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diff --git a/phys-0.txt b/phys-0.txt new file mode 100644 index 0000000..be0ef4c --- /dev/null +++ b/phys-0.txt @@ -0,0 +1,16994 @@ +The Project Gutenberg EBook of A Practical Physiology, by Albert F. Blaisdell + +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 www.gutenberg.org + + +Title: A Practical Physiology + +Author: Albert F. Blaisdell + +Release Date: December 14, 2003 [EBook #10453] + +Language: English + +Character set encoding: UTF-8 + +*** START OF THIS PROJECT GUTENBERG EBOOK A PRACTICAL PHYSIOLOGY *** + + + + +Produced by Distributed Proofreaders + + + + + +[Transcriber's Note: Figures 162-167 have been renumbered. In the +original, Figure 162 was labeled as 161; 163 as 162; etc.] + + + + +A Practical Physiology + +A Text-Book for Higher Schools + +By + +Albert F. Blaisdell, M.D. + +Author of "Child's Book of Health," "How to Keep Well," +"Our Bodies and How We Live," Etc., Etc. + + + + +Preface. + + + +The author has aimed to prepare a text-book on human physiology for use in +higher schools. The design of the book is to furnish a practical manual of +the more important facts and principles of physiology and hygiene, which +will be adapted to the needs of students in high schools, normal schools, +and academies. + +Teachers know, and students soon learn to recognize the fact, that it is +impossible to obtain a clear understanding of the functions of the various +parts of the body without first mastering a few elementary facts about +their structure. The course adopted, therefore, in this book, is to devote +a certain amount of space to the anatomy of the several organs before +describing their functions. + +A mere knowledge of the facts which can be gained in secondary schools, +concerning the anatomy and physiology of the human body, is of little real +value or interest in itself. Such facts are important and of practical +worth to young students only so far as to enable them to understand the +relation of these facts to the great laws of health and to apply them to +daily living. Hence, it has been the earnest effort of the author in this +book, as in his other physiologies for schools, to lay special emphasis +upon such points as bear upon personal health. + +Physiology cannot be learned as it should be by mere book study. The +result will be meagre in comparison with the capabilities of the subject. +The study of the text should always be supplemented by a series of +practical experiments. Actual observations and actual experiments are as +necessary to illuminate the text and to illustrate important principles in +physiology as they are in botany, chemistry, or physics. Hence, as +supplementary to the text proper, and throughout the several chapters, a +series of carefully arranged and practical experiments has been added. For +the most part, they are simple and can be performed with inexpensive and +easily obtained apparatus. They are so arranged that some may be omitted +and others added as circumstances may allow. + +If it becomes necessary to shorten the course in physiology, the various +sections printed in smaller type may be omitted or used for home study. + +The laws of most of the states now require in our public schools the study +of the effects of alcoholic drinks, tobacco, and other narcotics upon the +bodily life. This book will be found to comply fully with all such laws. + +The author has aimed to embody in simple and concise language the latest +and most trustworthy information which can be obtained from the standard +authorities on modern physiology, in regard to the several topics. + +In the preparation of this text-book the author has had the editorial help +of his esteemed friend, Dr. J. E. Sanborn, of Melrose, Mass., and is also +indebted to the courtesy of Thomas E. Major, of Boston, for assistance in +revising the proofs. + +Albert F. Blaisdell. + +Boston, August, 1897. + + + + +Contents. + + + +Chapter I. Introduction +Chapter II. The Bones +Chapter III. The Muscles +Chapter IV. Physical Exercise +Chapter V. Food and Drink +Chapter VI. Digestion +Chapter VII. The Blood and Its Circulation +Chapter VIII. Respiration +Chapter IX. The Skin and the Kidneys +Chapter X. The Nervous System +Chapter XI. The Special Sense +Chapter XII. The Throat and the Voice +Chapter XIII. Accidents and Emergencies +Chapter XIV. In Sickness and in Health + Care of the Sick-Room; Poisons and their Antidotes; Bacteria; + Disinfectants; Management of Contagious Diseases. +Chapter XV. Experimental Work in Physiology + Practical Experiments; Use of the Microscope; Additional Experiments; + Surface Anatomy and Landmarks. + +Glossary + +Index + + + + +Chapter I. + +Introduction. + + + +1. The Study of Physiology. We are now to take up a new study, and in +a field quite different from any we have thus far entered. Of all our +other studies,--mathematics, physics, history, language,--not one comes +home to us with such peculiar interest as does physiology, because +this is the study of ourselves. + +Every thoughtful young person must have asked himself a hundred questions +about the problems of human life: how it can be that the few articles of +our daily food--milk, bread, meats, and similar things--build up our +complex bodies, and by what strange magic they are transformed into hair, +skin, teeth, bones, muscles, and blood. + +How is it that we can lift these curtains of our eyes and behold all the +wonders of the world around us, then drop the lids, and though at noonday, +are instantly in total darkness? How does the minute structure of the ear +report to us with equal accuracy the thunder of the tempest, and the hum +of the passing bee? Why is breathing so essential to our life, and why +cannot we stop breathing when we try? Where within us, and how, burns the +mysterious fire whose subtle heat warms us from the first breath of +infancy till the last hour of life? + +These and scores of similar questions it is the province of this deeply +interesting study of physiology to answer. + +2. What Physiology should Teach us. The study of physiology is not +only interesting, but it is also extremely useful. Every reasonable person +should not only wish to acquire the knowledge how best to protect and +preserve his body, but should feel a certain profound respect for an +organism so wonderful and so perfect as his physical frame. For our bodies +are indeed not ourselves, but the frames that contain us,--the ships in +which we, the real selves, are borne over the sea of life. He must be +indeed a poor navigator who is not zealous to adorn and strengthen his +ship, that it may escape the rocks of disease and premature decay, and +that the voyage of his life may be long, pleasant, and successful. + +But above these thoughts there rises another,--that in studying physiology +we are tracing the myriad lines of marvelous ingenuity and forethought, as +they appear at every glimpse of the work of the Divine Builder. However +closely we study our bodily structure, we are, at our best, but imperfect +observers of the handiwork of Him who made us as we are. + +3. Distinctive Characters of Living Bodies. Even a very meagre +knowledge of the structure and action of our bodies is enough to reveal +the following distinctive characters: our bodies are continually +breathing, that is, they take in oxygen from the surrounding air; they +take in certain substances known as food, similar to those composing the +body, which are capable through a process called oxidation, or through +other chemical changes, of setting free a certain amount of energy. + +Again, our bodies are continually making heat and giving it out to +surrounding objects, the production and the loss of heat being so adjusted +that the whole body is warm, that is, of a temperature higher than that of +surrounding objects. Our bodies, also, move themselves, either one part +on another, or the whole body from place to place. The motive power is not +from the outside world, but the energy of their movements exists in the +bodies themselves, influenced by changes in their surroundings. Finally, +our bodies are continually getting rid of so-called waste matters, which +may be considered products of the oxidation of the material used as food, +or of the substances which make up the organism. + +4. The Main Problems of Physiology briefly Stated. We shall learn in +a subsequent chapter that the living body is continually losing energy, +but by means of food is continually restoring its substance and +replenishing its stock of energy. A great deal of energy thus stored up is +utilized as mechanical work, the result of physical movements. We shall +learn later on that much of the energy which at last leaves the body as +heat, exists for a time within the organism in other forms than heat, +though eventually transformed into heat. Even a slight change in the +surroundings of the living body may rapidly, profoundly, and in special +ways affect not only the amount, but the kind of energy set free. Thus the +mere touch of a hair may lead to such a discharge of energy, that a body +previously at rest may be suddenly thrown into violent convulsions. This +is especially true in the case of tetanus, or lockjaw. + +The main problem we have to solve in the succeeding pages is to ascertain +how it is that our bodies can renew their substance and replenish the +energy which they are continually losing, and can, according to the nature +of their surroundings, vary not only the amount, but the kind of energy +which they set free. + +5. Technical Terms Defined. All living organisms are studied usually +from two points of view: first, as to their form and structure; second, as +to the processes which go on within them. The science which treats of all +living organisms is called biology. It has naturally two +divisions,--morphology, which treats of the form and structure of +living beings, and physiology, which investigates their functions, or +the special work done in their vital processes. + +The word anatomy, however, is usually employed instead of morphology. +It is derived from two Greek words, and means the science of dissection. +Human anatomy then deals with the form and structure of the human +body, and describes how the different parts and organs are arranged, as +revealed by observation, by dissection, and by the microscope. + +Histology is that part of anatomy which treats of the minute +structure of any part of the body, as shown by the microscope. + +Human physiology describes the various processes that go on in the +human body in health. It treats of the work done by the various parts of +the body, and of the results of the harmonious action of the several +organs. Broadly speaking, physiology is the science which treats of +functions. By the word function is meant the special work which an +organ has to do. An organ is a part of the body which does a special +work. Thus the eye is the organ of sight, the stomach of digestion, and +the lungs of breathing. + +It is plain that we cannot understand the physiology of our bodies without +a knowledge of their anatomy. An engineer could not understand the working +of his engine unless well acquainted with all its parts, and the manner in +which they were fitted together. So, if we are to understand the +principles of elementary physiology, we must master the main anatomical +facts concerning the organs of the body before considering their special +functions. + +As a branch of study in our schools, physiology aims to make clear certain +laws which are necessary to health, so that by a proper knowledge of them, +and their practical application, we may hope to spend happier and more +useful, because healthier, lives. In brief, the study of hygiene, or +the science of health, in the school curriculum, is usually associated +with that of physiology.[1] + +6. Chemical Elements in the Body. All of the various complex +substances found in nature can be reduced by chemical analysis to about 70 +elements, which cannot be further divided. By various combinations of +these 70 elements all the substances known to exist in the world of nature +are built up. When the inanimate body, like any other substance, is +submitted to chemical analysis, it is found that the bone, muscle, teeth, +blood, etc., may be reduced to a few chemical elements. + +In fact, the human body is built up with 13 of the 70 elements, namely: +oxygen, hydrogen, nitrogen, chlorine, fluorine, carbon, phosphorus, +sulphur, calcium, potassium, sodium, magnesium, and iron. Besides +these, a few of the other elements, as silicon, have been found; but they +exist in extremely minute quantities. + +The following table gives the proportion in which these various elements +are present: + + Oxygen 62.430 per cent + Carbon 21.150 " " + Hydrogen 9.865 " " + Nitrogen 3.100 " " + Calcium 1.900 " " + Phosphorus 0.946 " " + Potassium 0.230 " " + Sulphur 0.162 " " + Chlorine 0.081 " " + Sodium 0.081 " " + Magnesium 0.027 " " + Iron 0.014 " " + Fluorine 0.014 " " + ----- + 100.000 + +As will be seen from this table, oxygen, hydrogen, and nitrogen, which are +gases in their uncombined form, make up ¾ of the weight of the whole +human body. Carbon, which exists in an impure state in charcoal, forms +more than ⅕ of the weight of the body. Thus carbon and the three gases +named, make up about 96 per cent of the total weight of the body. + +7. Chemical Compounds in the Body. We must keep in mind that, with +slight exceptions, none of these 13 elements exist in their elementary +form in the animal economy. They are combined in various proportions, the +results differing widely from the elements of which they consist. Oxygen +and hydrogen unite to form water, and water forms more than ⅔ of the +weight of the whole body. In all the fluids of the body, water acts as a +solvent, and by this means alone the circulation of nutrient material is +possible. All the various processes of secretion and nutrition depend on +the presence of water for their activities. + +8. Inorganic Salts. A large number of the elements of the body unite +one with another by chemical affinity and form inorganic salts. Thus +sodium and chlorine unite and form chloride of sodium, or common salt. +This is found in all the tissues and fluids, and is one of the most +important inorganic salts the body contains. It is absolutely necessary +for continued existence. By a combination of phosphorus with sodium, +potassium, calcium, and magnesium, the various phosphates are formed. + +The phosphates of lime and soda are the most abundant of the salts of the +body. They form more than half the material of the bones, are found in the +teeth and in other solids and in the fluids of the body. The special place +of iron is in the coloring matter of the blood. Its various salts are +traced in the ash of bones, in muscles, and in many other tissues and +fluids. These compounds, forming salts or mineral matters that exist in +the body, are estimated to amount to about 6 per cent of the entire +weight. + +9. Organic Compounds. Besides the inorganic materials, there exists +in the human body a series of compound substances formed of the union of +the elements just described, but which require the agency of living +structures. They are built up from the elements by plants, and are called +organic. Human beings and the lower animals take the organized +materials they require, and build them up in their own bodies into still +more highly organized forms. + +The organic compounds found in the body are usually divided into three +great classes: + + 1. Proteids, or albuminous substances. + 2. Carbohydrates (starches, sugars, and gums). + 3. Fats. + +The extent to which these three great classes of organic materials of the +body exist in the animal and vegetable kingdoms, and are utilized for the +food of man, will be discussed in the chapter on food (Chapter V.). The +Proteids, because they contain the element nitrogen and the others do +not, are frequently called nitrogenous, and the other two are known +as non-nitrogenous substances. The proteids, the type of which is egg +albumen, or the white of egg, are found in muscle and nerve, in glands, in +blood, and in nearly all the fluids of the body. A human body is estimated +to yield on an average about 18 per cent of albuminous substances. In the +succeeding chapters we shall have occasion to refer to various and allied +forms of proteids as they exist in muscle (myosin), coagulated blood +(fibrin), and bones (gelatin). + +The Carbohydrates are formed of carbon, hydrogen, and oxygen, the +last two in the proportion to form water. Thus we have animal starch, or +glycogen, stored up in the liver. Sugar, as grape sugar, is also found in +the liver. The body of an average man contains about 10 per cent of +Fats. These are formed of carbon, hydrogen, and oxygen, in which the +latter two are not in the proportion to form water. The fat of the body +consists of a mixture which is liquid at the ordinary temperature. + +Now it must not for one moment be supposed that the various chemical +elements, as the proteids, the salts, the fats, etc., exist in the body in +a condition to be easily separated one from another. Thus a piece of +muscle contains all the various organic compounds just mentioned, but they +are combined, and in different cases the amount will vary. Again, fat may +exist in the muscles even though it is not visible to the naked eye, and a +microscope is required to show the minute fat cells. + +10. Protoplasm. The ultimate elements of which the body is composed +consist of "masses of living matter," microscopic in size, of a material +commonly called protoplasm.[2] In its simplest form protoplasm +appears to be a homogeneous, structureless material, somewhat resembling +the raw white of an egg. It is a mixture of several chemical substances +and differs in appearance and composition in different parts of the body. + +Protoplasm has the power of appropriating nutrient material, of dividing +and subdividing, so as to form new masses like itself. When not built into +a tissue, it has the power of changing its shape and of moving from place +to place, by means of the delicate processes which it puts forth. Now, +while there are found in the lowest realm of animal life, organisms like +the amœba of stagnant pools, consisting of nothing more than minute +masses of protoplasm, there are others like them which possess a small +central body called a nucleus. This is known as nucleated protoplasm. + +[Illustration: Fig. 1.--Diagram of a Cell. + + A, nucleus; + B, nucleolus; + C, protoplasm. (Highly magnified) +] + +11. Cells. When we carry back the analysis of an organized body as +far as we can, we find every part of it made up of masses of nucleated +protoplasm of various sizes and shapes. In all essential features these +masses conform to the type of protoplasmic matter just described. Such +bodies are called cells. In many cells the nucleus is finely granular or +reticulated in appearance, and on the threads of the meshwork may be one +or more enlargements, called nucleoli. In some cases the protoplasm at the +circumference is so modified as to give the appearance of a limiting +membrane called the cell wall. In brief, then, a cell is a mass of +nucleated protoplasm; the nucleus may have a nucleolus, and the cell +may be limited by a cell wall. Every tissue of the human body is formed +through the agency of protoplasmic cells, although in most cases the +changes they undergo are so great that little evidence remains of their +existence. + +There are some organisms lower down in the scale, whose whole activity is +confined within the narrow limits of a single cell. Thus, the amœba +begins its life as a cell split off from its parent. This divides in its +turn, and each half is a complete amœba. When we come a little higher +than the amœba, we find organisms which consist of several cells, and a +specialization of function begins to appear. As we ascend in the animal +scale, specialization of structure and of function is found continually +advancing, and the various kinds of cells are grouped together into +colonies or organs. + +12. Cells and the Human Organism. If the body be studied in its +development, it is found to originate from a single mass of nucleated +protoplasm, a single cell with a nucleus and nucleolus. From this +original cell, by growth and development, the body, with all its various +tissues, is built up. Many fully formed organs, like the liver, consist +chiefly of cells. Again, the cells are modified to form fibers, such as +tendon, muscle, and nerve. Later on, we shall see the white blood +corpuscles exhibit all the characters of the amœba (Fig. 2). Even such +dense structures as bone, cartilage, and the teeth are formed from cells. + +[Illustration: Fig. 2.--Amœboid Movement of a Human White Blood +Corpuscle. (Showing various phases of movement.)] + +In short, cells may be regarded as the histological units of animal +structures; by the combination, association, and modification of these +the body is built up. Of the real nature of the changes going on within +the living protoplasm, the process of building up lifeless material into +living structures, and the process of breaking down by which waste is +produced, we know absolutely nothing. Could we learn that, perhaps we +should know the secret of life. + +13. Kinds of Cells. Cells vary greatly in size, some of the smallest +being only 1/3500 an inch or less in diameter. They also vary greatly in +form, as may be seen in Figs. 3 and 5. The typical cell is usually +_globular_ in form, other shapes being the result of pressure or of +similar modifying influences. The globular, as well as the large, flat +cells, are well shown in a drop of saliva. Then there are the _columnar_ +cells, found in various parts of the intestines, in which they are closely +arranged side by side. These cells sometimes have on the free surface +delicate prolongations called cilia. Under the microscope they resemble a +wave, as when the wind blows over a field of grain (Fig. 5). There are +besides cells known as _spindle, stellate, squamous_ or pavement, and +various other names suggested by their shapes. Cells are also described as +to their contents. Thus _fat_ and _pigment_ cells are alluded to in +succeeding sections. Again, they may be described as to their functions or +location or the tissue in which they are found, as _epithelial_ cells, +_blood_ cells (corpuscles, Figs. 2 and 66), _nerve_ cells (Fig. 4), and +_connective-tissue_ cells. + +14. Vital Properties of Cells. Each cell has a life of its own. It +manifests its vital properties in that it is born, grows, multiplies, +decays, and at last dies.[3] During its life it assimilates food, works, +rests, and is capable of spontaneous motion and frequently of locomotion. +The cell can secrete and excrete substance, and, in brief, presents nearly +all the phenomena of a human being. + +Cells are produced only from cells by a process of self-division, +consisting of a cleavage of the whole cell into parts, each of which +becomes a separate and independent organism. Cells rapidly increase in +size up to a certain definite point which they maintain during adult life. +A most interesting quality of cell life is motion, a beautiful form of +which is found in ciliated epithelium. Cells may move actively and +passively. In the blood the cells are swept along by the current, but the +white corpuscles, seem able to make their way actively through the +tissues, as if guided by some sort of instinct. + +[Illustration: Fig. 3.--Various Forms of Cells. + + A, columnar cells found lining various parts of the intestines (called + _columnar epithelium_); + B, cells of a fusiform or spindle shape found in the loose tissue under + the skin and in other parts (called _connective-tissue cells_); + C, cell having many processes or projections--such are found in + connective tissue, D, primitive cells composed of protoplasm with + nucleus, and having no cell wall. All are represented about 400 times + their real size. +] + +Some cells live a brief life of 12 to 24 hours, as is probably the case +with many of the cells lining the alimentary canal; others may live for +years, as do the cells of cartilage and bone. In fact each cell goes +through the same cycle of changes as the whole organism, though doubtless +in a much shorter time. The work of cells is of the most varied kind, and +embraces the formation of every tissue and product,--solid, liquid, or +gaseous. Thus we shall learn that the cells of the liver form bile, those +of the salivary glands and of the glands of the stomach and pancreas form +juices which aid in the digestion of food. + +15. The Process of Life. All living structures are subject to +constant decay. Life is a condition of incessant changes, dependent upon +two opposite processes, repair and decay. Thus our bodies are not +composed of exactly the same particles from day to day, or even from one +moment to another, although to all appearance we remain the same +individuals. The change is so gradual, and the renewal of that which is +lost may be so exact, that no difference can be noticed except at long +intervals of time.[4] (See under "Bacteria," Chapter XIV.) + +The entire series of chemical changes that take place in the living body, +beginning with assimilation and ending with excretion, is included in one +word, metabolism. The process of building up living material, or the +change by which complex substances (including the living matter itself) +are built up from simpler materials, is called anabolism. The +breaking down of material into simple products, or the changes in which +complex materials (including the living substance) are broken down into +comparatively simple products, is known as katabolism. This reduction +of complex substances to simple, results in the production of animal force +and energy. Thus a complex substance, like a piece of beef-steak, is built +up of a large number of molecules which required the expenditure of force +or energy to store up. Now when this material is reduced by the process of +digestion to simpler bodies with fewer molecules, such as carbon dioxid, +urea, and water, the force stored up in the meat as potential energy +becomes manifest and is used as active life-force known as _kinetic +energy_. + +16. Epithelium. Cells are associated and combined in many ways to +form a simple tissue. Such a simple tissue is called an epithelium or +surface-limiting tissue, and the cells are known as epithelial +cells. These are united by a very small amount of a cement substance which +belongs to the proteid class of material. The epithelial cells, from their +shape, are known as squamous, columnar, glandular, or ciliated. Again, the +cells may be arranged in only a single layer, or they may be several +layers deep. In the former case the epithelium is said to be simple; in +the latter, stratified. No blood-vessels pass into these tissues; the +cells derive their nourishment by the imbibition of the plasma of the +blood exuded into the subjacent tissue. + +[Illustration: Fig. 4.--Nerve Cells from the Gray Matter of the +Cerebellum. (Magnified 260 diameters.)] + +17. Varieties of Epithelium. The squamous or pavement epithelium +consists of very thin, flattened scales, usually with a small nucleus in +the center. When the nucleus has disappeared, they become mere horny +plates, easily detached. Such cells will be described as forming the outer +layer of the skin, the lining of the mouth and the lower part of the +nostrils. + +The columnar epithelium consists of pear-shaped or elongated cells, +frequently as a single layer of cells on the surface of a mucous membrane, +as on the lining of the stomach and intestines, and the free surface of +the windpipe and large air-tubes. + +The glandular or spheroidal epithelium is composed of round cells or +such as become angular by mutual pressure. This kind forms the lining of +glands such as the liver, pancreas, and the glands of the skin. + +The ciliated epithelium is marked by the presence of very fine +hair-like processes called cilia, which develop from the free end of the +cell and exhibit a rapid whip-like movement as long as the cell is alive. +This motion is always in the same direction, and serves to carry away +mucus and even foreign particles in contact with the membrane on which +the cells are placed. This epithelium is especially common in the air +passages, where it serves to keep a free passage for the entrance and exit +of air. In other canals a similar office is filled by this kind of +epithelium. + +18. Functions of Epithelial Tissues. The epithelial structures may be +divided, as to their functions, into two main divisions. One is chiefly +protective in character. Thus the layers of epithelium which form the +superficial layer of the skin have little beyond such an office to +discharge. The same is to a certain extent true of the epithelial cells +covering the mucous membrane of the mouth, and those lining the air +passages and air cells of the lungs. + +[Illustration: Fig. 5.--Various Kinds of Epithelial Cells + + A, columnar cells of intestine; + B, polyhedral cells of the conjunctiva; + C, ciliated conical cells of the trachea; + D, ciliated cell of frog's mouth; + E, inverted conical cell of trachea; + F, squamous cell of the cavity of mouth, seen from its broad surface; + G, squamous cell, seen edgeways. +] + +The second great division of the epithelial tissues consists of those +whose cells are formed of highly active protoplasm, and are busily engaged +in some sort of secretion. Such are the cells of glands,--the cells of the +salivary glands, which secrete the saliva, of the gastric glands, which +secrete the gastric juice, of the intestinal glands, and the cells of the +liver and sweat glands. + +19. Connective Tissue. This is the material, made up of fibers and +cells, which serves to unite and bind together the different organs and +tissues. It forms a sort of flexible framework of the body, and so +pervades every portion that if all the other tissues were removed, we +should still have a complete representation of the bodily shape in every +part. In general, the connective tissues proper act as packing, +binding, and supporting structures. This name includes certain tissues +which to all outward appearance vary greatly, but which are properly +grouped together for the following reasons: first, they all act as +supporting structures; second, under certain conditions one may be +substituted for another; third, in some places they merge into each other. + +All these tissues consist of a ground-substance, or matrix, cells, and +fibers. The ground-substance is in small amount in connective tissues +proper, and is obscured by a mass of fibers. It is best seen in hyaline +cartilage, where it has a glossy appearance. In bone it is infiltrated +with salts which give bone its hardness, and make it seem so unlike other +tissues. The cells are called connective-tissue corpuscles, cartilage +cells, and bone corpuscles, according to the tissues in which they occur. +The fibers are the white fibrous and the yellow elastic tissues. + +The following varieties are usually described: + + I. Connective Tissues Proper: + + 1. White Fibrous Tissue. + 2. Yellow Elastic Tissue. + 3. Areolar or Cellular Tissue. + 4. Adipose or Fatty Tissue. + 5. Adenoid or Retiform Tissue. + + II. Cartilage (Gristle): + + 1. Hyaline. + 2. White Fibro-cartilage. + 3. Yellow Fibro-cartilage. + + III. Bone and Dentine of Teeth. + +20. White Fibrous Tissue. This tissue consists of bundles of very +delicate fibrils bound together by a small amount of cement substance. +Between the fibrils protoplasmic masses (connective-tissue corpuscles) +are found. These fibers may be found so interwoven as to form a sheet, as +in the periosteum of the bone, the fasciæ around muscles, and the capsules +of organs; or they may be aggregated into bundles and form rope-like +bands, as in the ligaments of joints and the tendons of muscles. On +boiling, this tissue yields gelatine. In general, where white fibrous +tissue abounds, structures are held together, and there is flexibility, +but little or no distensibility. + +[Illustration: Fig. 6.--White Fibrous Tissue. (Highly magnified.)] + +21. Yellow Elastic Tissue. The fibers of yellow elastic tissue +are much stronger and coarser than those of the white. They are yellowish, +tend to curl up at the ends, and are highly elastic. It is these fibers +which give elasticity to the skin and to the coats of the arteries. The +typical form of this tissue occurs in the ligaments which bind the +vertebræ together (Fig. 26), in the true vocal cords, and in certain +ligaments of the larynx. In the skin and fasciæ, the yellow elastic is +found mixed with white fibrous and areolar tissues. It does not yield +gelatine on boiling, and the cells are, if any, few. + +[Illustration: Fig. 7.--Yellow Elastic Tissue. (Highly magnified.)] + +22. Areolar or Cellular Tissue. This consists of bundles of delicate +fibers interlacing and crossing one another, forming irregular spaces or +meshes. These little spaces, in health, are filled with fluid that has +oozed out of the blood-vessels. The areolar tissue forms a protective +covering for the tissues of delicate and important organs. + +23. Adipose or Fatty Tissue. In almost every part of the body the +ordinary areolar tissue contains a variable quantity of adipose or +fatty tissue. Examined by the microscope, the fat cells consist of a +number of minute sacs of exceedingly delicate, structureless membrane +filled with oil. This is liquid in life, but becomes solidified after +death. This tissue is plentiful beneath the skin, in the abdominal cavity, +on the surface of the heart, around the kidneys, in the marrow of bones, +and elsewhere. Fat serves as a soft packing material. Being a poor +conductor, it retains the heat, and furnishes a store rich in carbon and +hydrogen for use in the body. + +24. Adenoid or Retiform Tissue. This is a variety of connective +tissue found in the tonsils, spleen, lymphatic glands, and allied +structures. It consists of a very fine network of cells of various sizes. +The tissue combining them is known as adenoid or gland-like tissue. + +[Illustration: Fig. 8.--Fibro-Cartilage Fibers. (Showing network +surrounded cartilage cells.)] + +25. Cartilage. Cartilage, or gristle, is a tough but highly elastic +substance. Under the microscope cartilage is seen to consist of a +matrix, or base, in which nucleated cells abound, either singly or in +groups. It has sometimes a fine ground-glass appearance, when the +cartilage is spoken of as hyaline. In other cases the matrix is +almost replaced by white fibrous tissue. This is called white +fibro-cartilage, and is found where great strength and a certain +amount of rigidity are required. + +Again, there is between the cells a meshwork of yellow elastic fibers, and +this is called yellow fibro-cartilage (Fig. 8). The hyaline cartilage +forms the early state of most of the bones, and is also a permanent +coating for the articular ends of long bones. The white fibro-cartilage is +found in the disks between the bodies of the vertebræ, in the interior of +the knee joint, in the wrist and other joints, filling the cavities of the +bones, in socket joints, and in the grooves for tendons. The yellow +fibro-cartilage forms the expanded part of the ear, the epiglottis, and +other parts of the larynx. + +26. General Plan of the Body. To get a clearer idea of the general +plan on which the body is constructed, let us imagine its division into +perfectly equal parts, one the right and the other the left, by a great +knife severing it through the median, or middle line in front, backward +through the spinal column, as a butcher divides an ox or a sheep into +halves for the market. In a section of the body thus planned the skull and +the spine together are shown to have formed a tube, containing the brain +and spinal cord. The other parts of the body form a second tube (ventral) +in front of the spinal or dorsal tube. The upper part of the second tube +begins with the mouth and is formed by the ribs and breastbone. Below the +chest in the abdomen, the walls of this tube would be made up of the soft +parts. + +[Illustration: Fig. 9.--Diagrammatic Longitudinal Section of the Trunk and +Head. (Showing the dorsal and the ventral tubes.) + + A, the cranial cavity; + B, the cavity of the nose; + C, the mouth; + D, the alimentary canal represented as a simple straight tube; + E, the sympathetic nervous system; + F, heart; + G, diaphragm; + H, stomach; + K, end of spinal portion of cerebro-spinal nervous system. +] + +We may say, then, that the body consists of two tubes or cavities, +separated by a bony wall, the dorsal or nervous tube, so called +because it contains the central parts of the nervous system; and the +visceral or ventral tube, as it contains the viscera, or general +organs of the body, as the alimentary canal, the heart, the lungs, the +sympathetic nervous system, and other organs. + +The more detailed study of the body may now be begun by a description of +the skeleton or framework which supports the soft parts. + + + +Experiments. + + +For general directions and explanations and also detailed suggestions for +performing experiments, see Chapter XV. + + Experiment 1. _To examine squamous epithelium._ With an ivory + paper-knife scrape the back of the tongue or the inside of the lips or + cheek; place the substance thus obtained upon a glass slide; cover it + with a thin cover-glass, and if necessary add a drop of water. Examine + with the microscope, and the irregularly formed epithelial cells will be + seen. + + Experiment 2. _To examine ciliated epithelium._ Open a frog's + mouth, and with the back of a knife blade gently scrape a little of the + membrane from the roof of the mouth. Transfer to a glass slide, add a + drop of salt solution, and place over it a cover-glass with a hair + underneath to prevent pressure upon the cells. Examine with a microscope + under a high power. The cilia move very rapidly when quite fresh, and + are therefore not easily seen. + +For additional experiments which pertain to the microscopic examination of +the elementary tissues and to other points in practical histology, see +Chapter XV. + + [NOTE. Inasmuch as most of the experimental work of this chapter + depends upon the use of the microscope and also necessarily assumes a + knowledge of facts which are discussed later, it would be well to + postpone experiments in histology until they can be more + satisfactorily handled in connection with kindred topics as they are + met with in the succeeding chapters.] + + + + +Chapter II. + +The Bones. + + + +27. The Skeleton. Most animals have some kind of framework to support +and protect the soft and fleshy parts of their bodies. This framework +consists chiefly of a large number of bones, and is called the +skeleton. It is like the keel and ribs of a vessel or the frame of a +house, the foundation upon which the bodies are securely built. + +There are in the adult human body 200 distinct bones, of many sizes and +shapes. This number does not, however, include several small bones found +in the tendons of muscles and in the ear. The teeth are not usually +reckoned as separate bones, being a part of the structure of the skin. + +The number of distinct bones varies at different periods of life. It is +greater in childhood than in adults, for many bones which are then +separate, to allow growth, afterwards become gradually united. In early +adult life, for instance, the skull contains 22 naturally separate bones, +but in infancy the number is much greater, and in old age far less. + +The bones of the body thus arranged give firmness, strength, and +protection to the soft tissues and vital organs, and also form levers for +the muscles to act upon. + +28. Chemical Composition of Bone. The bones, thus forming the +framework of the body, are hard, tough, and elastic. They are twice as +strong as oak; one cubic inch of compact bone will support a weight of +5000 pounds. Bone is composed of earthy or mineral matter +(chiefly in the form of lime salts), and of animal matter +(principally gelatine), in the proportion of two-thirds of the former to +one-third of the latter. + +[Illustration: Fig. 10.--The Skeleton.] + +The proportion of earthy to animal matter varies with age. In infancy the +bones are composed almost wholly of animal matter. Hence, an infant's +bones are rarely broken, but its legs may soon become misshapen if walking +is allowed too early. In childhood, the bones still contain a larger +percentage of animal matter than in more advanced life, and are therefore +more liable to bend than to break; while in old age, they contain a +greater percentage of mineral matter, and are brittle and easily broken. + + Experiment 3. _To show the mineral matter in bone_. Weigh a large + soup bone; put it on a hot, clear fire until it is at a red heat. At + first it becomes black from the carbon of its organic matter, but at + last it turns white. Let it cool and weigh again. The animal matter has + been burnt out, leaving the mineral or earthy part, a white, brittle + substance of exactly the same shape, but weighing only about two-thirds + as much as the bone originally weighed. + + Experiment 4. _To show the animal matter in bone_. Add a + teaspoonful of muriatic acid to a pint of water, and place the mixture + in a shallow earthen dish. Scrape and clean a chicken's leg bone, part + of a sheep's rib, or any other small, thin bone. Soak the bone in the + acid mixture for a few days. The earthy or mineral matter is slowly + dissolved, and the bone, although retaining its original form, loses its + rigidity, and becomes pliable, and so soft as to be readily cut. If the + experiment be carefully performed, a long, thin bone may even be tied + into a knot. + + [Illustration: Fig. 11.--The fibula tied into a knot, after the hard + mineral matter has been dissolved by acid.] + +29. Physical Properties of Bone. If we take a leg bone of a sheep, or +a large end of beef shin bone, and saw it lengthwise in halves, we see two +distinct structures. There is a hard and compact tissue, like ivory, +forming the outside shell, and a spongy tissue inside having the +appearance of a beautiful lattice work. Hence this is called cancellous +tissue, and the gradual transition from one to the other is apparent. + +It will also be seen that the shaft is a hollow cylinder, formed of +compact tissue, enclosing a cavity called the medullary canal, which is +filled with a pulpy, yellow fat called _marrow_. The marrow is richly +supplied with blood-vessels, which enter the cavity through small openings +in the compact tissue. In fact, all over the surface of bone are minute +canals leading into the substance. One of these, especially constant and +large in many bones, is called the _nutrient foramen_, and transmits an +artery to nourish the bone. + +At the ends of a long bone, where it expands, there is no medullary canal, +and the bony tissue is spongy, with only a thin layer of dense bone around +it. In flat bones we find two layers or plates of compact tissue at the +surface, and a spongy tissue between. Short and irregular bones have no +medullary canal, only a thin shell of dense bone filled with cancellous +tissue. + +[Illustration: Fig 12.--The Right femur sawed in two, lengthwise. (Showing +arrangement of compact and cancellous tissue.)] + + Experiment 5. Obtain a part of a beef shin bone, or a portion of a + sheep's or calf's leg, including if convenient the knee joint. Have the + bone sawed in two, lengthwise, keeping the marrow in place. Boil, + scrape, and carefully clean one half. Note the compact and spongy parts, + shaft, etc. + + Experiment 6. Trim off the flesh from the second half. Note the + pinkish white appearance of the bone, the marrow, and the tiny specks of + blood, etc. Knead a small piece of the marrow in the palm; note the oily + appearance. Convert some marrow into a liquid by heating. Contrast this + fresh bone with an old dry one, as found in the fields. Fresh bones + should be kept in a cool place, carefully wrapped in a damp cloth, while + waiting for class use. + +A fresh or living bone is covered with a delicate, tough, fibrous +membrane, called the periosteum. It adheres very closely to the bone, +and covers every part except at the joints and where it is protected with +cartilage. The periosteum is richly supplied with blood-vessels, and plays +a chief part in the growth, formation, and repair of bone. If a portion of +the periosteum be detached by injury or disease, there is risk that a +layer of the subjacent bone will lose its vitality and be cast off.[5] + +30. Microscopic Structure of Bone. If a very thin slice of bone be +cut from the compact tissue and examined under a microscope, numerous +minute openings are seen. Around these are arranged rings of bone, with +little black bodies in them, from which radiate fine, dark lines. These +openings are sections of canals called _Haversian canals_, after Havers, +an English physician, who first discovered them. The black bodies are +minute cavities called _lacunæ_, while the fine lines are very minute +canals, _canaliculi_, which connect the lacunæ and the Haversian canals. +These Haversian canals are supplied with tiny blood-vessels, while the +lacunæ contain bone cells. Very fine branches from these cells pass into +the canaliculi. The Haversian canals run lengthwise of the bone; hence if +the bone be divided longitudinally these canals will be opened along their +length (Fig. 13). + +Thus bones are not dry, lifeless substances, but are the very type of +activity and change. In life they are richly supplied with blood from the +nutrient artery and from the periosteum, by an endless network of +nourishing canals throughout their whole structure. Bone has, therefore, +like all other living structures, a _self-formative_ power, and draws from +the blood the materials for its own nutrition. + +[Illustration: Fig. 13. + + A, longitudinal section of bone, by which the Haversian canals are seen + branching and communicating with one another; + B, cross section of a very thin slice of bone, magnified about 300 + diameters--little openings (Haversian canals) are seen, and around + them are ranged rings of bones with little black bodies (lacunæ), from + which branch out fine dark lines (canaliculi); + C, a bone cell, highly magnified, lying in lacuna. +] + + + +The Bones of the Head. + + +31. The Head, or Skull. The bones of the skeleton, the bony framework +of our bodies, may be divided into those of the head, the trunk, +and the limbs. + +The bones of the head are described in two parts,--those of the +cranium, or brain-case, and those of the face. Taken together, +they form the skull. The head is usually said to contain 22 bones, of +which 8 belong to the cranium and 14 to the face. In early childhood, the +bones of the head are separate to allow the brain to expand; but as we +grow older they gradually unite, the better to protect the delicate brain +tissue. + +32. The Cranium. The cranium is a dome-like structure, made up +in the adult of 8 distinct bones firmly locked together. These bones are: + + One Frontal, + Two Parietal, + Two Temporal + One Occipital, + One Sphenoid, + One Ethmoid. + +The frontal bone forms the forehead and front of the head. It is +united with the two parietal bones behind, and extends over the forehead +to make the roofs of the sockets of the eyes. It is this bone which, in +many races of man, gives a dignity of person and a beauty of form seen in +no other animal. + +The parietal bones form the sides and roof of the skull. They are +bounded anteriorly by the frontal bone, posteriorly by the occipital, and +laterally by the temporal and sphenoid bones. The two bones make a +beautiful arch to aid in the protection of the brain. + +The temporal bones, forming the temples on either side, are attached +to the sphenoid bone in front, the parietals above, and the occipital +behind. In each temporal bone is the cavity containing the organs of +hearing. These bones are so called because the hair usually first turns +gray over them. + +The occipital bone forms the lower part of the base of the skull, as +well as the back of the head. It is a broad, curved bone, and rests on the +topmost vertebra (atlas) of the backbone; its lower part is pierced by a +large oval opening called the _foramen magnum_, through which the spinal +cord passes from the brain (Fig. 15). + +The sphenoid bone is in front of the occipital, forming a part of the +base of the skull. It is wedged between the bones of the face and those of +the cranium, and locks together fourteen different bones. It bears a +remarkable resemblance to a bat with extended wings, and forms a series of +girders to the arches of the cranium. + +The ethmoid bone is situated between the bones of the cranium and +those of the face, just at the root of the nose. It forms a part of the +floor of the cranium. It is a delicate, spongy bone, and is so called +because it is perforated with numerous holes like a sieve, through which +the nerves of smell pass from the brain to the nose. + +[Illustration: Fig. 14.--The Skull] + +33. The Face. The bones of the face serve, to a marked extent, in +giving form and expression to the human countenance. Upon these bones +depend, in a measure, the build of the forehead, the shape of the chin, +the size of the eyes, the prominence of the cheeks, the contour of the +nose, and other marks which are reflected in the beauty or ugliness of the +face. + +The face is made up of fourteen bones which, with the exception of +the lower jaw, are, like those of the cranium, closely interlocked with +each other. By this union these bones help form a number of cavities which +contain most important and vital organs. The two deep, cup-like sockets, +called the orbits, contain the organs of sight. In the cavities of the +nose is located the sense of smell, while the buccal cavity, or mouth, is +the site of the sense of taste, and plays besides an important part in the +first act of digestion and in the function of speech. + +The bones of the face are: + + Two Superior Maxillary, + Two Malar, + Two Nasal, + Two Lachrymal, + Two Palate, + Two Turbinated, + One Vomer, + One Lower Maxillary. + +34. Bones of the Face. The superior maxillary or upper jawbones +form a part of the roof of the mouth and the entire floor of the orbits. +In them is fixed the upper set of teeth. + +The malar or cheek bones are joined to the upper jawbones, and help +form the sockets of the eyes. They send an arch backwards to join the +temporal bones. These bones are remarkably thick and strong, and are +specially adapted to resist the injury to which this part of the face is +exposed. + +The nasal or nose bones are two very small bones between the eye +sockets, which form the bridge of the nose. Very near these bones are the +two small lachrymal bones. These are placed in the inner angles of +the orbit, and in them are grooves in which lie the ducts through which +the tears flow from the eyes to the nose. + +The palate bones are behind those of the upper jaw and with them form +the bony part of the roof of the mouth. The inferior turbinated are +spongy, scroll-like bones, which curve about within the nasal cavities so +as to increase the surface of the air passages of the nose. + +The vomer serves as a thin and delicate partition between the two cavities +of the nose. It is so named from its resemblance to a ploughshare. + +[Illustration: Fig. 15.--The Base of the Skull. + + A, palate process of upper jawbone; + B, zygoma, forming zygomatic arch; + C, condyle for forming articulation with atlas; + D, foramen magnum; + E, occipital bone. +] + +The longest bone in the face is the inferior maxillary, or lower jaw. +It has a horseshoe shape, and supports the lower set of teeth. It is the +only movable bone of the head, having a vertical and lateral motion by +means of a hinge joint with a part of the temporal bone. + + +35. Sutures of the Skull. Before leaving the head we must notice the +peculiar and admirable manner in which the edges of the bones of the outer +shell of the skull are joined together. These edges of the bones resemble +the teeth of a saw. In adult life these tooth-like edges fit into each +other and grow together, suggesting the dovetailed joints used by the +cabinet-maker. When united these serrated edges look almost as if sewed +together; hence their name, sutures. This manner of union gives unity +and strength to the skull. + +In infants, the corners of the parietal bones do not yet meet, and the +throbbing of the brain may be seen and felt under these "soft spots," or +_fontanelles_, as they are called. Hence a slight blow to a babe's head +may cause serious injury to the brain (Fig. 14). + + + +The Bones of the Trunk. + + +36. The Trunk. The trunk is that central part of the body which +supports the head and the upper pair of limbs. It divides itself into an +upper cavity, the thorax, or chest; and a lower cavity, the +abdomen. These two cavities are separated by a movable, muscular +partition called the diaphragm, or midriff (Figs. 9 and 49). + +The bones of the trunk are variously related to each other, and some of +them become united during adult life into bony masses which at earlier +periods are quite distinct. For example, the sacrum is in early life made +up of five distinct bones which later unite into one. + +The upper cavity, or chest, is a bony enclosure formed by the +breastbone, the ribs, and the spine. It contains the heart and the lungs +(Fig. 86). + +The lower cavity, or abdomen, holds the stomach, liver, intestines, +spleen, kidneys, and some other organs (Fig. 59). + +The bones of the trunk may be subdivided into those of the spine, the +ribs, and the hips. + +The trunk includes 54 bones usually thus arranged: + + I. Spinal Column, 26 bones: + 7 Cervical Vertebræ. + 12 Dorsal Vertebræ. + 5 Lumbar Vertebræ. + 1 Sacrum. + 1 Coccyx. + + II. Ribs, 24 bones: + 14 True Ribs. + 6 False Ribs. + 4 Floating Ribs. + + III. Sternum. + + IV. Two Hip Bones. + + V. Hyoid Bone. + +37. The Spinal Column. The spinal column, or backbone, is a +marvelous piece of mechanism, combining offices which nothing short of +perfection in adaptation and arrangement could enable it to perform. It is +the central structure to which all the other parts of the skeleton are +adapted. It consists of numerous separate bones, called vertebræ. The +seven upper ones belong to the neck, and are called cervical +vertebræ. The next twelve are the dorsal vertebræ; these belong to +the back and support the ribs. The remaining five belong to the loins, and +are called lumbar vertebræ. On looking at the diagram of the backbone +(Fig. 9) it will be seen that the vertebræ increase in size and strength +downward, because of the greater burden they have to bear, thus clearly +indicating that an erect position is the one natural to man. + +[Illustration: Fig. 16.--The Spinal Column.] + +This column supports the head, encloses and protects the spinal cord, and +forms the basis for the attachment of many muscles, especially those which +maintain the body in an erect position. Each vertebra has an opening +through its center, and the separate bones so rest, one upon another, that +these openings form a continuous canal from the head to the lower part of +the spine. The great nerve, known as the spinal cord, extends from +the cranium through the entire length of this canal. All along the spinal +column, and between each two adjoining bones, are openings on each side, +through which nerves pass out to be distributed to various parts of the +body. + +Between the vertebræ are pads or cushions of cartilage. These act as +"buffers," and serve to give the spine strength and elasticity and to +prevent friction of one bone on another. Each vertebra consists of a body, +the solid central portion, and a number of projections called processes. +Those which spring from the posterior of each arch are the spinous +processes. In the dorsal region they are plainly seen and felt in thin +persons. + +The bones of the spinal column are arranged in three slight and graceful +curves. These curves not only give beauty and strength to the bony +framework of the body, but also assist in the formation of cavities for +important internal organs. This arrangement of elastic pads between the +vertebræ supplies the spine with so many elastic springs, which serve to +break the effect of shock to the brain and the spinal cord from any sudden +jar or injury. + +The spinal column rests on a strong three-sided bone called the +sacrum, or sacred-bone, which is wedged in between the hip bones and +forms the keystone of the pelvis. Joined to the lower end of the sacrum is +the coccyx, or cuckoo-bone, a tapering series of little bones. + + Experiment 7. Run the tips of the fingers briskly down the + backbone, and the spines of the vertebræ will be tipped with red so that + they can be readily counted. Have the model lean forward with the arms + folded across the chest; this will make the spines of the vertebræ more + prominent. + + Experiment 8. _To illustrate the movement of torsion in the spine, + or its rotation round its own axis_. Sit upright, with the back and + shoulders well applied against the back of a chair. Note that the head + and neck can be turned as far as 60° or 70°. Now bend forwards, so as to + let the dorsal and lumbar vertebræ come into play, and the head can be + turned 30° more. + + Experiment 9. _To show how the spinal vertebræ make a firm but + flexible column._ Take 24 hard rubber overcoat buttons, or the same + number of two-cent pieces, and pile them on top of each other. A thin + layer of soft putty may be put between the coins to represent the pads + of cartilage between the vertebræ. The most striking features of the + spinal column may be illustrated by this simple apparatus. + +38. How the Head and Spine are Joined together. The head rests upon +the spinal column in a manner worthy of special notice. This consists in +the peculiar structure of the first two cervical vertebræ, known as the +axis and atlas. The atlas is named after the fabled giant who +supported the earth on his shoulders. This vertebra consists of a ring of +bone, having two cup-like sockets into which fit two bony projections +arising on either side of the great opening (_foramen magnum_) in the +occipital bone. The hinge joint thus formed allows the head to nod +forward, while ligaments prevent it from moving too far. + +On the upper surface of the axis, the second vertebra, is a peg or +process, called the _odontoid process_ from its resemblance to a tooth. +This peg forms a pivot upon which the head with the atlas turns. It is +held in its place against the front inner surface of the atlas by a band +of strong ligaments, which also prevents it from pressing on the delicate +spinal cord. Thus, when we turn the head to the right or left, the skull +and the atlas move together, both rotating on the odontoid process of the +axis. + + +39. The Ribs and Sternum. The barrel-shaped framework of the chest is +in part composed of long, slender, curved bones called ribs. There +are twelve ribs on each side, which enclose and strengthen the chest; they +somewhat resemble the hoops of a barrel. They are connected in pairs with +the dorsal vertebræ behind. + +The first seven pairs, counting from the neck, are called the _true_ ribs, +and are joined by their own special cartilages directly to the breastbone. +The five lower pairs, called the _false_ ribs, are not directly joined to +the breastbone, but are connected, with the exception of the last two, +with each other and with the last true ribs by cartilages. These elastic +cartilages enable the chest to bear great blows with impunity. A blow on +the sternum is distributed over fourteen elastic arches. The lowest two +pairs of false ribs, are not joined even by cartilages, but are quite free +in front, and for this reason are called _floating_ ribs. + +The ribs are not horizontal, but slope downwards from the backbone, so +that when raised or depressed by the strong intercostal muscles, the size +of the chest is alternately increased or diminished. This movement of the +ribs is of the utmost importance in breathing (Fig. 91). + +The sternum, or breastbone, is a long, flat, narrow bone forming the +middle front wall of the chest. It is connected with the ribs and with the +collar bones. In shape it somewhat resembles an ancient dagger. + +40. The Hip Bones. Four immovable bones are joined together so as to +form at the lower extremity of the trunk a basin-like cavity called the +pelvis. These four bones are the sacrum and the coccyx, +which have been described, and the two hip bones. + +[Illustration: Fig. 17.--Thorax. (Anterior view.)] + +The hip bones are large, irregularly shaped bones, very firm and +strong, and are sometimes called the haunch bones or _ossa innominata_ +(nameless bones). They are united to the sacrum behind and joined to each +other in front. On the outer side of each hip bone is a deep cup, or +socket, called the _acetabulum_, resembling an ancient vinegar cup, into +which fits the rounded head of the thigh bone. The bones of the pelvis are +supported like a bridge on the legs as pillars, and they in turn contain +the internal organs in the lower part of the trunk. + +41. The Hyoid Bone. Under the lower jaw is a little horseshoe shaped +bone called the hyoid bone, because it is shaped like the Greek +letter upsilon (Υ). The root of the tongue is fastened to its bend, +and the larynx is hung from it as from a hook. When the neck is in its +natural position this bone can be plainly felt on a level with the lower +jaw and about one inch and a half behind it. It serves to keep open the +top of the larynx and for the attachment of the muscles, which move the +tongue. (See Fig. 46.) The hyoid bone, like the knee-pan, is not connected +with any other bone. + + + +The Bones of the Upper Limbs. + + +42. The Upper Limbs. Each of the upper limbs consist of the upper +arm, the forearm, and the hand. These bones are classified +as follows: + + Upper Arm: + Scapula, or shoulder-blade, + Clavicle, or collar bone, + Humerus, or arm bone, + + Forearm: + Ulna, + Radius, + + Hand: + 8 Carpal or wrist bones, + 5 Metacarpal bones, + 14 Phalanges, or finger bones, + +making 32 bones in all. + + +43. The Upper Arm. The two bones of the shoulder, the scapula +and the clavicle, serve in man to attach the arm to the trunk. The +scapula, or shoulder-blade, is a flat, triangular bone, placed point +downwards, and lying on the upper and back part of the chest, over the +ribs. It consists of a broad, flat portion and a prominent ridge or +_spine_. At its outer angle it has a shallow cup known as the _glenoid +cavity_. Into this socket fits the rounded head of the humerus. The +shoulder-blade is attached to the trunk chiefly by muscles, and is capable +of extensive motion. + +The clavicle, or collar bone, is a slender bone with a double curve +like an italic _f_, and extends from the outer angle of the shoulder-blade +to the top of the breastbone. It thus serves like the keystone of an arch +to hold the shoulder-blade firmly in its place, but its chief use is to +keep the shoulders wide apart, that the arm may enjoy a freer range of +motion. This bone is often broken by falls upon the shoulder or arm. + +The humerus is the strongest bone of the upper extremity. As already +mentioned, its rounded head fits into the socket of the shoulder-blade, +forming a ball-and-socket joint, which permits great freedom of motion. +The shoulder joint resembles what mechanics call a universal joint, for +there is no part of the body which cannot be touched by the hand. + +[Illustration: Fig. 18.--Left Scapula, or Shoulder-Blade.] + +When the shoulder is dislocated the head of the humerus has been forced +out of its socket. The lower end of the bone is grooved to help form a +hinge joint at the elbow with the bones of the forearm (Fig. 27). + +44. The Forearm. The forearm contains two long bones, the +ulna and the radius. The ulna, so called because it forms +the elbow, is the longer and larger bone of the forearm, and is on the +same side as the little finger. It is connected with the humerus by a +hinge joint at the elbow. It is prevented from moving too far back by a +hook-like projection called the _olecranon process_, which makes the sharp +point of the elbow. + +The radius is the shorter of the two bones of the forearm, and is on +the same side as the thumb. Its slender, upper end articulates with the +ulna and humerus; its lower end is enlarged and gives attachment in part +to the bones of the wrist. This bone radiates or turns on the ulna, +carrying the hand with it. + + Experiment 10. Rest the forearm on a table, with the palm up (an + attitude called supination). The radius is on the outer side and + parallel with the ulna If now, without moving the elbow, we turn the + hand (pronation), as if to pick up something from the table, the radius + may be seen and felt crossing over the ulna, while the latter has not + moved. + +[Illustration: Fig. 19.--Left Clavicle, or Collar Bone. (Anterior +surface.)] + +45. The Hand. The hand is the executive or essential part of the +upper limb. Without it the arm would be almost useless. It consists of 27 +separate bones, and is divided into three parts, the wrist, the +palm, and the fingers. + +[Illustration: Fig. 20.--Left Humerus.] + +[Illustration: Fig. 21.--Left Radius and Ulna.] + +The carpus, or wrist, includes 8 short bones, arranged in two rows of +four each, so as to form a broad support for the hand. These bones are +closely packed, and tightly bound with ligaments which admit of ample +flexibility. Thus the wrist is much less liable to be broken than if it +were to consist of a single bone, while the elasticity from having the +eight bones movable on each other, neutralizes, to a great extent, a +shock caused by falling on the hands. Although each of the wrist bones has +a very limited mobility in relation to its neighbors, their combination +gives the hand that freedom of action upon the wrist, which is manifest in +countless examples of the most accurate and delicate manipulation. + +The metacarpal bones are the five long bones of the back of the hand. +They are attached to the wrist and to the finger bones, and may be easily +felt by pressing the fingers of one hand over the back of the other. The +metacarpal bones of the fingers have little freedom of movement, while the +thumb, unlike the others, is freely movable. We are thus enabled to bring +the thumb in opposition to each of the fingers, a matter of the highest +importance in manipulation. For this reason the loss of the thumb disables +the hand far more than the loss of either of the fingers. This very +significant opposition of the thumb to the fingers, furnishing the +complete grasp by the hand, is characteristic of the human race, and is +wanting in the hand of the ape, chimpanzee, and ourang-outang. + +The phalanges, or finger bones, are the fourteen small bones arranged +in three rows to form the fingers. Each finger has three bones; each +thumb, two. + +The large number of bones in the hand not only affords every variety of +movement, but offers great resistance to blows or shocks. These bones are +united by strong but flexible ligaments. The hand is thus given strength +and flexibility, and enabled to accomplish the countless movements so +necessary to our well-being. + +In brief, the hand is a marvel of precise and adapted mechanism, capable +not only of performing every variety of work and of expressing many +emotions of the mind, but of executing its orders with inconceivable +rapidity. + + + +The Bones of the Lower Limbs. + + +46. The Lower Limbs. The general structure and number of the bones of +the lower limbs bear a striking similarity to those of the upper limbs. +Thus the leg, like the arm, is arranged in three parts, the thigh, +the lower leg, and the foot. The thigh bone corresponds to the +humerus; the tibia and fibula to the ulna and radius; the ankle to the +wrist; and the metatarsus and the phalanges of the foot, to the metacarpus +and the phalanges of the hand. + +The bones of the lower limbs may be thus arranged: + + Thigh: Femur, or thigh bone, + + Lower Leg: + Patella, or knee cap, + Tibia, or shin bone, + Fibula, or splint bone, + + Foot: + 7 Tarsal or ankle bones, + 5 Metatarsal or instep bones, + 14 Phalanges, or toes bones, + +making 30 bones in all. + +[Illustration: Fig. 22.--Right Femur, or Thigh Bone.] + +47. The Thigh. The longest and strongest of all the bones is the +femur, or thigh bone. Its upper end has a rounded head which fits into the +_acetabulum_, or the deep cup-like cavity of the hip bone, forming a +perfect ball-and-socket joint. When covered with cartilage, the ball fits +so accurately into its socket that it may be retained by atmospheric +pressure alone (sec. 50). + +The shaft of the femur is strong, and is ridged and roughened in places +for the attachment of the muscles. Its lower end is broad and irregularly +shaped, having two prominences called _condyles_, separated by a groove, +the whole fitted for forming a hinge joint with the bones of the lower leg +and the knee-cap. + + +48. The Lower Leg. The lower leg, like the forearm, consists of +two bones. The tibia, or shin bone, is the long three-sided bone +forming the front of the leg. The sharp edge of the bone is easily felt +just under the skin. It articulates with the lower end of the thigh bone, +forming with it a hinge joint. + +The fibula, the companion bone of the tibia, is the long, slender +bone on the outer side of the leg. It is firmly fixed to the tibia at each +end, and is commonly spoken of as the small bone of the leg. Its lower end +forms the outer projection of the ankle. In front of the knee joint, +embedded in a thick, strong tendon, is an irregularly disk-shaped bone, +the patella, or knee-cap. It increases the leverage of important +muscles, and protects the front of the knee joint, which is, from its +position, much exposed to injury. + +[Illustration: Fig. 23.--Patella, or Knee-Cap.] + +49. The Foot. The bones of the foot, 26 in number, consist of +the tarsal bones, the metatarsal, and the phalanges. The +tarsal bones are the seven small, irregular bones which make up the +ankle. These bones, like those of the wrist, are compactly arranged, and +are held firmly in place by ligaments which allow a considerable amount of +motion. + +One of the ankle bones, the _os calcis_, projects prominently backwards, +forming the heel. An extensive surface is thus afforded for the attachment +of the strong tendon of the calf of the leg, called the tendon of +Achilles. The large bone above the heel bone, the _astragalus_, +articulates with the tibia, forming a hinge joint, and receives the weight +of the body. + +The metatarsal bones, corresponding to the metacarpals of the hand, +are five in number, and form the lower instep. + +The phalanges are the fourteen bones of the toes,--three in each +except the great toe, which, like the thumb, has two. They resemble in +number and plan the corresponding bones in the hand. The bones of the foot +form a double arch,--an arch from before backwards, and an arch from side +to side. The former is supported behind by the os calcis, and in front by +the ends of the metatarsal bones. The weight of the body falls +perpendicularly on the astragalus, which is the key-bone or crown of the +arch. The bones of the foot are kept in place by powerful ligaments, +combining great strength with elasticity. + +[Illustration: Fig. 24.--Right Tibia and Fibula (Anterior surface.)] + +[Illustration: Fig. 25.--Bones of Right Foot. (Dorsal surface.)] + + + +The Joints. + + +50. Formation of Joints. The various bones of the skeleton are +connected together at different parts of their surfaces by joints, or +articulations. Many different kinds of joints have been described, but the +same general plan obtains for nearly all. They vary according to the kind +and the amount of motion. + +The principal structures which unite in the formation of a joint are: +bone, cartilage, synovial membrane, and ligaments. Bones make +the chief element of all the joints, and their adjoining surfaces are +shaped to meet the special demands of each joint (Fig. 27). The joint-end +of bones is coated with a thin layer of tough, elastic cartilage. This is +also used at the edge of joint-cavities, forming a ring to deepen them. +The rounded heads of bones which move in them are thus more securely held +in their sockets. + +Besides these structures, the muscles also help to maintain the +joint-surfaces in proper relation. Another essential to the action of the +joints is the pressure of the outside air. This may be sufficient to keep +the articular surfaces in contact even after all the muscles are removed. +Thus the hip joint is so completely surrounded by ligaments as to be +air-tight; and the union is very strong. But if the ligaments be pierced +and air allowed to enter the joint, the union at once becomes much less +close, and the head of the thigh bone falls away as far as the ligaments +will allow it. + +51. Synovial Membrane. A very delicate connective tissue, called the +synovial membrane, lines the capsules of the joints, and covers the +ligaments connected with them. It secretes the _synovia_, or joint oil, a +thick and glairy fluid, like the white of a raw egg, which thoroughly +lubricates the inner surfaces of the joints. Thus the friction and heat +developed by movement are reduced, and every part of a joint is enabled to +act smoothly. + +52. Ligaments. The bones are fastened together, held in place, and +their movements controlled, to a certain extent, by bands of various +forms, called ligaments. These are composed mainly of bundles of +white fibrous tissue placed parallel to, or closely interlaced with, one +another, and present a shining, silvery aspect. They extend from one of +the articulating bones to another, strongly supporting the joint, which +they sometimes completely envelope with a kind of cap (Fig. 28). This +prevents the bones from being easily dislocated. It is difficult, for +instance, to separate the two bones in a shoulder or leg of mutton, they +are so firmly held together by tough ligaments. + +While ligaments are pliable and flexible, permitting free movement, they +are also wonderfully strong and inextensible. A bone may be broken, or its +end torn off, before its ligaments can be ruptured. The wrist end of the +radius, for instance, is often torn off by force exerted on its ligaments +without their rupture. + +The ligaments are so numerous and various and are in some parts so +interwoven with each other, that space does not allow even mention of +those that are important. At the knee joint, for instance, there are no +less than fifteen distinct ligaments. + +53. Imperfect Joints. It is only perfect joints that are fully +equipped with the structures just mentioned. Some joints lack one or more, +and are therefore called imperfect joints. Such joints allow little or no +motion and have no smooth cartilages at their edges. Thus, the bones of +the skull are dovetailed by joints called sutures, which are immovable. +The union between the vertebræ affords a good example of imperfect joints +which are partially movable. + +[Illustration: Fig. 26.--Elastic Tissue from the Ligaments about Joints. +(Highly magnified.)] + +54. Perfect Joints. There are various forms of perfect joints, +according to the nature and amount of movement permitted. They an divided +into hinge joints, ball-and-socket joints and pivot joints. + +The hinge joints allow forward and backward movements like a hinge. +These joints are the most numerous in the body, as the elbow, the ankle, +and the knee joints. + +In the ball-and-socket joints--a beautiful contrivance--the rounded +head of one bone fits into a socket in the other, as the hip joint and +shoulder joint. These joints permit free motion in almost every direction. + +In the pivot joint a kind of peg in one bone fits into a notch in +another. The best example of this is the joint between the first and +second vertebræ (see sec. 38). The radius moves around on the ulna by +means of a pivot joint. The radius, as well as the bones of the wrist and +hand, turns around, thus enabling us to turn the palm of the hand upwards +and downwards. In many joints the extent of motion amounts to only a +slight gliding between the ends of the bones. + +55. Uses of the Bones. The bones serve many important and useful +purposes. The skeleton, a general framework, affords protection, +support, and leverage to the bodily tissues. Thus, the bones of +the skull and of the chest protect the brain, the lungs, and the heart; +the bones of the legs support the weight of the body; and the long bones +of the limbs are levers to which muscles are attached. + +Owing to the various duties they have to perform, the bones are +constructed in many different shapes. Some are broad and flat; +others, long and cylindrical; and a large number very irregular +in form. Each bone is not only different from all the others, but is also +curiously adapted to its particular place and use. + +[Illustration: Fig. 27.--Showing how the Ends of the Bones are shaped to +form the Elbow Joint. (The cut ends of a few ligaments are seen.)] + +Nothing could be more admirable than the mechanism by which each one of +the bones is enabled to fulfill the manifold purposes for which it was +designed. We have seen how the bones of the cranium are united by sutures +in a manner the better to allow the delicate brain to grow, and to afford +it protection from violence. The arched arrangement of the bones of the +foot has several mechanical advantages, the most important being that it +gives firmness and elasticity to the foot, which thus serves as a support +for the weight of the body, and as the chief instrument of locomotion. + +The complicated organ of hearing is protected by a winding series of +minute apartments, in the rock-like portion of the temporal bone. The +socket for the eye has a jutting ridge of bone all around it, to guard the +organ of vision against injury. Grooves and canals, formed in hard bone, +lodge and protect minute nerves and tiny blood-vessels. The surfaces of +bones are often provided with grooves, sharp edges, and rough projections, +for the origin and insertion of muscles. + +[Illustration: Fig. 28.--External Ligaments of the Knee.] + +56. The Bones in Infancy and Childhood. The bones of the infant, +consisting almost wholly of cartilage, are not stiff and hard as in after +life, but flexible and elastic. As the child grows, the bones become more +solid and firmer from a gradually increased deposit of lime salts. In time +they become capable of supporting the body and sustaining the action of +the muscles. The reason is that well-developed bones would be of no use to +a child that had not muscular strength to support its body. Again, the +numerous falls and tumbles that the child sustains before it is able to +walk, would result in broken bones almost every day of its life. As it is, +young children meet with a great variety of falls without serious injury. + +But this condition of things has its dangers. The fact that a child's +bones bend easily, also renders them liable to permanent change of shape. +Thus, children often become bow-legged when allowed to walk too early. +Moderate exercise, however, even in infancy, promotes the health of the +bones as well as of the other tissues. Hence a child may be kept too long +in its cradle, or wheeled about too much in a carriage, when the full use +of its limbs would furnish proper exercise and enable it to walk earlier. + +57. Positions at School. Great care must be exercised by teachers +that children do not form the habit of taking injurious positions at +school. The desks should not be too low, causing a forward stoop; or too +high, throwing one shoulder up and giving a twist to the spine. If the +seats are too low there will result an undue strain on the shoulder and +the backbone; if too high, the feet have no proper support, the thighs may +be bent by the weight of the feet and legs, and there is a prolonged +strain on the hips and back. Curvature of the spine and round shoulders +often result from long-continued positions at school in seats and at desks +which are not adapted to the physical build of the occupant. + +[Illustration: Fig. 29.--Section of the Knee Joint. (Showing its internal +structure) + + A, tendon of the semi-membranosus muscle cut across; + B, F, tendon of same muscle; + C, internal condyle of femur; + D, posterior crucial ligament; + E, internal interarticular fibro cartilage; + G, bursa under knee-cap; + H, ligament of knee-cap; + K, fatty mass under knee-cap; + L, anterior crucial ligament cut across; + P, patella, or knee-cap +] + +A few simple rules should guide teachers and school officials in providing +proper furniture for pupils. Seats should be regulated according to the +size and age of the pupils, and frequent changes of seats should be made. +At least three sizes of desks should be used in every schoolroom, and more +in ungraded schools. The feet of each pupil should rest firmly on the +floor, and the edge of the desk should be about one inch higher than the +level of the elbows. A line dropped from the edge of the desk should +strike the front edge of the seat. Sliding down into the seat, bending too +much over the desk while writing and studying, sitting on one foot or +resting on the small of the back, are all ungraceful and unhealthful +positions, and are often taken by pupils old enough to know better. This +topic is well worth the vigilance of every thoughtful teacher, especially +of one in the lower grades. + +58. The Bones in After Life. Popular impression attributes a less +share of life, or a lower grade of vitality, to the bones than to any +other part of the body. But really they have their own circulation and +nutrition, and even nervous relations. Thus, bones are the seat of active +vital processes, not only during childhood, but also in adult life, +and in fact throughout life, except perhaps in extreme old age. The final +knitting together of the ends of some of the bones with their shafts does +not occur until somewhat late in life. For example, the upper end of the +tibia and its shaft do not unite until the twenty-first year. The separate +bones of the sacrum do not fully knit into one solid bone until the +twenty-fifth year. Hence, the risk of subjecting the bones of young +persons to undue violence from injudicious physical exercise as in rowing, +baseball, football, and bicycle-riding. + +The bones during life are constantly going through the process of +absorption and reconstruction. They are easily modified in their growth. +Thus the continued pressure of some morbid deposit, as a tumor or cancer, +or an enlargement of an artery, may cause the absorption or distortion of +bones as readily as of one of the softer tissues. The distortion resulting +from tight lacing is a familiar illustration of the facility with which +the bones may be modified by prolonged pressure. + +Some savage races, not content with the natural shape of the head, take +special methods to mould it by continued artificial pressure, so that it +may conform in its distortion to the fashion of their tribe or race. This +custom is one of the most ancient and widespread with which we are +acquainted. In some cases the skull is flattened, as seen in certain +Indian tribes on our Pacific coast, while with other tribes on the same +coast it is compressed into a sort of conical appearance. In such cases +the brain is compelled, of course, to accommodate itself to the change in +the shape of the head; and this is done, it is said, without any serious +result. + +59. Sprains and Dislocations. A twist or strain of the ligaments and +soft parts about a joint is known as a sprain, and may result from a +great variety of accidents. When a person falls, the foot is frequently +caught under him, and the twist comes upon the ligaments and tissues of +the ankle. The ligaments cannot stretch, and so have to endure the wrench +upon the joint. The result is a sprained ankle. Next to the ankle, a +sprain of the wrist is most common. A person tries, by throwing out his +hand, to save himself from a fall, and the weight of the body brings the +strain upon the firmly fixed wrist. As a result of a sprain, the ligaments +may be wrenched or torn, and even a piece of an adjacent bone may be torn +off; the soft parts about the injured joint are bruised, and the +neighboring muscles put to a severe stretch. A sprain may be a slight +affair, needing only a brief rest, or it may be severe and painful enough +to call for the most skillful treatment by a surgeon. Lack of proper care +in severe sprains often results in permanent lameness. + +A fall or a blow may bring such a sudden wrench or twist upon the +ligaments as to force a bone out of place. This displacement is known as a +dislocation. A child may trip or fall during play and put his elbow +out of joint. A fall from horseback, a carriage, or a bicycle may result +in a dislocation of the shoulder joint. In playing baseball a swift ball +often knocks a finger out of joint. A dislocation must be reduced at once. +Any delay or carelessness may make a serious and painful affair of it, as +the torn and bruised parts rapidly swell and become extremely sensitive. + +60. Broken Bones. The bones, especially those of the upper limbs, are +often fractured or broken. The _simple_ fracture is the most common +form, the bone being broken in a single place with no opening through the +skin. When properly adjusted, the bone heals rapidly. Sometimes bones are +crushed into a number of fragments; this is a _comminuted_ fracture. +When, besides the break, there is an opening through the soft parts and +surface of the body, we have a _compound_ fracture. This is a serious +injury, and calls for the best surgical treatment. + +A bone may be bent, or only partly broken, or split. This is called "a +green-stick fracture," from its resemblance to a half-broken green stick. +This fracture is more common in the bones of children. + +Fractures may be caused by direct violence, as when a bone is broken at a +certain point by some powerful force, as a blow from a baseball bat or a +fall from a horse. Again, a bone may be broken by indirect violence, as +when a person being about to fall, throws out his hand to save himself. +The force of the fall on the hand often breaks the wrist, by which is +meant the fracture of the lower end of the radius, often known as the +"silver-fork fracture." This accident is common in winter from a fall or +slip on the ice. + +Sometimes bones are broken at a distance from the point of injury, as in a +fracture of the ribs by violent compression of the chest; or fracture may +occur from the vibration of a blow, as when a fall or blow upon the top of +the head produces fracture of the bones at the base of the brain.[6] + +61. Treatment for Broken Bones. When a bone is broken a surgeon is +needed to set it, that is, to bring the broken parts into their natural +position, and retain them by proper appliances. Nature throws out between +and around the broken ends of bones a supply of repair material known as +plastic lymph, which is changed to fibrous tissue, then to cartilage, and +finally to bone. This material serves as a sort of cement to hold the +fractured parts together. The excess of this at the point of union can be +felt under the skin for some time after the bone is healed. + +With old people a broken bone is often a serious matter, and may cripple +them for life or prove fatal. A trifling fall, for instance, may cause a +broken hip (popularly so called, though really a fracture of the neck of +the femur), from the shock of which, and the subsequent pain and +exhaustion, an aged person may die in a few weeks. In young people, +however, the parts of a broken bone will knit together in three or four +weeks after the fracture is reduced; while in adults, six or even more may +be required for firm union. After a broken bone is strong enough to be +used, it is fragile for some time; and great care must be taken, +especially with children, that the injured parts may not be broken again +before perfect union takes place.[7] + +62. The Effect of Alcohol upon the Bones. While the growth of the +bones occurs, of course, mainly during the earlier years of life, yet they +do not attain their full maturity until about the twenty-fifth year; and +it is stated that in persons devoted to intellectual pursuits, the skull +grows even after that age. It is plainly necessary that during this period +of bone growth the nutrition of the body should be of the best, that the +bones may be built up from pure blood, and supplied with all the materials +for a large and durable framework. Else the body will be feeble and +stunted, and so through life fall short of its purpose. + +If this bony foundation be then laid wrong, the defect can never be +remedied. This condition is seen in young persons who have been underfed +and overworked. But the use of alcoholic liquors produces a similar +effect, hindering bone cell-growth and preventing full development.[8] +The appetite is diminished, nutrition perverted and impaired, the stature +stunted, and both bodily and mental powers are enfeebled. + +63. Effect of Tobacco upon the Bones. Another narcotic, the +destructive influence of which is wide and serious, is tobacco. Its +pernicious influence, like that of alcohol, is peculiarly hurtful to the +young, as the cell development during the years of growth is easily +disturbed by noxious agents. The bone growth is by cells, and a powerful +narcotic like tobacco retards cell-growth, and thus hinders the building +up of the bodily frame. The formation of healthy bone demands good, +nutritious blood, but if instead of this, the material furnished for the +production of blood is poor in quality or loaded with poisonous narcotics, +the body thus defrauded of its proper building material becomes undergrown +and enfeebled. + +Two unfavorable facts accompany this serious drawback: one is, that owing +to the insidious nature of the smoky poison[9] (cigarettes are its worst +form) the cause may often be unsuspected, and so go on, unchecked; and the +other, that the progress of growth once interrupted, the gap can never be +fully made up. Nature does her best to repair damages and to restore +defects, but never goes backwards to remedy neglects. + + + +Additional Experiments. + + Experiment 11. Take a portion of the decalcified bone obtained from + Experiment 4, and wash it thoroughly in water: in this it is insoluble. + Place it in a solution of carbonate of soda and wash it again. Boil it + in water, and from it gelatine will be obtained. + + Experiment 12. Dissolve in hydrochloric acid a small piece of the + powdered bone-ash obtained from Experiment 3. Bubbles of carbon dioxid + are given off, indicating the presence of a carbonate. Dilute the + solution; add an excess of ammonia, and we find a white precipitate of + the phosphate of lime and of magnesia. + + Experiment 13. Filter the solution in the preceding experiment, and + to the filtrate add oxalate of ammonia. The result is a white + precipitate of the oxalate of lime, showing there is lime present, but + not as a phosphate. + + Experiment 14. To the solution of mineral matters obtained from + Experiment 3, add acetate of soda until free acetic acid is present, + recognized by the smell (like dilute vinegar); then add oxalate of + ammonia. The result will be a copious white precipitate of lime salts. + + Experiment 15. _To show how the cancellous structure of bone is + able to support a great deal of weight_. Have the market-man saw out a + cubic inch from the cancellous tissue of a fresh beef bone and place it + on a table with its principal layers upright. Balance a heavy book upon + it, and then gradually place upon it various articles and note how many + pounds it will support before giving way. + + Experiment 16. Repeat the last experiment, using a cube of the + decalcified bone obtained from Experiment 4. + + [NOTE. As the succeeding chapters are studied, additional experiments + on bones and their relation to other parts of the body, will readily + suggest themselves to the ingenious instructor or the thoughtful + student. Such experiments may be utilized for review or other + exercises.] + + + Review Analysis: The Skeleton (206 bones). + + / / 1 Frontal, + / / 2 Parietal, + / I. Cranium | 2 Temporal, + / (8 bones) | 1 Occipital, + / \ 1 Sphenoid, + | \ 1 Ethmoid. + | + | / 2 Superior Maxillary, + The Head | / 2 Malar, + (28 bones). | / 2 Nasal, + | II. Face | 2 Lachrymal Bones, + | (14 bones) | 2 Palate Bones, + | \ 2 Turbinated, + | \ 1 Vomer, + \ \ 1 Lower Maxillary. + \ + \ / Hammer, + \ III. The Ear | Anvil, + \ (6 bones) \ Stirrup. + + / / 7 Cervical Vertebræ. + / / 12 Dorsal Vertebræ, + / I. Spinal Column | 5 Lumbar Vertebræ, + | (26 bones) \ Sacrum, + | \ Coccyx. + The Trunk | + (54 bones). | / 7 True Ribs, + | II. The Ribs | 3 False Ribs, + | (24 bones) \ 2 Floating Ribs. + | + \ III. Sternum. + \ IV. Two Hip Bones. + \ V. Hyoid Bone. + + + + / / Scapula, + / I. Upper Arm | Clavicle, + | \ Humerus. + | + The Upper Limbs | II. Forearm / Ulna, + (64 bones). | \ Radius. + | + | / 8 Carpal Bones, + \ III. Hand | 5 Metacarpal Bones, + \ \ 14 Phalanges. + + / I. Thigh Femur. + / + | / Patella, + The Lower Limbs | II. Lower Leg | Tibia, + (60 bones). | \ Fibula. + | + | / 7 Tarsal Bones, + \ III. Foot | 5 Metatarsal Bones, + \ \ 14 Phalanges. + + + + + +Chapter III. + +The Muscles. + + + +64. Motion in Animals. All motion of our bodies is produced by means +of muscles. Not only the limbs are moved by them, but even the movements +of the stomach and of the heart are controlled by muscles. Every part of +the body which is capable of motion has its own special set of muscles. + +Even when the higher animals are at rest it is possible to observe some +kind of motion in them. Trees and stones never move unless acted upon by +external force, while the infant and the tiniest insect can execute a +great variety of movements. Even in the deepest sleep the beating of the +heart and the motion of the chest never cease. In fact, the power to +execute spontaneous movement is the most characteristic property of +living animals. + +65. Kinds of Muscles. Most of the bodily movements, such as affect +the limbs and the body as a whole, are performed by muscles under our +control. These muscles make up the red flesh or lean parts, which, +together with the fat, clothe the bony framework, and give to it general +form and proportion. We call these muscular tissues voluntary +muscles, because they usually act under the control of the will. + +The internal organs, as those of digestion, secretion, circulation, and +respiration, perform their functions by means of muscular activity of +another kind, that is, by that of muscles not under our control. This work +goes on quite independently of the will, and during sleep. We call the +instruments of this activity involuntary muscles. The voluntary +muscles, from peculiarities revealed by the microscope, are also known as +striped or striated muscles. The involuntary from their smooth, regular +appearance under the microscope are called the unstriped or non-striated +muscles. + +The two kinds of muscles, then, are the red, voluntary, striated +muscles, and the smooth, involuntary, non-striated muscles. + +66. Structure of Voluntary Muscles. The main substance which clothes +the bony framework of the body, and which forms about two-fifths of its +weight, is the voluntary muscular tissue. These muscles do not cover and +surround the bones in continuous sheets, but consist of separate bundles +of flesh, varying in size and length, many of which are capable of +independent movement. + +Each muscle has its own set of blood-vessels, lymphatics, and nerves. It +is the blood that gives the red color to the flesh. Blood-vessels and +nerves on their way to other parts of the body, do not pass through the +muscles, but between them. Each muscle is enveloped in its own sheath of +connective tissue, known as the fascia. Muscles are not usually +connected directly with bones, but by means of white, glistening cords +called tendons. + +[Illustration: Fig. 30.--Striated (voluntary) Muscular Fibers. + + A, fiber serparating into disks; + B, fibrillæ (highly magnified); + C, cross section of a disk +] + +If a small piece of muscle be examined under a microscope it is found to +be made up of bundles of fibers. Each fiber is enclosed within a +delicate, transparent sheath, known as the sarcolemma. If one of +these fibers be further examined under a microscope, it will be seen to +consist of a great number of still more minute fibers called +fibrillæ. These fibers are also seen marked cross-wise with dark +stripes, and can be separated at each stripe into disks. These cross +markings account for the name _striped_ or _striated_ muscle. + +The fibrillæ, then, are bound together in a bundle to form a fiber, which +is enveloped in its own sheath, the sarcolemma. These fibers, in turn, are +further bound together to form larger bundles called fasciculi, and +these, too, are enclosed in a sheath of connective tissue. The muscle +itself is made up of a number of these fasciculi bound together by a +denser layer of connective tissue. + + Experiment 17. _To show the gross structure of muscle._ Take a + small portion of a large muscle, as a strip of lean corned beef. Have it + boiled until its fibers can be easily separated. Pick the bundles and + fasciculi apart until the fibers are so fine as to be almost invisible + to the naked eye. Continue the experiment with the help of a hand + magnifying glass or a microscope. + +67. The Involuntary Muscles. These muscles consist of ribbon-shaped +bands which surround hollow fleshy tubes or cavities. We might compare +them to India rubber rings on rolls of paper. As they are never attached +to bony levers, they have no need of tendons. + +[Illustration: Fig. 31.--A, Muscular Fiber, showing Stripes, and Nuclei, b +and c. (Highly magnified.)] + +The microscope shows these muscles to consist not of fibers, but of long +spindle-shaped cells, united to form sheets or bands. They have no +sarcolemma, stripes, or cross markings like those of the voluntary +muscles. Hence their name of _non-striated_, or _unstriped_, and _smooth_ +muscles. + +The involuntary muscles respond to irritation much less rapidly than do +the voluntary. The wave of contraction passes over them more slowly and +more irregularly, one part contracting while another is relaxing. This may +readily be seen in the muscular action of the intestines, called +vermicular motion. It is the irregular and excessive contraction of the +muscular walls of the bowels that produces the cramp-like pains of colic. + +The smooth muscles are found in the tissues of the heart, lungs, +blood-vessels, stomach, and intestines. In the stomach their contraction +produces the motion by which the food is churned about; in the arteries +and veins they help supply the force by which the blood is driven along, +and in the intestines that by which the partly digested food is mainly +kept in motion. + +Thus all the great vital functions are carried on, regardless of the will +of the individual, or of any outward circumstances. If it required an +effort of the will to control the action of the internal organs we could +not think of anything else. It would take all our time to attend to +living. Hence the care of such delicate and important machinery has wisely +been put beyond our control. + +Thus, too, these muscles act instinctively without training; but the +voluntary need long and careful education. A babe can use the muscles of +swallowing on the first day of its life as well as it ever can. But as it +grows up, long and patient education of its voluntary muscles is needed to +achieve walking, writing, use of musical instruments, and many other acts +of daily life. + +[Illustration: Fig. 32.--A Spindle Cell of Involuntary Muscle. (Highly +magnified.)] + + Experiment 18. _To show the general appearance of the muscles._ + Obtain the lower part of a sheep's or calf's leg, with the most of the + lean meat and the hoof left on. One or more of the muscles with their + bundles of fibers, fascia, and tendons; are readily made out with a + little careful dissection. The dissection should be made a few days + before it is wanted and the parts allowed to harden somewhat in dilute + alcohol. + +68. Properties of Muscular Tissue. The peculiar property of living +muscular tissue is irritability, or the capacity of responding to a +stimulus. When a muscle is irritated it responds by contracting. By this +act the muscle does not diminish its bulk to any extent; it simply changes +its form. The ends of the muscle are drawn nearer each other and the +middle is thicker. + +Muscles do not shorten themselves all at once, but the contraction passes +quickly over them in the form of a wave. They are usually stimulated by +nervous action. The delicate nerve fibrils which end in the fibers +communicate with the brain, the center of the will power. Hence, when the +brain commands, a nervous impulse, sent along the nerve fibers, becomes +the exciting stimulus which acts upon the muscles and makes them shorter, +harder, and more rigid.[10] + +Muscles, however, will respond to other than this usual stimulus. Thus an +electrical current may have a similar effect. Heat, also, may produce +muscular contraction. Mechanical means, such as a sharp blow or pinching, +may irritate a muscle and cause it to contract. + +We must remember that this property of contraction is inherent and belongs +to the muscle itself. This power of contraction is often independent of +the brain. Thus, on pricking the heart of a fish an hour after removal +from its body, obvious contraction will occur. In this case it is not the +nerve force from the brain that supplies the energy for contraction. The +power of contraction is inherent in the muscle substance, and the stimulus +by irritating the nerve ganglia of the heart simply affords the +opportunity for its exercise. + +Contraction is not, however, the natural state of a muscle. In time it is +tired, and begins to relax. Even the heart, the hardest-working muscle, +has short periods of rest between its beats. Muscles are highly elastic as +well as contractile. By this property muscle yields to a stretching force, +and returns to its original length if the stretching has not been +excessive. + +[Illustration: Fig. 33.--Principal Muscles of the Body. (Anterior view.)] + +69. The Object of Contraction. The object of contraction is obvious. +Like rubber bands, if one end of a muscle be fixed and the other attached +to some object which is free to move, the contraction of the muscle will +bring the movable body nearer to the fixed point. A weight fastened to the +free end of a muscle may be lifted when the muscle contracts. Thus by +their contraction muscles are able to do their work. They even +contract more vigorously when resistance is opposed to them than when it +is not. With increased weight there is an increased amount of work to be +done. The greater resistance calls forth a greater action of the muscle. +This is true up to a certain point, but when the limit has been passed, +the muscle quickly fails to respond. + +Again, muscles work best with a certain degree of rapidity provided the +irritations do not follow each other too rapidly. If, however, the +contractions are too rapid, the muscles become exhausted and fatigue +results. When the feeling of fatigue passes away with rest, the muscle +recovers its power. While we are resting, the blood is pouring in fresh +supplies of building material. + + Experiment 19. _To show how muscles relax and contract_. Lay your + left forearm on a table; grasp with the right hand the mass of flesh on + the front of the upper arm. Now gradually raise the forearm, keeping the + elbow on the table. Note that the muscle thickens as the hand rises. + This illustrates the contraction of the biceps, and is popularly called + "trying your muscle" Reverse the act. Keep the elbow in position, bring + the forearm slowly to the table, and the biceps appears to become softer + and smaller,--it relaxes. + + Experiment 20. Repeat the same experiment with other muscles. With + the right hand grasp firmly the extended left forearm. Extend and flex + the fingers vigorously. Note the effect on the muscles and tendons of + the forearm. Grasp with the right hand the calf of the extended right + leg, and vigorously flex the leg, bringing it near to the body. Note the + contractions and relaxations of the muscles. + +70. Arrangement of Muscles. Muscles are not connected directly with +bones. The mass of flesh tapers off towards the ends, where the fibers +pass into white, glistening cords known as tendons. The place at +which a muscle is attached to a bone, generally by means of a tendon, is +called its origin; the end connected with the movable bone is its +insertion. + +There are about 400 muscles in the human body, all necessary for its +various movements. They vary greatly in shape and size, according to their +position and use. Some are from one to two feet long, others only a +fraction of an inch. Some are long and spindle-shaped, others thin and +broad, while still others form rings. Thus some of the muscles of the arm +and thigh are long and tapering, while the abdominal muscles are thin and +broad because they help form walls for cavities. Again, the muscular +fibers which surround and by their contraction close certain orifices, as +those of the eyelids and lips, often radiate like the spokes of a wheel. + +Muscles are named according to their shape, position, division of origin +or insertion, and their function. Thus we have the _recti_ (straight), and +the _deltoid_ (Δ, delta), the _brachial_ (arm), _pectoral_ +(breast), and the _intercostals_ (between the ribs), so named from their +position. Again, we have the _biceps_ (two-headed), _triceps_ +(three-headed), and many others with similar names, so called from the +points of origin and insertion. We find other groups named after their +special use. The muscles which bend the limbs are called _flexors_ while +those which straighten them are known as _extensors_. + +After a bone has been moved by the contraction of a muscle, it is brought +back to its position by the contraction of another muscle on the opposite +side, the former muscle meanwhile being relaxed. Muscles thus acting in +opposition to each other are called antagonistic. Thus the biceps serves +as one of the antagonists to the triceps, and the various flexors and +extensors of the limbs are antagonistic to one another. + +71. The Tendons. The muscles which move the bones by their +contraction taper for the most part, as before mentioned, into +tendons. These are commonly very strong cords, like belts or straps, +made up of white, fibrous tissue. + +Tendons are most numerous about the larger joints, where they permit free +action and yet occupy but little space. Large and prominent muscles in +these places would be clumsy and inconvenient. If we bend the arm or leg +forcibly, and grasp the inside of the elbow or knee joint, we can feel the +tendons beneath the skin. The numerous tendons in the palm or on the back +of the hand contribute to its marvelous dexterity and flexibility. The +thickest and strongest tendon in the body is the tendon of Achilles, +which connects the great muscles in the calf of the leg with the heel bone +(sec. 49). + +When muscles contract forcibly, they pull upon the tendons which transmit +the movement to the bones to which they are attached. Tendons may be +compared to ropes or cords which, when pulled, are made to act upon +distant objects to which one end is fastened. Sometimes the tendon runs +down the middle of a muscle, and the fibers run obliquely into it, the +tendon resembling the quill in a feather. Again, tendons are spread out in +a flat layer on the surface of muscles, in which case they are called +aponeuroses. Sometimes a tendon is found in the middle of a muscle as well +as at each end of it. + +[Illustration: Fig. 34.--The Biceps Muscle dissected to show its Tendons.] + +72. Synovial Sheaths and Sacs. The rapid movement of the tendons +over bony surfaces and prominences would soon produce an undue amount of +heat and friction unless some means existed to make the motion as easy as +possible. This is supplied by sheaths which form a double lining around +the tendons. The opposed surfaces are lined with synovial +membrane,[11] the secretion from which oils the sheaths in which the +tendons move. + +Little closed sacs, called synovial sacs or bursæ, similarly lined +and containing fluid, are also found in special places between two +surfaces where much motion is required. There are two of these bursæ near +the patella, one superficial, just under the skin; the other deep beneath +the bone (Fig. 29). Without these, the constant motion of the knee-pan and +its tendons in walking would produce undue friction and heat and +consequent inflammation. Similar, though smaller, sacs are found over the +point of the elbow, over the knuckles, the ankle bones, and various other +prominent points. These sacs answer a very important purpose, and are +liable to various forms of inflammation. + + Experiment 21. Examine carefully the tendons in the parts dissected + in Experiment 18. Pull on the muscles and the tendons, and note how they + act to move the parts. This may be also admirably shown on the leg of a + fowl or turkey from a kitchen or obtained at the market. + + Obtain the hoof of a calf or sheep with one end of the tendon of + Achilles still attached. Dissect it and test its strength. + +73. Mechanism of Movement. The active agents of bodily movements, as +we have seen, are the muscles, which by their contraction cause the bones +to move one on the other. All these movements, both of motion and of +locomotion, occur according to certain fixed laws of mechanics. The bones, +to which a great proportion of the muscles in the body are attached, act +as distinct levers. The muscles supply the power for moving the +bones, and the joints act as fulcrums or points of support. The weight of +the limb, the weight to be lifted, or the force to overcome, is the +resistance. + +74. Levers in the Body. In mechanics three classes of levers are +described, according to the relative position of the power, the fulcrum, +and the resistance. All the movements of the bones can be referred to one +or another of these three classes. + +Levers of the first class are those in which the fulcrum is between +the power and the weight. The crowbar, when used to lift a weight at one +end by the application of power at the other, with a block as a fulcrum, +is a familiar example of this class. There are several examples of this in +the human body. The head supported on the atlas is one. The joint between +the atlas and the skull is the fulcrum, the weight of the head is the +resistance. The power is behind, where the muscles from the neck are +attached to the back of the skull. The object of this arrangement is to +keep the head steady and balanced on the spinal column, and to move it +backward and forward. + +[Illustration: Fig. 35.--Showing how the Bones of the Arm serve as Levers. + + P, power; + W, weight; + F, fulcrum. +] + +Levers of the second class are those in which the weight is between +the fulcrum and the power. A familiar example is the crowbar when used for +lifting a weight while one end rests on the ground. This class of levers +is not common in the body. Standing on tiptoe is, however, an example. +Here the toes in contact with the ground are the fulcrum, the power is the +action of the muscles of the calf, and between these is the weight of the +body transmitted down the bones of the leg to the foot. + +Levers of the third class are those in which the power is applied at +a point between the fulcrum and weight. A familiar example is where a +workman raises a ladder against a wall. This class of levers is common in +the body. In bending the forearm on the arm, familiarly known as "trying +your muscle," the power is supplied by the biceps muscle attached to the +radius, the fulcrum is the elbow joint at one end of the lever, and the +resistance is the weight of the forearm at the other end. + + Experiment 22. _To illustrate how the muscles use the bones as + levers._ First, practice with a ruler, blackboard pointer, or any other + convenient object, illustrating the different kinds of levers until the + principles are familiar. Next, illustrate these principles on the + person, by making use of convenient muscles. Thus, lift a book on the + toes, by the fingers, on the back of the hand, by the mouth, and in + other ways. + + These experiments, showing how the bones serve as levers, may be + multiplied and varied as circumstances may require. + +75. The Erect Position. The erect position is peculiar to man. No +other animal naturally assumes it or is able to keep it long. It is the +result of a somewhat complex arrangement of muscles which balance each +other, some pulling backwards and some forwards. Although the whole +skeleton is formed with reference to the erect position, yet this attitude +is slowly learned in infancy. + +In the erect position the center of gravity lies in the joint between the +sacrum and the last lumbar vertebra. A line dropped from this point would +fall between the feet, just in front of the ankle joints. We rarely stand +with the feet close together, because that basis of support is too small +for a firm position. Hence, in all efforts requiring vigorous muscular +movements the feet are kept more or less apart to enlarge the basis of +support. + +Now, on account of the large number and flexibility of the joints, the +body could not be kept in an upright position without the cooperation of +certain groups of muscles. The muscles of the calf of the leg, acting on +the thigh bone, above the knee, keep the body from falling forward, while +another set in front of the thigh helps hold the leg straight. These thigh +muscles also tend to pull the trunk forward, but in turn are balanced by +the powerful muscles of the lower back, which help keep the body straight +and braced. + +The head is kept balanced on the neck partly by the central position of +the joint between the atlas and axis, and partly by means of strong +muscles. Thus, the combined action of these and other muscles serves to +balance the body and keep it erect. A blow on the head, or a sudden shock +to the nervous system, causes the body to fall in a heap, because the +brain has for the time lost its power over the muscles, and they cease to +contract. + +[Illustration: Fig. 36.--Diagram showing the Action of the Chief Muscles +which keep the Body Erect. (The arrows indicate the direction in which +these muscles act, the feet serving as a fixed basis.) [After Huxley.] + +_Muscles which tend to keep the body from falling forward._ + + A, muscles of the calf; + B, of the back of the thigh; + C, of the spinal column. + +_Muscles which tend to keep the body from falling backward._ + + D, muscles of the front of the leg; + E, of the front of the thigh; + F, of the front of the abdomen; + G, of the front of the neck. +] + +76. Important Muscles. There are scores of tiny muscles about the +head, face, and eyes, which, by their alternate contractions and +relaxations, impart to the countenance those expressions which reflect the +feelings and passions of the individual. Two important muscles, the +temporal, near the temples, and the masseter, or chewing muscle, +are the chief agents in moving the lower jaw. They are very large in the +lion, tiger, and other flesh-eating animals. On the inner side of each +cheek is the buccinator, or trumpeter's muscle, which is largely +developed in those who play on wind instruments. Easily seen and felt +under the skin in thin persons, on turning the head to one side, is the +sterno-cleido-mastoid muscle, which passes obliquely down on each +side of the neck to the collar bone--prominent in sculpture and painting. + +The chest is supplied with numerous muscles which move the ribs up and +down in the act of breathing. A great, fan-shaped muscle, called the +pectoralis major, lies on the chest. It extends from the chest to the +arm and helps draw the arm inward and forward. The arm is raised from the +side by a large triangular muscle on the shoulder, the deltoid, so +called from its resemblance to the Greek letter delta, Δ. The +biceps, or two-headed muscle, forms a large part of the fleshy mass +in front of the arm. Its use is to bend the forearm on the arm, an act +familiarly known as "trying your muscle." Its direct antagonist is the +three-headed muscle called the triceps. It forms the fleshy mass on +the back of the arm, its use being to draw the flexed forearm into a right +line. + +On the back and outside of the forearm are the extensors, which +straighten the wrist, the hand, and the fingers. On the front and inside +of the forearm are the flexors, which bend the hand, the wrist, and +the fingers. If these muscles are worked vigorously, their tendons can be +readily seen and felt under the skin. At the back of the shoulder a large, +spread-out muscle passes upward from the back to the humerus. From its +wide expanse on the back it is known as the latissimus dorsi +(broadest of the back). When in action it draws the arm downward and +backward, or, if one hangs by the hands, it helps to raise the body. It is +familiarly known as the "climbing muscle." + +[Illustration: Fig. 37.--A Few of the Important Muscles of the Back.] + +Passing to the lower extremity, the thigh muscles are the largest and the +most powerful in the body. In front a great, four-headed muscle, +quadriceps extensor, unites into a single tendon in which the +knee-cap is set, and serves to straighten the knee, or when rising from a +sitting posture helps elevate the body. On the back of the thigh are +several large muscles which bend the knee, and whose tendons, known as the +"hamstrings," are readily felt just behind the knee. On the back of the +leg the most important muscles, forming what is known as the calf, are the +gastrocnemius and the soleus. The first forms the largest part +of the calf. The soleus, so named from resembling a sole-fish, is a muscle +of broad, flattened shape, lying beneath the gastrocnemius. The tendons of +these two muscles unite to form the tendon of Achilles, as that hero +is said to have been invulnerable except at this point. The muscles of the +calf have great power, and are constantly called into use in walking, +cycling, dancing, and leaping. + +77. The Effect of Alcoholic Drinks upon the Muscles. It is found that +a man can do more work without alcohol than with it. After taking it there +may be a momentary increase of activity, but this lasts only ten or +fifteen minutes at the most. It is followed by a rapid reduction of power +that more than outweighs the momentary gain, while the quality of the work +is decidedly impaired from the time the alcohol is taken. + +Even in the case of hard work that must be speedily done, alcohol does not +help, but hinders its execution. The tired man who does not understand the +effects of alcohol often supposes that it increases his strength, when in +fact it only deadens his sense of fatigue by paralyzing his nerves. When +put to the test he is surprised at his self-deception. + +Full intoxication produces, by its peculiar depression of the brain and +nervous system, an artificial and temporary paralysis of the muscles, as +is obvious in the pitifully helpless condition of a man fully intoxicated. +But even partial approach to intoxication involves its proportionate +impairment of nervous integrity, and therefore just so much diminution of +muscular force. All athletes recognize this fact, as while training for a +contest, rigid abstinence is the rule, both from liquors and tobacco. This +muscular weakness is shown also in the unsteady hand, the trembling limbs +of the inebriate, his thick speech, wandering eye, and lolling head. + +78. Destructive Effect of Alcoholic Liquors upon Muscular Tissue. +Alcoholic liquors retard the natural chemical changes so essential to good +health, by which is meant the oxidation of the nutritious elements of +food. Careful demonstration has proved also that the amount of carbon +dioxide escaping from the lungs of intoxicated persons is from thirty to +fifty per cent less than normal. This shut-in carbon stifles the nervous +energy, and cuts off the power that controls muscular force. This lost +force is in close ratio to the retained carbon: so much perverted chemical +change, so much loss of muscular power. Not only the strength but the fine +delicacy of muscular action is lost, the power of nice control of the hand +and fingers, as in neat penmanship, or the use of musical instruments. + +To this perverted chemical action is also due the fatty degeneration so +common in inebriates, affecting the muscles, the heart, and the liver. +These organs are encroached upon by globules of fat (a hydrocarbon), +which, while very good in their proper place and quantity, become a +source of disorder and even of death when they abnormally invade vital +structures. Other poisons, as phosphorus, produce this fatty decay more +rapidly; but alcohol causes it in a much more general way. + +This is proved by the microscope, which plainly shows the condition +mentioned, and the difference between the healthy tissues and those thus +diseased. + +[Illustration: Fig. 38.--Principal Muscles on the Left Side of Neck. + + A, buccinator; + B, masseter; + C, depressor anguli oris; + D, anterior portion of the digastric; + E, mylo-hyoid; + F, tendon of the digastric; + G, sterno-hyoid; + H, sterno-thyroid; + K, omo-hyoid; + L, sternal origin of sterno-cleido-mastoid muscle; + M, superior fibers of deltoid; + N, posterior scalenus; + O, clavicular origin of sterno-cleido-mastoid; + P, sterno-cleido-mastoid; + R, trapezius; + S, anterior constrictor; + T, splenius capitis; + V, stylo-hyoid; + W, posterior portion of the digastric; + X, fasciculi of ear muscles; + Z, occipital. +] + + [NOTE. It was proposed during the Civil War to give each soldier in a + certain army one gill of whiskey a day, because of great hardship and + exposure. The eminent surgeon, Dr. Frank H. Hamilton of New York, thus + expressed his views of the question: "It is earnestly desired that no + such experiment will ever be repeated in the armies of the United + States. In our own mind, the conviction is established, by the + experience and observation of a life, that the regular routine + employment of alcoholic stimulants by man in health is never, under + any circumstances, useful. We make no exceptions in favor of cold or + heat or rain." + + "It seems to me to follow from these Arctic experiences that the + regular use of spirits, even in moderation, under conditions of great + physical hardship, continued and exhausting labor, or exposure to + severe cold cannot be too strongly deprecated." + + A. W. Greely, retired Brigadier General, U.S.A., and formerly leader + of the Greely Expedition.] + +79. Effect of Tobacco on the Muscles. That other prominent narcotic, +tobacco, impairs the energy of the muscles somewhat as alcohol does, by +its paralyzing effect upon the nervous system. As all muscular action +depends on the integrity of the nervous system, whatever lays its +deadening hand upon that, saps the vigor and growth of the entire frame, +dwarfs the body, and retards mental development. This applies especially +to the young, in the growing age between twelve or fourteen and twenty, +the very time when the healthy body is being well knit and compacted. + +Hence many public schools, as well as our national naval and military +academies, rigidly prohibit the use of tobacco by their pupils. So also +young men in athletic training are strictly forbidden to use it.[12] This +loss of muscular vigor is shown by the unsteady condition of the muscles, +the trembling hand, and the inability to do with precision and accuracy +any fine work, as in drawing or nice penmanship. + + + +Additional Experiments. + + Experiment 23. _ To examine the minute structure of voluntary + muscular fiber._ Tease, with two needles set in small handles, a bit of + raw, lean meat, on a slip of glass, in a little water. Continue until + the pieces are almost invisible to the naked eye. + + Experiment 24. Place a clean, dry cover-glass of about the width of + the slip, over the water containing the torn fragments. Absorb the + excess of moisture at the edge of the cover, by pressing a bit of + blotting-paper against it for a moment. Place it on the stage of a + microscope and examine with highest obtainable power, by light reflected + upward from the mirror beneath the stage. Note the apparent size of the + finest fibers; the striation of the fibers, or their markings, + consisting of alternate dim and bright cross bands. Note the arrangement + of the fibers in bundles, each thread running parallel with its + neighbor. + + Experiment 25. _To examine the minute structure of involuntary + muscular fiber, a tendon, or a ligament._ Obtain a very small portion of + the muscular coat of a cow's or a pig's stomach. Put it to soak in a + solution of one dram of bichromate of potash in a pint of water. Take + out a morsel on the slip of glass, and tease as directed for the + voluntary muscle. Examine with a high power of the microscope and note: + (1) the isolated cells, long and spindle-shaped, that they are much + flattened; (2) the arrangement of the cells, or fibers, in sheets, or + layers, from the torn ends of which they project like palisades. + + Experiment 26. Tease out a small portion of the tendon or ligament + in water, and examine with a glass of high power. Note the large fibers + in the ligament, which branch and interlace. + + Experiment 27. With the head slightly bent forwards, grasp between + the fingers of the right hand the edge of the left + sterno-cleido-mastoid, just above the collar bone. Raise the head and + turn it from left to right, and the action of this important muscle is + readily seen and felt. In some persons it stands out in bold relief. + + Experiment 28. The tendons which bound the space (popliteal) behind + the knee can be distinctly felt when the muscles which bend the knee are + in action. On the outer side note the tendons of the biceps of the leg, + running down to the head of the fibula. On the inside we feel three + tendons of important muscles on the back of the thigh which flex the leg + upon the thigh. + + Experiment 29. _To show the ligamentous action of the muscles._ + Standing with the back fixed against a wall to steady the pelvis, the + knee can be flexed so as to almost touch the abdomen. Take the same + position and keep the knee rigid. When the heel has been but slightly + raised a sharp pain in the back of the thigh follows any effort to carry + it higher. Flexion of the leg to a right angle, increases the distance + from the lines of insertion on the pelvic bones to the tuberosities of + the tibia by two or three inches--an amount of stretching these muscle + cannot undergo. Hence the knee must be flexed in flexion of the hip. + + Experiment 30. A similar experiment may be tried at the wrist. Flex + the wrist with the fingers extended, and again with the fingers in the + fist. The first movement can be carried to 90°, the second only to 30°, + or in some persons up to 60°. Making a fist had already stretched the + extensor muscles of the arm, and they can be stretched but little + farther. Hence, needless pain will be avoided by working a stiff wrist + with the parts loose, or the fingers extended, and not with a clenched + fist. + + + Review Analysis: Important Muscles. + + Location. + Name. Chief Function. + + + Head and Neck. + + Occipito-frontalis. moves scalp and raises eye brow. + Orbicularis palpebrarum. shuts the eyes. + Levator palpebrarum. opens the eyes. + Temporal. raise the lower jaw. + Masseter. " " " " + Sterno-cleido-mastoid. depresses head upon neck and neck upon chest. + Platysma myoides. depresses lower jaw and lower lip. + + + Trunk. + + Pectoralis major. draws arm across front of chest. + Pectoralis minor. depresses point of shoulder, + Latissimus dorsi. draws arm downwards and backwards. + Serratus magnus. assists in raising ribs. + Trapezius. Rhomboideus. backward movements of head and shoulder, + Intercostals. raise and depress the ribs. + External oblique. /various forward movements + Internal oblique. \ of trunk + Rectus abdominis. compresses abdominal viscera and acts upon + pelvis. + + Upper Limbs. + + Deltoid. carries arm outwards and upwards. + Biceps. flexes elbow and raises arm. + Triceps. extends the forearm. + Brachialis anticus. flexor of elbow. + Supinator longus. flexes the forearm. + Flexor carpi radialis. flexors of wrist. + Flexor carpi ulnaris. " " " + + + Lower Limbs. + + Gluteus maximus. adducts the thigh. + Adductors of thigh. draw the leg inwards. + Sartorius. crosses the legs. + Rectus femoris. flexes the thigh. + Vastus externus. extensor of leg. + Vastus internus. extensor of leg upon thigh. + Biceps femoris. flexes leg upon thigh. + Gracilis. flexes the leg and adducts thigh. + Tibialis anticus. draws up inner border of foot. + Peroneus longus. raises outer edge of foot, + Gastrocnemius. keep the body erect, and + Soleus. aid in walking and running. + + + + +Chapter IV. + +Physical Exercise. + + + +80. Importance of Bodily Exercise. Nothing is so essential to success +in life as sound physical health. It enables us to work with energy and +comfort, and better to endure unusual physical and mental strains. While +others suffer the penalties of feebleness, a lower standard of functional +activities, and premature decay, the fortunate possessor of a sound mind +in a sound body is better prepared, with proper application, to endure the +hardships and win the triumphs of life[13]. + +This element of physical capacity is as necessary to a useful and +energetic life, as are mental endowment and intellectual acquirement. +Instinct impels us to seek health and pleasure in muscular exercise. A +healthy and vigorous child is never still except during sleep. The +restless limbs and muscles of school children pent up for several hours, +feel the need of movement, as a hungry man craves food. This natural +desire for exercise, although too often overlooked, is really one of the +necessities of life. One must be in ill health or of an imperfect nature, +when he ceases to feel this impulse. Indeed, motion within proper bounds +is essential to the full development and perfect maintenance of the bodily +health. Unlike other machines, the human body becomes within reasonable +limits, stronger and more capable the more it is used. + +As our tenure of life at best is short, it is our duty to strive to live +as free as possible from bodily ills. It is, therefore, of paramount +importance to rightly exercise every part of the body, and this without +undue effort or injurious strain. + +Strictly speaking, physical exercise refers to the functional +activity of each and every tissue, and properly includes the regulation of +the functions and movements of the entire body. The word exercise, +however, is used usually in a narrower sense as applied to those movements +that are effected by the contraction of the voluntary muscles. + +Brief reference will be made in this chapter only to such natural and +systematic physical training as should enter into the life of every +healthy person. + +81. Muscular Activity. The body, as we have learned, is built up of +certain elementary tissues which are combined to make bones, muscles, +nerves, and other structures. The tissues, in turn, are made up of +countless minute cells, each of which has its birth, lives its brief +moment to do its work in the animal economy, is separated from the tissue +of which it was a part, and is in due time eliminated by the organs of +excretion,--the lungs, the skin, or the kidneys. Thus there is a +continuous process of growth, of decay, and removal, among the individual +cells of each tissue. + + [NOTE. The Incessant Changes in Muscular Tissue. "In every tiny + block of muscle there is a part which is really alive, there are parts + which are becoming alive, there are parts which have been alive, and + are now dying or dead; there is an upward rush from the lifeless to + the living, a downward rush from the living to the dead. This is + always going on, whether the muscle be quiet and at rest, or whether + it be active and moving,--some of the capital of living material is + being spent, changed into dead waste; some of the new food is always + being raised into living capital. But when the muscle is called upon + to do work, when it is put into movement, the expenditure is + quickened, there is a run upon the living capital, the greater, the + more urgent the call for action."--Professor Michael Foster.] + +These ceaseless processes are greatly modified by the activity of the +bodily functions. Every movement of a muscle, for instance, involves +change in its component cells. And since the loss of every atom of the +body is in direct relation to its activity, a second process is necessary +to repair this constant waste; else the body would rapidly diminish in +size and strength, and life itself would soon end. This process of repair +is accomplished, as we shall learn in Chapters VI. and VII., by the organs +of nutrition, which convert the food into blood. + +[Illustration: Fig. 39.--Showing how the Muscles of the Back may be +developed by a Moderate Amount of Dumb-Bell Exercise at Home. (From a +photograph.)] + +82. Effect of Exercise upon the Muscles. Systematic exercise +influences the growth and structure of the muscles of the body in a manner +somewhat remarkable. Muscular exercise makes muscular tissue; from the +lack of it, muscles become soft and wasted. Muscles properly exercised not +only increase in size, both as a whole and in their individual structure, +but are better enabled to get rid of material which tends to hamper their +movements. Thus muscular exercise helps to remove any needless +accumulation of fat, as well as useless waste matters, which may exist in +the tissues. As fat forms no permanent structural part of the organism, +its removal is, within limits, effected with no inconvenience. + +Muscular strength provides the joints with more powerful ligaments and +better developed bony parts. After long confinement to the bed from +disease, the joints have wasted ligaments, thin cartilages, and the bones +are of smaller proportions. Duly exercised muscles influence the size of +the bones upon which they act. Thus the bones of a well-developed man are +stronger, firmer, and larger than those of a feeble person. + +He who has been physically well trained, has both a more complete and a +more intelligent use of his muscles. He has acquired the art of causing +his muscles to act in concert. Movements once difficult are now carried on +with ease. The power of coördination is increased, so that a desired end +is attained with the least amount of physical force and nervous energy. In +learning to row, play baseball, ride the bicycle, or in any other +exercises, the beginner makes his movements in a stiff and awkward manner. +He will use and waste more muscular force in playing one game of ball, or +in riding a mile on his wheel, than an expert would in doing ten times the +work. He has not yet learned to balance one set of muscles against their +antagonists. + +[Illustration: Fig. 40.--The Standard Special Chest Weight. + +A convenient machine by means of which all the muscles of the body may be +easily and pleasantly exercised with sufficient variations in the +movements to relieve it of monotony. + +A space 6 ft wide, 6 ft deep, and 7 ft high nearly in front of the machine +is required for exercise.] + +In time, however, acts which were first done only with effort and by a +conscious will, become automatic. The will ceases to concern itself. By +what is called reflex action, memory is developed in the spinal cord and +the muscular centers (sec. 273). There is thus a great saving of actual +brain work, and one important cause of fatigue is removed. + +83. Effect of Exercise on Important Organs. The importance of +regular exercise is best understood by noting its effects upon the +principal organs of the body. As the action of the heart is increased both +in force and frequency during exercise, the flow of blood throughout the +body is augmented. This results from the force of the muscular +contractions which play their part in pressing the blood in the veins +onward towards the heart. Exercise also induces a more vigorous +respiration, and under increased breathing efforts the lung capacity is +increased and the size of the chest is enlarged. The amount of air +inspired and expired in a given time is much larger than if the body were +at rest. The blood is thus supplied with a much larger amount of oxygen +from the air inhaled, and gives off to the air a corresponding excess of +carbon dioxid and water. + +Again, exercise stimulates and strengthens the organs of digestion. The +appetite is improved, as is especially noted after exercise in the open +air. The digestion is more complete, absorption becomes more rapid, the +peristaltic movements of the bowels are promoted, and the circulation +through the liver is more vigorous. More food is taken to supply the force +necessary for the maintenance of the mechanical movements. Ample exercise +also checks the tendency towards a torpid circulation in the larger +digestive organs, as the stomach and the liver, so common with those who +eat heartily, but lead sedentary lives. In short, exercise may be regarded +as a great regulator of nutrition. + +Exercise increases the flow of blood through the small vessels of the +skin, and thus increases the radiation of heat from the surface. If the +exercise be vigorous and the weather hot, a profuse sweat ensues, the +rapid evaporation of which cools the body. The skin is thus a most +important regulator of the bodily temperature, and prevents any rise above +the normal which would otherwise result from vigorous exercise. (See secs. +226 and 241). + +84. Effect of Exercise upon the Personal Appearance. Judicious and +systematic exercise, if moderately employed, soon gives a more upright and +symmetrical figure, and an easier and more graceful carriage. Rounded +shoulders become square, the awkward gait disappears, and there is seen a +graceful poise to the head and a bearing of the body which mark those +whose muscles have been well trained. A perfectly formed skeleton and +well-developed muscles give the graceful contour and perfect outline to +the human body. The lean, soft limbs of those who have never had any +physical education, often look as if they belonged to persons recovering +from sickness. The effects of sound physical exercise are well exhibited +in the aspect of the neck, shoulders, and chest of one who has been well +trained. This is noticeable in gymnasts and others who practice upon the +horizontal bar, with chest weights, dumb-bells, and other apparatus which +develop more especially the muscles of the upper half of the trunk. + +[Illustration: Fig. 41.--Young Woman practicing at Home with the "Whitely +Exerciser." (From a photograph)] + +Exercise improves the condition of the tissues generally. They become more +elastic, and in all respects sounder. The skin becomes firm, clear, and +wholesome. Hence, every part of the surface of the body rapidly takes on a +change in contour, and soon assumes that appearance of vigor and soundness +which marks those of firm physical condition. The delicate, ruddy aspect +of the complexion, the swing about the body and the bearing of the head +and shoulders, of young women whose physical training has been efficient, +are in marked contrast with those characteristics in persons whose +education in this respect has been neglected. + +85. Effect of Unsuitable or Excessive Exercise. But exercise, like +everything else which contributes to our welfare, may be carried to +excess. The words excessive and unsuitable, when applied to muscular +exertion, are relative terms, and apply to the individual rather than to +amount of work done. Thus what may be excessive for one person, might be +suitable and beneficial to another. Then the condition of the individual, +rather than the character of the muscular work, is always a most important +factor. + +Breathlessness is, perhaps, the most common effect of undue exertion. Let +a middle-aged person, who is out of practice, run a certain distance, and +he is soon troubled with his breathing. The respirations become irregular, +and there is a sense of oppression in his chest. He pants, and his +strength gives out. His chest, and not his legs, has failed him. He is +said to be "out of breath." He might have practiced dumb-bells or rowed +for some time without inconvenience. + +The heart is often overstrained, and at times has been ruptured during +violent exertion, as in lifting an immense weight. The various forms of +heart-disease are common with those whose occupations involve severe +muscular effort, as professional athletes and oarsmen. Hæmorrhages of +various kinds, especially from the lungs, or rupture of blood-vessels in +the brain, are not uncommon results of over-exertion. + +Excessive repetition of muscular movements may lead to permanent +contractions of the parts involved. Thus sailors, mechanics, and others +frequently develop a rigidity of the tendons of the hand which prevents +the full extension of the fingers. So stenographers, telegraphers and +writers occasionally suffer from permanent contractions of certain muscles +of the arm, known as writer's cramp, due to their excessive use. But the +accidents which now and then may result from severe physical exertion, +should discourage no one from securing the benefits which accrue from +moderate and reasonable exercise. + +86. Muscular Fatigue. We all know how tiresome it is to hold the arm +outstretched horizontally even for a few moments. A single muscle, the +deltoid, in this case does most of the work. Even in a vigorous man, this +muscle can act no longer than four to six minutes before the arm drops +helpless. We may prolong the period by a strong effort of the will, but a +time soon comes when by no possible effort are we able to hold out the +arm. The muscle is said to be fatigued. It has by no means lost its +contractile power, for if we apply a strong electric stimulus to it, the +fatigue seems to disappear. Thus we see the functional power of a muscle +has a definite limit, and in fatigue that limit is reached. + +[Illustration: Fig. 42.--A Well-Equipped Gymnasium. (From a photograph.)] + +The strength of the muscle, its physical condition, the work it has done, +and the mental condition of the individual, all modify the state of +fatigue. In those difficult acts which involve a special effort of the +will, the matter of nerve exhaustion is largely concerned. Thus, the +incessant movements in St. Vitus' dance result in comparatively little +fatigue, because there is no association of the brain with the muscular +action. If a strong man should attempt to perform voluntarily the same +movements, he would soon have to rest. None of the movements which are +performed independently of the will, as the heart-beats and breathing +movements, ever involve the sensation of fatigue. As a result of fatigue +the normal irritability of muscular tissue becomes weakened, and its force +of contraction is lessened. There is, also, often noticed in fatigue a +peculiar tremor of the muscles, rendering their movements uncertain. The +stiffness of the muscles which comes on during severe exercise, or the day +after, are familiar results of fatigue. + +This sense of fatigue should put us on guard against danger. It is a kind +of regulator which serves in the ordinary actions of life to warn us not +to exceed the limits of useful exercise. Fatigue summons us to rest long +before all the force of the motor organs has been expended, just as the +sensation of hunger warns us that we need food, long before the body has +become weak from the lack of nourishment. + +We should never forget that it is highly essential to maintain an unused +reserve of power, just as a cautious merchant always keeps at the bank an +unexpended balance of money. If he overspends his money he is bankrupt, +and the person who overspends his strength is for the time physically +bankrupt. In each case the process of recovery is slow and painful. + +87. Rest for the Muscles. Rest is necessary for the tissues, that +they may repair the losses sustained by work; that is, a period of rest +must alternate with a period of activity. Even the heart, beating +ceaselessly, has its periods of absolute rest to alternate with those of +work. A steam-engine is always slowly, but surely, losing its fitness for +work. At last it stops from the need of repair. Unlike the engine, the +body is constantly renewing itself and undergoing continual repair. Were +it not for this power to repair and renew its various tissues, the body +would soon be worn out. + +This repair is really a renovation of the structure. Rest and work are +relative terms, directly opposed to each other. Work quickens the pulse +and the respiration, while rest slows both. During sleep the voluntary +muscles are relaxed, and those of organic life work with less energy. The +pulse and the respiration are less frequent, and the temperature lower +than when awake. Hence sleep, "tired Nature's sweet restorer," may be +regarded as a complete rest. + +The periods of rest should vary with the kind of exercise. Thus exercise +which produces breathlessness requires frequent but short rests. The +trained runner, finding his respiration embarrassed, stops a moment to +regain his breath. Exercises of endurance cause fatigue less quickly than +those of speed, but require longer rest. Thus a man not used to long +distances may walk a number of hours without stopping, but while fatigue +is slow to result, it is also slow to disappear. Hence a lengthy period of +rest is necessary before he is able to renew his journey. + +88. Amount of Physical Exercise Required. The amount of physical +exercise that can be safely performed by each person, is a most important +and practical question. No rule can be laid down, for what one person +bears well, may prove very injurious to another. To a certain extent, each +must be guided by his own judgment. If, after taking exercise, we feel +fatigued and irritable, are subject to headache and sleeplessness, or find +it difficult to apply the mind to its work, it is plain that we have been +taxing our strength unduly, and the warnings should be heeded. + +Age is an important factor in the problem, as a young man may do with +ease and safety, what might be injurious to an older person. In youth, +when the body is making its most active development, the judicious use of +games, sports, and gymnastics is most beneficial. In advanced life, both +the power and the inclination for exercise fail, but even then effort +should be made to take a certain reasonable amount of exercise. + +Abundant evidence shows that physical development is most active from +thirteen to seventeen years of age; this manifests itself clearly by +increase in weight. Hence this period of life is of great consequence. If +at this age a boy or girl is subjected to undue physical strain, the +development may suffer, the growth be retarded, and the foundation laid +for future ill health. + +[Illustration: Fig. 43.--Student exercising in the School Gymnasium on the +Rowing Machine. (From a photograph.)] + +The proper amount of exercise must vary greatly with circumstances. It may +be laid down as a fairly safe rule, that a person of average height and +weight, engaged in study or in any indoor or sedentary occupation, should +take an amount of exercise equivalent to walking five or six miles a day. +Growing children, as a rule, take more exercise than this, while most men +working indoors take far less, and many women take less exercise than men. +Exercise may be varied in many ways, the more the better; but for the most +part it should always be taken in the open air. + +89. Time for Exercise. It is not prudent to do hard work or take +severe exercise, just before or just after a full meal. The best time is +one or two hours after a meal. Vigorous exercise while the stomach is +busily digesting food, may prove injurious, and is apt to result sooner or +later in dyspepsia. On the other hand, severe exercise should not be taken +on an empty stomach. Those who do much work or study before breakfast, +should first take a light lunch, just enough to prevent any faint feeling. +With this precaution, there is no better time for moderate exercise than +the early morning. + +In the case of children, physical exercises should not be undertaken when +they are overtired or hungry. Neither is it judicious for adults to take +vigorous exercise in the evening, after a long and arduous day's work. + +90. Walking, Running, and Jumping. Walking is generally regarded as +the simplest and most convenient mode of taking exercise. Man is +essentially a walking animal. When taken with a special object in view, it +is the best and most pleasant of all physical activities. It is suited for +individuals of all ages and occupations, and for residents of every +climate. The child, the athlete, and the aged are all able to indulge in +this simple and effective means of keeping the body in health. + +In walking, the muscles of the entire body are brought into action, +and the movements of breathing and the circulation of the blood are +increased. The body should be erect, the chest thrown out, the head and +shoulders held back, and the stride long and elastic. It is an excellent +custom to add to the usefulness of this fine exercise, by deep, voluntary +inhalations of pure air. + +Running is an excellent exercise for children and young people, but +should be sparingly indulged in after the age of thirty-five. If it be +accompanied with a feeling of faintness, breathlessness, and palpitation +of the heart, the exercise is too severe, and its continuance may do +serious harm. Running as an exercise is beneficial to those who have kept +themselves in practice and in sound condition. It brings into play nearly +every muscle of the body, and thus serves to develop the power of +endurance, as well as strength and capacity for rapid movement. + +Jumping may well be left to boys and young men under twenty, but +skipping with a rope, allied to jumping, is an admirable and beneficial +form of exercise. It brings into action many muscles without putting undue +strain upon any particular group. + +91. Skating, Swimming, and Rowing. Skating is a delightful and +invigorating exercise. It calls into play a great variety of muscles, and +is admirably adapted for almost all ages. It strengthens the ankles and +helps give an easy and graceful carriage to the body. Skating is +especially valuable, as it can be enjoyed when other out-door exercises +are not convenient. + +Every child above ten years of age should be taught to swim. The art, +once mastered, is never forgotten. It calls into use a wide combination of +muscles. This accomplishment, so easily learned, should be a part of our +education, as well as baseball or bicycling, as it may chance to any one +to save his own life or that of a companion. + +In many respects rowing is one of the most perfect exercises at our +command. It expands the chest, strengthens the body, and gives tone to the +muscles of the abdomen. It is very suitable for girls and women, as no +other exercise is so well adapted to remedy the muscular defects so marked +in their sex. Even elderly persons can row day after day without +difficulty. The degree of muscular effort required, can be regulated so +that those with weak hearts and weak lungs can adjust themselves to the +exercise. + +92. Bicycling as an Exercise. The bicycle as a means of taking +exercise has come into popular use with remarkable rapidity. Sharp +competition bids fair to make the wheel more popular and less expensive +than ever. Its phenomenal use by persons of all ages and in all stations +of life, is proof of the enthusiasm with which this athletic exercise is +employed by women as well as by men. + +Mechanical skill has removed most of the risks to health and person which +once existed. A good machine, used by its owner with judgment, is the most +convenient, the safest, and the least expensive means of traveling for +pleasure or exercise. It is doing more than any other form of exercise to +improve the bodily condition of thousands whose occupations confine them +all day to sedentary work. Dependent upon no one but himself, the cyclist +has his means of exercise always at hand. No preparation is necessary to +take a spin of ten miles or so on the road, during a summer evening or +before breakfast. + +Bicycling brings into active use the muscles of the legs as well as those +of the trunk and arms. It seems to benefit those who suffer from +dyspepsia, constipation, and functional disorders of the liver. + +A special caution must be used against overdoing in cycling, for the +temptation by rivalry, making a record, by social competition on the road, +is stronger in this form of exercise than in any other, especially for +young folks. Many cases have occurred of permanent injury, and even loss +of life, from collapse simply by excessive exertion and exhaustion. + +93. Outdoor Games and Physical Education. While outdoor games +are not necessary to maintain health, yet we can scarcely overestimate the +part that the great games of baseball, football, tennis, golf, and +croquet, play in the physical development of young people. When played in +moderation and under suitable conditions, they are most useful and +beneficial exercises. They are played in the open air, and demand a great +variety of vigorous muscular movement, with a considerable amount of skill +and adroitness of action. These games not only involve healthful exercise, +but develop all those manly and wholesome qualities so essential to +success in life. + +A vigorous body is well-nigh essential to success, but equally important +are readiness of action, sound judgment, good temper, personal courage, a +sense of fair play, and above all, a spirit of honor. Outdoor games, when +played in a reasonable and honorable manner, are most efficient and +practical means to develop these qualities in young people. + + +94. The School and Physical Education. The advantages to be derived, +during the school period, from the proper care and development of the +body, should be understood and appreciated by school officials, teachers, +and parents. The school period is the best time to shape the lives of +pupils, not mentally or morally alone, but physically as well. This is the +time, by the use of a few daily exercises at school, to draw back the +rounding shoulders, to form the habit of sitting and standing erect, to +build up strong and comely arms and chests, and otherwise to train pupils +to those methods which will serve to ripen them into vigorous and +well-knit men and women. + +Teachers can by a little effort gain the knowledge requisite properly to +instruct their pupils in a few systematic exercises. Gratifying results +will follow just as the teacher and pupils evince interest and judgment in +the work. It is found by experience that pupils are not only quick to +learn, but look forward eagerly to the physical exercises as an +interesting change from the routine of school life. + +There should be a stated time for these school exercises, as for any other +duty. There can be practiced in the schoolroom a great variety of +interesting and useful exercises, which call for little or no expense for +apparatus. Such exercises should no more interfere with the children's +usual games than any other study does. Under no circumstances should the +play hours be curtailed. + +95. Physical Exercises in School. Physical exercises of some sort, +then, should be provided for pupils in our schools, especially in large +towns and cities, where there is little opportunity for outdoor games, and +they should form a part of the regular course of study. The object should +be the promotion of sound health rather than the development of muscle, or +performing feats of agility or strength. Exercises with dumb-bells and +wands, or even without any apparatus, practiced a few times a day, for +five minutes at a time, do a great deal of good. They relax the tension of +body and mind, and introduce an element of pleasure into the routine of +school life. They increase the breathing power and quicken the action of +the heart. + +[Illustration: Fig. 44.--Physical Exercises as carried on in Schools. +(From photographs.)] + + [NOTE. "In early boyhood and youth nothing can replace the active + sports so much enjoyed at this period; and while no needless + restrictions should be placed upon them, consideration should be paid + to the amount, and especially to the character, of the games pursued + by delicate youth. For these it would be better to develop the + weakened parts by means of systematic physical exercises and by + lighter sports."--Dr. John M. Keating on "Physical Development" in + Pepper's _Cyclopædia of the Diseases of Children_.] + +If vigorously and systematically carried out, these exercises invigorate +all the tissues and organs of the body, and stimulate them to renewed +activity. They serve to offset the lack of proper ventilation, faulty +positions at the desks, and the prolonged inaction of the muscles. To +secure the greatest benefit from physical training in school, it is +important that the pupils be interested in these exercises, and consider +them a recreation, and not a task[14]. + +96. Practical Points about Physical Exercise. The main object in +undertaking systematic and graduated physical exercises is not to learn to +do mere feats of strength and skill, but the better to fit the individual +for the duties and the work of life. Exercises should be considered with +reference to their availability from the learner's standpoint. The most +beneficial exercises ordinarily are the gentle ones, in which no strain is +put upon the heart and the respiration. The special aim is to secure the +equal use of all the muscles, not the development of a few. The +performance of feats of strength should never come within the scope of any +educational scheme. Exercises which call for sustained effort, violent +exertion, or sudden strain are best avoided by those who have had no +preparation or training. + +Regular exercise, not sudden and occasional prolonged exertion, is +necessary for health. The man or woman who works in an office or store all +the week, and on Sunday or a holiday indulges in a long spin on the +bicycle, often receives more harm than good from the exertion. Exercise +should be taken, so far as is convenient, in the open air, or in a large +and well-ventilated room.[15] + +After the more violent exercises, as baseball, football, a long ride on +the bicycle, or even after a prolonged walk, a warm bath should be taken +at the first convenient opportunity. Care should be taken to rub down +thoroughly, and to change a part or all of the clothing. Exercise is +comparatively valueless until the idea of taking it for health is quite +forgotten in the interest and pleasure excited by the occasion. No +exercise should be carried to such a degree as to cause fatigue or +exhaustion. Keep warmly clad after exercise, avoid chills, and always stop +exercising as soon as fatigue is felt. + +Wear clothing which allows free play to all the muscles of the body. The +clothing should be light, loose, and made of wool. Care should be taken +not to take cold by standing about in clothes which are damp with +perspiration. In brisk walking and climbing hills keep the mouth shut, +especially in cold weather, and breathe through the nose, regulating the +pace so that it can be done without discomfort. + + +97. Effect of Alcoholic Liquors and Tobacco upon Physical Culture. As +a result of the unusual attention given to physical culture in the last +few years, hundreds of special instructors are now employed in training +young people in the theory and practice of physical exercise. These expert +teachers, to do their work with thoroughness and discipline, recognize the +necessity of looking after the daily living of their students. The time of +rising and retiring, the hours of sleep, the dress, the care of the diet, +and many other details of personal health become an important part of the +training. + +Recognizing the fact that alcoholic drink and tobacco are so disastrous to +efficiency in any system of physical training, these instructors rigidly +forbid the use of these drugs under all circumstances. While this +principle is perhaps more rigorously enforced in training for athletic +contests, it applies equally to those who have in view only the +maintenance of health. + +Books on Physical Education. There are many excellent books on +physical education, which are easily obtained for reading or for +reference. Among these one of the most useful and suggestive is Blackie's +well-known book, "How to Get Strong and how to Stay so." This little book +is full of kindly advice and practical suggestions to those who may wish +to begin to practice health exercises at home with inexpensive apparatus. +For more advanced work, Lagrange's "Physiology of Bodily Exercise" and the +Introduction to Maclaren's "Physical Education" may be consulted. A +notable article on "Physical Training" by Joseph H. Sears, an Ex-Captain +of the Harvard Football Team, may be found in Roosevelt's "In Sickness and +in Health." + +Price lists and catalogues of all kinds of gymnastic apparatus are easily +obtained on application to firms handling such goods. + +Various Systems of Physical Exercises. The recent revival of popular +interest in physical education has done much to call the attention of the +public to the usefulness and importance of a more thorough and systematic +use of physical exercises, both at home and in the schools. It is not +within the scope of this book to describe the various systems of gymnastic +and calisthenic exercises now in common use in this country. For the most +part they have been modified and rearranged from other sources, notably +from the two great systems, i.e., Swedish and German. + +For a most comprehensive work on the Swedish system, the teacher is +referred to the "Swedish System of Educational Gymnastics," with 264 +illustrations, by Baron Nils Posse. There is also a small manual for +teachers, called "Handbook of School Gymnastics of the Swedish Systems," +by the same author. + + + + +Chapter V. + +Food and Drink. + + + +98. Why we need Food. The body is often compared to a steam-engine in +good working order. An engine uses up fuel and water to obtain from them +the energy necessary to do its work. So, we consume within our bodies +certain nutritious substances to obtain from them the energy necessary for +our activities. Just as the energy for the working of the engine is +obtained from steam by the combustion of fuel, so the energy possessed by +our bodies results from the combustion or oxidation within us of the food +we eat. Unless this energy is provided for the body it will have but +little power of doing work, and like an engine without steam, must soon +become motionless. + + +99. Waste and Repair. A steam-engine from the first stroke of its +piston-rod begins to wear out, and before long needs repair. All work +involves waste. The engine, unless kept in thorough repair, would soon +stop. So with our bodies. In their living cells chemical changes are +constantly going on; energy, on the whole, is running down; complex +substances are being broken up into simpler combinations. So long as life +lasts, food must be brought to the tissues, and waste products carried +away from them. It is impossible to move a single muscle, or even to think +for one moment, without some minute part of the muscular or brain tissue +becoming of no further use in the body. The transformation of dead matter +into living tissue is the ever-present miracle which life presents even in +its lowest forms. + +In childhood the waste is small, and the amount of food taken is more +than sufficient to repair the loss. Some of the extra food is used in +building up the body, especially the muscles. As we shall learn in Chapter +VIII., food is also required to maintain the bodily heat. Food, then, +is necessary for the production of energy, for the repair of the body, for +the building up of the tissues, and for the maintenance of bodily heat. + + +100. Nature of the Waste Material. An ordinarily healthy person +passes daily, on an average, by the kidneys about 50 ounces of waste +material, of which 96 per cent is water, and from the intestines, on an +average, 5½ ounces, a large proportion of which is water. By the skin, +in the shape of sweat and insensible perspiration, there is cast out about +23 ounces, of which 99 per cent is water; and by the lungs about 34 +ounces, 10 of which are water and the remainder carbon dioxid. + +Now if we omit an estimate of the undigestible remains of the food, we +find that the main bulk of what daily leaves the body consists of water, +carbon dioxid, and certain solid matters contained in solution in +the renal secretion and the sweat. The chief of these solid matters is +urea, a complex product made up of four elements,--carbon, hydrogen, +oxygen, and nitrogen. Water contains only two elements, hydrogen and +oxygen; and carbon dioxid also has only two, carbon and oxygen. Hence, +what we daily cast out of our bodies consists essentially of these four +elements in the form mainly of water, carbon dioxid, and urea. + +These waste products represent the oxidation that has taken place in +the tissues in producing the energy necessary for the bodily activities, +just as the smoke, ashes, clinkers, and steam represent the consumption of +fuel and water in the engine. Plainly, therefore, if we could restore to +the body a supply of these four elements equivalent to that cast out, we +could make up for the waste. The object of food, then, is to restore to +the body an amount of the four elements equal to that consumed. In other +words, and briefly: The purpose of food is to supply the waste of the +tissues and to maintain the normal composition of the blood. + +101. Classification of Foods. Foods may be conveniently divided into +four great classes, to which the name food-stuffs or alimentary +principles has been given. They correspond to the chief "proximate +principles" of which the body consists. To one or the other of these +classes all available foods belong[16]. The classification of food-stuffs +usually given is as follows: + + I. Proteids, or Nitrogenous Foods. + II. Starches and Sugars, or Carbohydrates. + III. Fats and Oils. + IV. Inorganic or Mineral Foods,--Water, Salt. + +102. Proteids; or Nitrogenous Foods. The proteids, frequently +spoken of as the nitrogenous foods, are rich in one or more of the +following organic substances: albumen, casein, fibrin, gelatine, myosin, +gluten, and legumin. + +The type of this class of foods is albumen, well known as the white of an +egg. The serum of the blood is very rich in albumen, as is lean meat. The +curd of milk consists mainly of casein. Fibrin exists largely in blood and +flesh foods. Gelatine is obtained from the animal parts of bones and +connective tissue by prolonged boiling. One of the chief constituents of +muscular fiber is myosin. Gluten exists largely in the cereals wheat, +barley, oats, and rye. The proteid principle of peas and beans is legumin, +a substance resembling casein. + +As the name implies, the proteids, or nitrogenous foods, contain nitrogen; +carbohydrates and fats, on the contrary, do not contain nitrogen. The +principal proteid food-stuffs are milk, eggs, flesh foods of all kinds, +fish, and the cereals among vegetable foods. Peas and beans are rich in +proteids. The essential use of the proteids to the tissues is to supply +the material from which the new proteid tissue is made or the old proteid +tissue is repaired. They are also valuable as sources of energy to the +body. Now, as the proteid part of its molecule is the most important +constituent of living matter, it is evident that proteid food is an +absolute necessity. If our diet contained no proteids, the tissues of +the body would gradually waste away, and death from starvation would +result. All the food-stuffs are necessary in one way or another to the +preservation of perfect health, but proteids, together with a certain +proportion of water and inorganic salts, are absolutely necessary for the +bare maintenance of animal life--that is, for the formation and +preservation of living protoplasm. + +103. Starches and Sugars. The starches, sugars, and gums, also known +as carbohydrates, enter largely into the composition of foods of +vegetable origin. They contain no nitrogen, but the three elements, +carbon, hydrogen, and oxygen, the last two in the same proportion as in +water. The starches are widely distributed throughout the vegetable +kingdom. They are abundant in potatoes and the cereals, and in arrowroot, +rice, sago, and tapioca. Starch probably stands first in importance among +the various vegetable foods. + +The sugars are also widely distributed substances, and include the +cane, grape, malt, maple, and milk sugars. Here also belong the gums and +cellulose found in fruit, cereals, and all vegetables which form the +basis of the plant cells and fibers. Honey, molasses, and manna are +included in this class. + +The physiological value of the starches and sugars lies in the fact that +they are oxidized in the body, and a certain amount of energy is thereby +liberated. The energy of muscular work and of the heat of the body comes +largely from the oxidation, or destruction, of this class of foods. Now, +inasmuch as we are continually giving off energy from the body, chiefly in +the form of muscular work and heat, it is evident that material for the +production of this energy must be taken in the food. The carbohydrates +constitute the bulk of our ordinary food. + +104. Fats and Oils. These include not only the ordinary fats of +meat, but many animal and vegetable oils. They are alike in +chemical composition, consisting of carbon and hydrogen, with a little +oxygen and no nitrogen. The principal kinds of fat used as food are the +fat of meat, butter, suet, and lard; but in many parts of the world +various vegetable oils are largely used, as the olive, palm, cotton seed, +cocoanut, and almond. + +The use of the fats in the body is essentially the same as that of the +starches and sugars. Weight for weight they are more valuable than the +carbohydrates as sources of energy, but the latter are more easily +digested, and more easily oxidized in the body. An important use of fatty +foods is for the maintenance of the bodily heat. The inhabitants of Arctic +regions are thus enabled, by large use of the fat and oil from the animals +they devour, to endure safely the severe cold. Then there is reason to +believe that fat helps the digestion of other foods, for it is found that +the body is better nourished when the fats are used as food. When more fat +is consumed than is required to keep up the bodily heat and to yield +working power, the excess is stored up in various parts of the body, +making a sort of reserve fuel, which may be drawn upon at any future time. + +105. Saline or Mineral Foods. All food contains, besides the +substances having potential energy, as described, certain saline +matters. Water and salts are not usually considered foods, but the results +of scientific research, as well as the experience of life, show that these +substances are absolutely necessary to the body. The principal mineral +foods are salt, lime, iron, magnesia, phosphorus, potash, and water. +Except common salt and water, these substances are usually taken only in +combination with other foods. + +These saline matters are essential to health, and when not present in due +proportion nutrition is disturbed. If a dog be fed on food freed from all +salines, but otherwise containing proper nutrients, he soon suffers from +weakness, after a time amounting to paralysis, and often dies in +convulsions. + +About 200 grains of common salt are required daily by an adult, but a +large proportion of this is in our food. Phosphate of lime is obtained +from milk and meats, and carbonate of lime from the hard water we drink. +Both are required for the bones and teeth. The salts of potash, which +assist in purifying the blood, are obtained from vegetables and fruits. An +iron salt is found in most foods, and sulphur in the yolk of eggs. + +106. Water. Water is of use chiefly as a solvent, and while not +strictly a food, is necessary to life. It enters into the construction of +every tissue and is constantly being removed from the body by every +channel of waste[17]. + +As a solvent water aids digestion, and as it forms about 80 per cent +of the blood, it serves as a carrier of nutrient material to all the +tissues of the body. + + + +Important Articles of Diet. + + +107. Milk. The value of milk as a food cannot be overestimated. +It affords nourishment in a very simple, convenient, and perfect form. It +is the sole food provided for the young of all animals which nourish their +young. It is an ideal food containing, in excellent proportions, all the +four elements necessary for growth and health in earlier youth. + +[Table: Composition of Food Materials. Careful analyses have been +made of the different articles of food, mostly of the raw, or uncooked +foods. As might be expected, the analyses on record differ more or less in +the percentages assigned to the various constituents, but the following +table will give a fair idea of the fundamental nutritive value of the more +common foods: + + + In 100 parts Water Proteid Fat Carbohydrate Ash + Digestible Cellulose + Meat 76.7 20.8 1.5 0.3 -- 1.3 + Eggs 73.7 12.6 12.1 -- -- 1.1 + Cheese 36-60 25-33 7-30 3-7 -- 3.4 + Cow's Milk 87.7 3.4 3.2 4.8 -- 0.7 + Wheat Flour 13.3 10.2 0.9 74.8 0.3 0.5 + Wheat Bread 35.6 7.1 0.2 55.5 0.3 1.1 + Rye Flour 13.7 11.5 2.1 69.7 1.6 1.4 + Rye bread 42.3 6.1 0.4 49.2 0.5 1.5 + Rice 13.1 7.0 0.9 77.4 0.6 1.0 + Corn 13.1 9.9 4.6 68.4 2.5 1.5 + Macaroni 10.1 9.0 0.3 79.0 0.3 0.5 + Peas and Beans 12-15 23-26 1½-2 49-54 4.7 2-3 + Potatoes 75.5 2.0 0.2 20.6 0.7 1.0 + Carrots 87.1 1.0 0.2 9.3 1.4 0.9 + Cabbage 90 2.3 0.5 4-6 1-2 1.3 + Fruit 84 0.5 -- 10 4 0.5 +] + +Cheese is the nitrogenous part of milk, which has been coagulated by the +use of rennet. The curd is then carefully dried, salted, and pressed. +Cheese is sometimes difficult of digestion, as on account of its solid +form it is not easily acted upon by the digestive fluids. + +108. Meats. The flesh of animals is one of our main sources of food. +Containing a large amount of proteid, it is admirably adapted for building +up and repairing the tissues of the body. The proportion of water is also +high, varying from 50 to 75 per cent. The most common meats used in +this country are beef, mutton, veal, pork, poultry, and game. + +Beef contains less fat and is more nutritious than either mutton or pork. +Mutton has a fine flavor and is easily digested. Veal and lamb, though +more tender, are less easily digested. Pork contains much fat, and its +fiber is hard, so that it is the most difficult to digest of all the +meats. Poultry and game have usually a small proportion of fat, but are +rich in phosphates and are valued for their flavor. + +109. Eggs. Consisting of about two-thirds water and the rest albumen +and fat, eggs are often spoken of as typical natural food. The white +of an egg is chiefly albumen, with traces of fat and salt; the yolk is +largely fat and salts. The yellow color is due partly to sulphur. It is +this which blackens a silver spoon. Eggs furnish a convenient and +concentrated food, and if properly cooked are readily digested. + +110. Fish. Fish forms an important and a most nutritious article of +diet, as it contains almost as much nourishment as butcher's meat. The +fish-eating races and classes are remarkably strong and healthy. Fish +is less stimulating than meat, and is thus valuable as a food for invalids +and dyspeptics. To be at its best, fish should be eaten in its season. As +a rule shell-fish, except oysters, are not very digestible. Some persons +are unable to eat certain kinds of fish, especially shell-fish, without +eruptions on the skin and other symptoms of mild poisoning. + +111. Vegetable Foods. This is a large and important group of foods, +and embraces a remarkable number of different kinds of diet. Vegetable +foods include the cereals, garden vegetables, the fruits, and other less +important articles. These foods supply a certain quantity of albumen and +fat, but their chief use is to furnish starches, sugars, acids, and salts. +The vegetable foods indirectly supply the body with a large amount of +water, which they absorb in cooking. + +112. Proteid Vegetable Foods. The most important proteid vegetable +foods are those derived from the grains of cereals and certain +leguminous seeds, as peas and beans. The grains when ground make the +various flours or meals. They contain a large quantity of starch, a +proteid substance peculiar to them called gluten, and mineral salts, +especially phosphate of lime. Peas and beans contain a smaller proportion +of starch, but more proteid matter, called legumin, or vegetable casein. +Of the cereal foods, wheat is that most generally useful. Wheat, and corn +and oatmeal form most important articles of diet. Wheat flour has starch, +sugar, and gluten--nearly everything to support life except fat. + +Oatmeal is rich in proteids. In some countries, as Scotland, it forms an +important article of diet, in the form of porridge or oatmeal cakes. + +Corn meal is not only rich in nitrogen, but the proportion of fat is also +large; hence it is a most important and nutritious article of food. Rice, +on the other hand, contains less proteids than any other cereal grain, and +is the least nutritious. Where used as a staple article of food, as in +India, it is commonly mixed with milk, cheese, or other nutritious +substances. Peas and beans, distinguished from all other vegetables by +their large amount of proteids--excel in this respect even beef, mutton, +and fish. They take the place of meats with those who believe in a +vegetable diet. + +113. Non-proteid Vegetable Foods. The common potato is the best type +of non-proteid vegetable food. When properly cooked it is easily +digested and makes an excellent food. It contains about 75 per cent of +water, about 20 per cent of carbohydrates, chiefly starch, 2 per cent of +proteids, and a little fat and saline matters. But being deficient in +flesh-forming materials, it is unfit for an exclusive food, but is best +used with milk, meat, and other foods richer in proteid substances. Sweet +potatoes, of late years extensively used as food, are rich in starch and +sugar. Arrowroot, sago, tapioca, and similar foods are nutritious, and +easily digested, and with milk furnish excellent articles of diet, +especially for invalids and children. + +Explanation of the Graphic Chart. The graphic chart, on the next +page, presents in a succinct and easily understood form the composition of +food materials as they are bought in the market, including the edible and +non-edible portions. It has been condensed from Dr. W. O. Atwater's +valuable monograph on "Foods and Diet." This work is known as the Yearbook +of the U.S. Department of Agriculture for 1894. + +KEY: 1, percentage of nutrients; 2, fuel value of 1 pound in calories. The +unit of heat, called a _calorie_, or gramme-degree, is the amount of heat +which is necessary to raise one gramme (15.43 grains) of water one degree +centigrade (1.8° Fahr.). A, round beef; B, sirloin beef; C, rib beef; D, +leg of mutton; E, spare rib of pork; F, salt pork; G, smoked ham; H, fresh +codfish; I, oysters; J, milk; K, butter; L, cheese; M, eggs; N, wheat +bread; O, corn meal; P, oatmeal; Q, dried beans; R, rice; S, potatoes; T, +sugar. + +This table, among other things, shows that the flesh of fish contains more +water than that of warm-blooded animals. It may also be seen that animal +foods contain the most water; and vegetable foods, except potatoes, the +most nutrients. Proteids and fats exist only in small proportions in most +vegetables, except beans and oatmeal. Vegetable foods are rich in +carbohydrates while meats contain none. The fatter the meat the less the +amount of water. Thus very lean meat may be almost four-fifths water, and +fat pork almost one-tenth water. + +[Illustration: Fig. 45.--Graphic Chart of the Composition of Food +Materials. Composition of Food Materials. Nutritive ingredients, refuse, +and fuel value. ] + +114. Non-proteid Animal Foods. Butter is one of the most digestible +of animal fats, agreeable and delicate in flavor, and is on this account +much used as a wholesome food. Various substitutes have recently come into +use. These are all made from animal fat, chiefly that of beef, and are +known as butterine, oleomargarine, and by other trade names. These +preparations, if properly made, are wholesome, and may be useful +substitutes for butter, from which they differ but little in composition. + +115. Garden Vegetables. Various green, fresh, and succulent +vegetables form an essential part of our diet. They are of importance +not so much on account of their nutritious elements, which are usually +small, as for the salts they supply, especially the salts of potash. It is +a well-known fact that the continued use of a diet from which fresh +vegetables are excluded leads to a disease known as scurvy. They are also +used for the agreeable flavor possessed by many, and the pleasant variety +and relish they give to the food. The undigested residue left by all green +vegetables affords a useful stimulus to intestinal contraction, and tends +to promote the regular action of the bowels. + +116. Fruits. A great variety of fruits, both fresh and dry, is +used as food, or as luxuries. They are of little nutritive value, +containing, as they do, much water and only a small amount of proteid, but +are of use chiefly for the sugar, vegetable acids, and salts they contain. + +In moderate quantity, fruits are a useful addition to our regular diet. +They are cooling and refreshing, of agreeable flavor, and tend to prevent +constipation. Their flavor and juiciness serve to stimulate a weak +appetite and to give variety to an otherwise heavy diet. If eaten in +excess, especially in an unripe or an overripe state, fruits may occasion +a disturbance of the stomach and bowels, often of a severe form. + +117. Condiments. The refinements of cookery as well as the craving +of the appetite, demand many articles which cannot be classed strictly as +foods. They are called condiments, and as such may be used in +moderation. They give flavor and relish to food, excite appetite and +promote digestion. Condiments increase the pleasure of eating, and by +their stimulating properties promote secretions of the digestive fluids +and excite the muscular contractions of the alimentary canal. + +The well-known condiments are salt, vinegar, pepper, ginger, nutmeg, +cloves, and various substances containing ethereal oils and aromatics. +Their excessive use is calculated to excite irritation and disorder of the +digestive organs. + +118. Salt The most important and extensively used of the condiments +is common salt. It exists in all ordinary articles of diet, but in +quantities not sufficient to meet the wants of the bodily tissues. Hence +it is added to many articles of food. It improves their flavor, promotes +certain digestive secretions, and meets the nutritive demands of the body. +The use of salt seems based upon an instinctive demand of the system for +something necessary for the full performance of its functions. Food +without salt, however nutritious in other respects, is taken with +reluctance and digested with difficulty. + +Salt has always played an important and picturesque part in the history of +dietetics. Reference to its worth and necessity abounds in sacred and +profane history. In ancient times, salt was the first thing placed on the +table and the last removed. The place at the long table, above or below +the salt, indicated rank. It was everywhere the emblem of hospitality. In +parts of Africa it is so scarce that it is worth its weight in gold, and +is actually used as money. Torture was inflicted upon prisoners of state +in olden times by limiting the food to water and bread, without salt. So +intense may this craving for salt become, that men have often risked their +liberty and even their lives to obtain it. + +119. Water. The most important natural beverage is pure water; in +fact it is the only one required. Man has, however, from the earliest +times preferred and daily used a variety of artificial drinks, among which +are tea, coffee, and cocoa. + +All beverages except certain strong alcoholic liquors, consist almost +entirely of water. It is a large element of solid foods, and our +bodies are made up to a great extent of water. Everything taken into the +circulating fluids of the body, or eliminated from them, is done through +the agency of water. As a solvent it is indispensable in all the +activities of the body. + +It has been estimated that an average-sized adult loses by means of the +lungs, skin, and kidneys about eighty ounces of water every twenty-four +hours. To restore this loss about four pints must be taken daily. About +one pint of this is obtained from the food we eat, the remaining three +pints being taken as drink. One of the best ways of supplying water to the +body is by drinking it in its pure state, when its solvent properties can +be completely utilized. The amount of water consumed depends largely upon +the amount of work performed by the body, and upon the temperature. + +Being one of the essential elements of the body, it is highly important +that water should be free from harmful impurities. If it contain the germs +of disease, sickness may follow its use. Without doubt the most important +factor in the spread of disease is, with the exception of impure air, +impure water. The chief agent in the spread of typhoid fever is +impure water. So with cholera, the evidence is overwhelming that filthy +water is an all-powerful agent in the spread of this terrible disease. + +120. Tea, Coffee, and Cocoa. The active principle of tea is called +theine; that of coffee, caffeine, and of cocoa, theobromine. They also +contain an aromatic, volatile oil, to which they owe their distinctive +flavor. Tea and coffee also contain an astringent called tannin, which +gives the peculiar bitter taste to the infusions when steeped too long. In +cocoa, the fat known as cocoa butter amounts to fifty per cent. + +121. Tea. It has been estimated that one-half of the human race now +use tea, either habitually or occasionally. Its use is a prolific source +of indigestion, palpitation of the heart, persistent wakefulness, and of +other disorders. When used at all it should be only in moderation. Persons +who cannot use it without feeling its hurtful effects, should leave it +alone. It should not be taken on an empty stomach, nor sipped after every +mouthful of food. + +122. Coffee. Coffee often disturbs the rhythm of the heart and causes +palpitation. Taken at night, coffee often causes wakefulness. This effect +is so well known that it is often employed to prevent sleep. Immoderate +use of strong coffee may produce other toxic effects, such as muscular +tremors, nervous anxiety, sick-headache, palpitation, and various +uncomfortable feelings in the cardiac region. Some persons cannot drink +even a small amount of tea or coffee without these unpleasant effects. +These favorite beverages are unsuitable for young people. + +123. Cocoa. The beverage known as cocoa comes from the seeds of the +cocoa-tree, which are roasted like the coffee berries to develop the +aroma. Chocolate is manufactured cocoa,--sugar and flavors being added to +the prepared seeds. Chocolate is a convenient and palatable form of highly +nutritious food. For those with whom tea and coffee disagree, it may be an +agreeable beverage. The large quantity of fat which it contains, however, +often causes it to be somewhat indigestible. + +124. Alcoholic Beverages. There is a class of liquids which are +certainly not properly food or drink, but being so commonly used as +beverages, they seem to require special notice in this chapter. In view +of the great variety of alcoholic beverages, the prevalence of their +use, and the very remarkable deleterious effects they produce upon the +bodily organism, they imperatively demand our most careful attention, both +from a physiological and an hygienic point of view. + +125. Nature of Alcohol. The ceaseless action of minute forms of plant +life, in bringing about the decomposition of the elaborated products of +organized plant or animal structures, will be described in more detail +(secs. 394-398). + +All such work of vegetable organisms, whether going on in the moulding +cheese, in the souring of milk, in putrefying meat, in rotting fruit, or +in decomposing fruit juice, is essentially one of fermentation, +caused by these minute forms of plant life. There are many kinds of +fermentation, each with its own special form of minute plant life or +micro-organism. + +In this section we are more especially concerned about that fermentation +which results from the decomposition of sweet fruit, plant, or other +vegetable, juices which are composed largely of water containing sugar and +flavoring matters. + +This special form of fermentation is known as alcoholic or vinous +fermentation, and the micro-organisms that cause it are familiarly termed +alcoholic ferments. The botanist classes them as _Saccharomycetes_, of +which there are several varieties. Germs of _Saccharomycetes_ are found on +the surfaces and stems of fruit as it is ripening. While the fruit remains +whole these germs have no power to invade the juice, and even when the +skins are broken the conditions are less favorable for their work than for +that of the moulds,[18] which are the cause of the rotting of fruit. + +But when fruit is crushed and its juice pressed out, the +_Saccharomycetes_ are carried into it where they cannot get the oxygen +they need from the air. They are then able to obtain oxygen by taking it +from the sugar of the juice. By so doing they cause a breaking up of the +sugar and a rearrangement of its elements. Two new substances are formed +in this decomposition of sugar, viz., carbon dioxid, which arises +from the liquid in tiny bubbles, and alcohol, a poison which +remains in the fermenting fluid. + +Now we must remember that fermentation entirely changes the nature of the +substance fermented. For all forms of decomposition this one law holds +good. Before alcoholic fermentation, the fruit juice was wholesome and +beneficial; after fermentation, it becomes, by the action of the minute +germs, a poisonous liquid known as alcohol, and which forms an essential +part of all intoxicating beverages. + +Taking advantage of this great law of fermentation which dominates the +realm of nature, man has devised means to manufacture various alcoholic +beverages from a great variety of plant structures, as ripe grapes, pears, +apples, and other fruits, cane juices, corn, the malt of barley, rye, +wheat, and other cereals. + +The process differs according to the substance used and the manner in +which it is treated, but the ultimate outcome is always the same, +viz., the manufacture of a beverage containing a greater or less +proportion of alcoholic poison. By the process of _distillation_, new and +stronger liquor is made. Beverages thus distilled are known as ardent +spirits. Brandy is distilled from wine, rum from fermented molasses, and +commercial alcohol mostly from whiskey. + +The poisonous element in all forms of intoxicating drinks, and the one so +fraught with danger to the bodily tissues, is the alcohol they +contain. The proportion of the alcoholic ingredient varies, being about 50 +per cent in brandy, whiskey, and rum, about 20 to 15 per cent in wines, +down to 5 per cent, or less, in the various beers and cider; but whether +the proportion of alcohol be more or less, the same element of danger is +always present. + +126. Effects of Alcoholic Beverages upon the Human System. One of the +most common alcoholic beverages is wine, made from the juice of grapes. As +the juice flows from the crushed fruit the ferments are washed from the +skins and stems into the vat. Here they bud and multiply rapidly, +producing alcohol. In a few hours the juice that was sweet and wholesome +while in the grape is changed to a poisonous liquid, capable of injuring +whoever drinks it. One of the gravest dangers of wine-drinking is the +power which the alcohol in it has to create a thirst which demands more +alcohol. The spread of alcoholism in wine-making countries is an +illustration of this fact. + +Another alcoholic beverage, common in apple-growing districts, is cider. +Until the microscope revealed the ferment germ on the "bloom" of the +apple-skin, very little was known of the changes produced in cider during +the mysterious process of "working." Now, when we see the bubbles of gas +in the glass of cider we know what has produced them, and we know too that +a poison which we do not see is there also in corresponding amounts. We +have learned, too, to trace the wrecked hopes of many a farmer's family to +the alcohol in the cider which he provided so freely, supposing it +harmless. + +Beer and other malt liquors are made from grain. By sprouting the grain, +which changes its starch to sugar, and then dissolving out the sugar with +water, a sweet liquid is obtained which is fermented with yeast, one kind +of alcoholic ferment. Some kinds of beer contain only a small percentage +of alcohol, but these are usually drunk in proportionately large amounts. +The life insurance company finds the beer drinker a precarious risk; the +surgeon finds him an unpromising subject; the criminal court finds him +conspicuous in its proceedings. The united testimony from all these +sources is that beer is demoralizing, mentally, morally, and physically. + +127. Cooking. The process through which nearly all food used by +civilized man has to pass before it is eaten is known as cooking. +Very few articles indeed are consumed in their natural state, the +exceptions being eggs, milk, oysters, fruit and a few vegetables. Man is +the only animal that cooks his food. Although there are savage races that +have no knowledge of cooking, civilized man invariably cooks most of his +food. It seems to be true that as nations advance in civilization they +make a proportionate advance in the art of cooking. + +Cooking answers most important purposes in connection with our food, +especially from its influence upon health. It enables food to be more +readily chewed, and more easily digested. Thus, a piece of meat when raw +is tough and tenacious, but if cooked the fibers lose much of their +toughness, while the connective tissues are changed into a soft and +jelly-like mass. Besides, the meat is much more readily masticated and +acted upon by the digestive fluids. So cooking makes vegetables and grains +softer, loosens their structure, and enables the digestive juices readily +to penetrate their substance. + +Cooking also improves or develops flavors in food, especially in animal +foods, and thus makes them attractive and pleasant to the palate. The +appearance of uncooked meat, for example, is repulsive to our taste, but +by the process of cooking, agreeable flavors are developed which stimulate +the appetite and the flow of digestive fluids. + +Another important use of cooking is that it kills any minute parasites or +germs in the raw food. The safeguard of cooking thus effectually removes +some important causes of disease. The warmth that cooking imparts to food +is a matter of no slight importance; for warm food is more readily +digested, and therefore nourishes the body more quickly. + +The art of cooking plays a very important part in the matter of health, +and thus of comfort and happiness. Badly cooked and ill-assorted foods are +often the cause of serious disorders. Mere cooking is not enough, but good +cooking is essential. + + + +Experiments. + + +Experiments with the Proteids. + +Experiment 31. As a type of the group of proteids we take the white +of egg, egg-white or egg-albumen. Break an egg carefully, so as not to mix +the white with the yolk. Drop about half a teaspoonful of the raw white of +egg into half a pint of distilled water. Beat the mixture vigorously with +a glass rod until it froths freely. Filter through several folds of muslin +until a fairly clear solution is obtained. + +Experiment 32. To a small quantity of this solution in a test tube +add strong nitric acid, and boil. Note the formation of a white +precipitate, which turns yellow. After cooling, add ammonia, and note that +the precipitate becomes orange. + +Experiment 33. Add to the solution of egg-albumen, excess of strong +solution of caustic soda (or potash), and then a drop or two of very +dilute solution (one per cent) of copper sulphate. A violet color is +obtained which deepens on boiling. + +Experiment 34. Boil a small portion of the albumen solution in a test +tube, adding drop by drop dilute acetic acid (two per cent) until a flaky +coagulum of insoluble albumen separates. + + +Experiments with Starch. + +Experiment 35. Wash a potato and peel it. Grate it on a nutmeg grater +into a tall cylindrical glass full of water. Allow the suspended particles +to subside, and after a time note the deposit. The lowest layer consists +of a white powder, or starch, and above it lie coarser fragments of +cellulose and other matters. + +Experiment 36. Examine under the microscope a bit of the above white +deposit. Note that each starch granule shows an eccentric hilum with +concentric markings. Add a few drops of very dilute solution of iodine. +Each granule becomes blue, while the markings become more distinct. + +Experiment 37. Examine a few of the many varieties of other kinds of +starch granules, as in rice, arrowroot, etc. Press some dry starch powder +between the thumb and forefinger, and note the peculiar crepitation. + +Experiment 38. Rub a few bits of starch in a little cold water. Put a +little of the mixture in a large test tube, and then fill with boiling +water. Boil until an imperfect opalescent solution is obtained. + +Experiment 39. Add powdered dry starch to cold water. It is +insoluble. Filter and test the filtrate with iodine. It gives no blue +color. + +Experiment 40. Boil a little starch with water; if there is enough +starch it sets on cooling and a paste results. + +Experiment 41. Moisten some flour with water until it forms a tough, +tenacious dough; tie it in a piece of cotton cloth, and knead it in a +vessel containing water until all the starch is separated. There remains +on the cloth a grayish white, sticky, elastic "gluten," made up of +albumen, some of the ash, and fats. Draw out some of the gluten into +threads, and observe its tenacious character. + +Experiment 42. Shake up a little flour with ether in a test tube, +with a tight-fitting cork. Allow the mixture to stand for an hour, shaking +it from time to time. Filter off the ether, and place some of it on a +perfectly clean watch glass. Allow the ether to evaporate, when a greasy +stain will be left, thus showing the presence of fats in the flour. + +Experiment 43. Secure a specimen of the various kinds of flour, and +meal, peas, beans, rice, tapioca, potato, etc. Boil a small quantity of +each in a test tube for some minutes. Put a bit of each thus cooked on a +white plate, and pour on it two or three drops of the tincture of iodine. +Note the various changes of color,--blue, greenish, orange, or yellowish. + + +Experiments with Milk. + +Experiment 44. Use fresh cow's milk. Examine the naked-eye character +of the milk. Test its reaction with litmus paper. It is usually neutral or +slightly alkaline. + +Experiment 45. Examine with the microscope a drop of milk, noting +numerous small, highly refractive oil globules floating in a fluid. + +Experiment 46. Dilute one ounce of milk with ten times its volume of +water. Add cautiously dilute acetic acid until there is a copious, +granular-looking precipitate of the chief proteid of milk (caseinogen), +formerly regarded as a derived albumen. This action is hastened by +heating. + +Experiment 47. Saturate milk with Epsom salts, or common salt. The +proteid and fat separate, rise to the surface, and leave a clear fluid +beneath. + +Experiment 48. Place some milk in a basin; heat it to about 100° F., +and add a few drops of acetic acid. The mass curdles and separates into a +solid curd (proteid and fat) and a clear fluid (the whey), which contains +the lactose. + +Experiment 49. Take one or two teaspoonfuls of fresh milk in a test +tube; heat it, and add a small quantity of extract of rennet. Note that +the whole mass curdles in a few minutes, so that the tube can be inverted +without the curd falling out. Soon the curd shrinks, and squeezes out a +clear, slightly yellowish fluid, the whey. + +Experiment 50. Boil the milk as before, and allow it to cool; then +add rennet. No coagulation will probably take place. It is more difficult +to coagulate boiled milk with rennet than unboiled milk. + +Experiment 51. Test fresh milk with red litmus paper; it should turn +the paper pale blue, showing that it is slightly alkaline. Place aside for +a day or two, and then test with blue litmus paper; it will be found to be +acid. This is due to the fact that lactose undergoes the lactic acid +fermentation. The lactose is converted into lactic acid by means of a +special ferment. + +Experiment 52. Evaporate a small quantity of milk to dryness in an +open dish. After the dry residue is obtained, continue to apply heat; +observe that it chars and gives off pungent gases. Raise the temperature +until it is red hot; allow the dish then to cool; a fine white ash will be +left behind. This represents the _inorganic matter_ of the milk. + + +Experiments with the Sugars. + +Experiment 53. Cane sugar is familiar as cooking and table sugar. The +little white grains found with raisins are grape sugar, or glucose. Milk +sugar is readily obtained of the druggist. Prepare a solution of the +various sugars by dissolving a small quantity of each in water. Heat each +solution with sulphuric acid, and it is seen to darken or char slowly. + +Experiment 54. Place some Fehling solution (which can be readily +obtained at the drug store as a solution, or tablets may be bought which +answer the same purpose) in a test tube, and boil. If no yellow +discoloration takes place, it is in good condition. Add a few drops of the +grape sugar solution and boil, when the mixture suddenly turns to an +opaque yellow or red color. + +Experiment 55. Repeat same experiment with milk sugar. + + + + +Chapter VI. + +Digestion. + + + +128. The Purpose of Digestion. As we have learned, our bodies are +subject to continual waste, due both to the wear and tear of their +substance, and to the consumption of material for the production of their +heat and energy. The waste occurs in no one part alone, but in all the +tissues. + +Now, the blood comes into direct contact with every one of these tissues. +The ultimate cells which form the tissues are constantly being bathed by +the myriads of minute blood-vessels which bring to the cells the raw +material needed for their continued renewal. These cells are able to +select from the nutritive fluid whatever they require to repair their +waste, and to provide for their renewed activity. At the same time, the +blood, as it bathes the tissues, sweeps into its current and bears away +the products of waste. + +Thus the waste occurs in the tissues and the means of repair are obtained +from the blood. The blood is thus continually being impoverished by having +its nourishment drained away. How, then, is the efficiency of the blood +maintained? The answer is that while the ultimate purpose of the food is +for the repair of the waste, its immediate destination is the blood.[19] + +129. Absorption of Food by the Blood. How does the food pass from the +cavity of the stomach and intestinal canal into the blood-vessels? There +are no visible openings which permit communication. It is done by what in +physics is known as _endosmotic_ and _exosmotic_ action. That is, whenever +there are two solutions of different densities, separated only by an +animal membrane, an interchange will take place between them through the +membrane. + +To illustrate: in the walls of the stomach and intestines there is a +network of minute vessels filled with blood,--a liquid containing many +substances in solution. The stomach and intestinal canal also contain +liquid food, holding many substances in solution. A membrane, made up of +the extremely thin walls of the blood-vessels and intestines, separates +the liquids. An exchange takes place between the blood and the contents of +the stomach and bowels, by which the dissolved substances of food pass +through the separating membranes into the blood. + +[Illustration: Fig. 46.--Cavities of the Mouth, Pharynx, etc. (Section in +the middle line designed to show the mouth in its relations to the nasal +fossæ, the pharynx, and the larynx.) + + A, sphenoidal sinus; + B, internal orifice of Eustachian tube; + C, velum palati; + D, anterior pillar of soft palate; + E, posterior pillar of soft palate; + F, tonsil; + H, lingual portion of the pharynx; + K, lower portion of the pharynx; + L, larynx; + M, section of hyoid bone; + N, epiglottis; + O, palatine arch +] + +This change, by which food is made ready to pass into the blood, +constitutes food-digestion, and the organs concerned in bringing +about this change in the food are the digestive organs. + +130. The General Plan of Digestion. It is evident that the digestive +organs will be simple or complex, according to the amount of change which +is necessary to prepare the food to be taken up by the blood. If the +requisite change is slight, the digestive organs will be few, and their +structure simple. But if the food is varied and complex in composition, +the digestive apparatus will be complex. This condition applies to the +food and the digestion of man. + +[Illustration: Fig. 47.--Diagram of the Structure of Secreting Glands. + + A, simple tubular gland; + B, gland with mouth shut and sac formed; + C, gland with a coiled tube; + D, plan of part of a racemose gland +] + +The digestive apparatus of the human body consists of the alimentary canal +and tributary organs which, although outside of this canal, communicate +with it by ducts. The alimentary canal consists of the mouth, the pharynx, +the œsophagus, the stomach, and the intestines. Other digestive organs +which are tributary to this canal, and discharge their secretions into it, +are the salivary glands,[20] the liver, and the pancreas. + +The digestive process is subdivided into three steps, which take place in +the mouth, in the stomach, and in the intestines. + +131. The Mouth. The mouth is the cavity formed by the lips, the +cheeks, the palate, and the tongue. Its bony roof is made up of the upper +jawbone on each side, and the palate bones behind. This is the _hard +palate_, and forms only the front portion of the roof. The continuation of +the roof is called the _soft palate_, and is made up of muscular tissue +covered with mucous membrane. + +The mouth continues behind into the throat, the separation between the two +being marked by fleshy pillars which arch up from the sides to form the +soft palate. In the middle of this arch there hangs from its free edge a +little lobe called the uvula. On each side where the pillars begin to +arch is an almond-shaped body known as the tonsil. When we take cold, +one or both of the tonsils may become inflamed, and so swollen as to +obstruct the passage into the throat. The mouth is lined with mucous +membrane, which is continuous with that of the throat, œsophagus, +stomach, and intestines (Fig. 51). + +132. Mastication, or Chewing. The first step of the process of +digestion is mastication, the cutting and grinding of the food by the +teeth, effected by the vertical and lateral movements of the lower jaw. +While the food is thus being crushed, it is moved to and fro by the varied +movements of the tongue, that every part of it may be acted upon by the +teeth. The advantage of this is obvious. The more finely the food is +divided, the more easily will the digestive fluids reach every part of it, +and the more thoroughly and speedily will digestion ensue. + +The act of chewing is simple and yet important, for if hurriedly or +imperfectly done, the food is in a condition to cause disturbance in the +digestive process. Thorough mastication is a necessary introduction to the +more complicated changes which occur in the later digestion. + +133. The Teeth. The teeth are attached to the upper and lower +maxillary bones by roots which sink into the sockets of the jaws. Each +tooth consists of a _crown_, the visible part, and one or more fangs, +buried in the sockets. There are in adults 32 teeth, 16 in each jaw. + +Teeth differ in name according to their form and the uses to which they +are specially adapted. Thus, at the front of the jaws, the incisors, +or cutting teeth, number eight, two on each side. They have a single root +and the crown is beveled behind, presenting a chisel-like edge. The +incisors divide the food, and are well developed in rodents, as squirrels, +rats, and beavers. + +Next come the canine teeth, or cuspids, two in each jaw, so called +from their resemblance to the teeth of dogs and other flesh-eating +animals. These teeth have single roots, but their crowns are more pointed +than in the incisors. The upper two are often called eye teeth, and the +lower two, stomach teeth. Next behind the canines follow, on each side, +two bicuspids. Their crowns are broad, and they have two roots. The +three hindmost teeth in each jaw are the molars, or grinders. These +are broad teeth with four or five points on each, and usually each molar +has three roots. + +The last molars are known as the wisdom teeth, as they do not usually +appear until the person has reached the "years of discretion." All animals +that live on grass, hay, corn, and the cereals generally, have large +grinding teeth, as the horse, ox, sheep, and elephant. + +The following table shows the teeth in their order: + + Mo. Bi. Ca. In. In. Ca. Bi. Mo. + + Upper 3 2 1 2 | 2 1 2 3 = 16 + | } = 32 + Lower 3 2 1 2 | 2 1 2 3 = 16 + +The vertical line indicates the middle of the jaw, and shows that on each +side of each jaw there are eight teeth. + +134. Development of the Teeth. The teeth just described are the +permanent set, which succeeds the temporary or milk teeth. +The latter are twenty in number, ten in each jaw, of which the four in the +middle are incisors. The tooth beyond on each side is an eye tooth, and +the next two on each side are bicuspids, or premolars. + +The milk teeth appear during the first and second years, and last until +about the sixth or seventh year, from which time until the twelfth or +thirteenth year, they are gradually pushed out, one by one, by the +permanent teeth. The roots of the milk teeth are much smaller than those +of the second set. + +[Illustration: Fig. 48.--Temporary and Permanent Teeth together. + +_Temporary teeth:_ + A, central incisors; + B lateral incisors; + C, canines; + D, anterior molars; + E, posterior molars + +_Permanent teeth:_ + F, central incisors; + H, lateral incisors; + K, canines; + L, first bicuspids; + M, second biscuspids; + N, first molars +] + +The plan of a gradual succession of teeth is a beautiful provision of +nature, permitting the jaws to increase in size, and preserving the +relative position and regularity of the successive teeth. + +[Illustration: Fig. 49.--Showing the Principal Organs of the Thorax and +Abdomen _in situ_. (The principal muscles are seen on the left, and +superficial veins on the right.)] + +135. Structure of the Teeth. If we should saw a tooth down through +its center we would find in the interior a cavity. This is the pulp +cavity, which is filled with the dental pulp, a delicate substance +richly supplied with nerves and blood-vessels, which enter the tooth by +small openings at the point of the root. The teeth are thus nourished like +other parts of the body. The exposure of the delicate pulp to the air, due +to the decay of the dentine, gives rise to the pain of toothache. + +Surrounding the cavity on all sides is the hard substance known as the +dentine, or tooth ivory. Outside the dentine of the root is a +substance closely resembling bone, called cement. In fact, it is true +bone, but lacks the Haversian canals. The root is held in its socket +by a dense fibrous membrane which surrounds the cement as the periosteum +does bone. + +[Illustration: Fig. 50.--Section of Face. (Showing the parotid and +submaxillary glands.)] + +The crown of the tooth is not covered by cement, but by the hard +enamel, which forms a strong protection for the exposed part. When +the teeth are first "cut," the surface of the enamel is coated with a +delicate membrane which answers to the Scriptural phrase "the skin of the +teeth." This is worn off in adult life. + +136. Insalivation. The thorough mixture of the saliva with the food +is called insalivation. While the food is being chewed, it is +moistened with a fluid called saliva, which flows into the mouth from +six little glands. There are on each side of the mouth three salivary +glands, which secrete the saliva from the blood. The parotid is +situated on the side of the face in front of the ear. The disease, common +in childhood, during which this gland becomes inflamed and swollen, is +known as the "mumps." The submaxillary gland is placed below and to +the inner side of the lower jaw, and the sublingual is on the floor +of the mouth, between the tongue and the gums. Each gland opens into the +mouth by a little duct. These glands somewhat resemble a bunch of grapes +with a tube for a stalk. + +The saliva is a colorless liquid without taste or smell. Its +principal element, besides water, is a ferment called _ptyalin_, which has +the remarkable property of being able to change starch into a form of +cane-sugar, known as maltose. + +Thus, while the food is being chewed, another process is going on by which +starch is changed into sugar. The saliva also moistens the food into a +mass for swallowing, and aids in speech by keeping the mouth moist. + +The activity of the salivary glands is largely regulated by their abundant +supply of nerves. Thus, the saliva flows into the mouth, even at the +sight, smell, or thought of food. This is popularly known as "making the +mouth water." The flow of saliva may be checked by nervous influences, as +sudden terror and undue anxiety. + + Experiment 56. _To show the action of saliva on starch_. Saliva for + experiment may be obtained by chewing a piece of India rubber and + collecting the saliva in a test tube. Observe that it is colorless and + either transparent or translucent, and when poured from one vessel to + another is glairy and more or less adhesive. Its reaction is alkaline to + litmus paper. + + Experiment 57. Make a thin paste from pure starch or arrowroot. + Dilute a little of the saliva with five volumes of water, and filter it. + This is best done through a filter perforated at its apex by a pin-hole. + In this way all air-bubbles are avoided. Label three test tubes _A, B_, + and _C_. In _A_, place starch paste; in _B_, saliva; and in _C_ one + volume of saliva and three volumes of starch paste. Place them for ten + minutes in a water bath at about 104° Fahrenheit. + + Test portions of all three for a reducing sugar, by means of Fehling's + solution or tablets.[21] _A_ and _B_ give no evidence of sugar, while + _C_ reduces the Fehling, giving a yellow or red deposit of cuprous + oxide. Therefore, starch is converted into a reducing sugar by the + saliva. This is done by the ferment ptyalin contained in saliva. + +137. The Pharynx and Œsophagus. The dilated upper part of the +alimentary canal is called the pharynx. It forms a blind sac above +the level of the mouth. The mouth opens directly into the pharynx, and +just above it are two openings leading into the posterior passages of the +nose. There are also little openings, one on each side, from which begin +the Eustachian tubes, which lead upward to the ear cavities. + +The windpipe opens downward from the pharynx, but this communication can +be shut off by a little plate or lid of cartilage, the epiglottis. +During the act of swallowing, this closes down over the entrance to the +windpipe, like a lid, and prevents the food from passing into the +air-passages. This tiny trap-door can be seen, by the aid of a mirror, if +we open the mouth wide and press down the back of the tongue with the +handle of a spoon (Figs. 46, 84, and 85). + +Thus, there are six openings from the pharynx; the œsophagus being +the direct continuation from it to the stomach. If we open the mouth +before a mirror we see through the fauces the rear wall of the pharynx. In +its lining membrane is a large number of glands, the secretion from which +during a severe cold may be quite troublesome. + +The œsophagus, or gullet, is a tube about nine inches long, +reaching from the throat to the stomach. It lies behind the windpipe, +pierces the diaphragm between the chest and abdomen, and opens into the +stomach. It has in its walls muscular fibers, which, by their worm-like +contractions, grasp the successive masses of food swallowed, and pass them +along downwards into the stomach. + +138. Deglutition, or Swallowing. The food, having been well chewed +and mixed with saliva, is now ready to be swallowed as a soft, pasty mass. +The tongue gathers it up and forces it backwards between the pillars of +the fauces into the pharynx. + +If we place the fingers on the "Adam's apple," and then pretend to +swallow something, we can feel the upper part of the windpipe and the +closing of its lid (epiglottis), so as to cover the entrance and prevent +the passage of food into the trachea. + +There is only one pathway for the food to travel, and that is down the +œsophagus. The slow descent of the food may be seen if a horse or +dog be watched while swallowing. Even liquids do not fall or flow down the +food passage. Hence, acrobats can drink while standing on their heads, or +a horse with its mouth below the level of the œsophagus. The food is +under the control of the will until it has entered the pharynx; all the +later movements are involuntary. + +[Illustration: Fig. 51.--A View into the Back Part of the Adult Mouth. +(The head is represented as having been thrown back, and the tongue drawn +forward.) + + A, B, incisors; + C, canine; + D, E, bicuspids; + F, H, K, molars; + M, anterior pillar of the fauces; + N, tonsil; + L, uvula; + O, upper part of the pharynx; + P, tongue drawn forward; + R, linear ridge, or raphé. +] + +139. The Stomach. The stomach is the most dilated portion of the +alimentary canal and the principal organ of digestion. Its form is not +easily described. It has been compared to a bagpipe, which it resembles +somewhat, when moderately distended. When empty it is flattened, and in +some parts its opposite walls are in contact. + +We may describe the stomach as a pear-shaped bag, with the large end to +the left and the small end to the right. It lies chiefly on the left side +of the abdomen, under the diaphragm, and protected by the lower ribs. The +fact that the large end of the stomach lies just beneath the diaphragm and +the heart, and is sometimes greatly distended on account of indigestion or +gas, may cause feelings of heaviness in the chest or palpitation of the +heart. The stomach is subject to greater variations in size than any other +organ of the body, depending on its contents. Just after a moderate meal +it averages about twelve inches in length and four in diameter, with a +capacity of about four pints. + +[Illustration: Fig. 52.--The Stomach. A, cardiac end; B, pyloric end, C, +lesser curvature, D, greater curvature] + +The orifice by which the food enters is called the cardiac opening, +because it is near the heart. The other opening, by which the food leaves +the stomach, and where the small intestine begins, is the pyloric +orifice, and is guarded by a kind of valve, known as the pylorus, or +gatekeeper. The concave border between the two orifices is called the +_small curvature_, and the convex as the _great curvature_, of the +stomach. + +140. Coats of Stomach. The walls of the stomach are formed by four +coats, known successively from without as serous, muscular, +sub-mucous, and mucous. The outer coat is the serous membrane +which lines the abdomen,--the peritoneum (note, p. 135). The second +coat is muscular, having three sets of involuntary muscular fibers. The +outer set runs lengthwise from the cardiac orifice to the pylorus. The +middle set encircles all parts of the stomach, while the inner set +consists of oblique fibers. The third coat is the sub-mucous, made up of +loose connective tissues, and binds the mucous to the muscular coat. +Lastly there is the mucous coat, a moist, pink, inelastic membrane, which +completely lines the stomach. When the stomach is not distended, the +mucous layer is thrown into folds presenting a corrugated appearance. + +[Illustration: Fig. 53.--Pits in the Mucous Membrane of the Stomach, and +Openings of the Gastric Glands. (Magnified 20 diameters.)] + +141. The Gastric Glands. If we were to examine with a hand lens the +inner surface of the stomach, we would find it covered with little pits, +or depressions, at the bottom of which would be seen dark dots. These dots +are the openings of the gastric glands. In the form of fine, wavy +tubes, the gastric glands are buried in the mucous membrane, their mouths +opening on the surface. When the stomach is empty the mucous membrane is +pale, but when food enters, it at once takes on a rosy tint. This is due +to the influx of blood from the large number of very minute blood-vessels +which are in the tissue between the rows of glands. + +The cells of the gastric glands are thrown into a state of greater +activity by the increased quantity of blood supply. As a result, soon +after food enters the stomach, drops of fluid collect at the mouths of the +glands and trickle down its walls to mix with the food. Thus these glands +produce a large quantity of gastric juice, to aid in the digestion of +food. + +142. Digestion in the Stomach. When the food, thoroughly mixed with +saliva, reaches the stomach, the cardiac end of that organ is closed as +well as the pyloric valve, and the muscular walls contract on the +contents. A spiral wave of motion begins, becoming more rapid as digestion +goes on. Every particle of food is thus constantly churned about in the +stomach and thoroughly mixed with the gastric juice. The action of the +juice is aided by the heat of the parts, a temperature of about 99° +Fahrenheit. + +The gastric juice is a thin almost colorless fluid with a sour taste +and odor. The reaction is distinctly acid, normally due to free +hydrochloric acid. Its chief constituents are two ferments called pepsin +and rennin, free hydrochloric acid, mineral salts, and 95 per cent of +water. + +[Illustration: Fig. 54.--A highly magnified view of a peptic or gastric +gland, which is represented as giving off branches. It shows the columnar +epithelium of the surface dipping down into the duct D of the gland, from +which two tubes branch off. Each tube is lined with columnar epithelial +cells, and there is a minute central passage with the "neck" at N. Here +and there are seen other special cells called parietal cells, P, which are +supposed to produce the acid of the gastric juice. The principal cells are +represented at C.] + +Pepsin the important constituent of the gastric juice, has the +power, in the presence of an acid, of dissolving the proteid food-stuffs. +Some of which is converted into what are called _peptones_, both soluble +and capable of filtering through membranes. The gastric juice has no +action on starchy foods, neither does it act on fats, except to dissolve +the albuminous walls of the fat cells. The fat itself is thus set free in +the form of minute globules. The whole contents of the stomach now assume +the appearance and the consistency of a thick soup, usually of a grayish +color, known as chyme. + +It is well known that "rennet" prepared from the calf's stomach has a +remarkable effect in rapidly curdling milk, and this property is utilized +in the manufacture of cheese. Now, a similar ferment is abundant in the +gastric juice, and may be called _rennin_. It causes milk to clot, and +does this by so acting on the casein as to make the milk set into a jelly. +Mothers are sometimes frightened when their children, seemingly in perfect +health, vomit masses of curdled milk. This curdling of the milk is, +however, a normal process, and the only noteworthy thing is its rejection, +usually due to overfeeding. + + Experiment 58. _To show that pepsin and acid are necessary for + gastric digestion._ Take three beakers, or large test tubes; label them + _A_, _B_, _C_. Put into _A_ water and a few grains of powdered pepsin. + Fill _B_ two-thirds full of dilute hydrochloric acid (one teaspoonful to + a pint), and fill _C_ two-thirds full of hydrochloric acid and a few + grains of pepsin. Put into each a small quantity of well-washed fibrin, + and place them all in a water bath at 104° Fahrenheit for half an hour. + + Examine them. In _A_, the fibrin is unchanged; in _B_, the fibrin is + clear and swollen up; in _C_, it has disappeared, having first become + swollen and clear, and completely dissolved, being finally converted + into peptones. Therefore, both acid and ferment are required for gastric + digestion. + + Experiment 59. Half fill with dilute hydrochloric acid three large + test tubes, labelled _A_, _B_, _C_. Add to each a few grains of pepsin. + Boil _B_, and make _C_ faintly alkaline with sodic carbonate. The + alkalinity may be noted by adding previously some neutral litmus + solution. Add to each an equal amount--a few threads--of well-washed + fibrin which has been previously steeped for some time in dilute + hydrochloric acid, so that it is swollen and transparent. Keep the tubes + in a water-bath at about 104° Fahrenheit for an hour and examine them at + intervals of twenty minutes. + + After five to ten minutes the fibrin in _A_ is dissolved and the fluid + begins to be turbid. In _B_ and _C_ there is no change. Even after long + exposure to 100° Fahrenheit there is no change in _B_ and _C_. + + After a variable time, from one to four hours, the contents of the + stomach, which are now called chyme, begin to move on in successive + portions into the next part of the intestinal canal. The ring-like + muscles of the pylorus relax at intervals to allow the muscles of the + stomach to force the partly digested mass into the small intestines. + This action is frequently repeated, until even the indigestible masses + which the gastric juice cannot break down are crowded out of the stomach + into the intestines. From three to four hours after a meal the stomach + is again quite emptied. + +A certain amount of this semi-liquid mass, especially the peptones, with +any saccharine fluids, resulting from the partial conversion of starch or +otherwise, is at once absorbed, making its way through the delicate +vessels of the stomach into the blood current, which is flowing through +the gastric veins to the portal vein of the liver. + +[Illustration: Fig. 55.--A Small Portion of the Mucous Membrane of the +Small Intestine. (Villi are seen surrounded with the openings of the +tubular glands.) [Magnified 20 diameters.]] + +143. The Small Intestine. At the pyloric end of the stomach the +alimentary canal becomes again a slender tube called the small +intestine. This is about twenty feet long and one inch in diameter, +and is divided, for the convenience of description, into three parts. + +The first 12 inches is called the duodenum. Into this portion opens +the bile duct from the liver with the duct from the pancreas, these having +been first united and then entering the intestine as a common duct. + +The next portion of the intestine is called the jejunum, because it +is usually empty after death. + +The remaining portion is named the ileum, because of the many folds +into which it is thrown. It is the longest part of the small intestine, +and terminates in the right iliac region, opening into the large +intestine. This opening is guarded by the folds of the membrane forming +the ileo-cæcal valve, which permits the passage of material from the +small to the large intestine, but prevents its backward movement. + +144. The Coats of the Small Intestine. Like the stomach, the small +intestine has four coats, the serous, muscular, sub-mucous, +and mucous. The serous is the peritoneum.[22] The muscular consists +of an outer layer of longitudinal, and an inner layer of circular fibers, +by contraction of which the food is forced along the bowel. The sub-mucous +coat is made up of a loose layer of tissue in which the blood-vessels and +nerves are distributed. The inner, or mucous, surface has a fine, velvety +feeling, due to a countless number of tiny, thread-like projections, +called villi. They stand up somewhat like the "pile" of velvet. It is +through these villi that the digested food passes into the blood. + +[Illustration: Fig. 56.--Sectional View of Intestinal Villi. (Black dots +represent the glandular openings.)] + +The inner coat of a large part of the small intestine is thrown into +numerous transverse folds called _valvulæ conniventes_. These seem to +serve two purposes, to increase the extent of the surface of the bowels +and to delay mechanically the progress of the intestinal contents. Buried +in the mucous layer throughout the length, both of the small and large +intestines, are other glands which secrete intestinal fluids. Thus, in the +lower part of the ileum there are numerous glands in oval patches known as +_Peyer's patches_. These are very prone to become inflamed and to ulcerate +during the course of typhoid fever. + +145. The Large Intestine. The large intestine begins in the +right iliac region and is about five or six feet long. It is much larger +than the small intestine, joining it obliquely at short distance from its +end. A blind pouch, or dilated pocket is thus formed at the place of +junction, called the cæcum. A valvular arrangement called the +ileo-cæcal valve, which is provided with a button-hole slit, forms a kind +of movable partition between this part of the large intestine and the +small intestine. + +[Illustration: Fig. 57.--Tubular Glands of the Small Intestines. + +A, B, tubular glands seen in vertical section with their orifices at C, +opening upon the membrane between the villi, D, villus (Magnified 40 +diameters)] + +Attached to the cæcum is a worm-shaped tube, about the size of a lead +pencil, and from three to four inches long, called the _vermiform +appendix_. Its use is unknown. This tube is of great surgical importance, +from the fact that it is subject to severe inflammation, often resulting +in an internal abscess, which is always dangerous and may prove fatal. +Inflammation of the appendix is known as _appendicitis_,--a name quite +familiar on account of the many surgical operations performed of late +years for its relief. + +The large intestine passes upwards on the right side as the ascending +colon, until the under side of the liver is reached, where it passes +to the left side, as the transverse colon, below the stomach. It +there turns downward, as the descending colon, and making an S-shaped +curve, ends in the rectum. Thus the large intestine encircles, in the +form of a horseshoe, the convoluted mass of small intestines. + +Like the small intestine, the large has four coats. The mucous coat, +however, has no folds, or villi, but numerous closely set glands, like +some of those of the small intestine. The longitudinal muscular fibers of +the large intestine are arranged in three bands, or bundles, which, being +shorter than the canal itself, produce a series of bulgings or pouches in +its walls. This sacculation of the large bowel is supposed to be designed +for delaying the onward flow of its contents, thus allowing more time for +the absorption of the liquid material. The blood-vessels and nerves of +this part of the digestive canal are very numerous, and are derived from +the same sources as those of the small intestine. + +146. The Liver. The liver is a part of the digestive apparatus, +since it forms the bile, one of the digestive fluids. It is a large +reddish-brown organ, situated just below the diaphragm, and on the right +side. The liver is the largest gland in the body, and weighs from 50 to 60 +ounces. It consists of two lobes, the right and the left, the right being +much the larger. The upper, convex surface of the liver is very smooth and +even; but the under surface is irregular, broken by the entrance and exit +of the various vessels which belong to the organ. It is held in its place +by five ligaments, four of which are formed by double folds of the +peritoneum. + +The thin front edge of the liver reaches just below the bony edge of the +ribs; but the dome-shaped diaphragm rises slightly in a horizontal +position, and the liver passes up and is almost wholly covered by the +ribs. In tight lacing, the liver is often forced downward out from the +cover of the ribs, and thus becomes permanently displaced. As a result, +other organs in the abdomen and pelvis are crowded together, and also +become displaced. + +147. Minute Structure of the Liver. When a small piece of the liver +is examined under a microscope it is found to be made up of masses of +many-sided cells, each about 1/1000 of an inch in diameter. Each group of +cells is called a _lobule_. When a single lobule is examined under the +microscope it appears to be of an irregular, circular shape, with its +cells arranged in rows, radiating from the center to the circumference. +Minute, hair-like channels separate the cells one from another, and unite +in one main duct leading from the lobule. It is the lobules which give to +the liver its coarse, granular appearance, when torn across. + +[Illustration: Fig. 58.--Diagrammatic Section of a Villus + + A, layer of columnar epithelium covering the villus; + B, central lacteal of villus; + C, unstriped muscular fibers; + D, goblet cell +] + +Now there is a large vessel called the portal vein that brings to the +liver blood full of nourishing material obtained from the stomach and +intestines. On entering the liver this great vein conducts itself as if it +were an artery. It divides and subdivides into smaller and smaller +branches, until, in the form of the tiniest vessels, called capillaries, +it passes inward among the cells to the very center of the hepatic +lobules. + +148. The Bile. We have in the liver, on a grand scale, exactly the +same conditions as obtain in the smaller and simpler glands. The +thin-walled liver cells take from the blood certain materials which they +elaborate into an important digestive fluid, called the bile.[23] +This newly manufactured fluid is carried away in little canals, called +_bile ducts_. These minute ducts gradually unite and form at last one main +duct, which carries the bile from the liver. This is known as the hepatic +duct. It passes out on the under side of the liver, and as it +approaches the intestine, it meets at an acute angle the cystic duct which +proceeds from the gall bladder and forms with it the common bile +duct. The common duct opens obliquely into the horseshoe bend of the +duodenum. + +The cystic duct leads back to the under surface of the liver, where +it expands into a sac capable of holding about two ounces of fluid, and is +known as the gall bladder. Thus the bile, prepared in the depths of +the liver by the liver cells, is carried away by the bile ducts, and may +pass directly into the intestines to mix with the food. If, however, +digestion is not going on, the mouth of the bile duct is closed, and in +that case the bile is carried by the cystic duct to the gall bladder. Here +it remains until such time as it is needed. + +149. Blood Supply of the Liver. We must not forget that the liver +itself, being a large and important organ, requires constant nourishment +for the work assigned to it. The blood which is brought to it by the +portal vein, being venous, is not fit to nourish it. The work is done by +the arterial blood brought to it by a great branch direct from the aorta, +known as the hepatic artery, minute branches of which in the form of +capillaries, spread themselves around the hepatic lobules. + +The blood, having done its work and now laden with impurities, is picked +up by minute veinlets, which unite again and again till they at last form +one great trunk called the hepatic vein. This carries the impure +blood from the liver, and finally empties it into one of the large veins +of the body. + +After the blood has been robbed of its bile-making materials, it is +collected by the veinlets that surround the lobules, and finds its way +with other venous blood into the hepatic vein. In brief, blood is brought +to the liver and distributed through its substance by two distinct +channels,--the portal vein and the hepatic artery, but it leaves +the liver by one distinct channel,--the hepatic vein. + +[Illustration: Fig. 59--Showing the Relations of the Duodenum and Other +Intestinal Organs. (A portion of the stomach has been cut away.)] + +150. Functions of the Liver. We have thus far studied the liver only +as an organ of secretion, whose work is to elaborate bile for future use +in the process of digestion. This is, however, only one of its functions, +and perhaps not the most important. In fact, the functions of the liver +are not single, but several. The bile is not wholly a digestive fluid, but +it contains, also, materials which are separated from the blood to be +cast out of the body before they work mischief. Thus, the liver ranks +above all others as an organ of excretion, that is, it separates +material of no further use to the body. + +Of the various ingredients of the bile, only the bile salts are of use in +the work of digestion, for they act upon the fats in the alimentary canal, +and aid somehow in their emulsion and absorption. They appear to be +themselves split up into other substances, and absorbed with the dissolved +fats into the blood stream again. + +The third function of the liver is very different from those already +described. It is found that the liver of an animal well and regularly fed, +when examined soon after death, contains a quantity of a carbohydrate +substance not unlike starch. This substance, extracted in the form of a +white powder, is really an animal starch. It is called glycogen, or +liver sugar, and is easily converted into grape sugar. + +The hepatic cells appear to manufacture this glycogen and to store it up +from the food brought by the portal blood. It is also thought the glycogen +thus deposited and stored up in the liver is little by little changed into +sugar. Then, as it is wanted, the liver disposes of this stored-up +material, by pouring it, in a state of solution, into the hepatic vein. It +is thus steadily carried to the tissues, as their needs demand, to supply +them with material to be transformed into heat and energy. + +151. The Pancreas. The pancreas, or sweetbread, is much smaller +than the liver. It is a tongue-like mass from six to eight inches long, +weighing from three to four ounces, and is often compared in appearance to +a dog's tongue. It is somewhat the shape of a hammer with the handle +running to a point. + +The pancreas lies behind the stomach, across the body, from right to left, +with its large head embraced in the horseshoe bend of the duodenum. It +closely resembles the salivary glands in structure, with its main duct +running from one end to the other. This duct at last enters the duodenum +in company with the common bile duct. + +The pancreatic juice, the most powerful in the body, is clear, +somewhat viscid, fluid. It has a decided alkaline reaction and is not +unlike saliva in many respects. Combined with the bile, this juice acts +upon the large drops of fat which pass from the stomach into the duodenum +and emulsifies them. This process consists partly in producing a fine +subdivision of the particles of fat, called an emulsion, and partly in a +chemical decomposition by which a kind of soap is formed. In this way the +oils and fats are divided into particles sufficiently minute to permit of +their being absorbed into the blood. + +Again, this most important digestive fluid produces on starch an action +similar to that of saliva, but much more powerful. During its short stay +in the mouth, very little starch is changed into sugar, and in the +stomach, as we have seen, the action of the saliva is arrested. Now, the +pancreatic juice takes up the work in the small intestine and changes the +greater part of the starch into sugar. Nor is this all, for it also acts +powerfully upon the proteids not acted upon in the stomach, and changes +them into peptones that do not differ materially from those resulting from +gastric digestion. The remarkable power which the pancreatic juice +possesses of acting on all the food-stuffs appears to be due mainly to the +presence of a specific element or ferment, known as _trypsin_. + + Experiment 60. _To show the action of pancreatic juice upon oils or + fats._ Put two grains of Fairchild's extract of pancreas into a + four-ounce bottle. Add half a teaspoonful of warm water, and shake well + for a few minutes; then add a tablespoonful of cod liver oil; shake + vigorously. + + A creamy, opaque mixture of the oil and water, called an emulsion, will + result. This will gradually separate upon standing, the pancreatic + extract settling in the water at the bottom. When shaken it will again + form an emulsion. + + Experiment 61. _To show the action of pancreatic juice on starch_. + Put two tablespoonfuls of _smooth_ starch paste into a goblet, and while + still so warm as just to be borne by the mouth, stir into it two grains + of the extract of pancreas. The starch paste will rapidly become + thinner, and gradually change into soluble starch, in a perfectly fluid + solution. Within a few minutes some of the starch is converted through + intermediary stages into maltose. Use the Fehling test for sugar. + +152. Digestion in the Small Intestines. After digestion in the +stomach has been going on for some time, successive portions of the +semi-digested food begin to pass into the duodenum. The pancreas now takes +on new activity, and a copious flow of pancreatic juice is poured along +its duct into the intestines. As the food is pushed along over the common +opening of the bile and pancreatic ducts, a great quantity of bile from +this reservoir, the gall bladder, is poured into the intestines. These two +digestive fluids are now mixed with the chyme, and act upon it in the +remarkable manner just described. + +[Illustration: Fig. 60.--Diagrammatic Scheme of Intestinal Absorption. + + A, mesentery; + B, lacteals and mesentery glands; + C, veins of intestines; + R.C, receptacle of the chyle (receptaculum chyli); + P V, portal vein; + H V, hepatic veins; + S.V.C, superior vena cava; + R.A, right auricle of the heart; + I.V.C, inferior vena cava. +] + +The inner surface of the small intestine also secretes a liquid called +intestinal juice, the precise functions of which are not known. The +chyme, thus acted upon by the different digestive fluids, resembles a +thick cream, and is now called chyle. The chyle is propelled along +the intestine by the worm-like contractions of its muscular walls. A +function of the bile, not yet mentioned, is to stimulate these movements, +and at the same time by its antiseptic properties to prevent putrefaction +of the contents of the intestine. + +153. Digestion in the Large Intestines. Digestion does not occur to +any great extent in the large intestines. The food enters this portion of +the digestive canal through the ileo-cæcal valve, and travels through it +slowly. Time is thus given for the fluid materials to be taken up by the +blood-vessels of the mucous membrane. The remains of the food now become +less fluid, and consist of undigested matter which has escaped the action +of the several digestive juices, or withstood their influence. Driven +onward by the contractions of the muscular walls, the refuse materials at +last reach the rectum, from which they are voluntarily expelled from the +body. + + + +Absorption. + + +154. Absorption. While food remains within the alimentary canal it is as +much outside of the body, so far as nutrition is concerned, as if it had +never been taken inside. To be of any service the food must enter the +blood; it must be absorbed. The efficient agents in absorption are the +blood-vessels, the lacteals, and the lymphatics. The process through which +the nutritious material is fitted to enter the blood, is called +absorption. It is a process not confined, as we shall see, simply to the +alimentary canal, but one that is going on in every tissue. + +The vessels by which the process of absorption is carried on are called +absorbents. The story, briefly told, is this: certain food materials +that have been prepared to enter the blood, filter through the mucous +membrane of the intestinal canal, and also the thin walls of minute +blood-vessels and lymphatics, and are carried by these to larger vessels, +and at last reach the heart, thence to be distributed to the tissues. + +155. Absorption from the Mouth and Stomach. The lining of the mouth +and œsophagus is not well adapted for absorption. That this does +occur is shown by the fact that certain poisonous chemicals, like cyanide +of potash, if kept in the mouth for a few moments will cause death. While +we are chewing and swallowing our food, no doubt a certain amount of water +and common salt, together with sugar which has been changed from starch by +the action of the saliva, gains entrance to the blood. + +In the stomach, however, absorption takes place with great activity. The +semi-liquid food is separated from the enormous supply of blood-vessels in +the mucous membrane only by a thin porous partition. There is, therefore, +nothing to prevent the exchange taking place between the blood and the +food. Water, along with any substances in the food that have become +dissolved, will pass through the partition and enter the blood-current. +Thus it is that a certain amount of starch that has been changed into +sugar, of salts in solution, of proteids converted into peptones, is taken +up directly by the blood-vessels of the stomach. + +156. Absorption by the Intestines. Absorption by the intestines is a +most active and complicated process. The stomach is really an organ more +for the digestion than the absorption of food, while the small intestines +are especially constructed for absorption. In fact, the greatest part of +absorption is accomplished by the small intestines. They have not only a +very large area of absorbing surface, but also structures especially +adapted to do this work. + +157. The Lacteals. We have learned in Section 144 that the mucous +lining of the small intestines is crowded with millions of little +appendages called villi, meaning "tufts of hair." These are only +about 1/30 of an inch long, and a dime will cover more than five hundred +of them. Each villus contains a loop of blood-vessels, and another vessel, +the lacteal, so called from the Latin word _lac_, milk, because of the +milky appearance of the fluid it contains. The villi are adapted +especially for the absorption of fat. They dip like the tiniest fingers +into the chyle, and the minute particles of fat pass through their +cellular covering and gain entrance to the lacteals. The milky material +sucked up by the lacteals is not in a proper condition to be poured at +once into the blood current. It is, as it were, in too crude a state, and +needs some special preparation. + +The intestines are suspended to the posterior wall of the abdomen by a +double fold of peritoneum called the mesentery. In this membrane are +some 150 glands about the size of an almond, called mesenteric +glands. Now the lacteals join these glands and pour in their fluid +contents to undergo some important changes. It is not unlikely that the +mesenteric glands may intercept, like a filter, material which, if allowed +to enter the blood, would disturb the whole body. Thus, while the glands +might suffer, the rest of the body might escape. This may account for the +fact that these glands and the lymphatics may be easily irritated and +inflamed, thus becoming enlarged and sensitive, as often occurs in the +axilla. + +Having been acted upon by the mesenteric glands, and passed through them, +the chyle flows onward until it is poured into a dilated reservoir for the +chyle, known as the receptaculum chyli. This is a sac-like expansion +of the lower end of the thoracic duct. Into this receptacle, situated at +the level of the upper lumbar vertebræ, in front of the spinal column, are +poured, not only the contents of the lacteals, but also of the lymphatic +vessels of the lower limbs. + +158. The Thoracic Duct. This duct is a tube from fifteen to eighteen +inches long, which passes upwards in front of the spine to reach the base +of the neck, where it opens at the junction of the great veins of the left +side of the head with those of the left arm. Thus the thoracic duct +acts as a kind of feeding pipe to carry along the nutritive material +obtained from the food and to pour it into the blood current. It is to be +remembered that the lacteals are in reality lymphatics--the +lymphatics of the intestines. + +[Illustration: Fig. 61.--Section of a Lymphatic Gland. + + A, strong fibrous capsule sending partitions into the gland; + B, partitions between the follicles or pouches of the _cortical_ or + outer portion; + C, partitions of the _medullary_ or central portion; + D, E, masses of protoplasmic matter in the pouches of the gland; + F, lymph-vessels which bring lymph _to_ the gland, passing into its + center; + G, confluence of those leading to the efferent vessel; + H, vessel which carries the lymph away _from_ the gland. +] + +159. The Lymphatics. In nearly every tissue and organ of the body +there is a marvelous network of vessels, precisely like the lacteals, +called the lymphatics. These are busily at work taking up and making +over anew waste fluids or surplus materials derived from the blood and +tissues generally. It is estimated that the quantity of fluid picked up +from the tissues by the lymphatics and restored daily to the circulation +is equal to the bulk of the blood in the body. The lymphatics seem to +start out from the part in which they are found, like the rootlets of a +plant in the soil. They carry a turbid, slightly yellowish fluid, called +lymph, very much like blood without the red corpuscles. + +Now, just as the chyle was not fit to be immediately taken up by the +blood, but was passed through the mesenteric glands to be properly worked +over, so the lymph is carried to the lymphatic glands, where it +undergoes certain changes to fit it for being poured into the blood. +Nature, like a careful housekeeper, allows nothing to be wasted that can +be of any further service in the animal economy (Figs. 63 and 64). + +The lymphatics unite to form larger and larger vessels, and at last join +the thoracic duct, except the lymphatics of the right side of the head and +chest and right arm. These open by the right lymphatic duct into the +venous system on the right side of the neck. + +The whole lymphatic system may be regarded as a necessary appendage to the +vascular system (Chapter VII.). It is convenient, however, to treat it +under the general topic of absorption, in order to complete the history of +food digestion. + +160. The Spleen and Other Ductless Glands. With the lymphatics may be +classified, for convenience, a number of organs called ductless or +blood glands. Although they apparently prepare materials for use in +the body, they have no ducts or canals along which may be carried the +result of their work. Again, they are called blood glands because it is +supposed they serve some purpose in preparing material for the blood. + +The spleen is the largest of these glands. It lies beneath the +diaphragm, and upon the left side of the stomach. It is of a deep red +color, full of blood, and is about the size and shape of the palm of the +hand. + +The spleen has a fibrous capsule from which partitions pass inwards, +dividing it into spaces by a framework of elastic tissue, with plain +muscular fibers. These spaces are filled with what is called the spleen +pulp, through which the blood filters from its artery, just as a fluid +would pass through a sponge. The functions of the spleen are not known. It +appears to take some part in the formation of blood corpuscles. In certain +diseases, like malarial fever, it may become remarkably enlarged. It may +be wholly removed from an animal without apparent injury. During digestion +it seems to act as a muscular pump, drawing the blood onwards with +increased vigor along its large vein to the liver. + +The thyroid is another ductless gland. It is situated beneath the +muscles of the neck on the sides of "Adam's apple" and below it. It +undergoes great enlargement in the disease called goitre. + +The thymus is also a blood gland. It is situated around the windpipe, +behind the upper part of the breastbone. Until about the end of the second +year it increases in size, and then it begins gradually to shrivel away. +Like the spleen, the thyroid and thymus glands are supposed to work some +change in the blood, but what is not clearly known. + +The suprarenal capsules are two little bodies, one perched on the top +of each kidney, in shape not unlike that of a conical hat. Of their +functions nothing definite is known. + + + +Experiments. + + +The action produced by the tendency of fluids to mix, or become equally +diffused in contact with each other, is known as _osmosis_, a form of +molecular attraction allied to that of adhesion. The various physical +processes by which the products of digestion are transferred from the +digestive canal to the blood may be illustrated in a general way by the +following simple experiments. + +The student must, however, understand that the necessarily crude +experiments of the classroom may not conform in certain essentials to +these great processes conducted in the living body, which they are +intended to illustrate and explain. + +[Illustration: Fig. 62.] + + Experiment 62. _Simple Apparatus for Illustrating Endosmotic + Action._ "Remove carefully a circular portion, about an inch in + diameter, of the shell from one end of an egg, which may be done without + injuring the membranes, by cracking the shell in small pieces, which are + picked off with forceps. A small glass tube is then introduced through + an opening in the shell and membranes of the other end of the egg, and + is secured in a vertical position by wax or plaster of Paris, the tube + penetrating the yelk. The egg is then placed in a wine-glass partly + filled with water. In the course of a few minutes, the water will have + penetrated the exposed membrane, and the yelk will rise in the + tube."--Flint's _Human Physiology_, page 293. + + Experiment 63. Stretch a piece of moist bladder across a glass + tube,--a common lamp-chimney will do. Into this put a strong saline + solution. Now suspend the tube in a wide mouthed vessel of water. After + a short time it will be found that a part of the salt solution has + passed through into the water, while a larger amount of water has passed + into the tube and raised the height of the liquid within it. + +161. The Quantity of Food as Affected by Age. The quantity of food +required to keep the body in proper condition is modified to a great +extent by circumstances. Age, occupation, place of residence, climate, and +season, as well as individual conditions of health and disease, are always +important factors in the problem. In youth the body is not only growing, +but the tissue changes are active. The restless energy and necessary +growth at this time of life cannot be maintained without an abundance of +wholesome food. This food supply for young people should be ample enough +to answer the demands of their keen appetite and vigorous digestion. + +In adult life, when the processes of digestion and assimilation are +active, the amount of food may without harm, be in excess of the actual +needs of the body. This is true, however, only so long as active muscular +exercise is taken. + +In advanced life the tissue changes are slow, digestion is less active, +and the ability to assimilate food is greatly diminished. Growth has +ceased, the energy which induced activity is gone, and the proteids are no +longer required to build up worn-out tissues. Hence, as old age +approaches, the quantity of nitrogenous foods should be steadily +diminished. + + Experiment 64. Obtain a sheep's bladder and pour into it a heavy + solution of sugar or some colored simple elixir, found at any drug + store. Tie the bladder carefully and place it in a vessel containing + water. After a while it will be found that an interchange has occurred, + water having passed into the bladder and the water outside having become + sweet. + + Experiment 65. Make a hole about as big as a five-cent piece in the + large end of an egg. That is, break the shell carefully and snip the + outer shell membrane, thus opening the space between the outer and inner + membranes. Now put the egg into a glass of water, keeping it in an + upright position by resting on a napkin-ring. There is only the inner + shell membrane between the liquid white of the egg (albumen) and the + water. + + An interchange takes place, and the water passes towards the albumen. As + the albumen does not pass out freely towards the water, the membrane + becomes distended, like a little bag at the top of the egg. + +162. Ill Effects of a too Generous Diet. A generous diet, even of +those who take active muscular exercise, should be indulged in only with +vigilance and discretion. Frequent sick or nervous headaches, a sense of +fullness, bilious attacks, and dyspepsia are some of the after-effects of +eating more food than the body actually requires. The excess of food is +not properly acted upon by the digestive juices, and is liable to undergo +fermentation, and thus to become a source of irritation to the stomach and +the intestines. If too much and too rich food be persistently indulged in, +the complexion is apt to become muddy, the skin, especially of the face, +pale and sallow, and more or less covered with blotches and pimples; the +breath has an unpleasant odor, and the general appearance of the body is +unwholesome. + +An excess of any one of the different classes of foods may lead to serious +results. Thus a diet habitually too rich in proteids, as with those who +eat meat in excess, often over-taxes the kidneys to get rid of the excess +of nitrogenous waste, and the organs of excretion are not able to rid the +tissues of waste products which accumulate in the system. From the blood, +thus imperfectly purified, may result kidney troubles and various diseases +of the liver and the stomach. + +163. Effect of Occupation. Occupation has an important influence upon +the quantity of food demanded for the bodily support. Those who work long +and hard at physical labor, need a generous amount of nutritious food. A +liberal diet of the cereals and lean meat, especially beef, gives that +vigor to the muscles which enables one to undergo laborious and prolonged +physical exertion. On the other hand, those who follow a sedentary +occupation do not need so large a quantity of food. Brain-workers who +would work well and live long, should not indulge in too generous a diet. +The digestion of heavy meals involves a great expenditure of nervous +force. Hence, the forces of the brain-worker, being required for mental +exertion, should not be expended to an unwarranted extent on the task of +digestion. + +164. Effect of Climate. Climate also has a marked influence on the +quantity of food demanded by the system. Much more food of all kinds is +consumed in cold than in warm climates. The accounts by travelers of the +quantity of food used by the inhabitants of the frigid zone are almost +beyond belief. A Russian admiral gives an instance of a man who, in his +presence, ate at a single meal 28 pounds of rice and butter. Dr. Hayes, +the Arctic traveler, states from personal observation that the daily +ration of the Eskimos is 12 to 15 pounds of meat. With the thermometer +ranging from 60 to 70° F. below zero, there was a persistent craving for +strong animal diet, especially fatty foods.[24] + +[Illustration: Fig. 63.--Lymphatics and Lymphatic Glands of the Axilla.] + +The intense cold makes such a drain upon the heat-producing power of the +body that only food containing the largest proportion of carbon is capable +of making up for the loss. In tropical countries, on the other hand, the +natives crave and subsist mainly upon fruits and vegetables. + +165. The Kinds of Food Required. An appetite for plain, well-cooked +food is a safe guide to follow. Every person in good health, taking a +moderate amount of daily exercise, should have a keen appetite for three +meals a day and enjoy them. Food should be both nutritious and digestible. +It is nutritious in proportion to the amount of material it furnishes for +the nourishment of the tissues. It is digestible in a greater or less +degree in respect to the readiness with which it yields to the action of +the digestive fluids, and is prepared to be taken up by the blood. This +digestibility depends partly upon the nature of the food in its raw state, +partly upon the effect produced upon it by cooking, and to some extent +upon its admixture with other foods. Certain foods, as the vegetable +albumens, are both nutritious and digestible. A hard-working man may grow +strong and maintain vigorous health on most of them, even if deprived of +animal food. + +While it is true that the vegetable albumens furnish all that is really +needed for the bodily health, animal food of some kind is an economical +and useful addition to the diet. Races of men who endure prolonged +physical exertion have discovered for themselves, without the teaching of +science, the great value of meat. Hence the common custom of eating meat +with bread and vegetables is a sound one. It is undoubtedly true that the +people of this country, as a rule, eat meat too often and too much at a +time. The judicious admixture of different classes of foods greatly aids +their digestibility. + +The great abundance and variety of food in this country, permit this +principle to be put into practice. A variety of mixed foods, as milk, +eggs, bread, and meat, are almost invariably associated to a greater or +less extent at every meal. + +Oftentimes where there is of necessity a sameness of diet, there arises a +craving for special articles of food. Thus on long voyages, and during +long campaigns in war, there is an almost universal craving for onions, +raw potatoes, and other vegetables. + +166. Hints about Meals. On an average, three meals each day, from +five to six hours apart, is the proper number for adults. Five hours is by +no means too long a time to intervene between consecutive meals, for it is +not desirable to introduce new food into the stomach, until the gastric +digestion of the preceding meal has been completed, and until the stomach +has had time to rest, and is in condition to receive fresh material. The +stomach, like other organs, does its work best at regular periods.[25] + +Eating out of mealtimes should be strictly avoided, for it robs the +stomach of its needed rest. Food eaten when the body and mind are wearied +is not well digested. Rest, even for a few minutes, should be taken before +eating a full meal. It is well to lie down, or sit quietly and read, +fifteen minutes before eating, and directly afterwards, if possible. + +Severe exercise and hard study just after a full meal, are very apt to +delay or actually arrest digestion, for after eating heartily, the vital +forces of the body are called upon to help the stomach digest its food. If +our bodily energies are compelled, in addition to this, to help the +muscles or brain, digestion is retarded, and a feeling of dullness and +heaviness follows. Fermentative changes, instead of the normal digestive +changes, are apt to take place in the food. + +167. Practical Points about Eating. We should not eat for at least +two or three hours before going to bed. When we are asleep, the vital +forces are at a low ebb, the process of digestion is for the time nearly +suspended, and the retention of incompletely digested food in the stomach +may cause bad dreams and troubled sleep. But in many cases of +sleeplessness, a trifle of some simple food, especially if the stomach +seems to feel exhausted, often appears to promote sleep and rest. + + [NOTE. The table on the next page shows the results of many + experiments to illustrate the time taken for the gastric digestion of + a number of the more common solid foods. There are a good many factors + of which the table takes no account, such as the interval since the + last meal, state of the appetite, amount of work and exercise, method + of cooking, and especially the quantity of food.] + + Table Showing the Digestibility of the More Common Solid Foods. + + Food How Time in + Cooked Stomach, + Hours + ------------------------------------------------- + Apples, sweet and mellow Raw 1½ + Apples, sour and hard " 2½ + Apple Dumpling Boiled 3 + Bass, striped, fresh Broiled 3 + Beans, pod Boiled 2½ + Beef, with salt only " 2¾ + " fresh, lean Raw 3 + " " " Fried 4 + " " " Roasted 3½ + " old, hard, salted Boiled 4¼ + Beefsteak Broiled 3 + Beets Boiled 3¾ + Bread, corn Baked 3¼ + " wheat, fresh " 3½ + Butter Melted 3½ + Cabbage, with vinegar Raw 2 + " " " Boiled 4½ + " heads Raw 2½ + Carrots Boiled 3¼ + Cheese, old, strong Raw 3½ + Chicken, full-grown Fricassee 2¾ + " soup Boiled 3 + Codfish, cured, dried " 2 + Corncake Baked 2¾ + Custard " 2¾ + Duck, domestic Roasted 4 + " wild " 4½ + Eggs, fresh, whipped Raw 1½ + " " 2 + " soft-boiled Boiled 3 + " hard-boiled " 3½ + " Fried 3½ + Fowl, domestic Boiled 4 + " " Roasted 4 + Gelatin Boiled 2½ + Goose Roasted 2½ + Green corn and beans Boiled 3¾ + Hash, meat and vegetables Warmed 2½ + Lamb Broiled 2½ + Liver " 2 + Milk Boiled 2 + " Raw 2¼ + Mutton, fresh Broiled 3 + " " Boiled 3 + " " Roasted 3¼ + Oysters, fresh Raw 2½ + " " Roasted 3¼ + " " Stewed 3½ + Parsnips Boiled 2½ + Pig Roasted 2½ + Pig's feet, soused Boiled 1 + Pork, recently salted " 4½ + " Fried 4¼ + " Raw 3 + " steaks Fried 3¼ + " Stewed 3 + " fat or lean Roasted 5¼ + Potatoes Baked 2½ + " Boiled 3½ + " Roasted 2½ + Rice Boiled 1 + Sago " 1¾ + Salmon, salted " 4 + Soup, barley " 1½ + " beans " 3 + " beef, vegetables, bread " 4 + " marrow bone " 4½ + " mutton " 3½ + Sponge Cake Baked 2½ + Suet, beef, fresh Boiled 5⅓ + " mutton " 4½ + Tapioca " 2 + Tripe, soused " 1 + Trout, salmon, fresh " 1½ + " " " Fried 1½ + Turkey, wild Roasted 2¼ + " domestic Boiled 2¼ + " " Roasted 2½ + Turnips Boiled 3½ + Veal Roasted 4 + " Fried 4½ + Venison, steaks Broiled 1½ + +The state of mind has much to do with digestion. Sudden fear or joy, or +unexpected news, may destroy the appetite at once. Let a hungry person be +anxiously awaiting a hearty meal, when suddenly a disastrous telegram is +brought him; all appetite instantly disappears, and the tempting food is +refused. Hence we should laugh and talk at our meals, and drive away +anxious thoughts and unpleasant topics of discussion. + +The proper chewing of the food is an important element in digestion. +Hence, eat slowly, and do not "bolt" large fragments of food. If +imperfectly chewed, it is not readily acted upon by the gastric juice, and +often undergoes fermentative changes which result in sour stomach, gastric +pain, and other digestive disturbance. + +If we take too much drink with our meals, the flow of the saliva is +checked, and digestion is hindered. It is not desireable to dilute the +gastric juice, nor to chill the stomach with large amount of cold liquid. + +Do not take food and drink too hot or too cold. If they are taken too +cold, the stomach is chilled, and digestion delayed. If we drink freely of +ice-water, it may require half an hour or more for the stomach to regain +its natural heat. + +It is a poor plan to stimulate a flagging appetite with highly spiced food +and bitter drinks. An undue amount of pepper, mustard, horseradish, +pickles, and highly seasoned meat-sauces may stimulate digestion for the +time, but they soon impair it. + + [NOTE. The process of gastric digestion was studied many years ago by + Dr. Beaumont and others, in the remarkable case of Alexis St. Martin, + a French-Canadian, who met with a gun-shot wound which left a + permanent opening into his stomach, guarded by a little valve of + mucous membrane. Through this opening the lining of the stomach could + be seen, the temperature ascertained, and numerous experiments made as + to the digestibility of various kinds of food. + + It was by these careful and convincing experiments that the foundation + of our exact knowledge of the composition and action of gastric juice + was laid. The modest book in which Dr. Beaumont published his results + is still counted among the classics of physiology. The production of + artificial fistulæ in animals, a method that has since proved so + fruitful, was first suggested by his work.] + +It cannot be too strongly stated that food of a simple character, well +cooked and neatly served, is more productive of healthful living than a +great variety of fancy dishes which unduly stimulate the digestive organs, +and create a craving for food in excess of the bodily needs. + +168. The Proper Care of the Teeth. It is our duty not only to take +the very best care of our teeth, but to retain them as long as possible. +Teeth, as we well know, are prone to decay. We may inherit poor and soft +teeth: our mode of living may make bad teeth worse. If an ounce of +prevention is ever worth a pound of cure, it is in keeping the teeth in +good order. Bad teeth and toothless gums mean imperfect chewing of the +food and, hence, impaired digestion. To attain a healthful old age, the +power of vigorous mastication must be preserved. + +One of the most frequent causes of decay of the teeth is the retention of +fragments of food between and around them. The warmth and moisture of the +mouth make these matters decompose quickly. The acid thus generated +attacks the enamel of the teeth, causing decay of the dentine. Decayed +teeth are often the cause of an offensive breath and a foul stomach. + +[Illustration: Fig. 64.--Lymphatics on the Inside of the Right Hand.] + +To keep the teeth clean and wholesome, they should be thoroughly cleansed +at bedtime and in the morning with a soft brush and warm water. Castile +soap, and some prepared tooth-powder without grit, should be used, and the +brush should be applied on both sides of the teeth. + +The enamel, once broken through, is never renewed. The tooth decays, +slowly but surely: hence we must guard against certain habits which injure +the enamel, as picking the teeth with pins and needles. We should never +crack nuts, crush hard candy, or bite off stout thread with the teeth. +Stiff tooth-brushes, gritty and cheap tooth-powders, and hot food and +drink, often injure the enamel. + +To remove fragments of food which have lodged between adjacent teeth, a +quill or wooden toothpick should be used. Even better than these is the +use of surgeon's floss, or silk, which when drawn between the teeth, +effectually dislodges retained particles. If the teeth are not regularly +cleansed they become discolored, and a hard coating known as _tartar_ +accumulates on them and tends to loosen them. It is said that after the +age of thirty more teeth are lost from this deposit than from all other +causes combined. In fact decay and tartar are the two great agents that +furnish work for the dentist.[26] + +169. Hints about Saving Teeth. We should exercise the greatest care +in saving the teeth. The last resort of all is to lose a tooth by +extraction. The skilled dentist will save almost anything in the shape of +a tooth. + +People are often urged and consent to have a number of teeth extracted +which, with but little trouble and expense, might be kept and do good +service for years. The object is to replace the teeth with an artificial +set. Very few plates, either partial or entire, are worn with real +comfort. They should always be removed before going to sleep, as there is +danger of their being swallowed. + +The great majority of drugs have no injurious effect upon the teeth. Some +medicines, however, must be used with great care. The acids used in the +tincture of iron have a great affinity for the lime salts of the teeth. As +this form of iron is often used, it is not unusual to see teeth very badly +stained or decayed from the effects of this drug. The acid used in the +liquid preparations of quinine may destroy the teeth in a comparatively +short time. After taking such medicines the mouth should be thoroughly +rinsed with a weak solution of common soda, and the teeth cleansed. + +170. Alcohol and Digestion. The influence of alcoholic drinks upon +digestion is of the utmost importance. Alcohol is not, and cannot be +regarded from a physiological point of view as a true food. The reception +given to it by the stomach proves this very plainly. It is obviously an +unwelcome intruder. It cannot, like proper foods, be transformed into any +element or component of the human body, but passes on, innutritious and +for the most part unappropriated. Taken even into the mouth, by any person +not hardened to its use, its effect is so pungent and burning as at once +to demand its rejection. But if allowed to pass into the stomach, that +organ immediately rebels against its intrusion, and not unfrequently +ejects it with indignant emphasis. The burning sensation it produces +there, is only an appeal for water to dilute it. + +The stomach meanwhile, in response to this fiery invitation, secretes from +its myriad pores its juices and watery fluids, to protect itself as much +as possible from the invading liquid. It does not digest alcoholic drinks; +we might say it does not attempt to, because they are not material +suitable for digestion, and also because no organ can perform its normal +work while smarting under an unnatural irritation. + +Even if the stomach does not at once eject the poison, it refuses to +adopt it as food, for it does not pass along with the other food material, +as chyme, into the intestines, but is seized by the absorbents, borne into +the veins, which convey it to the heart, whence the pulmonary artery +conveys it to the lungs, where its presence is announced in the breath. +But wherever alcohol is carried in the tissues, it is always an irritant, +every organ in turn endeavoring to rid itself of the noxious material. + +171. Effect of Alcoholic Liquor upon the Stomach. The methods by +which intoxicating drinks impair and often ruin digestion are various. We +know that a piece of animal food, as beef, if soaked in alcohol for a few +hours, becomes hard and tough, the fibers having been compacted together +because of the abstraction of their moisture by the alcohol, which has a +marvelous affinity for water. In the same way alcohol hardens and toughens +animal food in the stomach, condensing its fibers, and rendering it +indigestible, thus preventing the healthful nutrition of the body. So, if +alcohol be added to the clear, liquid white of an egg, it is instantly +coagulated and transformed into hard albumen. As a result of this +hardening action, animal food in contact with alcoholic liquids in the +stomach remains undigested, and must either be detained there so long as +to become a source of gastric disturbance, or else be allowed to pass +undigested through the pyloric gate, and then may become a cause of +serious intestinal disturbance.[27] + +This peculiar property of alcohol, its greedy absorption of water from +objects in contact with it, acts also by absorbing liquids from the +surface of the stomach itself, thus hardening the delicate glands, +impairing their ability to absorb the food-liquids, and so inducing +gastric dyspepsia. This local injury inflicted upon the stomach by all +forms of intoxicants, is serious and protracted. This organ is, with +admirable wisdom, so constructed as to endure a surprising amount of +abuse, but it was plainly not intended to thrive on alcoholic liquids. The +application of fiery drinks to its tender surface produces at first a +marked congestion of its blood-vessels, changing the natural pink color, +as in the mouth, to a bright or deep red. + +If the irritation be not repeated, the lining membrane soon recovers its +natural appearance. But if repeated and continued, the congestion becomes +more intense, the red color deeper and darker; the entire surface is the +subject of chronic inflammation, its walls are thickened, and sometimes +ulcerated. In this deplorable state, the organ is quite unable to perform +its normal work of digestion.[28] + +172. Alcohol and the Gastric Juice. But still another destructive +influence upon digestion appears in the singular fact that alcohol +diminishes the power of the gastric juice to do its proper work. Alcohol +coagulates the pepsin, which is the dissolving element in this important +gastric fluid. A very simple experiment will prove this. Obtain a small +quantity of gastric juice from the fresh stomach of a calf or pig, by +gently pressing it in a very little water. Pour the milky juice into a +clear glass vessel, add a little alcohol, and a white deposit will +presently settle to the bottom. This deposit contains the pepsin of the +gastric juice, the potent element by which it does its special work of +digestion. The ill effect of alcohol upon it is one of the prime factors +in the long series of evil results from the use of intoxicants. + +173. The Final Results upon Digestion. We have thus explained three +different methods by which alcoholic drinks exercise a terrible power for +harm; they act upon the food so as to render it less digestible; they +injure the stomach so as seriously to impair its power of digestion; and +they deprive the gastric juice of the one principal ingredient essential +to its usefulness. + +Alcoholic drinks forced upon the stomach are a foreign substance; the +stomach treats them as such, and refuses to go on with the process of +digestion till it first gets rid of the poison. This irritating presence +and delay weaken the stomach, so that when proper food follows, the +enfeebled organ is ill prepared for its work. After intoxication, there +occurs an obvious reaction of the stomach, and digestive organs, against +the violent and unnatural disturbance. The appetite is extinguished or +depraved, and intense headache racks the frame, the whole system is +prostrated, as from a partial paralysis (all these results being the voice +of Nature's sharp warning of this great wrong), and a rest of some days +is needed before the system fully recovers from the injury inflicted. + +It is altogether an error to suppose the use of intoxicants is necessary +or even desirable to promote appetite or digestion. In health, good food +and a stomach undisturbed by artificial interference furnish all the +conditions required. More than these is harmful. If it may sometimes seem +as if alcoholic drinks arouse the appetite and invigorate digestion, we +must not shut our eyes to the fact that this is only a seeming, and that +their continued use will inevitably ruin both. In brief, there is no more +sure foe to good appetite and normal digestion than the habitual use of +alcoholic liquors. + +174. Effect of Alcoholic Drinks upon the Liver. It is to be noted +that the circulation of the liver is peculiar; that the capillaries of the +hepatic artery unite in the lobule with those of the portal vein, and thus +the blood from both sources is combined; and that the portal vein brings +to the liver the blood from the stomach, the intestines, and the spleen. +From the fact that alcohol absorbed from the stomach enters the portal +vein, and is borne directly to the liver, we would expect to find this +organ suffering the full effects of its presence. And all the more would +this be true, because we have just learned that the liver acts as a sort +of filter to strain from the blood its impurities. So the liver is +especially liable to diseases produced by alcoholics. Post mortems of +those who have died while intoxicated show a larger amount of alcohol in +the liver than in any other organ. Next to the stomach the liver is an +early and late sufferer, and this is especially the case with hard +drinkers, and even more moderate drinkers in hot climates. Yellow fever +occurring in inebriates is always fatal. + +The effects produced in the liver are not so much functional as organic; +that is, not merely a disturbed mode of action, but a destruction of the +fabric of the organ itself. From the use of intoxicants, the liver +becomes at first irritated, then inflamed, and finally seriously diseased. +The fine bands, or septa, which serve as partitions between the hepatic +lobules, and so maintain the form and consistency of the organ, are the +special subjects of the inflammation. Though the liver is at first +enlarged, it soon becomes contracted; the secreting cells are compressed, +and are quite unable to perform their proper work, which indeed is a very +important one in the round of the digestion of food and the purification +of the blood. This contraction of the septa in time gives the whole organ +an irregularly puckered appearance, called from this fact a hob-nail liver +or, popularly, gin liver. The yellowish discoloration, usually from +retained or perverted bile, gives the disease the medical name of +cirrhosis.[29] It is usually accompanied with dropsy in the lower +extremities, caused by obstruction to the return of the circulation from +the parts below the liver. This disease is always fatal. + + +175. Fatty Degeneration Due to Alcohol. Another form of destructive +disease often occurs. There is an increase of fat globules deposited in +the liver, causing notable enlargement and destroying its function. This +is called fatty degeneration, and is not limited to the liver, but other +organs are likely to be similarly affected. In truth, this deposition of +fat is a most significant occurrence, as it means actual destruction of +the liver tissues,--nothing less than progressive death of the organ. This +condition always leads to a fatal issue. Still other forms of alcoholic +disease of the liver are produced, one being the excessive formation of +sugar, constituting what is known as a form of diabetes. + +176. Effect of Tobacco on Digestion. The noxious influence of +tobacco upon the process of digestion is nearly parallel to the effects of +alcohol, which it resembles in its irritant and narcotic character. +Locally, it stimulates the secretion of saliva to an unnatural extent, and +this excess of secretion diminishes the amount available for normal +digestion. + +Tobacco also poisons the saliva furnished for the digestion of food, and +thus at the very outset impairs, in both of these particulars, the general +digestion, and especially the digestion of the starchy portions of the +food. For this reason the amount of food taken, fails to nourish as it +should, and either more food must be taken, or the body becomes gradually +impoverished. + +The poisonous _nicotine_, the active element of tobacco, exerts a +destructive influence upon the stomach digestion, enfeebling the vigor of +the muscular walls of that organ. These effects combined produce +dyspepsia, with its weary train of baneful results. + +The tobacco tongue never presents the natural, clear, pink color, but +rather a dirty yellow, and is usually heavily coated, showing a disordered +stomach and impaired digestion. Then, too, there is dryness of the mouth, +an unnatural thirst that demands drink. But pure water is stale and flat +to such a mouth: something more emphatic is needed. Thus comes the +unnatural craving for alcoholic liquors, and thus are taken the first +steps on the downward grade. + +"There is no doubt that tobacco predisposes to neuralgia, vertigo, +indigestion, and other affections of the nervous, circulatory and +digestive organs."--W. H. Hammond, the eminent surgeon of New York city +and formerly Surgeon General, U.S.A. + +Drs. Seaver of Yale University and Hitchcock of Amherst College, +instructors of physical education in these two colleges, have clearly +demonstrated by personal examination and recorded statistics that the use +of tobacco among college students checks growth in weight, height, +chest-girth, and, most of all, in lung capacity. + + + +Additional Experiments. + + Experiment 66. Test a portion of _C_ (Experiment 57) with solution + of iodine; no blue color is obtained, as all the starch has disappeared, + having been converted into a reducing sugar, or maltose. + + Experiment 67. Make a thick starch paste; place some in test tubes, + labeled _A_ and _B_. Keep _A_ for comparison, and to _B_ add saliva, and + expose both to about 104° F. _A_ is unaffected, while _B_ soon becomes + fluid --within two minutes--and loses its opalescence; this liquefaction + is a process quite antecedent to the saccharifying process which + follows. + + Experiment 68. _To show the action of gastric juice on milk_. Mix + two teaspoonfuls of fresh milk in a test tube with a few drops of + neutral artificial gastric juice;[30] keep at about 100° F. In a short + time the milk curdles, so that the tube can be inverted without the curd + falling out. By and by _whey_ is squeezed out of the clot. The curdling + of milk by the rennet ferment present in the gastric juice, is quite + different from that produced by the "souring of milk," or by the + precipitation of caseinogen by acids. Here the casein (carrying with it + most of the fats) is precipitated in a neutral fluid. + + Experiment 69. To the test tube in the preceding experiment, add + two teaspoonfuls of dilute hydrochloric acid, and keep at 100° F. for + two hours. The pepsin in the presence of the acid digests the casein, + gradually dissolving it, forming a straw-colored fluid containing + peptones. The peptonized milk has a peculiar odor and bitter taste. + + Experiment 70. _To show the action of rennet on milk_. Place milk + in a test tube, add a drop or two of commercial rennet, and place the + tube in a water-bath at about 100° F. The milk becomes solid in a few + minutes, forming a _curd_, and by and by the curd of casein contracts, + and presses out a fluid,--the _whey_. + + Experiment 71. Repeat the experiment, but previously boil the + rennet. No such result is obtained as in the preceding experiment, + because the rennet ferment is destroyed by heat. + + Experiment 72. _To show the effect of the pancreatic ferment + (trypsin) upon albuminous matter_. Half fill three test tubes, _A, B, + C_, with one-per-cent solution of sodium carbonate, and add 5 drops of + liquor pancreaticus, or a few grains of Fairchild's extract of pancreas, + in each. Boil _B_, and make _C_ acid with dilute hydrochloric acid. + Place in each tube an equal amount of well-washed fibrin, plug the tubes + with absorbent cotton, and place all in a water-bath at about 100° F. + + Experiment 73. Examine from time to time the three test tubes in + the preceding experiment. At the end of one, two, or three hours, there + is no change in _B_ and _C_, while in _A_ the fibrin is gradually being + eroded, and finally disappears; but it does not swell up, and the + solution at the same time becomes slightly turbid. After three hours, + still no change is observable in _B_ and _C_. + + Experiment 74. Filter _A_, and carefully neutralize the filtrate + with very dilute hydrochloric or acetic acid, equal to a precipitate of + alkali-albumen. Filter off the precipitate, and on testing the filtrate, + peptones are found. The intermediate bodies, the albumoses, are not + nearly so readily obtained from pancreatic as from gastric digests. + + Experiment 75. Filter _B_ and _C_, and carefully neutralize the + filtrates. They give no precipitate. No peptones are found. + + Experiment 76. _To show the action of pancreatic juice upon the + albuminous ingredients (casein) of milk_. Into a four-ounce bottle put + two tablespoonfuls of cold water; add one grain of Fairchild's extract + of pancreas, and as much baking soda as can be taken up on the point of + a penknife. Shake well, and add four tablespoonfuls of cold, fresh milk. + Shake again. + + Now set the bottle into a basin of hot water (as hot as one can bear the + hand in), and let it stand for about forty-five minutes. While the milk + is digesting, take a small quantity of milk in a goblet, and stir in ten + drops or more of vinegar. A thick curd of casein will be seen. + + Upon applying the same test to the digested milk, no curd will be made. + This is because the pancreatic ferment (trypsin) has digested the casein + into "peptone," which does not curdle. This digested milk is therefore + called "peptonized milk." + + Experiment 77. _To show the action of bile_. Obtain from the + butcher some ox bile. Note its bitter taste, peculiar odor, and greenish + color. It is alkaline or neutral to litmus paper. Pour it from one + vessel to another, and note that strings of mucin (from the lining + membrane of the gall bladder) connect one vessel with the other. It is + best to precipitate the mucin by acetic acid before making experiments; + and to dilute the clear liquid with a little distilled water. + + Experiment 78. _Test for bile pigments_. Place a few drops of bile + on a white porcelain slab. With a glass rod place a drop or two of + strong nitric acid containing nitrous acid near the drop of bile; bring + the acid and bile into contact. Notice the succession of colors, + beginning with green and passing into blue, red, and yellow. + + Experiment 79. _To show the action of bile on fats_. Mix three + teaspoonfuls of bile with one-half a teaspoonful of almond oil, to which + some oleic acid is added. Shake well, and keep the tube in a water-bath + at about 100° F. A very good emulsion is obtained. + + Experiment 80. _To show that bile favors filtration and the + absorption of fats_. Place two small funnels of exactly the same size in + a filter stand, and under each a beaker. Into each funnel put a filter + paper; moisten the one with water (_A_) and the other with bile (_B_). + Pour into each an equal volume of almond oil; cover with a slip of glass + to prevent evaporation. Set aside for twelve hours, and note that the + oil passes through _B_, but scarcely any through _A_. The oil filters + much more readily through the one moistened with bile, than through the + one moistened with water. + + +Experiments with the Fats. + + Experiment 81. Use olive oil or lard. Show by experiment that they + are soluble in ether, chloroform and hot water, but insoluble in water + alone. + + Experiment 82. Dissolve a few drops of oil or fat in a teaspoonful + of ether. Let a drop of the solution fall on a piece of tissue or rice + paper. Note the greasy stain, which does not disappear with the heat. + + Experiment 83. Pour a little cod-liver oil into a test tube; add a + few drops of a dilute solution of sodium carbonate. The whole mass + becomes white, making an emulsion. + + Experiment 84. Shake up olive oil with a solution of albumen in a + test tube. Note that an emulsion is formed. + + + + +Chapter VII. + +The Blood and Its Circulation. + + + +177. The Circulation. All the tissues of the body are traversed by +exceedingly minute tubes called capillaries, which receive the blood from +the arteries, and convey it to the veins. These capillaries form a great +system of networks, the meshes of which are filled with the elements of +the various tissues. That is, the capillaries are closed vessels, and the +tissues lie outside of them, as asbestos packing may be used to envelop +hot-water pipes. The space between the walls of the capillaries and the +cells of the tissues is filled with lymph. As the blood flows along +the capillaries, certain parts of the plasma of the blood filter through +their walls into the lymph, and certain parts of the lymph filter through +the cell walls of the tissues and mingle with the blood current. The lymph +thus acts as a medium of exchange, in which a transfer of material takes +place between the blood in the capillaries and the lymph around them. A +similar exchange of material is constantly going on between the lymph and +the tissues themselves. + +This, then, we must remember,--that in every tissue, so long as the blood +flows, and life lasts, this exchange takes place between the blood within +the capillaries and the tissues without. + +The stream of blood _to_ the tissues carries to them the material, +including the all-important oxygen, with which they build themselves up +and do their work. The stream _from_ the tissues carries into the blood +the products of certain chemical changes which have taken place in these +tissues. These products may represent simple waste matter to be cast out +or material which may be of use to some other tissue. + +In brief, the tissues by the help of the lymph live on the blood. +Just as our bodies, as a whole, live on the things around us, the food and +the air, so do the bodily tissues live on the blood which bathes them in +an unceasing current, and which is their immediate air and food. + + +178. Physical Properties of Blood. The blood has been called the +life of the body from the fact that upon it depends our bodily existence. +The blood is so essentially the nutrient element that it is called +sometimes very aptly "liquid flesh." It is a red, warm, heavy, alkaline +fluid, slightly salt in taste, and has a somewhat fetid odor. Its color +varies from bright red in the arteries and when exposed to the air, to +various tints from dark purple to red in the veins. The color of the blood +is due to the coloring constituent of the red corpuscles, _hæmoglobin_, +which is brighter or darker as it contains more or less oxygen. + +[Illustration: Fig. 65.--Blood Corpuscles of Various Animals. (Magnified +to the same scale.) + + A, from proteus, a kind of newt; + B, salamander; + C, frog; + D, frog after addition of acetic acid, showing the central nucleus; + E, bird; + F, camel; + G, fish; + H, crab or other invertebrate animal +] + +The temperature of the blood varies slightly in different parts of the +circulation. Its average heat near the surface is in health about the +same, _viz_. 98½° F. Blood is alkaline, but outside of the body it soon +becomes neutral, then acid. The chloride of sodium, or common salt, which +the blood contains, gives it a salty taste. In a hemorrhage from the +lungs, the sufferer is quick to notice in the mouth the warm and saltish +taste. The total amount of the blood in the body was formerly greatly +overestimated. It is about 1/13 of the total weight of the body, and in a +person weighing 156 pounds would amount to about 12 pounds. + +179. Blood Corpuscles. If we put a drop of blood upon a glass slide, +and place upon it a cover of thin glass, we can flatten it out until the +color almost disappears. If we examine this thin film with a microscope, +we see that the blood is not altogether fluid. We find that the liquid +part, or plasma, is of a light straw color, and has floating in it a +multitude of very minute bodies, called corpuscles. These are of two +kinds, the red and the colorless. The former are much more +numerous, and have been compared somewhat fancifully to countless myriads +of tiny fishes in a swiftly flowing stream. + +180. Red Corpuscles. The red corpuscles are circular disks about +1/3200 of an inch in diameter, and double concave in shape. They tend to +adhere in long rolls like piles of coins. They are soft, flexible, and +elastic, readily squeezing through openings and passages narrower than +their own diameter, then at once resuming their own shape. + +The red corpuscles are so very small, that rather more than ten millions +of them will lie on a surface one inch square. Their number is so enormous +that, if all the red corpuscles in a healthy person could be arranged in a +continuous line, it is estimated that they would reach four times around +the earth! The principal constituent of these corpuscles, next to water, +and that which gives them color is _hæmoglobin_, a compound containing +iron. As all the tissues are constantly absorbing oxygen, and giving off +carbon dioxid, a very important office of the red corpuscles is to carry +oxygen to all parts of the body. + +181. Colorless Corpuscles. The colorless corpuscles are larger +than the red, their average diameter being about 1/2500 of an inch. While +the red corpuscles are regular in shape, and float about, and tumble +freely over one another, the colorless are of irregular shape, and stick +close to the glass slide on which they are placed. Again, while the red +corpuscles are changed only by some influence from without, as pressure +and the like, the colorless corpuscles spontaneously undergo active and +very curious changes of form, resembling those of the amœba, a very +minute organism found in stagnant water (Fig. 2). + +The number of both red and colorless corpuscles varies a great deal from +time to time. For instance, the number of the latter increases after +meals, and quickly diminishes. There is reason to think both kinds of +corpuscles are continually being destroyed, their place being supplied by +new ones. While the action of the colorless corpuscles is important to the +lymph and the chyle, and in the coagulation of the blood, their real +function has not been ascertained. + +[Illustration: Fig. 66.--Blood Corpuscles of Man. + + A, red corpuscles; + B, the same seen edgeways; + C, the same arranged in rows; + D, white corpuscles with nuclei. +] + + Experiment 85. _To show the blood corpuscles_. A moderately + powerful microscope is necessary to examine blood corpuscles. Let a + small drop of blood (easily obtained by pricking the finger with a + needle) be placed upon a clean slip of glass, and covered with thin + glass, such as is ordinarily used for microscopic purposes. + + The blood is thus spread out into a film and may be readily examined. At + first the red corpuscles will be seen as pale, disk-like bodies floating + in the clear fluid. Soon they will be observed to stick to each other by + their flattened faces, so as to form rows. The colorless corpuscles are + to be seen among the red ones, but are much less numerous. + +182. The Coagulation of the Blood. Blood when shed from the living +body is as fluid as water. But it soon becomes viscid, and flows less +readily from one vessel to another. Soon the whole mass becomes a nearly +solid jelly called a clot. The vessel containing it even can be +turned upside down, without a drop of blood being spilled. If carefully +shaken out, the mass will form a complete mould of the vessel. + +At first the clot includes the whole mass of blood, takes the shape of +the vessel in which it is contained, and is of a uniform color. But in a +short time a pale yellowish fluid begins to ooze out, and to collect on +the surface. The clot gradually shrinks, until at the end of a few hours +it is much firmer, and floats in the yellowish fluid. The white corpuscles +become entangled in the upper portion of clot, giving it a pale yellow +look on the top, known as the _buffy coat_. As the clot is attached to the +sides of the vessel, the shrinkage is more pronounced toward the center, +and thus the surface of the clot is hollowed or _cupped_, as it is called. +This remarkable process is known as coagulation, or the clotting of +blood; and the liquid which separates from the clot is called serum. +The serum is almost entirely free from corpuscles, these being entangled +in the fibrin. + +[Illustration: Fig. 67.--Diagram of Clot with Buffy Coat. + + A, serum; + B, cupped upper surface of clot; + C, white corpuscles in upper layer of clot; + D, lower portion of clot with red corpuscles. +] + +This clotting of the blood is due to the formation in the blood, after it +is withdrawn from the living body, of a substance called fibrin.[31] +It is made up of a network of fine white threads, running in every +direction through the plasma, and is a proteid substance. The coagulation +of the blood may be retarded, and even prevented, by a temperature below +40° F., or a temperature above 120° F. The addition of common salt also +prevents coagulation. The clotting of the blood may be hastened by free +access to air, by contact with roughened surfaces, or by keeping it at +perfect rest. + +This power of coagulation is of the most vital importance. But for this, +a very small cut might cause bleeding sufficient to empty the +blood-vessels, and death would speedily follow. In slight cuts, Nature +plugs up the wound with clots of blood, and thus prevents excessive +bleeding. The unfavorable effects of the want of clotting are illustrated +in some persons in whom bleeding from even the slightest wounds continues +till life is in danger. Such persons are called "bleeders," and surgeons +hesitate to perform on them any operation, however trivial, even the +extraction of a tooth being often followed by an alarming loss of blood. + + Experiment 86. A few drops of fresh blood may be easily obtained to + illustrate important points in the physiology of blood, by tying a + string tight around the finger, and piercing it with a clean needle. The + blood runs freely, is red and opaque. Put two or three drops of fresh + blood on a sheet of white paper, and observe that it looks yellowish. + + Experiment 87. Put two or three drops of fresh blood on a white + individual butter plate inverted in a saucer of water. Cover it with an + inverted goblet. Take off the cover in five minutes, and the drop has + set into a jelly-like mass. Take it off in half an hour, and a little + clot will be seen in the watery serum. + + Experiment 88. _To show the blood-clot._ Carry to the slaughter + house a clean, six or eight ounce, wide-mouthed bottle. Fill it with + fresh blood. Carry it home with great care, and let it stand over night. + The next day the clot will be seen floating in the nearly colorless + serum. + + Experiment 89. Obtain a pint of fresh blood; put it into a bowl, + and whip it briskly for five minutes, with a bunch of dry twigs. Fine + white threads of fibrin collect on the twigs, the blood remaining fluid. + This is "whipped" or defibrinated blood, which has lost the power of + coagulating spontaneously. + +183. General Plan of Circulation. All the tissues of the body depend +upon the blood for their nourishment. It is evident then that this vital +fluid must be continually renewed, else it would speedily lose all of its +life-giving material. Some provision, then, is necessary not only to have +the blood renewed in quantity and quality, but also to enable it to carry +away impurities. + +So we must have an apparatus of circulation. We need first a central +pump from which branch off large pipes, which divide into smaller and +smaller branches until they reach the remotest tissues. Through these +pipes the blood must be pumped and distributed to the whole body. Then we +must have a set of return pipes by which the blood, after it has carried +nourishment to the tissues, and received waste matters from them, shall be +brought back to the central pumping station, to be used again. We must +have also some apparatus to purify the blood from the waste matter it has +collected. + +[Illustration: Fig. 68.--Anterior View of the Heart. + + A, superior vena cava; + B, right auricle; + C, right ventricle; + D, left ventricle; + E, left auricle; + F, pulmonary vein; + H, pulmonary artery; + K, aorta; + L, right subclavian artery; + M, right common carotid artery; + N, left common carotid artery. +] + +This central pump is the heart. The pipes leading from it and +gradually growing smaller and smaller are the arteries. The very +minute vessels into which they are at last subdivided are +capillaries. The pipes which convey the blood back to the heart are +the veins. Thus, the arteries end in the tissues in fine, hair-like +vessels, the capillaries; and the veins begin in the tissues in +exceedingly small tubes,--the capillaries. Of course, there can be no +break in the continuity between the arteries and the vein. The apparatus +of circulation is thus formed by the heart, the arteries, the +capillaries, and the veins. + +184. The Heart. The heart is a pear-shaped, muscular organ +roughly estimated as about the size of the persons closed fist. It lies in +the chest behind the breastbone, and is, lodged between the lobes of the +lungs, which partly cover it. In shape the heart resembles a cone, the +base of which is directed upwards, a little backwards, and to the right +side, while the apex is pointed downwards, forwards, and to the left side. +During life, the apex of the heart beats against the chest wall in +the space between the fifth and sixth ribs, and about an inch and a half +to the left of the middle line of the body. The beating of the heart can +be readily felt, heard, and often seen moving the chest wall as it strikes +against it. + +[Illustration: Fig. 69.--Diagram illustrating the Structure of a Serous +Membrane. + + A, the viscus, or organ, enveloped by serous membrane; + B, layer of membrane lining cavity; + C, membrane reflected to envelop viscus; + D, outer layer of viscus, with blood-vessels at + E communicating with the general circulation. +] + +The heart does not hang free in the chest, but is suspended and kept in +position to some extent by the great vessels connected with it. It is +enclosed in a bell-shaped covering called the pericardium. This is +really double, with two layers, one over another. The inner or serous +layer covers the external surface of the heart, and is reflected back upon +itself in order to form, like all membranes of this kind, a sac without an +opening.[32] The heart is thus covered by the pericardial sac, but +is not contained inside its cavity. The space between the two membranes is +filled with serous fluid. This fluid permits the heart and the pericardium +to glide upon one another with the least possible amount of friction.[33] + +The heart is a hollow organ, but the cavity is divided into two parts by a +muscular partition forming a left and a right side, between which there is +no communication. These two cavities are each divided by a horizontal +partition into an upper and a lower chamber. These partitions, however, +include a set of valves which open like folding doors between the two +rooms. If these doors are closed there are two separate rooms, but if open +there is practically only one room. The heart thus has four chambers, two +on each side. The two upper chambers are called auricles from their +supposed resemblance to the ear. The two lower chambers are called +ventricles, and their walls form the chief portion of the muscular +substance of the organ. There are, therefore, the right and left auricles, +with their thin, soft walls, and the right and left ventricles, with their +thick and strong walls. + +185. The Valves of the Heart. The heart is a valvular pump, which +works on mechanical principles, the motive power being supplied by the +contraction of its muscular fibers. Regarding the heart as a pump, its +valves assume great importance. They consist of thin, but strong, +triangular folds of tough membrane which hang down from the edges of the +passages into the ventricles. They may be compared to swinging curtains +which, by opening only one way, allow the blood to flow from the auricles +to the ventricles, but by instantly folding back prevent its return. + +[Illustration: Fig. 70.--Lateral Section of the Right Chest. (Showing the +relative position of the heart and its great vessels, the œsophagus +and trachea.) + + A, inferior constrictor muscle (aids in conveying food down the + œsophagus); + B, œsophagus; + C, section of the right bronchus; + D, two right pulmonary veins; + E, great azygos vein crossing œsophagus and right bronchus to empty + into the superior vena cava; + F, thoracic duct; + H, thoracic aorta; + K, lower portion of œsophagus passing through the diaphragm; + L, diaphragm as it appears in sectional view, enveloping the heart; + M, inferior vena cava passing through diaphragm and emptying into + auricle; + N, right auricle; + O, section of right branch of the pulmonary artery; + P, aorta; + R, superior vena cava; + S, trachea. +] + +The valve on the right side is called the tricuspid, because it +consists of three little folds which fall over the opening and close it, +being kept from falling too far by a number of slender threads called +chordæ tendinæ. The valve on the left side, called the mitral, +from its fancied resemblance to a bishop's mitre, consists of two folds +which close together as do those of the tricuspid valve. + +The slender cords which regulate the valves are only just long enough to +allow the folds to close together, and no force of the blood pushing +against the valves can send them farther back, as the cords will not +stretch The harder the blood in the ventricles pushes back against the +valves, the tighter the cords become and the closer the folds are brought +together, until the way is completely closed. + +From the right ventricle a large vessel called the pulmonary artery +passes to the lungs, and from the left ventricle a large vessel called the +aorta arches out to the general circulation of the body. The openings +from the ventricles into these vessels are guarded by the semilunar +valves. Each valve has three folds, each half-moon-shaped, hence the +name semilunar. These valves, when shut, prevent any backward flow of the +blood on the right side between the pulmonary artery and the right +ventricle, and on the left side between the aorta and the left ventricle. + +[Illustration: Fig. 71.--Right Cavities of the Heart. + + A, aorta; + B, superior vena cava; + C, C, right pulmonary veins; + D, inferior vena cava; + E, section of coronary vein; + F, right ventricular cavity; + H, posterior curtain of the tricuspid valve; + K, right auricular cavity; + M, fossa ovalis, oval depression, partition between the auricles formed + after birth. +] + +186. General Plan of the Blood-vessels Connected with the Heart. +There are numerous blood-vessels connected with the heart, the relative +position and the use of which must be understood. The two largest veins in +the body, the superior vena cava and the inferior vena cava, +open into the right auricle. These two veins bring venous blood from all +parts of the body, and pour it into the right auricle, whence it passes +into the right ventricle. + +From the right ventricle arises one large vessel, the pulmonary +artery, which soon divides into two branches of nearly equal size, one +for the right lung, the other for the left. Each branch, having reached +its lung, divides and subdivides again and again, until it ends in +hair-like capillaries, which form a very fine network in every part of the +lung. Thus the blood is pumped from the right ventricle into the pulmonary +artery and distributed throughout the two lungs (Figs. 86 and 88). + +We will now turn to the left side of the heart, and notice the general +arrangement of its great vessels. Four veins, called the pulmonary +veins, open into the left auricle, two from each lung. These veins +start from very minute vessels the continuation of the capillaries of the +pulmonary artery. They form larger and larger vessels until they become +two large veins in each lung, and pour their contents into the left +auricle. Thus the pulmonary artery carries venous blood from the right +ventricle _to_ the lungs, as the pulmonary veins carry arterial blood +_from_ the lungs to the left auricle. + +From the left ventricle springs the largest arterial trunk in the body, +over one-half of an inch in diameter, called the aorta. From the +aorta other arteries branch off to carry the blood to all parts of the +body, only to be again brought back by the veins to the right side, +through the cavities of the ventricles. We shall learn in Chapter VIII. +that the main object of pumping the blood into the lungs is to have it +purified from certain waste matters which it has taken up in its course +through the body, before it is again sent on its journey from the left +ventricle. + + +187. The Arteries. The blood-vessels are flexible tubes through which +the blood is borne through the body. There are three kinds,--the +arteries, the veins, and the capillaries, and these differ +from one another in various ways. + +The arteries are the highly elastic and extensible tubes which carry +the pure, fresh blood outwards from the heart to all parts of the body. +They may all be regarded as branches of the aorta. After the aorta leaves +the left ventricle it rises towards the neck, but soon turns downwards, +making a curve known as the arch of the aorta. + +From the arch are given off the arteries which supply the head and arms +with blood. These are the two carotid arteries, which run up on each +side of the neck to the head, and the two subclavian arteries, which +pass beneath the collar bone to the arms. This great arterial trunk now +passes down in front of the spine to the pelvis, where it divides into two +main branches, which supply the pelvis and the lower limbs. + +The descending aorta, while passing downwards, gives off arteries to the +different tissues and organs. Of these branches the chief are the +coeliac artery, which subdivides into three great branches,--one +each to supply the stomach, the liver, and the spleen; then the renal +arteries, one to each kidney; and next two others, the mesenteric +arteries, to the intestines. The aorta at last divides into two main +branches, the common iliac arteries, which, by their subdivisions, +furnish the arterial vessels for the pelvis and the lower limbs. + +[Illustration: Fig. 72.--Left Cavities of the Heart. + + A, B, right pulmonary veins; + with S, openings of the veins; + E, D, C, aortic valves; + R, aorta; + P, pulmonary artery; + O, pulmonic valves; + H, mitral valve; + K, columnæ carnoeæ; + M, right ventricular cavity; + N, interventricular septum. +] + +The flow of blood in the arteries is caused by the muscular force of the +heart, aided by the elastic tissues and muscular fibers of the arterial +walls, and to a certain extent by the muscles themselves. Most of the +great arterial trunks lie deep in the fleshy parts of the body; but their +branches are so numerous and become so minute that, with a few exceptions, +they penetrate all the tissues of the body,--so much so, that the point +of the finest needle cannot be thrust into the flesh anywhere without +wounding one or more little arteries and thus drawing blood. + + +188. The Veins. The veins are the blood-vessels which carry the +impure blood from the various tissues of the body to the heart. They begin +in the minute capillaries at the extremities of the four limbs, and +everywhere throughout the body, and passing onwards toward the heart, +receive constantly fresh accessions on the way from myriad other veins +bringing blood from other wayside capillaries, till the central veins +gradually unite into larger and larger vessels until at length they form +the two great vessels which open into the right auricle of the heart. + +These two great venous trunks are the inferior vena cava, bringing +the blood from the trunk and the lower limbs, and the superior vena +cava, bringing the blood from the head and the upper limbs. These two +large trunks meet as they enter the right auricle. The four pulmonary +veins, as we have learned, carry the arterial blood from the lungs to +the left auricle. + +[Illustration: Fig. 73. + + A, part of a vein laid open, with two pairs of valves; + B, longitudinal section of a vein, showing the valves closed. +] + +A large vein generally accompanies its corresponding artery, but most +veins lie near the surface of the body, just beneath the skin. They may be +easily seen under the skin of the hand and forearm, especially in aged +persons. If the arm of a young person is allowed to hang down a few +moments, and then tightly bandaged above the elbow to retard the return of +the blood, the veins become large and prominent. + +The walls of the larger veins, unlike arteries, contain but little of +either elastic or muscular tissue; hence they are thin, and when empty +collapse. The inner surfaces of many of the veins are supplied with +pouch-like folds, or pockets, which act as valves to impede the backward +flow of the blood, while they do not obstruct blood flowing forward toward +the heart. These valves can be shown by letting the forearm hang down, and +sliding the finger upwards over the veins (Fig. 73). + +The veins have no force-pump, like the arteries, to propel their contents +towards their destination. The onward flow of the blood in them is due to +various causes, the chief being the pressure behind of the blood pumped +into the capillaries. Then as the pocket-like valves prevent the backward +flow of the blood, the pressure of the various muscles of the body urges +along the blood, and thus promotes the onward flow. + +The forces which drive the blood through the arteries are sufficient to +carry the blood on through the capillaries. It is calculated that the +onward flow in the capillaries is about 1/50 to 1/33 of an inch in a +second, while in the arteries the blood current flows about 16 inches in a +second, and in the great veins about 4 inches every second. + +[Illustration: Fig. 74.--The Structure of Capillaries. + +Capillaries of various sizes, showing cells with nuclei] + +189. The Capillaries. The capillaries are the minute, hair-like +tubes, with very thin walls, which form the connection between the ending +of the finest arteries and the beginning of the smallest veins. They are +distributed through every tissue of the body, except the epidermis and its +products, the epithelium, the cartilages, and the substance of the teeth. +In fact, the capillaries form a network of the tiniest blood-vessels, so +minute as to be quite invisible, at least one-fourth smaller than the +finest line visible to the naked eye. + +The capillaries serve as a medium to transmit the blood from the arteries +to the veins; and it is through them that the blood brings nourishment to +the surrounding tissues. In brief, we may regard the whole body as +consisting of countless groups of little islands surrounded by +ever-flowing streams of blood. The walls of the capillaries are of the +most delicate structure, consisting of a single layer of cells loosely +connected. Thus there is allowed the most free interchange between the +blood and the tissues, through the medium of the lymph. + +The number of the capillaries is inconceivable. Those in the lungs alone, +placed in a continuous line, would reach thousands of miles. The thin +walls of the capillaries are admirably adapted for the important +interchanges that take place between the blood and the tissues. + +190. The Circulation of the Blood. It is now well to study the +circulation as a whole, tracing the course of the blood from a +certain point until it returns to the same point. We may conveniently +begin with the portion of blood contained at any moment in the right +auricle. The superior and inferior venæ cavæ are busily filling the +auricle with dark, impure blood. When it is full, it contracts. The +passage leading to the right ventricle lies open, and through it the blood +pours till the ventricle is full. Instantly this begins, in its turn, to +contract. The tricuspid valve at once closes, and blocks the way backward. +The blood is now forced through the open semilunar valves into the +pulmonary artery. + +The pulmonary artery, bringing venous blood, by its alternate expansion +and recoil, draws the blood along until it reaches the pulmonary +capillaries. These tiny tubes surround the air cells of the lungs, and +here an exchange takes place. The impure, venous blood here gives up its +_débris_ in the shape of carbon dioxid and water, and in return takes up a +large amount of oxygen. Thus the blood brought to the lungs by the +pulmonary arteries leaves the lungs entirely different in character and +appearance. This part of the circulation is often called the lesser or +pulmonic circulation. + +The four pulmonary veins bring back bright, scarlet blood, and pour it +into the left auricle of the heart, whence it passes through the mitral +valve into the left ventricle. As soon as the left ventricle is full, it +contracts. The mitral valve instantly closes and blocks the passage +backward into the auricle; the blood, having no other way open, is forced +through the semilunar valves into the aorta. Now red in color from its +fresh oxygen, and laden with nutritive materials, it is distributed by the +arteries to the various tissues of the body. Here it gives up its oxygen, +and certain nutritive materials to build up the tissues, and receives +certain products of waste, and, changed to a purple color, passes from the +capillaries into the veins. + +[Illustration: Fig. 75.--Diagram illustrating the Circulation. + + 1, right auricle; + 2, left auricle; + 3, right ventricle; + 4, left ventricle; + 5, vena cava superior; + 6, vena cava inferior; + 7, pulmonary arteries; + 8, lungs; + 9, pulmonary veins; + 10, aorta; + 11, alimentary canal; + 12, liver; + 13, hepatic artery; + 14, portal vein; + 15, hepatic vein. +] + + +All the veins of the body, except those from the lungs and the heart +itself, unite into two large veins, as already described, which pour their +contents into the right auricle of the heart, and thus the grand round of +circulation is continually maintained. This is called the systemic +circulation. The whole circuit of the blood is thus divided into two +portions, very distinct from each other. + +191. The Portal Circulation. A certain part of the systemic or +greater circulation is often called the portal circulation, which +consists of the flow of the blood from the abdominal viscera through the +portal vein and liver to the hepatic vein. The blood brought to the +capillaries of the stomach, intestines, spleen, and pancreas is gathered +into veins which unite into a single trunk called the portal vein. +The blood, thus laden with certain products of digestion, is carried to +the liver by the portal vein, mingling with that supplied to the +capillaries of the same organ by the hepatic artery. From these +capillaries the blood is carried by small veins which unite into a large +trunk, the hepatic vein, which opens into the inferior vena cava. The +portal circulation is thus not an independent system, but forms a kind of +loop on the systemic circulation. + +The lymph-current is in a sense a slow and stagnant side stream of +the blood circulation; for substances are constantly passing from the +blood-vessels into the lymph spaces, and returning, although after a +comparatively long interval, into the blood by the great lymphatic trunks. + + Experiment 90. _To illustrate the action of the heart, and how it + pumps the blood in only one direction_. Take a Davidson or Household + rubber syringe. Sink the suction end into water, and press the bulb. As + you let the bulb expand, it fills with water; as you press it again, a + valve prevents the water from flowing back, and it is driven out in a + jet along the other pipe. The suction pipe represents the veins; the + bulb, the heart; and the tube end, out of which the water flows, the + arteries. + + [NOTE. The heart is not nourished by the blood which passes through + it. The muscular substance of the heart itself is supplied with + nourishment by two little arteries called the _coronary arteries_, + which start from the aorta just above two of the semilunar valves. The + blood is returned to the right auricle (not to either of the venæ + cavæ) by the _coronary vein_.] + +The longest route a portion of blood may take from the moment it leaves +the left ventricle to the moment it returns to it, is through the portal +circulation. The shortest possible route is through the substance of the +heart itself. The mean time which the blood requires to make a complete +circuit is about 23 seconds. + +192. The Rhythmic Action of the Heart. To maintain a steady flow of +blood throughout the body the action of the heart must be regular and +methodical. The heart does not contract as a whole. The two auricles +contract at the same time, and this is followed at once by the contraction +of the two ventricles. While the ventricles are contracting, the auricles +begin to relax, and after the ventricles contract they also relax. Now +comes a pause, or rest, after which the auricles and ventricles contract +again in the same order as before, and their contractions are followed by +the same pause as before. These contractions and relaxations of the +various parts of the heart follow one another so regularly that the result +is called the rhythmic action of the heart. + +The average number of beats of the heart, under normal conditions, is from +65 to 75 per minute. Now the time occupied from the instant the auricles +begin to contract until after the contraction of the ventricles and the +pause, is less than a second. Of this time one-fifth is occupied by the +contraction of the auricles, two-fifths by the contraction of the +ventricles, and the time during which the whole heart is at rest is +two-fifths of the period. + +193. Impulse and Sounds of the Heart. The rhythmic action of the +heart is attended with various occurrences worthy of note. If the hand be +laid flat over the chest wall on the left, between the fifth and sixth +ribs, the heart will be felt beating. This movement is known as the +beat or impulse of the heart, and can be both seen and felt on +the left side. The heart-beat is unusually strong during active bodily +exertion, and under mental excitement. + +The impulse of the heart is due to the striking of the lower, tense part +of the ventricles--the apex of the heart--against the chest wall at the +moment of their vigorous contraction. It is important for the physician to +know the exact place where the heart-beat should be felt, for the heart +may be displaced by disease, and its impulse would indicate its new +position. + +Sounds also accompany the heart's action. If the ear be applied over the +region of the heart, two distinct sounds will be heard following one +another with perfect regularity. Their character may be tolerably imitated +by pronouncing the syllables _lubb_, _dŭp_. One sound is heard +immediately after the other, then there is a pause, then come the two +sounds again. The first is a dull, muffled sound, known as the "first +sound," followed at once by a short and sharper sound, known as the +"second sound" of the heart. + +The precise cause of the first sound is still doubtful, but it is made at +the moment the ventricles contract. The second sound is, without doubt, +caused by the sudden closure of the semilunar valves of the pulmonary +artery and the aorta, at the moment when the contraction of the ventricles +is completed. + +[Illustration: Fig. 76.--Muscular Fibers of the Ventricles. + + A, superficial fibers common to both ventricles; + B, fibers of the left ventricle; + C, deep fibers passing upwards toward the base of the heart; + D, fibers penetrating the left ventricle +] + +The sounds of the heart are modified or masked by blowing "murmurs" when +the cardiac orifices or valves are roughened, dilated, or otherwise +affected as the result of disease. Hence these new sounds may often afford +indications of the greatest importance to physicians in the diagnosis of +heart-disease. + +194. The Nervous Control of the Heart. The regular, rhythmic movement +of the heart is maintained by the action of certain nerves. In various +places in the substance of the heart are masses of nerve matter, called +ganglia. From these ganglia there proceed, at regular intervals, +discharges of nerve energy, some of which excite movement, while others +seem to restrain it. The heart would quickly become exhausted if the +exciting ganglia had it all their own way, while it would stand still if +the restraining ganglia had full sway. The influence of one, however, +modifies the other, and the result is a moderate and regular activity of +the heart. + +The heart is also subject to other nerve influences, but from outside of +itself. Two nerves are connected with the heart, the pneumogastric +and the sympathetic (secs. 271 and 265). The former appears to be +connected with the restraining ganglia; the latter with the exciting +ganglia. Thus, if a person were the subject of some emotion which caused +fainting, the explanation would be that the impression had been conveyed +to the brain, and from the brain to the heart by the pneumogastric nerves. +The result would be that the heart for an instant ceases to beat. Death +would be the result if the nerve influence were so great as to restrain +the movements of the heart for any appreciable time. + +Again, if the person were the subject of some emotion by which the heart +were beating faster than usual, it would mean that there was sent from the +brain to the heart by the sympathetic nerves the impression which +stimulated it to increased activity. + +195. The Nervous Control of the Blood-vessels. The tone and caliber +of the blood-vessels are controlled by certain vaso-motor nerves, +which are distributed among the muscular fibers of the walls. These nerves +are governed from a center in the medulla oblongata, a part of the brain +(sec. 270). If the nerves are stimulated more than usual, the muscular +walls contract, and the quantity of the blood flowing through them and the +supply to the part are diminished. Again, if the stimulus is less than +usual, the vessels dilate, and the supply to the part is increased. + +Now the vaso-motor center may be excited to increased activity by +influences reaching it from various parts of the body, or even from the +brain itself. As a result, the nerves are stimulated, and the vessels +contract. Again, the normal influence of the vaso-motor center may be +suspended for a time by what is known as the inhibitory or +restraining effect. The result is that the tone of the blood-vessels +becomes diminished, and their channels widen. + +The effect of this power of the nervous system is to give it a certain +control over the circulation in particular parts. Thus, though the force +of the heart and the general average blood-pressure remain the same, the +state of the circulation may be very different in different parts of the +body. The importance of this local control over the circulation is of the +utmost significance. Thus an organ at work needs to be more richly +supplied with blood than when at rest. For example, when the salivary +glands need to secrete saliva, and the stomach to pour out gastric juice, +the arteries that supply these organs are dilated, and so the parts are +flushed with an extra supply of blood, and thus are aroused to greater +activity. + +Again, the ordinary supply of blood to a part may be lessened, so that the +organ is reduced to a state of inactivity, as occurs in the case of the +brain during sleep. We have in the act of blushing a visible example of +sudden enlargement of the smaller arteries of the face and neck, called +forth by some mental emotion which acts on the vaso-motor center and +diminishes its activity. The reverse condition occurs in the act of +turning pale. Then the result of the mental emotion is to cause the +vaso-motor nerves to exercise a more powerful control over the +capillaries, thereby closing them, and thus shutting off the flow of +blood. + + Experiment 91. Hold up the ear of a white rabbit against the light + while the animal is kept quiet and not alarmed. The red central artery + can be seen coursing along the translucent organ, giving off branches + which by subdivision become too small to be separately visible, and the + whole ear has a pink color and is warm from the abundant blood flowing + through it. Attentive observation will show also that the caliber of the + main artery is not constant; at somewhat irregular periods of a minute + or more it dilates and contracts a little. + +[Illustration: Fig. 77.--Some of the Principal Organs of the Chest and +Abdomen. (Blood vessels on the left, muscles on the right.)] + +In brief, all over the body, the nervous system, by its vaso-motor +centers, is always supervising and regulating the distribution of blood in +the body, sending now more and now less to this or that part. + +[Illustration: Fig. 78.--Capillary Blood-Vessels in the Web of a Frog's +Foot, as seen with the Microscope.] + +196. The Pulse. When the finger is placed on any part of the body +where an artery is located near the surface, as, for example, on the +radial artery near the wrist, there is felt an intermittent pressure, +throbbing with every beat of the heart. This movement, frequently visible +to the eye, is the result of the alternate expansion of the artery by the +wave of blood, and the recoil of the arterial walls by their elasticity. +In other words, it is the wave produced by throwing a mass of blood into +the arteries already full. The blood-wave strikes upon the elastic walls +of the arteries, causing an increased distention, followed at once by +contraction. This regular dilatation and rigidity of the elastic artery +answering to the beats of the heart, is known as the pulse. + +The pulse may be easily found at the wrist, the temple, and the inner side +of the ankle. The throb of the two carotid arteries may be plainly felt by +pressing the thumb and finger backwards on each side of the larynx. The +progress of the pulse-wave must not be confused with the actual current of +the blood itself. For instance, the pulse-wave travels at the rate of +about 30 feet a second, and takes about 1/10 of a second to reach the +wrist, while the blood itself is from 3 to 5 seconds in reaching the same +place. + +The pulse-wave may be compared to the wave produced by a stiff breeze on +the surface of a slowly moving stream, or the jerking throb sent along a +rope when shaken. The rate of the pulse is modified by age, fatigue, +posture, exercise, stimulants, disease, and many other circumstances. At +birth the rate is about 140 times a minute, in early infancy, 120 or +upwards, in the healthy adult between 65 and 75, the most common number +being 72. In the same individual, the pulse is quicker when standing than +when lying down, is quickened by excitement, is faster in the morning, and +is slowest at midnight. In old age the pulse is faster than in middle +life; in children it is quicker than in adults. + +[Illustration: Fig. 79.--Circulation in the Capillaries, as seen with the +Microscope.] + +As the pulse varies much in its rate and character in disease, it is to +the skilled touch of the physician an invaluable help in the diagnosis of +the physical condition of his patient. + + Experiment 92. _To find the pulse_. Grasp the wrist of a friend, + pressing with three fingers over the radius. Press three fingers over + the radius in your own wrist, to feel the pulse. + + Count by a watch the rate of your pulse per minute, and do the same with + a friend's pulse. Compare its characters with your own pulse. + + Observe how the character and frequency of the pulse are altered by + posture, muscular exercise, a prolonged, sustained, deep inspiration, + prolonged expiration, and other conditions. + +197. Effect of Alcoholic Liquors upon the Organs of Circulation. +Alcoholic drinks exercise a destructive influence upon the heart, the +circulation, and the blood itself. These vicious liquids can reach the +heart only indirectly, either from the stomach by the portal vein to the +liver, and thence to the heart, or else by way of the lacteals, and so to +the blood through the thoracic duct. But by either course the route is +direct enough, and speedy enough to accomplish a vast amount of ruinous +work. + +The influence of alcohol upon the heart and circulation is produced mainly +through the nervous system. The inhibitory nerves, as we have seen, hold +the heart in check, exercise a restraining control over it, very much as +the reins control an active horse. In health this inhibitory influence is +protective and sustaining. But now comes the narcotic invasion of +alcoholic drinks, which paralyze the inhibitory nerves, with the others, +and at once the uncontrolled heart, like the unchecked steed, plunges on +to violent and often destructive results. + +[Illustration: Fig. 80.--Two Principal Arteries of the Front of the Leg +(Anterior Tibial and Dorsalis Pedis).] + +This action, because it is quicker, has been considered also a stronger +action, and the alcohol has therefore been supposed to produce a +stimulating effect. But later researches lead to the conclusion that the +effect of alcoholic liquors is not properly that of a stimulant, but of a +narcotic paralyzant, and that while it indeed quickens, it also really +weakens the heart's action. This view would seem sustained by the fact +that the more the intoxicants are pushed, the deeper are the narcotic and +paralyzing effects. After having obstructed the nutritive and reparative +functions of the vital fluid for many years, their effects at last may +become fatal. + +This relaxing effect involves not only the heart, but also the capillary +system, as is shown in the complexion of the face and the color of the +hands. In moderate drinkers the face is only flushed, but in drunkards it +is purplish. The flush attending the early stages of drinking is, of +course, not the flush of health, but an indication of disease.[34] + +198. Effect upon the Heart. This forced overworking of the heart +which drives it at a reckless rate, cuts short its periods of rest and +inevitably produces serious heart-exhaustion. If repeated and continued, +it involves grave changes of the structure of the heart. The heart muscle, +endeavoring to compensate for the over-exertion, may become much +thickened, making the ventricles smaller, and so fail to do its duty in +properly pumping forward the blood which rushes in from the auricle. Or +the heart wall may by exhaustion become thinner, making the ventricles +much too large, and unable to send on the current. In still other cases, +the heart degenerates with minute particles of fat deposited in its +structures, and thus loses its power to propel the nutritive fluid. All +three of these conditions involve organic disease of the valves, and all +three often produce fatal results. + +199. Effect of Alcohol on the Blood-vessels. Alcoholic liquors injure +not only the heart, but often destroy the blood-vessels, chiefly the +larger arteries, as the arch of the aorta or the basilar artery of the +brain. In the walls of these vessels may be gradually deposited a morbid +product, the result of disordered nutrition, sometimes chalky, sometimes +bony, with usually a dangerous dilatation of the tube. + +In other cases the vessels are weakened by an unnatural fatty deposit. +Though these disordered conditions differ somewhat, the morbid results in +all are the same. The weakened and stiffened arterial walls lose the +elastic spring of the pulsing current. The blood fails to sweep on with +its accustomed vigor. At last, owing perhaps to the pressure, against the +obstruction of a clot of blood, or perhaps to some unusual strain of work +or passion, the enfeebled vessel bursts, and death speedily ensues from a +form of apoplexy. + +[Illustration: Fig. 81.--Showing the Carotid Artery and Jugular Vein on +the Right Side, with Some of their Main Branches. (Some branches of the +cervical plexus, and the hypoglossal nerve are also shown.)] + + [NOTE. "An alcoholic heart loses its contractile and resisting power, + both through morbid changes in its nerve ganglia and in its muscle + fibers. In typhoid fever, muscle changes are evidently the cause of + the heart-enfeeblement; while in diphtheria, disturbances in + innervation cause the heart insufficiency. 'If the habitual use of + alcohol causes the loss of contractile and resisting power by + impairment of both the nerve ganglia and muscle fibers of the heart, + how can it act as a heart tonic?'"--Dr. Alfred L. Loomis, Professor of + Medicine in the Medical Department of the University of the City of + New York.] + +200. Other Results from the Use of Intoxicants. Other disastrous +consequences follow the use of intoxicants, and these upon the blood. When +any alcohol is present in the circulation, its greed for water induces the +absorption of moisture from the red globules of the blood, the +oxygen-carriers. In consequence they contract and harden, thus becoming +unable to absorb, as theretofore, the oxygen in the lungs. Then, in turn, +the oxidation of the waste matter in the tissues is prevented; thus the +corpuscles cannot convey carbon dioxid from the capillaries, and this fact +means that some portion of refuse material, not being thus changed and +eliminated, must remain in the blood, rendering it impure and unfit for +its proper use in nutrition. Thus, step by step, the use of alcoholics +impairs the functions of the blood corpuscles, perverts nutrition, and +slowly poisons the blood. + +[Illustration: Fig. 82.--The Right Axillary and Brachial Arteries, with +Some of their Main Branches.] + + [NOTE. "Destroy or paralyze the inhibitory nerve center, and instantly + its controlling effect on the heart mechanism is lost, and the + accelerating agent, being no longer under its normal restraint, runs + riot. The heart's action is increased, the pulse is quickened, an + excess of blood is forced into the vessels, and from their becoming + engorged and dilated the face gets flushed, all the usual concomitants + of a general engorgement of the circulation being the result."--Dr. + George Harley, F.R.S., an eminent English medical author. + + "The habitual use of alcohol produces a deleterious influence upon the + whole economy. The digestive powers are weakened, the appetite is + impaired, and the muscular system is enfeebled. The blood is + impoverished, and nutrition is imperfect and disordered, as shown by + the flabbiness of the skin and muscles, emaciation, or an abnormal + accumulation of fat."--Dr. Austin Flint, Senior, formerly Professor of + the Practice of Medicine in Bellevue Medical College, and author of + many standard medical works. + + "The immoderate use of the strong kind of tobacco, which soldiers + affect, is often very injurious to them, especially to very young + soldiers. It renders them nervous and shaky, gives rise to + palpitation, and is a factor in the production of the irritable or + so-called "trotting-heart" and tends to impair the appetite and + digestion."--London _Lancet_. + + "I never smoke because I have seen the most efficient proofs of the + injurious effects of tobacco on the nervous system."--Dr. + Brown-Sequard, the eminent French physiologist. + + "Tobacco, and especially cigarettes, being a depressant upon the + heart, should be positively forbidden."--Dr. J. M. Keating, on + "Physical Development," in _Cyclopædia of the Diseases of + Children_.] + +201. Effect of Tobacco upon the Heart. While tobacco poisons more or +less almost every organ of the body, it is upon the heart that it +works its most serious wrong. Upon this most important organ its +destructive effect is to depress and paralyze. Especially does this apply +to the young, whose bodies are not yet knit into the vigor that can brave +invasion. + +The _nicotine_ of tobacco acts through the nerves that control the heart's +action. Under its baneful influence the motions of the heart are +irregular, now feeble and fluttering, now thumping with apparently much +force: but both these forms of disturbed action indicate an abnormal +condition. Frequently there is severe pain in the heart, often dizziness +with gasping breath, extreme pallor, and fainting. + +The condition of the pulse is a guide to this state of the heart. In this +the physician reads plainly the existence of the "tobacco heart," an +affection as clearly known among medical men as croup or measles. There +are few conditions more distressing than the constant and impending +suffering attending a tumultuous and fluttering heart. It is stated that +one in every four of tobacco-users is subject, in some degree, to this +disturbance. Test examinations of a large number of lads who had used +cigarettes showed that only a very small percentage escaped cardiac +trouble. Of older tobacco-users there are very few but have some warning +of the hazard they invoke. Generally they suffer more or less from the +tobacco heart, and if the nervous system or the heart be naturally feeble, +they suffer all the more speedily and intensely. + + + +Additional Experiments. + + Experiment 93. Touch a few drops of blood fresh from the finger, + with a strip of dry, smooth, neutral litmus paper, highly glazed to + prevent the red corpuscles from penetrating into the test paper. Allow + the blood to remain a short time; then wash it off with a stream of + distilled water, when a blue spot upon a red or violet ground will be + seen, indicating its _alkaline_ reaction, due chiefly to the sodium + phosphate and sodium carbonate. + + Experiment 94. Place on a glass slide a thin layer of defibrinated + blood; try to read printed matter through it. This cannot be done. + + Experiment 95. _To make blood transparent or laky_. Place in each + of three test tubes two or three teaspoonfuls of defibrinated blood, + obtained from Experiment 89, labeled _A, B_, and _C. A_ is for + comparison. To _B_ add five volumes of water, and warm slightly, noting + the change of color by reflected and transmitted light. By reflected + light it is much darker,--it looks almost black; but by transmitted + light it is transparent. Test this by looking at printed matter as in + Experiment 94. + + Experiment 96. To fifteen or twenty drops of defibrinated blood in + a test tube (labeled _D_) add five volumes of a 10-per-cent solution of + common salt. It changes to a very bright, florid, brick-red color. + Compare its color with _A, B_, and _C_. It is opaque. + + Experiment 97. Wash away the coloring matter from the twigs (see + Experiment 89) with a stream of water until the fibrin becomes quite + white. It is white, fibrous, and elastic. Stretch some of the fibers to + show their extensibility; on freeing them, they regain their elasticity. + + Experiment 98. Take some of the serum saved from Experiment 88 and + note that it does not coagulate spontaneously. Boil a little in a test + tube over a spirit lamp, and the albumen will coagulate. + + Experiment 99. _To illustrate in a general way that blood is + really a mass of red bodies which give the red color to the fluid in + which they float._ Fill a clean white glass bottle two-thirds full of + little red beads, and then fill the bottle full of water. At a short + distance the bottle appears to be rilled with a uniformly red liquid. + + Experiment 100. _To show how blood holds a mineral substance in + solution_. Put an egg-shell crushed fine, into a glass of water made + acid by a teaspoonful of muriatic acid. After an hour or so the + egg-shell will disappear, having been dissolved in the acid water. In + like manner the blood holds various minerals in solution. + + Experiment 101. _To hear the sounds of the heart_. Locate the heart + exactly. Note its beat. Borrow a stethoscope from some physician. Listen + to the heart-beat of some friend. Note the sounds of your own heart in + the same way. + + Experiment 102. _To show how the pulse may be studied_. "The + movements of the artery in the human body as the pulse-wave passes + through it may be shown to consist in a sudden dilatation, followed by a + slow contraction, interrupted by one or more secondary dilatations. This + demonstration may be made by pressing a small piece of looking-glass + about one centimeter square (⅔ of an inch) upon the wrist over the + radial artery, in such a way that with each pulse beat the mirror may be + slightly tilted. If the wrist be now held in such a position that + sunlight will fall upon the mirror, a spot of light will be reflected on + the opposite side of the room, and its motion upon the wall will show + that the expansion of the artery is a sudden movement, while the + subsequent contraction is slow and interrupted."--Bowditch's _Hints for + Teachers of Physiology_. + + [Illustration: Fig. 83.--How the Pulse may be studied by Pressing a + Mirror over the Radial Artery.] + + Experiment 103. _To illustrate the effect of muscular exercise in + quickening the pulse_. Run up and down stairs several times. Count the + pulse both before and after. Note the effect upon the rate. + + Experiment 104. _To show the action of the elastic walls of the + arteries._ Take a long glass or metal tube of small caliber. Fasten one + end to the faucet of a water-pipe (one in a set bowl preferred) by a + very short piece of rubber tube. Turn the water on and off alternately + and rapidly, to imitate the intermittent discharge of the ventricles. + The water will flow from the other end of the rubber pipe in jets, each + jet ceasing the moment the water is shut off. + + The experiment will be more successful if the rubber bulb attached to an + ordinary medicine-dropper be removed, and the tapering glass tube be + slipped on to the outer end of the rubber tube attached to the faucet. + + Experiment 105. Substitute a piece of rubber tube for the glass + tube, and repeat the preceding experiment. Now it will be found that a + continuous stream flows from the tube. The pressure of water stretches + the elastic tube, and when the stream is turned off, the rubber recoils + on the water, and the intermittent flow is changed into a continuous + stream. + + Experiment 106. _To illustrate some of the phenomena of + circulation._ Take a common rubber bulb syringe, of the Davidson, + Household, or any other standard make. Attach a piece of rubber tube + about six or eight feet long to the delivery end of the syringe. + + To represent the resistance made by the capillaries to the flow of + blood, slip the large end of a common glass medicine-dropper into the + outer end of the rubber tube. This dropper has one end tapered to a fine + point. + + Place the syringe flat, without kinks or bends, on a desk or table. + Press the bulb slowly and regularly. The water is thus pumped into the + tube in an intermittent manner, and yet it is forced out of the tapering + end of the glass tube in a steady flow. + + Experiment 107. Take off the tapering glass tube, or, in the place + of one long piece of rubber tube, substitute several pieces of glass + tubing connected together by short pieces of rubber tubes. The obstacle + to the flow has thus been greatly lessened, and the water flows out in + intermittent jets to correspond to the compression of the bulb. + + + + +Chapter VIII. + +Respiration. + + + +202. Nature and Object of Respiration. The blood, as we have learned, +not only provides material for the growth and activity of all the tissues +of the body, but also serves as a means of removing from them the products +of their activity. These are waste products, which if allowed to remain, +would impair the health of the tissues. Thus the blood becomes +impoverished both by the addition of waste material, and from the loss of +its nutritive matter. + +We have shown, in the preceding chapter, how the blood carries to the +tissues the nourishment it has absorbed from the food. We have now to +consider a new source of nourishment to the blood, _viz._, that which it +receives from the oxygen of the air. We are also to learn one of the +methods by which the blood gets rid of poisonous waste matters. In brief, +we are to study the set of processes known as respiration, by which +oxygen is supplied to the various tissues, and by which the principal +waste matters, or chief products of oxidation, are removed. + +Now, the tissues are continually feeding on the life-giving oxygen, and at +the same time are continually producing carbon dioxid and other waste +products. In fact, the life of the tissues is dependent upon a continual +succession of oxidations and deoxidations. When the blood leaves the +tissues, it is poorer in oxygen, is burdened with carbon dioxid, and has +had its color changed from bright scarlet to purple red. This is the +change from the arterial to venous conditions which has been described in +the preceding chapter. + +Now, as we have seen, the change from venous to arterial blood occurs in +the capillaries of the lungs, the only means of communication between the +pulmonary arteries and the pulmonary veins. The blood in the pulmonary +capillaries is separated from the air only by a delicate tissue formed of +its own wall and the pulmonary membrane. Hence a gaseous interchange, +the essential step in respiration, very readily takes place between the +blood and the air, by which the latter gains moisture and carbon dioxid, +and loses its oxygen. These changes in the lungs also restore to the dark +blood its rosy tint. + +The only condition absolutely necessary to the purification of the blood +is an organ having a delicate membrane, on one side of which is a thin +sheet of blood, while the other side is in such contact with the air that +an interchange of gases can readily take place. The demand for oxygen is, +however, so incessant, and the accumulation of carbon dioxid is so rapid +in every tissue of the human body, that an All-Wise Creator has provided a +most perfect but complicated set of machinery to effect this wonderful +purification of the blood. + +We are now ready to begin the study of the arrangement and working of the +respiratory apparatus. With its consideration, we complete our view of the +sources of supply to the blood, and begin our study of its purification. + +[Illustration: Fig. 84.--The Epiglottis.] + +203. The Trachea, or Windpipe. If we look into the mouth of a friend, +or into our own with a mirror, we see at the back part an arch which is +the boundary line of the mouth proper. There is just behind this a similar +limit for the back part of the nostrils. The funnel-shaped cavity beyond, +into which both the mouth and the posterior nasal passages open, is +called the pharynx. In its lower part are two openings; the +trachea, or windpipe, in front, and the œsophagus behind. + +The trachea is surmounted by a box-like structure of cartilage, about +four and one-half inches long, called the larynx. The upper end of +the larynx opens into the pharynx or throat, and is provided with a lid,-- +the epiglottis,--which closes under certain circumstances (secs. 137 +and 349). The larynx contains the organ of voice, and is more fully +described in Chapter XII. + +The continuation of the larynx is the trachea, a tube about three-fourths +of an inch in diameter, and about four inches long. It extends downwards +along the middle line of the neck, where it may readily be felt in front, +below the Adam's apple. + +[Illustration: Fig. 85.--Larynx, Trachea, and the Bronchi. (Front view.) + + A, epiglottis; + B, thyroid cartilage; + C, cricoid-thyroid membrane, connecting with the cricoid cartilage below, + all forming the larynx; + D, one of the rings of the trachea. +] + +The walls of the windpipe are strengthened by a series of cartilaginous +rings, each somewhat the shape of a horseshoe or like the letter C, being +incomplete behind, where they come in contact with the œsophagus. +Thus the trachea, while always open for the passage of air, admits of the +distention of the food-passage. + +204. The Bronchial Tubes. The lower end of the windpipe is just +behind the upper part of the sternum, and there it divides into two +branches, called bronchi. Each branch enters the lung of its own +side, and breaks up into a great number of smaller branches, called +bronchial tubes. These divide into smaller tubes, which continue +subdividing till the whole lung is penetrated by the branches, the +extremities of which are extremely minute. To all these branches the +general name of bronchial tubes is given. The smallest are only about +one-fiftieth of an inch in diameter. + +[Illustration: Fig. 86.--Relative Position of the Lungs, Heart, and its +Great Vessels. + + A, left ventricle; + B, right ventricle; + C, left auricle; + D, right auricle; + E, superior vena cava; + F, pulmonary artery; + G, aorta; + H, arch of the aorta; + K, innominate artery; + L, right common carotid artery; + M, right subclavian artery; + N, thyroid cartilage forming upper portion of the larynx; + O, trachea. +] + +Now the walls of the windpipe, and of the larger bronchial tubes would +readily collapse, and close the passage for air, but for a wise +precaution. The horseshoe-shaped rings of cartilage in the trachea and the +plates of cartilage in the bronchial tubes keep these passages open. +Again, these air passages have elastic fibers running the length of the +tubes, which allow them to stretch and bend readily with the movements of +the neck. + +205. The Cilia of the Air Passages. The inner surfaces of the +windpipe and bronchial tubes are lined with mucous membrane, continuous +with that of the throat, the mouth, and the nostrils, the secretion from +which serves to keep the parts moist. + +Delicate, hair-like filaments, not unlike the pile on velvet, called +cilia, spring from the epithelial lining of the air tubes. Their +constant wavy movement is always upwards and outwards, towards the mouth. +Thus any excessive secretion, as of bronchitis or catarrh, is carried +upwards, and finally expelled by coughing. In this way, the lungs are kept +quite free from particles of foreign matter derived from the air. +Otherwise we should suffer, and often be in danger from the accumulation +of mucus and dust in the air passages. Thus these tiny cilia act as +dusters which Nature uses to keep the air tubes free and clean (Fig. 5). + +[Illustration: Fig. 87.--Bronchial tube, with its Divisions and +Subdivisions. (Showing groups of air cells at the termination of minute +bronchial tubes.)] + +206. The Lungs. The lungs, the organs of respiration, are two +pinkish gray structures of a light, spongy appearance, that fill the chest +cavity, except the space taken up by the heart and large vessels. Between +the lungs are situated the large bronchi, the œsophagus, the heart +in its pericardium, and the great blood-vessels. The base of the lungs +rests on the dome-like diaphragm, which separates the chest from the +abdomen. This partly muscular and partly tendinous partition is a most +important factor in breathing. + +Each lung is covered, except at one point, with an elastic serous membrane +in a double layer, called the pleura. One layer closely envelops the +lung, at the apex of which it is reflected to the wall of the chest cavity +of its own side, which it lines. The two layers thus form between them a +Closed Sac a serous cavity (see Fig. 69, also note, p. 176). + +[Illustration: Fig. 88.--The Lungs with the Trachea, Bronchi, and Larger +Bronchial Tubes exposed. (Posterior view.) + + A, division of left bronchus to upper lobe; + B, left branch of the Pulmonary artery; + C, left bronchus; + D, left superior pulmonary vein; + E, left inferior pulmonary vein; + F, left auricle; + K, inferior vena cava; + L, division of right bronchus to lower lobe; + M, right inferior pulmonary vein; + N, right superior pulmonary vein; + O, right branch of the pulmonary artery; + P, division of right bronchus to upper lobe; + R, left ventricle; + S, right ventricle. +] + +In health the two pleural surfaces of the lungs are always in contact, and +they secrete just enough serous fluid to allow the surfaces to glide +smoothly upon each other. Inflammation of this membrane is called +_pleurisy_. In this disease the breathing becomes very painful, as the +secretion of glairy serum is suspended, and the dry and inflamed surfaces +rub harshly upon each other. + +The root of the lung, as it is called, is formed by the bronchi, two +pulmonary arteries, and two pulmonary veins. The nerves and lymphatic +vessels of the lung also enter at the root. If we only remember that all +the bronchial tubes, great and small, are hollow, we may compare the whole +system to a short bush or tree growing upside down in the chest, of which +the trachea is the trunk, and the bronchial tubes the branches of various +sizes. + +207. Minute Structure of the Lungs. If one of the smallest bronchial +tubes be traced in its tree-like ramifications, it will be found to end in +an irregular funnel-shaped passage wider than itself. Around this passage +are grouped a number of honeycomb-like sacs, the air cells[35] or +alveoli of the lungs. These communicate freely with the passage, and +through it with the bronchial branches, but have no other openings. The +whole arrangement of passages and air cells springing from the end of a +bronchial tube, is called an ultimate lobule. Now each lobule is a +very small miniature of a whole lung, for by the grouping together of +these lobules another set of larger lobules is formed. + +[Illustration: Fig. 89. + + A, diagrammatic representation of the ending of a bronchial tube in air + sacs or alveoli; + B, termination of two bronchial tubes in enlargement beset with air sacs + (_Huxley_); + C, diagrammatic view of an air sac. + + a lies within sac and points to epithelium lining wall; + b, partition between two adjacent sacs, in which run capillaries; + c, elastic connective tissue (_Huxley_). +] + +In like manner countless numbers of these lobules, bound together by +connective tissue, are grouped after the same fashion to form by their +aggregation the lobes of the lung. The right lung has three such +lobes; and the left, two. Each lobule has a branch of the pulmonary artery +entering it, and a similar rootlet of the pulmonary vein leaving it. It +also receives lymphatic vessels, and minute twigs of the pulmonary plexus +of nerves. + +[Illustration: Fig. 90.--Diagram to illustrate the Amounts of Air +contained by the Lungs in Various Phases of Ordinary and of Forced +Respiration.] + +The walls of the air cells are of extreme thinness, consisting of delicate +elastic and connective tissue, and lined inside by a single layer of thin +epithelial cells. In the connective tissue run capillary vessels belonging +to the pulmonary artery and veins. Now these delicate vessels running in +the connective tissue are surrounded on all sides by air cells. It is +evident, then, that the blood flowing through these capillaries is +separated from the air within the cells only by the thin walls of the +vessels, and the delicate tissues of the air cells. + +This arrangement is perfectly adapted for an interchange between the +blood in the capillaries and the air in the air cells. This will be more +fully explained in sec. 214. + +208. Capacity of the Lungs. In breathing we alternately take into and +expel from the lungs a certain quantity of air. With each quiet +inspiration about 30 cubic inches of air enter the lungs, and 30 cubic +inches pass out with each expiration. The air thus passing into and out of +the lungs is called tidal air. After an ordinary inspiration, the +lungs contain about 230 cubic inches of air. By taking a deep inspiration, +about 100 cubic inches more can be taken in. This extra amount is called +complemental air. + +After an ordinary expiration, about 200 cubic inches are left in the +lungs, but by forced expiration about one-half of this may be driven out. +This is known as supplemental air. The lungs can never be entirely +emptied of air, about 75 to 100 cubic inches always remaining. This is +known as the residual air. + +The air that the lungs of an adult man are capable of containing is thus +composed: + + Complemental air 100 cubic inches. + Tidal " 30 " " + Supplemental " 100 " " + Residual " 100 " " + ---- + Total capacity of lungs 330 " " + +If, then, a person proceeds, after taking the deepest possible breath, to +breath out as much as he can, he expels: + + Complemental air 100 cubic inches. + Tidal " 30 " " + Supplemental " 100 " " + ---- + 230 + +This total of 230 cubic inches forms what is called the vital +capacity of the chest (Fig. 90). + +209. The Movements of Breathing. The act of breathing consists of a +series of rhythmical movements, succeeding one another in regular order. +In the first movement, inspiration, the chest rises, and there is an +inrush of fresh air; this is at once followed by expiration, the +falling of the chest walls, and the output of air. A pause now occurs, and +the same breathing movements are repeated. + +The entrance and the exit of air into the respiratory passages are +accompanied with peculiar sounds which are readily heard on placing the +ear at the chest wall. These sounds are greatly modified in various +pulmonary diseases, and hence are of great value to the physician in +making a correct diagnosis. + +In a healthy adult, the number of respirations should be from 16 to 18 per +minute, but they vary with age, that of a newly born child being 44 for +the same time. Exercise increases the number, while rest diminishes it. In +standing, the rate is more than when lying at rest. Mental emotion and +excitement quicken the rate. The number is smallest during sleep. Disease +has a notable effect upon the frequency of respirations. In diseases +involving the lungs, bronchial tubes, and the pleura, the rate may be +alarmingly increased, and the pulse is quickened in proportion. + +210. The Mechanism of Breathing. The chest is a chamber with bony +walls, the ribs connecting in front with the breastbone, and behind with +the spine. The spaces between the ribs are occupied by the intercostal +muscles, while large muscles clothe the entire chest. The diaphragm serves +as a movable floor to the chest, which is an air-tight chamber with +movable walls and floor. In this chamber are suspended the lungs, the air +cells of which communicate with the outside through the bronchial +passages, but have no connection with the chest cavity. The thin space +between the lungs and the rib walls, called the pleural cavity, is in +health a vacuum. + +Now, when the diaphragm contracts, it descends and thus increases the +depth of the chest cavity. A quantity of air is now drawn into the lungs +and causes them to expand, thus filling up the increased space. As soon as +the diaphragm relaxes, returning to its arched position and reducing the +size of the chest cavity, the air is driven from the lungs, which then +diminish in size. After a short pause, the diaphragm again contracts, and +the same round of operation is constantly repeated. + +The walls of the chest being movable, by the contractions of the +intercostals and other muscles, the ribs are raised and the breastbone +pushed forward. The chest cavity is thus enlarged from side to side and +from behind forwards. Thus, by the simultaneous descent of the diaphragm +and the elevation of the ribs, the cavity of the chest is increased in +three directions,--downwards, side-ways, and from behind forwards. + +It is thus evident that inspiration is due to a series of muscular +contractions. As soon as the contractions cease, the elastic lung +tissue resumes its original position, just as an extended rubber band +recovers itself. As a result, the original size of the chest cavity is +restored, and the inhaled air is driven from the lungs. Expiration may +then be regarded as the result of an elastic recoil, and not of active +muscular contractions. + +[Illustration: Fig. 91.--Diagrammatic Section of the Trunk. (Showing the +expansion of the chest and the movement of the ribs by action of the +lungs.) [The dotted lines indicate the position during inspiration.]] + +211. Varieties of Breathing. This is the mechanism of quiet, normal +respiration. When the respiration is difficult, additional forces are +brought into play. Thus when the windpipe and bronchial tubes are +obstructed, as in croup, asthma, or consumption, many additional muscles +are made use of to help the lungs to expand. The position which asthmatics +often assume, with arms raised to grasp something for support, is from the +need of the sufferer to get a fixed point from which the muscles of the +arm and chest may act forcibly in raising the ribs, and thus securing more +comfortable breathing. + +The visible movements of breathing vary according to circumstances. In +infants the action of the diaphragm is marked, and the movements of the +abdomen are especially obvious. This is called abdominal breathing. In +women the action of the ribs as they rise and fall, is emphasized more +than in men, and this we call costal breathing. In young persons and in +men, the respiration not usually being impeded by tight clothing, the +breathing is normal, being deep and abdominal. + +Disease has a marked effect upon the mode of breathing. Thus, when +children suffer from some serious chest disease, the increased movements +of the abdominal walls seem distressing. So in fracture of the ribs, the +surgeon envelops the overlying part of the chest with long strips of firm +adhesive plaster to restrain the motions of chest respiration, that they +may not disturb the jagged ends of the broken bones. Again, in painful +diseases of the abdomen, the sufferer instinctively suspends the abdominal +action and relies upon the chest breathing. These deviations from the +natural movements of respiration are useful to the physician in +ascertaining the seat of disease. + +212. The Nervous Control of Respiration. It is a matter of common +experience that one's breath may be held for a short time, but the need of +fresh air speedily gets the mastery, and a long, deep breath is drawn. +Hence the efforts of criminals to commit suicide by persistent restraint +of their breathing, are always a failure. At the very worst, +unconsciousness ensues, and then respiration is automatically resumed. +Thus a wise Providence defeats the purpose of crime. The movements of +breathing go on without our attention. In sleep the regularity of +respiration is even greater than when awake. There is a particular part of +the nervous system that presides over the breathing function. It is +situated in that part of the brain called the medulla oblongata, and is +fancifully called the "vital knot" (sec. 270). It is injury to this +respiratory center which proves fatal in cases of broken neck. + +From this nerve center there is sent out to the nerves that supply the +diaphragm and other muscles of breathing, a force which stimulates them to +regular contraction. This breathing center is affected by the condition of +the blood. It is stimulated by an excess of carbon dioxid in the blood, +and is quieted by the presence of oxygen. + + Experiment 108. _To locate the lungs_. Mark out the boundaries of + the lungs by "sounding" them; that is, by _percussion_, as it is called. + This means to put the forefinger of the left hand across the chest or + back, and to give it a quick, sharp rap with two or three fingers. Note + where it sounds hollow, resonant. This experiment can be done by the + student with only imperfect success, until practice brings some skill. + + Experiment 109. Borrow a stethoscope, and listen to the respiration + over the chest on the right side. This is known as _auscultation_. Note + the difference of the sounds in inspiration and in expiration. Do not + confuse the heart sounds with those of respiration. The respiratory + murmurs may be heard fairly well by applying the ear flat to the chest, + with only one garment interposed. + + Experiment 110. Get a sheep's lungs, with the windpipe attached. + Ask for the heart and lungs all in one mass. Take pains to examine the + specimen first, and accept only a good one. Parts are apt to be hastily + snipped or mangled. Examine the windpipe. Note the horseshoe-shaped + rings of cartilage in front, which serve to keep it open. + + Experiment 111. Examine one bronchus, carefully dissecting away the + lung tissue with curved scissors. Follow along until small branches of + the bronchial tubes are reached. Take time for the dissection, and save + the specimen in dilute alcohol. Put pieces of the lung tissue in a basin + of water, and note that they float. + +The labored breathing of suffocation and of lung diseases is due to the +excessive stimulation of this center, caused by the excess of carbon +dioxid in the blood. Various mental influences from the brain itself, as +the emotions of alarm or joy or distress, modify the action of the +respiratory center. + +Again, nerves of sensation on the surface of the body convey influences to +this nerve center and lead to its stimulation, resulting in a vigorous +breathing movement. Thus a dash of cold water on the face or neck of a +fainting person instantly produces a deep, long-drawn breath. Certain +drugs, as opium, act to reduce the activity of this nerve center. Hence, +in opium poisoning, special attention should be paid to keeping up the +respiration. The condition of the lungs themselves is made known to the +breathing center, by messages sent along the branches of the great +pneumogastric nerve (page 276), leading from the lungs to the medulla +oblongata. + +213. Effects of Respiration upon the Blood. The blood contains three +gases, partly dissolved in it and partly in chemical union with certain of +its constituents. These are oxygen, carbon dioxid, and nitrogen. +The latter need not be taken into account. The oxygen is the +nourishing material which the tissues require to carry on their work. The +carbon dioxid is a waste substance which the tissues produce by their +activity, and which the blood carries away from them. + +As before shown, the blood as it flows through the tissues loses most of +its oxygen, and carbon dioxid takes its place. Now if the blood is to +maintain its efficiency in this respect, it must always be receiving new +supplies of oxygen, and also have some mode of throwing off its excess of +carbon dioxid. This, then, is the double function of the process of +respiration. Again, the blood sent out from the left side of the heart is +of a bright scarlet color. After its work is done, and the blood returns +to the right side of the heart, it is of a dark purple color. This change +in color takes place in the capillaries, and is due to the fact that there +the blood gives up most of its oxygen to the tissues and receives from +them a great deal of carbon dioxid. + +In brief, while passing through the capillaries of the lungs the blood has +been changed from the venous to the arterial blood. That is to say, the +blood in its progress through the lungs has rid itself of its excess of +carbon dioxid and obtained a fresh supply of oxygen.[36] + +214. Effects of Respiration upon the Air in the Lungs. It is well +known that if two different liquids be placed in a vessel in contact with +each other and left undisturbed, they do not remain separate, but +gradually mix, and in time will be perfectly combined. This is called +diffusion of liquids. The same thing occurs with gases, though the process +is not visible. This is known as the diffusion of gases. It is also true +that two liquids will mingle when separated from each other by a membrane +(sec. 129). In a similar manner two gases, especially if of different +densities, may mingle even when separated from each other by a membrane. + +In a general way this explains the respiratory changes that occur in the +blood in the lungs. Blood containing oxygen and carbon dioxid is flowing +in countless tiny streams through the walls of the air cells of the lungs. +The air cells themselves contain a mixture of the same two gases. A thin, +moist membrane, well adapted to allow gaseous diffusion, separates the +blood from the air. This membrane is the delicate wall of the capillaries +and the epithelium of the air cells. By experiment it has been found that +the pressure of oxygen in the blood is less than that in the air cells, +and that the pressure of carbon dioxid gas in the blood is greater than +that in the air cells. As a result, a diffusion of gases ensues. The +blood gains oxygen and loses carbon dioxid, while the air cells lose +oxygen and gain the latter gas. + +[Illustration: Fig. 92.--Capillary Network of the Air Cells and Origin of +the Pulmonary Veins. + + A, small branch of pulmonary artery; + B, twigs of the pulmonary artery anastomosing to form peripheral network + of the primitive air cells; + C, capillary network around the walls of the air sacs; + D, branches of network converging for form the veinlets of the pulmonary + veins. +] + +The blood thus becomes purified and reinvigorated, and at the same time is +changed in color from purple to scarlet, from venous to arterial. It is +now evident that if this interchange is to continue, the air in the cells +must be constantly renewed, its oxygen restored, and its excess of carbon +dioxid removed. Otherwise the process just described would be reversed, +making the blood still more unfit to nourish the tissues, and more +poisonous to them than before. + +215. Change in the Air in Breathing. The air which we exhale during +respiration differs in several important particulars from the air we +inhale. Both contain chiefly the three gases, though in different +quantities, as the following table shows. + + Oxygen. Nitrogen. Carbon Dioxid. + Inspired air contains 20.81 79.15 .04 + Expired air contains 16.03 79.58 4.38 + +That is, expired air contains about five per cent less oxygen and five per +cent more carbon dioxid than inspired air. + +The temperature of expired air is variable, but generally is higher than +that of inspired air, it having been in contact with the warm air +passages. It is also loaded with aqueous vapor, imparted to it like +the heat, not in the depth of the lungs, but in the upper air passages. + +Expired air contains, besides carbon dioxid, various impurities, many of +an unknown nature, and all in small amounts. When the expired air is +condensed in a cold receiver, the aqueous product is found to contain +organic matter, which, from the presence of _micro-organisms_, +introduced in the inspired air, is apt to putrefy rapidly. Some of these +organic substances are probably poisonous, either so in themselves, as +produced in some manner in the breathing apparatus, or poisonous as being +the products of decomposition. For it is known that various animal +substances give rise, by decomposition, to distinct poisonous products +known as _ptomaines_. It is possible that some of the constituents of the +expired air are of an allied nature. See under "Bacteria" (Chapter XIV). + +At all events, these substances have an injurious action, for an +atmosphere containing simply one per cent of pure carbon dioxid has very +little hurtful effect on the animal economy, but an atmosphere in which +the carbon dioxid has been raised one per cent by breathing is highly +injurious. + +The quantity of oxygen removed from the air by the breathing of an adult +person at rest amounts daily to about 18 cubic feet. About the same amount +of carbon dioxid is expelled, and this could be represented by a piece of +pure charcoal weighing 9 ounces. The quantity of carbon dioxid, however, +varies with the age, and is increased also by external cold and by +exercise, and is affected by the kind of food. The amount of water, +exhaled as vapor, varies from 6 to 20 ounces daily. The average daily +quantity is about one-half a pint. + +216. Modified Respiratory Movements. The respiratory column of air is +often used in a mechanical way to expel bodies from the upper air +passages. There are also, in order to secure special ends, a number of +modified movements not distinctly respiratory. The following peculiar +respiratory acts call for a few words of explanation. + +A sigh is a rapid and generally audible expiration, due to the +elastic recoil of the lungs and chest walls. It is often caused by +depressing emotions. Yawning is a deep inspiration with a stretching +of the muscles of the face and mouth, and is usually excited by fatigue or +drowsiness, but often occurs from a sort of contagion. + +Hiccough is a sudden jerking inspiration due to the spasmodic +contraction of the diaphragm and of the glottis, causing the air to rush +suddenly through the larynx, and produce this peculiar sound. Snoring +is caused by vibration of the soft palate during sleep, and is habitual +with some, although it occurs with many when the system is unusually +exhausted and relaxed. + +Laughing consists of a series of short, rapid, spasmodic expirations +which cause the peculiar sounds, with characteristic movements of the +facial muscles. Crying, caused by emotional states, consists of +sudden jerky expirations with long inspirations, with facial movements +indicative of distress. In sobbing, which often follows +long-continued crying, there is a rapid series of convulsive inspirations, +with sudden involuntary contractions of the diaphragm. Laughter, and +sometimes sobbing, like yawning, may be the result of involuntary +imitation. + + Experiment 112. _Simple Apparatus to Illustrate the Movements of + the Lungs in the Chest_.--T is a bottle from which the bottom has been + removed; D, a flexible and elastic membrane tied on the bottle, and + capable of being pulled out by the string S, so as to increase the + capacity of the bottle. L is a thin elastic bag representing the lungs. + It communicates with the external air by a glass tube fitted air-tight + through a cork in the neck of the bottle. When D is drawn down, the + pressure of the external air causes L to expand. When the string is let + go, L contracts again, by virtue of its elasticity. + + [Illustration: Fig. 93.] + +Coughing is produced by irritation in the upper part of the windpipe +and larynx. A deep breath is drawn, the opening of the windpipe is closed, +and immediately is burst open with a violent effort which sends a blast of +air through the upper air passages. The object is to dislodge and expel +any mucus or foreign matter that is irritating the air passages. + +Sneezing is like coughing; the tongue is raised against the soft +palate, so the air is forced through the nasal passages. It is caused by +an irritation of the nostrils or eyes. In the beginning of a cold in the +head, for instance, the cold air irritates the inflamed mucous membrane of +the nose, and causes repeated attacks of sneezing. + +217. How the Atmosphere is Made Impure. The air around us is +constantly being made impure in a great variety of ways. The combustion of +fuel, the respiration of men and animals, the exhalations from their +bodies, the noxious gases and effluvia of the various industries, together +with the changes of fermentation and decomposition to which all organized +matter is liable,--all tend to pollute the atmosphere. + +The necessity of external ventilation has been foreseen for us. The +forces of nature,--the winds, sunlight, rain, and growing vegetation,--all +of great power and universal distribution and application, restore the +balance, and purify the air. As to the principal gases, the air of the +city does not differ materially from that of rural sections. There is, +however, a vastly greater quantity of dust and smoke in the air of towns. +The breathing of this dust, to a greater or less extent laden with +bacteria, fungi, and the germs of disease, is an ever-present and most +potent menace to public and personal health. It is one of the main causes +of the excess of mortality in towns and cities over that of country +districts. + +This is best shown in the overcrowded streets and houses of great cities, +which are deprived of the purifying influence of sun and air. The fatal +effect of living in vitiated air is especially marked in the mortality +among infants and children living in the squalid and overcrowded sections +of our great cities. The salutary effect of sunshine is shown by the fact +that mortality is usually greater on the shady side of the street. + +218. How the Air is Made Impure by Breathing. It is not the carbon +dioxid alone that causes injurious results to health, it is more +especially the organic matter thrown off in the expired air. The +carbon dioxid which accompanies the organic matter is only the index. In +testing the purity of air it is not difficult to ascertain the amount of +carbon dioxid present, but it is no easy problem to measure the amount of +organic matter. Hence it is the former that is looked for in factories, +churches, schoolrooms, and when it is found to exceed .07 per cent it is +known that there is a hurtful amount of organic matter present. + +The air as expelled from the lungs contains, not only a certain amount of +organic matter in the form of vapor, but minute solid particles of +_débris_ and bacterial micro-organisms (Chap. XIV). The air thus +already vitiated, after it leaves the mouth, putrefies very rapidly. It is +at once absorbed by clothing, curtains, carpets, porous walls, and by many +other objects. It is difficult to dislodge these enemies of health even by +free ventilation. The close and disagreeable odor of a filthy or +overcrowded room is due to these organic exhalations from the lungs, the +skin, and the unclean clothing of the occupants. + +The necessity of having a proper supply of fresh air in enclosed +places, and the need of removal of impure air are thus evident. If a +man were shut up in a tightly sealed room containing 425 cubic feet of +air, he would be found dead or nearly so at the end of twenty-four hours. +Long before this time he would have suffered from nausea, headache, +dizziness, and other proofs of blood-poisoning. These symptoms are often +felt by those who are confined for an hour or more in a room where the +atmosphere has been polluted by a crowd of people. The unpleasant effects +rapidly disappear on breathing fresh air. + +219. The Effect on the Health of Breathing Foul Air. People are often +compelled to remain indoors for many hours, day after day, in shops, +factories, or offices, breathing air perhaps only slightly vitiated, but +still recognized as "stuffy." Such persons often suffer from ill health. +The exact form of the disturbance of health depends much upon the +hereditary proclivity and physical make-up of the individual. Loss of +appetite, dull headache, fretfulness, persistent weariness, despondency, +followed by a general weakness and an impoverished state of blood, often +result. + +Persons in this lowered state of health are much more prone to surfer from +colds, catarrhs, bronchitis, and pneumonia than if they were living in the +open air, or breathing only pure air. Thus, in the Crimean War, the +soldiers who lived in tents in the coldest weather were far more free from +colds and lung troubles than those who lived in tight and ill-ventilated +huts. In the early fall when typhoid fever is prevalent, the grounds of +large hospitals are dotted with canvas tents, in which patients suffering +from this fever do much better than in the wards. + +This tendency to inflammatory diseases of the air passages is aggravated +by the overheated and overdried condition of the air in the room occupied. +This may result from burning gas, from overheated furnaces and stoves, +hot-water pipes, and other causes. Serious lung diseases, such as +consumption, are more common among those who live in damp, overcrowded, or +poorly ventilated homes. + +220. The Danger from Pulmonary Infection. The germ of pulmonary +consumption, known as the bacillus tuberculosis, is contained in the +breath and the sputa from the lungs of its victims. It is not difficult to +understand how these bacilli may be conveyed through the air from the +lungs of the sick to those of apparently healthy people. Such persons may, +however, be predisposed, either constitutionally or by defective hygienic +surroundings, to fall victims to this dreaded disease. Overcrowding, poor +ventilation, and dampness all tend to increase the risk of pulmonary +infection. + +It must not be supposed that the tubercle bacillus is necessarily +transmitted directly through the air from the lungs of the sick to be +implanted in the lungs of the healthy. The germs may remain for a time in +the dust turn and _débris_ of damp, filthy, and overcrowded houses. In +this congenial soil they retain their vitality for a long time, and +possibly may take on more virulent infective properties than they +possessed when expelled from the diseased lungs.[37] + +[Illustration: Fig. 94. Example of a Micro-Organism--Bacillus Tuberculosis +in Spotum. (Magnified about 500 diameters.)] + +221. Ventilation. The question of a practicable and economical system +of ventilation for our homes, schoolrooms, workshops, and public +places presents many difficult and perplexing problems. It is perhaps due +to the complex nature of the subject, that ventilation, as an ordinary +condition of daily health, has been so much neglected. The matter is +practically ignored in building ordinary houses. The continuous renewal of +air receives little if any consideration, compared with the provision made +to furnish our homes with heat, light, and water. When the windows are +closed we usually depend for ventilation upon mere chance,--on the +chimney, the fireplace, and the crevices of doors and windows. The proper +ventilation of a house and its surroundings should form as prominent a +consideration in the plans of builders and architects as do the grading of +the land, the size of the rooms, and the cost of heating. + +The object of ventilation is twofold: First, to provide for the removal +of the impure air; second, for a supply of pure air. This must +include a plan to provide fresh air in such a manner that there shall be +no draughts or exposure of the occupants of the rooms to undue +temperature. Hence, what at first might seem an easy thing to do, is, in +fact, one of the most difficult of sanitary problems. + +222. Conditions of Efficient Ventilation. To secure proper +ventilation certain conditions must be observed. The pure air introduced +should not be far below the temperature of the room, or if so, the +entering current should be introduced towards the ceiling, that it may mix +with the warm air. + +Draughts must be avoided. If the circuit from entrance to exit is short, +draughts are likely to be produced, and impure air has less chance of +mixing by diffusion with the pure air. The current of air introduced +should be constant, otherwise the balance may occasionally be in favor of +vitiated air. If a mode of ventilation prove successful, it should not be +interfered with by other means of entrance. Thus, an open door may prevent +the incoming air from passing through its proper channels. It is desirable +that the inlet be so arranged that it can be diminished in size or closed +altogether. For instance, when the outer air is very cold, or the wind +blows directly into the inlet, the amount of cold air entering it may +lower the temperature of the room to an undesirable degree. + +In brief, it is necessary to have a thorough mixing of pure and impure +air, so that the combination at different parts of the room may be fairly +uniform. To secure these results, the inlets and outlets should be +arranged upon principles of ventilation generally accepted by authorities +on public health. It seems hardly necessary to say that due attention must +be paid to the source from which the introduced air is drawn. If it be +taken from foul cellars, or from dirty streets, it may be as impure as +that which it is designed to replace. + + + +Animal Heat. + + +223. Animal or Vital Heat. If a thermometer, made for the purpose, be +placed for five minutes in the armpit, or under the tongue, it will +indicate a temperature of about 98½° F., whether the surrounding +atmosphere be warm or cold. This is the natural heat of a healthy person, +and in health it rarely varies more than a degree or two. But as the body +is constantly losing heat by radiation and conduction, it is evident that +if the standard temperature be maintained, a certain amount of heat must +be generated within the body to make up for the loss externally. The heat +thus produced is known as animal or vital heat. + +This generation of heat is common to all living organisms. When the mass +of the body is large, its heat is readily perceptible to the touch and by +its effect upon the thermometer. In mammals and birds the heat-production +is more active than in fishes and reptiles, and their temperatures differ +in degree even in different species of the same class, according to the +special organization of the animal and the general activity of its +functions. The temperature of the frog may be 85° F. in June and 41° F. in +January. The structure of its tissues is unaltered and their vitality +unimpaired by such violent fluctuations. But in man it is necessary not +only for health, but even for life, that the temperature should vary only +within narrow limits around the mean of 98½° F. + +We are ignorant of the precise significance of this constancy of +temperature in warm-blooded animals, which is as important and peculiar as +their average height, Man, undoubtedly, must possess a superior delicacy +of organization, hardly revealed by structure, which makes it necessary +that he should be shielded from the shocks and jars of varying +temperature, that less highly endowed organisms endure with impunity. + +224. Sources of Bodily Heat. The heat of the body is generated by the +chemical changes, generally spoken of as those of oxidation, which are +constantly going on in the tissues. Indeed, whenever protoplasmic +materials are being oxidized (the process referred to in sec. 15 as +katabolism) heat is being set free. These chemical changes are of +various kinds, but the great source of heat is the katabolic process, +known as oxidation. + +The vital part of the tissues, built up from the complex classes of food, +is oxidized by means of the oxygen carried by the arterial blood, and +broken down into simpler bodies which at last result in urea, carbon +dioxid, and water. Wherever there is life, this process of oxidation is +going on, but more energetically in some tissues and organs than in +others. In other words, the minutest tissue in the body is a source of +heat in proportion to the activity of its chemical changes. The more +active the changes, the greater is the heat produced, and the greater the +amount of urea, carbon dioxid, and water eliminated. The waste caused by +this oxidation must be made good by a due supply of food to be built up +into protoplasmic material. For the production of heat, therefore, food is +necessary. But the oxidation process is not as simple and direct as the +statement of it might seem to indicate. Though complicated in its various +stages, the ultimate result is as simple as in ordinary combustion outside +of the body, and the products are the same. + +The continual chemical changes, then, chiefly by oxidation of combustible +materials in the tissues, produce an amount of heat which is efficient to +maintain the temperature of the living body at about 98½° F. This process +of oxidation provides not only for the heat of the body, but also for +the energy required to carry on the muscular work of the animal +organism. + +225. Regulation of the Bodily Temperature. While bodily heat is being +continually produced, it is also as continually being lost by the lungs, +by the skin, and to some extent, by certain excretions. The blood, in its +swiftly flowing current, carries warmth from the tissues where heat is +being rapidly generated, to the tissues or organs in which it is being +lost by radiation, conduction, or evaporation. Were there no arrangement +by which heat could be distributed and regulated, the temperature of the +body would be very unequal in different parts, and would vary at different +times. + +The normal temperature is maintained with slight variations throughout +life. Indeed a change of more than a degree above or below the average, +indicates some failure in the organism, or some unusual influence. It is +evident, then, that the mechanisms which regulate the temperature of the +body must be exceedingly sensitive. + +The two chief means of regulating the temperature of the body are the +lungs and the skin. As a means of lowering the temperature, the +lungs and air passages are very inferior to the skin; although, by giving +heat to the air we breathe, they stand next to the skin in importance. As +a regulating power they are altogether subordinate to the skin. + + Experiment 113. _To show the natural temperature of the body_. + Borrow a physician's clinical thermometer, and take your own + temperature, and that of several friends, by placing the instrument + under the tongue, closing the mouth, and holding it there for five + minutes. It should be thoroughly cleansed after each use. + +226. The Skin as a Heat-regulator. The great regulator of the bodily +temperature is, undoubtedly, the skin, which performs this function +by means of a self-regulating apparatus with a more or less double action. +First, the skin regulates the loss of heat by means of the vaso-motor +mechanism. The more blood passes through the skin, the greater will be +the loss of heat by conduction, radiation, and evaporation. Hence, any +action of the vaso-motor mechanism which causes dilatation of the +cutaneous capillaries, leads to a larger flow of blood through the skin, +and will tend to cool the body. On the other hand, when by the same +mechanism the cutaneous vessels are constricted, there will be a smaller +flow of blood through the skin, which will serve to check the loss of heat +from the body (secs. 195 and 270). + +Again, the special nerves of perspiration act directly as regulators +of temperature. They increase the loss of heat when they promote the +secretion of the skin, and diminish the loss when they cease to promote +it. + +The practical working of this heat-regulating mechanism is well shown by +exercise. The bodily temperature rarely rises so much as a degree during +vigorous exercise. The respiration is increased, the cutaneous capillaries +become dilated from the quickened circulation, and a larger amount of +blood is circulating through the skin. Besides this, the skin perspires +freely. A large amount of heat is thus lost to the body, sufficient to +offset the addition caused by the muscular contractions. + +It is owing to the wonderful elasticity of the sweat-secreting mechanism, +and to the increase in respiratory activity, and the consequent increase +in the amount of watery vapor given off by the lungs, that men are able to +endure for days an atmosphere warmer than the blood, and even for a short +time at a temperature above that of boiling water. The temperature of a +Turkish bath may be as high as 150° to 175° F. But an atmospheric +temperature may be considerably below this, and yet if long continued +becomes dangerous to life. In August, 1896, for instance, hundreds of +persons died in this country, within a few days, from the effects of the +excessive heat. + +A much higher temperature may be borne in dry air than in humid air, or +that which is saturated with watery vapor. Thus, a shade temperature of +100° F. in the dry air of a high plain may be quite tolerable, while a +temperature of 80° F. in the moisture-laden atmosphere of less elevated +regions, is oppressive. The reason is that in dry air the sweat evaporates +freely, and cools the skin. In saturated air at the bodily temperature +there is little loss of heat by perspiration, or by evaporation from the +bodily surface. + +This topic is again discussed in the description of the skin as a +regulator of the bodily temperature (sec. 241). + +227. Voluntary Means of Regulating the Temperature. The voluntary +factor, as a means of regulating the heat loss in man, is one of great +importance. Clothing retards the loss of heat by keeping in contact with +it a layer of still air, which is an exceedingly bad conductor. When a man +feels too warm and throws off his coat, he removes one of the badly +conducting layers of air, and increases the heat loss by radiation and +conduction. The vapor next the skin is thus allowed a freer access to the +surface, and the loss of heat by evaporation of the sweat becomes greater. +This voluntary factor by which the equilibrium is maintained must be +regarded as of great importance. This power also exists in the lower +animals, but to a much smaller extent. Thus a dog, on a hot day, runs out +his tongue and stretches his limbs so as to increase the surface from +which heat is radiated and conducted. + +The production, like the loss, of heat is to a certain extent under the +control of the will. Work increases the production of heat, and rest, +especially sleep, lessens it. Thus the inhabitants of very hot countries +seek relief during the hottest part of the day by a siesta. The quantity +and quality of food also influence the production of heat. A larger +quantity of food is taken in winter than in summer. Among the inhabitants +of the northern and Arctic regions, the daily consumption of food is far +greater than in temperate and tropical climates. + +228. Effect of Alcohol upon the Lungs. It is a well recognized fact +that alcohol when taken into the stomach is carried from that organ to the +liver, where, by the baneful directness of its presence, it produces a +speedy and often disastrous effect. But the trail of its malign power does +not disappear there. From the liver it passes to the right side of the +heart, and thence to the lungs, where its influence is still for harm. + +In the lungs, alcohol tends to check and diminish the breathing capacity +of these organs. This effect follows from the partial paralyzing influence +of the stupefying agent upon the sympathetic nervous system, diminishing +its sensibility to the impulse of healthful respiration. This diminished +capacity for respiration is clearly shown by the use of the _spirometer_, +a simple instrument which accurately records the cubic measure of the +lungs, and proves beyond denial the decrease of the lung space. + + "Most familiar and most dangerous is the drinking man's inability to + resist lung diseases."--Dr. Adoph Frick, the eminent German physiologist + of Zurich. + + "Alcohol, instead of preventing consumption, as was once believed, + reduces the vitality so much as to render the system unusually + susceptible to that fatal disease."--R. S. Tracy, M.D., Sanitary + Inspector of the N. Y. City Health Dept. + + "In thirty cases in which alcoholic phthisis was present a dense, + fibroid, pigmented change was almost invariably present in some portion + of the lung far more frequently than in other cases of + phthisis."--_Annual of Medical Sciences_. + + "There is no form of consumption so fatal as that from alcohol. + Medicines affect the disease but little, the most judicious diet fails, + and change of air accomplishes but slight real good.... In plain terms, + there is no remedy whatever for alcoholic phthisis. It may be delayed in + its course, but it is never stopped; and not infrequently, instead of + being delayed, it runs on to a fatal termination more rapidly than is + common in any other type of the disorder."--Dr. B. W. Richardson in + _Diseases of Modern Life_. + +229. Other Results of Intoxicants upon the Lungs. But a more potent +injury to the lungs comes from another cause. The lungs are the arena +where is carried on the ceaseless interchange of elements that is +necessary to the processes of life. Here the dark venous blood, loaded +with effete material, lays down its carbon burden and, with the +brightening company of oxygen, begins again its circuit. But the enemy +intrudes, and the use of alcohol tends to prevent this benign interchange. + +The continued congestion of the lung tissue results in its becoming +thickened and hardened, thus obstructing the absorption of oxygen, and the +escape of carbon dioxid. Besides this, alcohol destroys the integrity of +the red globules, causing them to shrink and harden, and impairing their +power to receive oxygen. Thus the blood that leaves the lungs conveys an +excess of the poisonous carbon dioxid, and a deficiency of the needful +oxygen. This is plainly shown in the purplish countenance of the +inebriate, crowded with enlarged veins. This discoloration of the face is +in a measure reproduced upon the congested mucous membrane of the lungs. +It is also proved beyond question by the decreased amount of carbon dioxid +thrown off in the expired breath of any person who has used alcoholics. + +The enfeebled respiration explains (though it is only one of the reasons) +why inebriates cannot endure vigorous and prolonged exertion as can a +healthy person. The hurried circulation produced by intoxicants involves +in turn quickened respiration, which means more rapid exhaustion of the +life forces. The use of intoxicants involves a repeated dilatation of the +capillaries, which steadily diminishes their defensive power, rendering +the person more liable to yield to the invasion of pulmonary diseases.[38] + +230. Effect of Alcoholics upon Disease. A theory has prevailed, to a +limited extent, that the use of intoxicants may act as a preventive of +consumption. The records of medical science fail to show any proof +whatever to support this impression. No error could be more serious or +more misleading, for the truth is in precisely the opposite direction. +Instead of preventing, alcohol tends to develop consumption. Many +physicians of large experience record the existence of a distinctly +recognized alcoholic consumption, attacking those constitutions broken +down by dissipation. This form of consumption is steadily progressive, and +always fatal. + +The constitutional debility produced by the habit of using alcoholic +beverages tends to render one a prompt victim to the more severe diseases, +as pneumonia, and especially epidemical diseases, which sweep away vast +numbers of victims every year. + +231. Effect of Tobacco upon the Respiratory Passages. The effects of +tobacco upon the throat and lungs are frequently very marked and +persistent. The hot smoke must very naturally be an irritant, as the mouth +and nostrils were not made as a chimney for heated and narcotic vapors. +The smoke is an irritant, both by its temperature and from its destructive +ingredients, the carbon soot and the ammonia which it conveys. It +irritates and dries the mucous membrane of the mouth and throat, producing +an unnatural thirst which becomes an enticement to the use of intoxicating +liquors. The inflammation of the mouth and throat is apt to extend up the +Eustachian tube, thus impairing the sense of hearing. + +But even these are not all the bad effects of tobacco. The inhalation of +the poisonous smoke produces unhealthful effects upon the delicate mucous +membrane of the bronchial tubes and of the lungs. Upon the former the +effect is to produce an irritating cough, with short breath and chronic +bronchial catarrh. The pulmonary membrane is congested, taking cold +becomes easy, and recovery from it tedious. Frequently the respiration is +seriously disturbed, thus the blood is imperfectly aërated, and so in turn +the nutrition of the entire system is impaired. The cigarette is the +defiling medium through which these direful results frequently invade the +system, and the easily moulded condition of youth yields readily to the +destructive snare. + +"The first effect of a cigar upon any one demonstrates that tobacco can +poison by its smoke and through the lungs."--London _Lancet_. + +"The action of the heart and lungs is impaired by the influence of the +narcotic on the nervous system, but a morbid state of the larynx, trachea, +and lungs results from the direct action of the smoke."--Dr. Laycock, +Professor of Medicine in the University of Edinburgh. + + + +Additional Experiments. + + Experiment 114. _To illustrate the arrangement of the lungs and the + two pleuræ._ Place a large sponge which will represent the lungs in a + thin paper bag which just fits it; this will represent the pulmonary + layer of the pleura. Place the sponge and paper bag inside a second + paper bag, which will represent the parietal layer of the pleura. Join + the mouths of the two bags. The two surfaces of the bags which are now + in contact will represent the two moistened surfaces of the pleuræ, + which rub together in breathing. + + Experiment 115. _To show how the lungs may be filled with air._ + Take one of the lungs saved from Experiment 110. Tie a glass tube six + inches long into the larynx. Attach a piece of rubber to one end of the + glass tube. Now inflate the lung several times, and let it collapse. + When distended, examine every part of it. + + Experiment 116. _To take your own bodily temperature or that of a + friend._ If you cannot obtain the use of a physician's clinical + thermometer, unfasten one of the little thermometers found on so many + calendars and advertising sheets. Hold it for five minutes under the + tongue with the lips closed. Read it while in position or the instant it + is removed. The natural temperature of the mouth is about 98½° F. + + Experiment 117. _To show the vocal cords._ Get a pig's windpipe in + perfect order, from the butcher, to show the vocal cords. Once secured, + it can be kept for an indefinite time in glycerine and water or dilute + alcohol. + + Experiment 118. _To show that the air we expire is warm._ Breathe + on a thermometer for a few minutes. The mercury will rise rapidly. + + Experiment 119. _To show that expired cur is moist_. Breathe on a + mirror, or a knife blade, or any polished metallic surface, and note the + deposit of moisture. + + Experiment 120. _To show that the expired air contains carbon + dioxid_. Put a glass tube into a bottle of lime water and breathe + through the tube. The A liquid will soon become cloudy, because the + carbon dioxid of the expired air throws down the lime held in solution. + + Experiment 121. "A substitute for a clinical thermometer may be + readily contrived by taking an ordinary house thermometer from its tin + case, and cutting off the lower part of the scale so that the bulb may + project freely. With this instrument the pupils may take their own and + each other's temperatures, and it will be found that whatever the season + of the year or the temperature of the room, the thermometer in the mouth + will record about 99° F. Care must, of course, be taken to keep the + thermometer in the mouth till it ceases to rise, and to read while it is + still in position."--Professor H. P. Bowditch. + + Experiment 122. _To illustrate the manner in which the movements of + inspiration cause the air to enter the lungs._ Fit up an apparatus, as + represented in Fig. 95, in which a stout glass tube is provided with a + sound cork, B, and also an air-tight piston, D, resembling that of an + ordinary syringe. A short tube, A, passing through the cork, has a small + India-rubber bag, C, tied to it. Fit the cork in the tube while the + piston is near the top. Now, by lowering the piston we increase the + capacity of the cavity containing the bag. The pressure outside the bag + is thus lowered, and air rushes into it through the tube, A, till a + balance is restored. The bag is thus stretched. As soon as we let go the + piston, the elasticity of the bag, being free to act, Movements of + drives out the air just taken in, and the piston returns to its former + place. + + [Illustration: Fig. 95. Apparatus for Illustrating the Movements of + Respiration.] + + It will be noticed that in this experiment the elastic bag and its tube + represent the lungs and trachea; and the glass vessel enclosing it, the + thorax. + +For additional experiments on the mechanics of respiration, see Chapter +XV. + + + + +Chapter IX. + +The Skin and the Kidneys. + + + +232. The Elimination of Waste Products. We have traced the food from +the alimentary canal into the blood. We have learned that various food +materials, prepared by the digestive processes, are taken up by the +branches of the portal vein, or by the lymphatics, and carried into the +blood current. The nutritive material thus absorbed is conveyed by the +blood plasma and the lymph to the various tissues to provide them with +nourishment. + +We have learned also that oxygen, taken up in the air cells of the lungs, +is being continually carried to the tissues, and that the blood is +purified by being deprived in the lungs of its excess of carbon dioxid. +From this tissue activity, which is mainly oxidation, are formed certain +waste products which, as we have seen, are absorbed by the capillaries and +lymphatics and carried into the venous circulation. + +In their passage through the blood and tissues, the albumens, sugars, +starches, and fats are converted into carbon dioxid, water, and urea, or +some closely allied body. Certain articles of food also contain small +amounts of sulphur and phosphorus, which undergo oxidation into sulphates +and phosphates. We speak, then, of carbon dioxid, salts, and water as +waste products of the animal economy. These leave the body by one of +the three main channels,--the lungs, the skin, or the kidneys. + +The elimination of these products is brought about by a special apparatus +called organs of excretion. The worn-out substances themselves +are called excretions, as opposed to secretions, which are +elaborated for use in the body. (See note, p. 121.) As already shown, the +lungs are the main channels for the elimination of carbon dioxid, and +of a portion of water as vapor. By the skin the body gets rid of a +small portion of salts, a little carbon dioxid, and a large +amount of water in the form of perspiration. From the kidneys +are eliminated nearly all the urea and allied bodies, the main +portion of the salts, and a large amount of water. In fact, +practically all the nitrogenous waste leaves the body by the kidneys. + +[Illustration: Fig. 96.--Diagrammatic Scheme to illustrate in a very +General Way Absorption and Excretion. + + A, represents the alimentary canal; + L, the pulmonary surface; + K, the surface of the renal epithelium; + S, the skin; + o, oxygen; + h, hydrogen,; + n, nitrogen. +] + + +233. The Skin. The skin is an important and unique organ of the +body. It is a blood-purifying organ as truly as are the lungs and the +kidneys, while it also performs other and complex duties. It is not merely +a protective covering for the surface of the body. This is indeed the most +apparent, but in some respectes, the lest important, of its functions. +This protective duty is necessary and efficient, as is proved by the +familiar experience of the pain when a portion of the outer skin has been +removed. + +The skin, being richly supplied with nerves, is an important organ of +sensibility and touch. In some parts it is closely attached to +the structures beneath, while in others it is less firmly adherent and +rests upon a variable amount of fatty tissue. It thus assists in relieving +the abrupt projections and depressions of the general surface, and in +giving roundness and symmetry to the entire body. The thickness of the +skin varies in different parts of the body. Where exposed to pressure and +friction, as on the soles of the feet and in the palms of the hands, it is +much thickened. + +The true skin is 1/12 to ⅛ of an inch in thickness, but in certain +parts, as in the lips and ear passages, it is often not more than 1/100 of +an inch thick. At the orifices of the body, as at the mouth, ears, and +nose, the skin gradually passes into mucous membrane, the structure of the +two being practically identical. As the skin is an outside covering, so is +the mucous membrane a more delicate inside lining for all cavities into +which the apertures open, as the alimentary canal and the lungs. + +[Illustration: Fig. 97.--A Layer of the Cuticle from the Palm of the Hand. +(Detached by maceration.)] + +The skin ranks as an important organ of excretion, its product being +sweat, excreted by the sweat glands. The amount of this excretion +evaporated from the general surface is very considerable, and is modified +as becomes necessary from the varied conditions of the temperature. The +skin also plays an important part in regulating the bodily +temperature(sec. 241). + +234. The Cutis Vera, or True Skin. The skin is remarkably complex in +its structure, and is divided into two distinct layers, which may be +readily separated: the deeper layer,--the true skin, dermis, or +corium; and the superficial layer, or outer skin,--the epidermis, +cuticle, or scarf skin. + +The true skin consists of elastic and white fibrous tissue, the +bundles of which interlace in every direction. Throughout this feltwork +structure which gradually passes into areolar tissue are numerous muscular +fibers, as about the hair-follicles and the oil glands. When these tiny +muscles contract from cold or by mental emotion, the follicles project +upon the surface, producing what is called "goose flesh." + +The true skin is richly supplied with blood-vessels and nerves, as when +cut it bleeds freely, and is very sensitive. The surface of the true skin +is thrown into a series of minute elevations called the papillæ, upon +which the outer skin is moulded. These abound in blood-vessels, +lymphatics, and peculiar nerve-endings, which will be described in +connection with the organ of touch (sec. 314). The papillæ are large +and numerous in sensitive places, as the palms of the hands, the soles of +the feet, and the fingers. They are arranged in parallel curved lines, and +form the elevated ridges seen on the surface of the outer skin (Fig. 103). + +235. The Epidermis, or Cuticle. Above the true skin is the epidermis. +It is semi-transparent, and under the microscope resembles the scales of a +fish. It is this layer that is raised by a blister. + +As the epidermis has neither blood-vessels, nerves, nor lymphatics, +it may be cut without bleeding or pain. Its outer surface is marked with +shallow grooves which correspond to the deep furrows between the papillæ +of the true skin. The inner surface is applied directly to the papillary +layer of the true skin, and follows closely its inequalities. The outer +skin is made up of several layers of cells, which next to the true skin +are soft and active, but gradually become harder towards the surface, +where they are flattened and scale-like. The upper scales are continually +being rubbed off, and are replaced by deeper cells from beneath. There are +new cells continually being produced in the deeper layer, which push +upward the cells already existing, then gradually become dry, and are cast +off as fine, white dust. Rubbing with a coarse towel after a hot bath +removes countless numbers of these dead cells of the outer skin. During +and after an attack of scarlet fever the patient "peels," that is, sheds +an unusual amount of the seal; cells of the cuticle. + +The deeper and more active layer of the epidermis, the _mucosum_, is made +up of cells some of which contain minute granules of pigment, or coloring +matter, that give color to the skin. The differences in the tint, as +brunette, fair, and blond, are due mainly to the amount of coloring matter +in these pigment cells. In the European this amount is generally small, +while in other peoples the color cells may be brown, yellow, or even +black. The pinkish tint of healthy skin, and the rosy-red after a bath are +due, not to the pigment cells, but to the pressure of capillaries in the +true skin, the color of the blood being seen through the semi-transparent +outer skin. + +[Illustration: Fig. 98.--Surface of the Palm of the Hand, showing the +Openings of the Sweat Glands and the Grooves between the Papillæ of the +Skin. (Magnified 4 diameters.) [In the smaller figure the same epidermal +surface is shown, as seen with the naked eye.]] + + Experiment 123. Of course the living skin can be examined only in a + general way. Stretch and pull it, and notice that it is elastic. Note + any liver spots, white scars, moles, warts, etc. Examine the outer skin + carefully with a strong magnifying glass. Study the papillæ on the + palms. Scrape off with a sharp knife a few bits of the scarf skin, and + examine them with the microscope. + +236. The Hair. Hairs varying in size cover nearly the entire body, +except a few portions, as the upper eyelids, the palms of the hands, and +the soles of the feet. + +The length and diameter of the hairs vary in different persons, especially +in the long, soft hairs of the head and beard. The average number of hairs +upon a square inch of the scalp is about 1000, and the number upon the +entire head is estimated as about 120,000. + +Healthy hair is quite elastic, and may be stretched from one-fifth to +one-third more than its original length. An ordinary hair from the head +will support a weight of six to seven ounces. The hair may become strongly +electrified by friction, especially when brushed vigorously in cold, dry +weather. Another peculiarity of the hair is that it readily absorbs +moisture. + +237. Structure of the Hair. The hair and the nails are structures +connected with the skin, being modified forms of the epidermis. A hair is +formed by a depression, or furrow, the inner walls of which consist of the +infolded outer skin. This depression takes the form of a sac and is called +the hair-follicle, in which the roots of the hair are embedded. At +the bottom of the follicle there is an upward projection of the true skin, +a papilla, which contains blood-vessels and nerves. It is covered +with epidermic cells which multiply rapidly, thus accounting for the rapid +growth of the hair. Around each papilla is a bulbous expansion, the hair +bulb, from which the hair begins to grow. + +[Illustration: Fig. 99.--Epidermis of the Foot. + +It will be noticed that there are only a few orifices of the sweat glands +in this region. (Magnified 8 diameters.)] + +The cells on the papillæ are the means by which the hairs grow. As these +are pushed upwards by new ones formed beneath, they are compressed, and +the shape of the follicle determines their cylindrical growth, the shaft +of the hair. So closely are these cells welded to form the cylinder, that +even under a microscope the hair presents only a fibrous appearance, +except in the center, where the cells are larger, forming the +medulla, or pith (Fig. 106). + +The medulla of the hair contains the pigment granules or coloring matter, +which may be of any shade between a light yellow and an intense black. It +is this that gives the great variety in color. Generally with old people +the pigment is absent, the cells being occupied by air; hence the hair +becomes gray or white. The thin, flat scales on the surface of the hair +overlap like shingles. Connected with the hair-follicles are small bundles +of muscular fibers, which run obliquely in the skin and which, on +shortening, may cause the hairs to become more upright, and thus are made +to "stand on end." The bristling back of an angry cat furnishes a familiar +illustration of this muscular action. + +[Illustration: Fig. 100.--Hair and Hair-Follicle. + + A, root of hair; + B, bulb of the hair; + C, internal root sheath; + D, external root sheath; + E, external membrane of follicle; + F, muscular fibers attached to the follicle; + H, compound sebaceous gland with its duct; + K, L, simple sebaceous gland; + M, opening of the hair-follicle. +] + +Opening into each hair-follicle are usually one or more sebaceous, or +oil, glands. These consist of groups of minute pouches lined with +cells producing an oily material which serves to oil the hair and keep the +skin moist and pliant. + +238. The Nails. The nails are also formed of epidermis cells +which have undergone compression, much like those forming the shaft of a +hair. In other words, a nail is simply a thick layer of horny scales built +from the outer part of the scarf skin. The nail lies upon very fine and +closely set papillæ, forming its matrix, or bed. It is covered at its +base with a fold of the true skin, called its root, from beneath +which it seems to grow. + +The growth of the nail, like that of the hair and the outer skin, is +effected by the production of new cells at the root and under surface. The +growth of each hair is limited; in time it falls out and is replaced by a +new one. But the nail is kept of proper size simply by the removal of its +free edge. + +239. The Sweat Glands. Deep in the substance of the true skin, or in +the fatty tissue beneath it, are the sweat glands. Each gland +consists of a single tube with a blind end, coiled in a sort of ball about +1/60 of an inch in diameter. From this coil the tube passes upwards +through the dermis in a wavy course until it reaches the cuticle, which it +penetrates with a number of spiral turns, at last opening on the surface. +The tubes consist of delicate walls of membrane lined with cells. The coil +of the gland is enveloped by minute blood-vessels. The cells of the glands +are separated from the blood only by a fine partition, and draw from it +whatever supplies they need for their special work. + +[Illustration: Fig. 101.--Concave or Adherent Surface of the Nail. + + A, border of the root; + B, whitish portion of semilunar shape (the lunula); + C, body of nail. The continuous line around border represents the free + edge. +] + +[Illustration: Fig. 102.--Nail in Position. + + A, section of cutaneous fold (B) turned back to show the root of the + nail; + B, cutaneous fold covering the root of the nail; + C, semi lunar whitish portion (lunula); + D, free border. +] + +With few exceptions every portion of the skin is provided with sweat +glands, but they are not equally distributed over the body. They are +fewest in the back and neck, where it is estimated they average 400 to the +square inch. They are thickest in the palms of the hands, where they +amount to nearly 3000 to each square inch. These minute openings occur in +the ridges of the skin, and may be easily seen with a hand lens. The +length of a tube when straightened is about 1/4 of an inch. The total +number in the body is estimated at about 2,500,000, thus making the entire +length of the tubes devoted to the secretion of sweat about 10 miles. + +240. Nature and Properties of Sweat. The sweat is a turbid, saltish +fluid with a feeble but characteristic odor due to certain volatile fatty +acids. Urea is always present in small quantities, and its proportion may +be largely increased when there is deficiency of elimination by the +kidneys. Thus it is often observed that the sweat is more abundant when +the kidneys are inactive, and the reverse is true. This explains the +increased excretion of the kidneys in cold weather. Of the inorganic +constituents of sweat, common salt is the largest and most important. Some +carbon dioxid passes out through the skin, but not more than 1/50 as much +as escapes by the lungs. + +The sweat ordinarily passes off as vapor. If there is no obvious +perspiration we must not infer that the skin is inactive, since sweat is +continually passing from the surface, though often it may not be apparent. +On an average from 1-1/2 to 4 pounds of sweat are eliminated daily from +the skin in the form of vapor. This is double the amount excreted by the +lungs, and averages about 1/67 of the weight of the body. + +The visible sweat, or sensible perspiration, becomes abundant during +active exercise, after copious drinking of cold water, on taking certain +drugs, and when the body is exposed to excessive warmth. Forming more +rapidly than it evaporates it collects in drops on the surface. The +disagreeable sensations produced by humid weather result from the fact +that the atmosphere is so loaded with vapor that the moisture of the skin +is slowly removed by evaporation. + + Experiment 124. Study the openings of the sweat glands with the aid + of a strong magnifying glass. They are conveniently examined on the + palms. + +A man's weight may be considerably reduced within a short time by loss +through the perspiration alone. This may explain to some extent the +weakening effect of profuse perspiration, as from night sweats of +consumption, convalescence from typhoid fever, or the artificial sweating +from taking certain drugs. + + +241. The Skin as a Regulator of the Temperature of the Body. We thus +learn that the skin covers and protects the more delicate structures +beneath it; and that it also serves as an important organ of excretion. By +means of the sweat the skin performs a third and a most important +function, _viz_., that of regulating the temperature of the body. + +The blood-vessels of the skin, like those of other parts of the body, are +under the control of the nervous system, which regulates their diameter. +If the nervous control be relaxed, the blood-vessels dilate, more blood +flows through them, and more material is brought to the glands of the skin +to be acted upon. External warmth relaxes the skin and its blood-vessels. +There results an increased flow of blood to the skin, with increased +perspiration. External cold, on the other hand, contracts the skin and its +blood-vessels, producing a diminished supply of blood and a diminished +amount of sweat. + +Now, it is a law of physics that the change from liquid to vapor involves +a loss of heat. A few drops of ether or of any volatile liquid placed on +the skin, produce a marked sense of coldness, because the heat necessary +to change the liquid into vapor has been drawn rapidly from the skin. This +principle holds good for every particle of sweat that reaches the mouth of +a sweat gland. As the sweat evaporates, it absorbs a certain amount of +heat, and cools the body to that extent. + + +242. How the Action of the Skin may be Modified. After profuse +sweating we feel chilly from the evaporation of a large amount of +moisture, which rapidly cools the surface. When the weather is very warm +the evaporation tends to prevent the bodily temperature from rising. On +the other hand, if the weather be cold, much less sweat is produced, the +loss of heat from the body is greatly lessened, and its temperature +prevented from falling. Thus it is plain why medicine is given and other +efforts are made to sweat the fever patient. The increased activity of the +skin helps to reduce the bodily heat. + +The sweat glands are under the control of certain nerve fibers originating +in the spinal cord, and are not necessarily excited to action by an +increased flow of blood through the skin. In other words, the sweat glands +may be stimulated to increased action both by an increased flow of blood, +and also by reflex action upon the vaso-dilator nerves of the parts. These +two agencies, while working in harmony through the vaso-dilators, produce +phenomena which are essentially independent of each other. Thus a strong +emotion, like fear, may cause a profuse sweat to break out, with cold, +pallid skin. During a fever the skin may be hot, and its vessels full of +blood, and yet there may be no perspiration. + +[Illustration: Fig. 103.--Papillæ of the Skin of the Palm of the Hand. + +In each papilla are seen vascular loops (dark lines) running up from the +vascular network below, the tactile corpuscles with their nerve branches +(white lines) which supply the papillæ.] + +The skin may have important uses with which we are not yet acquainted. +Death ensues when the heat of the body has been reduced to about 70° F., +and suppression of the action of the skin always produces a lowering of +the temperature. Warm-blooded animals usually die when more than half of +the general surface has been varnished. Superficial burns which involve a +large part of the surface of the body, generally have a fatal result due +to shock. + +If the skin be covered with some air-tight substance like a coating of +varnish, its functions are completely arrested. The bodily heat falls very +rapidly. Symptoms of blood-poisoning arise, and death soon ensues. The +reason is not clearly known, unless it be from the sudden retention of +poisonous exhalations. + +243. The Skin and the Kidneys. There is a close relationship between +the skin and the kidneys, as both excrete organic and saline matter. In +hot weather, or in conditions producing great activity of the skin, the +amount of water excreted by the kidneys is diminished. This is shown in +the case of firemen, stokers, bakers, and others who are exposed to great +heat, and drink heavily and sweat profusely, but do not have a relative +increase in the functions of the kidneys. In cool weather, when the skin +is less active, a large amount of water is excreted by the kidneys, as is +shown by the experience of those who drive a long distance in severe +weather, or who have caught a sudden cold. + +[Illustration: Fig. 104.--Magnified View of a Sweat Gland with its Duct. + +The convoluted gland is seen surrounded with big fat-cells, and may be +traced through the dermis to its outlet in the horny layers of the +epidermis.] + +244. Absorbent Powers of the Skin. The skin serves to some extent as +an organ for absorption. It is capable of absorbing certain +substances to which it is freely exposed. Ointments rubbed in, are +absorbed by the lymphatics in those parts where the skin is thin, as in +the bend of the elbow or knee, and in the armpits. Physicians use +medicated ointments in this way, when they wish to secure prompt and +efficient results. Feeble infants often grow more vigorous by having their +skin rubbed vigorously daily with olive oil. + +A slight amount of water is absorbed in bathing. Sailors deprived of +fresh water have been able to allay partially their intense thirst by +soaking their clothing in salt water. The extent to which absorption +occurs through the healthy skin is, however, quite limited. If the outer +skin be removed from parts of the body, the exposed surface absorbs +rapidly. Various substances may thus be absorbed, and rapidly passed into +the blood. When the physician wishes remedies to act through the skin, he +sometimes raises a small blister, and dusts over the surface some drug, a +fine powder, like morphine. + +The part played by the skin as an organ of touch will be considered +in sections 314 and 315. + + Experiment 125. _To illustrate the sense of temperature_. Ask the + person to close his eyes. Use two test tubes, one filled with cold and + the other with hot water, or two spoons, one hot and one cold. Apply + each to different parts of the surface, and ask the person whether the + touching body is hot or cold. Test roughly the sensibility of different + parts of the body with cold and warm metallic-pointed rods. + + Experiment 126. Touch fur, wood, and metal. The metal feels + coldest, although all the objects are at the same temperature. Why? + + Experiment 127. Plunge the hand into water at about 97°F. One + experiences a feeling of heat. Then plunge it into water at about 86°F.; + at first it feels cold, because heat is abstracted from the hand. Plunge + the other hand direct into water at 86°F. without previously placing it + in water at 97°F.,--it will feel pleasantly warm. + + Experiment 128. _To illustrate warm and cold spots_. With a blunt + metallic point, touch different parts of the skin. Certain points excite + the sensation of warmth, others of cold, although the temperatures of + the skin and of the instrument remain constant. + +245. Necessity for Personal Cleanliness. It is evident that the skin, +with its myriads of blood-vessels, nerves, and sweat and oil glands, is an +exceedingly complicated and important structure. The surface is +continually casting off perspiration, oily material, and dead scales. By +friction and regular bathing we get rid of these waste materials. If this +be not thoroughly done, the oily secretion holds the particles of waste +substances to the surface of the body, while dust and dirt collect, and +form a layer upon the skin. When we remember that this dirt consists of a +great variety of dust particles, poisonous matters, and sometimes germs of +disease, we may well be impressed with the necessity of personal +cleanliness. + +This layer of foreign matter on the skin is in several ways injurious to +health. It clogs the pores and retards perspiration, thus checking the +proper action of the skin as one of the chief means of getting rid of the +waste matters of the body. Hence additional work is thrown upon other +organs, chiefly the lungs and the kidneys, which already have enough to +do. This extra work they can do for only a short time. Sooner or later +they become disordered, and illness follows. Moreover, as this unwholesome +layer is a fertile soil in which bacteria may develop, many skin diseases +may result from this neglect. It is also highly probable that germs of +disease thus adherent to the skin may then be absorbed into the system. +Parasitic skin diseases are thus greatly favored by the presence of an +unclean skin. It is also a fact that uncleanly people are more liable to +take cold than those who bathe often. + +The importance of cleanliness would thus seem too apparent to need special +mention, were it not that the habit is so much neglected. The old and +excellent definition that dirt is suitable matter, but in the wrong place, +suggests that the place should be changed. This can be done only by +regular habits of personal cleanliness, not only of the skin, the hair, +the teeth, the nails, and the clothing, but also by the rigid observance +of a proper system in daily living. + +246. Baths and Bathing. In bathing we have two distinct objects in +view,--to keep the skin clean and to impart vigor. These are closely +related, for to remove from the body worn-out material, which tends to +injure it, is a direct means of giving vigor to all the tissues. Thus a +cold bath acts upon the nervous system, and calls out, in response to the +temporary abstraction of heat, a freer play of the general vital powers. +Bathing is so useful, both locally and constitutionally, that it +should be practiced to such an extent as experience proves to be +beneficial. For the general surface, the use of hot water once a week +fulfills the demands of cleanliness, unless in special occupations. +Whether we should bathe in hot or cold water depends upon circumstances. +Most persons, especially the young and vigorous, soon become accustomed to +cool, and even cold water baths, at all seasons of the year. + +The hot bath should be taken at night before going to bed, as in the +morning there is usually more risk of taking cold. The body is readily +chilled, if exposed to cold when the blood-vessels of the skin have been +relaxed by heat. Hot baths, besides their use for the purposes of +cleanliness, have a sedative influence upon the nervous system, tending to +allay restlessness and weariness. They are excellent after severe physical +or mental work, and give a feeling of restful comfort like that of sleep. + +[Illustration: Fig. 105.--Epithelial Cells from the Sweat Glands. The +cells are very distinct, with nuclei enclosing pigmentary granulations +(Magnified 350 times)] + +Cold baths are less cleansing than hot, but serve as an excellent +tonic and stimulant to the bodily functions. The best and most convenient +time for a cold bath is in the morning, immediately after rising. To the +healthy and vigorous, it is, if taken at this time, with proper +precautions, a most agreeable and healthful luxury. The sensation of +chilliness first felt is caused by the contraction of the skin and its +blood-vessels, so that the blood is forced back, as it were, into the +deeper parts of the body. This stimulates the nervous system, the +breathing becomes quicker and deeper, the heart beats more vigorously, +and, as a consequence, the warm blood is sent back to the skin with +increased force. This is known as the stage of reaction, which is best +increased by friction with a rough towel. This should produce the pleasant +feeling of a warm glow all over the body. + +A cold bath which is not followed by reaction is likely to do more harm +than good. The lack of this reaction may be due to the water being too +cold, the bath too prolonged, or to the bather being in a low condition of +health. In brief, the ruddy glow which follows a cold bath is the main +secret of its favorable influence. + +The temperature of the water should be adapted to the age and strength of +the bather. The young and robust can safely endure cold baths, that would +be of no benefit but indeed an injury to those of greater age or of less +vigorous conditions of health. After taking a bath the skin should be +rapidly and vigorously rubbed dry with a rough towel, and the clothing at +once put on. + +247. Rules and Precautions in Bathing. Bathing in cold water should +not be indulged in after severe exercise or great fatigue, whether we are +heated or not. Serious results have ensued from cold baths when the body +is in a state of exhaustion or of profuse perspiration. A daily cold bath +when the body is comfortably warm, is a safe tonic for almost all persons +during the summer months, and tends especially to restore the appetite. +Cold baths, taken regularly, render persons who are susceptible to +colds much less liable to them, and less likely to be disturbed by sudden +changes of temperature. Persons suffering from heart disease or from +chronic disease of an important organ should not indulge in frequent cold +bathing except by medical advice. Owing to the relaxing nature of hot +baths, persons with weak hearts or suffering from debility may faint while +taking them. + +Outdoor bathing should not be taken for at least an hour after a +full meal, and except for the robust it is not prudent to bathe with the +stomach empty, especially before breakfast. It is a wise rule, in outdoor +or sea bathing, to come out of the water as soon as the glow of reaction +is felt. It is often advisable not to apply cold water very freely to the +head. Tepid or even hot water is preferable, especially by those subject +to severe mental strain. But it is often a source of great relief during +mental strain to bathe the face, neck, and chest freely at bedtime with +cold water. It often proves efficient at night in calming the +sleeplessness which results from mental labor. + +Hot baths, if taken at bedtime, are often serviceable in preventing a +threatened cold or cutting it short, the patient going immediately to bed, +with extra clothing and hot drinks. The free perspiration induced helps to +break up the cold. + +Salt water acts more as a stimulant to the skin than fresh water. +Salt-water bathing is refreshing and invigorating for those who are +healthy, but the bather should come out of the water the moment there is +the slightest feeling of chilliness. The practice of bathing in salt water +more than once a day is unhealthful, and even dangerous. Only the +strongest can sustain so severe a tax on their power of endurance. Sea +bathing is beneficial in many ways for children, as their skin reacts well +after it. In all cases, brisk rubbing with a rough towel should be had +afterwards. + +[Illustration: Fig. 106.--Magnified Section of the Lower Portion of a Hair +and Hair-Follicle. + + A, membrane of the hair-follicle, cells with nuclei and pigmentary + granules; + B, external lining of the root sheath; + C, internal lining of the root sheath; + D, cortical or fibrous portion of the hair shaft; + E, medullary portion (pith) of shaft; + F, hair-bulb, showing its development from cells from A. +] + +The golden rule of all bathing is that it must never be followed by a +chill. If even a chilliness occur after bathing, it must immediately +be broken up by some appropriate methods, as lively exercise, brisk +friction, hot drinks, and the application of heat. + +Swimming is a most valuable accomplishment, combining bathing and +exercise. Bathing of the feet should never be neglected. Cleanliness of +the hair is also another matter requiring strict attention, especially in +children. + +248. Care of the Hair and Nails. The hair brush should not be too +stiff, as this increases the tendency towards scurfiness of the head. If, +however, the hair is brushed too long or too hard, the scalp is greatly +stimulated, and an increased production of scurf may result. If the head +be washed too often with soap its natural secretion is checked, and the +scalp becomes dry and scaly. The various hair pomades are as a rule +undesirable and unnecessary. + +The nails should be kept in proper condition, else they are not only +unsightly, but may serve as carriers of germs of disease. The nails are +often injured by too much interference, and should never be trimmed to the +quick. The upper surfaces should on no account be scraped. The nail-brush +is sufficient to cleanse them without impairing their smooth and polished +surfaces. + +[Illustration: Fig. 107.--Longitudinal Section of a Finger-Nail. + + A, last phalanx of the fingers; + B, true skin on the dorsal surface of the finger; + C, epidermis; + D, true skin; + E, bed of the nail; + F, superficial layer of the nail; + H, true skin of the pulp of the finger. +] + +249. Use of Clothing. The chief use of clothing, from a hygienic +point of view, is to assist in keeping the body at a uniform temperature. +It also serves for protection against injury, and for personal adornment. +The heat of the body, as we have learned, is normally about 98 1/2° F. +This varies but slightly in health. A rise of temperature of more than one +degree is a symptom of disturbance. The normal temperature does not vary +with the season. In summer it is kept down by the perspiration and its +rapid evaporation. In winter it is maintained by more active oxidation, by +extra clothing, and by artificial heat. + +The whole matter of clothing is modified to a great extent by climatic +conditions and local environments,--topics which do not come +within the scope of this book. + +250. Material Used for Clothing. It is evident that if clothing is to +do double duty in preventing the loss of heat by radiation, and in +protecting us from the hot rays of the sun, some material must be used +that will allow the passage of heat in either direction. The ideal +clothing should be both a bad conductor and a radiator of heat. At the +same time it must not interfere with the free evaporation of the +perspiration, otherwise chills may result from the accumulation of +moisture on the surface of the body. + +Wool is a bad conductor, and should be worn next the skin, both in +summer and winter, especially in variable climates. It prevents, better +than any other material, the loss of heat from the body, and allows free +ventilation and evaporation. Its fibers are so lightly woven that they +make innumerable meshes enclosing air, which is one of the best of +non-conductors. + +Silk ranks next to wool in warmth and porosity. It is much softer and +less irritating than flannel or merino, and is very useful for summer +wear. The practical objection to its general use is the expense. Fur +ranks with wool as a bad conductor of heat. It does not, however, like +wool, allow of free evaporation. Its use in cold countries is universal, +but in milder climates it is not much worn. + +Cotton and linen are good conductors of heat, but are not +absorbents of moisture, and should not be worn next the skin. They are, +however, very durable and easily cleansed. As an intermediate clothing +they may be worn at all seasons, especially over wool or silk. Waterproof +clothing is also useful as a protection, but should not be worn a longer +time than necessary, as it shuts in the perspiration, and causes a sense +of great heat and discomfort. + +The color of clothing is of some importance, especially if exposed +directly to the sun's rays. The best reflectors, such as white and light +gray clothing, absorb comparatively little heat and are the coolest, while +black or dark-colored materials, being poor reflectors and good +absorbents, become very warm. + +251. Suggestions for the Use of Clothing. Prudence and good sense +should guide us in the spring, in changing winter flannels or clothing for +fabrics of lighter weight. With the fickle climate in most sections of +this country, there are great risks of severe colds, pneumonia, and other +pulmonary diseases from carelessness or neglect in this matter. A change +from heavy to lighter clothing should be made first in the outer garments, +the underclothing being changed very cautiously. + +The two essentials of healthful clothing are cleanliness and +dryness. To wear garments that are daily being soiled by perspiration +and other cutaneous excretions, is a most uncleanly and unhealthful +practice. Clothing, especially woolen underclothing, should be frequently +changed. One of the objections to the use of this clothing is that it does +not show soiling to the same extent as do cotton and linen. + +Infectious and contagious diseases may be conveyed by the clothing. Hence, +special care must be taken that all clothing in contact with sick people +is burned or properly disinfected. Children especially are susceptible to +scarlet fever, diphtheria, and measles, and the greatest care must be +exercised to prevent their exposure to infection through the clothing. + +We should never sleep in a damp bed, or between damp sheets. The vital +powers are enfeebled during sleep, and there is always risk of pneumonia +or rheumatism. The practice of sitting with wet feet and damp clothing is +highly injurious to health. The surface of the body thus chilled may be +small, yet there is a grave risk of serious, if not of fatal, disease. No +harm may be done, even with clothing wet with water or damp with +perspiration, so long as exercise is maintained, but the failure or +inability to change into dry garments as soon as the body is at rest is +fraught with danger. + +Woolen comforters, scarfs, and fur mufflers, so commonly worn around the +neck, are more likely to produce throat troubles and local chill than to +have any useful effect. Harm ensues from the fact that the extra covering +induces local perspiration, which enfeebles the natural defensive power of +the parts; and when the warmer covering is removed, the perspiring surface +is readily chilled. Those who never bundle their throats are least liable +to suffer from throat ailments. + +252. Ill Effects of Wearing Tightly Fitting Clothing. The injury to +health caused by tight lacing, when carried to an extreme, is due to the +compression and displacement of various organs by the pressure exerted on +them. Thus the lungs and the heart may be compressed, causing short breath +on exertion, palpitation of the heart, and other painful and dangerous +symptoms. The stomach, the liver, and other abdominal organs are often +displaced, causing dyspepsia and all its attendant evils. The improper use +of corsets, especially by young women, is injurious, as they interfere +with the proper development of the chest and abdominal organs. The use of +tight elastics below the knee is often injurious. They obstruct the local +venous circulation and are a fruitful source of cold feet and of enlarged +or varicose veins. + +Tightly fitting boots and shoes often cause corns, bunions, and ingrowing +nails; on the other hand, if too loosely worn, they cause corns from +friction. Boots too narrow in front crowd the toes together, make them +overlap, and render walking difficult and painful. High-heeled boots throw +the weight of the body forwards, so that the body rests too much on the +toes instead of on the heels, as it should, thus placing an undue strain +upon certain groups of muscles of the leg, in order to maintain the +balance, while other groups are not sufficiently exercised. Locomotion is +never easy and graceful, and a firm, even tread cannot be expected. + +The compression of the scalp by a tight-fitting hat interferes with the +local circulation, and may cause headaches, neuralgia, or baldness, the +nutrition of the hair-follicles being diminished by the impaired +circulation. The compression of the chest and abdomen by a tight belt and +various binders interferes with the action of the diaphragm,--the most +important muscle of respiration. + +253. Miscellaneous Hints on the Use of Clothing. Children and old +people are less able to resist the extreme changes of temperature than are +adults of an average age. Special care should be taken to provide children +with woolen underclothing, and to keep them warm and in well-ventilated +rooms. Neither the chest nor limbs of young children should be unduly +exposed, as is often done, to the cold blasts of winter or the fickle +weather of early spring. Very young children should not be taken out in +extremely cold weather, unless quite warmly clad and able to run about. +The absurd notion is often entertained that children should be hardened by +exposure to the cold. Judicious "hardening" means ample exposure of +well-fed and well-clothed children. Exposure of children not thus cared +for is simple cruelty. The many sicknesses of children, especially +diseases of the throat and lungs, may often be traced directly to gross +carelessness, ignorance, or neglect with reference to undue exposure. The +delicate feet of children should not be injured by wearing ill-fitting or +clumsy boots or shoes. Many deformities of the feet, which cause much +vexation and trouble in after years, are acquired in early life. + +No one should sleep in any of the clothes worn during the day, not even in +the same underclothing. All bed clothing should be properly aired, by free +exposure to the light and air every morning. Never wear wet or damp +clothing one moment longer than necessary. After it is removed rub the +body thoroughly, put on at once dry, warm clothing, and then exercise +vigorously for a few minutes, until a genial glow is felt. Neglect of +these precautions often results in rheumatism, neuralgia, and diseases of +the chest, especially among delicate people and young women. + +Pupils should not be allowed to sit in the schoolroom with any outer +garments on. A person who has become heated in a warm room should not +expose himself to cold without extra clothing. We must not be in a hurry +to put on heavy clothes for winter, but having once worn them, they must +not be left off until milder weather renders the change safe. The cheaper +articles of clothing are often dyed with lead or arsenic. Hence such +garments, like stockings and colored underclothing, worn next the skin +have been known to produce severe symptoms of poisoning. As a precaution, +all such articles should be carefully washed and thoroughly rinsed before +they are worn. + + + +The Kidneys. + + +254. The Kidneys. The kidneys are two important organs in the +abdomen, one on each side of the spine. They are of a reddish-brown color, +and are enveloped by a transparent capsule made up of a fold of the +peritoneum. Embedded in fat, the kidneys lie between the upper lumbar +vertebræ, and the crest of the hip bone. The liver is above the right +kidney, and the spleen above the left, while both lie close against the +rear wall of the abdomen, with the intestines in front of them. The human +kidneys, though somewhat larger, are exactly of the same shape, color, and +general appearance as those of the sheep, so commonly seen in the markets. + +The kidneys are about four inches long, two inches across, one inch thick, +and weigh from 41/2 to 51/2 ounces each. The hollow or concave side of the +kidneys is turned inwards, and the deep fissure of this side, known as the +hilus, widens out to form the pelvis. Through the hilus the +renal artery passes into each kidney, and from each hilus passes outwards +the renal vein, a branch of the inferior vena cava. + +A tube, called the ureter, passes out from the concave border of each +kidney, turns downwards, and enters the bladder in the basin of the +pelvis. This tube is from 12 to 14 inches long, about as large as a goose +quill, and conveys the secretion of the kidneys to the bladder. + +255. Structure of the Kidneys. The pelvis is surrounded by +reddish cones, about twelve in number, projecting into it, called the +pyramids of Malpighi. The apices of these cones, known as the +_papillæ_, are crowded with minute openings, the mouths of the +uriniferous tubules, which form the substance of the kidney. These +lie parallel in the medullary or central structure, but On reaching the +cortical or outer layer, they wind about and interlace, ending, at last, +in dilated closed sacs called Malpighian capsules. + +[Illustration: Fig. 108.--Vertical Section of the Kidney. + + A, pyramids of Malpighi; + B, apices, or papillæ, of the pyramids, surrounded by subdivisions of + the pelvis known as cups or calices; + C, pelvis of the kidney; + D, upper end of ureter. +] + +256. Function of the Kidneys. The Malpighian capsules are really the +beginning of the tubules, for here the work of excretion begins. The thin +wall of the capillaries within each capsule separates the blood from the +cavity of the tubule. The blood-pressure on the delicate capillary walls +causes the exudation of the watery portions of the blood through the cell +walls into the capsule. The epithelial cell membrane allows the water of +the blood with certain salts in solution to pass, but rejects the albumen. +From the capsules, the excretion passes through the tubules into the +pelvis, and on through the ureters to the bladder. But the delicate +epithelial walls of the tubules through which it passes permit the inflow +of urea and other waste products from the surrounding capillaries. By this +twofold process are separated from the blood the fluid portions of the +renal secretion with soluble salts, and the urea with other waste +material. + +257. How the Action of the Kidneys may be Modified. The action of the +kidneys is subject to very marked and sudden modifications, especially +those operating through the nervous system. Thus whatever raises the +blood-pressure in the capillaries of the capsules, will increase the +quantity of fluid filtering through them. That is, the watery portion of +the secretion will be increased without necessarily adding to its solids. +So anything which lowers the blood-pressure will diminish the watery +portion of the secretion, that is, the secretion will be scanty, but +concentrated. + +The Renal Secretion.--The function of the kidneys is to secrete a +fluid commonly known as the urine. The average quantity passed in 24 hours +by an adult varies from 40 to 60 fluid ounces. Normal urine consists of +about 96 per cent of water and 4 per cent of solids. The latter consist +chiefly of certain nitrogenous substances known as urea and uric acid, a +considerable quantity of mineral salts, and some coloring matter. Urea, +the most important and most abundant constituent of urine, contains the +four elements, but nitrogen forms one-half its weight. While, therefore, +the lungs expel carbon dioxid chiefly, the kidneys expel nitrogen. Both of +these substances express the result of oxidations going on in the body. +The urea and uric acids represent the final result of the breaking down in +the body of nitrogenous substances, of which albumen is the type. + +Unusual constituents of the urine are _albumen, sugar_, and _bile_. When +albumen is present in urine, it often indicates some disease of the +kidneys, to which the term _albuminuria_ or Bright's Disease is applied. +The presence of grape sugar or glucose indicates the disease known as +diabetes. Bile is another unusual constituent of the urine, appearing in +_jaundice_. + +The bladder is situated in the pelvic cavity or in the lowest part of +the abdomen. When full, the bladder is pear-shaped; when empty, it is +collapsed and lies low in the pelvis. The functions of the bladder are to +collect and retain the urine, which has reached it drop by drop from the +kidneys through the ureters, until a certain quantity accumulates, and +then to expel it from the body. + +[Illustration: Fig. 109.--Vertical Section of the Back. (Showing kidneys +_in situ_ and the relative position of adjacent organs and vessels.) +[Posterior view.] + + A, 12th dorsal vertebra; + B, diaphragm; + C, receptaculum chyli; + D, small intestines +] + +In the kidneys, as elsewhere, the vaso-motor nerves are distributed +to the walls of the blood-vessels, and modify the quantity and the +pressure of blood in these organs. Thus, some strong emotion, like fear or +undue anxiety, increases the blood-pressure, drives more blood to the +kidneys, and causes a larger flow of watery secretion. When the atmosphere +is hot, there is a relaxation of the vessels of the skin, with a more +than ordinary flow of blood, which is thus withdrawn from the deeper +organs. The blood-pressure in the kidneys is not only diminished, but the +total quantity passing through them in a given time is much lessened. As a +result, the secretion of the kidneys is scanty, but it contains an unusual +percentage of solids. + +When the atmosphere is cold, the reverse is true. The cutaneous vessels +contract, the blood is driven to the deeper organs with increased +pressure, and there is a less amount of sweat, but an increased renal +secretion, containing a smaller proportion of solids. Certain drugs have +the power of increasing or diminishing the renal secretion. As the waste +matters eliminated by the kidneys are being constantly produced in the +tissues, the action of the renal organs is continuous, in marked contrast +with the intermittent flow of most of the secretions proper, as +distinguished from the excretions. + +258. Effects of Alcoholic Drinks upon the Kidneys. The kidneys differ +from some of the other organs in this: those can rest a while without any +harm to themselves, or to the body. We can keep the eyes closed for a few +days, if necessary, without injury, and in fact often with benefit; or, we +can abstain from food for some days, if need be, and let the stomach rest. +But the kidneys cannot, with safety, cease their work. Their duty in +ridding the blood of waste products, and of any foreign or poisonous +material introduced, must be done not only faithfully, but continually, or +the whole body at once suffers from the evil effects of the retained waste +matters. + +This vital fact is the key to the injurious results developed in the +kidneys by the use of alcoholic drinks. These two organs have large +blood-vessels conveying full amounts of blood to and from their +structures, and they feel very quickly the presence of alcohol. Alcoholic +liquors excite and irritate the delicate renal membranes, and speedily +disturb and eventually destroy their capacity to excrete the proper +materials from the blood. + +The continued congestion of the minute structure of the kidney cuts off +the needed nutrition of the organ, and forms the primary step in the +series of disasters. Sometimes from this continued irritation, with the +resulting inflammation, and sometimes from change of structure of the +kidney by fatty degeneration, comes the failure to perform its proper +function. Then, with this two-edged sword of disaster, the urea, which +becomes a poisonous element, and should be removed, is retained in the +system, while the albumen, which is essential to healthy blood, is +filtered away through the diseased kidney. + +259. Alcoholic Liquors as a Cause of Bright's Disease. The +unfortunate presence of albumen in the urine is often a symptom of that +insidious and fatal malady known as _albuminuria_ or Bright's disease, +often accompanied with dropsy and convulsions. One of the most constant +causes of this disease is the use of intoxicants. It is not at all +necessary to this fatal result that a person be a heavy drinker. Steady, +moderate drinking will often accomplish the work. Kidney diseases produced +by alcoholic drinks, are less responsive to medical treatment and more +fatal than those arising from any other known cause.[39] + + Experiment 129. Obtain a sheep's kidney in good order. Observe that + its shape is something like that of a bean, and note that the concave + part (hilus), when in its normal position, is turned towards the + backbone. Notice that all the vessels leave and enter the kidney at the + hilus. Observe a small thick-walled vessel with open mouth from which + may be pressed a few drops of blood. This is the renal artery. Pass a + bristle down it. With the forceps, or even with a penknife, lift from + the kidney the fine membrane enclosing it. This is the kidney capsule. + + Divide the kidney in halves by a section from its outer to near its + inner border. Do not cut directly through the hilus. Note on the cut + surfaces, on the outer side, the darker cortical portion, and on the + inner side, the smooth, pale, medullary portion. Note also the pyramids + of Malpighi. + + + + +Chapter X. + +The Nervous System. + + + +260. General View of the Nervous System. Thus far we have learned +something of the various organs and the manner in which they do their +work. Regarding our bodily structure as a kind of living machine, we have +studied its various parts, and found that each is designed to perform some +special work essential to the well-being of the whole. As yet we have +learned of no means by which these organs are enabled to adjust their +activities to the needs of other tissues and other organs. We are now +prepared to study a higher, a more wonderful and complex agency,--the +nervous system, the master tissue, which controls, regulates, and +directs every other tissue of the human body. + +The nervous system, in its properties and mode of action, is distinct from +all the other systems and organs, and it shares with no other organ or +tissue the power to do its special work. It is the medium through which +all impressions are received. It connects all the parts of the body into +an organism in which each acts in harmony with every other part for the +good of the whole. It animates and governs all movements, voluntary or +involuntary,--secretion, excretion, nutrition; in fact all the processes +of organic life are subject to its regulating power. The different organs +of the body are united by a common sympathy which regulates their action: +this harmonious result is secured by means of the nervous system. + +This system, in certain of its parts, receives impressions, and generates +a force peculiar to itself. We shall learn that there can be no physical +communication between or coördination of the various parts of organs, or +harmonious acts for a desire result, without the nerves. General +impressions, as in ordinary sensation, or special impressions, as in +sight, smell, taste, or hearing,--every instinct, every act of the will, +and every thought are possible only through the action of the nerve +centers. + +261. Nerve Cells. However complicated the structure of nerve tissue +in man seems to be, it is found to consist of only two different elements, +nerve cells and nerve fibers. These are associated and combined +in many ways. They are arranged in distinct masses called nerve +centers, or in the form of cords known as nerves. The former are +made up of nerve fibers; the latter of both cells and fibers. + +[Illustration: Fig. 110. Nerve Cells from the Spinal Cord.] + +Nerve cells, which may be regarded as the central organs of the nerve +fibers, consist of masses of cell protoplasm, with a large _nucleus_ and +_nucleolus_. They bear a general resemblance to other cells, but vary much +in size and shape. Nerve cells grow, become active, and die, as do other +cells. A number of processes branch off from them, some cells giving one +or two, others many. The various kinds of nerve cells differ much in the +shape and number of processes. One of the processes is a strand which +becomes continuous with the axis cylinder of the nerve fibers; that is, +the axis cylinders of all nerve fibers are joined in one place or another +with at least one cell. + +Each part of this system has its own characteristic cell. Thus we have in +the spinal cord the large, irregular cells with many processes, and in the +brain proper the three-sided cells with a process jutting out from each +corner. So characteristic are these forms of cells, that any particular +part of nerve structure may be identified by the kind of cells seen under +the microscope. Nerve cells and nerve fibers are often arranged in +groups, the various cells of the groups communicating with one another. +This clustered arrangement is called a nerve center. + +262. Nerve Fibers. The nerve fibers, the essential elements of +the nerves, somewhat resemble tubes filled with a clear, jelly-like +substance. They consist of a rod, or central core, continuous throughout +the whole length of the nerve, called the axis cylinder. This core is +surrounded by the white substance of Schwann, or medullary sheath, which +gives the nerve its characteristic ivory-white appearance. The whole is +enclosed in a thin, delicate sheath, known as neurilemma. + +[Illustration: Fig. 111.--Nerve Cells from the Gray Matter of the Brain.] + +The axis cylinder generally passes without any break from the nerve +centers to the end of the fibers.[40] The outer sheath (neurilemma) is +also continuous throughout the length of the fibers. The medullary sheath, +on the other hand, is broken at intervals of about 1/25 of an inch, and at +the same intervals nuclei are found along the fiber, around each of +which is a minute protoplasmic mass. Between each pair of nuclei the +sheath is interrupted. This point is known as the _node of Ranvier_. + +Some nerve fibers have no inner sheath (medullary), the outer alone +protecting the axis cylinder. These are known as the non-medullary fibers. +They are gray, while the ordinary medullary fibers are white in +appearance. The white nerve fibers form the white part of the brain +and of the spinal cord, and the greater part of the cerebro-spinal nerves. +The gray fibers occur chiefly in branches from the sympathetic +ganglia, though found to some extent in the nerves of the cerebro-spinal +system. + +In a general way, the nerve fibers resemble an electric cable wire with +its central rod of copper, and its outer non-conducting layer of silk or +gutta percha. Like the copper rod, the axis cylinder along which the nerve +impulse travels is the essential part of a nerve fiber. In a cut nerve +this cylinder projects like the wick of a candle. It is really the +continuation of a process of a nerve cell. Thus the nerve cells and nerve +fibers are related, in that the process of one is the axis cylinder and +essential part of the other. + +The separate microscopic threads or fibers, bound together in cords of +variable size, form the nerves. Each strand or cord is surrounded and +protected by its own sheath of connective tissue, made up of nerves. +According to its size a nerve may have one or many of these strands. The +whole nerve, not unlike a minute tendon in appearance, is covered by a +dense sheath of fibrous tissue, in which the blood-vessels and lymphatics +are distributed to the nerve fibers. + + +[Illustration: Fig. 112.--Medullated Nerve Fibers. + + A, a medullated nerve fiber, showing the subdivision of the medullary + sheath into cylindrical sections imbricated with their ends, a nerve + corpuscle with an oval nucleus is seen between the neurilemma and the + medullary sheath; + B, a medullated nerve fiber at a node or constriction of Ranvier, the + axis cylinder passes uninterruptedly from one segment into the other, + but the medullary sheath is interrupted. +] + +263. The Functions of the Nerve Cells and Nerve Fibers. The nerve +cells are a highly active mass of living material. They find their +nourishment in the blood, which is supplied to them in abundance. The +blood not only serves as nourishment, but also supplies new material, as +it were, for the cells to work over for their own force or energy. Thus +we may think of the nerve cells as a sort of a miniature manufactory, +deriving their material from the blood, and developing from it nervous +energy. + +The nerve fibers, on the other hand, are conductors of nervous energy. +They furnish a pathway along which the nerve energy generated by the cells +may travel. Made up as they are of living nerve substance, the fibers can +also generate energy, yet it is their special function to conduct +influences to and from the cells. + +[Illustration: Fig. 113.--Non-Medullated Fibers. + +Two nerve fibers, showing the nodes or constrictions of Ranvier and the +axis cylinder. The medullary sheath has been dissolved away. The deeply +stained oblong nuclei indicate the nerve corpuscles within the +neurilemma.] + +264. The Nervous System Compared to a Telegraphic System. In men and +other highly organized animals, nerves are found in nearly every tissue +and organ of the body. They penetrate the most minute muscular fibers; +they are closely connected with the cells of the glands, and are found in +the coats of even the smallest blood-vessels. They are among the chief +factors of the structure of the sense organs, and ramify through the skin. +Thus the nervous system is the system of organs through the functions of +which we are brought into relation with the world around us. When we hear, +our ears are bringing us into relation with the outer world. So sight +opens up to us another gateway of knowledge. + +It will help us the better to understand the complicated functions of the +nervous system, if we compare it to a telegraph line. The brain is the +main office, and the multitudes of nerve fibers branching off to all parts +of the body are the wires. By means of these, nerve messages are +constantly being sent to the brain to inform it of what is going on in +various parts of the body, and asking what is to be done in each case. The +brain, on receiving the intelligence, at once sends back the required +instructions. Countless messages are sent to and fro with unerring +accuracy and marvelous rapidity. + +Thus, when we accidentally pick up something hot, it is instantly +dropped. A nerve impulse passes from the nerves of touch in the fingers to +the brain, which at once hurries off its order along another set of nerves +for the hand to drop the burning object. These examples, so common in +daily life, may be multiplied to any extent. Almost every voluntary act we +perform is executed under the direction of the nervous system, although +the time occupied is so small that it is beyond our power to estimate it. +The very frequency with which the nerves act tends to make us forget their +beneficent work. + +265. Divisions of the Nervous System. This system in man consists of +two great divisions. The first is the great nerve center of the body, the +cerebro-spinal system, which rules the organs of animal life. This +includes the brain, the spinal cord, and the cerebro-spinal +nerves. Nerves are given off from the brain and the cord, and form the +mediums of communication between the external parts of the body, the +muscles or the sense organs, and the brain. + +The second part is the sympathetic system, which regulates the +organic life. This consists of numerous small nerve centers arranged in +oval masses varying greatly in size, called ganglia or knots. These +are either scattered irregularly through the body, or arranged in a double +chain of knots lying on the front of the spine, within the chest and +abdomen. From this chain large numbers of nerves are given off, which end +chiefly in the organs of digestion, circulation, and respiration. The +sympathetic system serves to bring all portions of the animal economy into +direct sympathy with one another. + +266. The Brain as a Whole. The brain is the seat of the +intellect, the will, the affections, the emotions, the memory, and +sensation. It has also many other and complex functions. In it are +established many reflex, automatic, and coordinating centers, which are as +independent of consciousness as are those of the spinal cord. + +The brain is the largest and most complex mass of nerve tissue in the +body, made up of an enormous collection of gray cells and nerve fibers. +This organ consists of a vast number of distinct ganglia, or separate +masses of nerve matter, each capable of performing separate functions, but +united through the cerebral action into a harmonious whole. + +[Illustration: Fig. 114.--The Upper Surface of the Cerebrum. (Showing its +division into two hemispheres, and also the convolutions)] + +The average weight of the adult human brain is about 50 ounces for men and +45 ounces for women. Other things being equal, the size and weight of the +brain bear a general relation to the mental power of the individual. As a +rule, a large, healthy brain stands for a vigorous and superior intellect. +The brains of many eminent men have been found to be 8 to 12 ounces above +the average weight, but there are notable exceptions. The brains of +idiots are small; indeed, any weight under a certain size, about 30 +ounces, seems to be invariably associated with an imbecile mind. + +The human brain is absolutely heavier than that of any other animal, +except the whale and elephant. Comparing the size of these animals with +that of man, it is instructive to notice how much larger in proportion to +the body is man's brain. The average proportion of the weight of the brain +to the weight of the body is greater in man than in most animals, being +about 1 to 36. In some small birds, in the smaller monkeys, and in some +rodents, the proportional weight of the brain to that of the body is even +greater than in man. + +267. The Cerebrum. The three principal masses which make up the brain +when viewed as a whole are: + + 1. The cerebrum, or brain proper. + 2. The cerebellum, or lesser brain. + 3. The medulla oblongata. + +The cerebrum comprises nearly seven-eighths of the entire mass, and +fills the upper part of the skull. It consists of two halves, the right +and left cerebral hemispheres. These are almost separated from each +other by a deep median fissure. The hemispheres are united at the bottom +of the fissure by a mass of white fibers passing from side to side. Each +of these hemispheres is subdivided into three lobes, so that the entire +cerebrum is made up of six distinct lobes. + +The cerebrum has a peculiar convoluted appearance, its deep folds being +separated by fissures, some of them nearly an inch in depth. + +It is composed of both white and gray matter. The former comprises the +greater part of the mass, while the latter is spread over the surface in a +layer of about ⅛ of an inch thick. The gray matter is the portion having +the highest functions, and its apparent quantity is largely increased by +being formed in convolutions. + +The convolutions of the cerebrum are without doubt associated with all +those higher actions which distinguish man's life; but all the +convolutions are not of equal importance. Thus it is probable that only +the frontal part of the brain is the intellectual region, while certain +convolutions are devoted to the service of the senses. + +The cerebrum is the chief seat of the sensations, the intellect, the will, +and the emotions. A study of cerebral injuries and diseases, and +experiments upon the lower animals, prove that the hemispheres, and more +especially the gray matter, are connected with mental states. The +convolutions in the human brain are more prominent than in that of the +higher animals, most nearly allied to man, although some species of +animals, not especially intelligent, have marked cerebral convolutions. +The higher races of men have more marked convolutions than those less +civilized. + +A view of the under surface of the brain, which rests on the floor of the +skull, shows the origin of important nerves, called the cranial +nerves, the cerebellum, the structure connecting the optic +nerves (optic commissure), the bridge of nervous matter (pons +Varolii) connecting the two hemispheres of the cerebellum, and lastly +numerous and well-marked convolutions. + +268. The Cerebellum. The cerebellum, or lesser brain, lies in +the back of the cranium, and is covered over in man by the posterior lobe +of the cerebrum. It is, at it were, astride of the back of the +cerebro-spinal axis, and consists of two hemispheres joined by a central +mass. On its under surface is a depression which receives the medulla +oblongata. The cerebellum is separated from the cerebrum by a +horizontal partition of membrane, a portion of the dura mater. In some +animals, as in the cat, this partition is partly bone. + +The cerebellum is connected with other parts of the nervous system by +strands of white matter on each side, radiating from the center and +divided into numerous branches. Around these branches the gray matter is +arranged in a beautiful manner, suggesting the leaves of a tree: hence its +name, arbor vitæ, or the tree of life. + +The functions of the cerebellum are not certainly known. It appears to +influence the muscles of the body so as to regulate their movements; that +is, it serves to bring the various muscular movements into harmonious +action. The mechanism by which it does this has not yet been clearly +explained. In an animal from which the cerebellum has been removed, the +functions of life do not appear to be destroyed, but all power of either +walking or flying straight is lost. + +[Illustration: Fig. 115.--A Vertical Section of the Brain. + + A, frontal lobe of the cerebrum; + B, parietal lobe; + C, parieto occipital lobe with fissure between this lobe and + D, the occipital lobe; + E, cerebellum; + F, arbor vitæ; + H, pons Varolu; + K, medulla oblongata; + L, portion of lobe on the opposite side of brain. + +The white curved band above H represents the corpus callosum.] + +Disease or injury of the cerebellum usually produces blindness, +giddiness, a tendency to move backwards, a staggering, irregular gait, and +a feeling of insecurity in maintaining various positions. There is no loss +of consciousness, or other disturbance of the mental functions. + +269. The Membranes of the Brain. The brain and spinal cord are +protected by three important membranes, known as the meninges,--the +dura mater, the arachnoid, and the pia mater. + +The outer membrane, the dura mater, is much thicker and stronger than +the others, and is composed of white fibrous and elastic connective +tissue. It closely lines the inner surface of the skull, and forms a +protective covering for the brain. Folds of it pass between the several +divisions of the brain and serve to protect them. + +The arachnoid is a thin membrane which lies beneath the dura mater. +It secretes a serous fluid which keeps the inner surfaces moist. + +The pia mater is a very delicate, vascular membrane which covers the +convolutions, dips into all the fissures, and even penetrates into the +interior of the brain. It is crowded with blood-vessels, which divide and +subdivide very minutely before they penetrate the brain. The membranes of +the brain are sometimes the seat of inflammation, a serious and painful +disease, commonly known as brain fever. + +270. The Medulla Oblongata. This is the thick upper part of the +spinal cord, lying within the cavity of the skull. It is immediately under +the cerebellum, and forms the connecting link between the brain and the +spinal cord. It is about an inch and a quarter long, and from one-half to +three-fourths of an inch wide at its upper part. The medulla +oblongata consists, like the spinal cord, of columns of white fibers +and masses of gray matter, but differently arranged. The gray matter is +broken up into masses which serve as centers of origin for various nerves. +The functions of the medulla oblongata are closely connected with the +vital processes. It is a great nerve tract for transmitting sensory and +motor impressions, and also the seat of a number of centers for reflex +actions of the highest importance to life. Through the posterior part of +the medulla the sensory impressions pass, that is, impressions from below +upwards to the brain resulting in sensation or feeling. In the anterior +part of the medulla, pass the nerves for motor transmission, that is, +nerve influences from above downwards that shall result in muscular +contractions in some part of the body. + +The medulla is also the seat of a number of reflex centers connected with +the influence of the nervous system on the blood-vessels, the movements of +the heart, of respiration, and of swallowing, and on the secretion of +saliva. This spot has been called the "vital knot." In the medulla also +are centers for coughing, vomiting, swallowing, and the dilatation of the +pupil of the eye. It is also in part the deep origin of many of the +'important cranial nerves. + +[Illustration: Fig. 116.--Illustrating the General Arrangement of the +Nervous System. (Posterior view.)] + +271. The Cranial Nerves. The cranial or cerebral nerves +consist of twelve pairs of nerves which pass from the brain through +different openings in the base of the skull, and are distributed over the +head and face, also to some parts of the trunk and certain internal +organs. These nerves proceed in pairs from the corresponding parts of each +side of the brain, chiefly to the organs of smell, taste, hearing, and +sight. + +The cranial nerves are of three kinds: sensory, motor, and both +combined, _viz_., mixed. + +Distribution and Functions of the Cranial Nerves. The cranial nerves +are thus arranged in pairs: + +The first pair are the olfactory nerves, which pass down through +the ethmoid bone into the nasal cavities, and are spread over the inner +surface of the nose. They are sensory, and are the special nerves of +smell. + +The second pair are the optic nerves, which, under the name of +the _optic tracts_, run down to the base of the brain, from which an optic +nerve passes to each eyeball. These are sensory nerves, and are devoted to +sight. + +The third, fourth, and sixth pairs proceed to the muscles of the +eyes and control their movements. These are motor nerves, the movers of +the eye. + +Each of the fifth pair of nerves is in three branches, and proceeds +mainly to the face. They are called tri-facial, and are mixed nerves, +partly sensory and partly motor. The first branch is purely sensory, and +gives sensibility to the eyeball. The second gives sensibility to the +nose, gums, and cheeks. The third (mixed) gives the special sensation of +taste on the front part of the tongue, and ordinary sensation on the inner +side of the cheek, on the teeth, and also on the scalp in front of the +ear. The motor branches supply the chewing muscles. + +The seventh pair, the facial, proceed to the face, where they +spread over the facial muscles and control their movements. The +eighth pair are the auditory, or nerves of hearing, and are +distributed to the special organs of hearing. + +The next three pairs of nerves all arise from the medulla, and escape +from the cavity of the skull through the same foramen. They are sometimes +described as one pair, namely, the eighth, but it is more convenient to +consider them separately. + +The ninth pair, the glosso-pharyngeal, are partly sensory and +partly motor. Each nerve contains two roots: one a nerve of taste, which +spreads over the back part of the tongue; the other a motor nerve, which +controls the muscles engaged in swallowing. + +The tenth pair, the pneumogastric, also known as the vagus +or wandering nerves, are the longest and most complex of all the cranial +nerves. They are both motor and sensory, and are some of the most +important nerves in the body. Passing from the medulla they descend near +the œsophagus to the stomach, sending off, on their way, branches to +the throat, the larynx, the lungs, and the heart. Some of their branches +restrain the movements of the heart, others convey impressions to the +brain, which result in quickening or slowing the movements of breathing. +Other branches pass to the stomach, and convey to the brain impressions +which inform us of the condition of that organ. These are the nerves by +which we experience the feelings of pain in the stomach, hunger, nausea, +and many other vague impressions which we often associate with that organ. + +[Illustration: Fig. 117.--Anterior View of the Medulla Oblongata. + + A, chiasm of the optic nerves; + B, optic tracts; + C, motor oculi communis; + D, fifth nerve; + E, motor oculi externus; + F, facial nerve; + H, auditory nerve; + I, glosso-pharyngeal nerve; + K, pneumogastric; + L, spinal accessory; + M, cervical nerves; + N, upper extremity of spinal cord; + O, decussation of the anterior pyramids; + R, anterior pyramids of the medulla oblongata; + S, pons Varolii. +] + +The eleventh pair, the spinal accessory, are strictly motor, and +supply the muscles of the neck and the back. + +The twelfth pair, the hypoglossal, are also motor, pass to the +muscles of the tongue, and help control the delicate movements in the act +of speech. + +272. The Spinal Cord. This is a long, rod-like mass of white nerve +fibers, surrounding a central mass of gray matter. It is a continuation of +the medulla oblongata, and is lodged in the canal of the spinal column. It +extends from the base of the skull to the lower border of the first lumbar +vertebra, where it narrows off to a slender filament of gray substance. + +The spinal cord is from 16 to 18 inches long, and has about the +thickness of one's little finger, weighing about 1-1/2 ounces. Like the +brain, it is enclosed in three membranes, which in fact are the +continuation of those within the skull. They protect the delicate cord, +and convey vessels for its nourishment. The space between the two inner +membranes contains a small quantity of fluid, supporting the cord, as it +were in a water-bath. It is thus guarded against shocks. + +The cord is suspended and kept in position in the canal by delicate +ligaments at regular intervals between the inner and outer membranes. +Finally, between the canal, enclosed by its three membranes, and the bony +walls of the spinal canal, there is considerable fatty tissue, a sort of +packing material, imbedded in which are some large blood-vessels. + +273. Structure of the Spinal Cord. The arrangement of the parts of +the spinal cord is best understood by a transverse section. Two fissures, +one behind, the other in front, penetrate deeply into the cord, very +nearly dividing it into lateral halves. In the middle of the isthmus which +joins the two halves, is a very minute opening, the _central canal_ of the +cord. This tiny channel, just visible to the naked eye, is connected with +one of the openings of the medulla oblongata, and extends, as do the +anterior and posterior fissures, the entire length of the cord. + +The spinal cord, like the brain, consists of gray and white matter, but +the arrangement differs. In the brain the white matter is within, and the +gray matter is on the surface. In the cord the gray matter is arranged in +two half-moon-shaped masses, the backs of which are connected at the +central part. The white matter, consisting mainly of fibers, running for +the most part in the direction of the length of the cord, is outside of +and surrounds the gray crescents. Thus each half or side of the cord has +its own gray crescent, the horns of which point one forwards and the other +backwards, called respectively the anterior and posterior cornua or horns. + +It will also be seen that the white substance itself, in each half of the +cord, is divided by the horns of the gray matter and by fibers passing +from them into three parts, which are known as the anterior, +posterior, and lateral columns. + + Experiment 130. Procure at the market an uninjured piece of the + spinal cord from the loin of mutton or the sirloin or the rib of beef. + After noting its general character while fresh, put it to soak in dilute + alcohol, until it is sufficiently hard to be cut in sections. + +274. The Spinal Nerves. From the gray matter on each side of the +spinal cord 31 spinal nerves are given off and distributed chiefly to +the muscles and the skin. They pass out at regular intervals on each side +of the canal, by small openings between the vertebræ. Having escaped from +the spine, they pass backwards and forwards, ramifying in the soft parts +of the body. The first pair pass out between the skull and the atlas, the +next between the atlas and the axis, and so on down the canal. The eighth +pair, called _cervical_, pass out in the region of the neck; twelve, +called _dorsal_, in the region of the ribs; five are _lumbar_, and five +_sacral_, while the last pair leave the cord near the coccyx. + +Each spinal nerve has two roots, one from the anterior, the other +from the posterior portion of the cord. These unite and run side by +side, forming as they pass between the vertebræ one silvery thread, or +nerve trunk. Although bound up in one bundle, the nerve fibers of the two +roots remain quite distinct, and perform two entirely different functions. + +After leaving the spinal cord, each nerve divides again and again into +finer and finer threads. These minute branches are distributed through the +muscles, and terminate on the surface of the body. The anterior roots +become motor nerves, their branches being distributed to certain +muscles of the body, to control their movements. The posterior roots +develop into sensory nerves, their branches being distributed through +the skin and over the surface of the body to become nerves of touch. In +brief, the spinal nerves divide and subdivide, to reach with their twigs +all parts of the body, and provide every tissue with a nerve center, a +station from which messages may be sent to the brain. + +[Illustration: Fig. 118.--Side View of the Spinal Cord. (Showing the +fissures and columns.) + + A, anterior median fissure; + B, posterior median fissure; + C, anterior lateral fissure; + D, posterior lateral fissure; + E, lateral column; + F, anterior column; + G, posterior column; + H, posterior median column; + K, anterior root; + L, posterior root; + M, ganglion of + N, a spinal nerve. +] + +275. The Functions of the Spinal Nerves. The messages which pass +along the spinal nerves to and from the brain are transmitted mostly +through the gray matter of the cord, but some pass along the white matter +on the outer part. As in the brain, however, all the active powers of the +cord are confined to the gray matter. The spinal nerves themselves have +nothing to do with sensation or will. They are merely conductors to carry +messages to and fro. They neither issue commands nor feel a sensation. +Hence, they consist entirely of white matter. + +276. Functions of the Spinal Cord. The spinal cord is the principal +channel through which all impulses from the trunk and extremities pass to +the brain, and all impulses to the trunk and extremities pass from the +brain. That is, the spinal cord receives from various parts of the body +by means of its sensory nerves certain impressions, and conveys them to +the brain, where they are interpreted. + +The cord also transmits by means of its motor nerves the commands of the +brain to the voluntary muscles, and so causes movement. Thus, when the +cord is divided at any point, compressed, as by a tumor or broken bone, or +disorganized by disease, the result is a complete loss of sensation and +voluntary movement below the point of injury. If by accident a man has his +spinal cord injured at some point, he finds he has lost all sensation and +power of motion below that spot. The impulse to movement started in his +brain by the will does not reach the muscles he wishes to move, because +traveling _down_ the spinal cord, it cannot pass the seat of injury. + +So the impression produced by pricking the leg with a pin, which, before +pain can be felt, must travel up the spinal cord to the brain, cannot +reach the brain because the injury obstructs the path. The telegraph wire +has been cut, and the current can no longer pass. + +277. The Spinal Cord as a Conductor of Impulses. The identity in +structure of the spinal nerves, whether motor or sensory, and the vast +number of nerves in the cord make it impossible to trace for any distance +with the eye, even aided by the microscope and the most skillful +dissection, the course of nerve fibers. The paths by which the motor +impulses travel down the cord are fairly well known. These impulses +originate in the brain, and passing down keep to the same side of the +cord, and go out by nerves to the same side of the body. + +The sensory impulses, however, soon after they enter the cord by the +nerve of one side, cross in the cord to the opposite side, up which they +travel to the brain. Thus the destruction of one lateral half of the cord +causes paralysis of motion on the _same side_ as the injury, but loss of +sensation on the _opposite side_, because the posterior portion destroyed +consists of fibers which have crossed from the opposite side. + +Experiment proves that if both roots of a spinal nerve be cut, all those +parts of the body to which they send branches become paralyzed, and have +neither sense of pain nor power of voluntary movement. The parts might +even be cut or burned without pain. It is precisely like cutting a +telegraph wire and stopping the current. + +[Illustration: Fig. 119.--The Base of the Brain. + + A, anterior lobe of the cerebrum; + B, olfactory nerve; + C, sphenoid portion of the posterior lobe; + D, optic chiasm; + E, optic tract; + F, abducens; + H, M, hemispheres of the cerebellum; + K, occipital portion of the occipital lobe; + L, fissure separating the hemispheres; + N, medulla oblongata; + O, olivary body; + P, antenor pyramids; + R, pons Valoru; + S, section of olfactory nerve, with the trunk removed to show sulcus in + which it is lodged; + T, anterior extremity of median fissure +] + +Experiment also proves that if only the posterior root of a spinal nerve +be cut, all sensation is lost in the parts to which the nerve passes, but +the power of moving these parts is retained. But if the anterior root +alone be divided, all power of motion in the parts supplied by that nerve +is lost, but sensation remains. From these and many other experiments, it +is evident that those fibers of a nerve which are derived from the +anterior root are motor, and those from the posterior root sensory, +fibers. Impulses sent _from_ the brain and spinal cord to muscles will, +therefore, pass along the anterior roots through those fibers of the +nerves which are derived from these (motor) roots. On the other hand, +impressions or sensations passing _to_ the brain will enter the spinal +cord and reach the brain through the posterior or sensory roots. + +278. The Spinal Cord as a Reflex Center. Besides this function of the +spinal cord as a great nerve conductor to carry sensations to the brain, +and bring back its orders, it is also an independent center for what +is called reflex action. By means of its sensory nerves it receives +impressions from certain parts of the body, and on its own authority sends +back instructions to the muscles by its motor nerves, without consulting +the brain. This constitutes reflex action, so called because the +impulse sent to the spinal cord by certain sensory nerves is at once +reflected or sent back as a motor impulse to the muscles. + +This reflex action is a most important function of the spinal cord. This +power is possessed only by the gray matter of the cord, the white +substance being simply a conductor. + +The cells of gray matter are found all along the cord, but are grouped +together in certain parts, notably in the cervical and lumbar regions. The +cells of the anterior horns are in relation with the muscles by means of +nerve fibers, and are also brought into connection with the skin and other +sensory surfaces, by means of nerve fibers running in the posterior part +of the cord. Thus there is established in the spinal cord, without +reference to the brain at all, a reflex mechanism. + +279. Reflex Centers. For the purpose of illustration, we might +consider the body as made up of so many segments piled one on another, +each segment presided over by a similar segment of spinal cord. Each +bodily segment would have sensory and motor nerves corresponding to its +connection with the spinal cord. The group of cells in each spinal segment +is intimately connected with the cells of the segments above and below. +Thus an impression reaching the cells of one spinal segment might be so +strong as to overflow into the cells of other segments, and thus cause +other parts of the body to be affected. + +Take as an example the case of a child who has eaten improper food, which +irritates its bowels. Sensory nerves of the bowels are disturbed, and +powerful impressions are carried up to a center in the spinal cord. These +impressions may now overflow into other centers, from which spasmodic +discharges of nerve energy may be liberated, which passing to the muscles, +throw them into violent and spasmodic contraction. In other words, the +child has a fit, or convulsion. All this disturbance being the result of +reflex action (the spasmodic motions being quite involuntary, as the brain +takes no part in them), the child meanwhile is, of course, entirely +unconscious and, however it may seem to be distressed, really suffers no +pain. + +Scattered along the entire length of the spinal cord, especially in the +upper part, are groups of nerve cells which preside over certain specific +functions of animal life; that is, definite collections of cells which +control definite functions. Thus there are certain centers for maintaining +the action of the heart, and the movements of breathing; and low down in +the cord, in the lumbar regions, are centers for the control of the +various abdominal organs. + +Numerous other reflex centers are described by physiologists, but enough +has been said to emphasize the great importance of the spinal cord as an +independent nerve center, besides its function as a conductor of +nervous impulses to and from the brain. + +280. The Brain as a Reflex Center. The brain, as we have just +stated, is the seat of consciousness and intelligence. It is also the seat +of many reflex, automatic, and coordinating centers. These give rise to +certain reflex actions which are as entirely independent of consciousness +as are those of the spinal cord. These acts take place independently of +the will, and often without the consciousness of the individual. Thus, a +sudden flash of light causes the eyes to blink, as the result of reflex +action. The optic nerves serve as the sensory, and the facial nerves as +the motor, conductors. The sudden start of the whole body at some loud +noise, the instinctive dodging a threatened blow, and the springing back +from sudden danger, are the results of reflex action. The result ensues in +these and in many other instances, without the consciousness of the +individual, and indeed beyond his power of control. + +281. The Importance of Reflex Action. Reflex action is thus a +marvelous provision of nature for our comfort, health, and safety. Its +vast influence is not realized, as its numberless acts are so continually +going on without our knowledge. In fact, the greater part of nerve power +is expended to produce reflex action. The brain is thus relieved of a vast +amount of work. It would be impossible for the brain to serve as a +"thinking center" to control every act of our daily life. If we had to +plan and to will every heart-beat or every respiration, the struggle for +life would soon be given up. + +The fact that the gray cells of the spinal cord can originate a countless +number of reflex and automatic activities is not only of great importance +in protecting the body from injury, but increases vastly the range of the +activities of our daily life. + +Even walking, riding the bicycle, playing on a piano, and numberless other +such acts may be reflex movements. To learn how, requires, of course, the +action of the brain, but with frequent repetition the muscles become so +accustomed to certain successive movements, that they are continued by +the cord without the control of the brain. Thus we may acquire a sort of +artificial reflex action, which in time becomes in a way a part of our +organization, and is carried on without will power or even consciousness. + +So, while the hands are busily doing one thing, the brain can be intently +thinking of another. In fact, any attempt to control reflex action is more +apt to hinder than to help. In coming rapidly down stairs, the descent +will be made with ease and safety if the spinal cord is allowed entire +charge of the act, but the chances of stumbling or of tripping are very +much increased if each step be taken as the result of the will power. The +reflex action of the cord may be diminished, or inhibited as it is called, +but this power is limited. Thus, we can by an effort of the will stop +breathing for a certain time, but beyond that the reflex mechanism +overcomes our will and we could not, if we would, commit suicide by +holding our breath. When we are asleep, if the palm of the hand be +tickled, it closes; when we are awake we can prevent it. + +[Illustration: Fig. 120.--Dr. Waller's Diagrammatic Illustration of the +Reflex Process. + +From the sentient surface (1) an afferent impulse passes along (2) to the +posterior root of the spinal cord, the nerve fibers of the posterior root +ending in minute filaments among the small cells of this part of the cord +(3). In some unknown way this impulse passes across the gray part of the +cord to the large cells of the anterior root (5), the cells of this part +being connected by their axis-cylinder with the efferent fibers (6). These +convey the stimulus to the fibers of the muscle (7), which accordingly +contract. Where the brain is concerned in the action the circuit is longer +through S and M.] + + Experiment 131. _To illustrate reflex action by what is called + knee-jerk._ Sit on a chair, and cross the right leg over the left one. + With the tips of the fingers or the back of a book, strike the right + ligamentum patellæ. The right leg will be raised and thrown forward with + a jerk, owing to the contraction of the quadriceps muscles. An + appreciable time elapses between the striking of the tendon and the + jerk. The presence or absence of the knee-jerk may be a most significant + symptom to the physician. + +282. The Sympathetic System. Running along each side of the spine, +from the base of the skull to the coccyx, is a chain of nerve knots, or +ganglia. These ganglia, twenty-four on each side, and their branches +form the sympathetic system, as distinguished from the cerebro-spinal +system consisting of the brain and spinal cord and the nerves springing +from them. The ganglia of the sympathetic system are connected with each +other and with the sensory roots of the spinal nerves by a network of gray +nerve fibers. + +At the upper end the chain of each side passes up into the cranium and is +closely connected with the cranial nerves. In the neck, branches pass to +the lungs and the heart. From the ganglia in the chest three nerves form a +complicated network of fibers, from which branches pass to the stomach, +the liver, the intestines, the kidneys, and other abdominal organs. A +similar network of fibers is situated lower down in the pelvis, from which +branches are distributed to the pelvic organs. At the coccyx the two +chains unite into a single ganglion. + +Thus, in general, the sympathetic system, while intimately connected with +the cerebro-spinal, forms a close network of nerves which specially +accompany the minute blood-vessels, and are distributed to the muscles of +the heart, the lungs, the stomach, the liver, the intestines, and the +kidneys--that is, the hollow organs of the body. + +283. The Functions of the Sympathetic System. This system exercises a +superintending influence over the greater part of the internal organs of +the body, controlling to a certain extent the functions of digestion, +nutrition, circulation, and respiration. The influence thus +especially connected with the processes of organic life is generally +different from, or even opposed to, that conveyed to the same organs by +fibers running in the spinal or cranial nerves. These impulses are beyond +the control of the will. + +[Illustration: Fig. 121.--The Cervical and Thoracic Portion of the +Sympathetic Nerve and its Main Branches. + + A, right pneumogastric; + B, spinal accessory; + C, glosso-pharyngeal; + D, right bronchus; + E, right branch of pulmonary artery; + F, one of the intercostal nerves; + H, great splanchnic nerve; + K, solar plexus; + L, left pneumogastric; + M, stomach branches of right pneumogastric; + N, right ventricle; + O, right auricle; + P, trunk of pulmonary artery; + R, aorta; S, cardiac nerves; + T, recurrent laryngeal nerve; + U, superior laryngeal nerve; + V, submaxillary ganglion; + W, lingual branch of the 5th nerve; + X, ophthalmic ganglion; + Y, motor oculi externus. +] + +Hence, all these actions of the internal organs just mentioned that are +necessary to the maintenance of the animal life, and of the harmony which +must exist between them, are controlled by the sympathetic system. But for +this control, the heart would stop beating during sleep, digestion would +cease, and breathing would be suspended. Gentle irritation of these +nerves, induced by contact of food in the stomach, causes that organ to +begin the churning motion needed for digestion. Various mental emotions +also have a reflex action upon the sympathetic system. Thus, terror +dilates the pupils, fear acts upon the nerves of the small blood-vessels +of the face to produce pallor, and the sight of an accident, or even the +emotions produced by hearing of one, may excite nausea and vomiting. + +The control of the blood-vessels, as has been stated (sec. 195), is +one of the special functions of the sympathetic system. Through the nerves +distributed to the muscular coats of the arteries, the caliber of these +vessels can be varied, so that at one moment they permit a large quantity +of blood to pass, and at another will contract so as to diminish the +supply. This, too, is beyond the control of the will, and is brought about +by the vaso-motor nerves of the sympathetic system through a reflex +arrangement, the center for which is the medulla oblongata. + +284. Need of Rest. The life of the body, as has been emphasized in +the preceding chapters, is subject to constant waste going on every +moment, from the first breath of infancy to the last hour of old age. We +should speedily exhaust our life from this continual loss, but for its +constant renewal with fresh material. This exhaustion of life is increased +by exertion, and the process of repair is vastly promoted by rest. Thus, +while exercise is a duty, rest is equally imperative. + +The eye, when exactingly used in fine work, should have frequent intervals +of rest in a few moments of darkness by closing the lids. The brain, when +urged by strenuous study, should have occasional seasons of rest by a +dash of cold water upon the forehead, and a brief walk with slow and deep +inspirations of fresh air. The muscles, long cramped in a painful +attitude, should be rested as often as may be, by change of posture or by +a few steps around the room. + +It is not entirely the amount of work done, but the continuity of +strain that wears upon the body. Even a brief rest interrupts this +strain; it unclogs the wheels of action. Our bodies are not designed for +continuous toil. An alternation of labor and rest diminishes the waste of +life. The benign process of repair cannot go on, to any extent, during +strenuous labor, but by interposing frequent though brief periods of rest, +we lessen the amount of exhaustion, refresh the jaded nerves, and the +remaining labor is more easily endured. + +285. Benefits of Rest. There is too little repose in our American +nature and in our modes of life. A sense of fatigue is the mute appeal of +the body for a brief respite from labor, and the appeal should, if +possible, be heeded. If this appeal be not met, the future exertion +exhausts far more than if the body had been even slightly refreshed. If +the appeal be met, the brief mid-labor rest eases the friction of toil, +and the remaining labor is more easily borne. The feeling that a +five-minute rest is so much time lost is quite an error. It is a gain of +physical strength, of mental vigor, and of the total amount of work done. + +The merchant burdened with the cares of business life, the soldier on the +long march, the ambitious student over-anxious to win success in his +studies, the housewife wearied with her many hours of exacting toil, each +would make the task lighter, and would get through it with less loss of +vital force, by occasionally devoting a few minutes to absolute rest in +entire relaxation of the strained muscles and overtaxed nerves. + +286. The Sabbath as a Day of Physiological Rest. The divine +institution of a Sabbath of rest, one day in seven, is based upon the +highest needs of our nature. Rest, to be most effective, should alternate +in brief periods with labor. + +It is sound physiology, as well as good morals and manners, to cease +from the usual routine of six days of mental or physical work, and rest +both the mind and the body on the seventh. Those who have succeeded best +in what they have undertaken, and who have enjoyed sound health during a +long and useful life, have studiously lived up to the mandates of this +great physiological law. It is by no means certain that the tendency +nowadays to devote the Sabbath to long trips on the bicycle, tiresome +excursions by land and sea, and sight-seeing generally, affords that real +rest from a physiological point of view which nature demands after six +days of well-directed manual or mental labor. + +287. The Significance of Sleep as a Periodical Rest. Of the chief +characteristics of all living beings none is so significant as their +periodicity. Plants as well as animals exhibit this periodic +character. Thus plants have their annual as well as daily periods of +activity and inactivity. Hibernating animals pass the winter in a +condition of unconsciousness only to have their functions of activity +restored in early spring. Human beings also present many instances of a +periodic character, many of which have been mentioned in the preceding +pages. Thus we have learned that the heart has its regular alternating +periods of work and rest. After every expiration from the lungs there is a +pause before the next inspiration begins. + +Now sleep is just another manifestation of this periodic and +physiological rest by which Nature refreshes us. It is during the periods +of sleep that the energy expended in the activities of the waking hours is +mainly renewed. In our waking moments the mind is kept incessantly active +by the demands made on it through the senses. There is a never-ceasing +expenditure of energy and a consequent waste which must be repaired. A +time soon comes when the brain cells fail to respond to the demand, and +sleep must supervene. However resolutely we may resist this demand, +Nature, in her relentless way, puts us to sleep, no matter what objects +are brought before the mind with a view to retain its attention.[41] + +288. Effect of Sleep upon the Bodily Functions. In all the higher +animals, the central nervous system enters once at least in the +twenty-four hours into the condition of rest which we call sleep. +Inasmuch as the most important modifications of this function are observed +in connection with the cerebro-spinal system, a brief consideration of the +subject is properly studied in this chapter. In Chapter IV. we learned +that repose was as necessary as exercise to maintain muscular vigor. So +after prolonged mental exertion, or in fact any effort which involves an +expenditure of what is often called nerve-force, sleep becomes a +necessity. The need of such a rest is self-evident, and the loss of it is +a common cause of the impairment of health. While we are awake and active, +the waste of the body exceeds the repair; but when asleep, the waste is +diminished, and the cells are more actively rebuilding the structure for +to-morrow's labor. The organic functions, such as are under the direct +control of the sympathetic nervous system,--circulation, respiration, and +digestion,--are diminished in activity during sleep. The pulsations of the +heart and the respiratory movements are less frequent, and the +circulation is slower. The bodily temperature is reduced, and the cerebral +circulation is diminished. The eyes are turned upward and inward, and the +pupils are contracted. + +The senses do not all fall to sleep at once, but drop off successively: +first the sight, then the smell, the taste, the hearing and lastly the +touch. The sleep ended, they awake in an inverse order, touch, hearing, +taste, smell, and sight. + +289. The Amount of Sleep Required. No precise rule can be laid down +concerning the amount of sleep required. It varies with age, occupation, +temperament, and climate to a certain extent. An infant whose main +business it is to grow spends the greater part of its time in sound sleep. +Adults of average age who work hard with their hands or brain, under +perfectly normal physiological conditions, usually require at least eight +hours of sleep. Some need less, but few require more. Personal +peculiarities, and perhaps habit to a great extent, exert a marked +influence. Some of the greatest men, as Napoleon I., have been very +sparing sleepers. Throughout his long and active life, Frederick the Great +never slept more than five or six hours in the twenty-four. On the other +hand, some of the busiest brain-workers who lived to old age, as William +Cullen Bryant and Henry Ward Beecher, required and took care to secure at +least eight or nine hours of sound sleep every night. + +In old age, less sleep is usually required than in adult life, while the +aged may pass much of their time in sleep. In fact, each person learns by +experience how much sleep is necessary. There is no one thing which more +unfits one for prolonged mental or physical effort than the loss of +natural rest. + +290. Practical Rules about Sleep. Children should not be played with +boisterously just before the bedtime hour, nor their minds excited with +weird goblin stories, or a long time may pass before the wide-open eyes +and agitated nerves become composed to slumber. Disturbed or insufficient +sleep is a potent factor towards producing a fretful, irritable child. + +At all ages the last hour before sleep should, if possible, be spent +quietly, to smooth the way towards sound and refreshing rest. The sleep +induced by medicine is very often troubled and unsatisfactory. Medicines +of this sort should not be taken except on the advice of a physician. + +While a hearty meal should not usually be taken just before bedtime, it is +not well to go to bed with a sense of positive faintness and hunger. +Rather, one should take a very light lunch of quite simple food as a +support for the next eight hours. + +[Illustration: Fig. 122.--Trunk of the Left Pneumogastric. + +(Showing its distribution by its branches and ganglia to the larynx, +pharynx, heart, lungs, and other parts.)] + +It is better, as a rule, not to engage in severe study during the hours +just before bedtime. Neither body nor mind being at its best after the +fatigues of the day, study at that time wears upon the system more, and +the progress is less than at earlier hours. One hour of morning or day +study is worth a much longer time late at night. It is, therefore, an +economy both of time and of nerve force to use the day hours and the early +evening for study. + +The so-called "cat naps" should never be made to serve as a substitute for +a full night's sleep. They are largely a matter of habit, and are +detrimental to some as well as beneficial to others. Late hours are +usually associated with exposure, excitement, and various other drains +upon the nerve force, and hence are injurious. + +It is better to sleep on one or other side than on the back. The head +should be somewhat raised, and a mattress is better than a feather bed. +The bedclothes should be sufficient, but not too heavy. Light tends to +prevent sleep, as do loud or abrupt sounds, but monotonous sounds aid it. + +291. Alcohol and the Brain. The unfortunate effects which alcoholic +drinks produce upon the brain and nervous system differ from the +destructive results upon other parts of the body in this respect, that +elsewhere the consequences are usually both less speedy and less obvious. +The stomach, the liver, and even the heart may endure for a while the +trespass of the narcotic poison, and not betray the invasion. But the +nervous system cannot, like them, suffer in silence. + +In the other parts of the body the victim may (to a certain extent) +conceal from others the suffering of which he himself is painfully +conscious. But the tortured brain instantly reveals the calamity and the +shame, while the only one who may not fully realize it is the victim +himself. Besides this, the injuries inflicted upon other organs affect +only the body, but here they drag down the mind, ruin the morals, and +destroy the character. + +The brain is indeed the most important organ of the body, as it presides +over all the others. It is the lofty seat of power and authority. Here the +king is on his throne. But if, by this malignant adversary, the king +himself be dethroned, his whole empire falls to ruins. + +292. How Alcohol Injures the Brain. The brain, the nerve centers, +and the nerves are all made up of nerve pulp, the softest and most +delicate tissue in the whole bodily structure. Wherever this fragile +material occurs in our bodies,--in the skull, the spine, the trunk, or the +limbs,--the all-wise Architect has carefully protected it from violence, +for a rough touch would injure it, or even tender pressure would disturb +its function. + +It is a further indication of the supreme importance of the brain, that +about one-fifth of the entire blood of the body is furnished to it. +Manifestly, then, this vital organ must be tenderly cared for. It must +indeed be well nourished, and therefore the blood sent to it must be +highly nutrient, capable of supplying oxygen freely. This condition is +essential to successful brain action. But intoxicants bring to it blood +surcharged with a poisonous liquid, and bearing only a limited supply of +oxygen. + +Another condition of a healthy brain is that the supply of blood to it +shall be equable and uniform. But under the influence of strong drink, the +blood pours into the paralyzed arteries a surging tide that floods the +head, and hinders and may destroy the use of the brain and the senses. +Still another requirement is that whatever is introduced into the cerebral +tissues, having first passed through the stomach walls and thence into the +blood, shall be bland, not irritating. But in the brain of the inebriate +are found not only the distinct odor but the actual presence of alcohol. +Thus we plainly see how all these three vital conditions of a healthy +brain are grossly violated by the use of intoxicants. + + "I think there is a great deal of injury being done by the use of + alcohol in what is supposed by the consumer to be a most moderate + quantity, to persons who are not in the least intemperate, and to people + supposed to be fairly well. It leads to degeneration of the tissues; it + damages the health; it injures the intellect. Short of drunkenness, that + is, in those effects of it which stop short of drunkenness, I should say + from my experience that alcohol is the most destructive agent we are + aware of in this country."--Sir William Gull, the most eminent English + physician of our time. + +293. Why the Brain Suffers from the Alcoholic Habit. We do not find +that the alcoholic habit has produced in the brain the same coarse +injuries that we see in other organs, as in the stomach, the liver, or the +heart. Nor should we expect to find them; for so delicate and so sensitive +is the structure of this organ, that a very slight injury here goes a +great way,--a disturbance may be overwhelming to the brain that would be +only a trifle to some of the less delicate organs. + +Alcohol has different degrees of affinity for different organs of the +body, but much the strongest for the cerebral tissues. Therefore the brain +feels more keenly the presence of alcohol than does any other organ. +Almost the moment that the poison is brought into the stomach, the nerves +send up the alarm that an invading foe has come. At once there follows a +shock to the brain, and very soon its paralyzed blood-vessels are +distended with the rush of blood. This first effect is, in a certain +sense, exhilarating, and from this arousing influence alcohol has been +erroneously considered a stimulant; but the falsity of this view is +pointed out elsewhere in this book. + +294. Alcohol, the Enemy of Brain Work. The healthy brain contains a +larger proportion of water than does any other organ. Now alcohol, with +its intense affinity for water, absorbs it from the brain, and thus +condenses and hardens its structure. One of the important elements of the +brain is its albumen; this also is contracted by alcohol. The nerve cells +and fibers gradually become shriveled and their activity is lowered, the +elasticity of the arteries is diminished, the membranes enveloping the +brain are thickened, and thus all proper brain nutrition is impaired. The +entire organ is slowly hardened, and becomes unfitted for the proper +performance of its delicate duties. In brief, alcohol in any and every +form is the enemy of successful and long-continued brain work. + +[Illustration: Fig. 123.--Nerve Trunks of the Right Arm.] + +295. Other Physical Results of Intoxicants. What are some of the +physical results observed? First, we note the failure of the vaso-motor +nerves to maintain the proper tone of the blood-vessels, as in the turgid +face and the congested cornea of the eye. Again, we observe the loss of +muscular control, as is shown by the drop of the lower lip, the thickened +speech, and the wandering eye. The spinal cord, too, is often affected and +becomes unable to respond to the demand for reflex action, as appears from +the trembling hands, the staggering legs, the swaying body, and the +general muscular uncertainty. All these are varied results of the +temporary paralysis of the great nerve centers. + +Besides, the sensibility of the nerves is deadened. The inebriate may +seize a hot iron and hardly know it, or wound his hand painfully and never +feel the injury. The numbness is not of the skin, but of the brain, for +the drunken man may be frozen or burned to death without pain. The senses, +too, are invaded and dulled. Double vision is produced, the eyes not being +so controlled as to bring the image upon corresponding points of the +retina. + +296. Diseases Produced by Alcohol. The diseases that follow in the +train of the alcoholic habit are numerous and fatal. It lays its +paralyzing hand upon the brain itself, and soon permanently destroys the +integrity of its functions. In some the paralysis is local only, perhaps +in one of the limbs, or on one side of the body; in others there is a +general muscular failure. The vitality of the nerve centers is so +thoroughly impaired that general paralysis often ensues. A condition of +insomnia, or sleeplessness, often follows, or when sleep does come, it is +in fragments, and is far from refreshing to the jaded body. + +In time follows another and a terrible disease known as _delirium +tremens_; and this may occur in those who claim to be only moderate +drinkers, rarely if ever intoxicated. It accompanies an utter breakdown of +the nervous system. Here reason is for the time dethroned, while at some +times wild and frantic, or at others a low, mumbling delirium occurs, with +a marked trembling from terror and exhaustion. + +There is still another depth of ruin in this downward course, and that is +_insanity_. In fact, every instance of complete intoxication is a case of +temporary insanity, that is, of mental unsoundness with loss of +self-control. Permanent insanity may be one of the last results of +intemperance. Alcoholism sends to our insane asylums a large proportion of +their inmates, as ample records testify. + +297. Mental and Moral Ruin Caused by Alcoholism. Alcoholism, the evil +prince of destroyers, also hastens to lay waste man's mental and moral +nature. Just as the inebriate's senses, sight, hearing, and touch, fail to +report correctly of the outer world, so the mind fails to preside properly +over the inner realm. Mental perceptions are dulled. The stupefied +faculties can hardly be aroused by any appeal. Memory fails. Thus the man +is disqualified for any responsible labor. No railroad company, no +mercantile house, will employ any one addicted to drinking. The mind of +the drunkard is unable to retain a single chain of thought, but gropes +about with idle questionings. The intellect is debased. Judgment is +impossible, for the unstable mind cannot think, compare, or decide. + +The once active power of the will is prostrate, and the victim can no +longer resist the feeblest impulse of temptation. The grand faculty of +self-control is lost; and as a result, the baser instincts of our lower +nature are now uppermost; greed and appetite rule unrestrained. + +But the moral power is also dragged down to the lowest depths. All the +finer sensibilities of character are deadened; all pride of personal +appearance, all nice self-respect and proper regard for the good opinion +of others, every sense of decorum, and at last every pretence of decency. +Dignity of behavior yields to clownish silliness, and the person lately +respected is now an object of pity and loathing. The great central +convictions of right and wrong now find no place in his nature; conscience +is quenched, dishonesty prevails. This is true both as to the solemn +promises, which prove mere idle tales, and also as to property, for he +resorts to any form of fraud or theft to feed the consuming craving for +more drink. + +298. Evil Results of Alcoholism Inherited. But the calamity does not +end with the offender. It may follow down the family line, and fasten +itself upon the unoffending children. These often inherit the craving for +drink, with the enfeebled nature that cannot resist the craving, and so +are almost inevitably doomed to follow the appalling career of their +parents before them. + +Nor does this cruel taint stop with the children. Even their descendants +are often prone to become perverse. As one example, careful statistics of +a large number of families, more than two hundred descended from +drunkards, show that a very large portion of them gave undoubted proof of +well-marked degeneration. This was plain in the unusual prevalence of +infant mortality, convulsions, epilepsy, hysteria, fatal brain diseases, +and actual imbecility.[42] + +It is found that the long-continued habitual user of alcoholic drinks, the +man who is never intoxicated, but who will tell you that he has drunk +whiskey all his life without being harmed by it, is more likely to +transmit the evil effects to his children than the man who has occasional +drunken outbreaks with intervals of perfect sobriety between. By his +frequently repeated small drams he keeps his tissues constantly +"alcoholized" to such an extent that they are seldom free from some of the +more or less serious consequences. His children are born with organisms +which have received a certain bias from which they cannot escape; they are +freighted with some heredity, or predisposition to particular forms of +degeneration, to some morbid tendency, to an enfeebled constitution, to +various defective conditions of mind and body. Let the children of such a +man attempt to imitate the drinking habits of the father and they quickly +show the effects. Moderate drinking brings them down. + +Among other consequences of an alcoholic inheritance which have been +traced by careful observers are: Morbid changes in the nerve centers, +consisting of inflammatory lesions, which vary according to the age in +which they occur; alcoholic insanity; congenital malformations; and a much +higher infant death rate, owing to lack of vitality, than among the +children of normal parents. + +Where the alcoholic inheritance does not manifest itself in some definite +disease or disorder, it can still be traced in the limitations to be found +in the drinking man's descendants. They seem to reach a level from which +they cannot ascend, and where from slight causes they deteriorate. The +parents, by alcoholic poisoning, have lowered the race stock of vitality +beyond the power of ascent or possibility to rise above or overcome the +downward tendency. + +Of course these effects of alcoholics differ widely according to the +degree of intoxication. Yet, we must not forget that the real nature of +inebriety is always the same. The end differs from the beginning only in +degree. He who would avoid a life of sorrow, disgrace, and shame must +carefully shun the very first glass of intoxicants. + +299. Opium. Opium is a gum-like substance, the dried juice of the +unripe capsule of the poppy. The head of the plant is slit with fine +incisions, and the exuding white juice is collected. When it thickens and +is moulded in mass, it becomes dark with exposure. _Morphine_, a white +powder, is a very condensed form of opiate; _laudanum_, an alcoholic +solution of marked strength; and _paregoric_, a diluted and flavored form +of alcoholic tincture. + +300. Poisonous Effects of Opium. Some persons are drawn into the use +of opium, solely for its narcotic and intoxicating influence. +Every early consent to its use involves a lurking pledge to repeat the +poison, till soon strong cords of the intoxicant appetite bind the now +yielding victim. + +Opium thus used lays its benumbing hand upon the brain, the mind is +befogged, thought and reasoning are impossible. The secretions of the +stomach are suspended, digestion is notably impaired, and the gastric +nerves are so deadened that the body is rendered unconscious of its needs. + +The moral sense is extinguished, persons once honest resort to fraud and +theft, if need be, to obtain the drug, till at last health, character, and +life itself all become a pitiful wreck. + +301. The Use of Opium in Patent Medicines. Some forms of this drug +are found in nearly all the various patent medicines so freely sold as a +cure-all for every mortal disease. Opiates are an ingredient in different +forms and proportions in almost all the soothing-syrups, cough medicines, +cholera mixtures, pain cures, and consumption remedies, so widely and +unwisely used. Many deaths occur from the use of these opiates, which at +first seem indeed to bring relief, but really only smother the prominent +symptoms, while the disease goes on unchecked, and at last proves fatal. + +These patent medicines may appear to help one person and be fraught with +danger to the next, so widely different are the effects of opiates upon +different ages and temperaments. But it is upon children that these fatal +results oftenest fall. Beyond doubt, thousands of children have been +soothed and soothed out of existence.[43] + +302. The Victim of the Opium Habit. Occasionally persons convalescing +from serious sickness where anodynes were taken, unwisely cling to them +long after recovery. Other persons, jaded with business or with worry, and +unable to sleep, unwisely resort to some narcotic mixture to procure rest. +In these and other similar cases, the use of opiates is always most +pernicious. The amount must be steadily increased to obtain the elusive +repose, and at best the phantom too often escapes. + +Even if the desired sleep is procured, it is hardly the coveted rest, but +a troubled and dreamy slumber, leaving in the morning the body quite +unrefreshed, the head aching, the mouth dry, and the stomach utterly +devoid of appetite. But far worse than even this condition is the slavish +yielding to the habit, which soon becomes a bondage in which life is shorn +of its wholesome pleasures, and existence becomes a burden. + + +303. Chloral. There are other preparations which have become +instruments of direful and often fatal injury. Chloral is a powerful +drug that has been much resorted to by unthinking persons to produce +sleep. Others, yielding to a morbid reluctance to face the problems of +life, have timidly sought shelter in artificial forgetfulness. To all such +it is a false friend. Its promises are treason. It degrades the mind, +tramples upon the morals, overpowers the will, and destroys life itself. + + +304. Cocaine, Ether, Chloroform, and Other Powerful Drugs. Another +dangerous drug is Cocaine. Ether and chloroform, those priceless +blessings to the human race if properly controlled, become instruments of +death when carelessly trifled with. Persons who have been accustomed to +inhale the vapor in slight whiffs for neuralgia or similar troubles do so +at imminent hazard, especially if lying down. They are liable to become +slowly unconscious, and so to continue the inhalation till life is ended. + +There is still another class of drugs often carelessly used, whose effect, +while less directly serious than those mentioned, is yet far from +harmless. These drugs, which have sprung into popular use since the +disease _la grippe_ began its dreaded career, include _phenacetine_, +_antipyrine_, _antifebrine_, and other similar preparations. These drugs +have been seized by the public and taken freely and carelessly for all +sorts and conditions of trouble. The random arrow may yet do serious harm. +These drugs, products of coal-oil distillation, are powerful depressants. +They lower the action of the heart and the tone of the nervous centers. +Thus the effect of their continued use is to so diminish the vigor of the +system as to aggravate the very disorder they are taken to relieve. + + +305. Effect of Tobacco on the Nervous System. That the use of tobacco +produces a pernicious effect upon the nervous system is obvious from the +indignant protest of the entire body against it when it is first used. Its +poisonous character is amply shown by the distressing prostration and +pallor, the dizziness and faintness, with extreme nausea and vomiting, +which follow its employment by a novice. + +The morbid effects of tobacco upon the nervous system of those who +habitually use it are shown in the irregular and enfeebled action of the +heart, with dizziness and muscular tremor. The character of the pulse +shows plainly the unsteady heart action, caused by partial paralysis of +the nerves controlling this organ. Old, habitual smokers often show an +irritable and nervous condition, with sleeplessness, due doubtless to lack +of proper brain nutrition. + +All these results tend to prove that tobacco is really a nerve poison, and +there is reason to suspect that the nervous breakdown of many men in +mature life is often due to the continued use of this depressing agent. +This is shown more especially in men of sedentary life and habits, as men +of active habits and out-door life, experience less of the ill effects of +tobacco. + +Few, if any, habitual users of tobacco ever themselves approve of it. They +all regret the habit, and many lament they are so enslaved to it that they +cannot throw it off. They very rarely advise any one to follow their +example. + +306. Effects of Tobacco on the Mind. With this continuously +depressing effect of tobacco upon the brain, it is little wonder that the +mind may become enfeebled and lose its capacity for study or successful +effort. This is especially true of the young. The growth and development +of the brain having been once retarded, the youthful user of tobacco +(especially the foolish cigarette-smoker) has established a permanent +drawback which may hamper him all his life. + +The young man addicted to the use of tobacco is often through its use +retarded in his career by mental languor or weakening will power, and by +mental incapacity. The keenness of mental perception is dulled, and the +ability to seize and hold an abstract thought is impaired. True, these +effects are not sharply obvious, as it would be impossible to contrast the +present condition of any one person with what it might have been. But the +comparison of large numbers conveys an instructive lesson. Scholars who +start well and give promise of a good future fail by the way. The honors +of the great schools, academies, and colleges are very largely taken by +the tobacco abstainers. This is proved by the result of repeated and +extensive comparisons of the advanced classes in a great number of +institutions in this country and in Europe. So true is this that any young +man who aspires to a noble career should bid farewell either to his +honorable ambition or to his tobacco, for the two very rarely travel +together. Consequently our military and naval academies and very many +seminaries and colleges prohibit the use of tobacco by their students. For +the same reasons the laws of many states very properly forbid the sale to +boys of tobacco, and especially of cigarettes. + + +307. Effect of Tobacco upon Character. Nor does tobacco spare the +morals. The tobacco-user is apt to manifest a selfish disregard of the +courtesies due to others. He brings to the presence of others a repulsive +breath, and clothing tainted with offensive odors. He poisons the +atmosphere that others must inhale, and disputes their rights to breathe a +pure, untainted air. The free use of tobacco by young people dulls the +acuteness of the moral senses, often leads to prevarication and deceit in +the indulgence, and is apt to draw one downward to bad associates. It is +not the speed but the direction that tells on the future character and +destiny of young men. + + + +Additional Experiments. + + Experiment 132. _To illustrate the cooperation of certain parts of + the body._ Tickle the inside of the nose with a feather. This does not + interfere with the muscles of breathing, but they come to the help of + the irritated part, and provoke sneezing to clear and protect the nose. + + Experiment 133. Pretend to aim a blow at a person's eye. Even if he + is warned beforehand, the lids will close in spite of his effort to + prevent them. + + Experiment 134. _To illustrate how sensations are referred to the + ends of the nerves_. Strike the elbow end of the ulna against anything + hard (commonly called "hitting the crazy bone") where the ulna nerve is + exposed, and the little finger and the ring finger will tingle and + become numb. + + Experiment 135. _To show that every nerve is independent of any + other._ Press two fingers closely together. Let the point of the finest + needle be carried ever so lightly across from one finger to another, and + we can easily tell just when the needle leaves one finger and touches + the other. + + Experiment 136. _To paralyze a nerve temporarily_. Throw one arm + over the sharp edge of a chair-back, bringing the inner edge of the + biceps directly over the edge of the chair. Press deep and hard for a + few minutes. The deep pressure on the nerve of the arm will put the arm + "asleep," causing numbness and tingling. The leg and foot often "get + asleep" by deep pressure on the nerves of the thigh. + + Experiment 137. Press the ulnar nerve at the elbow, the prickling + sensation is referred to the skin on the ulnar side of the hand. + + Experiment 138. Dip the elbow in ice-cold water; at first one feels + the sensation of cold, owing to the effect on the cutaneous + nerve-endings. Afterwards, when the trunk of the ulnar nerve is + affected, pain is felt in the skin of the ulnar side of the hand, where + the nerve terminates. + + + + +Chapter XI. + +The Special Senses. + + + +308. The Special Senses. In man certain special organs are set apart +the particular duty of which is to give information of the nature of the +relations which he sustains to the great world of things, and of which he +is but a mere speck. The special senses are the avenues by which we obtain +this information as to our bodily condition, the world around us, and the +manner in which it affects us. + +Animals high in the scale are affected in so many different ways, and by +so many agencies, that a subdivision of labor becomes necessary that the +sense avenues may be rigidly guarded. One person alone may be a sufficient +watch on the deck of a sloop, but an ocean steamer needs a score or more +on guard, each with his special duty and at his own post. Or the senses +are like a series of disciplined picket-guards, along the outposts of the +mind, to take note of events, and to report to headquarters any +information which may be within the range of their duty. + +Thus it is that we are provided with a number of special senses, by +means of which information is supplied regarding outward forces and +objects. These are touch, taste, smell, seeing, and hearing, to +which may be added the muscular sense and a sense of temperature. + + +309. General Sensations. The body, as we have learned, is made up of +a great number of complicated organs, each doing its own part of the +general work required for the life and vigor of the human organism. These +organs should all work in harmony for the good of the whole. We must have +some means of knowing whether this harmony is maintained, and of receiving +timely warning if any organ fails to do its particular duty. + +Such information is supplied by the common or general sensations. +Thus we have a feeling of hunger or thirst indicating the need of food, +and a feeling of discomfort when imperfectly clad, informing us of the +need of more clothing. + +To these may be added the sensation of pain, tickling, itching, and so on, +the needs of which arise from the complicated structure of the human body. +The great majority of sensations result from some stimulus or +outward agency; and yet some sensations, such as those of faintness, +restlessness, and fatigue seem to spring up within us in some mysterious +way, without any obvious cause. + +310. Essentials of a Sense Organ. Certain essentials are necessary +for a sensation. First, there is a special structure adapted to a +particular kind of influence. Thus the ear is formed specially for being +stimulated by the waves of sound, while the eye is not influenced by +sound, but responds to the action of light. These special structures are +called terminal organs. + +Again, a nerve proceeds from the special structure, which is in direct +communication with nerve cells in the brain at the region of +consciousness. This last point is important to remember, for if on +some account the impression is arrested in the connecting nerve, no +sensation will result. Thus a man whose spine has been injured may not +feel a severe pinch on either leg. The impression may be quite sufficient +to stimulate a nerve center in a healthy cord, so as to produce a marked +reflex act, but he has no sensation, because the injury has prevented the +impression from being carried up the cord to the higher centers in the +brain. + +311. The Condition of Sensation. It is thus evident that while an +impression may be made upon a terminal organ, it cannot strictly be called +a sensation until the person becomes conscious of it. The consciousness +of an impression is, therefore, the essential element of a sensation. + +It follows that sensation may be prevented in various ways. In the sense +of sight, for example, one person may be blind because the terminal organ, +or eye, is defective or diseased. Another may have perfect eyes and yet +have no sight, because a tumor presses on the nerve between the eye and +the brain. In this case, the impression fails because of the break in the +communication. Once more, the eye may be perfect and the nerve connection +unbroken, and yet the person cannot see, because the center in the brain +itself is injured from disease or accident, and cannot receive the +impression. + + +312. The Functions of the Brain Center in the Perception of an +Impression. Sensation is really the result of a change which occurs in +a nerve center in the brain, and yet we refer impressions to the various +terminal organs. Thus, when the skin is pinched, the sensation is referred +to the skin, although the perception is in the brain. We may think it is +the eyes that see objects; in reality, it is only the brain that takes +note of them. + +This is largely the result of education and habit. From a blow +on the head one sees flashes of light as vividly as if torches actually +dance before the eyes. Impressions have reached the seeing-center in the +brain from irritation of the optic nerve, producing the same effect as +real lights would cause. In this case, however, knowing the cause of the +colors, the person is able to correct the erroneous conclusion. + +As a result of a depraved condition of blood, the seeing-center itself may +be unduly stimulated, and a person may see objects which appear real. Thus +in an attack of delirium tremens, the victim of alcoholic poisoning sees +horrible and fantastic creatures. The diseased brain refers them as usual +to the external world; hence they appear real. As the sufferer's judgment +is warped by the alcoholic liquor, he cannot correct the impressions, and +is therefore deceived by them. + + +313. Organs of Special Sense. The organs of special sense, the means +by which we are brought into relation with surrounding objects, are +usually classed as five in number. They are sometimes fancifully called +"the five gateways of knowledge"--the skin, the organ of touch; the +tongue, of taste; the nose, of smell; the eye, of sight; +and the ear, of hearing. + +[Illustration: Fig. 124.--Magnified View of a Papilla of the Skin, with a +Touch Corpuscle.] + +314. The Organ of Touch. The organ of touch, or tactile sensibility, +is the most widely extended of all the special senses, and perhaps the +simplest. It is certainly the most precise and certain in its results. It +is this sense to which we instinctively appeal to escape from the +illusions into which the other senses may mislead us. It has its seat in +the skin all over the body, and in the mucous membrane of the nostrils. +All parts of the body, however, do not have this sense in an equal degree. + +In Chapter IX. we learned that the superficial layers of the skin covers +and dips in between the papillæ. We also learned that these papillæ are +richly provided with blood-vessels and sensory nerve fibers (sec. 234). +Now these nerve fibers terminate in a peculiar way in those parts of the +body which are endowed with a very delicate sense of touch. In every +papilla are oval-shaped bodies about 1/300 of an inch long, around which +the nerve fibers wind, and which they finally enter. These are called +touch-bodies, or tactile corpuscles, and are found in great +numbers on the feet and toes, and more scantily in other places, as on the +edges of the eyelids. + +Again, many of the nerve fibers terminate in corpuscles, the largest about +1/20 of an inch long, called Pacinian corpuscles. These are most +numerous in the palm of the hand and the sole of the foot. In the papillæ +of the red border of the lips the nerves end in capsules which enclose one +or more fibers, and are called end-bulbs. + +The great majority of the nerve fibers which supply the skin do not end in +such well-defined organs. They oftener divide into exceedingly delicate +filaments, the terminations of which are traced with the greatest +difficulty. + + +315. The Sense of Touch. Touch is a sensation of contact referred to +the surface of the body. It includes three things,--the sense of +contact, the sense of pressure, and the sense of heat and +cold. + +The sense of contact is the most important element in touch. By it we +learn of the form, size, and other properties of objects, as their +smoothness and hardness. As we all know, the sense of touch varies in +different parts of the skin. It is most acute where the outer skin is +thinnest. The tips of the fingers, the edges of the lips, and the tip of +the tongue are the most sensitive parts. + +Even the nails, the teeth, and the hair have the sense of touch in a +slight degree. When the scarf skin is removed, the part is not more +sensitive to sense of contact. In fact, direct contact with the +unprotected true skin occasions pain, which effectually masks the feeling +of touch. The sense of touch is capable of education, and is generally +developed to an extraordinary degree in persons who are deprived of some +other special sense, as sight or hearing. We read of the famous blind +sculptor who was said to model excellent likenesses, guided entirely by +the sense of touch. An eminent authority on botany was a blind man, able +to distinguish rare plants by the fingers, and by the tip of the tongue. +The blind learn to read with facility by passing their fingers over raised +letters of a coarse type. It is impossible to contemplate, even for a +moment, the prominence assigned to the sense of touch in the physical +organism, without being impressed with the manifestations of design--the +work of an all-wise Creator. + +316. Muscular Sense; Sense of Temperature; Pain. When a heavy object +is laid upon certain parts of the body, it produces a sensation of +pressure. By it we are enabled to estimate differences of weight. If +an attempt be made to raise this object, it offers resistance which the +muscles must overcome. This is known as the muscular sense. It +depends on sensory nerves originating in the muscles and carrying +impressions from them to the nerve centers. + +The skin also judges, to a certain extent, of heat and cold. +These sensations can be felt only by the skin. Direct irritation of a +nerve does not give rise to them. Thus, the exposed pulp of a diseased +tooth, when irritated by cold fluids, gives rise to pain, and not to a +sensation of temperature. Various portions of the body have different +degrees of sensibility in this respect. The hand will bear a degree of +heat which would cause pain to some other parts of the body. Then, again, +the sensibility of the outer skin seems to affect the sensibility to heat, +for parts with a thin skin can bear less heat than portions with a thick +cuticle. + + Experiment 139. _To illustrate how the sense of touch is a matter + of habit or education_. Shut both eyes, and let a friend run the tips of + your fingers first lightly over a hard plane surface; then press hard, + then lightly again, and the surface will seem to be concave. + + Experiment 140. Cross the middle over the index finger, roll a + small marble between the fingers; one has a distinct impression of two + marbles. Cross the fingers in the same way, and rub them against the + point of the nose. A similar illusion is experienced. + + Experiment 141. _To test the sense of locality_. Ask a person to + shut his eyes, touch some part of his body lightly with the point of a + pin, and ask him to indicate the part touched. + +As to the general temperature, this sense is relative and is much +modified by habit, for what is cold to an inhabitant of the torrid zone +would be warm to one accustomed to a very cold climate. + +Pain is an excessive stimulation of the sensory nerves, and in it all +finer sensations are lost. Thus, when a piece of hot iron burns the hand, +the sensation is the same as when the iron is very cold, and extreme cold +feels like intense heat. + +317. The Organ of Taste. The sense of taste is located chiefly +in the tongue, but may also be referred even to the regions of the fauces. +Taste, like touch, consists in a particular mode of nerve termination. + +The tongue is a muscular organ covered with mucous membrane, and is +richly supplied with blood-vessels and nerves. By its complicated +movements it is an important factor in chewing, in swallowing, and in +articulate speech. The surface of the tongue is covered with irregular +projections, called papillæ,--fine hair-like processes, about 1/12 of +an inch high. Interspersed with these are the fungiform papillæ. +These are shaped something like a mushroom, and may often be detected by +their bright red points when the rest of the tongue is coated. + +Towards the root of the tongue is another kind of papillæ, the +circumvallate, eight to fifteen in number, arranged in the form of +the letter V, with the apex directed backwards. These are so called +because they consist of a fungiform papilla surrounded by a fold of mucous +membrane, presenting the appearance of being walled around. + +In many of the fungiform and most of the circumvallate papillæ are +peculiar structures called taste buds or taste goblets. These +exist in great numbers, and are believed to be connected with nerve +fibers. These taste buds are readily excited by savory substances, and +transmit the impression along the connected nerve. + +The tongue is supplied with sensory fibers by branches from the fifth and +eighth pairs of cranial nerves. The former confers taste on the front part +of the tongue, and the latter on the back part. Branches of the latter +also pass to the soft palate and neighboring parts and confer taste on +them. The motor nerve of the tongue is the ninth pair, the hypoglossal. + +[Illustration: Fig. 125.--The Tongue. + + A, epiglottis; + B, glands at the base of tongue; + C, tonsil; + D, median circumvallate papilla, + E, circumvallate papillæ; + F, filiform papillæ; + H, furrows on border of the tongue; + K, fungiform papillæ. +] + +318. The Sense of Taste. The sense of taste is excited by stimulation +of the mucous membrane of the tongue and of the palate, affecting the ends +of the nerve fibers. Taste is most acute in or near the circumvallate +papillæ. The middle of the tongue is scarcely sensitive to taste, while +the edges and the tip are, as a rule, highly sensitive. + +Certain conditions are necessary that the sense of taste may be +exercised. First, the substance to be tasted must be in _solution_, or be +soluble in the fluids of the mouth. Insoluble substances are tasteless. If +we touch our tongue to a piece of rock crystal, there is a sensation of +contact or cold, but no sense of taste. On the other hand, when we bring +the tongue in contact with a piece of rock salt, we experience the +sensations of contact, coolness, and saline taste. + +Again, the mucous membrane of the mouth must be _moist_. When the mouth is +dry, and receives substances not already in solution, there is no saliva +ready to dissolve them; hence, they are tasteless. This absence of taste +is common with the parched mouth during a fever. + +The tongue assists in bringing the food in contact with the nerves, by +pressing it against the roof of the mouth and the soft palate, and thus is +produced the fullest sense of taste. + +319. Physiological Conditions of Taste. The tongue is the seat of +sensations which are quite unlike each other. Thus, besides the sense of +taste, there is the sensation of touch, pressure, heat and cold, burning +or acrid feelings, and those produced by the application of the tongue to +an interrupted electric current. These are distinct sensations, due to +some chemical action excited probably in the touch cells, although the +true tastes may be excited by causes not strictly chemical. Thus a smart +tap on the tongue may excite the sensation of taste. + +In the majority of persons the back of the tongue is most sensitive to +bitters, and the tip to sweets. Saline matters are perceived most +distinctly at the tip, and acid substances at the sides. The nerves of +taste are sensitive in an extraordinary degree to some articles of food +and certain drugs. For example, the taste of the various preparations of +quinine, peppermint, and wild cherry is got rid of with difficulty. + +Like the other special senses, that of taste may become fatigued. The +repeated tasting of one substance rapidly deadens the sensibility, +probably by over-stimulation. Some savors so impress the nerves of taste +that others fail to make any impression. This principle is used to make +disagreeable medicine somewhat tasteless. Thus a few cloves, or grains of +coffee, or a bit of pepper, eaten before a dose of castor oil, renders it +less nauseous. + +Flavor is something more than taste. It is in reality a mixed +sensation, in which smell and taste are both concerned, as is shown by the +common observation that one suffering from a cold in the head, which +blunts his sense of smell, loses the proper flavor of his food. So if a +person be blindfolded, and the nose pinched, he will be unable to +distinguish between an apple and an onion, if one be rubbed on the tongue +after the other. As soon as the nostrils are opened the difference is at +once perceived. + + Experiment 142. Put a drop of vinegar on a friend's tongue, or on + your own. Notice how the papillæ of the tongue start up. + + Experiment 143. Rub different parts of the tongue with the pointed + end of a piece of salt or gum-aloes, to show that the _back_ of the + tongue is most sensitive to salt and bitter substances. + + Experiment 144. Repeat the same with some sweet or sour substances, + to show that the _edges_ of the tongue are the most sensitive to these + substances. + + Experiment 145. We often fail to distinguish between the sense of + taste and that of smell. Chew some pure, roasted coffee, and it seems to + have a distinct taste. Pinch the nose hard, and there is little taste. + Coffee has a powerful odor, but only a feeble taste. The same is true of + garlic, onions, and various spices. + + Experiment 146. Light helps the sense of taste. Shut the eyes, and + palatable foods taste insipid. Pinch the nose, close the eyes, and see + how palatable one half of a teaspoonful of cod-liver oil becomes. + + Experiment 147. Close the nostrils, shut the eyes, and attempt to + distinguish by taste alone between a slice of an apple and one of a + potato. + +320. Modifications of the Sense of Taste. Taste is modified to a +great extent by habit, education, and other circumstances. Articles of +food that are unpleasant in early life often become agreeable in later +years. There is occasionally a craving, especially with people of a +peculiar nervous organization, for certain unnatural articles (as chalk +and laundry starch) which are eaten without the least repugnance. Again, +the most savory dishes may excite disgust, while the simplest articles may +have a delicious flavor to one long deprived of them. The taste for +certain articles is certainly acquired. This is often true of raw +tomatoes, olives, and especially of tobacco. + +The organs of taste and smell may be regarded as necessary accessories of +the general apparatus of nutrition, and are, therefore, more or less +essential to the maintenance of animal life. While taste and smell are +generally maintained until the close of life, sight and hearing are often +impaired by time, and may be altogether destroyed, the other vital +functions remaining unimpaired. + +321. Effect of Tobacco and Alcohol upon Taste. It would be remarkable +if tobacco should fail to injure the sense of taste. The effect produced +upon the tender papillæ of the tongue by the nicotine-loaded juices and +the acrid smoke tends to impair the delicate sensibility of the entire +surface. The keen appreciation of fine flavors is destroyed. The once +clear and enjoyable tastes of simple objects become dull and vapid; thus +highly spiced and seasoned articles of food are in demand, and then +follows continued indigestion, with all its suffering. + +Again, the burning, almost caustic effect of the stronger alcoholic +drinks, and the acrid pungency of tobacco smoke, are disastrous to the +finer perceptions of both taste and odors. + + +322. Smell. The sense of smell is lodged in the delicate +membrane which lines the nasal cavities. The floor, sides, and roof of +these cavities are formed by certain bones of the cranium and the face. +Man, in common with all air-breathing animals, has two nasal cavities. +They communicate with the outer air by two nostrils opening in front, +while two other passages open into the pharynx behind. + +To increase the area of the air passages, the two light, spongy turbinated +bones, one on each side, form narrow, winding channels. The mucous +membrane, with the branches of the olfactory nerve, lines the dividing +wall and the inner surfaces of these winding passages. Below all these +bones the lower turbinated bones may be said to divide the olfactory +chamber above from the ordinary air passages. + +[Illustration: Fig. 126.--Distribution of Nerves over the Interior of the +Nostrils. (Outer wall.) + + A, branches of the nerves of smell--olfactory nerve, or ganglion; + B, nerves of common sensation to the nostril; + E, F, G, nerves to the, palate springing from a ganglion at C; + H, vidian nerve, from which branches + D, I, and J spring to be distributed to the nostrils. +] + +The nerves which supply the nasal mucous membrane are derived from the +branches of the fifth and the first pair of cranial nerves,--the +olfactory. The latter, however, are the nerves of smell proper, and are +spread out in a kind of thick brush of minute nerve filaments. It is in +the mucous membrane of the uppermost part of the cavity of the nostril +that the nerve endings of smell proper reside. The other nerves which +supply the nostrils are those of common sensation (sec. 271). + + +323. The Sense of Smell. The sense of smell is excited by the contact +of odorous particles contained in the air, with the fibers of the +olfactory nerves, which are distributed over the delicate surface of +the upper parts of the nasal cavities. In the lower parts are the endings +of nerves of ordinary sensation. These latter nerves may be irritated by +some substance like ammonia, resulting in a powerfully pungent sensation. +This is not a true sensation of smell, but merely an irritation of a nerve +of general sensation. + +In ordinary quiet breathing, the air simply flows along the lower nasal +passages into the pharynx, scarcely entering the olfactory chamber at all. +This is the reason why, when we wish to perceive a faint odor, we sniff up +the air sharply. By so doing, the air which is forcibly drawn into the +nostrils passes up even into the higher olfactory chamber, where some of +the floating particles of the odorous material come into contact with the +nerves of smell. + +One of the most essential conditions of the sense of smell is that the +nasal passages be kept well bathed in the fluid secreted by the lining +membrane. At the beginning of a cold in the head, this membrane becomes +dry and swollen, thus preventing the entrance of air into the upper +chamber, deadening the sensibility of the nerves, and thus the sense of +smell is greatly diminished. + +The delicacy of the sense of smell varies greatly in different individuals +and in different animals. It is generally more acute in savage races. It +is highly developed in both the carnivora and the herbivora. Many animals +are more highly endowed with this sense than is man. The dog, for example, +appears to depend on the sense of smell almost as much as on sight. It is +well known, also, that fishes have a sense of smell. Fragments of bait +thrown into the water soon attract them to a fishing ground, and at depths +which little or no light can penetrate. Deer, wild horses, and antelopes +probably surpass all other animals in having a vivid sense of smell. + +Smell has been defined as "taste at a distance," and it is obvious that +these two senses not only form a natural group, but are clearly +associated in their physical action, especially in connection with the +perception of the flavor of food. The sense of odor gives us information +as to the quality of food and drink, and more especially as to the quality +of the air we breathe. Taste is at the gateway of the alimentary canal, +while smell acts as the sentinel of the respiratory tract. Just as taste +and flavor influence nutrition by affecting the digestive process, so the +agreeable odors about us, even those of the perfumes, play an important +part in the economy of life. + + +324. The Sense of Sight. The sight is well regarded as the +highest and the most perfect of all our senses. It plays so common and so +beneficent a part in the animal economy that we scarcely appreciate this +marvelous gift. Sight is essential not only to the simplest matters of +daily comfort and necessity, but is also of prime importance in the +culture of the mind and in the higher forms of pleasure. It opens to us +the widest and the most varied range of observation and enjoyment. The +pleasures and advantages it affords, directly and indirectly, have neither +cessation nor bounds. + +Apart from its uses, the eye itself is an interesting and instructive +object of study. It presents beyond comparison the most beautiful example +of design and artistic workmanship to be found in the bodily structure. It +is the watchful sentinel and investigator of the external world. Unlike +the senses of taste and smell we seem, by the sense of vision, to become +aware of the existence of objects which are entirely apart from us, and +which have no direct or material link connecting them with our bodies. And +yet we are told that in vision the eye is affected by something which is +as material as any substance we taste or smell. + + [NOTE. "The higher intelligence of man is intimately associated with + the perfection of the eye. Crystalline in its transparency, sensitive + in receptivity, delicate in its adjustments, quick in its motions, the + eye is a fitting servant for the eager soul, and, at times, the truest + interpreter between man and man of the spirit's inmost workings. The + rainbow's vivid hues and the pallor of the lily, the fair creations of + art and the glance of mutual affection, all are pictured in its + translucent depths, and transformed and glorified by the mind within. + Banish vision, and the material universe shrinks for us to that which + we may touch; sight alone sets us free to pierce the limitless abyss + of space."--M'Kendrick and Snodgrass's _Physiology of the Senses_.] + +Physicists tell us that this material, known as the _luminiferous ether_, +permeates the universe, and by its vibrations transmits movements which +affect the eye, giving rise to the sensation of light, and the perception +of even the most distant objects. Our eyes are so constructed as to +respond to the vibrations of this medium for the transmission of light. + + +325. The Eye. The eye, the outer instrument of vision, is a most +beautiful and ingenious machine. All its parts are arranged with such a +delicate adjustment to one another, and such an exquisite adaptation of +every part to the great object of the whole, that the eye is properly +regarded as one of the wonders of nature. + +The eyeball is nearly spherical in shape, but is slightly elongated +from before backwards. The front part is clear and transparent, and bulges +somewhat prominently to allow the entrance of the rays of light. The eye +rests in a bowl-shaped socket, called the orbit, formed by parts of +various bones of the head and face. The margins of this cavity are formed +of strong bone which can withstand heavy blows. The socket is padded with +loose, fatty tissue, and certain membranes, which serve as a soft and +yielding bed in which the eyeball can rest and move without injury. In a +severe sickness this fatty tissue is absorbed, and this fact explains the +sunken appearance of the eyes. + +The orbit is pierced through its posterior surface by an opening through +which the nerve of sight, the optic, passes to the eyeball. We may think +of the optic nerve holding the eyeball much as the stem holds the +apple. It is the function of this most important nerve to transmit +retinal impressions to the seat of consciousness in the brain, where they +are interpreted. + +The eye is bathed with a watery fluid, and protected by the eyelids and +the eyebrows; it is moved in various directions, by muscles, all of which +will soon be described. + +[Illustration: Fig. 127.--Section of the Human Eye.] + +326. The Coats of the Eyeball. The eyeball proper is elastic but +firm, and is composed of three coats, or layers, each of which +performs important functions. These coats are the sclerotic, the +choroid, and the retina. + +The sclerotic coat is the outside layer and enclosing membrane of the +eyeball. It is a tough, fibrous coat for the protection and maintenance of +the shape of the eye. It is white and glistening in appearance, and is in +part visible, to which the phrase, "the white of the eye," is applied. To +this coat, which serves as a kind of framework for the eye, are attached +the muscles which move the eyeball. In front of the globe, the sclerotic +passes into a transparent circular portion forming a window through which +one can see into the interior. This is the cornea. + +The cornea, a clear, transparent, circular disk, fits into the +sclerotic, somewhat as the crystal fits into the metallic case of a watch, +forming a covering for its dial. It projects from the general contour of +the eyeball, not unlike a rounded bay-window, and is often spoken of as +the "window of the eye." + +Lining the inner surface of the sclerotic is the second coat, the +choroid. It is dark in color and fragile in structure, and is made up +almost entirely of blood-vessels and nerves. As the choroid approaches the +front part of the eyeball, its parts become folded upon themselves into a +series of ridges, called ciliary processes. These folds gradually +become larger, and at last merge into the ciliary or accommodation +muscle of the eye. The circular space thus left in front by the +termination of the choroid is occupied by the iris, a thin, circular +curtain, suspended in the aqueous humor behind the cornea and in front of +the crystalline lens. In its center is a round opening for the admission +of light. + +This is the pupil, which appears as if it were a black spot. The back +of the iris is lined with dark pigment, and as the coloring matter is more +or less abundant, we may have a variety of colors. This pigment layer and +that of the choroid and retina absorb the light entering the eye, so that +little is reflected. + +The pupil appears black, just as the open doorway to a dark closet seems +black. The margin of the iris is firmly connected with the eyeball all +round, at the junction of the sclerotic and the cornea. + +327. The Retina. The third and innermost coat of the eyeball is the +retina. This is the perceptive coat, without which it would be impossible +to see, and upon which the images of external objects are received. It +lines nearly the whole of the inner surface of the posterior chamber, +resting on the inner surface of the choroid. It is with the retina, +therefore, that the vitreous humor is in contact. + +The retina is a very thin, delicate membrane. Although very thin, it +is made up of ten distinct layers, and is so complicated in structure that +not even a general description will be attempted in this book. It does not +extend quite to the front limits of the posterior chamber, but stops short +in a scalloped border, a little behind the ciliary processes. This is the +nerve coat of the eye, and forms the terminal organ of vision. It is +really an expansion of the ultimate fibers of the optic nerve, by means of +which impressions are sent to the brain. + +The retina contains curious structures which can be seen only with the aid +of the microscope. For instance, a layer near the choroid is made up of +nerve cells arranged in innumerable cylinders called "rods and cones," and +packed together not unlike the seeds of a sunflower. These rods and cones +are to be regarded as the peculiar modes of termination of the nerve +filaments of the eye, just as the taste buds are the modes of termination +of the nerve of taste in the tongue, and just as the touch corpuscles are +the terminations of the nerves in the skin. + + Experiment 148. Close one eye and look steadily at the small a in + the figure below. The other letters will also be visible at the same + time. If now the page be brought slowly nearer to the eye while the eye + is kept steadily looking at the small a, the large A will disappear at a + certain point, reappearing when the book is brought still nearer. + + [Illustration: a oAx] + + On the reappearance of the A it will be noted that it comes into view + from the inner side, the x being seen before it. If now we move the book + towards its original place, the A will again disappear, coming again + into view from the outer side when the o is seen before it. + +328. Inner Structure of the Eye. Let us imagine an eyeball divided +through the middle from above downwards. Let us now start in front and +observe its parts (Fig. 127). We come first to the cornea, which has +just been described. The iris forms a sort of vertical partition, +dividing the cavity of the eyeball into two chambers. + +[Illustration: Fig. 128.--Diagram illustrating the Manner in which the +Image of an Object is brought to a Focus on the Retina.] + +The anterior chamber occupies the space between the cornea and the +iris, and is filled with a thin, watery fluid called the aqueous +humor. + +The portion behind the iris forms the posterior chamber, and contains +the crystalline lens and a transparent, jelly-like fluid, the +vitreous humor. This fluid is never renewed, and its loss is +popularly described by the phrase, "when the eye runs out." + + Experiment 149. The retina is not sensitive where the optic nerve + enters the eyeball. This is called the "blind spot." Put two ink-bottles + about two feet apart, on a table covered with white paper. Close the + left eye, and fix the right steadily on the left-hand inkstand, + gradually varying the distance from the eye to the ink-bottle. At a + certain distance the right-hand bottle will disappear; but nearer or + farther than that, it will be plainly seen. + +The vitreous humor fills about four-fifths of the eyeball and prevents it +from falling into a shapeless mass. It also serves to hold the choroid and +the retina in position, and to maintain the proper relations of the inner +structures of the eye. + +The iris consists of a framework of connective tissue, the surface of +which is lined by cells containing pigment, which gives color to the eye. + +Bundles of involuntary muscular fibers are found in the substance of the +iris. Some are arranged in a ring round the margin of the pupil; others +radiate from it like the spokes of a wheel. When the circular fibers +contract, the pupil is made smaller, but if these fibers relax, the +radiating fibers cause the pupil to dilate more or less widely. + +329. The Crystalline Lens. Just behind the pupil and close to the iris is +a semi-solid, double-convex body, called the crystalline lens. It is +shaped like a magnifying glass, convex on each side, but with the +posterior surface more convex than the anterior. In health it is perfectly +clear and transparent, and highly elastic. When the lens becomes opaque, +from change in old age, or from ulcers or wounds, we have the disease +known as _cataract_. + +[Illustration: Fig. 129.--Diagram showing the Change in the Lens during +Accommodation. + +On the right the lens is arranged for distant vision, the ciliary muscle +is relaxed and the ligament D is tense, so flattening by its compression +the front of the lens C; on the left the muscle A is acting, and this +relaxes the ligament and allows the lens B to become more convex, and so +fitted for the vision of near objects.] + +The lens is not placed loosely in the eyeball, but is enclosed in a +transparent and elastic capsule suspended throughout its circumference by +a ligament called the suspensory ligament. This ligament not only +retains the lens in place, but is capable of altering its shape. In +ordinary conditions of the eye, this ligament is kept tense so that the +front part of the lens is flattened somewhat by the pressure on it. + +All around the edge, where the cornea, sclerotic, and choroid meet, is a +ring of involuntary muscular fibers, forming the ciliary muscle. When +these fibers contract, they draw forwards the attachment of the suspensory +ligament of the lens, the pressure of which on the lens is consequently +diminished. The elasticity of the lens causes it at once to bulge +forwards, and it becomes more convex. + +The ciliary muscle is thus known as the muscle of accommodation, +because it has the power to accommodate the eye to near and distant +objects. In this respect it corresponds in its use to the adjusting screw +in the opera-glass and the microscope. + + +330. The Eye Compared to the Photographic Camera. As an optical +instrument, the eye may be aptly compared, in many particulars, to the +photographic camera. The latter, of course, is much simpler in +structure. The eyelid forms the cap, which being removed, the light from +the object streams through the eye and passes across the dark chamber to +the retina behind, which corresponds to the sensitive plate of the camera. +The transparent structures through which the rays of light pass represent +the lenses. To prevent any reflected light from striking the plate and +interfering with the sharpness of the picture, the interior of the +photographic camera box is darkened. The pigmented layer of the choroid +coat represents this blackened lining. + +In the camera, the artist uses a thumb-screw to bring to a focus on the +sensitive plate the rays of light coming from objects at different +distances. Thus the lens of the camera may be moved nearer to or farther +from the object. In order to obtain clear images, the same result must be +accomplished by the eye. When the eye is focused for near objects, those +at a distance are blurred, and when focused for distant objects, those +near at hand are indistinct. Now, in the eye there is no arrangement to +alter the position of the lenses, as in the camera, but the same result is +obtained by what is called "accommodation." + +Again, every camera has an arrangement of diaphragms regulating the amount +of light. This is a rude contrivance compared with the iris, which by +means of its muscular fibers can in a moment alter the size of the pupil, +thus serving a similar purpose. + +[Illustration: Fig. 130.--Illustrating the manner in which the Image of an +Object is brought to a Focus in a Photographer's Camera.] + +331. The Refractive Media of the Eye. The eye is a closed chamber +into which no light can pass but through the cornea. All the rays that +enter the eye must also pass through the crystalline lens, which brings +them to a focus, as any ordinary lens would do. + +Now, if the media through which the light from an object passes to reach +the retina were all of the same density as the air, and were also plane +surfaces, an impression would be produced, but the image would not be +distinct. The action of the lens is aided by several refractive media +in the eye. These media are the cornea, the aqueous humor, and the +vitreous humor. By reason of their shape and density these media refract +the rays of light, and bring them to a focus upon the retina, thus aiding +in producing a sharp and distinct image of the object. Each point of the +image being the focus or meeting-place of a vast number of rays coming +from the corresponding point of the object is sufficiently bright to +stimulate the retina to action.[44] + +Thus, the moment rays of light enter the eye they are bent out of their +course. By the action of the crystalline lens, aided by the refractive +media, the rays of light that are parallel when they fall upon the normal +eye are brought to a focus on the retina. + +If the entire optical apparatus of the eye were rigid and immovable, one +of three things would be necessary, in order to obtain a clear image of an +object; for only parallel rays (that is, rays coming from objects distant +about thirty feet or more), are brought to a focus in the average normal +eye, unless some change is brought about in the refractive media. First, +the posterior wall of the eye must be moved further back, or the lens +would have to be capable of movement, or there must be some way of +increasing the focusing power of the lens. In the eye it is the convexity +of the lens that is altered so that the eye is capable of adjusting itself +to different distances.[45] + +[Illustration: Fig. 131.--The Actual Size of the Test-Type, which should +be seen by the Normal Eye at a Distance of Twenty Feet.] + +332. The More Common Defects of Vision. The eye may be free from +disease and perfectly sound, and yet vision be indistinct, because the +rays of light are not accurately brought to a focus on the retina. "Old +sight," known as presbyopia, is a common defect of vision in +advancing years. This is a partial loss of the power to accommodate the +eye to different distances. This defect is caused by an increase in the +density of the crystalline lens, and an accompanying diminution in the +ability to change its form. The far point of vision is not changed, but +the near point is removed so far from the eye, that small objects are no +longer visible. + +[Illustration: Fig. 132.--Diagram illustrating the Hypermetropic +(far-sighted) Eye. + +The image P′ of a point P falls behind the retina in the unaccommodated +eye. By means of a convex lens it may be focused on the retina without +accommodation (dotted lines). (To save space P is placed much too near the +eye.)] + +Hence, when a person about forty-five years of age complains of dim light, +poor print, and tired eyes, the time has come to seek the advice of an +optician. A convex lens may be needed to aid the failing power to increase +the convexity of the lens, and to assist it in bringing the divergent rays +of light to a focus. + +In "long sight," or hypermetropia both the near and far point of +vision are concerned, and there is no distinct vision at any distance +without a strain. It is a defect in the focus, dependent upon the form of +the eyes, and exists in childhood. The axis of the eyeball is too short, +and the focus falls beyond the retina, which is too near the cornea. In +childhood this strain may pass unnoticed, but, sooner or later it +manifests itself by a sense of fatigue, dizziness, and a blurred and +indistinct vision. The remedy is in the use of convex glasses to converge +parallel rays of light before they enter the eye. The muscles of +accommodation are thus relieved of their extra work. + +"Short sight," known as myopia, is one of the commonest defects of +vision. In this defect the axis of the eye, or the distance between the +cornea and the retina, is too long and the rays of light are brought to a +focus in front of the retina. The tendency to short-sightedness exists in +many cases at birth, and is largely hereditary. It is alarmingly common +with those who make a severe demand upon the eyes. During childhood there +is a marked increase of near-sightedness. The results of imprudence and +abuse, in matters of eyesight, are so disastrous, especially during school +life, that the question of short sight becomes one of paramount +importance. + + Experiment 150. With a hand-mirror reflect the sunlight on a white + wall. Look steadily at the spot for a full minute, and then let the + mirror suddenly be removed. The "complementary" color--a dark spot--will + appear. + + Experiment 151. _To show that impressions made upon the retina do + not disappear at once_. Look steadily at a bright light for a moment or + two, and then turn away suddenly, or shut the eyes. A gleam of light + will be seen for a second or two. + + Look steadily at a well-lighted window for a few seconds, and then turn + the eyes suddenly to a darkened wall. The window frame may be plainly + seen for a moment. + + Glance at the sun for a moment, close the eyes and the image of the sun + may be seen for a few seconds. + + Experiment 152. Take a round piece of white cardboard the size of a + saucer, and paint it in alternate rings of red and yellow,--two primary + colors. Thrust a pin through the center and rotate it rapidly. The eye + perceives neither color, but orange,--the secondary color. + + Experiment 153. To note the shadows cast upon the retina by opaque + matters in the vitreous humor (popularly known as floating specks, or + gossamer threads), look through a small pin-hole in a card at a bright + light covered by a ground-glass shade. + + Experiment 154. _To illustrate accommodation_. Standing near a + source of light, close one eye, hold up both forefingers not quite in a + line, keeping one finger about six or seven inches from the other eye, + and the other forefinger about sixteen to eighteen inches from the eye. + Look at the _near_ finger; a distinct image is obtained of it, while the + far one is blurred or indistinct. Look at the far image; it becomes + distinct, while the near one becomes blurred. Observe that in + accommodating for the near object, one is conscious of a distinct + effort. + +In many cases near-sightedness becomes a serious matter and demands +skillful advice and careful treatment. To remedy this defect, something +must be done to throw farther back the rays proceeding from an object so +that they will come to a focus exactly on the retina. This is done by +means of concave glasses, properly adjusted to meet the conditions of the +eyes. The selection of suitable glasses calls for great care, as much harm +may be done by using glasses not properly fitted to the eye. + +[Illustration: Fig. 133.--Diagram illustrating the Myopic (near-sighted) +Eye. + +The image P′ of a distant object P falls in front of the retina even +without accommodation. By means of a concave lens (L) the image may be +made to fall on the retina (dotted lines). (To save space P is placed much +too near the eye).] + +There is an optical condition of the eye known as astigmatism, in +which the cornea is usually at fault. In this defect of vision the +curvature of the cornea is greater in one meridian than in another. As a +result the rays from an object are not all brought to the same focus. +Objects appear distorted or are seen with unequal clearness. Glasses of a +peculiar shape are required to counteract this defect. + + +333. The Movements of the Eyes. In order that our eyes may be +efficient instruments of vision, it is necessary that they have the power +of moving independently of the head. The mechanical arrangement by which +the eyeballs are moved in different directions is quite simple. It is done +by six little muscles, arranged in three pairs, which, with one exception, +originate in the back of the cavity in which the eye rests. Four of these +muscles run a straight course and are called the _recti_. The remaining +two muscles bend in their course and are called _oblique_. The +coördination of these tiny muscles is marvellous in its delicacy, +accuracy, and rapidity of action. + +When, for any cause, the coördination is faulty, "cross eye," technically +called strabismus, is produced. Thus, if the internal rectus is +shortened, the eye turns in; if the external rectus, the eye turns out, +producing what is known as "wall eye." It is thus evident that the beauty +of the internal mechanism of the eye has its fitting complement in the +precision, delicacy, and range of movement conferred upon it by its +muscles. + +334. The Eyelids and Eyebrows. The eye is adorned and protected by +the eyelids, eyelashes, and eyebrows. + +[Illustration: Fig. 134.--Muscles of the Eyeball. + + A, attachment of tendon connected with the three recti muscles; + B, external rectus, divided and turned downward, to expose the internus + rectus; + C, inferior rectus; + D, internal rectus; + E, superior rectus; + F, superior oblique; + H, pulley and reflected portion of the superior oblique; + K, inferior oblique; L, levator palpebri superioris; + M, middle portion of the same muscle (L); + N, optic nerve. +] + +The eyelids, two in number, move over the front of the eyeball and +protect it from injury. They consist of folds of skin lined with mucous +membrane, kept in shape by a layer of fibrous material. Near the inner +surface of the lids is a row of twenty or thirty glands, known as the +_Meibomian glands_, which open on the free edges of each lid. When one of +these glands is blocked by its own secretion, the inflammation which +results is called a "sty." + +The inner lining membrane of the eyelids is known as the conjunctiva; +it is richly supplied with blood-vessels and nerves. After lining the lids +it is reflected on to the eyeballs. It is this membrane which is +occasionally inflamed from taking cold. + +The free edges of the lids are bordered with two or more rows of hairs +called the eyelashes, which serve both for ornament and for use. They +help to protect the eyes from dust, and to a certain extent to shade them. +Their loss gives a peculiar, unsightly look to the face. + +The upper border of the orbit is provided with a fringe of short, stiff +hairs, the eyebrows. They help to shade the eyes from excessive +light, and to protect the eyelids from perspiration, which would otherwise +cause serious discomfort. + + +335. The Lacrymal Apparatus. Nature provides a special secretion, the +tears, to moisten and protect the eye. The apparatus producing this +secretion consists of the lacrymal or tear gland and lacrymal +canals or tear passages (Fig. 136). + +Outside of the eyeball, in the loose, fatty tissue of the orbit, in the +upper and outer corner is the lacrymal or tear gland. It is +about the size of a small almond and from it lead several little canals +which open on the inner surface of the upper lid. The fluid from the gland +flows out by these openings over the eyeball, and is collected at the +inner or nasal corner. Here in each lid is a little reddish elevation, or +_lacrymal caruncle_, in which is an opening, communicating with a small +canal in the lid which joins the lacrymal sac, lodged between the +orbit and the bridge of the nose (Fig. 137). + +From this sac there passes a channel, the nasal duct, about one-half +of an inch long, leading into the lower portion of the nostril. The fluid +which has flowed over the eye is drained off by these canals into the +nose. During sleep this secretion is much diminished. When the eyes are +open the quantity is sufficient to moisten the eyeball, the excess being +carried into the nose so gradually that the attention is not attracted to +it. + +The lacrymal canals are at times blocked by inflammation of the nasal +duct, and the fluid collects in the corners of the eyelids and overflows +down the cheeks, producing much inconvenience. The lining membrane of the +eyelids through these canals is continuous with that of the nostrils. +Hence, when the lining membrane of the eye is red and swollen, as during a +cold, the nasal passages are also irritated, and when the nasal membrane +is inflamed, the irritation is apt to pass upwards and affect the eyelids. + +336. The Tears. The lacrymal or tear gland is under the control of the +nervous system. Thus, if anything irritates the eyelids, the sensory +nerves are stimulated and the impression is carried to the brain. Thence +the nerve impulses travel to the lacrymal glands, leading to an increased +flow of their secretion. The irritation of the sensory nerves in the nasal +passages by smelling such substances as onions, or pungent salts, often +causes a copious flow of tears. + +[Illustration: Fig. 135.--Lacrymal Gland and Ducts. + + A, lachrymal gland, the size of a small almond lodged in a shallow + depression in the bones of the orbit; + B, lachrymal ducts (usually seven), which form a row of openings into + the conjunctival fold. +] + +Various mental emotions, as joy and grief, may produce similar results. In +these cases the glands secrete the fluid in such quantities that it cannot +escape by the lacrymal canals, and the excess rolls over the cheeks as +tears. Excessive grief sometimes acts on the nerve centers in exactly the +opposite manner, so that the activity of the glands is arrested and less +fluid is secreted. This explains why some people do not shed tears in +times of deep grief. + + Experiment 155. Gently turn the inner part of your lower eyelid + down. Look in a mirror, and the small lacrymal point, or opening into + the nasal duct, may be observed. + +337. Color-blindness. There is an abnormal condition of vision called +color-blindness, in which the power of discrimination between different +colors is impaired. Experiment shows that ninety-six out of every one +hundred men agree as to the identity or the difference of color, while the +remaining four show a defective perception of color. + +The first may be said to have _normal vision_; the second are called +_color-blind_. It is a curious fact that ten times more men than women are +color-blind. + +In its true sense, color-blindness is always congenital, often +hereditary. This condition of abnormal vision is totally incurable. A +person may be color-blind and not know it until the defect is accidentally +revealed. The common form of defective color-vision is the inability to +distinguish between _red_ and _green_. As green lights mean safety, and +red lights danger, on railroads, on shipboard, and elsewhere, it becomes +of paramount importance that no one who is color-blind should be employed +in such service. Various tests are now required by statute law in many +states to be used for the detection of such defects of vision among +employees in certain occupations. + + +338. School Life and the Eyesight. The eyes of children need more +care than those of adults, because their eyes are still in the course of +development. The eyes, like any other organ which is yet to attain its +full growth, require more care in their use than one which has already +reached its full size. They are peculiarly liable to be affected by +improper or defective light. Hence the care of the eyes during school life +is a matter of the most practical importance. + +In no matter of health can the teacher do a more distinct service than in +looking after the eyesight of the pupils. Children suffering from +defective vision are sometimes punished by teachers for supposed +stupidity. Such pupils, as well as the deaf, are peculiarly sensitive to +their defects. Every schoolroom should have plenty of light; it should +come from either side or the rear, and should be regulated with suitable +shades and curtains. + +Pupils should not be allowed to form the bad habit of reading with the +book held close to the eyes. The long search on maps for obscure names +printed in letters of bad and trying type should be discouraged. Straining +the eyes in trying to read from slates and blackboards, in the last hour +of the afternoon session, or in cloudy weather, may do a lifelong injury +to the eyesight. Avoid the use, so far as possible, especially in a +defective light, of text-books which are printed on battered type and worn +plates. + +The seat and desk of each scholar should be carefully arranged to suit the +eyesight, as well as the bones and muscles. Special pains should be taken +with the near-sighted pupils, and those who return to school after an +attack of scarlet fever, measles, or diphtheria. + + Experiment 156. _To test color-blindness._ On no account is the + person being tested to be asked to name a color. In a large class of + students one is pretty sure to find some who are more or less + color-blind. The common defects are for red and green. + +Place worsteds on a white background in a good light. Select, as a test +color, a skein of light green color, such as would be obtained by mixing a +pure green with white. Ask the examinee to select and pick out from the +heap all those skeins which appear to him to be of the same color, whether +of lighter or darker shades. A color-blind person will select amongst +others some of the confusion-colors, _e.g._, pink, yellow. A colored plate +showing these should be hung up in the room. Any one who selects all the +greens and no confusion-colors has normal color vision. If, however, one +or more confusion-colors be selected, proceed as follows: select as a test +color a skein of pale rose. If the person be red-blind, he will choose +blue and violet; if green-blind, gray and green. + +Select a bright red skein. The red-blind will select green and brown; the +green-blind picks out reds or lighter brown. + +339. Practical Hints on the Care of the Eyes. The eye is an +exceedingly delicate and sensitive organ. While it is long-suffering, its +endurance has a limit. Like all the other organs of the body, the eyes are +better for moderate and rational use. More than any other organ they +require attention to the general health, as the condition of the skin, +exercise in the open air, good food, and proper habits of daily living. + +The tissues of the eyes are peculiarly sensitive to any general influence. +Certain constitutional diseases, like rheumatism, lead-poisoning, +diphtheria, and measles often affect the eyes. Special care should be +taken with children's eyes during and after an attack of measles and +scarlet fever. The eyes of young infants should not be exposed to glaring +lights or to the direct rays of the sun, as when taken out in baby +carriages. + +[Illustration: Fig. 136.--Showing the Relative Position of the Lacrymal +Apparatus, the Eyeball, and the Eyelids. + + A, lacrymal canals, with the minute orifices represented as two black + dots (puncta lacrymalia) to the right; + B, tendon of the orbicularis palpebrarum muscle; apparently under B is + seen the lacrymal sac. The minute openings of the Meibomian glands are + seen on the free margins of the eyelids. + +Below A is seen a small conical elevation, with black dots (the lacrymal +papilla or caruncle).] + +Glasses should be worn when they are needed. A failure to do this ususally +causes much unnecessary suffering. It is far from wise to postpone as long +as possible the first use of glasses. The selection and proper fitting of +glasses call for the combined skill of both the physician and the +optician. Obstinate headaches are often caused by defective vision, and +may disappear after discontinuing improper glasses. + +The habit of reading, in the cars or elsewhere, the daily paper and +poorly printed books, with their blurred and indistinct type, is a severe +strain on the accommodation apparatus of the eyes. It is a dangerous +practice to read in bed at night, or while lying down in a darkened or +shaded room. This is especially true during recovery from illness. The +muscles of the eyes undergo excessive strain in accommodating themselves +to the unnatural position. The battered type, wood-pulp paper, and poor +presswork, now so commonly used in the cheap editions of books and +periodicals, are often injurious to the eyesight. + +Reading-matter should not be held nearer to the eyes than is necessary to +make the print appear perfectly sharp and distinct. No print should be +read continuously that cannot be seen clearly at about eighteen inches. +Those who read music are especially liable to strain the eyes, because +exact vision is required to follow the notes. Persons who wear glasses for +reading should be careful to use them while reading music, and good light +is necessary to avoid any undue strain. + +After reading steadily for some time, the eyes should be rested by closing +them a short period or by looking at some distant object, even if only for +a few moments. The book, the sewing, and work generally, should be held as +far from the eyes as is compatible with good vision. The natural tendency +is to reverse this rule. We should never read, write, sew, stitch, or +otherwise use the eyes when they smart or tingle, or when the sight is dim +or blurred. The eyes are then tired and need a rest. Much injury may be +done by reading in twilight, or by artificial light in the early morning, +and by reading and working in badly lighted and ill-ventilated rooms. + +Good artificial light is much to be preferred to insufficient sunlight. +The artificial light should be sufficiently bright and steady; a fickering +light is always bad. Riding against a strong wind, especially on a +bicycle, may prove hurtful, at least for eyes that are inclined to any +kind of inflammation. The light reflected from snow is a common source of +injury to the eyes. It is a wise caution in passing from a dark room to +avoid looking immediately at the sun, an incandescent light, the +glistening snow, or other bright objects. + +The eyes should never be rubbed, or the fingers thrust into them,[46] and +much less when they are irritated by any foreign substance. The sooner the +offending substance is removed the better. + +[Illustration: Fig. 137.--Lacrymal Canals, Lacrymal Sac, and Nasal ducts, +opened by their Anterior Portion.] + +340. Effect of Alcohol upon the Eye. The earlier and slighter forms +of injury done to the eye by the use of intoxicants are quite familiar: +the watery condition of the eye and of the lids, and the red and bleared +aspect of the organ. Both are the result of chronic inflammation, which +crowds the blood into the vessels of the cornea, making them bloodshot and +visible. The nerves controlling the circulation of the eye are partially +paralyzed, and thus the relaxed vessels become distended. + +But more serious results ensue. Long use of intoxicants produces diseases +of the retina, involving in many cases marked diminution of acuteness as +well as quickness of vision, and at times distorted images upon the +surface of the retina. In other instances, the congestion of the optic +nerve is so serious as to involve a progressive wasting of that organ, +producing at first a hazy dimness of vision which gradually becomes worse +and worse, till total blindness may ensue. + +It is beyond question that a wide comparison of cases by careful +observers proves that a large fraction of those who indulge in strong +drink suffer from some form of disease of the eye. + + +341. Effect of Tobacco upon Vision. Tobacco, in its distribution of +evil effects, does not neglect the senses and especially the eye. A +variety of vicious results is produced. The pungent smoke inflames the +lids. The narcotic dilates the pupil, causing dimness and confusion of +vision. A diseased condition occurs with severe pain in the eye followed +by impaired vision. + +Oculists speak impressively of the ill effects of tobacco, and especially +of cigarettes, upon the eyes of the young. They mention a well-known +disease, tobacco blindness, usually beginning with color-blindness, and +progressing occasionally with increasing dimness of vision to entire loss +of sight.[47] + + +342. The Sense of Hearing. The structure of the human ear is much +more complicated than is generally supposed. It is an apparatus +constructed to respond to the waves of sound. As a whole, it may be +considered a peculiar form of nerve-ending. + +The external ear forms only a part of a most elaborate apparatus whereby +sound waves may be transmitted inwards to the real organ of hearing. The +really sensitive part of the ear, in which the auditory nerve ends, is +buried for protection deep out of sight in the bones of the head; so deep +that sounds cannot directly affect it. Some arrangement, therefore, is +required for conducting the sounds inwards to this true organ. + +[Illustration: Fig. 138.--The Pinna, or Auricle.] + +In studying the structure of the ear, and how it is fitted to respond to +sonorous vibrations, we may divide it into three parts: the +sound-conducting part, known as the external ear, the middle +ear, and the deeply placed nerve portion, the inner ear. + + +343. The External Ear. The external ear consists of an expanded +portion known as the pinna or _auricle_, and of a passage, the +auditory canal or _meatus_, leading inwards from it. The surface of +the auricle is convoluted to collect and transmit the vibrations of air by +which sound is produced the auditory canal conducts these vibrations to +the tympanic membrane. Many animals move the auricle in the direction of +the sound. Thus the horse pricks up its ears when it hears a noise, the +better to judge of the direction of sounds.[48] + +The external auditory meatus, the passage to the middle ear, is curved +and is about an inch and a quarter long. Near its outer portion are a +number of fine hairs slanting outwards to prevent the entrance of insects. +Embedded in the deeper parts of the canal are glands which secrete the +_cerumen_, or ear-wax, which keeps the canal moist, and helps to protect +it against foreign bodies and insects. As the result of a cold, this wax +may collect in sufficient quantities to block the passage, and to diminish +to a considerable extent the power of hearing. + + +344. The Middle Ear. At the inner end of the outer ear passage is the +tympanum, known as "the drum of the ear." It is a thin, oval membrane, +stretched at an angle across the deep end of the passage, which it +completely closes. The tympanum is thus a partition between the +passage of the outer ear and the cavity of the middle ear. On its inner +side is a small air chamber in the petrous portion of the temporal bone, +called the cavity of the tympanum. Its bony walls are lined with +mucous membrane similar to that lining the nose, mouth, and throat. On the +inner wall of the tympanum are two openings, the round window, or _foramen +rotundum_, and the oval window, or _foramen ovale_. + +The tympanic cavity communicates with the back part of the throat, by the +Eustachian tube. This tube is about one and a half inches long and +lined with mucous membrane similar to that of the tympanic chamber and the +throat. This passage is usually closed, but is opened in the act of +swallowing. In health there is no communication between the chamber of the +middle ear and the outside, except by the Eustachian tube. Thus a throat +cold, with redness and swelling of the mucous membrane, is usually +accompanied with some degree of deafness, because the swelling may block +the lumen of the tube, and thus prevent the free passage of air to and +fro. + +[Illustration: Fig. 139.--General View of the Organ of Hearing. + + A, pinna; + B, cavity of the concha, showing the orifices of a great number of + sebaceous glands; + C, external auditory meatus; + D, membrana tympani; + F, incus; + H, malleus; + K, handle of malleus applied to the internal surface of the membrana + tympani; + L, tensor tympani muscle; + between M and K is the tympanic cavity; + N, Eustachian tube; + O, P, semicircular canals; + R, internal auditory canal; + S, large nerve given off from the facial ganglion; + T, facial and auditory nerves. +] + +A most curious feature of the ear is the chain of tiny movable bones which +stretch across the cavity of the middle ear. They connect the tympanic +membrane with the labyrinth, and serve to convey the vibrations +communicated to the membrane across the cavity of the tympanum to the +internal ear. These bones are three in number, and from their shape are +called the <b>malleus</b>, or _hammer_, <b>incus</b>, or _anvil_; and +<b>stapes</b>, or _stirrup_. + +The hammer is attached by its long handle to the inner surface of the drum +of the ear. The round head is connected with the anvil by a movable joint, +while the long projection of the anvil is similarly connected with the +stirrup bone. The plate of the stirrup is fixed by a membrane into the +oval window of the inner wall of the tympanic chamber. + +These little bones are connected with each other and the tympanum by +ligaments and moved by three tiny muscles. Two are attached to the hammer, +and tighten and relax the drum; the other is attached to the stirrup, and +prevents it from being pushed too deeply into the oval window. + +[Illustration: Fig. 140.--Ear-Bones. (Anterior View.) + + 1, malleus, or hammer; + 2, incus, or anvil; + 3, stapes, or stirrup. +] + +345. The Internal Ear. This forms one of the most delicate and +complex pieces of mechanism in the whole body. It is that portion of the +organ which receives the impression of sound, and carries it directly to +the seat of consciousness in the brain. We are then able to say that we +hear. + +The internal ear, or bony labyrinth, consists of three distinct parts, or +variously shaped chambers, hollowed out in the temporal bone,--the +vestibule, the semicircular canals, and the cochlea, or snail's shell. + +[Illustration: Fig. 141.--A Cast of the External Auditory Canal. +(Posterior view)] + +The vestibule is the common cavity with which all the other portions +of the labyrinth connect. It is an oval-shaped chamber, about ⅓ of an +inch in diameter, occupying the middle part of the internal ear. It is on +the inner side of the oval window, which was closed, as we have seen, by +the stirrup bone. From one side of this vestibule, or central hall, the +three semicircular canals pass off, and from the other side, the cochlea. + +The three semicircular canals, so called from their shape, are +simply bony tubes about 1/20 of an inch in width, making a curve of about +1/4 of an inch in diameter. They pass out from the vestibule, and after +bending around somewhat like a hoop, they return again to the vestibule. +Each bony canal contains within it a membranous canal, at the end of which +it is dilated to form an _ampulla_. + + Experiment 157. _To vibrate the tympanic membrane and the little + ear-bones._ Shut the mouth, and pinch the nose tightly. Try to force air + through the nose. The air dilates the Eustachian tube, and is forced + into the ear-drum. The distinct crackle, or clicking sound, is due to + the movement of the ear-bones and the tympanic membrane. + +The cochlea, or snail's shell, is another chamber hollowed out in the +solid bone. It is coiled on itself somewhat like a snail's shell. There is +a central pillar, around which winds a long spiral canal. One passage from +the cochlea opens directly into the vestibule; the other leads to the +chamber of the middle ear, and is separated from it by the little round +window already described. + +The cochlea contains thousands of the most minute cords, known as the +fibers or _organ of Corti_.[49] Under the microscope they present the +appearance of the keyboard of a piano. These fibers appear to vibrate in +sympathy with the countless shades of sounds which daily penetrate the +ear. From the hair-like processes on these tightly stretched fibers, +auditory impulses appear to be transmitted to the brain. + +The tubes and chambers of the inner ear enclose and protect a delicate +membranous sac of exactly the same shape as themselves. Between the bony +walls of the passages and the membranous bag inside is a thin, clear +fluid, the _perilymph_. The membranous bag itself contains a similar +fluid, the _endolymph_. In this fluid are found some minute crystals of +lime like tiny particles of sand, called _otoliths_, or ear-stones. Every +movement of the fluid itself throws these grains from side to side. + +[Illustration: Fig. 142.--Bony internal Ear of Right Side. (Magnified; the +upper figure of the natural size.) + + A, oval window (foramen ovale); + B, C, D, semicircular canals; + * represents the bulging part (ampulla) of each canal; + E, F, G cochlea, H, round window (foramen rotundum). +] + +The auditory nerve, or nerve of hearing, passes to the inner ear, +through a passage in the solid bone of the skull. Its minute filaments +spread at last over the inner walls of the membranous labyrinth in two +branches,--one going to the vestibule and the ampullæ at the ends of the +semicircular canals, the other leading to the cochlea. + + +346. Mechanism of Hearing. Waves of sound reach the ear, and are +directed by the concha to the external passage, at the end of which they +reach the tympanic membrane. When the sound-waves beat upon this thin +membrane, it is thrown into vibration, reproducing in its movements the +character of the air-vibrations that have fallen upon it. + +Now the vibrations of the tympanic membrane are passed along the chain of +bones attached to its inner surface and reach the stirrup bone. The +stirrup now performs a to-and-fro movement at the oval window, passing the +auditory impulse inwards to the internal ear. + +Every time the stirrup bone is pushed in and drawn out of the oval +window, the watery fluid (the perilymph) in the vestibule and inner ear is +set in motion more or less violently, according to the intensity of the +sound. The membranous labyrinth occupies the central portion of the +vestibule and the passages leading from it. When, therefore, the perilymph +is shaken it communicates the impulse to the fluid (endolymph) contained +in the inner membranous bag. The endolymph and the tiny grains of ear-sand +now perform their part in this marvelous and complex mechanism. They are +driven against the sides of the membranous bag, and so strike the ends of +the nerves of hearing, which transmit the auditory impulses to the seat of +sensation in the brain. + +It is in the seat of sensation in the brain called the _sensorium_ that +the various auditory impulses received from different parts of the inner +ear are fused into one, and interpreted as sounds. It is the extent of the +vibrations that determines the loudness of the sound; the number of them +that determines the pitch. + + Experiment 158. Hold a ticking watch between the teeth, or touch + the upper incisors with a vibrating tuning-fork; close both ears, and + observe that the ticking or vibration is heard louder. Unstop one ear, + and observe that the ticking or vibration is heard loudest in the + stopped ear. + + Experiment 159. Hold a vibrating tuning-fork on the incisor teeth + until you cannot hear it sounding. Close one or both ears, and you will + hear it. + + Experiment 160. Listen to a ticking watch or a tuning-fork kept + vibrating electrically. Close the mouth and nostrils, and take either a + deep inspiration or deep expiration, so as to alter the tension of the + air in the tympanum; in both cases the sound is diminished. + + Experiment 161. With a blindfolded person test his sense of the + direction of sound, _e.g._, by clicking two coins together. It is very + imperfect. Let a person press both auricles against the side of the + head, and hold both hands vertically in front of each meatus. On a + person making a sound in front, the observed person will refer it to a + position behind him. + +347. Practical Hints on the Care of the Ear. This very delicate and +complicated organ is often neglected when skilled treatment is urgently +needed, and it is often ignorantly and carelessly tampered with when it +should be let alone. + +Never insert into the ear canal the corners of towels, ear spoons, the +ends of toothpicks, hairpins, or any other pointed instruments. It is a +needless and dangerous practice, usually causing, in time, some form of +inflammation. The abrasion of the skin in the canal thus produced affords +a favorable soil for the growth of vegetable parasites. + +[Illustration: Fig. 143.--Diagram of the Middle and Internal Ear.] + +This, in turn, may lead to a chronic inflammation of the canal and of the +tympanic membrane. Again, there is always risk that the elbow may be +jogged and the instrument pushed through the drum-head. There is, of +course, a natural impulse to relieve the itching of the ear. This should +be done with the tips of the fingers or not at all. + +The popular notion that something should be put into the ear to cure +toothache is erroneous. This treatment does not cure a toothache, and may +lead to an injury to the delicate parts of the ear. A piece of absorbent +cotton, carefully inserted into the ear, may be worn out of doors, when +the cold air causes pain, but should be removed on coming into the house. + +Frequent bathing in the cold water of ponds and rivers is liable to +injure both the ears and the general health. In salt-water bathing, the +force of the waves striking against the ears often leads to earache, +long-continued inflammation, or defective hearing; to diminish this risk, +insert into the ears a small plug of absorbent cotton. + +The ears are often carelessly exposed to cold water and inclement weather. +Very cold water should never be used to bathe the ears and nostrils. Bathe +moderately and gently in lukewarm water, using a wash-rag in preference to +a sponge; dry gently and thoroughly. Children's ears are often rudely +washed, especially in the auditory canal. This is not at all necessary to +cleanliness, and may result in a local inflammation. + +Never shout suddenly in a person's ear. The ear is not prepared for the +shock, and deafness has occasionally resulted. A sudden explosion, the +noise of a cannon, may burst the drum-head, especially if the Eustachian +tube be closed at the time. During heavy cannonading, soldiers are taught +to keep the mouth open to allow an equal tension of air. + +[Illustration: Fig. 144.--Section of Cochlea. + +From A straight downwards is the direction of the central column, to which +E points. B points to the projecting ridge, almost dividing the canal of +the tube into an upper compartment (D), and a lower (C).] + +Insects may gain entrance to the ears and occasion annoyance, pain, and +fright, perhaps leading to vomiting, even to convulsions, with nervous +children. A lighted lamp held at the entrance of the ear will often induce +the offending insect to crawl out towards the light. A few drops of warm +water, sweet oil, or molasses, dropped into the ear, will help remove the +intruder. + +When a discharge occurs from the ears, it is not best to plug them with +cotton wads. It only keeps in what should be got rid of. Do not go to +sleep with the head on a window sill or in any position, with the ears +exposed to draughts of cold or damp air. + +No effort should be made to remove the ear wax unless it accumulates +unduly. The skin of the canal grows outward, and the extra wax and dust +will be naturally carried out, if let alone. Never employ any of the many +articles or "drops," advertised to cure deafness. Neuralgic pain in the +canal, usually classed as earache, may be due to decayed or improperly +filled teeth. + +Quinine, so generally used in its many preparations for malaria, causes a +peculiar ringing or buzzing in the ears. This is a warning that it should +be taken in smaller doses, or perhaps stopped for a time. In some cases +quinine may produce temporary deafness. + +The practice of snuffing up cold water into the nostrils is occasionally +followed by an acute inflammation of the middle ear, some of the water +finding its way through the Eustachian tube into this part of the organ of +hearing. The nasal douche, so often advised as a home remedy for nasal +catarrh, should be used only with great caution, and always in accordance +with detailed directions from a physician. + +348. Effect of Tobacco upon the Hearing. The sense of hearing is +often injured by the use of tobacco. The irritating smoke filling all the +inner cavity of the mouth and throat, readily finds its way up the +Eustachian tube, dries the membrane, and irritates or inflames the +delicate mechanism of the inner ear. Thus may be produced a variety of +serious aural disturbances, such as unnatural noises, whistling, and +roaring, followed oftentimes by a partial loss of hearing. + +Hearing may be impaired by the use of alcoholic beverages. Alcohol +inflames the mucous membrane of the throat, then by its nearness the +lining of the Eustachian tube, and finally may injure the delicate +apparatus of the internal ear. + + + +Additional Experiments. + + Experiment 162. Use a small pair of wooden compasses, or an + ordinary pair of dividers with their points guarded by a small piece of + cork. Apply the points of the compasses lightly and simultaneously to + different parts of the body, and ascertain at what distance apart the + points are felt as two. The following is the order of sensibility: tip + of tongue, tip of the middle finger, palm, forehead, and back of hand. + + Experiment 163. Test as in preceding experiment the skin of the + arm, beginning at the shoulder and passing downwards. Observe that the + sensibility is greater as one tests towards the fingers, and also in the + transverse than in the long axis of the limb. In all cases compare the + results obtained on both sides of the body. + + Experiment 164. By means of a spray-producer, spray the back of the + hand with ether, and observe how the sensibility is abolished. + + Experiment 165. Touch your forehead with your forefinger; the + finger appears to feel the contact, but on rubbing the forefinger + rapidly over the forehead, it is the latter which is interpreted as + "feeling" the finger. + + Experiment 166. Generally speaking, the sensation of touch is + referred to the cutaneous surfaces. In certain cases, however, it is + referred even beyond this. Holding firmly in one hand a cane or a + pencil, touch an object therewith; the sensation is referred to the + extremity of the cane or pencil. + + If, however, the cane or pencil be held loosely in one's hand, one + experiences two sensations: one corresponding to the object touched, and + the other due to the contact of the rod with the skin. The process of + mastication affords a good example of the reference of sensations to and + beyond the periphery of the body. + + Experiment 167. Prepare a strong solution of sulphate of quinine + with the aid of a little sulphuric acid to dissolve it (_bitter_), a + five-per-cent solution of sugar (_sweet_), a ten-per-cent solution of + common salt (_saline_), and a one-per-cent solution of acetic acid + (_acid_). Wipe the tongue dry, and lay on its tip a crystal of sugar. It + is not tasted until it is dissolved. + + Experiment 168. Apply a crystal of sugar to the tip, and another to + the back of the tongue. The sweet taste is more pronounced at the tip. + + Experiment 169. Repeat the process with sulphate of quinine in + solution. It is scarcely tasted on the tip, but is tasted immediately on + the back part of the tongue. Test where salines and acids are tasted + most acutely. + + Experiment 170. _To illustrate the muscular sense_. Take two equal + iron or lead weights; heat one and leave the other cold. The cold weight + will feel the heavier. + + Experiment 171. Place a thin disk of _cold_ lead, the size of a + silver dollar, on the forehead of a person whose eyes are closed; remove + the disk, and on the same spot place two warm disks of equal size. The + person will judge the latter to be about the same weight, or lighter, + than the single cold disk. + + Experiment 172. Compare two similar wooden disks, and let the + diameter of one be slightly greater than that of the other. Heat the + smaller one to over 120° F., and it will be judged heavier than the + larger cold one. + + Experiment 173. _To illustrate the influence of excitation of one + sense organ on the other sense organs_. Small colored patches the shape + and color of which are not distinctly visible may become so when a + tuning-fork is kept vibrating near the ears. In other individuals the + visual impressions are diminished by the same process. + + On listening to the ticking of a watch, the ticking sounds feebler or + louder on looking at a source of light through glasses of different + colors. + + If the finger be placed in cold or warm water the temperature appears to + rise when a red glass is held in front of the eyes. + + Experiment 174. _Formation of an inverted image on the retina_. + Take a freshly removed ox-eye; dissect the sclerotic from that part of + its posterior segment near the optic nerve. Roll up a piece of blackened + paper in the form of a tube, black surface innermost, and place the eye + in it with the cornea directed forward. Look at an object--_e.g._, a + candle-flame--and observe the inverted image of the flame shining + through the retina and choroid, and notice how the image moves when the + candle is moved. + + Experiment 175. Focus a candle-flame or other object on the + ground-glass plate of an ordinary photographic camera, and observe the + small inverted image. + + Experiment 176. _To illustrate spherical aberration_. Make a + pin-hole in a blackened piece of cardboard; look at a light placed at a + greater distance than the normal distance of accommodation. One will see + a radiate figure with four to eight radii. The figures obtained from + opposite eyes will probably differ in shape. + + Experiment 177. Hold a thin wooden rod or pencil about a foot from + the eyes and look at a distant object. Note that the object appears + double. Close the right eye; the left image disappears, and _vice + versa_. + + Experiment 178. _To show the movements of the iris_. It is an + extremely beautiful experiment, and one that can easily be made. Look + through a pin-hole in a card at a uniform white surface as the white + shade of an ordinary reading-lamp. With the right eye look through the + pin-hole, the left eye being closed. Note the size of the (slightly + dull) circular visual field. Open the left eye, the field becomes + brighter and smaller (contraction of pupil); close the left eye, after + an appreciable time, the field (now slightly dull) is seen gradually to + expand. One can thus see and observe the rate of movements of his own + iris. + + [Illustration: Fig. 145.] + + Experiment 179. _To show the blind spot_. The left eye being shut, + let the right eye be fixed upon the cross as in Fig. 145. When the book + is held at arm's length, both cross and round spot will be visible; but + if the book be brought to about 8 inches from the eye, the gaze being + kept steadily upon the cross, the round spot will at first disappear, + but as the book, is brought still nearer both cross and round spot will + again be seen. + + Experiment 180. _To illustrate the duration of retinal + impressions_. On a circular white disk, about halfway between the center + and circumference, fix a small, black, oblong disk, and rapidly rotate + it by means of a rotating wheel. There appears a ring of gray on the + black, showing that the impression on the retina lasts a certain time. + + [Illustration: Fig. 146.--Optic Disks. + + The disk A, having black and white sectors, when rotated rapidly gives + an even gray tint as in B.] + + Experiment 181. Mark off a round piece of cardboard into black and + white sectors as in A (Fig. 146). Attach it so as to rotate it rapidly, + as on a sewing machine. An even gray tint will be produced as in B. + + Experiment 182._To illustrate imperfect visual judgments_. Make + three round black dots, A, B, C, of the same size, in the same line, and + let A and C be equidistant from B. Between A and B make several more + dots of the same size. A and B will then appear to be farther apart than + B and C. + + [Illustration: + * * * * * * * + A B C + ] + + For the same reason, of two squares absolutely identical in size, one + marked with alternately clear and dark cross-bands, and the other with + alternately clear and dark upright markings, the former will appear + broader and the latter higher than the other. + + Experiment 183. Make on a white card two squares of equal size. + Across the one draw _horizontal_ lines at equal distances, and in the + other make similar _vertical_ lines. Hold them at some distance. The one + with horizontal lines appears higher than it really is, while the one + with vertical lines appears broader, i.e., both appear oblong. + + Experiment 184. Look at the row of letters (S) and figures (8). To + + [Illustration: + S S S S S S S S 8 8 8 8 8 8 8 8 + ] + + some the upper halves of the letters and figures may appear to be of the + same size as the lower halves, to others the lower halves may appear + larger. Hold the figure upside down, and observe that there is a + considerable difference between the two, the lower halves being + considerably larger. + + Experiment 185. _To illustrate imperfect visual judgment_. The + length of a line appears to vary according to the angle and direction of + certain other lines in relation to it (Fig. 147). The length of the two + vertical lines is the same, yet B appears much longer than A. + + [Illustration: Fig. 147.--To show False Estimate of Size. + + \ / + \ / + /|\ | + / | \ | + | | + A | B | + | | + \ | / | + \|/ | + / \ + / \ + ] + + Experiment 186. In indirect vision the appreciation of direction is + still more imperfect. While leaning on a large table, fix a point on the + table, and then try to arrange three small pieces of colored paper in a + straight line. Invariably, the papers, being at a distance from the + fixation-point, and being seen by indirect vision, are arranged, not in + a straight line, but in the arc of a circle with a long radius. + + + +Chapter XII. + +The Throat and the Voice. + + + +349. The Throat. The throat is a double highway, as it were, +through which the air we breathe traverses the larynx on its way to the +lungs, and through which the food we swallow reaches the œsophagus +on its passage to the stomach. It is, therefore, a very important region +of the body, being concerned in the great acts of respiration and +digestion. + +The throat is enclosed and protected by various muscles and bony +structures, along which run the great blood-vessels that supply the head, +and the great nerve trunks that pass from the brain to the parts below. + +We have already described the food passages (Chapter VI.) and the +air passages (Chapter VIII.). + +To get a correct idea of the throat we should look into the wide-open +mouth of some friend. Depressing the tongue we can readily see the back +wall of the pharynx, which is common to the two main avenues leading +to the lungs and the stomach. Above, we notice the air passages, which +lead to the posterior cavities of the nose. We have already described the +hard palate, the soft palate, the uvula, and the tonsils (Fig. 46). + +On looking directly beyond these organs, we see the beginning of the +downward passage,--the pharynx. If now the tongue be forcibly drawn +forward, a curved ridge may be seen behind it. This is the +epiglottis, which, as we have already learned shuts down, like the +lid of a box, over the top of the larynx (secs. 137 and 203). + +The throat is lined with mucous membrane covered with ciliated epithelium, +which secretes a lubricating fluid which keeps the parts moist and +pliable. An excess of this secretion forms a thick, tenacious mass of +mucus, which irritates the passages and gives rise to efforts of hawking +and coughing to get rid of it. + +350. The Larynx. The larynx, the essential organ of voice, forms +the box-like top of the windpipe. It is built of variously shaped +cartilages, connected by ligaments. It is clothed on the outside with +muscles; on the inside it is lined with mucous membrane, continuous with +that of the other air passages. + +[Illustration: Fig. 148.--View of the Cartilages in front project and form +the lages and Ligaments of the "Adam's apple," plainly seen and Larynx. +(Anterior view.) + + A, hyoid bone; + B, thyro-hyoid membrane; + C, thyroid cartilage; + D, erico-thyroid membrane; + E, cricoid cartilage, lateral ligaments seen on each side; + F, upper ring of the trachea. + ("Adam's apple" is in the V-shaped groove on a line with B and C.) +] + +The larynx has for a framework two cartilages, the thyroid and the +cricoid, one above the other. The larger of these, called the +thyroid, from a supposed resemblance to a shield, consists of two +extended wings which join in front, but are separated by a wide interval +behind. The united edges in front project and form the "Adam's apple" +plainly seen and easily felt on most people, especially on very lean men. + +Above and from the sides rise two horns connected by bands to the hyoid +bone from which the larynx is suspended. This bone is attached by +muscles and ligaments to the skull. It lies at the base of the tongue, and +can be readily felt by the finger behind the chin at the angle of the jaw +and the neck (sec. 41 and Fig. 46). From the under side of the thyroid two +horns project downwards to become jointed to the cricoid. The thyroid thus +rests upon, and is movable on, the cricoid cartilage. + +The cricoid cartilage, so called from its fancied resemblance to a +signet-ring, is smaller but thicker and stronger than the thyroid, and +forms the lower and back part of the cavity of the larynx. This cartilage +is quite sensitive to pressure from the fingers, and is the cause of the +sharp pain felt when we try to swallow a large and hard piece of food not +properly chewed. + +[Illustration: Fig. 149.--Diagram of a Sectional of Nasal and Throat +Passages. + + C, nasal cavities; + T, tongue; + L, lower jaw; + M, mouth; + U, uvula; + E, epiglottis; + G, larynx; + O, œsophagus. +] + +On the upper edge of the cricoid cartilage are perched a pair of very +singular cartilages, pyramidal in shape, called the arytenoid, which +are of great importance in the production of the voice. These cartilages +are capped with little horn-like projections, and give attachment at their +anterior angles to the true vocal cords, and at their posterior +angles to the muscles which open and close the glottis, or upper +opening of the windpipe. When in their natural position the arytenoid +cartilages resemble somewhat the mouth of a pitcher, hence their name. + +351. The Vocal Cords. The mucous membrane which lines the various +cartilages of the larynx is thrown into several folds. Thus, one fold, the +free edge of which is formed of a band of elastic fibers, passes +horizontally outwards from each side towards the middle line, at the level +of the base of the arytenoid cartilages. These folds are called the true +vocal cords, by the movements of which the voice is produced. + +Above them are other folds of mucous membrane called the false vocal +cords, which take no part in the production of the voice. The +arrangement of the true vocal cords, projecting as they do towards the +middle line, reduces to a mere chink the space between the part of the +larynx above them and the part below them. This constriction of the larynx +is called the glottis. + +[Illustration: Fig. 150.--View of the Cartilages and Ligaments of Larynx. +(Posterior view.) + + A, epiglottis; + B, thyroid cartilage; + C, arytenoid cartilage; + D, ligament connecting lower cornu of the thyroid with the back of the + cricoid cartilage; + E, cricoid cartilage; + F, upper ring of the trachea. +] + +352. The Mechanism of the Voice. The mechanism of the voice may be +more easily understood by a study of Fig. 150. We have here the larynx, +viewed from behind, with all the soft parts in connection with it. On +looking down, the folds forming the true vocal cords are seen enclosing a +V-shaped aperture (the glottis), the narrow part being in front. + +The form of this aperture may be changed by the delicately coordinate +activities of the muscles of the larynx. For instance, the vocal cords may +be brought so closely together that the space becomes a mere slit. Air +forced through the slit will throw the edges of the folds into vibration +and a sound will be produced. + +The Variations in the form of the opening will determine the variations in +the sound. Now, if the various muscles of the larynx be relaxed, the +opening of the glottis is wider. Thus the air enters and leaves the larynx +during breathing, without throwing the cords into vibration enough to +produce any sound. + +We may say that the production of the voice is effected by an arrangement +like that of some musical instruments, the sounds produced by the +vibrations of the vocal cords being modified by the tubes above and below. +All musical sounds are due to movements or vibrations occurring with a +certain regularity, and they differ in loudness, pitch, and quality. +Loudness of the sound depends upon the extent of the vibrations, pitch on +the rapidity of the vibrations, and quality on the admixture of tones +produced by vibrations of varying rates of rapidity, related to one +another. + +[Illustration: Fig. 151.--Longitudinal Section of the Larynx. (Showing the +vocal cords.) + + A, epiglottis; + B, section of hyoid bone; + C, superior vocal cord; + D, ventricle of the larynx; + E, inferior vocal cord; + F, section of the thyroid cartilage; + H, section of anterior portion of the cricoid cartilage; + K, trachea; + L, section of the posterior portion of the cricoid cartilage; + M, arytenoid cartilage; + N, section of the arytenoid muscle. +] + +353. Factors in the Production of the Voice. Muscles which pass from +the cricoid cartilage to the outer angle of the arytenoids act to bring +the vocal cords close together, and parallel to one another, so that the +space between them is narrowed to a slit. A strong expiration now drives +the air from the lungs through the slit, between the cords, and throws +them into vibration. The vibration is small in amount, but very rapid. +Other muscles are connected with the arytenoid cartilages which serve to +seperate the vocal cords and to widely open the glottis. The force of the +outgoing current of air determines the extent of the movement of the +cords, and thus the loudness of the sound will increase with greater force +of expiration. + +We have just learned that the pitch of sound depends on the rapidity of +the vibrations. This depends on the length of cords and their tightness +for the shorter and tighter a string is, the higher is the note which its +vibration produces. The vocal cords of women are about one-third shorter +than those of men, hence the higher pitch of the notes they produce. In +children the vocal cords are shorter than in adults.[50] The cords of +tenor singers are also shorter than those of basses and baritones. The +muscles within the larynx, of course, play a very important part in +altering the tension of the vocal cords. Those qualities of the voice +which we speak of as sweet, harsh, and sympathetic depend to a great +extent upon the peculiar structure of the vocal cords of the individual. + +Besides the physical condition of the vocal cords, as their degree of +smoothness, elasticity, thickness, and so on, other factors determine the +quality of an individual's voice. Thus, the general shape and structure of +the trachea, the larynx, the throat, and mouth all influence the quality +of voice. In fact, the air passages, both below and above the vibrating +cords, act as resonators, or resounding chambers, and intensify and modify +the sounds produced by the cords. It is this fact that prompts skillful +teachers of music and elocution to urge upon their pupils the necessity of +the mouth being properly opened during speech, and especially during +singing. + + Experiment 187. _To show the anatomy of the throat_. Study the + general construction of the throat by the help of a hand mirror. Repeat + the same on the throat of some friend. + + Experiment 188. _To show the construction of the vocal organs_. Get + a butcher to furnish two windpipes from a sheep or a calf. They differ + somewhat from the vocal organs of the human body, but will enable us to + recognize the different parts which have been described, and thus to get + a good idea of the gross anatomy. + + One specimen should be cut open lengthwise in the middle line in front, + and the other cut in the same way from behind. + +354. Speech. Speech is to be distinguished from voice. It may exist +without voice, as in a whisper. Speech consists of articulated +sounds, produced by the action of various parts of the mouth, throat, and +nose. Voice is common to most animals, but speech is the peculiar +privilege of man. + +[Illustration: Fig. 152.--Diagramatic Horizontal Section of Larynx to show +the Direction of Pull of the Posterior Crico-Arytenoid Muscles, which +abduct the Vocal Cords. (Dotted lines show position in abduction.)] + +The organ of speech is perhaps the most delicate and perfect _motor_ +apparatus in the whole body. It has been calculated that upwards of 900 +movements per minute can be made by the movable organs of speech during +reading, speaking, and singing. It is said that no less than a hundred +different muscles are called into action in talking. Each part of this +delicate apparatus is so admirably adjusted to every other that all parts +of this most complex machinery act in perfect harmony. + +There are certain articulate sounds called vowel or vocal, from the fact +that they are produced by the vocal cords, and are but slightly modified +as they pass out of the mouth. The true vowels, _a, e, i, o, u_, can +all be sounded alone, and may be prolonged in expiration. These are the +sounds chiefly used in singing. The differences in their characters are +produced by changes in the position of the tongue, mouth, and lips. + +Consonants are sounds produced by interruptions of the outgoing +current of air, but in some cases have no sound in themselves, and serve +merely to modify vowel sounds. Thus, when the interruption to the outgoing +current takes place by movements of the lips, we have the _labial_ +consonants, _p_, _b_, _f_, and _v_. When the tongue, in relation with the +teeth or hard palate, obstructs the air, the _dental_ consonants, _d_, +_t_, _l_, and _s_ are produced. _Gutturals_, such as _k_, _g_, _ch_, _gh_, +and _r_, are due to the movements of the root of the tongue in connection +with the soft palate or pharynx. + +To secure an easy and proper production of articulate sounds, the mouth, +teeth, lips, tongue, and palate should be in perfect order. The +modifications in articulation occasioned by a defect in the palate, or in +the uvula, by the loss of teeth, from disease, and from congenital +defects, are sufficiently familiar. We have seen that speech consists +essentially in a modification of the vocal sounds by the accessory organs, +or by parts above the larynx, the latter being the essential vocal +instrument. + +Many animals have the power of making articulated sounds; a few have +risen, like man, to the dignity of sentences, but these are only by +imitation of the human voice. Both vowels and consonants can be +distinguished in the notes of birds, the vocal powers of which are +generally higher than those of mammals. The latter, as a rule, produce +only vowels, though some are also able to form consonants. + +Persons idiotic from birth are incapable of producing any other vocal +sounds than inarticulate cries, although supplied with all the internal +means of articulation. Persons deaf and dumb are in the same situation, +though from a different cause; the one being incapable of imitating, and +the other being deprived of hearing the sounds to be imitated. + +[Illustration: Fig. 153.--Direction of Pull of the Lateral +Crico-Arytenoids, which adduct the Vocal Cords. (Dotted lines show +position in adduction.)] + +In _whispering_, the larynx takes scarcely any part in the production of +the sounds; the vocal cords remain apart and comparatively slack, and the +expiratory blast rushes through without setting them in vibration. + +In _stammering_, spasmodic contraction of the diaphragm interrupts the +effort of expiration. The stammerer has full control of the mechanism of +articulation, but not of the expiratory blast. His larynx and his lips are +at his command, but not his diaphragm. To conquer this defect he must +train his muscles of respiration to calm and steady action during speech. +The _stutterer_, on the other hand, has full control of the muscles of +expiration. His diaphragm is well drilled, but his lips and tongue are +insubordinate. + +355. The Care of the Throat and Voice. The throat, exposed as it is +to unwholesome and overheated air, irritating dust of the street, +factories, and workshops, is often inflamed, resulting in that common +ailment, _sore throat_. The parts are red, swollen, and quite painful on +swallowing. Speech is often indistinct, but there is no hoarseness or +cough unless the uvula is lengthened and tickles the back part of the +tongue. Slight sore throat rarely requires any special treatment, aside +from simple nursing. + +The most frequent cause of throat trouble is the action of cold upon the +heated body, especially during active perspiration. For this reason a cold +bath should not be taken while a person is perspiring freely. The muscles +of the throat are frequently overstrained by loud talking, screaming, +shouting, or by reading aloud too much. People who strain or misuse the +voice often suffer from what is called "clergyman's sore throat." Attacks +of sore throat due to improper methods of breathing and of using the voice +should be treated by judicious elocutionary exercises and a system of +vocal gymnastics, under the direction of proper teachers. + +Persons subject to throat disease should take special care to wear +suitable underclothing, adapted to the changes of the seasons. Frequent +baths are excellent tonics to the skin, and serve indirectly to protect +one liable to throat ailments from changes in the weather. It is not +prudent to muffle the neck in scarfs, furs, and wraps, unless perhaps +during an unusual exposure to cold. Such a dress for the neck only makes +the parts tender, and increases the liability to a sore throat. + +Every teacher of elocution or of vocal music, entrusted with the training +of a voice of some value to its possessor, should have a good, practical +knowledge of the mechanism of the voice. Good voices are often injured by +injudicious management on the part of some incompetent instructor. It is +always prudent to cease speaking or singing in public the moment there is +any hoarseness or sore throat. + +The voice should not be exercised just after a full meal, for a full +stomach interferes with the free play of the diaphragm. A sip of water +taken at convenient intervals, and held in the mouth for a moment or two, +will relieve the dryness of the throat during the use of the voice. + + +356. Effect of Alcohol upon the Throat and Voice. Alcoholic beverages +seriously injure the throat, and consequently the voice, by causing a +chronic inflammation of the membrane lining the larynx and the vocal +cords. The color is changed from the healthful pink to red, and the +natural smooth surface becomes roughened and swollen, and secretes a tough +phlegm. + +The vocal cords usually suffer from this condition. They are thickened, +roughened, and enfeebled, the delicate vibration of the cords is impaired, +the clearness and purity of the vocal tones are gone, and instead the +voice has become rough and husky. So well known is this result that +vocalists, whose fortune is the purity and compass of their tones, are +scrupulously careful not to impair these fine qualities by convivial +indulgences. + + +357. Effect of Tobacco upon the Throat and Voice. The effect of +tobacco is often specially serious upon the throat, producing a disease +well known to physicians as "the smoker's sore throat." Still further, it +produces inflammation of the larynx, and thus entails disorders of the +vocal cords, involving rough voice and harsh tones. For this reason +vocalists rarely allow themselves to come under the narcotic influence of +tobacco smoke. It is stated that habitual smokers rarely have a normal +condition of the throat. + + + +Additional Experiments. + + Experiment 189. _To illustrate the importance of the resonating + cavity of the nose in articulation_. Pinch the nostrils, and try to + pronounce slowly the words "Lincoln," "something," or any other words + which require the sound of _m_, _ln_, or _ng_. + + [Illustration: Fig. 154.] + + Experiment 190. _To illustrate the passage of air through the + glottis._ Take two strips of India rubber, and stretch them over the + open end of a boy's "bean-blower," or any kind of a tube. Tie them + tightly with thread, so that a chink will be left between them, as shown + in Fig. 154. Force the air through such a tube by blowing hard, and if + the strips are not too far apart a sound will be produced. The sound + will vary in character, just as the bands are made tight or loose. + + Experiment 191. "A very good illustration of the action of the + vocal bands in the production of the voice may be given by means of a + piece of bamboo or any hollow wooden tube, and a strip of rubber, about + an inch or an inch and a half wide, cut from the pure sheet rubber used + by dentists. + + "One end of the tube is to be cut sloping in two directions, and the + strip of sheet rubber is then to be wrapped round the tube, so as to + leave a narrow slit terminating at the upper corners of the tube. + + "By blowing into the other end of the tube the edges of the rubber bands + will be set in vibration, and by touching the vibrating membrane at + different points so as to check its movements it may be shown that the + pitch of the note emitted depends upon the length and breadth of the + vibrating portion of the vocal bands."[51]--Dr. H. P. Bowditch. + + [NOTE. The limitations of a text-book on physiology for schools do not + permit so full a description of the voice as the subject deserves. For + additional details, the student is referred to Cohen's _The Throat and + the Voice_, a volume in the "American Health Primer Series." Price 40 + cents.] + + + + +Chapter XIII. + +Accidents and Emergencies. + + + +358. Prompt Aid to the Injured. A large proportion of the accidents, +emergencies, and sudden sicknesses that happen do not call for medical or +surgical attention. For those that do require the services of a physician +or surgeon, much can be often done before the arrival of professional +help. Many a life has been saved and much suffering and anxiety prevented +by the prompt and efficient help of some person with a cool head, a steady +hand, and a practical knowledge of what to do first. Many of us can recall +with mingled admiration and gratitude the prompt services rendered our +families by some neighbor or friend in the presence of an emergency or +sudden illness. + +In fact, what we have studied in the preceding chapters becomes tenfold +more interesting, instructive, and of value to us, if we are able to +supplement such study with its practical application to the treatment of +the more common and less serious accidents and emergencies. + +While no book can teach one to have presence of mind, a cool head, or to +restrain a more or less excitable temperament in the midst of sudden +danger, yet assuredly with proper knowledge for a foundation, a certain +self-confidence may be acquired which will do much to prevent hasty +action, and to maintain a useful amount of self-control. + +Space allows us to describe briefly in this chapter only a few of the +simplest helps in the more common accidents and emergencies +which are met with in everyday life.[52] + + 359. Hints as to what to Do First. Retain so far as possible your +presence of mind, or, in other words, keep cool. This is an all-important +direction. Act promptly and quietly, but not with haste. Whatever you do, +do in earnest; and never act in a half-hearted manner in the presence of +danger. Of course, a knowledge of what to-do and how to do it will +contribute much towards that self-control and confidence that command +success. Be sure and send for a doctor at once if the emergency calls for +skilled service. All that is expected of you under such circumstances +is to tide over matters until the doctor comes. + +[Illustration: Fig. 155.--Showing how Digital Compression should be +applied to the Brachial Artery.] + +Do not presume upon any smattering of knowledge you have, to assume any +risk that might lead to serious results. Make the sufferer comfortable by +giving him an abundance of fresh air and placing him in a restful +position. Do all that is possible to keep back the crowd of curious +lookers-on, whom a morbid curiosity has gathered about the injured person. +Loosen all tight articles of clothing, as belts, collars, corsets, and +elastics. Avoid the use of alcoholic liquors. They are rarely of any real +service, and in many instances, as in bleeding, may do much harm. + + +360. Incised and Lacerated Wounds. An incised or cut wound +is one made by a sharp instrument, as when the finger is cut with a +knife. Such a wound bleeds freely because the clean-cut edges do not favor +the clotting of blood. In slight cuts the bleeding readily ceases, and the +wound heals by primary union, or by "first intention," as surgeons call +it. + +Lacerated and contused wounds are made by a tearing or bruising +instrument, for example, catching the finger on a nail. Such wounds bleed +but little, and the edges and surfaces are rough and ragged. + +If the incised wound is deep or extensive, a physician is necessary to +bring the cut edges together by stitches in order to get primary union. +Oftentimes, in severe cuts, and generally in lacerations, there is a loss +of tissue, so that the wound heals by "second intention"; that is, the +wound heals from the bottom by a deposit of new cells called +_granulations_, which gradually fill it up. The skin begins to grow from +the edges to the center, covering the new tissue and leaving a cicatrix or +scar with which every one is familiar. + + +361. Contusion and Bruises. An injury to the soft tissues, caused by +a blow from some blunt instrument, or a fall, is a contusion, or +bruise. It is more or less painful, followed by discoloration due to +the escape of blood under the skin, which often may not be torn through. A +black eye, a knee injured by a fall from a bicycle, and a finger hurt by a +baseball, are familiar examples of this sort of injury. Such injuries +ordinarily require very simple treatment. + +The blood which has escaped from the capillaries is slowly absorbed, +changing color in the process, from blue black to green, and fading into a +light yellow. Wring out old towels or pieces of flannel in hot water, and +apply to the parts, changing as they become cool. For cold applications, +cloths wet with equal parts of water and alcohol, vinegar, and witch-hazel +may be used. Even if the injury is apparently slight it is always safe to +rest the parts for a few days. + +When wounds are made with ragged edges, such as those made by broken +glass and splinters, more skill is called for. Remove every bit of +foreign substance. Wash the parts clean with one of the many +antiseptic solutions, bring the torn edges together, and hold them in +place with strips of plaster. Do not cover such an injury all over with +plaster, but leave room for the escape of the wound discharges. For an +outside dressing, use compresses made of clean cheese-cloth or strips of +any clean linen cloth. The antiseptic _corrosive-sublimate gauze_ on sale +at any drug store should be used if it can be had. + +Wounds made by toy pistols, percussion-caps, and rusty nails and tools, if +neglected, often lead to serious results from blood-poisoning. A hot +flaxseed poultice may be needed for several days. Keep such wounds clean +by washing or syringing them twice a day with hot _antiseptics_, which are +poisons to _bacteria_ and kill them or prevent their growth. Bacteria are +widely distributed, and hence the utmost care should be taken to have +everything which is to come in contact with a wounded surface free from +the germs of inflammation. In brief, such injuries must be kept +_scrupulously neat_ and _surgically clean_. + +[Illustration: Fig. 156.--Dotted Line showing the Course of the Brachial +Artery.] + +The injured parts should be kept at rest. Movement and disturbance hinder +the healing process. + + +362. Bites of Mad Dogs. Remove the clothing at once, if only from the +bitten part, and apply a temporary ligature _above_ the wound. This +interrupts the activity of the circulation of the part, and to that +extent delays the absorption of the poisonous saliva by the blood-vessels +of the wound. A dog bite is really a lacerated and contused wound, and +lying in the little roughnesses, and between the shreds, is the poisonous +saliva. If by any means these projections and depressions affording the +lodgment can be removed, the poison cannot do much harm. If done with a +knife, the wound would be converted, practically, into an incised wound, +and would require treatment for such. + +If a surgeon is at hand he would probably cut out the injured portion, or +cauterize it thoroughly. Professional aid is not always at our command, +and in such a case it would be well to take a poker, or other suitable +piece of iron, heat it _red_ hot in the fire, wipe off and destroy the +entire surface of the wound. As fast as destroyed, the tissue becomes +white. An iron, even at a white heat, gives less pain and at once destroys +the vitality of the part with which it comes in contact. + +If the wound is at once well wiped out, and a stick of solid nitrate of +silver (lunar caustic) rapidly applied to the entire surface of the wound, +little danger is to be apprehended. Poultices and warm fomentations should +be applied to the injury to hasten the sloughing away of the part whose +vitality has been intentionally destroyed. + +Any dog, after having bitten a person, is apt, under a mistaken belief, to +be at once killed. This should not be done. There is no more danger from a +dog-bite, unless the dog is suffering from the disease called _rabies_ or +is "mad," than from any other lacerated wound. The suspected animal should +be at once placed in confinement and watched, under proper safeguards, for +the appearance of any symptoms that indicate rabies. + +Should no pronounced symptoms indicate this disease in the dog, a great +deal of unnecessary mental distress and worry can be saved both on the +part of the person bitten and his friends. + +363. Injuries to the Blood-vessels. It is very important to know the +difference between the bleeding from an artery and that from a vein. + +If an artery bleeds, the blood leaps in spurts, and is of a +bright scarlet color. + +If a vein bleeds, the blood flows in a steady stream, and is of a +dark purple color. + +If the capillaries are injured the blood merely oozes. + +Bleeding from an artery is a dangerous matter in proportion to the size of +the vessel, and life itself may be speedily lost. Hemorrhage from a vein +or from the capillaries is rarely troublesome, and is ordinarily easily +checked, aided, if need be, by hot water, deep pressure, the application +of some form of iron styptic, or even powdered alum. When an artery is +bleeding, always remember to make deep pressure between the wound and the +heart. In all such cases send at once for the doctor. + +[Illustration: Fig. 157.--Showing how Digital Compression should be +applied to the Femoral Artery.] + +Do not be afraid to act at once. A resolute grip in the right place with +firm fingers will do well enough, until a twisted handkerchief, stout +cord, shoestring, suspender, or an improvised tourniquet[53] is ready to +take its place. If the flow of blood does not stop, change the pressure +until the right spot is found. + +Sometimes it will do to seize a handful of dry earth and crowd it down +into the bleeding wound, with a firm pressure. Strips of an old +handkerchief, underclothing, or cotton wadding may also be used as a +compress, provided pressure is not neglected. + +In the after-treatment it is of great importance that the wound and the +dressing should be kept free from bacteria by keeping everything +surgically clean. + + +364. Where and how to Apply Pressure. The principal places in which +to apply pressure when arteries are injured and bleeding should always be +kept in mind. + + Experiment 192. _How to tie a square knot_. If the student would + render efficient help in accidents and emergencies, to say nothing of + service on scores of other occasions, he must learn how to tie a square + or "reef" knot. This knot is secure and does not slip as does the + "granny" knot. The square knot is the one used by surgeons in ligating + vessels and securing bandages. Unless one knew the difference, the + insecure "granny" knot might be substituted. + + [Illustration: Fig. 158.--Showing how a Square Knot may be tied with a + Cord and a Handkerchief.] + + A square knot is tied by holding an end of a bandage or cord in + each hand, and then passing the end in the _right_ hand over the one in + the left and tying; the end now in the _left_ hand is passed over the + one in the right and again tied. + +If in the finger, grasp it with the thumb and forefinger, and pinch +it firmly on each side; if in the hand, press on the bleeding spot, +or press with the thumb just above and in front of the wrist. + +For injuries below the elbow, grasp the upper part of the arm with +the hands, and squeeze hard. The main artery runs in the middle line of +the bend of the elbow. Tie the knotted cord here, and bend the forearm so +as to press hard against the knot. + +For the upper arm, press with the fingers against the bone on the +inner side, and just on the edge of the swell of the biceps muscle. Now we +are ready for the knotted cord. Take a stout stick of wood, about a foot +long, and twist the cord hard with it, bringing the knot firmly over the +artery. + +For the foot or leg, pressure as before, in the hollow behind +the knee, just above the calf of the leg. Bend the thigh towards the +abdomen and bring the leg up against the thigh, with the knot in the bend +of the knee. + + +365. Bleeding from the Stomach and Lungs. Blood that comes from the +lungs is bright red, frothy, or "soapy." There is rarely much; it usually +follows coughing, feels warm, and has a salty taste. This is a grave +symptom. Perfect rest on the back in bed and quiet must be insisted upon. +Bits of ice should be eaten freely. Loosen the clothing, keep the +shoulders well raised, and the body in a reclining position and absolutely +at rest. Do not give alcoholic drinks. + +Blood from the stomach is not frothy, has a sour taste, and is +usually dark colored, looking somewhat like coffee grounds. It is more in +quantity than from the lungs, and is apt to be mixed with food. Employ the +same treatment, except that the person should be kept flat on the back. + + +366. Bleeding from the Nose. This is the most frequent and the least +dangerous of the various forms of bleeding. Let the patient sit upright; +leaning forward with the head low only increases the hemorrhage. Raise the +arm on the bleeding side; do not blow the nose. Wring two towels out of +cold water; wrap one around the neck and the other properly folded over +the forehead and upper part of the nose. + +Add a teaspoonful of powdered _alum_ to a cup of water, and snuff it up +from the hand. If necessary, soak in alum water a piece of absorbent +cotton, which has been wound around the pointed end of a pencil or +penholder; plug the nostril by pushing it up with a twisting motion until +firmly lodged. + + +367. Burns or Scalds. Burns or scalds are dangerous in proportion to +their extent and depth. A child may have one of his fingers burned off +with less danger to life than an extensive scald of his back and legs. A +deep or extensive burn or scald should always have prompt medical +attendance. + +In burns by acids, bathe the parts with an alkaline fluid, as diluted +ammonia, or strong soda in solution, and afterwards dress the burn. + +In burns caused by lime, caustic potash, and other alkalies, soak the +parts with vinegar diluted with water; lemon juice, or any other diluted +acid. + +Remove the clothing with the greatest care. Do not pull, but carefully cut +and coax the clothes away from the burned places. Save the skin unbroken +if possible, taking care not to break the blisters. The secret of +treatment is to prevent friction, and to keep out the air. If +the burn is slight, put on strips of soft linen soaked in a strong +solution of baking-soda and water, one heaping table spoonful to a cupful +of water. This is especially good for scalds. + +[Illustration: Fig. 159.--Dotted Line showing the Course of the Femoral +Artery.] + +_Carron oil_ is one of the best applications. It is simply half +linseed-oil and half lime-water shaken together. A few tablespoonfuls of +carbolic acid solution to one pint may be added to this mixture to help +deaden the pain. Soak strips of old linen or absorbent cotton in this +time-honored remedy, and gently apply. + +If carbolized or even plain _vaseline_ is at hand, spread it freely on +strips of old linen, and cover well the burnt parts, keeping out the air +with other strips carefully laid on. Simple cold water is better than +flour, starch, toilet powder, cotton batting, and other things which are +apt to stick, and make an after-examination very painful. + +[Illustration: Fig. 160.--Showing how Hemorrhage from the Femoral Artery +may be arrested by the Use of an Improvised Apparatus (technically called +a _Tourniquet_).] + +368. Frost Bites. The ears, toes, nose, and fingers are occasionally +frozen, or frost-bitten. No warm air, warm water, or fire should be +allowed near the frozen parts until the natural temperature is nearly +restored. Rub the frozen part vigorously with snow or snow-water in a cold +room. Continue this until a burning, tingling pain is felt, when all +active treatment should cease. + +Pain shows that warmth and circulation are beginning to return. The after +effects of a frost bite are precisely like those of a burn, and require +similar treatment. Poultices made from scraped raw potatoes afford much +comfort for an after treatment. + + +369. Catching the Clothing on Fire. When the clothing catches fire, +throw the person down on the ground or floor, as the flames will tend +less to rise toward the mouth and nostrils. Then without a moment's delay, +roll the person in a carpet or hearth-rug, so as to stifle the flames, +leaving only the head out for breathing. + +If no carpet or rug can be had, then take off your coat, shawl, or cloak +and use it instead. Keep the flame as much as possible from the face, so +as to prevent the entrance of the hot air into the lungs. This can be done +by beginning at the neck and shoulders with the wrapping. + + +370. Foreign Bodies in the Throat. Bits of food or other small +objects sometimes get lodged in the throat, and are easily extracted by +the forefinger, by sharp slaps on the back, or expelled by vomiting. If it +is a sliver from a toothpick, match, or fishbone, it is no easy matter to +remove it; for it generally sticks into the lining of the passage. If the +object has actually passed into the windpipe, and is followed by sudden +fits of spasmodic coughing, with a dusky hue to the face and fingers, +surgical help must be called without delay. + +If a foreign body, like coins, pencils, keys, fruit-stones, etc., is +swallowed, it is not wise to give a physic. Give plenty of hard-boiled +eggs, cheese, and crackers, so that the intruding substance maybe enfolded +in a mass of solid food and allowed to pass off in the natural way. + + +371. Foreign Bodies in the Nose. Children are apt to push beans, +peas, fruit-stones, buttons, and other small objects, into the nose. +Sometimes we can get the child to help by blowing the nose hard. At other +times, a sharp blow between the shoulders will cause the substance to fall +out. If it is a pea or bean, which is apt to swell with the warmth and +moisture, call in medical help at once. + + +372. Foreign Bodies in the Ear. It is a much more difficult matter to +get foreign bodies out of the ear than from the nose. Syringe in a little +warm water, which will often wash out the substance. If live insects get +into the ear, drop in a little sweet oil, melted vaseline, salt and water, +or even warm molasses. + +If the tip of the ear is pulled up gently, the liquid will flow in more +readily. If a light is held close to the outside ear, the insect may be +coaxed to crawl out towards the outer opening of the ear, being attracted +by the bright flame. + +373. Foreign Bodies in the Eye. Cinders, particles of dust, and other +small substances, often get into the eye, and cause much pain. It will +only make bad matters worse to rub the eye. Often the copious flow of +tears will wash the substance away. It is sometimes seen, and removed +simply by the twisted corner of a handkerchief carefully used. If it is +not removed, or even found, in this way, the upper lid must be turned +back. + +[Illustration: Fig. 161.--Showing how the Upper Eyelid may be everted with +a Pencil or Penholder.] + +This is done usually as follows: Seize the lashes between the thumb and +forefinger, and draw the edge of the lid away from the eyeball. Now, +telling the patient to look down, press a slender lead-pencil or penholder +against the lid, parallel to and above the edge, and then pull the edge +up, and turn it over the pencil by means of the lashes. + +The eye is now readily examined, and usually the foreign body is easily +seen and removed. Do not increase the trouble by rubbing the eye after you +fail, but get at once skilled help. After the substance has been removed, +bathe the eye for a time with hot water. + +If lime gets into the eye, it may do a great amount of mischief, and +generally requires medical advice, or permanent injury will result. Until +such advice can be had, bathe the injured parts freely with a weak +solution of vinegar and hot water. + +374. Broken Bones. Loss of power, pain, and swelling are symptoms of +a broken bone that may be easily recognized. Broken limbs should always be +handled with great care and tenderness. If the accident happens in the +woods, the limb should be bound with handkerchiefs, suspenders, or strips +of clothing, to a piece of board, pasteboard, or bark, padded with moss or +grass, which will do well enough for a temporary splint. Always put a +broken arm into a sling after the splints are on. + +[Illustration: Fig. 162.--Showing how an Umbrella may be used as a +Temporary Splint in Fracture of the Leg.] + +Never move the injured person until the limb is made safe from further +injuries by putting on temporary splints. If you do not need to move the +person, keep the limb in a natural, easy position, until the doctor comes. + +Remember that this treatment for broken bones is only to enable the +patient to be moved without further injury. A surgeon is needed at once to +set the broken bone. + + +[Illustration: Fig. 163.--Showing how a Pillow may be used as a Temporary +Splint in Fracture of the Leg.] + +375. Fainting. A fainting person should be laid flat at once. Give +plenty of fresh air, and dash cold water, if necessary, on the head and +neck. Loosen all tight clothing. Smelling-salts may be held to the nose, +to excite the nerves of sensation. + +376. Epileptic and Hysterical Fits, Convulsions of Children. +Sufferers from "fits" are more or less common. In _epilepsy_, the sufferer +falls with a peculiar cry; a loss of consciousness, a moment of rigidity, +and violent convulsions follow. There is foaming at the mouth, the eyes +are rolled up, and the tongue or lips are often bitten. When the fit is +over the patient remains in a dazed, stupid state for some time. It is a +mistake to struggle with such patients, or to hold them down and keep them +quiet. It does more harm than good. + +See that the person does not injure himself; crowd a pad made from a +folded handkerchief or towel between the teeth, to prevent biting of the +lips or tongue. Do not try to make the sufferer swallow any drink. +Unfasten the clothes, especially about the neck and chest. Persons who are +subject to such fits should rarely go out alone, and never into crowded or +excited gatherings of any kind. + +_Hysterical fits_ almost always occur in young women. Such patients never +bite their tongue nor hurt themselves. Placing a towel wrung out in cold +water across the face, or dashing a little cold water on the face or +neck, will usually cut short the fit, speaking firmly to the patient at +the same time. Never sympathize too much with such patients; it will only +make them a great deal worse. + +377. Asphyxia. Asphyxia is from the Greek, and means an "absence of +pulse." This states a fact, but not the cause. The word is now commonly +used to mean _suspended animation_. When for any reason the proper supply +of oxygen is cut off, the tissues rapidly load up with carbon dioxid. The +blood turns dark, and does not circulate. The healthy red or pink look of +the lips and finger-nails becomes a dusky purple. The person is suffering +from a lack of oxygen; that is, from asphyxia, or suffocation. +It is evident there can be several varieties of asphyxia, as in apparent +drowning, strangulation and hanging, inhalation of gases, etc. + +The first and essential thing to do is to give fresh air. Remove the +person to the open air and place him on his back. Remove tight clothing +about the throat and waist, dash on cold water, give a few drops of +ammonia in hot water or hot ginger tea. Friction applied to the limbs +should be kept up. If necessary, use artificial respiration by the +Sylvester method (sec. 380). + +The chief dangers from poisoning by noxious gases come from the fumes of +burning coal in the furnace, stove, or range; from "blowing out" gas, +turning it down, and having it blown out by a draught; from the foul air +often found in old wells; from the fumes of charcoal and the foul air of +mines. + +378. Apparent Drowning. Remove all tight clothing from the neck, +chest, and waist. Sweep the forefinger, covered with a handkerchief or +towel, round the mouth, to free it from froth and mucus. Turn the body on +the face, raising it a little, with the hands under the hips, to allow any +water to run out from the air passages. Take only a moment for this. + +Lay the person flat upon the back, with a folded coat, or pad of any +kind, to keep the shoulders raised a little. Remove all the wet, clinging +clothing that is convenient. If in a room or sheltered place, strip the +body, and wrap it in blankets, overcoats, etc. If at hand, use bottles of +hot water, hot flats, or bags of hot sand round the limbs and feet. Watch +the tongue: it generally tends to slip back, and to shut off the air from +the glottis. Wrap a coarse towel round the tip of the tongue, and keep it +well pulled forward. + +The main thing to do is to keep up artificial respiration until the +natural breathing comes, or all hope is lost. This is the simplest way to +do it: The person lies on the back; let some one kneel behind the head. +Grasp both arms near the elbows, and sweep them upward above the head +until they nearly touch. Make a firm pull for a moment. This tends to fill +the lungs with air by drawing the ribs up, and making the chest cavity +larger. Now return the arms to the sides of the body until they press hard +against the ribs. This tends to force out the air. This makes artificially +a complete act of respiration. Repeat this act about fifteen times every +minute. + +[Illustration: Fig. 164.--The Sylvester Method. (First +movement--inspiration.)] + +All this may be kept up for several hours. The first sign of recovery is +often seen in the slight pinkish tinge of the lips or finger-nails. That +the pulse cannot be felt at the wrist is of little value in itself as a +sign of death. Life may be present when only the most experienced ear can +detect the faintest heart-beat. + +When a person can breathe, even a little, he can swallow. Hold +smelling-salts or hartshorn to the nose. Put one teaspoonful of the +aromatic spirits of ammonia, or even of ammonia water, into a half-glass +of hot water, and give a few teaspoonfuls of this mixture every few +minutes. Meanwhile do not fail to keep up artificial warmth in the most +vigorous manner. + +379. Methods of Artificial Respiration. There are several +well-established methods of artificial respiration. The two known as the +Sylvester and the Marshall Hall methods are generally accepted +as efficient and practical. + +[Illustration: Fig. 165.--The Sylvester Method. (Second +movement--expiration.)] + +380. The Sylvester Method. The water and mucus are supposed to have +been removed from the interior of the body by the means above described +(sec. 378). + +The patient is to be placed on his back, with a roll made of a coat or a +shawl under the shoulders; the tongue should then be drawn forward and +retained by a handkerchief which is placed across the extended organ and +carried under the chin, then crossed and tied at the back of the neck. An +elastic band or small rubber tube or a suspender may be used for the same +purpose. + +The attendant should kneel at the head and grasp the elbows of the +patient and draw them upward until the hands are carried above the head +and kept in this position until one, two, three, can be slowly counted. +This movement elevates the ribs, expands the chest, and creates a vacuum +in the lungs into which the air rushes, or in other words, the movement +produces _inspiration_. The elbows are then slowly carried downward, +placed by the side, and pressed inward against the chest, thereby +diminishing the size of the latter and producing _expiration_. + +These movements should be repeated about fifteen times each minute for at +least two hours, provided no signs of animation show themselves. + +381. The Marshall Hall Method. The patient should be placed face +downwards, the head resting on the forearm with a roll or pillow placed +under the chest; he should then be turned on his side, an assistant +supporting the head and keeping the mouth open; after an interval of two +or three seconds, the patient should again be placed face downward and +allowed to remain in this position the same length of time. This operation +should be repeated fifteen or sixteen times each minute, and continued +(unless the patient recovers) for at least two hours. + +[Illustration: Fig. 166.--The Marshall Hall Method. (First position.)] + +If, after using one of the above methods, evidence of recovery appears, +such as an occasional gasp or muscular movement, the efforts to produce +artificial respiration must not be discontinued, but kept up until +respiration is fully established. All wet clothing should then be removed, +the patient rubbed dry, and if possible placed in bed, where warmth and +warm drinks can be properly administered. A small amount of nourishment, +in the form of hot milk or beef tea, should be given, and the patient kept +quiet for two or three days. + +[Illustration: Fig. 167.--The Marshall Hall Method. (Second position.)] + +382. Sunstroke or Heatstroke. This serious accident, so far-reaching +oftentimes in its result, is due to an unnatural elevation of the bodily +temperature by exposure to the direct rays of the sun, or from the extreme +heat of close and confined rooms, as in the cook-rooms and laundries of +hotel basements, from overheated workshops, etc. + +There is sudden loss of consciousness, with deep, labored breathing, an +intense burning heat of the skin, and a marked absence of sweat. The main +thing is to lower the temperature. Strip off the clothing; apply chopped +ice, wrapped in flannel to the head. Rub ice over the chest, and place +pieces under the armpits and at the sides. If there is no ice, use sheets +or cloths wet with cold water. The body may be stripped, and sprinkled +with ice-water from a common watering-pot. + +If the skin is cold, moist, or clammy, the trouble is due to heat +exhaustion. Give plenty of fresh air, but apply no cold to the body. Apply +heat, and give hot drinks, like hot ginger tea. Sunstroke or heatstroke is +a dangerous affliction. It is often followed by serious and permanent +results. Persons who have once suffered in this way should carefully avoid +any risk in the future. + + + + +Chapter XIV. + +In Sickness and in Health. + + + +383. Arrangement of the Sick-room. This room, if possible, should be +on the quiet and sunny side of the house. Pure, fresh air, sunshine, and +freedom from noise and odor are almost indispensable. A fireplace as a +means of ventilation is invaluable. The bed should be so placed that the +air may get to it on all sides and the nurse move easily around it. +Screens should be placed, if necessary, so as to exclude superfluous light +and draughts. + +The sick-room should be kept free from all odors which affect the sick +unpleasantly, as perfumery, highly scented soaps, and certain flowers. +Remove all useless ornaments and articles likely to collect dust, as +unnecessary pieces of furniture and heavy draperies. A clean floor, with a +few rugs to deaden the footsteps, is much better than a woolen carpet. +Rocking-chairs should be banished from the sick-room, as they are almost +sure to disturb the sick. + +A daily supply of fresh flowers tends to brighten the room. Keep the +medicines close at hand, but all poisonous drugs should be kept carefully +by themselves and ordinarily under lock and key. A small table should be +placed at the bedside, and on it the bell, food tray, flowers and other +small things which promote the comfort of the patient. + +The nurse should not sleep with the patient. Sofas and couches are not +commonly comfortable enough to secure needed rest. A cot bed is at once +convenient and inexpensive, and can be readily folded and put out of sight +in the daytime. It can also be used by the patient occasionally, +especially during convalescence. + +384. Ventilation of the Sick-room. Proper ventilation is most +essential to the sick-room, but little provision is ordinarily made for so +important a matter. It is seldom that one of the windows cannot be let +down an inch or more at the top, a screen being arranged to avoid any +draught on the patient. Remove all odors by ventilation and not by +spraying perfumery, or burning pastilles, which merely conceal offensive +odors without purifying the air. During cold weather and in certain +diseases, the patient may be covered entirely with blankets and the +windows opened wide for a few minutes. + +Avoid ventilation by means of doors, for the stale air of the house, +kitchen smells, and noises made by the occupants of the house, are apt to +reach the sick-room. The entire air of the room should be changed at least +two or three times a day, in addition to the introduction of a constant +supply of fresh air in small quantities. + + +385. Hints for the Sick-room. Always strive to look cheerful and +pleasant before the patient. Whatever may happen, do not appear to be +annoyed, discouraged, or despondent. Do your best to keep up the courage +of sick persons under all circumstances. In all things keep in constant +mind the comfort and ease of the patient. + +Do not worry the sick with unnecessary questions, idle talk, or silly +gossip. It is cruel to whisper in the sick-room, for patients are always +annoyed by it. They are usually suspicious that something is wrong and +generally imagine that their condition has changed for the worse. + +Symptoms of the disease should never be discussed before the patient, +especially if he is thought to be asleep. He may be only dozing, and any +such talk would then be gross cruelty. Loud talking must, of course, be +avoided. The directions of the physician must be rigidly carried out in +regard to visitors in the sick-room. This is always a matter of foremost +importance, for an hour or even a night of needed sleep and rest may be +lost from the untimely call of some thoughtless visitor. A competent +nurse, who has good sense and tact, should be able to relieve the family +of any embarrassment under such circumstances. + +Do not ever allow a kerosene light with the flame turned down to remain in +the sick-room. Use the lamp with the flame carefully shaded, or in an +adjoining room, or better still, use a sperm candle for a night light. + +Keep, so far as possible, the various bottles of medicine, spoons, +glasses, and so on in an adjoining room, rather than to make a formidable +array of them on a bureau or table near the sick-bed. A few simple things, +as an orange, a tiny bouquet, one or two playthings, or even a pretty +book, may well take their place. + +The ideal bed is single, made of iron or brass, and provided with woven +wire springs and a hair mattress. Feather-beds are always objectionable in +the sick-room for many and obvious reasons. The proper making of a +sick-bed, with the forethought and skill demanded in certain diseases, is +of great importance and an art learned only after long experience. The +same principle obtains in all that concerns the lifting and the moving of +the sick. + +Sick people take great comfort in the use of fresh linen and fresh +pillows. Two sets should be used, letting one be aired while the other is +in use. In making changes the fresh linen should be thoroughly aired and +warmed and everything in readiness before the patient is disturbed. + + +386. Rules for Sick-room. Do not deceive sick people. Tell what is +proper or safe to be told, promptly and plainly. If a physician is +employed, carry out his orders to the very letter, as long as he visits +you. Make on a slip of paper a note of his directions. Make a brief record +of exactly what to do, the precise time of giving medicines, etc. This +should always be done in serious cases, and by night watchers. Then there +is no guesswork. You have the record before you for easy reference. All +such things are valuable helps to the doctor. + +Whatever must be said in the sick-room, say it openly and aloud. How often +a sudden turn in bed, or a quick glance of inquiry, shows that whispering +is doing harm! If the patient is in his right mind, answer his questions +plainly and squarely. It may not be best to tell all the truth, but +nothing is gained in trying to avoid a straightforward reply. + +Noises that are liable to disturb the patient, in other parts of the house +than the sick-room, should be avoided. Sounds of a startling character, +especially those not easily explained, as the rattling or slamming of +distant blinds and doors, are always irritating to the sick. + +Always attract the attention of a patient before addressing him, otherwise +he may be startled and a nervous spell be induced. The same hint applies +equally to leaning or sitting upon the sick-bed, or running against +furniture in moving about the sick-room. + + +387. Rest of Mind and Body. The great importance of rest for the sick +is not so generally recognized as its value warrants. If it is worry and +not work that breaks down the mental and physical health of the well, how +much more important is it that the minds and bodies of the sick should be +kept at rest, free from worry and excitement! Hence the skilled nurse does +her best to aid in restoring the sick to a condition of health by securing +for her patient complete rest both of mind and body. To this end, she +skillfully removes all minor causes of alarm, irritation, or worry. There +are numberless ways in which this may be done of which space does not +allow even mention. Details apparently trifling, as noiseless shoes, +quietness, wearing garments that do not rustle, use of small pillows of +different sizes, and countless other small things that make up the +refinement of modern nursing, play an important part in building up the +impaired tissues of the sick. + + +388. Care of Infectious and Contagious Diseases. There are certain +diseases which are known to be infectious and can be communicated from one +person to another, either by direct contact, through the medium of the +atmosphere, or otherwise. + +Of the more prevalent infectious and contagious diseases are +_scarlet fever, diphtheria, erysipelas, measles_, and _typhoid fever_. + +Considerations of health demand that a person suffering from any one of +these diseases should be thoroughly isolated from all other members of the +family. All that has been stated in regard to general nursing in previous +sections of this chapter, applies, of course, to nursing infectious and +contagious diseases. In addition to these certain special directions must +be always kept in mind. + +Upon the nurse, or the person having the immediate charge of the patient, +rests the responsibility of preventing the spread of infectious diseases. +The importance must be fully understood of carrying out in every detail +the measures calculated to check the spread or compass the destruction of +the germs of disease. + + +389. Hints on Nursing Infectious and Contagious Diseases. Strip the +room of superfluous rugs, carpets, furniture, etc. Isolate two rooms, if +possible, and have these, if convenient, at the top of the house. Tack +sheets, wet in some proper disinfectant, to the outer frame of the +sick-room door. Boil these sheets every third day. In case of diseases to +which young folks are very susceptible, send the children away, if +possible, to other houses where there are no children. + +Most scrupulous care should be taken in regard to cleanliness and neatness +in every detail. Old pieces of linen, cheese-cloth, paper napkins, should +be used wherever convenient or necessary and then at once burnt. All +soiled clothing that cannot well be burnt should be put to soak at once in +disinfectants, and afterward boiled apart from the family wash. Dishes and +all utensils should be kept scrupulously clean by frequent boiling. For +the bed and person old and worn articles of clothing that can be destroyed +should be worn so far as possible. + +During convalescence, or when ready to leave isolation, the patient should +be thoroughly bathed in water properly disinfected, the hair and nails +especially being carefully treated. + +Many details of the after treatment depend upon the special disease, as +the rubbing of the body with carbolized vaseline after scarlet fever, the +care of the eyes after measles, and other particulars of which space does +not admit mention here. + + + +Poisons and Their Antidotes. + + +390. Poisons. A poison is a substance which, if taken into the system +in sufficient amounts, will cause serious trouble or death. For +convenience poisons may be divided into two classes, irritants and +narcotics. + +The effects of irritant poisons are evident immediately after being +taken. They burn and corrode the skin or membrane or other parts with +which they come in contact. There are burning pains in the mouth, throat, +stomach, and abdomen, with nausea and vomiting. A certain amount of +faintness and shock is also present. + +With narcotic poisoning, the symptoms come on more slowly. After a +time there is drowsiness, which gradually increases until there is a +profound sleep or stupor, from which the patient can be aroused only with +great difficulty. There are some substances which possess both the +irritant and narcotic properties and in which the symptoms are of a mixed +character. + +391. Treatment of Poisoning. An antidote is a substance which will +either combine with a poison to render it harmless, or which will have a +directly opposite effect upon the body, thus neutralizing the effect of +the poison. Hence in treatment of poisoning the first thing to do, if you +know the special poison, is to give its antidote at once. + +If the poison is unknown, and there is any delay in obtaining the +antidote, the first thing to do is to remove the poison from the stomach. +Therefore cause vomiting as quickly as possible. This may be done by an +emetic given as follows: Stir a tablespoonful of mustard or of common +salt in a glass of warm water and make the patient swallow the whole. It +will usually be vomited in a few moments. If mustard or salt is not at +hand, compel the patient to drink lukewarm water very freely until +vomiting occurs. + +Vomiting may be hastened by thrusting the forefinger down the throat. Two +teaspoonfuls of the syrup of ipecac, or a heaping teaspoonful of powdered +ipecac taken in a cup of warm water, make an efficient emetic, especially +if followed with large amounts of warm water. + +It is to be remembered that in some poisons, as certain acids and +alkalies, no emetic should be given. Again, for certain poisons (except in +case of arsenic) causing local irritation, but which also affect the +system at large, no emetic should be given. + + +392. Reference Table of Common Poisons; Prominent Symptoms; Antidotes and +Treatment. The common poisons with their leading symptoms, treatment, +and antidotes, may be conveniently arranged for easy reference in the form +of a table. + +It is to be remembered, of course, that a complete mastery of the table of +poisons, as set forth on the two following pages, is really a physician's +business. At the same time, no one of fair education should neglect to +learn a few of the essential things to do in accidental or intentional +poisoning. + + + A Table of the More Common Poisons, + + With their prominent symptoms, antidotes, and treatment. + + Poison Prominent Symptoms Antidotes and Treatment + + _Strong Acids:_ + + Muriatic, Burning sensation in _No emetic_ Saleratus; + Nitric, mouth, throat, and chalk; soap; plaster from + Sulphuric (vitriol), stomach; blisters the wall; lime; magnesia; + Oxalic. about mouth; vomiting; baking soda (3 or 4 + great weakness teaspoonfuls in a glass of + water). + + _Alkalies_: + + Caustic potash and Burning sensation in _No emetic_ Olive oil + soda, the parts; severe pain freely; lemon juice, vinegar; + Ammonia, in stomach; vomiting; melted butter and vaseline; + Lye, difficulty in thick cream. + Pearlash, swallowing; cold skin; + Saltpeter. weak pulse. + + _Arsenic:_ + + Paris green, Intense pains in Vomit patient repeatedly, + Rough on rats, stomach and bowels; give hydrated oxide of iron + White arsenic, thirst; vomiting, with magnesia, usually kept + Fowler's solution, perhaps with blood; by druggists for emergencies; + Scheele's green. cold and clammy skin. follow with strong solution + of common salt and water. + + _Other Metallic Poisons_: + + Blue vitriol, Symptoms in general, Emetic with lead; none with + Copperas, same as in arsenical copper and iron; white of + Green vitriol, poisoning. With lead eggs in abundance with + Sugar of lead, and mercury there may copper; with iron and lead + Corrosive be a metallic taste in give epsom salts freely; + sublimate, the mouth. afterwards, oils, flour, and + Bedbug poison. water. _No emetic with + mercury;_ raw eggs; + milk, or flour, and water. + + _Phosphorus from_ + + Matches, rat Pain in the stomach; _Cause vomiting_. + poisons,etc. vomiting; purging; Strong soapsuds; + general collapse. magnesia in water. + Never give oils. + + _Opium:_ + Morphine, Sleepiness; dullness; _Cause vomiting_. Keep + Laudanum, stupor; "pin-hole" patient awake by any means, + Paregoric, pupils; slow especially by vigorous + Dover's powder, breathing; profuse walking; give strong coffee + Soothing syrups, sweat. freely; dash cold water on + Cholera and diarrhœa face and chest. + mixtures. + + + _Carbolic Acid:_ + Creasote. Severe pain in abdomen; _No emetic._ Milk or + odor of carbolic acid, flour and water; white of + mucous membrane in eggs. + around mouth white and + benumbed; cold and + clammy skin. + + _Aconite:_ + Wolfsbane Numbness everywhere, _Vomit patient freely._ + Monkshood great weakness; cold Stimulating drinks. + sweat. + + _Belladonna_ + Deadly Nightshade Eyes bright, with pupil _Vomit patient freely._ + Atropia enlarged; dry mouth and + throat. + + _Various Vegetable Poisons_ + Wild parsley, Stupor, nausea, great _Cause brisk vomiting_. + Indian tobacco, weakness and other Stimulating drinks. + Toadstools, symptoms according to + Tobacco plant, the poison. + Hemlock, + Berries of the mountain ash, + Bitter sweet etc. + +393. Practical Points about Poisons. Poisons should never be kept in +the same place with medicines or other preparations used in the household. +They should always be put in some secure place under lock and key. Never +use internally or externally any part of the contents of any package or +bottle unless its exact nature is known. If there is the least doubt +about the substance, do not assume the least risk, but destroy it at +once. Many times the unknown contents of some bottle or package has +been carelessly taken and found to be poison. + +Careless and stupid people often take, by mistake, with serious, and often +fatal, results, poisonous doses of carbolic acid, bed-bug poison, +horse-liniment, oxalic acid, and other poisons. A safe rule is to keep all +bottles and boxes containing poisonous substances securely bottled or +packed, and carefully labeled with the word POISON plainly written in +large letters across the label. Fasten the cork of a bottle containing +poison to the bottle itself with copper or iron wire twisted into a knot +at the top. This is an effective means of preventing any mistakes, +especially in the night. + +This subject of poisons assumes nowadays great importance, as it is a +common custom to keep about stables, workshops, bathrooms, and living +rooms generally a more or less formidable array of germicides, +disinfectants, horse-liniments, insect-poisons, and other preparations of +a similar character. For the most part they contain poisonous +ingredients. + + + +Bacteria. + + +394. Nature Of Bacteria. The word bacteria is the name applied to +very low forms of plant life of microscopic size. Thus, if hay be soaked +in water for some time, and a few drops of the liquid are examined under a +high power of the microscope, the water is found to be swarming with +various forms of living vegetable organisms, or bacteria. These +microscopic plants belong to the great fungus division, and consist of +many varieties, which may be roughly divided into groups, according as +they are spherical, rod-like, spiral, or otherwise in shape. + +Each plant consists of a mass of protoplasm surrounded by an +ill-defined cell wall. The bacteria vary cably in size. Some of the +rod-shaped varieties are from 1/12,000 to 1/8,000 of an inch in length, and +average about 1/50,000 of an inch in diameter. It has been calculated that +a space of one cubic millimeter would contain 250,000,000 of these minute +organisms, and that they would not weigh more than a milligram. + +[Illustration: Fig. 168.--Examples of Micro-Organisms called Bacteria. +(Drawn from photographs.) + + A, spheroidal bacteria (called _cocci_) in pairs; + B, same kind of bacteria in chains; + C, bacteria found in pus (grouped in masses like a bunch of grapes). + [Bacteria in A, B, and C magnified about 1000 diameters]. + D, bacteria found in pus (tendency to grow in the form of chains). + [Magnified about 500 diameters.] +] + +Bacteria are propagated in a very simple manner. The parent cell divides +into two; these two into two others, and so on. The rapidity with which +these organisms multiply under favorable conditions, makes them, in some +cases, most dangerous enemies. It has been calculated that if all of the +organisms survived, one bacterium would lead to the production of several +billions of others in twenty-four hours. + + +395. The Struggle of Bacteria for Existence. Like all kinds of living +things, many species of bacteria are destroyed if exposed to boiling water +or steam, but seem able to endure prolonged cold, far below the +freezing-point. Thus ice from ponds and rivers may contain numerous germs +which resume their activity when the ice is melted. Typhoid fever germs +have been known to take an active and vigorous growth after they have been +kept for weeks exposed in ice to a temperature below zero. + +The bacteria of consumption (bacillus tuberculosis) may retain their +vitality for months, and then the dried expectoration of the invalids may +become a source of danger to those who inhale air laden with such +impurities (sec. 220 and Fig. 94). + +Like other living organisms, bacteria need warmth, moisture, and some +chemical compound which answers for food, in order to maintain the +phenomena of life. Some species grow only in contact with air, others need +no more oxygen than they can obtain in the fluid or semi-fluid which they +inhabit. + + +396. Importance of Bacteria in Nature. We might well ask why the +myriads of bacteria do not devastate the earth with their marvelous +rapidity of propagation. So indeed they might, were it not for the winds, +rains, melting snow and ice which scatter them far and wide, and destroy +them. + +Again, as in countless other species of living organisms, bacteria are +subject to the relentless law which allows only the fittest to survive. +The bacteria of higher and more complex types devour those of a lower +type. Myriads perish in the digestive tract of man and other animals. The +excreta of some species of bacteria act as poison to destroy other +species. + +It is true from the strictest scientific point of view that all living +things literally return to the dust whence they came. While living they +borrow a few elementary substances and arrange them in new combinations, +by aid of the energy given them by the sun, and after a time die and leave +behind all they had borrowed both of energy and matter. + +Countless myriads of bacteria are silently at work changing dead animal +and vegetable matter into useful substances. In brief, bacteria prepare +food for all the rest of the world. Were they all destroyed, life upon +the earth would be impossible, for the elements necessary to maintain it +would be embalmed in the bodies of the dead. + +397. Action of Bacteria. In certain well-known processes bacteria +have the power of bringing about decomposition of various kinds. Thus a +highly organized fungus, like the yeast plant, growing in the presence of +sugar, has the power of breaking down this complex body into simpler ones, +_viz._, alcohol and carbon dioxid. + +In the same way, various forms of bacteria have the power of breaking down +complex bodies in their immediate neighborhood, the products depending +upon the substance, the kind of bacteria, and the conditions under which +they act. Thus the _bacteria lactis_ act upon the milk sugar present in +milk, and convert it into lactic acid, thus bringing about the souring of +milk. + +[Illustration: Fig. 169.--Examples of Pathogenic Bacteria. (Drawn from +photographs.) + + A, spiral form of bacteria found in cholera (Magnified about 1000 + diameters) + B, rod-shaped bacteria (called _bacilli_) from a culture obtained + in _anthrax_ or malignant fustule of the face. Diseased hides + carry this micro-organism, and thus may occasion disease among those + who handle hides and wool. (Magnified about 1000 diameters) +] + +Now, while most species of bacteria are harmless, some are the cause of +sickness and death when they gain admittance to the body under certain +conditions. These disease-producing bacteria (known as _pathogenic_), when +established in the blood and tissues of the body, bring about important +chemical changes, depending upon the species of bacteria, and also produce +a particular form of disease. The production of certain diseases by the +agency of bacteria has now been proved beyond all doubt. In yellow fever, +erysipelas, diphtheria, typhoid fever, consumption and other diseases, the +connection has been definitely established. + +The evil results these germs of disease produce vary greatly in kind and +severity. Thus the bacteria of Asiatic cholera and diphtheria may destroy +life in a few hours, while those of consumption may take years to produce +a fatal result. Again, the bacteria may attack some particular organ, or +group of organs, and produce mostly local symptoms. Thus in a boil there +is painful swelling due to the local effect of the bacteria, with slight +general disturbance. + +398. The Battle against Bacteria. When we reflect upon the terrible +ravages made by infectious diseases, and all their attendant evils for +these many years, we can the better appreciate the work done of late years +by tireless scientists in their efforts to modify the activity of +disease-producing bacteria. It is now possible to cultivate certain +pathogenic bacteria, and by modifying the conditions under which they are +grown, to destroy their violence. + +In brief, science has taught us, within certain limitations, how to +change the virulent germs of a few diseases into harmless microbes. + +399. Alcoholic Fermentation and Bacteria. Men of the lowest, as well +as of the highest, type of civilization have always known that when the +sugary juice of any fruit is left to itself for a time, at a moderately +warm temperature, a change takes place under certain conditions, and the +result is a liquid which, when drank, produces a pronounced effect upon +the body. In brief, man has long known how to make for himself alcoholic +beverages, by means of which he may become intoxicated with their +poisonous ingredients. + +Whether it is a degraded South Sea Islander making a crude intoxicant from +a sugary plant, a Japanese preparing his favorite alcoholic beverage from +the fermentation of rice by means of a fungus plant grown for the purpose, +a farmer of this country making cider from fermenting apple juice, or a +French expert manufacturing costly champagne by a complicated process, +the outcome and the intent are one and the same. The essential thing is +to produce an alcoholic beverage which will have a marked physiological +effect. This effect is poisonous, and is due solely to the +alcoholic ingredient, without which man would have little or no use +for the otherwise harmless liquid. + +While the practical process of making some form of alcoholic beverage has +been understood for these many centuries, the real reason of this +remarkable change in a wholesome fruit juice was not known until revealed +by recent progress in chemistry, and by the use of the microscope. We know +now that the change is due to fermentation, brought about from the +influence, and by the action, of bacteria (sec. 125). + +In other words, fermentation is the result of the growth of low form of +vegetable life known as an organised ferment. The ferment, whether it +be the commonly used brewer's yeast, or any other species of alcoholic +ferment, has the power to decompose or break down a large part of the +sugar present in the liquid into alcohol, which remains as a poison, +and _carbon dioxid_, which escapes more or less completely. + +Thus man, ever prone to do evil, was once obliged, in his ignorance, to +make his alcoholic drinks in the crudest manner; but now he has forced +into his service the latest discoveries in science, more especially in +bacteriology, that he may manufacture more scientifically and more +economically alcoholic beverages of all sorts and kinds, and distribute +them broadcast all over God's earth for the physical and moral ruin of the +people. + + + +Disinfectants. + + +400. Disinfectants, Antiseptics, and Deodorants. The word +disinfectant is synonymous with the term _bactericide_ or _germicide_. A +disinfectant is a substance which destroys infectious material. An +antiseptic is an agent which may hinder the growth, but does not +destroy the vitality, of bacteria. A deodorant is not necessarily a +disinfectant, or even an antiseptic, but refers to a substance that +destroys or masks offensive odors. + +401. Air and Water as Disinfectants. Nature has provided for our +protection two most efficient means of disinfection,--pure air (sec. +218) and pure water (sec. 119). The air of crowded rooms contains +large quantities of bacteria, whereas in pure air there are comparatively +few, especially after rain, which carries them to the earth. Living +micro-organisms have never been detected in breezes coming from the sea, +but in those blowing out from the shore large numbers may be found. + +In water tainted with organic matter putrefactive bacteria will flourish, +whereas pure water is fatal to their existence. Surface water, because it +comes from that part of the soil where bacteria are most active, and where +there is most organic matter, generally contains great quantities of these +organisms. In the deeper strata of the soil there is practically no +decomposition of organic matter going on, hence, water taken from deep +sources is comparatively free from bacteria. For this reason, deep well +water is greatly to be preferred for drinking purposes to that from +surface wells. + + +402. Disinfectants. It is evident that air and water are not always +sufficient to secure disinfection, and this must be accomplished by other +means. The destruction of infected material by fire is, of course, a sure +but costly means of disinfection. Dry heat, steam, and boiling water are +valuable disinfectants and do not injure most fabrics. These agents are +generally used in combination with various chemical disinfectants. + +Certain chemical agents that are capable of destroying micro-organisms +and their spores have come, of late years, into general use. A form of +mercury, called _corrosive sublimate_, is a most efficacious and powerful +germicide, but is exceedingly poisonous and can be bought only under +restrictions.[54] _Carbolic acid, chloride of lime, permanganate of +potash_, and various other preparations made from zinc, iron, and +petroleum, are the chemical disinfectants most commonly and successfully +used at the present time. There are also numerous varieties of commercial +disinfectants now in popular use, such as Platt's chlorides, +bromo-chloral, sanitas, etc., which have proved efficient germicides. + + + +Instructions for the Management of Contagious Diseases. + + +The following instructions for the management of contagious diseases were +prepared for the National Board of Health by an able corps of scientists +and experienced physicians. + +403. Instructions for Disinfection. Disinfection is the destruction +of the poisons of infectious and contagious diseases. Deodorizers, or +substances which destroy smells, are not necessarily disinfectants, and +disinfectants do not necessarily have an odor. Disinfection cannot +compensate for want of cleanliness nor of ventilation. + +404. Disinfectants to be Employed. 1. Roll sulphur (brimstone); for +fumigation. + +2. Sulphate of iron (copperas) dissolved in water in the proportion of one +and a half pounds to the gallon; for soil, sewers, etc. + + [NOTE. A most useful little manual to consult in connection with this + chapter is the _Hand-Book of Sanitary Information_, written by Roger + S. Tracy, Sanitary Inspector of the New York City Health Department. + Price, 50 cents.] + +3. Sulphate of zinc and common salt, dissolved together in water in the +proportion of four ounces sulphate and two ounces salt to the gallon; for +clothing, bed-linen, etc. + + +405. How to Use Disinfectants. 1. _In the sick-room._ The most +available agents are fresh air and cleanliness. The clothing, +towels, bed-linen, etc., should, on removal from the patient, and before +they are taken from the room, be placed in a pail or tub of the zinc +solution, boiling-hot, if possible. + +All discharges should either be received in vessels containing copperas +solution, or, when this is impracticable, should be immediately covered +with copperas solution. All vessels used about the patient should be +cleansed with the same solution. + +Unnecessary furniture, especially that which is stuffed, carpets, and +hangings, should, when possible, be removed from the room at the outset; +otherwise they should remain for subsequent fumigation and treatment. + +2. _Fumigation_. Fumigation with sulphur is the only practicable method +for disinfecting the house. For this purpose, the rooms to be disinfected +must be vacated. Heavy clothing, blankets, bedding, and other articles +which cannot be treated with zinc solution, should be opened and exposed +during fumigation, as directed below. Close the rooms as tightly as +possible, place the sulphur in iron pans supported upon bricks placed in +washtubs containing a little water, set it on fire by hot coals or with +the aid of a spoonful of alcohol, and allow the room to remain closed for +twenty-four hours. For a room about ten feet square, at least two pounds +of sulphur should be used; for larger rooms, proportionally increased +quantities.[55] + +3. _Premises_. Cellars, yards, stables, gutters, privies, cesspools, +water-closets, drains, sewers, etc., should be frequently and liberally +treated with copperas solution. The copperas solution is easily prepared +by hanging a basket containing about sixty pounds of copperas in a barrel +of water.[56] + +4. _Body and bed clothing, etc_. It is best to burn all articles which +have been in contact with persons sick with contagious or infectious +diseases. Articles too valuable to be destroyed should be treated as +follows: + +_(a)_ Cotton, linen, flannels, blankets, etc., should be treated with the +boiling-hot zinc solution; introduce piece by piece, secure thorough +wetting, and boil for at least half an hour. + +_(b)_ Heavy woolen clothing, silks, furs, stuffed bed-covers, beds, and +other articles which cannot be treated with the zinc solution, should be +hung in the room during fumigation, their surfaces thoroughly exposed and +pockets turned inside out. Afterward they should be hung in the open air, +beaten, and shaken. Pillows, beds, stuffed mattresses, upholstered +furniture, etc., should be cut open, the contents spread out and +thoroughly fumigated. Carpets are best fumigated on the floor, but should +afterward be removed to the open air and thoroughly beaten. + + +Books for Collateral Study. Among the many works which may be +consulted with profit, the following are recommended as among those most +useful: Parkes _Elements of Health_; Canfield's _Hygiene of the +Sick-Room;_ Coplin & Bevan's _Practical Hygiene;_ Lincoln's _School +Hygiene_; Edward Smith's _Health_; McSherrys _Health; American Health +Primers_ (12 little volumes, edited by Dr. Keen of Philadelphia); +Reynold's _Primer of Health_; Corfield's _Health_; Appleton's _Health +Primers;_ Clara S. Weeks' _Nursing_; Church's _Food_; Yeo's _Food in Health +and Disease;_ Hampton's _Nursing, its Principles and Practice_; Price's +_Nurses and Nursing;_ Cullinworth's _Manual of Nursing_; Wise's _Text-Book +of Nursing_ (2 vols.); and Humphrey's _Manual of Nursing_. + + + + +Chapter XV. + +Experimental Work in Physiology. + + + +406. The Limitations of Experimental Work in Physiology in Schools. +Unlike other branches of science taught in the schools from the +experimental point of view, the study of physiology has its limitations. +The scope and range of such experiments is necessarily extremely limited +compared with what may be done with the costly and elaborate apparatus of +the medical laboratory. Again, the foundation of physiology rests upon +systematic and painstaking dissection of the dead human body and the lower +animals, which mode of study very properly is not permitted in ordinary +school work. Experiments upon the living human body and the lower animals, +now so generally depended upon in our medical and more advanced scientific +schools, for obvious reasons can be performed only in a crude and quite +superficial manner in secondary schools. + +Hence in the study of physiology in schools many things must be taken for +granted. The observation and experience of medical men, and the +experiments of the physiologist in his laboratory must be depended upon +for data which cannot be well obtained at first hand by young students. + +407. Value of Experiments in Physiology in Secondary Schools. While +circumstances and regard for certain proprieties of social life forbid the +use of a range of experiments, in anatomy and physiology, such as are +permitted in other branches of science in secondary schools, it by no +means follows that we are shut out altogether from this most important and +interesting part of the study. However simple and crude the apparatus, the +skillful and enthusiastic teacher has at his command a wide series of +materials which can be profitably utilized for experimental instruction. +As every experienced teacher knows, pupils gain a far better knowledge, +and keep up a livelier interest in any branch of science, if they see with +their own eyes and do with their own hands that which serves to illuminate +and illustrate the subject-matter. + + [NOTE. For additional suggestions and practical helps on the subject + of experimental work in physiology the reader is referred to + Blaisdell's _How to Teach Physiology_, a handbook for teachers. A copy + of this pamphlet will be sent postpaid to any address by the + publishers of this book on receipt of ten cents.] + +The experimental method of instruction rivets the attention and arouses +and keeps alive the interest of the young student; in fact, it is the +only true method of cultivating a scientific habit of study[57]. The +subject-matter as set forth on the printed pages of this book should be +mastered, of course, but at the same time the topics discussed should be +illuminated and made more interesting and practical by a well-arranged +series of experiments, a goodly show of specimens, and a certain amount of +microscopical work. + + +408. The Question of Apparatus. The author well understands from +personal experience the many practical difficulties in the way of +providing a suitable amount of apparatus for classroom use. If there are +ample funds for this purpose, there need be no excuse or delay in +providing all that is necessary from dealers in apparatus in the larger +towns, from the drug store, markets, and elsewhere. In schools where both +the funds and the time for such purposes are limited, the zeal and +ingenuity of teachers and students are often put to a severe test. +Fortunately a very little money and a great deal of ingenuity and patience +will do apparent wonders towards providing a working supply of apparatus. + +It will be noticed that many of the experiments in the preceding chapters +of this book can be performed with very simple, and often a crude and +home-made sort of apparatus. This plan has been rigidly followed by the +author, first, because he fully realizes the limitations and restrictions +of the subject; and secondly, because he wishes to emphasize the fact that +expensive and complicated apparatus is by no means necessary to illustrate +the great principles of anatomy and physiology. + +409. Use of the Microscope. To do thorough and satisfactory work in +physiology in our higher schools a compound microscope is almost +indispensable. Inasmuch as many of our best secondary schools are equipped +with one or more microscopes for use in other studies, notably botany, it +is much less difficult than it was a few years ago to obtain this +important help for the classes in physiology. + +[Illustration: Fig. 170.--A Compound Microscope] + +For elementary class work a moderate-priced, but well-made and strong, +instrument should be provided. If the school does not own a microscope, +the loan of an instrument should be obtained for at least a few weeks from +some person in the neighborhood. + +The appearance of the various structures and tissues of the human body as +revealed by the microscope possesses a curious fascination for every +observer, especially for young people. No one ever forgets the first look +at a drop of blood, or the circulation of blood in a frog's foot as shown +by the microscope. + + [NOTE. For detailed suggestions in regard to the manipulation and use + of the microscope the student is referred to any of the standard works + on the subject. The catalogues of scientific-instrument makers of our + larger cities generally furnish a list of the requisite materials or + handbooks which describe the use of the various microscopes of + standard make. + + The author is indebted to Bergen's _Elements of Botany_ for the + following information concerning the different firms which deal in + microscopes. "Several of the German makers furnish excellent + instruments for use in such a course as that here outlined. The author + is most familar with the Leitz microscopes, which are furnished by Wm. + Krafft, 411 West 59th St., New York city, or by the Franklin + Educational Co., 15 and 17 Harcourt St., Boston. The Leitz Stand, No. + IV., can be furnished duty free (for schools only), with objectives 1, + 3, and 5, eye-pieces I. and III., for $24.50. If several instruments + are being provided, it would be well to have part of them equipped + with objectives 3 and 7, and eye-pieces I. and III. + + "The American manufacturers, Bausch & Lomb Optical Company, Rochester, + N.Y., and No. 130 Fulton St., New York city, have this year produced a + microscope of the Continental type which is especially designed to + meet the requirements of the secondary schools for an instrument with + rack and pinion coarse adjustment and serviceable fine adjustment, at + a low price. They furnish this new stand, 'AAB,' to schools and + teachers at 'duty-free' rates, the prices being for the stand with two + eye-pieces (any desired power), ⅔-inch and ¼-inch objectives, + $25.60, or with 2-inch, ⅔-inch, and ¼-inch objectives, and two + eye-pieces, $29.20. Stand 'A,' the same stand as the 'AAB,' without + joint and with sliding tube coarse adjustment (as in the Leitz Stand + IV.), and with three eye-pieces and ⅔-inch and ¼-inch objectives, + is furnished for $20.40. Stand 'A,' with two eye-pieces, ⅔-inch and + ⅙-inch objectives, $20.40."] + +410. The Use of the Skeleton and Manikin. The study of the bones by +the help of a skeleton is almost a necessity. To this intent, schools of a +higher grade should be provided both with a skeleton and a +manikin. If the former is not owned by the school, oftentimes a loan +of one can be secured of some medical man in the vicinity. Separate bones +will also prove useful. In fact, there is no other way to study properly +the structure and use of the bones and joints than by the bones +themselves. A good manikin is also equally serviceable, although not so +commonly provided for schools on account of its cost. + +411. The Question of Vivisection and Dissection. There should be no +question at all concerning vivisection. _In no shape or form should +it be allowed in any grade of our schools._ Nor is there any need of much +dissection in the grammar-school grades. A few simple dissections to +be performed with fresh beef-joints, tendons of turkey legs, and so on, +will never engender cruel or brutal feelings toward living things. In the +lower grades a discreet teacher will rarely advise his pupils to dissect a +dead cat, dog, frog, or any other animal. Instead of actual dissection, +the pupils should examine specimens or certain parts previously dissected +by the teacher,--as the muscles and tendons of a sheep, the heart of an +ox, the eye of a codfish, and so on. Even under these restrictions the +teacher should not use the knife or scissors before the class to open up +any part of the specimen. In brief, avoid everything that can possibly +arouse any cruel or brutal feeling on the part of young students. + +In the higher schools, in normal and other training schools, different +conditions prevail. Never allow vivisection in any form whatever, either +in school or at home. Under the most exact restrictions students in these +schools may be taught to make a few simple dissections. + +Most teachers will find, however, even in schools of a higher grade, that +the whole subject is fraught with many difficulties. It will not require +much oftentimes to provoke in a community a deal of unjust criticism. A +teacher's good sense and discretion are often put to a severe test. + + + +Additional Experiments. + + +To the somewhat extended list of experiments as described in the preceding +chapters a few more are herewith presented which may be used as +opportunity allows to supplement those already given. + + Experiment 193. _To examine white fibrous tissue._ Snip off a very + minute portion from the muscle of a rabbit, or any small animal recently + dead. Tease the specimen with needles, mount in salt solution and + examine under a high power. Note the course and characters of the + fibers. + + Experiment 194. _To examine elastic tissue._ Tease out a small + piece of ligament from a rabbit's leg in salt solution; mount in the + same, and examine as before. Note the curled elastic fibers. + + Experiment 195. _To examine areolar tissue._ Gently tease apart + some muscular fibers, noting that they are attached to each other by + connective tissue. Remove a little of this tissue to a slide and examine + as before. Examine the matrix with curled elastic fiber mixed with + straight white fibers. + + Experiment 196. _To examine adipose tissue._ Take a bit of fat from + the mesentery of a rabbit. Tease the specimen in salt solution and mount + in the same. Note the fat cells lying in a vascular meshwork. + + Experiment 197. _To examine connective tissues._ Take a very small + portion from one of the tendons of a rabbit, or any animal recently + dead; place upon a glass slide with a drop of salt solution; tease it + apart with needles, cover with thin glass and examine with microscope. + The fine wavy filaments will be seen. Allow a drop of dilute acetic acid + to run under the cover glass; the filaments will swell and become + transparent. + + Experiment 198. Tease out a small piece of ligament from the + rabbit's leg in salt solution; mount in the same, and examine under a + high power. Note the curled elastic fibers. + + Experiment 199. _A crude experiment to represent the way in which a + person's neck is broken._ Bring the ends of the left thumb and the left + second finger together in the form of a ring. Place a piece of a wooden + toothpick across it from the middle of the finger to the middle of the + thumb. Put the right forefinger of the other hand up through the front + part to represent the odontoid process of the axis, and place some + absorbent cotton through the other part to represent the spinal cord. + Push backwards with the forefinger with just enough force to break the + toothpick and drive its fragments on to the cotton. + + Experiment 200. _To illustrate how the pulse-wave is transmitted + along an artery._ Use the same apparatus as in Experiment 106, p. 201. + Take several thin, narrow strips of pine wood. Make little flags by + fastening a small piece of tissue paper on one end of a wooden + toothpick. Wedge the other end of the toothpick into one end of the + strips of pine wood. Use these strips like levers by placing them across + the long rubber tube at different points. Let each lever compress the + tube a little by weighting one end of it with a blackboard eraser or + book of convenient size. + + As the pulse-wave passes along under the levers they will be + successively raised, causing a slight movement of the tissue-paper + flags. + + Experiment 201. _The dissection of a sheep's heart._ Get a sheep's + heart with the lungs attached, as the position of the heart will be + better understood. Let the lungs be laid upon a dish so that the heart + is uppermost, with its apex turned toward the observer. + + The line of fat which extends from the upper and left side of the heart + downwards and across towards the right side, indicates the division + between the right and left ventricles. + + Examine the large vessels, and, by reference to the text and + illustrations, make quite certain which are the _aorta_, the _pulmonary + artery_, the _superior_ and _inferior venæ cavæ_, and the _pulmonary + veins_. + + Tie variously colored yarns to the vessels, so that they may be + distinguished when separated from the surrounding parts. + + Having separated the heart from the lungs, cut out a portion of the wall + of the _right ventricle_ towards its lower part, so as to lay the cavity + open. Gradually enlarge the opening until the _chordæ tendineæ_ and the + flaps of the _tricuspid valve_ are seen. Continue to lay open the + ventricle towards the pulmonary artery until the _semilunar valves_ come + into view. + + The pulmonary artery may now be opened from above so as to display the + upper surfaces of the semilunar valves. Remove part of the wall of the + right auricle, and examine the right auriculo-ventricular opening. + + The heart may now be turned over, and the _left ventricle_ laid open in + a similar manner. Notice that the mitral valve has only two flaps. The + form of the valves is better seen if they are placed under water, and + allowed to float out. Observe that the walls of the _left_ ventricle are + much thicker than those of the _right_. + + Open the left auricle, and notice the entrance of the _pulmonary veins_, + and the passage into the ventricle. + + The ventricular cavity should now be opened up as far as the aorta, and + the semilunar valves examined. Cut open the aorta, and notice the form + of the _semilunar valves_. + + Experiment 202. _To show the circulation in a frog's foot_ (see + Fig. 78, p. 192). In order to see the blood circulating in the membrane + of a frog's foot it is necessary to firmly hold the frog. For this + purpose obtain a piece of soft wood, about six inches long and three + wide, and half an inch thick. At about two inches from one end of this, + cut a hole three-quarters of an inch in diameter and cover it with a + piece of glass, which should be let into the wood, so as to be level + with the surface. Then tie up the frog in a wet cloth, leaving one of + the hind legs outside. Next, fasten a piece of cotton to each of the two + longest toes, but not too tightly, or the circulation will be stopped + and you may hurt the frog. + + Tie the frog upon the board in such a way that the foot will just come + over the glass in the aperture. Pull carefully the pieces of cotton tied + to the toes, so as to spread out the membrane between them over the + glass. Fasten the threads by drawing them into notches cut in the sides + of the board. The board should now be fixed by elastic bands, or by any + other convenient means, upon the stage of the microscope, so as to bring + the membrane of the foot under the object glass. + + The flow of blood thus shown is indeed a wonderful sight, and never to + be forgotten. The membrane should be occasionally moistened with water. + + Care should be taken not to occasion any pain to the frog. + + Experiment 203. _To illustrate the mechanics of respiration_[58] + (see Experiment 122, p. 234). "In a large lamp-chimney, the top of which + is closed by a tightly fitting perforated cork (A), is arranged a pair + of rubber bags (C) which are attached to a Y connecting tube (B), to be + had of any dealer in chemical apparatus or which can be made by a + teacher having a bunsen burner and a little practice in the manipulation + of glass (Fig. 171). From the center of the cork is attached a rubber + band by means of a staple driven through the cork, the other end of + which (D) is attached to the center of a disk of rubber (E) such as + dentists use. This disk is held to the edge of the chimney by a wide + elastic band (F). There is a string (G) also attached to the center of + the rubber disk by means of which the diaphragm may be lowered. + + [Illustration: Fig. 171.] + + Such is a description of the essentials of the model. The difficulties + encountered in its construction are few and easily overcome. In the + first place, the cork must be air-tight, and it is best made so by + pouring a little melted paraffin over it, care being taken not to close + the tube. The rubber bags were taken from toy balloon-whistles. + + In the construction of the diaphragm, it is to be remembered that it + also must be air-tight, and in order to resemble the human diaphragm, it + must have a conical appearance when at rest. In order to avoid making + any holes in the rubber, the two attachments (one of the rubber band, + and the other of the string) were made in this wise: the rubber was + stretched over a button having an eye, then under the button was placed + a smaller ring from an old umbrella; to this ring was attached the + rubber band, and to the eye of the button was fastened the operating + string. When not in use the diaphragm should be taken off to relieve the + strain on the rubber band." + + Experiment 204. _To illustrate the action of the intercostal + muscles_ (see sec. 210). The action of the intercostal muscles is not at + first easy to understand; but it will be readily comprehended by + reference to a model such as that represented in Fig. 172. This maybe + easily made by the student himself with four laths of wood, fastened + together at the corners, A, B, C, D, with pins or small screws, so as + to be movable. At the points E, F, G, H, pins are placed, to which + elastic bands may be attached (A). B D represents the vertebral column; + A C, the sternum; and A B and C D, the ribs. The elastic band F G + represents the _external_ intercostal muscles, and E H, the _internal_ + intercostals. + + [Illustration: Fig. 172.] + + If now the elastic band E H be removed, the remaining band, F G, will + tend to bring the two points to which it is attached, nearer together, + and the result will be that the bars A B and C D will be drawn upwards + (B), that is, in the same direction as the ribs in the act of + _inspiration_. When the elastic band E H is allowed to exert its force, + the opposite effect will be produced (C); in this case representing the + position of the ribs in an act of _expiration_. + + Experiment 205. Pin a round piece of bright red paper (large as a + dinner-plate) to a white wall, with a single pin. Fasten a long piece of + thread to it, so it can be pulled down in a moment. Gaze steadily at the + red paper. Have it removed while looking at it intently, and a greenish + spot takes its place. + + Experiment 206. Lay on different parts of the skin a small, square + piece of paper with a small central hole in it. Let the person close his + eyes, while another person gently touches the uncovered piece of skin + with cotton wool, or brings near it a hot body. In each case ask the + observed person to distinguish between them. He will always succeed on + the volar side of the hand, but occasionally fail on the dorsal surface + of the hand, the extensor surface of the arm, and very frequently on the + skin of the back. + + Experiment 207. _Wheatstone's fluttering hearts_. Make a drawing of + a red heart on a bright blue ground. In a dark room lighted by a candle + hold the picture below the level of the eyes and give it a gentle + to-and-fro motion. On continuing to look at the heart it will appear to + move or flutter over the blue background. + + Experiment 208. At a distance of six inches from the eyes hold a + veil or thin gauze in front of some printed matter placed at a distance + of about two feet. Close one eye, and with the other we soon see either + the letters distinctly or the fine threads of the veil, but we cannot + see both equally distinct at the same time. The eye, therefore, can form + a distinct image of a near or distant object, but not of both at the + same time; hence the necessity for accommodation. + + Experiment 209. Place a person in front of a bright light opposite + a window, and let him look at the light; or place one's self opposite a + well-illuminated mirror. Close one eye with the hand and observe the + diameter of the other pupil. Then suddenly remove the hand from the + closed eye: light falls upon it; at the same time the pupil of the other + eye contracts. + + Experiment 210. _To illustrate the blind spot. Marriott's + experiment_. On a white card make a cross and a large dot, either black + or colored. Hold the card vertically about ten inches from the right + eye, the left being closed. Look steadily at the cross with the right + eye, when both the cross and the circle will be seen. Gradually approach + the card toward the eye, keeping the axis of vision fixed on the cross. + At a certain distance the circle will disappear, i.e., when its image + falls on the entrance of the optic nerve. On bringing the card nearer, + the circle reappears, the cross, of course, being visible all the time + (see Experiment 180, p. 355). + + Experiment 211. _To map out the field of vision_. A crude method is + to place the person with his back to a window, ask him to close one eye, + stand in front of him about two feet distant, hold up the forefingers of + both hands in front of and in the plane of your own face. Ask the person + to look steadily at your nose, and as he does so observe to what extent + the fingers can be separated horizontally, vertically, and in oblique + directions before they disappear from his field of vision. + + Experiment 212. _To illustrate imperfect judgment of distance_. + Close one eye and hold the left forefinger vertically in front of the + other eye, at arm's length, and try to strike it with the right + forefinger. + + On the first trial one will probably fall short of the mark, and fail to + touch it. Close one eye, and rapidly try to dip a pen into an inkstand, + or put a finger into the mouth of a bottle placed at a convenient + distance. In both cases one will not succeed at first. + + In these cases one loses the impressions produced by the convergence of + the optic axes, which are important factors in judging of distance. + + Experiment 213. Hold a pencil vertically about twelve inches from + the nose, fix it with both eyes, close the left eye, and then hold the + right index finger vertically, so as to cover the lower part of the + pencil. With a sudden move, try to strike the pencil with the finger. In + every case one misses the pencil and sweeps to the right of it. + + Experiment 214. _To illustrate imperfect judgment of direction_. As + the retina is spherical, a line beyond a certain length when looked at + always shows an appreciable curvature. + + Hold a straight edge just below the level of the eyes. Its upper margin + shows a slight concavity. + + + +Surface Anatomy and Landmarks. + + +In all of our leading medical colleges the students are carefully and +thoroughly drilled on a study of certain persons selected as models. The +object is to master by observation and manipulation the details of what is +known as surface anatomy and landmarks. Now while detailed work of this +kind is not necessary in secondary schools, yet a limited amount of study +along these lines is deeply interesting and profitable. The habit of +looking at the living body with anatomical eyes and with eyes at our +fingers' ends, during the course in physiology, cannot be too highly +estimated. + +In elementary work it is only fair to state that many points of surface +anatomy and many of the landmarks cannot always be defined or located with +precision. A great deal in this direction can, however, be done in higher +schools with ingenuity, patience, and a due regard for the feelings of all +concerned. Students should be taught to examine their own bodies for this +purpose. Two friends may thus work together, each serving as a "model" to +the other. + +To the following syllabus may be added such other similar exercises as +ingenuity may suggest or time permit. + + + + +Syllabus. + + + +I. Bony Landmarks. + + +1. The _occipital protuberance_ can be distinctly felt at the back of +the head. This is always the thickest part (often three-quarters of an +inch or more) of the skull-cap, and is more prominent in some than in +others. The thinnest part is over the temples, where it may be almost as +thin as parchment. + +2. The working of the _condyle of the lower jaw_ vertically and from +side to side can be distinctly felt and seen in front of the ear. When the +mouth is opened wide, the condyle advances out of the glenoid cavity, and +returns to its socket when the mouth is shut. In front of the ear, lies +the zygoma, one of the most marked and important landmarks to the touch, +and in lean persons to the eye. + +3. The sliding movement of the _scapula_ on the chest can be properly +understood only on the living subject. It can move not only upwards and +downwards, as in shrugging the shoulders, backwards and forwards, as in +throwing back the shoulders, but it has a rotary movement round a movable +center. This rotation is seen while the arm is being raised from the +horizontal to the vertical position, and is effected by the cooperation of +the trapezius with the serratus magnus muscles. + +4. The _patella_, or knee-pan, the _two condyles of the tibia_, the +_tubercle on the tibia_ for the attachment of the ligament of the patella, +and the _head of the fibula_ are the chief bony landmarks of the knee. The +head of the fibula lies at the outer and back part of the tibia. In +extension of the knee, the patella is nearly all above the condyles. The +inner border of the patella is thicker and more prominent than the outer, +which slopes down toward its condyle. + +5. The short, front edge of the _tibia_, called the "shin," and the +broad, flat, subcutaneous surface of the bone can be felt all the way +down. The inner edge can be felt, but not so plainly. + +6. The head of the _fibula_ is a good landmark on the outer side of +the leg, about one inch below the top of the tibia. Note that it is placed +well back, and that it forms no part of the knee joint, and takes no share +in supporting the weight. The shaft of the fibula arches backwards and is +buried deep among the muscles, except at the lower fourth, which can be +distinctly felt. + +7. The _malleoli_ form the great landmarks of the ankle. The outer +malleolus descends lower than the inner. The inner malleolus advances more +to the front and does not descend so low as the outer. + +8. The line of the _clavicle_, or collar bone, and the projection of +the joint at either end of it can always be felt. Its direction is not +perfectly horizontal, but slightly inclined downwards. We can distinctly +feel the _spine_ of the scapula and its highest point, the _acromion_. + +9. Projecting beyond the acromion (the arm hanging by the side), we +can feel, through the fibers of the _deltoid_, the upper part of the +humerus. It distinctly moves under the hand when the arm is rotated. It is +not the head of the bone which is felt, but its prominences (the +tuberosities). The greater, externally; the lesser in front. + +10. The _tuberosities of the humerus_ form the convexity of the +shoulder. When the arm is raised, the convexity disappears,--there is a +slight depression in its place. The head of the bone can be felt by +pressing the fingers high up in the axilla. + +11. The _humerus_ ends at the elbow in two bony prominences (internal +and external condyles). The internal is more prominent. We can always feel +the _olecranon_. Between this bony projection of the ulna and the internal +condyle is a deep depression along which runs the ulna nerve (commonly +called the "funny" or "crazy" bone). + +12. Turn the hand over with the palm upwards, and the edge of the +_ulna_ can be felt from the olecranon to the prominent knob (styloid +process) at the wrist. Turn the forearm over with the palm down, and the +head of the ulna can be plainly felt and seen projecting at the back of +the wrist. + +13. The upper half of the _radius_ cannot be felt because it is so +covered by muscles; the lower half is more accessible to the touch. + +14. The three rows of projections called the "knuckles" are formed by +the proximal bones of the several joints. Thus the first row is formed by +the ends of the metacarpals, the second by the ends of the first +phalanges, and the third by the ends of the second phalanges. That is, in +all cases the line of the joints is a little in advance of the knuckles +and nearer the ends of the fingers. + + + +II. Muscular Landmarks. + + +1. The position of the _sterno-mastoid_ muscle as an important and +interesting landmark of the neck has already been described (p. 70). + +2. If the left arm be raised to a vertical position and dropped to a +horizontal, somewhat vigorously, the tapering ends of the _pectoralis +major_ and the tendons of the _biceps_ and _deltoid_ may be felt by +pressing the parts in the axilla between the fingers and thumb of the +right hand. + +3. The appearance of the _biceps_ as a landmark of the arm has +already been described (p. 70). The action of its antagonist, the +_triceps_, may be studied in the same manner. + +4. The _sartorius_ is one of the fleshy landmarks of the thigh, as +the biceps is of the arm, and the sterno-cleido-mastoid of the neck. Its +direction and borders may be easily traced by raising the leg,--a movement +which puts the muscle in action. + +5. If the model be directed to stand on tiptoe, both of the large +muscles of the calf, the _gastrocnemius_ and _soleus_, can be +distinguished. + +6. Direct the model, while sitting upright, to cross one leg over the +other, using his utmost strength. The great muscles of the inner thigh are +fully contracted. Note the force required to pull the legs to the ordinary +position. + +7. With the model lying in a horizontal position with both legs +firmly held together, note the force required to pull the feet apart while +the great muscles of the thigh are fully contracted. + +8. In forcible and resisted flexion of the wrist two tendons come up +in relief. On the outer side of one we feel the pulse at the wrist, the +radial artery here lying close to the radius. + +9. On the outer side of the wrist we can distinctly see and feel when +in action, the three extensor tendons of the thumbs. Between two of them +is a deep depression at the base of the thumb, which the French call the +"anatomical tobacco box." + +10. The relative position of the several extensor tendons on the back +of the wrist and fingers as they play in their grooves over the back of +the radius and ulna can be distinctly traced when the several muscles are +put in action. + +11. There are several strong tendons to be seen and felt about the +ankle. Behind is the _tendo Achillis_. It forms a high relief with a +shallow depression on each side of it. Behind both the inner and outer +ankle several tendons can be felt. Over the front of the ankle, when the +muscles are in action, we can see and feel several tendons. They start up +like cords when the action is resisted. They are kept in their proper +relative position by strong pulleys formed by the annular ligament. Most +of these tendons can be best seen by stand a model on one foot, _i.e._ in +unstable equilibrium. + + + +III. Landmarks of the Heart. + + +To have a general idea of the form and position of the _heart_, map its +outline with colored pencils or crayon on the chest wall itself, or on +some piece of clean, white cloth, tightly pinned over the clothing. A +pattern of the heart may be cut out of pasteboard, painted red, or papered +with red paper, and pinned in position outside the clothing. The apex of +the heart is at a point about two inches below the left nipple and one +inch to its sternal side. This point will be between the fifth and sixth +ribs, and can generally be determined by feeling the apex beat. + + + + +IV. Landmarks of a Few Arteries. + + +The pulsation of the _temporal_ artery can be felt in front of the ear, +between the zygoma and the ear. The _facial_ artery can be distinctly felt +as it passes over the upper jaw at the front edge of the masseter muscle. +The pulse of a sleeping child can often be counted at the anterior +fontanelle by the eye alone. + +About one inch above the clavicle, near the outer border of the +sterno-mastoid, we can feel the pulsation of the great _subclavian_ +artery. At the back of the knee the _popliteal_ artery can be felt +beating. The _dorsal_ artery of the foot can be felt beating on a line +from the middle of the ankle to the interval between the first and second +metatarsal bones. + +When the arm is raised to a right angle with the body, the _axillary_ +artery can be plainly felt beating in the axilla. Extend the arm with palm +upwards and the _brachial_ artery can be felt close to the inner side of +the biceps. The position of the _radial_ artery is described in Experiment +102. + + + + +Glossary. + + + +Abdomen (Lat. _abdo_, _abdere_, to conceal). The largest cavity of +the body, containing the liver, stomach, intestines, and other organs. + +Abductor (Lat. _abduco_, to draw from). A muscle which draws a limb +from the middle line of the body, or a finger or toe from the middle line +of the foot or hand. + +Absorbents (Lat. _absorbere_, to suck up). The vessels which take +part in the process of absorption. + +Absorption. The process of sucking up nutritive or waste matters by +the blood-vessels or lymphatics. + +Accommodation of the Eye. The alteration in the shape of the +crystalline lens, which accommodates, or adjusts, the eye for near or +remote vision. + +Acetabulum (Lat. _acetabulum_, a small vinegar-cup). The cup-shaped +cavity of the innominate bone for receiving the head of the femur. + +Acid (Lat. _acidus_, from _acere_, to be sour). A substance usually +sour, sharp, or biting to the taste. + +Acromion (Gr. ἀκρον the tip, and ᾧμος, the shoulder). The part of the scapula +forming the tip of the shoulder. + +Adam's Apple. An angular projection of cartilage in the front of the +neck. It may be particularly prominent in men. + +Adductor (Lat. _adduco_, to draw to). A muscle which draws towards +the middle line of the body, or of the hand or foot. + +Adenoid (Gr. ἀδήν, a gland). Tissue resembling gland tissue. + +Afferent (Lat. _ad_, to, and _fero_, to convey). Vessels or nerves +carrying the contents or impulses from the periphery to the center. + +Albumen, or Albumin (Lat. _albus_, white). An animal substance +resembling the white of an egg. + +Albuminuria. A combination of the words "albumin" and "urine." +Presence of _albumen_ in the _urine_. + +Aliment (Lat. _alo_, to nourish). That which affords nourishment; +food. + +Alimentary (Lat. _alimentum_, food). Pertaining to _aliment_, or +food. + +Alimentary Canal (Lat. _alimentum_). The tube in which the food is +digested or prepared for reception into the blood. + +Alkali (Arabic _al kali_, the soda plant). A name given to certain +substances, such as soda, potash, and the like, which have the power of +combining with acids. + +Alveolar (Lat. _alveolus_, a little hollow). Pertaining to the +alveoli, the _cavities_ for the reception of the teeth. + +Amœba (Gr. ἀμείβω, to change). A single-celled, protoplasmic organism, +which is constantly changing its form by protrusions and withdrawals of +its substance. + +Amœboid. Like an _amœba_. + +Ampulla (Lat. _ampulla_, a wine-flask). The dilated part of the +semicircular canals of the internal ear. + +Anabolism (Gr. ἀναβάλλω to throw or build up). The process by means of +which simpler elements are _built up_ into more complex. + +Anæsthetics (Gr. ἀν, without, and αἰσθησία, feeling). Those medicinal +agents which prevent the feeling of pain, such as chloroform, ether, +laughing-gas, etc. + +Anastomosis (Gr. ἀνά, by, and στόμα, a mouth). The intercommunication of +vessels. + +Anatomy (Gr. ἀνατέμνω, to cut up). The science which describes the +structure of living things. The word literally means dissection. + +Antiseptic (Lat. _anti_, against, and _sepsis_, poison). Opposing or +counter-acting putrefaction. + +Antrum (Lat. _antrum_, a cave). The cavity in the upper jaw. + +Aorta (Gr. ἀορτή, from ἀείρο, to raise up). The great artery that _rises +up_ from the left ventricle of the heart. + +Aponeurosis (Gr. ἀπό, from, and νεῦρον, a nerve). A fibrous membranous +expansion of a tendon; the nerves and tendons were formerly thought to be +identical structures, both appearing as white cords. + +Apoplexy (Gr. ἀποπληξία, a sudden stroke). The escape of blood from a +ruptured blood-vessel into the substance of the brain. + +Apparatus. A number of organs of various sizes and structures working +together for some special object. + +Appendages (Lat. _ad_ and _pendeo_, to hang from). Something +connected with a part. + +Aqueous Humor (Lat. _aqua_, water). The watery fluid occupying the +space between the cornea and crystalline lens of the eye. + +Arachnoid Membrane (Gr. ἀράχνη, a spider, and εἰδώς, like). The thin +covering of the brain and spinal cord, between the dura mater and the pia +mater. + +Arbor Vitæ. Literally, "the tree of life"; a name given to the +peculiar appearance presented by a section of the cerebellum. + +Areolar (Lat. _areola_, a small space, dim. of _area_). A term +applied to a connective tissue containing _small spaces_. + +Artery (Gr. ἀήρ, air, and τερέω, to contain). A vessel by which blood is +carried away from the heart. It was supposed by the ancients to contain +only air, hence the name. + +Articulation (Lat. _articulo_, to form a joint). The more or less +movable union of bones, etc.; a joint. + +Arytenoid Cartilages (Gr. ἀρύταινα, a ladle). Two small cartilages of the +larynx, resembling the mouth of a pitcher. + +Asphyxia (Gr. ἀ, without, and σφίξις, the pulse). Literally, "without +pulse." Condition caused by non-oxygenation of the blood. + +Assimilation (Lat. _ad_, to, and _similis_, like). The conversion of +food into living tissue. + +Asthma (Gr. ἆσθμα, a gasping). Spasmodic affection of the bronchial tubes +in which free respiration is interfered with, owing to their diminished +caliber. + +Astigmatism (Gr. ἀ, without, and στίγμα, a point). Irregular refraction +of the eye, producing a blurred image. + +Atrophy (Gr. ἀ, without, and τροφή, nourishment). Wasting of a part from +lack of nutrition. + +Auditory Nerve (Lat. _audio_, to hear). The special nerve of hearing. + +Auricle (Lat. _auricula_, a little ear). A cavity of the heart. + +Azygos (Gr. ἀ, without, and ζυγός, a yoke). Without fellow; not paired. + + +Bacteria (βακτήριον, a staff). A microscopic, vegetable organism; certain +species are active agents in fermentation, while others appear to be the +cause of infectious diseases. + +Bactericide (_Bacterium_ and Lat. _caedere_, to kill). Same as +_germicide_. + +Bile. The gall, or peculiar secretion of the liver; a viscid, yellowish +fluid, and very bitter to the taste. + +Biology (Gr. βίος, life, and λόγος, discourse). The science which treats +of living bodies. + +Bladder (Saxon _bleddra_, a bladder, a goblet). A bag, or sac, +serving as a receptacle of some secreted fluid, as the _gall bladder_, +etc. The receptacle of the urine in man and other animals. + +Bright's Disease. A group of diseases of the kidney, first described +by Dr. Bright, an English physician. + +Bronchi (Gr. βρόγχος, windpipe). The first two divisions, or branches, of +the trachea; one enters each lung. + +Bronchial Tubes. The smaller branches of the trachea within the +substance of the lungs terminating in the air cells. + +Bronchitis. Inflammation of the larger bronchial tubes; a "cold" +affecting the air passages. + +Bunion. An enlargement and inflammation of the first joint of the +great toe. + +Bursa. A pouch; a membranous sac interposed between parts which are +subject to movement, one on the other, to allow them to glide smoothly. + + +Callus (Lat. _calleo_, to be thick-skinned). Any excessive hardness +of the skin caused by friction or pressure. + +Canal (Lat. _canalis_, a canal). A tube or passage. + +Capillary (Lat. _capillus_, hair). The smallest blood-vessels, so +called because they are so minute. + +Capsule (Lat. _capsula_, a little chest). A membranous bag enclosing +a part. + +Carbon Dioxid, often called _carbonic acid_. The gas which is present +in the air breathed out from the lungs; a waste product of the animal +kingdom and a food of the vegetable kingdom. + +Cardiac (Gr. καρδία, the heart). The cardiac orifice of the stomach is +the upper one, and is near the heart; hence its name. + +Carnivorous (Lat. _caro_, flesh, and _voro_, to devour). Subsisting +upon flesh. + +Carron Oil. A mixture of equal parts of linseed oil and lime-water, +so called because first used at the Carron Iron Works in Scotland. + +Cartilage. A tough but flexible material forming a part of the +joints, air passages, nostrils, ear; gristle, etc. + +Caruncle (Lat. _caro_, flesh). The small, red, conical-shaped body at +the inner angle of the eye, consisting of a cluster of follicles. + +Casein (Lat. _caseus_, cheese). The albuminoid substance of milk; it +forms the basis of cheese. + +Catarrh. An inflammation of a mucous membrane, usually attended with +an increased secretion of mucus. The word is often limited to _nasal_ +catarrh. + +Cauda Equina (Lat., horse's tail). The collection of large nerves +descending from the lower end of the spinal cord. + +Cell (Lat. _cella_, a storeroom). The name of the tiny miscroscopic +elements, which, with slender threads or fibers, make up most of the body; +they were once believed to be little hollow chambers; hence the name. + +Cement. The substance which forms the outer part of the fang of a +tooth. + +Cerebellum (dim. for _cerebrum_, the brain). The little brain, +situated beneath the posterior third of the cerebrum. + +Cerebrum. The brain proper, occupying the upper portion of the skull. + +Ceruminous (Lat. _cerumen_, ear wax). A term applied to the glands +secreting cerumen, or _ear wax_. + +Chloral. A powerful drug and narcotic poison used to produce sleep. + +Chloroform. A narcotic poison generally used by inhalation; of +extensive use in surgical operations. It produces anæsthesia. + +Chondrin (Gr. χονδρός, cartilage). A kind of gelatine obtained by boiling +_cartilage_. + +Chordæ Tendineæ. Tendinous cords. + +Choroid (Gr. χορίον, skin, and εἶδος, form). The middle coat of the +eyeball. + +Chyle (Gr. χυλός, juice). The milk-like fluid formed by the digestion of +fatty articles of food in the intestines. + +Chyme (Gr. χυμός, juice). The pulpy +liquid formed by digestion in the stomach. + +Cilia (pl. of _cilium_, an eyelash). Minute hair-like processes found +upon the cells of the air passages and other parts. + +Ciliary Muscle. A small muscle of the eye which assists in +accommodation. + +Circumvallate (Lat. _circum_, around, and _vallum_, a rampart). +Surrounded by a rampart, as are certain papillæ of the tongue. + +Coagulation (Lat. _coagulo_, to curdle). Applied to the process by +which the blood clots or solidifies. + +Cochlea (Lat. _cochlea_, a snail shell). The spiral cavity of the +internal ear. + +Columnæ Carneæ. Fleshy projections in the ventricles of the heart. + +Commissure (Lat. _con_, together, and _mitto_, _missum_, to put). A +joining or uniting together. + +Compress. A pad or bandage applied directly to an injury to compress it. + +Concha (Gr. κόγχη, a mussel shell). The shell-shaped portion of the +external ear. + +Congestion (Lat. _con_, together, and _gero_, to bring). Abnormal +gathering of blood in any part of the body. + +Conjunctiva (Lat. _con_, together, and _jungo_, to join). A thin +layer of mucous membrane which lines the eyelids and covers the front of +the eyeball, thus joining the latter to the lids. + +Connective Tissue. The network which connects the minute parts of +most of the structures of the body. + +Constipation (Lat. _con_, together, and _stipo_, to crowd close). +Costiveness. + +Consumption (Lat. _consumo_, to consume). A disease of the lungs, +attended with fever and cough, and causing a decay of the bodily powers. +The medical name is _phthisis_. + +Contagion (Lat. _con_, with, and _tango_ or _tago_, to touch). The +communication of disease by contact, or by the inhalation of the effluvia +of a sick person. + +Contractility (Lat. _con_, together, and _traho_, to draw). The +property of a muscle which enables it to contract, or draw its extremities +closer together. + +Convolutions (Lat. _con_, together, and _volvo_, to roll). The +tortuous foldings of the external surface of the brain. + +Convulsion (Lat. _convello_, to pull together). A more or less +violent agitation of the limbs or body. + +Coördination. The manner in which several different organs of the +body are brought into such relations with one another that their functions +are performed in harmony. + +Coracoid (Gr. κόραξ, a crow, εἶδος, form). Shaped like a crow's beak. + +Cornea (Lat. _cornu_, a horn). The transparent horn-like substance +which covers a part of the front of the eyeball. + +Coronary (Lat. _corona_, a crown). A term applied to vessels and +nerves which encircle parts, as the _coronary_ arteries of the heart. + +Coronoid (Gr. κορώνη;, a crow). Like a crow's beak; thus the _coronoid_ +process of the ulna. + +Cricoid (Gr. κρίκος, a ring, and εἶδος, form). A cartilage of the larynx +resembling a seal ring in shape. + +Crystalline Lens (Lat. _crystallum_, a crystal). One of the humors of +the eye; a double-convex body situated in the front part of the eyeball. + +Cumulative. A term applied to the violent action from drugs which +supervenes after the taking of several doses with little or no effect. + +Cuticle (Lat. dim. of _cutis_, the skin). Scarf skin; the epidermis. + +Cutis (Gr. σκῦτος, a skin or hide). The true skin, also called the +_dermis_. + + +Decussation (Lat. _decusso_, _decussatum_, to cross). The _crossing_ +or running of one portion athwart another. + +Degeneration (Lat. _degenerare_, to grow worse, to deteriorate). A +change in the structure of any organ which makes it less fit to perform +its duty. + +Deglutition (Lat. _deglutire_, to swallow). The process of +swallowing. + +Deltoid. Having a triangular shape; resembling the Greek letter +Δ (_delta_). + +Dentine (Lat. _dens_, _dentis_, a tooth). The hard substance which +forms the greater part of a tooth; ivory. + +Deodorizer. An agent which corrects any foul or unwholesome odor. + +Dextrin. A soluble substance obtained from starch. + +Diabetes Mellitus (Gr. διά, through, βαίνω, to go, and μέλι, honey). +Excessive flow of sugar-containing urine. + +Diaphragm (Gr. διαφράσσω, to divide by a partition). A large, thin muscle +which separates the cavity of the chest from the abdomen. + +Diastole (Gr. διαστέλλω, to dilate). The _dilatation_ of the heart. + +Dietetics. That part of medicine which relates to diet, or food. + +Diffusion of Gases. The power of gases to become intimately mingled. + +Diplöe (Gr. διπλόω, to double, to fold). The osseous tissue between the +tables of the skull. + +Dipsomania (Gr. δίψα, thirst, and μανία, madness). An insatiable desire +for intoxicants. + +Disinfectants. Agents used to destroy the germs or particles of +living matter that are believed to be the causes of infection. + +Dislocation (Lat. _dislocare_, to put out of place). An injury to a +joint in which the bones are displaced or forced out of their sockets. + +Dissection (Lat. _dis_, apart, and _seco_, to cut). The cutting up of +an animal in order to learn its structure. + +Distal (Lat. _dis_, apart, and _sto_, to stand). Away from the +center. + +Duct (Lat. _duco_, to lead). A narrow tube. + +Duodenum (Lat. _duodeni_, twelve). The first division of the small +intestines, about twelve fingers' breadth long. + +Dyspepsia (Gr. -δύς, ill, and πέπτειν, to digest). A condition of the +alimentary canal in which it digests imperfectly. Indigestion. + +Dyspnœa (Gr. δύς, difficult, and πνέω, to breathe). Difficult breathing. + + +Efferent (Lat. _effero_, to carry out). _Bearing_ or _carrying +outwards_, as from the center to the periphery. + +Effluvia (Lat. _effluo_, to flow out). Exhalations or vapors coming +from the body, and from decaying animal or vegetable substances. + +Element. One of the simplest parts of which anything consists. + +Elimination (Lat. _e_, out of, and _limen, liminis_, a threshold). +The act of _expelling_ waste matters. Signifies, literally, "to throw out +of doors." + +Emetic (Gr. ἐμέω, to vomit). A medicine which causes vomiting. + +Emulsion (Lat. _emulgere_, to milk). Oil in a finely divided state, +suspended in water. + +Enamel (Fr. _émail_). Dense material covering the crown of a tooth. + +Endolymph (Gr. ἔνδον, within, and Lat. _lympha_, water). The fluid in +the membranous labyrinth of the ear. + +Endosmosis (Gr. ἔνδον, within, and ὠθέω, to push). The current from +without _inwards_ when diffusion of fluids takes place through a membrane. + +Epidemic (Gr. ἐπί, upon, and δέμος, the people). An extensively prevalent +disease. + +Epiglottis (Gr. ἐπί, upon, and γλόττις, the entrance to the windpipe). A +leaf-shaped piece of cartilage which covers the top of the larynx during +the act of swallowing. + +Epilepsy (Gr. ἐπίληψις, a seizure). A nervous disease accompanied by fits +in which consciousness is lost; the falling sickness. + +Ether (Gr. αἰθήρ, the pure, upper air). A narcotic poison. Used as an +anæsthetic in surgical operations. + +Eustachian (from an Italian anatomist named Eustachi). The tube which +leads from the throat to the middle ear, or tympanum. + +Excretion (Lat. _excerno_, to separate). The separation from the +blood of the waste matters of the body; also the materials excreted. + +Exosmosis (Gr. ἔξω, without, and ᾀθέω, to push). The current from within +_outwards_ when diffusion of fluids takes place through a membrane. + +Expiration (Lat. _expiro_, to breathe out). The act of forcing air +out of the lungs. + +Extension (Lat. _ex_, out, and _tendo_, to stretch). The act of +restoring a limb, etc., to its natural position after it has been flexed +or bent; the opposite of _flexion_. + + +Fauces. The part of the mouth which opens into the pharynx. + +Fenestra (Lat.). Literally, "a window." Fenestra ovalis and +fenestra rotunda, the oval and the round window; two apertures in the +bone between the tympanic cavity and the labyrinth of the ear. + +Ferment. That which causes fermentation, as yeast. + +Fermentation (Lat. _fermentum_, boiling). The process of undergoing +an effervescent change, as by the action of yeast; in a wider sense, the +change of organized substances into new compounds by the action of a +ferment. It differs in kind according to the nature of the ferment. + +Fiber (Lat. _fibra_, a filament). One of the tiny threads of which +many parts of the body are composed. + +Fibrilla. A little fiber; one of the longitudinal threads into which +a striped muscular fiber can be divided. + +Fibrin (Lat. _fibra_, a fiber). An albuminoid substance contained in +the flesh of animals, and also produced by the coagulation of blood. + +Flexion (Lat. _flecto_, to bend). The act of bending a limb, etc. + +Follicle (Lat. dim. of _follis_, a money bag). A little pouch or +depression. + +Fomentation (Lat. _foveo_, to keep warm). The application of any +warm, medicinal substance to the body, by which the vessels are relaxed. + +Foramen. A hole, or aperture. + +Frontal Sinus. A blind or closed cavity in the bones of the skull +just over the eyebrows. + +Fumigation (Lat. _fumigo_, to perfume a place). The use of certain +fumes to counteract contagious effluvia. + +Function (Lat. _functio_, a doing). The special duty of any organ. + + +Ganglion (Gr. γάγγλιν, a knot). A knot-like swelling in a nerve; a +smaller nerve center. + +Gastric (Gr. γαστήρ, stomach). Pertaining to the stomach. + +Gelatine (Lat. _gelo_, to congeal). An animal substance which +dissolves in hot water and forms a jelly on cooling. + +Germ (Lat. _germen_, a sprout, bud). Disease germ; a name applied to +certain tiny bacterial organisms which have been demonstrated to be the +cause of disease. + +Germicide (_Germ_, and Lat. _caedere_, to kill). Any agent which has +a destructive action upon living germs, especially _bacteria_. + +Gland (Lat. _glans_, an acorn). An organ consisting of follicles and +ducts, with numerous blood-vessels interwoven. + +Glottis (Gr. γλόττα, the tongue). +The narrow opening between the vocal cords. + +Glucose. A kind of sugar found in fruits, also known as grape sugar. + +Gluten. The glutinous albuminoid ingredient of cereals. + +Glycogen. Literally, "producing glucose." Animal starch found in +liver, which may be changed into glucose. + +Gram. Unit of metric system, 15.43 grains troy. + +Groin. The lower part of the abdomen, just above each thigh. + +Gustatory (Lat. _gusto_, _gustatum_, to taste). Belonging to the +sense of _taste_. + +Gymnastics (Gr. γυμνάξω, to exercise). The practice of athletic exercises. + + +Hæmoglobin (Gr. αἷμα, blood, and Lat. _globus_, a globe or globule). +A complex substance which forms the principal coloring constituent of the +red corpuscles of the blood. + +Hemispheres (Gr. ἡμί, half, and σφαῖρα, a sphere). Half a sphere, the +lateral halves of the cerebrum, or brain proper. + +Hemorrhage (Gr. αἷμα, blood, and ῥήγνυμι, to burst). Bleeding, or the +loss of blood. + +Hepatic (Gr. ἧπαρ, the liver). Pertaining to the liver. + +Herbivorous (Lat. _herba_, an herb, and _voro_, to devour). Applied +to animals that subsist upon vegetable food. + +Heredity. The predisposition or tendency derived from one's ancestors +to definite physiological actions. + +Hiccough. A convulsive motion of some of the muscles used in +breathing, accompanied by a shutting of the glottis. + +Hilum, sometimes written Hilus. A small fissure, notch, or +depression. A term applied to the concave part of the kidney. + +Homogeneous (Gr. ὁμός, the same, and γένος, kind). Of the _same kind_ +or quality throughout; uniform in nature,--the reverse of heterogeneous. + +Humor. The transparent contents of the eyeball. + +Hyaline (Gr. ὕαλος, glass). Glass-like, resembling glass in transparency. + +Hydrogen. An elementary gaseous substance, which, in combination with +oxygen, produces water. + +Hydrophobia (Gr. ὕδωρ, water, and φοβέομαι, to fear). A disease caused by +the bite of a rabid dog or other animal. + +Hygiene (Gr. ὑγἰεια health). The art of preserving health and preventing +disease. + +Hyoid (Gr. letter υ, and εἰδος, form, resemblance). The bone at the root +of the tongue, shaped like the Greek letter υ. + +Hypermetropia (Gr. ὑπέρ over, beyond, μέτρον, measure, and ώ̓ψ, the +eye). Far-sightedness. + +Hypertrophy (Gr. ὑπέρ, over, and τροφή, nourishment). Excessive growth; +thickening or enlargement of any part or organ. + + +Incisor (Lat. _incido_, to cut). Applied to the four front teeth of +both jaws, which have sharp, cutting edges. + +Incus. An anvil; the name of one of the bones of the middle ear. + +Indian Hemp. The common name of _Cannabis Indica_, an intoxicating +drug known as _hasheesh_ and by other names in Eastern countries. + +Inferior Vena Cava. The chief vein of the lower part of the body. + +Inflammation (Lat. prefix _in_ and _flammo_, to flame). A redness or +swelling of any part of the body with heat and pain. + +Insalivation (Lat. _in_ and _saliva_, the fluid of the mouth). The +mingling of the saliva with the food during the act of chewing. + +Inspiration (Lat. _inspiro, spiratum_, to breathe in). The act of +drawing in the breath. + +Intestine (Lat. _intus_, within). The part of the alimentary canal +which is continuous with the lower end of the stomach; also called the +bowels. + +Iris (Lat. _iris_, the rainbow). The thin, muscular ring which lies +between the cornea and crystalline lens, giving the eye its special color. + + +Jaundice (Fr. _jaunisse_, yellow). A disorder in which the skin and +eyes assume a yellowish tint. + + +Katabolism (Gr. καταβάλλω, to throw down). The process by means of which +the more complex elements are rendered more simple and less complex. The +opposite of _anabolism_. + + +Labyrinth. The internal ear, so named from its many windings. + +Lacrymal Apparatus (Lat. _lacryma_, a tear). The organs for forming +and carrying away the tears. + +Lacteals (Lat. _lac, lactis_, milk). The absorbent vessels of the +small intestines. + +Laryngoscope (Gr. λάρυγξ, larynx, and σκοπέω, to behold). An instrument +consisting of a mirror held in the throat, and a reflector to throw light +on it, by which the interior of the larynx is brought into view. + +Larynx. The cartilaginous tube situated at the top of the windpipe. + +Lens. Literally, a lentil; a piece of transparent glass or other +substance so shaped as either to converge or disperse the rays of light. + +Ligament (Lat. _ligo_, to bind). A strong, fibrous material binding +bones or other solid parts together. + +Ligature (Lat. _ligo_, to bind). A thread of some material used in +tying a cut or injured artery. + +Lobe. A round, projecting part of an organ, as of the liver, lungs, +or brain. + +Lymph (Lat. _lympha_, pure water). The watery fluid conveyed by the +lymphatic vessels. + +Lymphatic Vessels. A system of absorbent vessels. + + +Malleus. Literally, the mallet; one of the small bones of the middle +ear. + +Marrow. The soft, fatty substance contained in the cavities of bones. + +Mastication (Lat. _mastico_, to chew). The act of cutting and +grinding the food to pieces by means of the teeth. + +Meatus (Lat. _meo_, _meatum_, to pass). A _passage_ or canal. + +Medulla Oblongata. The "oblong marrow"; that portion of the brain +which lies upon the basilar process of the occipital bone. + +Meibomian. A term applied to the small glands between the conjunctiva +and tarsal cartilages, discovered by _Meibomius_. + +Membrana Tympani. Literally, the membrane of the drum; a delicate +partition separating the outer from the middle ear; it is sometimes +popularly called "the drum of the ear." + +Membrane. A thin layer of tissue serving to cover some part of the +body. + +Mesentery (Gr. μέσος, middle, and ἔντερον, the intestine). A duplicature +of the peritoneum covering the small _intestine_, which occupies the +_middle_ or center of the abdominal cavity. + +Metabolism (Gr. μεταβολή, change). The _changes_ taking place in cells, +whereby they become more complex and contain more force, or less complex +and contain less force. The former is constructive metabolism, or +_anabolism_; the latter, destructive metabolism, or _katabolism_. + +Microbe (Gr. μικρός, little, and βίος, life). A microscopic organism, +particularly applied to bacteria. + +Microscope (Gr. μικρός, small, and σκοπέω;, to look at). An optical +instrument which assists in the examination of minute objects. + +Molar (Lat. _mola_, a mill). The name applied to the three back +teeth at each side of the jaw; the grinders, or mill-like teeth. + +Molecule (dim. of Lat. _moles_, a mass). The smallest quantity into +which the mass of any substance can physically be divided. A molecule may +be chemically separated into two or more atoms. + +Morphology (Gr. μόρφη, form, and λόγος, discourse). The study of the laws +of form or structure in living beings. + +Motor (Lat. _moveo_, _motum_, to move). The name of the nerves which +conduct to the muscles the stimulus which causes them to contract. + +Mucous Membrane. The thin layer of tissue which covers those internal +cavities or passages which communicate with the external air. + +Mucus. The glairy fluid secreted by mucous membranes. + +Myopia (Gr. μύω, to shut, and ὤψ, the eye). A defect of vision dependent +upon an eyeball that is too long, rendering distant objects indistinct; +_near sight_. + +Myosin (Gr. μῶς, muscle). Chief proteid substance of muscle. + + +Narcotic (Gr. ναρκάω, to benumb). A medicine which, in poisonous doses, +produces stupor, convulsions, and sometimes death. + +Nerve Cell. A minute round and ashen-gray cell found in the brain and +other nervous centers. + +Nerve Fiber. An exceedingly slender thread of nervous tissue. + +Nicotine. The poisonous and stupefying oil extracted from tobacco. + +Nostril (Anglo-Saxon _nosu_, nose, and _thyrl_, a hole). One of the +two outer openings of the nose. + +Nucleolus (dim. of _nucleus_). A little nucleus. + +Nucleus (Lat. _nux_, a nut). A central part of any body, or that +about which matter is collected. In anatomy, a cell within a cell. + +Nutrition (Lat. _nutrio_, to nourish). The processes by which the +nourishment of the body is accomplished. + + +Odontoid (Gr. ὀδούς, a tooth, εἶδος, shape). The name of the bony peg of +the second vertebra, around which the first turns. + +Œsophagus. Literally, that which carries food. The tube leading +from the throat to the stomach; the gullet. + +Olecranon (Gr. ὠλένη, the elbow, and κρανίον, the top of the head). A +curved eminence at the upper and back part of the ulna. + +Olfactory (Lat. _olfacio_, to smell). Pertaining to the sense of +smell. + +Optic (Gr. ὀπτεύω, to see). Pertaining to the sense of sight. + +Orbit (Lat. _orbis_, a circle). The bony socket or cavity in which +the eyeball is situated. + +Organ (Lat. _organum_, an instrument or implement). A portion of the +body having some special function or duty. + +Osmosis (Gr. ὠσμός, impulsion). Diffusion of liquids through membranes. + +Ossa Innominata, pl. of Os Innominatum (Lat.). "Unnamed bones." The +irregular bones of the pelvis, unnamed on account of their non-resemblance +to any known object. + +Otoconia (Gr. οὖς, an ear, and κονία, dust). Minute crystals of lime in +the vestibule of the ear; also known as _otoliths_. + + +Palate (Lat. _palatum_, the palate). The roof of the mouth, +consisting of the hard and soft palate. + +Palpitation (Lat. _palpitatio_, a frequent or throbbing motion). A +violent and irregular beating of the heart. + +Papilla. The small elevations found on the skin and mucous membranes. + +Paralysis (Gr. παραλύω, to loosen; also, to disable). Loss of function, +especially of motion or feeling. Palsy. + +Parasite. A plant or animal that grows or lives on another. + +Pelvis. Literally, a basin. The bony cavity at the lower part of the +trunk. + +Pepsin (Gr. πέπτω, to digest). The active principle of the gastric juice. + +Pericardium (Gr. περί, about, and καρδία, heart). The sac enclosing the +heart. + +Periosteum (Gr. περί, around, ὀστέον, a bone). A delicate fibrous +membrane which invests the bones. + +Peristaltic Movements (Gr. περί, round, and στέλλω, to send). The slow, +wave-like movements of the stomach and intestines. + +Peritoneum (Gr. περιτείνω, to stretch around). The investing membrane of +the stomach, intestines, and other abdominal organs. + +Perspiration (Lat. _perspiro_, to breathe through). The sweat. + +Petrous (Gr. πέτρα, a rock). The name of the hard portion of the temporal +bone, in which are situated the drum of the ear and labyrinth. + +Phalanges (Gr. φάλαγξ, a body of soldiers closely arranged in ranks and +files). The bones of the fingers and toes. + +Pharynx (Gr. φάρμγξ, the throat). The cavity between the back of the +mouth and the gullet. + +Physiology (Gr. φύσις, nature, and λόγος, a discourse). The science of the +functions of living, organized beings. + +Pia Mater (Lat.). Literally, the tender mother; the innermost of the +three coverings of the brain. It is thin and delicate; hence the name. + +Pinna (Lat. a feather or wing). External cartilaginous flap of the +ear. + +Plasma (Gr. πλάσσω, to mould). Anything formed or moulded. The liquid +part of the blood. + +Pleura (Gr. πλευρά, the side, also a rib). A membrane covering the lung, +and lining the chest. + +Pleurisy. An inflammation affecting the pleura. + +Pneumogastric (Gr. πνεύμων, the lungs, and γαστήρ, the stomach). The chief +nerve of respiration; also called the _vagus_, or wandering nerve. + +Pneumonia. An inflammation affecting the air cells of the lungs. + +Poison (Fr. _poison_). Any substance, which, when applied externally, +or taken into the stomach or the blood, works such a change in the animal +economy as to produce disease or death. + +Pons Varolii. Bridge of Varolius. The white fibers which form a +_bridge_ connecting the different parts of the brain, first described by +_Varolius_. + +Popliteal (Lat. _poples_, _poplitis_, the ham, the back part of the +knee). The space _behind the knee joint_ is called the _popliteal_ space. + +Portal Vein (Lat. _porta_, a gate). The venous trunk formed by the +veins coming from the intestines. It carries the blood to the liver. + +Presbyopia (Gr. πρέσβυς, old, and ὤψ, the eye). A defect of the +accommodation of the eye, caused by the hardening of the crystalline +lens; the "far sight" of adults and aged persons. + +Process (Lat. _procedo_, _processus_, to proceed, to go forth). Any +projection from a surface; also, a method of performance; a procedure. + +Pronation (Lat. _pronus_, inclined forwards). The turning of the hand +with the palm downwards. + +Pronator. The group of muscles which turn the hand palm downwards. + +Proteids (Gr. πρῶτος, first, and εἶδος, form). A general term for the +albuminoid constitutents of the body. + +Protoplasm (Gr. πρῶτος, first, and πλάσσω, to form). A _first-formed_ +organized substance; primitive organic cell matter. + +Pterygoid (Gr. πτέρων, a wing, and εἶδος, form, resemblance). Wing-like. + +Ptomaine (Gr. πτῶμα, a dead body). One of a class of animal bases or +alkaloids formed in the putrefaction of various kinds of albuminous +matter. + +Ptyalin (Gr. σίαλον, saliva). A ferment principle in _saliva_, having +power to convert starch into sugar. + +Pulse (Lat. _pello, pulsum_, to beat). The throbbing of an artery +against the finger, occasioned by the contraction of the heart. Commonly +felt at the _wrist_. + +Pupil (Lat. _pupilla_). The central, round opening in the iris, +through which light passes into the interior of the eye. + +Pylorus (Gr. πυλουρός, a gatekeeper). The lower opening of the stomach, +at the beginning of the small intestine. + + +Reflex (Lat. _reflexus_, turned back). The name given to involuntary +movements produced by an excitation traveling along a sensory nerve to a +center, where it is turned back or reflected along motor nerves. + +Renal (Lat. _ren_, _renis_, the kidney). Pertaining to the _kidneys_. + +Respiration (Lat. _respiro_, to breathe frequently). The function of +breathing, comprising two acts,--_inspiration_, or breathing in, and +_expiration_, or breathing out. + +Retina (Lat. _rete_, a net). The innermost of the three tunics, or +coats, of the eyeball, being an expansion of the optic nerve. + +Rima Glottidis (Lat. _rima_, a chink or cleft). The _opening_ of the +glottis. + + +Saccharine (Lat. _saccharum_, sugar). The group of food substances +which embraces the different varieties of sugar, starch, and gum. + +Saliva. The moisture, or fluids, of the mouth, secreted by the +salivary glands; the spittle. + +Sarcolemma (Gr. σάρξ, flesh, and λέμμα, a husk). The membrane which +surrounds the contractile substance of a striped muscular fiber. + +Sclerotic (Gr. σκληρός, hard). The tough, fibrous, outer coat of the +eyeball. + +Scurvy. Scorbutus,--a disease of the general system, having prominent +skin symptoms. + +Sebaceous (Lat. _sebum_, fat). Resembling fat; the name of the oily +secretion by which the skin is kept flexible and soft. + +Secretion (Lat. _secerno_, _secretum_, to separate). The process of +separating from the blood some essential, important fluid; which fluid is +also called a _secretion_. + +Semicircular Canals. Three canals in the internal ear. + +Sensation. The perception of an external impression by the nervous +system. + +Serum. The clear, watery fluid which separates from the clot of the +blood. + +Spasm (Gr. σπασμός, convulsion). A sudden, violent, and involuntary +contraction of one or more muscles. + +Special Sense. A sense by which we receive particular sensations, +such as those of sight, hearing, taste, and smell. + +Sputum, pi. Sputa (Lat. _spuo_, _sputum_, to _spit_). The matter +which is coughed up from the air passages. + +Stapes. Literally, a stirrup; one of the small bones of the middle +ear. + +Stimulant (Lat. _stimulo_, to prick or goad on). An agent which +causes an increase of vital activity in the body or in any of its parts. + +Striated (Lat. _strio_, to furnish with channels). Marked with fine +lines. + +Styptics (Gr. στυπτικός astringent). Substances used to produce a +contraction or shrinking of living tissues. + +Subclavian Vein (Lat. _sub_, under, and _clavis_, a key). The great +vein bringing back the blood from the arm and side of the head; so called +because it is situated underneath the _clavicle_, or collar bone. + +Superior Vena Cava (Lat., upper hollow vein). The great vein of the +upper part of the body. + +Suture (Lat. _sutura_, a seam). The union of certain bones of the +skull by the interlocking of jagged edges. + +Sympathetic System of Nerves. A double chain of nervous ganglia, +situated chiefly in front of, and on each side of, the spinal column. + +Symptom (Gr. σύν, with, and πίπτω, to fall). A sign or token of disease. + +Synovial (Gr. σύν, with, and ὠόν, an egg). The liquid which lubricates +the joints; joint-oil. It resembles the white of a raw egg. + +System. A number of different organs, of similar structures, +distributed throughout the body and performing similar functions. + +Systemic. Belonging to the system, or body, as a whole. + +Systole (Gr. συστέλλω, to contract). The contraction of the heart, by +which the blood is expelled from that organ. + + +Tactile (Lat. _tactus_, touch). Relating to the sense of touch. + +Tartar. A hard crust which forms on the teeth, and is composed of +salivary mucus, animal matter, and a compound of lime. + +Temporal (Lat. _tempus_, time, and _tempora_, the temples). +Pertaining to the temples; so called because the hair begins to turn white +with age in that portion of the scalp. + +Tendon (Lat. _tendo_, to stretch). The white, fibrous cord, or band, +by which a muscle is attached to a bone; a sinew. + +Tetanus (Gr. τείνω, to stretch). A disease +marked by persistent contractions of all or some of the voluntary muscles; +those of the jaw are sometimes solely affected; the disorder is then +termed lockjaw. + +Thorax (Gr. θώραξ, a breast-plate). The upper cavity of the trunk of the +body, containing the lungs, heart, etc.; the chest. + +Thyroid (Gr. θυρέος, a shield, and εἶδος, form). The largest of +the cartilages of the larynx: its projection in front is called "Adam's +Apple." + +Tissue. Any substance or texture in the body formed of various +elements, such as cells, fibers, blood-vessels, etc., interwoven with each +other. + +Tobacco (Indian _tabaco_, the tube, or pipe, in which the Indians +smoked the plant). A plant used for smoking and chewing, and in snuff. + +Trachea (Gr. τραχύς, rough). The windpipe. + +Tragus (Gr. τράγος, a goat). The eminence in front of the opening of the +ear; sometimes hairy, like a goat's beard. + +Transfusion (Lat. _transfundo_, to pour from one vessel to another). +The operation of injecting blood taken from one person into the veins of +another. + +Trichina Spiralis. (A twisted hair). A minute species of parasite, or +worm, which infests the flesh of the hog: may be introduced into the human +system by eating pork not thoroughly cooked. + +Trochanter (Gr. τροχάω, to turn, to revolve). Name given to two +projections on the upper extremities of the femur, which give attachment +to the _rotator_ muscles of the thigh. + +Trypsin. The ferment principle in pancreatic juice, which converts +proteid material into peptones. + +Tubercle (Lat. _tuber_, a bunch). A pimple, swelling, or tumor. A +morbid product occurring in certain lung diseases. + +Tuberosity (Lat. _tuber, tuberis_, a swelling). A protuberance. + +Turbinated (Lat. _turbinatus_, from _turbo, turbinis_, a top). Formed +like a _top_; a name given to the bones in the outer wall of the nasal +fossæ. + +Tympanum (Gr. τύμπανον, a drum). The cavity of the middle ear, resembling +a drum in being closed by two membranes. + + +Umbilicus (Lat., the navel.) A round cicatrix or scar in the median +line of the abdomen. + +Urea (Lat. _urina_, urine). Chief solid constitutent of _urine_. +Nitrogenous product of tissue decomposition. + +Ureter (Gr. οὐρέω, to pass urine). +The tube through which the _urine_ is conveyed from the kidneys to the +bladder. + +Uvula (Lat. _uva_, a grape). The small, pendulous body attached to +the back part of the palate. + + +Vaccine Virus (Lat. _vacca_, a cow, and _virus_, poison). The +material derived from heifers for the purpose of vaccination,--the great +preventive of smallpox. + +Valvulae Conniventes. A name given to transverse folds of the mucous +membrane in the small intestine. + +Varicose (Lat. _varix_, a dilated vein). A distended or enlarged +vein. + +Vascular (Lat. _vasculum_, a little vessel). Pertaining to or +possessing blood or lymph vessels. + +Vaso-motor (Lat. _vas_, a vessel, and _moveo, motum_, to move). +Causing _motion_ to the _vessels_. Vaso-motor nerves cause contraction and +relaxation of the blood-vessels. + +Venæ Cavæ, pl. of Vena Cava. "Hollow veins." A name given to the +two great veins of the body which meet at the right auricle of the heart + +Venous (Lat. _vena_, a vein). Pertaining to, or contained within, a +vein. + +Ventilation. The introduction of fresh air into a room or building in +such a manner as to keep the air within it in a pure condition. + +Ventral (Lat. _venter, ventris_, the belly). Belonging to the +abdominal or belly cavity. + +Ventricles of the Heart. The two largest cavities of the heart. + +Vermiform (Lat. _vermis_, a worm, and _forma_, form). Worm-shaped. + +Vertebral Column (Lat. _vertebra_, a joint). The backbone; also +called the spinal column and spine. + +Vestibule. A portion of the internal ear, communicating with the +semicircular canals and the cochlea, so called from its fancied +resemblance to the vestibule, or porch, of a house. + +Villi (Lat. _villus_, shaggy hair). Minute, thread-like projections +upon the internal surface of the small intestine, giving it a velvety +appearance. + +Virus (Lat., poison). Foul matter of an ulcer; poison. + +Vital Knot. A part of the medulla oblongata, the destruction of which +causes instant death. + +Vitreous (Lat. _vitrum_, glass). Having the appearance of glass; +applied to the humor occupying the largest part of the cavity of the +eyeball. + +Vivisection (Lat. _vivus_, alive, and _seco_, to cut). The practice +of operating upon living animals, for the purpose of studying some +physiological process. + +Vocal Cords. Two elastic bands or ridges situated in the larynx; the +essential parts of the organ of voice. + + +Zygoma (Gr. ζυγώς, a yoke). The arch formed by the malar bone and the +zygomatic process of the temporal bone. + + + + +Index. + + +Absorption + from mouth and stomach + by the intestines +Accident and emergencies +Achilles, Tendon of +Air, made impure by breathing + Foul, effect of, on health +Alcohol, Effect of, on bones + Effect of, on muscles + Effect of, on muscular tissue + Effect of, on physical culture + Nature of + Effects of, on human system + and digestion + Effect of, on the stomach + and the gastric juice + Final results on digestion + Effects of, on the liver + Fatty degeneration due to + Effect of, on the circulation + Effect of, on the heart + Effect of, on the blood-vessels + Effect of, on the lungs + Other results of, on lungs + Effect of, on disease + Effect of, on kidneys +Alcohol + as cause of Bright's disease + and the brain + How, injures the brain + Why brain suffers from + the enemy of brain work + Other physical results of + Diseases produced by + Mental and moral ruin by + Evil results of, inherited + Effect of, on taste + Effect of, on the eye + Effect of, on throat and voice +Alcoholic beverages +Alcoholic fermentation and Bacteria +Anabolism defined +Anatomy defined +Antidotes for poisons +Antiseptics +Apparatus, Question of +Arm, Upper +Arteries +Astigmatism +Asphyxia +Atlas and axis +Atmosphere, how made impure + +Bacteria, Nature of +Bacteria, Struggle for existence of + Importance of, in Nature + Action of + Battle against +Baths and bathing +Bathing, Rules and precautions +Bicycling +Bile +Biology defined +Bladder +Bleeding, from stomach + from lungs + from nose + How to stop +Blood, Circulation of + Physical properties of + corpuscles + Coagulation of + General plan of circulation +Blood-vessels, Nervous control of + connected with heart + Effect of alcohol on + Injuries to +Bodies, living, Characters of +Body, General plan of +Bone, Chemical composition of + Physical properties of + Microscopic structure of +Bones, uses of, The + Kinds of + in infancy and childhood + positions at school + in after life + Broken + broken, Treatment for + Effect of alcohol on + Effect of tobacco on +Breathing, Movements of +Breathing, Mechanism of + Varieties of + Nervous control of + change in the air + Air, made impure by +Brain, as a whole + Membranes of + as a reflex center + Effects of alcohol on +Brain center, Functions of, in perception of impressions +Bright's disease caused by alcohol +Bronchial tubes +Burns or scalds + +Capillaries +Carbohydrates +Carpus +Cartilage + Hyaline + White fibro- + Yellow fibro- + Thyroid + Arytenoid + Cricoid +Cells + and the human organism + Kinds of + Vital properties of + Epithelial + Nerve +Cerebrum +Cerebellum +Chemical compounds in the body +Chloral +Chyle +Chyme +Cilia of air passages +Circulation + General plan of + Portal + Pulmonic + Systemic + Effect of alcohol on +Clavicle +Cleanliness, Necessity for +Clothing, Use of + Material used for + Suggestions for use of + Effects of tight-fitting + Miscellaneous hints on use of + Catching, on fire +Coagulation of blood +Cocaine, ether, and chloroform +Cochlea of ear +Cocoa +Coffee +Colon +Color-blindness +Complemental air +Compounds, Chemical + Organic +Condiments +Conjunctiva +Connective tissue +Consonants +Contagious diseases +Contraction, Object of +Contusions and bruises +Convulsions +Cooking +Coughing +Cornea +Corpuscles, Blood + Red + Colorless +Corti, Organ of +Cranial Nerves +Cranium, Bones of +Crying +Crystalline lens +Cuticle +Cutis vera, or true skin + +Degeneration, Fatty, due to alcohol +Deglutition, or swallowing +Deodorants +Diet, Important articles of + Effect of occupation on + Too generous + Effect of climate on +Digestion, Purpose of + General plan of + in small intestines + in large intestines + Effect of alcohol on +Disease, Effect of alcoholics upon +Diseases, infectious and contagious, Management of + Care of + Hints on nursing +Disinfectants + Air and water as + How to use +Dislocations +Dogs, mad, Bites of +Drowning, Apparent + Methods of treating + Sylvester method + Marshall Hall method +Duct, Hepatic + Cystic + Common bile + Thoracic + Nasal +Duodenum +Dura mater + +Ear, External + Middle + Bones of the + Internal + Practical hints on care of + Foreign bodies in +Eating, Practical points about +Eggs as food +Elements, Chemical, in the body +Epidermis, or cuticle +Epiglottis +Epithelium + Squamous + Columnar + Glandular + Ciliated +Epithelial tissues, Functions of +Erect position +Ethmoid bone +Eustachian tube +Excretion +Exercise, Physical + Importance of + Effect of, on muscles + Effect of, on important organs + Effect of, on personal appearance + Effect of excessive + Amount of, required + Time for + Physical, in school + Practical points about + Effect of alcohol and tobacco on +Experiments, Limitations of + Value of +Eye + Inner structure of + Compared to camera + Refractive media of + Movements of + Foreign bodies in + Practical hints on care of + Effect of alcohol on + Effect of tobacco on +Eyeball, Coats of +Eyelids and eyebrows +Eyesight in schools + +Face + Bones of the +Fainting +Fats + and oils +Femur +Fibrin +Fibula +Fish as food +Food and drink +Food, why we need it + Absorption of, by the blood + Quantity of, as affected by age + Kinds of, required +Foods, Classification of + Nitrogenous + Proteid + Saline or mineral + Vegetable + Proteid vegetable + Non-proteid vegetable + Non-proteid animal + Table of +Food materials, Table of + Composition of +Foot +Foul air, Effect of, on health +Frontal bone +Frost bites +Fruits as food + +Gall bladder +Garden vegetables +Gastric glands +Gastric juice, Effect of alcohol on +Glands + Mesenteric + Lymphatic + Ductless + Thyroid + Thymus + Suprarenal + Lacrymal +Glottis + +Hair + Structure of +Hair and nails, Care of +Hall, Marshall, method for apparent drowning +Hand +Haversian canals +Head and spine, how joined +Head, Bones of +Hearing, Sense of + Mechanism of + Effect of tobacco on +Heart + Valves of + General plan of blood-vessels connected with + Rhythmic action of + Impulse and sounds of + Nervous control of + Effect of alcohol on + Effect of tobacco on +Heat, Animal + Sources of +Hiccough +Hip bones +Histology defined +Humerus +Hygiene defined +Hyoid bone +Hypermetropia + +Ileum +Injured, Prompt aid to +Insalivation +Intestine, Small + Coats of small + Large +Intoxicants, Physical results of +Iris of the eye + +Jejunum +Joints + Imperfect + Perfect + Hinge + Ball-and-socket + Pivot + +Katabolism defined +Kidneys + Structure of + Function of + Action if, how modified + Effect of alcohol on +Kidneys and skin + +Lacrymal apparatus + gland +Lacteals +Landmarks, Bony + Muscular + heart + arteries +Larynx +Laughing +Lens, Crystalline +Levers in the body +Life, The process of +Ligaments +Limbs, Upper + Lower +Liver + Minute structure of + Blood supply of + Functions of + Effect of alcohol on +Lungs + Minute structure of + Capacity of + Effect of alcohol on + Bleeding from +Lymph +Lymphatics + +Mad dogs, Bites of +Malar bone +Mastication +Maxillary, Superior + Inferior +Meals, Hints about +Meats as food +Medulla oblongata +Membrane, Synovial + Serous + Arachnoid +Membranes, Brain +Mesentery +Metabolism defined +Metacarpal bones +Metatarsal bones +Microscope, Use of +Milk +Mineral foods +Morphology defined +Motion in animals +Mouth +Movement, Mechanism of +Muscles, Kinds of + voluntary, Structure of + involuntary, Structure of + Arrangement of + Important + Effect of alcohol on + Effect of tobacco on + Review analysis of + Rest for +Muscular tissue, Effect of alcohol on + Changes in + Properties of + activity + contraction + fatigue + sense +Myopia + +Nails + Care of +Nasal bones +Nerve cells + fibers + cells and fibers, Function of +Nerves, Cranial + Spinal + Motor + Sensory + spinal, Functions of +Nervous system, General view of + compared to telegraph system + Divisions of + Effect of alcohol on + Effect of tobacco on +Nitrogenous foods. +Non-proteid vegetable foods + animal foods +Nose, Bleeding from + Foreign bodies in + +Occipital bone +Œsophagus +Opium + Poisonous effects of + In patent medicines + Victim of the, habit +Organic compounds +Outdoor games +Oxidation + +Pain, Sense of +Palate bones +Pancreas +Pancreatic juice +Parietal bones +Patella +Pepsin +Pericardium +Periosteum +Peritoneum +Phalanges +Pharynx and œsophagus +Physical exercise +Physical education in school +Physical exercises in school +Physiology defined + Study of + what it should teach + Main problems of, briefly stated. +Physiological knowledge, Value of +Pia mater +Pneumogastric nerve +Poisons +Poisons, Table of + Antidotes for + Practical points about +Poisoning, Treatment of +Portal circulation +Portal vein +Presbyopia +Pressure, Where to apply +Proteids +Proteid vegetable foods +Protoplasm +Pulmonary artery + veins +Pulmonary infection +Pulse +Pupil of the eye + +Radius +Receptaculum chyli +Rectum +Reflex centers + in the brain +Reflex action, Importance of +Renal secretion +Residual air +Respiration, Nature and object of + Nervous control of + Effect of, on the blood + Effect of, on the air + Modified movements of + Effect of alcohol on + Effect of tobacco on + artificial, Methods of +Rest, for the muscles + Need of + Benefits of + The Sabbath, a day of + of mind and body +Retina +Ribs and sternum + +Saline or mineral foods +Saliva +Salt as food +Salts, Inorganic, in the body +Scalds or burns +Scapula +School, Physical education in + Positions at +School and physical education +Secretion +Semicircular canals +Sensations, General +Sensation, Conditions of +Sense, Organs of +Sense organ, The essentials of +Serous membranes +Sick-room, Arrangement of + Ventilation of + Hints for + Rules for +Sighing +Sight, Sense of +Skating, swimming, and rowing +Skeleton + Review analysis of +Skeleton and manikin, Use of +Skin, The + regulating temperature + Action of, how modified + Absorbent powers of + and the kidneys +Skull + Sutures of +Sleep, a periodical rest + Effect of, on bodily functions + Amount of, required + Practical rules about +Smell + Sense of +Sneezing +Snoring +Sobbing +Special senses +Speech +Sphenoid bone +Spinal column +Spinal cord + Structure of + Functions of + conductor of impulses + as a reflex center +Spinal nerves + Functions of +Spleen +Sprains and dislocations +Stammering +Starches and sugars +Sternum +Stomach + Coats of + Digestion in + Effect of alcohol on + Bleeding from +Strabismus +Stuttering +Sunstroke +Supplemental air +Suprarenal capsules +Sutures of skull +Sweat glands +Sweat, Nature of +Sylvester method for apparent drowning +Sympathetic system + Functions of +Synovial membrane + sheaths and sacs + +Taste, Organ of + Sense of +Taste, Physiological conditions of + Modifications of the sense + Effect of alcohol on + Effect of tobacco on +Tea +Tear gland and tear passages +Tears +Technical terms defined +Teeth + Development of + Structure of + Proper care of + Hints about saving +Temperature, Regulation of bodily + Skin as a regulator of + Voluntary regulation of + Sense of +Temporal bones +Tendon of Achilles +Tendons +Thigh +Thoracic duct +Throat + Care of + Effect of alcohol on + Effect of tobacco on + Foreign bodies in +Thymus gland +Thyroid gland +Tibia +Tidal air +Tissue, White fibrous + Connective + Yellow elastic + Areolar + Adipose + Adenoid + Muscular +Tissues, Epithelial +Tissues, epithelial, Varieties of + Functions of + Connective +Tobacco, Effect of, on bones + Effect of, on muscles + Effect of, on physical culture + Effect of, on digestion + Effect of, on the heart + Effect of, on the lungs + Effect of, on the nervous system + Effect of, on the mind + Effect of, on the character + Effect of, on taste + Effect of, on hearing + Effect of, on throat and voice +Touch, Organ of + Sense of +Trachea +Trunk, Bones of +Tympanum, Cavity of + +Ulna +Urine + +Valve, Mitral +Valves of the heart +Valves, Tricuspid + Semilunar +Vegetable foods +Veins +Ventilation + Conditions of efficient + of sick-room +Vestibule of ear +Vermiform appendix +Vision, Common defects of + Effect of tobacco on +Vivisection and dissection +Vocal cords +Voice, Mechanism of + Factors in the production of + Care of + Effect of alcohol on + Effect of tobacco on +Vowel sounds + +Walking, jumping, and running +Waste and repair +Waste material, Nature of +Waste products, Elimination of +Water as food +Whispering +Wounds, Incised and lacerated + +Yawning + + + + +Footnotes: + + + +[1] The Value of Physiological Knowledge. "If any one doubts the +importance of an acquaintance with the fundamental principles of +physiology as a means to complete living, let him look around and see how +many men and women he can find in middle life, or later, who are +thoroughly well. Occasionally only do we meet with an example of vigorous +health continued to old age; hourly do we meet with examples of acute +disorder, chronic ailment, general debility, premature decrepitude. +Scarcely is there one to whom you put the question, who has not, in the +course of his life, brought upon himself illness from which a little +knowledge would have saved him. Here is a case of heart disease consequent +on a rheumatic fever that followed a reckless exposure. There is a case of +eyes spoiled for life by overstudy. + +"Not to dwell on the natural pain, the gloom, and the waste of time and +money thus entailed, only consider how greatly ill health hinders the +discharge of all duties,--makes business often impossible, and always more +difficult; produces irritability fatal to the right management of +children, puts the functions of citizenship out of the question, and makes +amusement a bore. Is it not clear that the physical sins--partly our +ancestors' and partly our own--which produce this ill health deduct more +from complete living than anything else, and to a great extent make life a +failure and a burden, instead of a benefaction and a pleasure?"--Herbert +Spencer. + +[2] The word protoplasm must not be misunderstood to mean a substance of a +definite chemical nature, or of an invariable morphological structure; it +is applied to any part of a cell which shows the properties of life, and +is therefore only a convenient abbreviation for the phrase "mass of living +matter." + +[3] "Did we possess some optic aid which should overcome the grossness of +our vision, so that we might watch the dance of atoms in the double +process of making and unmaking in the living body, we should see the +commonplace, lifeless things which are brought by the blood, and which we +call food, caught up into and made part of the molecular whorls of the +living muscle, linked together for a while in the intricate figures of the +dance of life, giving and taking energy as they dance, and then we should +see how, loosing hands, they slipped back into the blood as dead, inert, +used-up matter."--Michael Foster, Professor of Physiology in the +University of Cambridge, England. + +[4] "Our material frame is composed of innumerable atoms, and each +separate and individual atom has its birth, life, and death, and then its +removal from the 'place of the living.' Thus there is going on a +continuous process of decay and death among the individual atoms which +make up each tissue. Each tissue preserves its vitality for a limited +space only, is then separated from the tissue of which it has formed a +part, and is resolved into its inorganic elements, to be in due course +eliminated from the body by the organs of excretion."--Maclaren's +_Physical Education_. + +[5] The periosteum is often of great practical importance to the surgeon. +Instances are on record where bones have been removed, leaving the +periosteum, within which the entire bone has grown again. The importance +of this remarkable tissue is still farther illustrated by experiments upon +the transplantation of this membrane in the different tissues of living +animals, which has been followed by the formation of bone in these +situations. Some years ago a famous surgeon in New York removed the whole +lower jawbone from a young woman, leaving the periosteum and even +retaining in position the teeth by a special apparatus. The entire jawbone +grew again, and the teeth resumed their original places as it grew. + +[6] The mechanism of this remarkable effect is clearly shown by an +experiment which the late Dr. Oliver Wendell Holmes used to take delight +in performing in his anatomical lectures at the Harvard Medical College. +He had a strong iron bar made into a ring of some eight inches in +diameter, with a space left between the ends just large enough to be +filled by an English walnut. The ring was then dropped to the floor so as +to strike on the convexity just opposite to the walnut, which invariably +was broken to pieces. + +[7] For the treatment of accidents and emergencies which may occur with +reference to the bones, see Chapter XIII. + +[8] "Besides the danger connected with the use of alcoholic drinks which +is common to them with other narcotic poisons, alcohol retards the growth +of young cells and prevents their proper development. Now, the bodies of +all animals are made up largely of cells, ... and the cells being the +living part of the animal, it is especially important that they should not +be injured or badly nourished while they are growing. So that alcohol in +all its forms is particularly injurious to young persons, as it retards +their growth, and stunts both body and mind. This is the theory of Dr. +Lionel S. Beale, a celebrated microscopist and thinker, and is quite +generally accepted."--Dr. Roger S. Tracy, of the New York Board of Health. + +[9] "In its action on the system nicotine is one of the most powerful +poisons known. A drop of it in a concentrated form was found sufficient to +kill a dog, and small birds perished at the approach of a tube containing +it."--Wood's _Materia Medica_. + +"Tobacco appears to chiefly affect the heart and brain, and I have +therefore placed it among cerebral and cardiac poisons."--Taylor's +_Treatise on Poisons_. + +[10] "Certain events occur in the brain; these give rise to other events, +to changes which travel along certain bundles of fibers called nerves, and +so reach certain muscles. Arrived at the muscles, these changes in the +nerves, which physiologists call nervous impulses, induce changes in the +muscles, by virtue of which these shorten contract, bring their ends +together, and so, working upon bony levers, bend the arm or hand, or lift +the weight."--Professor Michael Foster. + +[11] The synovial membranes are almost identical in structure with serous +membranes (page 176), but the secretion is thicker and more like the +white of egg. + +[12] "Smoking among students or men training for contests is a mistake. It +not only affects the wind, but relaxes the nerves in a way to make them +less vigorous for the coming contest. It shows its results at once, and +when the athlete is trying to do his best to win he will do well to avoid +it." Joseph Hamblen Sears, Harvard Coach, and Ex-Captain of the Harvard +Football Team, Article in _In Sickness and in Health_. + +[13] "There is no profession, there is no calling or occupation in which +men can be engaged, there is no position in life, no state in which a man +can be placed, in which a fairly developed frame will not be valuable to +him; there are many of these, even the most purely and highly +intellectual, in which it is essential to success--essential simply as a +means, material, but none the less imperative, to enable the mind to do +its work. Year by year, almost day by day, we see men (and women) falter +and fail in the midst of their labors; ... and all for want of a little +bodily stamina--a little bodily power and bodily capacity for the +endurance of fatigue, or protracted unrest, or anxiety, or +grief."--Maclaren's _Physical Education_. + +[14] "One half the struggle of physical training has been won when a boy +can be induced to take a genuine interest in his bodily condition,--to +want to remedy its defects, and to pride himself on the purity of his +skin, the firmness of his muscles, and the uprightness of his figure. +Whether the young man chooses afterwards to use the gymnasium, to run, to +row, to play ball, or to saw wood, for the purpose of improving his +physical condition, matters little, provided he accomplishes that +object."--Dr. D. A. Sargent, Director of the Hemenway Gymnasium at Harvard +University. + +[15] "It is _health_ rather than _strength_ that is the great requirement +of modern men at modern occupations; it is not the power to travel great +distances, carry great burdens, lift great weights, or overcome great +material obstructions; it is simply that condition of body, and that +amount of vital capacity, which shall enable each man in his place to +pursue his calling, and work on in his working life, with the greatest +amount of comfort to himself and usefulness to his fellowmen."--Maclaren's +_Physical Education_. + +[16] To this classification may be added what are called albuminoids, a +group of bodies resembling proteids, but having in some respects a +different nutritive value. Gelatine, such as is found in soups or table +gelatine is a familiar example of the albuminoids. They are not found to +any important extent in our raw foods, and do not therefore usually appear +in the analyses of the composition of foods. The albuminoids closely +resemble the proteids, but cannot be used like them to build up +protoplasm. + +[17] The amount of water in various tissues of the body is given by the +following table in parts of 1000: + + Solids. Liquids. + Enamel, 2 Blood, 791 + Dentine, 100 Bile, 864 + Bone, 486 Blood plasma, 901 + Fat, 299 Chyle, 928 + Cartilage, 550 Lymph, 958 + Liver, 693 Serum, 959 + Skin, 720 Gastric juice, 973 + Brain, 750 Tears, 982 + Muscle, 757 Saliva, 995 + Spleen, 758 Sweat, 995 + Kidney, 827 + Vitreous humor, 987 + +[18] The work of some kinds of moulds may be apparent to the eye, as in +the growths that form on old leather and stale bread and cheese. That of +others goes on unseen, as when acids are formed in stewed fruits. +Concerning the work of the different kinds of moulds. Troussart says: +"_Mucor mucedo_ devours our preserves; _Ascophora mucedo_ turns our bread +mouldy; _Molinia_ is nourished at the expense of our fruits; _Mucor +herbarium_ destroys the herbarium of the botanist; and _Choetonium +chartatum_ develops itself on paper, on the insides of books and on their +bindings, when they come in contact with a damp wall."--Troussart's +_Microbes, Ferments, and Moulds_. + +[19] "The physiological wear of the organism is constantly being repaired +by the blood; but in order to keep the great nutritive fluid from becoming +impoverished, the matters which it is constantly losing must be supplied +from some source out of the body, and this necessitates the ingestion of +articles which are known as food."--Flint's _Text-book of Human +Physiology_. + +[20] Glands. Glands are organs of various shapes and sizes, whose +special work it is to separate materials from the blood for further use in +the body, the products being known as secretion and excretion. +The means by which secretion and excretion are effected are, however, +identical. The essential parts of a gland consist of a basement membrane, +on one side of which are found actively growing cells, on the other is the +blood current, flowing in exceedingly thin-walled vessels known as the +capillaries. The cells are able to select from the blood whatever material +they require and which they elaborate into the particular secretion. In +Fig. 47 is illustrated, diagrammatically, the structure of a few typical +secreting glands. The continuous line represents the basement membrane. +The dotted line represents the position of the cells on one side of the +basement membrane. The irregular lines show the position of the +blood-vessels. + +[21] Tablets and other material for Fehling and additional tests for sugar +can be purchased at a drug store. The practical details of these and other +tests which assume some knowledge of chemistry, should be learned from +some manual on the subject. + +[22] The Peritoneum. The intestines do not lie in a loose mass in the +abdominal cavity. Lining the walls of this cavity, just as in a general +way, a paper lines the walls of a room, is a delicate serous membrane, +called the peritoneum. It envelops, in a greater or less degree, all +the viscera in the cavity and forms folds by which they are connected with +each other, or are attached to the posterior wall. Its arrangement is +therefore very complicated. When the peritoneum comes in contact with the +large intestine, it passes over it just as the paper of a room would pass +over a gas pipe which ran along the surface of the wall, and in passing +over it binds it down to the wall of the cavity. The small intestines are +suspended from the back wall of the cavity by a double fold of the +peritoneum, called the mesentery. The bowels are also protected from +external cold by several folds of this membrane loaded with fat. This is +known as the _great omentum_. + +The peritoneum, when in health, secretes only enough fluid to keep its +surface lubricated so that the bowels may move freely and smoothly on each +other and on the other viscera. In disease this fluid may increase in +amount, and the abdominal cavity may become greatly distended. This is +known as _ascites_ or dropsy. + +[23] The human bile when fresh is generally of a bright golden red, +sometimes of a greenish yellow color. It becomes quite green when kept, +and is alkaline in reaction. When it has been omited it is distinctly +yellow, because of its action on the gastric juice. The bile contains a +great deal of coloring matter, and its chief ingiedients are two salts of +soda, sodium taurocholate and glycocholate. + +[24] Nansen emphasizes this point in his recently published work, +_Farthest North_. + +[25] We should make it a point not to omit a meal unless forced to do so. +Children, and even adults, often have the habit of going to school or to +work in a hurry, without eating any breakfast. There is almost sure to be +a fainting, or "all-gone" feeling at the stomach before another mealtime. +This habit is injurious, and sure to produce pernicious results. + +[26] The teeth of children should be often examined by the dentist, +especially from the beginning of the second dentition, at about the sixth +year, until growth is completed. In infancy the mother should make it a +part of her daily care of the child to secure perfect cleanliness of the +teeth. The child thus trained will not, when old enough to rinse the mouth +properly or to use the brush, feel comfortable after a meal until the +teeth have been cleansed. The habit thus formed is almost sure to be +continued through life. + +[27] "If the amount of alcohol be increased, or the repetition become +frequent, some part of it undergoes acid fermentation in the stomach, and +acid eructations or vomitings occur. With these phenomena are associated +catarrh of the stomach and liver with its characteristic symptoms,--loss +of appetite, feeble digestion, sallowness, mental depression, and +headache."--James C. Wilson, Professor in the Jefferson Medical College, +Philadelphia. + +"Man has recourse to alcohol, not for the minute quantity of energy which +may be supplied by itself, but for its powerful influence on the +distribution of the energy furnished by other things. That influence is a +very complex one."--Professor Michael Foster. + +[28] "When constantly irritated by the direct action of alcoholic drinks, +the stomach gradually undergoes lasting structural changes. Its vessels +remain dilated and congested, its connective tissue becomes excessive, its +power of secreting gastric juice diminishes, and its mucous secretions +abnormally abundant."--H. Newell Martin, late Professor of Physiology in +Johns Hopkins University. + +"Chemical experiments have demonstrated that the action of alcohol on the +digestive fluids is to destroy its active principle, the pepsin, thus +confirming the observations of physiologists that its use gives ride to +the most serious disorders of the stomach and the most malignant +aberrations of the entire economy."--Professor E. C. Youmans, author of +standard scientific works. + +"The structural changes induced by habitual use of alcohol and the action +of this agent on the pepsin, seriously impair the digestive power. Hence +it is, that those who are habitual consumers of alcoholic fluids suffer +from disorders o digestion."--Robert Bartholow, recently Professor of +Materia Medica in the University of Pennsylvania. + +"Alcohol in any appreciable quantity diminishes the solvent power of the +gastric fluid so as to interfere with the process of digestion instead of +aiding it."--Professor W. B. Carpenter, the eminent English physiologist. + +[29] "Cirrhosis of the liver is notoriously frequent among drunkards, and +is in fact almost, though not absolutely, confined to them."--Robert T. +Edes, formerly Professor of Materia Medica in Harvard Medical College. + +"Alcohol acts on the liver by producing enlargement of that organ, and a +fat deposit, or 'hob-nailed' liver mentioned by the English +writers."--Professor W. B. Carpenter. + +[30] Preparation of Artificial Gastric Juice. _(a)_ Take part of the +cardiac end of the pig's stomach, which has been previously opened and +washed rapidly in cold water, and spread it, mucous surface upwards, on +the convex surface of an inverted capsule. Scrape the mucous surface +firmly with the back of a knife blade, and rub up the scrapings in a +mortar with fine sand. Add water, and rub up the whole vigorously for some +time, and filter. The filtrate is an artificial gastric juice. + +_(b)_ From the cardiac end of a pig's stomach detach the mucous membrane +in shreds, dry them between folds of blotting-paper, place them in a +bottle, and cover them with strong glycerine for several days. The +glycerine dissolves the pepsin, and on filtering, a glycerine extract with +high digestive properties is obtained. + +These artificial juices, when added to hydrochloric acid of the proper +strength, have high digestive powers. + +Instead of _(a)_ or _(b)_ use the artificial pepsin prepared for the +market by the wholesale manufacturers of such goods. + +[31] The cause of the clotting of blood is not yet fully understood. +Although the process has been thoroughly investigated we have not yet a +satisfactory explanation why the circulating blood does not clot in +healthy blood-vessels. The ablest physiologists of our day do not, as +formerly, regard the process as a so-called vital, but a purely chemical +one. + +[32] Serous Membranes.--The serous membranes form shut sacs, of which +one portion is applied to the walls of the cavity which it lines; the +other is reflected over the surface of the organ or organs contained in +the cavity. The sac is completely closed, so that no communication exists +between the serous cavity and the parts in its neighborhood. The various +serous membranes are the _pleura_ which envelops the lungs; the +_pericardium_ which surrounds the heart; the _peritoneum_ which invests +the viscera of the abdomen, and the _arachnoid_ in the spinal canal and +cranial cavity. In health the serous membranes secrete only sufficient +fluid to lubricate and keep soft and smooth the opposing surfaces. + +[33] A correct idea may be formed of the arrangement of the pericardium +around the heart by recalling how a boy puts on and wears his toboggan +cap. The pericardium encloses the heart exactly as this cap covers the +boy's head. + +[34] "Alcohol taken in small and single doses, acts almost exclusively on +the brain and the blood-vessels of the brain, whereas taken in large and +repeated doses its chief effects are always nervous effects. The first +effects of alcohol on the function of inhibition are to paralyze the +controlling nerves, so that the blood-centers are dilated, and more blood +is let into the brain. In consequence of this flushing of the brain, its +nerve centers are asked to do more work."--Dr. T. S. Clouston, Medical +Superintendent of the Royal Asylum, Edinburgh. + +"Alcoholic drinks prevent the natural changes going on in the blood, and +obstruct the nutritive and reparative functions."--Professor E. L. +Youmans, well-known scientist and author of _Class Book of Chemistry_. + +[35] The word "cell" is not used in this connection in its technical +signification of a histological unit of the body (sec. 12), but merely in +its primary sense of a small cavity + +[36] "The student must guard himself against the idea that arterial blood +contains no carbonic acid, and venous blood no oxygen. In passing through +the lungs venous blood loses only a part of its carbonic acid; and +arterial blood, in passing through the tissues, loses only a part of its +oxygen. In blood, however venous, there is in health always some oxygen; +and in even the brightest arterial blood there is actually more carbonic +acid than oxygen."--T. H. Huxley. + +[37] "Consumption is a disease which can be taken from others, and is not +simply caused by colds. A cold may make it easier to take the disease. It +is usually caused by germs which enter the body with the air breathed. The +matter which consumptives cough or spit up contains these germs in great +numbers--frequently millions are discharged in a single day. This matter +spit upon the floor, wall, or elsewhere is apt to dry, become pulverized, +and float in the air as dust. The dust contains the germs, and thus they +enter the body with the air breathed. The breath of a consumptive does not +contain the germs and will not produce the disease. A well person catches +the disease from a consumptive only by in some way taking in the matter +coughed up by the consumptive."--Extract from a circular issued by the +Board of Health of New York City. + +[38] "The lungs from the congested state of their vessels produced by +alcohol are more subject to the influence of cold, the result being +frequent attacks of bronchitis. It has been recognized of late years that +there is a peculiar form of consumption of the lungs which is very rapidly +fatal and found only in alcohol drinkers."--Professor H. Newell Martin. + +[39] "The relation to Bright's Disease is not so clearly made out as is +assumed by some writers, though I must confess to myself sharing the +popular belief that alcohol is one among its most important +factors."--Robert T. Edes, M.D. + +[40] Thus the fibers which pass out from the sacral plexus in the loins, +and extend by means of the great sciatic nerve and its branches to the +ends of the toes, may be more than a yard long. + +[41] Remarkable instances are cited to illustrate the imperative demand +for sleep. Gunner boys have been known to fall asleep during the height of +a naval battle, owing to the fatigue occasioned by the arduous labor in +carrying ammunition for the gunner. A case is reported of a captain of a +British frigate who fell asleep and remained so for two hours beside one +of the largest guns of his vessel, the gun being served vigorously all the +time. Whole companies of men have been known to sleep while on the march +during an arduous campaign. Cavalrymen and frontiersmen have slept soundly +in the saddle during the exhausting campaigns against the Indians. + +[42] According to the Annual Report of New York State Reformatory, for +1896, drunkenness among the inmates can be clearly traced to no less than +38 per cent of the fathers and mothers only. + +Drunkenness among the parents of 38 per cent of the prisoners in a +reformatory of this kind is a high and a serious percentage. It shows that +the demoralizing influence of drink is apt to destroy the future of the +child as well as the character of the parent. + +"There is a marked tendency in nature to transmit all diseased conditions. +Thus the children of consumptive parents are apt to be consumptive. But, +of all agents, alcohol is the most potent in establishing a heredity that +exhibits itself in the destruction of mind and body. There is not only a +propensity transmitted, but an actual disease of the nervous system."--Dr. +Willard Parker. + +[43] "It is very certain that many infants annually perish from this +single cause."--Reese's _Manual of Toxicology_. + +[44] If an eye removed from its socket be stripped posteriorly of the +sclerotic coat, an inverted image or the field of view will be seen on the +retina; but if the lens or other part of the refractive media be removed, +the image will become blurred or disappear altogether. + +[45] This change in the convexity of the lens is only a slight one, as the +difference in the focal point between rays from an object twenty feet +distant and one four inches distant is only one-tenth of an inch. While +this muscular action is taking place, the pupil contracts and the eyeballs +converge by the action of the internal rectus muscles. These three acts +are due to the third nerve (the motor oculi). This is necessary in order +that each part should he imprinted on the same portion of the retina, +otherwise there would be double vision. + +[46] The Germans have a quaint proverb that one should never rub his eyes +except with his elbows + +[47] "The deleterious effect of tobacco upon eyesight is an acknowledged +fact. The Belgian government instituted an investigation into the cause of +the prevalence of color-blindness. The unanimous verdict of the experts +making the examination was that the use of tobacco was one of the +principal causes of this defect of vision. + +"The dimness of sight caused by alcohol or tobacco has long been +clinically recognized, although not until recently accurately understood. +The main facts can now be stated with much assurance, since the +publication of an article by Uhthoff which leaves little more to be said. +He examined one thousand patients who were detained in hospital because of +alcoholic excess, and out of these found a total of eye diseases of about +thirty per cent. + +"Commonly both eyes are affected, and the progress of the disease is slow, +both in culmination and in recovery.... Treatment demands entire +abstinence."--Henry D. Noyes, Professor of Otology in the Bellevue +Hospital Medical College, New York. + +[48] "The student who will take a little trouble in noticing the ears of +the persons whom he meets from day to day will be greatly interested and +surprised to see how much the auricle varies. It may be a thick and clumsy +ear or a beautifully delicate one; long and narrow or short and broad, may +have a neatly formed and distinct lobule, or one that is heavy, ungainly, +and united to the cheek so as hardly to form a separate part of the +auricle, may hug the head closely or flare outward so as to form almost +two wings to the head. In art, and especially in medallion portraits, in +which the ear is a marked (because central) feature, the auricle is of +great importance"--William W. Keen, M.D., editor of Gray's _Anatomy_ + +[49] The organ of Corti is a very complicated structure which it is +needless to describe in this connection. It consists essentially of +modified ephithelial cells floated upon the auditory epithelium, or +basilar membrane, of the cochlea. There is a series of fibers, each made +of two parts sloped against each other like the rafters of a roof. It is +estimated that there are no less than 3000 of these arches in the human +ear, placed side by side in a continuous series along the whole length of +the basilar membrane. Resting on these arches are numbers of conical +epithelial cells, from the free surface of which bundles of stiff hairs +(cilia) project. The fact that these hair-cells are connected with the +fibers of the cochlear division of the auditory nerve suggests that they +must play an important part in auditory sensation. + +[50] The voices of boys "break," or "change," because of the sudden growth +or enlargement of the larynx, and consequent increase in length of the +vocal cords, at from fourteen to sixteen years of age. No such enlargement +takes place in the larynxes of girls: therefore their voices undergo no +such sudden change. + +[51] This experiment and several others in this book, are taken from +Professor Bowditch's little book called _Hints for Teachers of +Physiology_, a work which should be mastered by every teacher of +physiology in higher schools. + +[52] The teacher or student who is disposed to study the subject more +thoroughly and in more detail than is possible in a class text-book, will +find all that is needed in the following excellent books, which are +readily obtained by purchase, or may be found in the public libraries of +larger towns: Dulles' _Accidents and Emergencies;_ Pilcher's _First Aid in +Illness and Injury_; Doty's _Prompt Aid to the Injured;_ and Johnston's +"Surgical Injuries and Surgical Diseases," a special article in +Roosevelt's _In Sickness and in Health_. + +[53] "A tourniquet is a bandage, handkerchief, or strap of webbing, into +the middle of which a stone, a potato, a small block of wood, or any hard, +smooth body is tied. The band is tied loosely about the limb, the hard +body is held over the artery to be constricted, and a stick is inserted +beneath the band on the opposite side of the limb and used to twist the +band in such a way that the limb is tightly constricted thereby, and the +hard body thus made to compress the artery (Fig. 160). + +"The entire circumference of the limb may be constricted by any sort of +elastic band or rubber tube, or any other strong elastic material passed +around the limb several times on a stretch, drawn tight and tied in a +knot. In this way, bleeding may be stopped at once from the largest +arteries. The longer and softer the tube the better. It requires no skill +and but little knowledge of anatomy to apply it efficiently." Alexander B. +Johnson, Surgeon to Roosevelt Hospital, New York City. + +[54] Corrosive sublimate is probably the most powerful disinfectant known. +A solution of one part in 2000 will destroy microscopic organisms. Two +teaspoonfuls of this substance will make a solution strong enough to kill +all disease germs. + +[55] The burning of sulphur produces sulphurous acid, which is an +irrespirable gas. The person who lights the sulphur must, therefore, +immediately leave the room, and after the lapse of the proper time, must +hold his breath as he enters the room to open the windows and let out the +gas. After fumigation, plastered walls should be white-washed, the +woodwork well scrubbed with carbolic soap, and painted portions repainted. + +[56] Put copperas in a pail of water, in such quantity that some may +constantly remain undissolved at the bottom. This makes a saturated +solution. To every privy or water-closet, allow one pint of the solution +for every four persons when cholera is about. To keep privies from being +offensive, pour one pint into each seat, night and morning. + +[57] "While physiology is one of the biological sciences, it should be +clearly recognized that it is not, like botany or zoology, a science of +observation and description; but rather, like physics or chemistry, a +science of experiment. While the amount of experimental instruction (not +involving vivisection or experiment otherwise unsuitable) that may with +propriety be given in the high school is neither small nor unimportant, +the limitations to such experimental teaching, both as to kind and as to +amount, are plainly indicated. + +"The obvious limitations to experimental work in physiology in the high +school, already referred to, make it necessary for the student to acquire +much of the desired knowledge from the text-book only. Nevertheless, much +may be done by a thoughtful and ingenious teacher to make such knowledge +real, by the aid of suitable practical exercises and +demonstrations."--_Report of the Committee of Ten on Secondary School +Studies_. + +[58] This ingenious and excellent experiment is taken from the _New York +School Journal_ for May, 1897, for which paper it was prepared by Charles +D. Nason, of Philadelphia. + + + + + +End of Project Gutenberg's A Practical Physiology, by Albert F. 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