy substance. The <hi rend="font-style: +italic">red marrow</hi>, relations of which to the red corpuscles of the +blood have already been noted (page 27), occupies the minute spaces in +the spongy substance.</p> + +<p rend="text-align: center"> +<figure url="images/image94.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 94—<hi rend="font-weight: bold">Cross section of +bone showing minute structure.</hi> Magnified. 1. Surface layer of bone. +2. Deeper portion. 3. Haversian canals from which pass the canaliculi. +4. A lacuna. Observe arrangement of lacunæ at surface and in deeper +portion.</head> +<figDesc>Fig. 94</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Minute Structure of Bone.</hi>—A +microscopic examination of a thin slice of bone taken from the compact +substance shows this to be porous as well as the spongy substance. Two +kinds of small channels are found running through it in different +directions, known as the Haversian canals and the canaliculi (Fig. 94). +These serve the general purpose of distributing nourishment through the +bone. The <hi rend="font-style: italic">Haversian canals</hi> are larger +<pb n="220" /><anchor id="Pg220" />than the canaliculi and contain +small nerves and blood vessels, chiefly capillaries (Fig. 95). They +extend lengthwise through the bone. The <hi rend="font-style: +italic">canaliculi</hi> are channels for conveying lymph. They pass out +from the Haversian canals at right angles, going to all portions of the +compact substance except a thin layer at the surface. In the surface +layer of the bone the canaliculi are in communication with the +periosteum.</p> + +<p rend="text-align: center"> +<figure url="images/image95.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 95—<hi rend="font-weight: bold">Section showing +Haversian canal and contents</hi>, highly magnified (after Schäfer). 1. +Arterial capillary. 2. Venous capillary. 3. Nerve fibers. 4. Lymph +vessel.</head> +<figDesc>Fig. 95</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Bone Cells.</hi>—Surrounding the +Haversian canals are thin layers of bone substance called the <hi +rend="font-style: italic">laminæ</hi>, and within these are great +numbers of irregular bodies, known as the <hi rend="font-style: +italic">lacunæ</hi>. The walls of the lacunæ are hard and dense, but +within each is an open space. In this lies a flattened body, having a +nucleus, which is recognized as the <hi rend="font-style: italic">bone +cell</hi>, or the bone corpuscle (Fig. 96). It appears to be the work of +the bone cells to deposit mineral matter in the walls surrounding them +and in this way to supply the properties of hardness and stiffness to +the bones. The canaliculi connect with the lacunæ in all parts of the +bone, causing them to appear under the microscope like so many burs +fastened together by their projecting spines (Fig. 94).</p> + +<p rend="text-align: center"> +<figure url="images/image96.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 96—<hi rend="font-weight: bold">Bone cell</hi> +removed from the lacuna and very highly magnified. (From Quain's <hi +rend="font-style: italic">Anatomy</hi>.)</head> +<figDesc>Fig. 96</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">How the Bone Cells are +Nourished.</hi>—The bone cells, like all the other cells of the body, +are nourished by the lymph that escapes from the blood. This passes +through the canaliculi to the cells in the different parts of the bone, +as follows:</p> + +<p><pb n="221" /><anchor id="Pg221" />1. The cells in the +surface layer of the bone receive lymph from the capillaries in the +periosteum.<note place="foot"><p>The dependence of the outer layers of bone cells upon +the periosteum for nourishment causes a destruction of this membrane to +affect seriously the bone beneath, producing in many instances a decay +of the bone substance.</p></note> It gets to them through the short canaliculi that run out +to the surface.</p> + +<p>2. The cells within the interior of the bone receive their +nourishment from the small blood vessels in the Haversian canals. Lymph +from these vessels is conveyed to the cells through the canaliculi that +connect with the Haversian canals.</p> + +<p><hi rend="font-weight: bold">Plan and Purpose of the +Skeleton.</hi>—The framework of the body is such as to adapt it to a <hi +rend="font-style: italic">movable</hi> structure. Obviously the +different parts of the body cannot be secured to a foundation, as are +those of a stationary building, but must be arranged after a plan that +is conducive to motion. A moving structure, as a wagon or a bicycle, has +within it some strong central part to which the remainder is joined. The +same is true of the skeleton. That part to which the others are attached +is a long, bony axis, known as the <hi rend="font-style: italic">spinal +column</hi>. Certain parts, as the ribs and the skull, are attached +directly to the spinal column, while others are attached indirectly to +it. The arrangement of all the parts is such that the spinal column is +made the central, cohering portion of the skeleton and also of the whole +body.</p> + +<p>Besides the general arrangement of the parts of the skeleton, there +is such a grouping of the bones in each of its main divisions as will +enable them to serve definite purposes. In most places they form +mechanical devices for supplying special movements, and in certain +places they provide for the support or protection of important organs. +In most cases there is a definite combination of different bones, +forming what is called the bone group.</p> + +<p rend="text-align: center"> +<figure url="images/image97.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 97—The human skeleton.</head> +<figDesc>Fig. 97</figDesc> +</figure></p> + +<p><pb n="223" /><anchor id="Pg223" /><hi rend="font-weight: bold">Bone +Groups.</hi>—On account of the close relation between the bones of the +same group, they cannot profitably be studied as individual bones, but +each must be considered as a part of the group to which it belongs. By +first making out the relation of a given bone to its group, its value to +the whole body can be determined. The most important of the groups of +bones are as follows:</p> + +<p>1. <hi rend="font-style: italic">The Spinal Column.</hi>—This group +consists of twenty-four similarly shaped bones, placed one above the +other, called the <hi rend="font-style: italic">vertebræ</hi>, and two +bones found below the vertebræ, known as the sacrum and the coccyx (Fig. +98). These twenty-six bones supply the central axis of the body, support +the head and upper extremities, and inclose and protect the spinal +cord.</p> + +<p rend="text-align: center"> +<figure url="images/image98.png" rend="page-float: 'hp'; text-align: center; w40"> +<head><lb />Fig. 98—The spinal column.</head> +<figDesc>Fig. 98</figDesc> +</figure></p> + +<p>The upper seven vertebræ form the neck and are called the <hi +rend="font-style: italic">cervical</hi> vertebræ. They are smaller and +have greater freedom of motion than the others. The first and second +cervical vertebræ, known as the <hi rend="font-style: italic">atlas</hi> +and the <hi rend="font-style: italic">axis</hi>, are specially modified +to form a support for the head and provide for its movements. The head +rests upon the atlas, forming with it a hinge joint (used in nodding to +indicate "yes"); and the atlas turns upon an upward projection of the +axis forming a pivot joint (used in shaking the head to indicate +"no").</p> + +<p><pb n="224" /><anchor id="Pg224" />The next twelve vertebræ, in order below the cervical, are known as +the <hi rend="font-style: italic">thoracic</hi> vertebræ. They form the +back part of the framework of the thorax and have little freedom of +motion. The five vertebræ below the thoracic are known as the <hi +rend="font-style: italic">lumbar</hi> vertebræ. These bones are large +and strong and admit of considerable motion. Below the last lumbar +vertebra is a wedge-shaped bone which has the appearance of five +vertebræ fused together. This bone, known as the <hi rend="font-style: +italic">sacrum</hi>, connects with the large bones which form the pelvic +girdle. Attached to the lower end of the sacrum is a group of from two +to four small vertebræ, more or less fused, called the <hi +rend="font-style: italic">coccyx</hi>.</p> + +<p rend="text-align: center"> +<figure url="images/image99.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 99—<hi rend="font-weight: bold">Two views of a +lumbar vertebra.</hi> <hi rend="font-style: italic">A.</hi> From above. +<hi rend="font-style: italic">B.</hi> From the side. 1. Body. 2, 3, 4, +5. Projections from the neural arch.</head> +<figDesc>Fig. 99</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Joining of the Vertebræ.</hi>—A +typical vertebra consists of a heavy, disk-shaped portion in front, +called the <hi rend="font-style: italic">body</hi>, which is connected +with a ring-like portion behind, called the <hi rend="font-style: +italic">neural arch</hi>. The body and the neural arch together encircle +a round opening which is a part of the canal that contains the spinal +cord (Fig. 99). From the neural arch are seven bony projections, or +processes, three of which serve for the attachment of muscles and +ligaments, while the other four, two above and two below, are for the +interlocking of the vertebræ with each other. The separate vertebræ are +joined together in the spinal column, as follows:</p> + +<p><hi rend="font-style: italic">a.</hi> Between the bodies of adjacent +vertebræ are disks of elastic cartilage. Each disk is about one fourth +of an inch thick and is grown <pb n="225" /><anchor id="Pg225" />tight +onto the face of the vertebra above and also onto the face of the +vertebra below. By means of these disks a very close connection is +secured between the vertebræ on the front side of the column.</p> + +<p><hi rend="font-style: italic">b.</hi> On the back of the column, the +downward projections from the neural arch of each vertebra above fit +into depressions found in the neural arch of the vertebra below. This +<hi rend="font-style: italic">interlocking</hi> of the vertebræ, which +is most marked in the lumbar region, strengthens greatly the back +portion of the column.</p> + +<p><hi rend="font-style: italic">c.</hi> To further secure one bone upon +the other, numerous ligaments pass from vertebra to vertebra on all +sides of the column.</p> + +<p>2. <hi rend="font-style: italic">The Skull.</hi>—The skull is formed +by the close union of twenty-two irregular bones. These fall naturally +into two subgroups—the cranium and the face (Fig. 100). The <hi +rend="font-style: italic">cranium</hi> consists of eight thin, curved +bones which inclose the space, called the <hi rend="font-style: +italic">cranial cavity</hi>, that holds the brain. The <hi +rend="font-style: italic">face group</hi>, consisting of fourteen bones, +provides cavities and supports for the different organs of the face, and +supplies a movable part (the inferior maxillary) which, with the bones +above (superior maxillary), forms the machine for masticating the +food.</p> + +<p rend="text-align: center"> +<figure url="images/image100.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 100—<hi rend="font-weight: bold">The skull +(Huxley).</hi> The illustration shows most of the bones of the +skull.</head> +<figDesc>Fig. 100</figDesc> +</figure></p> + +<p>3. <hi rend="font-style: italic">The Thorax.</hi>—This group contains +twenty-four bones of similar form, called <hi rend="font-style: +italic">ribs</hi>, and a straight flat bone, called the <hi +rend="font-style: italic">sternum</hi>, or breastbone (Fig. 101). The +ribs connect with the spinal column behind, and all but the two lowest +ones connect with the sternum in front, and, by so doing, inclose the +thoracic cavity. As already stated (page 85),<pb n="226" /><anchor id="Pg226" /> the bones of the thorax form a +mechanical device, or machine, for breathing. The ribs are so arranged +that the volume of the thorax is increased by elevating them and +diminished by depressing them, enabling the air to be forced into and +out of the lungs.</p> + +<p rend="text-align: center"> +<figure url="images/image101.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 101—<hi rend="font-weight: bold">Bone groups of +trunk.</hi></head> +<figDesc>Fig. 101</figDesc> +</figure></p> + +<p>4. <hi rend="font-style: italic">The Shoulder and Pelvic +Girdles.</hi>—These groups form two bony supports—one at the upper and +the other at the lower portion of the trunk—which serve for the +attachment of the arms and legs (Fig. 101). The <hi rend="font-style: +italic">shoulder girdle</hi> is formed by four bones—two clavicles, or +collar bones, and two scapulæ, or shoulder blades. The clavicle on +either side connects with the upper end of the sternum and serves as a +<hi rend="font-style: italic">brace</hi> for the shoulder, while the +scapula forms a socket for the humerus (the large bone of the arm) and +supplies many places for the attachment of muscles.</p> + +<p>The <hi rend="font-style: italic">pelvic girdle</hi> consists of two +large bones of irregular shape, called the <hi rend="font-style: +italic">innominate</hi> bones. They connect behind with the sacrum and +in front they connect, through a small pad of cartilage, with each +other. On the inside of the girdle is a smooth, basin-shaped support for +the contents of the abdomen, but on the outside the bones are rough<pb n="227" /><anchor id="Pg227" /> and irregular and provide many +places for the attachment of muscles and ligaments. Each innominate bone +has a deep, round socket into which the end of the femur (the long bone +of the leg) accurately fits.</p> + +<p>5. <hi rend="font-style: italic">The Arm and Hand Groups.</hi>—A long +bone, the <hi rend="font-style: italic">humerus</hi>, connects the arm +with the shoulder and gives form to the upper arm. In the forearm are +two bones, the <hi rend="font-style: italic">radius</hi> and the <hi +rend="font-style: italic">ulna</hi>, which connect at one end with the +humerus and at the other with the bones of the wrist (Fig. 102).</p> + +<p rend="text-align: center"> +<figure url="images/image102.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 102—<hi rend="font-weight: bold">Bone groups of +arm and leg.</hi></head> +<figDesc>Fig. 102</figDesc> +</figure></p> + +<p>A group of eight small, round bones is found in the wrist, known as +the <hi rend="font-style: italic">carpal</hi> bones. These are arranged +in two rows and are movable upon one another. Five straight bones, the +<hi rend="font-style: italic">metacarpals</hi>, connect with the wrist +bones and form the framework for the palm of the hand. Attached to the +metacarpals are the bones of the fingers and thumb. These form an +interesting group of fourteen bones, called the <hi rend="font-style: +italic">phalanges of the fingers</hi> (Fig. 102).</p> + +<p>The bones of the hand provide a mechanical device, or machine, for +grasping, and the arm serves as a device for moving this grasping +machine from place to place. The work of the arm, in this respect, is +not unlike that of a revolving crane upon the end of which is a +grab-hook. The hand without the arm to move it about would be of little +use.</p> + +<p><pb n="228" /><anchor id="Pg228" />6. <hi rend="font-style: +italic">The Leg and Foot Groups.</hi>—These correspond in form and +arrangement to the bones of the arm and hand. Since, however, the leg +and foot are used for purposes different from those of the arm and hand, +certain differences in structure are to be found. The <hi +rend="font-style: italic">patella</hi>, or kneepan, has no corresponding +bone in the arm; and the <hi rend="font-style: italic">carpus</hi>, or +ankle, which corresponds to the wrist, contains seven instead of eight +bones. The bones of the foot and toes are the same in number as those of +the hand and fingers, but they differ greatly in size and form and have +less freedom of motion. The <hi rend="font-style: italic">femur</hi>, +which gives form to the thigh, is the longest bone of the body. The <hi +rend="font-style: italic">tibia</hi>, or shin bone, and the <hi +rend="font-style: italic">fibula</hi>, the slender bone by its side, +give form to the lower part of the leg (Fig. 102).</p> + +<p>The legs are mechanical devices (walking machines) for moving the +body from place to place. The feet serve both as supports for the body +and as levers for pushing the body forward. By their attachment to the +legs they may be placed in all necessary positions for supporting and +moving the body.</p> + +<p>The different bone groups are shown in Fig. 97 and named in Table +IV.</p> + +<p><hi rend="font-weight: bold">Adaptation to Special Needs.</hi>—When +any single bone is studied in its relation to the other members of the +group to which it belongs or with particular reference to its purpose in +the body, its adaptation to some special place or use is at once +apparent. Each bone serves some special purpose, and to this purpose it +is adapted by its form and structure. Long bones, like the humerus and +femur, are suited to giving strength, form, and stiffness to certain +parts, while irregular bones, like the vertebræ and the pelvic bones, +are fitted for supporting and protecting organs. Others, like the wrist +and ear bones, make possible a peculiar kind of motion, and still +others, like the ribs, are adapted to more than one purpose. The vast +differences in shape, size, structure, and surface among the various +bones are but the conditions that adapt them to particular forms of +service in the body.</p> + +<p><pb n="229" /><anchor id="Pg229" />TABLE IV - <hi rend="font-variant: +small-caps">The Principal Bones and their Grouping in the Body</hi></p> + +<list type="simple"> + + <item>I. AXIAL SKELETON + + <list type="simple"> + + <item>A. <hi rend="font-style: italic">Skull</hi>, 28. + + <list type="simple"> + + <item>1. Cranium, 8. + + <list type="simple"> + + <item><hi rend="font-style: italic">a.</hi> Frontal, + forehead 1</item> + + <item><hi rend="font-style: italic">b.</hi> Parietal 2</item> + + <item><hi rend="font-style: italic">c.</hi> Temporal, temple 2</item> + + <item><hi rend="font-style: italic">d.</hi> Occipital 1</item> + + <item><hi rend="font-style: italic">e.</hi> Sphenoid 1</item> + + <item><hi rend="font-style: italic">f.</hi> Ethmoid 1</item> + + </list></item> + + <item>2. Face, 14. + + <list type="simple"> + + <item><hi rend="font-style: italic">a.</hi> Inferior maxillary 1</item> + + <item><hi rend="font-style: italic">b.</hi> Superior maxillary 2</item> + + <item><hi rend="font-style: italic">c.</hi> Palatine, palate 2</item> + + <item><hi rend="font-style: italic">d.</hi> Nasal bones 2</item> + + <item><hi rend="font-style: italic">e.</hi> Vomer 1</item> + + <item><hi rend="font-style: italic">f.</hi> Inferior turbinated 2</item> + + <item><hi rend="font-style: italic">g.</hi> Lachrymal 2</item> + + <item><hi rend="font-style: italic">h.</hi> Malar, cheek bones 2</item> + + </list></item> + + <item>3. Bones of the Ears, 6. + + <list type="simple"> + + <item><hi rend="font-style: italic">a.</hi> Malleus 2</item> + + <item><hi rend="font-style: italic">b.</hi> Incus 2</item> + + <item><hi rend="font-style: italic">c.</hi> Stapes 2</item> + + </list></item> + + </list></item> + + <item>B. <hi rend="font-style: italic">Spinal Column</hi>, 26. + + <list type="simple"> + + <item>1. Cervical, or neck, vertebræ 7</item> + + <item>2. Dorsal, or thoracic, vertebræ 12</item> + + <item>3. Lumbar vertebræ 5</item> + + <item>4. Sacrum 1</item> + + <item>5. Coccyx 1</item> + + </list></item> + + <item>C. <hi rend="font-style: italic">Thorax</hi>, 25. + + <list type="simple"> + + <item>1. Ribs 24</item> + + <item>2. Sternum 1</item> + + </list></item> + + <item>D. <hi rend="font-style: italic">Hyoid</hi>, 1 (at base of tongue).</item> + + </list></item> + + <item>II. APPENDICULAR SKELETON + + <list type="simple"> + + <item>A. <hi rend="font-style: italic">Shoulder girdle</hi> 4. + + <list type="simple"> + + <item>1. Clavicle, collarbone. 2</item> + + <item>2. Scapula, shoulder blade 2</item> + + </list></item> + + <item>B. <hi rend="font-style: italic">Upper extremities</hi>, 60. + + <list type="simple"> + + <item>1. Humerus 2</item> + + <item>2. Radius 2</item> + + <item>3. Ulna 2</item> + + <item>4. Carpal, wrist bones 16</item> + + <item>5. Metacarpal 10</item> + + <item>6. Phalanges of fingers 28</item> + + </list></item> + + <item>C. <hi rend="font-style: italic">Pelvic girdle</hi>, 2. + + <list type="simple"> + + <item>1. Osinnominatum 2</item> + + </list></item> + + <item>D. <hi rend="font-style: italic">Lower extremities</hi>, 60. + + <list type="simple"> + + <item>1. Femur, thigh bone 2</item> + + <item>2. Tibia, shin bone 2</item> + + <item>3. Fibula 2</item> + + <item>4. Patella, kneepan 2</item> + + <item>5. Tarsal, ankle bones 14</item> + + <item>6. Metatarsal, instep bones 10</item> + + <item>7. Phalanges of toes 28</item> + + </list></item> + + </list></item> + +</list> + +<div> +<pb n="230" /><anchor id="Pg230" /> +<head>ARTICULATIONS</head> + +<p>Any place in the body where two or more bones meet is called an +articulation, or joint. At the place of meeting the bones are firmly +attached to each other, thereby securing the necessary coherence of the +skeleton. The large number of bones, and consequently of articulations, +are necessary for the different movements of the body and also on +account of the manner in which the skeleton develops, or grows. +Articulations are classed with reference to their freedom of motion, as +<hi rend="font-style: italic">movable</hi>, <hi rend="font-style: +italic">slightly movable</hi>, and <hi rend="font-style: +italic">immovable</hi> articulations.</p> + +<p>Most of the <hi rend="font-style: italic">immovable</hi> +articulations are found in the skull. Here irregular, tooth-like +projections from the different bones enable them to interlock with one +another, while they are held firmly together by a thin layer of +connective tissue. The wavy lines formed by articulations of this kind +are called <hi rend="font-style: italic">sutures</hi> (Fig. 100).</p> + +<p>The best examples of joints that are <hi rend="font-style: +italic">slightly</hi>, but not freely, <hi rend="font-style: +italic">movable</hi> are found in the front of the spinal column. The +cartilaginous pads between the vertebræ permit, by their elasticity, of +a slight bending of the column in different directions. These movements +are caused, not by one bone gliding over another, but by compressions +and extensions of the cartilage. Between the vertebræ in the back of the +spinal column, however, there is a slight movement of the bone surfaces +upon one another.</p> + +<p><hi rend="font-weight: bold">Structure of the Movable Joints.</hi>—By +far the most numerous and important of the joints are those that are +freely movable. Such joints are strongly constructed and endure great +strain without dislocation, and yet their parts move over each other +easily and without friction. The ends of the bones are usually enlarged +and have specially formed<pb n="231" /><anchor id="Pg231" /> projections or depressions which +fit into corresponding depressions or elevations on the bones with which +they articulate. In addition to this the articular surfaces are quite +smooth and dense, having no Haversian canals, and they are covered with +a layer of cartilage. Strong ligaments pass from one bone to the other +to hold each in its place (<hi rend="font-style: italic">A, </hi>Fig. +103). Some of these consist simply of bands, connecting the joint on its +different sides, while others form continuous sheaths around the +joint.</p> + +<p rend="text-align: center"> +<figure url="images/image103.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 103—<hi rend="font-weight: bold">Outside and +inside view of knee joint.</hi> 1. Tendons. 2. Ligaments. 3. Cartilage. +4. Space containing synovial fluid. This space is lined, except upon the +articular surfaces, by the synovial membrane.</head> +<figDesc>Fig. 103</figDesc> +</figure></p> + +<p>The interior of the joint, except where the bone surfaces rub upon +each other, is covered with a serous lining, called the <hi +rend="font-style: italic">synovial membrane</hi> (<hi rend="font-style: +italic">B</hi>, Fig. 103). This secretes a thick, viscid liquid, the <hi +rend="font-style: italic">synovial fluid</hi>, which prevents friction. +The synovial membrane does not cover the ends of the bones, but passes +around the joint and connects with the bones at their edges so as to +form a closed sac in which the fluid is retained.</p> + +<p><hi rend="font-weight: bold">Kinds of Movable Joints.—</hi>The +different kinds of movable joints are the ball and socket joint, the +hinge joint, the pivot joint, the condyloid joint, and the gliding +joint. These are constructed and admit of motion, as follows:</p> + +<p>1. In the <hi rend="font-style: italic">ball and socket</hi> joint +the ball-shaped end of one bone fits into a cup-shaped cavity in another +bone, called the socket. The best examples of such joints are<pb n="232" /><anchor id="Pg232" /> found at the hips and shoulders. +The ball and socket joint admits of motion in all directions.</p> + +<p>2. In the <hi rend="font-style: italic">hinge</hi> joint the bones +are grooved and fit together after the manner of a hinge. Hinge joints +are found at the elbows and knees and also in the fingers. The hinge +joint gives motion in but two directions—forward and backward.</p> + +<p>3. A <hi rend="font-style: italic">pivot</hi> joint is formed by the +fitting of a pivot-like projection of one bone into a ring-like +receptacle of a second bone, so that one, or the other, is free to turn. +A good example of the pivot joint is found at the elbow, where the +radius turns upon the humerus. Another example is the articulation of +the atlas with the axis vertebra as already noted. The pivot joint +admits of motion around an axis.</p> + +<p>4. The <hi rend="font-style: italic">condyloid</hi> joint is formed +by the fitting of the ovoid (egg-shaped) end of one bone into an +elliptical cavity of a second bone. Examples of condyloid joints are +found at the knuckles and where the wrist bones articulate with the +radius and ulna. They move easily in two directions, like hinge joints, +and slightly in other directions.</p> + +<p>5. <hi rend="font-style: italic">Gliding</hi> joints are formed by +the articulation of plain (almost flat) surfaces. Examples of gliding +joints are found in the articulations between the bones of the wrist and +those of the ankle. They are the simplest of the movable joints and are +formed by one bone gliding, or slipping, upon the surface of +another.</p> + +<p><hi rend="font-weight: bold">The Machinery of the Body.</hi>—A +machine is a contrivance for directing energy in doing work. A sewing +machine, for example, so directs the energy of the foot that it is made +to sew. Through its construction the machine is able to produce just +that form of motion needed for its work, and no other forms, so that +energy is not wasted in the production of useless motion. The places in +machines where parts rub or<pb n="233" /><anchor id="Pg233" /> turn upon each other are called +<hi rend="font-style: italic">bearings</hi>, and extra precautions are +taken in the construction and care of the bearings to prevent +friction.</p> + +<p>The body cannot properly be compared to any single machine, but must +be looked upon as a complex organization which employs a number of +different kinds of machines in carrying on its work. The majority of +these machines are found in the skeleton. The bones are the parts that +are moved, and the joints serve as bearings. Connected with the bones +are the muscles that supply energy, and attached to the muscles are the +nerves that control the motion. Other parts also are required for +rendering the machines of the body effective in doing work. These are +supplied by the tissues connected with the bones and the muscles.</p> +</div> + +<div> +<head>HYGIENE OF THE SKELETON</head> + +<p>Of chief concern in the hygiene of the skeleton is the proper <hi +rend="font-style: italic">adjustment</hi> of its parts. The efficiency +of any of the body machines is impaired by lack of proper adjustment. +Not only this, but because of the fact that the skeleton forms the +groundwork of the whole body—muscles, blood vessels, nerves, everything +in fact, being arranged with reference to it—any lack of proper +adjustment of the bones interferes generally with the arrangement and +work of tissues and organs. The displaced bones may even compress blood +vessels and nerves and interfere, in this way, with the nourishment and +control of organs remote from the places where the displacements occur. +For these reasons the proper adjustment of the different parts of the +skeleton supplies one of the essential conditions for preserving the +health.</p> + +<p><hi rend="font-weight: bold">Hygienic Importance of the Spinal +Column.</hi>—What has been said about the adjustment of the skeleton in +general applies with particular force to the spinal column. The spinal +column serves both as the central axis of the body and as the container +of the spinal cord. Thirty-one pairs<pb n="234" /><anchor id="Pg234" /> of nerves pass between the +vertebræ to connect the spinal cord with different parts of the body, +and two important arteries (the vertebral) pass through a series of +small openings in the bones of the neck to reach the brain. Unnatural +curves of the spine throw different parts of the body out of their +natural positions, diminish the thoracic and abdominal cavities, and, +according to the belief of certain physicians, compress the nerves that +pass from the cord to other parts of the body. Slightly misplaced +vertebræ in the neck, by compressing the vertebral arteries, may also +interfere with the supply of blood</p> + +<p rend="text-align: center"> +<figure url="images/image104.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 104—A tendency toward spinal curvature (after +Mosher)</head> +<figDesc>Fig. 104</figDesc> +</figure></p> + +<p rend="text-align: center"> +<figure url="images/image105.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 105—Effect on spinal column of improper position +in writing. (From Pyle's <hi rend="font-style: italic">Personal +Hygiene.</hi>)</head> +<figDesc>Fig. 105</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">How the Skeleton becomes +Deformed</hi>—We are accustomed to look upon the skeleton as a rigid +framework which can get out of its natural form only through severe +strain or by violence. This view is far from being correct. On account +of their necessary freedom of motion, the bones, especially those of the +spinal column, are easily slipped from their normal positions; and where +improper attitudes are frequently<pb n="235" /><anchor id="Pg235" /> assumed, or continued through +long periods of time, the skeleton gradually becomes deformed (Fig. +104). For example, the habit of always sleeping on the same side with a +high pillow may develop a bad crook in the neck; and the ugly curves, +assumed so frequently in writing <note place="foot"><p>It has been claimed that the introduction of vertical +writing has reduced the number of cases of spinal curvature originating +in the schoolroom, and statistics appear to prove the claim. It is +shown, on the other hand, that unnatural positions also are unnecessary +in the slanting system of writing, and that in either system the pupil +who is permitted to do so is liable to assume an improper position.</p></note> (Fig. 105), and also in standing, +when the weight is shifted too much on one foot, may become permanent. +Then the habit of reclining in a chair with the hips resting on the +front of the seat often deforms the back and causes a drooping of the +shoulders. In fact, slight displacements of the vertebræ come about so +easily <hi rend="font-style: italic">through incorrect positions</hi>, +that they may almost be said to "occur of themselves" where active +measures are not taken to preserve the natural form of the body. The +very few people who have perfectly formed bodies show to what an extent +has been overlooked an essential law of hygiene.</p> + +<p><hi rend="font-weight: bold">Prevention of Skeletal +Deformities.</hi>—Those deformities of the skeleton that are acquired +through improper positions are prevented by giving sufficient attention +to the positions assumed in sitting, standing, and sleeping, and also to +the posture in various kinds of work. In sitting the trunk should be +erect and the hips should touch the back of the chair. One should not +lounge in the ordinary chair. In standing the body should be erect, the +shoulders back and down, the chest pushed slightly up and forward, and +the chin slightly depressed, while the weight should, as a rule, rest +about equally on the two feet. The habit of leaning against some object +when standing (the pupil in<pb n="236" /><anchor id="Pg236" /> reciting often leans on his desk) +should be avoided. In sleeping the pillow should be of the right +thickness to support the head on a level with the spinal column and +should not be too soft. If one sleeps on his back, no pillow is +required. It is best not to acquire the habit of sleeping always on the +same side.</p> + +<p>Where one is compelled by his work to assume harmful positions, these +should be corrected by proper exercises, and by cultivating opposing +positions during the leisure hours. Much is to be accomplished through +those forms of physical exercise which develop the muscles whose work it +is to keep the body in an upright position.</p> + +<p><hi rend="font-weight: bold">School Furniture.</hi>—It has long been +observed that school children are more subject to curvature of the spine +and other deformities of the skeleton than the children who do not +attend school. While this is due largely to faulty positions assumed by +the pupils at their work, it has been suggested that the school +furniture may be in part to blame for these positions. Investigations of +this problem have shown that most of the school desks and seats in use +in our public schools are unhygienically constructed, in that they <hi +rend="font-style: italic">force</hi> pupils into unnatural positions. +School seats should support the pupil in a natural position, both in the +use of his books and in writing, and there are many arguments in favor +of the so-called "adjustable" school furniture. Fig. 106 shows the seat +and desk designed by the Boston, Mass., Schoolhouse Commission after +much study and experimenting and used in the Boston schools. This +furniture, which provides a seat adjustable for height, having a back +rest also adjustable for height, and a desk which is likewise provided +with a vertical adjustment, supplies all essential hygienic +requirements. It is to be hoped that school furniture of this character +may in the near future come into general use.</p> + +<p rend="text-align: center"> +<figure url="images/image106.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 106—Adjustable seat and desk used in schools of +Boston, Mass.</head> +<figDesc>Fig. 106</figDesc> +</figure></p> + +<p><pb n="237" /><anchor id="Pg237" /><hi rend="font-weight: +bold">Correction of Skeletal Deformities.</hi>—It is, of course, easier +to prevent deformities of the skeleton by giving attention to proper +positions, than to correct them after they have occurred. It should also +be noted that severe deformities cannot be corrected by the individual +for himself, but these must come under the treatment of specialists in +this line of medical work. In mild cases of spinal curvature, drooping +of the head, and round shoulders, the individual <hi rend="font-style: +italic">can</hi> benefit his condition. By working to "substitute a +correct attitude for the faulty one,"<note place="foot"><p>Lovett, <hi rend="font-style: italic">Lateral Curvature +of the Spine and Round Shoulders</hi>.</p></note> he can by persistence bring +about marked improvements. It is better, however, to have the advice and +aid of a physical director, where this is possible. It should also be +borne in mind that the correction of skeletal deformities requires +effort through a long period of time, especially where the deformities +are pronounced; and one lacking the will power to persist will not +secure all the results which he seeks.</p> + +<p><hi rend="font-weight: bold">"Setting Up" Exercises.</hi>—The +splendid carriage of students from military schools shows what may be +accomplished in securing erectness of form where proper attention is +given to this matter. The military student gets his fine form partly +through his exercises in handling arms, but mainly through his so-called +"setting up" drill. As a suggestion to one desiring to improve the form +of his body, a modification of the usual "setting up" drill is here +given:</p> + +<p>1. Standing erect, with the heels together, the feet at an angle of +45°, and hands at the sides, bring the arms to a horizontal position in +front, little fingers touching and nails down. From this position raise +the hands straight over the head, bringing the palms gradually together. +Then with a backward sweeping movement, return the hands again to the +sides. Repeat several times.</p> + +<p>2. With the feet as in the above exercise, bring the hands and the +arms to a level with the shoulders, palms down, elbows bent, middle +fingers of the two hands touching, and the extended thumbs touching the +chest. Keeping the palms down and the arms on a level with the<pb n="238" /><anchor id="Pg238" /> shoulders, extend the hands as +far sideward and backward as possible, returning each time to the first +position. As the hands move out, inhale deeply (through the nose), and +as they are brought back, exhale quickly (through the mouth). Repeat +several times.</p> + +<p>3. With the arms at the sides and the feet side by side and touching, +bring the hands in a circular movement to a vertical position over the +head, and lock the thumbs. Keeping the knees straight and the thumbs +locked, bend forward, letting the hands touch the ground if possible, +and then bring the body and hands again to the vertical position. Then +by a backward sweeping movement, return the hands again to the sides. +Repeat.</p> + +<p>While these exercises may be practiced whenever convenient, it is +best to set apart some special time each day for them, as on retiring at +night or on rising in the morning.</p> + +<p><hi rend="font-weight: bold">Hygienic Footwear.</hi>—A necessary aid +to erectness of position in standing and walking is a properly fitting +shoe. Heels that are too high tilt the body unnaturally forward, and +shoes that cause any kind of discomfort in walking lead to unnatural +positions in order to protect the feet. Shoes should fit snugly, being +neither too large nor too small. Many shoes, however, are unhygienically +constructed, and no attempt should be made to wear them. Certainly is +this true of styles that approach the "French heel" or the "toothpick +toe" (Fig. 107). However, many styles of shoes are manufactured that are +both hygienic and neat fitting. Rubber heels, on account of their +elasticity, are to be preferred to those made of leather.</p> + +<p rend="text-align: center"> +<figure url="images/image107.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 107—Heels and toes of unhygienic and of hygienic +footwear.</head> +<figDesc>Fig. 107</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Skeleton in Childhood and Old +Age.</hi>—Certain peculiarities are found to exist in the bones of +children and of old people which call for special care of the skeleton +during the first and last periods of life. The bones of children are +soft, lacking mineral matter, and are liable to become bent<pb n="239" /><anchor id="Pg239" /> For this reason, children who are +encouraged to walk at too early an age may bend the thigh bones, causing +the too familiar "bow-legs." These bones may also be bent by having +children sit on benches and chairs which are too high for the feet to +reach the floor, and which do not provide supports for the feet. +Wholesome food, fresh air, sunlight, and exercise are also necessary to +the proper development of the bones of children. Where these natural +conditions are lacking, as in the crowded districts of cities, children +often suffer from a disease known as "rickets," on account of which +their bones are unnaturally soft and easily bent.</p> + +<p>On account of the accumulation of mineral matter, the bones of +elderly people become brittle and are easily broken, and from lack of +vigor of the bone cells they heal slowly after such injuries occur. This +makes the breaking of a bone by an aged person a serious matter. Old +people should, as far as possible, avoid liabilities to falls, such as +going rapidly up and down stairs, or walking on icy sidewalks, and +should use the utmost care in getting about. In old people also the +cartilage between the bones softens, increasing the liability of getting +misshaped. Special attention, therefore, should be given to erectness of +form, and to such exercises as tend to preserve the natural shape of the +body.</p> + +<p><hi rend="font-weight: bold">Treatment of Fractures.</hi>—A fractured +bone always requires the aid of a surgeon, and no time should be lost in +securing his services. In the meantime the patient should be put in a +comfortable position, and the broken limb supported above the rest of +the body. Though the breaking of a bone is not, as a rule, a serious +mishap, it is necessary that the very best skill be employed in setting +it. Any failure to bring the ends of the broken bone into their +normal<pb n="240" /><anchor id="Pg240" /> relations permanently deforms the +limb and interferes with its use.</p> + +<p><hi rend="font-weight: bold">Dislocations and +Sprains.</hi>—Dislocations, if they be of the larger joints, also +require the aid of the surgeon in their reduction and sometimes in their +subsequent treatment. Simple dislocations of the finger joints, however, +may be reduced by pulling the parts until the bones can be slipped into +position.</p> + +<p><hi rend="font-style: italic">A sprain</hi>, which is an overstrained +condition of the ligaments surrounding a joint, frequently requires very +careful treatment. When the sprain is at all serious, a physician should +be called. Because of the limited supply of blood to the ligaments, they +are slow to heal, and the temptation to use the joint before it is fully +recovered is always great. Massage<note place="foot"><p>See "Hygiene of Muscles," Chapter XV.</p></note> judiciously applied to a sprained +joint, by bringing about a more rapid change in the blood and the lymph, +is beneficial both in relieving the pain, and in hastening recovery.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The skeleton, or framework +of the body, is a structure which is movable as a whole and in most of +its parts. It preserves the form of the body, protects important organs, +and supplies the mechanical devices, or machines, upon which the muscles +act in the production of motion. The skeleton is adapted to its purposes +through the number and properties of the bones, and through the +cartilage and connective tissue associated with the bones. The places +where the different bones connect one with another are known as joints, +and most of these admit of motion. The preservation of the natural form +of the skeleton is necessary, both for its proper action and for the +health of the body.</p> + +<p><pb n="241" /><anchor id="Pg241" /><hi rend="font-weight: bold">Exercises.</hi>—1. State the main +purpose of the skeleton. What is the necessity for so many bones in its +construction?</p> + +<p>2. How may the per cent of animal and of mineral matter in a bone be +determined?</p> + +<p>3. What properties are given the bones by the animal matter? What by +the mineral matter?</p> + +<p>4. Locate the bone cells. What is their special function?</p> + +<p>5. State the plan by which nourishment is supplied to the bone cells +in different parts of the bone.</p> + +<p>6. Give the uses of the periosteum.</p> + +<p>7. State the purpose of the Haversian canals. Of the canaliculi.</p> + +<p>8. Give functions of the spinal column.</p> + +<p>9. Name the different materials used in the construction of a joint +and the purpose served by each.</p> + +<p>10. Name four mechanical devices, or machines, found in the skeleton +and state the purpose served by each.</p> + +<p>11. Name one or more of the body machines not located in the +skeleton.</p> + +<p>12. Of what advantage is the peculiar shape of the lower jaw? Of the +ribs? Of the bones of the pelvic girdle?</p> + +<p>13. State the importance of preserving the natural form of the +skeleton. How are unnatural curves produced in the spinal column?</p> + +<p>14. How may slight deformities of the skeleton be corrected?</p> + +<p>15. What different systems are employed in the body in the production +of motion? What is the special function of each?</p> +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p>To obtain clear ideas of the form and functions of the bones, a +careful examination of a prepared and mounted skeleton is necessary. +Many of the bones, however, may be located and their general form made +out from the living body. Bones of the lower animals may also be studied +to advantage.</p> + +<p><hi rend="font-weight: bold">Experiments to show the Composition of +Bone.</hi>—1. Examine a slender bone, like that in a chicken's leg. Note +that it resists bending and is difficult to break. Note also that it is +elastic—that, when slightly bent, it will spring back.</p> + +<p>2. Soak such a bone over night in a mixture of one part hydrochloric +acid and four parts water. Then ascertain by bending, stretching, +and<pb n="242" /><anchor id="Pg242" /> twisting what properties the bone +has lost. The acid has dissolved out the mineral matter.</p> + +<p>3. Burn a small piece of bone in a clear gas flame, or on a bed of +coals, until it ceases to blaze and turns a white color. Can the bone +now be bent or twisted? What properties has it lost and what retained? +What substance has been removed from the bone by burning?</p> + +<p><hi rend="font-weight: bold">Observation on the Gross Structure of +Bone.</hi>—1. Procure a long, dry bone. (One that has lain out in the +field until it has bleached will answer the purpose excellently.) Test +its hardness, strength, and stiffness. Saw it in two a third of the +distance from one end, and saw the shorter piece in two lengthwise. +Compare the structure at different places. Find rough elevations on the +outside for the attachment of muscles, and small openings into the bone +for the entrance of blood vessels and nerves. Make drawings to represent +the sections.</p> + +<p>2. Procure a fresh bone from the butcher shop. Note the difference +between it and the dry bone. Examine the materials surrounding the sides +and covering the ends of the bone. Saw through the enlarged portion at +the end and examine the red marrow. Saw through the middle of the bone +and observe the yellow marrow.</p> + +<p><hi rend="font-weight: bold">To show the Minute Structure of the +Bone.</hi>—Prepare a section of bone for microscopic study as follows: +With a jeweler's saw cut as thin a slice as possible. Place this upon a +good-sized whetstone, not having too much grit, and keeping it wet rub +it under the finger, or a piece of leather, until it is thin enough to +let the light shine through. The section may then be washed and examined +with the microscope. If the specimen is to be preserved for future +study, it may be mounted in the usual way, but with <hi +rend="font-style: italic">hard</hi> balsam. Prepare and study both +transverse and longitudinal sections, making drawings. The sections +should be prepared from bones that are thoroughly dry but which have not +begun to decay.</p> + +<p><hi rend="font-weight: bold">To show the Structure of a +Joint.</hi>—Procure from a butcher the joint of some small animal (hog +or sheep). Cut it open and locate the cartilage, synovial membrane, and +ligaments. Observe the shape and surface of the rubbing parts and the +strength of the ligaments.</p> + +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="243" /><anchor id="Pg243" /> +<head>CHAPTER XV - THE MUSCULAR SYSTEM</head> + +<p>As already stated, the skeleton, the nervous system, and the muscular +system are concerned in the production of motion. The skeleton and the +nervous system, however, serve other purposes in the body, while the +muscular system is devoted exclusively to the production of motion. For +this reason it is looked upon as the special <hi rend="font-style: +italic">motor</hi> system. The muscular tissue is the most abundant of +all the tissues, forming about 41 per cent of the weight of the +body.</p> + +<p><hi rend="font-weight: bold">Properties of Muscles.</hi>—The ability +of muscular tissue to produce motion depends primarily upon two +properties—the property of irritability and the property of +contractility. <hi rend="font-style: italic">Irritability</hi> is that +property of a substance which enables it to respond to a stimulus, or to +act when acted upon. <hi rend="font-style: italic">Contractility</hi> is +the property which enables the muscle when stimulated to draw up, +thereby becoming shorter and thicker (a condition called contraction), +and when the stimulation ceases, to return to its former condition (of +relaxation). The property of contractility enables the muscles to +produce motion. Irritability is a condition necessary to their control +in the body.</p> + +<p><hi rend="font-weight: bold">Kinds of Muscular Tissue.</hi>—Three +kinds of muscular tissue are found in the body. These are known as the +<hi rend="font-style: italic">striated</hi>, or striped, muscular +tissue; the <hi rend="font-style: italic">non-striated</hi>, or plain, +muscular tissue; and the <hi rend="font-style: italic">muscular tissue +of the heart</hi>. These are made up of different kinds of muscle cells +and act in different ways to cause motion. The <pb n="244" /><anchor +id="Pg244" />striated muscular tissue far exceeds the others in amount +and forms all those muscles that can be felt from the surface of the +body. The non-striated muscle is found in the walls of the food canal, +blood vessels, air passages, and other tubes of the body; while the +muscular tissue of the heart is confined entirely to that organ.</p> + +<p><hi rend="font-weight: bold">Striated Muscle Cells.</hi>—The cells of +the striated muscles are slender, thread-like structures, having an +average length of 1-1/2 inches (35 millimeters) and a diameter of about +1/400 of an inch (60 μ). Because of their great length they are +called fibers, or fiber cells. They are marked by a number of dark, +transverse bands, or stripes, called striations,<note place="foot"><p>On account of the striations of these cells the muscles +which they form are called striated muscles.</p></note> which seem to divide +them into a number of sections, or disks (Fig. 108). A thin sac-like +covering, called the <hi rend="font-style: italic">sarcolemma</hi>, +surrounds the entire cell and just beneath this are a number of +nuclei.<note place="foot"><p>The striated muscle cells, having many nuclei, are said +to be multi-nucleated.</p></note></p> + +<p rend="text-align: center"> +<figure url="images/image108.png" rend="page-float: 'hp'; text-align: center; w40"> +<head><lb />Fig. 108—<hi rend="font-weight: bold">A striated +muscle cell</hi> highly magnified, showing striations and nuclei. +Attached to the cell is the termination of a nerve fiber.</head> +<figDesc>Fig. 108</figDesc> +</figure></p> + +<p>Within the sarcolemma are minute fibrils and a semiliquid substance, +called the <hi rend="font-style: italic">sarcoplasm</hi>. At each end +the cell tapers to a point from which the sarcolemma appears to continue +as a fine thread, and this, by attaching itself to the inclosing sheath, +holds the cell in place. Most of the muscle cells receive, at some +portion of their length, the termination of a nerve fiber. This +penetrates the sarcolemma and spreads out upon a kind of disk, having +several nuclei, known as the <hi rend="font-style: italic">end +plate</hi>.</p> + +<p><pb n="245" /><anchor id="Pg245" /><hi rend="font-weight: bold">The +"Muscle-organ."</hi>—We must distinguish between the term "muscle" as +applied to the muscular tissue and the term as applied to a working +group of muscular tissue, which is an organ. In the muscle, or +muscle-organ, is found a definite grouping of muscle fibers such as will +enable a large number of them to act together in the production of the +same movement. An examination of one of the striated muscles shows the +individual fibers to lie parallel in small bundles, each bundle being +surrounded by a thin layer of connective tissue. (See Practical Work.) +These small bundles are bound into larger ones by thicker sheaths and +these in turn may be bound into bundles of still larger size (Fig. 109). +The sheaths surrounding the fiber bundles are connected with one another +and also with the outer covering of the muscle, known as</p> + +<p rend="text-align: center"> +<figure url="images/image109.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 109—<hi rend="font-weight: bold">Diagram</hi> of +a section of a muscle, showing the perimysium and the bundles of fiber +cells.</head> +<figDesc>Fig. 109</figDesc> +</figure></p> + +<p rend="text-align: center"> +<figure url="images/image110.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 110—<hi rend="font-weight: bold">A muscle-organ +in position.</hi> The tendons connect at one end with the bones and at +the other end with the fiber cells and perimysium. (See text.)</head> +<figDesc>Fig. 110</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Perimysium.</hi>—The plan of the +muscle-organ is revealed through a study of the perimysium. This is not +limited to the surface of the muscle, as the name suggests, but properly +includes the sheaths that surround the bundles of fibers. Furthermore,<pb n="246" /><anchor id="Pg246" /> the surface perimysium and +that within the muscle are both continuous with the strong, white cords, +called <hi rend="font-style: italic">tendons</hi>, that connect the +muscles with the bones. By uniting with the bone at one end and blending +with the perimysium and fiber bundles at the other, the tendon forms a +very secure attachment for the muscle. The perimysium and the tendon are +thus the means through which the fiber cells in any muscle-organ are +made to <hi rend="font-style: italic">pull together</hi> upon the same +part of the body (Fig. 110).</p> + +<p><hi rend="font-weight: bold">Purpose of Striated Muscles.</hi>—The +striated muscles, by their attachments to the bones, supply motion to +all the mechanical devices, or machines, located in the skeleton. +Through them the body is moved from place to place and all the external +organs are supplied with such motion as they require. Because of the +attachment of the striated muscles to the skeleton, and their action +upon it, they are called <hi rend="font-style: italic">skeletal</hi> +muscles. As most of them are under the control of the will, they are +also called <hi rend="font-style: italic">voluntary</hi> muscles. They +are of special value in adapting the body to its surroundings.</p> + +<p><hi rend="font-weight: bold">Structure of the Non-striated +Muscles.</hi>—The cells of the non-striated muscles differ from those of +the striated muscles in being decidedly spindle-shaped and in having but +a single well-defined nucleus (Fig. 111). Furthermore, they have no +striations, and their connection with the nerve fibers is less marked. +They are also much smaller than the striated cells, being less than one +one-hundredth of an inch in length and one three-thousandth of an inch +in diameter.</p> + +<p>In the formation of the non-striated muscles, the cells are attached +to one another by a kind of muscle cement to form thin sheets or slender +bundles. These differ from the striated muscles in several particulars. +They are of a pale, whitish color, and they have no tendons. Instead +of<pb n="247" /><anchor id="Pg247" /> being attached to the bones, they +usually form a distinct layer in the walls of small cavities or of tubes +(Fig. 111). Since they are controlled by the part of the nervous system +which acts independently of the will, they are said to be <hi +rend="font-style: italic">involuntary</hi>. They contract and relax +slowly.</p> + +<p rend="text-align: center"> +<figure url="images/image111.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 111—<hi rend="font-weight: bold">Non-striated +muscle cells.</hi> <hi rend="font-style: italic">A.</hi> Cross section +of small artery magnified, showing (1) the layer of non-striated cells. +<hi rend="font-style: italic">B.</hi> Three non-striated cells highly +magnified.</head> +<figDesc>Fig. 111</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Work of the Non-striated +Muscles.</hi>—The work of the non-striated muscles, both in purpose and +in method, is radically different from that of the striated. They do not +change the <hi rend="font-style: italic">position</hi> of parts of the +body, as do the striated muscles, but they alter the <hi +rend="font-style: italic">size</hi> and <hi rend="font-style: +italic">shape</hi> of the parts which they surround. Their purpose, as a +rule, is to move, or control the movement of, materials within cavities +and tubes, and they do this by means of the <hi rend="font-style: +italic">pressure</hi> which they exert. Examples of their action have +already been studied in the propulsion of the food through the +alimentary canal and in the regulation of the flow of blood through the +arteries (pages 159 and 49). While they do not contract so quickly, nor +with such great force as the striated muscles, their work is more +closely related to the vital processes.</p> + +<p><hi rend="font-weight: bold">Structure of the Heart Muscle.</hi>—The +cells of the heart combine the structure and properties of the striated +and the non-striated muscle cells, and form an intermediate type between +the two. They are cross-striped like the striated cells, and are nearly +as wide, but are rather short (Fig. 112). Each cell has a well-defined +nucleus, but the sarcolemma is absent. They are placed end to end to +form fibers, and<pb n="248" /><anchor id="Pg248" /> many of the cells have branches +by which they are united to the cells in neighboring fibers. In this way +they interlace more or less with each other, but are also cemented +together. They contract quickly and with great force, but are not under +control of the will. Muscular tissue of this variety seems excellently +adapted to the work of the heart.</p> + +<p rend="text-align: center"> +<figure url="images/image112.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 112—<hi rend="font-weight: bold">Muscle cells +from the heart</hi>, highly magnified (after Schäfer).</head> +<figDesc>Fig. 112</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Muscular Stimulus.</hi>—The +inactive, or resting, condition of a muscle is that of relaxation. It +does work through contracting. It becomes active, or contracts, only +when it is being acted upon by some force outside of itself, and it +relaxes again when this force is withdrawn. Any kind of force which, by +acting on muscles, causes them to contract, is called a <hi +rend="font-style: italic">muscular stimulus</hi>. Electricity, chemicals +of different kinds, and mechanical force may be so applied to the +muscles as to cause them to contract. These are <hi rend="font-style: +italic">artificial</hi> stimuli. So far as known, muscles are stimulated +<hi rend="font-style: italic">naturally</hi> in but one way. This is +through the nervous system. The nervous system supplies a stimulus +called the <hi rend="font-style: italic">nervous impulse</hi>, which +reaches the muscles by the nerves, causing them to contract. By means of +nervous impulses, all of the muscles (both voluntary and involuntary) +are made to contract as the needs of the body for motion require.</p> + +<p><hi rend="font-weight: bold">Energy Transformation in the +Muscle.</hi>—The muscle serves as a kind of engine, doing work by the +transformation of potential into kinetic energy. Evidences of this are +found in the changes that accompany contraction. Careful study shows +that during any period of contraction oxygen and food materials are +consumed, waste products, such as carbon dioxide, are produced, and heat +is<pb n="249" /><anchor id="Pg249" /> liberated. Furthermore, the <hi +rend="font-style: italic">blood supply to the muscle</hi> is such that +the materials for providing energy may be carried rapidly to it and the +products of oxidation as rapidly removed. Blood vessels penetrate the +muscles in all directions and the capillaries lie very near the +individual cells (Fig. 113). Provision is made also, through the nervous +system, for <hi rend="font-style: italic">increasing</hi> the blood +supply when the muscle is at work. From these facts, as well as from the +great force with which the muscle contracts, one must conclude that the +muscle is a <hi rend="font-style: italic">transformer of +energy</hi>—that within its protoplasm, chemical changes take place +whereby the potential energy of oxygen and food is converted into the +kinetic energy of motion.</p> + +<p rend="text-align: center"> +<figure url="images/image113.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 113—<hi rend="font-weight: +bold">Capillaries</hi> of muscles.</head> +<figDesc>Fig. 113</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Plan of Using Muscular Force.</hi>—Two +difficulties have to be overcome in the using of muscular force in the +body. The first of these is due to the fact that the muscles exert their +force <hi rend="font-style: italic">only when they contract</hi>. They +can pull but not push. Hence, in order to bring about the opposing +movements<note place="foot"><p>Every movement in the body has its opposing movement. +This is necessary both on account of the work to be accomplished and for +preserving the natural form of the body.</p></note> of the body, each muscle must work against some force that +produces a result directly opposite to that which the muscle produces. +Some of the muscles (those of breathing) work against the elasticity of +certain parts of the body; others (those that hold the body in an +upright position), to some extent against gravity; and others<pb n="250" /><anchor id="Pg250" /> (the non-striated muscle in +arteries), against pressure. But in most cases, <hi rend="font-style: +italic">muscles work against muscles</hi>.</p> + +<p rend="text-align: center"> +<figure url="images/image114.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 114—<hi rend="font-weight: bold">The muscle +pair</hi> that operates the forearm. For names of these muscles, see +Fig. 119.</head> +<figDesc>Fig. 114</figDesc> +</figure></p> + +<p>The striated, or skeletal, muscles are nearly all arranged after the +last-named plan. As a rule a pair of muscles is so placed, with +reference to a joint, that one moves the part in one direction, and the +other moves it in the opposite direction. From the kinds of motion which +the various muscle pairs produce, they are classified as follows:</p> + +<p>1. <hi rend="font-style: italic">Flexors and Extensors.</hi>—The +flexor muscles bend and the extensors straighten joints (Fig. 114).</p> + +<p>2. <hi rend="font-style: italic">Adductors and Abductors.</hi>—The +adductors draw the limbs into positions parallel with the axis of the +body and the abductors draw them away.</p> + +<p>3. <hi rend="font-style: italic">Rotators</hi> (two kinds).—The +rotators are attached about pivot joints and bring about twisting +movements.</p> + +<p>4. <hi rend="font-style: italic">Radiating and Sphincter Muscles. +</hi>—The radiating muscles open and the sphincter muscles close the +natural openings of the body, such as the mouth.</p> + +<p>The pupil should locate examples of the different kinds of muscle +pairs in his own body.</p> + +<p><hi rend="font-weight: bold">Exchange of Muscular Force for +Motion.</hi>—The second difficulty to be overcome in the use of muscular +force in the body is due to the fact that the muscles contract through +<hi rend="font-style: italic">short</hi> distances, while it is +necessary for most of them to move portions of the body through <hi +rend="font-style: italic">long</hi> distances. It may be easily shown +that the longest muscles of the body do not shorten more than three or +four inches during<pb n="251" /><anchor id="Pg251" /> contraction. To bring about the +required movements of the body, which in some instances amount to four +or five feet, requires that a large proportion of the muscular force be +exchanged for motion. The machines of the skeleton, while providing for +motion in definite directions, also provide the means whereby <hi +rend="font-style: italic">strong forces</hi>, acting through <hi +rend="font-style: italic">short distances</hi>, are made to produce +movements of <hi rend="font-style: italic">less force</hi>, through <hi +rend="font-style: italic">long distances</hi>. The mechanical device +employed for this purpose is known as</p> + +<p><hi rend="font-weight: bold">The Lever.</hi>—The lever may be +described as a stiff bar which turns about a fixed point of support, +called the <hi rend="font-style: italic">fulcrum</hi>. The force applied +to the bar to make it turn is called the <hi rend="font-style: +italic">power</hi>, and that which is lifted or moved is termed the <hi +rend="font-style: italic">weight</hi>. The weight, the power, and the +fulcrum may occupy different positions along the bar and this gives rise +to the three kinds of levers, known as levers of the first class, the +second class, and the third class (Fig. 115). In levers of the <hi +rend="font-style: italic">first class</hi> the fulcrum occupies a +position somewhere between the power and the weight. In the <hi +rend="font-style: italic">second class</hi> the weight is between the +fulcrum and the power. In the <hi rend="font-style: italic">third +class</hi> the power is between the fulcrum and the weight.</p> + +<p rend="text-align: center"> +<figure url="images/image115.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 115—<hi rend="font-weight: bold">Classes of +levers. I.</hi> Two levers of first class showing fulcrums in different +positions. II. Lever of second class. III. Lever of third class. <hi +rend="font-style: italic">F.</hi> Fulcrum. <hi rend="font-style: +italic">P.</hi> Power. <hi rend="font-style: italic">W.</hi> Weight. <hi +rend="font-style: italic">a.</hi> Power-arm. <hi rend="font-style: +italic">b.</hi> Weight-arm.</head> +<figDesc>Fig. 115</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Application to the Body.</hi>—In the +body the bones serve as levers; the turning points, or fulcrums, are +found at the joints; the muscles supply the power; and parts of the<pb n="252" /><anchor id="Pg252" /> body, or things to be lifted, +serve as weights. For these levers to <hi rend="font-style: +italic">increase</hi> the motion of the muscles, it is necessary that +the muscles be attached to the bones <hi rend="font-style: italic">near +the joints</hi>, and that the parts to be moved be located at some +distance from the joints. In other words the (muscle) power-arm must be +<hi rend="font-style: italic">shorter</hi> than the (body) +weight-arm.<note place="foot"><p>The distance from the fulcrum to the power is called the +<hi rend="font-style: italic">power-arm</hi> and the distance from the +fulcrum to the weight is called the <hi rend="font-style: +italic">weight-arm</hi> (Fig. 115).</p></note></p> + +<p>Examining Fig. 116, it is seen that the distances moved by the power +and weight vary as their respective distances from the fulcrum. That is +to say, if the weight is twice as far from the fulcrum as the power, it +will move through twice the distance, and if three times as far, through +three times the distance. Thus the muscles, by acting through short +distances (on the short arms of levers), are able to move portions of +the body (located on the long arms) through long distances. Can all +three classes of levers be used in this way in the body?</p> + +<p rend="text-align: center"> +<figure url="images/image116.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 116—<hi rend="font-weight: bold">Motion +producing levers.</hi> Diagrams show relative distances moved by the +power and weight in levers having the power nearer the fulcrum than is +the weight. <hi rend="font-style: italic">F.</hi> Fulcrum. <hi +rend="font-style: italic">P, P'.</hi> Power. <hi rend="font-style: +italic">W, W'.</hi> Weight.</head> +<figDesc>Fig. 116</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Classes of Levers found in the +Body.</hi>—Practically all of the levers of the body belong either to +the first class or the third class. In both of these the muscle power +can be applied to the short arm of the lever, thereby moving the body +weight through a longer distance than the muscle contracts (Fig. 116). +In the levers of the second class, however, the weight occupies this +position, being situated <hi rend="font-style: italic">between</hi> the +power and fulcrum (Fig. 117). The weight,<pb n="253" /><anchor id="Pg253" /> therefore, <hi rend="font-style: +italic">cannot</hi> move farther than the power in this lever. It must +always move a shorter distance. While such a lever is of great advantage +in lifting heavy weights outside of the body, it cannot be used for +increasing the motion of the muscles. For this reason no well-defined +levers of the second class are present in the body.<note place="foot"><p>The foot in lifting the body on tiptoe appears at first +thought to be a lever of the second class, the body being the weight and +the toe serving as the fulcrum. However, if the distance which the body +is raised is compared with the distance which the muscle shortens, it is +found that the <hi rend="font-style: italic">supposed</hi> weight has +moved <hi rend="font-style: italic">farther</hi> than the power (Fig. +118). It will also be noted that the muscle which furnishes the power is +attached at its upper end to the "weight." These facts show clearly that +we are not here dealing with a lever of the second class. The foot in +this instance acts as a lever of the first class with the fulcrum at the +ankle joint and the toe pressing against the earth, which is the <hi +rend="font-style: italic">actual</hi> weight. Since the earth is +immovable, the body is lifted or pushed upward, somewhat as a fulcrum +support is made to move when it is too weak to hold up the weight that +is being lifted. In other words, we have the same lever action in the +foot in lifting the body as we have when one lies face downward, and, +bending the knee, lifts some object on the toes.</p></note></p> + +<p rend="text-align: center"> +<figure url="images/image117.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 117—<hi rend="font-weight: bold">Weight lifting +levers.</hi> Diagrams show relative distances moved by the power and +weight in levers having the weight nearer the fulcrum than is the power. +<hi rend="font-style: italic">F.</hi> Fulcrum. <hi rend="font-style: +italic">P, P'.</hi> Power. <hi rend="font-style: italic">W, W'.</hi> +Weight.</head> +<figDesc>Fig. 117</figDesc> +</figure></p> + +<p rend="text-align: center"> +<figure url="images/image118.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 118—<hi rend="font-weight: bold">Diagram of the +foot lever.</hi> <hi rend="font-style: italic">F.</hi> Fulcrum at ankle +joint. <hi rend="font-style: italic">W.</hi> Body weight expressed as +pressure against the earth. While the muscle power acts through the +distance <hi rend="font-style: italic">ab</hi>, the fulcrum support +(body) is forced through the distance <hi rend="font-style: +italic">FE</hi>.</head> +<figDesc>Fig. 118</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Loss of Muscular Force.</hi>—Using a +small spring balance for measuring the power, a light stick for a lever, +and a small piece of metal for a weight, and arranging these to +represent some lever of the body (as the<pb n="254" /><anchor id="Pg254" /> forearm), it is easily shown that +the gain in motion causes a corresponding loss in muscular power. (See +Practical Work.) If, for example, the balance is attached two inches +from the fulcrum and the weight twelve inches, the pull on the balance +is found to be six times greater than the weight that is being lifted. +If other positions are tried, it is found that the power exerted in each +case is as many times greater than the weight as the weight-arm is times +longer than the power-arm.</p> + +<p>Applying this principle to the levers of the body, it is seen that +the gain in motion is at the expense of muscular force, or, as we say, +<hi rend="font-style: italic">muscular force is exchanged for +motion</hi>. This exchange is greatly to the advantage of the body; for +while the ability to lift heavy weights is important, the ability to +move portions of the body rapidly and through long distances is much +more to be desired.</p> + +<p><hi rend="font-weight: bold">Important Muscles.</hi>—There are about +five hundred separate muscles in the body. These vary in size, shape, +and plan of attachment, to suit their special work. Some of those that +are prominent enough to be felt at the surface are as follows:</p> + +<p><hi rend="font-style: italic">Of the head</hi>: The <hi +rend="font-style: italic">temporal</hi>, in the temple, and the <hi +rend="font-style: italic">masseter</hi>, in the cheek. These muscles are +attached to the lower jaw and are the chief muscles of mastication.</p> + +<p><hi rend="font-style: italic">Of the neck</hi>: The <hi +rend="font-style: italic">sterno-mastoids</hi>, which pass between the +mastoid processes, back of the ears, and the upper end of the sternum. +They assist in turning the head and may be felt at the sides of the neck +(Fig. 119).</p> + +<p><hi rend="font-style: italic">Of the upper arm</hi>: The <hi +rend="font-style: italic">biceps</hi> on the front side, the <hi +rend="font-style: italic">triceps</hi> behind, and the <hi +rend="font-style: italic">deltoid</hi> at the upper part of the arm +beyond the projection of the shoulder.</p> + +<p rend="text-align: center"> +<figure url="images/image119.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 119—Back and front views of important muscles.</head> +<figDesc>Fig. 119</figDesc> +</figure></p> + +<p><hi rend="font-style: italic">Of the forearm</hi>: The <hi +rend="font-style: italic">flexors</hi> of the fingers, on the front<pb n="256" /><anchor id="Pg256" /> side, and the <hi +rend="font-style: italic">extensors</hi> of the fingers, on the back of +the forearm (Fig. 119).</p> + +<p><hi rend="font-style: italic">Of the hand</hi>: The <hi +rend="font-style: italic">adductor pollicis</hi> between the thumb and +the palm.</p> + +<p><hi rend="font-style: italic">Of the trunk</hi>: The <hi +rend="font-style: italic">pectoralis major</hi>, between the upper front +part of the thorax and the shoulder; the <hi rend="font-style: +italic">trapezius</hi>, between the back of the shoulders and the spine; +the <hi rend="font-style: italic">rectus abdominis</hi>, passing over +the abdomen from above downward; and the <hi rend="font-style: +italic">erector spinæ</hi>, found in the small of the back.</p> + +<p><hi rend="font-style: italic">Of the hips</hi>: The <hi +rend="font-style: italic">glutens maximus</hi>, fastened between the +lower back part of the hips and the upper part of the femur.</p> + +<p><hi rend="font-style: italic">Of the upper part of the leg</hi>: The +<hi rend="font-style: italic">rectus femoris</hi>, the large muscle on +the front of the leg which connects at the lower end with the +kneepan.</p> + +<p><hi rend="font-style: italic">Of the lower leg</hi>: The <hi +rend="font-style: italic">tibialis anticus</hi> on the front side, +exterior to the tibia, and the <hi rend="font-style: +italic">gastrocnemius</hi>, the large muscle in the calf of the leg. +This is the largest muscle of the body, and is connected with the heel +bone by the <hi rend="font-style: italic">tendon of Achilles</hi> (Fig. +119).</p> + +<p>The use of these muscles is, in most instances, easily determined by +observing the results of their contraction.</p> + +<div> +<head>HYGIENE OF THE MUSCLES</head> + +<p>The hygiene of the muscles is almost expressed by the one word <hi +rend="font-style: italic">exercise</hi>. It is a matter of everyday +knowledge that the muscles are developed and strengthened by use, and +that they become weak, soft, and flabby by disuse. The effects of +exercise are, however, not limited to the large muscles attached to the +skeleton, but are apparent also upon the involuntary muscles, whose work +is so closely related to the vital processes. While it is true that +exercise cannot be applied directly to the involuntary muscles, it is +also true that exercise of the voluntary muscles causes<pb n="257" /><anchor id="Pg257" /> a greater activity on the part of +those that are involuntary and is indirectly a means of exercising +them.</p> + +<p><hi rend="font-weight: bold">Exercise and Health.</hi>—In addition to +its effects upon the muscles themselves, exercise is recognized as one +of the most fundamental factors in the preservation of the health. +Practically every process of the body is stimulated and the body as a +whole invigorated by exercise properly taken. On the other hand, a lack +of exercise has an effect upon the entire body somewhat similar to that +observed upon a single muscle. It becomes weak, lacks energy, and in +many instances actually loses weight when exercise is omitted. This +shows exercise to supply an actual need and to be in harmony with the +nature and plan of the body.</p> + +<p><hi rend="font-weight: bold">How Exercise benefits the Body.</hi>—In +accounting for the healthful effects of exercise, it must be borne in +mind that the body is essentially a motion-producing structure. +Furthermore, its plan is such that the movements of its different parts +aid indirectly the vital processes. The student will recall instances of +such aid, as, for example, the assistance rendered by muscular +contractions in the circulation of the blood and lymph, due to the +valves in veins and lymph vessels, and the assistance rendered by +abdominal movements in the propulsion of materials through the food +canal. A fact not as yet brought out, however, is that <hi +rend="font-style: italic">exercise stimulates nutritive changes in the +cells</hi>, thereby imparting to them new vigor and vitality. While this +effect of exercise cannot be fully accounted for, two conditions that +undoubtedly influence it are the following:</p> + +<p>1. Exercise causes the blood to circulate more rapidly.</p> + +<p>2. Exercise increases the movement of the lymph through the lymph +vessels.</p> + +<p>The increase in the flow of the blood and the lymph<pb n="258" /><anchor id="Pg258" /> causes changes to take place more +rapidly in the liquids around the cells, thereby increasing the supply +of food and oxygen, and hastening the removal of waste.</p> + +<p><hi rend="font-weight: bold">One should plan for Exercise.</hi>—Since +exercise is demanded by the nature and plan of the body, to neglect it +is a serious matter. People do not purposely omit exercise, but from +lack of time or from its interference with the daily routine of duties, +the needed amount is frequently not taken. Especially is this true of +students and others who follow sedentary occupations. People of this +class should plan for exercise as they plan for the other great needs of +the body—food, sleep, clothing, etc. It is only by making a sufficient +amount of muscular work or play a regular part of the daily program that +the needs of the body for exercise are adequately supplied.</p> + +<p><hi rend="font-weight: bold">Amount and Kind of Exercise.</hi>—The +amount of exercise required varies greatly with different individuals, +and definite recommendations cannot be made. For each individual also +the amount should vary with the physical condition and the other demands +made upon the energy. One in health should exercise sufficiently to keep +the muscles firm to the touch and the body in a vigorous condition.</p> + +<p>Of the many forms of exercise from which one may choose, the question +is again one of individual adaptability and convenience. While the +different forms of exercise vary in their effects and may be made to +serve different purposes, the consideration of these is beyond the scope +of an elementary text. As a rule one will not go far wrong by following +his inclinations, observing of course the conditions under which +exercise is taken to the best advantage.</p> + +<p><hi rend="font-weight: bold">General Rules for Healthful +Exercise.</hi>—That exercise may secure the best results from the +standpoint of health, a number of conditions should be observed: 1. It +should<pb n="259" /><anchor id="Pg259" /> not be excessive or carried to +the point of exhaustion. Severe physical exercise is destructive to both +muscular and nervous tissues. 2. It should, if possible, be of an +interesting nature and taken in the open air. 3. It should be +counter-active, that is, calling into play those parts of the body that +have not been used during the regular work.<note place="foot"><p><hi rend="font-style: italic">Walking</hi> is considered +one of the very best forms of counter-active exercise for the brain +worker (page 328).</p></note> 4. It should be directed +toward the weak rather than toward the strong parts of the body. 5. When +one is already tired from study, or other work, it should be taken with +moderation or omitted for the time being. (For exercise of the heart +muscle and the muscular coat of the blood vessels see pages 55 and +57.)</p> + +<p><hi rend="font-weight: bold">Massage.</hi>—In lieu of exercise taken +in the usual way, similar effects are sometimes obtained by a systematic +rubbing, pressing, stroking, or kneading of the skin and the muscles by +one trained in the art. This process, known as massage, may be gentle or +vigorous and is subject to a variety of modifications. Massage is +applied when one is unable to take exercise, on account of disease or +accident, and also in the treatment of certain bodily disorders. A weak +ankle, wrist, or other part of the body, or even a bruise, may be +greatly benefited by massage. The flow of blood and lymph is stimulated, +causing new materials to be passed to the affected parts and waste +materials to be removed. Massage, however, should never be applied to a +boil, or other infected sore. The effect in this case would be to spread +the infection and increase the trouble.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—Motion is provided for in +the body mainly through the muscle cells. These are grouped into working +parts, called muscles, which in turn are attached to the movable parts +of the body. The striated muscles, as a<pb n="260" /><anchor id="Pg260" /> rule, are attached to the +mechanical devices found in the skeleton, and bring about the voluntary, +movements. The non-striated muscles surround the parts on which they +act, and produce involuntary movements. Both, however, are under the +control of the nervous system. To bring about the opposing movements of +the body, the striated muscles are arranged in pairs; and to increase +their motion, the bones are used as levers. Physical exercise is +necessary both for the development of the muscles and for the health and +vigor of the entire body.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. Compare the striated +and non-striated muscles with reference to structure, location, and +method of work.</p> + +<p>2. In what respects is the muscular tissue of the heart like the +striated, and in what respects like the non-striated, muscular +tissue?</p> + +<p>3. If muscles could push as well as pull, would so many be needed in +the body? Why?</p> + +<p>4. Locate muscles that work to some extent against elasticity and +gravity.</p> + +<p>5. Locate five muscles that act as flexors; five that act as +extensors; two that act as adductors; and two as abductors. Locate +sphincter and radiating muscles.</p> + +<p>6. By what means does the nervous system control the muscles?</p> + +<p>7. Give proofs of the change of potential into kinetic energy during +muscular contraction.</p> + +<p>8. Define the essential properties of muscular tissue and state the +purpose served by each.</p> + +<p>9. Describe a lever. For what general purpose are levers used in the +body? What other purpose do they serve outside of the body?</p> + +<p>10. Why are levers of the second class not adapted to the work of the +body?</p> + +<p>11. Name the class of lever used in bending the elbow; in +straightening the elbow; in raising the knee; in elevating the toes; and +in biting. Why is one able to bite harder with the back teeth than with +the front ones when the same muscles are used in both cases?</p> + +<p>12. Measure the distance from the middle of the palm of the hand to +the center of the elbow joint. Find the attachment of the tendon of the +biceps muscle to the radius and measure its distance to the<pb n="261" /><anchor id="Pg261" /> center of the elbow joint. From +these distances calculate the force with which the biceps contracts in +order to support a weight of ten pounds on the palm of the hand.</p> + +<p>13. How does exercise benefit the health? How does a short walk +"clear the brain" and enable one to study to better advantage?</p> + +<p>14. When exercisers taken for its effects upon the health, what +conditions should be observed?</p> +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p>The reddish muscle found in a piece of beef is a good example of +striated muscle. The clear ring surrounding the intestine of a cat +(shown by cross section) and the outer portion of the preparation from +the cow's stomach, sold at the butcher shop under the name of <hi +rend="font-style: italic">tripe</hi>, are good examples of non-striated +muscular tissue. The heart of any animal, of course, shows the heart +muscle.</p> + +<p><hi rend="font-weight: bold">To show the Structure of Striated +Muscle.</hi>—Boil a tough piece of beef, as a cut from the neck, until +the connective tissue has thoroughly softened. Then with some pointed +instrument, separate the main piece into its fiber bundles and these in +turn into their smallest divisions. The smallest divisions obtainable +are the muscle cells or fibers.</p> + +<p><hi rend="font-weight: bold">To show Striated Fibers.</hi>—Place a +small muscle from the leg of a frog in a fifty-per-cent solution of +alcohol and leave it there for half a day or longer. Then cover with +water on a glass slide, and with a couple of fine needles tease out the +small muscle threads. Protect with a cover glass and examine with a +microscope, first with a low and then with a high power. The striations, +sarcolemma, and sometimes the nuclei and nerve plates, may be +distinguished in such a preparation.</p> + +<p><hi rend="font-weight: bold">To show Non-striated Cells.</hi>—Place +a clean section of the small intestine of a cat in a mixture of one part +of nitric acid and four parts of water and leave for four or five hours. +Thoroughly wash out the acid with water and separate the muscular layer +from the mucous membrane. Cover a small portion of the muscle with water +on a glass slide and tease out, with needles, until it is as finely +divided as possible. Examine with a microscope, first with a low and +then with a high power. The cells appear as very fine, spindle-shaped +bodies.</p> + +<p><hi rend="font-weight: bold">To illustrate Muscular Stimulus and +Contraction.</hi>—Separate the muscles at the back of the thigh of a +frog which has just been killed and draw the large sciatic nerve to the +surface. Cut this as high up as possible and, with a sharp knife and a +small pair of scissors, dissect it<pb n="262" /><anchor id="Pg262" /> +out to the knee. Now cut out entirely the large muscle of the calf of +the leg (the gastrocnemius), but leave attached to it the nerve, the +lower tendon, and the bones of the knee. Mount on an upright support, as +shown in Fig. 120, and fasten the tendon to a lever below by a thread or +small wire hook:</p> + +<p rend="text-align: center"> +<figure url="images/image120.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 120—<hi rend="font-weight: bold">Apparatus</hi> +for demonstrating properties of muscles.</head> +<figDesc>Fig. 120</figDesc> +</figure></p> + +<p>1. Lay the nerve over the ends of the wires from a small battery +which are attached to the support at <hi rend="font-style: +italic">A</hi>, and arrange a second break in the circuit at <hi +rend="font-style: italic">B</hi>. At this place the battery circuit is +made and broken either by a telegraph key or by simply touching and +separating the wires. Note that the muscle gives a single contraction, +or twitch, both when the current is made and when it is broken.</p> + +<p>2. Remove the current and pinch the end of the nerve, noting the +result. With very fine wires, connect the battery directly to the ends +of the muscle. Stimulate by making and breaking the current as before. +In this experiment the muscle cells are stimulated by the direct action +of the current and not by the current acting on the nerve.</p> + +<p>3. With the wires attached to either the muscle or the nerve, make +and break the current in rapid succession. This causes the muscle to +enter into a second contraction before it has relaxed from the first, +and if the shocks follow in rapid succession, to continue in the +contracted state. This condition, which represents the method of +contraction of the muscles in the body, is called <hi rend="font-style: +italic">tetanus</hi>.</p> + +<p>NOTE.—In these experiments a twitching of the muscle is frequently +observed when no stimulus is being applied. This is due to the drying +out of the nerve and is prevented by keeping it wet with a physiological +salt solution. (See footnote, page 38.)</p> + +<p><hi rend="font-weight: bold">To show the Action of Levers.</hi>—With +a light but stiff wooden bar, a spring balance, and a wedge-shaped +fulcrum, show:</p> + +<p>1. The position of the weight, the fulcrum, and the power in the +different classes of levers, and also the weight-arm and the power-arm +in each case.</p> + +<p>2. The direction moved by the power and the weight respectively in +the use of the different classes of levers.</p> + +<p>3. That when the power-arm and weight-arm are equal, the power equals +the weight and moves through the same distance.</p> + +<p><pb n="263" /><anchor id="Pg263" />4. That when the power-arm is longer than the weight-arm, +the weight is greater, but moves through a shorter distance than the +power.</p> + +<p>5. That when the weight-arm is longer than the power-arm, the power +is greater and moves through a shorter distance than the weight.</p> + +<p><hi rend="font-weight: bold">To show the Loss of Power in the Use of +the Body Levers.</hi>—Construct a frame similar to, but larger than, +that shown in Fig. 120, (about 12 inches high), and hang a small spring +balance (250 grams capacity) at the place where the muscle is attached. +Fasten the end of a lever to the upright piece, at a point on a level +with the end of the balance hook. (The nail or screw used for this +purpose must pass loosely through the lever, and serve as a pivot upon +which it can turn.) The lever should consist of a light piece of wood, +and should have a length at least three times as great as the distance +from the hook to the turning point. Connect the balance hook with the +lever by a thread or string, and then hang upon it a small body of known +weight. Note the amount of force exerted at the balance in order to +support the weight at different places on the lever. At what point is +the force just equal to the weight? Where is it twice as great? Where +three times? Show that the force required to support the weight +increases proportionally as the weight-arm and as the distance through +which the weight may be moved by the lever. Apply to the action of the +biceps muscle in lifting weights on the forearm.</p> + +<p><hi rend="font-weight: bold">A Study of the Action of the Biceps +Muscle.</hi>—Place the fingers upon the tendon of the biceps where it +connects with the radius of the forearm. With the forearm resting upon +the table, note that the tendon is somewhat loose and flaccid, but that +with the slightest effort to raise the forearm it quickly tightens. Now +transfer the fingers to the body of the muscle, and sweep the forearm +through two or three complete movements, noting the changes in the +length and thickness of the muscle. Lay the forearm again on the table, +back of hand down, and place a heavy weight (a flatiron or a hammer) +upon the hand. Note the effort required to raise the weight, and then +shift it along the arm. Observe that the nearer it approaches the elbow +the lighter it seems. Account for the difference in the effort required +to raise the weight at different places. Does the effort vary as the +distance from the tendon?</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="264" /><anchor id="Pg264" /> +<head>CHAPTER XVI - THE SKIN</head> + +<p>Protective coverings are found at all the exposed surfaces of the +body. These vary considerably at different places, each being adapted to +the conditions under which it serves. The most important ones are the +<hi rend="font-style: italic">skin</hi>, which covers the entire +external surface of the body; the <hi rend="font-style: italic">mucous +membrane</hi>, which lines all the cavities that communicate by openings +with the external surface; and the <hi rend="font-style: italic">serous +membrane</hi>, which, including the synovial membranes, lines all the +closed cavities of the body. In addition to the protection which it +affords, the skin is one of the means by which the body is brought into +proper relations with its surroundings. It is because of this function +that we take up the study of the skin at this time.</p> + +<p><hi rend="font-weight: bold">The Skin</hi> is one of the most complex +structures of the body, and serves several distinct purposes. It is +estimated to have an area of from 14 to 16 square feet, and to have a +thickness which varies from less than one eighth to more than one fourth +of an inch. It is thickest on the palms of the hands and the soles of +the feet, the places where it is most subject to wear. It is made up of +two distinct layers—an outer layer called the <hi rend="font-style: +italic">epidermis</hi>, or cuticle, and an inner layer called the <hi +rend="font-style: italic">dermis</hi>, or cutis vera (Fig. 121).</p> + +<p><hi rend="font-weight: bold">The Dermis.</hi>—This is the thicker and +heavier of the two layers, and is made up chiefly of connective tissue. +The network of tough fibers which this tissue supplies, <pb n="265" +/><anchor id="Pg265" /> forms the essential body of the dermis and gives +to it its power of resistance. It is on account of the connective tissue +that the skins of animals can be converted into leather by tanning. A +variety of structures, including blood and lymph vessels, oil and +perspiratory glands, hair follicles, and nerves, are found embedded in +the connective tissue (Fig. 122). These aid in different ways in the +work of the skin.</p> + +<p rend="text-align: center"> +<figure url="images/image121.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 121—<hi rend="font-weight: bold">Section of +skin</hi> magnified, <hi rend="font-style: italic">a, b.</hi> Epidermis, +<hi rend="font-style: italic">b.</hi> Pigment layer. <hi +rend="font-style: italic">c.</hi> Papillæ, <hi rend="font-style: +italic">d.</hi> Dermis. <hi rend="font-style: italic">e.</hi> Fatty +tissue. <hi rend="font-style: italic">f, g, h.</hi> Sweat gland and +duct. <hi rend="font-style: italic">i, k.</hi> Hair and follicle. <hi +rend="font-style: italic">l.</hi> Oil gland.</head> +<figDesc>Fig. 121</figDesc> +</figure></p> + +<p>On the outer surface of the dermis are numerous <pb n="266" /><anchor id="Pg266" />elevations, called <hi +rend="font-style: italic">papillæ</hi>. These average about one +one-hundredth of an inch in height, and one two hundred and fiftieth of +an inch in diameter. They are most numerous on the palms of the hands, +the soles of the feet, and the under surfaces of the fingers and toes. +At these places they are larger than in other parts of the body, and are +closely grouped, forming the parallel curved ridges which cover the +surfaces. Each papilla contains a loop of capillaries and a small nerve, +and many of them are crowned with touch corpuscles (page 342).</p> + +<p rend="text-align: center"> +<figure url="images/image122.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 122—<hi rend="font-weight: bold">Diagram</hi> of +section of skin showing its different structures.</head> +<figDesc>Fig. 122</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Epidermis</hi> is much thinner than +the dermis. It is made up of several layers of cells which are flat and +scale-like at the surface, but are rounded in form where the epidermis +joins the dermis. The epidermis has the appearance of being <hi +rend="font-style: italic">moulded onto</hi> the dermis, filling up the +depressions between the papillæ and having corresponding irregularities +(Fig. 121). No blood vessels are found in the epidermis, its nourishment +being derived from the lymph which reaches it from the dermis. Only the +part next to the dermis is made up of <hi rend="font-style: +italic">living</hi> cells. These are active, however, in the formation +of new cells, which take the place of those that are worn off at the +surface. Some of the cells belonging to the inner layer of epidermis +contain <hi rend="font-style: italic">pigment granules</hi>, which give +the skin its color (Fig.<pb n="267" /><anchor id="Pg267" /> 121). The +epidermis contains no nerves and is therefore non-sensitive. The hair +and the nails are important modifications of the epidermis.</p> + +<p><hi rend="font-weight: bold">A Hair</hi> is a slender cylinder, +formed by the union of epidermal cells, which grows from a kind of pit +in the dermis, called the <hi rend="font-style: italic">hair +follicle</hi>. The oval and somewhat enlarged part of the hair within +the follicle is called the <hi rend="font-style: italic">root</hi>, or +<hi rend="font-style: italic">bulb</hi>, and the uniform cylinder beyond +the follicle is called the <hi rend="font-style: italic">shaft</hi>. +Connected with the sides of the follicles are the <hi rend="font-style: +italic">oil</hi>, or <hi rend="font-style: italic">sebaceous, +glands</hi> (Figs. 121 and 122). These secrete an oily liquid which +keeps the hair and cuticle soft and pliable. Attached to the inner ends +of the follicles are small, involuntary muscles whose contractions cause +the roughened condition of the skin that occurs on exposure to cold.</p> + +<p><hi rend="font-weight: bold">A Nail</hi> is a tough and rather horny +plate of epidermal tissue which grows from a depression in the dermis, +called the <hi rend="font-style: italic">matrix</hi>. The back part of +the nail is known as the <hi rend="font-style: italic">root</hi>, the +middle convex portion as the <hi rend="font-style: italic">body</hi>, +and the front margin as <hi rend="font-style: italic">the free edge</hi> +(Fig. 123). Material for the growth of the nail is derived from the +matrix, which is lined with active epidermal cells and is richly +supplied with blood vessels. Cells added to the root cause the nail to +grow in length (forward) and cells added to the under surface cause it +to grow in thickness. The cuticle adheres to the nail around its entire +circumference so that the covering over the dermis is complete.</p> + +<p rend="text-align: center"> +<figure url="images/image123.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 123—<hi rend="font-weight: bold">Section of end +of finger</hi> showing nail in position.</head> +<figDesc>Fig. 123</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Functions of the Skin.</hi>—The chief +function of the skin is that of protection. It is able to protect the +body on account of the tough connective tissue in the dermis, the +non-sensitive cells of the epidermis, and also by the touch<pb n="268" /><anchor id="Pg268" /> corpuscles and their connecting +nerve fibers. This protection is of at least three kinds, as +follows:</p> + +<p>1. <hi rend="font-style: italic">From mechanical injuries</hi> such +as might result from contact with hard, rough, or sharp objects. The +main quality needed for resisting mechanical injuries is <hi +rend="font-style: italic">toughness</hi>, and this is supplied both by +the epidermis and by the connective tissue of the dermis.</p> + +<p>2. <hi rend="font-style: italic">From chemical injuries</hi> caused +by contact with various chemical agents, as acids, alkalies, and the +oxygen of the air. The epidermis, being of such a nature as to resist to +a considerable extent the action of chemical agents, affords protection +from these substances. <note place="foot"><p>The epidermis does not afford complete protection +against chemicals, many of them being able to destroy it quickly. The +rule of washing the skin immediately after contact with strong chemical +agents should always be followed.</p></note></p> + +<p>3. <hi rend="font-style: italic">From disease germs</hi> which are +everywhere present. The epidermis is the main protective agent against +attacks of germs, but should the epidermis be broken, they meet with +further resistance from the fluids of the dermis and the white +corpuscles of the blood.</p> + +<p>4. <hi rend="font-style: italic">From an excessive evaporation of +liquid from the surface of the body</hi>. In the performance of this +function, the skin is an important means of keeping the tissues soft and +the blood and lymph from becoming too concentrated.</p> + +<p><hi rend="font-weight: bold">Other Functions of the +Skin.</hi>—Through the perspiratory glands the skin is an <hi +rend="font-style: italic">organ of excretion</hi>. While the secretion +from a single gland is small, the waste that leaves the body through all +of the perspiratory glands is considerable <note place="foot"><p>"Rough calculations have placed the number of sweat +glands on the entire body at about 2,000,000." Rettger, <hi +rend="font-style: italic">Studies in Advanced Physiology</hi>.</p></note> (page 206). By means of +the nerves terminating in the touch corpuscles, the skin serves as the +<hi rend="font-style: italic">organ of touch</hi>, or feeling (Chapter +XX). To a slight extent also the skin<pb n="269" /><anchor id="Pg269" /> may absorb liquid substances, these +being taken up by the blood and lymph vessels, and perform a respiratory +function, throwing off carbon dioxide. But the most important function +of the skin, in addition to protection, is that of serving as</p> + +<p><hi rend="font-weight: bold">An Organ of Adaptation.</hi>—Forming, as +it does, the boundary between the body and its physical environment, the +skin is perhaps the most important agent through which the body is +adapted to its immediate surroundings. Evidence of this is found in the +great variety of influences which are able to affect the body through +their action upon the nerves in the skin, and in the changes which the +epidermis undergoes on exposure. The latter function is especially +marked in the lower animals, the coverings of epidermal tissue (hair, +scales, feathers, etc.) adapting each species to the physical conditions +under which it lives. In man the most striking example of adaptation +through the skin is seen in the variations in the quantity of blood +circulating through it, corresponding to the changes in the temperature +outside of the body. These variations are of great importance, having to +do with the</p> + +<p><hi rend="font-weight: bold">Maintenance of the Normal +Temperature.</hi>—It is necessary to the continuance of life that the +temperature of the body be kept at a nearly uniform degree, called the +<hi rend="font-style: italic">normal temperature</hi>, which is about +98.6° F. The maintenance of the normal temperature depends mainly upon +four conditions: the chemical changes at the cells, the circulation of +the blood, the nervous system, and <hi rend="font-style: italic">the +skin</hi>. The chemical changes produce the heat, the blood in its +circulation distributes the heat over the body, and the nervous system +controls the heat-producing and distributing processes (page 320). The +skin is the chief means by which the body<pb n="270" /><anchor id="Pg270" /> gets rid of an excess of heat +and, by so doing, avoids overheating. <note place="foot"><p>Heat also leaves the body by the lungs, partly by the +respired air and partly through the evaporation of moisture from the +lung surfaces. Respiration in some animals, as the dog, is the chief +means of cooling the body.</p></note></p> + +<p><hi rend="font-weight: bold">How the Skin cools the Body.</hi>—The +skin is a means of ridding the body of an excess of heat in at least two +ways:</p> + +<p>1. <hi rend="font-style: italic">By the conduction and radiation of +heat from its surface</hi> as from a stove. This goes on all the time, +but varies with the amount of heat brought to the surface by the +blood.</p> + +<p>2. <hi rend="font-style: italic">By the evaporation of the +perspiration.</hi> It is a well-established and easily demonstrated +principle that liquids in evaporating use up heat.(See Practical Work.) +It is also a matter of everyday experience that the perspiration has a +cooling effect upon the body and that its flow increases with the amount +of heat to be gotten rid of. The quantity of perspiration secreted, and +of heat disposed of through its evaporation, also varies with the amount +of blood circulating through the skin.</p> + +<p><hi rend="font-weight: bold">Temperature Regulation by the +Skin.</hi>—Variations in the quantity of blood circulating through the +skin enable this organ to throw off just the right amount of heat for +keeping the body at the normal temperature. If it is necessary for the +body to rid itself of an excess of heat, the quantity of blood +circulating in the skin is increased. This brings the blood near the +surface, where more heat can be radiated and where it may cause an +increase in the perspiration. On the other hand, if the body is in +danger of losing too much heat, the circulation diminishes in the skin +and increases in the internal organs. This stops the rapid loss of heat +from the surface. The skin in this work<pb n="271" /><anchor id="Pg271" /> is of +course made to cooperate with other parts of the body. That it is not +the only organ concerned in regulating the escape of heat is seen in the +results that follow sensations either of chilliness or of heat at the +surface.</p> + +<p><hi rend="font-weight: bold">Effects of Heat and Cold +Sensations.</hi>—Sensations, or feelings, of heat and cold are made +possible through the nerves which connect the brain with the <hi +rend="font-style: italic">temperature corpuscles</hi>, found in the skin +(page 343). As the warm blood recedes from the skin, a sensation of cold +is felt, but when the blood returns, there is again the feeling of +warmth. The sensation of cold prompts one to seek a warmer place, or to +put on more clothing; while the sensation of heat, if it be oppressive, +leads to activities of an opposite kind. Prompted in this way by the +sensations from the skin, one voluntarily supplies the external +conditions, such as clothing and heat, that affect the body +temperature.</p> + +<p><hi rend="font-weight: bold">Alcohol and the Regulation of +Temperature.</hi>—Alcohol, through its effect upon the nervous system, +interferes seriously with the regulation of the body temperature. By +dilating the capillaries, it increases the circulation in the skin and +leads to an undue loss of heat. At the same time the excess of blood in +the skin causes a <hi rend="font-style: italic">feeling of warmth</hi> +which has led to the erroneous belief that alcohol is a heat producer. +If taken on a cold day, it deceives one about his true condition and +leads to a wasting of heat when it should be carefully economized. Not +only is alcohol of no value in maintaining the body temperature, but if +taken during severe exposure to cold, it becomes a menace to life +itself. Arctic, explorers and others exposed to severe cold have found +that they withstand cold far better when no alcohol at all is +used.<note place="foot"><p>"The story is told of some woodsmen who were overtaken +by a severe snowstorm and had to spend the night away from camp; they +had a bottle of whisky, and, chilled to the bone, some imbibed freely while +others refused to drink. Those who drank soon felt comfortable and went +to sleep in their improvised shelter; those who did not drink felt very +uncomfortable throughout the night and could get no sleep, but in the +morning they were alive and able to struggle back to camp, while their +companions who had used alcohol were frozen to death.... This, if true, +was of course an extreme case; but it accords with the universal +experience of arctic travelers and of lumbermen and hunters in the +northern woods, that the use of alcohol during exposure to cold, +although contributing greatly to one's comfort for the time being, is +generally followed by undesirable or dangerous results."—HOUGH AND +SEDGWICK: <hi rend="font-style: italic">The Elements of Hygiene and +Sanitation</hi>.</p></note></p> + +<div> +<pb n="272" /><anchor id="Pg272" /> +<head>HYGIENE OF THE SKIN</head> + +<p>Much of the hygiene of the skin is included in the problems of +keeping it warm and clean. It is kept warm by clothing; bathing is the +method of keeping it clean.</p> + +<p><hi rend="font-weight: bold">Clothing</hi> should be warm and +loose-fitting. Woolen fabrics are to be preferred in winter to cotton +because, being poorer conductors of heat, they afford better protection +from the cold. But wool fails to absorb the perspiration rapidly from +the skin and to pass it to the outside where it is evaporated. This, +together with its tendency to irritate, makes woolen clothing somewhat +objectionable for wearing next to the skin. This objection, however, is +obviated by woolen underwear which is lined by a thin weaving of +cotton.</p> + +<p><hi rend="font-weight: bold">Bathing.</hi>—The solid material from +the perspiration, which is left on the skin, together with the oil from +the oil glands and the dirt from the outside, tends to close up the +pores and develop offensive odors. Keeping the skin clean is, for these +reasons, necessary from both a health and a social standpoint. While one +should always keep clean, the frequency of the bath will depend upon the +season, the occupation of the individual, and the nature and amount of +the perspiration. As to the kind of bath to be taken and the precautions +to be observed, no specific rules can be laid down. These must be +determined by<pb n="273" /><anchor id="Pg273" /> the facilities at hand and by the +health and natural vigor of the bather. Severe chilling of the body +should be avoided, especially by those in delicate health. If a hot bath +is taken, one should dash cold water over the body on finishing. One +should then quickly dry and rub the body with a coarse towel. The dash +of cold water closes the pores of the skin and lessens the liability of +taking cold.</p> + +<p><hi rend="font-weight: bold">The Tonic Bath.</hi>—The cold bath has +been found to have a beneficial effect upon the general health beyond +its effect upon the skin. When taken with care as to the length of time +and the degree of cold, decided tonic effects are observed on the +circulation and on the nervous system. The rapid changes of temperature +vigorously exercise the non-striated muscles of the blood vessels (page +57) and the nerves controlling them. The irritability of the nervous +system in general is also lessened. For this reason the cold bath is one +of the best means of keeping both mind and body in good condition during +the warm months. Sponging off the body with cold or tepid water before +retiring is also an excellent aid in securing sound sleep during the hot +summer nights.</p> + +<p>Danger from the cold bath arises through the shock to the nervous +system and the loss of heat from the body. It is avoided by using water +whose temperature is not too low and by limiting the time spent in the +bath. A brisk rubbing with a coarse towel should always follow the cold +bath. People past middle age are, as a rule, not benefited by the cold +bath; and those in delicate health, especially if inclined toward +rheumatism, are likely to be affected injuriously by it.</p> + +<p><hi rend="font-weight: bold">Care of the Complexion.</hi>—A good +complexion is a natural accompaniment of good health and depends +primarily<pb n="274" /><anchor id="Pg274" /> upon two conditions—a +clear skin and an active circulation of the blood through it. Clearness +of the skin depends largely upon the elimination of waste material from +the body, and where the solid wastes are not effectively removed through +the natural channels (the liver, kidneys, and bowels), blotches, +sallowness of the skin, and skin eruptions are likely to result. In +seeking to clear the complexion, attention must be given to all those +agencies that favor the elimination of waste, and especially should +there be a free and thorough evacuation of the bowels each day. The +general health should also be looked after, attention being given to +exercise, fresh air, proper food,<note place="foot"><p>Foods that are difficult to digest, or which cause +disturbances of the digestive organs (a coated tongue being one +indication), have a bad effect upon the skin. It is in this way that the +use of tea and coffee by some people induces a sallow or "muddy" +condition of the complexion.</p></note> sufficient sleep, etc.</p> + +<p>Bathing is the chief means employed for increasing the circulation in +the skin, although exercise which is sufficiently vigorous to cause one +to perspire freely is a valuable aid. A daily bath of warm or hot water, +finished off with a dash of cold, followed by a thorough rubbing of the +entire surface, and this by a kneading of the skin with the thumbs and +fingers, will in most cases bring about the desired results. A little +olive oil, thoroughly worked into the skin during the kneading process, +is beneficial where one lacks flesh or where the skin is dry and thin. +The olive oil is also beneficial where the baths are exhausting or +render one susceptible to cold. In rubbing and kneading, the skin should +not be bruised or irritated.</p> + +<p>The much advertised "complexion beautifiers" which are applied +directly to the face frequently have the effect of clogging the pores +and of causing eruptions of the skin. <pb n="275" /><anchor id="Pg275" />On the other hand, certain +authorities state that the cold cream preparations may be of advantage +in giving the skin a desired softness, and that when judiciously used +(the face being cleansed after each application) they do no harm. Of the +different kinds of face powder those prepared from rice are considered +the least injurious.</p> + +<p><hi rend="font-weight: bold">Treatment of Skin Wounds.</hi>—Skin +wounds which may not be serious in themselves frequently become so +through getting infected with germs. Blood poisoning often results from +such infections, one of the worst forms being <hi rend="font-style: +italic">tetanus</hi>, or lockjaw. A wound should be kept clean, and if +it shows signs of infection, it should be washed with some antiseptic +solution. Or, it may be cleansed with pure warm water and then covered +with some antiseptic ointment,<note place="foot"><p>A most valuable antiseptic ointment is prepared by the +druggist from the following formula:</p> + +<p rend="display">Lanolin, 25 grams.<lb /> +Ichthyol, 6 grams.<lb /> +Yellow vaseline, 20 grams.</p> + +<p>This is applied as a thin layer on the surface, except in the case of +boils or abscesses. In treating these a heavy layer is spread over the +affected part and then covered with absorbent cotton or a thin piece of +clean cotton cloth.</p></note> of which there are a number on the +market. A weak solution of carbolic acid (one part acid to twenty-five +parts of water) makes an excellent antiseptic wash. It may be used not +only for cleansing wounds, but also in counteracting the poisonous +effects that follow the bites of insects.</p> + +<p>A wound resulting from the bite of an animal (cat or dog), even +though slight, should receive more serious attention, and as soon as +possible after the occurrence. Such wounds should be cauterized, and for +this purpose pure carbolic, acid (undiluted with water) may be used. A +wooden toothpick is dipped into the acid and this is worked about in the +wound. The acid is then washed out with warm water. A deep wound from a +rusty nail or<pb n="276" /><anchor id="Pg276" /> a thorn should be treated in the +same manner and should be kept open, not being allowed to heal at the +surface first. If one has reason to believe he has been bitten by a mad +dog, the wound should be cauterized as above, and a physician should be +summoned at once. Deep wounds from explosives, or other causes, should +also receive the attention of the physician. Many cases of lockjaw +result every year from wounds inflicted by the toy pistols, +firecrackers, etc., used in our Fourth of July celebrations. These are +due to the embedding in the skin or flesh of small solid particles on +which are lockjaw germs. Wounds of this nature should, of course, +receive the attention of the physician.</p> + +<p><hi rend="font-weight: bold">Care of the Nails.</hi>—Relief from a +blood blister under the nail is secured by boring a small hole through +the nail with the sharp point of a sterilized penknife (page 38). This +simple bit of surgery not only relieves the pain, but is frequently the +only means of saving the nail. Ingrown toe nails are relieved by +scraping a broad strip in the middle of the nail until very thin. This +relieves the pressure, preventing the sides of the nail from being +forced into the toe. While the finger nails should be trimmed in a +curve, corresponding to the end of the finger, it is recommended that +the toe nails be cut straight across (Fig. 124), as this method +diminishes the pressure from the shoe and keeps the nails from +ingrowing. Shoes that pinch the toes should, of course, not be worn +(page 238).</p> + +<p rend="text-align: center"> +<figure url="images/image124.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 124—Proper method of trimming nails of +toes.</head> +<figDesc>Fig. 124</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Care of the Hair.</hi>—Occasional +washing of the hair is beneficial, but too much wetting causes decay of +the hair roots, which leads to its falling out. The worst enemy of the +hair is dandruff. A method of removing dandruff which is highly +recommended is that of rubbing olive oil<pb n="277" /><anchor id="Pg277" /> into the scalp and later of +removing this with a cleansing shampoo. The olive oil is placed on the +scalp with a medicine dropper and thoroughly rubbed in with the fingers. +After three or four hours the hair is washed with soap and water (any +good toilet soap will do) and rinsed with pure water. The hair is then +dried, the surplus water being removed with a coarse towel. Where the +dandruff is very troublesome, this treatment may be given once or twice +a week; but in mild cases once a month is sufficient. Massage of the +scalp, by increasing the circulation at the hair roots, is beneficial, +but irritation by a fine-tooth comb, a stiff hair brush, or by other +means should be avoided. Frequent brushing and combing, however, are +necessary both for the good appearance of the hair and for spreading the +oil secreted by the glands at the hair roots.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The skin forms the +external covering of the body and also serves additional purposes. It is +a most important agency in adapting the body to its physical +surroundings, as shown by the part which it plays in the regulation of +the body temperature. The skin should be kept clean and active, and skin +wounds, even though small, should be guarded against infection.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. Name an example of +each of the protective coverings of the body.</p> + +<p>2. Compare the dermis and the epidermis with reference to thickness, +composition, and function.</p> + +<p>3. To what is the color of the skin due? How is the color of the skin +affected by the sunlight?</p> + +<p>4. What modifications of the epidermis are found on our bodies? What +are found on the body of a chicken?</p> + +<p>5. What different kinds of protection are provided by the skin?</p> + +<p>6. How does the perspiration cool the body?</p> + +<p>7. What change occurs in the circulation in the skin when the body is +becoming too cold? When becoming too warm? What is the purpose of these +changes?</p> + +<p><pb n="278" /><anchor id="Pg278" />8. How does alcohol cause one to +<hi rend="font-style: italic">feel</hi> warm when he may be losing too +much of his heat?</p> + +<p>9. What precaution should be observed by one in poor health, in +taking a bath?</p> + +<p>10. How may the cold bath be a means of improving the general +health?</p> +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">Observations on the Skin and its +Appendages.</hi>—Examine the palm of the hand with a lens. Note the +small ridges which correspond to the rows of papillæ beneath the +cuticle. In these find small pits, which are the openings of the sweat +glands.</p> + +<p>2. Examine the epidermis on the back of the hand and palm. At which +place is it thickest and most resisting? Is it of uniform thickness over +the palm? Try picking it with a pin at the thickest place, noting if +pain is felt. Inference?</p> + +<p>3. Examine a finger nail. Is the free edge or the root the thickest? +Trim closely the thumb nail and the nail of the middle finger of one +hand and try to pick up a pin, or other minute object, from a smooth, +hard surface. The result indicates what use of the nails? Suggest other +uses.</p> + +<p>4. Examine with a microscope under a low power hairs from a variety +of animals, as the horse, dog, cat, etc., noting peculiarities of form +and surface.</p> + +<p><hi rend="font-weight: bold">To illustrate Cooling Effects of +Evaporation.</hi>—1. Wet the back of the hand and move it through the +air to hasten evaporation. Observe that, as the hand dries, a sensation +of cold is felt. Repeat the experiment, using ether, alcohol, or +gasolene instead of the water, noting the differences in results. These +liquids evaporate faster than water.</p> + +<p>2. Wet the bulb of a thermometer with alcohol or water. Move it +through the air to hasten evaporation. Note and account for the fall of +the mercury.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="279" /><anchor id="Pg279" /> +<head>CHAPTER XVII - STRUCTURE OF THE NERVOUS SYSTEM</head> + +<p><hi rend="font-weight: bold">Coördination and Adjustment.</hi>—If we +consider for a moment the movements of the body, we cannot fail to note +the coöperation of organs, one with another. In the simple act of +whittling a stick one hand holds the stick and the other the knife, +while the movements of each hand are such as to aid in the whittling +process. Examples of coöperation are also found in the taking of food, +in walking, and in the performance of different kinds of work. Not only +is coöperation found among the external organs, but our study of the +vital processes has shown that the principle of coöperation is carried +out by the internal organs as well. The fact that all the activities of +the body are directed toward a common purpose makes the coöperation of +its parts a necessity. The term "coördination" is employed to express +this coöperation, or working together, of the different parts of the +body.</p> + +<p>A further study of the movements of the body shows that many of them +have particular reference to things outside of it. In going about one +naturally avoids obstructions, and if anything is in the way he walks +around or steps over it. Somewhat as a delicate instrument (the +microscope for example) is altered or adjusted, in order to adapt it to +its work, the parts of the body, and the body as a whole, have to be <hi +rend="font-style: italic">adjusted</hi> to their surroundings. This is +seen in the attitude assumed in sitting and in standing, in the position +of the hands for different kinds<pb n="280" /><anchor id="Pg280" /> of work, in the variations of the +circulation of the blood in the skin, and in the movements for +protecting the body.<note place="foot"><p>In a larger sense adjustment includes all those +activities by means of which the body is brought into proper relations +with its environment, including the changes which the body makes in its +surroundings to <hi rend="font-style: italic">adapt them</hi> to its +purposes.</p></note></p> + +<p><hi rend="font-weight: bold">Work of the Nervous System.</hi>—How are +the different activities of the body controlled and coördinated? How is +the body adjusted to its surroundings? The answer is found in the study +of the nervous system. Briefly speaking, the nervous system controls, +coördinates, and adjusts the different parts of the body by fulfilling +two conditions:</p> + +<p>1. It provides a complete system of connections throughout the body, +thereby bringing all parts into communication.</p> + +<p>2. It supplies a means of controlling action (the so-called impulse) +which it passes along the nervous connections from one part of the body +to another.</p> + +<p>The present chapter deals with the first of these conditions; the +chapter following, with the second.</p> + +<p><hi rend="font-weight: bold">The Nerve Skeleton.</hi>—If all the +other tissues are removed, leaving only the nervous tissue, a complete +skeleton outline of the body still remains. This nerve skeleton, as it +has been called, has the general form of the framework of bones, but +differs from it greatly in the fineness of its structures and the extent +to which it represents every portion of the body. An examination of a +nerve skeleton, or a diagram of one (Fig. 125), shows the main +structures of the nervous system and their connection with the different +parts of the body.</p> + +<p>Corresponding to the skull and the spinal column is a central nervous +axis, made up of two parts, the <hi rend="font-style: italic">brain</hi> +and the <hi rend="font-style: italic">spinal cord</hi>. From this +central axis white, cord-like bodies emerge and pass to different parts +of the body. <pb n="281" /><anchor id="Pg281" />These are called <hi +rend="font-style: italic">nerve trunks</hi>, and the smaller branches +into which they divide are called <hi rend="font-style: +italic">nerves</hi>. The nerves also undergo division until they +terminate as fine thread-like structures in all parts of the body. The +distribution of nerve terminations, however, is not uniform, as might be +supposed, but the skin and important organs like the heart, stomach, and +muscles are the more abundantly supplied. On many of the nerves are +small rounded masses, called <hi rend="font-style: italic">ganglia</hi>, +and from many of these small nerves also emerge. At certain places the +nerves and ganglia are so numerous as to form a kind of network, known +as a <hi rend="font-style: italic">plexus</hi>.</p> + +<p rend="text-align: center"> +<figure url="images/image125.png" rend="page-float: 'hp'; text-align: center; w40"> +<head><lb />Fig. 125—<hi rend="font-weight: bold">Diagram of +nerve skeleton.</hi> The illustration shows the extent and general +arrangement of the nervous tissue. <hi rend="font-style: italic">A.</hi> +Brain. <hi rend="font-style: italic">B.</hi> Spinal cord. <hi +rend="font-style: italic">N.</hi> Nerve trunks and nerves. <hi +rend="font-style: italic">G.</hi> Ganglia.</head> +<figDesc>Fig. 125</figDesc> +</figure></p> + +<p>It is through these structures—brain and spinal cord, nerve trunks +and nerves, ganglia and nerve terminations—that connections are +established between all parts of the body, but more especially between +the surface of the body and the organs within.</p> + +<p><hi rend="font-weight: bold">The Neurons, or Nerve Cells.</hi>—While +a hasty examination of the nerve skeleton is sufficient to show the +connection<pb n="282" /><anchor id="Pg282" /> of the nervous system with all +parts of the body, no amount of study of its gross structures reveals +the nature of its connections or suggests its method of operation. +Insight into the real nature of the nervous system is obtained only +through a study of its minute structural elements. These, instead of +being called cells, as in the case of the other tissues, are called <hi +rend="font-style: italic">neurons</hi>. The use of this term, instead of +the simpler one of nerve cell, is the result of recent advances in our +knowledge of the nervous system.<note place="foot"><p>Almost to the present time, physiologists have described +the nervous system as being made up of two kinds of structural elements +which were called <hi rend="font-style: italic">nerve cells</hi> and <hi +rend="font-style: italic">nerve fibers</hi>. The nerve cells were +supposed to form the ganglia and the fibers to form the nerves. Recent +investigators, however, employing new methods of microscopic study, have +established the fact that the so-called nerve cell and nerve fiber are +but two divisions of the same thing and that the nervous system is made +up of, not two, but one kind of structural element. The term "neuron" is +used to denote this structural element, or <hi rend="font-style: +italic">complete nerve cell</hi>.</p></note></p> + +<p rend="text-align: center"> +<figure url="images/image126.png" rend="page-float: 'hp'; text-align: center; w40"> +<head><lb />Fig. 126—<hi rend="font-weight: bold">Diagram of a +mon-axonic neuron</hi> (greatly enlarged except as to length). The +central thread in the axon is the axis cylinder.</head> +<figDesc>Fig. 126</figDesc> +</figure></p> + +<p>The neurons are in all respects cells. They differ widely, however, +from all the other cells of the body and are, in some respects, the most +remarkable of all cells. They are characterized by minute extensions, or +prolongations, which in some instances extend to great distances. Though +the neurons in certain parts of the body differ greatly in form and size +from those in other parts of the body, most of them may be included in +one or the other of two classes, known as <hi rend="font-style: +italic">mon-axonic</hi> neurons and <hi rend="font-style: +italic">di-axonic</hi> neurons.</p> + +<p><hi rend="font-weight: bold">Mon-axonic Neurons.</hi>—Neurons of +this<pb n="283" /><anchor id="Pg283" /> class consist of three distinct +parts, known as the cell-body, the dendrites, and the axon (Fig. +126).</p> + +<p>The <hi rend="font-style: italic">cell-body</hi> has in itself the +form of a complete cell and was at one time so described. It consists of +a rounded mass of protoplasm, containing a well-defined nucleus. The +protoplasm is similar to that of other cells, but is characterized by +the presence of many small granules and has a slightly grayish +color.</p> + +<p>The <hi rend="font-style: italic">dendrites</hi> are short extensions +from the cell-body. They branch somewhat as the roots of a tree and form +in many instances a complex network of tiny rootlets. Their protoplasm, +like that of the cell-body, is more or less granular. The dendrites +increase greatly the surface of the cell-body, to which they are related +in function.</p> + +<p>The <hi rend="font-style: italic">axon</hi>, or nerve fiber, is a +long, slender extension from the cell-body, which connects with some +organ or tissue. It was at one time described as a distinct nervous +element, but later study has shown it to be an outgrowth from the +cell-body. The mon-axonic neurons are so called from their having but a +single axon.</p> + +<p><hi rend="font-weight: bold">Di-axonic Neurons.</hi>—Neurons +belonging to this class have each a well-defined cell-body and two +axons, but no parts just like the dendrites of mon-axonic neurons. The +cell-body is smooth and rounded, and its axons extend from it in +opposite directions (Fig. 127).</p> + +<p rend="text-align: center"> +<figure url="images/image127.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 127—<hi rend="font-weight: bold">Diagram of a +di-axonic neuron.</hi> The diagram shows only the conducting portion of +the axon, or axis cylinder.</head> +<figDesc>Fig. 127</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Structure of the Axon.</hi>—The axon, or +nerve fiber, has practically the same structure in both classes of +neurons, being composed in most cases of three distinct parts. In<pb n="284" /><anchor id="Pg284" /> the center, and running the +entire length of the axon, is a thread-like body, called the <hi +rend="font-style: italic">axis cylinder</hi> (Fig. 126). The axis +cylinder is present in all axons and is the part essential to their +work. It may be considered as an extension of the protoplasm from the +cell-body. Surrounding the axis cylinder is a thick, whitish-looking +layer, known as the <hi rend="font-style: italic">medullary sheath</hi>, +and around this is a thin covering, called the <hi rend="font-style: +italic">primitive sheath</hi>, or neurilemma. The medullary sheath and +the primitive sheath are not, strictly speaking, parts of the nerve +cell, but appear to be growths that have formed around it. Certain of +the axons have no primitive sheath and others are without a medullary +sheath.<note place="foot"><p>Many of the axons in the brain and spinal cord have no +primitive sheath. Axons without the medullary sheath are found in the +sympathetic nerves. These are known as non-medullated axons and they +have a gray instead of a white color.</p></note></p> + +<p><hi rend="font-weight: bold">Form and Length of Axons.</hi>—Where the +axons terminate they usually separate into a number of small divisions, +thereby increasing the number of their connections. Certain axons are +also observed to give off branches before the place of termination is +reached (Fig. 131). These collateral branches, by distributing +themselves in a manner similar to the main fiber, greatly extend the +influence of a single neuron.</p> + +<p>In the matter of length, great variation is found among the axons in +different parts of the body. In certain parts of the brain, for example, +are fibers not more than one one-hundredth of an inch in length, while +the axons that pass all the way from the spinal cord to the toes have a +length of more than three feet. Between these extremes practically all +variations in length are found.</p> + +<p><hi rend="font-weight: bold">Arrangements of the +Neurons.</hi>—Nowhere in the body do the neurons exist singly, but they +are everywhere connected with each other to form the different +structures observed in the nerve skeleton. Two general plans of +connection are to be observed, known as the anatomical and the +physiological, or, more simply speaking, as the "side-by-side" and +"end-to-end" plans. The side-by-side<pb n="285" /><anchor id="Pg285" /> plan is seen in that +disposition of the neurons which enables them to form the nerves and the +ganglia, as well as the brain and spinal cord. The end-to-end +connections are necessary to the work which the neurons do.</p> + +<p><hi rend="font-weight: bold">Side-by-side Connections.</hi>—On +separating the ganglia and nerves into their finest divisions, it is +found that the nerves consist of axons, while the ganglia are made up +mainly of cell-bodies and dendrites. The axons lie side by side in the +nerve, being surrounded by the same protective coverings, while the +cell-bodies form a rounded mass or cluster, which is the ganglion (Fig. +128). But the axons, in order to connect with the cell-bodies, must +terminate within the ganglion, so that they too form a part of it. To +some extent, also, axons pass through ganglia with which they make no +connection. The neurons in the brain and spinal cord also lie side by +side, but their arrangement is more complex than that in the nerves and +ganglia.</p> + +<p rend="text-align: center"> +<figure url="images/image128.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 128—<hi rend="font-weight: bold">Diagrams +illustrating arrangement of neurons.</hi> <hi rend="font-style: +italic">A, B.</hi> Ganglia and short segments of nerves. 1. Ganglion. 2. +Nerve. In the ganglion of <hi rend="font-style: italic">A</hi> are +end-to-end connections of different neurons; in the ganglion of <hi +rend="font-style: italic">B</hi> are the cell-bodies of di-axonic +neurons. <hi rend="font-style: italic">C.</hi> Section of a nerve trunk. +1. Epineurium consisting chiefly of connective tissue. 2. Bundles of +nerve fibers. 3. Covering of fiber bundle, or perineurium. 4. Small +artery and vein.</head> +<figDesc>Fig. 128</figDesc> +</figure></p> + +<p><pb n="286" /><anchor id="Pg286" />The side-by-side arrangement of the neurons shows clearly the +structure of the ganglia and nerves. The nerve is seen to be a bundle of +axons, or nerve fibers, held together by connective tissue, while the +ganglion is little more than a cluster of cell-bodies. Their connection +is necessarily very close, for the same group of neurons will form, with +their axons, the nerve, and, with their cell-bodies, the ganglion (Fig. +128).</p> + +<p><hi rend="font-weight: bold">End-to-end Connections.</hi>—These +consist of loose end-to-end unions of the fiber branches of certain +neurons with the dendrites of other neurons. The purpose of such +connections is to provide the means of communication between different +parts of the body. There appears to be no actual uniting of the fiber +branches with the dendrites, but they come into relations sufficiently +close to establish <hi rend="font-style: italic">conduction +pathways</hi>, and these extend throughout the body (Fig. 129). They +connect all parts of the body with the brain and spinal cord, while +connections within the brain and cord bring the parts into communication +with each other.</p> + +<p rend="text-align: center"> +<figure url="images/image129.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 129—<hi rend="font-weight: bold">Diagram of a +nerve path</hi> starting at the skin, extending through the spinal cord, +and passing out to muscles. A division of this path also reaches the +brain.</head> +<figDesc>Fig. 129</figDesc> +</figure></p> + +<p><pb n="287" /><anchor id="Pg287" /><hi rend="font-weight: bold">Nature of the Nervous System.</hi>—The +nervous system represents the sum total of the neurons in the body. In +some respects it may be compared to the modern telephone system. The +neurons, like the electric wires, connect different places with a +central station (the brain and spinal cord), and through the central +station connections are established between the different places in the +system. As the separate wires are massed together to form cables, the +neurons are massed to form the gross structures of the nervous system. +The nervous system, however, is so radically different from anything +found outside of the animal body that no comparison can give an adequate +idea of it. We now pass to a study of the gross structures observed in +the nerve skeleton.</p> + +<p><hi rend="font-weight: bold">Divisions of the Nervous +System.</hi>—While all of the nervous structures are very closely +blended, forming one complete system for the entire body, this system +presents different divisions which may, for convenience, be studied +separately. As physiologists have become better acquainted with the +human nervous system, different schemes of classification have been +proposed. The following outline, based upon the location of the +different parts, presents perhaps the simplest view of the entire group +of nervous structures:</p> + +<p rend="text-align: center"> +<figure url="images/image129a.png" rend="page-float: 'hp'; text-align: center; w95"> +<figDesc>Table</figDesc> +</figure></p> + +<p><pb n="288" /><anchor id="Pg288" /><hi rend="font-weight: bold">The +Central Division.</hi>—This division of the nervous system lies within +the cranial and spinal cavities, and consists of the brain and the +spinal cord. The brain occupying the cranial cavity and the spinal cord +in the spinal cavity connect with each other through the large opening +at the base of the skull to form one continuous structure. The brain and +cord are the most complicated portions of the nervous system, and the +ones most difficult to understand.</p> + +<p rend="text-align: center"> +<figure url="images/image130.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 130—<hi rend="font-weight: bold">Diagram of +divisions of brain.</hi></head> +<figDesc>Fig. 130</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Brain.</hi>—The brain, which is the +largest mass of nervous tissue in the body, weighs in the average sized +man about 50 ounces, and in the average sized woman about 44 ounces.<note place="foot"><p>The difference in weight between the brain of man and +that of woman is due mainly to the fact that man's body is, as a rule, +considerably larger than that of woman's.</p></note> +It may be roughly divided into three parts, which are named from their +positions (in lower animals) the forebrain, the midbrain, and the +hindbrain (Fig. 130). The forebrain consists almost entirely of a single +part, known as</p> + +<p><hi rend="font-weight: bold">The Cerebrum.</hi>—The cerebrum +comprises about seven eighths of the entire brain, and occupies all the +front, middle, back, and upper portions of the cranial cavity, spreading +over and concealing, to a large extent, the parts beneath. The surface +layer of the cerebrum is called the <hi rend="font-style: +italic">cortex</hi>. This is made up largely of cell-bodies, and has a +grayish appearance.<note place="foot"><p>The nervous tissues present, at different places, two +colors—one white, and the other a light gray. Great significance was +formerly attached to these colors, because it was supposed that they +represented two essentially different kinds of nervous matter. It is now +known that the protoplasm in all parts of the neuron proper—cell-body, axis cylinder, and dendrites—has a +grayish color, while the coverings of most of the fibers are white. +Hence gray matter in any part of the nervous system indicates the +presence of cell-bodies, and white matter the presence of nerve +fibers.</p></note> The cortex is greatly increased in<pb n="289" /><anchor id="Pg289" /> area by the presence everywhere +of ridge-like <hi rend="font-style: italic">convolutions</hi>, between +which are deep but narrow depressions, called <hi rend="font-style: +italic">fissures</hi>. The interior of the cerebrum consists mainly of +nerve fibers, or axons, which give it a whitish appearance. These fibers +connect with the cell-bodies in the cortex (Fig. 131).</p> + +<p>The cerebrum is a double organ, consisting of two similar divisions, +called the <hi rend="font-style: italic">cerebral hemispheres</hi>. +These are separated by a deep groove, extending from the front to the +back of the brain, known as the <hi rend="font-style: italic">median +fissure</hi>. The hemispheres, however, are closely connected by a great +band of underlying nerve fibers, called the <hi rend="font-style: +italic">corpus callosum</hi>.</p> + +<p rend="text-align: center"> +<figure url="images/image131.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 131—<hi rend="font-weight: bold">Microscope +drawing</hi> of a neuron from cerebral cortex. <hi rend="font-style: +italic">a.</hi> Short segment of the axis cylinder with collateral +branches.</head> +<figDesc>Fig. 131</figDesc> +</figure></p> + +<p>At the base of the cerebrum three large masses of cell-bodies are to +be found. One of these, a double mass, occupies a central position +between the hemispheres, and is called the <hi rend="font-style: +italic">optic thalami</hi>. The other two occupy front central positions +at the base of either hemisphere, and are known as the <hi +rend="font-style: italic">corpora striata</hi>, or the striate +bodies.</p> + +<p><hi rend="font-weight: bold">The Midbrain</hi> is a short, rounded, +and compact body that lies immediately beneath the cerebrum, and +connects<pb n="290" /><anchor id="Pg290" /> it with the hindbrain. On account +of the great size of the cerebrum, the midbrain is entirely concealed +from view when the other parts occupy their normal positions. However, +if the cerebrum is pulled away from the hindbrain, it is brought into +view somewhat as in Fig. 130.</p> + +<p>The midbrain carries upon its back and upper surface four small +rounded masses of cell-bodies, called the <hi rend="font-style: +italic">corpora quadrigemina</hi>. The upper two of these bodies are +connected with the eyes; the lower two appear to have some connection +with the organs of hearing. On the front and under surface, the midbrain +separates slightly as if to form two pillars, which are called the <hi +rend="font-style: italic">crura cerebri</hi>, or cerebral peduncles. +These contain the great bundles of nerve fibers that connect the +cerebrum with the parts of the nervous system below.</p> + +<p><hi rend="font-weight: bold">The Hindbrain</hi> lies beneath the back +portion of the cerebrum, and occupies the enlargement at the base of the +skull. It forms about one eighth of the entire brain, and is composed of +three parts—the cerebellum, the pons, and the bulb.</p> + +<p><hi rend="font-weight: bold">The Cerebellum</hi> is a flat and +somewhat triangular structure with its upper surface fitting into the +triangular under surface of the back of the cerebrum. It is divided into +three lobes—a central lobe and two lateral lobes—and weighs about two +and one half ounces. In its general form and appearance, as well as in +the arrangement of its cell-bodies and axons, the cerebellum resembles +the cerebrum. It differs from the cerebrum, however, in being more +compact, and in having its surface covered with narrow, transverse +ridges instead of the irregular and broader convolutions (Fig. 132).</p> + +<p><hi rend="font-weight: bold">The Pons</hi>, or pons Varolii, named +from its supposed resemblance to a bridge, is situated in front of the +cerebellum, and is readily recognized as a circular expansion which +extends forward from that body. It consists largely of<pb n="291" /><anchor id="Pg291" /> bands of nerve fibers, between +which are several small masses of cell-bodies. The fibers connect with +different parts of the cerebellum and with parts above.</p> + +<p rend="text-align: center"> +<figure url="images/image132.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 132—<hi rend="font-weight: bold">Human +brain</hi> viewed from below. <hi rend="font-style: italic">C.</hi> +Cerebrum. <hi rend="font-style: italic">Cb.</hi> Cerebellum. <hi +rend="font-style: italic">M.</hi> Midbrain. <hi rend="font-style: +italic">P.</hi> Pons. <hi rend="font-style: italic">B.</hi> Bulb. I-XII. +Cranial nerves.</head> +<figDesc>Fig. 132</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Bulb</hi>, or medulla oblongata, is, +properly speaking, an enlargement of the spinal cord within the cranial +cavity. It is somewhat triangular in shape, and lies immediately below +the cerebellum. It contains important clusters of cell-bodies, as well +as the nerve fibers that pass from the spinal cord to the brain.</p> + +<p><pb n="292" /><anchor id="Pg292" /><hi rend="font-weight: bold">The +Spinal Cord.</hi>—This division of the central nervous system is about +seventeen inches in length and two thirds of an inch in diameter. It +does not extend the entire length of the spinal cavity, as might be +supposed, but terminates at the lower margin of the first lumbar +vertebra.<note place="foot"><p>In very early life the spinal cord entirely fills the +spinal cavity, but as the body develops the cord grows less rapidly than +the spinal column, and, as a consequence, separates at the lower end +from the inclosing bony column.</p></note> It connects at the upper end with the bulb, and terminates +at the lower extremity in a number of large nerve roots, which are +continuous with the nerves of the hips and legs (Fig. 133). Two deep +fissures, one in front and the other at the back, extend the entire +length of the cord, and separate it into two similar divisions. These +are connected, however, along their entire length by a central band +consisting of both gray and white matter.</p> + +<p rend="text-align: center"> +<figure url="images/image133.png" rend="page-float: 'hp'; text-align: center; w30"> +<head><lb />Fig. 133—<hi rend="font-weight: bold">Spinal +cord</hi>, showing on one side the nerves and ganglia with which it is +closely related in function. <hi rend="font-style: italic">A.</hi> Bulb. +<hi rend="font-style: italic">B.</hi> Cervical enlargement. <hi +rend="font-style: italic">C.</hi> Lumbar enlargement. <hi +rend="font-style: italic">D.</hi> Termination of cord. <hi +rend="font-style: italic">E.</hi> Nerve roots that occupy the spinal +cavity below the cord. <hi rend="font-style: italic">P.</hi> Pons. <hi +rend="font-style: italic">D.G.</hi> Dorsal root ganglia. <hi +rend="font-style: italic">S.G.</hi> Sympathetic ganglia. <hi +rend="font-style: italic">N.</hi> Nerve trunks to upper and lower +extremities.</head> +<figDesc>Fig. 133</figDesc> +</figure></p> + +<p>The arrangement of the neurons of the spinal cord is just the reverse +of<pb n="293" /><anchor id="Pg293" /> that in the cerebrum—the center +being occupied by a double column of cell-bodies, which give it a +grayish appearance, while the fibers occupy the outer portion of the +cord, giving it a whitish appearance.</p> + +<p>The spinal cord is not uniform in thickness, but tapers slightly, +though not uniformly, from the upper toward the lower end. At the places +where the nerves from the arms and legs enter the cord two enlargements +are to be found, the upper being called the <hi rend="font-style: +italic">cervical</hi> and the lower the <hi rend="font-style: +italic">lumbar enlargement</hi>. These, on account of the difference in +length between the cord and the spinal cavity, are above—the lower one +considerably above—the places where the limbs which they supply join the +trunk (Fig. 133).</p> + +<p><hi rend="font-weight: bold">Arrangement of the Neurons of the Brain +and Cord.</hi>—The cell-bodies in the brain and spinal cord are +collected into groups, and their fibers extend from these groups to +places that may be near or remote. Guided by the white and gray colors +of the nervous tissue, and also by the structures revealed by the +microscope, physiologists have made out three general schemes in the +grouping of cell-bodies, as follows:</p> + +<p>1. <hi rend="font-style: italic">That of surface distribution</hi>, +the cell-bodies forming a thin but continuous layer over a given +surface. This is the plan in the cerebrum and cerebellum, and here are +found devices for increasing the surface: the cerebrum having +convolutions, the cerebellum transverse ridges.</p> + +<p>2. <hi rend="font-style: italic">That of collections of cell-bodies +into rounded masses.</hi> Such masses are found in the bulb, the pons, +the midbrain, and the base of the cerebrum.</p> + +<p>3. <hi rend="font-style: italic">That of arrangement in a continuous +column.</hi> This is the plan in the spinal cord. It matters not at what +place the spinal cord be cut, a central area of gray matter, resembling +in form the capital letter H, is always found.</p> + +<p>The fibers connecting with the cell-bodies in the brain and spinal +cord are gathered into bundles or tracts, and these pass through +different parts somewhat as follows:</p> + +<p>1. <hi rend="font-style: italic">In the cerebrum</hi> they extend in +three general directions, forming three classes of fibers. The first +connect different localities in the same hemisphere, and are known as +<hi rend="font-style: italic">association</hi> fibers (<hi +rend="font-style: italic">A</hi>, Fig. 134). The second make connection +between the two hemispheres, and form<pb n="294" /><anchor id="Pg294" /> +the corpus callosum. These are known as <hi rend="font-style: +italic">commissural</hi> fibers (<hi rend="font-style: italic">C</hi>, +Fig. 134). The third connect the cerebrum with the parts of the nervous +system below, and are called <hi rend="font-style: +italic">projection</hi> fibers (<hi rend="font-style: italic">P</hi>, +Fig. 134).</p> + +<p>2. <hi rend="font-style: italic">In the cerebellum</hi> both +association and commissural fibers are found. Bands of fibers, passing +upward toward the cerebrum and downward toward the cord, connect this +part of the brain with other parts of the nervous system.</p> + +<p rend="text-align: center"> +<figure url="images/image134.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 134—<hi rend="font-weight: +bold">Semi-diagrammatic representation of a section through the right +cerebral hemisphere</hi>, showing fiber tracts. <hi rend="font-style: +italic">A.</hi> Association fibers. <hi rend="font-style: +italic">C.</hi> Commissural fibers. <hi rend="font-style: +italic">P.</hi> Projection fibers. The cell-bodies with which the fiber +bundles connect are in the surface layer or cortex.</head> +<figDesc>Fig. 134</figDesc> +</figure></p> + +<p>3. <hi rend="font-style: italic">In the midbrain, bulb, and spinal +cord</hi> fibers are found: first, that connect these parts with the +cerebrum<note place="foot"><p>Fibers passing between the spinal cord and the cerebrum +cross to opposite sides—most of them at the bulb, but many within the +cord—so that the right side of the cerebrum is connected with the left +side of the body, and <hi rend="font-style: italic">vice versa</hi>. +This accounts for the observed fact that disease or accidental injury of +one side of the cerebrum causes loss of motion or of feeling in the +opposite side of the body.</p></note> and cerebellum above; second,<pb n="295" /><anchor id="Pg295" /> +that pass into and become a part of the nerves of the body; and third, +that connect the opposite sides of these parts together.</p> + +<p><hi rend="font-weight: bold">The Peripheral Division.</hi>—The +peripheral division of the nervous system includes all the nervous +structures found outside of the brain and spinal cord. These consist of +the cranial, spinal, and sympathetic nerves, and of various small +ganglia, all of which are closely connected with the central system.</p> + +<p><hi rend="font-weight: bold">Spinal Nerves and Dorsal-root +Ganglia.</hi>—The spinal nerves comprise a group of thirty-one pairs, +which connect the spinal cord with different parts of the trunk, with +the upper, and with the lower extremities. Each nerve joins the cord by +two roots, these being named from their positions the <hi +rend="font-style: italic">ventral</hi>, or anterior, root and the <hi +rend="font-style: italic">dorsal</hi>, or posterior, root. The two roots +blend together within the spinal cavity to form a single nerve trunk, +which passes out between the vertebræ. On the dorsal root of each +spinal nerve is a small ganglion which is named, from its position, the +<hi rend="font-style: italic">dorsal-root ganglion</hi>. (Consult Figs. +133 and 135, and also Fig. 125.)</p> + +<p><hi rend="font-weight: bold">Double Nature of Spinal +Nerves.</hi>—Charles Bell, in 1811, made the remarkable discovery that +each spinal nerve is double in function. He found the portion connecting +with the cord by the dorsal root to be concerned in the <hi +rend="font-style: italic">production of feeling</hi> and the portion +connecting by the ventral root to be concerned in the <hi +rend="font-style: italic">production of motion</hi>. In keeping with +these functions, the two divisions of the nerve are made up of different +kinds of fibers, as follows:</p> + +<p>1. The dorsal-root divisions, of the fibers of di-axonic neurons, the +cell-bodies of which form the dorsal-root ganglia (Fig. 135).</p> + +<p>2. The ventral-root divisions, of the fibers of mon-axonic<pb n="296" /><anchor id="Pg296" /> neurons, the cell-bodies of which +are in the gray matter of the cord.</p> + +<p>The first convey impulses to the cord and are called <hi +rend="font-style: italic">afferent</hi> neurons;<note place="foot"><p>In general, <hi rend="font-style: italic">afferent</hi> +neurons or fibers are those that convey impulses <hi rend="font-style: +italic">toward</hi> the central nervous system (brain and cord), while +<hi rend="font-style: italic">efferent</hi> neurons or fibers are those +that convey impulses <hi rend="font-style: italic">from</hi> the central +system.</p></note> the second convey +impulses from the cord and are known as <hi rend="font-style: +italic">efferent</hi> neurons. Thus, by forming a part of the nerve +pathways between the skin and the brain, the dorsal divisions of these +nerves aid in the production of feeling; and by completing pathways to +the muscles, the ventral divisions aid in the production of motion +(Figs. 129, 135, and 141).</p> + +<p rend="text-align: center"> +<figure url="images/image135.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 135—<hi rend="font-weight: bold">Connection of +spinal nerves with the cord.</hi> On the right is shown a nerve pathway +from the skin to the muscle. A division of this pathway reaches the +brain.</head> +<figDesc>Fig. 135</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Cranial Nerves.</hi>—From the under +front surface of the brain, twelve pairs of nerves emerge and pass to +the head, neck, and upper portions of the trunk. These, the cranial +nerves, have names suggestive of their function or distribution and, in +addition, are given numbers which indicate the order in which they leave +the brain (Fig. 136). Unlike the spinal nerves, the cranial nerves +present great variety among themselves, scarcely any two of them being +alike in function or in their connection with different parts of the +body. Several of them have to do with the special senses, and are for +this reason very important. They<pb n="297" /><anchor id="Pg297" /> connect the brain with the +different parts of the head, neck, and trunk, as follows:</p> + +<p>1. The first pair (<hi rend="font-style: italic">olfactory</hi> +nerves; nerves of smell; afferent) connect with the mucous membrane of +the nostrils (Fig. 136).</p> + +<p>2. The second pair (<hi rend="font-style: italic">optic</hi> nerves; +nerves of sight; afferent) connect with the retina of the eyes.</p> + +<p>3. The third, fourth, and sixth pairs (<hi rend="font-style: +italic">motores oculi;</hi> control muscles of the eyes; efferent) +connect with the internal and external muscles of the eyeballs (Fig. +136).</p> + +<p rend="text-align: center"> +<figure url="images/image136.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 136—<hi rend="font-weight: bold">Diagram +suggesting the distribution and functions of the cranial nerves</hi> +(Colton). See also Fig. 132.</head> +<figDesc>Fig. 136</figDesc> +</figure></p> + +<p>4. The fifth pair (<hi rend="font-style: italic">trigeminal</hi> +nerves; nerves of feeling<pb n="298" /><anchor id="Pg298" /> to the face, of taste to the +front of the tongue, and of control of muscles of mastication; afferent +and efferent) connect with the skin of the face, the mucous membrane of +the mouth, the teeth, and the muscles of mastication.</p> + +<p>5. The seventh pair (<hi rend="font-style: italic">facial</hi> +nerves; control muscles that give the facial expressions; efferent) +connect with the muscles just beneath the skin of the face.</p> + +<p>6. The eighth pair (<hi rend="font-style: italic">auditory</hi> +nerves; nerves of hearing; afferent) connect with the internal ear.</p> + +<p>7. The ninth pair (<hi rend="font-style: +italic">glossopharyngeal</hi> nerves; nerves of taste to back of tongue +and of muscular control of pharynx; afferent and efferent) connect with +the back surface of the tongue and with the muscles of the pharynx.</p> + +<p>8. The tenth pair (<hi rend="font-style: italic">vagus</hi>, or +pneumogastric, nerves; nerves of feeling and of muscular control; +afferent and efferent) connect with the heart, larynx, lungs, and +stomach. They have the widest distribution of any of the cranial +nerves.</p> + +<p>9. The eleventh pair (<hi rend="font-style: italic">spinal +accessory</hi> nerves; control muscles of neck; efferent) connect with +the muscles of the neck.</p> + +<p>10. The twelfth pair (<hi rend="font-style: italic">hypoglossal</hi> +nerves; control muscles of the tongue; efferent) connect with the +muscles of the tongue.</p> + +<p><hi rend="font-weight: bold">Sympathetic Ganglia and Nerves.</hi>—The +sympathetic ganglia are found in different parts of the body, and vary +in size from those which are half an inch in diameter to those that are +smaller than the heads of pins. The largest and most important ones are +found in two chains which lie in front, and a little to either side, of +the spinal column, and extend from the neck to the region of the pelvis +(Figs. 125 and 133). The number of ganglia in each of these chains is +about twenty-four. They are connected<pb n="299" /><anchor id="Pg299" /> on either side by the right and +left sympathetic nerves which extend vertically from ganglion to +ganglion. In addition to the ganglia forming these chains, important +ones are found in the head (outside of the cranial cavity) and in the +plexuses of the thorax and the abdomen.</p> + +<p>The sympathetic ganglia receive nerves from the central division of +the nervous system, but connect with glands, blood vessels, and the +intestinal walls through fibers from their own cell-bodies. Some of +these latter fibers join the spinal nerves, and some blend with each +other to form small sympathetic nerves.</p> + +<p><hi rend="font-weight: bold">Protection of Brain and Spinal +Cord.</hi>—On account of their delicate structure, the brain and spinal +cord require the most complete protection. In the first place, they are +surrounded by the bones of the head and spinal column; these not only +shield them from the direct effects of physical force, but by their +peculiar construction prevent, to a large degree, the passage of jars +and shocks to the parts within. In the second place, they are surrounded +by three separate membranes, as follows:</p> + +<p>1. The <hi rend="font-style: italic">dura</hi>, or dura mater, a +thick, dense, and tough membrane which lines the bony cavities and forms +supporting partitions.</p> + +<p>2. The <hi rend="font-style: italic">pia</hi>, or pia mater, a thin, +delicate membrane, containing numerous blood vessels, that covers the +surface of the brain and cord.</p> + +<p>3. The <hi rend="font-style: italic">arachnoid</hi>, a membrane of +loose texture, that lies between the dura and the pin.</p> + +<p>Finally, within the spaces of the arachnoid is a lymph-like liquid +which completely envelops the brain and the cord, and which, by serving +as a watery cushion, protects them from jars and shocks. Thus the brain +and cord are directly shielded by bones, by membranes, and by the <pb +n="300" /><anchor id="Pg300" />liquid which surrounds them. They are +also protected from jars resulting from the movements of the body by the +general elasticity of the skeleton.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The nervous system +establishes connections between all parts of the body, and provides a +stimulus by means of which they are controlled. It is made up of a +special form of cells, called neurons. The neurons form the different +divisions of the nervous system, and also serve as the active agents in +carrying on its work. Through a side-by-side method of joining they form +the nerves, ganglia, spinal cord, and brain; and by a method of +end-to-end joining they connect places remote from each other, and +provide for nervous movements through the body. The nervous system, may +in some respects be compared to a complicated system of telephony, in +which the chains of neurons correspond to the wires, and the brain and +spinal cord to the central station.</p> + +<p>Exercises.—1. Give the meaning of the term "coördination." Supply +illustrations.</p> + +<p>2. What two general conditions are supplied in the body by the +nervous system?</p> + +<p>3. Compare the skeleton outline of the nervous system with the bony +skeleton.</p> + +<p>4. Sketch outlines of mon-axonic and di-axonic neurons.</p> + +<p>5. Give two differences between the neurons and the other cells of +the body.</p> + +<p>6. Describe the two general methods of connecting neurons in the +body. What purpose is accomplished by each method?</p> + +<p>7. Name and locate the principal divisions of the nervous system.</p> + +<p>8. Draw an outline of the brain (side view), locating each of its +principal divisions.</p> + +<p>9. If a pencil were placed over the ear, what portions of the brain +would be above it and what below?</p> + +<p>10. Describe briefly the cerebrum, the cerebellum, the midbrain, the +pons, and the bulb.</p> + +<p><pb n="301" /><anchor id="Pg301" />11. Locate and +describe the cortex. State purpose of the convolutions.</p> + +<p>12. State the general differences between the cranial and the spinal +nerves.</p> + +<p>13. Locate and give the number of the dorsal-root ganglia. Locate and +give the approximate number of the sympathetic ganglia.</p> + +<p>14. Show how the two portions of the spinal nerves are formed—the one +from the mon-axonic and the other from the di-axonic neurons.</p> + +<p>15. Enumerate the different agencies through which the brain and +spinal cord are protected.</p> + +<p>16. What cranial nerves contain afferent fibers? What ones contain +efferent fibers? What ones contain both afferent and efferent +fibers?</p> + +<p>17. In what respects is the nervous system similar to a system of +telephony? In what respects is it different?</p> + +<div> +<head>PRACTICAL WORK</head> + +<p>Examine a model of the brain, identifying the different divisions and +noting the position and relative size of the different parts (Fig. 137). +Observe the convolutions of the cerebrum and compare these with the +parallel ridges of the cerebellum. If the model is dissectible, study +the arrangement of the cell-bodies (gray matter) and the distribution of +the fiber bundles (white matter). Note the connection of the cranial +nerves with the under side.</p> + +<p rend="text-align: center"> +<figure url="images/image137.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 137—Model for demonstrating the brain +(dissectible).</head> +<figDesc>Fig. 137</figDesc> +</figure></p> + +<p>A prepared nervous system of a frog (such as may be obtained from +supply houses) should also be examined. Observe the appearance and +general distribution of the nerves and their connection with the brain +and spinal cord. If such a preparation is not at hand, some small animal +may be dissected to show the main divisions of the nervous system, as +follows:</p> + +<p><hi rend="font-weight: bold">Dissection of the Nervous System</hi> +(by the teacher).—For this purpose a half-grown cat is generally the +best available material. This <pb n="302" /><anchor id="Pg302" />should +be killed with chloroform and secured to a board as in the dissection of +the abdomen (page 169). Open the abdominal cavity and remove the +contents, tying the alimentary canal where it is cut, and washing out +any blood which may escape. Dissect for the nervous system in the +following order:</p> + +<p>1. Cut away the front of the chest, exposing the heart and lungs. +Find on each side of the heart a nerve which passes by the side of the +pericardium to the diaphragm. These nerves assist in controlling +respiration and are called the <hi rend="font-style: +italic">phrenic</hi> nerves. Find other nerves going to different parts +of the thorax.</p> + +<p>2. Remove the heart and lungs. Find in the back part of the thoracic +cavity, on each side of the spinal column, a number of small "knots" of +nervous matter joined together by a single nerve. These are sympathetic +ganglia. Where the neck joins the thorax, find two sympathetic ganglia +much larger than the others.</p> + +<p>3. Cut away the skin from the shoulder and upper side of the fore +leg. By separating the muscles and connective tissue where the leg joins +the thorax, find several nerves of considerable size. These connect with +each other, forming a network called the <hi rend="font-style: +italic">brachial plexus</hi>. From here nerves pass to the thorax and to +the fore leg.</p> + +<p>4. From the brachial plexus trace out the nerves which pass to +different parts of the fore leg. In doing this separate the muscles with +the fingers and use the knife only where it is necessary to expose the +nerves. Note that some of the branches pass into the muscles, while +others connect with the skin.</p> + +<p>5. Remove the skin from the upper portion of one of the hind legs and +separate the muscles carefully until a large nerve is found. This is one +of the divisions of the <hi rend="font-style: italic">sciatic</hi> +nerve. Carefully trace it to the spinal cord, cutting away the bone +where necessary, and find the connections of its branches with the cord. +Then trace it toward the foot, discovering its branches to different +muscles and to the skin.</p> + +<p>6. Unjoint the neck and remove the head. Examine the spinal cord +where exposed. Cut away the bone sufficiently to show the connection +between the cord and one of the spinal nerves. On the dorsal root of one +of the nerves find a small ganglion. What is it called?</p> + +<p>7. Fasten the head to a small board and remove the scalp. Saw through +the skull bones in several directions. Pry off the small pieces of +bones, exposing the upper surface of the brain. Study its membranes, +convolutions, and divisions.</p> + +<p><pb n="303" /><anchor id="Pg303" />8. With +a pair of bone forceps, or nippers, break away the skull until the +entire brain can be removed from the cavity. Examine the different +divisions, noting the relative position and size of the parts.</p> + +<p>9. With a sharp knife cut sections through the different parts, +showing the positions of the "gray matter" and of the "white +matter."</p> + +<p>NOTE.—If the entire class is to examine one specimen, it is generally +better to have the dissecting done beforehand and the parts separated +and tacked to small boards. This will permit of individual examination. +Sketches of the sciatic nerve, brachial plexus, and of sections through +the brain and spinal cord should be made.</p> + +<p><hi rend="font-weight: bold">Location of Nerves in the +Body.</hi>—Several of the nerves of the body lie sufficiently near the +surface to be located by pressure and are easily recognized as sensitive +cords. Slight pressure from the fingers reveals the presence of nerves +in the grooves of the elbow (the crazy bone), between the muscles on the +inner side of the arm near the shoulder, and in the hollow part of the +leg back of the knee. These are all large nerves. Small nerves may be +located in the same manner in the face and neck.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="304" /><anchor id="Pg304" /> +<head>CHAPTER XVIII - PHYSIOLOGY OF THE NERVOUS SYSTEM</head> + +<p>In the preceding chapter was pointed out the method by which the +different parts of the body are brought into communication by the +neurons or nerve cells. We are now to study the means whereby the +neurons are made to control and coördinate the different parts of the +body and bring about the necessary adjustment of the body to its +surroundings. This work of the neurons naturally has some relation to +their properties.</p> + +<p><hi rend="font-weight: bold">Properties of Neurons.</hi>—The work of +the neurons seems to depend mainly upon two properties—the property of +irritability and the property of conductivity. <hi rend="font-style: +italic">Irritability</hi> was explained, in the study of the muscles +(page 243), as the ability to respond to a stimulus. It has the same +meaning here. The neurons, however, respond more readily to stimuli than +do the muscles and are therefore more irritable. Moreover, they are +stimulated by all the forces that induce muscular contraction and by +many others besides. They are by far the most irritable portions of the +body.</p> + +<p><hi rend="font-style: italic">Conductivity</hi> is the property which +enables the effect of a stimulus to be transferred from one part of a +neuron to another. On account of this property, an excitation, or +disturbance, in any part of a neuron is conducted or carried to all the +other parts. Thus a disturbance at the distant ends of the dendrites +causes a movement toward the cell-body and, reaching the cell-body, the +disturbance is<pb n="305" /><anchor id="Pg305" /> passed through it into the axon. +This movement through the neuron is called the <hi rend="font-style: +italic">nervous impulse</hi>.</p> + +<p><hi rend="font-weight: bold">Purpose of the Impulse. </hi>—Though +the nature of the nervous impulse is not understood, <note place="foot"><p>At different times the nervous impulse has been regarded +as a current of electricity; as a progressive chemical change, likened +to that in a burning fuse; as a mechanical vibration, such as may be +passed over a stretched rope; and as a molecular disturbance accompanied +by an electrical discharge. The velocity of the nervous impulse, which +is only about one hundred feet per second, proves that it is not a +current of electricity. It takes place with little or no exhaustion of +the cell protoplasm and consequently is not due to chemical action. And +the loose, relaxed condition of the nerves prevents their transmission +of physical vibrations, like those on a stretched rope. The view that +the impulse is a progressive molecular disturbance, accompanied by an +electrical discharge, has much evidence in its favor, but it has only +recently been proposed and is likely to be modified upon fuller +investigation.</p></note> its purpose is +quite apparent. It is the means employed by the nervous system for +controlling and coördinating the different parts of the body. The +arrangement of the neurons enables impulses to be started in certain +parts of the nervous system, and the property of conductivity causes +them to be passed <hi rend="font-style: italic">as stimuli </hi>to other +parts. This enables excitation at one place to bring about action at +another place.</p> + +<p>Acting as stimuli, the impulses seem able to produce two distinct +effects: first, to throw resting organs into action and to increase the +activity of organs already at work; and second, to diminish the rate, or +check entirely, the activity of organs. Impulses producing the first +effect are called <hi rend="font-style: italic">excitant</hi> impulses; +those producing the second effect, <hi rend="font-style: +italic">inhibitory</hi> impulses.</p> + +<p><hi rend="font-weight: bold">Functions of the Parts of +Neurons.</hi>—The <hi rend="font-style: italic">cell-body</hi> serves as +a nutritive center from which the other parts derive nourishment. Proof +of this is found in the fact that when any part of the neuron is +separated from the cell-body, it dies, while the cell-body and the parts +attached to the cell-body<pb n="306" /><anchor id="Pg306" /> may continue to live. In +addition to this the cell-body probably reënforces the nervous +impulse.</p> + +<p>The <hi rend="font-style: italic">dendrites</hi> serve two purposes: +first, they extend the surface of the cell-body, thereby enabling it to +absorb a greater amount of nourishment from the surrounding lymph; +second, they act as <hi rend="font-style: italic">receivers of +stimuli</hi> from other neurons. The same impulse does not pass from one +neuron to another. An impulse in one neuron, however, is able to excite +the neuron with which it makes an end-to-end connection, so that a +series of impulses is produced along a given nerve path (Fig. 129).</p> + +<p>The special <hi rend="font-style: italic">function of the axon</hi> +is to transmit the impulse. By its length, structure, and property of +conductivity it is especially adapted to this purpose. The axis +cylinder, however, is the only part of the axon concerned in the +transmission. The primitive sheath and the medullary layer protect the +axis cylinder, and, according to some authorities, serve to insulate it. +The medullary sheath may also aid in the nourishment of the axis +cylinder.</p> + +<p><hi rend="font-weight: bold">Nerve Stimuli.</hi>—While the +properties of irritability and conductivity supply a necessary cause for +the production and transmission of nervous impulses, these alone are not +sufficient to account for their origin. An additional cause is necessary—a +force not found in the nerve protoplasm, but one which, by its +action on the protoplasm, makes it produce the impulse. In this respect, +the neuron does not differ essentially from the cell of a muscle. Just +as the muscle cell requires a stimulus to make it contract, so does the +neuron require a stimulus to start the impulse. Hence, in accounting for +the activities of the body, it is not sufficient to say they are caused +by nervous impulses. We must also investigate the <hi rend="font-style: +italic">nerve stimuli</hi>—the means through which the nervous impulses +are started. Most of these<pb n="307" /><anchor id="Pg307" /> are found outside of the body and +are known as external stimuli.</p> + +<p><hi rend="font-weight: bold">Action of External Stimuli.</hi>—In the +arrangement of the nervous system the most favorable conditions are +provided for the reception of external stimuli. Not only do vast numbers +of neurons terminate at the surface of the body,<note place="foot"><p>The surface of the body includes the linings of the air +passages, food canal, and certain cavities, as well as the external +covering or skin.</p></note> but they connect +there with delicate structures, called <hi rend="font-style: +italic">sense organs</hi>. The purpose of the sense organs is to <hi +rend="font-style: italic">sensitize</hi> (make sensitive) the +terminations of the neurons. This they do by supplying special +structures through which the stimuli can act to the best advantage upon +the nerve endings. Moreover, there are different kinds of sense organs, +and these cause the neurons to be sensitive to different kinds of +stimuli. Acting through the sense organs adapted for receiving them, +light, sound, heat, cold, and odors all act as stimuli for starting +impulses. Indeed, the arrangement is so complete that the nervous system +is subjected to the action of external stimuli in some form practically +all the time. The work of the sense organs is further considered in +Chapters XX, XXI, and XXII.</p> + +<p><hi rend="font-weight: bold">How External Stimuli act on Internal +Organs.</hi>—For stimulating the neurons not connected with the body +surface we are dependent, so far as known, upon the nervous impulses. An +impulse started by the external stimulus goes only so far as its neuron +extends. But it serves as a stimulus for the neuron with which the first +connects and starts an impulse in this connecting neuron, the point of +stimulation being where the fiber terminations of the first neuron make +connection with the dendrites of the second. This impulse in turn +stimulates the next neuron, and so on, producing a series of impulses +along a given nerve path. <pb n="308" /><anchor id="Pg308" />In this way the effect of an +external stimulus may reach and bring about action in any part of the +body. This is in brief the general plan of inducing action in the +various organs of the body. This plan, however, is varied according to +circumstances, and at least three well-defined forms of action are +easily made out. These are known as <hi rend="font-style: italic">reflex +action, voluntary action</hi>, and <hi rend="font-style: +italic">secondary reflex action</hi>.</p> + +<p><hi rend="font-weight: bold">Reflex Action.</hi>—When some sudden or +strong stimulus acts upon the nerve terminations at the surface of the +body, an immediate response is frequently observed in some quick +movement. The jerking away of the hand on accidentally touching a hot +stove, the winking of the eyes on sudden exposure to danger, and the +quick movements from slight electrical shocks are familiar examples. The +explanation of reflex action is that external stimuli start impulses in +neurons terminating at the surface of the body and these, in turn, +excite impulses in neurons which pass from the spinal cord or brain to +the muscles (Fig. 138). Since there is an apparent turning back of the +impulses by the cord or brain, the resulting movements are termed <hi +rend="font-style: italic">reflex</hi>.<note place="foot"><p>Derived from the Latin <hi rend="font-style: +italic">re</hi>, back, and <hi rend="font-style: italic">flectere</hi>, +to turn or bend.</p></note></p> + +<p rend="text-align: center"> +<figure url="images/image138.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 138—<hi rend="font-weight: bold">Diagram +illustrating reflex action of an external organ.</hi></head> +<figDesc>Fig. 138</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Reflex Action and the Mind.</hi>—If one +carefully studies the reflex actions of his own body, he will find that +they<pb n="309" /><anchor id="Pg309" /> occur at the time, or even a +little before the time, that he realizes what has happened. If a feather +is brought in contact with the more sensitive parts of the face of a +sleeping person, there is a twitching of the skin and sometimes a +movement of the hand to remove the offending substance. Surgeons +operating upon patients completely under the influence of chloroform, +and therefore completely unconscious, have observed strong reflex +actions. These and other similar cases indicate clearly that reflex +action occurs <hi rend="font-style: italic">independently</hi> of the +mind—that the mind neither causes nor controls it. If a further proof of +this fact were needed, it is supplied by experiments upon certain of the +lower animals,<note place="foot"><p>A frog from which the brain has been removed is +suspended with its feet downward and free to move. If a toe is pinched, +the foot is drawn away, and if dilute acid, or a strong solution of +salt, is placed on the tender skin, the feet are moved as if to take +away the irritating substance. This of course shows that reflex action +can take place independently of the brain.</p> + +<p>Now if the spinal cord is also destroyed, there is no response when +the irritation of the skin is repeated. The animal remains perfectly +quiet, because the destruction of the cord has interrupted the reflex +action pathway. This shows that some part of the central nervous system +is necessary to reflex action.</p></note> which live for a while after the removal of the brain. +These experiments show that the nervous impulses that produce reflex +action need only pass through the spinal cord and do not reach the +cerebrum, the organ of the mind.</p> + +<p><hi rend="font-weight: bold">The Reflex Action Pathway.</hi>—By study +of the impulses that produce any reflex action, a rather definite +pathway may be made out, having the following divisions:</p> + +<p>1. <hi rend="font-style: italic">From the surface of the body to the +central nervous system</hi> (usually the spinal cord). This, the <hi +rend="font-style: italic">afferent</hi> division, is made up of +di-axonic neurons, and these have (in the case of the spinal nerves) +their cell-bodies in the dorsal root ganglia (page 295). They are acted +upon by external stimuli, while their impulses in turn act on the +neurons in the spinal cord.</p> + +<p><pb n="310" /><anchor id="Pg310" />2. <hi rend="font-style: italic">Through the central system</hi> +(spinal cord or base of brain). This, the <hi rend="font-style: +italic">intermediate</hi> division, may be composed of mon-axonic +neurons, or it may consist of branches from the afferent neurons. In the +case of separate neurons, these are acted upon by impulses from the +afferent neurons, while their impulses serve in turn as stimuli to other +neurons within the cord (Fig. 129).</p> + +<p>3. <hi rend="font-style: italic">From the central nervous system to +the muscles.</hi> This, the <hi rend="font-style: italic">efferent</hi> +division, is made up of mon-axonic neurons. Most of these have their +cell-bodies in the gray matter of the cord, while their fibers pass into +the spinal nerves by the ventral roots.<note place="foot"><p>Review description of the spinal nerves, page 295.</p></note> They may be stimulated by +impulses either from the intermediate neurons, or from branches of the +afferent neurons. Their impulses reach and stimulate the muscles.</p> + +<p><hi rend="font-weight: bold">Reflex Action in Digestion.</hi>—The +flowing of the saliva, when food is present in the mouth, is an example +of reflex action. In this case, however, the organ excited to activity +is a gland instead of a muscle. The food starts the impulses, and these, +acting through the bulb, reach and stimulate the salivary glands. In a +similar manner food excites the glands that empty their fluids into the +stomach and intestines, and stimulates the muscular coats of these +organs to do their part in the digestive process. To a considerable +extent, neurons having their cell-bodies in the sympathetic ganglia are +concerned in these actions (Fig. 139).</p> + +<p rend="text-align: center"> +<figure url="images/image139.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 139—Diagram illustrating reflex action in its +relation to the food canal. The nerve path in this case includes +sympathetic neurons.</head> +<figDesc>Fig. 139</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Reflex Action in the Circulation of the +Blood.</hi>—On sudden exposure<pb n="311" /><anchor id="Pg311" /> to cold, the small arteries going +to the skin quickly diminish in size, check the flow of blood to the +surface, and prevent too great a loss of heat. In this case, impulses +starting at the surface of the body are transmitted to the bulb and then +through the efferent neurons to the muscles in the walls of the +arteries. In a somewhat similar manner, heat leads to a relaxation of +the arterial walls and an increase in the blood supply to the skin. +Other changes in the blood supply to different parts of the body are +also of the nature of reflex actions. As in the work of digestion, +neurons having their cell-bodies in the sympathetic ganglia aid in the +control of the circulation.</p> + +<p><hi rend="font-weight: bold">Purposes of Reflex Action.</hi>—The +examples of reflex action so far considered illustrate its two main +purposes—(1) protection, and (2) a means of controlling important +processes.</p> + +<p>The pupil has but to study carefully the reflex actions of his own +body for a period, say of two or three weeks, in order to be convinced +of their protective value. He will observe that portions of his body +have, on exposure to danger, been moved to places of safety, while in +some instances, like falling, his entire body has been adjusted to new +conditions. He will also find that reflex action is quicker, and for +that reason offers in some cases better protection, than movements +directed by the mind. In digestion and circulation are found the best +examples of the control of important processes through reflex +action.</p> + +<p><hi rend="font-weight: bold">Voluntary Action.</hi>—It is observed +that reflex action, in the sense that it has so far been considered, is +not the usual mode of action of the external organs, but is, instead, a +kind of emergency action, due to unusual conditions and excitation by +strong stimuli. Voluntary actions, on the other hand, represent the +ordinary, or normal, action of these organs. They comprise the movements +of the body of which we are conscious and which are <hi +rend="font-style: italic">controlled by the mind</hi>. But while they +are of a higher order than reflex<pb n="312" /><anchor id="Pg312" /> actions and are under <hi +rend="font-style: italic">intelligent</hi> direction, they are brought +about in much the same manner.</p> + +<p><hi rend="font-weight: bold">Voluntary Action Pathways</hi> differ in +but one essential respect from those of reflex action. They pass through +the cerebrum, the organ of the mind (Fig. 140). This is necessary in +order that the mind may control the action. From all portions of the +body surface, afferent pathways may be traced to the cerebrum; and from +the cerebrum efferent pathways extend to all the voluntary organs. A +complex system of intermediate neurons, found mostly in the brain, join +the afferent with the efferent pathways. The voluntary pathways are not +distinct from, but include, reflex pathways, a fact which explains why +the same external stimulus may excite both reflex and voluntary action +(Fig. 141).</p> + +<p rend="text-align: center"> +<figure url="images/image140.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 140—<hi rend="font-weight: bold">Diagram of a +voluntary action pathway.</hi></head> +<figDesc>Fig. 140</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Choice in Voluntary Action.</hi>—In +reflex action a given stimulus, acting in a certain way; produces each +time the same result. This is not the case with voluntary action, the +difference being <hi rend="font-style: italic">due to the mind</hi>. In +these actions the external stimulus first excites the mind, and the +resulting mental processes—perhaps as memory of previous +experiences—supply a variety of facts, any of which may act as stimuli +to action. Before the action takes place, however, <pb n="313" /><anchor +id="Pg313" />some one fact must be singled out from among the mental +processes excited. This fact becomes the <hi rend="font-style: +italic">exciting stimulus</hi> and leads to action. It follows, +therefore, that the action which finally occurs is not necessarily the +result of an immediate external stimulus, but of a <hi rend="font-style: +italic">selected</hi> stimulus—one which is the result of choice.</p> + +<p rend="text-align: center"> +<figure url="images/image141.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 141—<hi rend="font-weight: bold">Diagram of +voluntary action pathways</hi> including reflex pathways.</head> +<figDesc>Fig. 141</figDesc> +</figure></p> + +<p>Not only does the element of choice enter into the selection of the +proper stimulus, but it also enters into the time, nature, and intensity +of the action. For these reasons it is frequently impossible to trace +voluntary actions back to their actual stimuli. The pupil will recognize +the element of choice in such simple acts as picking up some object from +the street, complying with a request, and purchasing some article from a +store.</p> + +<p><hi rend="font-weight: bold">Reflex and Voluntary Action +Compared.</hi>—Certain likenesses and differences, already suggested in +these two forms of action, may now be more fully pointed out. Reflex and +voluntary action are alike in that the primary cause of each is some +outside force or condition which has impressed itself upon the nervous +system. They are also alike in the general direction taken by the +impulses in producing the action. The impulses are, first, from the +surface of the body to the central nervous system; second,<pb n="314" +/><anchor id="Pg314" /> through the central system; and third, from the +central nervous system to the active tissues of the body.</p> + +<p>Their chief differences are to be found, first, in the pathways +followed by the impulses, which are through the cerebrum (the organ of +the mind) in voluntary action, but in reflex action are only through the +spinal cord or the lower parts of the brain; and second, in the fact +that voluntary action is under the direction of the mind, while reflex +action is not. It would seem, therefore, that the statement sometimes +made that "voluntary action is reflex action plus the mind" is not far +from correct. Mind, however, is the important factor in this kind of +action.</p> + +<p><hi rend="font-weight: bold">Secondary Reflex Action.</hi>—Everyday +experience teaches that any voluntary action becomes easier by +repetition. A given act performed a number of times under conscious +direction establishes a condition in the nervous system that enables it +to occur without that direction and very much as reflex actions occur. +Actions of this kind are known as secondary reflex actions, or as <hi +rend="font-style: italic">acquired reflexes</hi>. Walking, writing, and +numerous other movements pertaining to the occupation which one follows +are examples of such reflexes. These activities are at first entirely +voluntary, but by repetition they gradually become reflex, requiring +only the stimulus to start them.</p> + +<p>The advantages to the body of its acquired reflexes are quite +apparent. The mind does not have to attend to the selection and +direction of stimuli and, to that extent, is left free for other work. A +good example of this is found in writing, where the mind apparently +gives no heed to the movements of the hand and is only concerned in what +is being written. The student will easily supply other illustrations of +the advantages of secondary reflex action.</p> + +<p><pb n="315" /><anchor id="Pg315" />The development of secondary +reflexes probably consists in the establishment of fixed pathways for +impulses through the nervous system. Through the branching of the nerve +fibers many pathways are open to the impulses. But in repeating the same +kind of action the impulses are guided into particular paths, or +channels. In time these paths become so well established that the +impulses flow along them without conscious direction and it is then +simply necessary that some stimulus starts the impulses. By following +the established pathways, these reach the right destination and produce +the desired result. According to this view, secondary reflex action is +but a higher phase of ordinary reflex action—a kind of reflex action, +the conditions of which have been established by the mind through +repetition. (See functions of the cerebellum, page 317.)</p> + +<p><hi rend="font-weight: bold">Habits.</hi>—People are observed to act +differently when exposed to the same conditions, or when acted upon by +the same stimuli. This is explained by saying they have different +habits. By <hi rend="font-style: italic">habits</hi> are meant certain +general modes of action that have been acquired by repetition. Certain +acts repeated again and again have established conditions in the nervous +system which enable definite forms of action to be excited, somewhat +after the manner of reflex action. On account of habits, therefore, the +actions of the individual are more or less <hi rend="font-style: +italic">predisposed</hi>. What he will do under certain conditions may +be foretold from his habits. Habits simply represent, a higher order of +secondary reflexes—those more closely associated with the mental life +and character than are the lower forms.</p> + +<p>Habits, in common with other forms of secondary reflex action, serve +the important purpose of <hi rend="font-style: italic">economizing the +nervous energy</hi>. However, if pernicious habits are formed instead of +those that are useful, they are detrimental from both a moral and +physical standpoint. Youth is recognized as the period in which +fundamental habits are formed and character is largely determined. +Therefore parents<pb n="316" /><anchor id="Pg316" /> and teachers do +wisely when they insist upon the formation of right habits by the +young.</p> + +<p><hi rend="font-weight: bold">Functions of Divisions of the Nervous +System.</hi>—The relationship between the different parts of the nervous +system is very close and one part does not work independently of other +parts. At the same time the general work of the nervous system requires +that its different divisions serve different purposes:</p> + +<p>1. The peripheral divisions of the nervous system are concerned in the +transmission of impulses between the surface of the body and the central +system and between the central system and the active tissues. The nerves +are the carriers of the impulses. The ganglia contain the cell-bodies +which serve as nutritive centers; and, in the case of the sympathetic +ganglia, these cell-bodies are the places where the fiber terminations +of one neuron connect with, and stimulate, other neurons.</p> + +<p>2. The gray matter in the spinal cord, bulb, pons, and midbrain +(through the cell-bodies, fiber terminations, and short neurons which +they contain) completes the reflex action pathways between the surface +of the body and the voluntary muscles, and also between the surface of +the body and the organs of circulation and digestion.</p> + +<p>3. The white matter of the spinal cord, bulb, pons, and midbrain (by +means of the fibers of which they are largely composed) forms +connections with, and passes impulses between, the various parts of the +central nervous system.</p> + +<p>4. The bulb, because of certain special reflex-action pathways +completed through it, is the portion of the central nervous system +concerned in the control of respiration, circulation, and the secretion +of liquids.</p> + +<p><hi rend="font-weight: bold">Work of the Sympathetic Ganglia and +Nerves.</hi>—The neurons which form these ganglia aid in controlling the +vital processes, especially digestion<pb n="317" /><anchor id="Pg317" /> +and circulation. These neurons are controlled for the most part by +fibers from the bulb and spinal cord, and cannot for this reason be +looked upon as forming an independent system. Their chief purpose seems +to be that of spreading the influence of neurons from the central system +over a wider area than they would otherwise reach. For example, a single +neuron passing out from the spinal cord may, by terminating in a +sympathetic ganglion, stimulate a large number of neurons, each of which +will in turn stimulate the cells of muscles or of glands. Because of +this function, the sympathetic neurons are sometimes called <hi +rend="font-style: italic">distributing</hi> neurons.</p> + +<p><hi rend="font-weight: bold">Functions of the +Cerebellum.</hi>—Efforts to discover some <hi rend="font-style: +italic">special</hi> function of the cerebellum have been in the main +unsuccessful. Its removal from animals, instead of producing definite +results, usually interferes in a mild way with a number of activities. +The most noticeable results are a general weakness of the muscles and an +inability on the part of the animal to balance itself. This and other +facts, including the manner of its connection with other parts of the +nervous system, have led to the belief that the cerebellum is the chief +organ for the <hi rend="font-style: italic">reflex</hi> coördination of +muscular movements, especially those having to do with the balancing of +the body. In this connection it is subordinate to and under the control +of the cerebrum. Of the relations which the cerebellum sustains to the +cerebrum and to the different parts of the body, the following view is +quite generally held:</p> + +<p>In the development of secondary reflexes, as already described, +conditions are established in the cerebellum, such that given stimuli +may act <hi rend="font-style: italic">reflexively</hi> through it and +produce definite results in the way of muscular contraction. After the +establishment of these conditions, afferent impulses from the eyes, +ears, skin, and other places, under the general direction of the +cerebrum, may cause such actions as the balancing of the body, walking, +etc., as well as the delicate and varied movements of the hand. This +view of its functions makes of the cerebellum the great center of +secondary reflex action.</p> + +<p><hi rend="font-weight: bold">Functions of the Cerebrum.</hi>—While +the work of the cerebrum is closely related to that of the general +nervous system, it, more than any other part, exercises functions +peculiar to itself. The cerebrum is the part of the nervous system upon +which our varied experiences leave their impressions and through which +these impressions are made<pb n="318" /><anchor id="Pg318" /> to +influence the movements of the body. But the power to alter, postpone, +or entirely inhibit, nervous movements is but a part of the general work +ascribed to the cerebrum as <hi rend="font-style: italic">the organ of +the mind</hi>. Numerous experiments performed upon the lower animals, +together with observations on man, show the cerebrum to be the seat of +the mental activities, and to make possible, in some way, the processes +of consciousness, memory, volition, imagination, emotion, thought, and +sensation.</p> + +<p><hi rend="font-weight: bold">Localization of Cerebral +Functions.</hi>—Many experiments have been performed with a view to +determining whether the entire cerebrum is concerned in each of its +several activities or whether special functions belong to its different +parts. These experiments have been made upon the lower animals and the +results thus obtained compared with observations made upon injured and +imperfectly developed brains in man. The results have led to the +conclusion that certain forms of the work of the cerebrum are <hi +rend="font-style: italic">localized</hi> and that some of its parts are +concerned in processes different from those of others.</p> + +<p rend="text-align: center"> +<figure url="images/image142.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 142—<hi rend="font-weight: bold">Location of +cerebral functions.</hi> Diagram of cerebrum, showing most of the areas +whose functions are known.</head> +<figDesc>Fig. 142</figDesc> +</figure></p> + +<p>The work of locating the functions of different parts of the cerebrum +forms one of the most interesting chapters in the history of brain +physiology. The portions having to do with sight, voluntary motion, +speech, and hearing have been rather accurately determined, while +considerable evidence as to the location of other functions has been +secured. Much of the cerebral surface, however, is still undetermined +(Fig. 142).</p> + +<div> +<head>NERVOUS CONTROL OF IMPORTANT PROCESSES</head> + +<p><hi rend="font-weight: bold">Circulation of the Blood.</hi>—1. <hi +rend="font-style: italic">Control of the Heart.</hi>—The ability to +contract at regular intervals has been shown to reside in the heart <pb +n="319" /><anchor id="Pg319" />muscle. Among other proofs is that +furnished by cold-blooded animals, like the frog, whose heart remains +active for quite a while after its removal from the body. These +automatic contractions, however, are not sufficient to meet all the +demands made upon the circulation. The needs of the tissues for the +constituents of the blood vary with their activity, and it is therefore +necessary to vary frequently the force and rapidity of the heart's +contractions. Such changes the heart itself is unable to bring +about.</p> + +<p>For the purpose of controlling the rate and force of its +contractions, the heart is connected with the central nervous system by +two kinds of fibers:</p> + +<p><hi rend="font-style: italic">a.</hi> Fibers that convey <hi +rend="font-style: italic">excitant</hi> impulses to the heart to quicken +its movements.</p> + +<p><hi rend="font-style: italic">b.</hi> Fibers that convey <hi +rend="font-style: italic">inhibitory</hi> impulses to the heart to +retard its movements.</p> + +<p>The cell-bodies of the excitant fibers are found in the sympathetic +ganglia, but fibers from the bulb connect with and control them. The +cell-bodies of the inhibitory fibers are located in the bulb, from where +their fibers pass to the heart as a part of the vagus nerve.</p> + +<p>In addition to the fibers above mentioned, are those that convey +impulses <hi rend="font-style: italic">from</hi> the heart to the bulb. +These connect with neurons that in turn connect with blood vessels and +with them act reflexively, when the heart is likely to be overstrained, +to cause a dilation of the blood vessels. This lessens the pressure +which the heart must exert to empty itself of blood. These fibers serve, +in this way, as a kind of safety valve for the heart.</p> + +<p>2. <hi rend="font-style: italic">Control of Arteries.</hi>—Changes in +the rate and force of the heart's contractions can be made to correspond +only to the <hi rend="font-style: italic">general</hi> needs of the +body. When the blood supply to a particular organ is to be increased or +diminished, this is accomplished through the muscular coat in the +arteries. The connection of the arterial muscle with the sympathetic +ganglia and the method by which they vary the flow of blood to different +organs has already been explained (pages 311 and 49), so that only the +location of the controlling neurons need be noted here. These, like the +controlling neurons of the heart, have their cell-bodies in the bulb. It +thus appears that the entire control of the circulation is effected in a +reflex manner through the nerve centers in the bulb. These centers are +stimulated by conditions that relate to the movement of the blood +through the body.</p> + +<p><pb n="320" /><anchor id="Pg320" /><hi rend="font-weight: +bold">Respiration.</hi>—Efferent fibers connect the different muscles of +respiration with a cluster of cell-bodies in the bulb, called the <hi +rend="font-style: italic">respiratory center</hi>. This center together +with the nerves and muscles in question form an automatic, or +self-acting, mechanism similar in some respects to that of the heart. +Through the impulses passing from the respiratory center to the muscles, +a rhythmic action is maintained sufficient to satisfy the usual needs of +the body for oxygen. The demand of the body for oxygen, however, varies +with its activities, and to such variations the respiratory center alone +is unable to respond. The regulating factor in the respiratory movements +has been found to be the condition of the blood with reference to the +presence of oxygen and carbon dioxide. If the blood contains much carbon +dioxide and little oxygen, it acts as a strong stimulus to the +respiratory center, causing it, in turn, to stimulate the respiratory +muscles with greater intensity and frequency. On the other hand, if the +blood contains much oxygen and little carbon dioxide, it acts only as a +mild stimulus. This explains how physical exercise increases the +breathing, since the muscles at work consume more oxygen than when +resting and give more carbon dioxide and other wastes to the blood.</p> + +<p>The respiratory center is also connected by afferent nerves with the +mucous membrane of the air passages. Irritation of the nerve endings in +this membrane causes impulses to pass to the center, and this leads, by +reflex action, to such modifications of the respiratory acts as sneezing +and coughing. There is also a connection between the cerebrum and the +respiratory center. This is shown by the fact that one can voluntarily +change the rate and force of the respiratory movements, and further by +the fact that emotions affect the breathing.</p> + +<p><hi rend="font-weight: bold">Regulation of the Body +Temperature.</hi>—As explained in the study of the skin (page 270), the +nervous system regulates the body temperature by controlling the +circulation of the blood through the skin and the internal organs. This +is accomplished by stimulating in a reflex manner the muscles in the +walls of certain arteries. To prevent the body from getting too hot, +muscles in the arteries going to the skin relax, thereby allowing more +blood to flow to the surface, where the heat can be disposed of through +radiation and through the evaporation of the perspiration. On the other +hand, if the body is in danger of losing too much heat, the muscles in +the walls of arteries going to the skin are made to contract and those +to internal organs relax, so that less blood flows to the skin and more +to the internal organs. In this<pb n="321" /><anchor id="Pg321" /> way +the nervous system adjusts the circulation to suit the conditions of +temperature outside of and within the body and, in so doing, maintains +the normal body temperature.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The nervous system is able +to control, coördinate, and adjust the different organs of the body +through its intimate connection with all parts and through a stimulus +(the nervous impulse) which it supplies and transmits. Nervous impulses, +excited by external stimuli, follow definite paths and cause activity in +the different parts of the body. All such pathways are through the +central nervous system. In reflex action the impulses are mainly through +the spinal cord, but to some extent through the bulb, pons, and +midbrain. In voluntary action they pass through the cerebrum—a condition +that leads to important modifications in the results. The cerebrum, in +addition to controlling the voluntary movements, is able to establish +the necessary conditions for secondary reflex actions, such as walking, +writing, etc. Although certain of the divisions of the nervous system +exercise special functions, all parts of it are closely related.</p> + +<p>Exercises.—1. Give the function of each of the parts of a neuron.</p> +<p>2. State the purpose of the nervous impulse.</p> + +<p>3. Show that the exciting cause of bodily action is outside of the +nervous system and, to a large extent, outside of the body.</p> + +<p>4. Describe the arrangement that enables stimuli outside of the body +to cause action within the body.</p> + +<p>5. Describe a reflex action and show how it is brought about.</p> + +<p>6. Distinguish between afferent, efferent, and intermediate +neurons.</p> + +<p>7. Draw diagrams showing the impulse pathways in voluntary and in +reflex action.</p> + +<p>8. What purposes are served by the sympathetic neurons?</p> + +<p>9. Describe the method of control of the circulatory and digestive +processes. How do reflex actions protect the body?</p> + +<p><pb n="322" /><anchor id="Pg322" />10. Compare voluntary and reflex +action. In what sense are all the activities of the body reflex?</p> + +<p>11. In what sense is walking voluntary? In what sense is it +reflex?</p> + +<p>12. How does secondary reflex action lessen the work of the nervous +system?</p> + +<p>13. State the special functions of the nerves, ganglia, spinal cord, +bulb, cerebellum, and cerebrum.</p> + +<p>14. State the importance of the formation of correct habits.</p> + +<p rend="text-align: center"> +<figure url="images/image143.png" rend="page-float: 'hp'; text-align: center; w55"> +<head><lb />Fig. 143—Nerve board for demonstrating nerve +pathways.</head> +<figDesc>Fig. 143</figDesc> +</figure></p> + +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">To demonstrate Nerve Pathways.</hi>—A +smooth board, 2x6 ft., is painted black, and upon this is drawn in white +a life-size outline of the body. Pieces of cord of different colors and +lengths are knotted to represent mon-axonic and di-axonic neurons. These +are then pinned or tacked to the board in such a manner as to represent +the connections in the different kinds of nerve pathways. Fig. 143 shows +such a board with connections for a reflex action and a voluntary action +of the same muscle.</p> + +<p><hi rend="font-weight: bold">Study of the "Knee Jerk" Reflex.</hi>—A +boy is seated on a chair with the legs crossed. With a small pointer he +is given a light, quick blow on the upper margin of the patella at the +point of connection of the tendon. The stroke will usually be followed +by a reflex movement of the foot. Does this take place independently of +the mind? (The one upon whom the experiment is being performed should +assume a relaxed condition and make no effort either to cause or prevent +the movement.) Can the movement be<pb n="323" /><anchor id="Pg323" /> +inhibited (prevented)? Repeat the experiment, effort being made to +prevent the movement, but not by contracting opposing muscles.</p> + +<p>Other reflex actions adapted to class study are those of the eyes, +such as the closing of the lids on moving objects near them and the +dilating of the pupils when the eyes are shaded. The involuntary jerking +of the head on bringing the prongs of a vibrating tuning fork in contact +with the end of the nose is also a reflex action which can be studied to +advantage.</p> + +<p><hi rend="font-weight: bold">To determine the Reaction +Time.</hi>—Have several pupils join hands, facing outwards, making a +complete circle, excepting one gap. Give a signal by touching the hand +of one pupil at the end of the line. Let this pupil communicate the +signal, by pressure of the other hand, to the next pupil and so on +around, having the last pupil raise the free hand at close of the +experiment. Note carefully the time, preferably with a stop watch, +required to complete the experiment and divide this by the number of +pupils, to get the average reaction time. The experiment may be repeated +with boys only and then with girls, comparing their average reaction +time.</p> + +<p><hi rend="font-weight: bold">Reflex Action of the Salivary +Glands.</hi>—Place a small pinch of salt upon the tongue and note the +flow of saliva into the mouth. Try other substances, as starch, bits of +wood, and sugar. What appears to be the natural stimulus for these +glands? Compare with reflex actions of the muscles.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="324" /><anchor id="Pg324" /> +<head>CHAPTER XIX - HYGIENE OF THE NERVOUS SYSTEM</head> + +<p>The far-reaching effects and serious nature of disorders of the +nervous system are sufficient reasons for considering carefully those +conditions that make or mar its efficiency. Controlling all the +activities of the body and affecting through its own condition the +welfare of all the organs, the hygiene of the nervous system is, in a +large measure, the hygiene of the entire body. Moreover, it is known +that some of our worst diseases, including paralysis and insanity, are +disorders of the nervous system and are prevented in many instances by a +proper mode of living.</p> + +<p><hi rend="font-weight: bold">The Main Problem.</hi>—Many of our +nervous disorders are undoubtedly due to the age in which we live. Our +modern civilization, with all its facilities for human advancement and +enjoyment, throws an extra strain upon the nervous system. Educational +and social standards are higher than ever before and life in all its +phases is more complex. Since we can hardly change the conditions under +which we live, and probably would not if we could, we must learn to +adapt or adjust ourselves to them so as to secure for the nervous system +such relief as it requires. This adjustment is sometimes difficult, even +when the actual needs of the nervous system are known.</p> + +<p>The healthful action of the nervous system requires, on the one hand, +exercise, but on the other hand, a certain condition of quietude, or <hi +rend="font-style: italic">poise</hi>—a state which is directly opposed +to that of restlessness. The conditions of modern<pb n="325" /><anchor +id="Pg325" /> life seem able to force upon the nervous system all the +exercise that it needs, and more (whether it be of the right kind or +not), so that the main problem of to-day seems to be that of conserving, +or economizing, the nervous energy and of preventing nervous waste.</p> + +<p><hi rend="font-weight: bold">Wasteful Forms of Nervous +Activity.</hi>—There are without doubt many forms of activity that waste +the vital forces of the body and lead to nervous exhaustion. Take, for +example, the rather common habit of worrying over the trivial things of +life. Certainly the nervous energy spent in this way cannot be used in +doing useful work, but must be counted as so much loss to the body. One +who would use his nervous system to the best advantage must find some +way of preventing waste of this kind.<note place="foot"><p>Where a deep-seated cause for worry exists, there may be +occasion for grave concern. Many people have become insane through +continued worry about some <hi rend="font-style: italic">one</hi> thing. +In cases of this kind the sufferer needs the aid of sympathetic friends, +and sometimes of the physician, in getting the mind away from the +exciting cause. A change of scene, a visit, or some new employment is +frequently recommended, where the actual cause for the worry cannot be +removed.</p></note></p> + +<p>Undue excitement, as well as pleasurable dissipations, also tend +toward nervous exhaustion. And while the fact is recognized that +pleasurable activities supply a necessary mental exercise, the limit of +healthful endurance must be watched and <hi rend="font-style: +italic">excesses of all kinds avoided</hi>. Intense emotional states are +found to be exhausting in the extreme; and the suppression of such +undesirable feelings as anger, fear, jealousy, and resentment are of +immense value in the hygiene of the nervous system.</p> + +<p><hi rend="font-weight: bold">The Habit of Self-control.</hi>—Much of +the needless waste of nervous energy, including that of worrying over +trivial matters, may be prevented through the exercise of self-control. +From the standpoint of the nervous system, the present age differs from +the past mainly in supplying a<pb n="326" /><anchor id="Pg326" /> greater number and variety +of nerve stimuli. Self-control means the ability to suppress activities +that would result from undesirable stimuli and to direct the bodily +activities into channels that are profitable. Self-control, therefore, +is not only to be exercised on occasions of great emergency, but in the +everyday affairs of life as well. It is even more important that the +daily toiler at his task be able to keep the petty annoyances of life +from acting as irritants to his nervous system than that he keep cool +during some great calamity. The habit of self-control is acquired mainly +through the persistent effort to prevent any and all kinds of petty +annoyances from affecting the nerves or the temper.</p> + +<p><hi rend="font-weight: bold">Nervousness.</hi>—Self-control is much +more easily practiced by some than by others. This is due partly to +habit, but is also due to an actual difference in the degree of +sensitiveness, or irritability, of the nervous systems of different +people. One whose nervous system tends to respond too readily to any and +all kinds of stimuli is said to be "nervous." This condition is in some +instances inherited, but is in most cases due to the wasteful +expenditure of nervous energy or to the action of some drug upon the +body. Excess of mental work, too much reading, long-continued anxiety, +eye strain, and the use of tea, coffee, alcohol, tobacco, or other +drugs, including many of those taken as medicines, are known to cause +nervousness. Nervousness is not only a source of great annoyance, both +to one's self and to others, but is a menace to the general health.</p> + +<p>The first step toward securing relief from such a condition is the +removal of the cause. The habits should be inquired into and excesses of +all kinds discontinued. In some instances it may be necessary to <hi +rend="font-style: italic">have the eyes <pb n="327" /><anchor id="Pg327" />examined</hi> and +glasses fitted by a competent oculist.<note place="foot"><p>Any part of the body which is overworked or which works +at a disadvantage tends to disturb, more or less, the entire nervous +system and to produce nervousness. Especially is this true of such +delicate and highly sensitive structures as the eyes. If the eyes do not +focus properly or if the muscles that move the eyeballs are out of their +natural adjustment, extra work is thrown upon these delicate parts. One +of the first and sometimes the only indication of eye strain is that of +some disturbance of the nervous system. For this reason it is important +to carefully test the eyes in determining the cause of nervousness (page +385).</p></note> The nervous energy should be +carefully economized and the habit of self-control diligently +cultivated. Special exercises that have for their purpose the equalizing +of the circulation and the strengthening of the blood vessels of the +neck and the brain also have beneficial effects.</p> + +<p><hi rend="font-weight: bold">Nervous Overstrain.</hi>—Both mental and +physical overwork tends to weaken the nervous system and to produce +nervousness. Where hard mental work is long continued, or where it is +carried on under excitement, a tense nervous condition is developed +which is decidedly weakening in its effects. The causes which lead to +such a condition, and in fact overwork of all kinds, should if possible +be avoided. Where this is not possible, and in many cases it is not, the +period of overwork should be followed by one of rest, recreation, and +plenty of sleep. To the overworked in body or in mind, nothing is more +important from a hygienic, as well as moral, standpoint, than the right +use of the <hi rend="font-style: italic">one rest day in seven</hi>. The +best interests of our modern civilization <hi rend="font-style: +italic">require</hi> that the Sabbath be kept as a quiet, rest-giving +day.</p> + +<p><hi rend="font-weight: bold">Disturbed Circulation of the +Brain.</hi>—Nervousness not infrequently is accompanied by an increase +in the circulation of the brain and disappears when this condition is +relieved. Though mental work and excitement tend naturally to increase +the circulation in the brain, this should subside with rest and relief +from excitement. When there is a tendency<pb n="328" /><anchor id="Pg328" /> for this condition to become +permanent, effort should be made looking for relief. Increasing the +circulation in the lower extremities by hot or cold foot baths, or by +much walking, is found to be most beneficial. Special exercises of the +muscles of the neck are also recommended as a means of relieving this +condition.<note place="foot"><p>One form of neck exercise recommended for this purpose +is easily taken on retiring at night. Lying flat on the back, without a +pillow, lift the head slowly from the bed and let it as slowly settle +back to the level of the body. Repeat several times, lying on the back, +and then again on the face and again on each side. Practice these +exercises every night during an interval of a month or until relief is +secured.</p></note></p> + +<p><hi rend="font-weight: bold">Hygienic Value of Work.</hi>—Within +reasonable limits, both mental and physical work are conducive to the +vigor of the nervous system. Through work the energies of the body find +their natural outlet, and this prevents dissipation and the formation of +bad habits. Even hard work does not injure the nervous system, and +severe mental exertion may be undergone, provided the proper hygienic +conditions are observed. The nervous disorders suffered by brain workers +are not, as a rule, due to the work which the brain does, but to +violation of the laws of health, especially the law of exercise. Such +persons should observe the general laws of hygiene and especially should +they practice daily those forms of physical exercise that tend to +counteract the effects of mental work.</p> + +<p><hi rend="font-weight: bold">Physical Exercise</hi> properly taken is +beneficial to the nervous system through both direct and indirect +effects. A large proportion of the nerve cells have for their function +the production of motion, and these are called into play only through +muscular activity. Then, as already suggested, physical exercise +counteracts the unpleasant effects of mental work. Hard study causes an +excess of blood to be sent to the brain and a diminished amount<pb n="329" /><anchor id="Pg329" /> to the arms and to the legs. +Physical exercise redistributes the blood and equalizes the circulation. +Light exercise should, therefore, follow hard study. The student before +retiring at night is greatly aided in getting to sleep and is put in a +better condition for the next day's work by ten to fifteen minutes of +light gymnastics. A daily walk of two or three miles is also an +excellent means of counteracting the effects of mental work. The brain +worker should, however, avoid violent exercise or the carrying of any +kind of exercise to exhaustion.</p> + +<p><hi rend="font-weight: bold">Sleep</hi>, and plenty of it, is one of +the first requirements of the nervous system. It is during sleep that +the exhausted brain cells are replenished. To shorten the time for sleep +is to weaken the brain and to lessen its working force. No one should +attempt to get along with less than eight hours of sleep each day and +most people require more. Children require more sleep than adults. Those +under six years should have from eleven to twelve hours of sleep per +day. Children between six and ten years should have at least ten +hours.</p> + +<p><hi rend="font-weight: bold">Insomnia</hi>, or sleeplessness, on +account of its effects upon the nervous system, is to be regarded as a +serious condition, and hygienic means for relieving it should be +diligently sought. Having its cause in nervousness, a disturbed +circulation of the brain, or some form of nervous exhaustion, it is +benefited through relieving these conditions and in the manner already +described. Of course the external conditions for aiding sleep should not +be overlooked. The bed should be comfortable, and the room should be +cool, well ventilated, dark, and quiet. The inducing of sleep by means +of drugs is a dangerous practice and should never be resorted to except +under the direction of the physician.</p> + +<p><pb n="330" /><anchor id="Pg330" /><hi rend="font-weight: +bold">Effects of Heat and Cold.</hi>—Heat and cold both have their +effects upon the nervous system. Heat increases the nervous +irritability, while cold acts as a natural sedative to the nerves. A +nervous person is made more nervous by an overheated atmosphere, but +derives beneficial effects from exposing the body freely to cold air and +water. The tonic cold bath (page 273), if taken with the usual +precautions, can be used to good advantage in diminishing nervousness. +The taking of outdoor exercise in cold weather is, for the same reason, +an excellent practice.</p> + +<p><hi rend="font-weight: bold">Effect of Emotional States.</hi>—We have +already noted the effect of certain emotional states upon the digestion +of the food (page 162). Emotional states are also known to interfere +with breathing and with the action of the heart. Such effects are +explained through the close relation of the mind to the work of the +nervous system in general. While certain emotional states, such as fear, +anger, melancholia, and the impulse to worry, interfere seriously with +the normal action of the nervous system, others, such as contentment, +cheerfulness, and joy, are decidedly beneficial in their effects. How +important, then, is the habit of suppressing the states that are harmful +and of cultivating those that are beneficial. From a hygienic, as well +as social, standpoint a cheerful, happy disposition is worth all the +effort necessary for its attainment.</p> + +<p><hi rend="font-weight: bold">The Nervous Condition of Children</hi> +should be a matter of deep concern on the part of both parents and +teachers. In the home, as well as in the school, the child may be +"pushed" until the nervous system receives permanent injury. Exhaustion +of nerve cells is produced through too many and too vivid impressions +being made upon the immature brain. The child should be protected +from<pb n="331" /><anchor id="Pg331" /> undue excitement. He should have +the benefit of outdoor exercise and should be early inured to cold. He +should be shielded from the poisoning effects of tea, coffee, tobacco, +alcohol, and other drugs. He should have impressed upon him the habit of +self-control. He should not be indulged in foolish caprices or whims, +but should be taught to be content with plain, wholesome food and with +the simple forms of enjoyment.</p> + +<p><hi rend="font-weight: bold">Influences at School.</hi>—School life +is necessarily a great strain upon the child. Night study added to the +work of the day makes a heavy burden for elementary pupils to bear. +Though the legal school age is usually fixed at six years, delicate +children should be kept out of school until they are seven or eight +years old, provided they have good homes. In addition to the excitation +incident to studying and reciting lessons, conditions frequently arise +both in the schoolroom and upon the playground that create a feeling of +fear or dread in the minds of children. Quarrels and feuds among the +children and the bullying of big boys on the playground may work untold +harm. All conditions tending to develop fear, uneasiness, or undue +excitement on the part of children should receive the attention of those +in authority.</p> + +<p><hi rend="font-weight: bold">Excessive Reading</hi> is a frequent +cause of injury to the nervous systems of children. This has a bad +effect, both on account of too many impressions being made upon the mind +and also on account of the strain to the eyes. Then if the reading +consists mostly of light fiction, the mind is directed away from the +really important things of life. The reading of children should be +thoughtfully controlled, both as to quality and quantity. Exciting +stories should, as a rule, be excluded, but a taste for biography, +historical and scientific writings, and for the great works<pb n="332" /><anchor id="Pg332" /> of literature should be +cultivated. Simple fairy tales which have a recognized value in +developing the imagination of the child need not be omitted, but it is +of vital importance that the "story-reading habit" be not formed.</p> + +<p><hi rend="font-weight: bold">Effects of Drugs.</hi>—Because of its +delicacy of structure a number of chemical compounds, or drugs, are able +to produce injurious effects upon the nervous system. Some of these are +violent poisons, while others, in small quantities, are mild in their +action. Certain drugs, in addition to their immediate effects, bring +about changes in the nervous system which cause an unnatural appetite, +or craving, that leads to their continued use. This is the case with +alcohol, the intoxicating substance in the usual saloon drinks, and with +nicotine, the stimulating drug in tobacco. The same is also true of +morphine, chloral, and several other drugs used as medicines. The <hi +rend="font-style: italic">danger of becoming a slave</hi> to some +useless and pernicious habit should dissuade one from the use of drugs +except in cases of positive emergency.</p> + +<p><hi rend="font-weight: bold">Alcohol and the Nervous +System.</hi>—Alcohol, as already shown, injures practically all portions +of the body; but it has its worst effects upon the nervous system. +Through its action on this system, it interferes with the circulation of +the blood, produces a condition of "temporary insanity" called +intoxication, weakens the will, and eventually dethrones the reason. +Worst of all, it produces a condition of "chronic poisoning" which +manifests itself in an unnatural craving, and this causes it to be used +by the victim even when he knows he is "drinking to his own +destruction." Though its use in small quantities does not, as a rule, +produce such marked effects upon the nervous system, it develops the +"craving," and this is apt in time to lead to its use in larger +quantities. But even if this does not occur, the practice is +objectionable for its unhygienic effects<pb n="333" /><anchor id="Pg333" +/> in general.<note place="foot"><p>Insurance statistics show that habitual <hi +rend="font-style: italic">moderate drinkers</hi> do not live so long as +abstainers.</p></note> Tippling with such mild +solutions of alcohol as light wine, beer, and hard cider is, for these +reasons, a dangerous pastime.</p> + +<p><hi rend="font-weight: bold">Alcohol and Crime.</hi>—It is sometimes +stated that no one who leaves alcohol alone will be injured by it. This +is true only of its direct effects; not of its indirect effects. +Whenever a crime is committed somebody is injured, and alcohol is known +to be a chief cause of crime. Alcohol causes crime through the loss of +self-control, seen especially in intoxication, and also because of the +moroseness and quarrelsomeness which it developes in certain +individuals. Indirectly it causes crime through the poverty which it +engenders and through its influence in bringing about social conditions +out of which crime develops. Everything considered, the free use of +alcohol is incompatible with the nervous health and moral tone of a +community.</p> + +<p><hi rend="font-weight: bold">Nicotine and the Nervous +System.</hi>—Nicotine is an oily substance which is extracted from the +tobacco plant. Its action on the nervous system is in general that of a +poison. Taken in small quantities, it is a mild stimulant and, if the +doses are repeated, a habit is formed which is difficult to break. +Tobacco is used mainly for the stimulating effect of this drug. While +not so serious in its results as the alcohol and other drug habits, the +use of tobacco is of no benefit, is a continual and useless expense, +and, in many instances, causes a derangement of the healthy action of +the body.<note place="foot"><p>Organs very frequently affected by tobacco are the heart +and the eyes. It induces, as already stated (page 56), a dangerous +nervous derangement called "tobacco heart," and it causes a serious +disorder of the retina (retinitis) which leads in some instances to loss +of vision. Tobacco smoke also acts as an irritant to the delicate lining +of the eyes, especially when the tobacco is smoked indoors.</p></note><pb n="334" /><anchor id="Pg334" /> With the bad effects of the +nicotine must be included those of questionable substances added to the +tobacco by the manufacturer, either for their agreeable flavor or for +adulteration.</p> + +<p><hi rend="font-weight: bold">Relation of Age to the Effects of +Nicotine.</hi>—The use of tobacco by the young is especially to be +deplored. In addition to the harmful effects observed in those of mature +years, nicotine interferes with the normal development of the body and +lays, in many instances, the foundation for physical and mental weakness +in later life. The cigarette is decidedly harmful, especially when +inhalation is practiced, its deadening effects being in part due to the +wrappers, some of which have been shown to contain arsenic and other +poisonous drugs. While dulling the intellect and weakening the body, +cigarette smoking also tends to make criminals of boys.<note place="foot"><p>Of 4117 boys in the Illinois State Reformatory, 4000 +used tobacco, and over 3000 were cigarette smokers. Dr. Hutchison, of +the Kansas State Reformatory, says: "Using cigarettes is the cause of +the downfall of more of the inmates of this institution than all other +vicious habits combined."</p></note> Parents, +teachers, school officers, and all who have the good of mankind at heart +should take every precaution, including that of setting a good example, +to prevent the formation of the tobacco habit by those of immature +years.</p> + +<p><hi rend="font-weight: bold">Habit versus Self-control.</hi>—The +power of self-control, already emphasized for its importance in the +economical expenditure of the nervous energy, is of vital importance in +its relation to the habits of the body. Self-control is the chief +safeguard against the formation of bad habits and is the only means of +redemption from such habits after they have once been formed. The +persistent cultivation of the power to control the appetites and the +passions, as well as all forms of activity which tend to injure the body +or debase the character, gives a tone to the nervous system<pb n="335" /><anchor id="Pg335" /> which increases the self-respect +and raises the individual to a <hi rend="font-style: italic">higher +plane of life</hi>. The worst habits <hi rend="font-style: +italic">can</hi> be broken and good ones formed in their stead, if only +there is sufficient determination to accomplish these results. Failure +comes from not having the mind thoroughly "made up" and from not having, +back of the desire to do better, "the strong will of a righteous +determination."</p> + +<p><hi rend="font-weight: bold">Effects of External +Conditions.</hi>—While the inner life and habits have most to do with +the hygiene of the nervous system, a certain amount of attention may +properly be given to those conditions outside of the body which affect +directly or indirectly the state of this system. Noise, disorder, and +confusion act as nervous irritants, but quiet, order, and system have +the opposite effect. There is, therefore, much in the management of the +office, factory, schoolroom, or home that has to do with the real +hygiene of the nerves as well as with the efficiency of the work that is +being done. The suppression of distracting influences not only enables +the mind to be given fully to the work in hand, but actually prevents +waste of nervous energy. Although the responsibility for securing the +best conditions for work rests primarily with those in charge, it is +also true that each individual in every organization may contribute to +the order or disorder that prevails.</p> + +<p><hi rend="font-weight: bold">Social Relations.</hi>—In considering +the external conditions that affect the nervous system, the fact must +not be overlooked that man is a social being and has to adjust himself +to an established social order. His relations to his fellow-men, +therefore, affect strongly his nervous condition and theirs also. For +this reason the best hygiene of the nervous system is based upon <hi +rend="font-style: italic">moral</hi> as well as physical right living. +Along with the power of self-control and the maintenance of a correct +nervous poise, there should be a proper regard<pb n="336" /><anchor id="Pg336" /> for the welfare of others. On +account of the ease with which one individual may disturb the nervous +state of another, those social forms and customs which tend to establish +harmonious relations among men are truly hygienic in their effects, and +may well be carried out in spirit as well as "in letter."</p> + +<p>It is also a fact that a given mental state in one person tends to +excite a like state in those with whom he associates. How important, +then, that each and all cultivate, as habits, the qualities of +cheerfulness, kindness, and good-will, instead of the opposite states of +mind. Especially in the family, and other groups of closely associated +individuals, should the nervous effect of one member upon the others be +considered and every effort made to secure and maintain harmonious +relations.</p> + +<p><hi rend="font-weight: bold">The High Ideal.</hi>—Everything +considered, the conditions most favorable to the healthfulness of the +nervous system are in harmony with what our greatest teachers have +pointed to as the higher plane of living. On this account a true +conception of the value and meaning of life is of the greatest +importance. <hi rend="font-style: italic">An ever present, strong desire +to live a vigorous, but simple and noble, life</hi> will suggest the +proper course to pursue when in doubt and will stimulate the power of +self-control. It will lead to the stopping of "nerve leaks" and to the +maintenance of harmonious relations with one's fellows. It will cause +one to recoil from the use of alcohol and other nerve poisons, as from a +deadly serpent, seeing the end in the beginning, and will be the means +eventually of leading the body into its greatest accomplishments.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The nervous system, on +account of its delicate structure, is liable to injury through wrong +methods of using it and also through the introduction of drugs, or +poisons, into the body. There are also found<pb n="337" /><anchor id="Pg337" /> in our methods of living and +systems of education conditions that tend to waste the nervous energy. +To protect the nervous system from all these threatened dangers +requires, among other things, the power of self-control. This enables +the individual to direct his life according to his highest ideals and to +free himself from habits known to be injurious. Children must have their +nervous systems safeguarded by parents and teachers. Especially must +they be kept from becoming enslaved to some drug, such as alcohol or the +nicotine of tobacco.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. In what respect is +the hygiene of the nervous system the hygiene of the entire body?</p> + +<p>2. Of what value in the hygiene of the nervous system is the power of +self-control? How is the habit of self-control formed?</p> + +<p>3. Name several forms of activity that waste the nervous energy.</p> + +<p>4. Name several influences that react unfavorably on the nervous +systems of children.</p> + +<p>5. How may too much reading prove injurious to the nervous +system?</p> + +<p>6. What forms of physical exercise are beneficial to the brain +worker?</p> + +<p>7. Why is the use of alcohol even in small quantities to be regarded +as a dangerous practice?</p> + +<p>8. Name several causes of nervousness.</p> + +<p>9. What are the unanswerable arguments for preventing the use of +tobacco by the young?</p> + +<p>10. Why do cigarettes have a more harmful effect upon the body than +other forms of tobacco?</p> + +<p>11. Enumerate conditions in the schoolroom that dissipate the nervous +energy of pupils; that economize it.</p> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="338" /><anchor id="Pg338" /> +<head>CHAPTER XX - PRODUCTION OF SENSATIONS</head> + +<p>Our study of the nervous system has shown that impulses arising at +the surface of the body are able, through connecting neurons, to bring +about various activities. Moving along definite pathways, they induce +motion in the muscles, and in the glands the secretion of liquids. It is +now our purpose to consider the effect produced by afferent impulses +upon the brain and, through the brain, upon the mind.<note place="foot"><p>The term "mind" is used in this and preceding chapters +in its popular, not technical, sense.</p></note> This effect is +manifested in a variety of similar forms, known as</p> + +<p><hi rend="font-weight: bold">The Sensations.</hi>—Sensations +constitute the lowest forms of mental activity. Roughly speaking, they +are the states of mind experienced as the <hi rend="font-style: +italic">direct</hi> result of impulses reaching the brain. In a sense, +just as impulses passing to the muscles cause motion, impulses passing +to the brain cause sensations. The feeling which results from the hand's +touching a table is a sensation and so also is the pain which is caused +by an injury to the body. The mental action in each case is due to +impulses passing to the brain. Care must be exercised by the beginner, +however, not to confuse sensations with the nervous impulses, on the one +hand, or with <hi rend="font-style: italic">secondary</hi> mental +effects, such as emotion or imagination, on the other. Sensations are +properly regarded as the first conscious effects of the afferent +impulses and as the <hi rend="font-style: italic">beginning stage</hi> +in the series of mental processes that may take place on account of +them.</p> + +<p><pb n="339" /><anchor id="Pg339" />In some way, not understood, the +mind associates the sensation with the part of the body from which the +impulses come. Pain, for example, is not felt at the brain where the +sensation is produced, but at the place where the injury occurs. This +association, by the mind, of the sensations with different parts of the +body, is known as "localizing the sensation."</p> + +<p><hi rend="font-weight: bold">Sensation Stimuli.</hi>—While the +sensations are dependent upon the afferent impulses, the afferent +impulses are in turn dependent upon causes outside of the nervous +system. If these are removed, the sensations cease and they do not start +up again unless the exciting influences are again applied. Any agency, +such as heat or pressure, which, by acting on the neurons of the body, +is able to produce a sensation, may be called a <hi rend="font-style: +italic">sensation stimulus</hi>. It has perhaps already been observed +that the stimuli that lead to voluntary action, as well as those that +produce reflex action of the muscles, cause sensations at the same time. +From this we may conclude that sensation stimuli are the same in +character as those that excite motion. On the other hand, it should be +noted that sensations are constantly resulting from stimuli that are of +too mild a nature to cause motion.</p> + +<p><hi rend="font-weight: bold">Classes of Sensations.</hi>—Perhaps as +many as twenty distinct sensations, such as pain, hunger, touch, etc., +are recognized. If these are studied with reference to their origin, it +will be seen that some of them result from the action of definite forms +of stimuli upon the neurons terminating in sense organs; while the +others, as a rule, arise from the action of indefinite stimuli upon +neurons in parts of the body that do not possess sense organs. The +members of the first class—and these include the sensations of touch, +temperature, taste, smell, hearing, and sight—are<pb n="340" /><anchor id="Pg340" /> known as the <hi +rend="font-style: italic">special</hi> sensations. The others, including +the sensations of pain, hunger, thirst, nausea, fatigue, comfort, +discomfort, and those of disease, are known as <hi rend="font-style: +italic">organic</hi>, or general, sensations. These two classes of +sensations differ in their purpose in the body as well as in the manner +of their origin.</p> + +<p><hi rend="font-weight: bold">Purposes of Sensations.</hi>—Any given +sensation is related to the stimulus which excites it as an <hi +rend="font-style: italic">effect</hi> to a <hi rend="font-style: +italic">cause</hi>. It starts up or stops, increases in intensity or +diminishes, according to the action of the exciting stimulus. As the +stimuli are outside of the nervous system, and in the majority of cases +outside of the body, the sensations indicate to the mind what is taking +place either in the body itself or in its surroundings. They supply, in +other words, the means through which the mind acquires information. By +means of the special sensations, a knowledge of the physical +surroundings of the body is gained, and through the organic sensations +the needs of the body and the state of the various organs are indicated. +In general, sensations are made to serve two great purposes in the body, +as follows:</p> + +<p>1. They provide the necessary conditions for intelligent and +purposeful action on the part of the body.</p> + +<p>2. They supply the basis for +the higher mental activities, as perception, memory, thought, +imagination, and emotion.</p> + +<p>Intelligent action is impossible without a knowledge both of the +bodily organs and of the body's surroundings. Protection and the +regulation of the work of an organ necessitate a knowledge of its +condition, while the adapting and adjusting of the body to its +surroundings require a knowledge of what those surroundings are. The +dependence of all the higher forms of mental activity upon sensations is +recognized by psychologists and is easily<pb n="341" /><anchor id="Pg341" /> demonstrated by a study of the +manner in which we acquire knowledge. "Without sensation there can be no +thought."</p> + +<p><hi rend="font-weight: bold">Steps in the Production of +Sensations.</hi>—The steps in the production of sensations are not +essentially different from those in the production of reflex action. +First of all, external stimuli act upon the fiber terminations in the +sense organs, or elsewhere, starting impulses in the neurons. These pass +into the central nervous system and there excite neurons which in turn +discharge impulses into the cerebrum. The result is to arouse an +activity of the mind—a sensation. The steps in the production of any <hi +rend="font-style: italic">special</hi> sensation naturally involve the +following parts:</p> + +<p>1. A sense organ where the terminations of the neurons are acted +upon by the stimulus.</p> + +<p>2. A chain of neurons which connect the sense organ with the +brain.</p> + +<p>3. The part of the cerebrum which produces the sensation.</p> + +<p><hi rend="font-weight: bold">Sense Organs.</hi>—The sense organs are +not parts of the afferent neurons, but are structures of various kinds, +in which the neurons terminate. Their function is to enable the +sensation stimuli to start the impulses. By directing, concentrating, or +controlling the stimuli, the sense organs enable them to act to the best +advantage upon the neurons. When it is recognized that such widely +different forces as light waves, sound waves, heat, pressure, and odors +are enabled by them to stimulate neurons, the importance of these organs +becomes apparent. As would naturally be inferred, the construction of +any sense organ has particular reference to the nature of the stimulus +which it is to receive. This is most apparent in the sense organs of +sight and hearing.</p> + +<p><pb n="342" /><anchor id="Pg342" /><hi rend="font-weight: +bold">Simple Forms of Sense Organs.</hi>—The simplest form of a sense +organ (if such it may be called) is one found among the various tissues. +It consists of the terminal branches of nerve fibers which spread over a +small area of cells, as a network or plexus. Such endings are numerous +in the skin and muscles.</p> + +<p>Next in order of complexity are the so-called <hi rend="font-style: +italic">end-bulbs</hi>. These consist of rounded, or elongated, +connective tissue capsules, within which the nerve fibers terminate. On +the inside the fibers lose their sheaths and divide into branches, which +wind through the capsule. End-bulbs are abundant in the lining membrane +of the eye, and are found also in the skin of the lips and in the +tissues around the joints.</p> + +<p>Slightly more complex than the end-bulbs are the <hi +rend="font-style: italic">touch corpuscles</hi>. These are elongated +bulb-like bodies, having a length of about one three-hundredth of an +inch, and occupying the papillæ of the skin (Fig. 144). They are +composed mainly of connective tissue. Each corpuscle receives the +termination of one or more nerve fibers. These, on entering, lose the +medullary sheath and separate into a number of branches that penetrate +the corpuscle in different directions.</p> + +<p rend="text-align: center"> +<figure url="images/image144.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 144—<hi rend="font-weight: bold">A touch +corpuscle</hi> highly magnified. (See text.)</head> +<figDesc>Fig. 144</figDesc> +</figure></p> + +<p>The largest of the simple forms of sense organs are bodies visible to +the naked eye and called, from their discoverer Pacini, the <hi +rend="font-style: italic">Pacinian corpuscles</hi>. They lie along the +course of nerves in many parts of the body, and have the general form of +grains of wheat. (See Practical Work.) The Pacinian corpuscles are +composed of connective tissue<pb n="343" /><anchor id="Pg343" /> +arranged in separate layers around a narrow central cavity called the +core (Fig. 145). Within the core is the termination of a large nerve +fiber. These corpuscles are found in the connective tissue beneath the +skin, along tendons, around joints, and among the organs of the +abdominal cavity.</p> + +<p rend="text-align: center"> +<figure url="images/image145.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 145—<hi rend="font-weight: bold">Pacinian +corpuscle</hi>, magnified. <hi rend="font-style: italic">A.</hi> +Medullated nerve fiber. <hi rend="font-style: italic">B.</hi> Axis +cylinder terminating in small bulb at <hi rend="font-style: +italic">C.</hi> <hi rend="font-style: italic">D.</hi> Concentric layers +of connective tissue. <hi rend="font-style: italic">E.</hi> Inner +bulb.</head> +<figDesc>Fig. 145</figDesc> +</figure></p> + +<p>The simple forms of sense organs have a more or less general +distribution over the body, and are concerned in the production of at +least three special sensations. These are <hi rend="font-style: +italic">touch, temperature</hi>, and the <hi rend="font-style: +italic">muscular sensation</hi>.</p> + +<p><hi rend="font-weight: bold">Touch</hi>, or feeling, is perhaps the +simplest of the sensations. The sense organs employed are the touch +corpuscles, and the external stimulus is some form of pressure or +impact. Pressure applied to the skin, by acting on the fiber +terminations in the corpuscles, starts the impulses that give rise to +the sensation. The touch corpuscles render the fiber terminations so +sensitive that the slightest pressure is able to arouse sensations of +touch. It is found that <hi rend="font-style: italic">a change of +pressure</hi>, rather than pressure that is constant, is the active +stimulus. That all parts of the skin are not equally sensitive to +pressure, and that the mind does not interpret equally well the +sensations from different parts, are facts easily demonstrated by +experiment. (See Practical Work.)</p> + +<p><hi rend="font-weight: bold">The Temperature +Sensation.</hi>—Temperature sensations,<pb n="344" /><anchor id="Pg344" /> like those of touch, are limited +almost entirely to the skin. They are of two kinds, and are designated +as <hi rend="font-style: italic">heat</hi> sensations and as <hi +rend="font-style: italic">cold</hi> sensations. Whether the sense organs +for temperature are different from those of touch is not known. It is +known, however, that the same corpuscles do not respond alike to heat, +cold, and pressure.</p> + +<p><hi rend="font-style: italic">A Change of Temperature</hi>, rather +than any specific degree of heat or cold, is the active temperature +stimulus. The sensation of warmth is obtained when the temperature of +the skin is being raised, and of cold when it is being lowered. This +explains why in going into a hallway from a heated room one receives a +sensation of cold, while in coming into the same hallway from the +outside air he receives a sensation of warmth. It is for the same reason +that we are able to distinguish only the relative, not the actual, +temperature of bodies.</p> + +<p><hi rend="font-weight: bold">Muscular Sensations.</hi>—These are +sensations produced by impulses arising at the muscles. Such impulses +originate at the fiber terminations which are found in both the muscles +and their tendons. By muscular sensations one is conscious of the +location of a contracting muscle and of the degree of its tension. They +also make it possible to judge of the weight of objects.</p> + +<p rend="text-align: center"> +<figure url="images/image146.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 146—<hi rend="font-weight: bold">Sense organs of +taste.</hi> <hi rend="font-style: italic">A.</hi> Map of upper surface +of tongue, showing on the left the different kinds of papillæ, and on +the right the areas of taste (after Hall). Area sensitive to bitter +(——); to acid (....); to salt (—.—.—.—); to sweet (————). <hi +rend="font-style: italic">B.</hi> Section through a papilla. <hi +rend="font-style: italic">n.</hi> Small nerve connecting with taste buds +at <hi rend="font-style: italic">d. e.</hi> Epithelium. <hi +rend="font-style: italic">C.</hi> Single taste bud magnified. <hi +rend="font-style: italic">n.</hi> Nerve, the fibers of which terminate +between the spindle-shaped cells <hi rend="font-style: italic">a. +e.</hi> Epithelial cells.</head> +<figDesc>Fig. 146</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Sensation of Taste.</hi>—The sense +organs of taste are found chiefly in the mucous membrane covering the +upper surface of the tongue. Scattered over this surface are a number of +rounded elevations, or large papillæ (A, Fig. 146). Toward the back of +the tongue two rows of these, larger than the others, converge to meet +at an angle, where is located a papilla of exceptional size. Surrounding +each papilla is a narrow depression, within which are found the sense +organs of taste (B, Fig. 146). These are called, from their shape, <hi +rend="font-style: italic">taste buds</hi>, and each bud contains a +central<pb n="345" /><anchor id="Pg345" /> cavity which communicates +with the surface by a small opening—<hi rend="font-style: italic">the +gustatory pore</hi>. Within this cavity are many slender, spindle-shaped +cells which terminate in hair-like projections at the end nearest the +pore, but in short fibers at the other end. Nerve fibers enter at the +inner ends of the buds and spread out between the cells (<hi +rend="font-style: italic">C</hi>, Fig. 146). These fibers pass to the brain as parts of two pairs of nerves—those +from the front of the tongue joining the trigeminal nerve, and those +from the back of the tongue, the glossopharyngeal nerve.</p> + +<p>The gustatary, or <hi rend="font-style: italic">taste stimulus</hi>, +is some chemical or physical condition of substances which is manifested +only when they are in a liquid state. For this reason <hi +rend="font-style: italic">only liquid substances can be tasted</hi>. +Solids to be tasted must first be dissolved.</p> + +<p><pb n="346" /><anchor id="Pg346" />The different taste sensations are described as bitter, sweet, sour, +and saline, and in the order named are recognized as the tastes of +quinine, sugar, vinegar, and salt. As to how these different tastes are +produced, little is known. Flavors such as vanilla and lemon, and the +flavors of meats and fruits, are really smelled and not tasted. Taste +serves two main purposes: it is an aid in the selection of food and it +is a means of stimulating the digestive glands (page 161).</p> + +<p rend="text-align: center"> +<figure url="images/image147.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 147—<hi rend="font-weight: bold">Sense organ of +smell.</hi> <hi rend="font-style: italic">A.</hi> Distribution of nerves +in outer wall of nasal cavity. 1. Turbinated bones. 2. Branch of fifth +pair of nerves. 3. Branches of olfactory nerve. 4. Olfactory bulb. <hi +rend="font-style: italic">B.</hi> Diagram showing connection of neurons +concerned in smell.</head> +<figDesc>Fig. 147</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Sensation of Smell.</hi>—The sense +organs of smell are found in the mucous membrane lining the upper +divisions of the nasal cavities. Here are found two kinds of cells in +great abundance—column-shaped epithelial cells and the cells which are +recognized as the sense organs of smell. These olfactory cells are +spindle-shaped, having at one end a slender, thread-like projection +which reaches the surface, and at the other end a fiber which joins an +olfactory nerve (B, Fig. 147). In fact, the olfactory cells<pb n="347" +/><anchor id="Pg347" /> resemble closely the cell-bodies of neurons, and +are thought to be such. The divisions of the olfactory nerve pass +through many small openings in the ethmoid bone to connect with the +olfactory bulbs, which in turn connect with the cerebrum (A, Fig. +147).</p> + +<p><hi rend="font-weight: bold">The Olfactory Stimulus.</hi>—Only +substances in the gaseous state can be smelled. From this it is inferred +that the stimulus is supplied by gas particles. Solids and liquids are +smelled because of the gas particles which separate from them. The +substance which is smelled must be kept moving through the nostrils and +made to come in direct contact with the olfactory cells. There is +practically no limit to the number of distinct odors that may be +recognized.</p> + +<p><hi rend="font-weight: bold">Value of Smell.</hi>—Although the sense +of smell is not so acute in man as in some of the lower animals, it is, +nevertheless, a most important and useful gift. It is the only sense +that responds to matter in the gaseous state, and is, for this reason, +the only natural means of detecting harmful constituents of the +atmosphere. In this connection it has been likened to a sentinel +standing guard over the air passages. Many gases are, however, without +odor, and for this reason cannot be detected by the nostrils. It is of +especial importance that gases which are likely to become mixed with the +air supply to the body have odor, even though the odor be disagreeable. +The bad odors of illuminating gas and of various compounds of the +chemical laboratory, since they serve as danger signals to put one +exposed to them on his guard, are of great protective value.</p> + +<p><hi rend="font-weight: bold">Sight and Hearing.</hi>—The sense organs +of sight and hearing are highly complicated structures, and will be +considered in the chapters following.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—Sensations are certain +activities of the mind that result from excitations within the body or +at its<pb n="348" /><anchor id="Pg348" /> surface. These cause the +neurons to discharge impulses which on reaching the cerebrum cause the +sensations. Sensations are necessary for intelligent and purposeful +action and for acquiring all kinds of knowledge. To enable the stimuli +to act to the best advantage in starting the impulses, special devices, +called sense organs, are employed. These receive the terminations of the +neurons, and by their special structure enable the most delicate stimuli +to start impulses. The simpler forms of sense organs are those of touch, +temperature, taste, and smell.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. Compare sensations +and reflex actions with reference to their nature and cause. Give steps +in the production of each.</p> + +<p>2. Give examples of sensation stimuli. State the purpose of sense +organs.</p> + +<p>3. How do general sensations differ from special sensations?</p> + +<p>4. Of what value is pain in the protection of the body?</p> + +<p>5. Show that sensations lead to the higher forms of mental activity, +such as emotion and imagination.</p> + +<p>6. Of what value to the body is the "localizing of the +sensation"?</p> + +<p>7. What kinds of sense organs are found in the skin? State the +purpose of each.</p> + +<p>8. Through what sense avenues is one made aware of solids, of +liquids, and of gases?</p> + +<p>9. Of what special protective value is the sense of smell?</p> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">To demonstrate the Pacinian +Corpuscles.</hi>—Spread out the mesentery from the intestine of a cat +and hold it between the eye and the light: Pacinian corpuscles will +appear as small translucent bodies having the general form of grains of +wheat. Secure a portion of the mesentery over a circular opening in a +thin piece of cork and examine it with a microscope of low power. Follow +the course of the nerve fiber to the nerve from which it branches.</p> + +<p><hi rend="font-weight: bold">To show Relative Sensitiveness of +Different Parts of the Skin.</hi>—Holding a bristle between the fingers, +bring the end in contact with the skin, noting the amount of pressure +necessary to cause a sensation of<pb n="349" /><anchor id="Pg349" /> +touch. Test the lips, tongue, tips of fingers, and palm and back of +hand, trying different sizes of bristles. Has the degree of +sensitiveness any relation to the thickness of the cuticle?</p> + +<p><hi rend="font-weight: bold">To show Perceptive Differences of +Different Portions of the Skin.</hi>—Place the points of a pair of +dividers on the back of the hand of one who looks in the opposite +direction. Is one point felt or two? Repeat several times, changing the +distance between the points until it is fully determined how near the +two points must be placed in order to be felt as one. In like manner +test other parts of the body, as the tips of the fingers and the back of +the neck. Compare results obtained at different places.</p> + +<p><hi rend="font-weight: bold">To locate Warm and Cold Sensation +Spots.</hi>—Slowly and evenly draw a blunt-pointed piece of metal over +the back of the neck. If it be of the same temperature as the skin, only +touch sensations will be experienced. If it be a little colder (the +temperature of the room) sensations of cold will be felt at certain +spots. If slightly warmer than the body, heat sensation spots will be +found on other parts of the skin. If the heat and cold sensation spots +be marked and tested from day to day they will be found to remain +constant as to position. Inference.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<pb n="350" /><anchor id="Pg350" /> +<head>CHAPTER XXI - THE LARYNX AND THE EAR</head> + +<p>Man is a social being. His inclinations are not to live alone, but to +be a part of that great human organization known as society. For men to +work together, to be mutually helpful one to another, requires the +ability to exchange ideas and this in turn requires some means of +communication.<note place="foot"><p>The problem of social adjustment is but a phase of the +general problem of establishing proper relations between the body and +its surroundings.</p></note> One means of communication is found in certain +movements of the atmosphere, known as <hi rend="font-style: +italic">sound waves</hi>. In the exchange of ideas by this means there +are employed two of the most interesting divisions of the body—the +larynx and the ear. The first is an instrument for the production of +sound waves; the second is the sense organ which enables the sound waves +to act as stimuli to the nervous system.</p> + +<p><hi rend="font-weight: bold">Nature of Sound Waves.</hi>—If some +sonorous body, as a bell, be struck, it is given a quivering, or +vibratory, motion. This is not confined to the bell, but is imparted to +the air and other substances with which the bell comes in contact. These +take up the movements and pass them to objects more remote, and they in +turn give them to others, until a very considerable distance is reached. +Such progressive vibrations are known as waves, and, since they act as +stimuli to the organs of hearing, they are called <hi rend="font-style: +italic">sound waves</hi>. Sound waves <hi rend="font-style: +italic">always originate in vibrating bodies</hi>.<note place="foot"><p>A vibrating body is one having a to-and-fro movement, +like that of a clock pendulum or the string of a violin on sounding. +Bodies to give out sound waves must vibrate rapidly, making not less than sixteen +vibrations per second. The upper limit of hearing being about 40,000 +vibrations per second, certain bodies may even vibrate too rapidly to be +heard.</p></note><pb n="351" /><anchor id="Pg351" /> They are transmitted chiefly <hi +rend="font-style: italic">by the air</hi>, which, because of its +lightness, elasticity, and abundance, readily takes up the vibrations +and spreads them in all directions (Fig. 148).</p> + +<p>While these vibratory movements of the atmosphere are correctly +classified as waves, they bear little resemblance to the waves on water. +Instead of being made of crests and troughs, as are the water waves, the +sound waves consist of alternating successions of slightly condensed and +rarefied layers of air. Then, while the general movement of the water +waves is that of ever widening circles <hi rend="font-style: +italic">over a surface</hi>, the sound waves spread as enlarging +spherical shells <hi rend="font-style: italic">through</hi> the air. In +sound waves, as in all other waves, however, it is only the form of the +wave that moves forward. The individual particles of air that make up +the wave simply vibrate back and forth.</p> + +<p rend="text-align: center"> +<figure url="images/image148.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 148—Diagram illustrating the spreading of sound +waves through air.</head> +<figDesc>Fig. 148</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">How Sound Waves act as Stimuli.</hi>—Any +sound wave represents a small but definite amount of energy, this being +a part of the original force that acted on the vibrating body to set it +in motion. The hammer, for instance, in striking a bell imparts to it a +measurable quantity of energy, which the bell in turn imparts to the +air. This energy is in the sound waves and is communicated to the<pb n="352" /><anchor id="Pg352" /> bodies against which they +strike.<note place="foot"><p>Somewhat as the waves on a body of water impart motion +to the sticks and weeds along the shore, sound waves are able to cause +bodies that are small or that are delicately poised to vibrate.</p></note> Though the force exerted by most sound waves is, indeed, very +slight, it is sufficient to enable them to act as stimuli to the nervous +system.</p> + +<p><hi rend="font-weight: bold">How Sounds Differ.</hi>—Three distinct +effects are produced by sound waves upon the nerves of hearing, and +through them upon the mind. These are known as <hi rend="font-style: +italic">pitch, intensity</hi>, and <hi rend="font-style: +italic">quality</hi>, and they are dependent upon the vibrations of the +sound-producing bodies.</p> + +<p><hi rend="font-style: italic">Pitch</hi>, which has reference to the +height, or degree of sharpness, of tones, is determined by the rapidity +of the vibrations of the vibrating body. The more rapid the vibrations, +the higher the pitch, the number of vibrations doubling for each musical +interval known as the octave.</p> + +<p><hi rend="font-style: italic">Intensity</hi> is the energy, or force, +of the sound waves. This is recognized by the strength of the sensation +and is expressed by the term <hi rend="font-style: +italic">loudness</hi>. Intensity is governed mainly by the width of the +vibrations of the vibrating body, and the width depends upon the force +applied to the body to make it vibrate.</p> + +<p><hi rend="font-style: italic">Quality</hi> is that peculiarity of +sound that enables tones from different instruments to sound +differently, although they may have the same pitch and intensity. +Quality depends upon the fact that most tones are complex in nature and +result from the blending together of simple tones of different +pitch.</p> + +<p><hi rend="font-weight: bold">Reënforcement of Sound Waves.</hi>—The +sound vibrations from small bodies are not infrequently reënforced by +surrounding conditions so that their outgoing waves reach farther and +are more effective than waves from larger bodies. This is true of the +sound waves produced by most musical instruments and also those produced +by the human larynx. Such reënforcement is effected in two general +ways—by sounding boards and by inclosed columns of air. Stringed +instruments—violin, guitar, piano, etc.—employ sounding boards, while +wind instruments, as the flute, pipe organ, and the various kinds of +horns, employ air columns for reënforcing their vibrations. In the use +of the sounding board, the vibrations are communicated to a larger +surface, and in the use of the air column the vibrations are +communicated to the inclosed air. (See Practical Work.)</p> + +<p><pb n="353" /><anchor id="Pg353" /><hi rend="font-weight: bold">Value of +Sound Waves to the Body.</hi>—From a physiological standpoint, the value +of sound waves is not easily overestimated. In addition to the use made +of them in the communication of ideas, they serve the purpose of +protecting the body, and in the sphere of music provide one of the most +elevating forms of entertainment. Sounds from different animals, as well +as from inanimate objects, may also be the means of supplying needed +information. The existence of two kinds of sound instruments in the +body—the one for the production, the other for the detection, of +sound—is certainly suggestive of the ability of the body to adjust +itself to, and to make use of, its physical environment. Both the larynx +and the ear are constructed with special reference to the nature and +properties of sound waves.</p> + +<div> +<head>THE LARYNX</head> + +<p><hi rend="font-weight: bold">The Sound-producing Mechanism of the +Body</hi> consists of the following parts:</p> + +<p>1. Delicately arranged bodies that are easily set in vibration.</p> + +<p>2. An arrangement for supplying the necessary force for making these +bodies vibrate.</p> + +<p>3. Contrivances for modifying the vibrating parts so as to produce +changes in pitch and intensity.</p> + +<p>4. Parts that reënforce the vibrations.</p> + +<p>5. Organs by means of which the sounds are converted into the forms +of speech.</p> + +<p>The central organ in this complex mechanism is</p> + +<p><hi rend="font-weight: bold">The Larynx.</hi>—The larynx forms a part +of the air passages, being a short tube at the upper end of the trachea. +Mucous membrane lines the inside of it and muscles cover most of the +outer surface. The framework<pb n="354" /><anchor id="Pg354" /> is made +of cartilage. At the top it is partly encircled by a small bone (the +hyoid), and its opening into the pharynx is guarded by a flexible lid, +called the <hi rend="font-style: italic">epiglottis</hi>. The cartilage +in its walls is in eight separate pieces, but the greater portion of the +structure is formed of two pieces only. These are known as the <hi +rend="font-style: italic">thyroid cartilage</hi> and the <hi +rend="font-style: italic">cricoid cartilage</hi> (Fig. 149). Both can be +felt in the throat—the thyroid as the projection known as "Adam's +apple," and the cricoid as a broad ring just below.</p> + +<p rend="text-align: center"> +<figure url="images/image149.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 149—The +larynx.—<hi rend="font-style: italic">A.</hi> Outside view. <hi +rend="font-style: italic">B.</hi> Vertical section through larynx, +showing inside. 1. Thyroid cartilage. 2. Cricoid cartilage. 3. Trachea. +4. Hyoid bone. 5. Epiglottis. 6. Vocal cord. 7. False vocal cord. 8. +Lining of mucous membrane.</head> +<figDesc>Fig. 149</figDesc> +</figure></p> + +<p>The <hi rend="font-style: italic">thyroid cartilage</hi> consists of +two V-shaped pieces, one on either side of the larynx, meeting at their +points in front, and each terminating at the back in an upward and a +downward projection. Between the back portions of the thyroid is a space +equal to about one third of the circumference of the larynx. This is +occupied by the greater portion of the <hi rend="font-style: +italic">cricoid cartilage</hi>. This cartilage <pb n="355" /><anchor +id="Pg355" />has the general shape of a signet ring and is so placed +that the part corresponding to the signet fits into the thyroid space, +while the ring portion encircles the larynx just below the thyroid. +Muscles and connective tissue pass from the thyroid to the cricoid +cartilage at all places, save one on each side, where the downward +projections of the thyroid form hinge joints with the cricoid. These +joints permit of motion of either cartilage upon the other.</p> + +<p>At the summit of the cricoid cartilage, on each side, is a small +piece of triangular shape, called the <hi rend="font-style: +italic">arytenoid cartilage</hi>. Each arytenoid is movable on the +cricoid and is connected with one end of a vocal cord.</p> + +<p rend="text-align: center"> +<figure url="images/image150.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 150—<hi rend="font-weight: bold">Vocal +cords</hi> as seen from above. <hi rend="font-style: italic">A.</hi> In +producing sound, <hi rend="font-style: italic">B.</hi> During quiet +breathing.</head> +<figDesc>Fig. 150</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Vocal Cords</hi> are formed by two +narrow strips of tissue which, connecting with the thyroid cartilage in +front and the arytenoid cartilages behind, lie in folds of the mucous +membrane. They have the general appearance of ridge-like projections +from the sides of the larynx, but at their edges they are sharp and +smooth. The open space between the cords is called the <hi +rend="font-style: italic">glottis</hi>. When sound is not being +produced, the glottis is open and has a triangular form, due to the +spreading apart of the arytenoid cartilages and the attached cords. But +when sound is being produced, the glottis is almost completely closed by +the cords. Above the vocal cords, and resembling them in <pb n="356" /><anchor id="Pg356" />appearance, are two other folds of membrane, +called the <hi rend="font-style: italic">false vocal cords</hi> (B, Fig. +149). The false cords do not produce sound, but they aid in the closing +of the glottis.</p> + +<p><hi rend="font-weight: bold">How the Voice is Produced.</hi>—The +voice is produced through the vibrations of the vocal cords. A special +set of muscles draws the arytenoid cartilages toward each other, thereby +bringing their edges very near and parallel to each other in the +passage. At the same time other muscles act on the thyroid and cricoid +cartilages to separate them at the top and give the cords the necessary +tension. With the glottis now almost closed, blasts of air from the +lungs strike the sharp edges of the cords and set them in vibration +(Fig. 150). The vocal cords do not vibrate as strings, like the strings +of a violin, but somewhat as reeds, similar to the reeds of a French +harp or reed organ.</p> + +<p>The location of the vocal cords in the air passages enables the lungs +and the muscles of respiration to aid in the production of the voice. It +is their function to supply the necessary force for setting the cords in +vibration. The upper air passages (mouth, nostrils, and pharynx) supply +resonance chambers for reënforcing the vibrations from the vocal cords, +thereby greatly increasing their intensity. In ordinary breathing the +vocal cords are in a relaxed condition against the sides of the larynx +and are not acted upon by the air as it enters or leaves the lungs.</p> + +<p><hi rend="font-weight: bold">Pitch and Intensity of the +Voice.</hi>—Changes in the pitch of the voice are caused mainly by +variations in the tension of the cords, due to the movements of the +thyroid and cricoid cartilages upon each other.<note place="foot"><p>Some idea of how the movements of the cartilages change +the tension of the cords may be obtained by holding the fingers on the +larynx, between the thyroid and cricoid cartilages, and making tones +first of low and then of high pitch. For the high tones the cartilages are pulled together in +front, and for the low tones they separate. As they pull together in +front, they of course separate behind and above, where the cords are +attached.</p></note> In the production of +tones of very high pitch, the vibrating portions of the cords<pb n="357" /><anchor id="Pg357" /> are thought to be actually +shortened by their margins being drawn into contact at the back. This +raises the pitch in the same manner as does the shortening of the +vibrating portion of a violin string.</p> + +<p>The <hi rend="font-style: italic">intensity</hi>, or loudness, of the +voice is governed by the force with which the air is expelled from the +lungs. The vibrations of the cords, however, are greatly reënforced by +the peculiar structure of the upper air passages, as stated above.</p> + +<p><hi rend="font-weight: bold">Production of Speech.</hi>—The sounds +that form our speech or language are produced by modifying the +vibrations from the vocal cords. This is accomplished by "mouthing" the +sounds from the larynx. The distinct sounds, or words, are usually +complex in nature, being made up of two or more elementary sounds. These +are classed either as <hi rend="font-style: italic">vowels</hi> or <hi +rend="font-style: italic">consonants</hi> and are represented by the +different letters of the alphabet. The vowel sounds are made with the +mouth open and are more nearly the pure vibrations of the vocal cords. +The consonants are modifications of the vocal cord vibrations produced +by the tongue, teeth, lips, and throat.</p> + +<p><hi rend="font-weight: bold">Words and their Significance.</hi>—In +the development of language certain ideas have become associated with +certain sounds so that the hearing of these sounds suggests the ideas. +Our words, therefore, consist of so many sound signals, each capable of +arousing a definite idea in the mind. To talk is to express ideas +through these signals, and to listen is to assume an attitude of mind +such that the signals may be interpreted. In learning a language, both +the sounds of the words and their associated ideas are<pb n="358" /><anchor id="Pg358" /> mastered, this being necessary to +their practical use in exchanging ideas. From spoken language man has +advanced to written language, so that the sight of the written or +printed word also arouses in the mind the associated idea.</p> +</div> + +<div> +<head>THE EAR</head> + +<p><hi rend="font-weight: bold">The Ear</hi> is the sense organ which +enables sound waves to so act upon afferent neurons as to excite +impulses in them. The effect upon the mind which these impulses produce +is known as the <hi rend="font-style: italic">sensation of hearing</hi>. +In the performance of its function the ear receives and transmits sound +waves and also concentrates them upon a suitable exposure of nerve +cells. It includes three parts—the <hi rend="font-style: +italic">external ear</hi>, the <hi rend="font-style: italic">middle +ear</hi>, and the <hi rend="font-style: italic">internal ear</hi>.</p> + +<p><hi rend="font-weight: bold">External Ear.</hi>—The external ear +consists of the part on the outside of the head called the <hi +rend="font-style: italic">pinna</hi>, or auricle, and the tube leading +into the middle ear, called the <hi rend="font-style: italic">auditory +canal</hi> (Fig. 151). The pinna by its peculiar shape aids to some +extent the entrance of sound waves into the auditory canal.<note place="foot"><p>It is only the central portion of the pinna that aids +the entrance of sound into the auditory canal. If by accident the outer +portion of the pinna is removed, there is no impairment of the +hearing.</p></note> It +consists chiefly of cartilage. The auditory canal is a little more than +an inch in length and one fourth of an inch in diameter, and is closed +at its inner end by a thin, but important membrane, called</p> + +<p><hi rend="font-weight: bold">The Membrana Tympani.</hi>—This +membrane consists of three thin layers. The outer layer is continuous +with the lining of the auditory canal; the inner is a part of the lining +of the middle ear; and the middle is a fine layer of connective tissue. +Being thin and delicately poised, the membrana tympani is easily made to +vibrate by the sound<pb n="359" /><anchor id="Pg359" /> waves that enter the auditory +canal. In this way it serves as a receiver of sound waves from the air. +It also protects</p> + +<p rend="text-align: center"> +<figure url="images/image151.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 151—<hi rend="font-weight: bold">Diagram of +section through the ear</hi>, showing relations of its various parts. +(See text.)</head> +<figDesc>Fig. 151</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Middle Ear.</hi>—The middle ear, or +tympanum,<note place="foot"><p>The middle ear is also called the <hi rend="font-style: +italic">ear drum</hi>, and, by the same system of naming, the membrana +tympani is referred to as the <hi rend="font-style: italic">drum +membrane</hi>.</p></note> consists of an irregular cavity in the temporal bone which +is lined with mucous membrane and filled with air. It is connected with +the pharynx by a slender canal called the <hi rend="font-style: +italic">Eustachian tube</hi>. Extending across the middle ear and +connecting with the membrana tympani on one side, and with a membrane +closing a small passage to the internal ear on the other, is a tiny +bridge formed of three small bones. These bones, named in their order +from the membrana tympani, are the <hi rend="font-style: +italic">malleus</hi>, the <hi rend="font-style: italic">incus</hi>, and +the <hi rend="font-style: italic">stapes</hi> (Fig. 151). Where the +malleus joins the membrane is a small muscle whose contraction has the +effect of tightening<pb n="360" /><anchor id="Pg360" /> the membrane. The Eustachian +tube admits air freely to the middle ear, providing in this way for an +equality of atmospheric pressure on the two sides of the drum membrane. +The bridge of bones and the air in the middle ear receive vibrations +from the membrana tympani and communicate them to the membrane of the +internal ear.</p> + +<p><hi rend="font-weight: bold">Purposes of the Middle Ear. </hi>—The +middle ear serves two important purposes. In the first place, it makes +it possible for sound waves to set the membrana tympani in vibration. +This membrane could not be made to vibrate by the more delicate of the +sound waves if it were stretched over a bone, or over some of the softer +tissues, or over a liquid. Its vibration is made possible by the +presence of air on <hi rend="font-style: italic">both</hi> sides, and +this condition is supplied, on the inner side, by the middle ear. The +Eustachian tube, by providing for an <hi rend="font-style: +italic">equality</hi> of pressure on the two sides of the membrane, also +aids in this purpose.</p> + +<p>In the second place, the middle ear provides a means for <hi +rend="font-style: italic">concentrating the force of the sound +waves</hi> as they pass from the membrana tympani to the internal ear. +This concentration is effected in the following manner:</p> + +<p>1. The bridge of bones, being pivoted at one point to the walls of +the middle ear, forms a lever in which the malleus is the long arm, and +the incus and stapes the short arm, their ratio being about that of +three to two. This causes the incus to move through a shorter distance, +but with greater force than the end of the malleus.</p> + +<p>2. The area of the membrana tympani is about twenty times as great as +the membrane of the internal ear which is acted upon by the stapes. The +force from the larger surface is, therefore, concentrated by the bridge +of bones upon the smaller surface. By the combination of these two +devices, the waves striking upon the membrane of the internal ear are +rendered some thirty times more effective than are the same waves +entering the auditory canal.</p> + +<p><hi rend="font-weight: bold">The Internal Ear</hi>, or labyrinth, +occupies a series of irregular channels in the petrous process of the +temporal bone.<note place="foot"><p>The inner projection of the temporal bone is known as +the petrous process.</p></note> It is very complicated in structure, and at the same +time is very small. Its greatest length is not more<pb n="361" /><anchor id="Pg361" /> than three +fourths of an inch and its greatest diameter not more than one half of +an inch. It is filled with a liquid which at one place is called the <hi +rend="font-style: italic">perilymph</hi>, and at another place the <hi +rend="font-style: italic">endolymph</hi>. It is a double organ, being +made up of an outer portion which lies next to the bone, and which +surrounds an inner portion of the same general form. The outer portion +is surrounded by a membrane which serves as periosteum to the bone and, +at the same time, holds the liquid belonging to this part, called the +perilymph. The inner portion, called the <hi rend="font-style: +italic">membranous labyrinth</hi>, consists essentially of a closed +membranous sac, which is filled with the endolymph. The auditory nerve +terminates in this portion of the internal ear. Three distinct divisions +of the labyrinth have been made out, known as the <hi rend="font-style: +italic">vestibule</hi>, the <hi rend="font-style: italic">semicircular +canals</hi>, and the <hi rend="font-style: italic">cochlea</hi> (Fig. +152).</p> + +<p rend="text-align: center"> +<figure url="images/image152.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 152—<hi rend="font-weight: bold">General form, +of internal ear.</hi> The illustration represents the structures of the +internal ear surrounded by a thin layer of bone. 1. Vestibule. 2. +Cochlea. 3. Semicircular canals. 4. Fenestra ovalis. 5. Fenestra +rotunda.</head> +<figDesc>Fig. 152</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Vestibule</hi> forms the central +portion of the internal ear and is somewhat oval in shape. It is in +communication with the middle ear through a small opening in the bone, +called the <hi rend="font-style: italic">fenestra ovalis</hi>, at which +place it is separated from the middle ear only by a thin membrane. Sound +waves enter the liquids of the internal ear at this point, the foot of +the stapes being attached to the membrane. <pb n="362" /><anchor +id="Pg362" />Six other openings lead off from the vestibule at +different places. One of these enters the cochlea. The other five open +into</p> + +<p><hi rend="font-weight: bold">The Semicircular Canals.</hi>—These +canals, three in number, pass through the bone in three different +planes. One extends in a horizontal direction and the other two +vertically, but each plane is at right angles to the other two. Both +ends of each canal connect with the vestibule, though two of them join +by a common opening. The inner membranous labyrinth is continuous +through each canal, and is held in position by small strips of +connective tissue.</p> + +<p>The purpose of the semicircular canals is not understood. It is +known, however, that they are not used in hearing. On the other hand, +there is evidence to the effect that they act as equilibrium sense +organs, exciting sensations necessary for balancing the body. Their +removal or injury, while having no effect upon the hearing, does +interfere with the ability to keep the body in an upright position.</p> + +<p rend="text-align: center"> +<figure url="images/image153.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 153—Diagram showing the divisions of cochlear +canal.</head> +<figDesc>Fig. 153</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Cochlea</hi> is the part of the +internal ear directly concerned in hearing. It consists of a coiled tube +which makes two and one half turns around a central axis and bears a +close resemblance to a snail shell (Figs. 151 and 152). It differs in +plan from a snail shell, however, in that its interior space is divided +into three distinct channels, or canals. These lie side by side and are +named, from their relations to other parts, the <hi rend="font-style: +italic">scala vestibula</hi>, the <hi rend="font-style: italic">scala +tympani</hi>, and the <hi rend="font-style: italic">scala media</hi>. +Any vertical section of the cochlea shows all three of these channels +(Fig. 153).</p> + +<p><pb n="363" /><anchor id="Pg363" /><hi rend="font-weight: +bold">The Scala Vestibula and the Scala Tympani</hi> appear in cross +section as the larger of the canals. The former, so named from its +connection with the vestibule, occupies the upper position in all parts +of the coil. The latter lies below at all places, and is separated from +the channels above partly by a margin of bone and partly by a membrane. +It receives its name from its termination at the tympanum, or middle +ear, from which it is separated only by a thin membrane.<note place="foot"><p>A small opening in the bone at this place is called the +<hi rend="font-style: italic">fenestra rotunda</hi>.</p></note> Both the +scala vestibula and the scala tympani belong to the outer portion of the +internal ear and are, for this reason, filled with the perilymph. At +their upper ends they communicate with each other by a small opening, +making by this means one continuous canal through the cochlea. This +canal passes from the vestibule to the tympanum and, in so doing, goes +entirely around</p> + +<p><hi rend="font-weight: bold">The Scala Media.</hi>—This division of +the cochlea lies parallel to and between the other two divisions. It is +above the scala tympani and below the scala vestibula, and is separated +from each by a membrane. The scala media belongs to the membranous +portion of the internal ear and is, therefore, filled with the +endolymph. It receives the terminations of fibers from the auditory +nerve and may be regarded as the true sense organ of hearing. The nerve +fibers terminate upon the membrane known as the <hi rend="font-style: +italic">basilar membrane</hi>, which separates it from the scala +tympani. This membrane extends the length of the cochlear canals, and is +stretched between a projecting shelf of bone on one side and the outer +wall of the cochlea on the other. It is covered with a layer of +epithelial cells, some of which have small, hair-like projections and +are known as the <hi rend="font-style: italic">hair cells</hi>. Above +the membrane, and resting partly upon it, are two<pb n="364" /><anchor id="Pg364" /> rows of rod-like bodies, called +the <hi rend="font-style: italic">rods of Corti</hi>. These, by leaning +toward each other, form a kind of tunnel beneath. They are exceedingly +numerous, numbering more than 6000, and form a continuous series along +the margin of the membrane.</p> + +<p rend="text-align: center"> +<figure url="images/image154.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 154—<hi rend="font-weight: bold">Diagram</hi> +illustrating passage of sound waves through the ear.</head> +<figDesc>Fig. 154</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">How We Hear.</hi>—The sound waves which +originate in vibrating bodies are transmitted by the air to the external +ear. Passing through the auditory canal, the waves strike against the +membrana tympani, setting it into vibration. By the bridge of bones and +the air within the middle ear the vibrations are carried to and +concentrated upon the liquid in the internal ear (Fig. 154). From here +the vibrations pass through the channels of the cochlea and set into +vibration the contents of the scala media and different portions of the +basilar membrane. This serves as a stimulus to the fibers of the +auditory nerve, causing them to transmit impulses which, on passing to +the brain, produce the sensation of hearing.</p> + +<p>Much of the peculiar structure of the cochlea is not understood. Its +minute size and its location in the temporal bone make its study +extremely difficult. The connection of the scala vestibula with the +scala tympani, and this with the middle ear, is necessary for the +passage of vibrations through the internal ear. Its liquids, being +practically incompressible and surrounded on all sides by bones, could +not otherwise yield to the movements of the stapes. (See Practical +Work.) The rods of Corti are thought to act as dampers on the basilar +membrane, to prevent the continuance of vibrations when once they are +started.</p> + +<p><hi rend="font-weight: bold">Detection of Pitch.</hi>—The method of +detecting tones of different pitch<pb n="365" /><anchor id="Pg365" /> is +not understood. Several theories have been advanced with reference to +its explanation, one of the most interesting being that proposed by +Helmholtz. This theory is based on our knowledge of sympathetic +vibrations. The basilar membrane, while continuous throughout, may be +regarded as made up of many separate cords of different lengths +stretched side by side. A tone of a given pitch will set into vibration +only certain of these cords, while tones of different pitch will set +others into vibration.</p> + +<p>Another theory is that the basilar membrane responds to all kinds of +vibrations and the analysis of sound takes place in the brain.</p> + +<p>A third view is that the filaments from the hair cells, rather than +the basilar membrane, respond to the vibrations and in turn stimulate +the terminations of the nerve fibers.</p> + +<p rend="text-align: center"> +<figure url="images/image155.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 155—<hi rend="font-weight: bold">Diagram</hi> +showing how wax may plug the auditory canal and cause deafness.</head> +<figDesc>Fig. 155</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Hygiene of the Ear.</hi>—The ear, being +a delicate organ, is frequently injured by careless or rough treatment. +The removal of the ear wax by the insertion of pointed instruments has +been found to interfere with the natural method of discharge and to +irritate the membrane. It should never be practiced. It is unnecessary +in the healthy ear thus to cleanse the auditory canal, as the wax is +passed by a natural process to where it is easily removed by a damp +cloth. If the natural process is obstructed, clean warm water and a soft +linen cloth may be employed in cleansing the canal, without likelihood +of injury. Clean warm water may also be introduced into the auditory +canal as a harmless remedy in relieving inflammation of the auditory +canal and of the middle ear. Children's ears are easily injured, and it +goes without saying that they should never be pulled nor boxed.</p> + +<p>It frequently happens that a mass of wax collects in the auditory +canal and closes the passage so completely as to<pb n="366" /><anchor id="Pg366" /> cause deafness (Fig. 155). This +may come about without pain and so gradually that one does not think of +seeking medical aid. Such masses are easily removed by the physician, +the hearing being then restored. Both for painful disturbances of the +ear and for the gradual loss of hearing, the physician should be +consulted.</p> + +<p><hi rend="font-weight: bold">The Hearing of School +Children.</hi>—School children not infrequently have defective hearing +and for this reason are slow to learn. The hearing is easily tested with +a watch, the normal ear being able to hear the watch tick at a distance +of at least two feet. Pupils with defective hearing should, of course, +have medical attention, and in the classroom should be seated where they +can hear to the best advantage.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—Sound waves constitute the +external stimuli for the sensation of hearing. They consist of +progressive vibratory movements of the air that originate in vibrating +bodies. Through the larynx and the ear, sound waves are utilized by the +body in different ways, but chiefly as a means of communication. The +larynx produces sound waves which are reënforced and modified by the +air passages. The ear supplies suitable conditions for the action of +sound waves upon nerve cells. Both the ear and the larynx are +constructed with special reference to the nature and properties of sound +waves, and they illustrate the body's ability to adjust itself to, and +to make use of, its physical environment.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. For what different +purposes are sound waves employed in the body?</p> + +<p>2. How do sound waves originate? How are they transmitted? How do +they differ from the waves on water?</p> + +<p>3. How are sound waves able to act as nerve stimuli?</p> + +<p>4. Describe two methods of reënforcing sound waves. Which method is +employed in the body?</p> + +<p><pb n="367" /><anchor id="Pg367" />5. Name all the parts of the body +that are directly or indirectly concerned in the production of +sound.</p> + +<p>6. Describe the larynx.</p> + +<p>7. Describe the condition of the vocal cords in speaking and in +ordinary breathing.</p> + +<p>8. How are sounds differing in pitch and intensity produced by the +larynx?</p> + +<p>9. How is the sound produced by the vocal cords changed into +speech?</p> + +<p>10. What parts of the ear are concerned in transmitting sound +waves?</p> + +<p>11. Give the purposes of the middle ear.</p> + +<p>12. Trace a sound wave from a bell to the basilar membrane, and trace +the impulse that it causes from there to the brain.</p> + +<p>13. Give the purpose of the Eustachian tubes; of the rods of Corti; +of the semicircular canals.</p> + +<p>14. Give directions for the proper care of the ear.</p> +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">To illustrate the Origin of +Sound.</hi>—1. Strike a bell an easy blow and hold some light substance, +as a pith ball attached to a thread, against the side, noting the +result. 2. Sound a tuning fork by striking it against the table. Test it +for vibrations as above, or by letting the vibrating prongs touch the +surface of water. 3. Pluck a string of a guitar or violin, and find +proof that it is vibrating while giving out sound.</p> + +<p><hi rend="font-weight: bold">To show the Transmission of +Sound.</hi>—1. Vibrate a tuning fork and press the stem against a table +or desk. The vibrations which are reënforced in this way will be heard +in all parts of the room. Now press one end of a wooden rod, as a broom +handle, against the table, and bring the stem of the vibrating fork +against the other end. The vibrations now move down the stick to the +table, from whence they are communicated to the air. Observe that the +sound waves, to reach the ear, must pass through the rod, the table, and +the air. 2. Fasten the tuning fork to a flat piece of cork by pressing +the stem into a small hole in the center. Vibrate the fork and let the +cork rest on the surface of water in a half-filled tumbler on the table. +The sound will, as before, pass to the table and then to the air. +Observe that in this case the vibrations are transmitted by a liquid, a +solid, and by the air.<pb n="368" /><anchor id="Pg368" /> Compare this action with the transmission of sound waves by different +portions of the ear.</p> + +<p><hi rend="font-weight: bold">To show Effects of Sound Waves.</hi>—1. +Place two large tuning forks of the same pitch, and mounted on thin +boxes for reënforcing their vibrations, near each other on a table. +Vibrate one of the forks for a moment and then stop it by means of the +hand. Observe that the other fork has been set in vibration. (This +experiment does not work with forks of different pitch.) 2. While +holding a thin piece of paper against a comb with the open lips, produce +musical tones with the vocal cords. These will set the paper in +vibration, producing the so-called "comb music." 3. Examine the disk in +a telephone which is set in vibration by the voice. Observe that it is a +thin disk and, like the membrane of the ear, has air on both sides of +it.</p> + +<p><hi rend="font-weight: bold">To show the Reënforcement of +Sound.</hi>—1. Vibrate a tuning fork in the air, noting the feebleness +of the tone produced. Then hold the stem against a door or the top of a +table, noting the difference. 2. Hold a vibrating tuning fork over a +tall jar, or bottle, and gradually add water. If the vessel is +sufficiently tall, a depth will be reached where the air in the vessel +reënforces the sound from the fork. 3. Hold a vibrating fork over the +mouth of a small fruit jar, partly covered with a piece of cardboard. By +varying the size of the opening, a position will be found where the +sound is reënforced. If not successful at first, try bottles and jars of +different sizes.</p> + +<p><hi rend="font-weight: bold">To illustrate the Manner of Vibration of +the Liquid in the Internal Ear.</hi>—Tie a piece of dental rubber over +the end of a glass or wooden tube about half an inch in diameter and six +inches in length. Fill the tube entirely full of water and, without +spilling, tie a piece of thin rubber tightly over the other end. Holding +the tube horizontally, press the rubber in at one end and note that it +is pushed out at the other end. Make an imitation of a vibration with +the finger against the rubber at one end of the tube and note the effect +at the other end. To what do the tube and the rubber on the ends of the +tube correspond in the internal ear?</p> + +<p rend="text-align: center"> +<figure url="images/image156.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 156—<hi rend="font-weight: bold">Simple +apparatus</hi> for demonstrating the larynx.</head> +<figDesc>Fig. 156</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">To show the Plan of the Larynx.</hi>—Cut +from stiff paper four pieces of different shapes as indicated in Fig. +156. (The piece to the left should have a length of about six inches, +the others proportionally<pb n="369" /><anchor id="Pg369" /> large.) +The largest represents the thyroid cartilage, the next in size the +cricoid, and the two smallest the arytenoid cartilages. By means of +pins, or threads, connect these with each other according to the +description of the larynx on page 253. With this simple model the +movements of the different cartilages and their effect upon the vocal +cords may be illustrated.</p> + +<p><hi rend="font-weight: bold">To show the Relation of the Movements of +the Vocal Organs to the Production of Different Sounds.</hi>—1. Lightly +grasp the larynx with the fingers while talking. Observe the changes, +both in the position and shape of the larynx, in the production of +sounds of different pitch. 2. Observe the difference in the action of +the muscles of respiration in the production of loud and faint sounds. +3. Pronounce slowly the vowels, A, E, I, O, U, and the consonants C, F, +K, M, R, S, T, and V, noting the shape of the mouth, the position of the +tongue, and the action of the lips in each case.</p> + +<p><hi rend="font-weight: bold">To demonstrate the Ear.</hi>—Examine a +dissectible model of the ear, locating and naming the different parts. +Trace as far as possible the path of the sound waves and find the +termination of the auditory nerve. Note also the relative size of the +parts, and calculate the number of times the model is larger than the +natural ear. <hi rend="font-style: italic">Suggestion</hi>: The greatest +diameter of the internal ear is about three fourths of an inch.</p> + +<p>In an extended course it is a profitable exercise to dissect the ear +of a sheep or calf, observing the auditory canal, middle ear, bridge of +bones, and the tympanic membrane with attached malleus and tensor +tympanic muscle. Pass a probe from the nasal pharynx through the +Eustachian tube into the middle ear. With bone forceps or a fine saw, +split open the petrous portion of the temporal bone and observe the +cochlea and the semicircular canals. By a careful dissection other parts +of interest may also be shown.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<pb n="370" /><anchor id="Pg370" /> +<index index="toc" /><index index="pdf" /> +<head>CHAPTER XXII - THE EYE</head> + +<p>Sight is considered the most important of the sensations. It is the +chief means of bringing the body into proper relations with its +surroundings and, even more than the sensation of hearing, is an avenue +for the reception of ideas. The sense organs for the production of sight +are the eyes; the external stimulus is</p> + +<p><hi rend="font-weight: bold">Light.</hi>—Light, like sound, consists +of certain vibrating movements, or waves. They differ from sound waves, +however, in form, velocity, and in method of origin and transmission. +Light waves are able to pass through a vacuum, thus showing that they +are not dependent upon air for their transmission. They are supposed to +be transmitted by what the physicist calls ether—a highly elastic and +exceedingly thin substance which fills all space and penetrates all +matter. As a rule, light waves originate in bodies that are highly +heated, being started by the vibrations of the minute particles of +matter.</p> + +<p>Light is influenced in its movements by various conditions. In a +substance of uniform density it moves with an unchanging velocity and in +a straight line. If it enters a less dense, or rarer, substance, its +velocity increases; if one more dense, its velocity diminishes; and if +it enters either the rarer or denser substance in any direction other +than perpendicularly, it is bent out of its course, or <hi +rend="font-style: italic">refracted</hi>. If it strikes against a body +lying in its course, it may be thrown off (<hi rend="font-style: +italic">reflected</hi>), or it may enter the body and either be passed +on through (<hi rend="font-style: italic">transmitted</hi>) or <hi +rend="font-style: italic">absorbed</hi> (Fig. 157). Light which is +absorbed is transformed into heat.</p> + +<p><pb n="371" /><anchor id="Pg371" /><hi rend="font-weight: bold">Kinds of Reflection.</hi>—Waves of light +striking against the smooth surface of a mirror are thrown off in +definite directions, depending on the angle at which they strike. +(Illustrate by holding a mirror in the direct rays of the sun.) But +light waves that strike rough surfaces are reflected in practically all +directions and apparently without reference to the angle at which they +strike. (Illustrate by placing a piece of white paper in the direct rays +of the sun. It matters not from what direction it is viewed, waves of +light strike the eye.) This kind of reflection is called <hi +rend="font-style: italic">diffusion</hi>, and it serves the important +purpose of making objects visible. The light waves passing out in all +directions from objects which have received light from the sun, or some +other luminous body, enable them to be seen.</p> + +<p rend="text-align: center"> +<figure url="images/image157.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 157—<hi rend="font-weight: bold">Diagram +illustrating passage of light waves.</hi>On the right the light is +transmitted by the glass, reflected by the mirror, refracted by the +prism, and absorbed by the black cloth. On the left the light from the +candle forms an image by passing through a small hole in a cardboard and +falling upon a screen.</head> +<figDesc>Fig. 157</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Formation of Images.</hi>—Another +principle necessary to seeing is that of refraction. <hi +rend="font-style: italic">Refraction</hi> means the bending, or turning, +of light from a straight course. One of the most interesting effects of +refraction is the formation of images of objects, such as may be +accomplished by light from them passing in a certain manner through +convex lenses. If, for example, a convex lens be moved back and +forth<pb n="372" /><anchor id="Pg372" /> between a candle and a screen in +a dimly lighted room, a position will be found where a picture of the +candle falls upon the screen. This picture, called the <hi +rend="font-style: italic">image</hi>, results from the refraction of the +candle light in passing through the lens.</p> + +<p rend="text-align: center"> +<figure url="images/image158.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 158—<hi rend="font-weight: bold">Diagram +illustrating formation of images.</hi> On the right the image is formed +by a double convex lens; on the left by the lenses of the eye. The +candle flame represents a luminous, or light-giving, body; but light +passes from the large arrow by reflection. (See text.)</head> +<figDesc>Fig. 158</figDesc> +</figure></p> + +<p>In order to form an image, the light waves spreading out from the +object must be brought together, or focused. Focusing means literally +the bringing of light to a point, but it is evident in the formation of +an image that all the waves are not brought to a single point. If they +were, there would be no image. In the example of the candle given above, +the explanation is as follows:</p> + +<p>The light from the candle comes from a great number of separate and +distinct points in the candle flame. The lens, by its peculiar shape, +bends the waves coming from any single point so that they are brought to +a corresponding point on the screen. Furthermore, the points of focused +light are made to occupy the same relative positions on the screen as +the points from which they emanate in the candle flame (Fig. 158). This +is why the area of light on the screen has the same form as the candle, +or makes an image of it. The same explanation applies if, instead of the +luminous candle, a body that simply reflects light, as a book, is +used.</p> + +<p><hi rend="font-weight: bold">The Problem of Seeing.</hi>—What we call +<hi rend="font-style: italic">seeing</hi> is vastly more than the +stimulation of the brain through the action of light upon afferent +neurons. It is the <hi rend="font-style: italic">perceiving </hi>of all +the different things that make up our surroundings. If<pb n="373" /><anchor id="Pg373" /> one looks toward the clear sky, +he receives a <hi rend="font-style: italic">sensation of light</hi>, but +sees no object. He may also get a sensation of light with the eyelids +closed, if he turn the eyes toward the window or some bright light. But +how different when the light from various objects enters the eyes. There +is apparently no consciousness of light, but instead a consciousness of +the size, form, color, and position of the objects. <hi +rend="font-style: italic">Seeing is perceiving objects.</hi> Stimulation +by the light waves is only the means toward this end. The chief problem +in the study of sight is that of determining <hi rend="font-style: +italic">how light waves enable us to become conscious of +objects.</hi></p> + +<p><hi rend="font-weight: bold">Sense Organs of Sight.</hi>—The sense +organs of sight consist mainly of the two eyeballs. Each of these is +located in a cavity of the skull bones, called the <hi rend="font-style: +italic">orbit</hi>, where it is held in position by suitable tissues and +turned in different directions by a special set of muscles. A cup-shaped +receptacle is provided within the orbit, by layers of fat, and a smooth +surface is supplied by a double membrane that lies between the fat and +the eyeball. In front the eyeballs are provided with movable coverings, +called the <hi rend="font-style: italic">eyelids</hi>. These are +composed of dense layers of connective tissue, covered on the outside by +the skin and lined within by a sensitive membrane, called the <hi +rend="font-style: italic">conjunctiva</hi>. At the base of the lids the +conjunctiva passes to the eyeball and forms a firmly attached covering +over its front surface. This membrane prevents the passage of foreign +materials back of the eyeball, and by its sensitiveness stimulates +effort for the removal of irritating substances from beneath the lids. +The eyelashes and the eyebrows are also a means of protecting the +eyeballs.</p> + +<p><hi rend="font-weight: bold">The Eyeball</hi>, or globe of the eye, +is a device for <hi rend="font-style: italic">focusing</hi> light upon a +sensitized nervous surface which it incloses and protects. In shape it +is nearly spherical, being about <pb n="374" /><anchor id="Pg374" />an +inch in diameter from right to left and nine tenths of an inch both in +its vertical diameter and from front to back. It has the appearance of +having been formed by the union of two spherical segments of different +size. The smaller segment, which forms about one sixth of the whole, is +set upon the larger and forms the projecting transparent portion in +front. The walls of the eyeballs are made up of three separate layers, +or coats—an <hi rend="font-style: italic">outer coat</hi>, a <hi +rend="font-style: italic">middle coat</hi>, and an <hi rend="font-style: +italic">inner coat</hi> (Fig. 159).</p> + +<p rend="text-align: center"> +<figure url="images/image159.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 159—<hi rend="font-weight: bold">Diagram of the +eyeball in position.</hi> 1. Yellow spot. 2. Blind spot. 3. Retina. 4. +Choroid coat. 5. Sclerotic coat. 6. Crystalline lens. 7. Suspensory +ligament. 8. Ciliary processes and ciliary muscle. 9. Iris containing +the pupil. 10. Cornea. 11. Lymph duct. 12. Conjunctiva. 13. Inferior and +superior recti muscles. 14. Optic nerve. 15. Elevator muscle of eyelid. +16. Bone. <hi rend="font-style: italic">A.</hi> Posterior chamber +containing the vitreous humor. <hi rend="font-style: italic">B.</hi> +Anterior chamber containing the aqueous humor.</head> +<figDesc>Fig. 159</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Outer Coat</hi> surrounds the entire +globe of the eye and consists of two parts—the sclerotic coat and the +cornea. The <hi rend="font-style: italic">sclerotic coat</hi> covers the +greater portion of the larger spherical segment and is recognized in +front as "the white of the eye." It is composed mainly of fibrous +connective tissue and is dense, opaque, and tough. It preserves the form +of the eyeball and protects the portions within. It is pierced at the +back by a small opening which admits the<pb n="375" /><anchor id="Pg375" /> optic nerve, and in front it +becomes changed into the peculiar tissue that makes up the cornea.</p> + +<p>The <hi rend="font-style: italic">cornea</hi> forms the transparent +covering over the lesser spherical segment of the eyeball, shading into +the sclerotic coat at its edges. It has a complex structure, consisting +in the main of a transparent form of connective tissue. It serves the +purpose of admitting light into the eyeball.</p> + +<p><hi rend="font-weight: bold">The Middle Coat</hi> consists of three +connected portions—the <hi rend="font-style: italic">choroid coat</hi>, +the <hi rend="font-style: italic">ciliary processes</hi>, and the <hi +rend="font-style: italic">iris</hi>. These surround the larger spherical +segment. All three parts are rich in blood vessels, containing the blood +supply to the greater portion of the eyeball.</p> + +<p>The <hi rend="font-style: italic">choroid coat</hi> lies immediately +beneath the sclerotic coat at all places except a small margin toward +the front of the eyeball. It is composed chiefly of blood vessels and a +delicate form of connective tissue that holds them in place. It contains +numerous pigment cells which give it a dark appearance and serve to +absorb surplus light. Near where the sclerotic coat joins the cornea, +the choroid coat separates from the outer wall and, by folding, forms +many slight projections into the interior space. These are known as the +<hi rend="font-style: italic">ciliary processes</hi>. The effect of +these folds is to collect a large number of capillaries into a small +space and to give this part of the eyeball an extra supply of blood. +Between the ciliary processes and the sclerotic coat is a small muscle, +containing both circular and longitudinal fibers, called the <hi +rend="font-style: italic">ciliary muscle</hi>.</p> + +<p>The <hi rend="font-style: italic">iris</hi> is a continuation of the +choroid coat across the front of the eyeball. It forms a dividing +curtain between the two spherical segments and gives the color to the +eye. At its center is a circular opening, called the <hi +rend="font-style: italic">pupil</hi>, which admits light to the back of +the eyeball. By varying the<pb n="376" /><anchor id="Pg376" /> size of the pupil, the iris is +able to regulate the amount of light which passes through and it employs +for this purpose two sets of muscular fibers. One set of fibers forms a +thin band which encircles the pupil and serves as a sphincter to +diminish the opening. Opposing this are radiating fibers which are +attached between the inner and outer margins of the iris. By their +contraction the size of the opening is increased. Both sets of fibers +act reflexively and are stimulated by variations in the light falling +upon the retina.</p> + +<p rend="text-align: center"> +<figure url="images/image160.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 160—<hi rend="font-weight: bold">Diagram showing +main nervous elements in the retina.</hi> Light waves stimulate the rods +and cones at back surface of the retina, starting impulses which excite +the ganglion cells at the front surface. Fibers from the ganglion cells +pass into the optic nerve.</head> +<figDesc>Fig. 160</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">The Inner Coat, or Retina.</hi>—This is +a delicate membrane containing the expanded termination of the optic +nerve. It rests upon the choroid coat and spreads over about two thirds +of the back surface of the eyeball. Although not more than one fiftieth +of an inch in thickness, it presents a very complex structure, +essentially nervous, and is<pb n="377" /><anchor id="Pg377" /> made up of several distinct +layers. Of chief importance in the outer layer are the cells which are +acted upon directly by the light and are named, from their shape, the +<hi rend="font-style: italic">rods</hi> and <hi rend="font-style: +italic">cones</hi>. In contact with these, but occupying a separate +layer, are the ends of small afferent nerve cells. These in turn +communicate with nerve cells in a third layer, known as the ganglion +cells, that send their fibers into the optic nerve (Fig. 160).</p> + +<p>In the center of the retina is a slight oval depression having a +faint yellowish color, and called, on that account, the <hi +rend="font-style: italic">yellow spot</hi>. This is the part of the +retina which is most sensitive to light. Directly over the place of +entrance of the optic nerve is a small area from which the rods and +cones are absent and which, therefore, is not sensitive to light. This +is called the <hi rend="font-style: italic">blind spot</hi>. (See +Practical Work.)</p> + +<p><hi rend="font-weight: bold">The Crystalline Lens.</hi>—Immediately +back of the iris and touching it is a transparent, rounded body, called +the crystalline lens. This is about one fourth of an inch thick and one +third of an inch through its long diameter, and is more curved on the +back than on the front surface. It is inclosed in a thin sheath, called +the <hi rend="font-style: italic">membranous capsule</hi>, which +connects with a divided sheath from the sides of the eyeball, called the +<hi rend="font-style: italic">suspensory ligament</hi> (Fig. 159). Both +the lens and the capsule are highly elastic.</p> + +<p><hi rend="font-weight: bold">Chambers and "Humors" of the +Eyeball.</hi>—The crystalline lens together with the suspensory ligament +and the ciliary processes form a partition across the eyeball. This +divides the eye space into two separate compartments, which are filled +with the so-called "humors" of the eye. The front cavity of the eyeball, +which is again divided in part by the iris, is filled with the <hi +rend="font-style: italic">aqueous</hi> humor. This is a clear, +lymph-like liquid which contains an occasional<pb n="378" /><anchor id="Pg378" /> white corpuscle. It has a +feeble motion and is slowly added to and withdrawn from the eye. It is +supplied mainly by the blood vessels in the ciliary processes and finds +a place of exit through a small lymph duct at the edge of the cornea +(Fig. 159).</p> + +<p>The back portion of the eyeball is filled with a soft, transparent, +jelly-like substance, called the <hi rend="font-style: +italic">vitreous</hi> humor. It is in contact with the surface of the +retina at the back and with the attachments of the lens in front, being +surrounded by a thin covering of its own, called the <hi +rend="font-style: italic">hyaloid membrane</hi>. The aqueous and +vitreous humors aid in keeping the eyeball in shape and also in +focusing.</p> + +<p><hi rend="font-weight: bold">How we see Objects.</hi>—To see an +object at least four things must happen:</p> + +<p>1. Light must pass from the object into the eye. Objects cannot be +seen where there is no light or where, for some reason, it is kept from +entering the eye.</p> + +<p>2. The light from the object must be focused (made to form an image) +on the retina. In forming the image, an area of the retina is stimulated +which corresponds to <hi rend="font-style: italic">the form of the +object</hi>.</p> + +<p>3. Impulses must pass from the retina to the brain, stimulating it to +produce the sensations.</p> + +<p>4. The sensations must be so interpreted by the mind as to give an +impression of the object.</p> + +<p><hi rend="font-weight: bold">Focusing Power of the Eyeball.</hi>—The +eyeball is essentially a device for focusing light. All of its +transparent portions are directly concerned in this work, and the +portions that are not transparent serve to protect and operate these +parts and hold them in place. Of chief importance are the crystalline +lens and the cornea. Both of these are lenses. The cornea with its +inclosed liquid is a plano-convex lens, while the crystalline lens +is<pb n="379" /><anchor id="Pg379" /> double convex.<note place="foot"><p>Consult some work on physics on the different kinds of +lenses and their uses.</p></note> Because of the +great difference in density between the air on the outside and the +aqueous humor within, the cornea is the more powerful of the two. The +crystalline lens, however, performs a special work in focusing which is +of great importance. The iris also aids in focusing since it, through +the pupil, regulates the amount of light entering the back chamber of +the eyeball and causes it to fall in the center of the crystalline lens, +the part which focuses most accurately.</p> + +<p rend="text-align: center"> +<figure url="images/image161.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 161—<hi rend="font-weight: bold">Diagram showing +changes in shape of crystalline lens</hi> to adapt it to near and +distant vision.</head> +<figDesc>Fig. 161</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Accommodation.</hi>—A difficulty in +focusing arises from the fact that the degree of divergence of the light +waves entering the eye from different objects, varies according to their +distance. Since the waves from any given point on an object pass out in +straight lines in all directions, the waves that enter the eye from +distant objects are at a different angle from those that enter from near +objects. In reality waves from distant objects are practically parallel, +while those from very near objects diverge to a considerable degree. To +adjust the eye to different distances requires some change in the +focusing parts that corresponds to the differences in the divergence of +the light.<pb n="380" /><anchor id="Pg380" /> This change, called <hi +rend="font-style: italic">accommodation</hi>, occurs in the crystalline +lens.<note place="foot"><p>With respect to its adjustments the eye does not differ +in principle from various other optical instruments, such as the +microscope, telescope, photographer's camera, etc., which, in their use, +form images of objects. These all require some adjustment of their +parts, called focusing, which adapts them to the distance. The eye's +method of focusing, however, differs from that of most optical +instruments, in that the adjustment is brought about through changes in +the curvature of a lens.</p></note> In the process of accommodation, changes occur in the shape of +the crystalline lens, as follows:</p> + +<p>1. In looking from a distant to a near object, the lens becomes more +convex, <hi rend="font-style: italic">i.e.</hi>, rounder and thicker +(Fig. 161). This change is necessary because the greater divergence of +the light from the near objects requires a greater converging power on +the part of the lens.<note place="foot"><p>The converging power of convex lenses varies as the +curvature—the greater the curvature, the greater the converging +power.</p></note></p> + +<p>2. In looking from near to distant objects, the lens becomes flatter +and thinner (Fig. 161). This change is necessary because the less +divergent waves from the distant objects require less converging power +on the part of the lens.</p> + +<p>The method employed in changing the shape of the lens is difficult +to determine and different theories have been advanced to account for +it. The following, proposed by Helmholtz, is the theory most generally +accepted:</p> + +<p>The lens is held in place back of the pupil by the suspensory +ligament. This is attached at its inner margin to the membranous +capsule, and at its outer margin to the sides of the eyeball, and +entirely surrounds the lens. It is drawn perfectly tight so that the +sides of the eyeball exert a continuous tension, or pull, on the +membranous capsule, which, in its turn, exerts pressure on the sides of +the lens, tending to flatten it. This arrangement brings the elastic +force of the eyeball into opposition to the elastic force of the lens. +The ciliary muscle plays between these opposing forces in the following +manner:</p> + +<p><hi rend="font-style: italic">To thicken the lens</hi>, the ciliary +muscle contracts, pulling forward the suspensory ligament and releasing +its tension on the membranous<pb n="381" /><anchor id="Pg381" /> +capsule. This enables the lens to thicken on account of its own elastic +force. <hi rend="font-style: italic">To flatten the lens</hi>, the +ciliary muscle relaxes, the elastic force of the eyeball resumes its +tension on the suspensory ligament, and the membranous capsule resumes +its pressure on the sides of the lens. This pressure, overcoming the +elastic force of the lens, flattens it.</p> + +<p><hi rend="font-weight: bold">Movements of the Eyeballs.</hi>—In order +that the light may enter the eyeballs to the best advantage, they must +be moved in various directions. These movements are brought about +through the action of six small muscles attached to each eyeball. Four +of these, named, from their positions, the superior, inferior, internal, +and external recti muscles, are attached at one end to the sides of the +eyeball and at the other end to the back of the orbit (Fig. 162). These, +in the order named, turn the eyes upward, downward, inward, and outward. +The other two, the superior and inferior oblique muscles, aid in certain +movements of the recti muscles and, in addition, serve to rotate the +eyes slightly. The movements of the eyeballs are similar to those of +ball and socket joints.</p> + +<p rend="text-align: center"> +<figure url="images/image162.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 162—<hi rend="font-weight: bold">Exterior +muscles of eyeball.</hi></head> +<figDesc>Fig. 162</figDesc> +</figure></p> + +<p> <hi rend="font-weight: bold">Binocular Vision.</hi>—In addition to +directing the eyeballs so that light may enter them to the best +advantage from different objects, the<pb n="382" /><anchor id="Pg382" /> +muscles also enable two eyes to be used as one. Whenever the eyes are +directed toward the same object, an image of this object is formed on +the retina of each. Double vision is prevented only by having the images +fall on corresponding places in the two eyes. This is accomplished by +the muscles. In each act of seeing, it becomes the task of the superior +and inferior recti muscles to keep the eyes in the same plane, and of +the external and internal recti muscles to give just the right amount of +convergence. If slight pressure is exerted against one of the eyes, the +action of the muscles is interfered with and, as a consequence, one sees +double. The advantages of two eyes over one in seeing lie in the greater +distinctness and broader range of vision and in the greater correctness +of judgments of distance.</p> + +<p><hi rend="font-weight: bold">Visual Sensations.</hi>—The visual +sensations include those of <hi rend="font-style: italic">color</hi> and +those of a <hi rend="font-style: italic">general sensibility to +light</hi>. Proof of the existence of these types of sensation is found +in color blindness, a defect which renders the individual unable to +distinguish certain colors when he is still able to see objects. Color +sensations are the results of light waves of different lengths acting on +the retina. While the method by which waves of one length produce one +kind of sensation and those of another length a different sensation is +not understood, the cones appear to be the portions of the retina acted +on to produce the color. On the other hand, the rods are sensitive to +all wave lengths and give general sensibility to light.</p> + +<p><hi rend="font-weight: bold">Visual Perceptions.</hi>—"Seeing" is +very largely the mental interpretation of the primary sensations and the +conditions under which they occur. For example, our ability to see +objects in their natural positions when their images are inverted on the +retina is explained by the fact that we are not conscious of the retinal +image, but of the mind's interpretation of it through experience. +Experience has also taught us to locate objects in the direction toward +which it is necessary to turn the eyes in order to see them. In other +words, we see objects in the direction from which the light enters the +eyes. That the object is not always in that direction is shown by the +image in the mirror. The apparent size and form of objects are +inferences, and they are based in part upon the size and form of the +area of the retina stimulated. We judge of distance by the effort +required to converge the eyes upon the objects, by the amount of +divergence of the waves entering the pupil, and also by the apparent +size of the object.</p> + +<p><pb n="383" /><anchor id="Pg383" /><hi rend="font-weight: bold">The Lachrymal Apparatus.</hi>—Seeing +requires that the light penetrate to the retina. For this reason all the +structures in front of the retina are transparent. One of these +structures, the cornea, on account of its exposure to the air, is liable +to become dry, like the skin, and to lose its transparency. To preserve +the transparency of the cornea, and also to lubricate the eyelids and +aid in the removal of foreign bodies, a secretion, called <hi +rend="font-style: italic">tears</hi>, is constantly supplied.</p> + +<p rend="text-align: center"> +<figure url="images/image163.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 163—<hi rend="font-weight: bold">Diagram of +irrigating system of the eye.</hi> After wetting the eyeball the tears +may also moisten the air entering the lungs.</head> +<figDesc>Fig. 163</figDesc> +</figure></p> + +<p>The lachrymal, or tear, glands are situated at the upper and outer +margins of the orbits. They have the general structure of the salivary +glands and discharge their liquid by small ducts beneath the upper lids. +From here the tears spread over the surfaces of the eyeballs and find +their way in each eye to two small canals whose openings may be seen on +the edges of the lids near the inner corner (Fig. 163). These canals +unite to form the <hi rend="font-style: italic">nasal duct</hi>, which +conveys the tears to the nasal cavity on the same side of the nose. When +by evaporation the eyeball becomes too dry, the lids close reflexively +and spread a fresh layer of tears over the surface. Any excess is passed +into the nostrils, where it aids in moistening the air entering the +lungs.</p> + +<div> +<head>HYGIENE OF THE EYE</head> + +<p><hi rend="font-weight: bold">Defects in Focusing.</hi>—The delicacy +and complexity of the sense organs of sight render them liable to a +number of imperfections, or defects, the most frequent and important +being those of focusing. Such defects not only result<pb n="384" /><anchor id="Pg384" /> in the imperfect vision of +objects, but they throw an extra strain upon the nervous system and may +render the process of seeing exceedingly painful.</p> + +<p>A normal eye is able, when relaxed, to focus light accurately from +objects which are twenty feet or more away and to accommodate itself to +objects as near as five inches. An eye is said to be <hi +rend="font-style: italic">myopic</hi>, or <hi rend="font-style: +italic">short-sighted</hi>, when it is unable to focus light waves from +distant objects, but can only distinguish the objects which are near at +hand. In such an eye the ball is too long for the converging power of +the lenses, and the image is formed in front of the retina (<hi +rend="font-style: italic">C</hi>, Fig. 164).</p> + +<p rend="text-align: center"> +<figure url="images/image164.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 164—<hi rend="font-weight: bold">Diagrams +illustrating long-sightedness and short-sightedness</hi>, and method of +remedying these defects by lenses. <hi rend="font-style: italic">A.</hi> +Normal eye. <hi rend="font-style: italic">B.</hi> Long-sighted eye. <hi +rend="font-style: italic">C.</hi> Short-sighted eye.</head> +<figDesc>Fig. 164</figDesc> +</figure></p> + +<p>A <hi rend="font-style: italic">long-sighted</hi>, or <hi +rend="font-style: italic">hypermetropic</hi>, eye is one which can focus +light from distant objects, but not from near objects. In such an eye +the ball is too short for the converging power of the lenses and the +image tends to form back of the retina (<hi rend="font-style: +italic">B</hi>, Fig. 164). These defects in focusing are remedied by +wearing glasses with lenses so shaped as to counteract them. +Short-sightedness is corrected by concave lenses and long-sightedness by +convex lenses, as shown in diagrams above.</p> + +<p><hi rend="font-style: italic">Astigmatism</hi> is another defect in +the focusing power of the eye. In astigmatism the parts of the eye fail +to form the image in the same plane, so that all portions of the object +do not appear equally distinct. Certain parts of it are indistinct, or +blurred. The cause is found in some<pb n="385" /><anchor id="Pg385" /> difference in curvature of the +surfaces of the cornea or crystalline lens. It is corrected by lenses so +ground as to correct the particular defects present in a given eye.</p> + +<p>Whenever defects in focusing are present, particularly in +astigmatism, extra work is thrown on the ciliary muscle as well as the +muscles that move the eyeballs. The result is frequently to induce a +condition, known as <hi rend="font-style: italic">muscle weakness</hi>, +which renders it difficult to use the eyes. Even after the defect in +focusing has been remedied, the muscles recover slowly and must be used +with care. For this reason glasses should be fitted by a competent +oculist<note place="foot"><p>An oculist is a physician who specializes in diseases of +the eye.</p></note> as soon as a defect is known to exist. When one is unduly +nervous, or suffers from headache, the eyes should be examined for +defects in focusing (page 326).</p> + +<p><hi rend="font-weight: bold">Eye Strain and Disease.</hi>—The extra +work thrown upon the nervous system through seeing with defective eyes, +especially in reading and other close work, is now recognized as an +important cause of disease. Through the tax made upon the nervous system +by the eyes, there may be left an insufficient amount of nervous energy +for the proper running of the vital processes. As a result there is a +decline of the health. Ample proof that eye strain interferes with the +vital processes and causes ill health, is found in the improvements that +result when, by means of glasses, this is relieved.</p> + +<p><hi rend="font-weight: bold">The Eyes of School Children.</hi>—School +children often suffer from defects of vision which render close work +burdensome, and cause headache, general nervousness, and disease. +Furthermore, the visual defects may be unknown both to themselves and to +their parents. Pupils showing indications of eye-strain should be +examined by an oculist,<pb n="386" /><anchor id="Pg386" /> and fitted with glasses should +defects be discovered.<note place="foot"><p>Some of the more common symptoms of eye strain are +nervousness, headache, insomnia, irritations of the eyelids, +sensitiveness to bright light, and pain in the use of the eyes.</p></note> The precaution, adopted by many schools, of +having the eyes of all children examined by a competent physician +employed for the purpose, is most excellent and worthy of imitation.</p> + +<p><hi rend="font-weight: bold">Reading Glasses.</hi>—Many people whose +eyes are weak, because slightly defective, find great relief in the use +of special glasses for reading and other close work. By using such +glasses they may postpone the time when they are compelled to wear +glasses constantly. It is in the close work that the extra strain comes +upon the eyes, and if this is relieved, one can much better withstand +the work of distant vision. The reading glasses should be fitted by a +competent oculist, and used only for the purpose for which they are +intended.</p> + +<p><hi rend="font-weight: bold">General Precautions in the Use of the +Eyes.</hi>—If proper care is exercised in the use of the eyes, many of +their common ailments and defects may be avoided. Any one, whether his +eyes are weak or strong, will do well to observe the following +precautions:</p> + +<p>1. Never read in light that is very intense or very dim. 2. When the +eyes hurt from reading, stop using them. 3. Never hold a book so that +the smooth page reflects light into the eyes. The best way is to sit or +stand so that the light passes over the shoulder to the book. 4. Never +study by a lamp that is not shaded. 5. Practice cleanliness in the care +of the eyes. Avoid rubbing the eyes with the fingers unless sure the +fingers are clean.</p> + +<p>If the eyes are weak, use them less and avoid, if possible, reading +by artificial light. Weak eyes are sometimes<pb n="387" /><anchor id="Pg387" /> benefited by bathing them in warm +water, or with water containing enough salt to make them smart slightly. +Boracic acid dissolved in water (40 grains to 4 ounces of distilled +water) is also highly recommended as a wash for weak eyes.</p> + +<p rend="text-align: center"> +<figure url="images/image165.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 165—<hi rend="font-weight: bold">Method of +procedure in lifting the eyelid</hi> (Pyle).</head> +<figDesc>Fig. 165</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Removal of Foreign Bodies from the +Eyes.</hi>—Foreign bodies embedded in the eyeball should be removed by +the oculist or physician. Small particles of dust or cinder may be +removed without the aid of the physician, by exercising proper care. +First let the tears, if possible, wash the offending substance to the +corner of the eye, or edge of the lid, where it can be removed with a +soft cloth. If it sticks to the ball or the under surface of the lid, it +will be necessary to find where it is located, and then dislodge it from +its position. Begin by examining the lower lid. Pull it down +sufficiently to expose the inner surface, and, if the foreign substance +be there, wipe it off with the hem of a clean handkerchief. If it is not +under the lower lid, it will be necessary to fold back the upper lid. +"The patient is told to look down, the edge of the lid and the lashes +are seized with the forefinger and thumb of the right hand (Fig. 165), +and the lid is drawn at first downward and forward away from the globe; +then upward and backward over the point of the thumb or forefinger of +the left hand, which is held stationary on the lid, and acts as a +fulcrum."<note place="foot"><p>Pyle, <hi rend="font-style: italic">Personal +Hygiene</hi>.</p></note> The foreign body is now removed in<pb n="388" /><anchor id="Pg388" /> the same manner as from the lower +lid. A large lens may be used to good advantage in finding the +irritating substance.</p> + +<p><hi rend="font-weight: bold">Strong Chemicals in the +Eyes.</hi>—Students in the laboratory frequently, through accident, get +strong chemicals, as acids and bases, in the eyes. The first thing to do +in such cases is quickly and thoroughly to <hi rend="font-style: +italic">flood the eyes with water</hi>. Any of the chemical which +remains may then be counteracted by the proper reagent, care being taken +to use a very dilute solution. To counteract an acid, use sodium +bicarbonate (cooking soda), and for bases use a very dilute solution of +acetic acid (vinegar). To guard against getting the counteractive agent +too strong for the inflamed eye, it should first be tried on an eye that +has not been injured.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—The nervous impulses that +cause the sensation of sight are started by light waves falling upon a +sensitized nervous surface, called the retina. By means of refractive +agents, forming a part of the eyeball in front of the retina, light from +different objects is focused and made to form images of the objects upon +the surface. In this way the light is made to stimulate a portion of the +retina corresponding to the form of the object. This, <hi +rend="font-style: italic">the image method of stimulation</hi>, enables +the mind to recognize objects and to locate them in their various +positions. While the greater portion of the eyeball is concerned in the +focusing of light, the crystalline lens, operated by the ciliary muscle, +serves as the special instrument of accommodation. Muscles attached to +the eyeballs turn them in different directions, and so adjust them with +reference to each other that double vision is avoided.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. Under what conditions +are light waves reflected, refracted, and absorbed?</p> + +<p><pb n="389" /><anchor id="Pg389" />2. Why does the body not need a +light-producing apparatus, corresponding to the larynx in the production +of sound?</p> + +<p>3. How is the light from a candle made to form an image?</p> + +<p>4. What different things must happen in order that one may see an +object?</p> + +<p>5. Make a sectional drawing of the eyeball, locating and naming all +the parts.</p> + +<p>6. Of what parts are the outer, middle, and inner coats of the +eyeball made up?</p> + +<p>7. What portions of the eyeball reflect light? What absorb light? +What transmit light? What refract light?</p> + +<p>8. Show how the iris, the crystalline lens, the retina, the ciliary +muscle, and the cornea aid in seeing.</p> + +<p>9. Trace a wave of light from a visible object to the retina.</p> + +<p>10. Why does not the inverted image on the retina cause us to see +objects upside down?</p> + +<p>11. What change occurs in the shape of the crystalline lens when we +look from distant to near objects? From near to distant objects? Why are +these changes necessary? How are they brought about?</p> + +<p>12. How does the method of adjustment, or accommodation, of the +eyeball differ from that of a telescope or a photographer's camera?</p> + +<p>13. With two eyes how are we kept from seeing double?</p> + +<p>14. What different purposes are served by the tears. Trace them from +the lachrymal glands to the nostrils.</p> + +<p>15. Show how the proper lenses remedy short- and +long-sightedness.</p> + +<p>16. Describe the conjunctiva and give its functions. Why should it be +so sensitive?</p> + +<p>17. How may eye strain cause disease in parts of the body remote from +the eyes?</p> + +<p>18. How does "image stimulation" differ from light stimulation in +general?</p> +</div> + +<div> +<head>PRACTICAL WORK</head> + +<p><hi rend="font-weight: bold">To illustrate Simple Properties of +Light.</hi>—1. Heat an iron or platinum wire in a clear gas flame. +Observe that when a high temperature is reached it gives out light or +becomes luminous.</p> + +<p>2. Cover one hand with a white and the other with a black piece of +cloth, and hold both for a short time in the direct rays of the sun. +Note and account for the difference in temperature which is felt.</p> + +<p><pb n="390" /><anchor id="Pg390" />3. Stand a book or a block of wood +by the side of an empty pan in the sunlight, so that the end of the +shadow falls on the bottom of the pan. Mark the place where the shadow +terminates and fill the pan with water. Account for the shadow's +becoming shorter.</p> + +<p>4. Place a coin in the center of an empty pan and let the members of +the class stand where the coin is barely out of sight over the edges of +the pan. Fill the pan with water and account for the coin's coming into +view. Show by a drawing how light, in passing from the water into the +air, is so bent as to enter the eye.</p> + +<p>5. With a convex lens, in a darkened room, focus the light from a +candle flame so that it falls on a white screen and forms an image of +the candle. Observe that the image is inverted. In a well-lighted room +focus the light from a window upon a white screen. Show that, as the +distance from the window to the screen is changed, the position of the +lens must also be changed. (Accommodation.)</p> + +<p>6. Hold a piece of cardboard, about eight inches square and having a +smooth, round hole an eighth of an inch in diameter in the center, in +front of a lighted candle in a darkened room. Back of the opening place +a muslin or paper screen (Fig. 157). Observe that a dim image is formed. +Account for the fact that it is inverted. Hold a lens between the +cardboard and the screen so that the light passes through it also. The +image should now appear smaller and more distinct.</p> + +<p rend="text-align: center"> +<figure url="images/image166.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 166—<hi rend="font-weight: bold">Diagram</hi> +for proving presence of the blind spot.</head> +<figDesc>Fig. 166</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">To prove the Presence of the Blind +Spot.</hi>—Close the left eye and with the right gaze steadily at the +spot on the left side of this page (Fig. 166). Then starting with the +book a foot or more from the face, move it slowly toward the eye. A +place will be found where the spot on the right entirely disappears. On +bringing it nearer, however, it is again seen. As the book is moved +forward or backward, the position of the<pb n="391" /><anchor id="Pg391" +/> image of this spot changes on the retina. When the spot cannot be +seen, it is because the image falls on the blind spot.</p> + +<p><hi rend="font-weight: bold">Dissection of the Eyeball.</hi>—Procure +from the butcher two or three eyeballs obtained from cattle. After +separating the fat, connective tissue, and muscle, place them in a +shallow vessel and cover with water. Insert the blade of a pair of sharp +scissors at the junction of the sclerotic rotic coat with the cornea and +cut from this point nearly around the entire circumference of the +eyeball, passing near the optic nerve. Spread open in the water and +identify the different parts from the description in the text. Open the +second eyeball in water by cutting away the cornea. Examine the parts in +front of the lens.</p> + +<p rend="text-align: center"> +<figure url="images/image167.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 167—<hi rend="font-weight: bold">Model</hi> for +demonstrating the eyeball.</head> +<figDesc>Fig. 167</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">To illustrate Accommodation.</hi>—Paste +together the ends of a strip of stiff writing paper (two by five inches) +making a ring a little less than three inches in diameter. This is to +represent the crystalline lens. Now paste a piece of thin paper (two by +seven inches) upon a second strip of the same size, leaving an open +place in the middle for the insertion of the paper lens. A flexible +piece of cardboard (three by twelve inches) is now bent into the form of +a half circle and to its ends are fastened the strips of paper +containing the ring. Make a small hole in each of the four corners of +the bent cardboard. Through these holes pass two loops of thread, or +fine string, in opposite directions, letting the ends hang loose from +the cardboard.</p> + +<p>When everything is in position, the tension from the cardboard +flattens the paper lens, while pulling the strings releases this tension +and permits the lens to become more rounded. With this simple device the +changes in the curvature of the lens for near and distant vision are +easily shown.</p> +</div> +</div> + +<div rend="page-break-before: always"> +<pb n="392" /><anchor id="Pg392" /> +<index index="toc" /><index index="pdf" /> +<head>CHAPTER XXIII - THE GENERAL PROBLEM OF KEEPING WELL</head> + +<p rend="display">"To cure was the voice of the Past: to prevent is the divine +whispering of To-day."</p> + +<p>As stated in the introduction to our study, the fundamental law of +hygiene is the law of harmony: <hi rend="font-style: italic">Habits of +living must harmonize with the plan of the body.</hi> Having acquainted +ourselves with the plan of the body, we may now review briefly those +conditions that help or hinder its various activities. The hygiene +already presented in connection with the study of the various organs may +be condensed into general rules, or laws, as follows:</p> + +<p>1. Of exercise: Exercise daily the important groups of muscles.</p> + +<p>2. Of form: Preserve the natural form of the body.</p> + +<p>3. Of energy: Observe regular periods of rest and exercise and avoid +exhaustion.</p> + +<p>4. Of nutriment: Eat moderately of a well-cooked and well-balanced +diet and drink freely of pure water.</p> + +<p>5. Of respiration: Breathe freely and deeply of pure air and spend a +part of each day out of doors.</p> + +<p>6. Of nervous poise: Suppress wasteful and useless forms of nervous +activity, avoid nervous strain, and practice cheerfulness.</p> + +<p>7. Of cleanliness: Keep the body and its immediate surroundings +clean.</p> + +<p>8. Of restraint: Abstain from the unnecessary use of<pb n="393" /><anchor id="Pg393" /> drugs as well as from the +practice of any form of activity known to be harmful to the body.</p> + +<p>9. Of elimination: Observe all the conditions that favor the regular +discharge of waste materials from the body.</p> + +<p>Obedience to these laws is of vast importance in the proper +management of the body. They should, indeed, be so thoroughly impressed +upon the mind as to become fixed habits. There are, however, other +conditions that relate to this problem, and it is to these that we now +turn. These conditions have reference more specifically to</p> + +<p><hi rend="font-weight: bold">The Prevention of Disease.</hi>—While +the average length of life is not far from thirty-five years, the length +of time which the average individual is capable of living is, according +to some of the lowest estimates, not less than seventy years. This +difference is due to disease. People do not, as a rule, die on account +of the wearing out of the body as seen in extreme old age, but on +account of the various ills to which flesh is heir. It is true that many +people meet death by accident and not a few are killed in wars, but +these numbers are small in comparison with those that die of bodily +disorders. The prevention of disease is the greatest of all human +problems. Though the fighting of disease is left largely to the +physician, much is to be gained through a more general knowledge of its +causes and the methods of its prevention.</p> + +<p><hi rend="font-weight: bold">Causes of Disease.</hi>—Disease, which +is some <hi rend="font-style: italic">derangement of the vital +functions</hi>, may be due to a variety of causes. Some of these causes, +such as hereditary defects, are remote and beyond the control of the +individual. Others are the result of negligence in the observance of +well-recognized hygienic laws. Others still are of the nature of +influences, such as climate, the house in which one<pb n="394" /><anchor id="Pg394" /> lives, or one's method of gaining +a livelihood, that produce changes in the body, imperceptible at the +time, but, in the long run, laying the foundations of disease. And last, +and most potent, are the minute living organisms, called microbes or +germs, that find their way into the body. Although there are two general +kinds of germs, known as <hi rend="font-style: italic">bacteria</hi> +(one-celled plants) and <hi rend="font-style: italic">protozoa</hi> +(one-celled animals), most of our germ diseases are caused by +bacteria.</p> + +<p><hi rend="font-weight: bold">Effects of Germs.</hi>—While there are +many kinds of germs that have no ill effect upon the body and others +that are thought to aid it in its work, there are many well-known +varieties that produce effects decidedly harmful. They gain an entrance +through the lungs, food canal, or skin, and, living upon the fluids and +tissues, multiply with great rapidity until they permeate the entire +body. Not only do they destroy the protoplasm, but they form waste +products, called <hi rend="font-style: italic">toxins</hi>, which act as +poisons. Diseases caused by germs are known as infectious, or +contagious, diseases.<note place="foot"><p>"An infectious disease is one in which disease germs +infect (that is, invade) the body from without. Among the infectious +diseases are some that are quite directly and quickly conveyed from +person to person and to these the term contagious is applied. Formerly a +sharp line was drawn between infection and contagion, but to-day it is +recognized that no such line exists."—HOUGH AND SEDGWICK, <hi +rend="font-style: italic">The Elements of Hygiene and +Sanitation.</hi></p></note> The list is a long one and includes smallpox, +measles, diphtheria, scarlet fever, typhoid fever, tuberculosis, la +grippe, malaria, yellow fever, and others of common occurrence. In +addition to the diseases that are well pronounced, it is probable that +germs are responsible also for certain bodily ailments of a milder +character.<note place="foot"><p>The arctic explorer, Nansen, states that during all the +time that his party was exposed to the low temperature of the arctic +region, no one was attacked by a cold, but on returning to a warmer +climate they were subject to colds as usual. The difference he +attributes to the absence of germs in the severe arctic climate. There +seems to be no doubt but that most of our common colds are due to +attacks of germs.</p></note></p> + +<p><pb n="395" /><anchor id="Pg395" /><hi rend="font-weight: +bold">Avoidance of Germ Diseases.</hi>—The problem of preventing +diseases caused by germs is an exceedingly difficult one and no solution +for all diseases has yet been found. One's chances of avoiding such +diseases, however, may be greatly enhanced:</p> + +<p>1. By strengthening the body through hygienic living so that it +offers greater resistance to the invasions of germs.</p> + +<p>2. By living as far as possible under conditions that are unfavorable +to germ life.</p> + +<p>3. By understanding the agencies through which disease germs are +spread from person to person.</p> + +<p><hi rend="font-weight: bold">Conditions Favorable and Unfavorable for +Germs.</hi>—Conditions favorable for germ life are supplied by animal +and vegetable matter, moisture, and a moderate degree of warmth. Hence +disease germs may be kept alive in damp cellars and places of filth. +Even living rooms that are poorly lighted or ventilated may harbor them. +Water may, if it contain a small per cent of organic matter, support +such dangerous germs as those of typhoid fever. Fresh air, sunlight, +dryness, cleanliness, and a high temperature, on the other hand, are +destructive of germs. The germs in impure water, as already noted (page +165), are destroyed by boiling.</p> + +<p><hi rend="font-weight: bold">How Germs are Spread.</hi>—Some of the +more common methods by which the germs of disease are spread, and by so +doing find new victims, are as follows:</p> + +<p>1. <hi rend="font-style: italic">By Means of Foods.</hi>—Foods, on +account of the locality in which they are produced or the method of +gathering or of handling-them, may become contaminated with germs, which +are then transported with the foods to the consumer.</p> + +<p>2. <hi rend="font-style: italic">By Means of Dust.</hi>—Material +containing germs, <hi rend="font-style: italic">e.g.</hi>, discharges +from the throat and lungs, will on drying<pb n="396" /><anchor id="Pg396" /> form dust. This is lifted with +other fine particles by the air and may be carried quite a distance. The +dust from public halls and other places where people congregate is the +kind most likely to contain disease germs. Dust should be breathed as +little as possible and only through the nostrils. Where one is +compelled, as in sweeping, to breathe dust-laden air for some time, he +should inhale through a moistened sponge, or cloth, tied in front of the +nostrils.</p> + +<p>3. <hi rend="font-style: italic">By Means of Domestic Pets and +Different Kinds of Household Vermin.</hi>—Germs sticking to the bodies +of small animals are carried about and may be easily communicated to +people. By this means, rats, mice, bedbugs, etc., where such exist, are +frequently the means of spreading disease; and particularly dangerous, +on this account, is the common house fly. Feeding as it does on filth of +all kinds, it is easy for it to transfer the bacteria that may stick to +its body to the food which is supplied to the table. The proper +screening of houses and the destruction of material in which flies may +develop, such as the refuse from stables, are necessary precautions.</p> + +<p>Germs are spread also by the clothing of people, by railroad and +steamship lines, by the mails, and by the natural elements. In fact, any +kind of carrier, in or upon which germs can live, may serve as a means +of spreading those of certain kinds.</p> + +<p><hi rend="font-weight: bold">Public Sanitation.</hi>—The general +conditions under which germs may thrive and some of the means by which +they are scattered, emphasize the practical value of measures which have +for their purpose the making of one's surroundings more wholesome and +hygienic. Such measures may be directed both toward one's immediate +surroundings—the home—and toward the neighborhood, town, or city in<pb n="397" /><anchor id="Pg397" /> which one lives. The hygienic +conditions of primary importance in every city or town are as +follows:</p> + +<p>1. An adequate public supply of pure water.</p> + +<p>2. An efficient system of underground pipes for the removal of +sewage.</p> + +<p>3. An efficient system for removing from the streets and alleys +everything of the nature of waste.</p> + +<p>4. Prevention, by enforcement of ordinances, of spitting upon +sidewalks and the floors of public halls and conveyances.</p> + +<p>5. A hospital or sanitarium in which people can be cared for when +sick with infectious diseases.</p> + +<p>In the larger cities other hygienic measures demand attention, such +as provisions for parks and playgrounds, the proper housing of the poor +of the city, and the suppression of the smoke and dust nuisances. +Crowded together as people are in the cities, the welfare of each +individual depends in a large measure upon the welfare of all. Hence the +problems of public sanitation are matters in which all are vitally +concerned.</p> + +<p><hi rend="font-weight: bold">Sanitary Conditions of the +Home.</hi>—The home, being the feeding and resting place for the entire +family, is the most important factor in one's physical, as well as +moral, environment. For this reason there is no place where careful +attention to hygienic requirements will yield better results. Much of +the danger from germs may be prevented by instituting and maintaining +proper sanitary conditions in and about the home.</p> + +<p>One of the first requisites of the home is a suitable location for +the house. The house should be built upon ground that is well drained, +and if natural drainage be lacking, artificial drainage must be +supplied. It should not be situated nearer than a quarter of a mile to +any<pb n="398" /><anchor id="Pg398" /> marsh or swamp and, if so near as +that, it ought to be on the side from which the wind usually blows. A +stone foundation should be provided, and at least eighteen inches of +ventilated air space should be left between the ground and the floor. +Ample provisions must be made for pure air and sunlight in all the +rooms. The cellar, if one is desired, needs to be constructed with +special care. It should be perfectly dry and provided with windows for +light and ventilation. Adequate means must also be provided, by sewage +pipes and other methods, for the disposal of all waste. Where drainage +pipes are provided, care must be taken to prevent the entrance of sewer +gas into the house and also the passage of material from these pipes +into the water supply. The placing and connecting of sewer pipes should, +of course, be under the direction of a plumber.</p> + +<p><hi rend="font-weight: bold">The Water Supply.</hi>—Since water +readily takes up and holds the impurities with which it comes in +contact, it should be exposed as little as possible in the process of +collecting. Where cistern water is used, care must be taken to prevent +filth from the roof (Fig. 168), water pipes, or soil from getting into +the reservoir. Water should be collected from the roof only after it has +rained long enough for the roof and pipes to have been thoroughly +cleaned. The cistern should have no leaks (Fig. 169), and the top should +be tightly closed to prevent the entrance of small animals and +rubbish.</p> + +<p rend="text-align: center"> +<figure url="images/image168.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 168—<hi rend="font-weight: bold">Contamination +of cistern water</hi> by birds nesting in the gutter trough.</head> +<figDesc>Fig. 168</figDesc> +</figure></p> + +<p>Shallow wells are to be condemned, as a rule, because of the +likelihood of surface drainage (Fig. 169), and water from springs +should, for the same reason, be used with<pb n="399" /><anchor id="Pg399" /> caution. Deep wells that are kept +clean usually may be relied on to furnish water free from organic +impurities, but such water often holds in solution so much of mineral +impurities as to render it unfit for drinking. The presence in water of +any considerable quantity of the compounds of iron or calcium makes it +objectionable for regular use.</p> + +<p rend="text-align: center"> +<figure url="images/image169.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 169—<hi rend="font-weight: bold">Sources of +contamination of cistern and well water.</hi> +Illustration shows liability of contamination from surface drainage and +from entrance of filth at top.</head> +<figDesc>Fig. 169</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Hygienic Housekeeping.</hi>—However +carefully a house has been constructed from a sanitary standpoint, the +constant care of an intelligent housekeeper is required to keep it a +healthful place in which to live. Daily cleaning and airing of all +living rooms are necessary, while such places as the kitchen, the +cellar, and the closets need extra thoughtfulness and, at times, hard +work. Moreover, the problem is not all indoors. The immediate premises +must be kept clean and sightly, and all decaying vegetable and animal +matter should be removed. Home sanitation consists,<pb n="400" /><anchor id="Pg400" /> not of one, but of many, +problems, all more or less complex. None of these can be slighted or +turned over to a novice.</p> + +<p><hi rend="font-weight: bold">Destruction of Infectious +Material.</hi>—At times the housekeeping has to be directed especially +toward hygienic requirements, such an occasion being the sickness of one +of the inmates with some contagious disease. Unless special precautions +are taken, the disease will spread to other members of the household and +may reach people in the neighborhood. Not only must great care be +exercised that nothing used in connection with the sick shall serve as a +carrier of disease, but germs passing from the patient should, as far as +possible, be actually destroyed. All discharges from the body likely to +contain bacteria, should be burned or treated with disinfectants and +buried deeply at a remote distance from the water supply to the +house.</p> + +<p>After recovery all clothing, bedding, and furniture used in +connection with the sick should be disinfected or burned. The room also +in which the sick was cared for should be thoroughly disinfected and +cleaned; in some instances the woodwork ought to be repainted and the +walls repapered or calcimined. The purpose is, of course, to destroy all +germs and prevent, by this means, a recurrence of the disease.</p> + +<p><hi rend="font-weight: bold">Fumigation.</hi>—To destroy germs in the +air or adhering to the walls of rooms, furniture, clothing, etc., +fumigation is employed. This is accomplished by saturating the air of +rooms with some vapor or gas which will destroy the germs. Fumigation is +quite generally employed in the general cleaning after the patient +leaves his room. This, to be effective, must be thorough. Formaldehyde +is considered the best disinfectant for this purpose, and it should be +evaporated with heat in the proportion of one half pint of the 40 per +cent solution to 1000 cu. ft. of space. Since formaldehyde is +inflammable and easily boils<pb n="401" /><anchor id="Pg401" /> over, it +has to be evaporated with care. It should be boiled in a tall vessel (a +tin or copper vessel which holds about four times the quantity to be +evaporated) over a quick fire, the room being tightly closed (openings +around windows and doors plugged with cotton or cloth). After three or +four hours the room may be opened and thoroughly aired. Since +formaldehyde is most disagreeable to breathe, one should not attempt to +occupy the room until it is free from the gas. This will require a day +or more of thorough ventilation.</p> + +<p><hi rend="font-weight: bold">Facts Relating to the Spread of Certain +Diseases.</hi>—The problem of preventing disease in general often +resolves itself into the problem of preventing the spread of some +particular disease. It is then of vital importance to know the special +method by which the germs of this disease leave the body of the patient +and are conveyed to the bodies of others. Some of these methods are +novel in the extreme, and are not at all in accord with prevailing +notions. Particularly is this true of that disease known as</p> + +<p><hi rend="font-weight: bold">Malaria, or Malarial Fever.</hi>—This +disease, so common in warm climates and also prevalent to a large extent +in the temperate zones, is due to animal germs (protozoa), which attack +and destroy the red corpuscles of the blood. These germs, it is found, +pass from malarial patients to others through the agency of a variety of +mosquitoes known as <hi rend="font-style: italic">Anopheles</hi>. In +sucking the blood of a malarial patient, the mosquito first infects her +own body.<note place="foot"><p>An interesting biological fact is that the female <hi +rend="font-style: italic">Anopheles</hi>, and not the male, sucks the +blood of animals and is the cause of the spreading of malaria.</p></note> In the body of the mosquito the germs undergo an essential +stage of their development, after which they are injected beneath the +skin of whomsoever the mosquito feeds upon. For the spreading of +malaria, then, two conditions are necessary: first, there must be people +who have the disease; and second, there must be in the neighborhood the +special variety of mosquito that spreads the disease.<pb n="402" /><anchor id="Pg402" /> If either condition be lacking, +the disease is not spread. The malarial mosquito (<hi rend="font-style: +italic">Anopheles</hi>) may be distinguished from the harmless variety +(<hi rend="font-style: italic">Culex</hi>) by the position which it +assumes in resting, as shown in Fig. 170.</p> + +<p rend="text-align: center"> +<figure url="images/image170.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 170—<hi rend="font-weight: bold">Mosquitoes</hi> +in resting position. (From Howard's <hi rend="font-style: +italic">Mosquitoes</hi>.) On left the malarial mosquito (<hi +rend="font-style: italic">Anopheles</hi>); on the right the harmless +mosquito (<hi rend="font-style: italic">Culex</hi>).</head> +<figDesc>Fig. 170</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Remedies against Mosquitoes.</hi>—The +natural method of preventing the spread of malaria is, of course, the +destruction of mosquitoes. This is accomplished by draining pools of +water where they are likely to breed, and by covering pools of water +that cannot be drained with crude petroleum or kerosene. The kerosene, +by destroying the larvae, prevents the development of the young. In +communities where such measures have been diligently carried out, the +mosquito pest has been practically eliminated. Other methods are also +under investigation, such as the stocking of shallow bodies of water +with varieties of fish that feed upon the mosquito larvae.</p> + +<p rend="text-align: center"> +<figure url="images/image171.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 171—<hi rend="font-weight: bold">Stegomyia</hi>, +the yellow-fever mosquito (after Howard).</head> +<figDesc>Fig. 171</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Yellow Fever.</hi>—This scourge of the +tropics is, like malaria,<pb n="403" /><anchor id="Pg403" /> caused by +animal germs. It is also propagated in the same manner as malaria, but +by a different variety of mosquito (<hi rend="font-style: +italic">Stegomyia</hi>, Fig. 171). The stamping out of yellow fever in +Havana, the Panama Canal Zone, and other places, through the destruction +of this variety of mosquito, affords ample proof of the correctness of +the "mosquito theory."</p> + +<p rend="text-align: center"> +<figure url="images/image172.png" rend="page-float: 'hp'; text-align: center; w95"> +<head><lb />Fig. 172—<hi rend="font-weight: bold">Consumption +germs</hi> from the spit of one having the disease. Highly magnified and +stained. (Huber's <hi rend="font-style: italic">Consumption and +Civilization</hi>.)</head> +<figDesc>Fig. 172</figDesc> +</figure></p> + +<p><hi rend="font-weight: bold">Consumption</hi>, or tuberculosis of the +lungs, spoken of as the "white plague," was among the first diseases +shown to be due to bacteria. Consumption is now recognized as an +infectious disease, though not so readily communicated as some other +diseases. Several methods are recognized by which the germs are passed +from the sick to the well, the most important being as follows:</p> + +<p>1. By personal contact of the sick with the well, especially in +kissing.</p> + +<p>2. By the sputum, or spit, which, if allowed to dry, is blown about +as dust and breathed into the lungs<note place="foot"><p>The habit of spitting upon the floors of public +buildings and street cars, and also upon sidewalks, is now recognized as +a most dangerous practice. Not only consumptives, but people with throat +affections, may do no end of harm in the spreading of disease by +carelessness in this respect.</p></note> (Fig. 172).</p> + +<p>3. By means of objects (drinking cups, tableware, etc.) that have +been handled by consumptives.</p> + +<p><pb n="404" /><anchor id="Pg404" />4. By +infectious material associated with houses or rooms in which +consumptives have lived.</p> + +<p>These methods of spreading consumption suggest the necessity for the +greatest care, on the part of both the patient and those having him in +charge.<note place="foot"><p>For further information on the care of consumptives, +consult Huber's <hi rend="font-style: italic">Consumption and +Civilization</hi>.</p></note> The material coughed up from the lungs and throat should be +collected on cloths or paper handkerchiefs and afterwards burned. The +house where a consumptive has lived should be disinfected, repapered or +calcimined, and thoroughly cleaned before it is again occupied. The +inside woodwork should also be repainted. The approaches to the house +where the patient may have expectorated should be disinfected and +cleaned. Since the germs are able to live in the soil, fresh lime or +wood ashes should be spread around the doorsteps and along the +walks.</p> + +<p><hi rend="font-weight: bold">Typhoid Fever</hi>, one of our most +dangerous diseases, is caused by germs (bacteria) that enter the body +through the food canal. They attack certain glands in the walls of the +small intestine, where they produce toxins that pass with the germs to +all parts of the body. Typhoid fever germs spread from those having the +disease to others, chiefly through the discharges from the bowels and +the kidneys. The germs contained in these, if not destroyed by +disinfectants, find their way into the soil, or into sewage, where they +may be picked up by water and widely distributed. Finding suitable +places, such as those containing decaying material, the germs may +rapidly increase in number, and from these sources find their way into +the bodies of new victims. They are likely, on account of manures, to +get on vegetables; on account of uncleanly methods of milking, to get +into the milk supply; and from sewerage outlets,<pb n="405" /><anchor id="Pg405" /> to get into the oysters +that grow in bays and harbors near seaboard cities; but they are most +frequently introduced into the body through the drinking of impure +water.</p> + +<p><hi rend="font-weight: bold">Diphtheria</hi>, also known as +"membranous croup," is caused by germs that attack the membranes of the +throat. This most dangerous of children's diseases is spread chiefly by +discharges from the mouth and throat. These should be collected on +cloths and burned, or rendered harmless with disinfectants. The disease +may be spread also by objects brought into contact with the mouth, such +as cups, toys, pencils, etc. Children are known to have diphtheria germs +in the mouth for some time after recovering from the disease, and +should, for this reason, be kept away from other children until +pronounced safe by the physician.</p> + +<p>The <hi rend="font-style: italic">antitoxin method</hi> of treating +diphtheria has robbed this disease of much of its terror, yet it not +infrequently happens that the physician is called too late to administer +this remedy to the best advantage. Since certain cases of diphtheria are +likely to be mistaken for croup, the parent frequently does not realize +the serious condition of the child. A croupy cough <hi rend="font-style: +italic">that lasts through the day</hi>, or a sore throat which shows +small white patches, are indications of diphtheria.</p> + +<p><hi rend="font-weight: bold">Scarlet Fever, Measles, Chicken Pox, and +Smallpox</hi>, on account of the eruptions of the skin which attend +them, are classed as eruptive diseases. As the eruptions heal, scales +separate from the skin, and these are supposed to be the chief means of +spreading the germs. Attention must be given to the destruction of these +scales by burning or thoroughly disinfecting all objects, such as +clothing, bedding, etc., that may serve as carriers of them. Those +having eruptive diseases should be confined to their rooms as long as +the scales continue to separate from the body.</p> + +<p><pb n="406" /><anchor id="Pg406" /><hi rend="font-weight: bold">Vaccination.</hi>—The method +of preventing smallpox known as vaccination, which has been practiced +since its discovery in 1796 by Jenner, has always proved effective. In +some instances the sore arm causes considerable inconvenience, but this +generally results from neglect to cleanse the arm thoroughly before +applying the virus, or from contact of the sore with the clothing later. +The virus should be applied by a physician and the wound should be +protected after the operation. If discomfort is felt when it "takes," +medical advice should be sought.</p> + +<p><hi rend="font-weight: bold">Isolation</hi>, or quarantining, is a +most important method of combating contagious diseases. By removing the +sick from the well many outbreaks of disease are quickly checked. +Isolation of individual patients, and sometimes of infected +neighborhoods, is absolutely necessary; and while this works a hardship +to the few, it is frequently the only safeguard of the many. The +community, on the other hand, should make ample provision for the care +of the afflicted in the way of hospitals, or sanitaria, and if it is +deemed necessary to remove people from their homes, they should not be +subjected to unnecessary hardship.</p> + +<p>Where one is sick from some contagious disease in the home and there +is liability of communicating it to the other members of the family, <hi +rend="font-style: italic">room isolation</hi> should be practiced. +Infection cannot spread through solid walls, and where the doors, and +the cracks around the doors, are kept completely closed and the usual +precautions are observed by those attending the patient, the other +inmates of the house can be protected from the disease.</p> + +<p><hi rend="font-weight: bold">The Physician and His Work.</hi>—In +combating disease the services of the physician are a prime necessity. +The special knowledge which he has at his command enables the conflict +to be carried on according to scientific requirements<pb n="407" /><anchor id="Pg407" /> and vastly increases the +chances for recovery. He should be called early and his directions +should be carefully followed. Everything, however, must not be left to +the physician, for recovery depends as much upon proper nursing and +feeding as upon the drugs that are administered. Of great importance is +<hi rend="font-style: italic">the saving of the energy of the +patient</hi>, and to accomplish this visitors should, as a rule, be +excluded from the sick room.</p> + +<p><hi rend="font-weight: bold">Precautions in Recovery from +Disease.</hi>—Many diseases, if severe, not only leave the body in a +weakened condition, but may, through the toxins which the germs deposit, +cause untold harm if the patient leaves his bed or resumes his usual +activities too soon. Especially is this true of typhoid fever,<note place="foot"><p>As typhoid fever is a disease of the small intestine, +great care must be exercised in taking food and in the bodily movements. +Solids greatly irritate the diseased lining of the intestine, and the +weakened walls may actually be broken through by pressure resulting from +moving about.</p></note> +diphtheria, scarlet fever, and measles. Rheumatism and affections of the +heart, lungs, kidneys, and other bodily organs frequently follow these +diseases, as the result of slight exposure or exertion before the body +has sufficiently recovered from the effects of the toxins. To guard +against such results, certain physicians require their patients to keep +their beds for a week, or longer, after apparent recovery from diseases +like typhoid fever, diphtheria, and scarlet fever.</p> + +<p><hi rend="font-weight: bold">Relation of Vocation to +Disease.</hi>—With a few exceptions, the pursuit of one's vocation, or +calling in life, does not supply either the quantity or the kind of +activity that is most in harmony with the plan of the body. Especially +is this true of work that requires most of the time to be spent indoors, +or which exercises but a small portion of the body. The effect of such +vocations, if not counteracted, <pb n="408" /><anchor id="Pg408" />is to weaken certain +organs, thereby disturbing the functional equilibrium of the body—a +result that may be brought about either by the overwork of particular +organs or by lack of exercise of others. Herein lies the explanation of +the observed fact that people of the same calling in life have similar +diseases.</p> + +<p><hi rend="font-weight: bold">A Special Problem for the Brain +Worker.</hi>—Farthest removed from those forms of activity which +harmonize with the plan of the body, and which therefore are most +hygienic, is that class of workers known as the professional class, or +the "brain workers." This class includes not only the members of the +learned professions—law, medicine, and the ministry—but a vast army of +business men, engineers, teachers, stenographers, office clerks, etc., a +class that is ever increasing as our civilization advances. It is this +class in particular that must give attention to those conditions that +indirectly, but profoundly, influence the bodily well-being and must +seek to obviate if possible such weaknesses as the occupation +induces.</p> + +<p><hi rend="font-weight: bold">The Remedy</hi> lies in two +directions—that of spending sufficient time away from one's work to +allow the body to recover its normal condition, and that of +counteracting the effect of the work by special exercise or other means. +In many cases the first symptoms of weakness indicate a suitable remedy. +Thus exhaustion from overwork suggests rest and recreation. The +diverting of too much blood from other parts of the body to the brain +suggests some form of exercise which will equalize the circulation. If +feebleness of the digestive organs is being induced, some natural method +of increasing the blood supply to these organs is to be looked for. And +effects arising from lack of fresh air and sunlight are counteracted by +spending more time out of doors.</p> + +<p><pb n="409" /><anchor id="Pg409" /><hi rend="font-weight: bold">Exercise as a Counteractive Agent.</hi>—In +counteracting tendencies to disease and in the maintenance of the +functional equilibrium of the body, no agent has yet been discovered of +greater importance than physical exercise, when applied systematically +and persistently. This may consist of exercises that call into play all +the muscles of the body, or which are concentrated upon special parts. +When general tonic effects are desired, the exercise should be well +distributed; but when counteractive or remedial effects are wanted, it +must be applied chiefly to the parts that are weak or that have not been +called into action by the regular work. Unfortunately, health is +sometimes confused with physical strength and exercise is directed +toward the stronger parts of the body with the effect of making them +still stronger. Not only is health not to be measured by the pounds that +one can lift or by some gymnastic feat that one can perform, but the +possession of great muscular power may, if the heart and other vital +organs be not proportionally strong, prove a menace to the health. This +being true, one having his health primarily in view will use physical +exercise, in part at least, as a means of building up organs that are +weak. Since the body, like a chain, can be no stronger than its weakest +part, this is clearly the logical method of fortifying it against +disease.</p> + +<p><hi rend="font-weight: bold">Value of Work.</hi>—Although there may +exist in one's vocation certain tendencies to disease, it must not be +inferred that work in itself is detrimental to health. Health demands +activity, and those forms of activity that provide a regular and +systematic outlet for one's surplus energy and compel the formation of +correct habits of eating, sleeping, and recreating best serve the +purpose. Work furnishes activity of this kind and serves<pb n="410" /><anchor id="Pg410" /> also as a safeguard against the +unhealthful and immoral habits contracted so often from idleness. Even +physical exercise which has for its purpose the reënforcement of the +body against disease may frequently consist of useful work without +diminishing its hygienic effects.</p> + +<p><hi rend="font-weight: bold">The Mental Attitude.</hi>—While a proper +thoughtfulness and care for the body is both desirable and necessary, it +is also true that over-anxiety about, or an unnatural attention to, the +needs of the body reacts unfavorably upon the nervous system. Observance +of the laws of health, therefore, should be natural and without special +effort—a matter of habit. The attention should never be turned with +anxiety upon any organ or process, but the mental attitude should at all +times be that of <hi rend="font-style: italic">confidence in the power +of the body organization to do its work</hi>. Fear and morbidity, which +are disturbing and paralyzing factors, should be supplanted by courage, +cheerfulness, and hopefulness.</p> + +<p>Let it be borne in mind that hygienic living requires nothing more +than the application of the same intelligence and practical common sense +to the care of the body that the skillful mechanic applies to an +efficient, but delicate, machine. And, just as in the case of the +machine, care of the body keeps its efficiency at the maximum and +lengthens the period that it may be used. This end and aim of hygienic +living is best attained by cultivating that attitude of mind toward the +body that avoids interference in the vital processes and permits the +natural appetites, sensations, and desires to indicate very largely the +body's needs.</p> + +<p><hi rend="font-weight: bold">Attitude toward Habit-forming +Drugs.</hi>—Among the different substances introduced into the body, +either as foods or as medicines, are a number which have the effect of +<pb n="411" /><anchor id="Pg411" />developing an artificial appetite or +craving which leads to their continued use. Since the effect of such +substances is usually harmful and since they tend to engraft themselves +upon communities as social customs, they present a twofold relation to +the general problem of keeping well. The individual may be injured +through the personal use which he makes of them, or he may be injured +through the effect which they have upon relatives or friends or upon +society at large. Since our social environment is a factor in health +little less important than our physical environment, the conditions that +make for their continuance should be more generally understood.</p> + +<p><hi rend="font-weight: bold">How Social Agencies perpetuate the Use +of Habit-forming Drugs.</hi>—When the use of some habit-forming drug has +risen to the importance of a general custom, a number of conditions +arise which tend to continue its use, even though the fact may be quite +generally known that the substance does harm. In the first place, those +who have formed the habit suffer inconvenience and distress when +deprived of its use. In the second place, a number of people will have +become interested in the production and sale of the substance, and these +will lose financially if it is discontinued. In the third place, those +of the rising generation will, from imitation or persuasion, be +constantly acquiring the habit before they are sufficiently mature to +decide what is best for them. Thus may the use of a substance most +harmful, such as the opium of the Chinese, be indefinitely continued—a +species of slavery from which the individual finds it hard to +escape.</p> + +<p>Such is human nature and such are the forces and influences of human +society, that the freeing of a people from the bondage of some +habit-forming drug cannot be accomplished without strenuous and +persistent effort. Education,<pb n="412" /><anchor id="Pg412" /> persuasion, the good example of +abstainers, and legal restrictions must be pitted against the forces +that make for its continuance. Such a struggle is now in progress in all +civilized countries relative to the use of alcoholic beverages.<note place="foot"><p>Alcoholic beverages include all the various kinds of +drinks that owe their stimulating properties to a substance, ethyl +alcohol (C<hi rend="vertical-align: sub">2</hi>H<hi rend="vertical-align: sub">5</hi>OH), which is made from sugar by the process of +fermentation. They include <hi rend="font-style: italic">malt +liquors</hi>, such as beer and ale, which contain from three to eight +per cent of alcohol; <hi rend="font-style: italic">wines</hi>, such as +claret, hock, sherry, and champagne, which contain from five to twenty +per cent of alcohol; and <hi rend="font-style: italic">distilled +liquors</hi>, such as brandy, whisky, rum, and gin, which contain from +thirty to sixty-five per cent of alcohol. Alcoholic beverages all +contain constituents other than alcohol, these varying with the +materials from which they are made and with the processes of +manufacture. The distilled liquors are so called from the fact that +their alcohol has been separated from the fermenting substances by +distillation.</p></note></p> + +<p><hi rend="font-weight: bold">How the Use of Alcohol became a Social +Custom.</hi>—The general use of alcohol as a beverage may be accounted +for by three facts. Alcohol is a habit-forming drug; it has a +stimulating effect which many have found agreeable; and being a product +of the fermentation of fruit juices and other liquids containing sugar, +it is easily obtained. Through the operation of these causes the human +family became habituated very early to the use of alcohol. The "wine" of +primitive man, however, did little harm as compared with the alcoholic +liquors of modern times. It was a weak solution and on account of the +crude methods of manufacture and storage could only be produced in +limited quantities. Perhaps the worst effect of its early use was the +establishment of a general belief in its power to benefit, since this +laid the foundation for excess in its use when the developments of a +later period made it possible.</p> + +<p>During the eleventh century the method of making alcoholic drinks +from starch-producing substances, such as wheat, barley, and potatoes, +became quite generally known, and also the method of concentrating them +by distillation.<pb n="413" /><anchor id="Pg413" /> This knowledge made +possible the manufacture of alcoholic drinks in large quantities and in +considerable variety. Alcoholic indulgence was now no longer the pastime +of the few, but the privilege of all. Its evil effects followed as a +matter of course; and as these became more and more apparent, there +began the struggle to restrict the consumption of alcohol which has +continued with varying success to the present time.</p> + +<p><hi rend="font-weight: bold">Counts against Alcohol.</hi>—The +statements found in different parts of this book relative to the effects +of alcohol upon the body may here be summarized as follows:—</p> + +<p>1. Alcohol has an injurious effect upon the white corpuscles of the +blood and lessens the power of the body to resist attacks of disease +(pages 35, 98).</p> + +<p>2. Alcohol injures the heart and the blood vessels (page 56).</p> + +<p>3. Alcohol causes diseases of the liver and kidneys and interferes +with the discharge of waste through these organs (pages 210, 212).</p> + +<p>4. Alcohol interferes seriously with the regulation of the body +temperature (page 271).</p> + +<p>5. Alcohol is one of the worst enemies to the nervous system (pages +326, 332-334. 336, 337).</p> + +<p>6. Through its effect upon the nervous system and through its +interference with the production of bodily energy (page 195), alcohol +greatly diminishes the efficiency of the individual.</p> + +<p>7. The taking of alcohol in amounts that apparently do not harm the +tissues is, nevertheless, liable to produce a habit which leads to its +use in amounts that are decidedly harmful.</p> + +<p><hi rend="font-weight: bold">Alcohol and the Social +Environment.</hi>—Our social environment includes the people with whom +we are directly or<pb n="414" /><anchor id="Pg414" /> indirectly associated. The +presence in any community of those who are immoral, inefficient, or +defective, places a burden upon those who are mentally and physically +capable and renders them liable to results which are the outgrowth of +weakness or viciousness. The fact that alcohol causes pauperism, crime, +and general inefficiency, thereby rendering the social environment less +conducive to what is best in life, is plainly evident. To realize how +alcohol harms the individual through its effects upon society in +general, one has only to take into account his dependence upon society +for intellectual and moral stimuli, for industrial and economic +opportunity, for protection, and for general conditions that make for +health and happiness. As we strive to improve our physical environment, +so should we also strive for the betterment of social conditions.</p> + +<p><hi rend="font-weight: bold">Industrial Use of +Alcohol.</hi>—Interesting and instructive in this connection is the fact +that alcohol is, after all, a substance capable of rendering great +service to humanity. The injury which it causes is the result of its +misuse. Though unfit for introduction into the human body, except in the +most guarded manner, it is adapted to a great variety of uses outside of +the body. A combustible substance which is readily convertible into a +gas, it may be substituted for gasoline in the cooking of food, lighting +of dwellings, and the running of machinery. As a solvent for gums, +resins, essential oils, etc., it is used in the preparation of +varnishes, extracts, perfumes, medicines, and numerous other substances +of everyday use. Through its chemical interactions, it is used in the +manufacture of ether, chloroform, explosives, collodion, celluloid, +dyestuffs, and artificial silk. In fact, alcohol is stated by one +authority to be, next to water, the most valuable liquid known.<note place="foot"><p>Duncan, <hi rend="font-style: italic">The Chemistry of +Commerce</hi>.</p></note></p> + +<p>Opposed to an extensive use of alcohol for industrial purposes is the +guard which the government must keep over its manufacture on account of +its use in beverages. Though alcohol may be profitably manufactured and +sold at thirty cents per gallon, the government revenue stamp of $2.08 +per gallon practically prohibits its use for many purposes. A step +toward a wider application to industrial purposes has been taken<pb n="415" /><anchor id="Pg415" /> by the law +permitting the sale of so-called "denatured"<note place="foot"><p>Alcohol is "denatured" by adding substances to it such +as wood alcohol, which render its use as a beverage impossible.</p></note> alcohol without the tax +for revenue. This law has proved beneficial to some extent, though the +practical solution of the problem is still remote.</p> + +<p><hi rend="font-weight: bold">Nicotine and Social Custom.</hi>—The +influences which brought about a general use of tobacco are similar to, +though not identical with, those that engrafted alcohol upon society. +The drug nicotine is a habit-forming substance and the plant producing +it is easily cultivated.<note place="foot"><p>The tobacco plant, <hi rend="font-style: +italic">Nicotiana tobacum</hi>, is a native of America, and the use of +tobacco began with the American Indians. It was taken back to Europe by +the early explorers, Sir Walter Raleigh being credited with introducing +it to the nobility of England.</p></note> Its immediate effect upon the user is +generally agreeable, acting as a stimulant to some, but having a +soothing effect upon the nerves of others. Moreover, a strong deterring +factor in its use is lacking, since its harmful effects are not readily +discernible and by many are avoided through moderation in its use.</p> + +<p>As with alcohol, tobacco is conveniently used to promote sociability +among men, a fact which has much to do with its very general use. If it +could be limited to social purposes, it would likely do little harm, but +the habit, once started, is continued without reference to sociability—a +matter of selfish indulgence. In fact, one effect of tobacco is to cause +the user to become less sensitive to the rights of others, this being +evidenced by smokers who do not hesitate to make rooms and public halls +almost unbearable to those unaccustomed to tobacco.</p> + +<p><hi rend="font-weight: bold">Counts against Nicotine.</hi>—The +physiological objections to the use of tobacco, as already stated +(pages 56, 92, 326, 333, 336), are the following:—</p> + +<p>1. The use of tobacco before one reaches maturity<pb n="416" /><anchor id="Pg416" /> +stunts the growth. The boy who uses it cannot develop into so strong and +capable a man as he would by leaving it alone.</p> + +<p>2. Tobacco injures the heart.</p> + +<p>3. Tobacco injures the air passages, especially when inhalation is +practiced.</p> + +<p>4. Tobacco injures the nervous system and by this means interferes in +a general way with the bodily processes. For the same reason it +interferes with mental and moral development, the cigarette being a +chief cause of criminal tendencies in boys.</p> + +<p>5. In some cases tobacco injures the vision.</p> + +<p>6. The tobacco habit is expensive and is productive of no good +results.</p> + +<p><hi rend="font-weight: bold">Tobacco and the Rising +Generation.</hi>—The problem of limiting the use of tobacco to the point +where it would do slight harm, in comparison to what it now does, would +be solved if those under twenty years of age could be kept from using +it. But few would then acquire the habit, and those who did would not be +so seriously injured. In our own country it lies within the province of +the home and the school to bring about this result. The fact that +parents use tobacco is no reason why the boys should also indulge. The +decided difference in effects upon the young and upon the mature makes +this point very clear. Laws protecting boys from the evil effects of +tobacco, not only cigarettes, but other forms as well, are both just and +necessary.</p> + +<p><hi rend="font-weight: bold">Social Custom and the Caffeine +Habit.</hi>—By suitable processes a white, crystalline solid, easily +soluble in water, can be separated from the leaves of tea, and from the +berry of the coffee plant. This is the drug caffeine, the substance +which gives to tea and coffee their stimulating properties,<pb n="417" +/><anchor id="Pg417" /> but not their agreeable flavors. Less injurious, +on the whole, than either alcohol or tobacco, caffeine has come into +general use in much the same way as these substances. In a sense, +however, caffeine is more deceptive than either alcohol or nicotine, +because the usual mode of preparing tea and coffee gives them the +appearance of real foods. The housewife who would feel condemned in +purchasing caffeine put up as a drug somehow feels justified when she +extracts it from plant products in the regular preparation of the +meal.</p> + +<p><hi rend="font-weight: bold">Counts against Caffeine.</hi>—People of +vigorous constitutions and of active outdoor habits are injured but +slightly, if at all, by either tea or coffee when these are used in +moderation. As already stated (pages 56, 167, 326, 329), they do harm +when used to excess and, in special cases, in very small amounts, in one +of the following ways:—</p> + +<p>1. By stimulating the nervous system, thereby causing nervousness and +insomnia and interfering with vital organs.</p> + +<p>2. By introducing a waste which forms uric acid into the body, +thereby throwing an extra burden upon the organs of elimination.</p> + +<p>In this connection it may also be stated that there appears to be +little, if any, real advantage to the healthy body from the use of +either tea or coffee, beyond that of temporary stimulation and the +gratification of an appetite artificially acquired. Hence the large sums +of money expended for these substances in this country yield no adequate +returns.</p> + +<p><hi rend="font-weight: bold">Caffeine Restrictions +Necessary.</hi>—Though with many the cup of tea or coffee at breakfast +does no harm, but gives an added pleasure to the meal, there is no +question but that the use of caffeine beverages should be greatly +curtailed. Children should not be permitted to drink either<pb n="418" +/><anchor id="Pg418" /> tea or coffee. Brain workers and indoor dwellers +generally should use these substances very sparingly, and people having +a tendency to indigestion, nervousness, constipation, rheumatism, or +diseases of the heart, kidneys, or liver frequently find it best to omit +them altogether.</p> + +<p><hi rend="font-weight: bold">Caffeine and "Soft" Drinks.</hi>—Recently +the practice has sprung up of using caffeine as a constituent +of certain drinks supplied at the soda-water fountains. Such drinks +usually purport to be made from the kola nut, which contains caffeine, +or to consist of extracts from the plants which yield cocoa and +chocolate, when in reality they consist of artificial mixtures to which +caffeine has been added. Those using these beverages are stimulated as +they would be by tea or coffee and soon acquire the habit which makes +them regular customers. Chief harm comes to the children who frequent +the soda fountains and to those who, on account of constitutional +tendencies, should avoid caffeine in all of its forms. It is generally +understood that the so-called "soft" drinks are harmless. If this +reputation is to be maintained, those containing caffeine must be +excluded.</p> + +<p><hi rend="font-weight: bold">Danger from Certain Medicinal +Agents.</hi>—Among the most valuable drugs used by the physician in the +treatment of disease are several, such as morphine, chloral, and +cocaine, which possess the habit-forming characteristic. Sad indeed are +the cases in which some pernicious drug habit has been formed through +the reckless administration of such medicines. Even the taking of such a +drug as quinine as a "tonic" tends to develop a dependence upon +stimulation which is equivalent to a habit. In the same list come also +the drugs that are taken to relieve a frequently recurring +indisposition, such as headache. The so-called headache powders are most +harmful in their<pb n="419" /><anchor id="Pg419" /> effects upon the nervous system +and should be carefully avoided.<note place="foot"><p>Most headaches are the result either of eye strain or of +digestive disturbances, such as indigestion and constipation, and are to +be relieved through the work of the oculist or through attention to the +hygiene of the digestive system.</p></note></p> + +<p><hi rend="font-weight: bold">Stimulants in Health +Unnecessary.</hi>—Stimulants have been aptly styled "the whips of the +nervous system." The healthy nervous system, however, like the +well-disposed and well-fed horse, needs no whip, but is irritated and +harmed through its use. Even in periods of weakness and depression, +stimulants are usually not called for, but a more perfect provision for +hygienic needs. Rest, relaxation, sleep, proper food, and avoidance of +irritation, not stimulants, are the great restorers of the nervous +system. A surplus of nervous energy gained through natural means is more +conducive to health and effective work than any result that can possibly +be secured through drugs. Then withal comes the satisfaction of knowing +that one has the expression of his real self in the way in which he +feels and in what he accomplishes—not a "whipped-up" condition that must +be paid for by weakness or suffering later on.</p> + +<p><hi rend="font-weight: bold">Summary.</hi>—To solve the problem of +keeping well, one must live the life which is in closest harmony with +the plan of the body. Such a life, because of differences in physical +organization, as well as differences in environment and occupation, +cannot be the same for all. All, however, may observe the conditions +under which the body can be used without injuring it and the special +hygienic laws relative to the care of different organs. Causes of +disease, whether they be in one's environment, vocation, in his use of +foods or drugs, or in his mode of recreation, must either be avoided or +counteracted.</p> + +<p>While the problem is beset with such difficulties as lack of +sufficient knowledge, inherited weakness, and time and opportunity<pb n="420" /><anchor id="Pg420" /> for doing what is +known to be best for the body, yet study and work that have for their +aim the preservation or improvement of the health are always worth +while. <hi rend="font-style: italic">Health is its own reward.</hi> The +expression of the poet,</p> + +<lg> +<l rend="text-indent: 4">"Each morn to feel a fresh delight to wake to life,</l> +<l rend="text-indent: 2">To rise with bounding pulse to meet whate'er of work, of care, of strife,</l> +<l rend="text-indent: 4">day brings to me,"</l> +</lg> + +<p rend="text-indent: 0">suggests the <hi rend="font-style: italic">joy</hi> of being well. +But the ultimate realization of one's aims and ambitions in life and the +actual prolongation of one's period of usefulness are <hi +rend="font-style: italic">higher and more enduring rewards</hi>.</p> + +<p><hi rend="font-weight: bold">Exercises.</hi>—1. Summarize the +different laws of hygiene. Upon what one fundamental law are these +based?</p> + +<p>2. State the important differences between a condition of health and +one of disease.</p> + +<p>3. In what general ways may disease originate in the body?</p> + +<p>4. Describe a model sanitary home. With what special hygienic +problems has the housekeeper to deal?</p> + +<p>5. Describe a method of collecting a wholesome supply of cistern +water. State possible objections to well and spring water.</p> + +<p>6. What means may be employed in preventing the spread of contagious +diseases?</p> + +<p>7. By what means are malaria, typhoid fever, diphtheria, and +tuberculosis spread from one individual to another?</p> + +<p>8. Why are extra precautions necessary in the recovery from certain +diseases, as typhoid fever, diphtheria, and scarlet fever?</p> + +<p>9. How may one's vocation become a cause of disease? What conditions +in the life of a student may, if uncounteracted, lead to poor +health?</p> + +<p>10. Of what special value are the parks and pleasure grounds in a +city to the health of its inhabitants?</p> + +<p>11. Discuss the hygienic value of work.</p> + +<p>12. What conditions lead to the continuance of habit-forming +substances after their use has become general?</p> + +<p>13. How is it possible for one not using alcohol to be injured by +this substance?</p> + +<p>14. Discuss the effect of alcoholic abuse upon social +environment.</p> + +<p>15. Summarize the rewards of hygienic living.</p> + +<div> +<pb n="421" /><anchor id="Pg421" /> +<head>SUMMARY OF PART II</head> + +<p>For the maintenance of life the needs of the cells must be supplied +and <hi rend="font-style: italic">the body as a whole must be brought +into proper relations with its surroundings</hi>. The last-named +condition requires that the body be moved from place to place; that its +parts be controlled and coördinated; and that it be adjusted in its +various activities to external physical conditions. To accomplish these +results there are employed:</p> + +<p>1. The skeleton, or bony framework, which preserves the form of the +body and supplies a number of mechanical devices, or machines, for +causing a variety of special movements.</p> + +<p>2. The muscular system, which supplies the energy necessary for +executing the movements of the body.</p> + +<p>3. The nervous system, which (<hi rend="font-style: italic">a</hi>) +controls and coördinates the various activities and (<hi +rend="font-style: italic">b</hi>) provides for the <hi rend="font-style: +italic">intelligent</hi> adjustment of the body to its environment. +(Review Summary of Part I, page 215, and consult Fig. 92, page 214.)</p> +</div> +</div> +</div> + +<div rend="page-break-before: always"> +<pb n="422" /><anchor id="Pg422" /> +<index index="toc" /><index index="pdf" /> +<head>APPENDIX</head> + +<p><hi rend="font-weight: bold">Equipment.</hi>—Nearly all of the +apparatus and materials called for in this book may be found in the +physical, chemical, and biological laboratories of the average high +school. There should be ready, however, for frequent and convenient use, +the following: One or more compound microscopes with two-thirds and +one-fifth inch objectives; a set of prepared and mounted slides of the +various tissues of the body; a set of dissecting instruments, including +bone forceps; a mounted human skeleton and a manikin or a set of +physiological charts; a set of simple chemical apparatus including +bottles, flasks, test tubes, and evaporating dishes; and a Bunsen burner +or some other means of supplying heat.</p> + +<p>The few chemicals required may be obtained from a drug store or from +the chemical laboratory. Access to a work bench having a set of +carpenter's tools will enable one to prepare many simple pieces of +apparatus as they are needed.</p> + +<p><hi rend="font-weight: bold">Physiological Charts</hi> are easily +prepared by teachers or pupils by carefully enlarging the more important +illustrations found in text-books or by working out original sketches +and diagrams. These, if drawn on heavy Manila paper, may be hung on the +wall as needed and preserved indefinitely. By the use of colors, +necessary contrasts are drawn and emphasis placed on parts as desired. +The author has for a number of years used such home-made charts in his +teaching and has found them quite satisfactory. His plan has been to +draw on heavy Manila paper, cut in sizes of two by three feet, the +general outline in pencil and then to mark over this with the desired +colors. There is of course an opportunity for producing results that are +artistic as well as practical, and if one has time and artistic skill, +better results can be obtained. Many of the cuts in this book are +excellently suited to enlargement and, if properly executed, will +provide a good set for general class purposes.</p> + +<p><hi rend="font-weight: bold">Models.</hi>—The use of prepared models +of the different bodily organs is strongly urged. These may be so used +in elementary courses as to obviate much of the dissections upon lower +animals. Although the actual tissues cannot be so well portrayed, the +general form and construction of organs are much better shown. Models +well adapted to class or laboratory work are easily obtained through +supply houses. Illustrations of several of these are shown in connection +with the "Practical Work."</p> +</div> + +<div rend="page-break-before: always"> +<index index="toc" /><index index="pdf" /> +<head>INDEX</head> + +<p rend="text-indent: 0">Abdomen; dissection of, <ref target="Pg169">169</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Abdominal cavity, <ref target="Pg007">7</ref>, <ref target="Pg138">138</ref>, <ref target="Pg152">152</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Absorption, <ref target="Pg173">173</ref>-<ref target="Pg186">186</ref>.<lb /> +Defined, <ref target="Pg018">18</ref>, <ref target="Pg173">173</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Accommodation, <ref target="Pg379">379</ref>.<lb /> +To illustrate, <ref target="Pg391">391</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Acid reactions, <ref target="Pg171">171</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Acquired reflexes, <ref target="Pg314">314</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Adipose tissue, <ref target="Pg005">5</ref>, <ref target="Pg178">178</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Afferent neurons, <ref target="Pg296">296</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Air, <ref target="Pg076">76</ref>.<lb /> +Changes it undergoes in lungs, <ref target="Pg101">101</ref>.<lb /> +Complemental, <ref target="Pg089">89</ref>, <ref target="Pg103">103</ref>.<lb /> +Reserve, <ref target="Pg089">89</ref>, <ref target="Pg103">103</ref>.<lb /> +Residual, <ref target="Pg089">89</ref>, <ref target="Pg103">103</ref>.<lb /> +Tidal, <ref target="Pg088">88</ref>, <ref target="Pg103">103</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Air passages, <ref target="Pg080">80</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Albuminoids, <ref target="Pg119">119</ref>.<lb /> +Purpose served by, <ref target="Pg121">121</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Alcohol,<lb /> +A cause of crime, <ref target="Pg333">333</ref>.<lb /> +Effects on circulation, <ref target="Pg055">55</ref>, <ref target="Pg056">56</ref>.<lb /> +Effects on digestion, <ref target="Pg167">167</ref>.<lb /> +Effects on energy supply, <ref target="Pg195">195</ref>.<lb /> +Effects on respiratory organs, <ref target="Pg098">98</ref>.<lb /> +Effects on social environment, <ref target="Pg413">413</ref>.<lb /> +Effect on temperature regulation, <ref target="Pg271">271</ref>.<lb /> +Effects on waste elimination, <ref target="Pg212">212</ref>.<lb /> +General considerations, <ref target="Pg412">412</ref>-<ref target="Pg415">415</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Alimentary canal, coats of, <ref target="Pg138">138</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Alimentary muscles, work of, <ref target="Pg159">159</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Alkaline reactions, <ref target="Pg171">171</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Alveoli, <ref target="Pg082">82</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Amylopsin, <ref target="Pg155">155</ref>, <ref target="Pg156">156</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Anatomy, defined, <ref target="Pg001">1</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Animal heat, <ref target="Pg192">192</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Anopheles, <ref target="Pg401">401</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Antiseptic ointment, <ref target="Pg275">275</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Antitoxin, <ref target="Pg405">405</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Appetite, natural, <ref target="Pg163">163</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Aqueous humor, <ref target="Pg377">377</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Arachnoid, <ref target="Pg299">299</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Arteries, <ref target="Pg047">47</ref>.<lb /> +Bronchial, <ref target="Pg084">84</ref>.<lb /> +Functions of, <ref target="Pg051">51</ref>.<lb /> +Pulmonary, <ref target="Pg084">84</ref>.<lb /> +Renal, <ref target="Pg202">202</ref>.<lb /> +To illustrate elasticity of, <ref target="Pg062">62</ref>.<lb /> +Why elastic, <ref target="Pg048">48</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Articulations, <ref target="Pg230">230</ref>-<ref target="Pg232">232</ref>.<lb /> +Kinds of, <ref target="Pg230">230</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Assimilation, <ref target="Pg018">18</ref>, <ref target="Pg182">182</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Astigmatism, <ref target="Pg384">384</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Atlas, <ref target="Pg223">223</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Atoms, defined, <ref target="Pg105">105</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Attraction sphere, <ref target="Pg015">15</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Auditory canal, <ref target="Pg358">358</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Auricles, <ref target="Pg042">42</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Axis, <ref target="Pg223">223</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Axis cylinder, <ref target="Pg284">284</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Axon, <ref target="Pg283">283</ref>.<lb /> +Form and length of, <ref target="Pg284">284</ref>.<lb /> +Function of, <ref target="Pg306">306</ref>.<lb /> +Structure of, <ref target="Pg284">284</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Bacteria, <ref target="Pg394">394</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ball-and-socket joint, <ref target="Pg231">231</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Basement membrane, <ref target="Pg197">197</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Basilar membrane, <ref target="Pg363">363</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Bathing, <ref target="Pg272">272</ref>, <ref target="Pg274">274</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Biceps muscle, action of, <ref target="Pg263">263</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Bicuspids, <ref target="Pg143">143</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Bile, <ref target="Pg154">154</ref>, <ref target="Pg155">155</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Binocular vision, <ref target="Pg381">381</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Blind spot, <ref target="Pg377">377</ref>.<lb /> +To prove presence of, <ref target="Pg390">390</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Blood, <ref target="Pg024">24</ref>-39.<lb /> +Changes in, <ref target="Pg034">34</ref>.<lb /> +Checking flow from wounds, <ref target="Pg058">58</ref>.<lb /> +Coagulation of, <ref target="Pg031">31</ref>.<lb /> +Experiments with, <ref target="Pg037">37</ref>-39.<lb /> +Flow of, how regulated, <ref target="Pg050">50</ref>.<lb /> +Functions of, <ref target="Pg033">33</ref>.<lb /> +Hygiene of, <ref target="Pg034">34</ref>-36.<lb /> +Physical properties of, <ref target="Pg024">24</ref>.<lb /> +Quantity of, <ref target="Pg033">33</ref>.<lb /> +Supply to lungs, <ref target="Pg082">82</ref>.<lb /> +Velocity of, <ref target="Pg054">54</ref>.<lb /> +Where found, <ref target="Pg024">24</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Blood platelets, <ref target="Pg025">25</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Blood pressure, <ref target="Pg052">52</ref>, <ref target="Pg070">70</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Blood pressure and velocity, <ref target="Pg052">52</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Blood vessels, to strengthen, <ref target="Pg057">57</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Body, organization of, <ref target="Pg019">19</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Bone groups, <ref target="Pg223">223</ref>-<ref target="Pg229">229</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Bones, <ref target="Pg216">216</ref>-<ref target="Pg242">242</ref>.<lb /> +Adaptation of, <ref target="Pg228">228</ref>.<lb /> +Composition, <ref target="Pg217">217</ref>.<lb /> +Gross structure of, <ref target="Pg218">218</ref>.<lb /> +Minute structure of, <ref target="Pg219">219</ref>.<lb /> +Observation on gross structure, <ref target="Pg241">241</ref>.<lb /> +Properties of, <ref target="Pg217">217</ref>.<lb /> +Table of, <ref target="Pg229">229</ref>.<lb /> +To show composition of, <ref target="Pg241">241</ref>.<lb /> +To show minute structure of, <ref target="Pg242">242</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Bowels, rules for care of, <ref target="Pg166">166</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Brachial plexus, <ref target="Pg302">302</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Brain, <ref target="Pg280">280</ref>, <ref target="Pg288">288</ref>-<ref target="Pg291">291</ref>.<lb /> +Disturbed circulation, <ref target="Pg327">327</ref>.<lb /> +Protection of, <ref target="Pg299">299</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Brain workers, <ref target="Pg408">408</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Breathing, <hi rend="font-style: italic">see</hi> Respiration.<lb /> +Causes of shallow, <ref target="Pg092">92</ref>.<lb /> +Illustrated, <ref target="Pg087">87</ref>.<lb /> +To prevent shallow, <ref target="Pg092">92</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Breathing exercises, <ref target="Pg093">93</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Bronchus, <ref target="Pg080">80</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Bulb, <ref target="Pg291">291</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Cæcum, <ref target="Pg151">151</ref>, <ref target="Pg158">158</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Calcium carbonate, <ref target="Pg122">122</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Calcium phosphate, <ref target="Pg122">122</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Calorie, defined, <ref target="Pg126">126</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cane sugar, <ref target="Pg120">120</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Canines, <ref target="Pg143">143</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Capillaries, <ref target="Pg050">50</ref>, <ref target="Pg064">64</ref>, <ref target="Pg249">249</ref>.<lb /> +Blood pressure at, <ref target="Pg070">70</ref>.<lb /> +Functions of, <ref target="Pg051">51</ref>.<lb /> +Work of, <ref target="Pg174">174</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Carbohydrates, <ref target="Pg119">119</ref>, <ref target="Pg125">125</ref>.<lb /> +Purpose served by, <ref target="Pg121">121</ref>.<lb /> +Storage of, <ref target="Pg177">177</ref>.<lb /> +Tests for, <ref target="Pg135">135</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Carbon, <ref target="Pg134">134</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Carbon dioxide,<lb /> +Final disposition of, <ref target="Pg111">111</ref>.<lb /> +Preparation, <ref target="Pg115">115</ref>.<lb /> +Pressure, <ref target="Pg110">110</ref>.<lb /> +Properties, <ref target="Pg110">110</ref>, <ref target="Pg115">115</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cardiac cycle, <ref target="Pg046">46</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cardiac orifice, <ref target="Pg147">147</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Carpals, <ref target="Pg227">227</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Carpus, <ref target="Pg228">228</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cell body, <ref target="Pg283">283</ref>.<lb /> +Functions of, <ref target="Pg305">305</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cell-division, <ref target="Pg016">16</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cell nucleus, <ref target="Pg014">14</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cell reproduction, <ref target="Pg016">16</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cell structure, <ref target="Pg014">14</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cell surroundings, <ref target="Pg017">17</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cell wall, <ref target="Pg015">15</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cells, <ref target="Pg013">13</ref>-23.<lb /> +Bone, how nourished, <ref target="Pg220">220</ref>.<lb /> +Ciliated epithelial, <ref target="Pg081">81</ref>.<lb /> +Food supply to, <ref target="Pg180">180</ref>.<lb /> +General work of, <ref target="Pg017">17</ref>.<lb /> +Importance of, <ref target="Pg015">15</ref>.<lb /> +Passage of materials to, <ref target="Pg183">183</ref>.<lb /> +Relation to nutrient fluid, <ref target="Pg020">20</ref>.<lb /> +Specialized, <ref target="Pg197">197</ref>.<lb /> +Special work of, <ref target="Pg018">18</ref>.<lb /> +Striated muscle, <ref target="Pg244">244</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cerebellum, <ref target="Pg290">290</ref>.<lb /> +Functions of, <ref target="Pg317">317</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cerebral functions, localization of, <ref target="Pg318">318</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cerebral hemispheres, <ref target="Pg289">289</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cerebral peduncles, <ref target="Pg290">290</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cerebrum, <ref target="Pg288">288</ref>.<lb /> +Functions of, <ref target="Pg317">317</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Chlorine, <ref target="Pg135">135</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cholesterine, <ref target="Pg155">155</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Chordæ tendineæ, <ref target="Pg043">43</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Choroid coat, <ref target="Pg375">375</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Chyme, <ref target="Pg150">150</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cigarettes, <ref target="Pg333">333</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cilia, <ref target="Pg081">81</ref>.<lb /> +To observe, <ref target="Pg101">101</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ciliary muscle, <ref target="Pg375">375</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ciliary processes, <ref target="Pg375">375</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Circulation of blood, <ref target="Pg040">40</ref>-64.<lb /> +Causes of, <ref target="Pg054">54</ref>.<lb /> +Discovery of, by Harvey, <ref target="Pg040">40</ref>.<lb /> +Divisions of, <ref target="Pg051">51</ref>, <ref target="Pg052">52</ref>.<lb /> +Effects of exercise upon, <ref target="Pg063">63</ref>.<lb /> +Effects of gravity upon, <ref target="Pg064">64</ref>.<lb /> +In a frog's foot, <ref target="Pg064">64</ref>.<lb /> +Organs of, <ref target="Pg040">40</ref>-54.<lb /> +Routes to, <ref target="Pg174">174</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Coagulation,<lb /> +Causes of, <ref target="Pg031">31</ref>.<lb /> +Purpose of, <ref target="Pg032">32</ref>.<lb /> +Time required for, <ref target="Pg033">33</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cochlea, <ref target="Pg362">362</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Coffee,<lb /> +Effects on complexion, <ref target="Pg274">274</ref>.<lb /> +Effects on digestion, <ref target="Pg167">167</ref>.<lb /> +Effects on heart, <ref target="Pg056">56</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Colds, <ref target="Pg193">193</ref>.<lb /> +Serious nature of, <ref target="Pg094">94</ref>.<lb /> +To cure, <ref target="Pg094">94</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Colon, parts of, <ref target="Pg158">158</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Complexion, care of, <ref target="Pg273">273</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Compound, defined, <ref target="Pg104">104</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Conduction pathways, <ref target="Pg286">286</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Conductivity, <ref target="Pg304">304</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Condyloid joint, <ref target="Pg232">232</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Conjunctiva, <ref target="Pg373">373</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Consumption, <hi rend="font-style: italic">see</hi> Tuberculosis.</p> + +<p rend="text-indent: -2; margin-left: 2">Control of arteries, <ref target="Pg319">319</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Convolutions, <ref target="Pg289">289</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Coördination, defined, <ref target="Pg279">279</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cornea, <ref target="Pg375">375</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Corpora quadrigemina, <ref target="Pg290">290</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Corpora striata, <ref target="Pg289">289</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Corpus callosum, <ref target="Pg289">289</ref>, <ref target="Pg293">293</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cortex, <ref target="Pg288">288</ref>, <ref target="Pg294">294</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Coughing, <ref target="Pg081">81</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cranial cavity, <ref target="Pg007">7</ref>, <ref target="Pg225">225</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cranial nerves, <ref target="Pg296">296</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Crura cerebri, <ref target="Pg290">290</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Crystalline lens, <ref target="Pg380">380</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Culex, <ref target="Pg402">402</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Cytoplasm, <ref target="Pg015">15</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Defects in focusing, <ref target="Pg383">383</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Deformities of skeleton, <ref target="Pg233">233</ref>-<ref target="Pg236">236</ref>.<lb /> +Correction of, <ref target="Pg236">236</ref>.<lb /> +Prevention of, <ref target="Pg235">235</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Deglutition, <ref target="Pg145">145</ref>.<lb /> +Steps in, <ref target="Pg146">146</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Dendrites, <ref target="Pg283">283</ref>, <ref target="Pg306">306</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Dentine, <ref target="Pg143">143</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Dermis, <ref target="Pg264">264</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Dextrose, <ref target="Pg030">30</ref>, <ref target="Pg120">120</ref>, <ref target="Pg150">150</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Diaphragm, <ref target="Pg088">88</ref>.<lb /> +To illustrate action of, <ref target="Pg102">102</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Diastole, <ref target="Pg046">46</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Diaxonic neuron, <ref target="Pg283">283</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Diet, one-sided, <ref target="Pg124">124</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Diffusion, <ref target="Pg371">371</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Digestion, <ref target="Pg130">130</ref>-<ref target="Pg172">172</ref>.<lb /> +Hygiene of, <ref target="Pg160">160</ref>.<lb /> +Nature of, <ref target="Pg130">130</ref>.<lb /> +Not a simple process, <ref target="Pg131">131</ref>.<lb /> +Of fat, <ref target="Pg156">156</ref>.<lb /> +Purpose of, <ref target="Pg177">177</ref>.<lb /> +Stomach, <ref target="Pg148">148</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Digestive fluids, <ref target="Pg132">132</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Digestive organs, <ref target="Pg160">160</ref>.<lb /> +Table of, <ref target="Pg138">138</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Digestive processes, <ref target="Pg130">130</ref>, <ref target="Pg141">141</ref>.<lb /> +Illustrated, <ref target="Pg137">137</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Diphtheria, <ref target="Pg094">94</ref>, <ref target="Pg405">405</ref>.<lb /> +Care after, <ref target="Pg211">211</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Disaccharides, <ref target="Pg120">120</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Disease, <ref target="Pg392">392</ref>-<ref target="Pg412">412</ref>.<lb /> +Causes of, <ref target="Pg393">393</ref>.<lb /> +Eruptive, <ref target="Pg405">405</ref>.<lb /> +Precautions in recovery from, <ref target="Pg407">407</ref>.<lb /> +Prevention of, <ref target="Pg393">393</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Dislocations, <ref target="Pg239">239</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Dorsal-root ganglia, <ref target="Pg295">295</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Drill, "setting up," <ref target="Pg237">237</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Drugs, effects of, <ref target="Pg035">35</ref>, <ref target="Pg055">55</ref>, <ref target="Pg129">129</ref>, <ref target="Pg332">332</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Duodenum, <ref target="Pg151">151</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Dura, <ref target="Pg299">299</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Ear, <ref target="Pg358">358</ref>.<lb /> +Hygiene of, <ref target="Pg365">365</ref>.<lb /> +To demonstrate, <ref target="Pg369">369</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ear drum, <ref target="Pg359">359</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Efferent neurons, <ref target="Pg296">296</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Element, defined, <ref target="Pg104">104</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Elevators of the ribs, <ref target="Pg087">87</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Emetics, <ref target="Pg151">151</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Emotional states, effects of, <ref target="Pg330">330</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">End bulbs, <ref target="Pg342">342</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Endocardium, <ref target="Pg042">42</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Endolymph, <ref target="Pg361">361</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">End-plate, <ref target="Pg244">244</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">End-to-end connections, <ref target="Pg286">286</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Energy, <ref target="Pg107">107</ref>, <ref target="Pg186">186</ref>-<ref target="Pg196">196</ref>.<lb /> +Bodily control of, <ref target="Pg192">192</ref>.<lb /> +From sun to cells, <ref target="Pg191">191</ref>.<lb /> +How plants store sun's, <ref target="Pg189">189</ref>.<lb /> +Increasing one's bodily, <ref target="Pg194">194</ref>.<lb /> +In food and oxygen, <ref target="Pg190">190</ref>.<lb /> +Kinds of, <ref target="Pg186">186</ref>.<lb /> +Methods of storing, <ref target="Pg187">187</ref>, <ref target="Pg188">188</ref>.<lb /> +Transformation of, in muscle, <ref target="Pg248">248</ref>, <ref target="Pg249">249</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Enzymes, <ref target="Pg132">132</ref>, <ref target="Pg155">155</ref>.<lb /> +Of the tissues, <ref target="Pg184">184</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Epidermis, <ref target="Pg264">264</ref>, <ref target="Pg266">266</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Epiglottis, <ref target="Pg080">80</ref>, <ref target="Pg354">354</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Epithelium, <ref target="Pg139">139</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Eruptive diseases, <ref target="Pg405">405</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Esophagus, <ref target="Pg146">146</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Eustachian tube, <ref target="Pg359">359</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Excessive reading, <ref target="Pg331">331</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Excitant impulse, <ref target="Pg305">305</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Excretion, <ref target="Pg197">197</ref>-<ref target="Pg213">213</ref>.<lb /> +Defined, <ref target="Pg018">18</ref>.<lb /> +Necessity for, <ref target="Pg201">201</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Exercise, <ref target="Pg256">256</ref>, <ref target="Pg257">257</ref>, <ref target="Pg328">328</ref>, <ref target="Pg409">409</ref>.<lb /> +General rules for, <ref target="Pg259">259</ref>.<lb /> +Results of, <ref target="Pg257">257</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Exhaustion, nervous, <ref target="Pg211">211</ref>.<lb /> +Results of, <ref target="Pg195">195</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">External ear, <ref target="Pg358">358</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">External stimuli, action of, <ref target="Pg307">307</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Eye, <ref target="Pg370">370</ref>-<ref target="Pg391">391</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Eyeball, <ref target="Pg373">373</ref>.<lb /> +Chambers of, <ref target="Pg377">377</ref>.<lb /> +Focusing power of, <ref target="Pg378">378</ref>.<lb /> +Movements of, <ref target="Pg381">381</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Eyelids, <ref target="Pg373">373</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Eyes,<lb /> +Care of, <ref target="Pg386">386</ref>.<lb /> +Removal of foreign bodies from, <ref target="Pg387">387</ref>,<lb /> +Strong chemicals in, <ref target="Pg388">388</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Eye strain, <ref target="Pg211">211</ref>.<lb /> +And disease, <ref target="Pg385">385</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Fat, <ref target="Pg030">30</ref>, <ref target="Pg149">149</ref>, <ref target="Pg162">162</ref>.<lb /> +Digestion of, <ref target="Pg156">156</ref>.<lb /> +Emulsification of, <ref target="Pg157">157</ref>.<lb /> +Purpose served by, <ref target="Pg121">121</ref>.<lb /> +Route taken by, <ref target="Pg175">175</ref>.<lb /> +Tests for, <ref target="Pg137">137</ref>.<lb /> +Where stored, <ref target="Pg178">178</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Fatty acid, <ref target="Pg156">156</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Fenestra ovalis, <ref target="Pg361">361</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Fenestra rotunda, <ref target="Pg363">363</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ferments, <hi rend="font-style: italic">see</hi> Enzymes.</p> + +<p rend="text-indent: -2; margin-left: 2">Fibrin, <ref target="Pg031">31</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Fibrin ferment, <ref target="Pg032">32</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Fibrinogen, <ref target="Pg030">30</ref>, <ref target="Pg031">31</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Fissures, <ref target="Pg289">289</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Food, <ref target="Pg117">117</ref>-<ref target="Pg137">137</ref>.<lb /> +Advantages of coarse, <ref target="Pg167">167</ref>.<lb /> +Classes of, <ref target="Pg118">118</ref>, <ref target="Pg119">119</ref>.<lb /> +Composition of, <ref target="Pg124">124</ref>.<lb /> +Dangers from impure, <ref target="Pg165">165</ref>.<lb /> +Defined, <ref target="Pg117">117</ref>.<lb /> +Elements supplied by, <ref target="Pg134">134</ref>.<lb /> +Excess of proteid, <ref target="Pg208">208</ref>.<lb /> +Frequency of taking, <ref target="Pg165">165</ref>.<lb /> +Materials, table of, <ref target="Pg126">126</ref>, <ref target="Pg126">126</ref>.<lb /> +Nitrogenous, <ref target="Pg119">119</ref>.<lb /> +Order of taking, <ref target="Pg161">161</ref>.<lb /> +Preparation of, <ref target="Pg164">164</ref>.<lb /> +Purity of, <ref target="Pg128">128</ref>.<lb /> +Quantity of, <ref target="Pg164">164</ref>.<lb /> +Simple, <ref target="Pg118">118</ref>.<lb /> +Variety, <ref target="Pg128">128</ref>.<lb /> +With reference to digestive changes, <ref target="Pg132">132</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Foot lever, diagram of, <ref target="Pg253">253</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Foot-pound, <ref target="Pg196">196</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Foot-wear, hygienic, <ref target="Pg238">238</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Fractures, treatment of, <ref target="Pg239">239</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Fumigation, <ref target="Pg400">400</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Furniture, school, <ref target="Pg236">236</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Gall bladder, <ref target="Pg154">154</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ganglia, <ref target="Pg281">281</ref>.<lb /> +Dorsal-root, <ref target="Pg295">295</ref>.<lb /> +Sympathetic, <ref target="Pg298">298</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Gastric glands, <ref target="Pg147">147</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Gastric juice, to illustrate action of, <ref target="Pg172">172</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Gelatine, <ref target="Pg218">218</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Germ diseases, avoidance of, <ref target="Pg394">394</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Germs, <ref target="Pg029">29</ref>, <ref target="Pg394">394</ref>, <ref target="Pg395">395</ref>.<lb /> +How spread, <ref target="Pg395">395</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Glands, <ref target="Pg197">197</ref>-<ref target="Pg213">213</ref>.<lb /> +Digestive, <ref target="Pg140">140</ref>.<lb /> +Ductless, <ref target="Pg208">208</ref>.<lb /> +Excretory, work of, <ref target="Pg201">201</ref>.<lb /> +Gastric, <ref target="Pg147">147</ref>.<lb /> +Kinds of, <ref target="Pg197">197</ref>, <ref target="Pg198">198</ref>.<lb /> +Lymphatic, <ref target="Pg068">68</ref>, <ref target="Pg208">208</ref>.<lb /> +Perspiratory, <ref target="Pg206">206</ref>.<lb /> +Salivary, <ref target="Pg144">144</ref>.<lb /> +Structure of, <ref target="Pg197">197</ref>.<lb /> +Thymus, <ref target="Pg208">208</ref>.<lb /> +Thyroid, <ref target="Pg208">208</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Gliding joint, <ref target="Pg232">232</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Glottis, <ref target="Pg355">355</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Glycogen, <ref target="Pg120">120</ref>, <ref target="Pg177">177</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Grape sugar, tests for, <ref target="Pg120">120</ref>, <ref target="Pg136">136</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Gross anatomy, defined, <ref target="Pg001">1</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Gullet, <ref target="Pg146">146</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Gustatory pore, <ref target="Pg345">345</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Gustatory stimulus, <ref target="Pg345">345</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Habits, <ref target="Pg315">315</ref>, <ref target="Pg334">334</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hair, <ref target="Pg267">267</ref>.<lb /> +Care of, <ref target="Pg276">276</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hair cells, <ref target="Pg363">363</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hair follicle, <ref target="Pg267">267</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Haversian canals, <ref target="Pg219">219</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hearing, defective, <ref target="Pg366">366</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Heart, <ref target="Pg041">41</ref>.<lb /> +Care of, <ref target="Pg055">55</ref>.<lb /> +Connection with arteries and veins, <ref target="Pg045">45</ref>.<lb /> +Difference in parts of, <ref target="Pg044">44</ref>.<lb /> +How it does its work, <ref target="Pg045">45</ref>.<lb /> +Observations on, <ref target="Pg060">60</ref>, <ref target="Pg061">61</ref>, <ref target="Pg062">62</ref>.<lb /> +Sounds of the, <ref target="Pg047">47</ref>.<lb /> +Valves of, <ref target="Pg043">43</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Heart muscle, structure of, <ref target="Pg247">247</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Heat and cold, effects of, <ref target="Pg330">330</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hemoglobin, <ref target="Pg026">26</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hepatic artery, <ref target="Pg154">154</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hepatic veins, <ref target="Pg154">154</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hindbrain, <ref target="Pg290">290</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hinge joint, <ref target="Pg231">231</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Histology, defined, <ref target="Pg001">1</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Humerus, <ref target="Pg227">227</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hyaloid membrane, <ref target="Pg378">378</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hydrochloric acid, <ref target="Pg149">149</ref>, <ref target="Pg150">150</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hydrogen, <ref target="Pg134">134</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hygiene,<lb /> +Defined, <ref target="Pg002">2</ref>.<lb /> +General aim of, <ref target="Pg002">2</ref>.<lb /> +General laws of, <ref target="Pg002">2</ref>, <ref target="Pg392">392</ref>.<lb /> +Of digestion, <ref target="Pg160">160</ref>.<lb /> +Of skeleton, <ref target="Pg238">238</ref>.<lb /> +Relation of physiology and anatomy to, <ref target="Pg003">3</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hygienic housekeeping, <ref target="Pg399">399</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Hypoglossal nerves, <ref target="Pg298">298</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Ileo-cæcal valve, <ref target="Pg151">151</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ileum, <ref target="Pg151">151</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Images,<lb /> +Diagram illustrating, <ref target="Pg372">372</ref>.<lb /> +Formation of, <ref target="Pg371">371</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Incisors, <ref target="Pg143">143</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Incus, <ref target="Pg359">359</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Infectious diseases, <ref target="Pg394">394</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Infundibula, <ref target="Pg080">80</ref>, <ref target="Pg084">84</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Inhibitory impulse, <ref target="Pg305">305</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Insomnia, <ref target="Pg329">329</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Inspiratory force, <ref target="Pg070">70</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Intercellular material, production of, <ref target="Pg013">13</ref>, <ref target="Pg018">18</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Internal ear, <ref target="Pg360">360</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Intestinal juice, <ref target="Pg152">152</ref>, <ref target="Pg157">157</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Iris, <ref target="Pg375">375</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Iron, <ref target="Pg135">135</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Irritability, <ref target="Pg006">6</ref>, <ref target="Pg243">243</ref>, <ref target="Pg304">304</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Isolation, <ref target="Pg406">406</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Jejunum, <ref target="Pg151">151</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Joints, <ref target="Pg230">230</ref>-<ref target="Pg232">232</ref>, <ref target="Pg242">242</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Kidneys, <ref target="Pg201">201</ref>.<lb /> +Blood supply to, <ref target="Pg204">204</ref>.<lb /> +Cortex of, <ref target="Pg204">204</ref>.<lb /> +Inflammation of, <ref target="Pg211">211</ref>.<lb /> +Pelvis of, <ref target="Pg202">202</ref>.<lb /> +Structure, <ref target="Pg202">202</ref>.<lb /> +Symptoms of diseased, <ref target="Pg211">211</ref>.<lb /> +Work of, <ref target="Pg205">205</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Knee jerk reflex, <ref target="Pg322">322</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Lachrymal glands, <ref target="Pg383">383</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lacteals, work of, <ref target="Pg174">174</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lacunæ, <ref target="Pg220">220</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Laminæ, <ref target="Pg220">220</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Large intestine, <ref target="Pg157">157</ref>.<lb /> +Division of, <ref target="Pg158">158</ref>.<lb /> +Work of, <ref target="Pg159">159</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Larynx, <ref target="Pg080">80</ref>, <ref target="Pg353">353</ref>-<ref target="Pg357">357</ref>.<lb /> +To show plan of, <ref target="Pg368">368</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lever, <ref target="Pg251">251</ref>.<lb /> +Application to the body, <ref target="Pg251">251</ref>.<lb /> +Classes of, in body, <ref target="Pg251">251</ref>.<lb /> +Producing motion, diagram of, <ref target="Pg252">252</ref>.<lb /> +To show action of, <ref target="Pg252">252</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Leucocytes, <ref target="Pg027">27</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Levulose, <ref target="Pg120">120</ref>, <ref target="Pg150">150</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Life, maintenance of, <ref target="Pg020">20</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Light, <ref target="Pg370">370</ref>, <ref target="Pg371">371</ref>.<lb /> +Simple properties, illustrated, <ref target="Pg389">389</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Light waves, diagram illustrating passage of, <ref target="Pg370">370</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lime water, to prepare, <ref target="Pg101">101</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Liver, <ref target="Pg052">52</ref>, <ref target="Pg152">152</ref>-<ref target="Pg155">155</ref>, <ref target="Pg178">178</ref>.<lb /> +Protection of, <ref target="Pg210">210</ref>.<lb /> +Work of, <ref target="Pg206">206</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lockjaw, <ref target="Pg276">276</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Longsightedness, <ref target="Pg384">384</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lung capacity, diagram illustrating, <ref target="Pg089">89</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lung diseases, out-door cure for, <ref target="Pg098">98</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lungs, <ref target="Pg077">77</ref>-<ref target="Pg103">103</ref>.<lb /> +Capacity of, <ref target="Pg088">88</ref>.<lb /> +Changes air undergoes in, <ref target="Pg101">101</ref>.<lb /> +Excretory work of, <ref target="Pg207">207</ref>.<lb /> +Interchange of gases in, <ref target="Pg088">88</ref>.<lb /> +Observations of, <ref target="Pg100">100</ref>.<lb /> +Supply of blood to, <ref target="Pg082">82</ref>.<lb /> +To estimate capacity of, <ref target="Pg103">103</ref>.<lb /> +Weakest portions of, <ref target="Pg092">92</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lymph, <ref target="Pg065">65</ref>-75.<lb /> +Composition, <ref target="Pg066">66</ref>.<lb /> +Movements at the cells, <ref target="Pg071">71</ref>.<lb /> +Origin of, <ref target="Pg065">65</ref>.<lb /> +Physical properties, <ref target="Pg066">66</ref>.<lb /> +Where it enters the blood, <ref target="Pg070">70</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lymph movements, causes of, <ref target="Pg069">69</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lymph spaces, <ref target="Pg066">66</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Lymph vessels, <ref target="Pg066">66</ref>.<lb /> +Variable pressure on the walls of, <ref target="Pg070">70</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Magnesium, <ref target="Pg135">135</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Malarial fever, <ref target="Pg401">401</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Malleus, <ref target="Pg359">359</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Malpighian capsules, <ref target="Pg203">203</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Maltose, <ref target="Pg120">120</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Massage, <ref target="Pg259">259</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Mastication,<lb /> +Muscles of, <ref target="Pg144">144</ref>.<lb /> +Slow, <ref target="Pg145">145</ref>.<lb /> +Thorough, <ref target="Pg160">160</ref>.<lb /> +To show importance of, <ref target="Pg171">171</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Matrix, <ref target="Pg267">267</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Measles, <ref target="Pg094">94</ref>.<lb /> +Care after, <ref target="Pg211">211</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Median fissures, <ref target="Pg289">289</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Medulla oblongata, <ref target="Pg291">291</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Medullary sheath, <ref target="Pg284">284</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Membrana tympani, <ref target="Pg358">358</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Membrane,<lb /> +Active, <ref target="Pg173">173</ref>.<lb /> +Basement, <ref target="Pg197">197</ref>.<lb /> +Basilar, <ref target="Pg363">363</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Membranous capsule, <ref target="Pg377">377</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Membranous labyrinth, <ref target="Pg361">361</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Mesentery, <ref target="Pg152">152</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Metacarpals, <ref target="Pg227">227</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Midbrain, <ref target="Pg289">289</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Middle ear, <ref target="Pg359">359</ref>.<lb /> +Purposes of, <ref target="Pg360">360</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Milk sugar, <ref target="Pg120">120</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Mineral salts, <ref target="Pg030">30</ref>.<lb /> +Uses, <ref target="Pg121">121</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Moderate drinkers, <ref target="Pg333">333</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Molars, <ref target="Pg143">143</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Molecules, defined, <ref target="Pg105">105</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Mon-axonic neuron, diagram of, <ref target="Pg282">282</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Mono-saccharides, <ref target="Pg120">120</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Mosquitoes, <ref target="Pg401">401</ref>-<ref target="Pg403">403</ref>.<lb /> +Remedies against, <ref target="Pg402">402</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Mouth, <ref target="Pg141">141</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Movable joints,<lb /> +Kinds of, <ref target="Pg231">231</ref>.<lb /> +Structure of, <ref target="Pg230">230</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Mucous membrane, <ref target="Pg080">80</ref>, <ref target="Pg264">264</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Mucus, <ref target="Pg139">139</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Muscle organ, <ref target="Pg245">245</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Muscles, <ref target="Pg243">243</ref>-<ref target="Pg263">263</ref>.<lb /> +Alimentary, <ref target="Pg189">189</ref>.<lb /> +Important, <ref target="Pg254">254</ref>-<ref target="Pg256">256</ref>.<lb /> +Intercostal, <ref target="Pg087">87</ref>.<lb /> +Of mastication, <ref target="Pg144">144</ref>.<lb /> +Properties of, <ref target="Pg243">243</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Muscular force, plan of using, <ref target="Pg249">249</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Muscular sensations, <ref target="Pg344">344</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Muscular stimulus, <ref target="Pg248">248</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Muscular stimulus and contraction, to illustrate, <ref target="Pg261">261</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Muscular tissue, kinds of, <ref target="Pg243">243</ref>, <ref target="Pg244">244</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Nails, <ref target="Pg267">267</ref>.<lb /> +Care of, <ref target="Pg276">276</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nasal duct, <ref target="Pg383">383</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Neck exercise, <ref target="Pg328">328</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nerve cells, <ref target="Pg281">281</ref>, <ref target="Pg282">282</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nerve fibers, <ref target="Pg282">282</ref>, <ref target="Pg293">293</ref>, <ref target="Pg294">294</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nerve path, diagram of, <ref target="Pg286">286</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nerve pathways, to demonstrate, <ref target="Pg322">322</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nerves, <ref target="Pg281">281</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nerve skeleton, <ref target="Pg280">280</ref>.<lb /> +Diagram of, <ref target="Pg281">281</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nerve stimuli, <ref target="Pg306">306</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nerve trunks, <ref target="Pg281">281</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nervous activity, wasteful forms of, <ref target="Pg325">325</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nervous control of,<lb /> +Body temperature, <ref target="Pg320">320</ref>.<lb /> +Circulation of blood, <ref target="Pg318">318</ref>.<lb /> +Respiration, <ref target="Pg320">320</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nervous energy, economizing of, <ref target="Pg315">315</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nervous impulse, <ref target="Pg248">248</ref>, <ref target="Pg305">305</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nervousness, <ref target="Pg326">326</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nervous system, <ref target="Pg279">279</ref>-<ref target="Pg337">337</ref>.<lb /> +Diagram of, <ref target="Pg287">287</ref>.<lb /> +Dissection of, <ref target="Pg302">302</ref>.<lb /> +Divisions of, <ref target="Pg287">287</ref>.<lb /> +Hygiene of, <ref target="Pg324">324</ref>-<ref target="Pg337">337</ref>.<lb /> +Nature of, <ref target="Pg287">287</ref>.<lb /> +Physiology of, <ref target="Pg304">304</ref>-<ref target="Pg323">323</ref>.<lb /> +Work of, <ref target="Pg280">280</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Neural arch, <ref target="Pg224">224</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Neurilemma, <ref target="Pg284">284</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Neurons, <ref target="Pg281">281</ref>, <ref target="Pg282">282</ref>.<lb /> +Arrangement of, <ref target="Pg284">284</ref>, <ref target="Pg293">293</ref>.<lb /> +Diagram, illustrating, <ref target="Pg285">285</ref>.<lb /> +Properties of, <ref target="Pg304">304</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nicotine,<lb /> +Effects of, <ref target="Pg333">333</ref>.<lb /> +Relation of age to effects, <ref target="Pg333">333</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nitrogen, <ref target="Pg134">134</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Non-striated cells, to show, <ref target="Pg261">261</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Non-striated muscles,<lb /> +Purpose of, <ref target="Pg246">246</ref>.<lb /> +Structure of, <ref target="Pg246">246</ref>.<lb /> +Work of, <ref target="Pg247">247</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Normal temperature, <ref target="Pg269">269</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nosebleed, <ref target="Pg058">58</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nucleoplasm, <ref target="Pg014">14</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nutrients (<hi rend="font-style: italic">see</hi> Foods),<lb /> +Composition of, <ref target="Pg135">135</ref>.<lb /> +Relative quantity needed, <ref target="Pg123">123</ref>.<lb /> +Routes taken by, <ref target="Pg175">175</ref>.<lb /> +Tests for, <ref target="Pg136">136</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Nutriment, storage of, <ref target="Pg177">177</ref>-<ref target="Pg180">180</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Olfactory stimulus, <ref target="Pg347">347</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Opsonins, <ref target="Pg034">34</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Optic thalami, <ref target="Pg289">289</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Orbit, <ref target="Pg373">373</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Organ, defined, <ref target="Pg007">7</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Organism, defined, <ref target="Pg019">19</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Organization, defined, <ref target="Pg010">10</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Osmosis, <ref target="Pg072">72</ref>.<lb /> +At the cells, <ref target="Pg072">72</ref>.<lb /> +To illustrate, <ref target="Pg075">75</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ossein, <ref target="Pg218">218</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Overstudy, <ref target="Pg211">211</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Oxidation, defined, <ref target="Pg106">106</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Oxygen, <ref target="Pg104">104</ref>-<ref target="Pg117">117</ref>.<lb /> +Combined, <ref target="Pg105">105</ref>, <ref target="Pg113">113</ref>.<lb /> +Free, <ref target="Pg105">105</ref>, <ref target="Pg113">113</ref>.<lb /> +How it unites, <ref target="Pg105">105</ref>.<lb /> +Main uses of, <ref target="Pg108">108</ref>.<lb /> +Movement a necessity, <ref target="Pg106">106</ref>, <ref target="Pg108">108</ref>, <ref target="Pg115">115</ref>.<lb /> +Movement in body, <ref target="Pg106">106</ref>, <ref target="Pg108">108</ref>, <ref target="Pg115">115</ref>.<lb /> +Nature of, <ref target="Pg104">104</ref>.<lb /> +Passage of, from cells, <ref target="Pg110">110</ref>.<lb /> +Passage of, through blood, <ref target="Pg109">109</ref>.<lb /> +Passage of, toward cells, <ref target="Pg109">109</ref>.<lb /> +Preparation of, <ref target="Pg113">113</ref>.<lb /> +Pressure, <ref target="Pg109">109</ref>.<lb /> +Properties of, <ref target="Pg113">113</ref>.<lb /> +Purpose of, in the body, <ref target="Pg106">106</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Oxyhemoglobin, <ref target="Pg027">27</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Pacinian corpuscles, <ref target="Pg342">342</ref>, <ref target="Pg343">343</ref>.<lb /> +To demonstrate, <ref target="Pg348">348</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pancreas, <ref target="Pg155">155</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pancreatic juice, <ref target="Pg155">155</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Papillæ, <ref target="Pg266">266</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Patent medicines, <ref target="Pg166">166</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pelvic girdle, <ref target="Pg226">226</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pepsin, <ref target="Pg149">149</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Peptones, <ref target="Pg149">149</ref>, <ref target="Pg176">176</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pericardium, <ref target="Pg041">41</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Perilymph, <ref target="Pg361">361</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Perimysium, <ref target="Pg245">245</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Periosteum, <ref target="Pg218">218</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Peritoneum, <ref target="Pg180">180</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Perspiration, <ref target="Pg207">207</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pharynx, <ref target="Pg145">145</ref>.<lb /> +Openings into, <ref target="Pg145">145</ref>, <ref target="Pg146">146</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Phosphorus, <ref target="Pg135">135</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Phrenic nerve, <ref target="Pg302">302</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Physiological salt solution, <ref target="Pg038">38</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Physiology, defined, <ref target="Pg002">2</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pia, <ref target="Pg299">299</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pigment granules, <ref target="Pg266">266</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pinna, <ref target="Pg358">358</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pitch, detection of, <ref target="Pg365">365</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pivot joint, <ref target="Pg232">232</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Plasma, <ref target="Pg025">25</ref>, <ref target="Pg029">29</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pleura, <ref target="Pg084">84</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Plexus, <ref target="Pg281">281</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pneumonia, <ref target="Pg094">94</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pons, <ref target="Pg290">290</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pons Varolii, <ref target="Pg290">290</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Portal vein, <ref target="Pg154">154</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Primitive sheath, <ref target="Pg284">284</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Proteids, <ref target="Pg161">161</ref>.<lb /> +Circulating, <ref target="Pg179">179</ref>.<lb /> +Kinds of, <ref target="Pg118">118</ref>.<lb /> +Purposes of, <ref target="Pg119">119</ref>.<lb /> +Supplied by, <ref target="Pg125">125</ref>.<lb /> +Tests for, <ref target="Pg135">135</ref>, <ref target="Pg136">136</ref>.<lb /> +Tissue, <ref target="Pg179">179</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Proteoses, <ref target="Pg149">149</ref>, <ref target="Pg176">176</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Protoplasm, <ref target="Pg014">14</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Protozoa, <ref target="Pg394">394</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ptyalin, <ref target="Pg145">145</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Public sanitation, <ref target="Pg396">396</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pulp cavity, <ref target="Pg143">143</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pupil, <ref target="Pg375">375</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pure food law, <ref target="Pg128">128</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pus, <ref target="Pg028">28</ref>, <ref target="Pg029">29</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pyloric orifice, <ref target="Pg147">147</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Pyramids, <ref target="Pg202">202</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Quarantine, <ref target="Pg406">406</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Radius, <ref target="Pg227">227</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Reaction time, to determine, <ref target="Pg323">323</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Reading glasses, <ref target="Pg386">386</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Receptacle of the chyle, <ref target="Pg068">68</ref>, <ref target="Pg170">170</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Rectum, <ref target="Pg158">158</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Red corpuscles, <ref target="Pg025">25</ref>.<lb /> +Disappearance of, <ref target="Pg027">27</ref>.<lb /> +Function of, <ref target="Pg026">26</ref>.<lb /> +Origin of, <ref target="Pg027">27</ref>.<lb /> +To examine, <ref target="Pg038">38</ref>.<lb /> +To prepare models of, <ref target="Pg039">39</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Red marrow, <ref target="Pg219">219</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Reënforcement of sound, <ref target="Pg352">352</ref>, <ref target="Pg356">356</ref>, <ref target="Pg368">368</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Reflection, kinds of, <ref target="Pg371">371</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Reflex action, <ref target="Pg308">308</ref>.<lb /> +Diagram illustrating, <ref target="Pg310">310</ref>.<lb /> +In circulation of blood, <ref target="Pg311">311</ref>.<lb /> +In digestion, <ref target="Pg310">310</ref>.<lb /> +Purposes of, <ref target="Pg311">311</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Reflex action and mind, <ref target="Pg308">308</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Reflex action pathway, <ref target="Pg309">309</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Refraction, <ref target="Pg371">371</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Rennin, <ref target="Pg149">149</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Respiration, <ref target="Pg076">76</ref>-<ref target="Pg103">103</ref>.<lb /> +Artificial, <ref target="Pg097">97</ref>.<lb /> +Internal, <ref target="Pg089">89</ref>.<lb /> +Lung, <ref target="Pg076">76</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Retina, <ref target="Pg376">376</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Retinitis, <ref target="Pg333">333</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Rheumatism,<lb /> +Effects on the heart, <ref target="Pg056">56</ref>.<lb /> +Sequel to other diseases, <ref target="Pg407">407</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Right lymphatic duct, <ref target="Pg067">67</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Rods and cones, <ref target="Pg377">377</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Rods of Corti, <ref target="Pg364">364</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Sacrum, <ref target="Pg224">224</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Saliva, <ref target="Pg145">145</ref>.<lb /> +Composition of, <ref target="Pg145">145</ref>.<lb /> +Uses of, <ref target="Pg145">145</ref>.<lb /> +To show action on starch, <ref target="Pg171">171</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Salivary glands, <ref target="Pg144">144</ref>.<lb /> +Kinds of, <ref target="Pg144">144</ref>.<lb /> +Reflex action of, <ref target="Pg323">323</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sanitation, defined, <ref target="Pg002">2</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sarcolemma, <ref target="Pg244">244</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sarcoplasm, <ref target="Pg244">244</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Scala media, <ref target="Pg363">363</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Scala tympani, <ref target="Pg363">363</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Scala vestibula, <ref target="Pg363">363</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Scarlet fever, care after, <ref target="Pg211">211</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sciatic nerve, <ref target="Pg302">302</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sclerotic coat, <ref target="Pg374">374</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Secondary reflex action, <ref target="Pg314">314</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Secretions, <ref target="Pg197">197</ref>.<lb /> +Kinds of, <ref target="Pg200">200</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Secretory process, nature of, <ref target="Pg199">199</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Seeing, problem of, <ref target="Pg372">372</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Self-control, <ref target="Pg326">326</ref>, <ref target="Pg334">334</ref>.<lb /> +Habit of, <ref target="Pg325">325</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Semicircular canals, <ref target="Pg362">362</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Semilunar valves, <ref target="Pg044">44</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sensations, <ref target="Pg338">338</ref>-<ref target="Pg349">349</ref>.<lb /> +Classes of, <ref target="Pg339">339</ref>.<lb /> +Production of, <ref target="Pg338">338</ref>, <ref target="Pg349">349</ref>.<lb /> +Purposes of, <ref target="Pg340">340</ref>.<lb /> +Special, <ref target="Pg340">340</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sensations (<hi rend="font-style: italic">continued</hi>).<lb /> +Steps in production of, <ref target="Pg341">341</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sensation stimuli, <ref target="Pg339">339</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sense organs, simple forms of, <ref target="Pg341">341</ref>, <ref target="Pg342">342</ref></p> + +<p rend="text-indent: -2; margin-left: 2">Serous coat, <ref target="Pg140">140</ref>, <ref target="Pg148">148</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Serous membrane, <ref target="Pg264">264</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Serum albumin, <ref target="Pg030">30</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Serum globulin, <ref target="Pg030">30</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Shortsightedness, <ref target="Pg384">384</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Shoulder girdle, <ref target="Pg226">226</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sight, organs of, <ref target="Pg373">373</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sigmoid flexure, <ref target="Pg158">158</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Simple life, <ref target="Pg410">410</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Skeleton, <ref target="Pg216">216</ref>-<ref target="Pg243">243</ref>.<lb /> +How deformed, <ref target="Pg234">234</ref>.<lb /> +Hygiene of, <ref target="Pg233">233</ref>.<lb /> +Plan of, <ref target="Pg221">221</ref>.<lb /> +Purpose of, <ref target="Pg221">221</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Skin, <ref target="Pg264">264</ref>-<ref target="Pg277">277</ref>.<lb /> +As regulator of temperature, <ref target="Pg270">270</ref>.<lb /> +Experiments on, <ref target="Pg349">349</ref>.<lb /> +Functions of, <ref target="Pg267">267</ref>, <ref target="Pg268">268</ref>.<lb /> +Observations on skin, <ref target="Pg278">278</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Skin wounds, treatment of, <ref target="Pg275">275</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Skull, <ref target="Pg225">225</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sleep, <ref target="Pg329">329</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Small intestine, <ref target="Pg151">151</ref>.<lb /> +Mucous membrane of, <ref target="Pg151">151</ref>.<lb /> +Muscular coat of, <ref target="Pg152">152</ref>.<lb /> +As organ of absorption, <ref target="Pg173">173</ref>.<lb /> +Parts of, <ref target="Pg151">151</ref>.<lb /> +Serous coat of, <ref target="Pg152">152</ref>.<lb /> +Work of, <ref target="Pg157">157</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Smell,<lb /> +Sensation of, <ref target="Pg346">346</ref>.<lb /> +Value of, <ref target="Pg347">347</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sneezing, <ref target="Pg081">81</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sodium, <ref target="Pg135">135</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sodium carbonate, <ref target="Pg155">155</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sodium chloride, <ref target="Pg122">122</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Soft palate, <ref target="Pg141">141</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Solution, <ref target="Pg131">131</ref>.<lb /> +Kinds of, <ref target="Pg073">73</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Solution theory, <ref target="Pg156">156</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Solvents, <ref target="Pg131">131</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sound,<lb /> +To illustrate origin of, <ref target="Pg367">367</ref>.<lb /> +To show transmission of, <ref target="Pg367">367</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sound waves,<lb /> +As stimuli, <ref target="Pg331">331</ref>.<lb /> +Nature of, <ref target="Pg350">350</ref>.<lb /> +Reënforcement of, <ref target="Pg352">352</ref>.<lb /> +To show effects of, <ref target="Pg368">368</ref>.<lb /> +Value of, <ref target="Pg353">353</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Speech, production of, <ref target="Pg357">357</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Spinal column, <ref target="Pg223">223</ref>-<ref target="Pg225">225</ref>.<lb /> +Hygiene of, <ref target="Pg233">233</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Spinal cord, <ref target="Pg280">280</ref>.<lb /> +Protection of, <ref target="Pg299">299</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Spinal nerves, <ref target="Pg295">295</ref>.<lb /> +Double nature of, <ref target="Pg295">295</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Spitting, <ref target="Pg403">403</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Spleen, <ref target="Pg208">208</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sprains, <ref target="Pg239">239</ref>, <ref target="Pg240">240</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Stapes, <ref target="Pg359">359</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Starch, <ref target="Pg162">162</ref>.<lb /> +Action of, on saliva, <ref target="Pg171">171</ref>.<lb /> +Animal, <ref target="Pg120">120</ref>.<lb /> +Tests for, <ref target="Pg136">136</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Steapsin, <ref target="Pg155">155</ref>, <ref target="Pg156">156</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Stegomyia, <ref target="Pg403">403</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sternum, <ref target="Pg225">225</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Stomach, <ref target="Pg147">147</ref>.<lb /> +Mucous membrane of, <ref target="Pg147">147</ref>.<lb /> +Muscular action of, <ref target="Pg150">150</ref>.<lb /> +Muscular coat, <ref target="Pg148">148</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Serous coat, <ref target="Pg148">148</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Storage of nutriment, <ref target="Pg177">177</ref>-<ref target="Pg179">179</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">"Strenuous life," <ref target="Pg410">410</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Striated fibers, to show, <ref target="Pg261">261</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Striated muscles, to show, <ref target="Pg261">261</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Stroma, <ref target="Pg025">25</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sugars, kinds, <ref target="Pg120">120</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sulphur, <ref target="Pg135">135</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Supra-renal bodies, <ref target="Pg208">208</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Suspensory ligament, <ref target="Pg377">377</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sutures, <ref target="Pg230">230</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Sympathetic ganglia and nerves, <ref target="Pg298">298</ref>.<lb /> +Work of, <ref target="Pg316">316</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Synovial fluid, <ref target="Pg231">231</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Synovial membrane, <ref target="Pg231">231</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">System, defined, <ref target="Pg020">20</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Systole, <ref target="Pg046">46</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Taste buds, <ref target="Pg345">345</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tea,<lb /> +Effects on digestion, <ref target="Pg167">167</ref>.<lb /> +Effects on heart, <ref target="Pg056">56</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tears, <ref target="Pg383">383</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Teeth, <ref target="Pg142">142</ref>.<lb /> +Care of <ref target="Pg163">163</ref>.<lb /> +Kinds of, <ref target="Pg143">143</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Temperature,<lb /> +Body, <ref target="Pg207">207</ref>.<lb /> +Corpuscles, <ref target="Pg271">271</ref>, <ref target="Pg345">345</ref>.<lb /> +Sensation, <ref target="Pg343">343</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tendon of Achilles, <ref target="Pg256">256</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tendons, <ref target="Pg246">246</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tests for foods, <ref target="Pg136">136</ref>, <ref target="Pg137">137</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tetanus, <ref target="Pg262">262</ref>, <ref target="Pg275">275</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Thoracic cavity, <ref target="Pg007">7</ref>, <ref target="Pg085">85</ref>, <ref target="Pg100">100</ref>, <ref target="Pg102">102</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Thoracic duct, <ref target="Pg067">67</ref>, <ref target="Pg170">170</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Thorax, <ref target="Pg085">85</ref>.<lb /> +Bones of, <ref target="Pg225">225</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tissue enzymes, <ref target="Pg182">182</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tissues, <ref target="Pg004">4</ref>.<lb /> +Complex nature of, <ref target="Pg013">13</ref>.<lb /> +Defined, <ref target="Pg020">20</ref>.<lb /> +General purposes of, <ref target="Pg005">5</ref>.<lb /> +Kinds of, <ref target="Pg005">5</ref>, <ref target="Pg006">6</ref>.<lb /> +Observations on, <ref target="Pg012">12</ref>.<lb /> +Properties of, <ref target="Pg006">6</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tobacco, effect on heart, <ref target="Pg056">56</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">"Tobacco heart," <ref target="Pg056">56</ref>, <ref target="Pg333">333</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tongue, <ref target="Pg143">143</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tonic bath, <ref target="Pg273">273</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Touch, <ref target="Pg343">343</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Touch corpuscles, <ref target="Pg342">342</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Toxins, <ref target="Pg394">394</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Trachea, <ref target="Pg080">80</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Trypsin, <ref target="Pg155">155</ref>, <ref target="Pg156">156</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tuberculosis, <ref target="Pg090">90</ref>, <ref target="Pg092">92</ref>, <ref target="Pg094">94</ref>, <ref target="Pg098">98</ref>.<lb /> +How communicated, <ref target="Pg403">403</ref>.<lb /> +Outdoor treatment, <ref target="Pg098">98</ref>.<lb /> +To prevent, <ref target="Pg404">404</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Tympanum, <ref target="Pg359">359</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Typhoid fever, <ref target="Pg404">404</ref>, <ref target="Pg407">407</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Ulna, <ref target="Pg227">227</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Urea, <ref target="Pg110">110</ref>, <ref target="Pg205">205</ref>, <ref target="Pg207">207</ref>, <ref target="Pg210">210</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ureters, <ref target="Pg170">170</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Uriniferous tubules, <ref target="Pg203">203</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Vaccination, <ref target="Pg406">406</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Valves,<lb /> +Advantages of, in veins, <ref target="Pg049">49</ref>, <ref target="Pg063">63</ref>.<lb /> +Mitral, <ref target="Pg043">43</ref>.<lb /> +Position of, in veins, <ref target="Pg063">63</ref>.<lb /> +Purposes of, <ref target="Pg049">49</ref>, <ref target="Pg063">63</ref>.<lb /> +Tricuspid, <ref target="Pg043">43</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Veins, <ref target="Pg047">47</ref>.<lb /> +Functions of, <ref target="Pg051">51</ref>.<lb /> +Renal, <ref target="Pg202">202</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ventilation, <ref target="Pg094">94</ref>.<lb /> +Rules for, <ref target="Pg095">95</ref>, <ref target="Pg096">96</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Ventricles, <ref target="Pg042">42</ref>.<lb /> +To illustrate action of, <ref target="Pg062">62</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Vermiform appendix, <ref target="Pg158">158</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Vertebræ, <ref target="Pg223">223</ref>-<ref target="Pg225">225</ref>.<lb /> +Interlocking of, <ref target="Pg225">225</ref>.<lb /> +Joining of, <ref target="Pg224">224</ref>.<lb /> +Kinds, <ref target="Pg223">223</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Vestibule, <ref target="Pg361">361</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Villi, <ref target="Pg152">152</ref>.<lb /> +Parts of, <ref target="Pg173">173</ref>, <ref target="Pg174">174</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Visual perceptions, <ref target="Pg382">382</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Visual sensations, <ref target="Pg382">382</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Vitreous humor, <ref target="Pg378">378</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Vocal cords, <ref target="Pg355">355</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Voice, <ref target="Pg353">353</ref>-<ref target="Pg357">357</ref>.<lb /> +How produced, <ref target="Pg356">356</ref>.<lb /> +Pitch and intensity, <ref target="Pg356">356</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Voluntary action, <ref target="Pg311">311</ref>, <ref target="Pg312">312</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Voluntary action pathways, <ref target="Pg312">312</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Vomiting, <ref target="Pg151">151</ref>, <ref target="Pg152">152</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Waste material, passage from body, <ref target="Pg210">210</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Wastes, <ref target="Pg030">30</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Water,<lb /> +Importance of, <ref target="Pg123">123</ref>.<lb /> +Supply of, <ref target="Pg398">398</ref>.<lb /> +Value of, <ref target="Pg210">210</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Water-vapor, <ref target="Pg208">208</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">White corpuscles, <ref target="Pg027">27</ref>, <ref target="Pg028">28</ref>.<lb /> +Functions of, <ref target="Pg029">29</ref>.<lb /> +To examine, <ref target="Pg039">39</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Work,<lb /> +Hygienic value of, <ref target="Pg328">328</ref>, <ref target="Pg409">409</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Worry, <ref target="Pg211">211</ref>.</p> + +<milestone unit="tb" /> + +<p rend="text-indent: -2; margin-left: 2">Yellow fever, <ref target="Pg403">403</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Yellow marrow, <ref target="Pg218">218</ref>.</p> + +<p rend="text-indent: -2; margin-left: 2">Yellow spot, <ref target="Pg377">377</ref>.</p> + + +</div> + +</body> + +<back rend="page-break-before: right"> +<div> +<pgIf output="pdf"> + <then> + <div> + <divGen type="pgfooter" rend="page-break-before: right" /> + </div> + </then> + <else> + <div> + <head>Footnotes</head> + <divGen type="footnotes" /> + </div> + <div> + <divGen type="pgfooter" rend="page-break-before: right" /> + </div> + </else> +</pgIf> +</div> + +</back> +</text> +</TEI.2> + +<!-- +A WORD FROM PROJECT GUTENBERG + + +This file should be named 18779-0.tei. + +This and all associated files of various formats will be found in: + + + http://www.gutenberg.org/dirs/1/8/7/7/18779/ + + +Updated editions will replace the previous one — the old editions will be +renamed. + +Creating the works from public domain print editions means that no one +owns a United States copyright in these works, so the Foundation (and +you!) can copy and distribute it in the United States without permission +and without paying copyright royalties. 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