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diff --git a/old/68830-0.txt b/old/68830-0.txt deleted file mode 100644 index 10b7112..0000000 --- a/old/68830-0.txt +++ /dev/null @@ -1,11884 +0,0 @@ -The Project Gutenberg eBook of The nutrition of man, by Russell H. -Chittenden - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world 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. If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: The nutrition of man - -Author: Russell H. Chittenden - -Release Date: August 24, 2022 [eBook #68830] - -Language: English - -Produced by: Thiers Halliwell, Mark C. Orton and the Online Distributed - Proofreading Team at https://www.pgdp.net (This file was - produced from images generously made available by The - Internet Archive) - -*** START OF THE PROJECT GUTENBERG EBOOK THE NUTRITION OF MAN *** - -[Transcriber's notes: - -The text of this e-book has been preserved in its original form -apart from correction of the typographic errors listed below. -Illustrations have been repositioned adjacent to relevant tabulated -data, and the List of Illustrations adjusted accordingly. On -p.72 an image of the Xanthin formula incorrectly shows a double -bond between a carbon and nitrogen atom – the correct formula -is shown on the next page – and there is a date discrepancy on -p. 248 between the text and the illustration caption (November -18/February 27). Footnotes have been repositioned below the -relevant paragraphs. - -Typographic corrections: - - enyzmes → enzymes - oxgyen → oxygen - enyzme → enzyme - Futher → Further - mechancial → mechanical - rythmical → rhythmical - economcially → economically - circulirinden → circulirenden - SUBJECT → SUBJECTS - equibrium → equilibrium - availibility → availability - (166) grams → (166 grams) - accusstomed → accustomed - Glassner → Glässner - strach → starch -] - - - - -THE NUTRITION OF MAN - - - - - THE - - NUTRITION OF MAN - - BY - - RUSSELL H. CHITTENDEN, Ph.D., LL.D., Sc.D. - - AUTHOR OF “PHYSIOLOGICAL ECONOMY IN NUTRITION,” ETC. - PROFESSOR OF PHYSIOLOGICAL CHEMISTRY - AND DIRECTOR OF THE SHEFFIELD - SCIENTIFIC SCHOOL OF YALE UNIVERSITY - - - WITH ILLUSTRATIONS - - - NEW YORK - FREDERICK A. STOKES COMPANY - PUBLISHERS - - - - - _Copyright, 1907_, - BY FREDERICK A. STOKES COMPANY - - _All rights reserved_ - - - May, 1907 - - - _FIFTH PRINTING_ - - - - -PREFACE - - -The present book is the outcome of a course of eight lectures delivered -before the Lowell Institute of Boston in the early part of 1907. - -In this presentation of the subject the attempt has been made to -give a systematic account of our knowledge regarding some of the -more important processes of nutrition, with special reference to the -needs of the body for food. In doing this, the facts accumulated by -painstaking observations and experiments during recent years in our -laboratory have been incorporated with data from other sources and -brought into harmony, so far as possible, with the modern trend of -physiological thought. - -Numerous experimental results, hitherto unpublished, have been -introduced, notably in Chapter VII, in which a few of the data recently -obtained in our laboratory with dogs are presented in some detail, -since they afford evidence of the error of the current arguments -concerning the necessity of a high proteid intake by man, as based on -the results of earlier investigators with high proteid animals. - -It is hoped that the facts and arguments here presented will help to -arouse a more general interest in the subject of human nutrition, as -right methods of living promise so much for the health and happiness of -the individual and of the community. - - - - -CONTENTS - - - CHAPTER I PAGE - - FOODS AND THEIR DIGESTION 1 - - TOPICS: The purpose of nutrition. The food of man. Proteid foods. - Carbohydrate foods. Fats. Food as fuel. Composition of foodstuffs. - Availability of foods. Food as source of energy. Various factors in - the nourishment of the body. Processes of digestion. Secretion of - saliva. Function of saliva. Enzymes. Reversible action of enzymes. - Specificity of enzymes. Mastication. Gastric secretion. Components - of gastric juice. Action of gastric juice. Muscular movements - of stomach. Time foods remain in stomach. Importance of stomach - digestion. Processes of the small intestine. Secretion of pancreatic - juice. Chemical changes in small intestine. Destruction of proteid - food. Significance of the breaking down of proteid. Change of fatty - foods and carbohydrates in intestine. Digestion practically complete - at end of small intestine. Putrefaction held in check. Digestion a - prelude to utilization of food. - - - CHAPTER II - - ABSORPTION, ASSIMILATION, AND THE PROCESSES OF METABOLISM 39 - - TOPICS: Physiological peculiarities in absorption. Chemical changes - in epithelial walls of intestine. Two pathways for absorbed - material. Function of the liver as a regulator of carbohydrate. - Absorption of proteid products. Assimilation of food products. - Anabolism. Katabolism. Metabolism. Processes of metabolism. Older - views regarding oxidation. Discoveries of Lavoisier. The views of - Liebig. Theory of luxus consumption. Oxidation in the body not simple - combustion. Oxygen not the cause of the decompositions. Oxidation not - confined to any one place. Intracellular enzymes. Living cells the - guiding power in katabolism. Some intermediary products of tissue - metabolism. Chemical structure of different proteids. Decomposition - products of nucleoproteids. Relation to uric acid. Action of specific - intracellular enzymes. Creatin and creatinin. Relation to urea. - Proteid katabolism a series of progressive chemical decompositions. - Intracellular enzymes as the active agents. - - - CHAPTER III - - THE BALANCE OF NUTRITION 77 - - TOPICS: Body equilibrium. Nitrogen equilibrium. Carbon equilibrium. - Loss of nitrogen during fasting. Influence of previous diet on loss - of nitrogen in fasting. Output of carbon during fasting. Influence - of pure proteid diet on output of nitrogen. Influence of fat on - proteid metabolism. Effect of carbohydrate on nitrogen metabolism. - Storing up of proteid by the body. Transformation of energy in the - body. Respiration calorimeter. Basal energy exchange of the body. - Circumstances influencing energy exchange. Effect of food on heat - production. Respiratory quotient and its significance. Influence of - muscle work on energy exchange. Elimination of carbon dioxide during - work and with different diets. Effect of excessive muscular work - on energy exchange. Oxygen consumption under different conditions. - Output of matter and energy subject to great variation. Body - equilibrium and approximate nitrogen balance to be expected in health. - - - CHAPTER IV - - SOURCE OF THE ENERGY OF MUSCLE WORK, WITH SOME THEORIES OF - PROTEID METABOLISM 119 - - TOPICS: Relation of muscle work to energy exchange. Views of Liebig. - Experimental evidence. Relation of nitrogen excretion to muscle - work. Significance of the respiratory quotient in determining - nature of the material oxidized. Fats and carbohydrates as source - of energy by muscles. Utilization of proteid as a source of energy. - Formation of carbohydrate from proteid. Significance of proteid - metabolism. Theories of Carl Voit. Morphotic proteid. Circulating - proteid. General conception of proteid metabolism on the basis of - Voit’s theories. Pflüger’s views of proteid metabolism. Rapidity of - elimination of food nitrogen. Methods by which nitrogen is split off - from proteid. Theories of Folin. Significance of creatinin and of the - percentage distribution of excreted nitrogen. Endogenous or tissue - metabolism. Exogenous or intermediate metabolism. Needs of the body - for proteid food possibly satisfied by quantity sufficient to meet - the demands of tissue or endogenous metabolism. Bearings of Folin’s - views on current theories and general facts of proteid metabolism. - Large proteid reserve and voluminous exogenous metabolism probably - not needed. Importance of feeding experiments in determining the true - value of different views. - - - CHAPTER V - - DIETARY HABITS AND TRUE FOOD REQUIREMENTS 153 - - TOPICS: Dietetic customs of mankind. Origin of dietary standards. - True food requirements. Arguments based on custom and habit. - Relationship between food consumption and prosperity. Erroneous - ideas regarding nutrition. Commercial success and national wealth - not the result of liberal dietary habits. Instinct and craving not - wise guides to follow in choice and quantity of food. Physiological - requirements and dietary standards not to be based on habits and - cravings. Old-time views regarding temperate use of food. The sayings - of Thomas Cogan. The teachings of Cornaro. Experimental results - obtained by various physiologists. Work of the writer on true proteid - requirements. Studies with professional men. Nitrogen equilibrium - with small amounts of food. Sample dietaries. Simplicity in diet. - Nitrogen requirement per kilogram of body-weight. Fuel value of the - daily food. Experiments with University athletes. Nitrogen balance - and food consumption. Sample dietaries. Adequacy of a simple diet. - - - CHAPTER VI - - FURTHER EXPERIMENTS AND OBSERVATIONS BEARING ON TRUE FOOD - REQUIREMENTS 191 - - TOPICS: Dietary experiments with a detail of soldiers from the United - States Army. General character of the army ration. Samples of the - daily dietary adopted. Rate of nitrogen metabolism attained. Effect - on body-weight. Nitrogen balance with lowered proteid consumption. - Influence of low proteid on muscular strength of soldiers and - athletes. Effect on fatigue. Effect on physical endurance. Fisher’s - experiments on endurance. Dangers of underfeeding. Dietary - observations on fruitarians. Observations on Japanese. Recent dietary - changes in Japanese army and navy. Observations of Dr. Hunt on - resistance of low proteid animals to poisons. Conclusions. - - - CHAPTER VII - - THE EFFECT OF LOW PROTEID DIET ON HIGH PROTEID ANIMALS 229 - - TOPICS: A wide variety of foods quite consistent with temperance in - diet. Safety of low proteid standards considered. Arguments based - on the alleged effects of low proteid diet on high proteid animals. - Experiments of Immanuel Munk with dogs. Experiments of Rosenheim. - Experiments of Jägerroos. Comments on the above experiments. The - experiments of Watson and Hunter on rats. The writer’s experiments - with dogs. Details of the results obtained with six dogs. Comparison - of the results with those of previous investigators. Effect of a - purely vegetable diet on dogs. Different nutritive value of specific - proteids considered. Possible influence of difference in chemical - constitution of individual proteids. Effect of low proteid diet on - the absorption and utilization of food materials in the intestine - of dogs. General conclusions from the results of experiments with - animals. - - - CHAPTER VIII - - PRACTICAL APPLICATIONS WITH SOME ADDITIONAL DATA 266 - - TOPICS: Proper application of the results of scientific research - helpful to mankind. Dietary habits should be brought into conformity - with the true needs of the body. The peculiar position of proteid - foods emphasized. The evil effects of overeating. What the new - dietary standards really involve. The actual amounts of foodstuffs - required. Relation of nutritive value to cost of foods. The - advantages of simplicity in diet. A sample dietary for a man of - 70 kilograms body-weight. A new method of indicating food values. - Moderation in the daily dietary leads toward vegetable foods. The - experiments of Dr. Neumann. The value of fruits as food. The merits - of animal and vegetable proteids considered in relation to the - bacterial processes in the intestine. A notable case of simplicity - in diet. Intelligent modification of diet to the temporary needs of - the body. Diet in summer and winter contrasted. Value of greater - protection to the kidneys. Conclusion. - - - INDEX 303 - - - - -LIST OF ILLUSTRATIONS - - - FACING PAGE - - Photograph of one of the athletes 190 - - Photograph of soldiers taken at the close of the experiment 194 - - Photograph of soldiers taken at the close of the experiment 195 - - Photograph of Fritz at the close of the experiment 200 - - Photographs of the dogs experimented with - - Subject No. 5 August 19, 1905 248 - Subject No. 5 November 18, 1905 248 - Subject No. 5 April 24, 1906 248 - Subject No. 5 June 27, 1906 248 - - Subject No. 3 August 19, 1905 251 - Subject No. 3 November 18, 1905 251 - Subject No. 3 April 24, 1906 251 - Subject No. 3 June 27, 1906 251 - - Subject No. 13 January 2, 1906 252 - Subject No. 13 February 27,1906 252 - Subject No. 13 April 24, 1906 252 - Subject No. 13 June 19, 1906 252 - - Subject No. 15 January 2, 1906 252 - Subject No. 15 February 27, 1906 252 - Subject No. 15 April 24, 1906 253 - Subject No. 15 June 19, 1906 252 - - Subject No. 20 January 2, 1906 252 - Subject No. 20 February 27, 1906 252 - Subject No. 20 April 24, 1906 252 - Subject No. 20 June 19, 1906 252 - - Subject No. 17 January 2, 1906 256 - Subject No. 17 February 27, 1906 256 - Subject No. 17 April 24, 1906 252 - Subject No. 17 June 27, 1906 252 - - - - -THE NUTRITION OF MAN - - - - -CHAPTER I - -FOODS AND THEIR DIGESTION - - TOPICS: The purpose of nutrition. The food of man. Proteid foods. - Carbohydrate foods. Fats. Food as fuel. Composition of foodstuffs. - Availability of foods. Food as source of energy. Various factors in - the nourishment of the body. Processes of digestion. Secretion of - saliva. Function of saliva. Enzymes. Reversible action of enzymes. - Specificity of enzymes. Mastication. Gastric secretion. Components - of gastric juice. Action of gastric juice. Muscular movements - of stomach. Time foods remain in stomach. Importance of stomach - digestion. Processes of the small intestine. Secretion of pancreatic - juice. Chemical changes in small intestine. Destruction of proteid - food. Significance of the breaking down of proteid. Change of fatty - foods and carbohydrates in intestine. Digestion practically complete - at end of small intestine. Putrefaction held in check. Digestion a - prelude to utilization of food. - - -One of the great mysteries of life is the power of growth, that -harmonious development of composite organs and tissues from simple -protoplasmic cells, with the ultimate formation of a complex organism -with its orderly adjustment of structure and function. Equally -mysterious is that wonderful power of rehabilitation by which the cells -of the body are able to renew their living substance and to maintain -their ceaseless activity through a period, it may be of fourscore -years, before succumbing to the inevitable fate that awaits all organic -structures. This bodily activity, visible and invisible, is the result -of a third mysterious process, more or less continuous as long as life -endures, of chemical disintegration, decomposition, and oxidation, by -which arises the evolution of energy to maintain the heat of the body -and the power for mental and physical work. - -These three main functions constitute the purpose of nutrition. The -growth of the adult man from the tiny cell or germ that marks his -simple beginning is at the expense of the food material he absorbs and -assimilates. The rehabilitation of the cells, or the composite tissues -of the fully developed organism, is accomplished through utilization -of the daily food, whereby cell substance is renewed and all losses -made good. The energy which manifests itself in the form of heat and -mechanical or mental work, _i. e._, the energy by which the vital -machinery is maintained in ceaseless activity, comes from the breaking -down of the food materials by means of which, as the saying goes, the -body is nourished. The body thus becomes the centre of different lines -of activity, the food serving as the material out of which new cells -and tissues are constructed, old cells revivified, and energy for -running the bodily machinery derived. Development, growth, and vital -activity all depend upon the availability of food in proper amounts and -proper quality. - -The food of man is composed mainly of organic materials, for while, -as Dr. Curtis[1] has expressed it, “the plant can make organic matter -out of inorganic elements, just this the animal cannot do at all. -The thing of legs and locomotion, of spine and speech, can build -his organic walls only out of organic bricks ruthlessly ripped from -existing walls of other animals or plants.” It is true that man has -need of certain inorganic salts in his daily diet, but they are in -the nature of aids to nutrition (aside from such as are necessary for -the formation of bone and teeth), contributing in some measure toward -regulation and control of nutritive processes rather than as a source -of energy to the body. Inorganic substances, however, are an integral -part of the essential tissues and organs of the body, being combined -with the organic constituents of the living cells. Indeed, electrolytes -are perhaps the substances that put life into the proteids of the -protoplasm, and it is truly important for the integrity and functional -power of living cells that the proportion of inorganic constituents -therein be kept in a constant condition of quality and quantity. -Still, the food of mankind is essentially organic in nature, and while -it may be exceedingly varied in character, ranging from the simple -vegetable dietary of the natives of India and the Far East to the -voluminous admixture of varied forms of animal and vegetable foodstuffs -so acceptable to the _bon vivant_ of our western civilization, the -principles contained therein are few in number. - - [1] Edward Curtis, M.D. Nature and Health: Henry Holt & Co., New - York. 1906. p. 39. - -The organic foodstuffs are of three distinct types and are classified -under three heads, viz.: Proteids or Albuminous foodstuffs, -Carbohydrates, and Fats. All animal and vegetable foods, whatever -their nature and whatever their origin, are composed simply of -representatives of one or more of these three classes of food -principles. - -Proteid substances are characterized by containing about 16 per cent -of nitrogen. In addition, they contain on an average 52 per cent of -carbon, 7 per cent of hydrogen, 23 per cent of oxygen, and 0.5–2.0 per -cent of sulphur. A certain class of proteids, known as nucleoproteids -because of their occurrence in the nuclei of cells, contain likewise -a small amount of phosphorus in organic combination. Proteid or -albuminous substances constitute the chemical basis of all living -cells, whether animal or vegetable. This means, expressed in different -language, that the organic substance of all organs and tissues, whether -of animals or plants, is made up principally of proteid matter. Proteid -substances occupy, therefore, a peculiar position in the nutrition of -man and of animals in general. They constitute the class of essential -foodstuffs without which life is impossible. For tissue-building and -for the renewal of tissues and organs, or their component cells, -proteid or albuminous foodstuffs are an absolute requirement. The -vital part of all tissue is proteid, and only proteid food can serve -for its growth or renewal. Hence, no matter how generous the supply -of carbohydrates and fats, without some admixture of proteid food the -body will weaken and undergo “nitrogen starvation.” It is to be noted, -however, that while the element nitrogen (16 per cent) gives character -to the proteid or albuminous foodstuffs, so that they are frequently -spoken of or classified as the “nitrogenous foodstuffs,” it is not the -nitrogen _per se_ that is so essential for the nutrition of the body. -Man lives in an atmosphere of oxygen and nitrogen. He can and does -absorb and utilize the free oxygen of the air he breathes; indeed, -it is absolutely essential for his existence, but the free nitrogen -likewise drawn into the lungs at each inspiration is of no avail for -the needs of the body. Further, there are many compounds of nitrogen, -some of them closely allied to the proteid foodstuffs in chemical -composition, which are just as useless as free nitrogen in meeting the -wants of the body for nitrogenous foods. - -Dame Nature is very discriminating; she demands a definite form of -nitrogenous compound, some peculiar or specific grouping of the -nitrogen element with other elements in the food that can make good -the waste of proteid tissue. In the inactive and fibrous tissues of -animals, such as are found in bones, tendons, and ligaments, there is -present a substance known as collagen, which, when boiled with water, -as in the making of soups, is transformed into gelatin. This body, -because of its close chemical relationship to proteid or albuminous -substances, is known as an albuminoid. Yet, though it has essentially -the same chemical composition as ordinary albuminous substances and -shows many of the reactions characteristic of the latter, it cannot -take the place of true proteid in building up or repairing the tissues -of the body. To quote again from Dr. Curtis: “Tissue is nitrogenous, so -that, of course, only nitrogenous food can serve for its making; but -of the two kinds of nitrogenous principles, proteids and albuminoids, -behold, proteids only are of avail! Why this is so is unknown, since -albuminoid is equally nitrogenous with proteid; but so it is--proteid -and proteid alone can fulfil the high function of furnishing the -material basis of life. Gelatin cannot even go to make the very kind -of tissue of which itself is a derivative. Alongside of its brother -proteid, gelatin stands as a prince of the blood whose escutcheon bears -the ‘bend sinister.’ Such a one, though of royal lineage, may never -aspire to the throne.” It is thus quite clear that the true proteid -foods are tissue builders in the broadest sense of the term, and it is -equally evident that they are absolutely essential for life, since no -other kind or form of foodstuff can take their place in supplying the -needs of the body. Every living cell, whether of heart, muscle, brain, -or nerve, requires its due allowance of proteid material to maintain -its physiological rhythm. No other foodstuff stands in such intimate -relationship to the vital processes, but so far as we know at present -any form of true proteid, whether animal or vegetable, will serve the -purpose. - -Carbohydrates include two closely related classes of compounds, viz., -sugars and starches. They are entirely free from nitrogen, containing -only carbon (44.4 per cent), hydrogen (6.2 per cent), and oxygen -(49.4 per cent), and hence are classified as non-nitrogenous foods. -Obviously, they cannot serve as tissue builders, but by oxidation they -yield energy for heat and work. They constitute an easily oxidizable -form of fuel, and when supplied in undue amounts they may undergo -transformation within the body into fat, which is temporarily -deposited in tissues and organs for future needs. - -Fats, like carbohydrates, are free from nitrogen, but differ from -them in containing a much larger percentage of carbon, and hence have -greater fuel value per pound. Fats contain on an average 76.5 per cent -of carbon, 11.9 per cent of hydrogen, and 11.5 per cent of oxygen. With -their larger content of carbon and smaller proportion of oxygen, fats -are less easily oxidizable than sugars, requiring a larger intake of -oxygen for their combustion, but when oxidized they yield more heat per -pound than carbohydrates. - -Fats and carbohydrates are thus seen to be the natural fuel foodstuffs -of the body. They cannot serve for the upbuilding or renewal of tissue, -but by oxidation they constitute an economical fuel for maintaining -body temperature and for power to run the bodily machinery. It should -be remembered, however, that anything capable of being burned in -the body may serve as fuel material; hence proteid food, though of -specific value as a tissue builder, may likewise by its oxidation yield -energy for heat and work, but its combustion, owing to the content of -nitrogen, is never complete. Further, its use as fuel is uneconomical -and undesirable for reasons to be discussed later, but it is well to -know that its oxidation, though incomplete, is accompanied by the -liberation of energy, as in the oxidation of non-nitrogenous foods. A -portion of the carbon, hydrogen, and oxygen of the proteid molecule -will burn within the body to gaseous products, as do sugars and fats, -but there remains a nucleus of nitrogen, with some carbon, hydrogen, -and oxygen, which resists combustion and must be gotten rid of by the -combined labors of liver and kidneys. Fats and carbohydrates, on the -other hand, undergo complete combustion to simple gaseous products, -carbon dioxide and water, which are easily removed by the lungs, skin, -etc. - -These three classes of foodstuffs exist in a great variety of -combinations or admixtures in nature. In many cases, noticeably in -milk, all three occur together in fairly large quantities. In animal -foods, such as meats, fish, etc., proteid and fat alone are found, -while in perfectly lean meat proteid only is present, excepting a -small amount of fat. Again, the white of the egg contains proteid -alone. Hence, a meat and egg diet would be essentially a proteid diet. -In vegetable foods, as in the cereals, there is found an admixture -of proteid and starch, the latter predominating in many cases, as in -wheat flour. The following table,[2] showing the chemical composition -of various food materials, may be of service in throwing light on the -relative distribution of the three classes of foodstuffs in natural -products. - - [2] The data composing this table are taken from Bulletin 28 (Revised - Edition), United States Department of Agriculture, Office of - Experiment Stations. - - -THE CHEMICAL COMPOSITION OF SOME COMMON FOOD MATERIALS - - +----------------------+--------+--------+--------+--------+--------+----------+ - | Food Materials. |Proteid.| Carbo- | Fat. | Water. |Mineral |Fuel Value| - | | |hydrate.| | | Matter.|per pound.| - +----------------------+--------+--------+--------+--------+--------+----------+ - | |per cent|per cent|per cent|per cent|per cent| calories | - |Fresh beef, loin, | | | | | | | - | lean, edible portion | 24.2 | 0 | 3.7 | 70.8 | 1.3 | 615 | - |Fresh beef, round, | | | | | | | - | lean, edible portion | 22.3 | 0 | 2.8 | 73.6 | 1.3 | 540 | - |Fresh Porterhouse | | | | | | | - | steak, edible portion| 21.9 | 0 | 20.4 | 60.0 | 1.0 | 1270 | - |Fresh beef liver | 21.0 | 1.7 | 4.5 | 71.2 | 1.6 | 605 | - |Fresh beef tongue | 19.0 | 0 | 9.2 | 70.8 | 1.0 | 740 | - |Fresh sweetbreads | 16.8 | 0 | 12.1 | 70.9 | 1.6 | 825 | - |Fresh beef kidney | 16.9 | 0.4 | 4.8 | 76.7 | 1.2 | 520 | - |Cooked beef, roasted | 22.3 | 0 | 28.6 | 48.2 | 1.3 | 1620 | - |Cooked round steak | 27.6 | 0 | 7.7 | 63.0 | 1.8 | 840 | - |Broiled tenderloin | | | | | | | - | steak | 23.5 | 0 | 20.4 | 54.8 | 1.2 | 1300 | - |Dried beef, canned | 39.2 | 0 | 5.4 | 44.8 | 11.2 | 960 | - |Stewed kidneys, | | | | | | | - | canned | 18.4 | 2.1 | 5.1 | 71.9 | 2.5 | 600 | - |Fresh corned beef, | | | | | | | - | edible portion | 15.3 | 0 | 26.2 | 53.6 | 4.9 | 1395 | - |Fresh breast of veal, | | | | | | | - | lean | 21.2 | 0 | 8.0 | 70.3 | 1.0 | 730 | - |Fresh leg of lamb, | | | | | | | - | edible portion | 19.2 | 0 | 16.5 | 63.9 | 1.1 | 1055 | - |Lamb chops, broiled | 21.7 | 0 | 29.9 | 47.6 | 1.3 | 1665 | - |Roast leg of lamb, | | | | | | | - | edible portion | 19.4 | 0 | 12.7 | 67.1 | 0.8 | 900 | - |Roast leg of mutton, | | | | | | | - | edible portion | 25.9 | 0 | 22.6 | 50.9 | 1.2 | 1420 | - |Fresh lean ham | 25.0 | 0 | 14.4 | 60.0 | 1.3 | 1075 | - |Smoked ham, fat, | | | | | | | - | edible portion | 14.8 | 0 | 52.3 | 27.9 | 3.7 | 2485 | - |Chicken, broilers, | | | | | | | - | edible portion | 21.5 | 0 | 2.5 | 74.8 | 1.1 | 505 | - |Turkey, edible portion| 21.1 | 0 | 22.9 | 55.5 | 1.0 | 1360 | - |Roast turkey, edible | | | | | | | - | portion | 27.8 | 0 | 18.4 | 52.0 | 1.2 | 1295 | - |Fricasseed chicken, | | | | | | | - | edible portion | 17.6 | 2.4 | 11.5 | 67.5 | 1.0 | 855 | - |Fresh cod, dressed | 11.1 | 0 | 0.2 | 58.5 | 0.8 | 215 | - |Fresh mackerel, edible| | | | | | | - | portion | 18.7 | 0 | 7.1 | 73.4 | 1.2 | 645 | - |Fresh halibut, steaks | 18.6 | 0 | 5.2 | 75.4 | 1.0 | 565 | - |Fresh shad, edible | | | | | | | - | portion | 18.8 | 0 | 9.5 | 70.6 | 1.3 | 750 | - |Fresh smelt, edible | | | | | | | - | portion | 17.6 | 0 | 1.8 | 79.2 | 1.7 | 405 | - |Cooked bluefish, | | | | | | | - | edible portion | 26.1 | 0 | 4.5 | 68.2 | 1.2 | 670 | - |Broiled Spanish | | | | | | | - | mackerel, edible | | | | | | | - | portion | 23.2 | 0 | 6.5 | 68.9 | 1.4 | 715 | - |Salt codfish, edible | | | | | | | - | portion | 25.4 | 0 | 0.3 | 53.5 | 24.7 | 410 | - |Salt mackerel, edible | | | | | | | - | portion | 22.0 | 0 | 22.6 | 42.2 | 13.2 | 1345 | - |Canned salmon, edible | | | | | | | - | portion | 21.8 | 0 | 12.1 | 63.5 | 2.6 | 915 | - |Canned sardines, | | | | | | | - | edible portion | 23.0 | 0 | 19.7 | 52.3 | 5.6 | 162 | - |Fresh round clams | 6.5 | 4.2 | 0.4 | 86.2 | 2.7 | 215 | - |Fresh oysters, solid | 6.0 | 3.3 | 1.3 | 88.3 | 1.1 | 230 | - |Fresh hen’s eggs | 13.4 | 0 | 10.5 | 73.7 | 1.0 | 720 | - |Boiled hen’s eggs | 13.2 | 0 | 12.0 | 73.2 | 0.8 | 765 | - |Butter | 1.0 | 0 | 85.0 | 11.0 | 3.0 | 3605 | - |Full cream cheese | 25.9 | 2.4 | 33.7 | 34.2 | 3.8 | 1950 | - |Whole cow’s milk | 3.3 | 5.0 | 4.0 | 87.0 | 0.7 | 325 | - |Corn meal, unbolted | 8.4 | 74.0 | 4.7 | 11.6 | 1.3 | 1730 | - |Oatmeal | 16.1 | 67.5 | 7.2 | 7.3 | 1.9 | 1860 | - |Rice | 8.0 | 79.0 | 0.3 | 12.3 | 0.4 | 1630 | - |Wheat flour, entire | | | | | | | - | wheat | 13.8 | 71.9 | 1.9 | 11.4 | 1.0 | 1675 | - |Boiled rice | 2.8 | 24.4 | 0.1 | 72.5 | 0.2 | 525 | - |Shredded wheat | 10.5 | 77.9 | 1.4 | 8.1 | 2.1 | 1700 | - |Macaroni | 13.4 | 74.1 | 0.9 | 10.3 | 1.3 | 1665 | - |Brown bread | 5.4 | 47.1 | 1.8 | 43.6 | 2.1 | 1050 | - |Wheat bread or rolls | 8.9 | 56.7 | 4.1 | 29.2 | 1.1 | 1395 | - |Whole wheat bread | 9.4 | 49.7 | 0.9 | 38.4 | 1.3 | 1140 | - |Soda crackers | 9.8 | 73.1 | 9.1 | 5.9 | 2.1 | 1925 | - |Oyster crackers | 11.3 | 70.5 | 10.5 | 4.8 | 2.9 | 1965 | - |Ginger bread | 5.8 | 63.5 | 9.0 | 18.8 | 2.9 | 1670 | - |Sponge cake | 6.3 | 65.9 | 10.7 | 15.3 | 1.8 | 1795 | - |Lady fingers | 8.8 | 70.6 | 5.0 | 15.0 | 0.6 | 1685 | - |Apple pie | 3.1 | 42.8 | 9.8 | 42.5 | 1.8 | 1270 | - |Custard pie | 4.2 | 26.1 | 6.3 | 62.4 | 1.0 | 830 | - |Squash pie | 4.4 | 21.7 | 8.4 | 64.2 | 1.3 | 840 | - |Indian meal pudding | 5.5 | 27.5 | 4.8 | 60.7 | 1.5 | 815 | - |Tapioca pudding | 3.3 | 28.2 | 3.2 | 64.5 | 0.8 | 720 | - |Fresh asparagus | 1.8 | 3.3 | 0.2 | 94.0 | 0.7 | 105 | - |Fresh lima beans | 7.1 | 22.0 | 0.7 | 68.5 | 1.7 | 570 | - |Dried lima beans | 18.1 | 65.9 | 1.5 | 10.4 | 4.1 | 1625 | - |Dried beans | 22.5 | 59.6 | 1.8 | 12.6 | 3.5 | 1605 | - |Cooked beets | 2.3 | 7.4 | 0.1 | 88.6 | 1.6 | 185 | - |Fresh cabbage, edible | | | | | | | - | portion | 1.6 | 5.6 | 0.3 | 91.5 | 1.0 | 145 | - |Green corn, edible | | | | | | | - | portion | 3.1 | 19.7 | 1.1 | 75.4 | 0.7 | 470 | - |Dried peas | 24.6 | 62.0 | 1.0 | 9.5 | 2.9 | 1655 | - |Green peas | 7.7 | 16.9 | 0.5 | 74.6 | 1.0 | 465 | - |Raw potatoes, edible | | | | | | | - | portion | 2.2 | 18.4 | 0.1 | 78.3 | 1.0 | 385 | - |Boiled potatoes | 2.5 | 20.9 | 0.1 | 75.5 | 1.0 | 440 | - |Fresh tomatoes | 0.9 | 3.9 | 0.4 | 94.3 | 0.5 | 105 | - |Baked beans, canned | 6.9 | 19.6 | 2.5 | 68.9 | 2.1 | 600 | - |Apples, edible portion| | | | | | | - | steak | 0.4 | 14.2 | 0.5 | 84.6 | 3.0 | 290 | - |Bananas, yellow, | | | | | | | - | edible portion | 1.3 | 22.0 | 0.6 | 75.3 | 0.8 | 460 | - |Fresh cranberries | 0.4 | 9.9 | 0.6 | 88.9 | 0.2 | 215 | - |Oranges, edible | | | | | | | - | portion | 0.8 | 11.6 | 0.2 | 86.9 | 0.5 | 240 | - |Peaches, edible | | | | | | | - | portion | 0.7 | 9.4 | 0.1 | 89.4 | 0.4 | 190 | - |Fresh strawberries | 1.0 | 7.4 | 0.6 | 90.4 | 0.6 | 180 | - |Dried prunes, edible | | | | | | | - | portion | 2.1 | 73.3 | 0.0 | 22.3 | 2.3 | 1400 | - |Almonds, edible | | | | | | | - | portion | 21.0 | 17.3 | 54.9 | 4.8 | 2.0 | 3030 | - |Peanuts, edible | | | | | | | - | portion | 25.8 | 24.4 | 38.6 | 9.2 | 2.0 | 2560 | - |Pine nuts, edible | | | | | | | - | portion | 33.9 | 6.9 | 49.4 | 6.4 | 3.4 | 2845 | - |Brazil nuts, edible | | | | | | | - | portion | 17.0 | 7.0 | 66.8 | 5.3 | 3.9 | 3265 | - |Soft-shell walnuts, | | | | | | | - | edible portion | 16.6 | 16.1 | 63.4 | 2.5 | 1.4 | 3285 | - +----------------------+--------+--------+--------+--------+--------+----------+ - -In commenting on these figures, reference to which will be made from -time to time in other connections, it may be wise to emphasize the -large amount of water almost invariably present in natural foodstuffs. -Further, it is to be noted that, in animal products especially, the -variations in proteid-content are in large measure coincident with -variations in the amount of water present. In other words, foods -of animal origin if freed entirely of water would, as a rule, show -essentially the same percentage of proteid matter. Fat is naturally -variable, according to the condition of the animal at the time it was -slaughtered. Among the vegetable products, carbohydrate, mainly in the -form of starch, becomes exceedingly conspicuous, though proteid is by -no means lacking. Indeed, in some cereals, as in oatmeal, in dried peas -and beans, the content of proteid will average as high as in fresh -beef, while in addition 50–70 per cent of the entire substance is made -up of carbohydrate. Again, in the edible nuts, the content of proteid -runs high, in some cases higher than in fresh beef, while at the same -time carbohydrate and fat are noticeably large. Further, it is to be -noted that in nuts there is here and there some striking individuality, -as in pine nuts and Brazil nuts, both of which show a noticeable lack -of carbohydrate as contrasted with peanuts, almonds, and walnuts; a -fact of some importance in cases where a vegetable food rich in proteid -is desired, but with freedom from starch. - -Another generality, to be thoroughly understood, is that while the -figures given for proteid express quite clearly and with reasonable -degree of accuracy the relative amounts of proteid matter present in -the foodstuffs in question, there may be important differences in -availability of which the percentage figures give no suggestion. In -other words, the analytical data deal solely with the total content -of proteid, while there is needed in addition information as to the -relative digestibility, or availability by the body, of the different -kinds of proteid food. For example, roast mutton, cream cheese, and -dried peas contain approximately the same amount of proteid. Are we -then to infer that these three foods have the same nutritive value so -far as proteid is concerned? Surely not, since no account is taken of -the relative digestibility of the three foods. It is one of the axioms -of physiology that the true nutritive value of any proteid food is -dependent not alone upon the amount of proteid contained therein, but -upon the quantity of proteid that can be digested and absorbed; or, -in other words, made available for the needs of the body. The same -rule holds good for both fats and carbohydrates, but as proteid is the -more important foodstuff, and is as a rule taken more sparingly, the -question of availability has greater import with the proteid foods. - -The availability or digestibility of foods can be determined only by -physiological experiment. By making a comparison for a definite period -of time of the amount of a given food ingredient consumed and the -amount that passes unchanged through the intestine, an estimate of its -digestibility can be made. The result, to be sure, is not wholly free -from error, since we cannot always distinguish between the undigested -food and so-called metabolic products coming from the digestive juices -and from the walls of the intestine; but the errors are not large, and -results so obtained are full of meaning. In a general way it may be -stated that with animal foods, such as meats, eggs, and milk, about -97 per cent of the contained proteid is digested and thereby rendered -available for the body. With ordinary vegetable foods, on the other -hand, as they are usually prepared for consumption, only about 85 per -cent of the proteid is made available. This is partially due to the -presence in the vegetable tissue of cellulose, which in some measure -prevents that thorough attack of the proteid by the digestive juices -which occurs with animal foods. With a mixed diet, _i. e._, with -a variable admixture of animal and vegetable foods, it is usually -considered that about 92 per cent of the proteid contained therein will -undergo digestion. - -Regarding differences in the availability of fats, it may be stated -that, as a rule, the fatty matter contained in vegetable foods is less -readily, or less thoroughly, digested than that present in foods of -animal origin. In the latter, about 95 per cent of the fat is digested -and absorbed. This figure, however, is generally taken as representing -approximately the digestibility or availability of the fat contained -in man’s daily dietary, since by far the larger proportion of the fat -consumed is of animal origin. Carbohydrates, on the other hand, are -much more easily utilized by the body. Naturally, sugars, owing to -their great solubility and ready diffusibility, offer little difficulty -in the way of easy digestion; but starches likewise, though not so -readily assimilable, are digested, as a rule, to the extent of 98 per -cent or more of the amount consumed. It is thus evident that in any -estimate of the food value of a given diet, chemical composition is to -be checked by the digestibility or availability of the food ingredients. - -As has been stated several times, the proteid foodstuffs are the more -important, since proteid matter is essential to animal life. Man -must have a certain amount of proteid food to maintain the body in a -condition of strength and vigor. The other essential is that the daily -food furnish sufficient energy to meet the needs of the body for heat -and power. This means that in addition to proteid, which primarily -serves a particular purpose, there must be enough non-nitrogenous food -(either carbohydrate or fat or both) to provide the requisite fuel -for oxidation or combustion to meet the demands of the body for heat -and for work; both of which are subject to great variation owing to -differences in the temperature of the surrounding air, and especially -because of variations in the degree of bodily activity. The energy -which a given foodstuff will yield can be ascertained by laboratory -experiment, in which a definite weight of the substance is burned or -oxidized in a calorimetric bomb under conditions where the exact amount -of heat liberated can be accurately measured. The fuel, or energy, -value so obtained is expressed in calories or heat units. A calorie may -be defined as the amount of heat required to raise 1 gram of water 1° -C., or, to be more exact, the amount of heat required to raise 1 gram -of water from 15° to 16° C. This unit is usually spoken of as the small -calorie, to distinguish it from the large calorie, which represents -the amount of heat required to raise 1 kilogram of water 1° C. Hence, -the large calorie is equal to one thousand small calories. When burned -in a calorimeter, 1 gram of carbohydrate yields on an average 4100 -gram-degree units of heat, or small calories; 1 gram of fat yields 9300 -small calories. Both of these non-nitrogenous foods burn or oxidize to -the same products--viz., carbon dioxide and water--when utilized in -the body as when burned in the calorimeter; hence, the figures given -represent the physiological heat of combustion, per gram, of the two -classes of foodstuffs. Obviously, the fuel values of different foods -belonging to the same group or class will show slight variation, but -the above figures represent average values. - -Unlike fats and carbohydrates, proteids are not burned completely -in the body; hence, the physiological fuel value of a proteid is -less than the value obtained by oxidation in a bomb calorimeter. In -the body, proteids yield certain decomposition products which are -removed through the excreta, and which represent a certain quantity of -potential energy thus lost to the economy. The average fuel value of -proteids burned outside of the body is placed at 5711 calories per -gram,[3] or 5.7 large calories. Deducting the heat value of the proteid -decomposition products contained in the excreta, the physiological fuel -value of proteids is reduced on an average to about 4.1 large calories -per gram.[4] Rubner considers that the physiological fuel value of -vegetable proteids is somewhat less than that of animal proteids; -conglutin, for example, yielding 3.96 calories, as contrasted with 4.3 -calories furnished by egg-albumin, or 4.40 calories from casein. On a -mixed diet, where 60 per cent of the ingested proteid food is of animal -origin and 40 per cent vegetable, the fuel value available to the body -would be about 4.1 calories per gram of proteid, on the assumption -that the physiological heat value of vegetable proteids averages 3.96 -calories per gram and that of animal proteids 4.23 calories per gram -(Rubner). - - [3] Stohmann: Ueber den Wärmewerth der Bestandtheile der - Nahrungsmittel. Zeitschr. f. Biol., Band 31, p. 373. - - [4] See Rubner: Calorimetrische Untersuchungen. Zeitschr. f. Biol., - Band 21, p. 250. Also, Rubner: Die Quelle der thierischen Wärme. - Ibid., Band 30, p. 73. - -At present, we accept for all purposes of computation the following -figures as representing the physiological or available (to the body) -fuel value of the three classes of organic foodstuffs: - - 1 gram of proteid 4.1 Large Calories - 1 gram of fat 9.3 " " - 1 gram of carbohydrate 4.1 " " - -From these data, it is evident at a glance that 1 gram of fat is -isodynamic with 2.27 grams of either carbohydrate or proteid; and -since carbohydrate and fat are of use to the body mainly because -of their energy value, it is obvious that 50 grams of fat taken as -food will be of as much service to the body as 113 grams of starch. -In view of the relatively high fuel value of fats, it follows that -the physiological heat of combustion of any given food material will -correspond largely with the content of fat therein. This is quite -apparent from the data given in the table showing chemical composition -of food materials, where the fuel value per pound is seen to run more -or less closely parallel with the percentage of fat. Experience, as -well as direct physiological experiment, teaches us, however, that fat -and carbohydrate cannot be interchanged indefinitely, because of the -difficulty in utilization of fat when the amount is increased beyond -a certain point. Personal experience provides ample evidence of the -difference in availability between the two classes of foodstuffs. -Carbohydrates are easily utilizable, fats with more difficulty. Palate, -as well as stomach, rebels at large quantities of fat; a statement that -certainly holds good for most civilized people, though exceptions may -be found, as in the Esquimeaux and certain savage races. - -In the nourishment of the body, the various factors that aid in the -utilization of food are of great moment and must not be overlooked. It -is not enough that the body be supplied with the proper proportion of -nutrients, with sufficient proteid to meet the demand for nitrogen, and -with carbohydrate and fat adequate to yield the needed energy; but all -those physiological processes which have to do with the preparation -of the foodstuffs for absorption into the circulating blood and lymph -must be in effective working order. There is an intricacy of detail -here which calls for careful oversight, and it is one of the functions -of the nervous system to control and regulate both the mechanical and -the chemical processes that are concerned in this seemingly automatic -progression of foodstuffs from their entry into the mouth cavity to -their final discharge from the alimentary tract, after removal of the -last vestige of true nutritive material. - -Mastication; deglutition; secretion of the various digestive juices, -saliva, gastric juice, pancreatic juice, bile, intestinal juice, etc.; -peristalsis, or the rhythmical movements of the muscular walls of the -gastro-intestinal tract; the solvent action of the several digestive -fluids on the different types of foodstuffs; the absorption of the -products formed as a preliminary step in their transportation to the -tissues and organs of the body, where they are to serve their ultimate -purpose in nutrition; the interaction of these several processes one on -the other; and, finally, the influence of the various nerve fibres and -nerve centres concerned in the control of these varied activities,--all -must work together in harmony and precision if the full measure of -available nitrogen and energy-yielding material is to be extracted -and absorbed from the ingested food, without undue expenditure of -physiological labor. Further, the various processes of cell and tissue -metabolism, by which the absorbed food material is built up into living -protoplasm, and the chemical processes of oxidation, hydrolysis, -reduction, etc., by which the intra and extra cellular material is -broken down progressively into varied katabolic or excretory products, -with liberation of energy; all these must move forward harmoniously -and with due regard to the preservation of an even balance between -intake and outgo, if the nutrition of the body is to be maintained at -a proper level, and with that degree of physiological economy which is -coincident with good health and high efficiency. - -We may well pause here and consider briefly some of these processes -which play so prominent a part in the proper utilization of the three -classes of organic foodstuffs. The first digestive fluid which the -ingested food comes in contact with is the saliva. Sensory nerve -fibres, chiefly of the glossopharyngeal and lingual nerves which supply -the mouth and tongue, are stimulated by the sapid substances of the -food, and likewise by mere contact of the food particles with the -mucous membrane lining the mouth cavity as the food is masticated and -rolled about prior to deglutition. Impulses communicated in this way -to the above sensory nerves are transmitted to certain nerve centres -in the medulla oblongata, whence impulses are reflected back through -secretory nerves going to the individual salivary glands, thereby -calling forth a secretion. The production of saliva is thus a simple -reflex act, in which the food consumed serves as a true stimulant or -excitant. Pawlow,[5] indeed, claims a certain degree of adaptability -of the secretion to the character of the food taken into the mouth. -Thus, he finds that dry, solid food excites a large flow of saliva, -such as would be needed to masticate it properly and bring it into a -suitable condition for swallowing. On the other hand, foods containing -an abundance of water cause only a scanty flow of saliva. The situation -of this secretory centre in the medulla, and the many branchings of -nerve cells in this locality would naturally suggest the possibility -of salivary secretion being incited by stimuli from a variety of -sources. This is indeed the case, and it is worthy of note that a flow -of saliva may result from stimulation of the sensory fibres of the -vagus nerves as well as of the splanchnic and sciatic, thus indicating -how a given secreting gland may be called into activity by impulses -or stimuli which come to the centre through very indirect and devious -pathways. Further, the secretory centre may be stimulated, and likewise -inhibited, by impulses which have their origin in higher nerve centres -in the brain. These facts are of great importance in throwing light -upon the ways in which a secretion like saliva is called forth and its -digestive action thus made possible. The thought and the odor of savory -food cause the mouth to water, the flow of saliva so incited being -the result of psychical stimulation. Similarly, fear, embarrassment, -and anxiety frequently cause a dry mouth and parched throat through -inhibition of the secretory centre by impulses which have their origin -in higher centres in the brain. - - [5] Pawlow: The Work of the Digestive Glands. Translated by Thompson. - London, 1902. - -The application of these facts to our subject is perfectly obvious, -since they suggest at once how the production or secretion of an -important digestive fluid--upon which the utilization of a given class -of foodstuffs may be quite dependent--is controlled and modified -through the nervous system by a variety of circumstances. We might -reason that the appearance, odor, and palatability of food are factors -of prime importance in its utilization by the body; that the æsthetics -of eating are not to be ignored, since they have an important influence -upon the flow of the digestive secretions. A peaceful mind, pleasurable -anticipation, freedom from care and anxiety, cheerful companionship, -all form desirable table accessories which play the part of true -psychical stimuli in accelerating the flow of the digestive juices -and thus pave the way for easy and thorough digestion. Further, it is -easy to see how thorough mastication of food may prolong mechanical -stimulation of the salivary glands and thus increase the flow of the -secretion, while the longer stay of sapid substances in the mouth -cavity increases the duration of the chemical stimulation of the -sensory fibres of the lingual and glossopharyngeal nerves. In this -connection, we may cite the view recently advanced by Pawlow that the -individual salivary glands respond normally to different stimuli. Thus, -there are three pairs of salivary glands concerned in the production -of saliva,--the submaxillary, parotid, and sublingual,--all of which -pour their secretions through separate ducts into the mouth cavity. By -experiment, Pawlow has found that in the dog the submaxillary gland -yields a copious flow of saliva when stimulated by acids, the chewing -of meats, the sight of food, etc., while the parotid gland fails to -respond. On the other hand, the latter gland responds with an abundant -secretion when dry food, such as dry powdered meat, dried bread, etc., -is placed in the mouth. With this gland, the inference is that dryness -is the active stimulus. - -As a digestive secretion, saliva serves several important purposes. By -moistening the food it renders mastication and deglutition possible; -its natural alkalinity tends to neutralize somewhat such acidity as may -be present in the food; it dissolves various solid substances, thus -making a solution capable of stimulating the taste nerves; lastly, -and most important, it has a marked digestive and solvent action on -starchy foods. A large proportion of the non-nitrogenous food consumed -by man--in most countries--is composed of some form of starch, and this -the body cannot use until it has undergone conversion into soluble -forms, such as dextrins and sugar. This it is the function of saliva to -accomplish, and it owes its activity in this direction to the presence -of a soluble ferment or enzyme known as ptyalin. - -Enzymes, which play so important a part in all digestive processes, -are a peculiar class of substances produced by the living cells -which constitute the various secreting glands. They are of unknown -composition, and are peculiar in that the chemical changes they induce -are the result of what is termed catalysis, _i. e._, contact. That -is, the enzyme or catalyzer does not enter into the reaction, it is -not destroyed or used up, but by its mere presence sets in motion or -accelerates a reaction between two other substances. The ordinary -illustration from the inorganic world is spongy platinum, which, if -placed in contact with a mixture of oxygen and hydrogen, causes the two -gases to unite with formation of water, although the two gases alone at -ordinary temperature will not so combine. In this reaction the platinum -is not altered, neither does it apparently enter into the reaction; it -is a simple catalyzer. The chemical nature of the change which most -digestive enzymes produce is usually defined as hydrolytic, in which -the substance undergoing transformation is made to combine with water, -thus becoming hydrolyzed, this reaction generally being accompanied -by a cleavage or splitting of the molecule into simpler substances. -It is to be noted further that enzymes are specific in their action. -An enzyme that acts upon starch, for example, cannot act on proteids -or fats. Some digestive fluids have the power of producing changes -in different classes of foodstuffs, but such diversity of action is -always assumed to be due to the presence in the same fluid of different -enzymes. Emil Fischer[6] has advanced the theory that the specificity -of an enzyme is related to the geometrical structure of the substance -undergoing change; _i. e._, that each enzyme is capable of acting upon -or attaching itself only to such molecules as have a definite structure -with which the enzyme is in harmony. Or, the enzyme may be considered -as a key which will fit only into the lock (structure) of the molecule -it acts upon. - - [6] Emil Fischer: Bedeutung der Stereochemie für die Physiologie. - Zeitschr. für physiologische Chemie, Band 26, p. 60. - -One characteristic feature of enzymes is the incompleteness of their -action. Thus, the enzyme of saliva transforms starch by a series of -progressive changes into soluble starch, two or more dextrins, and -the sugar maltose as the chief end-product. A mixture of starch paste -and saliva under ordinary conditions, however, never results in the -formation of a hundred per cent of maltose, but there always remains -a variable amount of dextrin which appears to resist further change. -This is apparently due to what is known as the reversible action of -enzymes. Thus, the chemical reactions involved here are reversible -actions, _i. e._, they take place in opposite directions. The catalyzer -not only accelerates or incites a reaction in the direction of breaking -down the substance acted upon, but it also aids in the recomposition -of the products so formed into the original or kindred substance. With -reversible reactions of this sort the opposite changes sooner or later -strike an equilibrium, which remains constant until some alteration in -the conditions brings about an inequality and the reactions proceed -until a new equilibrium is established. In the body, however, where -the circulating blood and lymph provide facilities for the speedy -removal by absorption of the soluble products formed, the reaction may -proceed until the original substance undergoing change is completely -transformed into the characteristic end-product. This reversible -action of enzymes is an important feature, and helps explain certain -nutritional changes to be referred to later. Whether all enzymes behave -in this way is not as yet determined. - -Another peculiarity of digestive enzymes is their extreme sensitiveness -to changes in their environment. Powerful in their ability to transform -relatively large quantities of a given foodstuff into simple products -better adapted for absorption and utilization by the body, they are, -however, quickly checked in their action, and even destroyed, when -the conditions surrounding them are slightly interfered with. They -require for their best action a temperature closely akin to that of the -healthy body, and any great deviation therefrom will result at once -in an inhibition of their activity. Further, they demand a certain -definite reaction of the fluid or mixture, if their working power -is to be maintained at the maximum. Indeed, many enzymes, like the -ptyalin of saliva, are quickly destroyed if the reaction is greatly -changed. Enzymes are thus seen to be more or less unstable substances, -endowed with great power as digestive agents, but sensitive to a high -degree and working advantageously only under definite conditions. Many -perversions of digestion and of nutrition are connected not only with -a lack of the proper secretion of some one or more digestive enzyme, -but also with the lack of proper surroundings for the manifestation of -normal or maximum activity. - -With these statements before us, we can readily picture for ourselves -the initial results following the ingestion of starch-containing foods -properly cooked; and it may be mentioned here that the cooking is an -essential preliminary, for uncooked starch cannot be utilized in any -degree by man. With the mind in a state of pleasurable anticipation, -with freedom from care and worry, which are so liable to act as -deterrents to free secretion, and with the food in a form which appeals -to the eye as well as to the olfactories, its thorough mastication -calls forth and prolongs vigorous salivary secretion, with which the -food becomes intimately intermingled. Salivary digestion is thus at -once incited, and the starch very quickly commences to undergo the -characteristic change into soluble products. As mouthful follows -mouthful, deglutition alternates with mastication, and the mixture -passes into the stomach, where salivary digestion can continue for a -limited time only, until the secretion of gastric juice eventually -establishes in the stomach-contents a distinct acid reaction, when -salivary digestion ceases through destruction of the starch-converting -enzyme. Need we comment, in view of the natural brevity of this -process, upon the desirability for purely physiological reasons of -prolonging within reasonable limits the interval of time the food -and saliva are commingled in the mouth cavity? It seems obvious, in -view of the relatively large bulk of starch-containing foods consumed -daily, that habits of thorough mastication should be fostered, with -the purpose of increasing greatly the digestion of starch at the very -gateway of the alimentary tract. It is true that in the small intestine -there comes later another opportunity for the digestion of starch; but -it is unphysiological, as it is undesirable, for various reasons, not -to take full advantage of the first opportunity which Nature gives for -the preparation of this important foodstuff for future utilization. -Further, thorough mastication, by a fine comminution of the food -particles, is a material aid in the digestion which is to take place in -the stomach and intestine. Under normal conditions, therefore, and with -proper observance of physiological good sense, a large proportion of -the ingested starchy foods can be made ready for speedy absorption and -consequent utilization through the agency of salivary digestion. - -Nowhere in the body do we find a more forcible illustration of -economical method in physiological processes than in the mechanism -of gastric secretion. Years ago, it was thought that the flow of -gastric juice was due mainly to mechanical stimulation of the gastric -glands by contact of the food material with the lining membrane of the -stomach. This, however, is not the case, as Pawlow has clearly shown, -and it is now understood that the flow of gastric juice is started -by impulses which have their origin in the mouth and nostrils; the -sensations of eating, the smell, sight, and taste of food serving -as psychical stimuli, which call forth a secretion from the stomach -glands, just as the same stimuli may induce an outpouring of saliva. -These sensations, as Pawlow has ascertained, affect secretory centres -in the brain, and impulses are thus started which travel downward to -the stomach through the vagus nerves, and as a result gastric juice -begins to flow. This process, however, is supplemented by other forms -of secretion, likewise reflex, which are incited by substances, ready -formed in the food, and by substances--products of digestion--which -are manufactured from the food in the stomach. Soups, meat juice, and -the extractives of meat, likewise dextrin and kindred products, when -present in the stomach, are especially active in provoking secretion. -Substances which in themselves have less flavor, as water, milk, etc., -are far less effective in this direction, while the white of eggs and -bread are entirely without action in directly stimulating secretion. -When the latter foods have been in the stomach for a time, however, -and the proteid material has undergone partial digestion, then -absorption of the products so formed calls forth energetic secretion of -gastric juice. It is thus seen that there are three distinct ways--all -reflex--by which gastric juice is caused to flow into the stomach as a -prelude to gastric digestion. Further, it has been shown by Pawlow that -there is a relationship between the volume and character of the gastric -juice secreted and the amount and composition of the food ingested, -thus suggesting a certain adjustment in the direction of physiological -economy well worthy of note. A diet of bread, for example, leads to the -secretion of a smaller volume of gastric juice than a corresponding -weight of meat produces, but the juice secreted under the influence of -bread is richer in pepsin and acid, _i. e._, it has a greater digestive -action than the juice produced by meat. The suggestion is that gastric -juice assumes different degrees of concentration, with different -proportions of acid and pepsin, to meet the varying requirements of a -changing dietary. - -As has been indicated, pepsin and hydrochloric acid are the important -constituents of gastric juice. It is noteworthy, however, that it is -the combination of the two that is effective in digestion. Pepsin -without acid is of no avail, and acid without pepsin can accomplish -little in the digestion of food. Pepsin and acid are secreted by -different gland cells in the stomach, and gastric insufficiency, or -so-called indigestion, may arise from either a condition of apepsia -or from hypoacidity. It is worthy of comment that the amount of -hydrochloric acid secreted during 24 hours by the normal individual, -under ordinary conditions of diet, amounts to what would constitute -a fatal dose of acid if taken at one time in concentrated form. At -the outset of gastric secretion, the fluid shows only a slight degree -of acidity, but as secretion proceeds, the acidity rises to 0.2–0.3 -per cent of hydrochloric acid. The main action of gastric juice is -exerted on proteid foods, which under its influence are gradually -dissolved and converted into soluble products known as proteoses and -peptones. It is a process of peptonization, in which the proteid of -the food is gradually broken down into so-called hydrolytic cleavage -products. The enzyme, like the ptyalin of saliva, is influenced by -temperature, maximum digestive action being manifested at about 38° C., -the temperature of the body. Further, a certain degree of acidity is -essential for procuring the highest degree of efficiency. Ordinarily, -it is stated that digestive action proceeds best in the presence of 0.2 -per cent hydrochloric acid, but what is more essential for vigorous -digestion is a certain relationship between the acid, pepsin, and -proteid undergoing digestion. As pepsin and the amount of proteid -are increased, the amount of acid, and its percentage somewhat, must -be correspondingly increased if digestion is to be maintained at the -maximum. - -Another important function of gastric juice is that of curdling milk, -due to the presence in the secretion of a peculiar enzyme known as -rennin. The latter ferment acts upon the casein of milk,--the chief -proteid constituent,--transforming it into a related substance commonly -called paracasein. This then reacts with the calcium salts present in -milk, forming an insoluble curd or calcium compound. From this point -on, the digestion of milk-casein by gastric juice is the same as that -of any other solid proteid, it being gradually transformed by the -pepsin-acid into soluble cleavage products. Why gastric juice should -be provided with this special enzyme, capable of acting solely on -the casein of milk, can only be conjectured, but we may assume that -it has to do with the economical use of this important food. As the -sole nutriment of the young, milk occupies a peculiar position as a -foodstuff, and being a liquid, its proteid constituent might easily -escape complete digestion were it to pass on too hastily through the -gastro-intestinal tract. Experiment has shown that when liquid food -alone is taken into the stomach it is pushed forward into the small -intestine in a comparatively short time. Curdled as it is by rennin, -however, casein must stay for a longer period in the stomach, like any -other solid food, and its partial digestion by gastric juice thereby -made certain. For the reasons above stated, it is apparent why milk -should not be treated as a drink in our daily diet. Remembering that -when milk reaches the stomach it is converted into a solid clot or -curd, there is obvious reason for sipping it, instead of taking it by -the glassful, thereby favoring the formation of small, individual clots -instead of one large curd, and thus facilitating instead of retarding -digestion. - -Among other factors in gastric digestion, the muscular movements of the -stomach walls are to be emphasized, since we have here a mechanical aid -to digestion of no small moment, and likewise a means of accomplishing -the onward movement of the stomach contents. The outer walls of the -stomach are composed of a thick layer of circular muscular fibres, -especially conspicuous at the pyloric end of the organ, where the -latter is joined on to the intestine; a smaller, less conspicuous -layer of longitudinal muscle fibres, and some oblique fibres. At the -pylorus, the circular fibres are so arranged as to form a structure -which, aided by a peculiar folding of the inner mucous membrane, -serves as a sphincter, closing off the stomach from the duodenum, the -beginning of the small intestine. The movements of the stomach were -first made the subject of careful investigation by Dr. Beaumont in his -study of the celebrated case of Alexis St. Martin, a French Canadian, -who, in 1822, was accidentally wounded by the discharge of a musket, -with the resultant formation of a permanent fistulous opening in the -stomach. Dr. Beaumont, in the description[7] of his observations, -writes that “by the alternate contractions and relaxations of these -bands (of muscle) a great variety of motion is induced on this -organ (the stomach), sometimes transversely, and at other times -longitudinally. These alternate contractions and relaxations, when -affecting the transverse diameter, produce what are called _vermicular_ -or _peristaltic_ motions.... When they all act together, the effect is -to lessen the cavity of the stomach, and to press upon the contained -aliment, if there be any in the stomach. These motions not only produce -a constant disturbance, or _churning_ of the contents of this organ, -but they compel them, at the same time, to revolve around the interior, -from point to point, and from one extremity to the other.” Of more -recent investigations, the most important are those made by Cannon,[8] -with the X-ray apparatus. From these later studies, it is evident -that Dr. Beaumont’s view of the entire stomach being involved in a -general rotary movement is not correct, since in reality the movements -are confined mainly to the pyloric end of the stomach, the fundus or -portion nearer the œsophagus not being directly involved. This means -that when food material passes into the stomach, it may remain at the -fundic end for some time more or less undisturbed before admixture with -the gastric juice occurs, and under such conditions, until acidity -creeps in, the salivary digestion of starch can continue. - - [7] The Physiology of Digestion. By William Beaumont, M.D. Second - Edition, 1847, p. 100. - - [8] W. B. Cannon: The Movements of the Stomach studied by means of - the Röntgen Rays. American Journal of Physiology, vol. 1, p. 359. - -According to the observations of Cannon, the contractile movements -of the stomach commence shortly after the entrance of food, the -contractions starting from about the middle of the stomach and passing -on toward the pylorus. These waves of contraction follow each other -very closely, certainly not more than one or two minutes apart, and -perhaps less, while the resulting movements bring about an intimate -commingling of food and gastric juice in the pyloric portion of the -stomach; followed by a gradual diffusion of the semi-fluid mixture into -the fundus accompanied by a gradual displacement of the more solid -food in the latter region. These movements of the stomach are more or -less automatic, arising from stimuli--the acid secreted--originating -in the stomach itself, although it is considered that the movements -are subject to some regulation from extrinsic nerve fibres, such as -the vagi and the splanchnics. As digestion proceeds and the mass in -the stomach becomes more fluid, the pyloric sphincter relaxes and a -certain amount of the fluid material is forced into the intestine by -the pressure of the contraction wave. This is repeated at varying -intervals, depending presumably in some measure upon the consistency -of the mass in the stomach, until after some hours of digestion the -stomach is completely emptied. - -Especially interesting and suggestive are the experiments made by -Cannon[9] on the length of time the different types of foodstuffs -remain in the stomach. Using cats as subjects, he found that fats -remain for a long period in the stomach; they leave that organ slowly, -the discharge into the intestine being at about the same rate as the -absorption of fat from the small intestine or its passage into the -large intestine. Carbohydrate foods, on the other hand, begin to leave -the stomach soon after their ingestion. They pass out rapidly, and at -the end of two hours reach a maximum amount in the small intestine -almost twice the maximum for proteids, and two and a half times the -maximum for fats, both of which maxima are reached only at the end of -four hours. Carbohydrates remain in the stomach about half as long as -proteids. Proteids, Cannon finds, frequently do not leave the stomach -at all during the first half-hour after they are eaten. After two -hours, they accumulate in the small intestine to a degree only slightly -greater than that reached by carbohydrates an hour and a half earlier. -The departure of proteids from the stomach is therefore slower at -first than that of either fats or carbohydrates. When a mixture of -equal parts of carbohydrates and proteids is fed, the discharge from -the stomach is intermediate in rapidity. When fat is added to either -carbohydrates or proteids it retards the passage of both foodstuffs -through the pylorus. - - [9] W. B. Cannon: The Passage of different Food-stuffs from the - Stomach and through the Small Intestine. American Journal of - Physiology, vol. 12, p. 387. - -It is evident from what has been stated that the gastric digestion of -proteid foods is a comparatively slow process, involving several hours -of time; and further, that food material in general remains in the -stomach for varying periods, dependent upon its chemical composition. -It would appear further, that relaxation of the pyloric sphincter, -allowing passage of chyme into the intestine, must depend somewhat upon -chemical stimulation, as this offers the most plausible explanation -of the diversity of action seen with the different foodstuffs. As -has been pointed out, gastric digestion is primarily a process for -the conversion of proteid food into soluble products. It would be -a mistake, however, to assume that the digestion of proteid foods -is complete in the stomach. Stomach digestion is to be considered -more as a preliminary step, paving the way for further changes to be -carried forward by the combined action of intestinal and pancreatic -juice in the small intestine. The importance of gastric digestion -is frequently overrated. It is unquestionably an important process, -but not absolutely essential for the maintenance of life. Dogs have -lived and flourished with their stomachs removed, the intestine being -joined to the œsophagus. The intestine is a much more important part -of the alimentary tract; it is likewise far more sensitive to changing -conditions than the stomach, and undoubtedly one function of the -latter organ is to protect the intestine and preserve it from insult. -The stomach may be compared to a vestibule or reservoir, capable of -receiving without detriment moderately large amounts of food, together -with fluid, in different forms and combinations, with the power to hold -them there until by action of the gastric juice they are so transformed -that their onward passage into the intestine can be permitted with -perfect safety. Then, small portions of the properly prepared material -may be discharged from time to time through the pylorus without danger -of overloading the intestine, and in a form capable of undergoing rapid -and complete digestion. Further, the stomach as a reservoir is very -useful in bringing everything to a proper and constant temperature -before allowing its entry into the intestine. Another fact of some -importance is that, contrary to the general view, absorption from -the stomach of the products of digestion is not very rapid under -ordinary conditions. Even water and soluble salts pass very slowly into -the circulation from the stomach. Like the partially digested food -material, they are carried forward through the pyloric sphincter into -the intestine, where absorption of all classes of material is most -marked. - -It is in the small intestine that both digestion and absorption are -seen at their best. It is here that all three classes of foodstuffs -are acted upon simultaneously through the agency of the pancreatic -juice, intestinal juice, and bile. Here, too, are witnessed some of the -most complicated and interesting reactions and changes occurring in -the whole range of digestive functions. Especially noteworthy is the -peculiar mechanism by which the secretion of pancreatic juice is set -up and maintained. On demand, pancreatic juice is manufactured in the -pancreas and poured into the intestine just beyond the pylorus through -a small duct--the duct of Wirsung. Secretion is started by contact of -the acid contents of the stomach with the mucous membrane of the small -intestine, so that as soon as the acid chyme passes through the pyloric -sphincter there commences an outflow of pancreatic juice into the -intestine. While acid is plainly the inciting agent in this secretory -process, its action is indirect. It does not cause secretion through -reflex action on nerve fibres, but it acts upon a substance formed in -the mucous membrane of the intestine, transforming it into _secretin_, -which is absorbed by the blood and carried to the pancreas, where it -excites secretory activity. As would be expected from the foregoing -statements, the secretion of pancreatic juice commences very soon after -food finds its way into the stomach, and naturally increases in amount -with the onward passage of acid chyme into the intestine, the maximum -flow being obtained in the neighborhood of the third or fourth hour, -after which the secretion gradually decreases. In man, it is estimated -on the basis of one or two observations that the amount secreted during -24 hours is about 700 cc., or a pint and a half. Careful experiments, -however, tend to show that the quantity of secretion depends in some -measure at least upon the character of the food, and also that the -composition of the secretion varies with the character of the food. -Thus, on a diet composed mainly of meat, the proteid-digesting enzyme -is especially conspicuous, while on a bread diet, with its large -content of starch, the starch-digesting enzyme is increased in amount. -In other words, there is suggested the possibility of an adaptation in -the composition of the secretion to the character of the food to be -digested. - -Pancreatic juice is an alkaline fluid, rather strongly alkaline -in fact, from its content of sodium carbonate, and is especially -characterized by the presence of at least three distinct enzymes; -viz., trypsin, a proteid-digesting ferment; lipase, a fat-splitting -enzyme; and amylopsin, a starch-digesting enzyme. It has already been -pointed out how dependent the secretion of pancreatic juice is upon the -co-operation of the intestinal mucous membrane. A similar dependence -is found when the digestive activity of the secretion is studied. As -just stated, pancreatic juice contains a proteid-digesting enzyme. -This statement, however, is not strictly correct, for if the secretion -is collected through a cannula so that it does not come in contact -with the mucous membrane of the intestine, it is found free from any -digestive action on proteids. The secretion is activated, however, by -contact with the duodenal membrane. Expressed in different language, -pancreatic juice as it is secreted by the gland does not contain -ready-formed trypsin; it does contain, however, an inactive pro-enzyme, -which, under the influence of a specific substance contained in the -intestinal mucous membrane, known as enterokinase, is transformed -into the active enzyme trypsin. There is thus seen another suggestive -example of the close physiological relationship between the small -intestine and the activity of the pancreatic gland, or its secretion. - -The chemical changes taking place in the small intestine are many -and varied. The acid chyme, with its admixture of semi-digested food -material, as it passes through the pyloric sphincter into the small -intestine, is at once brought into immediate contact with bile, -pancreatic juice, and intestinal juice, all of which are more or less -alkaline in reaction. As a result, the acidity of the gastric juice -is rapidly overcome, and the enzyme pepsin, which up to this point -could exert its characteristic digestive action, is quickly destroyed -by the accumulating alkaline salts. Pepsin digestion thus gives way -to trypsin digestion,--most effective in an alkaline medium,--and the -proteids of the food, already semi-digested by pepsin-acid, are further -transformed by trypsin; aided and abetted by another enzyme, known as -erepsin, secreted by the mucous membrane of the intestine. These two -enzymes are much more powerful agents than pepsin. It is true that they -begin work where pepsin left off, but most striking is the character -of the end-products which result from their combined action, since they -are small molecules and there is a surprising diversity of them. In -other words, while gastric digestion breaks down the proteid foodstuffs -into soluble bodies, such as proteoses and peptones closely related -to the original proteids, in pancreatic digestion as it takes place -in the intestine there is a profound breaking down, or disruption of -the proteid molecule into a row of comparatively simple nitrogenous -fragments, many of them crystalline bodies; such as leucin, tyrosin, -glutaminic acid, aspartic acid, arginin, lysin, histidin, etc., known -chemically as monoamino-acids and diamino-acids. We have no means -of knowing to how great an extent these more profound disruptive -changes of the proteid molecule take place in the intestine. Whether -practically all of the ingested proteid food is broken down into these -relatively simple compounds prior to absorption, or whether only a -small fraction suffers this change, cannot be definitely stated. - -A few years ago, the majority of physiologists held to the view that -in the digestion of proteid food all that was essential was its -conversion into soluble and diffusible forms which would permit of -ready absorption into the blood. The belief was prevalent that, since -the proteid of the food was destined to make good the proteid of the -blood and through the latter the proteids of the tissues, any change -beyond what was really necessary for absorption of the proteid would -be uneconomical and indeed wasteful. On the other hand, due weight -must be given to the fact that in trypsin digestion, proteid can be -quickly broken down into simple nitrogenous compounds, and that in the -enzyme erepsin, present in the mucous membrane of the intestine, we -have an additional ferment very efficient in bringing about cleavage -of proteoses and peptone into amino-acids. From these latter facts it -might be argued that, in the digestion of proteid foodstuffs by the -combined action of gastric and pancreatic juice in the alimentary -tract, a large proportion of the proteid is destined to undergo -complete conversion into amino-acids, and that from these fragments the -body, by a process of synthesis, can construct its own peculiar type of -proteid. - -This latter suggestion is worthy of a moment’s further consideration. -As is well known, every species of animal has its own particular -type of proteid, adapted to its particular needs. The proteids of -one species directly injected into the blood of another species are -incapable of serving as nutriment to the body, and frequently act as -poisons. Man in his wide choice of food consumes a great variety of -proteids, all different in some degree from the proteids of his own -tissues. Is it not possible, therefore, that it is the true function -of pancreatic and intestinal digestion to break down the different -proteids of the food completely into simple fragments, so that the body -can reconstruct after its own particular pattern the proteids essential -for its nourishment? Or, we can follow the suggestion contained in the -work of Abderhalden,[10] who finds that in the long continued digestion -of various proteids by pancreatic juice there results in addition to -the amino-acids a very resistant residue, non-proteid in nature, which -is termed polypeptid. In other words, Abderhalden believes that pepsin, -trypsin, and erepsin are not capable of bringing about a _complete_ -breaking down of proteids into amino-acids, but that there always -remains a nucleus of the proteid not strictly proteid in nature, though -related thereto,--polypeptid,--which may serve as a starting-point for -the synthesis or construction of new proteid molecules, the various -amino-acids being employed to finish out the structure and give the -particular character desired. This view, however, is rendered somewhat -untenable by the more recent experiments of Cohnheim,[11] who claims -that proteids can be _completely_ broken down by pepsin, trypsin, -and erepsin, and consequently polypeptids would hardly be available -for the synthesis of proteids. Moreover, Bergell and Lewin[12] have -ascertained that there is present in the liver an enzyme or ferment -which has the power of digesting or breaking down certain dipeptids -and polypeptids into amino-acids. Hence, it follows that if any -polypeptids are absorbed from the intestine, they would naturally be -carried to the liver, where further cleavage into fragments suitable -for synthetical processes might occur. In any event, there is good -ground for the belief that the more or less complete disruption of the -proteid molecule into small fragments renders possible a synthetical -construction of new proteid to meet the demands of the organism; a fact -of great importance in our conception of the possibilities connected -with this phase of proteid nutrition. - - [10] Emil Abderhalden: Abbau und Aufbau der Eiweisskörper im - thierischen Organismus. Zeitschr. f. physiologische Chemie, Band 44, - p. 27. - - [11] Otto Cohnheim: Zur Spaltung des Nahrungseiweisses im Darm. - Zeitschrift f. physiologische Chemie, Band 49, p. 64. - - [12] Bergell and Lewin: Zeitschrift für experimentelle Pathologie und - Therapie, Band 3, p. 425. - -Fatty foods undergo little or no chemical alteration until they reach -the small intestine. During their stay in the stomach they naturally -become liquid from the heat of the body, and there is more or less -liberation of fat from the digestive action of gastric juice on cell -walls, connective tissues, etc. Most food fat is in the form of -so-called neutral fat, which must undergo hydrolysis or saponification -before it can be absorbed and thus made available for the body. This -is accomplished by the enzyme lipase, or steapsin, of the pancreatic -juice, aided indirectly by the presence of bile. Under the influence -of this fat-splitting enzyme all neutral fats, whether animal or -vegetable, are broken apart, through hydrolysis, into glycerin and a -free fatty acid; the latter reacting in some measure with the sodium -carbonate of the pancreatic juice to form a sodium salt, or soluble -soap, while perhaps the larger part of the fatty acid is held in -solution by the bile present. Soap, free acid, and glycerin are then -absorbed from the intestine and are found again combined in the lymph -as neutral fat. In this way the fats of the food are rendered available -for the nourishment of the body. - -The next important chemical change taking place in the small intestine -is that induced by the amylopsin of the pancreatic juice, which, acting -in essentially the same manner as the ptyalin of saliva, converts -any unaltered starch into dextrins and sugar. The latter substance, -maltose, is exposed to the action of another enzyme contained in the -intestinal secretion termed maltase, which transforms it into dextrose, -a monosaccharide. - -In these ways the proteids, fats, and carbohydrates of the food are -gradually digested, so far as conditions will admit, digestion being -practically completed by the time the material reaches the ileocæcal -valve at the beginning of the large intestine. Throughout the length -of the small intestine absorption proceeds rapidly; water, salts, and -the products of digestion passing out from the intestine into the -circulating blood and lymph. At the ileocæcal valve, however, the -contents of the intestine are practically as fluid as at the beginning -of the small intestine, due to the fact that water is continually being -secreted into the intestine. In the large intestine, the contents -become less and less fluid through reabsorption of the water, and as -the propulsive movements of the circular and longitudinal muscle fibres -of the intestinal wall carry the material onward toward the rectum, -the last portions of available nutriment are absorbed. Finally, in -varying degree, certain putrefactive changes are observed in the large -intestine involving a breaking down of some residual proteid matter, -through the agency of micro-organisms almost invariably present, with -formation of such substances as indol, skatol, phenol, fatty acids, -etc. These processes, however, in health are held rigidly in check, -and count for little in fitting the food for absorption. Digestion, on -the other hand, extending as we have seen from the mouth cavity to the -ileocæcal valve, is the handmaiden of nutrition, preparing all three -classes of organic foodstuffs for their passage into the circulating -blood and lymph, and thus paving the way for their utilization by the -hungry tissue cells. - - - - -CHAPTER II - -ABSORPTION, ASSIMILATION, AND THE PROCESSES OF METABOLISM - - TOPICS: Physiological peculiarities in absorption. Chemical changes - in epithelial walls of intestine. Two pathways for absorbed - material. Function of the liver as a regulator of carbohydrate. - Absorption of proteid products. Assimilation of food products. - Anabolism. Katabolism. Metabolism. Processes of metabolism. Older - views regarding oxidation. Discoveries of Lavoisier. The views of - Liebig. Theory of luxus consumption. Oxidation in the body not simple - combustion. Oxygen not the _cause_ of the decompositions. Oxidation - not confined to any one place. Intracellular enzymes. Living cells - the guiding power in katabolism. Some intermediary products of tissue - metabolism. Chemical structure of different proteids. Decomposition - products of nucleoproteids. Relation to uric acid. Action of specific - intracellular enzymes. Creatin and creatinin. Relation to urea. - Proteid katabolism a series of progressive chemical decompositions. - Intracellular enzymes as the active agents. - - -Digestion being completed, and the available portion of the foodstuffs -thereby converted into forms suitable for absorption, the question -naturally arises, In what manner are these products transported -from the alimentary tract to the tissues and organs of the body? In -attempting to answer this question, we shall find many illustrations -of the precise and undeviating methods which prevail in the processes -of nutrition. For example, it would seem plausible to assume that the -different forms of sugar entering into man’s ordinary diet, all of -them being soluble, would be directly absorbed and at once utilized, -but such is far from being the case. Milk-sugar and cane-sugar, both -appearing in greater or less degree in our daily dietaries, if -introduced directly into the blood, are at once excreted through the -kidneys unchanged. The body cannot use them, and they are gotten rid -of as speedily as possible, much as if they were poisons. When taken -by way of the mouth, however, they are utilized, simply because in -the intestine two enzymes are present there, known as lactase and -invertase, which break each of the sugars apart into two smaller -molecules. In other words, milk-sugar and cane-sugar are disaccharides, -and if they are to be absorbed in forms capable of being made use -of by the body they must be split apart into simpler sugars, viz., -monosaccharides, such as dextrose, levulose, etc. The great bulk of the -carbohydrate food consumed by man is in the form of starch, and this, -as we have seen, is converted into maltose by the action of saliva and -pancreatic juice. Maltose, however, like cane-sugar, is a disaccharide, -and the body has no power to burn it or utilize it directly; but in the -intestine and elsewhere is an enzyme termed maltase, which breaks up -maltose into two molecules of the monosaccharide dextrose, and this the -body can use. Man frequently consumes starch to the extent of a pound a -day, and if utilized it must all undergo transformation into maltose, -and then into dextrose. There is no apparent reason why maltose should -not be absorbed and assimilated as readily as dextrose, but so urgent -is the necessity for this conversion into dextrose that in the blood -itself there is present maltase, to effect the transformation of any -maltose that may gain entrance there. We are here face to face with -a simple fact in nutrition. The body cannot utilize disaccharides -directly. Why it is so we cannot say, but the fact is a good -illustration of the principle that nothing can be taken for granted in -our study of nutrition. - -For years, physiologists assumed that the ordinary physical laws of -osmosis, imbibition, and diffusion were quite adequate to explain -the passage of digested food materials into the blood and lymph. -If a substance was soluble and diffusible, that was sufficient; it -would quite naturally be absorbed in harmony with its diffusion -velocity. This, however, is not wholly true, since experiment shows -that the rapidity of absorption of diffusible substances through -the wall of the intestine is by no means always proportional to the -diffusion velocity of the substance. The lining membrane of the -small intestine, where absorption mainly takes place, is not to be -compared to a dead parchment membrane. On the contrary, it is made -up of living protoplasmic cells; absorption is not a physical, but a -physiological, process, in which the living epithelium cells stand as -guardians of the portals, ready to challenge and, if need be, modify -the rate of passage. Osmosis and diffusion undoubtedly play some part -in absorption, but they alone are not sufficient to account for what -actually takes place in the absorption of digestion products, and other -substances from the living intestine. - -The primary products formed in the digestion of proteid foods--the -proteoses and peptones--afford another illustration of physiological -peculiarity in absorption. These bodies are readily soluble and -quite diffusible, yet they are never found to any extent in the -circulating blood and lymph during health. It is of course possible, -as has been previously suggested, that as soon as formed they undergo -transformation into simpler decomposition products in the small -intestine; but this is by no means certain. If proteoses and peptones -are injected directly into the blood, they cause a marked disturbance, -influencing at once blood-pressure, affecting the coagulability of -the blood, and in many other ways exhibiting a pronounced deleterious -action which at once indicates they are out of their normal -environment. They are not at home in the circulating blood, and the -latter medium gets rid of them as speedily as possible; they behave -like veritable poisons, and yet they are the primary products formed -in the digestion of all proteid foodstuffs. On the basis of all -physical laws governing diffusion they should be absorbed, and help to -renew the proteids of the blood and later the proteids of the tissues. -Yet, as we have said, they are not normally present in the blood or -lymph. Apparently, in the very act of absorption, as they pass through -the epithelial cells of the intestinal wall, before they gain entrance -to the blood stream, they undergo transformation into serum-albumin -and globulin, the characteristic blood proteids. The other alternative -is that, as previously mentioned, they are completely broken down -in the intestine into amino-acids, etc., and these simpler products -synthesized, as they pass through the intestinal wall toward the blood, -into serum-albumin and globulin. Certainly as yet, there is no evidence -that the amino-acids, as such, go through the epithelial cells of the -intestine; they are not found in the blood or lymph to any appreciable -extent, yet the proteids of the blood are reinforced in some manner by -the products of proteid digestion. Whichever view is correct, one thing -is perfectly obvious, viz., that in the act of absorption the products -resulting from the gastric and pancreatic digestion of proteid foods -are exposed to some influence, presumably in the epithelial cells of -the intestinal wall, by which there is a reconstruction of proteid. -Further, the proteid substances so formed are of the type peculiar to -the blood of that particular species of animal. The proteids of beef, -mutton, chicken, oatmeal, or bread go to make the proteids of human -blood. - -From these statements, it is obvious that what we term absorption is -something more than a simple diffusion of soluble substances from -the alimentary tract into the blood current. The process is much -more complex than appears on the surface, and our lack of definite -knowledge, in spite of numerous efforts to unravel the mystery, -merely strengthens the view that we are dealing here with an obscure -physiological problem, and not a simple physical one. Digestion induces -a splitting up of the food proteid into fragments, large or small, -while incidental to absorption there is apparently a reconstruction, -or synthesis, of proteid from the fragments so formed. The process -seems somewhat costly, physiologically speaking, yet when one considers -the variety of proteids consumed as food, it is easy to comprehend -how essential it is that in some manner, as in absorption, there be -opportunity for construction of the specific proteids of the blood and -lymph. - -We find an analogous process in the absorption of fats. As we have -seen, the fats of the food are broken apart in the small intestine into -glycerin and free fatty acid, a portion of the latter, and perhaps all, -combining with the alkali of the intestinal juices to form soluble -soaps, or sodium salts of the respective fatty acids. The neutral fats -present in animal and vegetable foods are all alike in containing -the glyceryl radicle, but they differ in the character of the fatty -acids present. Further, one form of animal fat, like that from beef, -may contain quite a different proportion of stearin, palmitin, and -olein than is present in the fat of another animal, like mutton. By -digestion, however, they are all broken apart into fatty acid and -glycerin. These acids and their salts can be readily detected in the -intestine, but they are not found in the blood or lymph, yet shortly -after fatty food is taken the lymph is seen to be milky from fat. -Obviously, the fatty acids liberated in the intestine are absorbed, -either as soluble soaps or as free fatty acids dissolved in bile, but -as they pass through the epithelial cells of the intestine into the -lacteal radicles, there is a synthesis or reconstruction of fat; and -as a result, neutral fats and not soaps are found in the lymph. Here, -then, we have a process quite analogous to what apparently occurs in -the absorption of proteid, though less complex; and it is possible that -this is one of the factors which aids in the formation of a specific -fat mixture corresponding, in a measure, to the type of fat present -in the particular species. It is well understood that the fat of an -animal’s tissues may be modified somewhat by the character of the -fat fed, yet in spite of this there is a certain degree of constancy -in composition which calls for explanation. Sheep and oxen feeding -in the same pasture have fat widely different in the proportion of -stearin, palmitin, etc. The fat of man’s tissues is fairly definite -in composition, yet he eats a great variety of fatty foods. One man -may consume large amounts of hard mutton fat with its relatively large -content of stearin, while another individual may take his fat mainly in -the form of the soft butter fats, with their relatively large content -of olein and palmitin. In both cases, the fat of the man’s tissues will -be essentially the same. To be sure, the changes that take place in the -tissue cells, reinforced by the construction of fat from other sources, -may be partly responsible for this constancy of composition, but the -transformations incidental to absorption are quite possibly, in some -measure, helpful thereto. - -The great bulk of the digested food material is absorbed from the small -intestine, and there are two pathways open through which the absorbed -material can gain access to the blood. The one path leads directly to -the liver, and substances taking this course are exposed to the action -of this organ, before they enter into the general circulation. The -other path is through the lacteal or lymphatic system, and constitutes -a roundabout way for substances to enter the blood stream, since -they must first pass through the thoracic duct before entering the -main circulation. As a general truth, it may be stated that fats are -absorbed through the latter channel, while carbohydrates and proteids -follow the first path. The innumerable blood capillaries in the villi -of the intestine take up the products resulting from the digestion -of proteids and carbohydrates, through which they are passed into -the portal vein, and thereby distributed throughout the liver. This -means that both carbohydrates and proteids--or their decomposition -products--are exposed to a variety of possible changes in this large -glandular organ, before they can enter into the tissues of the body. -As we have seen, practically all carbohydrate food is converted into -a monosaccharide, principally dextrose, in the alimentary tract; and -it is in this form of a simple sugar that the carbohydrate passes into -the blood. This might easily mean a pound of sugar absorbed during -the twenty-four hours, and would obviously give to the blood a high -degree of concentration, unless the excess was quickly disposed of. -Sugar is very diffusible, and if it accumulates to any extent in the -blood it is quickly gotten rid of by excretion through the kidneys. -This, however, is wasteful, physiologically and otherwise, and does not -ordinarily occur except in diseased conditions. Further, physiologists -have learned that a certain small, but definite, amount of sugar in the -blood is a necessary requirement in nutrition, and it is the function -of the liver to maintain the proper carbohydrate level. - -We must again emphasize the great importance of carbohydrate food; -there is a far larger amount of starchy food consumed than of any -other foodstuff, and it is more readily available as a source of -energy. Its presence in the blood, in the form of sugar, is constantly -demanded, but it must be kept within the proper limits for the uses -of the different tissues and organs of the body. The liver serves as -an effective regulator, maintaining, in spite of all fluctuations -in the supply and demand, a definite percentage of sugar such as is -best adapted to keep the tissues of the body in a normal and healthy -condition. This regulation by the liver is rendered possible through -the ability of the hepatic cells to transform the sugar brought to -the gland into glycogen, so-called animal starch, which is stored -up in the liver until such time as it is needed by the body. The -process is one of dehydration, the reverse of what takes place in the -intestine when ordinary starch is converted into maltose and dextrose. -The efficiency of this regulating mechanism depends also upon the -ability of the liver to transform glycogen into sugar, presumably -through the agency of an enzyme in the hepatic cells. Hence, glycogen -may be looked upon as a temporary reserve supply of carbohydrate, -manufactured and stored in the liver during digestion, when naturally -large amounts of sugar are passing into the portal blood, and to be -drawn upon whenever from any cause the content of sugar in the blood -threatens to fall below normal. Obviously, there must be some delicate -machinery for the adjustment of these opposite changes in the liver, -and we may well believe that it is associated with the composition -of the blood itself, which in some fashion stimulates and inhibits, -as may be required, the functional activity of the liver, or its -component cells. In any event, we have in this so-called glycogenic -function of the liver a most effective means for accomplishing the -complete and judicious utilization of all the sugar formed from the -carbohydrates of the food, after it has once passed beyond the confines -of the alimentary tract into the blood; preventing all loss, and at -the same time guarding against all danger, from undue accumulation -of sugar in the circulation. We see, too, how wise the provision -that all sugar should pass from the alimentary canal into the portal -circulation and not by way of the lymphatics, since by the latter -channel the regulating action of the liver would be mainly lost. -Further, recalling how soluble and diffusible sugar is, we may well -marvel that it practically all passes from the intestine by way of -the blood, and escapes entry into the lymphatics. Surely, this marked -shunning of the other equally accessible pathway affords a striking -illustration of selective action such as might be expected in a -physiological process, but not in harmony with the ordinary physical -laws of osmosis or diffusion. In conformity with this statement, it may -be mentioned that appropriate experiments have clearly demonstrated -that the different sugars available as food are not absorbed from the -intestine in harmony with their diffusion velocity, but show deviations -therefrom which can be explained only on the ground that the intestinal -wall exercises some selective action, due to the living cells composing -it. Likewise interesting in their bearing on nutrition are the -observations of Hofmeister,[13] who finds by experiments on dogs that -the assimilation limit of the different sugars shows marked variation. -Thus, dextrose, levulose, and cane-sugar have the highest assimilation, -while milk-sugar is far less easily and completely assimilated. If this -is equally true of man, it indicates that starchy foods, with their -ultimate conversion into dextrose, are to be ranked as having a high -assimilation limit, thus affording additional evidence of their high -nutritive value. - - [13] Franz Hofmeister: Ueber Resorption und Assimilation der - Nährstoffe. Archiv f. d. exper. Pathol. u. Pharm., Band 25, p. 240. - -In the absorption of proteid products, their passage from the intestine -by way of the portal circulation insures exposure to the action of the -hepatic cells, before they are distributed by the general circulation -throughout the body. It is only under conditions of an excessive -intake of proteid foods that their products are absorbed by way of the -lymphatics. These points are clearly established, and there is every -ground for believing that substantial reasons exist to account for -this single line of departure. Just what the liver does, however, is -uncertain. In fact, as already indicated, there is lack of definite -knowledge as to how far the proteid foods are broken down in digestion, -prior to absorption. The combined action of pepsin, trypsin, and -erepsin, if sufficiently long continued, can accomplish a complete -disruption of the proteid molecule. We are inclined to assume in a -general way that the “proteids taken as food cannot find a place in -the economy of the animal body till they have been, as it were, melted -down and recast.”[14] How far this melting down or disruption extends -in normal digestion, we do not at present know. As already stated, -neither proteoses and peptones, nor the amino-acids, are found in -the blood stream in sufficient amounts, or with that frequency, to -suggest absorption in these forms. Possibly, as some physiologists have -suggested, the amount of any of these products to be found at any one -time in a given quantity of blood is too small for certain recognition, -yet in the twenty-four hours the amount passing from intestine to -liver might be sufficiently large to equal the total proteid absorbed. -We can, however, at present only conjecture, and must rest content -with the simple statement that in the digestion of the proteid -foodstuffs, proteoses, peptones, and amino-acids are formed, and that -by transformation or total reconstruction of these products, special -types of proteid are manufactured either in the epithelial cells of -the intestinal walls during absorption, or elsewhere in the body after -absorption. If this latter is the case, the liver might readily be -regarded as a likely spot for the synthesis to occur. - - [14] J. B. Leathes: Problems in Animal Metabolism. Blakiston’s Son - and Co., 1906, p. 123. - -Bearing in mind what has been said regarding the production of specific -types of proteid by every species of animal, we can the more readily -conceive of a synthesis “out of fragments of the original molecules -rearranged and put together in new combinations, by processes in -which the intestine can hardly be supposed to play a part.” This, -the liver might well be assumed as capable of accomplishing, and if -we were disposed to accept this view we might use as an argument the -fact that the products of proteid digestion are taken directly to -this organ, before being cast loose in the tissues and organs of the -body. There is perhaps as good ground for assuming that a synthesis -or reconstruction of proteid takes place all over the body; that, as -suggested by Leathes, “the synthesis of proteids is a function of every -cell in the body, each one for itself, and that the material out of -which all proteids in the body are made is not proteid in any form, -but the fragments derived from proteids by hydrolysis, probably the -amido-acids, which in different combinations and different proportions -are found in all proteids, and into which they are all resolved by the -processes, autolytic or digestive, which can be carried out in every -cell in the body.” It is certainly a reasonable hypothesis, and since -we lack positive knowledge it cannot at present be disproved. All that -we can affirm in the light of established fact is that the products of -proteid digestion are absorbed from the intestine by way of the portal -circulation, and that either in their passage through the intestinal -wall, or later on in the liver or elsewhere, there is a construction of -new proteid to meet the wants of the body. The liver, indeed, may be -effective in both construction and destruction of proteid, but there is -no way of telling at present just how far it acts in either direction. - -Regarding the absorption of fats, a single statement will suffice, in -addition to what has already been said. Fats gain access to the general -circulation by passing from the intestine into the lacteal radicles, -thence into the lymphatics, whence they move onward into the thoracic -duct, and from there are emptied into the great veins at the neck. A -small amount is apparently absorbed in the form of soap by the portal -circulation, but by far the larger amount of fat gains access to the -blood stream without going through the liver. - - * * * * * - -In these ways, the blood and lymph are continually supplied with -proteid, fat, and carbohydrate from the ingested food, and as these -fluids surround and permeate the organized elements of the tissues, the -latter are enabled to gain what they need to maintain their nutritive -balance. Living matter is essentially unstable; it is the seat of -chemical changes of various kinds, anabolic or constructive, and -katabolic or destructive. The more comprehensive term “metabolic” is -applied to all of these changes that take place in living matter. In -anabolism, the dead, inert proteids, fats, and carbohydrates are more -or less assimilated and made a part of the living matter of the tissue -cells, while at the same time a certain amount of the food material, -probably the larger amount, is simply stored as such, or left to -circulate in the blood and lymph, without being raised to the higher -level of living protoplasm. In katabolism, this accumulated material, -and in some degree the living substance itself, is broken down or -disintegrated with liberation of the stored-up energy, which manifests -itself in the form of heat and mechanical work. At times, the anabolic -processes predominate and there is a relatively large accumulation -of stored-up materials; while at other times, katabolism, with its -attendant chemical decompositions, predominates, and the body loses -correspondingly. The point to be emphasized here is that the living -body, with its multitude of living cells, is the seat of incessant -change. Construction and destruction are continually going forward -side by side; sometimes the one and sometimes the other predominating, -according to existing conditions. The living protoplasm with its -attendant storage material is, under ordinary conditions, constantly -being made good from the assimilated food, a part of which is raised to -the dignity of living matter and becomes an integral part of the living -cells, while the larger portion is simply stored for future uses, or -circulates in the blood and lymph which bathe them. Doubtless, this -storage or circulating material is the main source of the energy which -constantly flows from the cells in the form of heat and of work, as a -result of the disruptive changes that constitute katabolism. - -Worthy of special notice is the fact that cell protoplasm is -essentially proteid in nature; water and proteid make up the larger -part of its substance, to which are added small proportions of -carbohydrate, fat, and mineral matter. Proteid is the basis of cell -protoplasm; it is the chemical nucleus of living matter, and owing to -the large size of its molecule, with its large number of contained -atoms, is capable of many combinations and many alterations. Most of -the reactions characteristic of katabolism centre around this proteid, -but the disruptive changes that occur undoubtedly involve more largely -the circulating materials present in the blood and lymph, and which -bathe the cells, rather than the so-called fixed, or organ proteid, of -the cell substance itself. Still, while the circulating blood and lymph -furnish largely the substances which are made to undergo disintegration -in katabolism, the living protoplasmic cell is the controlling power -which regulates the extent and character of the decompositions, -and proteid matter is the chemical basis of protoplasm. From these -statements, we again have suggested the significant importance of the -proteid foods in nutrition, since they alone can furnish the material -which constitutes the chemical basis of living cells. The human body, -which represents the highest form of animal life, is merely, as stated -by another, “literally a nation of cells derived from a single cell -called the ovum, living together, but dividing the work, transformed -variously into tissues and organs, and variously surrounded by -protoplasm products” (Waller). - -The processes involved in metabolism are not easily unravelled. The -word itself is simple, but it is employed to designate that complex of -“chemical changes in living organisms which constitute their life, the -changes by which their food is assimilated and becomes part of them, -the changes which it undergoes while it shares their life, and finally -those by which it is returned to the condition of inanimate matter. -Gathered together under this one phrase are some of the most intricate -and inaccessible of natural phenomena. It implies also, and gently -insists on the idea, that all the phenomena of life are at bottom -chemical reactions” (Leathes). Regarding the processes of anabolism, as -in the construction of living protoplasm out of inert food materials, -we can say nothing. This is altogether beyond our ken at present, and -doubtless will remain so, since it involves a chemical alteration, or -change, akin to that of bringing the dead to life. With the processes -of katabolism, however, we may hope for more satisfactory results; and, -indeed, to-day we have considerable information of value as to some of -the methods, at least, which are the cause of this phase of nutrition. -This knowledge, however, has been slow of attainment. - -In the earlier years of the sixteenth century, when anatomy and -physiology were beginning to make progress, the savants of that day, -hampered as they were by grave misconceptions and by the lack of -any understanding of chemical phenomena, could not take advantage, -naturally, of the suggestion that as wood burns or oxidizes in the air -with liberation of heat, so might the food substances, absorbed by the -body, undergo oxidation in the tissues and thus give rise to animal -heat. Such suggestions were at that time as a closed book, and so we -find Vesalius, in 1543, teaching the Galenic doctrines in physiology -then prevalent. The conception of heat production, as it existed at -that time, may be inferred from the following quotation:[15] “The parts -of the food absorbed from the alimentary canal are carried by the -portal blood to the liver, and by the influence of that great organ -are converted into blood. The blood thus enriched by the food is by -the same great organ endued with the nutritive properties summed up -in the phrase ‘natural spirits.’ But blood thus endowed with natural -spirits is still crude blood, unfitted for the higher purposes of the -blood in the body. Carried from the liver by the vena cava to the right -side of the heart, some of it passes from the right ventricle through -innumerable invisible pores in the septum to the left ventricle. As the -heart expands it draws from the lungs through the vein-like artery air -into the left ventricle. And in that left cavity, the blood which has -come through the septum is mixed with the air thus drawn in, and by the -help of that heat, which is innate in the heart, which was placed there -as the source of the heat of the body by God in the beginning of life, -and which remains there until death, is imbued with further qualities, -is laden with ‘vital spirits,’ and so fitted for its higher duties. The -air thus drawn into the left heart by the pulmonary vein, at the same -time tempers the innate heat of the heart and prevents it from becoming -excessive.” In other words, heat was considered as a divine gift, and -as can readily be seen, there was an utter lack of appreciation of the -use of air in breathing. Even van Helmont, who lived in 1577–1644, and -was in a sense an alchemist, still gave credence to the spirits, viz., -that the food absorbed from the stomach and intestine is in the liver -endued with natural spirits, while in the heart the natural spirits -are converted into vital spirits, and in the brain the vital spirits -are transformed into animal spirits.[16] Later, Malpighi discovered -the true structure of the lungs, and Borelli, in 1680, exposed the -erroneous views then prevalent regarding the purpose of breathing. -It is not true, says Borelli, that the use of breathing is to cool -the excessive heat of the heart or to ventilate the vital flame, but -we must believe that this great machinery of the lungs, with their -accompanying blood vessels, is for some grand purpose. In a long and -vigorous argument, he contends that the “air taken in by breathing is -the chief cause of the life of animals, far more essential than the -working of the heart and the circulation of the blood.” He quotes the -experiments of Boyle, who showed in 1660 “that even in a partial vacuum -brought about by his air pump, flame was extinguished and life soon -came to an end; the candle went out and the mouse or the sparrow died.” - - [15] Taken from Sir Michael Foster’s “Lectures on the History - of Physiology during the Sixteenth, Seventeenth, and Eighteenth - Centuries.” Cambridge, 1901, p. 12. - - [16] See Foster’s Lectures, p. 136. - -At this time, and for long afterwards, the belief was prevalent -that the air taken up by the blood in the lungs was the air of the -atmosphere in its entirety. No one appears to have thought of the -possibility of only a part of the air being used, for at that time -there was no suspicion that air was a mixture of substances. Mayow, -however, in 1668, showed that it was not the whole air which was -employed for respiration, but a particular part only. At this time, -great attention was being given to a study of nitre or saltpetre; its -wonderful properties in combustion were being recognized, and Mayow, -who was a chemist of repute, claimed that it had its origin partly -in the air and partly in the earth. The air “which surrounds us, and -which, since by its tenuity escapes the sharpness of our eyes, seems -to those who think about it to be an empty space, is impregnated -with a certain universal salt, of a nitro-saline nature, that is to -say, with a vital, fiery, and in the highest degree fermentative -spirit,” to which the name of “igneo-aereus” was applied. Nitre was -shown to be composed of a _sal fixum_ or sal alkali,--potash as it -is now called,--and was obviously derived from the earth, while the -other part of nitre was made up of the _spiritus acidus_, or nitric -acid. For a time it was supposed that the whole of this _spiritus -acidus_ was contained in the atmosphere, but it was soon recognized -that this could not be the case, since nitric acid was found to be a -corrosive liquid, destructive to life and quite incapable of supporting -combustion. Hence, Mayow concluded that only a part of the acid -exists in the atmosphere, viz., that part which he termed _spiritus -nitro-aereus_. In combustion, there is something in the air which is -necessary for the burning of every flame, unless perchance igneo-aereal -particles should pre-exist in the thing to be burnt. These igneo-aereal -particles form “the more active and subtle part of air which is thus -necessary for combustion, exist in nitre and indeed constitute its -‘more active and fiery part.’” Mayow fully recognized that burning -and breathing involved in a measure the same process; both consisted -in the consumption of the igneo-aereal particles present in the air. -“If a small animal and a lighted candle be shut up in the same vessel, -the entrance into which of air from without be prevented, you will see -in a short time the candle go out, nor will the animal long survive -its funeral torch. Indeed, [says Mayow] I have found by observation -that an animal shut up in a flask together with a candle will continue -to breathe for not much more than half the time than it otherwise -would, that is, without the candle.” Something contained in the air, -necessary alike for supporting combustion and for sustaining life, -passes from the air into the blood. Mayow expressed his thoughts in -these words: “And indeed it is very probable that certain particles -of a nitro-saline nature, and those very subtle, nimble, and of very -great fermentative power, are separated from the air by the aid of the -lungs and introduced into the mass of the blood. And so necessary for -life of every kind is that aereal salt (constituent) that not even -plants can grow in earth the access of air to which is shut off. But -if that same earth be exposed to air and so forthwith impregnated with -that fecundating salt, it at once becomes fit again for growing.”[17] -Mayow fully appreciated the importance of his nitro-aereal particles in -the processes of life; he had indeed a fairly accurate conception of a -sound theory of animal heat; he saw that they were equally necessary -for burning, or combustion, and for respiration, and so was enabled to -draw a parallelism between the two processes; he pointed out that they -were essential for the ordinary activity of the muscles of the body, -that as muscle work was increased more particles from the air were -required; indeed, he clearly foresaw the need which the body had for -these igneo-aereal particles in all the chemical processes of life. And -thus was foreshadowed a conception of oxidation, a hundred years before -Priestley evolved his phlogiston theories and Lavoisier discovered -oxygen. - - [17] Quoted from Foster’s Lectures, p. 195. - -The discoveries of Lavoisier, published in 1789, led to a clear -understanding of combustion as a process of oxidation, and paved the -way for a fuller knowledge of the part played by the oxygen of the -air in the chemical reactions going on in the animal body. Lavoisier -showed that the oxygen drawn into the lungs with the air breathed was -used in the body for the oxidation of certain substances, carbon being -transformed thereby into carbon dioxide, and hydrogen into water. -Further, he noted that these oxidations were carried forward on a -large scale, and he emphasized the importance of oxygen as being the -true cause of the varied decompositions taking place in the living -body. The larger the amount of oxygen inspired, the more extensive -the oxidation, and consequently the rate of respiration as modifying -the intake of oxygen served in his opinion as a regulator to control -the extent of the oxidative processes. He pointed out that a definite -relationship existed between the amount of work done by the body and -the oxygen consumed; greater muscular activity, lower temperature of -the surrounding air, the activities attending the digestive functions, -all seemed to be associated with a greater utilization of oxygen. -Oxidation was the pivot around which all the chemical reactions of the -body seemed to centre. Lavoisier, however, was not a physiologist, and -he was, quite naturally perhaps, led into some errors. For example, -he considered that the process of combustion or oxidation took place -in the lungs, certain fluids rich in carbon and hydrogen formed in -the different organs of the body being brought there for exposure to -the inspired oxygen. Further, his views implied a simple and complete -combustion, in which complex substances rich in carbon were directly -and completely oxidized to carbon dioxide and water, in much the same -manner as combustion occurs outside the body. Again, he assumed that -the amount of oxygen taken into the lungs determined the extent of -oxidation, just as the use of the bellows, by increasing the draft of -air, causes the fire to burn more brightly. - -To Liebig (1842) the next great advance was due. This phenomenally -clear-minded man, while recognizing at their full value the fundamental -theories advanced by Lavoisier, saw and fully appreciated their -incompleteness, and he likewise understood their failure to explain -many of the phenomena of life more familiar to the physiological mind -than to that of a simple chemist like Lavoisier. Liebig had made a -special study of the chemical composition of foodstuffs, and likewise -of the tissues and organs of the body. He had, moreover, given great -attention to the decomposition products formed in the body, especially -the nitrogenous substances excreted through the kidneys, as well as the -carbon dioxide and water passed out through the lungs and skin. It was -not strange, therefore, that he should take exception to Lavoisier’s -view that oxidation in the body consisted in the combustion of a -fluid, rich in carbon and hydrogen, which was brought to the lungs. -On the contrary, Liebig contended that it was the organic compounds, -proteids, fats, and carbohydrates, that underwent oxidation, and not -necessarily in the lungs, but all over the body, wherever organs and -tissues were active. Especially noteworthy was the view advanced by -Liebig, and upheld for many years, that of these three classes of -compounds the proteids alone served for the construction of organized -tissues, like muscle, and that in the activity of this tissue, as -in muscle contraction or muscle work, the energy for the work was -derived solely from the breaking down or oxidation of this organized -proteid. On this ground he termed the proteid foodstuffs “plastic,” or -tissue-building foods. Liebig further pointed out that the substances -of the body have the power of combining with and holding on to the -inspired oxygen, and that fats and carbohydrates, _i. e._, the -non-nitrogenous compounds, easily undergo oxidation or combustion, and -thereby furnish the heat of the body. For this reason he termed the -corresponding foodstuffs “respiratory” foods. Proteids, on the other -hand, according to Liebig’s view, are capable of combustion only in -slight degree. The cause of the decomposition of proteid substances in -the body was to be traced solely to muscle work, _i. e._, the energy -of muscle contraction, or muscle work, was derived from the breaking -down of the proteids of the muscle tissue, and work was the stimulus -which brought about proteid decomposition. Non-nitrogenous substances -played no part in these reactions; muscle work was without influence -on these compounds, oxygen being the sole stimulus which led to their -combustion, and heat was the sole product of the combustion. - -If Liebig’s theory is correct, that the proteids of the body are -decomposed only as the result or the accompaniment of muscle work, and -the proteids of the food are used up only as they take the place of the -organized proteid so metabolized, it follows that with a like degree of -muscular activity a given body will always decompose the same amount -of proteid. If excess of proteid food is taken, the surplus will be -stored in the tissues, or, in other words, the excretion of nitrogen -will not be influenced by the amount of proteid consumed in the food. -This was the line of argument made use of by various physiologists[18] -who were disposed to criticise Liebig’s view, and quite naturally the -question was soon made the subject of many experiments. It will suffice -here merely to say that many concordant results were obtained, showing -that an abundance of proteid food leads to an increase in the excretion -of nitrogen, muscle activity remaining at a constant level. Hence, as -Voit states, some other ground than muscle work must be sought as the -true cause of proteid katabolism. Consequently, we find this hypothesis -of Liebig replaced by the theory of “luxus consumption,” in which it -is maintained that while whatever proteid is used up by the work of -the muscle must be made good from the proteid of the food, any excess -of proteid absorbed from the intestinal canal is to be considered as -“luxus,” and like the non-nitrogenous foods may be burned up in the -blood, by the oxygen therein, without being previously organized. -Hence, we see suggested two causes for the decomposition of proteid in -the body, viz., the work of the muscle and the oxygen of the blood. -Further, as stated by C. Voit,[19] the nitrogen excretion of the hungry -or fasting animal affords, according to these views, a measure of the -extent to which tissue proteid must be broken down in the maintenance -of life, and of the amount of proteid food necessary to be consumed in -order to make good the loss; viz., the minimum proteid requirement. -Again, since any excess of proteid food beyond this minimal -requirement, according to the theory, is destined to be burned up in -the blood, or elsewhere, to furnish heat the same as non-nitrogenous -foods, it follows that the excess of proteid food can be replaced by -non-nitrogenous aliment. - - [18] See C. Voit: Hermann’s Handbuch der physiologie des - Gesammt-Stoffwechsels. Band 6, Theil 1, p. 269, 1881. - - [19] Loc. cit., p. 270. - -Oxidation, however, is the keynote in any explanation of the processes -of metabolism, whether nitrogenous or non-nitrogenous matter is -involved. Both alike undergo oxidation, but it is not simple oxidation -or combustion that we have to deal with. In the time of Lavoisier, as -already stated, it was thought that oxygen alone was the cause of the -decomposition going on in the body, but simply increasing the intake -of air or oxygen, as in quickened breathing or deeper inspiration, -does not increase correspondingly the rate of oxidation. In other -words, it is not a direct combination of oxygen with the carbon and -hydrogen of the foodstuffs, or tissue elements, that takes place in -the body, but rather a gradual, progressive decomposition of complex -organic compounds into simpler products; made possible, however, by the -agency of the oxygen carried from the lungs by the circulating blood. -It was demonstrated years ago that animals breathing pure oxygen do -not consume any more of the gas than when breathing ordinary air, and -likewise no more carbon dioxide is produced in the one case than in -the other. Fifty years ago, Liebig and other physiologists showed that -frogs’ muscle placed in an atmosphere free of oxygen could be made to -contract or do work for some considerable time, and with liberation -of heat. This fact implies a breaking down of muscle substance into -simpler bodies, but there is here no free oxygen to act as the inciting -cause; indeed, what actually occurs is a cleavage or splitting up -of substances in the muscle tissue, but at the expense of oxygen in -some form of combination in the muscle. This oxygen must have been -taken from the blood at some previous time and stored in the tissue -for future use. Again, as C. Voit has expressed it, if oxygen were -really the immediate cause of the decompositions taking place in the -organism, we should expect combustion to occur in harmony with the -well-known relationship of the three classes of organic foodstuffs to -oxygen. In other words, fats would undergo combustion most readily, -carbohydrates next, and lastly the nitrogenous or albuminous compounds. -In reality, however, proteid matter is decomposed in largest quantity; -a generous addition of proteid food is always accompanied by an -increased consumption of oxygen. Yet oxygen is not the inciting cause -of the proteid decomposition, as is seen from the fact that in muscle -work, where the intake of oxygen is greatly increased, there is no -noticeable change in the amount of proteid material broken down. -Plainly, in the body we have to deal not with a direct oxidation of -the complex compounds of the tissues or of the food, but rather with -a gradual cleavage of these higher compounds into simpler substances, -these latter undergoing progressively a still further breaking down -with intake of oxygen. To repeat, oxygen is not the _cause_ of the -decompositions within the body, but the extent of the breaking down of -the tissue or food material is the determining factor in the amount -of oxygen taken on and used up. The products of decomposition contain -more oxygen than the original substances undergoing the breaking down -process, which means that oxygen is taken from the blood and used in -the physiological combustion that is going on. It is not, however, -strictly a combustion process; it is more complicated and more gradual -than ordinary combustion, involving first of all a series of what may -be termed oxidative cleavages, in which large molecules are gradually, -step by step, broken down into simpler molecules, and these latter then -oxidized to still simpler forms. Hence, we find the oxidative changes -preceded by a variety of alterations in which oxygen may take no part -whatever; such as hydrolytic cleavage, where the elements of water are -taken on as a necessary step in the cleavage process; dissociation of -a simple sort, as when a large molecule breaks up directly into smaller -molecules, etc. - -These statements by no means detract from the importance of oxygen in -the katabolic processes of the body, but it is physiological oxidation -that we have to do with, and not simple combustion. Oxygen is not the -direct cause of the transformations taking place in the body. As one -looks over the history of progress in our knowledge of nutrition from -the time of Lavoisier to the present, it is easy to note the gradual -change of view regarding oxidation in the living organism. Step by -step, it has been demonstrated that there are many factors involved in -this breaking down of complex substances; that while oxygen is an ever -present requirement, there are other equally important factors to be -taken into account. The contrast between the older views and those now -current is clearly shown by the difference in attitude regarding the -_place_ in the body where oxidation occurs. Thus, in the earlier days, -when the view was gradually gaining ground that nutritional changes -were mainly the result of oxidation, and that the oxygen drawn into the -lungs in inspiration was a primary factor, then, as we have seen, the -lungs were considered as the laboratory where the transformation takes -place. This view, however, was soon exploded, and next we find the -blood, the lymph, and other fluids, but especially the blood, looked on -as the locality where oxidation occurs. This was indeed quite a natural -view to hold, since the blood is the carrier of oxygen, but we now -know, in harmony with the fact that the breaking down of complex food -material is a complicated process, involving various kinds of chemical -change, that these katabolic processes are not located in any one -place, but occur all over the body wherever there are active tissues. -As has been previously stated, the human body is a “nation” of cells, -all of which are more or less active, and it is in these miniature -laboratories mainly that oxidation and all the other nutritional -changes coincident to life take place. Muscle tissue and nerve tissue, -the large secreting glands, such as the liver, stomach, and pancreas, -all are the seat of oxidative and other changes which we class under -the broad term of nutritional. To these cells, therefore, we must -look for an explanation of the causes of oxidation, and the other -transformations of a kindred nature that take place in the body. - -In our brief survey of digestion, and of the methods there followed -for the proper utilization of the organic foodstuffs, it was seen -that the unorganized ferments or enzymes are the active agents in -accomplishing the breaking down of proteids, and the less profound -alteration of fats and carbohydrates. Is it not possible that the -tissues of the body are likewise supplied with enzymes of various -types, and that upon these powerful agents rests the responsibility -for the different kinds of decomposition, oxidation and other changes, -that take place in the body? Some years ago much interest was aroused -by the observation that certain glands in the body, if simply warmed -at body temperature with water, in the presence of some germicidal -agent sufficient to prevent putrefactive changes, underwent what is -now termed autodigestion, _i. e._, a process of self-digestion, with -formation of various products, notably such as would naturally result -from the breaking down of proteid material by ordinary proteolytic -enzymes. This would seem to imply the presence in the glands of -a proteid-splitting enzyme, the products formed being proteoses, -peptones, amino-acids, etc., just such products as result from the -action of trypsin. To-day, we know that practically all tissues and -organs can, under suitable conditions, undergo autolysis, and in many -instances the enzymes themselves can be separated from the tissues by -appropriate treatment. Liver, muscle, lymph glands, spleen, kidneys, -lungs, thymus, etc., all contain what are very appropriately called -intracellular enzymes. These enzymes are of various kinds. Especially -conspicuous are the hydrolytic, proteid-splitting enzymes, which -behave in a manner quite similar to, if not identical with, that of -the digestive enzymes of the gastro-intestinal tract, _i. e._, pepsin, -trypsin, and erepsin. Further, there are other hydrolytic cleavages -taking place in tissue cells, such as the cleavage of fats, due as we -now know to intracellular enzymes of the lipase type, and by which -neutral fats are split apart into glycerin and fatty acid. Again, there -are in many organs intracellular enzymes which act upon the complex -nucleoproteids of the tissue, causing them to break apart into proteid -and nucleic acid, the latter being further broken down by other enzymes -with liberation of the contained nuclein or purin bases. Many other -chemical reactions are brought about by specific enzymes of various -kinds, present in the cells of particular glandular organs. Thus, -intracellular enzymes have been found, as in the liver, which are able -to transform amino-acids into amides, and still others capable of -splitting up amides. - -Equally important, and even more suggestive, are the data which have -been collected recently regarding oxidative processes in the tissues -of the body. Specific ferments, known as oxidases, are found widely -distributed in many organs and tissues, and it is difficult to escape -the conclusion that as intracellular enzymes they have an important -part to play in some, at least, of the transformations characteristic -of tissue katabolism.[20] As a single example, mention may be made of -aldehydase, which accomplishes the oxidation of substances having the -structure of aldehydes into corresponding acids. Ferments or enzymes -of this class are found in the liver, spleen, salivary glands, lungs, -brain, kidneys, etc., and they may well be considered as important -agents in the chemical transformations going on in the tissues of -the body. It would take us too far afield to enter into a detailed -consideration of these intracellular enzymes; it must suffice to -emphasize the general fact that in all the tissues and organs of the -body there are present a large number of enzymes of different types, -endowed with different lines of activity, and consequently capable -of accomplishing a great variety of results in metabolism. Oxidation -may still be a dominant feature in nutrition, oxidative changes may -characterize more or less every tissue and organ in the body, but the -processes are subtle and are not to be defined in harmony with simple -chemical or physical laws. The living cell, with its intracellular -enzymes, is the guiding and controlling power by which the processes of -katabolism are regulated in harmony with the needs of the body. Complex -organic matter is broken down step by step in the various tissues, with -gradual liberation of the contained energy; processes of hydrolytic -cleavage alternate with processes of oxidation, the molecules acted -upon growing smaller with each downward step, until at last the final -end-products are reached, viz., carbon dioxide, water, and urea, which -the body eliminates through various channels as true physiological -waste-products. - - [20] See M. Jacoby: Ueber die Bedeutung der intracellulären Fermente - für die Physiologie und Pathologie. Ergebnisse der Physiologie, - Erster Jahrgang, 1. Abtheilung, p. 230. - -It will be advisable for us to consider briefly some of these -intermediary products of tissue metabolism, since in any discussion -of nutritive changes it is quite essential to have some understanding -of the chemical relationship existing between the various products -which result from the breaking down of proteid and other materials in -tissue katabolism. This is especially true of proteid material, since -in the gradual disintegration of this substance in tissue metabolism -many intermediary bodies are formed, which undoubtedly exercise some -physiological influence prior to their transformation into simpler -bodies, with ultimate formation of the final product, urea. As has -been pointed out so many times, the proteid foods are peculiar in that -they alone contain the necessary nitrogen, and in the peculiar form -able to meet the physiological requirements of the body. Variations in -the proteid intake are of necessity accompanied by variations in the -formation of nitrogenous intermediary products, and both quality and -quantity of these substances must be given due attention in any study -of nutrition. Further, it is only by an understanding of the general -or ground structure of proteids that we can hope to attain knowledge -of the processes going on in the different tissues and organs in -connection with metabolism, while a true appreciation of the chemical -peculiarities of the individual proteids will help to explain the -different nutritional value of vegetable as contrasted with animal -proteids. - -Our understanding of the chemical structure of any organic substance -is based primarily upon a study of the decomposition products which -result from its breaking down, under the influence of various chemical -agencies. Simple proteid substances when acted upon by pancreatic -juice reinforced by the enzyme erepsin, or when boiled with dilute -acids, undergo hydrolytic cleavage with ultimate formation of a large -number of relatively simple bodies, mostly amino-acids, the chemical -structure of which throws some light upon the nature of the proteid. -Thus, in the pancreatic digestion of proteid in the intestine we may -adopt the following scheme as showing in a general way the progressive -transformation that occurs, understanding at the same time that like -transformations may be accomplished by corresponding intracellular -enzymes in the tissues and organs of the body; and further, that by the -long-continued action of hydrolytic agents there is a complete breaking -down into amino-acids and other simple products. - - Native Proteid - /\ - / \ - / \ - Protoproteose Heteroproteose : Primary proteoses - | | - Deuteroproteose Deuteroproteose : Secondary proteoses - | | - Peptone Peptone - | | - Amino-acids Amino-acids - -Among these end-products, or amino-acids, are leucin, tyrosin, aspartic -acid, glutaminic acid, glycocoll, arginin, lysin, histidin, and -likewise the peculiar aromatic body tryptophan. The chemical make-up -of these substances may be indicated by the following structural -formulæ, which, if even only partially understood, will suggest to the -non-chemical mind some idea of close chemical relationship: - - CH(NH_{2})COOH - / CH(NH_{2})COOH - CH_{2} | - \ CH_{2}-COOH - CH_{2}-COOH - - Glutaminic acid Aspartic acid - - CH_{3} - CH_{2}-NH_{2} \ - | CH-CH_{2}-CH(NH_{2})-COOH - COOH / - CH_{3} - - Glycocoll Leucin - - OH - / - C_{6}H_{4} - \ - CH_{2}-CH(NH_{2})COOH - - Tyrosin - C·CH_{2}·CH·(NH_{2})·COOH - / \\ - C_{6}H_{4} CH - \ / - NH - - Tryptophan - - CH_{2}-NH CH_{2}-NH_{2} CH--N - | \ | || \\ - CH_{2} C--NH_{2} CH_{2} || CHµ - | // | || / - CH_{2} NH CH_{2} C--NH - | | | - CH·NH_{2} CH_{2} CH_{2} - | | | - COOH CH-NH_{2} CH-NH_{2} - | | - COOH COOH - - Arginin Lysin Histidin - -In these various decomposition products there is apparent certain -definite lines of resemblance, on which is based one or more -suggestions regarding possible ways in which these chemical groups are -linked, or bound together, in the proteid molecule. Thus, there is -apparently present a complex or nucleus which may be indicated as - - | | - HC-NH-CO- also HC-NH-C(NH)- - | | - -The proteid molecule is presumably built up of amino-acids variously -joined together, this synthesis being accomplished, doubtless, by the -condensation of different types of amino-acids, in which the first -of the above groups represents the more common method of union. We -may indeed conjecture that such methods of condensation take place in -the human body, in the epithelial cells of the intestine, and in the -tissues in general; and that by such methods, construction of proteid -is accomplished out of the various fragments split off by digestion, -etc. In a tentative way, the principle may be illustrated by the fusion -of leucin and glutaminic acid,--following Hofmeister’s suggestion,--in -which a still larger complex is formed: - - : : - --CO-:-NH--CH--CO--NH--CH--CO-:-NH-- - : | | : - C_{4}H_{9} (CH_{2})_{2} - | - CO·OH - - Leucin Glutaminic acid - -In this way, step by step, the proteid molecule is built up, and -naturally in katabolism the proteid breaks down along certain definite -lines of cleavage, with formation of katabolic products containing -those groups, or chemical nuclei, which characterize the different -proteid molecules. For it is to be clearly understood that there are -many different forms of proteid, perhaps superficially alike, but -possessed of physiological individuality. This is well illustrated -by the two primary proteoses formed in digestion. As will be -recalled, there are at first two proteoses produced, protoproteose -and heteroproteose. These are, superficially at least, not radically -unlike; they possess essentially the same percentage composition, but -when broken down by vigorous chemical methods they show a totally -different make-up. In other words, at the very beginning of digestion -there is a splitting up of the proteid into two parts, which have -quite a different chemical structure, as is clearly indicated by the -difference in the character and amount of the decomposition products -yielded by hydrolytic cleavage. Thus, heteroalbumose as derived from -blood-fibrin contains 39 per cent of its total nitrogen in basic form, -_i. e._, in a form which goes over into the basic bodies, arginin, -lysin, and histidin, etc. On the other hand, protoalbumose from the -same source yields hardly 25 per cent of basic nitrogen. Further, -heteroalbumose yields only a very small amount of tyrosin, while -protoalbumose gives on decomposition a large amount of this substance. -Again, heteroalbumose furnishes a large yield of leucin and glycocoll, -while protoalbumose gives no glycocoll and only a little leucin. -Obviously, these two proteoses have an inner structure quite divergent -one from the other, and owing to this fact they must play a quite -different rôle in metabolism. - -Even greater differences in inner chemical structure are found among -native proteids. By way of illustration, we may take egg-albumin, -the casein of cow’s milk, gliadin of wheat, and the edestin of hemp -seed. These are all typical proteids; they are all useful as food, but -they are radically different in their inner chemical structure, as is -clearly indicated by the following data,[21] which show the percentage -yield of the different amino-acids and ammonia: - - [21] These data were furnished the writer by Dr. Thomas B. Osborne, - and represent in large measure the results of his own chemical work. - - +--------+-------+--------+----------+--------+------+---------+--------+ - | | | |Glutaminic| | | | | - | |Leucin.|Tyrosin.| Acid. |Arginin.|Lysin.|Histidin.|Ammonia.| - +--------+-------+--------+----------+--------+------+---------+--------+ - |Egg- | | | | | | | | - | albumin| 6.1 | 1.1 | 9.0 | ... | ... | ... | 1.6 | - |Casein | 10.5 | 4.5 | 10.7 | 4.8 | 5.8 | 2.6 | 1.9 | - |Gliadin | 5.7 | 1.2 | 37.3 | 3.2 | 0 | 0.6 | 5.1 | - |Edestin | 19.9 | 2.7 | 14.0 | 14.2 | 1.6 | 2.2 | 2.3 | - +--------+-------+--------+----------+--------+------+---------+--------+ - -These are not mere technical differences, but they represent -divergences of structure which cannot help counting as material factors -in nutritional processes. Especially noticeable is the large yield of -glutaminic acid from wheat proteid, as contrasted with the proteid -(casein) of animal origin. As a rule, glutaminic acid forms a larger -proportion of the decomposition products of vegetable than of animal -proteids. Similarly, arginin is present in much larger proportion -in most vegetable proteids than in most animal proteids. While many -other data more or less trustworthy might be added, these figures -will suffice to emphasize the main point under discussion, viz., that -individual proteids show marked variation in the amount of the several -amino-acids which serve as corner-stones or nuclei in the building -up of the molecule, and consequently they must yield correspondingly -different katabolic products when serving the body as food. - -Turning now to another phase of tissue metabolism, we may consider -briefly the nucleoproteids and their characteristic decomposition -products; bodies which are widely distributed as cleavage products -formed in the disintegration of most cell protoplasm, and having -special interest in nutrition because of their chemical relationship -to that well-known substance, uric acid. Nucleoproteids of some type -are found in all cells; consequently they are present in all tissues, -in all glandular organs, and their widespread distribution constitutes -evidence of their great physiological importance. Nucleoproteids are -compound substances made up of some form of proteid and nucleic acid. -By simple hydrolysis with dilute mineral acids they are broken down -into proteid, phosphoric acid, and one or more bodies known as nuclein -bases. Of these latter substances, there are four well-defined bodies, -viz., adenin, hypoxanthin, guanin, and xanthin, which from their -peculiar chemical constitution are known as “purin bases.” In the -body, there is present in many cells a peculiar intracellular enzyme -termed _nuclease_, which has the power of liberating these purin bases -from their combination as a component part of tissue nucleoproteids, -or of the contained nucleic acid. In autolysis or self-digestion of -many glands, such as the spleen, thymus, etc., this chemical reaction -is easily induced by action of the contained nuclease. Further, the -liberated purin bases then undergo change because of the presence of -certain deamidizing enzymes, and as a result guanin is transformed into -xanthin, and adenin is converted into hypoxanthin. These ferments are -true intracellular enzymes, and are termed respectively _guanase_ and -_adenase_. The real essence of the reaction they accomplish is clearly -indicated by the following formulæ, which likewise show the chemical -nature and relationship of the four substances: - - HN--CO HN--CO - | | | | - H_{2}N·C C--NH + H_{2}O = CO C--NH + NH_{3} - || || \ || || \ - || || CH || || CH - || || // || || // - N--C--N HN--C--N - - Guanin Xanthin - - N==C·NH_{2} HN--CO - | | | | - HC C--NH + H_{2}O = HC C--NH + NH_{3} - || || \ || || \ - || || CH || || CH - || || // || || // - N--C--N N--C--N - - Adenin Hypoxanthin - -These two enzymes are typical hydrolyzing enzymes, but it is to be -noted that there is not only a taking on of water with a retention of -the oxygen, but there is also a giving off of ammonia, by which the -transformation is made possible. Adenin is known as an amino-purin -and guanin as an amino-oxypurin, while hypoxanthin is an oxypurin and -xanthin a dioxypurin. In other words, the two intracellular enzymes -are able to transform the two amino-purins into the corresponding -oxypurins; _i. e._, the enzymes are deamidizing ferments, liberating -the NH_{2} group of the adenin and guanin and thus forming two new -compounds. These reactions, though more or less technical, are -emphasized in this way not merely because they illustrate the action -of intracellular enzymes in intermediary metabolism, thus affording a -striking example of the gradual changes that take place in ordinary -katabolic processes, but especially because they throw light upon the -production of another substance common in body metabolism, viz., uric -acid. It has long been known that nucleoproteids, nucleins, and other -compounds containing these purin radicles, when taken as food, cause -at once an increased output of uric acid, and it has been clearly -recognized that in some way this latter substance, as a product of -metabolism, must come from the transformation of nuclein bases. To-day, -we understand that in many tissues, as in the liver, spleen, lungs, -and muscle, there is present a peculiar oxidizing ferment, an oxidase, -by the action of which hypoxanthin can be converted into xanthin, and -the latter directly oxidized to uric acid. This conversion into uric -acid is purely a process of oxidation, brought about by a typical -intracellular oxidase, known specifically as “xanthin oxidase,” the -reaction involved being as follows: - - HN--CO HN--CO - | | | | - CO C--NH + O = CO C--NH - | || \ | || \ - | || CH | || CO - | || // | || / - HN--C--N HN--C--NH - - Xanthin Uric acid - -From these several reactions, it is clear how various intracellular -enzymes working one after the other are able gradually to evolve uric -acid from tissue nucleoproteids. Further, it is to be noted that there -is another tissue oxidase--contained principally in the kidneys, -muscle, and liver--which has the power of oxidizing and thus destroying -uric acid, with formation, among other substances, of urea. Remembering -that urea has the following chemical constitution - - NH_{2} - / - C==O - \ - NH_{2} - -it is easy to see, by comparison of the formulæ, how uric acid might -easily yield two molecules of urea through simple oxidation. In this -way, excess of uric acid produced in the body can be converted into -urea, and in this harmless form be excreted from the system. - -Finally, reference should be made here to several other products of -tissue metabolism, products of the breaking down of proteid matter in -the body, since they are liable to prove of interest to us in other -connections. Thus creatin, abundant in the muscle and other places; the -related substance creatinin, present in the urine; methyl guanidin, -a decomposition product of creatin; and urea, all call for a word of -description. The chemical relationship of these bodies is clearly -indicated by the following formulæ: - - NH_{2} NH------- - / / \ - C==NH C==NH CO - \ \ / - N(CH_{3})CH_{2}COOH N(CH_{3})CH_{2} - - Creatin Creatinin - - NH_{2} NH_{2} - / / - C==NH C==O - \ \ - NH(CH_{3}) NH_{2} - - Methyl guanidin Urea - -Creatinin is chemically the anhydride of creatin, _i. e._, it can be -formed from creatin by the simple extraction of one molecule of water, -H_{2}O. Creatin, by hydrolytic cleavage, will break down into one -molecule of urea and one molecule of sarcosin or methyl glycocoll, as -shown in the following equation: - - NH_{2} NH_{2} - / CH_{2}·NH·(CH_{3}) / - C==NH + H_{2}O = | + C==O - \ COOH \ - N (CH_{3}) CH_{2}COOH NH_{2} - - Creatin Sarcosin Urea - -Methyl guanidin is a decomposition product of creatin, while guanidin, -as can be seen from the formula, is like urea, excepting that the -group NH replaces the oxygen of urea. These simple statements will -suffice for our present purpose, viz., to indicate the more or less -close chemical relationships existing between many of these nitrogenous -decomposition products resulting from proteid katabolism; also to -suggest how by slight chemical alteration one decomposition product -may be resolved into another related substance in the processes of -katabolism. Our conception of the processes involved in proteid -katabolism is that of a series of progressive chemical decompositions, -in which intracellular enzymes play the all-important part. The -intermediary products formed are definite bodies because of the -specific nature of the active enzymes, and, secondly, because of the -chemical nature of the substances acted upon. In other words, oxidation -in the animal body takes the shape of a series of well-defined chemical -reactions, in which chemical constitution and specific enzyme action -are the predetermining cause. In the absence of the particular chemical -groups, the oxidase is unable to bring about oxidation, or, given the -proper compound or mother substance in the absence of the specific -oxidase, there is no oxidation. Hence, oxidation in the animal body -is not the result of simple combustion, but, on the contrary, it -consists of a series of orderly chemical processes, each one of which -is presided over by an intracellular enzyme, specific in its nature, -in that it is capable of acting only upon substances having a certain -definite constitution, and leading invariably to a certain definite -result. The processes which years ago were considered as due to the -peculiar vital properties of the tissue cells, and which were supposed -to be entirely dependent upon their morphological and functional -integrity, are now seen to be due primarily to a great variety of -enzymes, manufactured indeed by the living cells, but capable of -manifesting their activity even when free from the influence of the -living protoplasm. The varied processes of tissue katabolism are the -result of orderly and progressive chemical changes, in which cleavage, -hydrolysis, reduction, oxidation, deamidization, etc., alternate with -each other under the influence of specific enzymes, where chemical -constitution and the structural make-up of the various molecules are -determining factors in the changes produced. - - - - -CHAPTER III - -THE BALANCE OF NUTRITION - - TOPICS: Body equilibrium. Nitrogen equilibrium. Carbon equilibrium. - Loss of nitrogen during fasting. Influence of previous diet on loss - of nitrogen in fasting. Output of carbon during fasting. Influence - of pure proteid diet on output of nitrogen. Influence of fat on - proteid metabolism. Effect of carbohydrate on nitrogen metabolism. - Storing up of proteid by the body. Transformation of energy in the - body. Respiration calorimeter. Basal energy exchange of the body. - Circumstances influencing energy exchange. Effect of food on heat - production. Respiratory quotient and its significance. Influence of - muscle work on energy exchange. Elimination of carbon dioxide during - work and with different diets. Effect of excessive muscular work - on energy exchange. Oxygen consumption under different conditions. - Output of matter and energy subject to great variation. Body - equilibrium and approximate nitrogen balance to be expected in health. - - -Man, strictly speaking, is always in a condition of unequilibrium. If -placed upon a large and sensitive pair of scales with the opposite -side exactly counterpoised, he will be found to lose weight constantly -until water or food are taken, when the losses of an hour or two may -be made good, or perchance more than balanced. The human body is a -maelstrom of chemical changes; chemical decompositions are taking place -continuously at the expense of the proteids, fats, and carbohydrates -of the tissues and of the food, the stored-up energy of these organic -compounds being thereby transformed into the active or “kinetic” -forms of heat and motion; while carbon dioxide, water, urea, and -some few other nitrogenous substances are being continually formed as -the normal waste products of these tissue changes, and constantly or -intermittently excreted. In other words, the body is in a perpetual -condition of chemical oscillation, constantly consuming its own -substance, rejecting the waste products which result, and giving off -energy in the several forms characteristic of living beings. The -condition of the body plainly depends upon the relation which it is -able to maintain between the income and the expenditure of matter -and energy. If the income equals the output, the body is kept in a -condition approaching equilibrium; if the intake exceeds the outgo, the -body adds to its capital of matter and energy; while if the expenditure -is greater than the income, the accumulated capital is drawn upon; -and this, if continued indefinitely, results in a drain upon the bank -which must eventually end in disaster. It is comparatively easy, -however, for man to maintain his body in a condition of equilibrium -from day to day; _i. e._, the losses of the morning can be made good -at luncheon, or the expenditures of an entire day counterbalanced by -a corresponding addition to capital the following day, in which case -the body may be said to be in balance. It is necessary, however, to -discriminate between body equilibrium, meaning thereby the maintenance -from day to day of a constant body-weight, and nitrogen equilibrium, -or carbon equilibrium. In the latter cases, what is meant is that the -intake of nitrogen, or of carbon, exactly equals the output of these -two elements. It is quite possible, however, to have a condition of -nitrogen equilibrium without the body being in a state of balance, as -when the outgo of carbon exceeds the intake of carbon, or when there is -an increased output of water. - -As a rule, it may be stated that when a man puts out less carbon and -less nitrogen than he takes in he must be gaining in weight; the only -exception being the possible case of an increased excretion of water, -which might more than counterbalance the gain. On the other hand, if -he gives off more carbon and more nitrogen than he takes in, the body -must lose in weight. Where the output of carbon is beyond the amount of -carbon ingested, the lost carbon represents a drain upon body fat. In -a reversal of this condition, _i. e._, where the carbon taken in is in -excess of the outgo, the body is gaining in fat. Theoretically, gain -or loss of carbon may mean gain or loss of either carbohydrate or fat, -but practically stored-up carbon generally stands for accumulated fat; -and, correspondingly, loss of carbon represents a withdrawal from the -store of adipose tissue, since glycogen and sugar from a quantitative -standpoint figure only slightly in these metabolic processes. When the -body excretes more nitrogen than is taken in during a given period, -there is only one interpretation possible, viz., that the body is -losing proteid or flesh. If, on the other hand, the nitrogen import -exceeds the outgo, then the body must be gaining flesh. Here, again, -there is the theoretical possibility that gain or loss of nitrogen -might represent increase or decrease of proteid in some glandular -organ, or even in the blood; but practically it is the relatively -bulky muscle tissue, with its high content of proteid matter, that is -most subject to change in metabolism. Finally, it is easy to see how, -knowing the percentage of nitrogen in proteid and the percentage of -carbon in fat, one can calculate from the nitrogen and carbon lost or -gained the amounts of proteid or fat added to the capital stock, or -withdrawn from the store of nutritive material. - -When there is no income, as in fasting, the body loses rapidly, living -during the hunger period upon its store of energy-containing material. -Many careful observations have been made upon people who have fasted -for long periods, some as long as thirty days, the income consisting -solely of water. The following figures[22] show the daily excretion of -nitrogen in several notable cases: - - [22] Taken from Landergren: Untersuchungen über die Eiweissumsetzung - des Menschen. Skandinavisches Archiv für Physiologie, Band 14, p. - 112; and from A. Magnus-Levy: v. Noorden’s Handbuch der Pathologie - des Stoffwechsels, 1906, p. 312. - - +-----------------+-------------+-------------+-------------+ - | | Breithaupt. | Cetti. | Succi. | - | Day of Fasting. | 59.9 Kilos. | 56.5 Kilos. | 62.4 Kilos. | - +-----------------+-------------+-------------+-------------+ - | | grams | grams | grams | - | 0 | 13.0 | 13.5 | 16.2 | - | 1 | 10.0 | 13.6 | 13.8 | - | 2 | 9.9 | 12.6 | 11.0 | - | 3 | 13.3 | 13.1 | 13.9 | - | 4 | 12.8 | 12.4 | 12.8 | - | 5 | 11.0 | 10.7 | 12.8 | - | 6 | 9.9 | 10.1 | 10.1 | - | 7 | ... | 10.9 | 9.4 | - | 8 | ... | 8.9 | 8.4 | - | 9 | ... | 10.8 | 7.8 | - | 10 | ... | 9.5 | 6.7 | - +-----------------+-------------+-------------+-------------+ - -In Succi’s case, the fasting was continued for thirty days. The daily -average loss of nitrogen from the 11th to the 15th day was 5.8 grams; -from the 16th to the 20th day, 5.3 grams; from the 20th to the 25th -day, 4.7 grams; and from the 26th to the 30th day, 5.3 grams. A daily -loss of 5.3 grams of nitrogen means a breaking down, or using up, of 33 -grams of proteid, or a little more than one ounce. On the sixth day of -fasting, all three of these subjects showed essentially the same daily -loss of nitrogen; viz., 10 grams, which implies a using up of 62.5 -grams of proteid material. We must not be led astray by these figures, -however, or draw too hasty conclusions therefrom regarding the -requirements of the body for proteid food. Noting the close agreement -in the nitrogen output of the three subjects on the sixth day, combined -with the fact that their body-weight was essentially the same, we -might infer that 62.5 grams of proteid matter represents the amount of -nitrogenous food necessary to maintain nitrogen equilibrium and keep -the body in a condition of balance. Such a conclusion, however, would -be quite erroneous for several reasons. First, a man fasting, if he was -in an ordinary condition of nutrition prior to the fast, has in his -tissues a large store of fat. It is considered that in fasting only -about 10–12 per cent of the total energy of the body is derived from -tissue proteid; the major part comes from the fat stored up. When there -is no income to make good the loss, the body must naturally draw upon -its own store. A certain amount of proteid must be used up daily, but -in addition there are the energy requirements to be considered. These -are met mainly by fat and carbohydrate, and so long as fat endures -proteid will be drawn upon only, or mainly, to meet the nitrogen -requirement; but if the fat gives out, then proteid must be used in -larger quantity, as a source of energy. Hence in fasting, the daily -loss of nitrogen will be governed largely by the condition of the body -as regards fat. Thus, Munk has reported the case of a well-nourished -and fat person, suffering from disease of the brain, who gave off daily -in the later stages of starvation only one-third the amount of nitrogen -voided by Cetti, who had been poorly nourished. Obviously, in fasting, -as soon as the adipose tissue of the body has been largely used up, -there will be an increase in the amount of tissue proteid consumed, -since under such conditions the heat of the body and the energy of -muscular work (work of the heart and involuntary muscles) must come -from the decomposition of proteid. In harmony with this statement, it -is frequently observed that in cases of starvation there comes toward -the end a sudden and marked increase in the output of nitrogen. - -Secondly, the elimination of nitrogen during the earlier days of -fasting is governed in large measure by the character and extent of -the diet on the days just preceding the fast. This is well illustrated -by some experiments conducted by C. Voit on a dog. In the first series -of experiments, the dog received daily 2500 grams of meat prior to -fasting; in the second series, 1500 grams of meat were fed daily before -the fast; while in the third series, a mixed diet relatively poor -in proteid was given. The following figures[23] show the amounts of -proteid used up by the dog (calculated from the nitrogen excreted) each -day of the fasting period, under the different conditions: - - [23] Expressed in this form from Voit’s figures by A. Magnus-Levy. - Loc. cit., p. 311. - - +------------------+---------------+----------------+---------------+ - | | First Series. | Second Series. | Third Series. | - +------------------+---------------+----------------+---------------+ - | | grams | grams | grams | - |First fasting day | 175 | 77 | 40 | - |Second " " | 72 | 54 | 33 | - |Third " " | 56 | 46 | 30 | - |Fourth " " | 50 | 53 | 36 | - |Fifth " " | 36 | 43 | 35 | - |Sixth " " | 39 | 37 | 37 | - +------------------+---------------+----------------+---------------+ - -We see very clearly in these experiments the effects of the large -quantities of proteid fed on the destruction of proteid in the early -days of fasting. When the body is rich in proteid from food previously -taken, the metabolism of nitrogenous matter is very large at first, -as in the first series of experiments. Indeed, in this series, even -on the fifth day of fasting, the amount of proteid metabolized was -larger than on the second day of the third series. We have here a -forcible illustration of the physiological axiom that excess of proteid -matter in the tissues, or in the blood, stimulates proteid metabolism; -and it affords convincing proof of the contention that in the first -days of fasting the output of nitrogen, or the amount of proteid used -up, will depend in large measure upon the proteid condition of the -body at the time of the fast. Equally noticeable is the fact that -there comes a time--the sixth day in the above experiment--when the -nitrogen output reaches a common level, irrespective of the previous -proteid condition of the body. Further, it is easy to see that the -greater loss of nitrogen, _i. e._, the large breaking down of proteid -during the first few days of fasting, in those cases where proteid -food has been freely taken, suggests the existence in the tissues of -two forms of proteid. We may term them, following the nomenclature of -Voit, as circulating and morphotic, or tissue, proteid; or, we may -designate them as labile and stable forms of proteid. In other words, -following the usually accepted view, this circulating or labile proteid -represents reserve or surplus material which is easily decomposed -and hence rapidly gotten rid of, while the stable proteid is more -slowly oxidized, and its metabolism may be taken as representing more -nearly the real necessities of the body. However this may be, it is -plainly manifest that the nitrogen output, meaning the metabolism of -proteid matter, during hunger or fasting is modified by a variety of -circumstances, notably the previous nutritive condition of the body as -regards both fat and proteid. It is hardly necessary to add that the -amount of muscular work performed is another factor of importance in -this connection. Fat in the body represents inert material stored up -mainly for nutritive purposes; hence, in hunger it is used largely, and -serves to protect more important tissues. Thus, experiments have shown -that in long periods of fasting, adipose tissue may be consumed to the -extent of 97 per cent of the total amount present, while the heart and -nervous tissue will not lose over 3 per cent of their tissue substance. -The influence of tissue fat upon the consumption of proteid during -hunger can thus be fully appreciated. - -The output of carbon during fasting may be illustrated by the following -experiment[24] made upon a young man, the nitrogen data being included -for comparison, and likewise the intake of food, in terms of nitrogen -and carbon, preceding the fast and for two days following the fast. The -fasting was of five days’ duration. - - [24] Taken from Johansson, Landergren, Sondén, and Tiegerstedt: - Beiträge zur Kenntniss des Stoffwechsels beim hungernden Menschen. - Skandinavisches Archiv für Physiologie, Band 7, p. 29. - - +------+--------------+---------------------+------------------------+ - | | | Intake. | Output. | - | Day. | Body-weight. +---------+-----------+------------+-----------+ - | | | Carbon. | Nitrogen. | Carbon.[25]| Nitrogen. | - +------+--------------+---------+-----------+------------+-----------+ - | | kilos | grams | grams | grams | grams | - | 2 | 67.4 | 438.7 | 30.96 | 303.4 | 25.81 | - | 3 | 66.9 | 0 | 0 | 197.6 | 12.17 | - | 4 | 65.7 | 0 | 0 | 188.8 | 12.85 | - | 5 | 64.8 | 0 | 0 | 183.2 | 13.61 | - | 6 | 63.9 | 0 | 0 | 180.8 | 13.69 | - | 7 | 63.1 | 0 | 0 | 176.2 | 11.47 | - | 8 | 63.9 | 439.9 | 35.65 | 270.5 | 26.83 | - | 9 | 65.5 | 391.7 | 23.68 | 258.8 | 19.46 | - +------+--------------+---------+-----------+------------+-----------+ - - [25] The carbon output represents the total carbon of the expired - air, urine, and excrement. - -On the non-fasting days, the intake consisted of an ordinary food -mixture of proteids, fats, and carbohydrates, with a small addition -of alcohol. The point to be emphasized here, however, is that the -carbon-content was more than sufficient to meet the needs of the body. -Thus, it will be observed that on all three of the days when food was -taken, the income of carbon was far in excess of the output. In other -words, on the day preceding the beginning of the fast the body stored -up 135 grams of carbon, and on the day following the fast the body -retained 169 grams of carbon to help make good the loss. Similarly, -the amount of proteid food taken in on the day prior to the fast was -considerably in excess of the needs of the body, 5.1 grams of nitrogen -equivalent to 31.8 grams of proteid being stored for future use. -Plainly, the man was not in either carbon or nitrogen balance prior -to the fast, but was taking far more food than the needs of the body -called for. This fact may be emphasized by noting that the total fuel -value of the daily food, plus the fuel value of the alcohol, amounted -on an average to about 4200 large calories, while the fuel value of the -material metabolized on the feeding days averaged only 2500 calories. -Looking at the figures showing the output of carbon, as well as of -nitrogen, during the fasting days, it is to be seen that in the early -days of fasting, the metabolism of the body tends to remain at a fairly -constant level, especially when figured per kilogram of body-weight. - -To fully appreciate what takes place in a man of the above body-weight -fasting for five days (though living on a large excess of food prior to -the fast), the daily losses of carbon and nitrogen may be translated -into terms of fat and proteid. If it is assumed that the total carbon, -aside from what necessarily belongs to the proteid indicated by the -nitrogen figures, comes from the oxidation of fat, it is easy to -compute the amounts of fat and proteid metabolized, or destroyed, each -day of the fasting period. These are shown in the following table: - - +------+--------------+--------------+ - | Day. | Proteid | Fat | - | | metabolized. | metabolized. | - +------+--------------+--------------+ - | | grams | grams | - | 3 | 76.1 | 206.1 | - | 4 | 80.3 | 191.6 | - | 5 | 85.1 | 181.2 | - | 6 | 85.6 | 177.6 | - | 7 | 71.7 | 181.2 | - +------+--------------+--------------+ - -Finally, if from these figures we calculate the fuel value of the -proteid and fat oxidized per day, it is possible to gain a fairly clear -conception of the part played by these two classes of tissue material -during fasting, in furnishing the heat of the body and the energy for -muscular motion, etc. - - +------+---------------+---------------+-------------+ - | | Fuel Value of | Fuel Value of | Total | - | Day. | the Proteid | the Fat | Fuel Value. | - | | metabolized. | metabolized. | | - +------+---------------+---------------+-------------+ - | | calories | calories | calories | - | 3 | 303 | 1916 | 2220 | - | 4 | 320 | 1781 | 2102 | - | 5 | 339 | 1684 | 2024 | - | 6 | 341 | 1651 | 1992 | - | 7 | 286 | 1684 | 1970 | - +------+---------------+---------------+-------------+ - -These somewhat general statements, with the illustrations given, will -serve in a brief way to emphasize some of the essential features of -metabolism in the fasting individual; where there is no income of -energy-containing material, and where the body must draw entirely -upon its store of accumulated fat and proteid to keep the machinery -in motion, maintain body temperature, and do the tasks of every-day -life. When it is remembered that persons have fasted for periods of -thirty days or longer without succumbing, it is evident that the body -of the well-nourished man has a large reserve of nutritive material, -which can be drawn upon in cases of emergency. At the same time, the -facts presented show us that in the early days of fasting the actual -amounts of tissue proteid and body fat consumed are not large. In -Cetti’s case, on the sixth day of fasting the metabolized nitrogen -amounted to 10 grams, which implies a loss of 62.5 grams of proteid. -At this rate of loss, one pound of dry proteid matter in the form of -tissue proteid would meet the wants of a man of 130 pounds body-weight -for seven and a half days, provided of course there was a reasonable -stock of fat to help satisfy the energy requirements. Finally, we may -again emphasize the fact that the loss of nitrogen in the fasting man -is by no means a measure of the minimal proteid requirement. By feeding -fat, or carbohydrate, or both, the output of nitrogen can be materially -diminished, although naturally we cannot establish a nitrogen balance -by so doing, since the income is free from nitrogen; but we can -postpone for a time the approach of nitrogen starvation. - -We may next profitably consider the effect of a pure proteid diet--such -as lean meat free from fat--on the output of nitrogen. In studying this -problem, we at once meet with several important and surprising facts. -First, we are led to see that, strange as it may seem, every addition -of proteid to the diet results in an increased excretion of nitrogen. -In other words, increase of proteid income is followed at once by an -increase in the metabolism of proteid, with a corresponding outgo of -nitrogen. The hungry or fasting man with his income entirely cut off, -and consequently suffering from a heavy drain upon his capital stock, -would be expected, when suddenly supplied with fresh capital in the -form of meat or other kind of proteid food, to hold on firmly to this -all-important foodstuff; but such is not the case. It is impossible, -for example, to establish nitrogen equilibrium by an income of proteid -equal to what the individual during fasting is found to metabolize. -As stated by another, “It is one of the cardinal laws of proteid -metabolism that the store of nitrogenous substances in the body is not -increased by, or not in proportion to, an increase in the nitrogen -intake.” The principle is well illustrated in the fasting experiment -just described. On the fifth day of fasting, the nitrogen output -amounted to 11.4 grams. On the day following, the man took 35.6 grams -of nitrogen in the form of proteid, while the excretion of nitrogen for -that day rose to 26.8 grams. In other words, although deprived of all -proteid income for five days, and during that period drawing entirely -upon his proteid capital, the man was wholly unable to avail himself of -the proteid so abundantly supplied at the close of the fast and make -good the losses of the preceding days; only a small proportion of the -proteid income could be retained. If a dog fed on a definite quantity -of meat suddenly has his proteid income increased, there is at once an -acceleration of proteid metabolism, and a corresponding increase in the -output of nitrogen. Addition of still more proteid to his income is -followed by an accumulation of a portion of the proteid; but this tends -to decrease gradually, while there is a corresponding daily increase -in the excretion of nitrogen. In this manner, there finally results a -condition of nitrogenous equilibrium or nitrogen balance. - -Again, an animal brought into nitrogen equilibrium by excessive -proteid feeding, if suddenly given a small amount of meat per day, -tends to put out nitrogen from its own tissues. This tissue loss, -however, decreases slowly, and eventually the animal is quite likely -to re-establish nitrogen equilibrium at a lower level. There is, in -other words, a strong tendency for the body to pass into a condition -of nitrogen balance under different conditions of proteid feeding, -even after a long period of nitrogen loss and with an abundance of -proteid in the intake. The starving body, as we have seen, cannot make -use of all the nitrogen fed, although we can well conceive its great -need for all the proteid available. A certain amount of the proteid -fed, or its contained nitrogen, is at once passed out of the body and -lost, even though the organism be gasping, as it were, for proteid to -make good the drain incidental to long fasting. A recent writer[26] -has suggested that some explanation for these anomalies may be found -in the supposition “that a long succession of generations in the past, -which have lived from choice or necessity on a diet rich in proteids, -have handed down to us, as an inheritance, a constitution in which -arrangements exist for the removal of nitrogen from a considerable -part of this proteid. The fact that the amount of proteid taken is -re-adjusted to suit the actual needs of the body, though it makes -these arrangements unnecessary, will not necessarily remove them. The -denitrifying enzyme, which has been trained to keep guard over the -entrances by which nitrogenous substances are admitted into the body, -will continue to levy its toll of nitrogen, even when the amount of -proteid presented to it is no more than the tissues which it serves -actually require.” - - [26] Leathes: Problems in Animal Metabolism. Philadelphia, 1906, p. - 157. - -As an illustration of how the body behaves with a low nitrogen intake -followed by a sudden increase in the income of proteid, some data from -an experiment performed by Sivén[27] on himself may be cited: - - [27] Sivén: Zur Kenntniss des Stoffwechsels beim erwachsenen - Menschen, mit besonderer Berücksichtigung des Eiweissbedarfs. - Skandinavisches Archiv für Physiologie, Band 11, p. 308. - - +--------+--------------+-------------+-----------+----------+ - | | | Nitrogen of | Nitrogen | Nitrogen | - | Date. | Body-weight. | the Food. | excreted. | Balance. | - +--------+--------------+-------------+-----------+----------+ - | | kilos | grams | grams | grams | - | Nov. 6 | 65.4 | 2.69 | 8.31 | -5.62 | - | 7 | 65.4 | 2.69 | 5.37 | -2.68 | - | 8 | 65.1 | 2.69 | 5.71 | -3.02 | - | 9 | 65.3 | 2.69 | 4.88 | -2.19 | - | 10 | 65.0 | 2.69 | 4.32 | -1.63 | - | 11 | 64.9 | 2.69 | 4.25 | -1.56 | - | 12 | 64.9 | 2.69 | 4.47 | -1.78 | - | 13 | 64.6 | 2.96 | 4.88 | -1.92 | - | 14 | 64.4 | 2.96 | 4.30 | -1.44 | - | 15 | 64.3 | 2.96 | 4.75 | -1.79 | - | 16 | 64.4 | 2.96 | 4.36 | -1.40 | - | 17 | 64.4 | 2.96 | 4.13 | -1.17 | - | 18 | 64.4 | 2.96 | 4.35 | -1.39 | - | 19 | 64.4 | 2.96 | 4.32 | -1.36 | - | 20 | 64.4 | 2.96 | 4.22 | -1.26 | - | 21 | 64.0 | 2.96 | 4.06 | -1.10 | - | | | | +----------+ - | | | | | -31.31 | - | | | | | | - | 22 | 64.1 | 4.02 | 4.22 | -0.20 | - | 23 | 64.4 | 4.02 | 4.35 | -0.33 | - | 24 | 64.4 | 4.02 | 4.21 | -0.19 | - | 25 | 64.4 | 4.02 | 4.40 | -0.38 | - | | | | +----------+ - | | | | | -1.10 | - | | | | | | - | 26 | 64.2 | 8.24 | 6.56 | +1.68 | - | 27 | 64.4 | 13.45 | 8.67 | +4.78 | - | 28 | 64.4 | 13.66 | 10.54 | +3.12 | - | 29 | 64.0 | 13.45 | 11.10 | +2.35 | - | 30 | 64.2 | 13.24 | 12.83 | +0.41 | - | Dec. 1 | 64.2 | 13.24 | 11.70 | +1.54 | - | 2 | 63.9 | 12.61 | 12.00 | +0.61 | - | | | | +----------+ - | | | | | +14.49 | - | | | | | | - | 3 | 64.0 | 22.93 | 16.24 | +6.69 | - | 4 | 63.9 | 22.41 | 21.47 | +0.94 | - | 5 | 63.9 | 22.41 | 23.10 | -0.69 | - | 6 | 63.6 | 23.35 | 23.12 | +0.23 | - | 7 | 63.9 | 23.04 | 22.82 | +0.22 | - | 8 | 63.8 | 22.62 | 22.86 | -0.24 | - | | | | +----------| - | | | | | +6.15 | - +--------+--------------+-------------+-----------+----------+ - -I have ventured to give these data in some detail, because of their -exceeding great interest in several directions aside from the point -under discussion. Confining our attention to the nitrogen exchange, it -is to be observed that for a period of two weeks Sivén lived on less -than 3 grams of nitrogen per day, and without any excessive intake -of carbohydrate or fat. During this time, the body naturally was in -a condition of minus balance as regards nitrogen, the output being -considerably larger than the income. The total amount of nitrogen lost -in the period, 31 grams, corresponds to a breaking down of 193 grams of -tissue proteid, or over one-third of a pound. On increasing the income -of nitrogen to 4 grams per day, the nitrogen loss still continued, -though at a much lower rate; indeed, the body is seen to approach very -closely to a condition of nitrogen equilibrium. Still further increase -of the nitrogen income to 13 grams per day was followed at once by a -slight accumulation of proteid, and the body showed a decided plus -balance of nitrogen, as on November 27. This, however, is seen to -decrease gradually with a corresponding daily increase in the outgo of -nitrogen, until on December 2 the body was once more practically in -nitrogenous equilibrium. On again increasing the nitrogen income, to 23 -grams per day, the same process was repeated, although in this case the -body more quickly approached a condition of nitrogen balance. - -We see in these data striking confirmation of the statement that the -nitrogen outgo tends to keep pace with the income of nitrogen, the -body always striving to maintain a condition of nitrogen equilibrium. -Consequently, the fasting man having lost largely of his store of -proteid can replace the latter only slowly, even though he eats -abundantly of proteid food. Thus, Sivén in the week ending December 2, -though taking over 13 grams of nitrogen a day, retained in his body -only 14.5 grams of nitrogen during the entire seven days; while in the -six days following, with a daily intake of 23 grams of nitrogen, he -gained only about 8 grams additional. The human body does not readily -store up proteid, and this is true no matter how greatly the tissues -are in need of replenishment. - -If the daily income is reinforced by the addition of carbohydrate or -fat, there is observed a decided influence on the outgo of nitrogen; -the rate or extent of proteid metabolism is at once modified, fat and -carbohydrate both having a direct saving effect on proteid. Neither fat -nor carbohydrate can prevent the katabolism of proteid, but they can -and do decrease it, and thus serve as proteid-sparers. In the fasting -body, or where there is only an intake of proteid, the latter material, -except for the fat contained in the tissues, must serve the double -purpose of meeting the specific nitrogen requirements of the body and -furnishing the requisite energy. The energy requirements, however, can -be met more advantageously by either of the non-nitrogenous foodstuffs, -and just so far as they are oxidized, so far will there be a saving of -proteid. Herein lies the philosophy of a mixed diet, with its natural -intermingling of proteid, fat, and carbohydrate. For the same reason, -the body of a man rich in fat will in fasting lose far less proteid -per day than the lean man; or, if fed with a given amount of proteid -food, the fat man may attain nitrogen equilibrium, or even store up a -little proteid, while on the same diet the lean man will lose proteid. -Further, if a man is in nitrogen balance with a given amount of proteid -food, the addition of fat or carbohydrate to the diet will permit of a -reduction in the amount of proteid necessary to maintain nitrogenous -equilibrium. Fat, however, when added to food, does not always protect -proteid to the extent possibly suggested by the preceding statements. -The following data from oft-quoted experiments by Voit[28] on dogs will -serve to illustrate: - - [28] C. Voit: Hermann’s Handbuch der Physiologie des - Gesammtstoffwechsels, Band 6, p. 130. - - +-----------------------++-----------------------------+ - | Food. || Flesh. | - +-----------+-----------++--------------+--------------+ - | Meat. | Fat. || Metabolized. | On the Body. | - +-----------+-----------++--------------+--------------+ - | grams | grams || grams | grams | - | 1500 | 0 || 1512 | -12 | - | 1500 | 150 || 1474 | +26 | - | | || | | - | 500 | 0 || 556 | -56 | - | 500 | 100 || 520 | -20 | - +-----------+-----------++--------------+--------------+ - -It is to be observed that in both of these experiments the fairly large -addition of fat results in a saving of proteid, but the sparing effect -in the first experiment amounts to only 38 grams of proteid for the -150 grams of fat added. In the second experiment, however, there is -a saving of 36 grams of proteid, although only 100 grams of fat were -fed. The radical point of difference in the two experiments is the -amount of proteid ingested. Proteid food stimulates proteid metabolism; -it likewise accelerates the metabolism of non-nitrogenous matter, -consequently the sparing or protecting effect of fat on proteid is -most conspicuous when the intake of proteid is relatively small. Only -under such conditions, does fat protect in large degree the consumption -of proteid in the body. In the ordinary, daily, dietary of man, with -its great variety of food materials and with its proteid-content not -exceeding 125 grams, fat is apt to be a conspicuous element, and under -such conditions its sparing effect on proteid metabolism is most -marked. Further, it must not be forgotten, as Voit originally pointed -out, that the adipose tissue of the body acts like the food-fat, and -consequently the proteid-sparing effect of the former may be added to -that of the latter. - -The addition of carbohydrate to a meat diet produces at once a saving -in the decomposition of proteid, as shown in the following figures, -covering an experiment of two days: - - Meat. Sugar. Proteid metabolized. - 500 grams. 200 grams. 502 grams. - 500 0 564 - -Without the sugar, there was a minus balance of 64 grams of proteid, -but addition of the carbohydrate caused practically a saving of all -of this, with establishment of essentially a nitrogen balance. The -sparing of proteid by carbohydrate is greater than by fats, a fact -of considerable dietetic importance which is well illustrated by the -following experiments (on dogs) taken from Voit: - - +-------------------------------++-------------------------------------+ - | Food. || Flesh. | - +-------+-----------------------++--------------+----------------------+ - | Meat. | Non-nitrogenous Food. || Metabolized. | Balance of the Body. | - +-------+-----------------------++--------------+----------------------+ - | grams | grams || grams | grams | - | 500 | 250 Fat || 558 | -58 | - | 500 | 300 Sugar || 466 | +34 | - | 500 | 200 Sugar || 505 | -5 | - | 800 | 250 Starch || 745 | +55 | - | 800 | 200 Fat || 773 | +27 | - | 2000 | 200–300 Starch || 1792 | +208 | - | 2000 | 250 Fat || 1883 | +117 | - +-------+-----------------------++--------------+----------------------+ - -In considering the results of this experiment, it must be remembered -that the calorific or fuel value of fat as compared with carbohydrate -is as 9.3 : 4.1; in other words, fats have a fuel value of more than -twice that of carbohydrates. In spite of this fact, it is clearly -evident that carbohydrates as a class--for the different sugars and -starches act alike in this respect--are far more efficient than fats -in saving proteid. Thus, with an income of 500 grams of meat and 250 -grams of fat, the body of the animal lost 58 grams of proteid, while -with a like amount of meat and 300 grams of sugar the body not only -saved the 58 grams, but in addition stored 34 grams of proteid, showing -a plus balance to that extent. The sparing of proteid by carbohydrate -amounts on an average, according to Voit, to 9 per cent--in the highest -cases to 15 per cent--of the proteid given, while the saving produced -by fat averages only 7 per cent. Further, increasing quantities of -carbohydrates in the food diminish the rate of proteid metabolism much -more regularly and constantly than increasing quantities of fat. We -may attribute this difference in action, in a measure at least, to the -greater ease in oxidation and utilization of the carbohydrate. In any -event, starches and sugars are most valuable adjuncts to the daily -diet, because of this marked proteid-saving power, while their fuel -value adds just so much to the total energy intake. - -A more striking illustration of the action of carbohydrate in sparing -proteid is seen in experiments on man, where the nitrogen intake is -reduced to a minimum, so as to constitute a condition of specific -nitrogen-hunger. In such a case, increasing amounts of carbohydrate -added to the intake reduce enormously the using up of tissue proteid. -The following experiment with a young man 22 years old and 71.3 kilos -body-weight, reported by Landergren,[29] affords good evidence of the -extent to which this proteid sparing power may manifest itself. - - [29] Landergren: Untersuchungen über die Eiweissumsetzung des - Menschen, Skandinavisches Archiv für Physiologie, Band 14, p. 114. - -We see here the nitrogen consumption fall to the exceedingly low level -of 3.34 grams per day, or 0.047 gram per kilo of body-weight. To -appreciate the full significance of this drop in the extent of proteid -metabolism, we may recall that Succi, with a body-weight of only 62.4 -kilos, on the seventh day of fasting excreted 9.4 grams of nitrogen, -corresponding to a metabolism of 58.7 grams of tissue proteid. In -other words, with an intake of only 5.6 grams of proteid, the addition -of 908 grams of carbohydrate, with a total fuel value of 3745 calories, -reduced the consumption of tissue proteid to 20.8 grams. The same -individual, if fasting, would undoubtedly have used up at least 70 -grams of tissue proteid. - - +----+------------------------------------------++---------++------------+ - | | Intake. || Output. || | - |Day.+--------+-----+--------+--------+---------++---------++ Proteid | - | |Proteid.| Fat.| Carbo- |Alcohol.|Calories.||Nitrogen ||metabolized.| - | | | |hydrate.| | ||of Urine.|| | - +----+--------+-----+--------+--------+---------++---------++------------+ - | | grams |grams| grams | grams | || grams || grams | - | 1 | 35.2 | 6.1 | 507 | 26.6 | 2465.9 || 12.16 || 76.0 | - | 2 | 28.7 | 4.7 | 787 | 26.6 | 3574.3 || 8.37 || 52.3 | - | 3 | 28.8 | 4.7 | 841 | 26.6 | 3796.1 || 5.02 || 31.3 | - | 4 | 28.3 | 4.9 | 839 | 13.3 | 3690.5 || 4.50 || 28.1 | - | 5 | 5.4 | .. | 898 | .... | 3703.9 || 4.01 || 25.0 | - | 6 | 6.0 | .. | 931 | .... | 3841.7 || 3.36 || 21.0 | - | 7 | 5.6 | .. | 908 | .... | 3745.8 || 3.34 || 20.8 | - +----+--------+-----+--------+--------+---------++---------++------------+ - -It is evident from what has been said that both of these -non-nitrogenous foods, fat and carbohydrate, play a very important -part in nutrition, because of their ability to maintain in a measure -the integrity of tissue proteid. When we recall that a diet of pure -proteid, such as meat or eggs, must be excessive in quantity in order -to meet the energy requirements of the body, and that the stimulating -action of proteid food serves to whip up body metabolism, we can -appreciate at full measure the great physiological economy which -results from the addition of carbohydrate and fat to the daily diet. -The establishment of nitrogenous equilibrium is made possible at a much -lower level by the judicious addition of these two non-nitrogenous -foodstuffs. The same principle may be illustrated in another way, viz., -by noting the effect on tissue proteid of withdrawal of a portion of -the fat or carbohydrate of the intake, in the case of a person nearly -or quite in nitrogen balance. The following experiment[30] affords a -good example of what will occur under such treatment: - - [30] An experiment by Miura, quoted from A. Magnus-Levy in v. - Noorden’s Handbuch der Pathologie des Stoffwechsels, 1906, p. 331. - - +-------+---------------------------------------++---------+----------+ - | | Income. || |Balance of| - | +---------+-----+-------------+---------+|Output of| Nitrogen | - | |Nitrogen.| Fat.|Carbohydrate.|Calories.||Nitrogen.| in Body. | - +-------+---------+-----+-------------+---------++---------+----------+ - |Av. of | grams |grams| grams | || grams | | - |3 days | 15.782 |40.47| 289.6 | 1955 || 14.927 | +0.862 | - |Nov. 30| 15.782 |40.34| 177.3 | 1493 || 14.959 | +0.830 | - |Dec. 1| 15.782 |40.34| 177.3 | 1493 || 17.546 | -1.757 | - | 2| 15.782 |40.34| 177.3 | 1493 || 18.452 | -2.663 | - +-------+---------+-----+-------------+---------++---------+----------+ - | Average of the last two days -2.210 | - +---------------------------------------------------------------------+ - -Starting with the body in a condition of plus nitrogen balance, _i. -e._, with a mixed diet more than sufficient to maintain the tissue -proteid intact, the reduction of the fuel value of the food from 1955 -to 1493 calories by cutting off 112 grams of carbohydrate per day was -followed by a gradual, but marked, increase in the output of nitrogen; -indicating thereby the extent to which the body proteid was then drawn -upon to make good the loss of energy-containing income. The body showed -at the close of the experiment a minus nitrogen balance averaging -2.2 grams per day, or a loss of 13.8 grams of tissue proteid, which -would obviously have continued, under the above conditions, until the -body was exhausted. In other words, the 112 grams of carbohydrate, -if added to the diet on December 3 and the following days, would -have quickly saved the daily loss of 2.4 grams of nitrogen, and thus -changed the drain of tissue proteid to an actual gain, with consequent -establishment of a growing plus balance. - -It is obvious from what has been stated, that in man the body can -accomplish a storing of proteid only when the intake is reinforced by -substantial additions of fat or carbohydrate. It is plainly a matter of -great physiological importance that the body should be able to increase -at times its reserve of proteid. This, however, cannot apparently be -accomplished on a large scale under ordinary conditions. Any storing -up of nutritive material in excess, whether it be proteid or fat, -necessarily involves overfeeding, _i. e._, the taking of an amount of -food beyond the capacity of the body to metabolize at the time. Fat, -as we know, may be stored in large quantities, and it is in cases of -overfeeding with non-nitrogenous foods that we find accumulation of -fat most marked. Overfeeding with proteid, however, does not lead to -corresponding results, owing primarily to the peculiar physiological -properties of proteid; its general stimulating effect on metabolism, -the tendency of the body to establish nitrogenous equilibrium at -different levels, and the fact emphasized by von Noorden that flesh -deposition is primarily a function of the specific energy of developing -cells. In other words, the protoplasmic cells of the body are more -important factors in the storing or holding on to proteid than an -excess of proteid-containing food. - -It is generally considered as a settled fact, that in man it is -impossible to accomplish any large permanent storing or deposition of -flesh by overfeeding. Similarly, it is understood that the muscular -strength of man cannot be greatly increased by an excessive intake of -food. The only conditions under which there is ordinarily any marked -and permanent flesh deposition are such as are connected with the -regenerative energy of living cells. Thus, as von Noorden has stated, -an accumulation or storing of tissue proteid is seen especially in the -growing body, where new cells are being rapidly constructed; also in -the adult where growth may have ceased, but where increased muscular -work has resulted in an hypertrophy or enlargement of the muscular -tissue; and lastly in those cases where, owing to previous insufficient -food or to the wasting away of the body incidental to disease, the -proteid content of the tissues has been more or less diminished, and -consequently an abundance of proteid food is called for and duly -utilized to make good the loss. In some oft-quoted experiments by -Krug, conducted on himself, it was observed that with an abundant food -intake, sufficient to furnish 2590 calories per day (44 calories per -kilo of body-weight), a condition approaching nitrogenous equilibrium -was easily maintained. On then increasing the fuel value of the food -to 4300 calories (71 calories per kilo of body-weight) by addition -of fat and carbohydrate, there was during a period of fifteen days a -sparing of 49.5 grams of nitrogen or 309 grams of proteid, which would -correspond to about 1450 grams, or three pounds, of fresh muscle. It -is to be noted, however, that of this excess of calories added to the -intake only 5 per cent was made use of for flesh deposit, the remaining -95 per cent going to make fat. - -Again, we may call attention to the well-known fact that in feeding -animals for food, while fat may be laid on in large amounts, flesh -cannot be so increased by overfeeding. In this matter, however, race -and individuality count for considerable. Thus, there is on record a -more recent series of experiments conducted by Dapper[31] on himself -which shows some remarkable results. Starting with a daily diet not -excessive in amount, he was able by an addition of only 80 grams of -starch to accomplish a laying up of 3.32 grams of nitrogen per day for -a period of twelve days, or a total gain of 39.8 grams of nitrogen, -equal to 248 grams of proteid. It may be said that the gain of proteid -or flesh here for the twelve days was no greater than in the preceding -case (fifteen days), but the difference lies in the fact that Krug -accomplished his gain by increasing the daily intake from 2590 to 4300 -calories, an amount which he found too large to be eaten with comfort, -while the later investigator raised the fuel value of his daily food -from 2930 to only 3250 calories. As the experiments by Dapper contain -other points of interest bearing on the question before us, we may -advantageously consider them somewhat in detail. The following table -gives the more important results: - - [31] Max Dapper: Ueber Fleischmast beim Menschen. Inaug. Disser. - Marburg, 1902. - - +----+-----+--------------+-------------------+--------+------------------+ - |No. | | | Food Composition. | | | - |of |Dura-| Character +---------+---------+Nitrogen|Maxima and Minima | - |Exp.|tion.| of Food. |Nitrogen.|Calories.|Balance.|of Nitrogen-gain. | - +----+-----+--------------+---------+---------+--------+------------------+ - | |days | | grams | | grams | grams | - | 1 | 6 |Ordinary mixed| 20.25 | 2930 | +2.18 |+3.2 on 4th day. | - | | | diet | | | |+1.5 on 6th day. | - | | | | | | | | - | 2 | 12 |Ditto + 80 | 20.09 | 3250 | +3.32 |+4.75 on 2d day. | - | | | grams starch | | | |+4.65 on 12th day.| - | | | | | | |+2.30 on 8th day. | - | | | | | | | | - | 3 | 9 |Ditto + 80 | 24.58 | 3400 | +2.55 |+5.98 on 1st day. | - | | | grams starch,| | | |+4.73 on 2d day. | - | | | + 40 grams | | | |+0.50 on 6th day. | - | | | plasmon | | | |+1.60 on 9th day. | - +----+-----+--------------+---------+---------+--------+------------------+ - -As we look at these results, the nitrogen gain for the first and -second days of the third experiment and the first day of the second -experiment may well attract our attention, since they show an -astonishing laying by of proteid, or gain of flesh, under the influence -of a comparatively small increase in the fuel value of the food. A -gain of 5.98 grams of nitrogen means 37.3 grams of proteid, or more -than an ounce; by no means an inconsiderable addition for one day to -the store of tissue proteid. In the third experiment, where plasmon -(dried, milk proteid) was added to the diet, there is to be noted a -gradual falling off in the proteid-sparing power, which may perhaps -be interpreted as implying that the body was practically saturated -with proteid, and that owing to this fact the body was unable to -continue its laying hold of nitrogen. In the entire period of 21 -days, however, the body had succeeded in accumulating a store of 62.8 -grams of nitrogen, or 392 grams of proteid, and this without adding -very largely to the intake of non-nitrogenous matter. This experiment -affords a striking illustration of the ability of the body to “fatten -on nitrogen,” but it is very doubtful if such results can generally -be obtained. Lüthje,[32] however, has reported a large retention of -nitrogen on a diet containing 50 grams of nitrogen daily, with a fuel -value of 4000 calories. It is more than probable that there existed -in these particular cases some personal peculiarity or idiosyncrasy -which favored the proteid-sparing power. The personal coefficient of -nutrition is not to be ignored; it shows itself in many ways, and the -above results are to be counted among those that are exceptional and -not the rule. In the words of Magnus-Levy, “a given diet with Cassius -may lead to different results than with Anthony.” - - [32] Zeitschrift für klinische Medizin, Band 44, p. 22. - -For the study of many questions in nutrition, it becomes necessary to -determine accurately the transformations of energy within the body -as contrasted with the transformation of matter; the total income -and outgo of energy, measured in terms of heat, are to be compared -one with the other and a balance struck. Further, in studying the -metabolism of carbohydrate and fat it is necessary to determine the -output of gaseous products through the lungs and skin; to estimate the -excretion of carbon dioxide and water, and the intake of oxygen. For -these purposes, a special form of apparatus known as a respiration -calorimeter is employed. The double name is indicative of the twofold -character of the apparatus, viz., a suitably constructed chamber so -arranged as to permit of measuring at the same time the respiratory -products and the energy given off from the body. The form of apparatus -best known to-day, and with which exceedingly satisfactory work has -been done, is the Atwater-Rosa apparatus, as modified by Benedict. It -consists essentially of a respiration chamber, in reality an air-tight, -constant-temperature room (with walls of sheet metal, outside of which -are two concentric coverings of wood completely surrounding it, with -generous air spaces between), sufficiently large to admit of a man -living in it for a week or more at a time. Connected with the chamber -is a great variety of complex apparatus for maintaining and analyzing -the supply of oxygen, determining the amount of carbon dioxide and -of water, etc., etc. As an apparatus for measuring heat, the chamber -may be described as “a constant-temperature, continuous-flow water -calorimeter, so devised and manipulated that gain or loss of heat -through the walls of the chamber is prevented, and the heat generated -within the chamber cannot escape in any other way than that provided -for carrying it away and measuring it.”[33] - - [33] For an account of the respiration calorimeter and the great - diversity of apparatus accessory thereto, together with a description - of the methods of measurement, analysis, etc., see Publication No. - 42, Carnegie Institution of Washington, “A Respiration Calorimeter - with Appliances for the Direct Determination of Oxygen.” By W. O. - Atwater and F. G. Benedict. - -In illustration of the efficiency of an apparatus of this description, -and of the close agreement obtainable by direct calorimetric -measurement with the estimated energy, as figured from the materials -oxidized in the body, we may quote the following data from Dr. -Benedict’s report, referred to in the footnote. The subject was a young -man who had been fasting for five days. The experiment deals with the -metabolism on the first day after the fast, when a diet composed mainly -of milk was made use of, containing 53.31 grams of proteid, 211.87 -grams of fat, and 75.41 grams of carbohydrate. The following table -shows the results of the experiment: - - +--------------------------+--------+---------+---------+--------+-----------------+ - | Heat of Combustion of | (d) | (e) | (f) | | Heat Measured | - | Food and Excreta as | Avail- | Total |Estimated| Heat | Greater or | - | Determined by Bomb | able | Energy | Energy |Measured| Less than | - | Calorimeter. | Energy |from Body| from | by | Estimated. | - +--------+--------+--------+ from |Material | Material|Respira-+--------+--------+ - | (a) | (b) | (c) | Food. |Gained or| Oxidized| tion | | | - | Food. | Excre- | Urine. | a-(b+c)|Lost.[34]| in the | Calor- | Amount.|Propor- | - | | ment. | | | | Body. | imeter.| | tion. | - | | | | | | d-e | | | | - +--------+--------+--------+--------+---------+---------+--------+--------+--------+ - |calories|calories|calories|calories|calories | calories|calories|calories|per cent| - | 2569 | 149 | 103 | 2317 | +229 | 2088 | 2113 | +25 | +1.2 | - +--------+--------+--------+--------+---------+---------+--------+--------+--------+ - - [34] In the experiment, the body lost 29.16 grams of proteid = 165 - calories, but gained fat and glycogen = 393 calories. Hence, there - were 229 calories gained from body material. - -As is seen from the above figures, the total fuel value of the food -was 2569 calories. The fuel value of the unoxidized portion of the -food contained in the excreta was 149 + 103 calories, leaving as the -available energy of the food 2317 calories. This must be further -corrected by the fact, mentioned in the footnote, that a portion of -the food was stored as fat and glycogen, while the body lost at the -same time a small amount of proteid. Making the necessary correction -for these causes, we find 2088 calories as the energy from material -oxidized in the body. The actual output of energy as measured by the -calorimeter was 2113 calories, only 1.2 per cent greater than the -estimated amount. - -By aid of the respiration calorimeter, many important questions in -nutrition can be more or less accurately answered, especially such as -relate to the total energy requirements of the body. The law of the -conservation of energy obtains in the human body as elsewhere, and if -we can measure with accuracy the total heat output, with any energy -liberated in the form of work, and at the same time determine the total -excretion of carbon dioxide, water, nitrogen, etc., together with the -intake of oxygen, it becomes not only possible to ascertain the energy -requirements of the body under different conditions, but, aided by -data obtainable through study of the exchange of matter, we can draw -important conclusions concerning the sources of the energy, _i. e._, -whether from proteid, fat, or carbohydrate. - -It is obvious that a man asleep, or lying quietly at rest, in the -calorimeter, especially when he has been without food for some hours, -furnishes suitable conditions for ascertaining the minimal energy -requirements of the body. Under such conditions, bodily activity and -heat output are at their lowest, and we are thus afforded the means of -determining what is frequently called the basal energy exchange of the -body. The following table taken from Magnus-Levy, and embodying results -from many sources, shows the heat production during sleep, calculated -for 24 hours, of various individuals of different body-weight and of -different body surface. - -I venture to present these individual results, rather than make a -general statement simply, because it is important to recognize the -fact that the basal energy exchange differs according to body-weight, -extent of body surface, and the condition of the body. In the table, -the results are arranged in the order of body-weight, and it is -plain to see that the absolute energy exchange is greater with heavy -persons than with light, yet the energy exchange does not increase -in proportion to increase of body-weight. With a man of 83 kilos -body-weight, the basal exchange is only 30–40 per cent higher than -in a man of 43 kilos body-weight. In other words, the man of small -body-weight has, per kilo, a much higher basal exchange than the -heavier man. The energy exchange is more closely proportional to the -extent of body surface than to weight. - - +-------------+----------------+--------------+ - | Body-weight | Total Calories | Calories per | - | of the | for 24 Hours. | Kilo of | - | Individual. | | Body-weight. | - +-------------+----------------+--------------+ - | kilos | | | - | 43.2 | 1333 | 30.9 | - | 48.0 | 1214 | 25.3 | - | 50.0 | 1315 | 25.9 | - | 53.0 | 1527 | 28.8 | - | 55.0 | 1590 | 28.9 | - | 56.5 | 1519 | 26.8 | - | 57.2 | 1560 | 27.3 | - | 58.0 | 1510 | 26.0 | - | 62.5 | 1431 | 22.9 | - | 63.0 | 1418 | 22.5 | - | 63.0 | 1492 | 23.7 | - | 64.0 | 1656? | 25.8 | - | 64.9 | 1475 | 22.7 | - | 65.0 | 1498 | 23.0 | - | 65.0 | 1445 | 22.2 | - | 67.5 | 1608 | 23.8 | - | 67.5 | 1621 | 24.0 | - | 70.0 | 1661 | 23.7 | - | 70.0 | 1620 | 23.1 | - | 71.2 | 1787 | 25.1 | - | 72.6 | 1550 | 21.3 | - | 72.7 | 1657 | 22.8 | - | 73.0 | 1584 | 21.7 | - | 73.0 | 1630 | 22.4 | - | 75.6 | 1670 | 22.1 | - | 82.0 | 1556 | 19.0 | - | 82.7 | 2030? | 24.5 | - | 83.5 | 1670 | 20.0 | - | 88.3 | 2019? | 22.9 | - | 90.4 | 1773 | 19.6 | - +-------------+----------------+--------------+ - -As Richet has expressed it, the basal energy exchange is inversely -proportional to the body-weight and directly proportional to the body -surface. This is in harmony with the view advanced by v. Hösslin, “that -all the important physiological activities of the body, including -of course its internal work and the consequent heat production, are -substantially proportional to the two-thirds power of its volume, and -that since the external surface bears the same ratio to the volume, -a proportionality necessarily exists between heat production and -surface.”[35] - - [35] See Armsby: Principles of Animal Nutrition, p. 368. - -There are, however, many circumstances that modify, or influence, -energy exchange. Thus, the taking of food, with all the attendant -processes of digestion, assimilation, etc., involves an expenditure of -energy not inconsiderable. This has been experimentally demonstrated -on man by several investigators. With fatty food, Magnus-Levy found -that his subject lying upon a couch, as completely at rest as possible, -produced in the 24 hours 1547 calories when 94 grams of fat were eaten, -and 1582 calories when 195 grams of fat were consumed. The increase of -heat production over the basal energy exchange was 10 and 58 calories -respectively. With a mixed diet, where proteid food is a conspicuous -element, the increase in heat production is much more marked. Thus, -in some experiments reported from Sweden the following data were -obtained:[36] - - [36] Taken from Armsby: Principles of Animal Nutrition, p. 383. - - +---------+---------------------+------------------+ - | Day. | Energy of the Food. | Heat Production. | - +---------+---------------------+------------------+ - | | calories | calories | - | First | 4141 | .... | - | Second | 4277 | 2705 | - | Third | 0 | 2220 | - | Fourth | 0 | 2102 | - | Fifth | 0 | 2024 | - | Sixth | 0 | 1992 | - | Seventh | 0 | 1970 | - | Eighth | 4355 | 2436 | - | Ninth | 3946 | 2410 | - +---------+---------------------+------------------+ - -We see here an increase of 495 calories per day in heat production, -due to metabolism of the food ingested. In other words, with a basal -energy exchange of 2022 calories, the average of the five fasting days, -energy equivalent to 495 calories was expended in taking care of the -ingested food. It should be added, however, that the daily ration here -was somewhat excessive, 4193 calories being considerably in excess -of the requirements of the body. Finally, it should be stated that of -the several classes of foods, proteids cause the greatest increase in -metabolism and fats the least. - -In studying heat production in the body under varying conditions, -one of the important aids in drawing conclusions as to the character -of the body material burned up is the respiratory quotient. This is -the relationship, or ratio, of the oxygen absorbed to the oxygen of -the carbon dioxide eliminated, viz., CO_{2}/O_{2}. Carbohydrates -(C_{6}H_{12}O_{6}, C_{12}H_{22}O_{11}) all contain hydrogen and oxygen -in the proportion to form water, H_{2}O, and in their oxidation they -need of oxygen only such quantity as will suffice to oxidize the carbon -(C) of the sugar to carbon dioxide (CO_{2}). Carbohydrates, starch -and sugars, have a respiratory quotient of 1.00. Fat, on the other -hand, has a respiratory quotient of 0.7, and proteid, 0.8. Hence, it -is easy to see that the respiratory quotient will approach nearer to -unity as the quantity of carbohydrate burned in the body is increased. -Similarly, the respiratory quotient will grow smaller the larger the -amount of fat burned up. Practically, we never find a respiratory -quotient of 1.0 or 0.7, because there is always some oxidation of -proteid in the body. If, by way of illustration, we assume that the -energy of the body under given conditions comes from proteid to the -extent of 15 per cent, while the remaining 85 per cent is derived from -the oxidation of carbohydrate, the respiratory quotient will be 0.971. -If, however, the 85 per cent of energy comes from fat, the respiratory -quotient will change to 0.722. In the resting body, as in the early -morning hours, after a night’s sleep and before food is taken, the -respiratory quotient is generally in the neighborhood of 0.8. When, -however, as sometimes happens, the quotient at this time of day -approaches 0.9, it must be assumed that sugar is being burned in the -body, presumably from carbohydrate still circulating from the previous -day’s intake. - -As can easily be seen, any special drain upon either fat or -carbohydrate in the processes of the body will be indicated at once -by a corresponding change in the respiratory quotient. This we shall -have occasion to notice later on, in considering the source of the -energy of muscle contraction. Further, the respiratory quotient will -naturally change in harmony with transformations in the body which -involve alterations in oxygen-content, without the oxygen of the -inspired air being necessarily involved; as in the formation of a -substance poor in oxygen, such as fat, from a substance rich in oxygen, -such as carbohydrate. Moreover, the reversal of this reaction, as -in the formation of sugar from proteid with a taking on of oxygen, -will produce a corresponding effect upon the respiratory quotient. -As Magnus-Levy has clearly pointed out, in the formation of fat from -carbohydrate, carbon dioxide is produced in large amount without the -oxygen of the inspired air being involved at all. In such a change, -100 grams of starch will yield about 42 grams of fat, while at the -same time 45 grams of carbon dioxide will be produced. This might -cause the respiratory quotient to rise as high as 1.38. Again, in -the formation of sugar from proteid, the respiratory quotient may -sink very decidedly, the changes involved being accompanied by a -taking on of oxygen from the air, without, however, any corresponding -increase of carbon dioxide in the expired air. Assuming a manufacture -of 60 grams of dextrose from 100 grams of proteid, _i. e._, from the -non-nitrogenous moiety of the proteid molecule, a respiratory quotient -of 0.613 would be possible. Thus, a diabetic patient, living upon a -carbohydrate-free diet, consuming only proteid and fat, may show a -respiratory quotient of 0.613–0.707. These illustrations will suffice -to show how chemical alterations taking place in the body, involving -transformations of proteid, fat, and carbohydrate of the tissues -and of the food, may produce alterations in the respiratory quotient -without necessarily being directly connected with intake of oxygen or -output of carbon dioxide through the lungs; and how, conversely, the -respiratory quotient becomes a factor of great significance in throwing -light upon the character of the nutritive changes taking place in the -body. - -Among the various conditions that influence the energy exchange of -the body, muscle work stands out as the most conspicuous. It needs no -argument to convince one that all forms of muscular activity involve -liberation of the energy stored up in the tissues of the body; and -consequently that all work accomplished means chemical decomposition, -in which complex molecules are broken down into simple ones with -liberation of the contained energy, the energy exchange being -proportional to the amount of work done. As we have seen, the basal -energy exchange of the normal individual is ascertained by studying his -heat production while at rest--best during sleep--without food, when -involuntary muscle activity and heat production are at their lowest. -The maximum energy exchange is seen in the individual at hard muscular -work. Heat production is then at its highest, as can be ascertained -by direct calorimetric observation; or, by studying the output of -excretory products, which measure the extent of the oxidative processes -from which comes the energy for the accomplishment of the work. As -an illustration of the general effect of muscular work on the energy -exchange of the body, we may cite a summary of some results reported by -Atwater and Benedict,[37] the figures given being average results, from -several individuals, and covering different periods of time. Though -not strictly comparable in all details, they are sufficiently so to -illustrate the main principle. - - [37] Atwater and Benedict: Experiments on the Metabolism of Matter - and Energy in the Human Body 1900–1902. Bulletin No. 136, Office of - Experiment Stations, U. S. Department of Agriculture, 1903, p. 141. - - -HEAT GIVEN OFF BY BODY, INCLUDING FOR WORK EXPERIMENTS THE HEAT -EQUIVALENT OF THE EXTERNAL MUSCULAR WORK. - - +----------------+--------+---------------------------------------+--------+ - | | Total | Rates per Hour. | | - | | Amount +-------------------+-------------------+ Average| - | Kind of | of Heat| Day Periods. | Night Periods. | for | - | Experiment. | in 24 | | | 24 | - | | Hours. +---------+---------+---------+---------+ Hours. | - | | |7 A.M. to|1 P.M. to|7 P.M. to|1 A.M. to| | - | | | 1 P.M. | 7 P.M. | 1 A.M. | 7 A.M. | | - +----------------+--------+---------+---------+---------+---------+--------+ - | |calories| calories| calories| calories| calories|calories| - |Rest experiments| 2262 | 106.3 | 104.4 | 98.3 | 67.9 | 94.3 | - +----------------+--------+---------+---------+---------+---------+--------+ - |Work experiments|} | | | | | | - | Heat eliminated|} 4225 | 231.7 | 235.6 | 118.1 | 78.4 | 166.6 | - | | | | | | | | - |Heat equivalent |} | | | | | | - | of external |} 451 | 58.5 | 56.8 | ... | ... | ... | - | muscular work |} | | | | | | - +----------------+--------+---------+---------+---------+---------+--------+ - | Total | 4676 | 290.2 | 292.4 | 118.1 | 78.4 | 194.8 | - +----------------+--------+---------+---------+---------+---------+--------+ - -The work done in these experiments was on a stationary bicycle in the -calorimeter, and the heat equivalent was calculated from measurements -made by an ergometer attached to the bicycle. We are not concerned here -with details, but simply with the general question of the influence of -muscular work upon the energy exchange of the body. We note that the -work of the day periods, 7 A. M. to 7 P. M., resulted, in the several -cases brought together under the average figures, in an increased heat -production amounting to more than 100 per cent. Further, we observe -that in the body, as in all machines, only a fraction of the energy -liberated by the accelerated chemical decomposition, or oxidation, -was manifested as mechanical work, the larger part by far being heat -eliminated and lost. Thus, Zuntz has found that, in man, about 35 per -cent of the extra energy of the food used in connection with external -muscular work is available for that work. This, however, shows a -noticeably higher degree of efficiency than is generally obtainable -by the best steam or oil engines. Lastly, attention may be called to -the fact that after the work of the day was finished at 7 P. M., the -next period of six hours still showed an accelerated metabolism, as -contrasted with what took place during absolute rest. - -As bearing upon the exchange of matter in the body in connection with -muscular work, and as showing the relationship which exists here -between energy exchange and exchange of matter, we may quote a few -data relating to the elimination of carbon dioxide; remembering that -this substance represents particularly the final oxidation product in -the body of carbonaceous materials, such as fat and carbohydrate. The -following data, taken from Atwater and Benedict,[38] being results of -experiments upon the subject “J. C. W.,” are of value as showing the -variations in output of carbon dioxide that may be expected under the -conditions described: - - [38] Loc. cit., pp. 130 and 131. - - +------------------+---------+---------+-----------+---------+----------+ - | | | | | | Extra | - | | Rest Ex-| Rest Ex-| Work Ex- | Work Ex-| Severe | - | Period. |periments|periments| periments |periments| Work | - | | without | with |with Carbo-| with |Experiment| - | | Food. | Food. | hydrate |Fat Diet.| with | - | | | | Diet. | |Fat Diet. | - +------------------+---------+---------+-----------+---------+----------+ - | | grams | grams | grams | grams | grams | - | 7 A.M. to 1 P.M. | 189.6 | 230.4 | 694.0 | 642.3 | 907.0 | - | 1 P.M. to 7 P.M. | 172.6 | 232.0 | 705.6 | 634.8 | 821.3 | - | 7 P.M. to 1 A.M. | 167.2 | 196.6 | 260.1 | 230.3 | 842.7 | - | 1 A.M. to 7 A.M. | 146.7 | 153.1 | 161.1 | 157.6 | 502.6 | - +------------------+---------+---------+-----------+---------+----------+ - |Total for 24 hours| 676.1 | 812.1 | 1820.8 | 1665.0 | 3073.6 | - +------------------+---------+---------+-----------+---------+----------+ - -In considering these figures bearing on the output of carbon dioxide -under the conditions specified, we note at once a correspondence with -the total energy exchange, as indicated in the preceding table. As -previously stated, we are at present dealing simply with generalities, -and the important point to be observed here is that muscular work--7 A. -M. to 7 P. M.--in the work experiments, increases enormously the output -of carbon dioxide. We see clearly emphasized a connection between the -total energy exchange of the body, as expressed in calories or heat -units, and the oxidation of carbonaceous material, of which carbon -dioxide is the natural oxidation product. We note that on the cessation -of work--7 P. M. to 7 A. M.--the output of carbon dioxide tends to drop -back to the level characteristic of the corresponding period in rest, -with or without food. In the experiment with “extra severe muscular -work,” the results are different simply because here the subject -worked sixteen hours, necessitating a portion of the work being done -at night-time. Finally, it should be mentioned that the differences in -output of carbon dioxide in these experiments are somewhat greater than -in many experiments of this type, although all show the same general -characteristics. This may be explained, as stated by the authors from -whom the data are taken, “by the fact that J. C. W. was a larger and -heavier man than any of the others; that the differences in diet were -wider, and that the amounts of external muscular work were larger in -these experiments than in those with the other subjects.” - -If we pass from experiments of this type, conducted in a calorimeter, -to those cases where competitive trials of endurance are held by -trained athletes, _i. e._, where external muscular activity is pushed -to the extreme limit, we then see even more strikingly displayed the -effect of work in increasing the energy exchange of the body. One of -the best illustrations of this type of experiment is to be found in the -observations made in connection with the six-day bicycle race held in -New York City, at the Madison Square Garden, in December, 1898.[39] -The observations in question were made upon three of the athletes, -one of whom withdrew early in the fourth day, while the others -continued until the close of the race--142 consecutive hours--winning -the first and fourth places, respectively. The following table gives -the computation of energy of the material metabolized, exclusive of -body-fat lost: - - [39] See W. O. Atwater and H. C. Sherman: The effect of severe - and prolonged muscular work on food consumption, digestion, and - metabolism. Bulletin No. 98, Office of Experiment Stations, U. S. - Department of Agriculture. - - +------------+-------------+--------------+-------------+ - | Subject. | Duration of | Total Energy | Average per | - | | Experiment. | Metabolized. | Day. | - +------------+-------------+--------------+-------------+ - | | days | calories | calories | - | Miller | 6 | 28917 | 4820 | - | Albert | 6 | 36441 | 6074 | - | Pilkington | 3 | 13301 | 4464 | - +------------+-------------+--------------+-------------+ - -Miller, the winner of the race, who averaged a daily energy exchange -of 4820 calories, rode 2007 miles during the week, and finished the -race without physical or mental weakness resulting from the fatigue and -strain. During the first five days, he rode about 21 hours a day and -slept only 1 hour. Albert, who weighed a few pounds less than Miller, -covered 1822 miles in 109 hours, with an average daily exchange of -6074 calories. We may add a table (on the following page) showing the -balance of income and outgo of nitrogen in these three subjects, as -being of general interest in this connection. The figures given are -averages per day. - - +----------+-----+---------------------------------+-------------------+ - | |Dura-| Income in Food. | Nitrogen. | - | Subject. |tion +-----+-----+------+--------+-----+------+------+-----+ - | | of | | |Carbo-| | | | In | | - | |Exp. | Pro | Fat.| hy- | Fuel | In | In |Excre-|Loss.| - | | |teid.| |drate.| Value. |Food.|Urine.|ment. | | - +----------+-----+-----+-----+------+--------+-----+------+------+-----+ - | |days |grams|grams|grams |calories|grams|grams |grams |grams| - |Miller | 6 | 169 | 181 | 585 | 4770 | 29.4| 36.2 | 1.8 | 8.6 | - |Albert | 6 | 179 | 198 | 559 | 6095 | 29.1| 33.7 | 2.5 | 7.1 | - |Pilkington| 3 | 211 | 178 | 509 | 4610 | 36.0| 38.9 | 2.2 | 5.1 | - +----------+-----+-----+-----+------+--------+-----+------+------+-----+ - -The special significance of these data, as bearing upon the topic -under discussion, is that apparently all three of the subjects were -drawing in a measure upon their body material. As stated by Atwater -and Sherman, Pilkington lost per day 5.1 grams of nitrogen; that is -to say, the total nitrogen excreted exceeded the total nitrogen of -the food by 5.1 grams per day, corresponding to 33 grams of proteid, -which must have been drawn from the supply in the body. If we assume -that lean flesh contains 25 per cent of proteid, this would mean about -4-3/4 ounces per day. The other two subjects, Miller and Albert, lost -from the body per day 8.6 grams and 7.1 grams respectively of nitrogen, -which would imply a loss of about 54 grams and 44 grams of body proteid -respectively, or 8 ounces and 6-1/4 ounces of lean flesh per day. It is -evident, therefore, that none of the three subjects consumed sufficient -food to avoid loss of body proteid, under the existing conditions of -muscular activity. Indeed, it may be noted in Miller’s case that the -average fuel value of the food per day was 4770 calories, while the -average expenditure of energy per day was 4820 calories. We should -naturally expect, however, that any small deficiency in fuel value -would be made good by a call upon body fat. “Why the body should use -its own substance under such circumstances is a question which at -present cannot be satisfactorily answered. The fact that such was the -case, each of the contestants who finished the race consuming during -the period body protein equivalent to 2 or 3 pounds of lean flesh, and -that no injury resulted therefrom, would seem to indicate that these -men had stores of protein which could be metabolized to aid in meeting -the demands put upon the body by the severe exertion, without robbing -any of the working parts, and at the same time relieving the system -of a part of the labor of digestion. Possibly, the ability to carry -such a store of available protein is one of the factors which make for -physical endurance.”[40] This possibility we shall have occasion to -discuss in another connection. At present, the facts presented are to -be accepted as accentuating the general law that the energy exchange -of the body, everything else being equal, is increased proportionally -to increase in the extent of external muscular activity. It may be -noted that Albert, who did considerably less work than Miller, showed -a much larger exchange of energy than the latter athlete. This, -however, is to be connected with the fact that his fuel intake was 1300 -calories larger per day than Miller’s; in other words, the conditions -were not equal. This fact also calls to mind the observations of -Schnyder,[41] who, studying the relationship between muscular activity -and the production of carbon dioxide, maintained that the quantity of -this excretory product formed depends less upon the amount of work -accomplished than upon the intensity of the exertion; efficiency in -muscular work varying greatly with the condition of the subject, and -his familiarity with the particular task involved. - - [40] Atwater and Sherman. Loc. cit., p. 51. - - [41] L. Schnyder: Muskelkraft und Gaswechsel. Zeitschrift für - Biologie, Band 33, p. 289. - -From what has been said, it is obvious that oxygen consumption, as -well as output of carbon dioxide, must vary enormously with variations -in the muscular activity of the body. The one important factor -influencing the quantities of oxygen and carbon dioxide exchanged in -the lungs, _i. e._, the extent of the respiratory interchange, is -muscular activity; and since, as we have seen, carbonaceous material -is the substance mainly oxidized in muscle work, it follows, as -carbon dioxide is excreted principally through the lungs, that the -respiratory interchange becomes in good measure an indicator of the -extent of chemical decomposition incidental to external work. If we -recall that man, on an average, at each inspiration draws in about 500 -cubic centimeters of air (30 cubic inches), and that for the 24 hours -he averages 15 breaths a minute, it is easy to see that in one minute -the average man will inspire 7.5 litres of air, or 450 litres an hour, -with a total of 10,800 litres for the entire day, which is equivalent -to about 380 cubic feet. This would be a volume of air just filling a -room 7-1/3 feet in length, width, and height. Inspired air loses to the -body 4.78 volumes per cent of oxygen, while expired air contains an -excess of 4.34 volumes per cent of carbon dioxide. In muscular work, -respiration is increased in frequency and in depth. The volume of air -exchanged in the lungs during severe labor may be increased sevenfold, -while oxygen consumption and carbon dioxide excretion are frequently -increased 7–10 times. The following figures, being values for one -minute, show the effect on oxygen consumption of walking on a level and -climbing, the subject being a man of 55.5 kilos body-weight:[42] - - [42] G. Katzenstein: Ueber die Einwirkung der Muskelthätigkeit auf - den Stoffverbrauch des Menschen. Pflüger’s Archiv für die gesammte - Physiologie, Band 49, p. 330. Also Magnus-Levy: v. Noorden’s Handbuch - der Pathologie der Stoffwechsel, p. 233. - - +------------------+----------------------------------------+-----------+ - | |Oxygen Consumption in Cubic Centimeters.| | - | +---------+------------------------------+ | - | | | After Deducting Value | | - | Form of Work. | | for Rest. |Respiratory| - | | Total. +-----------+------------------+ Quotient. | - | | | | For Each | | - | | | Total. | Kilo of Moving | | - | | | | Weight. | | - +------------------+---------+-----------+------------------+-----------+ - |Standing at rest | 263.75 | .... | .... | 0.801 | - |Walking on a level| 763.00 | 499.25 | 8.990 | 0.805 | - |Climbing | 1253.20 | 989.45 | 17.819 | 0.801 | - +------------------+---------+-----------+------------------+-----------+ - -Remembering that these figures represent the oxygen consumption for -only one minute of time, it is easy to see the striking effect of -moderate and vigorous exercise on respiratory interchange. Simply -walking along a level suffices to increase the consumption of oxygen -threefold over what occurs when the body stands at rest. When the more -vigorous exercise attendant on lifting the body up a steep incline -is attempted, most striking is the great increase in the amount of -oxygen consumed. We thus see another forcible illustration of the -influence of muscular activity upon the exchange of matter in the -body, and a further confirmation of the statement, so many times made, -that oxidation--especially the oxidation of fats and carbohydrates by -which large quantities of heat are set free, easily convertible into -mechanical energy--is a primary factor in the metabolic processes, by -which the machinery of the living man is able to work so efficiently. - -Finally, we cannot avoid the conclusion that the outgoings of the body, -in the form of matter and energy, are subject to great variation, -incidental to the degree of activity of the day or hour. The ordinary -vicissitudes of life, bringing days of physical inaction, followed -perhaps by periods of unusual activity; changes in climatic conditions, -with their influence upon heat production in the body; alterations in -the character and amount of the daily dietary, etc.,--all seemingly -combine as natural obstacles to the maintenance of a true nutritive -balance. Outgo, however, must be met by adequate amounts of proper -intake if there is to be an approach toward a balance of nutrition. -In some way the normal, healthy man does maintain, approximately at -least, a condition of balance; not necessarily for every hour or for -every day, but the intake and outgo if measured for a definite period, -not too short, say for a week or two, will be found to approach each -other very closely. Body equilibrium and approximate nitrogen balance -may be reasonably looked for, as well as a balance of total energy, in -the case of a healthy man leading a life which conforms to ordinary -physiological requirements. The man who, on the other hand, consciously -or unconsciously, continues an intake way beyond the outgo, whose daily -income of nitrogen and total fuel value far exceeds the requirements -of his body, obviously lives with an accumulating plus balance, which -ordinarily shows itself in increasing body-weight and with a storing -away of fat. - -Equally conspicuous is the effect of an inadequate income of proper -nutriment; a food supply which persistently fails to furnish the -available nitrogen and total energy value called for by the body under -the conditions prevailing, will inevitably result in a minus balance, -which, if continued too long, must of necessity tax the body’s store -to the danger limit. At the same time, the well-nourished individual, -without being unduly burdened by a bulky store of energy-containing -material, is always supplied with a sufficient surplus to meet all -rational demands, when from any cause the intake fails, for brief -periods of time, to be commensurate with the needs of the body. It is -reasonable to believe, however, that in the maintenance of good health, -and the preservation of a high degree of efficiency, the body should be -kept in a condition approaching a true nutritive balance. - - - - -CHAPTER IV - -SOURCE OF THE ENERGY OF MUSCLE WORK, WITH SOME THEORIES OF PROTEID -METABOLISM - - TOPICS: Relation of muscle work to energy exchange. Views of Liebig. - Experimental evidence. Relation of nitrogen excretion to muscle - work. Significance of the respiratory quotient in determining - nature of the material oxidized. Fats and carbohydrates as source - of energy by muscles. Utilization of proteid as a source of energy. - Formation of carbohydrate from proteid. Significance of proteid - metabolism. Theories of Carl Voit. Morphotic proteid. Circulating - proteid. General conception of proteid metabolism on the basis of - Voit’s theories. Pflüger’s views of proteid metabolism. Rapidity of - elimination of food nitrogen. Methods by which nitrogen is split off - from proteid. Theories of Folin. Significance of creatinin and of the - percentage distribution of excreted nitrogen. Endogenous or tissue - metabolism. Exogenous or intermediate metabolism. Needs of the body - for proteid food possibly satisfied by quantity sufficient to meet - the demands of tissue or endogenous metabolism. Bearings of Folin’s - views on current theories and general facts of proteid metabolism. - Large proteid reserve and voluminous exogenous metabolism probably - not needed. Importance of feeding experiments in determining the true - value of different views. - - -As we have already seen, every form of muscular activity begets an -increase in the energy exchange of the body. Between the two extremes -of absolute rest and excessive muscular exertion, we find differences -of 2000 calories or more per day as representing the degree of chemical -decomposition corresponding to the particular state of muscular -activity. The work of the involuntary muscles, such as have to do with -peristalsis, respiration, rhythmical beat of the heart, etc., is a -relatively constant factor, though naturally subject to some variation, -as has been pointed out in other connections. External muscular -activity, however, is the one factor above all others that modifies the -rate of energy exchange. A little longer walk, a heavier load to carry, -a steeper hill to climb, any increase great or small in the activity -of the muscles of the body, means a corresponding increase in chemical -decomposition, with increased output of the ordinary products of tissue -oxidation. The material so consumed, or oxidized, must be made good -to hold the body in equilibrium; the supplies drawn upon are to be -replaced, if the tissues of the body are to be kept in a proper state -of efficiency. - -What is the nature of the material used up in connection with muscle -work? As can readily be seen, this is an important question, for on its -answer depends, in some measure at least, the character of the proper -intake, or food, to be supplied in order to make good the loss. If the -energy of mechanical work, the energy of muscle contraction, comes from -the breaking down of proteid matter alone, then obviously excessive -muscular work would need to be accompanied, or followed, by a generous -supply of proteid food. If, on the other hand, external work means -liberation of energy solely from non-nitrogenous materials, then it -is equally clear that fats and carbohydrates are the proper foods to -offset the drain incidental to vigorous muscular action. - -The views of Liebig, briefly referred to in a previous chapter, held -sway over physiologists for many years. His dictum that proteid foods -were true plastic foods, entering into the structure of the tissues -of the body, and that they alone were the real sources of muscular -energy, met for a time with no opposition. It was not until the advent -of a more critical spirit, accompanied by a fuller appreciation of -the necessity of experimental evidence, that physiologists began to -test with scientific accuracy the validity of the current views. It -is worthy of note that long prior to this time, even before oxygen -was discovered, the far-sighted and resourceful John Mayow, in his -work with the various “spirits” of the body and their relation to -respiration, etc., evolved the view that muscular power has its origin -in the combustion of fat brought to the muscles by the blood and burned -there by aid of a gas or “spirit” taken from the air by the lungs, and -likewise carried to the muscles by the circulating blood. Considering -the time when Mayow lived and the dearth of true scientific knowledge -as we measure it to-day, his hypothesis was a wonderful forestalling of -present views. - -It is quite obvious that the views of Liebig, if true, admit of easy -proof; since, if the energy of muscular power comes from the breaking -down of proteid, there should be a certain parallelism between the -output of nitrogen from the body and the amount of muscular work -accomplished, everything else being equal. As stated in a previous -chapter, such study of this question as was made soon disclosed the -fact that the one element above all others that seemed to influence the -output of nitrogen was the intake of proteid food. Thus, the English -investigators, Lawes and Gilbert, found by experimenting with animals -that when the latter were kept under uniform conditions of muscular -work, the amount of nitrogen excreted ran parallel with the intake -of nitrogen. Further, in the early experiments of Voit, the results -obtained clearly showed that variations in the amount of work performed -were practically without influence on the excretion of nitrogenous -waste products. - -The experiment, however, that came as a death blow to the theories of -Liebig was that of Fick and Wislicenus,[43] who in 1865 made an ascent -of the Faulhorn, 6500 feet high, using a diet wholly non-nitrogenous. -From the nitrogen excreted they were able, of course, to calculate the -amount of proteid oxidized in the body during the period of work, and -found that the proteid consumed could not have furnished, at the most, -more than one-half the energy required to lift the weights of their -bodies to the top of the high peak. Further, they observed that neither -during the work period, nor immediately after, was there any noticeable -increase in the excretion of nitrogen. Obviously, as they state, the -oxidation of proteid matter in the body cannot be the exclusive source -of the energy of muscular contraction, since the measurable amount -of external work performed in the ascent of the mountain was far -greater than the equivalent of the energy capable of being furnished -by the proteid actually burned. To which may be added the fact that -considerable energy, not measurable in their experiment, must have -been employed in the work of the involuntary muscles of the body; thus -increasing by so much the difference between the muscular work actually -accomplished and the available energy from proteid consumed. It is true -that minor criticisms regarding certain details of the experiment can -be offered to-day, such as the fact that the men were, in a measure, -in a state of “nitrogen starvation,” etc., but these criticisms do -not in any degree militate against the main thesis that the energy of -muscular contraction does not come exclusively from the consumption or -breaking down of proteid, either of food or tissue. Vigorous and even -severe muscular work does not necessarily increase the decomposition -of proteid material. Dogs made to run in large treadmills, with the -same diet as on resting days, were found to excrete practically no -more nitrogen than during the days of rest. Occasionally, however, -in some one experiment the output of nitrogen would show an increase -over the output on resting days. Further, experiments made with horses -led to essentially the same result, except that greater increase in -the excretion of nitrogen was observed than with dogs. This increase -in nitrogen output, however, as a concomitant of increased muscular -activity, could be prevented by adding to the amount of carbohydrate -food. - - [43] See Gesammelte Schriften von Adolf Fick. Ueber die Entstehung - der Muskelkraft. Band 2, p. 85. Würzburg, 1903. - -While experiments of this nature, on man and animals, all tended to -show little or no increase in the excretion of nitrogen, as a result -of muscle work; and likewise no increase in the output of sulphur and -phosphorus, thus strengthening the view that muscular energy is not the -result of proteid disintegration, there was observed marked increase -in the consumption of oxygen, and in the excretion of carbon dioxide. -Non-nitrogenous matter was thus at once suggested as the material -with which muscle chiefly does its work. There is to-day no question -of the general truth of this statement, yet there are other aspects -of the problem to be considered before we can lay it aside. Pflüger, -working with dogs, and Argutinsky, experimenting on himself by arduous -mountain climbing, reached conclusions seemingly quite opposed to what -has just been said. Their results, however, admit of quite a different -interpretation from what they were disposed to attach to them. Thus, -Pflüger[44] would go back to the old view that all muscle work is at -the expense of proteid material, because lean dogs fed mainly, or -entirely, on meat and made to do an excessive amount of work were found -by him to excrete nitrogen somewhat in proportion to the amount of work -done. Argutinsky,[45] likewise, in his mountain climbing carried to the -point of fatigue, and with a high proteid intake likewise, saw in the -increased output of nitrogen a suggestion of the same idea. In reality, -however, their results merely prove that, under some circumstances, -proteid may serve as the chief source of muscular energy; as when the -body is poor in fat and carbohydrate, or when the intake consists -solely of proteid matter. In other words, muscular work may result in -an increased excretion of nitrogen when the work is very severe, and -there is not a corresponding increase in the fats or carbohydrates -(fuel ingredients) of the food. In the words of Bunge,[46] “we might -assume _à priori_, on teleological grounds, that in the performance -of its most important functions the organism is to a certain extent -independent of the quality of its food. As long as non-nitrogenous -food is supplied in adequate quantity or is stored up in the tissues, -muscular work is chiefly maintained from this store. When it is gone -the proteids are attacked.” - - [44] Pflüger: Die Quelle der Muskelkraft. Pflüger’s Archiv für die - gesammte Physiologie, Band 50, p. 98. - - [45] Argutinsky: Muskelarbeit und Stickstoffumsatz. Ibid., Band 46, - p. 552. - - [46] Bunge: Textbook of Physiological and Pathological Chemistry. - Second English Edition, 1902, p. 352. - -There is no question that the energy of muscular contraction can come -from all three classes of organic foodstuffs. Voluntary muscular -movement is under the control of the nervous system, and when the -stimulus is applied the muscle is bound to contract, provided of -course there is sufficient energy-containing material present to -furnish the means. Muscle tissue, like other tissues and organs, has -a certain power of adaptability, by which it is able to do its work, -even though it is not adequately supplied with its preferred nutrient. -While proteid is plainly not the material from which the energy of -muscular contraction is ordinarily derived, it is equally evident -that in emergency, as when the usual store of carbohydrate and fat is -wanting, proteid can be drawn upon, and in such cases vigorous work -may be attended with increased nitrogen output. In harmony with this -statement, we find on record in recent years many experiments, both -with man and animals, where severe muscular labor is accompanied by an -excretion of nitrogen beyond what occurs on days of rest; but by simply -adding to the intake of non-nitrogenous food this increased outgo of -nitrogen is at once checked. With moderate work, the nitrogen outgo -is rarely influenced; it is only when the work becomes excessive, or -the store of non-nitrogenous reserve is small and the intake of the -latter food is limited, that proteid matter is drawn upon to supply the -required energy. - -Recalling what has been said regarding the significance of the -respiratory quotient, it is obvious that we have here a means of -acquiring information as to the character of the material that is -burned up in the body during muscular work. Increased metabolism -of carbohydrate will necessarily result in raising the respiratory -quotient, and if the latter food material alone is involved the -respiratory quotient must naturally approach 1.0. Zuntz, however, has -clearly shown that vigorous muscular activity does not materially -change the respiratory quotient; except in cases of very severe work, -where the oxygen-supply of the muscles is interfered with. Indeed, the -muscles may be made to do work sufficient to increase the consumption -of oxygen threefold or more, without any change in the respiratory -quotient being observed. And as there is frequently no change whatever -in the output of nitrogen under these conditions, it follows that the -energy of the muscle work must have come from the decomposition of -non-nitrogenous material. If carbohydrates alone were involved, the -respiratory quotient would obviously undergo change. Since, however, -this remains practically stationary, we are led to the conclusion that -fat must be involved in large degree, in addition to carbohydrate. - -In this connection, it is a significant fact that with _fasting_ -animals, where the store of carbohydrate material is more or less used -up, severe muscle work may be accomplished without any appreciable -increase in nitrogen output, thus showing that proteid material is not -involved and clearly pointing to fat as the source of the muscular -energy. Thus, in an experiment referred to by Leathes, a dog on the -sixth and seventh day of starvation was made to do work in a treadmill -equivalent to climbing to a height of 1400 meters, yet the output -of nitrogen was increased from six to only six and a half grams. -Obviously, not much of the energy of this muscle work could have come -from the breaking down of proteid, but it must have been derived mainly -from the oxidation of fat. There is abundant evidence that fat can be -used as a source of energy by muscles, as well as carbohydrates and -proteids, and there is every reason for believing that the yield of -work for a given amount of chemical energy in the form of fat is as -good as in the case of either of the other two substances. In fact, the -observations of Zuntz show that fat can be used just as economically -by the body for muscle work as either carbohydrates or proteid. Thus, -in one experiment,[47] he determined the oxygen-consumption and -respiratory quotient in a man resting and working on three different -diets--one principally fat, one principally carbohydrate, and the other -principally proteid--and found that slightly less oxygen and energy -were required to do work on the fat diet than on the others. This is -clearly shown in the following table: - - [47] Quoted from Leathes: Problems in Animal Metabolism, p. 100. - - +------------+------------------+------------------+------+----------------+ - | | | | | Per | - | | Resting. | Working. |Kilo- | Kilogram-meter | - | | | |gram- | of Work. | - | Diet +--------+---------+--------+---------+meters+------+---------+ - |Principally.| Oxygen |Respira- | Oxygen |Respira- | of |Oxygen|Calories.| - | |Used per| tory |Used per| tory | Work | Used.| | - | | Minute.|Quotient.| Minute.|Quotient.| Done.| | | - +------------+--------+---------+--------+---------+------+------+---------+ - | | c.c. | | c.c. | | | c.c. | | - |Fat | 319 | 0.72 | 1029 | 0.72 | 354 | 2.01 | 9.39 | - |Carbohydrate| 277 | 0.90 | 1029 | 0.90 | 346 | 2.17 | 10.41 | - |Proteid | 306 | 0.80 | 1127 | 0.80 | 345 | 2.38 | 11.35 | - +------------+--------+---------+--------+---------+------+------+---------+ - -From these data, we see that per kilogram-meter of work less energy -was required and less oxygen consumed with fat than with either of the -other two foodstuffs; but practically, fat and carbohydrate as sources -of muscle energy have about the same value. - -Much stress is ordinarily laid upon the importance of a large intake -of proteid food whenever the body is called upon to perform severe, or -long-continued, muscular work; but in view of what has been stated it -may be questioned whether there is any real physiological justification -for such custom. The pedestrian Weston,[48] who in 1884 walked 50 miles -a day for 100 consecutive days, was found by Blyth during a period of -five days to consume in his food 37.2 grams of nitrogen a day, while he -excreted only 35.3 grams, leaving a balance of 1.9 grams of nitrogen -per day apparently stored in the body. His daily food during this -period was composed of 262 grams of proteid, 64.6 grams of fat, and 799 -grams of carbohydrate, with an estimated fuel value of 4850 calories. -Yet he performed this large amount of work daily, and still laid by a -certain amount of proteid on a ration, the energy value of which would -not ordinarily be considered high for the muscular work to be done. -Fourteen years prior to this, Weston, while in New York, was carefully -studied by Dr. Flint during a period of 15 days, on 5 of which he -walked a total of 317 miles. His diet was essentially a proteid diet, -consisting principally of beef extract, oatmeal gruel, and raw eggs. -Nitrogen intake and output were carefully compared during the days of -rest and during the days of work, with the results tabulated. - - [48] This and the following account of Weston are taken from Bulletin - No. 98, U. S. Department of Agriculture, Office of Experiment - Stations. The effect of severe and prolonged muscular work on food - consumption, digestion, and metabolism. By W. O. Atwater and H. C. - Sherman, p. 13. - - +--------------+----------------+--------+--------------------------+ - | | | | Nitrogen. | - | | | +-----+------+------+------+ - | | |Duration| In | In | In |Gain +| - | Period. | Occupation. |of Test.|Food.|Urine.|Excre-| or | - | | | | | |ment. |Loss -| - +--------------+----------------+--------+-----+------+------+------+ - | | | days |grams|grams |grams |grams | - |Fore period |Comparative rest| 5 | 22.0| 18.7 | 1.4 | +1.9 | - | | | | | | | | - |Working period|Walking 62 miles|{ | | | | | - | | per day |{ 5 | 13.2| 21.6 | 1.6 |-10.0 | - | | | | | | | | - |After period |Rest | 5 | 28.6| 22.0 | 2.2 | +4.4 | - +--------------+----------------+--------+-----+------+------+------+ - -In this case it will be noted that the daily ration was comparatively -small, and, further, that during the working period the subject -consumed much less proteid than on the resting days. Moreover, when -we remember that the total energy value of his diet must have been -quite small, it is not at all strange that in the laborious task of -walking 62 miles a day he should have temporarily drawn upon his store -of body proteid to the extent of 62.5 grams, or 10 grams of nitrogen a -day. Such experiences, however, do not by any means constitute proof -that in excessive muscular work there is need for the consumption of -correspondingly increased quantities of proteid food, or that the -energy of muscular work comes preferably from the breaking down of -proteid material. Carbohydrate and fat unquestionably take precedence -over proteid in this respect, and we may accept as settled the view -that in all practical ways carbohydrate and fat stand on an equal -footing as sources of muscular energy. Less clear, perhaps, is the -question as to how these two radically different types of organic -material are utilized by the muscle. It has been a favorite belief -among some physiologists that the contracting muscle makes use of -only one substance as the direct source of its energy, and that this -substance is the sugar dextrose. This view would seemingly imply that -fat and proteid must undergo alteration prior to their utilization -by the muscle; that, possibly, the carbon of the fat and proteid -is transformed into sugar before the muscle can make use of it. So -far as fat is concerned, this view is not supported by the facts -available, since experiments show that the heat and energy liberated -in the utilization of a given amount of fat in muscle work are in -harmony with the energy value of the fat; in other words, the fat is -apparently burned, or oxidized, directly, without undergoing previous -transformation into any form of carbohydrate; or, if transformation -does occur, under some conditions, it must take place within the muscle -and without loss of energy. The practical significance of these facts -is at once apparent, for if fat, in order to be available as a source -of muscle energy, must first undergo conversion into sugar, it would -be far more economical from a physiological standpoint to replace the -fat of the diet with carbohydrate in any attempt to provide suitable -nourishment for the working muscle. We may safely conclude, however, -that fat and carbohydrate, as previously suggested, are in reality both -capable of direct metabolism by the muscular tissue, and that each is -of value as a source of muscular energy in proportion to its heat of -combustion, yielding substantially the same proportion of its potential -energy in the form of mechanical work. - -Regarding the utilization of proteid as a source of energy by the -muscle, there are many grounds for believing that here the body -has to deal with certain alterations, before the proteid can be -made available. We may indeed conjecture the transformation of a -non-nitrogenous portion of the proteid molecule into carbohydrate, as -a necessary step in its utilization for muscle work. It is certainly -true that in the ordinary katabolic processes, through which proteid -passes, there is a tendency for the nitrogen-containing portion to -be quickly split off and eliminated, leaving a carbonaceous residue -which may represent as much as 80 per cent of the total energy of the -original proteid. This so-called carbon moiety of the proteid molecule -is apparently much less rapidly oxidized than the nitrogenous portion, -and may indeed be temporarily stored in the body, in the form of fat or -carbohydrate.[49] We have very convincing proof that the carbohydrate -glycogen can be formed from proteid. Thus, the feeding of proteid to -warm-blooded animals may be accompanied by an accumulation of glycogen -in the liver. This is interpreted as meaning that in the cleavage -of proteid by digestion the various nitrogenous products formed are -somewhere, probably in the liver, still further acted upon; the -contained nitrogen with some of the carbon being converted into urea, -while the non-nitrogenous residue is transformed into glycogen, or -sugar. That some such change takes place, or, more specifically, that -carbohydrate does result from proteid is more strikingly shown in human -beings suffering with diabetes. In severe forms of this disease, all -carbohydrate food consumed is rapidly eliminated through the kidneys in -the form of sugar, the body having lost the power of burning sugar. If -such a person is placed upon a diet composed exclusively of proteid, -sugar still continues to be excreted, and there is observed a certain -definite relationship between the nitrogen output and the excretion of -sugar, thus implying that they have a common origin. - - [49] See Leo Langstein: Die Kohlehydratbildung aus Eiweiss. - Ergebnisse der Physiologie, Band 3, Erster Theil, p. 456. - - See also, Lüthje: Zur Frage der Zuckerbildung aus Eiweiss. Archiv für - d. gesammte Physiologie, Band 106, p. 160. - -Further, there are certain drugs, such as phloridzin, which, when -introduced into the circulation, set up a severe diabetes and -glycosuria. Dogs treated in this way, fed solely on proteid or even -starved for some time, will continue to excrete sugar, and as in the -previous instance, there is observed a certain definite ratio between -the nitrogen output and the elimination of sugar; thus leading to -the conclusion that both arise from the destruction of the proteid -molecule. Careful study of this ratio of dextrose to nitrogen has led -Lusk to the conclusion that full 58 per cent of the proteid may undergo -conversion into sugar in the body. Hence, it is easy to see how in -muscle work, when proteid is the sole source of the energy of muscular -contraction, the work accomplished may still result from the direct -oxidation of carbohydrate material, indirectly derived from the proteid -molecule. It requires no argument, however, to convince one that such a -procedure for the normal individual is less economical physiologically -than a direct utilization of carbohydrate and fat, introduced as such -and duly incorporated with the muscle substance. Consequently, in the -nourishment of the body for vigorous muscular work, there is reason -in a diet which shall provide an abundance of carbohydrate and fat; -proteid being added thereto only in amounts sufficient to meet the -ordinary requirements of the body for nitrogen and to furnish, it may -be, proper pabulum for the development of fresh muscle fibres, where, -as in training, effort is being made to strengthen the muscle tissue -and so enable it to do more work. Increase in proteid food may help to -make new tissue, but the source of the energy of muscle work is to be -found mainly in the breaking down of the non-nitrogenous materials, -carbohydrate and fat. - -In view of these facts, we may advantageously consider next the real -significance of the proteid metabolism of the body. As we have seen, a -meal rich in proteid leads at once--within a few hours--to an excretion -of urea equivalent to full 50 per cent of the nitrogen of the ingested -proteid, while a few hours later finds practically all of the nitrogen -of the intake eliminated from the body. Further, it is to be remembered -that in a general way this occurs no matter what the condition of the -body may be at the time and no matter how large or small the amount of -proteid consumed. In other words, there is practically no appreciable -storing of nitrogen or proteid for future needs,--at least none that is -proportional to the increase in nitrogen intake, even though the body -be in a condition approximating to nitrogen starvation. Moreover, it -is to be recalled that the increased proteid metabolism attendant on -increased intake of proteid food is accompanied by an acceleration of -the metabolism of non-nitrogenous matter; thus resulting in a stirring -up of tissue change, with consequent oxidation and loss of a certain -proportion of accumulated fat and carbohydrate. Coincident with this -increased excretion of nitrogen, the output of carbon dioxide is -likewise increased somewhat, due as is believed mainly to increased -metabolism of the involuntary muscle fibres of the gastro-intestinal -tract, by action of which the accelerated peristalsis so characteristic -of food intake is accomplished. Further, the increased output of -carbon dioxide, under these conditions, is to be attributed also to -the greater activity of the digestive and excretory organs, naturally -stimulated to greater functional power by the presence of proteid -foods and their decomposition products. Still, as stated by Leathes, -“the two main end-products of proteid metabolism, urea and carbonic -acid, are, to a great extent, produced independently of each other, -and the reactions which result in the discharge of the nitrogen are -not those in which energy is set free, work done, and carbonic acid -produced.” In other words, there is suggested what we have already -referred to, viz., that in proteid metabolism a nitrogenous portion of -the proteid molecule is quickly split off and gotten rid of, while the -non-nitrogenous part may be reserved for future oxidation, serving as -a source of muscle energy or for other purposes. This being so, it is -plain that “proteid metabolism in so far as it is concerned with the -evolution of energy, proteid metabolism in its exothermic stages, may -be almost entirely non-nitrogenous metabolism” (Leathes). - -Is there any advantage to the body, however, in this carbonaceous -residue of the proteid molecule over simple carbohydrate and fat? -Can the processes of the body be accomplished more economically, -or more advantageously, with a daily diet so constructed that the -tissues and organs must depend mainly upon this carbon moiety of -the proteid molecule for their energy-yielding material? It has been -one of the physiological dogmas of the past, that the tissues and -organs of the body, or rather their constituent cells, preferred to -use proteid for all their needs whenever it was available. If proteid -were wanting, either because of insufficient intake, or because of -excessive activity, then the tissue cells would draw upon their store -of non-nitrogenous material. Food proteid and tissue proteid, however, -were the materials preferred by the organism, so ran the argument, and -the large and incessant output of nitrogen which accompanied the intake -of proteid was accepted as proof of the general truth of this idea. -We might well question wherein lies the great advantage to the body -in this continual excretion of nitrogen; whether the loss of energy -in handling and removing the nitrogenous portion of the necessarily -large proteid intake, in order to render available the non-nitrogenous -part of the molecule, might not more than compensate for the supposed -gain? But the truly astonishing fact that the output of nitrogen runs -parallel with the intake of proteid, that the body cannot store up -nitrogen to any large extent, has been taken as conclusive evidence -that the organism prefers to use proteid for all of its requirements. -Truly, we might just as well argue that this significant rise in -the excretion of nitrogen after partaking of a proteid meal is an -indication that the body has no need of this excess of nitrogen; that -it is indeed a possible source of danger, since the system strives -vigorously to rid itself of the surplus, and that the energy-needs of -the body can be much more advantageously and economically met from fat -and carbohydrate than from the carbonaceous residue resulting from the -disruption of the proteid molecule. - -In discussing these questions, we shall need to refer to several of -the current theories concerning proteid metabolism, notably, the -theories of Voit, Pflüger, and Folin. In 1867 Carl Voit,[50] of -Munich, advanced the view that the proteid material of the body exists -in two distinct forms, viz., as “morphotic” or “organized” proteid, -representing proteid which has actually become a part of the living -units of the body, _i. e._, an integral part of the living tissues; -and “circulating” proteid, or that which exists in the internal meshes -of the tissue, or in the surrounding lymph and circulating blood. -The real point of distinction here is that while one portion of the -body proteid is raised to the higher plane of living matter, _i. e._, -becomes a component part of the living protoplasm, another and perhaps -larger portion is outside of the morphological framework of the tissue, -constituting a sort of internal medium which bathes the living cells, -and acts as middleman between the blood and lymph on the one side and -the living cells on the other. According to Voit’s view, it is this -circulating proteid that undergoes metabolism; the proteid of the food -after digestion and absorption being carried to the different tissues -and organs, and then, without becoming an integral part of the living -protoplasm of the cells, it is broken down under the influence of -the latter. Obviously, small numbers of tissue cells are constantly -dying, their proteid matter passing into solution, where it likewise -undergoes metabolism. In other words, according to Voit, the great -bulk of the proteid undergoing katabolism is the circulating proteid, -derived more or less directly from the food, and which at no time has -been a part of the tissue framework; while a smaller, but more constant -amount, represents the breaking down of tissue cells. This conception -of proteid metabolism is akin to our conception of morphological and -physiological destruction. In the words of Foster: “We know that an -epithelial cell, as notably in the case of the skin, may be bodily -cast off and its place filled by a new cell; and probably a similar -disappearance of and renewal of histological units takes place in all -the tissues of the body to a variable extent. But in the adult body -these histological transformations are, in the cases of most of the -tissues, slow and infrequent. A muscle, for instance, may suffer very -considerable wasting and recover from that wasting without any loss or -renewal of its elementary fibres. And it is obvious that the metabolism -of which we are now speaking does not involve any such shifting of -histological units. On the other hand, we find these histological -units, the muscle fibre or the gland cell, for instance, living on -their internal medium, the blood, or rather on the lymph, which is -the middleman between themselves and the actual blood flowing in the -vascular channels.” - - [50] See Voit: Hermann’s Handbuch der Physiologie, Band 6, p. 301. - -Voit claims that the proteid dissolved in the fluids of the body -is more easily decomposable than that which exists combined in -organized form, or as more or less insoluble tissue proteid; and it -is this soluble and circulating form which, under the influence of -the living cells, undergoes destruction or metabolism. We know, as -has been previously stated, that oxidation does not take place to -any extent in the circulating blood, and similarly there is every -reason for believing that proteid metabolism does not occur in this -menstrum. Metabolism is limited mainly to the active tissues of the -body, but according to the present conception of the matter it does -not occur at the expense of the proteid of the living cells, but -involves material contained in the fluids bathing the cells; _i. e._, -it is not the organized proteid that undergoes metabolism, but the -proteid circulating in and about the internal meshes of the cells and -tissues, the living cell being the active agent in controlling the -process. Further, this view lessens the difficulty of understanding -the elimination of nitrogen after a meal rich in proteid. If it was -necessary to assume that all the proteid of our daily food is built -up into living protoplasm before katabolism occurs, it would be -exceedingly difficult to explain the sudden and rapid elimination of -nitrogen which follows the ingestion of proteid. For example, we can -hardly imagine that merely eating an excess of proteid food will lead -to an actual breaking down of the living framework of the tissues, -equivalent to the amount of nitrogen which the body at once eliminates. -Voit’s theory, on the other hand, supposes a twofold origin of the -nitrogen excreted; one part, the larger and variable portion, comes -from the direct metabolism of the circulating proteid, being the -immediate result of the ingested food and varying in amount with the -quantity of proteid food consumed; the other, smaller and less variable -in amount, has its origin in the metabolism of the true tissue proteid, -or the actual living framework of the body. - -In a fasting animal, the tissues and organs of the body still contain -a large proportion of proteid matter, yet only a small fraction of -this proteid is eliminated each day, hardly 1 per cent. If, however, -proteid is absorbed from the intestine, proteid metabolism is at once -increased, and the excretion of nitrogen may be fifteen times greater -than during hunger. In other words, the extent of proteid metabolism -is not at all proportional to the total amount of proteid contained -in the body as a whole, but runs parallel in a general way with the -quantity of proteid absorbed from the intestine. Obviously, the newly -absorbed proteid is quite different in nature from the proteid which -in much larger amounts is deposited throughout the body, since it is -not organized and is so much more easily decomposable (Voit). This is -the circulating proteid of the body; it exists in solution, and it is a -significant fact that, according to Voit, the chemical transformations -that characterize proteid katabolism occur only in solution. The -organized proteid, on the other hand, is in a state of suspension, -and its katabolism, which is relatively very small, is preceded by -solution of the proteid in the fluids of the tissue, after which -its further breaking down is assumed to be the same as that of the -circulating proteid. This latter view is a fundamental part of the Voit -theory; in long-continued fasting, for example, the living protoplasm -of the various tissues and organs is of necessity drawn upon for the -nourishment of the more vital parts of the body, such as the brain, -spinal cord, etc., consequently the organized proteid is gradually -dissolved and then decomposed, after it has become liquefied and has -thus lost its organized structure. - -In this conception of proteid metabolism, we picture the different -organs and tissues of the body as being permeated by a fluid which -carries variable amounts of nutritive material, the quantity of the -latter determining in a way the extent of the proteid katabolism which -shall take place. As the proteid of the food passes into the blood and -lymph, the fluids bathing the cells are correspondingly enriched, and -as a result, proteid katabolism is accelerated in parallel degree. -During hunger, on the other hand, the organized proteid of the tissue -cells is gradually liquefied and passes out into the current of the -circulating fluids. As before stated, the organized proteid as such is -never decomposed; it must first enter into solution, and then under -the influence of the living cells it undergoes disruption in the same -manner as the circulating proteid. It is thus evident that the tissue -cells and the circulating fluids permeating them bear an ever changing -relationship to each other. Excess of circulating proteid will be -attended by increased katabolism, while at the same time there may be -some accumulation of proteid in the cells, and indeed some conversion -into organized proteid. During fasting, hunger, or with an insufficient -intake of proteid food, the current will naturally be in the opposite -direction, and organized proteid will slowly, but surely, be drawn -upon. - -Again, we may ask in view of these facts, of what real use to the -body is this large katabolism of circulating proteid? We can easily -understand the need of proteid to supply the loss incidental to the -breaking down of organized or true tissue proteid, but this we are led -to believe is very small in amount. Is there any real need for proteid -beyond this requirement? The physiological fuel value of proteid is -no greater than that of carbohydrate and considerably less than half -that of fat, consequently there is on the surface no apparent reason -why proteid should be used for its energy value in preference to the -non-nitrogenous foodstuffs. Further, as we have seen, the energy of -muscle work comes mainly, at least, from the breaking down of fat and -carbohydrate; proteid, in the case of the well-nourished individual, -ordinarily playing no part in this important line of energy exchange. -Lastly, in the katabolism of proteid there is the large proportion -of nitrogenous matter to be split off and disposed of before the -carbon moiety of the molecule can be rendered available. Here, we have -involved not only a loss of energy, but in addition a certain amount of -what appears to be useless labor thrown upon the liver, kidneys, and -other organs. Is there any wonder that the thoughtful physiologist, -looking at the facts and theories presented by the Voit conception -of proteid katabolism, should ask wherein lies the value to the body -of this high rate of metabolism of circulating proteid, a rate of -metabolism which is seemingly governed primarily by the amount of -proteid food ingested? - -Turning next to Pflüger’s[51] views regarding proteid katabolism, we -find a totally different outlook. Here, the supposition prevails that -the plasma of the blood and lymph, with its contained proteid, is the -food of the organs or their cells, but that before this food material -can undergo katabolism it must first be absorbed by the cell and built -up into the living protoplasm of the tissue. In other words, according -to the views expressed by Pflüger, katabolism must be preceded by -organization of the proteid. Expressed in still different language, -the proteid material circulating in blood and lymph must be eaten up -by the hungry cells and, by appropriate anabolic processes, made an -integral part of the living protoplasm before disassimilation can -occur. Further, according to Pflüger’s conception of these processes, -there is a radical difference in the chemical nature of living -protoplasm as compared with that of the so-called circulating proteid. -The latter is looked upon as being comparatively stable, resisting -oxidation in high degree, and hence not prone to undergo metabolism. -Living protoplasm, on the other hand, is characterized by instability, -suffering oxidation with the greatest ease, and hence readily broken -down in the ordinary processes of katabolism. Assuming for the moment -the correctness of this theory, we see at a glance that all disruption -of proteid matter in the body must be preceded by the upbuilding of the -proteid into living protoplasm. There can be no destruction of proteid -until the latter has been raised to the high plane of living matter. -The dead, inert circulating proteid can serve simply as food for the -living cells, and cannot undergo katabolism until it has been built up -into the organized structure of the tissue or organ. Even though we -grant that a small proportion of proteid may suffer katabolism without -previous organization, it does not materially modify the general trend -of the argument that, according to Pflüger’s hypothesis, proteid -katabolism is essentially a process involving the disruption of living -protoplasm. - - [51] Eduard Pflüger: Ueber einige Gesetze des Eiweissstoffwechsels - (mit besonderer Berücksichtigung der Lehre vom sogenannten - “circulirenden Eiweiss”). Archiv f. d. gesammte Physiologie, Band 54, - p. 333. - -Consider what this means in the light of facts already presented. -Remembering that the one factor above all others influencing the rate -of proteid katabolism is the amount of proteid food taken in, and that -the output of nitrogen, no matter what the previous condition of the -body or the amount of proteid food ingested, runs more or less parallel -with the consumption of proteid, we are forced to the conclusion, in -accepting this hypothesis, that there must be superhuman activity in -the building up of living protoplasm, only to be followed, however, by -its immediate and more or less complete breaking down. Further, think -of the daily or periodical fluctuation in the construction of bioplasm, -coincident with variations in the amount of proteid food consumed, and -the corresponding destruction of bioplasm as indicated by the daily -output of nitrogen. Imagine, if you will, the concrete case of a man -of 70 kilos body-weight eating a daily ration containing 125 grams -of proteid, the nitrogen equivalent of which is practically excreted -within twenty-four hours, and are we not wise in hesitating to believe -that all of that proteid has been so quickly built up into living or -organized tissue only to be immediately broken down and thrown out of -the body? Think of the enormous activity implied in the manufacture -of this bioplasm in the time allotted, and for what? Apparently, so -that it can be broken down again. But such energy as is liberated in -the breaking-down process might be derived far more economically by -simple destruction of the proteid, as contained in the meshes of the -tissue elements, without assuming a preliminary conversion into living -protoplasm. Obviously, we have here a theory which does not help us in -arriving at any very satisfactory conception of proteid metabolism. -The facts which Pflüger and his followers bring forward in support of -the theory are not very convincing, or at least not sufficiently so to -carry conviction in the face of a natural disinclination to believe in -the necessity of such a profound anabolic process, merely as a prelude -to the speedy destruction of the finished product. Finally, we may add -that if all proteid katabolized in the body must first be raised to the -high level of living protoplasm before the final disruption can occur, -it may be prudent to keep the daily intake of this foodstuff down to a -level somewhat commensurate with the real needs of the body. - -As has been stated many times in the course of this presentation, -the most striking feature of proteid metabolism is the rapidity with -which large quantities of proteid consumed as food are broken down, -and the contained nitrogen eliminated from the body as urea. A few -hours will suffice to accomplish the more or less complete destruction -of food proteid; and any theory of proteid metabolism, to be at all -satisfactory, must explain this peculiar phenomenon. According to -recent investigations, it seems probable that some, at least, of the -cleavage products of proteid formed during intestinal digestion are -not built up into new proteid, but are at once eliminated mainly in -the form of urea, without becoming a part of either the so-called -circulating proteid, or the living protoplasm of the body. It will be -recalled that under the influence of the digestive enzymes, trypsin -and erepsin, proteid foodstuffs may be broken down while undergoing -intestinal digestion into monamino- and diamino-acids, such as -leucin, tyrosin, arginin, lysin, etc. A certain proportion of these -comparatively simple substances may be directly absorbed by the -portal circulation and carried to the liver, where they may undergo -conversion into urea. In this way, some portion of the nitrogen of -the ingested food may be quickly eliminated from the system. As has -been stated in another connection, we are not sure at present how -far proteid decomposition of the kind indicated takes place normally -in the body. We merely know that there are present in the intestine, -enzymes capable of splitting up proteid into these small fragments, and -that substances of this type when made to circulate through the liver -are transformed into urea. These facts, coupled with the well-known -tendency of the nitrogen of proteid food to appear in the excretions -a few hours after the food in question has been consumed, naturally -suggests a direct breaking down of proteid along the lines indicated, -with a possible retention of a carbonaceous residue (nitrogen-free) -for subsequent oxidation, as a source of energy for heat or work. -Obviously, all of the proteid food cannot behave in this manner, for -if such were the case there would be no proteid available for making -good the normal waste incidental to tissue changes. Either a certain -amount of proteid escapes this profound alteration produced by the -proteolytic enzymes in question, or else a certain proportion of these -simple decomposition products is synthesized in the intestine, or in -the tissues of the body, to form new proteid for the regeneration of -cell protoplasm. However this may be, we have presented in this view -a plausible explanation of the prompt appearance of food nitrogen in -the excretions, and without compelling belief in a theory, such as -Pflüger’s, which taxes one’s credulity to the utmost. To be sure, -as a prominent writer on physiology has recently said, such a view -stands opposed to our conceptions of the importance of proteid food; -but it seems possible, in the light of accumulating knowledge, that -our conceptions of the part played by proteid foods in the nutrition -of man have not been strictly logical, or quite in accord with true -physiological reasoning. - -Again, in this connection, we may ask the question, why is it that the -body provides such an effective method for the speedy breaking down -of proteid food and the prompt elimination of the contained nitrogen? -Whatever the means made use of by the organism in accomplishing this, -the result is the same; the nitrogen of the ingested food is, in large -measure, quickly gotten rid of. We clearly recognize the all-important -position of proteid foods in the nutrition of the body, but there -appears a certain inconsistency in this prompt removal of the -nitrogen-containing portion of the proteid molecule. The nitrogenous -part of the proteid food is, physiologically considered, the -all-important part. It is the only source of nitrogen available to the -system, and yet apparently the larger proportion of this nitrogenous -material is not utilized in any recognizable way, but is eliminated as -quickly as possible. Is it not within the limits of possibility that -these methods, whatever may be the exact mechanism involved, are merely -a means of getting rid of a surplus of proteid for which the body has -no real need? This question I shall try to answer later on in another -connection, but we may advantageously keep this possibility in mind -while we are discussing these theories of proteid metabolism. - -It is obvious, in the light of present knowledge, that there must -be a certain amount of true tissue proteid broken down each day, -independent of that larger metabolism coincident with the intake of -proteid food. However much this more voluminous proteid katabolism may -fluctuate, owing to variations in the intake of proteid, and whatever -the significance of this latter phase of metabolism, it is self-evident -that there must be a steady, constant metabolism, upon which the life -of the various tissues and organs of the body depends, and by which -the proteid integrity of the tissue cells is maintained. This implies -a certain degree of true tissue change, in which definite amounts of -proteid material are broken down and the resultant loss made good from -the proteid intake. No matter what specific name be applied to this -form of proteid katabolism, its existence is clearly recognized. It is -obviously a form of metabolism distinct, and probably quite different, -from that form, more variable in extent, which is associated with the -intake of proteid food. Plainly, if there is truth in these statements, -there should be some data available by means of which these two lines -of proteid katabolism can be more or less sharply differentiated. - -Thanks especially to the work of Folin,[52] these data are now -apparently at hand, and the facts which he has accumulated with -painstaking care seem destined to throw additional light upon our -conception of proteid metabolism. It will be remembered that in the -breaking down of proteid, the great bulk of its contained nitrogen is -eliminated in the form of urea. In addition, a certain smaller amount -of nitrogen is excreted in the forms of creatinin and uric acid. As -we have seen, the total output of nitrogen, which measures the extent -to which proteid is decomposed in the body, varies with the intake of -proteid food; but it is found that the proportion of nitrogen excreted -in the forms of urea and uric acid varies with the extent of the -metabolism. In other words, quantitative changes in the daily proteid -katabolism are accompanied by pronounced changes in the distribution of -the excreted nitrogen. Let us take a single illustration from Folin’s -results; the case of a healthy man who on one day--July 13--consumed -a proteid-rich diet, and on the other day--July 20--was living on a -diet containing only about 1 gram of nitrogen. The composition of -the excretion through the kidneys on these two days is shown in the -following table: - - [52] Otto Folin: Laws Governing the Chemical Composition of Urine. - American Journal of Physiology, vol. 13, p. 66. A theory of Protein - Metabolism. Ibid., vol. 13, p. 117. - - +--------------------+-----------------------+---------------------+ - | | July 13. | July 20. | - +--------------------+-----------------------+---------------------+ - | Volume of urine | 1170 c.c. | 385 c.c. | - | Total nitrogen | 16.80 grams | 3.60 grams | - | Urea-nitrogen | 14.70 " = 87.5% | 2.20 " = 61.7% | - | Uric acid-nitrogen | 0.18 " = 1.1% | 0.09 " = 2.5% | - | Creatinin-nitrogen | 0.58 " = 3.6% | 0.60 " = 17.2% | - +--------------------+-----------------------+---------------------+ - -Here we see, as would be expected, that on the high proteid diet, there -was a large excretion of total nitrogen and of urea; while on the low -proteid diet, nitrogen and urea were correspondingly diminished. The -point to attract our attention, however, is the marked difference in -the percentage of urea-nitrogen in the two cases; a difference which -amounts to about 26 per cent. A similar difference is to be noted in -the percentage of uric acid-nitrogen. Lastly, it is to be observed that -in spite of the great difference in the extent of metabolism on the -two days--an excretion of 16.8 grams of nitrogen, as contrasted with -3.6 grams--the _amount_ of creatinin-nitrogen is essentially the same. -Folin finds that these peculiarities in the percentage distribution -of excreted nitrogen hold good in all cases where there is this wide -divergence in the amount of proteid katabolized, and, further, that -there is a gradual and regular transition from the one extreme to the -other. He sees in these results evidence that there are in the body -two forms of proteid katabolism, essentially independent and quite -different. One kind is extremely variable in quantity, while the other -tends to remain constant. The variable form has its own particular -kind of waste products, of which urea is the chief. The constant -katabolism, on the other hand, is largely represented by creatinin -and to a lesser degree by uric acid. The more the total katabolism is -reduced, the more prominent become creatinin and uric acid, products -of the constant katabolism; while urea, as chief representative of the -variable katabolism, becomes less conspicuous. Folin suggests the term -_endogenous_ or _tissue_ metabolism for the constant variety, while the -variable form he would name _exogenous_ or _intermediate_ metabolism. - -In these suggestions we have not theory only, but a number of very -important facts which plainly must have some significance. Take, -for example, the excretion of creatinin. It is a characteristic -nitrogenous waste product, but its elimination from the body is wholly -independent of quantitative changes in the total amount of nitrogen -excreted. In other words, the amount of creatinin eliminated is a -constant quantity for a given individual under ordinary conditions, -no matter how great the variation in the amount of proteid food, -provided no meat is eaten. Meat must be avoided in testing this point, -since meat contains a certain amount of creatin, or other components, -which would be excreted as creatinin. Further, it is found that every -individual has his own specific creatinin excretion, which fact again -emphasizes the idea that this substance is a product of true tissue -katabolism, having no connection with that variable metabolism, of -which urea is the striking representative. These are facts which cannot -be ignored. They are well established by the careful observations of -Folin, and they are confirmed by a large number of observations made in -our own laboratory. Turn now to that other, more conspicuous, product -of proteid katabolism, urea. With a so-called average proteid intake, -about 88–90 per cent of the excreted nitrogen will be in the form of -urea, but, as Folin states, “with every decided diminution in the -quantity of total nitrogen eliminated, there is a pronounced reduction -in the per cent of that nitrogen represented by urea. When the daily -total nitrogen elimination has been reduced to 3 grams or 4 grams, -about 60 per cent of it only is in the form of urea.” Here, we have the -chief product of exogenous metabolism, a substance quite distinct from -creatinin, just as the process by which it originates is likewise quite -distinct. - -Exogenous metabolism is plainly a process of quite a different order -from that of endogenous, or tissue metabolism. The latter involves -oxidation, while the former consists essentially of a series of -hydrolytic cleavages which result in a rapid elimination of the -proteid-nitrogen as urea. In this conception of exogenous katabolism, -we have essentially the same viewpoint as was previously taken in -attempting to explain how excess of proteid food can be so quickly -decomposed, and its nitrogen removed from the body. Whether the -hydrolytic cleavage is accomplished solely by trypsin and erepsin, -whether it takes place only in the intestine and in the liver, -or whether other glands and tissues are involved, is at present -immaterial; the essential point is that we have in the body a variety -of proteid katabolism, quite different from true tissue katabolism, the -extent of which is dependent primarily upon the amount of proteid food -consumed. The process involved is one which aims at the rapid removal -of the proteid-nitrogen as urea; without incorporation of the absorbed -proteid, or its decomposition products, either as an integral or -adherent part of the tissue proteid. Hydrolytic cleavage is eminently -fitted to accomplish this with the least expenditure of energy, while -the carbonaceous residue of the proteid thus freed from nitrogen can be -transformed into carbohydrate, or directly oxidized as the needs of the -body demand. - -As one considers these views so admirably worked out by Folin, the -question naturally arises, if the real demands of the body for proteid -food will not be adequately met by the quantity necessary to satisfy -the true tissue metabolism? We may well believe, with Folin, that “only -a small amount of proteid, namely, that necessary for the endogenous -metabolism, is needed. The greater part of the proteid furnished with -so-called standard diets, like Voit’s, _i. e._, that part representing -the exogenous metabolism, is not needed; or, to be more specific, its -nitrogen is not needed. The organism has developed special facilities -for getting rid of such excess of nitrogen, so as to get the use of -the carbonaceous part of the proteid containing it.” In endogenous -metabolism, we have a steady, constant process quite independent of -the amount of proteid food, and absolutely indispensable for the -maintenance of life. So far as we know at present, its representative -creatinin is, for a given individual, the same in amount during -fasting as when a rich, meat-free, proteid diet is taken. The one -factor that seemingly determines the amount of creatinin eliminated is -the weight of the individual, or more exactly the weight of the true -tissue elements of the body, as distinct from fat or adipose tissue. -Endogenous or tissue katabolism obviously calls for a certain quantity -of proteid to maintain equilibrium, but this is small in amount as -compared with the usual intake of proteid foods. The average man, with -his ordinary dietetic habits, consumes more nitrogen than the body can -possibly make use of. The excess is not stored up, “because the actual -need of nitrogen is so small that an excess is always furnished with -the food, except, of course, in carefully planned experiments” (Folin). - -We have seen at what low levels of proteid intake, nitrogen equilibrium -can be established, and we may well have faith in the conception of an -endogenous proteid katabolism which involves only minimal quantities of -proteid. Further, we have observed the constant tendency of the body -to maintain a condition of nitrogenous equilibrium, even with varying -income, and how slow the body is to lay by nitrogen on a rich proteid -diet, even when long deprived of proteid food; a fact difficult of -explanation except on the assumption that the real need of the body for -nitrogen is small, and that the tissues habitually carry a relatively -large reserve of nitrogenous material. We may assume with Folin that -“all the living protoplasm in the animal organism is suspended in a -fluid very rich in proteid, and on account of the habitual use of more -nitrogenous food than the tissues can use as proteid the organism -is ordinarily in possession of approximately the maximum amount of -reserved proteid in solution that it can advantageously retain. -When the supply of food proteid is stopped, the excess of reserve -proteid inside the organism is still sufficient to cause a rather -large destruction of proteid during the first day or two of proteid -starvation, and after that the proteid katabolism is very small, -provided sufficient non-nitrogenous food is available. But even then, -and for many days thereafter, the protoplasm of the tissues has still -an abundant supply of dissolved proteid, and the normal activity of -such tissues as the muscles is not at all impaired or diminished. When -30 grams or 40 grams of nitrogen have been lost by an average-sized -man during a week or more of abstinence from nitrogenous food the -living muscle tissues are still well supplied with all the proteid -they can use. That this is so, is indicated on the one hand by the -unchanged creatinin elimination, and on the other by the fact that one -experiences no feeling of unusual fatigue or of inability to do one’s -customary work. Because the organism at the end of such an experiment -still has an abundance of available proteid in the nutritive fluids, -it is at once seemingly wasteful with nitrogen when a return is made -to nitrogenous food. This is why it only gradually, and only under -the prolonged pressure of an excessive supply of food-proteid again -acquires its original maximum store of this reserve material.” - -We may reasonably suppose that the reserve of proteid present in the -body is contained in the fluid media, and not as a part of the living -protoplasm. Further, we are apparently justified in the belief that -the sole form of proteid katabolism which is vitally important for the -welfare of the body is the endogenous katabolism. This must be provided -for adequately and indeed liberally, and in addition there should be -sufficient intake to keep up an abundant supply of reserve proteid, but -beyond these necessities there would seem to be no legitimate demand -for additional proteid. The voluminous exogenous proteid katabolism so -conspicuous in most individuals would seem to have no justification -in fact, or in physiological reasoning. What good, for example, can -be accomplished by this constant splitting off of nitrogen, with its -subsequent speedy removal from the body? The organism can neither use -it nor store it up, and why therefore should this daily burden of an -excessive and accelerated proteid katabolism be borne? As we have seen, -the energy of muscle work is derived mainly, and can come wholly, from -the breaking down of non-nitrogenous materials, fats and carbohydrates. -The very fact that an intake of say 120 grams of proteid is followed -at once by the removal of the larger part of the contained nitrogen, -as a result of the exogenous katabolism of the body, would seemingly -warrant the view that the proteid so decomposed might advantageously be -replaced by a corresponding amount of carbohydrate. In muscle work, as -in heat production, carbohydrate and fat are the materials burned up, -or oxidized. Proteid, on the other hand, is not so oxidized, at least -not the nitrogen-containing portion of the molecule. - -There are apparent only two possible reasons for assuming a need on -the part of the body for the high exogenous katabolism of proteid so -commonly observed. The one is that the carbonaceous residue left after -the cleavage of nitrogen from the proteid molecule is better adapted -for the needs of the body than either carbohydrate or fat. Although -this does not seem very probable, it is of course a possibility and -merits consideration. Feeding experiments, with a comparatively small -proteid intake, continued over a sufficient length of time, would show -conclusively how much weight should be attached to this hypothesis. The -other possibility is that the body may derive some advantage from the -presence, in the tissues and fluids, of the varied nitrogenous cleavage -products split off from proteid so abundantly in exogenous katabolism. -These substances are mainly amino-acids on their way to urea, and there -is no apparent reason why they should be of service to the organism. -Still, the processes going on in the tissues and organs of the body are -intricate and not wholly understood, and we can conceive of some useful -function of which as yet we have no knowledge. In the construction of -tissue proteid, for example, as in a possible synthesis out of the -fragments formed by hydrolytic cleavage, it is not impossible that -certain corner-stones are needed, and that in order to obtain these -there must be a more or less wasteful breaking down of food-proteid. -However improbable this may seem, it, like the preceding hypothesis, -can be tested in a way by adequate feeding experiments, which shall -determine the effect on the body of a low proteid intake continued over -a long period of time. On the other hand, it is equally plausible, and -for some reasons more probable, to assume that this excessive exogenous -katabolism may be in a measure prejudicial to the best interests of the -body; that the many nitrogenous fragments formed in the efforts of the -organism to prevent undue accumulation of reserve proteid may in the -long run do as much harm as good. - -Further, there is reason in the question whether the continual carrying -of excessive amounts of nitrogen reserves in the shape of soluble -proteid in the blood and lymph, and in the meshes of tissue and cell -protoplasm, is advantageous for the maintenance of the highest degree -of efficiency? We all recognize that an excessive accumulation of fat -is distinctly disadvantageous to the welfare of the body, and there -is, physiologically speaking, equally good ground for considering that -the storage of unorganized proteid in amounts beyond all possible -requirements of the body may be equally undesirable. Because less -tangible to the eye, the accumulation of unnecessary proteid is not -so easily recognizable, but this fact does not diminish the possible -danger which such accumulation may constitute. It must be granted, -however, that we are dealing here with hypotheses and not facts, but -though hypothetical the suggestions made are of sufficient moment to -merit attention and experimental study. In a later chapter, we shall -have occasion to present some facts bearing on these questions. - -In the meantime, we may lay due stress upon the significance of these -views regarding proteid katabolism. We must accept as settled the -general idea that there are two distinct forms of proteid katabolism -within the body; one form representing the decay of tissue or cell -protoplasm, small in amount, with its own particular decomposition -products, and absolutely essential for the continuance of life. -The other form, the so-called exogenous katabolism, runs a totally -different course with distinctive side-products and end-products; it -is variable in extent, in harmony with variations in proteid intake, -and subject to the suspicion that at the level ordinarily maintained -it constitutes a menace to the preservation of that high degree of -efficiency which is an attribute of good health. - - - - -CHAPTER V - -DIETARY HABITS AND TRUE FOOD REQUIREMENTS - - TOPICS: Dietetic customs of mankind. Origin of dietary standards. - True food requirements. Arguments based on custom and habit. - Relationship between food consumption and prosperity. Erroneous - ideas regarding nutrition. Commercial success and national wealth - not the result of liberal dietary habits. Instinct and craving not - wise guides to follow in choice and quantity of food. Physiological - requirements and dietary standards not to be based on habits and - cravings. Old-time views regarding temperate use of food. The sayings - of Thomas Cogan. The teachings of Cornaro. Experimental results - obtained by various physiologists. Work of the writer on true proteid - requirements. Studies with professional men. Nitrogen equilibrium - with small amounts of food. Sample dietaries. Simplicity in diet. - Nitrogen requirement per kilogram of body-weight. Fuel value of the - daily food. Experiments with university athletes. Nitrogen balance - and food consumption. Sample dietaries. Adequacy of a simple diet. - - -Having acquired information regarding the principles of metabolism -and the general laws governing the nutrition of the body, we may -next consider briefly the dietetic habits of mankind, with a view -to learning how far such habits coincide with actual nutritive -requirements. Eventually, we shall need to ask the questions: What are -the _true_ nutritive requirements of the body? How much food and what -kinds of food does the ordinary individual doing an average amount -of work need each day in order to preserve body equilibrium, and to -maintain health, strength, and vigor under the varying conditions -of life? What amount of nitrogen or proteid, and what the total -calorific value required to supply the physiological needs of the -body? How closely do the so-called “normal diets” and “standard diets,” -which have met with such general acceptance, conform to a rational -conception of true physiological needs? These are vital questions of -great physiological and economic importance, and they are not easily -answered; but theoretical considerations based on scientific data, and -experimental evidence combined with practical experience, should point -the way to some very definite conclusions. - -Observations made in many countries regarding the dietetic customs and -habits of the people have resulted in the establishment of certain -dietary standards, which have been more or less generally adopted -as representing the requirements of the body. As a prelude to the -discussion of this question, let us consider briefly some of the -results of these dietary studies. In Sweden, laborers doing hard work -were found by Hultgren and Landergren to consume daily, on an average, -189 grams of proteid, 714 grams of carbohydrate, and 110 grams of fat, -with a total fuel value for the day’s ration of 4726 large calories. -In Russia, workmen at moderately hard labor, having perfect freedom of -choice in their food, were found by Erisman to take daily 132 grams of -proteid, 584 grams of carbohydrate, and 79 grams of fat, this ration -having a fuel value of 3675 calories. In Germany, soldiers in active -service consumed daily, according to Voit, 145 grams of proteid, 500 -grams of carbohydrate, and 100 grams of fat, with a fuel value of 3574 -calories. In Italy, laborers doing a moderate amount of work were found -by Lichtenfelt to consume daily 115 grams of proteid, 696 grams of -carbohydrate, and 26 grams of fat, with a fuel value of 3655 calories. -In France, Gautier states that the ordinary laborer working eight -hours a day must have 135 grams of proteid, 700 grams of carbohydrate, -and 90 grams of fat daily, with a fuel value of 4260 calories. In -England, weavers were found to take daily 151 grams of proteid, with -carbohydrates and fats sufficient to make the total fuel value of the -day’s ration equal to 3475 calories. In Austria, farm laborers consumed -daily 159 grams of proteid, with carbohydrates and fats sufficient to -raise the fuel value of the food to 5096 calories. - - +----------------------------------+----------------+----------------+ - | Subjects. |Proteid consumed|Total Fuel Value| - | | Daily. | of Daily Food. | - +----------------------------------+----------------+----------------+ - | | grams | calories | - |Swedish laborers, at hard work | 189 | 4726 | - |Russian workmen, moderate work | 132 | 3675 | - |German soldiers, active service | 145 | 3574 | - |Italian laborers, moderate work | 115 | 3655 | - |French laborers, eight hours’ work| 135 | 4260 | - |English weavers | 151 | 3475 | - |Austrian farm laborers | 159 | 5096 | - | | | | - | American Subjects. | | | - | | | | - |Man with very hard muscular work | 175 | 5500 | - |Man with hard muscular work | 150 | 4150 | - |Man with moderately active | | | - | muscular work | 125 | 3400 | - |Man with light to moderate | | | - | muscular work | 112 | 3050 | - |Man at “sedentary” or woman with | | | - | moderately active work | 100 | 2700 | - +----------------------------------+----------------+----------------+ - -Observations of this order might be multiplied indefinitely, but -the above will suffice to give a general idea of the average food -consumption of European peoples doing a moderate amount of work. These -data, however, must be supplemented by the observations made in our own -country, which have been very extensive, through the “investigations on -the nutrition of man in the United States,” carried on by the Office -of Experiment Stations in the Department of Agriculture, under the -efficient leadership of Atwater. As stated by Messrs. Langworthy and -Milner, in an official bulletin issued in 1904, dietary studies of the -actual food consumption of people of different classes in different -parts of the United States have been made during the years 1894 to -1904 on about 15,000 persons,--men, women, and children,--as a result -of which it is indicated that “the actual food requirements of persons -under different conditions of life and work” vary from 100 to 175 grams -of proteid per day, with a total fuel value ranging from 2700 to 5500 -calories. For comparison, the various data may be tabulated as shown on -page 155. - -These figures by no means represent maximum food consumption. Thus, -studies have been made on fifty Maine lumbermen,[53] where the intake -of proteid food averaged 185 grams per day, with a total fuel value of -6400 calories. Further, dietary studies of university boat crews[54] -have shown fairly high results. The Yale University crew, while at -Gales Ferry, averaged per man during seven days 171 grams of proteid, -171 grams of fat, and 434 grams of carbohydrate, with a total fuel -value of 4070 calories per day. The members of the Harvard University -crew showed an average daily consumption of 160 grams of proteid, 170 -grams of fat, and 448 grams of carbohydrate, with a total fuel value -of 4074 calories. It is also reported that a football team of college -students in the University of California consumed daily, per man, 270 -grams of proteid, 416 grams of fat, and 710 grams of carbohydrate, with -a total fuel value of 7885 calories. These figures may be contrasted, -however, with the data obtained in a study of the dietary habits of -fourteen professional men’s families, where the average amount of -proteid consumed daily was 104 grams, fat 125 grams, and carbohydrate -423 grams, with a total fuel value of 3325 calories. - - [53] Bulletin No. 149. Woods and Mansfield. Studies of the Food of - Maine Lumbermen. U. S. Department of Agriculture, 1904. - - [54] Bulletin No. 75. Atwater and Bryant. Office of Experiment - Stations, U. S. Department of Agriculture, 1900. - -Leaving out of consideration the extremes given, it is undoubtedly true -that, within certain rather wide limits, there is an apparent tendency -for people of different nations, having a free choice of food and not -restricted by expense, to consume daily approximately the same amounts -of nutrients; to use what may be called liberal rather than small -amounts of food; and, lastly, to consume food somewhat in proportion -to the amount of work done. It is perhaps, therefore, not strange that -students of nutrition should have taken these results, obtained by the -statistical method, as indicating the actual needs of the body for -food, and that so-called “standard diets” and “normal diets” should -have been constructed, based upon these and corresponding data. Thus, -we have the widely adopted “Voit standard,” composed of proteid 118 -grams, carbohydrate 500 grams, and fat 56 grams, with a total fuel -value of 3055 calories, as the amount of food required daily by a man -of 70 kilos body-weight doing a moderate amount of work. These figures -were obtained by Voit as an average of the food consumption of a large -number of laboring men in Germany, and they carried additional weight -because at that time Voit and others thought they had evidence that -nitrogenous equilibrium could not be maintained for any length of time -on smaller amounts of proteid. - -The figures given in the preceding table under the head of American -subjects constitute the “Atwater standards,” and as already indicated, -are based upon the dietetic habits of over 15,000 persons under -different conditions of life and physical activity. In the words of -the official Bulletin, these standards covering the quantities of food -per day “are intended to show the actual food requirements of persons -under different conditions of life and work.” Here, however, lies an -assumption which seems to meet with wide acceptance, but for which it -is difficult to conceive any logical reason. The thousands of dietary -studies made on peoples all over the world, affording more or less -accurate information regarding the average amounts of proteid, fat, -and carbohydrate consumed under varying conditions, are indeed most -interesting and important, as affording information regarding dietetic -customs and habits; but, the writer fails to see any reason why such -data need be assumed to throw any light on the actual food requirements -of the body. In the words of another, “Food should be ingested in just -the proper amount to repair the waste of the body; to furnish it with -the energy it needs for work and warmth; to maintain it in vigor; -and, in the case of immature animals, to provide the proper excess -for normal growth, in order to be of the most advantage to the body” -(Benedict). - -Any habitual excess of food, over and above what is really needed -to meet the actual wants of the body, is not only uneconomical, but -may be distinctly disadvantageous. Voit, among others, has clearly -emphasized the general principle that the smallest amount of proteid, -with non-nitrogenous food added, that will suffice to keep the body in -a state of continual vigor is the ideal diet. My own conception of the -true food requirements of the body has been expressed in the statement -that man needs of proteids, fats, and carbohydrates sufficient to -establish and maintain physiological and nitrogen equilibrium; -sufficient to keep up that strength of body and mind that is essential -to good health, to maintain the highest degree of physical and mental -activity with the smallest amount of friction and the least expenditure -of energy, and to preserve and heighten, if possible, the ordinary -resistance of the body to disease germs. The smallest amount of food -that will accomplish these ends is, I think, the ideal diet. There must -truly be enough to supply the real needs of the body, but any great -surplus over and above what is actually called for may in the long run -prove an undesirable addition. With these thoughts in mind, may we -not reasonably ask why it should be assumed that there is any tangible -connection between the dietetic habits of a people and their true -physiological needs? - -Arguments predicated on custom, habit, and usage have no physiological -basis that appeals strongly to the impartial observer. Man is -a creature of habits; he is quick to acquire new ones when his -environment affords the opportunity, and he is prone to cling to old -ones when they minister to his sense of taste. The argument that -because the people of a country, constituting a given class, eat -a certain amount of proteid food daily, the quantity so consumed -must be an indication of the amount needed to meet the requirements -of the body, is as faulty as the argument that because people of a -given community are in the habit of consuming a certain amount of -wine each day at dinner their bodies must necessarily be in need of -the stimulant, and that consequently alcohol is a true physiological -requirement. A large proportion of mankind is addicted to the tobacco -habit, and to many persons the after-dinner cigar is as essential to -comfort as the dinner itself; but would any one think of arguing that -tobacco is one of the physiological needs of the body? - -It is said that dietary studies made all over the civilized world -“show that a moderately liberal quantity of protein is demanded by -communities occupying leading positions in the world.... It certainly -seems more than a remarkable coincidence that peoples varying so widely -in regard to nationality, climatic and geographical conditions, and -dietetic habits, should show such agreement in respect to consumption -of protein and energy.” Again, we hear it said that “whatever may be -true of a few individuals, with communities a generally low condition -of mental and physical efficiency, thrift, and commercial success, is -coincident with a low proportion of protein in the diet.” The writer, -however, fails to find evidence in the results afforded by dietary -studies that there is any causal relationship between the amount of -proteid food consumed and the mental or physical supremacy of the -people of a given nation or community. Cause and effect are liable to -become reversed in arguments of this kind. It is certainly just as -plausible to assume that increase in the consumption of proteid follows -in the footsteps of commercial and other forms of prosperity, as to -argue that prosperity or mental and physical development are the result -of an increased intake of proteid food. - -Proteid foods are usually costly, and the ability of a community to -indulge freely in this form of dietetic luxury depends in large measure -upon its commercial prosperity. The palate is an extremely sensitive -organ, and the average individual properly derives great satisfaction -from the pleasurable effects of tasty articles of food. Furthermore, -there are many curious and quite unphysiological notions abroad -regarding foods, which tend to incite persons to unnecessary excess -and extravagance whenever they acquire the means to do so. The latter -point is well illustrated by the more or less prevalent opinion that a -cut of tenderloin steak is more nutritious than a cut of round steak. -It is true that the former is apt to be more tender, to have a little -finer flavor; but the round steak, when properly prepared, is just as -nutritious, and equally capable of meeting the needs of the body, as -the more expensive tenderloin. With increasing prosperity, we turn at -once, as a rule, to the more tasty and appetizing viands, partly to -satisfy the craving of appetite and palate, and partly because there -is an inherent belief that these varied delicacies, accessible to the -prosperous community, count as an aid to health and strength. The poor -laborer, with his small wage, is restricted to a certain low level -of dietary variety, and must likewise be economical as to quantity, -but on the first opportunity afforded by a fuller purse he is apt -to pass from corned beef to a fresh roast with its more appetizing -flavor; to eschew brown bread in favor of the white loaf, and in many -other ways to evince his desire for a dietary which, though perhaps no -more nutritious, appeals because of its finer flavor, more appetizing -appearance, and greater variety. He is in the same position as the -smoker who, limited by his purse to a five-cent cigar after dinner, -quickly passes to a cigar of better flavor as soon as his finances -warrant the indulgence. At the same time, if prosperity continues, our -laborer will speedily pass to a higher level of proteid intake and -greater fuel value, through increased consumption of meat and butter, -together with other articles rich in proteid and fat. - -In this connection, we may emphasize a fact of some significance in its -bearing on dietetic customs; viz., that ever since Liebig advanced his -theory that proteid material is the sole source of muscular energy, -there has been a deep-rooted belief that meat is the most efficient -kind of food for keeping up the strength of the body, and hence -especially demanded by all whose work is mainly physical. Although this -view, as we have seen, has been thoroughly disproved, the idea is still -more or less generally held that an abundance of meat is a necessary -requisite for a good day’s work, a view which undoubtedly accounts in -some measure for the tendency toward a high proteid intake, evinced by -many of the laboring class whose means will permit the necessary outlay. - -Increased consumption of proteid food may be coincident with thrift and -commercial success, but there is no justification for the belief that -these are the result of changed dietary conditions. The dietary of our -New England forefathers was, according to all accounts, exceedingly -limited as compared with that of to-day, but it is doubtful if the -present generation is any better developed, physically or mentally, -than the stalwart and vigorous people who opened up this country to -civilization. To-day, as a nation, we have greater wealth, and our -commercial prosperity has become phenomenal; but would any one think -for a moment that these characteristics are attributable to the -large consumption of proteid food so common to this generation of -the American people? No, increased wealth simply paves the way for -greater freedom in the choice of food; increased commercial success -and business prosperity throw open avenues which formerly were closed; -greater variety of animal foods, and vegetable foods as well, rich in -proteid, are made easily accessible, and appeal to eye and palate on -all sides; appetite and craving for food are abnormally stimulated, -and dietetic habits and customs change accordingly. In the words of -another, “the one thing that primitive, barbarous, and civilized man -alike long for is an abundance of the ‘flesh-pots of Egypt.’ The -very first use the latter makes of his increased power and financial -resources is to buy new, rare, and expensive kinds of meat.” With these -facts before us, it is difficult to accept the assumption that dietetic -customs afford any indication of the food requirements of the body. To -the physiologist such a view does not appeal, since there is a lack of -any scientific evidence that carries conviction. - -But it may be asked, is not appetite a safe guide to follow? Do not -the cravings of the stomach and the so-called pangs of hunger merit -consideration? Is it not the part of wisdom to follow inclination in -the choice and quantity of our food? Can we not safely rely upon these -factors as an index of the real needs of the body? If these questions -are to be answered in the affirmative, then it is plain that a study -of dietetic customs will tell us definitely how much food and what -kinds of food are required daily to supply the true wants of the body. -There are writers who claim that instinct is a perfectly safe guide to -follow; that it is far superior to reason; but it is to be noticed -that most of these writers, if they have any physiological knowledge -to draw upon, are sooner or later prone to admit that the body has -certain definite needs which it is the purpose of food to supply, with -the added implication that any surplus of food over and above what is -necessary to meet these demands is entirely uncalled for. Thus, one -such writer states that “the man in the street follows his God-given -instincts and plods peacefully along to his three square meals a day, -consisting of anything he can find in the market, and just as much of -it as he can afford, with special preference for rich meats, fats, and -sugars.” Yet this same writer, a little later, emphasizes the fact that -“every particle of the energy which sparkles in our eyes, which moves -our muscles, which warms our imaginations, is sunlight cunningly woven -into our food by the living cell, whether vegetable or animal. Every -movement, every word, every thought, every aspiration represents the -expenditure of precisely so much energy derived from food.” Why, then, -would it not be wise to ascertain how much energy is so expended, on -an average, during the day’s activity and govern the intake of food -accordingly? Why not apply an intelligent supervision in place of -following an instinct which, in the words of the author just quoted, -leads one on to consume “anything he can find in the market and just as -much of it as he can afford”? Truly, if dietetic customs and the habits -of mankind are the results of instinct working in this fashion, there -cannot be much value in the data obtained by observing the quantities -of food mankind is in the habit of eating. Dietary standards based on -such observations must be open to the suspicion of representing values -far above the actual needs of the body. - -Habits and cravings are certainly very unreliable indices of true -physiological requirements. Man is constantly acquiring new habits, and -these in time become second nature, forcing him to practise that which -he has become accustomed to, regardless of whether it is beneficial -or otherwise. The celebrated philosopher, John Locke, in his essay on -education, says: “I do not think all people’s appetites are alike ... -but this I think, that many are made gourmands and gluttons by custom, -that were not so by nature; and I see in some countries, men as lusty -and strong, that eat but two meals a day, as others that have set their -stomachs by a constant usage, like Larums, to call on them for four or -five.” Again, the so-called cravings of appetite are largely artificial -and mainly the result of habit. A habit once acquired and persistently -followed soon has us in its grasp, and then any deviation therefrom is -very apt to disturb our physiological equilibrium. The system makes -complaint, and we experience a craving, it may be, for that to which -the body has become accustomed. There has thus come about a sentiment -that the cravings of the appetite for food are to be fully satisfied, -that this is merely obedience to nature’s laws. In reality, there is -no foundation for such a belief; any one with a little persistence can -change his or her habits of life, change the whole order of cravings, -thereby indicating that the latter are essentially artificial, and that -they have no necessary connection with the welfare or needs of the -body. The man who for some reason deems it advisable to adopt two meals -a day in place of three or four, at first experiences a certain amount -of discomfort, but eventually the new habit becomes a part of the daily -routine, and the man’s life moves forward as before, with perfect -comfort and without a suggestion of craving, or a pang of hunger. -Dietetic requirements, and standard dietaries, are not to be founded -upon the so-called cravings of appetite and the instinctive demands -for food, but upon reason and intelligence, reinforced by definite -knowledge of the real necessities of the bodily machinery. - -The standards which have been adopted more or less generally throughout -the civilized world, based primarily on the assumption that man -instinctively and independently selects a diet that is best adapted -to his individual needs, are open to grave suspicion. The view that -the average food consumption of large numbers of individuals and -communities must represent the true nutritive requirements of the -people is equally untenable. Naturally, there is general recognition -of the principle that food requirements are necessarily modified by -a variety of circumstances, such as age, sex, body-weight, bodily -activity, etc. It is obvious that the man of 140 pounds body-weight -needs less proteid than the man of 170 pounds, and that the man who -does a large amount of physical work demands a larger calorific -value in his daily diet, _i. e._, more carbohydrate and fat, than -the sedentary individual. The growing child, in proportion to his -body-weight, plainly needs more proteid for the upbuilding of tissue, -and there are many conditions of disease where special dietetic -treatment is undoubtedly called for. Our contention, however, and one -which we believe to be perfectly justifiable, is that the true food -requirements of the body, under any conditions, cannot be ascertained -with any degree of accuracy by observations of what people are in the -habit of eating; that customs and habits are not a safe index of true -physiological needs. On the contrary, we are inclined to the belief -that direct physiological experimentation, covering a sufficient length -of time and with an adequate number of individuals, will prove far more -efficient in affording a true estimate of the quality and quantity of -food best adapted for the maintenance of good health, strength, and -vigor. - -Before considering these latter points, it is interesting to note, in -passing, that during the last four centuries many thoughtful men have -called attention to the apparent excessive use of food. There seems -to have been in many quarters a more or less prevalent opinion that -custom and habit were leading people on to methods of living, which -were not in accord with the best interests of the community. It must be -remembered, however, that arguments of this kind, even fifty years ago, -could have been founded only on general observation and the application -of common sense, since there were then no sound physiological data -on which to predicate an opinion, or base a conclusion. Still, there -were men of authority who attempted to lay before the people a proper -conception of the temperate use of food. We have not the time here to -consider many of these pleas, but I venture to call attention to the -somewhat celebrated book published by the physician Thomas Cogan in -1596, under the title “The Haven of Health,” and dedicated “to the -right honorable and my verie good lord, Sir Edward Seymour, Knight and -Earl of Hertford.” Under the subject of diet, this old-time writer -says: “The second thing that is to be considered of meates is the -quantitie, which ought of all men greatly to be regarded, for therein -lyeth no small occasion of health or sickness, of life or death. For -as want of meate consumeth the very substance of our flesh, so doth -excesse and surfet extinguish and suffocate naturall heat wherein life -consisteth.” Again, “Use a measure in eating, that thou maist live -long: and if thou wilst be in health, then hold thine hands. But the -greatest occasion why men passe the measure in eating, is varitie of -meats at one meale. Which fault is most common among us in England -farre above all other nations. For such is our custome by reason of -plentie (as I think) that they which be of abilitie, are served with -sundry sortes of meate at one meale. Yea the more we would welcome our -friends the more dishes we prepare. And when we are well satisfied with -one dish or two, then come other more delicate and procureth us by that -meanes, to eate more than nature doth require. Thus varietie bringeth -us to excesse, and sometimes to surfet also. But Phisicke teacheth -us to faede moderately upon one kinde of meate only at one meale, or -at leastwise not upon many of contrarie natures.... This disease, (I -mean surfet) is verie common: for common is that saying and most true: -That more die by surfet than by the sword. And as Georgius Pictorius -saith, all surfet is ill, but of bread worst of all. And if nature be -so strong in many, and they be not sicke upon a full gorge, yet they -are drowsie and heavie, and more desirous to loyter than to labor, -according to that old maeter, when the belly is full, the bones would -be at rest. Yea the minde and wit is so oppressed and overwhelmed with -excesse that it lyeth as it were drowned for a time, and unable to use -his force.” - -Cogan likewise makes some interesting statements regarding the effects -of custom on the consumption of proteid food, especially meats. Quoting -further from this author: “The fourth thing that is to be considered -in meats is custome. Which is of such force in man’s bodie both in -sicknesse and in health, that it countervaileth nature itselfe, and is -therefore called of Galen in sundry places, an other nature. Whereof he -giveth a notable example, where he sheweth that an olde woman of Athens -used a long time, to eate Hemlocke (which is a ranke poison) first a -little quantitie, and afterwarde more, till at length she could eate so -much without hurt as would presently poison another.... So that custome -in processe of time may alter nature.” Finally, we may quote one last -saying of Cogan’s, because of the good sense and wisdom displayed -in the sentiment, as true to-day as when it was written more than -three hundred years ago: “Neither is it good for any man that is in -perfect health, to observe any custome in dyet precisely, as Arnoldus -teacheth upon the same verses in these wordes: Every man should so -order himselfe, that he might be able to suffer heate and cold, and -all motions, and meats necessary, so as he might change the houres of -sleeping and waking, and his dwelling and lodging without harme: which -thing may be done if we be not too precise in keeping custome, but -otherwise use things unwonted. Which sentence of Arnoldus agraeth verie -well to that of Cornelius Celsus: He that is sound and in good health, -and at libertie, should bind himselfe to no rules of dyet. To need -neither Phisition or Chirurgion, he must use a diverse order of life, -and be sometimes in the countrie, sometime in the towne, sometimes -hunt, and sometime hawke. But some man may demand of me how this may -agree with that saying of the scholar of Salernus ‘if you would be free -from physicians, let these three be your physician, a cheerful mind, -rest, and a moderate diet.’ Whereunto I answer, that a moderate dyet -is alwaies good, but not a precise dyet: for a moderate diet is, as -Terence speaketh in Andria: To take nothing too much: which alwaies -is to be observed. But if a man accustome himselfe to such meats and -drinks as at length will breed some inconvenience in his bodie, or to -sleepe or to watch, or any other thing concerning the order of his -life, such custome must naedes be amended and changed, yet with good -discretion, and not upon the sudden: because sudden changes bring harme -and weaknesse, as Hippocrates teacheth. He therefore that will alter -any custome in dyet rightly, must do it with three conditions, which -are expressed by Hippocrates. Change is profitable, if it be rightly -used, that is, if it be done in the time of health, and at leisure, and -not upon the sudden.” - -This noteworthy book written by Cogan was preceded by the writings -of Louis Cornaro, the Venetian, who forty years before had published -the first edition of his celebrated book, “The Temperate Life,” and -who was a most ardent advocate of the benefits to be derived by -living temperately, especially in matters of diet. The simple diet -which served for the nourishment of the oldest peoples of Syria, -Greece, Egypt, and of the Romans when they were at the height of -their prosperity and culture, was advocated by Cornaro as conducing -to longevity, better health, and greater comfort of mind and body. -Himself a striking example of the effects of a reasonable abstinence in -diet (the last edition of his book having been written at the age of -ninety-five), his teachings have continued to attract attention down to -the present day; and although we have no values in grams or calories -expressive of his average food consumption, it is quite evident that -Cornaro lived a very abstemious life, eating little of the heavier -articles of diet common to his time and country. It is perhaps not -strictly physiological to refer to these cases, yet they have value -as representing a sentiment, common to the centuries now passed, that -benefit was to be derived by mankind from greater care in the taking of -food; that prevalent customs and habits were leading the people into -intemperate modes of life, and that these were surely tending toward -the physical and mental deterioration of the nation. We may attach much -or little weight to these conclusions, but there is a certain degree of -significance in the views, current then as now, that dietetic customs -and habits have no real connection with bodily requirements. - -Passing down to our own times, we find physiologists, by the aid -of scientific methods, studying the effects of smaller amounts of -food (smaller than custom prescribes) on the condition of the body, -thereby evincing a certain degree of skepticism concerning the dietary -standards based on habit and usage. This has been especially true -regarding the nitrogen requirement, or the need for proteid food. -As has been clearly pointed out in other connections, there are -two distinct needs which the body has for food; one for proteid or -nitrogen, the other for energy-yielding material. According to the -Voit standard, a man of average body-weight doing a moderate amount -of work requires daily 118 grams of proteid food, or about 16 grams of -metabolizable nitrogen, with fat and carbohydrate sufficient to yield -a total fuel value of over 3000 large calories. As we have seen, the -fuel value of the food must of necessity be a variable quantity because -of variations in bodily activity. The more muscular work performed, -the greater must be the intake of carbohydrate and fat, if the body -is to be kept in equilibrium. With proteid or nitrogen, however, the -case is quite different, since with adequate amounts of non-nitrogenous -food, proteid is not drawn upon for the energy of muscular work. -We can conceive of the nitrogen requirement, therefore, as being -a constant factor in the well-nourished individual and dependent -primarily upon body-weight, or more exactly, upon the weight of true -proteid-containing tissue. Obviously, whatever else happens, there must -be enough proteid food taken daily to maintain the body in nitrogen -equilibrium. If this can be accomplished only by the ingestion of 16 -grams of metabolizable nitrogen, then it is plain that the daily ration -must contain at least 118 grams of proteid food; _i. e._, it must -conform approximately at least to ordinary usage. - -This question has been studied by many investigators, with very -interesting and suggestive results. Thus, in 1887, Hirschfeld[55] -reported some experiments on himself, twenty-four years of age and -weighing 73 kilos. His ordinary diet contained daily 100 to 130 grams -of proteid, and the amount of nitrogen excreted varied from 16 to 20 -grams per day, corresponding to a metabolism of proteid equal to the -amount ingested. In other words, the body was essentially in nitrogen -equilibrium. Then, for a period of fifteen days, during which he was -unusually active, he lived on a diet in which the content of proteid -corresponded to only 6 grams of nitrogen per day, and yet he remained -in nitrogen equilibrium. The diet made use of was composed essentially -of milk, eggs, rice, potatoes, bread, butter, sugar, and coffee, with -some wine and beer, and on two days a little meat. It is to be observed -that the nitrogen or proteid intake per day was only one-third of what -he was accustomed to consume. In a second experiment, covering ten -days, similar results were obtained. So that evidence was afforded that -a young and vigorous man can maintain his body in nitrogen equilibrium, -for fifteen consecutive days at least, on an amount of proteid food -equal to only one-third of the minimal requirement called for by common -usage. Plainly, the difference between a daily consumption of 118 grams -of proteid food and 40 grams represents a large percentage saving, -both of proteid and in the metabolism of proteid matter with all the -attendant transformations. In these experiments, however, the subject -consumed relatively large amounts of non-nitrogenous food, notably -butter, of which on some days he took as much as 100 grams. The average -fuel value of his food ranged from 3750 to 3916 calories per day; a -fact of some importance, since it is to be remembered that both fat and -carbohydrate tend to protect proteid metabolism. - - [55] Felix Hirschfeld: Untersuchungen über den Eiweissbedarf des - Menschen. Pflüger’s Archiv f. d. gesammte Physiologie, Band 41, p. - 533. - -In an experiment reported in 1889 by Carl Voit[56], on a vegetarian -weighing about 57 kilos, it was found that with a purely vegetable -diet the subject was able, for a few days at least, to maintain his -body in essentially a condition of nitrogen equilibrium on a daily -diet containing 8.4 grams of nitrogen, corresponding to 52.5 grams -of proteid. In addition, there was a large consumption of starchy -food with some fat. Klemperer,[57] experimenting with two young men, -having a body-weight of 64 and 65.5 kilos, respectively, was able to -keep them in a condition of nitrogenous equilibrium for a period of -eight days on 4.38 grams and 3.58 grams of nitrogen per day. The diet, -however, had a large fuel value, 5020 calories per day, and contained -in addition to the small amount of proteid, 264 grams of fat, 470 -grams of carbohydrate, and 172 grams of alcohol. Breisacher,[58] in an -experiment on himself, using a mixed diet composed of 67.8 grams of -proteid, 494.2 grams of carbohydrate, and 60.5 grams of fat per day, -with a total fuel value of 2866 calories, observed a daily excretion -of nitrogen during thirty days of 8.23 grams. This corresponds to a -metabolism of 51.4 grams of proteid, thus showing that the 67 grams -of food-proteid taken was quite sufficient to maintain nitrogen -equilibrium for the above length of time. - - [56] Carl Voit: Ueber die Kost eines Vegetariers. Zeitschrift für - Biologie, Band 25, p. 232. - - [57] Klemperer: Untersuchungen über Stoffwechsel und Ernährung in - Krankheiten. Zeitschrift für klin. Medizin, Band 16, p. 550. - - [58] L. Breisacher: Ueber die Grösse des Eiweissbedarfs beim - Menschen. Deutsche med. Wochenschrift. 1891. No. 48. - -Caspari and Glässner[59] have reported observations made on two -vegetarians, a man and his wife, aged 49 and 48 years respectively, who -had lived for some years exclusively on a vegetable diet. The man had -a body-weight of 68.8 kilos, while the woman weighed 58 kilos. During -five days, the man consumed per day, on an average, 7.83 grams of -nitrogen and 4559 calories. This corresponds to 0.114 gram of nitrogen -per kilo of body-weight, and 66 calories per kilo. On this diet, the -man gained slightly in weight and showed a plus nitrogen balance of -5.2 grams for the five days. In other words, even this low nitrogen or -proteid intake was more than sufficient to meet the wants of his body. -The wife, during the same period of time, consumed per day 5.33 grams -of nitrogen and 2715 calories, corresponding to 0.092 gram of nitrogen -per kilo of body-weight and 47 calories per kilo. On this diet, the -woman gained 0.9 kilo in weight during the five days, and like the -man, she showed a plus nitrogen balance of 2.45 grams for the entire -period. The somewhat noted experiments of Sivén have been referred to -in another connection, and it will suffice to recall the fact that -he was able, with a body-weight of 60 kilos, to establish nitrogen -equilibrium on 6.26 grams of nitrogen, and for a day or two on 4.5 -grams of nitrogen, with a total fuel value of only 2444 calories in the -day’s ration. - - [59] W. Caspari: Physiologische Studien über Vegetarianismus. Bonn. - 1905. p. 13. - -These few illustrations will serve to indicate that, so far as the -maintenance of nitrogen equilibrium is concerned during short periods -of time, there is no necessity for the consumption of proteid food in -such amounts as common usage dictates. The high proteid intake called -for by the “standard dietaries,” and the ordinary practices of mankind, -is not needed to establish a condition of nitrogen equilibrium. It -would seem, however, as if results of this nature, presented from -time to time by various investigators, have been considered more in -the light of scientific curiosities than as data having an important -bearing on physiological processes. So strong has been the hold upon -the medical and physiological mind of the necessity of high proteid -that such figures as the above have merely excited comment, without -weakening in any measure the prevalent conviction that health, -strength, and the power to work necessitate a high rate of proteid -exchange. - -To one willing to accept the data as having possible significance there -arises at once the question, How long can the body be maintained in -nitrogen equilibrium on such relatively small quantities of proteid -food? In other words, can experiments of this nature, extending over -comparatively short periods of time, be safely accepted as a reliable -means of measuring the proteid requirements of the body for indefinite -periods? Suppose, says the critic, we grant that the body can maintain -itself in nitrogen equilibrium for a week or two on a very small amount -of proteid food, what proof have we that in the long run the body will -be benefited thereby, or even able to exist in a condition of normal -strength and vigor? In other words, is a low proteid diet, one that -seems sufficient to maintain the body in nitrogen equilibrium, a wholly -safe one to follow? May there not be other elements to be considered, -aside from nitrogen equilibrium, which, if fully understood, would -satisfactorily account for the customs of mankind, in which perhaps -man’s instincts have been followed for the betterment of the race? It -was with a view to learning more concerning these questions that five -years ago the writer commenced systematic, experimental, work upon the -nutrition of man, with special reference to his nitrogen requirements. -The experiments and observations have been continued up to the present -time, with many suggestive results, some of which will now be referred -to.[60] - - [60] In presenting the general results of these experiments, the - writer has drawn freely from his book, “Physiological Economy in - Nutrition,” published by the Frederick A. Stokes Company, New York, - 1904. - -One group of subjects was composed of professional men, professors and -instructors in the university, whose work was mainly mental rather -than physical, though by no means excluding the latter. Of this group, -two cases will be referred to with some regard for detail, since in -no other way can so striking a picture be presented of the effects -produced. The first subject weighed 65 kilos in the fall of 1902, and -at that time was nearly 47 years of age. His dietetic habits were in -accord with common practice, and his daily consumption of proteid food -averaged close to 118 grams. With a clear recognition of the principle -that the habits of a lifetime should not be too suddenly changed, a -very gradual reduction in the total amount of food, and especially of -proteid matter, was made. This finally resulted, with this particular -subject, in the complete abolition of breakfast, with the exception of -a small cup of coffee. A light lunch was taken at noontime, followed by -a more substantial dinner at night. There was no change to a vegetable -diet, but naturally any attempt to cut off largely the amount of -proteid food necessarily results in a marked diminution in the quantity -of animal food or meats. It is a somewhat singular though suggestive -fact, that a change of this order gradually results in a stronger -liking for simple foods, with their more delicate flavor, accompanied -by a diminished desire for the heavier animal foods. - -As the day’s ration was gradually reduced in amount, the body-weight -began to fall off, until after some months it became stationary at 57 -kilos, at which point it has remained practically constant for over -three years. The sixteen pounds of weight lost was composed, mainly at -least, of superfluous fat. For a period of nine months, from October, -1903, to the end of June, 1904, the amount of proteid material broken -down in the body was determined each day. The average daily metabolism -of nitrogen for the entire period of nearly nine months amounted to -5.69 grams. For the last two months, it averaged 5.4 grams per day. -Analyses made from time to time since these figures were obtained show -that the subject is still living at the same low level of nitrogen -metabolism. In fact, the data available afford satisfactory proof -that for a period covering over three years this particular person -has subsisted on an amount of proteid food equal to a metabolism of -not more than 5.8 grams of nitrogen per day. It may be asked why the -subject should have continued such a low proteid diet after the nine -months’ period was completed? In reply, it may be said that the new -habit has taken a firm hold, and entirely supplanted the dietetic -desires and cravings of the preceding years. Further, the improved -condition of health, freedom from minor ailments that formerly caused -inconvenience and discomfort, and the greater ability to work without -fatigue, have all combined to place the new habit on a firm basis, from -which there is no desire to change. - -Consider for a moment what this lowered consumption of proteid food -really amounts to, as compared with ordinary usage and the so-called -dietary standards. The latter call for at least 118 grams of proteid -or albuminous food daily, of which 105 grams should be absorbable, in -order to maintain the body in a condition of nitrogen equilibrium, -and in a state of physical vigor and general tone. This would mean a -daily metabolism and excretion of at least 16 grams of nitrogen. Our -subject, however, excreted per day, during nine months, only 5.69 grams -of nitrogen, which means a metabolism of 35.6 grams of proteid; _i. -e._, about one-third the amount ordinarily deemed necessary to meet -man’s requirement for proteid food. But was our subject in nitrogen -equilibrium on this small amount of proteid food? We answer yes, as the -following balance period shows: - - Output. - Nitrogen in Nitrogen through Weight of Excrement - Food. Kidneys. (dry). - March 20 6.989 grams. 5.91 grams. 3.6 grams. - 21 6.621 5.52 .. - 22 6.082 5.94 12.0 - 23 6.793 5.61 18.5 - 24 5.057 4.31 23.0 - 25 6.966 5.39 16.9 - ----- ---- ---- - 74.0 grams contain - 6.42% N. - - 38.508 32.68 + 4.75 grams nitrogen. - ------ -------------------------- - 38.508 grams nitrogen. 37.43 grams nitrogen. - - Nitrogen balance for six days = +1.078 grams. - Nitrogen balance per day = +0.179 gram. - -In this particular period of six days, the body was really gaining a -little nitrogen, _i. e._, storing away a small amount of proteid for -future use, although it may be granted that the amount was too small to -have any special significance. During this period, the average daily -intake of nitrogen was 6.4 grams, equal to 40 grams of proteid food. -The average daily output of nitrogen through kidneys and excrement was -6.24 grams. The average daily output of metabolized nitrogen, through -the kidneys, was 5.44 grams, corresponding to the breaking down of 34 -grams of proteid material. Further, it should be stated that the total -calorific value of the daily food during this period was less than 2000 -calories. Let me add now a final balance period taken at the close of -the nine months’ trial: - - Output. - Nitrogen in Nitrogen through Weight of Excrement - Food. Kidneys. (dry). - June 23 6.622 grams. 5.26 grams. 10.6 grams. - 24 6.331 5.30 30.7 - 25 4.941 4.43 14.2 - 26 5.922 4.66 11.9 - 27 5.486 4.98 15.2 - ----- ---- ---- - 82.6 grams contain - 6.08% N. - - 29.302 24.63 + 5.022 grams nitrogen. - ------ -------------------------- - 29.302 grams nitrogen. 29.652 grams nitrogen. - - - Nitrogen balance for five days = -0.350 gram. - Nitrogen balance per day = -0.070 gram. - -In this period of five days, the average daily intake of nitrogen was -5.86 grams, corresponding to 36.6 grams of proteid food. The average -daily output of metabolized nitrogen was 4.92 grams, implying the -breaking down in the body of only 30.7 grams of proteid material -per day. The fuel value of the daily food, calculated as closely as -possible, was less than 2000 calories. The body was essentially in -nitrogen equilibrium, the minus balance being too small to have any -special significance. - -It will be instructive to consider next the actual character and amount -of the diet made use of on several of these balance days: - - -_March 21._ - - Breakfast.--Coffee 119 grams, cream 30 grams, sugar 9 grams. - - Lunch.--One shredded wheat biscuit 31 grams, cream 116 grams, wheat - gem 33 grams, butter 7 grams, tea 185 grams, sugar 10 grams, cream - cake 53 grams. - - Dinner.--Pea soup 114 grams, lamb chop 24 grams, boiled sweet potato - 47 grams, wheat gems 76 grams, butter 13 grams, cream cake 52 grams, - coffee 61 grams, sugar 10 grams, cheese crackers 16 grams. - - Total nitrogen content of the day’s food = 6.621 grams. - - -_June 24._ - - Breakfast.--Coffee 96 grams, cream 32 grams, sugar 8 grams. - - Lunch.--Creamed codfish 89 grams, baked potato 95 grams, butter 10 - grams, hominy gems 58 grams, strawberries 86 grams, sugar 26 grams, - ginger snaps 47 grams, water. - - Dinner.--Cold tongue 14 grams, fried potato 48 grams, peas 60 grams, - wheat gems 30 grams, butter 11 grams, lettuce-orange salad with - mayonnaise dressing 155 grams, crackers 22 grams, cream cheese 14 - grams, ginger snaps 22 grams, coffee 58 grams, sugar 10 grams. - - Total nitrogen content of the day’s food = 6.331 grams. - - -_June 25._ - - Breakfast.--Coffee 101 grams, cream 36 grams, sugar 13 grams. - - Lunch.--Omelette 50 grams, bacon 9 grams, French fried potato 23 - grams, biscuit 29 grams, butter 8 grams, ginger snaps 42 grams, cream - cheese 17 grams, iced tea 150 grams, sugar 15 grams. - - Dinner.--Wheat popovers 57 grams, butter 10 grams, lettuce-orange - salad with mayonnaise dressing 147 grams, crackers 22 grams, cream - cheese 21 grams, cottage pudding 82 grams, coffee 48 grams, sugar 11 - grams. - - Total nitrogen content of the day’s food = 4.941 grams. - - -_June 27._ - - Breakfast.--Coffee 112 grams, cream 22 grams, sugar 10 grams. - - Lunch.--Roast lamb 9 grams, baked potato 90 grams, wheat gems 47 - grams, butter 12 grams, iced tea 250 grams, sugar 25 grams, vanilla - éclair 47 grams. - - Dinner.--Lamb chop 32 grams, creamed potato 107 grams, asparagus 49 - grams, bread 35 grams, butter 17 grams, lettuce-orange salad with - mayonnaise dressing 150 grams, crackers 21 grams, cream cheese 12 - grams, coffee 63 grams, sugar 9 grams. - - Total nitrogen content of the day’s food = 5.486 grams. - - -It can be seen that there was nothing especially peculiar in these -dietaries, aside from their simplicity, except that the quantities -were small. Meat was not excluded; there was no approach to a cereal -diet; there were no fads involved, nothing but simple moderation -in the amounts of nitrogen-containing foods. Further, there was -perfect freedom of choice; full latitude to consider personal likes -and dislikes in the selection of foods; anything that appealed to -the appetite could be eaten, with the simple restriction that the -amount taken must be small. During the balance days, naturally, every -article of food had to be carefully weighed and analyzed, which fact -undoubtedly tended to limit in some degree the variety of foods chosen, -since increase in the number of articles meant increased labor in -analysis. Quite noticeable, however, was the extreme constancy in the -nitrogen-content of the daily diet, even on those days when the food -was not weighed. In other words, there had been gradually acquired -a new habit of food consumption, and the individual, unconsciously -perhaps, rarely overstepped the limits fixed by the new level of -proteid metabolism. This is a fact that has been conspicuous in nearly -all of our experiments, where freedom of choice in the taking of food -has been followed; and is in harmony with the view that after a lower -level of proteid metabolism has once been established, and the body has -become accustomed to the new conditions, there is little tendency for -any marked deviation from the new standards of food consumption. - -With maintenance of body-weight, together with nitrogen equilibrium -through all these months; and with health, strength, and mental and -physical vigor unimpaired, there is certainly ground for the belief -that the real needs of the body were as fully met by the lowered -consumption of proteid food as by the quantities called for by the -customary standards. Finally, it should be noted that this particular -subject was small in weight, and hence did not need so much proteid -as a man of heavier body-weight would require. In recognizing this -principle, we may for future comparison calculate the nitrogen -requirement of the body, on the basis of the present results, per kilo -of body-weight. With the weight of the subject placed at 57 kilos, and -with an average daily excretion of nitrogen amounting to practically -5.7 grams, it is plain that this individual was quite able to maintain -a condition of equilibrium with a metabolism of 0.1 gram of nitrogen -per kilo of body-weight. Translated into terms of proteid matter, this -would mean a utilization by the body of 0.625 gram of proteid daily -per kilo of body-weight. Regarding the fuel value of the daily food, -we need not be more precise than to emphasize the fact that so far as -could be determined, on the basis of chemical composition, the heat -value of the food rarely exceeded 1900 calories per day. If we make a -liberal allowance, for the sake of precaution, it would seem quite safe -to say that this particular individual, under the conditions of life -and bodily activity prevailing, did not apparently need of fuel value -more than 2000 calories per day, which would correspond to 35 calories -per kilo of body-weight. - -Let us turn now to the second subject in this group, a man of 76 kilos -body-weight, 32 years of age, and of strong physique. His active life -in the laboratory called for greater physical exertion than the former -subject, and consequently there was need for greater consumption of -non-nitrogenous food, with the accompanying increase in fuel value of -the day’s ration. As in the preceding case, there was no prescribing -of food, but a gradual and voluntary diminution of proteid material. -During the last seven months and a half of the experiment, the average -daily excretion of nitrogen through the kidneys amounted to 6.53 grams, -equivalent to a metabolism of 40.8 grams of proteid matter daily; a -little more than one-third the minimal quantity called for by common -usage. At first, the body-weight of the subject gradually fell until it -reached 70 kilos, at which point it remained fairly constant during the -last five months. That the quantity of food taken was quite sufficient -to maintain the body in a condition of nitrogen equilibrium is apparent -from the results of a comparison of income and outgo of nitrogen, as -shown in the following table: - - Output. - Nitrogen in Nitrogen through Weight of Excrement - Food. Kidneys. (dry). - May 18 8.668 grams. 6.06 grams. 14 grams. - 19 6.474 7.17 39 - 20 6.691 6.33 30 - -- - 21 8.345 6.78 83 contain 6.06% N. - = 5.03 grm. N. - 22 7.015 5.70 .. - 23 9.726 5.75 38 - 24 10.424 6.39 57 - ------ ---- -- - 95 contain 5.76% N. - = 5.47 grm. N. - ---- - 10.50 grm. N. - - 57.343 44.18 + 10.50 grams nitrogen. - ------ ------------- - 57.343 grams N. 54.68 grams nitrogen. - - Nitrogen balance for seven days = +2.663 grams. - Nitrogen balance per day = +0.380 gram. - -The average daily intake of nitrogen was 8.192 grams, equivalent to -51.2 grams of proteid food. The average amount of nitrogen excreted -through the kidneys each day was 6.31 grams, corresponding to a -metabolism of 39.43 grams of proteid matter. The plus balance of 0.380 -gram of nitrogen per day shows that not only was the amount of proteid -food consumed quite adequate to meet the demands of the body, but the -latter was able to store up 2.3 grams of proteid per day. Regarding -the character of the food taken by this subject, it should be stated -that there was gradually developed a tendency toward a pure vegetarian -diet. During the last seven months of the experiment, meats were -almost entirely excluded. The diet voluntarily selected thus differed -decidedly from that of the preceding subject in that it was much more -bulky, contained a larger proportion of undigestible vegetable matter, -and was richer in fats and carbohydrates, with a corresponding increase -in fuel value. The exact character of the daily dietary is indicated -by the following data of food consumption, on four of the days of the -above balance period: - - -_May 19._ - - Breakfast.--Banana 102 grams, wheat rolls 50 grams, coffee 150 grams, - cream 50 grams, sugar 21 grams. - - Lunch.--Omelette 20 grams, bread 57 grams, hominy 137 grams, syrup 68 - grams, potatoes 128 grams, coffee 100 grams, cream 50 grams, sugar 21 - grams. - - Dinner.--Tomato purée 200 grams, bread 24 grams, fried sweet potato - 100 grams, spinach 70 grams, Indian meal 100 grams, syrup 25 grams, - coffee 100 grams, cream 40 grams, sugar 21 grams. - - Total nitrogen content of the day’s food = 6.474 grams. - - -_May 20._ - - Breakfast.--Sliced orange 140 grams, coffee 100 grams, cream 30 - grams, sugar 21 grams. - - Lunch.--Lima beans 40 grams, mashed potato 250 grams, bread 28 grams, - fried hominy 115 grams, syrup 48 grams, coffee 100 grams, cream 30 - grams, sugar 21 grams. - - Dinner.--Consommé 150 grams, string beans 140 grams, mashed potato - 250 grams, rice croquette 93 grams, syrup 25 grams, cranberry jam 95 - grams, bread 19 grams, coffee 100 grams, cream 30 grams, sugar 21 - grams. - - Total nitrogen content of the day’s food = 6.691 grams. - - -_May 21._ - - Breakfast.--Banana 153 grams, coffee 150 grams, cream 30 grams, sugar - 21 grams. - - Lunch.--Potato croquette 229 grams, bread 25 grams, tomato 123 grams, - Indian meal 109 grams, syrup 48 grams, coffee 100 grams, cream 20 - grams, sugar 14 grams. - - Dinner.--Bean soup 100 grams, bacon 5 grams, fried potato 200 grams, - bread 31 grams, lettuce-orange salad 47 grams, prunes 137 grams, - coffee 100 grams, cream 25 grams, sugar 21 grams, banana 255 grams. - - Total nitrogen content of the day’s food = 8.345 grams. - - -_May 23._ - - Breakfast.--Banana 229 grams, coffee 125 grams, cream 25 grams, sugar - 21 grams. - - Lunch.--Consommé 75 grams, scrambled egg 15 grams, bread 58 grams, - apple sauce 125 grams, fried potato 170 grams, rice croquette 197 - grams, syrup 68 grams, coffee 100 grams, cream 30 grams, sugar 21 - grams. - - Dinner.--Vegetable soup 100 grams, potato croquette 198 grams, bread - 73 grams, bacon 7 grams, string beans 120 grams, water ice 77 grams, - banana 270 grams, coffee 100 grams, cream 30 grams, sugar 14 grams. - - Total nitrogen content of the day’s food = 9.726 grams. - - -While the critic might justly say that these dietaries lack variety -and would not appeal to a fastidious taste, there is force in the -illustration which they afford of a simple diet being quite adequate -to meet the wants of the body. Further, it should be emphasized that -there is no special virtue in any of these dietaries, aside from their -simplicity and low content of nitrogen. They represent individual -taste and selection. Any other form of diet would answer as well, -provided there was not too large an intake of proteid, and provided -further the fuel value of the day’s ration was sufficient to meet the -requirements for heat and work. Again, it might be said that with this -latter subject the daily consumption of proteid food was considerably -larger than with the first subject. This is indeed true, but it must be -remembered that the second subject had a body-weight of 70 kilos during -the last seven months, while the first subject weighed only 57 kilos. -Obviously, with this marked difference in the weight of living tissue -there must be a corresponding difference in the extent of proteid -katabolism, and consequently a difference in the demand for proteid -food. - -As we have seen, the smaller subject for a period of many months -showed a proteid katabolism equal to 0.1 gram of nitrogen, per kilo -of body-weight, daily. The second and larger subject, on a totally -different diet, for seven months and a half, metabolized daily, on -an average, 6.53 grams of nitrogen. Taking the weight of the body at -70 kilos, it is readily seen that the nitrogen metabolized daily per -kilo of body-weight was 0.093 gram, almost identical with the rate of -nitrogen exchange found with the first subject. It is certainly very -suggestive that these two individuals with their marked difference -in body-weight, under different degrees of physical activity, and -living on different forms of diet, with only the one point in common -of voluntary restriction in the amount of proteid food, until a new -habit had been acquired and a new level of proteid metabolism attained, -should have quite independently reached exactly the same level of -nitrogen exchange per kilo of body-weight. And when it is remembered -that this was attained by the daily consumption of not more than -one-third to one-half the minimal amount of proteid food called for -by the dietetic customs of mankind, and with maintenance of all the -characteristics of good health through this comparatively long period -of time, there certainly seems to be justification for the opinion -that the consumption of proteid food, as practised by the people of -the present generation, is far in excess of the needs of the body. -Referring for a moment to the calorific value of the food used by the -second subject, in the last balance period, it is to be noted that the -heat value per day averaged 2448 calories, as estimated on the basis of -the chemical composition of the food. This would amount to 34 calories -per kilo. Whether this figure is strictly correct is immaterial; it is -certainly sufficiently so to warrant the statement that the needs of -the body were fully met by an intake of food below the standards set -by usage, and that maintenance of nitrogen equilibrium on a greatly -diminished consumption of proteid food is possible without increasing -the intake of non-nitrogenous matter. - -Finally, as affording additional evidence, we may refer to a third -subject in this group, a man of 65 kilos body-weight, 26 years of age, -who for a period of six consecutive months maintained body-weight, -nitrogen equilibrium, and a general condition of good health, with a -proteid metabolism equal to 7.81 grams of nitrogen per day. During the -last two months of the experiment, the average excretion of nitrogen -per day amounted to 6.68 grams, corresponding to a metabolism of -0.102 gram of nitrogen per kilo of body-weight. This figure, it will -be noted, is practically identical with the values obtained with the -preceding subjects, calculated to the same unit of weight. Further, -this third subject did not reduce his nitrogen intake by an exclusion -of meat, but made use of his ordinary diet gradually reduced in amount. -His daily consumption of proteid food averaged 55 grams, or 8.83 grams -of nitrogen, and on this amount of proteid, without increasing the -intake of fats and carbohydrates, he was quite able to do his work with -preservation of physiological equilibrium. - -Views so radically different from those commonly accepted can be made -to carry weight, only by the accumulation of supporting evidence -obtained under widely different conditions of life, and by methods -which will defy criticism. It might be argued, and with perhaps some -justification, that while professional men, with freedom from muscular -work, may be able to live without detriment on a relatively small -amount of proteid food, such a conclusion would not be warranted for -the great majority of mankind with their necessarily greater muscular -activity. We are confronted at once with the oft-heard statement that -the laboring man requires more proteid food; he has a more vigorous -appetite, and he must take an abundance of meat and other foods -rich in proteid, if he is to maintain his ability as a worker. Note -the statements already made in other connections regarding the food -consumption of Maine lumbermen, of men on the football team, of trained -athletes in general. These men consume large amounts of proteid daily, -because their work demands it. If the demand did not really exist, they -would not so agree in the use of high proteid standards, so runs the -argument. The custom certainly does exist and is almost universally -followed; men in training for athletic events deem it necessary to -consume large amounts of proteid food. Custom and long experience -sanction a high proteid diet, rich in nitrogen, for the development -and maintenance of that strength and vigor that help to make the -accomplished athlete. It is common knowledge to-day, however, that the -energy of muscle work does not have its origin in the breaking down of -proteid material, certainly not when there is an adequate amount of -fat and carbohydrate in the diet. A high proteid intake must therefore -be called for because of some subtle quality, not at present fully -understood. It must not be subjected to criticism, however, because it -is sanctioned by custom, habit, and common usage. - -Still, I have ventured to experiment somewhat with a group of eight -university athletes, all trained men, and with some surprising results. -We have not space for details, but it may be mentioned that the men -were young, from 22 to 27 years of age, and were experts in some field -of athletic work. By a preliminary study of their ordinary dietetic -habits, it was found that they were all large consumers of proteid -food, with a corresponding high rate of proteid katabolism. One subject -of 92 kilos body-weight, during ten days, showed an average daily -excretion through the kidneys of 22.79 grams of nitrogen, implying a -metabolism of 142 grams of proteid matter per day. On one of these -days, the nitrogen excretion reached the high figure of 31.99 grams, -corresponding to a metabolism of about 200 grams of proteid matter. -Calculated per kilo of body-weight, this means a metabolism of 0.35 -gram of nitrogen, or three and a half times the amount needed by the -three professional men for the maintenance of nitrogen equilibrium. -These subjects, with an intelligent comprehension of the point -at issue, and with full freedom in the choice of food, gradually -diminished their daily consumption of proteid material, at the same -time cutting down very markedly the total consumption of food. The -experiment extended through five months, and during the last two -months, the average daily excretion of metabolized nitrogen of the -eight men amounted to 8.81 grams per man. This corresponds to a -metabolism of 55 grams of proteid matter. - -Further, the average daily output of nitrogen through the kidneys -during the preceding two months was in many cases nearly, if not quite, -as low as during the last two months of the experiment. If we contrast -this average daily exchange of 8.81 grams of nitrogen with the average -output prior to the change in diet, it is easy to see that the men were -living on about one-half the amount of proteid food they were formerly -accustomed to take. Moreover, if the metabolized nitrogen for each -individual, with one exception, is calculated per kilo of body-weight, -it is seen to vary from 0.108 gram to 0.134 gram; somewhat higher than -was observed with the older professional men, but not conspicuously so. -Again, it is to be emphasized that the lowered intake of proteid food -with these men was quite adequate to maintain their bodies in nitrogen -equilibrium. We may cite a single case by way of illustration: - - Output. - Nitrogen of Nitrogen through Weight of Excrement - Food. Kidneys. (dry). - May 18 8.119 grams. 5.75 grams. .. grams. - 19 9.482 6.64 15 - 20 10.560 8.45 .. - 21 8.992 8.64 .. - 22 9.025 8.53 .. - 23 8.393 7.69 89 - 24 7.284 7.34 24 - ----- ---- --- - 128 grams contain - 6.40 % N. - - 61.855 53.04 + 8.192 grams nitrogen. - ------ ----------------- - 61.855 grams nitrogen. 61.232 grams nitrogen. - - Nitrogen balance for seven days = +0.623 gram. - Nitrogen balance per day = +0.089 gram. - -The daily intake of nitrogen during this balance period averaged 8.83 -grams, corresponding to 55.1 grams of proteid food. The metabolized -nitrogen eliminated through the kidneys averaged 7.58 grams per day, -thus showing a daily average metabolism of 47.37 grams of proteid -matter. With a body-weight of 63 kilos, this individual was maintaining -equilibrium on a metabolism of 0.120 gram of nitrogen per kilo of -body-weight. The fuel value of the day’s food as estimated did not -exceed 2800 calories, thus substantiating the general statement that -there is no need for increasing the fuel value of the food in any -attempt to maintain a lower nitrogen level. This particular individual, -in his choice of food, unconsciously drifted--as he expressed -it--toward a simple vegetable diet, without, however, excluding meat -entirely. The following four dietaries will serve to illustrate the -character and amount of his daily food: - - -_May 21._ - - Breakfast.--Banana 106 grams, boiled Indian meal 150 grams, cream 50 - grams, sugar 21 grams, bread 59 grams, butter 16 grams. - - Lunch.--Lamb chop 37 grams, potato croquette 105 grams, tomato 216 - grams, bread 55 grams, butter 13 grams, sugar 14 grams, water ice 143 - grams. - - Dinner.--Bean soup 100 grams, bacon 10 grams, fried egg 22 grams, - fried potato 100 grams, lettuce salad 63 grams, coffee 100 grams, - cream 50 grams, sugar 21 grams, stewed prunes 247 grams. - - Total nitrogen content of the day’s food = 8.992 grams. - - -_May 22._ - - Breakfast.--Orange 60 grams, oatmeal 207 grams, roll 46 grams, butter - 14 grams, coffee 150 grams, cream 150 grams, sugar 35 grams. - - Lunch.--Boiled potato 150 grams, boiled onions 145 grams, macaroni - 130 grams, fried rice 138 grams, syrup 48 grams, ice cream 160 grams, - cake 26 grams. - - Dinner.--Celery soup 150 grams, spinach 100 grams, mashed potato 100 - grams, bread 19 grams, coffee 100 grams, cream 50 grams, sugar 7 - grams, strawberry short-cake 169 grams. - - Total nitrogen content of the day’s food = 9.025 grams. - - -_May 23._ - - Breakfast.--Sliced banana 201 grams, cream 100 grams, sugar 28 grams, - griddle cakes 103 grams, syrup 48 grams. - - Lunch.--Consommé 150 grams, rice croquette 140 grams, syrup 48 grams, - fried potato 100 grams, bread 36 grams, butter 15 grams, apple sauce - 90 grams, coffee 75 grams, sugar 7 grams. - - Dinner.--Vegetable soup 100 grams, bacon 20 grams, potato croquette - 50 grams, string beans 120 grams, macaroni 104 grams, bread 26 grams, - water ice 184 grams. - - Total nitrogen content of the day’s food = 8.393 grams. - - -_May 24._ - - Breakfast.--Orange 80 grams, fried rice 186 grams, syrup 72 grams, - coffee 100 grams, cream 50 grams, sugar 21 grams. - - Lunch.--Celery soup 125 grams, bread 34 grams, butter 19 grams, - boiled onion 127 grams, boiled potato 150 grams, tomato sauce 50 - grams, stewed prunes 189 grams, cream 50 grams. - - Dinner.--Tomato soup 125 grams, bread 21 grams, fried potato 100 - grams, spinach 130 grams, cream pie 158 grams, coffee 100 grams, - cream 50 grams, sugar 14 grams. - - Evening.--Ginger ale 250 grams. - - Total nitrogen content of the day’s food = 7.284 grams. - - -Here, again, we have dietaries not particularly attractive to every -one, but they represent the choice of an individual who was following -his own preferences, and like the preceding dietaries they are -characterized by simplicity. In any event, they were quite adequate -for the wants of the body, and their value to us lies in the proof -they afford that a relatively small intake of proteid food will not -only bring about and maintain nitrogen equilibrium for many months, -and probably indefinitely, but that such a form of diet is equally as -effective with vigorous athletes, accustomed to strenuous muscular -effort, as with professional men of more sedentary habits. Further, -these many months of observation with different individuals all lead to -the opinion that there are no harmful results of any kind produced by -a reduction in the amount of proteid food to a level commensurate with -the actual needs of the body. Body-weight, health, physical strength, -and muscular tone can all be maintained, in partial illustration of -which may be offered two photographs of one of the eight athletes -taken toward the end of the experiment; pictures which are certainly -the antithesis of enfeebled muscular structure, or diminished physical -vigor. - -[Illustration: STAPLETON - -_Photograph taken in the middle of the experiment, in April_] - - - - -CHAPTER VI - -FURTHER EXPERIMENTS AND OBSERVATIONS BEARING ON TRUE FOOD REQUIREMENTS - - TOPICS: Dietary experiments with a detail of soldiers from the United - States army. General character of the army ration. Samples of the - daily dietary adopted. Rate of nitrogen metabolism attained. Effect - on body-weight. Nitrogen balance with lowered proteid consumption. - Influence of low proteid on muscular strength of soldiers and - athletes. Effect on fatigue. Effect on physical endurance. Fisher’s - experiments on endurance. Dangers of underfeeding. Dietary - observations on fruitarians. Observations on Japanese. Recent dietary - changes in Japanese army and navy. Observations of Dr. Hunt on - resistance of low proteid animals to poisons. Conclusions. - - -General acceptance of a new theory, or a new point of view, can be -expected only when there is an adequate amount of scientific evidence -on which the theory can safely rest. Facts cannot be ignored, and the -larger the amount of supporting evidence the more certain becomes -the general truth of the theory to which it points. Corroborative -evidence, therefore, is always desirable, and he who would open up a -new point of view must be zealous in accumulating facts to uphold his -position. Critics there are without number who are ever ready to pick -flaws in an argument or overturn a theory, especially if the one or -the other stands opposed to their own point of view. This, however, -is highly advantageous for the advance of sound knowledge, since it -necessarily prompts the advocate to search in all directions for added -data, by which he can build a bulwark of fact sufficient to defy just -criticism. Further, the true scientific spirit demands persistent -and painstaking effort in the search after truth, that error and -misconception may be avoided. - -In harmony with these ideas, our attempt to ascertain the real needs of -the body for proteid food led us to enlarge our evidence by a series -of experiments with still another body of men, _i. e._, a detail of -soldiers from the United States army.[61] This was a somewhat more -difficult and ambitious undertaking, since the number of subjects -involved was larger, and because with this group of men we could not -expect quite that high degree of intelligent co-operation afforded by -the preceding subjects. Still, this very fact was in a sense an added -inducement, since it offered the opportunity of experimenting with a -body of men who naturally would not take kindly to anything that looked -like deprivation, and whose continued co-operation could be expected -only by satisfying their natural demands for food. If this could be -accomplished by an intelligent prescription in their daily diet, and -the experiment brought to a successful conclusion, with maintenance of -body-weight, nitrogen equilibrium, health, strength, and general vigor; -with an intake of proteid food essentially equal to that adopted by the -preceding subjects, corroborative evidence of the highest value would -be obtained. - - [61] In presenting the general results of these experiments, the - writer has drawn freely from his book, “Physiological Economy in - Nutrition,” published by the Frederick A. Stokes Company, New York, - 1904. - -The detail was composed of a detachment of twenty men from the -Hospital Corps of the army, under the command of a first lieutenant -and assistant surgeon. They were located in a convenient house near -to the laboratory, where they lived during their six months’ stay in -New Haven, under military discipline, and subject to the constant -surveillance of the commanding officer and the non-commissioned -officers. Having well-trained cooks and assistants, with all necessary -facilities for preparing and serving their food, with members of -the laboratory staff to superintend the weighing of the food as it -was placed before the men, and with intelligent clerks to attend -to the many details connected with such an undertaking, a somewhat -unique physiological experiment was started. Thirteen members of the -detachment really took part in the experiment as subjects, and they -represented a great variety of types: of different ages, nationalities, -temperaments, and degrees of intelligence. They were men accustomed -to living an active life under varying conditions, and they naturally -had great liking for the pleasures of eating. Further, it should be -remembered that, although the men had volunteered for the experiment, -they had no personal interest whatever in the principles involved, -and it could not be expected that they would willingly incommode -themselves, or suffer any great amount of personal inconvenience. -Again, there were necessary restrictions placed upon their movements, -when relieved from duty, which constituted something of a hardship in -the minds of many of the men and added to the irksomeness and monotony -of their daily life. Regularity of life was insisted upon, and this -was a condition which brought to some of the men a new experience. -These facts are mentioned because their recital will help to make clear -that, from the standpoint of the men, there were certain depressing -influences connected with the experiment which would add to any -personal discomfort caused by restriction of diet. - -The ordinary army ration to which these men were accustomed was rich in -proteid, especially in meat, and during the first few days they were -allowed to follow their usual dietary habits, in order that data might -be obtained bearing on their average food consumption. The details of -one day’s food intake will suffice to show the average character and -amount of the food eaten per man: - - Breakfast.--Beefsteak 222 grams, gravy 68 grams, fried potatoes 234 - grams, onions 34 grams, bread 144 grams, coffee 679 grams, sugar 18 - grams. - - Dinner.--Beef 171 grams, boiled potatoes 350 grams, onions 55 grams, - bread 234 grams, coffee 916 grams, sugar 27 grams. - - Supper.--Corned beef 195 grams, potatoes 170 grams, onions 21 grams, - bread 158 grams, fruit jelly 107 grams, coffee 450 grams, sugar 21 - grams. - -It is not necessary to comment upon the large proportion of proteid -matter in the day’s ration; the three large portions of meat testify -clearly enough to that fact, while the three equally large volumes of -coffee indicate a natural disposition toward generous consumption of -anything available. Habit, reinforced by inclination, had evidently -placed these men on a high plane of food consumption. - -For a period of six months, a daily dietary was prescribed for the -subjects; the food for each meal and for every man being of known -composition, each article being carefully weighed, while the content of -nitrogen in the day’s ration was so graded as to bring about a gradual -reduction in the amount of proteid ingested. The rate of proteid -katabolism was likewise determined each day by careful estimation of -the excreted nitrogen, balance experiments being made from time to -time in order to ascertain if the men were in a condition of nitrogen -equilibrium. Finally, it should be mentioned that the subjects lived -a fairly active life, having each day a certain amount of prescribed -exercise in the university gymnasium, in addition to the regular drill -and other duties associated with their usual work. - -[Illustration: _Photograph of the soldiers taken at the close of the -experiment_] - -[Illustration: _Photograph of the soldiers taken at the close of the -experiment_] - -As just stated, the amount of proteid food was gradually reduced, -three weeks being taken to bring the amount down to a level somewhat -commensurate with the estimated needs of the body. This naturally -resulted in diminishing largely the intake of meat, though by no means -entirely excluding it. Effort was constantly made to introduce as -much variety as was possible with simple foods, though the main problem -with this group of men was to keep the volume of the food up to such -a point as would dispel any notion that they were not having enough -to eat. A second problem, which at first threatened trouble, was the -fear of the men, as they saw the proportion of meat gradually drop -off, that they were destined to lose their strength; but fortunately, -they very soon began to realize that their fears in this direction -were groundless, and a little later their personal experience opened -their eyes to possible advantages which quickly drove away all further -thought of danger, and made them quite content to continue the -experiment. We may introduce here a few samples of the daily food given -to the men after they had reached their lower level of proteid intake: - - -_January 15._ - - Breakfast.--Wheat griddle cakes 200 grams, syrup 50 grams, one cup - coffee[62] 350 grams. - - Dinner.--Codfish balls (4 parts potato, 1 part fish, fried in pork - fat) 150 grams, stewed tomato 200 grams, bread 75 grams, one cup - coffee 350 grams, apple pie 95 grams. - - Supper.--Apple fritters 200 grams, stewed prunes 125 grams, bread 50 - grams, butter 15 grams, one cup tea 350 grams. - - Total nitrogen content of the day’s food = 8.560 grams. - - - [62] The coffee was prepared with milk and sugar. - - -_January 16._ - - Breakfast.--Soft oatmeal 150 grams, milk 100 grams, sugar 30 grams, - bread 30 grams, butter 10 grams, one cup coffee 350 grams. - - Dinner.--Baked macaroni with a little cheese 200 grams, stewed tomato - 200 grams, bread 50 grams, tapioca-peach pudding 150 grams, one cup - coffee 350 grams. - - Supper.--Fried bacon 20 grams, French fried potato 100 grams, bread - 75 grams, jam 75 grams, one cup tea 350 grams. - - Total nitrogen content of the day’s food = 7.282 grams. - - -_March 1._ - - Breakfast.--Fried rice 150 grams, syrup 50 grams, baked potato 150 - grams, butter 10 grams, one cup coffee 350 grams. - - Dinner.--Thick pea soup 250 grams, boiled onions 150 grams, boiled - sweet potato 150 grams, bread 75 grams, butter 20 grams, one cup - coffee 350 grams. - - Supper.--Celery-lettuce-apple salad 120 grams, crackers 32 grams, - American cheese 20 grams, potato chips 79 grams, one cup tea 350 - grams, rice custard 100 grams. - - Total nitrogen content of the day’s food = 7.825 grams. - - -_March 3._ - - Breakfast.--Boiled hominy 175 grams, milk 125 grams, sugar 25 grams, - baked potato 150 grams, butter 10 grams, one cup coffee 350 grams. - - Dinner.--Hamburg steak with much bread, fat, and onions 150 grams, - boiled potato 250 grams, bread 75 grams, butter 10 grams, one cup - coffee 350 grams. - - Supper.--Tapioca-peach pudding 250 grams, bread 75 grams, butter 20 - grams, jam 75 grams, one cup tea 350 grams. - - Total nitrogen content of the day’s food = 8.750 grams. - - -_March 6._ - - Breakfast.--Sliced banana 100 grams, fried Indian meal 150 grams, - syrup 50 grams, baked potato 150 grams, butter 10 grams, one cup - coffee 350 grams. - - Dinner.--Corned beef 50 grams, boiled cabbage 200 grams, mashed - potato 250 grams, bread 75 grams, fried rice 100 grams, jam 75 grams, - one cup coffee 350 grams. - - Supper.--Crackers 32 grams, butter 10 grams, sardine 14 grams, sponge - cake 150 grams, apple sauce 150 grams, one cup tea 350 grams. - - Total nitrogen content of the day’s food = 10.265 grams. - - -_March 30._ - - Breakfast.--Sliced banana 250 grams, fried hominy 150 grams, butter - 10 grams, syrup 75 grams, one cup coffee 350 grams. - - Dinner.--Codfish balls 125 grams, mashed potato 250 grams, stewed - tomato 200 grams, bread 35 grams, apple sauce 200 grams, one cup - coffee 350 grams. - - Supper.--Chopped fresh cabbage with salt, pepper, and vinegar 75 - grams, bread 50 grams, butter 20 grams, fried sweet potato 250 grams, - cranberry sauce 200 grams, sponge cake 50 grams, one cup tea 350 - grams. - - Total nitrogen content of the day’s food = 9.356 grams. - - -_March 31._ - - Breakfast.--Fried Indian meal 100 grams, syrup 75 grams, baked potato - 250 grams, butter 20 grams, one cup coffee 350 grams. - - Dinner.--Tomato soup, thick, with potatoes and onions boiled in, 300 - grams, scrambled egg 50 grams, mashed potato 200 grams, bread 50 - grams, butter 10 grams, one cup coffee 350 grams. - - Supper.--Fried bacon 20 grams, boiled potato 200 grams, butter 10 - grams, bread pudding 150 grams, sliced banana 200 grams, one cup tea - 350 grams. - - Total nitrogen content of the day’s food = 8.420 grams. - - -_April 1._ - - Breakfast.--Fried hominy 150 grams, syrup 75 grams, baked potato 200 - grams, butter 20 grams, one cup coffee 350 grams. - - Dinner.--Baked spaghetti 200 grams, mashed potato 250 grams, boiled - turnip 150 grams, bread 35 grams, butter 10 grams, apple sauce 200 - grams, one cup coffee 350 grams. - - Supper.--Fried bacon 25 grams, fried sweet potato 200 grams, bread - 35 grams, butter 20 grams, jam 100 grams, apple-tapioca pudding 300 - grams, one cup tea 350 grams. - - Total nitrogen content of the day’s food = 7.342 grams. - - -These dietaries are fair samples of the daily food given the men -during the last five months of the experiment. If we place the intake -of nitrogen at 8.5 grams per day, or even 9 grams daily, it would -mean at the most an average daily consumption of 56 grams of proteid; -viz., about one-third the amount they were accustomed to take under -their ordinary modes of life. Of greater interest, however, is -the rate of proteid katabolism shown by these men under the above -conditions of diet, during the five months’ period. The average -daily output of metabolized nitrogen for each man ranged from 7.03 -grams--the lowest--to 8.91 grams--the highest. An excretion of 7.03 -grams of nitrogen per day means a katabolism, or breaking down, of -43.9 grams of proteid matter; while the excretion of 8.91 grams of -nitrogen corresponds to a katabolism of 55.6 grams of proteid. The -grand average, _i. e._, the average daily output of nitrogen of all -the men for the five months’ period amounted to 7.8 grams per man, -corresponding to an average daily katabolism of 48.75 grams of proteid. -The heaviest man of the group had a body-weight of 74 kilograms, while -his average daily output of metabolized nitrogen amounted to 7.84 -grams. This corresponds to 0.106 gram of metabolized nitrogen per kilo -of body-weight; a figure which agrees quite closely with the lowest -figures obtained with the preceding subjects when calculated to the -same unit of weight. Many of the men, however, metabolized considerably -more nitrogen or proteid in proportion to their body-weight, due in a -measure at least to the fact that they were being fed more liberally -with proteid food than was really necessary for the needs of the body. -In this group, we have a body of men doing a reasonable amount of -physical work, who lived without discomfort for five consecutive months -on a daily consumption of proteid food not much, if any, greater than -one-third the amount called for by common usage, and the average fuel -value of which certainly did not exceed 3000 calories per day. Indeed, -so far as could be determined on the basis of chemical composition, the -heat value of the food was quite a little less than this figure would -imply. - -If the relatively small amount of proteid food made use of in this -trial was inadequate for the real necessities of the body, some -indication of it would be expected to reveal itself, with at least some -of the men, by the end of the period. One criticism frequently made is -that the subject draws in some measure upon his store of body material. -Should this be the case, it is evident that body-weight--in such a -long experiment as this--will gradually but surely diminish. Further, -the subject will show a minus nitrogen balance, _i. e._, there will -be a constant tendency for the body to give off more nitrogen than it -takes in. As bearing on the first point, the following table showing -the body-weights of the men at the commencement of the experiment -in October, and at the close of the experiment in April will be of -interest: - - -TABLE OF BODY-WEIGHTS - - +-------------+----------------+----------------+ - | | October, 1903 | April, 1904 | - +-------------+----------------+----------------+ - | | kilos | kilos | - | Steltz | 52.3 | 53.0 | - | Zooman | 54.0 | 55.0 | - | Coffman | 59.1 | 58.0 | - | Morris | 59.2 | 59.0 | - | Broyles | 59.4 | 61.0 | - | Loewenthal | 60.1 | 59.0 | - | Sliney | 61.3 | 60.6 | - | Cohn | 65.0 | 62.6 | - | Oakman | 66.7 | 62.1 | - | Henderson | 71.3 | 71.0 | - | Fritz | 76.0 | 72.6 | - | Bates | 72.7 | 64.3 (Feb.) | - | Davis | 59.3 | 57.2 (Jan.) | - +-------------+----------------+----------------+ - -As is readily seen, five of the men practically retained their weight -or made a slight gain. Of the others, Coffman, Loewenthal, Sliney, and -Cohn lost somewhat, but the amount was very small. Further, the loss -occurred during the first few weeks of the experiment, after which -their weight remained practically stationary. Fritz and Oakman lost -weight somewhat more noticeably, but this loss likewise occurred during -the earlier part of the trial. The accompanying photographs of Fritz, -taken at the close of the experiment, show plainly that such loss -of weight as he suffered did not detract from the appearance of his -well-developed musculature. Certainly, the photographs do not show any -signs of nitrogen starvation, or suggest the lack of any kind of food. - -Of all the men, Bates was the only one who underwent any great loss of -weight. He, however, was quite stout, and the work in the gymnasium, -reinforced by the change in diet, brought about what was for him a very -desirable loss of body-weight. It is evident, therefore, that there was -no marked or prolonged loss of body-weight as a result of the continued -use of the low proteid diet. Regarding the second point, viz., nitrogen -equilibrium, the following illustrations will suffice to indicate the -relationship existing between the income and outgo of nitrogen. A -balance experiment with each of the men, lasting seven days, February -29 to March 6, is here shown, the figures given being the daily -averages for the period: - - +-------------+----------+-----------+-------------+----------+ - | | Nitrogen | Nitrogen | Nitrogen of | Nitrogen | - | | of Food. | of Urine. | Excrement. | Balance. | - +-------------+----------+-----------+-------------+----------+ - | | grams | grams | grams | grams | - | Oakman | 9.52 | 7.24 | 1.76 | +0.52 | - | Henderson | 9.40 | 7.90 | 1.00 | +0.50 | - | Morris | 9.49 | 6.05 | 2.30 | +1.14 | - | Coffman | 9.53 | 7.92 | 1.47 | +0.14 | - | Steltz | 9.62 | 7.16 | 1.95 | +0.51 | - | Loewenthal | 9.64 | 7.00 | 1.71 | +0.95 | - | Cohn | 9.27 | 7.63 | 1.41 | +0.23 | - | Zooman | 9.49 | 7.13 | 1.76 | +0.60 | - | Sliney | 9.52 | 8.08 | 1.92 | -0.48 | - | Broyles | 9.43 | 7.01 | 1.19 | +1.23 | - | Fritz | 9.37 | 6.36 | 1.81 | +1.20 | - +-------------+----------+-----------+-------------+----------+ - -[Illustration: FRITZ - -_At the close of the experiment_] - -With one exception, all of the men were plainly having more proteid -food than was necessary to maintain the body in nitrogen -equilibrium, the plus nitrogen balance in most cases being fairly -large. It is only necessary to remember that a gain to the body of 1 -gram of nitrogen means a laying by of 6.25 grams of proteid, and with -such a gain per day it is apparent that the men were really being -supplied with an excess of proteid food. This view is supported by the -fact that a later balance experiment, when considerably less proteid -food was being given, still showed many of the men in a condition -of plus balance, or with a minus balance so small as to indicate -essentially nitrogen equilibrium. The following figures, being daily -averages of a balance period about the first of April, may be offered -in evidence: - - +-------------+----------+-----------+-------------+----------+ - | | Nitrogen | Nitrogen | Nitrogen of | Nitrogen | - | | of Food. | of Urine. | Excrement. | Balance. | - +-------------+----------+-----------+-------------+----------+ - | | grams | grams | grams | grams | - | Broyles | 8.66 | 6.63 | 1.87 | +0.16 | - | Fritz | 8.13 | 5.77 | 1.63 | +0.73 | - | Loewenthal | 8.51 | 6.51 | 2.02 | -0.02 | - | Steltz | 8.32 | 6.50 | 1.88 | -0.06 | - | Cohn | 8.29 | 6.25 | 1.55 | +0.49 | - | Morris | 8.45 | 6.49 | 2.27 | -0.31 | - | Oakman | 8.62 | 7.04 | 1.87 | -0.29 | - +-------------+----------+-----------+-------------+----------+ - -A daily intake of 8.5 grams of nitrogen means the consumption of -53 grams of proteid. Under these conditions of diet, the average -daily amount of nitrogen metabolized was 6.45 grams, corresponding -to 40.3 grams of proteid. The men were practically in a condition -of nitrogen equilibrium, so that we are apparently justified in the -general statement that the simple dietary followed with these men -during the six months’ experiment, and which was accompanied by an -average daily metabolism, after the first three weeks, of 7.8 grams of -nitrogen, was certainly sufficient to maintain both body-weight and -nitrogen equilibrium. Lastly, emphasis may be laid upon the fact that -these values for nitrogen do not necessarily represent the minimal -proteid requirement of the human body, since it is a well-established -physiological principle that by increase of non-nitrogenous food -the rate of proteid katabolism can always be further diminished; a -principle which is plainly in harmony with the view that a high rate of -proteid exchange is not a necessary requisite for the welfare of the -body. - -The experimental results presented afford very convincing proof that -so far as body-weight and nitrogen equilibrium are concerned, the -needs of the body are fully met by a consumption of proteid food -far below the fixed dietary standards, and still further below the -amounts called for by the recorded habits of mankind. General health -is equally well maintained, and with suggestions of improvement that -are frequently so marked as to challenge attention. Most conspicuous, -however, though something that was entirely unlooked for, was the -effect observed on the muscular strength of the various subjects. -When the experiments were planned, it was deemed important to arrange -for careful quantitative tests of the more conspicuous muscles of the -body, with a view to measuring any loss of strength that might occur -from the proposed reduction in proteid food. The thought that prompted -this action was a result of the latent feeling that somehow muscular -strength must be dependent more or less upon the proteid constituents -of the muscles, and that consequently the cutting down of proteid food -would inevitably be felt in some degree. The most that could be hoped -for was that muscle tone and muscular strength might be maintained -unimpaired. Hence, we were at first quite astonished at what was -actually observed. - -With the soldier detail, fifteen distinct strength tests were made -with each man during the six months’ period, by means of appropriate -dynamometer tests applied to the muscles of the back, legs, chest, -upper arms, and forearms, reinforced by quarter-mile run, vault, and -ladder tests, etc. The so-called “total strength” of the man was -computed by multiplying the weight of the body by the number of times -the subject was able to push up (strength of triceps muscles) and pull -up (strength of biceps muscles) his body while upon the parallel bars, -to this product being added the strength (dynamometer tests) of hands, -legs, back, and chest. It should be added that all of these tests were -made quite independently in the university gymnasium by the medical -assistants and others in charge of the work there. It will suffice for -our purpose to give here the strength tests of the various members of -the soldier detail at the beginning and close of the experiment. - - -TOTAL STRENGTH - - +------------+----------+---------+ - | | October. | April. | - +------------+----------+---------+ - | Broyles | 2560 | 5530 | - | Coffman | 2835 | 6269 | - | Cohn | 2210 | 4002 | - | Fritz | 2504 | 5178 | - | Henderson | 2970 | 4598 | - | Loewenthal | 2463 | 5277 | - | Morris | 2543 | 4869 | - | Oakman | 3445 | 5055 | - | Sliney | 3245 | 5307 | - | Steltz | 2838 | 4581 | - | Zooman | 3070 | 5457 | - +------------+----------+---------+ - -Without exception, we note with all of the men a phenomenal gain in -strength, which demands explanation. Was it all due to the change in -diet? Probably not, for these men at the beginning of the experiment -were untrained, and it is not to be assumed that months of practical -work in the gymnasium would not result in a certain amount of physical -development, with corresponding gain in muscular skill and power. -Putting this question aside for the moment, however, it is surely -proper to emphasize this fact; viz., that although the men for a -period of five months were restricted to a daily diet containing -only one-third to one-half the amount of proteid food they had been -accustomed to, there was no loss of physical strength; no indication -of any physical deterioration that could be detected. In other words, -the men were certainly not being weakened by the lowered intake of -proteid food. This is in harmony with the principle, already discussed, -that the energy of muscle work comes primarily from the breaking down -of non-nitrogenous material, and consequently a diminished intake of -proteid food can have no inhibitory effect, provided, of course, there -is an adequate amount of proteid ingested to satisfy the endogenous -requirements of the tissues. - -On the other hand, recalling the large number of nitrogenous cleavage -products which result from the breaking down of proteid material, we -can conceive of an exaggerated exogenous proteid katabolism which -may flood the tissues and the surrounding lymph with a variety of -nitrogenous waste products, having an inhibitory effect upon the -muscle fibres themselves, or upon the peripheral endings of the motor -nerves, by which the muscles are prevented, directly or indirectly, -from working at their highest degree of efficiency. This being true, -a reduction of the exogenous katabolism to a level more nearly -commensurate with the real needs of the body might result in a marked -increase in the functional power of the tissue. However this may -be, the fact remains that all of the subjects showed this great -gain in strength; and furthermore, there was a noticeable gain in -self-reliance and courage in their athletic work, both of which are -likewise indicative of an improved condition of the body. How far these -improvements are attributable to training and to the more regular life -the men were leading, and how far to the change in diet, cannot be -definitely determined. We may venture the opinion, however, for reasons -to be made clear shortly, that the change in diet was in a measure -at least responsible for the increased efficiency. As the writer has -already expressed it, there must be enough food to make good the -daily waste of tissue, enough food to furnish the energy of muscular -contraction, but any surplus over and above what is necessary to supply -these needs is not only a waste, but may prove an incubus, retarding -the smooth working of the machinery and detracting from the power of -the organism to do its best work. - -Let us now turn our attention for a moment to the group of university -athletes, remembering that these men had been in training for many -months, and some of them for several years, prior to the commencement -of the trial with a reduced proteid intake. In the words of the -director of the gymnasium, “These eight men were in constant practice -and in the pink of condition; they were in ‘training form’ when they -began the changed diet.” Some of them had gained marked distinction for -their athletic work; one during the early months of the test won the -Collegiate and All-around Inter-collegiate Championship of America. -Compare now the strength tests of these men as taken at the beginning -and end of the five months’ experiment, during which they reduced their -daily intake of proteid food more than fifty per cent: - - -TOTAL STRENGTH - - +----------------+----------+----------+ - | | January. | June. | - +----------------+----------+----------+ - | G. W. Anderson | 4913 | 5722 | - | W. L. Anderson | 6016 | 9472 | - | Bellis | 5993 | 8165 | - | Callahan | 2154 | 3983 | - | Donahue | 4584 | 5917 | - | Jacobus | 4548 | 5667 | - | Schenker | 5728 | 7135 | - | Stapleton | 5351 | 6833 | - +----------------+----------+----------+ - -It is to be observed that the majority of these trained men showed at -the first trial in January a total strength test approximately equal to -that of the soldier detail at the close of their experiment. This by no -means implies that the latter men owed their gain in strength wholly -to the systematic training they had undergone, but it is certainly -plausible to assume that in a measure this was the case. In any event, -it is plain that the long-continued low proteid diet of the soldiers -had not interfered with a progressive muscular development, and the -attainment of a high degree of muscular strength. - -The noticeable feature in the figures obtained with the athletes, -however, is the striking difference between the January and June -results. Every man, without exception, showed a decided gain in his -muscular power as measured by the strength tests. This improvement, to -be sure, was not so marked as with the soldiers; a fact to be expected, -since with these men the element of training and the acquisition -of proficiency in athletic work could have played no part in the -observed gain. Further, most of the tests indicated that the gain was -progressive, each month showing an improvement, in harmony with the -growing effect of the diminished proteid intake. With these subjects, -the only tangible change in their mode of life which could in any sense -be considered as responsible for their gain in strength was the change -in diet. Consequently, it seems perfectly justifiable to conclude that -the observations presented afford reasonable proof of the beneficial -effects of a lowered proteid intake upon the muscular strength of man. - -The significance of such a conclusion is manifestly obvious. It -confirms and gives added force to the observations that man can -profitably maintain nitrogen equilibrium, and body-weight, upon a -much smaller amount of proteid food than he is accustomed to consume. -It harmonizes with the view that the normal requirements of the body -for food, under which health, strength, and maximum efficiency are -best maintained, are on a far lower level than the ordinary practices -of mankind would lead one to believe. The widespread opinion that -a rich proteid diet, with the correspondingly high rate of proteid -metabolism, is a necessity for the preservation of bodily strength and -vigor, is seen to be without foundation; for even the most conservative -estimate of the real value of these strength tests must carry with -it the conviction that lowering the consumption of proteid food does -not at least result in any weakening of the body. This is a fact of -vital importance, for it needs no argument to convince even the most -optimistic that while it might be possible to maintain body-weight -and nitrogen equilibrium on a small amount of proteid food, such a -form of physiological economy would not only be of no advantage to -the individual, but would be positively injurious if there was a -gradual weakening of the muscles of the body with decrease of physical -strength, vigor, and endurance. - -Another fact to be emphasized in this connection was the conviction, -gradually acquired by many of the subjects, that they suffered -less from fatigue after vigorous muscular effort than formerly. -This was especially conspicuous in the case of Donahue, whose work -on the Varsity basket-ball team called for vigorous exercise. It is -interesting to note that this athlete, of 63 kilos body-weight, for the -last four months of the experiment showed an average daily katabolism -of 7.45 grams of nitrogen, corresponding to a breaking down of 46.5 -grams of proteid material daily. Yet, with this low rate of proteid -exchange, he maintained his position on the team with satisfaction to -all, and with the consciousness of improved physical condition and -greater freedom from fatigue. Other subjects, as the laboratory workers -of the professional group, observed that the customary late afternoon -fatigue, coincident with the continued walking and standing about the -laboratory, gradually became far less conspicuous than usual; so that -there seemed to be a consensus of opinion that in some way the change -in diet was conducive to greater freedom from muscular weariness. - -It is well understood by physiologists that the ability of a muscle -to do work is inhibited by any condition that tends to depress the -general nutritive state of the body, or that interferes with the local -nutrition of the muscle or muscles involved. On the other hand, there -are certain well-recognized conditions that tend to augment the power -of the muscle, notably an increased circulation of blood through the -tissue, the taking of food, and especially the introduction of sugar. -Further, experiments have shown that when a given set of muscles has -been made to work excessively, other muscles of the body quite remote -will share in the fatigue, thus implying that muscular weariness and -the diminished power to do work are connected with what may be termed -fatigue products, which are distributed by means of the circulation. In -this way, muscles and nerve endings alike are exposed to the inhibitory -influence of waste products of unknown composition, formed in the -muscle, and as previously stated, we may conceive of an exaggerated -exogenous katabolism, with excessive proteid intake, by which muscular -fatigue and weariness may be augmented; hence, the beneficial effect in -this direction of a more rational food consumption, by which proteid -katabolism shall be reduced to a true physiological level. - -With these marked effects on strength and fatigue, it is reasonable -to assume that some corresponding action may be exerted on physical -endurance. As is well known, strength and endurance, though related, -are quite distinct and can be separately measured. Strength tests, -however, as usually carried out in gymnasium work, do involve in -considerable degree the question of endurance, since it is customary to -use as one of the factors in estimating total strength the number of -times the man can pull up, or push up, his body on the parallel bars. -Strictly speaking, however, the strength of a muscle is measured by the -maximum force it can exert in a single contraction, while its endurance -is estimated from the number of times it can contract well within the -limit of its strength. - -It is well known that endurance, both physical and mental, is one of -the most variable of the human faculties, and it is usually considered -that exercise or training is the chief cause of the differences so -frequently seen. The Maine guide will row a boat or paddle a canoe -for the entire day without undue fatigue, while the novice, though -he may have the necessary strength, lacks the endurance to continue -the task longer than a few hours. As expressed by Professor Fisher, -“Some persons are tired by climbing a flight of stairs, whereas the -Swiss guides, throughout the summer season, day after day spend the -entire time in climbing the Matterhorn and other peaks; some persons -are ‘winded’ by running a block for a street car, whereas a Chinese -coolie will run for hours on end; in mental work, some persons are -unable to apply themselves more than an hour at a time, whereas -others, like Humboldt, can work almost continuously through eighteen -hours of the day.” Again, Fisher states that “among some 75 tests -of different persons holding their arms horizontal, many were found -whose arms actually dropped against their will inside of 10 minutes, -whereas several were able to hold them up over 1 hour, and one man held -them 3 hours and 20 minutes, or a round 200 minutes, and then dropped -them voluntarily. Similarly with deep knee-bending, some persons were -found physically unable to rise again from the stooping posture after -accomplishing less than 500 bendings, whereas several succeeded in -stooping 1000 times, and in one case, 2400.” Here, we have inherent -differences in endurance not associated with training or exercise, and -the question may well be asked, What is the cause of these radical -variations in the ability to repeat a simple muscular exertion? - -Hitherto, little attention has been paid to the possible influence of -diet upon this faculty. It has always been assumed that endurance, -like physical strength, is augmented by a rich proteid diet, but it -has never been considered that diet by itself was a factor of any -great moment as compared with training or persistent exercise. It is -true that claims have been advanced from time to time concerning the -beneficial effects on endurance of a vegetable diet, and vegetarians -have frequently presented glowing reports of the great increase in -endurance they have experienced, but little attention has been given to -such statements, and the matter has remained more or less in obscurity. - -Recently, Professor Irving Fisher,[63] of Yale, has conducted an -interesting experiment on the influence of a change in diet on -endurance, having the co-operation of nine healthy students as -subjects. The experiment extended through five months, with endurance -tests at the beginning, middle, and end of the period. At the outset, -the men consumed daily an average of 2830 calories, of which 210 -were in the form of flesh foods, such as meats, poultry, fish and -shell-fish; 2.6 calories of proteid being ingested for each pound of -body-weight. At the close of the experiment, the per capita calories -had fallen to 2220, of which only 30 were in flesh foods, and the -proteid had fallen to 1.4 calories per pound of body-weight. In other -words, the total calories of the daily ration had dropped off about 25 -per cent, the proteid about 40 per cent, and the flesh foods over 80 -per cent, or to about one-sixth of their original amount. - - [63] Through the kindness of Professor Fisher, the writer has had the - opportunity of reading the report of this work, which at this writing - is not published, and he has drawn upon it freely for the following - statements of fact. - -To determine the endurance of the subjects, six simple gymnastic -tests were employed, and one of mental endurance. The physical tests -consisted of (1) in rising on the toes as often as possible; (2) deep -knee-bending, or stooping as far as possible and rising to the standing -posture, repeating as often as possible; (3) while lying on the back, -raising the legs from the floor to a vertical position and lowering -them again, repeating to the point of physical exhaustion; (4) raising -a 5-lb. dumb-bell (with the triceps) in each hand from the shoulder up -to the highest point above the head, repeating to the point of physical -exhaustion; (5) holding the arms from the sides horizontally for as -long a time as possible; (6) raising a dumb-bell (with the biceps) in -one hand from a position in which the arm hangs free, to the shoulder -and back, repeating to the point of physical exhaustion. This test was -taken with four successive dumb-bells of decreasing weight, viz., 50, -25, 10, and 5 pounds respectively. The mental test consisted in adding -specified columns of figures as rapidly as possible, the object being -to find out whether the rapidity of performing such work tended to -improve during the experiment. - -The following table shows the results of the three sets of physical -tests made in January, March, and June: - - -TESTS OF PHYSICAL ENDURANCE WITH THE NINE SUBJECTS - - +-------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ - | |Time.| B. | E. | Lq. | Lw. | M. | P. | R. | T. | W. | - +-------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ - |1. Rising on |Jan. | 300 |1007 | 333 | 69 | 127 |1482 | 702 | 900 |1263 | - | toes |Mar. | 400 |1265 |2620 | 65 | 400 | | 831 |1500 | | - | |June | 500 |1061 |3000 | 85 |1500 |1800 |1263 |1800 |3350 | - | | | | | | | | | | | | - |2. Deep knee-|Jan. | 82 | 142 | 70 | 48 | 132 | 208 | 374 | 129 | 404 | - | bending |Mar. | | | 191 | 47 | | | | | | - | |June | 200 | 81 | 202 | 58 | 155 | 230 | 453 | 250 | 508 | - | | | | | | | | | | | | - |3. Leg |Jan. | 25 | 52 | 9 | 22 | 30 | 27 | 50 | 23 | 30 | - | raising |Mar. | | | | 33 | | 34 | | | 40 | - | |June | 33 | 38 | 20 | 35 | 31 | 37 | 103 | 19 | 53 | - | | | | | | | | | | | | - |4. 5lb. |Jan. | 75 | 138 | 78 | 38 | 51 | 44 | 100 | 83 | 185 | - | Dumb-bell |Mar. | | | 106 | | | | | | | - | (triceps) |June | 127 | 59 | 80 | 51 | 75 | 56 | 104 | 101 | 501 | - | | |m. s.|m. s.|m. s.|m. s.|m. s.|m. s.|m. s.|m. s.|m. s.| - |5. Holding |Jan. | 5–0 | 1–33| 4–7 | 3–37| 3–30| 5–39| 2–5 | 3–22|11–0 | - | arms |Mar. | | | | | 5–49| | | |15–35| - | horizontal|June | 9–36| 2–56| 3–50| 3–0 | 6–5 |10–1 | 3–16| 3–24|23–45| - | | | | | | | | | | | | - |6. 25lb. |Jan. | 50 | 18 | 16 | 6 | 20 | 11 | 10 | 25 | 54 | - | Dumb-bell |June | 105 | 10 | 26 | 33 | 30 | 29 | 27 | 75 | 108 | - | (biceps) | | | | | | | | | | | - +-------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ - -The data presented show a marked improvement in March and June over the -record made at the beginning of the experiment in January, except in -the case of one subject, E. As Fisher states, the increased endurance -observed can be ascribed only to dietetic causes, since no other -factors of known significance could have aided in the result. The -dietetic changes, as we have seen, consisted in a slight reduction of -the total amount of food consumed daily, but with a large reduction of -the proteid element, especially from flesh foods. It is significant, -says Fisher, that the only man whose strength and endurance showed any -decrease was E, “whose case was exceptional in almost all respects. -His reduction in quantity of food, except for a spurt at the end, was -less than of most of the men; his reduction in proteid, with the same -exception, was the least of all; his reduction in quantity of flesh -foods was the least of all.” He stands out conspicuously as the one man -whose endurance failed to improve. The mental test carried out with the -subjects pointed to “a slight increase in mental quickness,” but the -adding test was too short to be of great value. - -We see in these results another confirmation of the view that the -welfare of the body is not impaired by a marked reduction in the amount -of proteid food; on the contrary, benefit results in the increased -efficiency which manifests itself in various directions. Physical -endurance is an asset not to be ignored, and like the strength of an -individual, it may well be fostered by the recognition and practice of -a principle which seemingly has a firm physiological basis. Whether -the fatigue poisons come from the excessive exogenous katabolism of -proteids in general, or whether they are derived directly in a measure -from flesh foods, need not be considered here; the main point is that -by lowering the rate of proteid katabolism, which necessarily compels a -reduction in the amount of flesh foods, there is a diminished quantity -of nitrogenous waste floating about in the body. Further, we need -not criticise too closely the method by which the reduction of food -is accomplished; whether it be by encouraging mastication, with a -view to better tasting and fuller enjoyment of the food, to the point -of involuntary swallowing; or whether we follow natural taste and -appetite, reinforced by the use of reason, with a full appreciation -of the principle that the welfare of the body is best subserved by a -quantity of food commensurate with true physiological needs. - -In making this presentation of the true food requirements of the -body as based on the results of physiological experimentation and -observation, I am by no means unmindful of the dangers of underfeeding; -but this is a condition comparatively rare. When occurring, as stated -by Dr. Curtis, “it is either because of dyspepsia, in which case it -really is involuntary, or comes from some silly notion born of a -combination of innate mental crookedness and that ‘little knowledge’ -that is a dangerous thing.” Overfeeding is the predominant dietetic -sin, and with the prevailing dietary standards, as fixed by common -usage, there is good ground for believing that it will continue for -many years to come. Reason tells us, however, in the practice of our -personal nutrition, to steer a middle course between physiological -excess on the one side, and the minimal food requirement on the other. -To quote again from Dr. Curtis,[64] who has expressed the matter very -forcibly, “The physiological chemist can easily draw a line on the -Scylla (starvation) side of the channel. A dietary whereby the system -gets less than it pays out is, obviously, a dangerous veer toward -starvation rock. But on the Charybdis (stuffing) side, just as the -whirlpool itself has no well-defined border, the channel boundary is -not so easily marked. The case is exactly analogous to the stoking of -a furnace. The proportion of ash to live coals is a telltale as to -_under_feeding, but not as to _over_feeding. With undersupply of fuel -the ashes overbalance the live coals, and the fire is thus foretold to -be going out. But with an oversupply the fire simply burns the faster: -all the fuel continues to be consumed; the more coal simply makes the -more ash, so that equilibrium is not disturbed, although maintained -at a higher level. To argue, therefore, that a given dietary is none -too large, because the balance between the material receipts and -expenditures of the economy is not upset, would be like saying that a -given furnace-fire is certainly none too hot, since the ashes raked -out of the fire-box just correspond to the amount of coal shovelled -in. The same would be equally true of a slower fire consuming much -less fuel. The philosophy of the matter is, then, to find the minimum -of steam that will run the engine, and then maintain a fire somewhat -hotter than the exact requirement, in order to run no risk of failure; -or, to return to the metaphor already employed, the would-be careful -liver must simply note how close to Scylla other voyagers have sailed -with safety, and then steer his own bark accordingly.” - - [64] Edward Curtis, M. D.: Nature and Health. New York, Henry Holt & - Co. 1906. p. 71. - -As one looks through the many careful dietary studies that have been -made in recent years, it is easy to find striking illustrations of -people, and communities of people, who have lived for long periods -of time on dietaries so strikingly simple and meagre that it seems -difficult at first glance to believe their daily needs could have been -entirely satisfied. Yet, such observations are quite in accord with -the facts we have been presenting, and they afford additional evidence -that the artificial dietary standards that have been set up are widely -at variance with the real requirements of the body for food. It may -be quite true that many of the people referred to have been and are -faddists, with peculiar notions regarding food, based on religious or -other scruples, but that has no bearing on the main contention that -they have lived for many years on amounts of food ridiculously small -as compared with the ordinary customs of mankind. Thus, in Professor -Jaffa’s report[65] of investigations made among fruitarians and Chinese -of California is an interesting account of a dietary study of a family -of fruitarians, consisting of two women and three children. They had -all been fruitarians from five to seven years, their diet being limited -to nuts and fruit, except for the addition of celery, honey, olive -oil, and occasionally a small amount of prepared cereal food. This -family was in the habit of taking only two meals a day; at 10.30 in -the morning and at 5 o’clock in the afternoon. The first meal always -consisted of nuts and fruit, the nuts being eaten first. At the second -meal, nuts were usually replaced by olive oil and honey. The nuts made -use of were almonds, Brazil nuts, pine nuts, pignolias (a variety of -pine nuts), and walnuts. Fruits, both fresh and dried, were used, -the former including apples, apricots, bananas, figs, grapes, olives -(pickled), oranges, peaches, pears, plums, and tomatoes. The dried -fruits were dates and raisins. - - [65] Bulletin No. 107, Office of Experiment Stations, U. S. - Department of Agriculture, 1901, from which the descriptions given - have been taken. - -On this limited dietary of raw, uncooked food, with a complete absence -of the high-proteid animal foods, and the ordinary vegetables, legumes, -etc., and without eggs or milk, this family, with three growing -children, had lived all these years. Note now what Jaffa observed -regarding their food consumption. The first subject, a woman 33 years -of age and weighing 90 pounds, was studied for twenty consecutive days, -all the food eaten being carefully weighed and its chemical composition -determined. As a result, it was found that the average amount of food -consumed per day was: proteid, 33 grams; fat, 59 grams; carbohydrate, -150 grams; with a total fuel value of 1300 calories. The other members -of the family were studied in a similar manner, one of the children -being the subject on two separate occasions. The table (on page 217), -showing the average daily food consumption, gives a summary of the -results obtained. - - +--------------------------------+--------+-----+------+--------+--------+ - | | | | | |Proteid | - | | | |Carbo-| Fuel |per Kilo| - | |Proteid.|Fat. | hyd- | Value. | Body- | - | | | | rate.| |weight. | - +--------------------------------+--------+-----+------+--------+--------+ - | | grams |grams|grams |calories| grams | - |Woman, 33 years old, | | | | | | - | Weight 90 lbs. (40.9 kilos) | 33 | 59 | 150 | 1300 | 0.80 | - |Woman, 30 years old, | | | | | | - | Weight 104 lbs. (47.3 kilos) | 25 | 57 | 90 | 1040 | 0.52 | - |Girl, 13 years old, | | | | | | - | Weight 75-1/2 lbs. (34.3 kilos)| 26 | 52 | 157 | 1235 | 0.75 | - |Boy, 9 years old, | | | | | | - | Weight 43 lbs. (19.5 kilos) | 27 | 56 | 152 | 1255 | 1.38 | - |Girl, 6 years old, | | | | | | - | Weight 30-1/2 lbs. (13.9 kilos)| 24 | 58 | 134 | 1190 | 1.72 | - |Girl, 7 years old, | | | | | | - | Weight 34 lbs. (15.4 kilos) | 40 | 72 | 134 | 1385 | 2.59 | - +--------------------------------+--------+-----+------+--------+--------+ - -As Professor Jaffa states, the tentative dietary standard for a -woman at light work calls for 90 grams of proteid daily, with a fuel -value of 2500 calories. Both of these women were light in weight, -and furthermore had no occasion to do much physical work; but even -so, a daily consumption of only 0.8 gram and 0.52 gram of proteid, -respectively, per kilo of body-weight, with the small calorific values -indicated, represents a phenomenally small amount of food. And yet -Jaffa, in referring to the woman with the lowest intake of food, states -that even this small quantity of food, judging from the appearance -and manner of the subject, “seemed sufficient for her needs, enabling -her to do her customary housework and take care of her two nieces -and nephew.” Regarding the children, it is stated that the commonly -accepted American dietary standard for a child 13 years old and of an -average activity calls for about 90 grams of proteid and 2450 calories. -As is seen from the table, however, the 13-year-old girl consumed of -proteid less than one-third, and of fuel value only about 60 per cent -of the amount called for; yet, says Jaffa, “notwithstanding the facts -brought out by this comparison, the subject had all the appearances of -a well-fed child in excellent health and spirits.” - -We need not consume time in discussing the details of this experimental -study, though the facts are interesting and suggestive, for it is only -the general question of proteid requirement and calorific value that -has interest for us at present. The fact is perfectly clear that this -family of fruitarians, young and old, were quite able to live and -thrive on a diet, the value of which in proteid and calories was at as -low a level as was attained in our experimental studies. The rock of -starvation, however, was not touched or even sighted by the voyagers -down this stream of nutrition. We may all agree that it would be -preferable, as a rule, to acquire the proteids, fats, and carbohydrates -of our diet from a greater variety of sources than did the fruitarians; -we might well complain at a dietary so limited in quality; but the -point to be emphasized is that the low intake of proteid and the low -fuel value were quite adequate for meeting the needs of the body. “It -is a difficult matter,” says Professor Jaffa, “to draw any general -conclusions from the foregoing dietaries without being unjust to -the subjects. It would appear, upon examining the recorded data and -comparing the results with commonly accepted standards, that all the -subjects were decidedly undernourished, even making allowances for -their light weight. But when we consider that the two adults have lived -upon this diet for seven years, and think they are in better health -and capable of more work than they ever were before, we hesitate to -pronounce judgment. The three children, though below the average in -height and weight, had the appearance of health and strength. They ran -and jumped and played all day like ordinary healthy children, and were -said to be unusually free from colds and other complaints common to -childhood.” - -Turning now to a larger community,--the island nation of Japan,--whose -exploits in war have recently attracted the attention of the civilized -world, we find a people the great majority of whom have remained -untouched by the prodigality of western civilization, and whose customs -and habits still bear the imprint of simplicity and frugality. After -the restoration of Japan and the reorganization of the government in -1867, much attention was directed to the methods of living and to the -dietary habits of the people, with the result that during the last -twenty-five years there have been slowly accumulating many important -data bearing on the food consumption of the people. These have recently -been brought together in an interesting volume by Kintaro Oshima, and -published[66] in the English language. - - [66] A Digest of Japanese Investigations on the Nutrition of Man. - Bulletin No. 159, Office of Experiment Stations, U. S. Department of - Agriculture, 1905. - - +-----------------------+--------+--------------------------------+ - | | |Digestible Nutrients and Energy | - | | | per Man per Day. | - | Subjects. | Body- +--------+-----+--------+--------+ - | |weight. |Proteid.| Fat.| Carbo- | Fuel | - | | | | |hydrate.| Value. | - +-----------------------+--------+--------+-----+--------+--------+ - | | kilos | grams |grams| grams |calories| - |School business agent |57.5 | 65.3 |11.3 | 493.8 | 2467 | - |Physician |.... | 61.9 | 8.0 | 468.5 | 2315 | - |Merchant |47.6 | 81.5 |19.6 | 366.2 | 2082 | - |Medical student |49.0 | 74.8 |11.2 | 326.9 | 1811 | - |Medical student |48.5 | 64.7 | 5.1 | 469.6 | 2305 | - |Military cadets |.... | 72.3 |11.7 | 618.1 | 3021 | - |Prisoners without work |47.6[67]| 36.3 | 5.6 | 360.4 | 1726 | - |Prisoners at light work|48.0[67]| 43.1 | 6.2 | 443.9 | 2112 | - |Prisoners at hard work |.... | 56.7 | 7.5 | 610.8 | 2884 | - |Physician |40.2 | 48.3 |15.5 | 438.2 | 2201 | - |Hygienic assistant |40.5 | 46.5 |19.7 | 485.3 | 2430 | - |Medical student |51.0 | 42.8 |14.0 | 438.2 | 2163 | - |Police prisoners |.... | 42.7 | 8.7 | 387.3 | 1896 | - |Army surgeon |54.0 | 79.3 |11.7 | 502.0 | 2567 | - |Soldier |66.7 | 75.8 |13.5 | 563.8 | 2828 | - |Soldier |61.0 | 58.8 |11.3 | 467.8 | 2330 | - |Soldier |56.7 | 55.2 |10.9 | 459.6 | 2276 | - +-----------------------+--------+--------+-----+--------+--------+ - - [67] Average weight of twenty subjects. - -As is well known, the great majority of the people of Japan live -mainly on a vegetable diet. It is also known to physiologists at least -that Japanese dietaries are characterized by a relatively small amount -of proteid, though since the passage of the Food Supply Act of the navy -in 1884, the proteid-content of the navy ration has been decidedly -increased. It will be interesting to note a few of the results collated -by Oshima, and some of the conclusions that he draws from the data -presented. The foregoing table shows a few of the more striking results -of the dietary studies obtained with various classes of people, where -the food used was largely vegetable, but generally with some admixture -of fish or meat. - -The figures presented, which represent the actual amounts of food -consumed, with proper correction for the indigestible portion, show -a much smaller intake of proteid than is common with European and -American people; indeed, both proteid and fuel value are very much -less than common practices call for among western peoples, even when -due allowance is made for differences in body-weight. To quote from -Oshima, “Probably the most interesting of the dietary studies are -those with poorer classes, which comprise by far the larger part of -the population. The dietaries of the miscellaneous class, including -employees, prisoners, etc., consisted largely of vegetable foods -and supplied on an average 59 grams of proteid and 2190 calories of -energy per man per day.” Especially suggestive were the results of -a study made with a military colonist, a type of man very common in -Japan; in reality farmers who live at home, but have military drill at -certain fixed times. The subject was carefully selected under advice -of officers in charge of the district, and weighed 59.9 kilograms. His -diet consisted solely of cereals and vegetables, being identical with -that of the people in the rural districts of Japan. His daily food was -found to be composed of 46.3 grams of digestible proteid, with a fuel -value of 2703 calories. - -Even more striking were the results obtained in a study of the dietary -habits of three healthy natives of Formosa, employed as day laborers -at the military hospital. They weighed respectively 60.9, 55, and 54.8 -kilograms. The main portion of their diet was rice, supplemented, -however, by a little salt fish, salted melon, spinach, ginger, and -greens. The daily amount of proteid ingested was 48.0 grams (37.4 grams -of digestible proteid), with a total fuel value of 1948 calories. A -composite sample of urine covering seven days showed an average daily -output of metabolized nitrogen of 6.93 grams, corresponding to a -breaking down of 43.3 grams of proteid. - -Especially interesting also is a series of experiments with -professional men, reported by Oshima, in which attention was paid to -nitrogen balance. The following table shows the essential results: - - +--------+-------+----------+-----------------------------------------+ - | | | | Digestible Nutrients and Energy | - | | | | per Man per Day. | - |Subject.| Body- |Character +--------+-----+--------+--------+--------+ - | |weight.| of Food. |Proteid.| Fat.| Carbo- | Fuel |Nitrogen| - | | | | | |hydrate.| Value. |Balance.| - +--------+-------+----------+--------+-----+--------+--------+--------+ - | | kilos | | grams |grams| grams |calories| | - | N. K. | 43.1 |mixed diet| 72.7 |18.3 | 380.7 | 2091 | + | - | S. A. | 49.5 |mixed diet| 69.8 |20.2 | 410.7 | 2222 | + | - | N. K. | 42.9 |mixed diet| 64.4 | 8.5 | 396.3 | 2028 | + | - | N. K. | 43.2 |mixed diet| 62.8 | 8.7 | 433.2 | 2178 | + | - | N. K. | 43.0 |vegetable | 68.5 |19.7 | 433.0 | 2303 | + | - | N. K. | 43.9 |vegetable | 36.8 | 6.6 | 381.0 | 1824 | - | - | N. K. | 42.4 |vegetable | 40.5 | 8.7 | 462.6 | 2200 | + | - | S. A. | 49.6 |vegetable | 34.4 | 7.5 | 451.9 | 2119 | - | - | S. A. | 49.9 |vegetable | 43.5 | 9.1 | 500.0 | 2376 | + | - +--------+-------+----------+--------+-----+--------+--------+--------+ - -It is to be observed that in all of the above experiments, excepting -two, the subjects gained nitrogen even with the low proteid intake and -the small fuel value of the day’s food. Particularly noteworthy, in -harmony with previous statements, are the results of the sixth and -seventh experiments. In the sixth experiment, the subject was not able -to maintain nitrogen equilibrium on a diet containing 36.8 grams of -digestible proteid and having a fuel value of 1825 calories, but by -raising the intake of carbohydrate food (seventh experiment) to 462 -grams daily, thereby increasing the fuel value of the daily ration -to 2200 calories (with a slight increase in the proteid incidental -thereto), the body was able to change its previous loss of nitrogen -into a gain; in other words, the added carbohydrate served as a -protector of proteid. - -The series of experiments as a whole, however, is to be considered -in the light of additional data bearing on the dietary customs of a -people who for generations have apparently lived and thrived on a daily -ration noticeably low in its content of proteid, as well as low in its -calorific value. As Oshima states, “It is probably fair to infer that -the amount of proteid in the dietaries of the classes living largely on -vegetable foods (and they constitute the larger part of the population) -may not be very far from 60 grams per day,” or 45 grams of digestible -proteid. It is reasonable to assume that the people live in this way -from force of habit or of necessity, and we may agree with Baelz, a -professor connected with the medical faculty of Tokyo University, “that -their diet is sufficient from a physiological standpoint.” Doubtless a -mixed diet, with a larger proportion of animal food, did their means -readily permit, would offer some advantages from the standpoint of -palatability and variety, but it is questionable if any material gain -in health or strength would result. “It is sometimes remarked,” says -Oshima, “that the peasants in the rural districts of Japan, living -largely on vegetable food, are really healthier and stronger than -people of the better classes, who live on a mixed diet, and the better -physical condition of the former is commonly believed to be due to -their diet.” This, however, is a difficult matter to decide, since -there are so many other factors that are liable to play a part, such as -the general conditions of life which are so widely different in the two -classes. - -It is plainly evident that the daily diet of the great bulk of the -Japanese people has been characterized by a very low proteid standard, -as contrasted with the standards and usages of the majority of -European and American people. The fact is brought forward merely as -confirmatory evidence, on a large scale, of the perfect safety of -lowering the consumption of proteid food to somewhere near the level of -the physiological requirements of the body. Generations of low proteid -feeding, with the temperance and simplicity in dietary matters thereby -implied, have certainly not stood in the way of phenomenal development -and advancement when the gateway was opened for the ingress of modern -ideas from western civilization. Many changes are sure to follow in -the footsteps of the nation’s progress, and among these it is safe to -prophesy that as public and private wealth, and resources in general, -increase, the dietary of the people will gradually assume a more varied -character with corresponding increase in volume. Whether such a change -will prove of real benefit to the race, time alone can determine. - -Having said so much concerning the Japanese, it is proper that a few -additional statements should be made. The stature and general physique -of the people could be advantageously improved. Is this a question of -dietary, or is it connected with some condition of life on which the -daily food has no bearing; or is it, perchance, a racial characteristic -so deeply ingrained that conditions of environment are without -noticeable influence? These questions cannot be definitely answered -at present. Finally, we may call attention to the dietary changes -inaugurated in recent years in connection with the new organization of -the imperial army and navy. With a view to increasing the efficiency of -the men, following the customs of other countries, an act was passed -increasing the amount of proteid food in the navy dietary. Oshima’s -report of the various steps taken to accomplish this end, with the -results that followed, is interesting in several ways. - -“A large part of the rice was to be replaced by bread, and meats were -to be used liberally. The experience, during the first year that -this ration was tried, indicated that bread and meat could not be -advantageously substituted immediately for the rice, because most of -the marines were unaccustomed to these food materials; consequently, -a modification of the ration was introduced in 1885, whereby a -rice-barley mixture was adopted in place of the bread. Barley was -considered at that time as a better article of food than rice, on -account of its higher proteid content, but later investigations showed -that the digestibility of the nutrients of barley was small. In 1886, -an effort was again made to substitute bread for the rice-barley -mixture. In 1890, the ration allowance was reduced by one-fifth and -an amount of money equivalent to the cost of the reduction in diet -was given to each marine with which to buy accessory food according -to his own choice. In 1898, the reduction was made one-tenth, instead -of one-fifth as in previous years. In 1900, the cash allowance was -abolished and a new ration adopted.” This ration contains about 150 -grams of proteid (animal and vegetable food) and has a fuel value of -over 3000 calories. In all of these changes, the proportion of rice was -greatly reduced. - -Probably, one of the chief reasons why persistent efforts were made -to improve the dietary of the navy was the prevalence among the men -of the disease known as beriberi. “While no satisfactory explanation -as to the cause of the disease was offered, it was generally believed -that there was some very close relation between the disease and the -rice diet” (Oshima). During the years 1878–1883 inclusive, nearly 33 -per cent of the marines suffered from beriberi. With the adoption of -the new ration in 1884, in which a large part of the rice was replaced -by bread and other articles, and with better hygienic conditions, -this disease immediately began to disappear, and during the six years -after the adoption of the new diet only 16 per cent of the marines -were affected by the disease. Later on, hardly more than two or three -cases a year were recorded. Advocates of a high proteid diet bring -forward this illustration as an evidence of the danger connected with -a lowered proteid intake; _i. e._, that the nutrition of the body -will be impaired and diseases of various sorts liable to follow. Yet, -Oshima is very careful to state, “It should be especially noted that -here no attempt has been made to indicate the cause of beriberi or the -relation between the disease and the diet.” That rice in itself can be -a cause of the disease is not to be considered for a moment. Further, -so far as any facts are concerned, the writer can see no ground for -considering that a low rate of proteid metabolism has in itself any -direct connection with the disease. From a dietary standpoint, it seems -far more plausible to assume that the great restriction in variety of -foods, so strikingly manifest in the dietary of the poorer people of -Japan, results in a lack of some one or more elements which conduces to -the disease, just as in scurvy the lack of _fresh_ vegetables on long -voyages was liable to be followed by an epidemic of this disease. - -Consider the natural character of the dietary of the great bulk -of the Japanese people, determined as it was by adverse financial -circumstances. As Oshima states, “The rural population of the -interior depends very largely or entirely upon a vegetable diet. -Fish is eaten perhaps once or twice a month, and meat once or twice -a year, if at all. The poorer working classes in the cities also -use very little animal food. But the poorer classes in the city and -the peasantry of the rural districts comprise nearly 75 per cent of -the total population, and it is therefore safe to assume that this -proportion lives chiefly, or wholly, upon vegetable diet. And this, -it may be observed, means vegetarianism literally. The so-called -lacto-vegetarianism is unknown in Japan. Cows are scarce, and milk -and other dairy products are expensive, and such as are available are -consumed almost entirely by the wealthier people in the cities.” It is -also to be noted that the amount of fat in Japanese dietaries is very -small. The reported data indicate that the usual vegetable dietaries -contain only about 10 grams of fat per day, while even in the average -mixed dietaries the amount rarely rises above 20 grams per day. In -other words, the ordinary food of the Japanese was characterized by -great lack of variety, and with such a preponderance of carbohydrate -materials of a limited kind that it is easy to conceive of a possible -dearth of some essential or accessory element, necessary for the -preservation of that nutritive balance which aids in protection against -disease. - -If the resistance of the body to disease germs and toxic influences in -general is really diminished by reducing the consumption of proteid -food below the set dietary standards, then obviously here lies a -tangible reason for the maintenance of a high proteid intake. I know -of only one series of scientific observations that bears directly on -this question. Dr. Reid Hunt of Washington has studied recently the -power of resistance to the poison acetonitrile of animals kept for some -time upon a reduced proteid diet. “My experiments,” says Dr. Hunt, -“showed in all cases that the resistance was much increased.” In other -words, the animals that had been fed a low proteid ration were able to -endure a much larger dose of the poison than corresponding animals on -their customary diet; “they resisted 2–3 times the ordinary fatal dose -of acetonitrile.” This general subject, however, is obviously a very -important one, and merits further experimental study under a diversity -of conditions. - -In conclusion, the facts here presented bearing on food requirements, -especially those that relate to the need for proteid food, are -seemingly harmonious in indicating that the physiological necessities -of the body are fully met by a much more temperate use of food than is -commonly practised. Dietary standards based on the habits and usages -of prosperous communities are not in accord with the data furnished -by exact physiological experimentation. Nitrogen equilibrium can be -maintained on quantities of proteid food fully fifty per cent less -than the every-day habits of mankind imply to be necessary, and this -without increasing unduly the consumption of non-nitrogenous food. A -daily metabolism of proteid matter equal to an exchange of 0.10–0.12 -gram of nitrogen per kilogram of body-weight is quite adequate for -physiological needs, provided a sufficient amount of non-nitrogenous -foods--fats and carbohydrates--is taken to meet the energy requirements -of the body. - -The long-continued experiments on many individuals, representing -different types and degrees of activity, all agree in indicating that -equilibrium can be maintained indefinitely on these smaller quantities -of food, and that health and strength can be equally well preserved, -to say nothing of possible improvement. The lifelong experience of -individuals and of communities affords sufficient corroborative -evidence that there is perfect safety in a closer adherence to -physiological needs in the nutrition of the body, and that these needs, -so far as proteid food is concerned, are in harmony with the theory -of an endogenous metabolism, or true tissue metabolism, in which the -necessary proteid exchange is exceedingly limited in quantity. There -are many suggestions of improvement in bodily health, of greater -efficiency in working power, and of greater freedom from disease, in -a system of dietetics which aims to meet the physiological needs of -the body without undue waste of energy and unnecessary drain upon the -functions of digestion, absorption, excretion, and metabolism in -general; a system which recognizes that the smooth running of man’s -bodily machinery calls for the exercise of reason and intelligence, and -is not to be intrusted solely to the dictates of blind instinct or to -the leadings of a capricious appetite. - - - - -CHAPTER VII - -THE EFFECT OF LOW PROTEID DIET ON HIGH PROTEID ANIMALS - - TOPICS: A wide variety of foods quite consistent with temperance in - diet. Safety of low proteid standards considered. Arguments based - on the alleged effects of low proteid diet on high proteid animals. - Experiments of Immanuel Munk with dogs. Experiments of Rosenheim. - Experiments of Jägerroos. Comments on the above experiments. The - experiments of Watson and Hunter on rats. The writer’s experiments - with dogs. Details of the results obtained with six dogs. Comparison - of the results with those of previous investigators. Effect of a - purely vegetable diet on dogs. Different nutritive value of specific - proteids considered. Possible influence of difference in chemical - constitution of individual proteids. Effect of low proteid diet on - the absorption and utilization of food materials in the intestine - of dogs. General conclusions from the results of experiments with - animals. - - -Man is by choice an omnivorous creature; he reaches out ordinarily in -all directions for as wide a variety of foods as his circumstances and -surroundings will allow. He rightly cultivates a taste for foods that -have individuality of flavor, and derives pleasure and satisfaction -from the eating of delicacies that appeal to palate and to reason. -All this he can do without becoming an epicure or a glutton, and -without violation of physiological laws or disregard of the teachings -of temperance. As a being endowed with reason and intelligence he is, -however, necessarily mindful of the possible deleterious effect of -undue quantities of food, as he is likewise mindful of the desirability -of avoiding certain varieties of food which personal experience has -taught him are fraught with possible danger. Care and prudence in diet -are legitimate outcomes of a reasonable interest in the welfare of the -body, upon which so largely depend the happiness and working power of -the individual. - -The adoption of dietary habits that aim to accord with the -physiological requirements of the body does not compel a crucifying of -the flesh or a disregard of personal likes and dislikes. A reasonable -intelligence combined with a disposition to exercise the same degree -of judgment and care in the nutrition of the body as is expended on -other matters, of no greater importance, pertaining to the individual, -to the household, or to business interests, are all that is needed to -bring about harmony between every-day dietary habits and the nutritive -requirements of the body. There is no occasion, unless one finds -pleasure and satisfaction in so doing, to resort to a limited dietary -of nuts and fruits, to become an ardent disciple of vegetarianism, -to adopt a cereal diet, to abjure meats entirely, or to follow in an -intensive fashion any particular dietary hobby, except so far as may -be necessary to insure an adequate amount of non-nitrogenous foods to -meet the energy requirements of the body without unduly increasing -the intake of proteid or nitrogenous food. Naturally, a man leading -a life of great physical activity with the consequent demand for a -large energy-yielding intake will be compelled to resort largely to -vegetable foods, rich in starch and poor in proteid, or to eat largely -of fatty foods. Reliance on meats and animal foods in general, under -such conditions, would plainly involve a high proteid intake with a -consequent high nitrogen metabolism, with the chance that even then the -energy requirement would not be fully met. - -In view of all that has been said, reinforced by the various facts -brought forward as evidence, we must recognize the value of the -non-nitrogenous foods as a source of energy, and this means plainly -food from the plant kingdom. In any rational diet, vegetable foods of -low nitrogen-content must predominate, while animal foods with their -higher nitrogen values must be greatly subordinate in amount, if the -nitrogen or proteid metabolism of the body is to be maintained at a -level commensurate with true physiological requirements. But there -comes the ever-recurring question, Are the lower proteid standards -quite safe to follow? Are we warranted in turning aside from the -teachings based on the habits and customs of mankind? Many reasons have -already been presented which seemingly justify an affirmative answer, -while the experimental results and the observations on various groups -of people, covering years of time, speak with no uncertainty regarding -the element of safety, and indicate clearly that the absolute proteid -requirement of the body is quite small; much smaller indeed than -the amount of proteid food consumed by the average individual would -seemingly imply. - -Probably the most striking evidence, certainly of an experimental -nature, so far presented against the safety of a relatively low -proteid diet for man is that based on the results of several studies -made to ascertain the effect of a reduced proteid intake on so-called -high proteid animals. Animal kind may be divided into three groups -according to the nature of their food, viz., high proteid feeders, such -as carnivorous animals in general, of which the dog is a good type; -omnivorous or moderate proteid consumers, to which class man belongs; -and low proteid consumers, such as herbivorous animals. Three series of -experiments have been reported by independent workers on the effects of -reducing the amount of proteid food in the diet of dogs. The results -of these experiments were of such a character that it has come to be -understood that animals of this type cannot exist for any great length -of time on a low proteid diet. It is affirmed that in a relatively -short period the animals reach such a state that they either die, or -are in such poor condition that they must be fed a more liberal amount -of proteid to maintain them alive. The explanation offered is that the -low proteid diet results “in a loss of the power of absorption from the -intestinal tract, caused apparently by a change in the condition of the -epithelial cells, as well as by a diminished secretion of the digestive -juices.” - -The argument based on this evidence is that while a high proteid animal -feels at once, or almost immediately, the deleterious effect of a -reduction in the amount of proteid food, an omnivorous animal may be -more tardy in manifesting the injurious action, which, however, is sure -to follow sooner or later from any material reduction of proteid below -the customary standards. In other words, man as a moderate proteid -consumer can endure for a time even large reductions in the amount -of proteid food, but eventually there will be manifested some of the -disastrous results obtained with dogs. Here, we have a somewhat serious -indictment, one that merits careful consideration. To be sure, it may -be objected that between dog and man there is a wide gulf, and that -there is no justification for assuming that these two types of animal -life have anything in common. Still, the experience of many years -has taught the physiologist that much light can be thrown upon the -processes of higher types of life by a study of what occurs in lower -forms, and on the subject of nutrition any one of experience would -hesitate to cast out of court the evidence gathered from observation of -what occurs among the higher animals. It will be the part of wisdom, -therefore, to scrutinize somewhat carefully the character of this -evidence obtained from a study of the behavior of dogs toward a low -proteid diet. - -The first series of experiments was made in 1891 by the late Immanuel -Munk of Berlin, privat docent of physiology at the University, followed -by further experiments in 1893.[68] Four dogs in all were studied. The -diet made use of was “fleischmehl” (dried meat ground to a powder), -fat (suet), and rice boiled together with water. We may refer briefly -to the details of one experiment. The dog weighed 10.4 kilograms, and -at first was given a daily diet composed of 85 grams of rice, 29 grams -of fat, and 30 grams of the flesh meal. This ration contained 30.3 -grams of proteid, 31 grams of fat, and 66 grams of carbohydrate, with -a total fuel value of 663 calories, or 63 calories per kilogram of -body-weight. On this diet, there was at the outset a slight loss of -body-weight, after which both body equilibrium and nitrogen equilibrium -were practically maintained. After this preliminary period of three -weeks, the day’s diet was altered by replacing 15 grams of the proteid -by 15 grams of rice, so that the daily ration consisted of 15.3 grams -of proteid (with 2.42 grams of nitrogen), 31 grams of fat, and 81 grams -of carbohydrate, with essentially the same fuel value per kilo of -body-weight as before. Later, the fuel value of the food was further -increased by raising the amount of rice to 125 grams per day, the day’s -ration then consisting of 15.5 grams of proteid, 37 grams of fat, and -96 grams of carbohydrate, with a total fuel value of 780 physiological -heat units, or 78 calories per kilo. On this diet, nitrogen equilibrium -was maintained and the animal gained somewhat in body-weight. By the -seventh week, however, Munk reports that the animal began to show -signs of change; there was loss of appetite, absorption of the daily -food was impaired, both proteid and fat failing in large degree to be -utilized, while nitrogen equilibrium could no longer be maintained. -This condition continued during the next week, aggravated by vomiting -and accompanied by loss of strength and vigor. At the beginning of -the tenth week of this low proteid ration, the animal was in a very -poor condition, with complete loss of appetite, little inclination to -take food, etc. On feeding a liberal diet of fresh meat, as much as -250 grams per day, with some fat (50 grams a day), the animal speedily -recovered its appetite, and in a short time was in normal condition, -absorption of food and utilization of the same being as complete as at -the beginning of the experiment. - - [68] Ueber die Folgen einer ausreichenden, aber eiweissarmen Nahrung. - Ein Beitrag zur Lehre vom Eiweissbedarf. Virchow’s Archiv für - pathologische Anatomie und Physiologie, Band 132, p. 91. - -It is not necessary to give further details bearing on the three -additional experiments. It will suffice to quote the general -conclusions which Munk drew from the various results obtained, viz., -that a low proteid intake in the case of dogs causes a loss of -appetite, weakness, vomiting, etc., while body-weight and nitrogen -equilibrium are difficult or impossible to maintain. More specifically, -Munk’s observations led him to state that for dogs of ten kilograms -body-weight a daily intake of 0.255 gram of nitrogen per kilo of -body-weight is not sufficient to maintain the normal condition of the -body, even when the fuel value of the day’s food amounts to more than -100 calories per kilo. In order to have the animal continue in nitrogen -and body equilibrium, the daily food must contain at least 0.31 gram of -nitrogen per kilogram of body-weight, with sufficient non-nitrogenous -food to yield over 100 calories per kilo. - -Let us now pass to the experiments made by Rosenheim,[69] which were -carried on at about the same date as Munk’s. In the first experiment, -the dog weighed 11.3 kilograms, and was fed daily a low proteid ration -having a fuel value of 1447 calories and containing 2.825 grams of -nitrogen. This ration was reduced in a short time to a still lower -plane, viz., to 1066 calories and 2.525 grams of nitrogen daily. The -food as then given was composed of 170 grams of rice, 50 grams of -fat, and 25 grams of chopped meat, on which the dog gained weight and -preserved nitrogen equilibrium. For six weeks, or thereabouts, the -animal maintained its normal condition, after which it began to show -symptoms of a general disturbance, with lack of appetite and weakness -accompanied by a condition of icterus. Addition of meat extract to -the diet to improve the flavor was without any appreciable effect. -During the next two weeks, the condition of the animal steadily grew -worse, although the body-weight remained practically stationary and -nitrogen equilibrium was maintained. A week later, the animal died in -a condition of exhaustion, without having manifested any symptoms of -disturbed metabolism. There was found a marked catarrhal condition -of the mucous membrane of the gastro-intestinal tract, with a fatty -degeneration or metamorphosis of the glandular apparatus, but nothing -sufficiently specific to account for the peculiar manner of death. - - [69] Theodor Rosenheim: Ueber den Gesundheitsschädigenden Einfluss - eiweissarmer Nahrung. DuBois-Reymond’s Archiv für Physiologie, - 1891, p. 341. Also, Weiterer Untersuchungen über die Schädlichkeit - eiweissarmer Nahrung. Pflüger’s Archiv f. d. gesammte Physiologie, - Band 54, p. 61, 1893. - -A second experiment with a dog of 5.8 kilograms, fed on meat, fat, and -rice, led to essentially the same results as the preceding experiment. -At the end of the first month, there appeared indications that the -animal was not well, loss of appetite being marked, with disturbance -of the stomach accompanied by occasional vomiting. These symptoms -disappeared quickly when the animal was given for a few days large -quantities of meat. On returning to the original low proteid diet, -with its large content of rice, the symptoms gradually reappeared. -At the end of two months the animal had again lost its appetite, and -before the end of the fifth month the subject was dead. Post-mortem -examination showed especially a strong fatty degeneration of the -epithelial cells of the mucous membrane of the stomach and intestine. -Rosenheim concludes that a diet poor in proteid is unhealthful for -dogs, and that a daily ration containing even 0.32 gram of nitrogen -per kilogram of body-weight, and with a fuel value of 110 calories per -kilo, is not sufficient to maintain the animal in a condition of health. - -The next series of experiments was made by Jägerroos[70] of Finland. -This investigator was evidently impressed by the unfavorable and -monotonous character of the diet made use of by the preceding -investigators, and sought to introduce a little variety, recognizing -also that with a carnivorous animal it is difficult to reduce the -proteid to a low level and maintain the necessary fuel value, without -introducing foodstuffs to which the animal is wholly unaccustomed. In -the first experiment, the dog had a body-weight of 5.77 kilograms, and -at the beginning was fed daily 40 grams of meat and 100 grams of sugar, -equal to 0.31 gram of nitrogen and 80 calories per kilo of body-weight. -The experiment continued for eight months, sugar being replaced in part -by butter, and occasionally bread, fat, and wheat meal being used in -proper amount to yield the given nitrogen and fuel values. During the -last five months, the intake of nitrogen per day averaged 0.29 gram -per kilo, with a fuel value amounting to 89 calories daily per kilo of -body-weight. During this period, the animal maintained a plus nitrogen -balance for a large part of the time. The experiment was then continued -for two months longer, with a gradual diminution in the nitrogen of the -food and in the fuel value, the animal dying at the end of the tenth -month. - - [70] B. H. Jägerroos: Ueber die Folgen einer ausreichenden, aber - eiweissarmen Nahrung. Skandinavisches Archiv für Physiologie, Band - 13, p. 375, 1902. - -In a second experiment, the dog made use of weighed at the beginning -11.97 kilograms. During the first five months, the average intake of -nitrogen amounted daily to 0.29 gram per kilo, while the average fuel -value of the food (meat, fat, and sugar) was 76 calories per kilo -daily. In the middle of the seventh month the animal was quite ill, -with poor appetite, vomiting, etc. Body-weight began to fall off, and -the animal soon died. With both of these animals, the experiment ended -suddenly by a sharp and short illness. - -Jägerroos, however, believed that both animals died from a severe -case of infection, and not as the result of the diminished intake of -proteid. This view was fully substantiated, in his opinion, by the -evidence furnished on bacteriological and morphological examination. -There was no pathological alteration and no fatty degeneration in the -intestinal epithelium; nothing to indicate any connection between the -lowered proteid intake and the death of the animal. To be sure, the -long-continued diet poor in nitrogen might have diminished the power -of resistance of the body, but no proof of this is offered. There -was indicated merely a simple infection, as shown by the presence -of Streptococcus and Bacterium coli communis in the blood. But, as -Jägerroos states, one might well conceive of a lowered power of -resistance on the part of the body, due not to any change in diet, -but to the long-continued confinement in a cage with the enforced -inactivity and lack of freedom. It is to be noted, furthermore, that -here there was no sign of a gradual and progressive weakening of -the body, no indication of any disturbance of the digestive tract -with diminished power of absorption of either fat or proteid. On the -contrary, there was a sudden and sharp attack of some infectious -disease by which the animals quickly succumbed. Jägerroos was of the -opinion that in the absence of this infection the animals would have -continued to live for a long period of time. - -If a low proteid diet works so inimically on high proteid animals as -Munk and Rosenheim thought, it would naturally be expected that the -small proteid ration followed so long by Jägerroos would have resulted -in the appearance of marked symptoms, at least a gradual and persistent -falling off in body-weight, inability to maintain nitrogen equilibrium, -etc.; but none of these things occurred. In Munk’s first experiment, -the animal was given no fresh meat whatever during four weeks. Is it -not quite possible that in the abrupt cutting off of this wonted form -of food a disturbance may have been set up in the gastro-intestinal -tract, which paved the way for the more serious results that followed? -Jägerroos used only fresh, uncooked meat in his experiments, and laid -great stress upon the importance of not departing any more than was -necessary from the accustomed form of diet. The writer is strongly of -the opinion that sufficient stress has not been laid upon this phase of -the subject. A satisfactory diet for dog as for man must meet ordinary -hygienic requirements; it must not only be sufficient in amount, but -it must be easily digestible, of accustomed flavor, appealing to eye, -nostrils, and palate, with reasonable variation occasionally and of -moderate volume. With due regard to these conditions, I believe with -Jägerroos that not much attention need be paid to the proportion -of nitrogen therein, for however small the amount it will be found -sufficient to meet the needs of the body. - -These are the results, collectively, so frequently used to point -a moral for man: Beware of the possible danger of reducing the -consumption of proteid food below the commonly accepted dietary -standards! We must admit, however, that there is a woeful lack of -agreement in these results, and it is difficult to prevent a shadow of -doubt from creeping over us as we try to depict for ourselves the way -in which a low proteid ration exerts its deleterious effect on dogs. -I do not believe that radical changes in diet, whether they involve -increase or decrease in total quantities, or in specific elements of -the diet, can be made suddenly without danger of some disturbance of -the gastro-intestinal tract or other parts of the economy, either -in dog or man. It is reasonable to believe also that a high proteid -feeder, like a dog, with his more limited dietary, will be far more -sensitive to great changes than omnivorous man with his wider range of -foodstuffs. Moreover, there is just as good ground for believing that -in any animal, excess of proteid is as dangerous as a low proteid diet. -Too great a disturbance in the nutritive balance, whether it involves -excess or reduction in the amount of a given foodstuff, is liable to be -attended with serious disturbance in any sensitive organism. - -In illustration of these statements, we have some recent results -obtained by Watson and Hunter[71] upon the influence of diet on -growth and nutrition. These investigators find that young rats--two -and a half months old--when fed upon a diet composed exclusively of -horse-flesh, which is chiefly proteid matter with some fat, succumb -very quickly, for some reason. Of fourteen young rats fed on this meat -diet, six died on the third day. On the morning of this day, as the -authors state, “the rats appeared to be in their usual health, but -an hour after feeding one of them was lying on its side apparently -unconscious. In a few minutes others were affected. They appeared to be -paralyzed, they felt cold to the touch, exhibited symptoms of tetany, -and speedily became unconscious. Six succumbed within half-an-hour. Of -the remainder, some showed similar symptoms, although in less degree, -and they recovered when the diet was changed to bread and skim milk.” -After two days of the so-called normal diet, composed of bread and skim -milk, the remaining eight rats were again placed on an exclusive meat -diet. They appeared now to have acquired a certain degree of immunity, -for although they exhibited symptoms of deranged nutrition, these were -gradually recovered from and they gained in weight. At the end of the -eighth month, five of the animals were still alive and in apparent good -health, but their growth was permanently stunted. With an exclusive -diet of ox-flesh, young rats were much more liable to thrive, although -their growth was distinctly retarded. - - [71] Chalmers Watson, M.D., and Andrew Hunter, M.B.: Observations - on Diet. The Influence of Diet on Growth and Nutrition. Journal of - Physiology, Vol. XXXIV, p. 112, 1906. - -This difference in the behavior of the animals towards the two -forms of proteid food is to be attributed to the fact that ox-flesh -contains more fat than horse-flesh, and consequently the diet with -this form of meat was less exclusively proteid in character. Further, -there were some indications that horse-flesh is less digestible than -ox-flesh. Another fact, showing the far-reaching effect of a distinctly -unphysiological diet, is the marked influence of pure meat food on the -progeny. Thus, of 93 rats born of meat-fed parents only 19 were alive -at the end of two months, while of 97 young born of bread and milk-fed -rats, 82 were alive and in apparent health at the end of the same -period. - -As illustrating how foods that have, superficially at least, -approximately the same chemical composition may react differently -in the animal body we have the observations of Watson on rats fed -with porridge, made by boiling oatmeal with water and skim milk, -as contrasted with a diet of bread and skim milk, the two diets -having essentially the same composition. Of fourteen young rats fed -exclusively on porridge, all, with the exception of two that were -withdrawn, succumbed within five months, while the bread and milk-fed -animals thrived as usual. Adult rats, however, can live for prolonged -periods and maintain their weight on a porridge diet. It is believed -that the difference in the behavior of young rats to these two closely -allied forms of diet, is due to a difference in the digestibility of -the food, the porridge being presumably less readily digested by the -young animals than bread. With the more fully developed digestive -powers of the adult animals, however, this difference in availability -practically disappears as a potent factor in their nutrition. Finally, -mention may be made of the fact that a pure rice diet, notably -deficient in proteid, arrests the growth of young rats and leads to a -fatal issue within three months, while adult rats placed on such a -diet lose weight rapidly and die in about the same time. All of these -facts bearing on the nutrition of animals quite remote from man have -significance as showing how any wide departure from a physiological -diet, for that particular species or type, may lead to very undesirable -results, and they warn us not to be too hasty in drawing far-reaching -conclusions and sweeping deductions from a few experiments with a given -species of animal. - -Recurring now to the experiments made with dogs, there is certainly -suggested an element of danger in a low proteid diet, which, if the -experiments are taken at their face value and the conclusions derived -therefrom applied to man, needs careful consideration. Jägerroos -plainly was not inclined toward the belief that a low nitrogen intake -was the cause of the unfortunate results that attended his experiments. -Still, his animals did die from some cause, and thereby his position -was weakened. Munk and Rosenheim, on the other hand, from their -experiments were apparently convinced that a low proteid intake was -inimical to dogs, and it will be remembered Rosenheim concluded that -“a daily ration containing even 0.32 gram of nitrogen per kilogram of -body-weight, and with a fuel value of 110 calories per kilo, is not -sufficient to maintain the animal in a condition of health.” If this -is really true, there is some ground for the arguments advanced by -critical writers regarding the general subject of nitrogen requirements -of man. The evidence and the arguments, however, have always seemed to -the present writer frail and faulty; but recognizing the hold they have -taken on physiologists and the way they are usually applied to man, I -have attempted to test the matter experimentally under conditions which -would yield trustworthy and conclusive results. - -The question how far results obtained with dogs can be applied safely -to man may be open to discussion, but we must first be sure of our -facts before arguments or conclusions of any kind are warranted. It is -to be remembered that dogs are as sensitive in many ways as man, and no -physiological experiment covering a long period of time can be carried -out with any hope of success unless there is due regard for proper -hygienic conditions, some degree of variety in diet, and reasonable -opportunities for fresh air and occasional exercise. I fancy that -even the most vigorous and hardy man, if confined for six consecutive -months in a room just large enough to furnish requisite air-space and -to permit of extending his body at full length, would find himself -at the end of such a period in a condition far from healthful, even -though there were perfect freedom of choice in diet. If, however, there -were added to the above conditions monotony in diet extending through -many months, there would be no occasion for surprise if the individual -lost appetite and strength, and showed signs of disturbance of the -gastro-intestinal tract. - -It is doubtful if there is full appreciation of the possible effect -of monotony, in the ordinary dietary experiments on dogs. Man quickly -feels the effect; the sportsman camping in the woods by brook or lake -enjoys his first meal of speckled trout and has no thought of ever -becoming tired of such a delicacy; but as trout cooked in various ways -continue to be placed before him three times a day, and with perhaps -very little else, he soon passes into a frame of mind where salt pork -would be a luxury, and where he would prefer to go hungry rather than -eat the delicacy, if indeed he has appetite to eat anything. Is it -strange that dogs confined in cages barely large enough to permit of -their turning around, and fed day after day and month after month with -exactly the same amount of desiccated meat, fat, and rice, should show -signs and symptoms, if nothing worse, of disturbed nutrition? It is -necessary in experiments of this kind that the animals be confined -for given periods, at least, since otherwise it would be impossible -to determine the extent of nitrogen excretion and the rate of proteid -katabolism, etc. It is possible, however, to limit the time of close -confinement to, say, ten consecutive days, this to be followed by a -like period of comparative freedom, thus insuring opportunities for an -abundance of fresh air and exercise. - -The experiments of which I wish to speak, and which had for their -object a study of the effect of low proteid diet on dogs, as types -of high proteid animals, were carried out at our laboratory in the -Sheffield Scientific School and were made possible by liberal grants -from the Carnegie Institution of Washington, thus providing means for -securing the requisite number of chemical assistants. The experiments -were conducted on a somewhat large scale, over twenty dogs being made -use of, while many of the experiments extended through a full year. -The results in their entirety are not yet ready for publication, but -I am able to present in a general way observations on six dogs, which -will serve as an ample illustration of what may be expected with high -proteid animals when living on a low proteid diet under healthful -conditions. All of the six dogs whose cases are here presented were fed -on a mixed diet, with some fresh meat each day; bread, cracker dust, -milk, lard, and rice being the other foods drawn upon to complete the -dietary. The animals were fed twice a day, each meal being accurately -weighed and of definite chemical composition. A large, light, and -airy room, kept scrupulously clean, and in the winter time properly -heated by steam, served as their main abiding place. In this room -were a suitable number of smaller compartments, the walls of which -were composed of open lattice work (of iron), so as not to interfere -with light or air, and yet adequate to keep the dogs apart. These -compartments were not cages in the ordinary sense, but were truly large -and roomy. The entire floor under the dogs was composed of metal, the -joints all soldered, the floor being sloped to a metal gutter in front -so that all the compartments could be flushed out each morning and kept -sweet and clean. In pleasant weather, immediately after their first -meal, the dogs were taken out of doors to a large enclosure near by, -where they were allowed perfect freedom until about four o’clock, when -they were taken in for their second meal (between four and five o’clock -in the afternoon). The outdoor enclosure was inaccessible to every one -except the holder of the key, and the dogs while there were wholly free -from annoyance. Once every month, during a period of ten consecutive -days, each dog was confined in the metabolism cage so as to admit of -the collection of all excreta, in order to make a determination of -the nitrogen balance. Practically, therefore, each dog was in close -confinement only one-third of the month, the remaining two-thirds -being spent in much more congenial surroundings. I have entered thus -fully into a description of the conditions prevailing, because I deem -them exceedingly important, and because therein undoubtedly lies the -explanation of the striking contrast between our results and those of -the earlier investigators of this subject. - -In considering the outcome of our experiments, it may be wise to enter -into some detail concerning the first case to be presented. The animal -employed in this experiment was designated as No. 5, and weighed on -July 27, 1905, 17.2 kilograms; it was apparently full grown, but was -thin and had the appearance of being underfed. At first, it was given -daily 172 grams of meat, 124 grams of cracker dust, and 72 grams of -lard, the day’s ration containing 8.66 grams of nitrogen and having a -fuel value of 1389 calories.[72] These figures are equivalent to 80 -calories, and 0.50 gram of nitrogen, per kilogram of body-weight. The -animal took kindly to the diet, but on August 3 it refused to eat and -seemed to have a little fever. The next day it was better, but for -the three following days its appetite was poor, and only a portion -of the daily food was eaten. Body-weight began to fall off, and was -soon at 15.5 kilograms. On the 7th of August, a dose of vermifuge -was given, after which the appetite returned and the animal appeared -in good spirits. From this time forward it seemed in perfect health, -with good appetite, and showed the usual vivacity and playfulness of -dog-kind. The diet as specified was continued unchanged until August -25, a balance experiment covering a period of ten days, from the 15th -to the 24th of August inclusive, being carried out, in which the -nitrogen of the intake was compared with the output for each day. From -the accompanying table, where are given the average values of all the -balance periods of the experiment, it is to be seen that during this -first period the animal was laying on or gaining an average of 2 grams -of nitrogen per day. - - [72] The fuel value of the food was calculated from the data given - in Bulletin No. 28, U. S. Department of Agriculture. All figures for - nitrogen were obtained by exact chemical analysis. - - -SUBJECT No. 5. DAILY AVERAGES - - +----------------+-------+-----------------------+-------------------------+------+ - | | | Food. | Output. | | - | | +------+-------+--------+---------+-------+-------+ | - | | Body- | |Nitro- | Fuel | Nitro- | Nitro-| Nitro-|Nitro-| - | Date. |weight.|Total |gen per| Value | gen | gen | gen | gen | - | | |Nitro-| Kilo |per Kilo| through |through|through| Bal- | - | | | gen. | Body- | Body- | Kid- |Excre- | Hair. | ance | - | | | |weight.| weight.|neys.[73]| ment. | |+ or -| - +----------------+-------+------+-------+--------+---------+-------+-------+------+ - | 1905 | kilos | grams| gram |calories| grams | gram | gram |grams | - |Aug. 15-Aug. 24 | 15.8 | 8.66 | 0.54 | 87.3 | 5.44 | 0.70 | 0.52 |+2.00 | - |Sept. 6-Sept. 15| 17.1 | 4.76 | 0.27 | 72.4 | 3.41 | 0.32 | 0.48 |+0.55 | - |Oct. 8-Oct. 17 | 17.6 | 4.76 | 0.27 | 71.8 | 3.54 | 0.54 | 0.49 |+0.19 | - |Nov. 22-Dec. 1 | 16.9 | 4.77 | 0.28 | 72.0 | 3.76 | 0.39 | 0.32 |+0.30 | - | 1906 | | | | | | | | | - |Jan. 2-Jan. 11 | 17.2 | 4.07 | 0.23 | 72.0 | 3.19 | 0.54 | 0.35 |-0.01 | - |Jan. 30-Feb. 8 | 18.0 | 4.07 | 0.23 | 69.0 | 2.87 | 0.54 | 0.62 |+0.04 | - |Feb. 27-Mar. 8 | 18.2 | 5.18 | 0.28 | 73.0 | 3.69 | 0.66 | 0.74 |+0.09 | - |Mar. 27-Apr. 5 | 18.3 | 5.23 | 0.28 | 73.0 | 3.66 | 0.84 | 0.48 |+0.25 | - |Apr. 24-May 3 | 19.1 | 5.22 | 0.27 | 68.0 | 3.76 | 0.38 | 0.48 |+0.60 | - |May 22-May 31 | 19.4 | 5.22 | 0.26 | 65.0 | 3.44 | 0.31 | 0.48 |+0.99 | - |June 17-June 26 | 20.0 | 5.24 | 0.26 | 67.0 | 3.50 | 0.71 | 0.48 |+0.55 | - +----------------+-------+------+-------+--------+---------+-------+-------+------+ - - [73] All through the balance periods the dogs were catheterized each - morning to insure complete collection of the twenty-four hours’ urine. - -On August 25, a radical change was made in the diet, by reducing the -amount of meat to 70 grams daily, thereby lowering the intake of -nitrogen to 4.76 grams, or 0.27 gram per kilo of body-weight; the -cracker dust and lard being kept at essentially the same levels as -before. This diet was continued through the next balance period, the -dog in the meantime gaining in body-weight, and showing for the second -balance period an average gain by the body of half a gram of nitrogen -per day. The food was then altered by substituting bread for the -cracker dust, but so adjusted that the nitrogen and fuel values of the -day’s food remained practically unchanged. There was still, however, a -gain in body-weight and a slight gain in body nitrogen. At the close -of the third balance period, the diet was again altered, one-half of -the meat being replaced by milk, while cracker dust was substituted -for the bread. The morning meal consisted of 170 grams of milk, 86 -grams of cracker dust, and 18 grams of lard, while the afternoon meal -was composed of 35 grams of meat, 63 grams of cracker, and 35 grams of -lard. The day’s ration, however, still contained 4.76 grams of nitrogen -and had a fuel value of 1249 calories. This diet was maintained until -November 20, when the animal was again placed on a daily ration of meat -(69 grams), bread (166 grams), and lard (80 grams), with a total fuel -value of 1228 calories and 4.77 grams of nitrogen. This was continued -until December 2, the dog still showing a plus nitrogen balance, but -with a little loss in body-weight. On December 2, the diet was again -changed by substituting milk for a portion of the meat, but the -nitrogen and fuel values were maintained at the same level as before. -After a week, December 9, the food was modified as follows: the morning -meal contained 170 grams of milk, 110 grams of rice, and 11 grams of -lard, while the afternoon meal was composed of 35 grams of meat, 81 -grams of rice, and 30 grams of lard. The total nitrogen content of the -day’s ration was 4.07 grams, while the fuel value was 1255 calories. At -this time, the animal weighed 17.1 kilograms, consequently the intake -of nitrogen had been reduced to 0.23 gram per kilo of body-weight, -while the fuel value stood at 73 calories per kilogram. This diet was -continued until February 9, the balance period, between January 2 and -11, showing that the animal was in nitrogen equilibrium, in spite of -the material reduction in the intake of proteid, and that body-weight -was increasing. The next balance period, January 30 to February 8, -showed still further gain in weight with continuance of nitrogen -equilibrium. On February 9, the diet was changed by returning to 70 -grams of meat, 158 grams of cracker dust, and 60 grams of lard, with a -daily intake of 0.28 gram of nitrogen per kilo of body-weight. - -In this manner, the experiment was continued with frequent changes in -the character of the diet, but always maintaining essentially the same -values in nitrogen and calories as shown in the table, until June 27; -having extended through just eleven months, with the animal at the -close of the experiment still gaining in body-weight, with a steady -plus balance of nitrogen, and with every indication of good health and -strength. For ten months the animal lived with perfect comfort and in -good condition on an average daily intake of 0.26 gram of nitrogen -per kilogram of body-weight, and with an average fuel value of 70.3 -calories per kilo. Further, it is to be observed that at no time -during the ten months did the daily intake of nitrogen rise above 0.28 -gram per kilo, while during one month it fell to 0.23 gram per kilo. -Similarly, the fuel value of the daily food never exceeded 73 calories -per kilo, while at times it dropped as low as 67 and 65 calories per -kilo. That this diet was more than sufficient, both in nitrogen and -fuel value, is indicated by the steady increase in body-weight and by -the plus nitrogen balances observed in most of the periods throughout -the experiment. Indeed, with the comparatively low degree of muscular -activity which this animal was accustomed to, it would have been unwise -to have kept the subject much longer on a diet so rich as the above, -since there would have been danger of detriment to its health and good -condition. When these results are contrasted with the statements of -Munk and Rosenheim, the latter of whom found that even 0.32 gram of -nitrogen and 110 calories per kilo were insufficient to maintain dogs -in a condition of health, it is plain that for some reason our results -are quite at variance with their findings. - -The accompanying photographs, taken on August 19, 1905, February 27, -April 24, and at the close of the experiment on June 27, 1906, show the -appearance of the animal at the respective dates, and indicate more -clearly than words can express the actual condition of the animal. - -[Illustration: _Subject No. 5._ _August 19, 1905_] - -[Illustration: _Subject No. 5._ _November 18, 1905_] - -[Illustration: _Subject No. 5._ _April 24, 1906_] - -[Illustration: _Subject No. 5._ _June 27, 1906_] - -Turning now to a second subject, designated as dog No. 3, the -experiment with which lasted for nearly an entire year, the following -general statements may be made. The animal was a small black and white -fox terrier, weighing on July 6, 1905, 6.5 kilograms. It was a nervous, -affectionate little creature, far less phlegmatic than the animal just -described, always on the alert for a petting, and unceasingly active. -For these reasons, it seemingly required per kilogram of body-weight a -little more food than the preceding animal; a fact also in harmony with -the general law that small animals, per unit of body-weight, need more -food than larger ones. The diet made use of was of the same general -character as employed with the preceding animal, and was changed -from time to time to give requisite variety and to insure freedom from -too great monotony. The accompanying table, showing daily averages -during the twelve balance periods, gives all necessary information -regarding the outcome of the experiment. - - -SUBJECT No. 3. DAILY AVERAGES - - +----------------+-------+-----------------------+-----------------------+------+ - | | | Food. | Output. | | - | | +------+-------+--------+-------+-------+-------+ | - | | Body- | |Nitro- | Fuel | Nitro-| Nitro-| Nitro-|Nitro-| - | Date. |weight.|Total |gen per| Value | gen | gen | gen | gen | - | | |Nitro-| Kilo |per Kilo|through|through|through| Bal- | - | | | gen. | Body- | Body- | Kid- |Excre- | Hair. | ance | - | | | |weight.| weight.| neys. | ment. | |+ or -| - +----------------+-------+------+-------+--------+-------+-------+-------+------+ - | 1905 | kilos | grams| gram |calories| grams | gram | gram | gram | - |July 18-July 28 | 6.8 | 5.88 | 0.84 | 79.0 | 5.58 | 0.43 | 0.05 |-0.18 | - |Aug. 15-Aug. 24 | 7.1 | 3.44 | 0.49 | 77.4 | 3.35 | 0.17 | 0.13 |-0.21 | - |Sept. 6-Sept. 15| 6.9 | 2.11 | 0.30 | 80.0 | 1.93 | 0.21 | 0.07 |-0.10 | - |Oct. 8-Oct. 17 | 6.9 | 2.10 | 0.30 | 80.0 | 1.83 | 0.20 | 0.07 | 0 | - |Nov. 22-Dec. 1 | 6.0 | 1.83 | 0.31 | 80.0 | 1.48 | 0.21 | 0.11 |+0.03 | - | 1906 | | | | | | | | | - |Jan. 2-Jan. 11 | 5.6 | 1.63 | 0.29 | 81.0 | 1.54 | 0.17 | 0.08 |-0.16 | - |Jan. 30-Feb. 8 | 5.5 | 1.63 | 0.30 | 82.0 | 1.60 | 0.15 | 0.05 |-0.17 | - |Feb. 27-Mar. 8 | 5.5 | 1.78 | 0.32 | 84.0 | 1.66 | 0.17 | 0.05 |-0.10 | - |Mar. 27-Apr. 5 | 5.7 | 1.98 | 0.34 | 81.0 | 1.75 | 0.21 | 0.06 |-0.04 | - |Apr. 24-May 3 | 5.7 | 1.98 | 0.34 | 83.0 | 1.68 | 0.13 | 0.13 |+0.04 | - |May 22-May 31 | 5.8 | 1.98 | 0.34 | 80.0 | 1.77 | 0.13 | 0.11 |-0.03 | - |June 17-June 26 | 6.0 | 1.98 | 0.33 | 77.0 | 1.53 | 0.21 | 0.07 |+0.17 | - +----------------+-------+------+-------+--------+-------+-------+-------+------+ - -It will be observed that during the first three months the animal -showed a tendency to gain in weight slightly, recalling that its -initial weight on July 6 was 6.5 kilograms. Later, the weight fell -off a little, but in March it showed an upward movement, though very -gradual. With the amount of proteid food given, it is evident that -the animal needed about 80 calories per kilo to maintain a condition -of body-equilibrium. Nitrogen equilibrium was practically maintained -throughout the larger portion of the twelve months, but evidently the -animal required 0.31–0.33 gram of nitrogen per kilogram of body-weight. -Attention may be directed, in view of the results reported by Munk -regarding loss of the power of absorption and utilization of proteid -food, to the figures showing the average daily output of nitrogen -through the excrement. It is plain from the data presented, that this -animal was not suffering from any trouble of this order; indeed, the -utilization of proteid food throughout the entire experiment was -exceedingly complete, as shown by the relatively small loss of nitrogen -through the excrement, thus implying vigorous and unimpaired digestion, -together with thorough absorption of the products formed. - -The accompanying photographs show the appearance of the animal on -August 19, 1905, November 18, 1905, April 3 and June 27, 1906, the -close of the experiment. - -[Illustration: _Subject No. 3._ _August 19, 1905_] - -[Illustration: _Subject No. 3._ _November 18, 1905_] - -[Illustration: _Subject No. 3._ _April 24, 1906_] - -[Illustration: _Subject No. 3._ _June 27, 1906_] - -Passing now to the third subject, we have an experiment of somewhat -shorter duration, viz., of nine months, but sufficiently long to -afford ample opportunity for any deleterious effect to manifest -itself. The initial weight of the dog, No. 13, was 14.5 kilograms on -September 14. The lowest intake of nitrogen was 0.26 gram per kilo -of body-weight per day, while the fuel value of the daily food was -during one period reduced to 55 calories per kilo. A daily proteid -consumption equalling 0.30 gram of nitrogen per kilo, with a total -fuel value in the day’s food of 66–70 calories per kilo, was clearly -quite sufficient to maintain nitrogen equilibrium and body-weight; -indeed, toward the end of the experiment, the animal commenced to gain -in weight quite noticeably on the above diet, and was laying by fairly -large amounts of nitrogen daily. The accompanying table gives the -average daily nitrogen exchange, etc., of the nine balance periods, -while the photographs, taken on the dates indicated under each, show -the appearance of the animal at various times. - -SUBJECT No. 13. DAILY AVERAGES - - +---------------+-------+-----------------------+-----------------------+------+ - | | | Food. | Output. | | - | | +------+-------+--------+-------+-------+-------+ | - | | Body- | |Nitro- | Fuel | Nitro-| Nitro-| Nitro-|Nitro-| - | Date. |weight.|Total |gen per| Value | gen | gen | gen | gen | - | | |Nitro-| Kilo |per Kilo|through|through|through| Bal- | - | | | gen. | Body- | Body- | Kid- |Excre- | Hair. | ance | - | | | |weight.| weight.| neys. | ment. | |+ or -| - +---------------+-------+------+-------+--------+-------+-------+-------+------+ - | 1905 | kilos | grams| gram |calories| grams | gram | gram | gram | - |Sept. 24-Oct. 3| 14.0 | 7.22 | 0.52 | 86.0 | 6.40 | 0.71 | 0.19 |-0.08 | - |Nov. 5-Nov. 14 | 13.0 | 4.78 | 0.35 | 80.0 | 4.29 | 0.37 | 0.25 |-0.13 | - |Dec. 19-Dec. 28| 13.4 | 3.70 | 0.27 | 72.0 | 2.86 | 0.49 | 0.13 |+0.22 | - | 1906 | | | | | | | | | - |Jan. 16-Jan. 25| 14.1 | 3.72 | 0.26 | 70.0 | 3.16 | 0.61 | 0.16 |-0.21 | - |Feb. 13-Feb. 22| 14.3 | 4.26 | 0.30 | 78.0 | 3.54 | 0.67 | 0.37 |-0.32 | - |Mar. 13-Mar. 22| 14.1 | 3.62 | 0.26 | 55.0 | 3.29 | 0.46 | 0.14 |-0.27 | - |Apr. 10-Apr. 19| 14.2 | 4.59 | 0.32 | 73.0 | 2.84 | 0.51 | 0.10 |+1.14 | - |May 8-May 17 | 14.2 | 4.59 | 0.32 | 71.0 | 3.56 | 0.48 | 0.18 |+0.37 | - |June 5-June 14 | 15.3 | 4.58 | 0.30 | 66.0 | 2.98 | 0.55 | 0.28 |+0.77 | - +---------------+-------+------+-------+--------+-------+-------+-------+------+ - -[Illustration: _Subject No. 13._ _January 2, 1906_] - -[Illustration: _Subject No. 13._ _February 27, 1906_] - -[Illustration: _Subject No. 13._ _April 24, 1906_] - -[Illustration: _Subject No. 13._ _June 19, 1906_] - -Results of the same general tenor with dogs No. 15 and No. 20 are seen -in the appended tables, while the accompanying photographs testify -clearly to the general good condition of the animals up to the end of -the experiments. In No. 20 particularly, the great gain in body-weight -is to be noted, even though the fuel value of the food was reduced as -low as 64 calories per kilo, with the nitrogen intake at 0.28 gram per -kilo daily. Plainly, the day’s food could have been diminished still -more, with perfect safety to both body and nitrogen equilibrium. - - -SUBJECT No. 15. DAILY AVERAGES - - +---------------+-------+-----------------------+-----------------------+------+ - | | | Food. | Output. | | - | | +------+-------+--------+-------+-------+-------+ | - | | Body- | |Nitro- | Fuel | Nitro-| Nitro-| Nitro-|Nitro-| - | Date. |weight.|Total |gen per| Value | gen | gen | gen | gen | - | | |Nitro-| Kilo |per Kilo|through|through|through| Bal- | - | | | gen. | Body- | Body- | Kid- |Excre- | Hair. | ance | - | | | |weight.| weight.| neys. | ment. | |+ or -| - +---------------+-------+------+-------+--------+-------+-------+-------+------+ - | 1905 | kilos | grams| gram |calories| grams | gram | gram | gram | - |Nov. 5-Nov. 14| 9.2 | 3.35 | 0.36 | 82.0 | 2.95 | 0.11 | 0.14 |+0.15 | - |Dec. 19-Dec. 28| 8.9 | 2.61 | 0.30 | 75.0 | 2.47 | 0.12 | 0.12 |-0.10 | - | 1906 | | | | | | | | | - |Jan. 16-Jan. 25| 8.7 | 2.60 | 0.30 | 79.9 | 2.15 | 0.21 | 0.16 |+0.08 | - |Feb. 13-Feb. 16| 8.5 | 2.61 | 0.30 | 82.0 | 2.37 | 0.20 | 0.15 |-0.11 | - |Mar. 13-Mar. 22| 8.7 | 2.82 | 0.32 | 80.0 | 2.68 | 0.17 | 0.19 |-0.22 | - |Apr. 10-Apr. 19| 9.0 | 2.80 | 0.31 | 82.0 | 2.14 | 0.26 | 0.09 |+0.31 | - |May 8-May 17| 9.5 | 2.83 | 0.30 | 75.0 | 2.26 | 0.30 | 0.12 |+0.15 | - |June 5-June 14| 10.2 | 2.81 | 0.27 | 70.0 | 2.26 | 0.28 | 0.24 |+0.03 | - +---------------+-------+------+-------+--------+-------+-------+-------+------+ - -[Illustration: _Subject No. 15._ _January 2, 1906_] - -[Illustration: _Subject No. 15._ _February 27, 1906_] - -[Illustration: _Subject No. 15._ _April 24, 1906_] - -[Illustration: _Subject No. 15._ _June 19, 1906_] - - -SUBJECT No. 20. DAILY AVERAGES - - +---------------+-------+-----------------------+-----------------------+------+ - | | | Food. | Output. | | - | | +------+-------+--------+-------+-------+-------+ | - | | Body- | |Nitro- | Fuel | Nitro-| Nitro-| Nitro-|Nitro-| - | Date. |weight.|Total |gen per| Value | gen | gen | gen | gen | - | | |Nitro-| Kilo |per Kilo|through|through|through| Bal- | - | | | gen. | Body- | Body- | Kid- |Excre- | Hair. | ance | - | | | |weight.| weight.| neys. | ment. | |+ or -| - +---------------+-------+------+-------+--------+-------+-------+-------+------+ - | 1905 | kilos | grams| gram |calories| grams | gram | gram | gram | - |Dec. 6-Dec. 15 | 15.9 | 8.35 | 0.52 | 82.0 | 6.03 | 0.74 | 0.38 |+1.20 | - | 1906 | | | | | | | | | - |Jan. 16-Jan. 25| 16.4 | 4.47 | 0.27 | 73.0 | 3.61 | 0.55 | 0.15 |+0.16 | - |Feb. 13-Feb. 22| 17.2 | 4.45 | 0.25 | 72.0 | 3.92 | 0.36 | 0.13 |+0.04 | - |Mar. 13-Mar. 22| 17.4 | 5.00 | 0.28 | 72.0 | 5.49 | 0.33 | 0.10 |-0.92 | - |Apr. 10-Apr. 19| 18.4 | 5.60 | 0.30 | 69.0 | 4.88 | 0.52 | 0.18 |+0.02 | - |May 8-May 17 | 19.6 | 5.58 | 0.28 | 69.0 | 3.85 | 0.75 | 0.38 |+0.60 | - |June 5-June 14 | 19.7 | 5.59 | 0.28 | 64.0 | 4.69 | 0.45 | 0.40 |+0.05 | - +---------------+-------+------+-------+--------+-------+-------+-------+------+ - -[Illustration: _Subject No. 20._ _January 2, 1906_] - -[Illustration: _Subject No. 20._ _February 27, 1906_] - -[Illustration: _Subject No. 20._ _April 24, 1906_] - -[Illustration: _Subject No. 20._ _June 19, 1906_] - -The illustrations so far presented, with the general agreement in the -character of the results, might perhaps be interpreted as indicating -that there is no difficulty whatever in bringing a high proteid -consumer, like a dog, down to a low level of proteid consumption. -This, however, would be a false impression. Much depends upon the -character of the proteid food, at least where any attempt at rapid -change is made, for a certain modicum of meat or other animal food -seems a necessary part of the daily diet if health and strength are -to be maintained. A dog transferred suddenly from a daily ration in -which meat and milk are conspicuous elements to a diet in which these -are wholly wanting is very liable to show disturbing symptoms almost -immediately. One case may be cited in illustration of these statements. -On September 29, 1905, dog No. 17, weighing 18.2 kilos, was placed on -a daily diet composed of 70 grams of fresh meat, 442 grams of milk, -300 grams of bread, and 28 grams of lard. This ration contained 9.06 -grams of nitrogen and had a fuel value of 1465 calories, or 0.5 gram -of nitrogen and 80 calories per kilogram of body-weight. On October -11, the animal weighed 18.6 kilograms and was in perfect condition. On -the 13th, the meat was reduced to 34 grams per day, but the milk was -increased in amount so as to maintain the same nitrogen intake and fuel -value as before. This diet was continued until November 3, a balance -experiment covering ten days from October 22 to the 31 inclusive, -showing that the animal was laying by a little nitrogen. On November -3, the diet was changed to milk, bread, and lard, the fuel value being -maintained at 80 calories per kilo daily, while the nitrogen intake -was reduced to 0.30 gram per kilo. On this diet, the animal seemed to -thrive perfectly, and at the end of two weeks showed a body-weight of -18.2 kilograms. November 19, the milk was withdrawn, the bread being -increased so as to keep the daily nitrogen intake and the fuel value -unchanged. The day’s food was now composed of bread and lard solely, -but, as just stated, the nitrogen and fuel values were unaltered. In -four days’ time, however, a change began to creep over the animal; the -appetite diminished, and there was apparent a condition of lassitude -and general weakness which deterred the animal from moving about as -usual. - -During the next week the animal grew steadily worse, and would eat -only when coaxed with a little milk or with bread softened with milk, -the diet of bread and lard being invariably refused. There was marked -disturbance of the gastro-intestinal tract; bloody discharges were -frequent; the mucous membrane of the mouth was greatly inflamed and -very sore; body-weight fell off, and the animal was in a very enfeebled -condition. This continued until December 4, with every indication that -the animal would not long survive, but by feeding carefully with a -little milk and occasionally some meat, improvement finally manifested -itself, and by December 18 there was good appetite, provided bread was -not conspicuous in the food. Body-weight, which had fallen to 15.5 -kilos, was being slowly regained, and on December 30 the animal was -again placed on a weighed diet, consisting of 70 grams of meat, 442 -grams of milk, 210 grams of cracker dust, and 10 grams of lard. This -diet contained 8.26 grams of nitrogen and had a fuel value of 1330 -calories, equivalent to 0.5 gram nitrogen and 80 calories per kilogram -of body-weight. On January 12, 1906, the weight of the animal was 16.7 -kilos, while in general condition there was nothing to be desired. The -food was then modified by diminishing the amounts of meat and milk fed -daily by one-half, thus reducing the nitrogen intake to 0.35 gram per -kilo of body-weight, but maintaining the fuel value of the food at 80 -calories per kilo. Under this régime, body-weight still increased, -and on January 27 was 17.5 kilograms. A balance period, shown in the -accompanying table, extending from January 30 to February 8, affords -ample evidence that the body was laying by nitrogen. - - -SUBJECT No. 17. DAILY AVERAGES - - +---------------+-------+-----------------------+-----------------------+------+ - | | | Food. | Output. | | - | | +------+-------+--------+-------+-------+-------+ | - | | Body- | |Nitro- | Fuel | Nitro-| Nitro-| Nitro-|Nitro-| - | Date. |weight.|Total |gen per| Value | gen | gen | gen | gen | - | | |Nitro-| Kilo |per Kilo|through|through|through| Bal- | - | | | gen. | Body- | Body- | Kid- |Excre- | Hair. | ance | - | | | |weight.| weight.| neys. | ment. | |+ or -| - +---------------+-------+------+-------+--------+-------+-------+-------+------+ - | 1905 | kilos | grams| gram |calories| grams | gram | gram | gram | - |Oct. 22-Oct. 31| 18.3 | 9.06 | 0.49 | 80.0 | 7.73 | 0.66 | 0.28 |+0.39 | - | 1906 | | | | | | | | | - |Jan. 30-Feb. 8 | 17.6 | 5.77 | 0.33 | 78.0 | 4.12 | 0.44 | 0.21 |+1.00 | - |Feb. 27-Mar. 8 | 17.9 | 5.31 | 0.30 | 72.0 | 4.59 | 0.59 | 0.37 |-0.24 | - |Mar. 27-Apr. 5 | 18.1 | 5.33 | 0.29 | 70.0 | 5.63 | 0.89 | 0.27 |-1.52 | - |Apr. 24-May 3 | 18.4 | 5.90 | 0.32 | 68.0 | 5.06 | 0.49 | 0.30 |+0.05 | - |May 22-May 31 | 18.6 | 5.90 | 0.31 | 67.0 | 5.25 | 0.53 | 0.43 |-0.31 | - |June 17-June 26| 19.9 | 5.89 | 0.29 | 70.0 | 4.29 | 0.39 | 0.28 |+0.93 | - +---------------+-------+------+-------+--------+-------+-------+-------+------+ - -In all of the subsequent months, a small amount of meat was a part of -the daily food, but as is seen from the table of balance periods, the -total nitrogen intake and the fuel value of the food were reduced to -even lower levels per kilogram of body-weight. Yet the animal gained -steadily, until at the latter part of June the weight was considerably -above that noted at the commencement of the experiment in the preceding -October. Further, the animal was in nitrogen equilibrium or even -gaining nitrogen, and in perfect condition of health and vigor, as -is indicated by the accompanying photographs taken at the different -periods stated. Especially to be emphasized is the fact that during the -last six months of the experiment, the daily intake of nitrogen and the -fuel value of the food were as low or even lower than in November, when -the daily diet was limited to bread and lard. The disastrous result -which showed itself at once on this latter diet, with all animal food -excluded, was not due to low proteid or to deficiency in fuel value, -but simply to the fact that the animal for some reason could not -adjust itself to a simple dietary of bread and fat, although there was -ample available nitrogen and fuel value for the body’s needs. Something -was lacking, which meat or milk could supply, and this something was -indispensable for the maintenance of the normal nutritional rhythm. - -[Illustration: _Subject No. 17._ _January 2, 1906_] - -[Illustration: _Subject No. 17._ _February 27, 1906_] - -[Illustration: _Subject No. 17._ _April 24, 1906_] - -[Illustration: _Subject No. 17._ _June 27, 1906_] - -This is by no means an exceptional case, but we can cite many other -examples of like results where the animal when restricted to a purely -vegetable diet, such as bread, pea-soup, bean soup, etc., reinforced by -an animal fat, quickly passed from a condition of health into a state -of utter wretchedness, with serious gastro-intestinal disturbance. -The results are not to be attributed to the lower utilization of the -vegetable food, for the disastrous effect is too quickly manifest, and -further, often shows itself when the animal plainly has a large store -of available nutriment in its own tissues. - -This experiment with dog No. 17 has been dwelt upon at some length, -because it illustrates a very important principle in the nutrition -of a high proteid and carnivorous animal. As before stated, it is -not a question of high or low proteid simply, but involves possibly -the more subtle question of the relative value of specific forms of -proteid food. It will be noted that this statement is made somewhat -guardedly, in harmony with the caution necessarily called for in view -of our lack of knowledge regarding the possible need of the animal’s -body for extraneous principles which only meat, milk, or other animal -products can supply. Inorganic salts, nitrogenous extractives, and -other substances without any appreciable fuel value, are quite likely -to be of primary importance in controlling and regulating the various -processes of the body, which combine to maintain the condition of -normal nutrition. With a diet restricted to one or two vegetable -products, it is quite conceivable that something may be lacking -which the system demands, though it cannot be measured in terms of -nitrogen or calories. It may be said that man thrives on a purely -vegetable diet, but while this is unquestionably true, it must be -remembered that man with his free choice of food has recourse, as a -rule, to a large variety of vegetable products from many sources, -and consequently there is great likelihood of his absorbing from -these varied products such supplementary matters as may be needed. On -this question, we are in a realm of doubt and uncertainty, but the -possibilities suggested must not be ignored, for they may contain a -germ of truth of the utmost importance. The fact remains, however, that -a dog when restricted to a purely vegetable dietary does not thrive; a -little animal food seems necessary to keep up health and strength, and -this suffices even though the daily nitrogen intake and fuel value of -the food are restricted to a level below that of the vegetable dietary. - -With these facts before us, it is difficult to avoid the conclusion -that some significance may attach to the specific nature of the -proteid. Of course, we must not overlook the radical difference in -dietary habits of man and dog. Man as an omnivorous creature has for -generations been accustomed to partake largely of vegetable foods, -and as a result his digestive tract and his system as a whole has -become acclimated, as it were, to the nutritive effects of vegetable -matter. Dogs, on the other hand, are typical carnivores, and their -habits for generations have led in an opposite direction, so that their -gastro-intestinal tracts and their systems have become accustomed -to the effects of a diet in which animal food largely predominates. -Whether these deeply ingrained characteristics are responsible in -any large measure for the difference in behavior of man, on a purely -vegetable diet, and dogs is open to question. It would certainly not be -strange if such were the case, but as we look at the facts collected in -our study of this subject, it is somewhat impressive to note how well -dogs thrive on a relatively large amount of vegetable food, provided -there is a modicum of animal food added thereto. In other words, -these high proteid consumers are apparently quite able to utilize the -vegetable foods, but there is something lacking in such a dietary -which the body has great need of. Is it not quite possible, as already -suggested, that the specific nature of the proteid counts for something -in nutrition? The question cannot be answered definitely at present, -but there are certain facts slowly accumulating which make the question -a pertinent one in this connection. - -Thus, it is becoming evident, as was pointed out in an earlier chapter, -that the many proteid substances occurring in the animal and vegetable -kingdoms are more or less unlike each other in their chemical make-up. -They yield different decomposition products, or the same products -in widely different proportion, when broken down by the action of -hydrolyzing agents; and when we recall that the digestive enzymes of -the body convert the proteids of the food into these same end-products, -it is plain that in the assimilation and utilization of the proteid -foodstuffs the body has to deal with these various chemical units. -Hence, an animal suddenly restricted to a dietary in which all of the -proteid is furnished by bread might be seriously incommoded, either by -the excess of certain amino-acids resulting therefrom, or by a lack -of certain other end-products to which its body is accustomed. As an -example, we may take the three typical proteids of the wheat kernel, -gliadin, glutenin, and leucosin, and note the very striking difference -in the proportion of certain of the decomposition products of each, as -reported by Osborne and Clapp.[74] - - [74] See Osborne and Clapp: The Chemistry of the Protein Bodies of - the Wheat Kernel. American Journal of Physiology, vol. 17, p. 231. - - +-----------------+-------------+-------------+-------------+ - | | | | | - | | Gliadin. | Glutenin. | Leucosin. | - | | | | | - +-----------------+-------------+-------------+-------------+ - | | per cent | per cent | per cent | - | Leucin | 5.61 | 5.95 | 11.34 | - | Lysin | 0 | 1.92 | 2.75 | - | Arginin | 3.16 | 4.72 | 5.94 | - | Glutaminic acid | 37.33 | 23.42 | 6.73 | - | Ammonia | 5.11 | 4.01 | 1.41 | - | Aspartic acid | 0.58 | 0.91 | 3.35 | - | Tyrosin | 1.20 | 4.25 | 3.34 | - +-----------------+-------------+-------------+-------------+ - -It is obvious from these figures that the three proteids of the wheat -kernel are radically different from each other. Contrast, for example, -the content of glutaminic acid in gliadin with the amount in leucosin. -With such striking differences in chemical make-up, it is reasonable -to assume that corresponding differences in physiological action or -food values may exist. Further, “in respect to the amount of these -amino-acids, leucosin more nearly resembles the animal proteins than -the seed proteins thus far examined, and in this connection it is -interesting to note that leucosin occurs chiefly if not wholly in the -embryo of this seed and is probably one of its ‘tissue’ proteins, in -contrast to the ‘reserve’ proteins of the endosperm of which gliadin -and glutenin form the chief part” (Osborne and Clapp). In other words, -animal proteids, such as those of meat, are characterized like leucosin -by a small content of glutaminic acid and ammonia; while leucin, lysin, -aspartic acid, and arginin are relatively more abundant. Until we know -more on this subject, however, any broad generalization would be out -of place, but certainly there is justification for the supposition -that in these differences in chemical constitution are to be found -explanation of some of the peculiarities common to certain varieties of -proteid food. Wheat flour, aside from its starch, is composed mainly -of glutenin and gliadin with their large content of glutaminic acid. -Meat proteids, on the other hand, like leucosin, contain only a small -fraction of this acid, and, with the other differences indicated, -meat proteid and wheat proteid as food for dogs or other high proteid -consumers may reasonably be expected to have at the least very unequal -values. And if we go a step beyond this and suppose that in the -formation of true tissue proteid or the living protoplasm of the cell, -certain of these end-products of proteid decomposition are absolutely -indispensable, we can easily picture for ourselves a dearth of such -building stones in the long-continued use of a diet which lacks that -particular proteid from which the necessary building stones can be -split off in adequate number. - -It has been said, notably by Munk, that in dogs fed for some time on -a low proteid diet there is a diminished power of absorption from the -intestinal tract, associated with weakened digestion. If it is true -that a lowered proteid intake results in a diminished utilization of -the ingested food, that efficiency in the digestion and absorption of -foodstuffs is impaired, it can only be interpreted as meaning that -some injurious influence has been exerted on the epithelial cells of -the intestine or the adjacent gland cells. We have, however, failed -to find any evidence of deleterious action in the dogs that we have -experimented with, where due regard was paid to maintaining a diet -suitable for the physiological needs of the body. In the experiments -that we have cited, both nitrogen intake and the fuel value of the food -per day were lower than in Munk’s experiments, but the utilization of -fat and proteid was not sensibly affected. The following tables give -the results with ten dogs (including the six dogs already described) -for lengths of time ranging from seven to twelve months, the periods -indicated being each of ten days’ duration and occurring once each -month. In the first table, the utilization of fat is shown, the -figures given being based on determinations of the amount of fat -contained in the excrement. Knowing the amount of fat in the daily -food and the amount which passed through the intestine, it is easy to -calculate the percentage of fat utilized. - - -UTILIZATION OF FAT IN PERCENTAGES. - - +----------+-------------------------------------------------+ - | | Dogs. | - | Periods. +----+----+----+----+----+----+----+----+----+----+ - | | 1 | 2 | 3 | 4 | 5 | 12 | 13 | 15 | 17 | 20 | - +----------+----+----+----+----+----+----+----+----+----+----+ - | 1 | 97 | 96 | 93 | 97 | 97 | 96 | 96 | 98 | 98 | 95 | - | 2 | 96 | 96 | 98 | 98 | 98 | 94 | 95 | 97 | 98 | 95 | - | 3 | 98 | 97 | 97 | 99 | 96 | 97 | 97 | 98 | 94 | 98 | - | 4 | 98 | 96 | 97 | 97 | 96 | 94 | 95 | 98 | 97 | 97 | - | 5 | 96 | .. | 94 | 98 | 97 | 95 | 95 | 98 | 97 | 96 | - | 6 | 97 | 98 | 94 | 98 | 97 | 96 | 94 | 97 | 96 | 97 | - | 7 | 97 | 98 | 98 | 97 | 96 | 93 | 95 | 97 | 98 | 96 | - | 8 | .. | .. | 98 | 96 | 96 | 96 | 93 | 97 | .. | .. | - | 9 | .. | .. | 98 | 97 | 98 | .. | 97 | 98 | .. | .. | - | 10 | .. | .. | 98 | 97 | 98 | .. | .. | .. | .. | .. | - | 11 | .. | .. | 97 | 92 | 97 | .. | .. | .. | .. | .. | - | 12 | .. | .. | 97 | 97 | .. | .. | .. | .. | .. | .. | - +----------+----+----+----+----+----+----+----+----+----+----+ - -It is perfectly plain from these results that there was no falling off -in the utilization of fat; the percentage amount digested and absorbed, -as in dogs 3 and 4, was just as large at the end of the twelve months’ -experiment as at the beginning. Clearly, a so-called low nitrogen -intake with dogs does not lead to any loss of power in the utilization -of the fat of the food. This being so, it is equally clear that the -arguments based on Munk’s results in this direction, and applied to -man, are without adequate foundation. - - -UTILIZATION OF NITROGEN IN PERCENTAGES. - - +----------+-------------------------------------------------+ - | | Dogs. | - | Periods. +----+----+----+----+----+----+----+----+----+----+ - | | 1 | 2 | 3 | 4 | 5 | 12 | 13 | 15 | 17 | 20 | - +----------+----+----+----+----+----+----+----+----+----+----+ - | 1 | 95 | 91 | 92 | 94 | 91 | 91 | 90 | 93 | 92 | 91 | - | 2 | 92 | 94 | 94 | 95 | 93 | 90 | 92 | 96 | 92 | 87 | - | 3 | 91 | 92 | 90 | 91 | 88 | 89 | 86 | 95 | 89 | 91 | - | 4 | 90 | 85 | 90 | 92 | 91 | 82 | 83 | 91 | 83 | 93 | - | 5 | 90 | 82 | 88 | 92 | 86 | 85 | 84 | 96 | 91 | 90 | - | 6 | 86 | 87 | 89 | 83 | 86 | 89 | 87 | 94 | 91 | 86 | - | 7 | 87 | 87 | 90 | 83 | 87 | 83 | 88 | 90 | 93 | 91 | - | 8 | .. | .. | 90 | 83 | 84 | 81 | 89 | 89 | .. | .. | - | 9 | .. | .. | 89 | 87 | 92 | .. | 87 | 89 | .. | .. | - | 10 | .. | .. | 93 | 85 | 94 | .. | .. | .. | .. | .. | - | 11 | .. | .. | 93 | 81 | 86 | .. | .. | .. | .. | .. | - | 12 | .. | .. | 89 | 92 | .. | .. | .. | .. | .. | .. | - +----------+----+----+----+----+----+----+----+----+----+----+ - -The figures in the above table were obtained by determining the -amount of nitrogen in the dried excrement from the animals, _i. e._ -the amount that passed through the intestine unchanged;[75] and -knowing the content of nitrogen in the daily food, the percentage of -unabsorbed nitrogen was then easily calculated, after which by simple -subtraction the percentage of utilized nitrogen was found. At first -glance, it would appear that as the experiments proceeded utilization -of nitrogen was less complete. In a sense, this was true, but it was -not connected with any impairment of the digestive or absorptive -powers of the intestine. It must be remembered that in the earlier -periods a larger proportion of the ingested nitrogen was in the form of -readily digestible meat, but as the latter was reduced in amount larger -proportions of vegetable food were introduced in order to maintain the -desired fuel value, and consequently the percentage of non-absorbable -nitrogen was increased. The well-known difference in the availability -of animal and vegetable proteid has already been referred to in other -connections; a difference due not so much to any inherent quality in -the digestibility of the two forms of proteid as to the presence of -cellulose and other material in the vegetable food which retards in -some measure the action of the digestive juices. To this cause must -be ascribed the slight falling off in the utilization of nitrogen -noticeable in most of the experiments. If, however, the figures are -compared with those usually obtained on a diet largely vegetable in -nature, it will be seen that the utilization of nitrogen by these dogs -was in no sense abnormal. - - [75] There is an unavoidable error here, since the excrement contains - not only undigested food, but also contains some nitrogenous matter - derived from the secretions of the intestine, etc. - -These experiments on the influence of a low proteid diet on dogs, as -a type of high proteid consumers, taken in their entirety, afford -convincing proof that such animals can live and thrive on amounts of -proteid and non-nitrogenous food far below the standards set by Munk -and Rosenheim. The deleterious results reported by these investigators -were not due to the effects of low proteid or to diminished consumption -of non-nitrogenous foods, but are to be ascribed mainly to non-hygienic -conditions, or to a lack of care and physiological good sense in the -prescription of a narrow dietary not suited to the habits and needs -of this class of animals. Further, it is obvious that the more or -less broad deductions so frequently drawn from the experiments of -Munk and Rosenheim, especially in their application to mankind, are -entirely unwarranted and without foundation in fact. Our experiments -offer satisfying proof that not only can dogs live on quantities -of proteid food per day smaller than these investigators deemed -necessary, and with a fuel value far below the standard adopted by -them; but, in addition, that these animals are quite able on such a -diet to gain in body-weight and to lay by nitrogen, thereby indicating -that even smaller quantities of food might suffice to meet their true -physiological requirements. - -The results of these experiments with dogs, which we have recorded in -such detail, are in perfect harmony with the conclusions arrived at by -our experiments and observations with man, and serve to strengthen the -opinion, so many times expressed, that the dietary habits of mankind -and the dietary standards based thereon are not always in accord with -the true physiological requirements of the body. If these views are -correct, and the facts presented seemingly indicate that they are, -it is time for enlightened people to give heed to such suggestions, -that their lives may be ordered more nearly in accord with the best -interests of the body. Physiological economy in nutrition is not a -myth, but a reality full of promise for the welfare of the individual -and of the community in general. Ignorance on dietary matters should -give place to an intelligent comprehension of the body’s needs, and an -adequate understanding of how best to meet the legitimate demands of -the system for nourishment under given conditions of life. It is said -that more than half the earnings of the working people of this country -is spent for food. Here, we have suggested another form of economy as -worthy of consideration; less important perhaps than that which relates -to health and strength, but still calling for thoughtful attention. We -cannot afford to be ignorant of these things; we must have definite -knowledge of the actual facts, and these can only be obtained by -careful research and investigation. - -As a prominent writer on nutrition has well said, “The health and -strength of all are intimately dependent upon their diet. Yet most -people understand very little about what their food contains, how it -nourishes them, whether they are economical or wasteful in buying and -preparing it for use, and whether or not the food they eat is rightly -fitted to the demands of their bodies. The result of this ignorance is -great waste in the purchase and use of food, loss of money, and injury -to health” (Atwater). We all recognize the general force and truth of -this statement, but there is a surprising lack of appreciation of the -full significance of what is involved thereby. If it is true that the -demands of the body for proteid food--which of all foods is the most -expensive--are fully met by an amount equal to one-half that ordinarily -consumed, and that health and strength are more satisfactorily -maintained thereby, it is easy to see how the acquisition of dietary -habits leading to consumption of food in harmony with physiological -needs will result in a fruitful twofold economy; viz., economy in -expenditure, and of still greater moment, economy in the activities of -the body by which food and its waste products are cared for. - - - - -CHAPTER VIII - -PRACTICAL APPLICATIONS WITH SOME ADDITIONAL DATA - - TOPICS: Proper application of the results of scientific research - helpful to mankind. Dietary habits should be brought into conformity - with the true needs of the body. The peculiar position of proteid - foods emphasized. The evil effects of overeating. What the new - dietary standards really involve. The actual amounts of foodstuffs - required. Relation of nutritive value to cost of foods. The - advantages of simplicity in diet. A sample dietary for a man of - 70 kilograms body-weight. A new method of indicating food values. - Moderation in the daily dietary leads toward vegetable foods. The - experiments of Dr. Neumann. The value of fruits as food. The merits - of animal and vegetable proteids considered in relation to the - bacterial processes in the intestine. A notable case of simplicity - in diet. Intelligent modification of diet to the temporary needs of - the body. Diet in summer and winter contrasted. Value of greater - protection to the kidneys. Conclusion. - - -Knowledge has value in proportion to the benefit it confers, directly -or indirectly, on the human race. Every new scientific fact or -principle brought to light promises help in the understanding of -Nature’s laws, and when rightly interpreted and properly applied is -sure to aid in the advancement and prosperity of the individual and of -the community. Proper methods of living, economical adjustment of the -intake to the varying needs of the body, avoidance of excessive waste -of foodstuffs and of energy, are all desirable precepts, which rational -people presumably are inclined to follow so far as their knowledge and -understanding of the subject will permit. Here, as elsewhere, false -teaching may be exceedingly mischievous and lead to costly errors; -while blind reliance upon customs, instinct, and superstitions is -hardly in keeping with twentieth-century progress. - -Modern scientific methods should give us help in dietetics, as in -other branches of hygiene and practical medicine. A few short years -ago, diphtheria was a scourge which brought misery to many a home, -for there was at hand no adequate means of combating the disease; but -scientific research has given us new light, and placed at our command a -weapon of inestimable value. Do we hesitate to use it when the occasion -arises, because it happens to be out of keeping with old-time customs -and traditions? No, we recognize the possibility of help, and as the -need is urgent we turn to it quickly, with hope and thankfulness that -scientific progress has opened up a pathway of escape from a threatened -calamity. - -Not many years ago we drank freely of such water as was at hand, -without realization of danger from bacteria or disease germs, looking -on epidemics of typhoid fever perhaps as a visitation of Divine -Providence, in punishment of our many sins and to be borne meekly and -with resignation. But all this has changed through the researches of -bacteriologists and chemists; scientific facts of the utmost importance -have been clearly established; a classification of water-borne -diseases has been adopted, and we realize fully that diseases of this -order can be kept from our doors by proper precautions applied to -our water supply. To-day, epidemics of typhoid fever are traceable -solely to the ignorance or carelessness of the individual or of the -commonwealth, and the exemption which we of the present generation -have from this class of diseases is directly due to the application of -precautionary measures based on the information furnished by scientific -investigation. It is proper for us to use caution in the acceptance of -new ideas, but not that form of caution which refuses change on the -ground that what has been is sufficiently good for the present and the -future. The point of view is ever changing with advance of knowledge, -and it is not profitable to exclude opportunities for improvement -in personal hygiene and general good health, any more than in other -matters that affect the prosperity of the individual or the community. - -Dietary habits should be brought into conformity with the true needs of -the body. Excessive consumption of proteid food, especially, should be -avoided on the ground that it is not only unnecessary and wasteful, but -is liable to bring penalties of its own, most undesirable and wholly -uncalled for. We may, perhaps, accept these statements at their full -value, and yet have a shadow of doubt in our minds as to whether, after -all, dietary customs do not harmonize sufficiently at least with true -nutritive requirements. All the data that we have presented in the -preceding chapters, however, have seemingly given a positive answer to -such doubts, and indicate quite clearly that the results of scientific -study are opposed to the prevailing dietary standards, especially -as regards proteid food. As the celebrated physiologist Bunge has -expressed it, “The necessity for a daily consumption of 100 grams of -proteid is incomprehensible, so long as we do not know of any function -of the body in the performance of which the chemical potential energies -of the destroyed proteid are used up.” - -Perfectly trustworthy evidence is at hand showing that the needs of -the body for potential energy can be fully met, and indeed are more -advantageously met, by the non-nitrogenous foods, carbohydrates and -fats. The energy of muscle work, as we have seen, comes preferably -from the breaking down of non-nitrogenous material, so that there is -no special call for proteid in connection with increased muscular -activity. In fact, it would appear that the need for proteid food -by man is limited to the requirements of growth and development, -reinforced by the amount called for in that form of tissue exchange -which we have emphasized under the term “endogenous proteid -metabolism,” or true tissue metabolism. To be sure, there must be a -certain reserve of proteid, available in case of emergency, but this is -easily established without resorting to excessive feeding. - -The peculiar position which proteid foods occupy in man’s dietary -naturally make them the central figure, around which the other foods -are grouped. No other form of food can take the place of proteid; a -certain amount is needed each day to make good the loss of tissue -material broken down in endogenous katabolism, and consequently our -choice and combination of the varied articles of diet made use of -should be regulated by the amount of proteid they contain. But while -proteid foods occupy this commanding position, it is not necessary -or desirable that they should exceed the other foodstuffs in amount, -or indeed approach them in quantity. We must be ever mindful of -the fact, so many times expressed, that proteid does not undergo -complete oxidation in the body to simple gaseous products like the -non-nitrogenous foods, but that there is left behind a residue of -non-combustible matter--solid oxidation products--which are not -so easily disposed of. In the forceful language of another, “The -combustion of proteid within the organism yields a solid ash which must -be raked down by the liver and thrown out by the kidneys. Now when -this task gets to be over-laborious, the laborers are likely to go on -strike. The grate, then, is not properly raked; clinkers form, and -slowly the smothered fire glows dull and dies” (Curtis). - -Even though no such dire fate overtakes one, the penalties of excessive -proteid consumption are found in many ills, for which perhaps the -victim seeks in vain a logical explanation; gastro-intestinal -disturbance, indigestion, intestinal toxæmia, liver troubles, bilious -attacks, gout, rheumatism, to say nothing of many other ailments, -some more and some less serious, are associated with the habitual -overeating of proteid food. But excessive food consumption is by no -means confined to the proteid foodstuffs; general overfeeding is a -widespread evil, the marks of which are to be detected on all sides, -and in no uncertain fashion. One of the most common signs of excessive -food consumption is the tendency toward obesity, a condition which -is distinctly undesirable and may prove decidedly injurious. Undue -accumulation of fat is not only a mechanical obstacle to the proper -activity of the body as a whole, but it interferes with the freedom -of movement of such muscular organs as the heart and stomach, thereby -interposing obstacles to the normal action of these structures. -Further, whenever undue fat formation is going on in the body, there is -the ever present danger that the lifeless fat may replace the living -protoplasm of the tissue cells and so give rise to a condition known as -“fatty degeneration.” While a superabundance of fat in the body is a -sure telltale of overeating, the absence of obesity is by no means an -indication that excess of food is being avoided. There is here, in man -as in animal kind, much idiosyncrasy; some persons, especially those -endowed with a long and large frame, tend to keep thin even though -they eat excessively, while others grow fat much more readily. As a -well-known physician has expressed it, “In the one case, the subject -burns, instantly and mercilessly, every stick of fuel delivered at his -door, whether or not he needs the resulting hot fire roaring within, -while the other, miser-like, hoards the rest in vast piles, filling the -house from cellar to garret.” - -Temperance in diet, like temperance in other matters, leads to good -results, and our physiological evidence points out plainly, like -a signpost all can read, that there is no demand on the part of -the body for such quantities of food as custom and habit call for. -Healthfulness and longevity are the prizes awarded for the successful -pursuance of a temperate life, modelled in conformity with Nature’s -laws. Intemperance, on the other hand, in diet as in other matters, -is equally liable to be followed by disaster. A physician of many -years’ experience, with opportunities for observation among different -classes of people, has written, “that overeating tends to shrink the -span of life in proportion as it expands the liver is demonstrable -both directly and indirectly. Let any actuary of life-insurance be -asked his experience with heavy-weight risks, where the waist measures -more than the chest, and the long-drawn face of the businessman, at -memory of lost dollars, will make answer without need of words. Then -let be noted the physique of the blessed ones that attain to green old -age, and, in nine cases out of ten, spry old boys--no disparagement, -but all honor in the phrase--will be found to be modelled after the -type of octogenarian Bryant or nonogenarian Bancroft--the whitefaced, -wiry, and spare, as contrasted with the red-faced, the pursy, and the -stout. It is true, as has already been mentioned, that in old age -much of an adventitious obesity is absorbed and disappears, but the -Bryant-Bancroft type is that of a subject who never has been fat at -all. And just such is preëminently the type that rides easily past the -fourscore mark, reins well in hand, and good for many another lap in -the race of life.”[76] - - [76] Edward Curtis, M.D.: Nature and Health, p. 70. Henry Holt & - Company, New York, 1906. - -With these thoughts before us, we may consider briefly just what is -involved in these new dietary standards that aim to conform more -closely with actual body needs. Referring at first to proteid food, it -may be wise to again emphasize the fact that the weight of the body, -_i. e._, the weight of the proteid-containing tissues, as contrasted -with excessive fat accumulation, is one of the important factors not to -be overlooked when determining the dietary needs of a given individual. -As must be perfectly clear, from all that has been said, the man of -170 pounds’ body-weight has more proteid tissue to nourish than the -man of 130 pounds’ weight, and consequently what will satisfy the -requirements of the latter individual will not suffice for the former. -We must understand distinctly that no general statement can be made -applicable to mankind at large, but due consideration must be given to -the size and weight of the individual structure. We have found that -the average need for proteid food by adults is fully met by a daily -metabolism equal to an exchange of 0.12 gram of nitrogen per kilogram -of body-weight. This means a katabolism of three-fourths of a gram of -proteid matter daily, per kilogram. - -Remembering, however, that the intake of proteid food must be somewhat -in excess of the actual proteid katabolism, since not all of the -proteid of the food is available, and as this is a variable amount -depending upon the proportion of animal and vegetable foods with their -different degrees of digestibility and availability, we may place the -required intake of proteid at 0.85 gram per kilogram of body-weight, -still keeping to maximum figures for safety’s sake. Hence, for a man -weighing 70 kilograms or 154 pounds, there would be required daily -59.5 grams--say 60 grams--of proteid food to meet the needs of the -body. These are perfectly trustworthy figures, with a reasonable margin -of safety, and carrying perfect assurance of being really more than -sufficient to meet the true wants of the body; adequate to supply all -physiological demands for reserve proteid, and able to cope with the -erratic requirements of personal idiosyncrasies. It will be observed -that such an intake of proteid food daily is equal to one-half the Voit -standard for a man of this weight, while it is still further below the -Atwater standard and far below the common practices of the majority of -mankind in Europe and America, as indicated by the published dietary -studies. - -It may not be out of place to state at this point that in the writer’s -opinion the use of the terms “standard diet” and “dietary standards,” -etc., is objectionable, since such usage seems to demand a certain -degree of definiteness in the daily diet for which there is no -justification. As in the use of the term “normal diet,” there is danger -of misinterpretation, and of the assumption that dietary habits should -be regulated strictly in accord with certain set principles. This I -believe to be altogether wrong; there should be, on the contrary, -full latitude for individual freedom, but freedom governed by an -intelligence that appreciates the significance of scientific fact -and is willing to mould custom and habit into accord with them. What -is needed to-day is not so much an acceptance of the view that man -requires daily 0.85 gram of proteid per kilogram of body-weight, as a -full appreciation of the general principle, which our definite figures -have helped to work out, that the requirements of the body for proteid -food are far below the customary habits of mankind, and that there is -both economy and gain in various directions to be derived by following -the general precepts which this view leads to. In other words, there -is no advantage, but, on the contrary, much bother and worriment, in -attempting to follow out in practice the details of our more or less -exact physiological experiments. - -The general teaching which they afford, however, can be adopted and -put in practice in our daily lives, without striving to follow too -closely the so-called standards which our experiments have led to. -Again, the sample dietaries adopted in our experiments have no special -virtue, aside from the general principle they teach that simple foods -are quite adequate for the nourishment of the body, and that the amount -of nitrogen or proteid they contain was sufficient to meet the demands -of the particular individuals consuming it. Broadening intelligence on -matters of food composition is called for on all sides, and as this -is acquired together with due appreciation of the relative nutritive -values of proteid, fat, and carbohydrate, there is placed at our -command the power of intelligent discrimination, with the ability -to apply the principles set forth in our own way, in harmony with -personal likes and dislikes. - -To the majority of us, not very familiar with the percentage -composition of ordinary food materials, and unaccustomed to the -weighing of food in grams, the figures given from time to time may -have failed to convey a very definite impression regarding the actual -amounts of the various foods made use of. Further, our ideas concerning -the bulk of many of the common articles of food necessary to furnish -the 60 grams of proteid required daily by a man of 70 kilograms -body-weight may be somewhat hazy. The following table, however, will be -of service in this direction: - - -SIXTY GRAMS OF PROTEID ARE CONTAINED IN - - Fuel Value[77] - One-half pound fresh lean beef, loin 308 calories - Nine hens’ eggs 720 - Four-fifths pound sweetbread 660 - Three-fourths pound fresh liver 432 - Seven-eighths pound lean smoked bacon 1820 - Three-fourths pound halibut steak 423 - One-half pound salt codfish, boneless 245 - Two-and one-fifth pounds oysters, solid 506 - One-half pound American pale cheese 1027 - Four pounds whole milk (two quarts) 1300 - Five-sixths pound uncooked oatmeal 1550 - One and one-fourth pounds shredded wheat 2125 - One pound uncooked macaroni 1665 - One and one-third pounds white wheat bread 1520 - One and one-fourth pounds crackers 2381 - One and two-thirds pounds flaked rice 2807 - Three-fifths pound dried beans 963 - One and seven-eighths pounds baked beans 1125 - One-half pound dried peas 827 - One and eleven-twelfths pounds potato chips 5128 - Two-thirds pound almonds 2020 - Two-fifths pound pine nuts, pignolias 1138 - One and two-fifths pounds peanuts 3584 - Ten pounds bananas, edible portion 4600 - Ten pounds grapes 4500 - Eleven pounds lettuce 990 - Fifteen pounds prunes 5550 - Thirty-three pounds apples 9570 - - [77] Fuel value of the quantity needed to furnish the sixty grams of - proteid. - -The figures in this table are instructive in many ways. First, it is -to be noted that the daily proteid requirement of sixty grams can -be obtained from one-half pound of lean meat (uncooked), of which -the loin steak is a type. Subject to some variations in content of -water, an equivalent weight of lean flesh of any variety, lamb, veal, -poultry, etc., will furnish approximately the same amount of proteid. -With fish, such as halibut steak, and with liver, three-quarters of a -pound are required; while with sweetbreads, four-fifths of a pound are -needed to furnish the requisite amount of proteid. Of salt codfish, -one-half pound will provide the same amount of proteid as an equivalent -weight of fresh beef; while with lean smoked bacon the amount rises -to seven-eighths of a pound. Among the vegetable products, it is to -be observed that dried peas and beans, almonds and pine nuts, are as -rich in proteid as the above-mentioned animal foods, essentially the -same weights being called for to provide the daily requirement of -proteid. The same is true of cheese, the variety designated having such -a composition that one-half pound is the equivalent, so far as the -content of proteid is concerned, of a like amount of fresh beef. We -must not be unmindful of the fact previously mentioned, however, that -there are differences in digestibility among these various foodstuffs -which tend to lower somewhat the availability of the vegetable -products, also of the cheese, thereby necessitating a slight increase -in the amount of these foods required to equal the value to the body of -lean meat. - -Secondly, passing to the other extreme in our list, we find indicated -types of foods exceedingly poor in proteid, such as the fruits; -notably, bananas, grapes, prunes, apples, etc., also lettuce, and in -less degree potatoes. These are the kinds of food that may legitimately -attract by their palatability, but do not add materially to our intake -of proteid even when consumed in relatively large amounts. Thirdly, we -see clearly indicated a radical difference between the animal foods -and those of vegetable origin, in that with the former the fuel value -of the quantity necessary to furnish the sixty grams of proteid is -very small, as compared with a like amount of the average vegetable -product. One-half pound of lean meat, for example, with its 60 grams of -proteid, has a fuel value of only 308 calories, while two-thirds of a -pound of almonds has a fuel value of 2020 calories, and one-half pound -of dried peas 827 calories. Naturally, this is mainly a question of -the proportion of fat or oil present. With fat meat, as in bacon, the -calorific value rises in proportion to increase in the amount of fat, -the proteid decreasing in greater or less measure. - -The main point to be emphasized in this connection, however, is that a -high proteid animal food, like lean meat, eggs, fish, etc., obviously -cannot alone serve as an advantageous food for man. We see at once the -philosophy of a mixed diet. Let us assume that our average man of 70 -kilograms body-weight needs daily 2800 calories. On this assumption, -if he were to depend entirely upon lean beef for his sustenance, he -would require daily four and a half pounds of such meat, which amount -would furnish nine times the quantity of proteid needed by his system. -The same would be more or less true of other kindred animal products. -On the other hand, certain vegetable foods on our list, such as flaked -rice, crackers, and shredded wheat, contain proteid, with carbohydrate -and fat, in such proportion that the energy requirement would be met -essentially by the same quantity as served to furnish the necessary -proteid. Passing to the other extreme among the vegetable products, as -in potatoes and bananas, for example, we find fuel value predominating -largely over proteid content. The ideal diet, however, is found in a -judicious admixture of foodstuffs of both animal and vegetable origin. -Wheat bread, reinforced by a little butter or fat bacon to add to its -calorific value, shredded wheat with rich cream, crackers with cheese, -bread and milk, eggs with bacon, meat with potatoes, etc.; the common, -every-day household admixtures, provide combinations which can easily -be made to accord with true physiological requirements. The same may be -equally true of the more complicated dishes evolved by the high art of -modern cookery. - -Lastly, our table throws light upon certain questions of household -economy. The cost of foods is regulated mainly not by the value of the -nutrients contained therein, but by other factors of quite a different -nature. Relationship between supply and demand naturally counts here -as in other directions, but our demand is liable to be based not upon -food values, but rather upon delicacy of flavor, palatability, and -other kindred fancies, some real and some imaginary. Ordinary crackers -can be purchased for ten cents a pound, but if we desire a little -stronger flavor of salt and a special box to hold them, we pay eighteen -cents a pound. Rolled very thin and thus made more delicate, they cost -twenty-five cents, while sold under a special name and perhaps tied -with a blue ribbon they cost thirty-five cents a pound. Their nutritive -value per pound is the same in all cases, but we pay something for -the increased labor of preparation and a good deal for the added -attractiveness to eye and palate. We pay twenty-two cents a pound for -round steak, thirty-two cents for loin steak, and seventy-five cents a -pound for sweetbreads, the high price of the latter being regulated by -the relative scarcity of the article and not by its food value. As our -table indicates, the real value of sweetbread as a source of proteid -is only a little more than half that of lean beef. Its fuel value, -however, is somewhat more than that of beef, but a little fat added -to the latter will more than compensate and at a trifling cost. When -we can afford it, we pay the increased price for sweetbreads simply -because their delicacy and flavor are attractive to us. We should -not do it under the mistaken idea that we are indulging in a highly -nutritive article of food, for as a matter of fact it is not only less -nutritive than a corresponding weight of lean beef, but in addition -it possesses certain qualities, in its high purin-content, that are a -menace to good health if indulged in too freely. - -Where expense must be carefully guarded, or where the condition of the -family purse is such that conflicting demands must be intelligently -considered in order to insure wise expenditure and the greatest -permanent good of the many, it is well to remember that price is no -guarantee whatever of real nutritive value. Two quarts of milk will -furnish half the daily fuel requirement of our average man and the -entire proteid requirement, while its cost is only sixteen cents. -Reinforced by a pound loaf of wheat bread, the energy requirement for -the day would be fully met, with surplus nitrogen to store up for -future needs, and at an additional cost of only ten cents. A mixture in -this proportion, however, would not be strictly physiological, since -it is wasteful of proteid, but it may serve to illustrate the point. -A better illustration is found in an admixture, quite adequate to -supply the daily needs of our average man, both for proteid and energy, -composed of one-quarter of a pound of lean beef, two-thirds of a pound -of bread, and half a pound of butter, and at a total cost not to exceed -thirty cents. The contrast of such prices with what is so commonly -paid for table delicacies is somewhat striking; it could be made still -more so by drawing upon many common vegetable foods, rich alike in -proteid and in fuel value, the cost of which is even less than the -simple food mixtures just referred to. It is not necessary, however, to -enlarge upon this question; it is sufficient to merely emphasize the -fact that the exaggerated demand of our present generation for dietetic -luxuries is leading us far away from the proverbially simple life of -our forefathers, and without adding in any way to the effectiveness of -the daily diet. On the contrary, it is in part responsible for the high -proteid consumption of the present day, with its attendant evils, and -involves a large and unnecessary expenditure without adequate return. -The wants of the body for food are far more advantageously met by a -simple dietary, moderate in amount and at an expense comparatively -slight. - -A recent writer,[78] in the “British Medical Journal,” a practitioner -of medicine in the Highlands of Scotland, has said that these are -“facts of common experience in the Highlands of Scotland, and probably -among the peasantry of other countries also, where the old beliefs and -customs have not too readily given way to the luxuries of civilization. -Oatmeal in one form or another is a daily ingredient in the diet of a -Highland peasant. The potato also is a staple food, and is consumed in -large quantities with salt herring or other fish, and perhaps in some -cases salt mutton or pork. Milk and eggs are used by most. The growing -consumption of tea, however, and the increasing relish for sweets, -candy, pastry, and biscuits, threaten to destroy the old way of living. -A typical day’s diet for a crofter or fisherman who still believes in -the traditional diet would be somewhat like this: - - Breakfast.--Oatmeal porridge or brose with milk; bread, butter, and tea. - Dinner.--Potatoes galore and herrings, or other salt fish. - Supper.--Porridge and milk, or oat bread and cheese, and tea. - - [78] Aran Coirce: British Medical Journal, April 7, 1906, p. 829. - -“I have often been assured by shepherds that they could work all -day ‘on the hill’ after a breakfast of oatmeal brose and milk, -without fatigue and without feeling hungry, returning in the evening -to partake of a dish of broth, potatoes, and salt mutton. In these -diets, proteid forms a very small proportion, and yet a hardier race -than these shepherds and fishermen cannot be found.” It should be -added that “brose” consists of a few handfuls of oatmeal, to which -is added boiling water, the mixture being stirred vigorously and -placed for a few minutes near the fire. It is then eaten with milk, or -better, with cream. In the absence of positive data, it can only be -asserted that the above dietary stands for simplicity and frugality. -Its proteid-content may be low, but the amount of proteid taken per -day by these Highlanders will obviously depend upon the _quantity_ -of food consumed. Oatmeal is fairly rich in proteid, and it is quite -conceivable that the amount eaten daily may be such as to result in a -high proteid exchange. - -It will be profitable for us to gain, if possible, a fairly clear idea -of the quantities of food requisite for our average man of 70 kilograms -body-weight; _i. e._, the amounts necessary to provide 60 grams of -proteid and 2800 calories. With this end in view, we may outline a -simple dietary, expressed in terms that will convey a clear impression, -showing what may be eaten without overstepping the required limits of -proteid or total calories: - - -BREAKFAST - - Proteid Calories - One shredded wheat biscuit 3.15 grams 106 - 30 grams - One teacup of cream 3.12 206 - 120 grams - One German water roll 5.07 165 - 57 grams - Two one-inch cubes of butter 0.38 284 - 38 grams - Three-fourths cup of coffee 0.26 ... - 100 grams - One-fourth teacup of cream 0.78 51 - 30 grams - One lump of sugar ... 88 - 10 grams ----- --- - 12.76 850 - - -LUNCH - - Proteid Calories - One teacup homemade chicken soup 5.25 grams 60 - 144 grams - One Parker-house roll 3.38 110 - 38 grams - Two one-inch cubes of butter 0.38 284 - 38 grams - One slice lean bacon 2.14 65 - 10 grams - One small baked potato 1.53 55 - 2 ounces, 60 grams - One rice croquette 3.42 150 - 90 grams - Two ounces maple syrup ... 166 - 60 grams - One cup of tea with one slice lemon ... .. - One lump of sugar ... 38 - 10 grams ----- --- - 16.10 928 - - -DINNER - - Proteid Calories - One teacup cream of corn soup 3.25 72 - 130 grams - One Parker-house roll 3.38 110 - 38 grams - One-inch cube of butter 0.19 142 - 19 grams - One small lamb chop, broiled 8.51 92 - lean meat, 30 grams - One teacup of mashed potato 3.34 175 - 167 grams - Apple-celery lettuce salad with mayonnaise dressing 0.62 75 - 50 grams - One Boston cracker, split 1.32 47 - 2 inches diameter, 12 grams - One-half inch cube American cheese 3.35 50 - 12 grams - One-half teacup of bread pudding 5.25 150 - 85 grams - One demi-tasse coffee ... .. - One lump of sugar ... 38 - 10 grams ----- --- - 29.21 951 - -The grand totals for the day, with this dietary, amount to 58.07 grams -of proteid and 2729 calories. It is of course understood that these -figures are to be considered as only approximately correct, but the -illustration will suffice, perhaps, to give a clearer understanding of -the actual quantities of food involved in a daily ration approaching -the requirements for a man of 70 kilograms body-weight. Further, there -may be suggested by the figures given for proteid and fuel value of -the different quantities of foods, a clearer conception of how much -given dietary articles count for in swelling the total values of a -day’s intake. Moreover, it is easy to see how the diet can be added to -or modified in a given direction. If a little more proteid is desired -without changing materially the fuel value of the food a boiled egg can -be added to the breakfast, for example. An average-sized egg (of 53 -grams) contains 6.9 grams of proteid, while it will increase the fuel -value of the food by only 80 calories. Or, if more vegetable proteid is -wished for, a soup of split-peas can be introduced, without changing -in any degree the calorific value of the diet. Thus, one teacup of -split-pea soup (144 grams) contains 8.64 grams of proteid, while the -fuel value of this quantity may be only 94 calories. The addition of -one banana (160 grams) will increase fuel value 153 calories, but will -add only 2.28 grams of proteid. If it is desired to increase fuel -value without change in the proteid-content of the food, recourse can -always be had to butter, fat of meat, additional oil in salads, or to -syrup and sugar. - -Such a menu as is roughly outlined, however, has perhaps special value -in emphasizing how largely the proteid intake is increased by foods -other than meats, and which are not conspicuously rich in proteid -matter. All wheat products, for example, while abounding in starch, -still show a large proportion of proteid. Thus, shredded wheat biscuit -(1 ounce), which is a type of many kindred wheat preparations, from -bread and biscuit to the various so-called breakfast foods, yields -about 3 grams of proteid per ounce and approximately 100 calories. -Even potato, which is conspicuously a carbohydrate food owing to its -large content of starch, yields of nitrogen the equivalent of at least -three-fourths of a gram of proteid per ounce. If larger volume is -desired without much increase in real food value, there are always -available green foods, such as lettuce, celery, greens of various -sorts, fruits, such as apples, grapes, oranges, etc. Too great reliance -on meats as a type of concentrated food, on the other hand, augments -largely the intake of proteid, and adds a relatively small amount to -the fuel value of the day’s ration. - -An ingenious method of indicating food values, which promises to -be of service in sanatoria and under other conditions where it is -desirable to record or correct the diet of a large number of persons, -has been devised recently by Professor Fisher.[79] The method aims to -save labor, and is likewise designed to visualize the magnitude and -proportions of the diet. The food is measured by calories instead of -by weight, a “standard portion” of 100 large calories being the unit -made use of. In carrying out the method, foods are served at table in -“standard portions,” or multiples thereof. In the words of Fisher, the -amount of milk served, for example, “instead of being a whole number of -ounces, should be 4.9 ounces--the amount that contains 100 calories. -This ‘standard portion’ constitutes about two-thirds of an ordinary -glass of milk. Of the 100 calories which it contains 19 will be in the -form of proteid, 52 in fat, and 29 in carbohydrate.” In the carrying -out of this plan, it is evident that the weight of any food yielding -100 calories becomes a measure of the degree of concentration. From -the standpoint of fuel value, olive oil is probably one of the most -concentrated of foods, approximately one-third of an ounce containing -100 calories. The following table, taken from Fisher’s description -of his method, will serve to show the amounts of several foods -constituting a “standard portion,” and also the number of calories in -the form of proteid, fat, and carbohydrate: - - [79] Irving Fisher: A new method for indicating food values. American - Journal of Physiology, vol. 15, p. 417, 1906. - - +-----------------------+-------------+--------+--------+--------+--------+ - | Name of Food | Weight | | | | | - | and “Portion” | containing |Proteid.| Fat. | Carbo- | Total. | - | roughly estimated. |100 Calories.| | |hydrate.| | - +-----------------------+------+------+--------+--------+--------+--------+ - | |ounces|grams |calories|calories|calories|calories| - |Almonds, a dozen | 0.53 | 15 | 13.0 | 77.0 | 10 | 100 | - |Bananas, one large | 3.50 | 98 | 5.0 | 5.0 | 90 | 100 | - |Bread, a large slice | 1.30 | 37 | 13.0 | 6.0 | 81 | 100 | - |Butter, an ordinary pat| 0.44 | 13 | 0.5 | 99.5 | .. | 100 | - |Eggs, one large | 2.10 | 60 | 32.0 | 68.0 | .. | 100 | - |Oysters, a dozen | 6.80 | 190 | 49.0 | 22.0 | 29 | 100 | - |Potatoes, one | 3.60 | 100 | 10.0 | 1.0 | 89 | 100 | - |Whole milk, | | | | | | | - | two-thirds glass | 4.90 | 140 | 19.0 | 52.0 | 29 | 100 | - |Beef sirloin, | | | | | | | - | a small piece | 1.40 | 40 | 31.0 | 69.0 | .. | 100 | - |Sugar, five teaspoons | 0.86 | 24 | .... | .... | 100 | 100 | - +-----------------------+------+------+--------+--------+--------+--------+ - -Obviously, to make use of the “calories per cent” method a table such -as the above, covering all common foodstuffs and showing the weight of -each food constituting a standard portion, together with the calories -of proteid, fat, and carbohydrate in this portion, is necessary. The -chief advantage of the method, however, is that it lends itself readily -to geometrical representation and affords an easy means of determining -the constituents of combinations of different foods by use of a simple -mechanism, for a description of which reference must be made to the -original paper. - -Any attempt to follow a daily routine which accords with the true -needs of the body leads necessarily toward foods derived from the -plant kingdom, with the adoption of simple dietary habits, and with -greater freedom from the exciting influence of the richer animal -foods. There is, however, virtue in a simple dietary that appeals and -satisfies, and in so doing testifies to the completeness with which -it meets the physiological requirements of the body. A physician,[80] -writing in the “British Medical Journal,” says: “I determined to give -the minimum-of-proteid diet a fair trial in my own case. The result -was that I was relieved of a life-long tendency to acid dyspepsia and -occasional sick headache; my fitness for work, my appetite and relish -for food, were increased, without any diminution, but rather a slight -increase, in my weight. My practice extends over a wide area of rough -mountainous country involving long journeys on cycle, on foot, driving, -and in open boats, in fair and foul weather. The muscular exertion -and endurance necessary for the work would seem to require a large -proportion of proteid and a generous diet altogether, but since I began -to experiment I have suffered less than formerly from fatigue, and seem -to eat in all a smaller quantity of food. My diet consists of: - - [80] Aran Coirce: British Medical Journal, April 7, 1906, p. 829. - - Breakfast, 8.30 A.M.--Oatmeal cakes, bread and butter, about 1 cubic - inch of cheese or bloater paste, marmalade, and one breakfast cup of - tea. - - Lunch, 1.30 P.M.--Same as breakfast, with occasionally a boiled egg, - and sometimes coffee instead of tea. - - Dinner, 7 P.M.--Thick soup containing vegetables, with bread, - followed by suet pudding or fruit tart; or vegetable stew, containing - 2 or 3 ounces of meat, with boiled potatoes, followed by milk pudding - and jam, and occasionally a cup of black coffee.” - -This statement of personal experience is in close accord with -statements that have come to the writer in hundreds of letters during -the past two or three years, from persons who have for some reason -chosen to follow a more abstemious mode of life. Such testimony has a -certain measure of value in that it offers corroborative evidence of -the beneficial effects of a moderate diet, more closely in accord with -the actual demands of the body for food. It does not, however, carry -quite that degree of assurance that scientific evidence, gathered by -careful observers and controlled by weights and measures that hold the -imagination in check, affords; and so we may turn to a different type -of testimony, presented in an elaborate research by Dr. Neumann,[81] -of the Hygienic Institute at Kiel, an experiment on himself extending -through a total of 746 days. - - [81] Dr. med. et phil. R. O. Neumann: Experimentelle Beiträge zur - Lehre von dem täglichen Nahrungsbedarf des Menschen unter besonderer - Berücksichtigung der notwendigen Eiweissmenge. Archiv für Hygiene, - Band 45, p. 1, 1902. - -The experiment was divided into three periods. In the first period of -ten months the subject, with a body-weight of 66.5 kilograms, consumed -daily on an average the amounts of food indicated in the following -table. In this same table are also included the daily values, based on -the preceding data, for a body-weight of 70 kilograms. Thirdly, the -table likewise shows the amounts of utilizable food contained in the -foodstuffs actually eaten, on the basis of 70 kilos body-weight. - - -AVERAGE DAILY FOOD FOR TEN MONTHS - - +------------+-----------------+----------------+-----------------+ - | |Actually consumed|Calculated for a| Utilizable Food | - | | by the Subject, | Body-weight of |for a Body-weight| - | | 66.5 Kilos | 70 Kilos | of 70 Kilos | - +------------+-----------------+----------------+-----------------+ - |Proteid | 66.1 grams | 69.1 grams | 57.3 grams | - |Fat | 83.5 | 90.2 | 81.2 | - |Carbohydrate| 230.0 | 242.0 | 225.0 | - |Alcohol | 43.7 | 45.6 | 41.0 | - |Fuel value | 2309 calories | 2427 calories | 2199 calories | - +------------+-----------------+----------------+-----------------+ - -During this period of ten months, the body-weight of the subject -remained practically constant, or indeed showed a slight gain up to 67 -kilograms. All the functions of the body, and the general condition -of good health, were in no wise impaired; so that in the words of the -subject, the amount of food eaten must have been sufficient for the -needs of the body. Somewhat striking is the fact that of the 2309 -calories in the daily food, more than one-fourth was derived from the -beer consumed daily (1200 c.c.). Also noticeable is the relatively -small amount of carbohydrate taken daily, only about one-half the -quantity designated by Voit as the average requirement of German -laborers. Finally, it is to be observed that during this period of -ten months, the daily consumption of food as calculated for a man of -70 kilograms body-weight, based on the actual food consumption of the -subject with a weight of 66.5 kilos, was not widely different from our -own statement of 60 grams of proteid and 2800 calories. The tendency, -however, in Dr. Neumann’s experiment was toward lower fuel values and -somewhat higher proteid consumption. - -In a second period of 50 days, with a slightly larger daily intake, -Dr. Neumann observed that his body was laying by nitrogen, _i. e._, -storing up proteid on a daily diet of 76.5 grams of proteid and with -sufficient fat and carbohydrate to furnish a total fuel value of 2658 -calories. In the final period of 8 months, the following data were -obtained: - - -AVERAGE DAILY FOOD FOR EIGHT MONTHS - - +------------+-----------------+----------------+-----------------+ - | |Actually consumed|Calculated for a| Utilizable Food | - | | by the Subject, | Body-Weight of |for a Body-Weight| - | | 71.5 Kilos. | 70 Kilos. | of 70 Kilos. | - +------------+-----------------+----------------+-----------------+ - |Proteid | 76.2 grams | 74.0 grams | 61.4 grams | - |Fat | 109.0 | 106.1 | 95.5 | - |Carbohydrate| 168.9 | 164.2 | 152.7 | - |Alcohol | 5.5 | 5.3 | 4.7 | - |Fuel value | 2057 calories | 1999 calories | 1766 calories | - +------------+-----------------+----------------+-----------------+ - -During this period, it is to be noted that the fuel value of the -day’s food averaged only 2057 calories, which for a body-weight of -70 kilograms would amount to less than 2000 calories. The proteid -consumption, however, was larger than we have found to be necessary -for a man of the above weight. Still, the facts are in harmony with -the general principle that there is no necessity for a daily intake -of food such as common usage dictates, there being obviously a wide -difference between a minimal daily consumption of 118 grams of proteid -and 3000 or more calories, such as is assumed to be needed by a man of -70 kilos, and 74 grams of proteid with 1999 calories. Under the latter -conditions, the subject gained a kilogram in weight during the eight -months, while the establishment of nitrogen equilibrium testifies to -the now generally accepted view that it is quite possible for the body -to establish nitrogen equilibrium at different levels, _i. e._, with -different quantities of proteid food and different fuel values. - -The diet made use of by Neumann was a mixed one, containing a great -variety of animal and vegetable foods, but withal simple and moderate -in quantity. Calculated per kilogram of body-weight, the average -consumption of food material per day during the three periods was as -indicated in the following table: - - -DAILY FOOD CONSUMPTION PER KILOGRAM OF WEIGHT - - +-------------+--------+-----+-------------+--------+--------+ - | |Proteid.| Fat.|Carbohydrate.|Alcohol.|Calories| - +-------------+--------+-----+-------------+--------+--------+ - | | grams |grams| grams | grams | | - |First Period | 0.99 | 1.3 | 34.5 | 0.56 | 34.7 | - |Second Period| 1.10 | 2.3 | 33.4 | . . | 59.7 | - |Third Period | 1.00 | 1.5 | 23.4 | 0.07 | 28.5 | - +-------------+--------+-----+-------------+--------+--------+ - -The average of daily food consumption for the total of 746 days was as -follows: 74.2 grams proteid, 117 grams fat, 213 grams carbohydrate, and -2367 calories. On such a diet, during this long period, equilibrium was -satisfactorily maintained, thereby furnishing additional evidence that -quantities of food way below the so-called normal amounts are quite -adequate to meet the needs of the body. There is no conflict whatever -between these results and our own; they both point in the same general -direction. Perhaps the one thing that needs to be again emphasized, -however, in view of the low fuel values used by Neumann, is that while -they proved quite adequate in his case, the demand in this direction is -governed largely by the degree of bodily activity. In fact, Neumann’s -results with fuel values are in perfect harmony with the data obtained -by us with professional men, but the writer is inclined to believe that -for the majority of mankind, with the varying degrees of activity and -muscular exertion called for, a somewhat larger number of heat units is -desirable, and indeed on many occasions demanded. - -Still, it is perfectly obvious that custom has greatly exaggerated -the fuel values required in ordinary muscular work, and such results -as are here presented tend to emphasize the true relationship between -actual requirements and fuel intake. Further, it must not be overlooked -that the rate of proteid katabolism is governed in large measure by the -amount of non-nitrogenous food, and consequently a too narrow margin in -the consumption of the latter will obviously result in a higher rate -of proteid exchange. We are inclined to the belief that a satisfactory -degree of bodily efficiency is more liable to be maintained with a -somewhat larger consumption of carbohydrate food, combined with a -reduction in proteid food to a level nearer our own figures. It will -be observed that the average amount of carbohydrate taken daily by -Neumann, during the 746 days, was only 213 grams, while the daily -consumption of fat averaged 117 grams. These figures are interesting -and instructive in many ways, especially as indicating the ease with -which the body accommodates itself to a relatively low intake of -proteid food, combined with a small proportion of starches and sugars. -This relationship between carbohydrate and fat might well occur at -times as a natural result of personal taste, but as a general rule it -is probably better, from the standpoint of digestibility and general -availability, for the daily food to contain a larger proportion of -carbohydrate. - -Under this head, I would lay special stress upon the value to the -body of the natural sugars as well as of starch. We are inclined to -deprecate the widespread use of candy, especially among children, and -there is no doubt that the too lavish use of sugar in such concentrated -form does at times do harm; but when eaten as an integral part of the -many available fruits its use cannot be too highly lauded, for both -young and old. Oranges, grapes, prunes, dates, plums, and bananas are -especially to be commended, and in lesser degree peaches, apricots, -pears, apples, figs, strawberries, raspberries, and blueberries. In -all of these fruits, it is the sugar especially that gives food value -to the article, while the mild acids and other extractives, together -with the water of the fruit, help in other ways in the maintenance -of good health. Where personal taste and inclination are favorably -disposed, the first six fruits named can be partaken of freely, and the -diet of the young, especially, can be advantageously modified by the -liberal use of such articles of food. - -Of the other fruits, apples when thoroughly ripe are above reproach -if properly masticated, but the raw fruit is somewhat indigestible -when swallowed in too large pieces, and may cause trouble to a -delicate stomach. A baked apple, on the other hand, is both savory and -wholesome, and if served with sugar and cream, for example, constitutes -a most healthful and satisfying article of food. Peaches, apricots, -and strawberries as ripe fruits are likewise exceedingly valuable, but -here personal idiosyncrasy frequently comes to the fore, especially -with strawberries, and prohibits their free use. The peculiar acidity -of these latter fruits is occasionally a source of trouble, which -leads to their avoidance; but this is far less liable to happen with -people living on a low proteid diet with its greater freedom from purin -derivatives, or uric acid antecedents. Further, there is a tendency -on the part of some individuals to suffer from acid fermentation with -too liberal use of starches and sugar, but as a rule the advantages -of ordinary starchy and natural sugar-containing foods cannot be -overestimated. It is certainly wise to give them a conspicuous place in -the daily dietary and to encourage their use, especially by children. - -As has been stated in several connections, a diet which conforms to the -true nutritive requirements of the body must necessarily lead toward -vegetable foods. In no other satisfactory way can excess of proteid be -avoided, and at the same time the proper calorific value be obtained. -This, however, does not mean vegetarianism, but simply a greater -reliance upon foods from the plant kingdom, with a corresponding -diminution in the typical animal foods. This raises the question of the -possible relation of diet to the bacterial processes of the intestine, -knowing, as we do, that the latter are of primary importance in the -causation of certain forms of auto-intoxication, etc. Recent studies -have indicated that the bacterial flora of carnivorous animals is -quite different from that of herbivorous animals, and this being so, -it is easy to see how a predominance of vegetable or animal food may -modify the bacterial conditions of the intestinal tract in man. Dr. -Herter[82] has reported the presence in the intestines of cats, dogs, -tigers, lion, and wolf of many spore-holding bacilli, as well as free -spores and vegetative forms of anærobic organisms; some of which at -least are decidedly pathogenic when injected into the subcutaneous -connective tissue, leading to serious and even fatal results within -twenty-four hours. With herbivorous animals, on the other hand, such as -the buffalo, goat, horse, elephant, etc., the predominating organisms -are of a different order from those found in the intestines of the -carnivora; proving practically non-pathogenic, or only slightly so, -when injected subcutaneously, and less disposed to produce putrefactive -changes or other chemical decompositions. - - [82] C. A. Herter: Character of the Bacterial Flora of Carnivorous - and Herbivorous Animals. Science, December 28, 1906, p. 859. - -In the words of Dr. Herter, “These differences in the appearance -and behavior of the bacteria derived from typical carnivora and -herbivora suggest that the habit of living upon a diet consisting -exclusively of raw meat entails differences in the types of bacteria -that characterize the contents of the large intestine. The occurrence -of considerable numbers of spore-bearing organisms in the carnivora -points to the presence of anærobic putrefactive forms in great -numbers. The results of subcutaneous inoculations into guinea-pigs -bear out this view and indicate that the numbers of organisms capable -of producing a hemorrhagic œdema with tissue necrosis, with or without -gas-production, are very considerable.... The observations recorded are -of much interest in relation to the bacterial processes and nutrition -of herbivorous as distinguished from carnivorous animals, and are -significant furthermore for the interpretation of bacterial conditions -found in man. The question arises whether the abundant use of meat over -a long period of time may not favor the development of much larger -numbers of spore-bearing putrefactive anærobes in the intestinal tract -than would be the case were a different type of proteid substituted for -meat.” While it may be said truly that observations of this character -are as yet not sufficiently numerous or conclusive to warrant positive -or sweeping statements, yet there is a suggestion here well worthy of -thoughtful consideration in its general bearing on the nutrition of -mankind. - -Simplicity in diet, with or without complete abstinence from meat, -is often resorted to as a means of relief from bodily ailments, and -such cases sometimes afford striking illustrations of the adequacy -and benefits of a relatively low intake of food. Cases of this sort, -perhaps, are more frequently observed among elderly people, where the -daily requirements are not so great as with younger and more active -persons, but they offer evidence in support of our main thesis that -dietary habits are no guarantee of bodily requirements. I have in mind -the details of an exceedingly interesting case reported with much care -by Dr. Fenger;[83] the case of a man who at 61 years of age, after a -long period of poor health, brought himself quickly into a condition of -sound health by a daily diet characterized by extreme simplicity and -with an exceedingly low fuel value. The daily diet made use of during -the fifteen years the subject was under examination consisted of the -following articles: - - [83] Dr. S. Fenger: Beiträge zur Kenntniss des Stoffwechsels im - Greisenalter. Skandinavisches Archiv für Physiologie, Band 16, p. - 222, 1904. - - 1889–1892: 1 egg, 1 quart of oatmeal soup, 2 quarts of skim milk, - 1-1/2 ounces of red wine, 1/4 ounce of sugar. - - 1892–1894: 2 eggs, 1 quart of oatmeal soup, 2 quarts of skim milk, - 1-1/2 ounces of red wine, 1/4 ounce of sugar. - - 1894–1900: 3 eggs, 1 pint of oatmeal soup, 2 quarts of skim milk, - 1-1/2 ounces of red wine, 1/4 ounce of sugar, 2 ounces of plum and - raspberry juice. - - 1900–1903: 3 eggs, 1 pint of barley soup, 3 pints of sweet milk, 1 - pint of buttermilk, 1-1/2 ounces of red wine, 1/4 ounce of sugar, 2 - ounces of plum and raspberry juice. - -It will be observed that during these fifteen years the subject -partook of no meat whatever, and further, that the diet was wholly -in fluid form. At the close of this long period, the subject, being -then 75 years of age, was reported as well and in good health, with -satisfactory physical condition for a person of his years. He was a -man of small body-weight, only 42 kilograms, but during this period -of voluntary restriction in diet, he suffered no loss. It is perhaps -worthy of comment also that all through this lengthy period no salt -was taken other than what was naturally present in the simple foods -made use of. The point to attract our attention especially, however, is -that for fifteen years, during which the quality and quantity of this -man’s food was carefully observed, body-weight, general good health, -and physical vigor were all maintained, together with freedom from the -ills of previous years and with a daily diet characterized by extreme -simplicity. The chemical composition of the diet was likewise peculiar, -particularly in its exceedingly low fuel value. The following table -shows the amounts of proteid, fat, and carbohydrate consumed daily -during the four periods designated: - - +---------+--------+-----+--------+---------+---------+---------+ - | | | | Carbo- | |Calories | Proteid | - | Period. |Proteid.|Fat. |hydrate.|Calories.| per | per | - | | | | | |Kilogram.|Kilogram.| - +---------+--------+-----+--------+---------+---------+---------+ - | | grams |grams| grams | | | grams | - |1889–1892| 79.8 | 21.7| 152.0 | 1125 | 26 | 1.90 | - |1892–1894| 85.2 | 27.0| 152.0 | 1200 | 28 | 2.03 | - |1894–1900| 87.0 | 30.1| 150.1 | 1230 | 29 | 2.07 | - |1900–1903| 84.4 | 73.7| 148.3 | 1600 | 38 | 2.00 | - +---------+--------+-----+--------+---------+---------+---------+ - -Especially noticeable here is the low intake of fat and carbohydrate, -with the corresponding low fuel value, and also the relatively high -consumption of proteid, averaging 2.0 grams daily per kilogram of -body-weight. Dr. Fenger concludes that for a man of this age and -weight, with the relative inactivity characteristic of old age, a heat -value in the intake of 30 calories per kilogram of body-weight is quite -sufficient for the needs of the body. This may be quite true, but to -maintain nitrogen equilibrium under such conditions requires a larger -intake of proteid food than is desirable. It will be observed that in -the last period of four years a very decided change in the diet was -instituted; proteid was diminished somewhat, but the noticeable change -was the decided increase in fat, produced in large measure by the -substitution of whole milk, with its contained cream, for skim milk. In -the words of Dr. Fenger, this change was necessitated by the appearance -of gout in the subject. From superficial examination of the dietary of -the preceding eleven years there would seem no occasion for criticising -the subject for high living, and yet I believe we are quite within the -limits of reason in saying that the proteid exchange for a subject of -this body-weight was altogether too high. The heat requirements of the -body were being met in an unnecessarily large degree from the breaking -down of proteid material, with consequent formation of excessive -nitrogenous waste, among which uric acid was plainly conspicuous. - -One comment to be made here is that meat and other rich -purin-containing foodstuffs are not the only source of gout and uric -acid. Excessive proteid katabolism, both exogenous and endogenous, is -a possible source of danger in this respect, and the above subject, -though living on an exceptionally simple diet, was consuming far more -proteid per kilogram of body-weight than was necessary or desirable. -Increase of fatty food naturally served to diminish the rate of proteid -katabolism, and this could have been advantageously accompanied by -a still greater reduction in the amount of proteid ingested, and a -larger addition of non-nitrogenous foodstuffs. In old age, there is -naturally a slowing down of the metabolic processes, and both nitrogen -equilibrium and body equilibrium can be satisfactorily maintained by a -relatively small intake of food and with gain to the body; but there -is every reason to believe that economy in proteid food can be more -advantageously adopted than economy in non-nitrogenous foodstuffs. - -Finally, we may call attention to the many possibilities of an -intelligent modification of the daily diet to the temporary needs -of the individual. The season of the year, summer and winter, the -climate, the degree of activity of the body, the state of health, -temporary ailments, etc., all present special conditions which admit -of particular dietetic treatment. In hot summer weather, for example, -there is plainly less need for food than in the cold winter season, -especially for fat with its high calorific value. During the cold part -of the year, the lower temperature of the surrounding air, with the -tendency toward greater muscular activity, calls for more extensive -chemical decomposition in order to meet the demand for heat, and the -energy of muscular contraction. There is perhaps no special reason for -any material change in the amount of proteid food consumed in the two -seasons, except in so far as it may seem desirable at times to take -advantage of the well-known stimulating properties of proteid to whip -up the general metabolism of the body, in harmony with the principle -that all metabolic processes may need spurring to meet the demands of a -greatly lowered temperature in the surrounding air. - -Fuel value, however, should be increased somewhat during the winter -months in our climate. Fat promises the largest amount of energy, -but there is more of a tendency to store up excess of fat than of -carbohydrate, hence the latter foods have certain advantages as a -source of the additional energy needed during cold weather. In warm -weather, it should be our aim to diminish unnecessary heat production -as much as possible, though it must be remembered that the body is -to be maintained approximately at least in equilibrium, and this -calls for an adequate amount of food. Lighter foods, however, may be -advantageously employed, such as fruits, vegetables, fresh fish, etc. -Fats and fat meats especially are to be avoided, not only because -there is no specific need for them, but particularly on account of a -greater sensitiveness of the gastro-intestinal tract during the hot -seasons of the year, that is liable to result in a disturbance whenever -undue quantity of rich or heavy food is taken. Further, in hot summer -weather we may advantageously live more largely on foods served cold, -and thereby avoid the heat ordinarily introduced into the body by -hot fluids and solids. These, however, are all obvious physiological -truths, constituting a form of physiological good sense the application -of which calls for no special expert knowledge. - -Less obvious, though no less important, is the partial protection -that can be afforded to weakened or disabled kidneys by judgment and -discrimination in the matter of diet. In acute or chronic nephritis, -forms of so-called Bright’s disease, is there not danger of overtaxing -organs already weakened by placing upon them the daily duty of -excreting large amounts of solid nitrogenous waste, as well as of the -various inorganic salts which are so intimately associated with many of -the organic foodstuffs? The consumption of excessive and unnecessary -amounts of proteid food simply means the ultimate formation of just -so much more urea, uric acid, etc., which must be passed out through -the kidneys. In the words of Bunge, “There is no organ in our body so -mercilessly ill treated as the kidneys. The stomach reacts against -overloading. The kidneys are obliged to let everything pass through -them, and the harm done to them is not felt till it is too late to -avoid the evil consequences.” It would seem the part of wisdom, -therefore, to adjust the daily intake of proteid food to as low a -level as is consistent with the true needs of the body, in those cases -where the kidneys are at all enfeebled, or where it seems desirable to -exercise due precaution as a possible means of prevention. - -Equal care is frequently called for in connection with the mineral -matters which enter so largely into many natural foodstuffs, or which -are introduced as condiments. As an illustration, we may note one or -two peculiarities in the distribution of sodium and potassium salts -in the tissues of the body. Potassium is an indispensable constituent -of every living cell, and the latter has the power of absorbing and -holding on to such amounts of this particular element as may be -necessary for the functional activity of the tissue of which it is a -part. Sodium, on the other hand, stands in a different relationship -to living structures. It is widely distributed, but in the higher -animals, as in man, sodium salts are most abundant in the fluids of -the body, notably in the plasma of the blood. Herbivorous animals have -a strong liking for sodium chloride or common salt, but this is not -true of carnivorous animals; indeed, the latter animals have a great -dislike for salty articles of food. Vegetable products are all rich in -potassium salts, whereas ordinary animal foods, such as meat, eggs, -milk, and blood, are relatively poor in this element. - -It is claimed that the abundance of potassium salts in vegetable foods -is the cause of the apparent need for sodium chloride by herbivorous -animals, and in lesser degree by man. This is explained by supposing -that when the salts of potassium reach the blood by absorption of the -vegetable foods, an interchange takes place with the sodium chloride -of the blood plasma. “Chloride of potassium and the sodium salt of the -acid which was combined with the potassium are formed. Instead of the -chloride of sodium, therefore, the blood now contains another sodium -salt, which did not form part of the normal composition of the blood, -or at any rate not in so large a proportion. A foreign constituent -or an excess of a normal constituent, _i. e._, sodium carbonate, -has arisen in the blood. But the kidneys possess the function of -maintaining the same composition of the blood, and of thus eliminating -every abnormal constituent and any excess of a normal constituent. The -sodium salt formed is therefore ejected by the kidneys, together with -the chloride of potassium, and the blood becomes poorer in chlorine -and sodium. Common salt is therefore withdrawn from the organism by -the ingestion of potassium salts. This loss can only be made up from -without, and this explains the fact that animals which live on a diet -rich in potassium, have a longing for salt” (Bunge). It is certainly a -fact worthy of note that man takes only one salt as such in addition -to those that are naturally present in his food, and it is equally -significant that sodium chloride is by no means lacking in ordinary -foodstuffs. If the individual lives entirely on animal foods, he has no -desire for salt, but as soon as he adopts a vegetable diet the craving -for salt shows itself. Vegetable foods, however, are not all alike in -their content of potassium salts; some, like rice, contain relatively -little, while others, like potatoes, peas, and beans, are comparatively -rich in this element. - -We may recognize in these statements a physiological demand for a -certain amount of salt, especially when vegetable foods enter into -the daily dietary, but there is no justification for the employment -of such quantities as are generally made use of. Where the vegetable -food is largely rice, a small fraction of a gram of salt is really -sufficient for all physiological purposes; and in those cases where -ordinary cereals, legumes, potatoes, etc., constitute the chief part -of the dietary, a few grams of salt, at the most, will suffice to meet -the daily needs. Common usage, however, frequently raises the amount -consumed to 25 grams or more per day, the bulk of which is at once -eliminated through the kidneys; thereby entailing a certain amount -of renal activity, which must, it would seem, constitute something -of a strain upon organs ordinarily hard worked at the best. “Do we -not impose too great a task upon them, and may it not be fraught -with serious consequences? When on a diet of meat and bread, without -salt, we excrete not more than from 6 to 8 grams of alkaline salts -in twenty-four hours. With a diet of potatoes, and a corresponding -addition of salt, over 100 grams of alkaline salts pass through the -kidneys in the day. May not there be danger in this? The habit of -drinking spirituous liquors, which moreover is reckoned one of the -causes of chronic nephritis, also brings about the immoderate use of -salt, and thus one sin against nature leads to another” (Bunge). - -The moral we would draw (from these observations) is that in weakened -conditions of the kidneys there is reason in reducing the rate of -proteid exchange to the lowest level consistent with the maintenance -of equilibrium and the preservation of strength and vigor, thereby -diminishing the amount of nitrogenous waste to be eliminated and the -consequent strain upon these organs. Further, there is suggested -moderation in the amount of salt to be used daily, and some -circumspection in the amount and quality of vegetable foods consumed -in order to regulate more effectually the quantity of saline waste to -be handled by the kidneys. These conclusions are just as worthy of -consideration as the more obvious rule that in diabetes or glycosuria -proper precaution must be observed in the eating of carbohydrate -foods. In gout and rheumatism, accumulated physiological knowledge -teaches plainly the necessity of avoiding those foods that are rich in -purin-containing compounds. Uric acid owes its origin in part at least -to substances of this class; and as an ounce of prevention is worth -more than a pound of cure, we may by proper moderation in the use of -such foods save ourselves from the disagreeable effects of accumulated -uric acid deposits. - -In conclusion, the nutrition of man, if it is to be carried out by the -individual in a manner adapted to obtaining the best results, involves -an intelligent appreciation of the needs of the body under different -conditions of life, and a willingness to accept and put in practice the -principles that scientific research has brought to light, even though -such principles stand opposed to old-time traditions and customs. The -master words which promise help in the carrying out of an intelligent -plan of living are moderation and simplicity; moderation in the amount -of food consumed daily, simplicity in the character of the dietary, in -harmony with the old saying that man _eats to live_ and not lives to -eat. In so doing there is promise of health, strength, and longevity, -with increased efficiency, as the reward of obedience to Nature’s -laws. - - - - -INDEX - - - A - - Abderhalden, Emil, 35 - - Absorption, a physiological process, 41 - diffusion as a factor in, 41 - from the stomach, 31 - in intestine, 37 - of fats, 43, 49 - of fats, in dogs on low proteid diet, 233, 261 - of food products, by blood, 44 - of peptones, 41 - of proteid in dogs on low proteid diet, 233, 262 - of proteid products, 47 - of proteoses, 41 - osmosis, as factor in, 41 - paths of, 44 - reconstruction of proteid during, 42 - selective action, of sugars, 47 - - Acid, aspartic, 34, 67, 259 - glutaminic, 34, 259 - hydrochloric, 25, 26 - uric, 73 - uric, excretion of, as influenced by diet, 144 - - Acids, amino, 34 - diamino, 34 - - Adenase, 71 - - Adenin, 72 - - Aldehydase, 64 - - Amino acids, 34, 67 - - Ammonia, 70, 259 - - Amylopsin, 32 - - Anabolism, 50 - - Animals, influence of low proteid diet on high proteid, 231, 233, 243 - - Animal starch, _see_ Glycogen - - Appetite, in relation to food requirements, 162 - - Arginin, 34, 68, 70, 259 - - Argutinsky, views on muscle work, 123 - - Aspartic acid, 34, 67, 259 - - Assimilation limits of sugars, 47 - - Athlete, photograph of, 190 - - Athletes, fuel value of food of, on low proteid diet, 198 - strength tests of, on low proteid diet, 206 - true proteid requirement of, 186 - - Atwater and Benedict, 109, 111 - - Autodigestion (_see_ Autolysis), 63 - - Autolysis, 12 - - Availability, of foods, 12 - of carbohydrates, as source of energy, 45 - - - B - - Bacterial flora in intestine, of carnivora, 292 - of herbivora, 292 - - Bacterial processes in intestine, in relation to food, 292 - - Balance, nutritive, as affected by various factors, 117, 118 - - Basal energy exchange, 104 - - Beaumont, William, on movements of stomach, 27 - - Benedict, F. G., _see_ Atwater and Benedict - - Bergell and Lewin, 36 - - Beriberi, and diet, 224 - - Blood, absorption of food products by, 44 - behavior of disaccharides when introduced into, 39 - effects of injection of proteoses and peptones into, 41 - relation of sugar in, to glycogen, 46 - sugar in, 45 - - Body, amounts of food required to furnish proteid needs of, 274 - efficiency of, as a machine, 111 - equilibrium, 78 - nature of oxidation in the, 60 - needs of nitrogen by, 4 - needs for food by, 169 - needs and dietary habits, 268 - needs of proteid by, 268, 272 - relation of oxygen to decompositions in, 61 - resistance, _see_ Resistance - sample dietary supplying needs of, 280 - site of oxidation in, 62 - surface, relation to energy exchange, 104, 105 - surface, relation to nitrogen requirement in dogs, 248 - - Body-weight, on low proteid diet, 175, 181, 185, 190, 199, 245–255 - relation to proteid requirement, 184, 188, 198, 227 - - Bright’s disease, _see_ Nephritis - - Breisacher, L., on minimum proteid requirement, 172 - - Bunge, 124 - - - C - - Calorie, 14 - - Calorimeter, respiration, 102 - - Cane sugar, assimilation limit of, 47 - behavior when introduced into blood, 39 - utilization of, 40 - - Cannon, W. B., on muscular movements of stomach, 28, 29 - - Carbon dioxide, output in rest, 111, 112 - dioxide, output during work, 111, 123 - equilibrium, 84 - excretion, during fasting, 84 - moiety of proteid, 129 - - Carnivora, bacterial flora in intestine of, 292 - - Carbohydrates, as food, 6 - as fuel, 6 - as heat producers, 58 - as proteid sparers, 92 - as source of energy, 128 - as source of energy in fasting, 81 - as source of energy in work, 58 - availability of, 13 - availability of, as source of energy, 45 - composition of, 5 - formation from proteid, 129 - fuel value of, 15 - in foodstuffs, 7 - liver as regulator of, 45 - respiratory quotient of, 107 - - Casein, cleavage products of, 70 - - Caspari and Glässner, on minimum proteid requirement in man, 172 - - Cellulose, in vegetables, influence on digestion, 263 - - Chemical character of proteid, influence on nutrition, 256 - composition of foodstuffs, 7 - - Circulating proteid, 134 - - Clapp, S. H. - (_see_ Osborne and Clapp, on proteid cleavage products), 258 - - Cleavage, oxidative, 61 - - Climbing, oxygen consumption in, 116 - - Cogan, Thomas, on temperance in food, 166 - - Cohnheim, Otto, on proteid decomposition, 36 - - Composition, of proteid, 3 - of carbohydrate, 5 - of fat, 6 - - Cornaro, Louis, on temperance in food, 168 - - Cost of foods in relation to nutritive value, 277 - - Creatin, 74 - - Creatinin, 74 - excretion, as influenced by diet, 144 - - Curtis, Edward, Nature and Health, 2, 5, 214 - - - D - - Dapper, Max, 99 - - Dangers of underfeeding, 214 - - Degeneration, fatty, 270 - - Deuteroproteose, 67, 69 - - Dextrins, 21, 37 - - Dextrose, 37 - assimilation, limit of, 47 - utilization of, 40 - - Diabetes, phloridzin, 130 - - Diamino acids, 34 - - Diet, and beriberi, 224 - and renal activity, 297 - effects of exclusive proteid, upon rats, 239 - effects of intemperance in, 270 - effects of rice, on rats, 240 - fat absorption in dogs on low proteid, 233, 261 - influence of, on creatin in excretion, 144 - exclusive proteid, on progeny in rats, 240 - on growth in rats, 239 - monotony in, 242 - on oxygen consumption in man at rest, 126 - on oxygen consumption in man at work, 126 - on respiratory quotient in man at rest, 126 - on respiratory quotient in man at work, 126 - rice, on growth in rats, 240 - on urea excretion, 144 - on uric acid excretion, 144 - vegetable, upon dogs, 254, 256 - in relation to nephritis, 297 - in relation to nitrogen distribution in urine, 144 - in relation to seasons of the year, 296 - of Highlanders, 279 - low proteid, influence on body-weight in dogs, 245, 249, 250, - 251, 252, 255 - nitrogen excretion during severe work on exclusive proteid, 123, 124 - philosophy of a mixed, 92, 276 - relation of endurance to low proteid, 210, 212 - relation of inorganic salts to, 299, 300 - relation of work to, 126 - relation of vegetable food to low proteid, 291 - sample, of soldiers, 194 - sample, in experiments on true proteid requirement in man, 178, - 182, 189, 195 - simplicity in, advantages of, 279, 293 - temperance in, 270 - utilization of fat in dogs on low proteid, 261 - utilization of nitrogen in dogs on low proteid, 262 - variety in, 229, 242 - - Diets, normal, _see_ Standard diets - standard, 155 - - Dietary habits, in relation to needs of body, 268 - of fruitarians, 215 - of Japanese, 225 - sample, supplying needs of body, 280 - standards, use of the term, 272 - - Dietetic customs of mankind, 154 - - Dietetics, habit in, 159 - - Diffusion, as factor in absorption, 41 - - Digestibility, _see_ Availability - - Digestion, gastric, of proteids, 26 - importance of gastric, 30 - influence of cellulose in vegetables on, 263 - in the stomach, 25 - object of gastric, 30 - of fat, in intestine, 36 - of fat, in stomach, 36 - of starch, 21 - products of pancreatic, of fats, 36 - products of pancreatic, of proteids, 34, 67 - products of pancreatic, of starch, 37 - products of salivary, 21 - salivary, in stomach, 23 - - Digestive products, reconstruction of proteid from, 42 - - Disease, relation of excessive proteid consumption to, 269 - - Dogs, effects of low proteid diet on, 232–236, 245–255 - fasting experiments on, 82 - fat absorption in, on low proteid diet, 233, 261 - fuel value requirement of, 234, 236, 245–255 - influence of low proteid diet upon body-weight in, 245–255 - influence of vegetable diet on, 254, 256 - nitrogen requirement of, 234, 235, 236, 245–255 - photographs of, 248 - proteid absorption in, on low proteid diet, 233, 262 - proteid requirement, experiments by Munk, 232 - proteid requirement, experiments by Rosenheim, 234 - proteid requirement, experiments by Jägerroos, 236 - proteid requirement, experiments by author, 243 - utilization of fat in, on low proteid diet, 261 - utilization of nitrogen in, on low proteid diet, 262 - - Disaccharides, utilization of, 40 - - - E - - Edestin, cleavage products of, 70 - - Efficiency of body, as a machine, 111 - - Egg albumin, cleavage products of, 70 - - Endogenous metabolism, 145, 146 - - Endurance, relation of, to low proteid diet, 210, 212 - - Energy, availability of carbohydrates, as source of, 45 - basal exchange, 104 - carbohydrate as source of, 128 - carbohydrate as source of, in fasting, 81 - conservation of, in man, 103 - exchange, effect of muscular work, 109, 110, 113, 115 - exchange, factors modifying, 105, 106 - exchange, in relation to work, 119 - exchange proportional to body surface, 104, 105 - fat as source of, 128 - fat as source of, in fasting 81 - foods as source of, 15 - metabolism of, in man, 103 - of muscle contraction, 121 - origin of, in fasting, 81 - output, in man, 103 - produced by man, 106 - proteid as source of, 122, 123, 124, 129 - proteid as source of, in fasting, 81 - source of, in body, 21, 121 - source of, during fasting, in work, 125 - - Enterokinase, 33 - - Enzymes, deamidizing, 71, 72 - in gastric juice, 25 - in pancreatic juice, 32 - in saliva, 20 - intracellular, 63, 71, 72, 75 - reversible action of, 21 - specificity of, 21 - - Equilibrium, carbon, 84 - nitrogenous, 78 - of body, 78 - - Erepsin, 34 - - Exchange, basal energy, 104 - of energy, as affected by work, 109, 110, 113, 115, 119 - of energy, factors modifying, 105, 106 - of energy, relation to body surface, 104, 105 - - Exogenous metabolism, 145, 146 - - - F - - Fasting, carbohydrates as source of energy in, 81 - excretion of carbon during, 84 - excretion of nitrogen during, 80, 82, 84 - experiments on dogs, 82 - experiments on man, 80, 84 - fat as source of energy in, 81 - fuel value during, 86 - fuel value of fat, metabolized during, 86 - metabolism of fat during, 84 - nitrogen excretion during, 80, 82, 84 - origin of energy in, 81 - proteid as source of energy in, 81 - proteid metabolism during, 83 - relation of nitrogen excretion to work during, 125 - source of energy for work during, 125 - - Fat, absorption, 43, 49 - absorption in dogs on low proteid diet, 233, 261 - as food, 6 - as fuel, 6 - as source of energy, 128 - as source of energy during work, 58 - as source of energy in fasting, 81 - composition of, 6 - digestion of, in intestine, 36 - digestion of, in stomach, 36 - fuel value of, 15 - fuel value of, metabolized during fasting, 86 - hydrolysis of, 36 - influence of feeding, on body fat, 44 - in foodstuffs, 7 - laying on of, from overfeeding, 98, 99 - metabolism during fasting, 84, 86 - respiratory quotient of, 107 - saponification of, 36 - specificity of body, 44 - synthesis of, 43 - utilization of, in dogs on low proteid diet, 261 - - Fats, availability of, 13 - as heat producers, 58 - as proteid sparers, 92 - - Fatty degeneration, 270 - - Fatigue, relation to low proteid diet, 208 - - Fenger, S., 293 - - Fick and Wislicenus, on source of muscular energy, 121 - - Fischer, Emil, 21 - - Fisher, Irving, on endurance and low proteid diet, 210 - on method of indicating food values, 283 - - Folin, Otto, theory of proteid metabolism, 144 - - Food, absorption and utilization of, in dogs on low proteid diet, 261, 262 - amounts, required for proteid needs of body, 274 - as fuel, 6 - as source of energy, 15 - availability of, 12 - carbohydrates as, 6 - character of, in relation to bacterial processes in intestine, 292 - consumption and obesity, 270 - consumption, relation to prosperity, 160 - fats as, 6 - fuel value of, 274 - of fruitarians, 217 - in experiments on proteid requirement, athletes, 198 - in experiments on proteid requirement, professional men, 178, 180, 185 - in experiments on proteid requirement, soldiers, 198 - of Japanese, 219, 221 - fuel value requirement of, in dogs, 234, 236, 245–255 - influence of, on respiratory quotient, 107 - needs of body for, 169 - of man, 2 - proteids as, 3, 5 - real need of body for proteid, 272 - relation of appetite to, 162 - relation of nutritive value and cost of, 277 - requirements, factors modifying, 165 - temperance in, 166, 168 - value of fruits as, 290 - values of, method of indicating, 283 - - Foods, respiratory, 58 - time, remain in stomach, 29, 30 - - Foodstuffs, carbohydrate in, 7 - composition of, 7 - fat in, 7 - fuel value of, 7 - inorganic salts in, 7 - organic, 3 - plastic, 58 - proteid in, 7 - water in, 7 - - Fritz, photograph of, 199 - - Fruitarians, dietary of, 215 - fuel value of food of, 217 - proteid consumption of, 217 - - Fruits, value of, as food, 290 - - Fuel, carbohydrate as, 6 - fat as, 6 - proteid as, 6 - - Fuel value, in fasting, 86 - of carbohydrate, 15 - of fat, 15 - of fat metabolized during fasting, 86 - of food, in experiments on proteid requirement, athletes, 188 - of food, in experiments on proteid requirement, professional men, - 178, 180, 185 - of food, in experiments on proteid requirement, soldiers, 198 - of food of fruitarians, 217 - of food of Japanese, 219, 221 - of foods, 274 - of foodstuffs, 7 - of proteid, 15 - of proteid metabolized during fasting, 86 - requirement in the dog, experiments by Munk, 234 - requirement in the dog, experiments by Rosenheim, 236 - requirement in the dog, experiments by Jägerroos, 236 - requirement in the dog, experiments by author, 245–255 - - - G - - Gastric digestion, importance of, 30 - object of, 30 - products of, 26 - - Gastric juice, action on milk, 26 - composition of, 25, 26 - functions of, 25, 27 - hydrochloric acid in, 25, 26 - influence of diet upon flow of, 25 - pepsin in, 25 - psychical stimulation of, 24 - - Gastric secretion, 24 - - Gelatin, as food, 4, 5 - - Glässner, _see_ Caspari and Glässner - - Gliadin, cleavage products of, 70, 259 - - Glutaminic acid, 34, 67, 70, 259 - - Glutenin, cleavage products of, 259 - - Glycerin, 36 - - Glycocoll, 67 - - Glycogen, formation from proteid, 130 - in liver, 46 - relation to sugar of blood, 46 - - Growth, influence of diet on, in rats, 239 - - Guanase, 71 - - Guanin, 72 - - - H - - Habit, in dietetics, 159 - - Heat, furnished by fats and carbohydrates, 58 - production during sleep, 104, 105 - production in work, 110 - - Herbivora, bacterial flora in intestine of, 292 - - Herter, C. A., on bacterial flora, 292 - - Hirschfeld, Felix, on minimum proteid requirement, 170 - - Histidin, 34, 68, 70 - - Hofmeister, Franz, on sugar assimilation, 47 - - Hunt, Reid, on low proteid diet and body resistance, 226 - - Hunter, Andrew, _see_ Watson and Hunter - - Hydrochloric acid, in gastric juice, 25, 26 - - Hydrolysis, of fats, 36 - - Hypoxanthin, 72 - - - I - - Indol, 37 - - Inorganic salts, and renal activity, 298, 300 - in foodstuffs, 7 - in nutrition, 2 - relation to diet, 299, 300 - - Intemperance in diet, effects of, 270 - - Intermediary metabolism, _see_ Exogenous metabolism - - Intestine, absorption in, 37 - chemical changes in, 33 - putrefaction in, 37 - bacterial flora of, 292 - - Invertase, 40 - - - J - - Jägerroos, B. H., on proteid requirement in the dog, 236 - - Japanese Army and Navy, rations of, 224 - - Japanese, dietary of, 225 - fuel value of food of, 219, 221 - proteid consumption by, 219, 221 - - - K - - Katabolism, 50 - nature of proteid, 75 - oxygen in, 62 - relation to intracellular enzymes, 75 - - Klemperer, on proteid requirement, 171 - - - L - - Lactase, 40 - - Lavoisier, views on oxidation, 56 - - Leucin, 34, 67, 70, 259 - - Leucosin, cleavage products of, 259 - - Levulose, assimilation limits of, 47 - - Lewin, _see_ Bergell and Lewin - - Liebig, views on oxidation, 57, 120 - - Lipase, 32 - - Lipolysis, by pancreatic juice, 36 - - Liver, function of, as regulator of carbohydrate, 45 - glycogen in, 46 - synthesis of proteid by, 48 - - Luxus consumption, of proteid, 59 - - Lüthje, 101 - - Lymphatics, absorption of food products by, 44 - - Lysin, 34, 68, 70, 259 - - - M - - Maltose, 21, 37 - behavior when introduced into blood, 39 - - Man, conservation of energy in, 103 - energy produced by, 106 - experiments on oxygen consumption in, 126 - fasting experiments on, 80, 84 - food of, 2 - metabolism of energy in, 103 - minimum proteid requirement in, 170, 171, 172, 174–208 - work experiments on, 110–116 - - Mastication, importance of, 23 - - Meat, influence on growth in rats, 239 - - Metabolic changes as influencing respiratory quotient, 108 - - Metabolism, 51 - and old age, 296 - endogenous, 145 - exogenous, 145 - Folin’s theory of proteid, 144 - influence of proteid on, 83 - influence of carbohydrates on proteid, 92, 94, 95, 96, 97 - influence of fat on proteid, 92, 93, 96, 97 - influence of proteid on proteid, 88 - of energy in man, 103 - of fat during fasting, 84, 86 - oxidation in, 60 - of proteid during fasting, 83, 86 - Pflüger’s theory of proteid, 138 - processes of, 51 - significance of exogenous and endogenous proteid, 49 - significance of proteid, 131 - Voit’s theory of proteid, 134 - - Methyl glycocoll, _see_ Sarcosin - - Methyl guanidin, 74 - - Milk sugar, assimilation limit of, 47 - behavior when introduced into blood, 39 - utilization of, 40 - - Mineral matter, _see_ Inorganic salts - - Minimum proteid requirement, 59 - - Mixed diet, philosophy of a, 92, 276 - - Monotony of diet, influence of, 242 - - Morphotic proteid, 134 - - Munk, Immanuel, on proteid requirement in the dog, 232 - - Muscular movements of stomach, 27–30 - - - N - - Needs of body for food, 169 - - Nephritis, in relation to diet, 297 - - Neumann, R. O., on low proteid diet, 286 - - Nitrogen, distribution of, in the urine in relation to diet, 144 - needs by body, 4 - utilization of, in dogs on low proteid diet, 262 - - Nitrogen excretion, as influenced by proteid, 59, 87, 90 - during fasting, 80, 84 - during work in fasting, 125 - during excessive work, 114, 127 - during hard work on proteid diet, 123, 124 - in experiments on proteid requirement, in dogs, 245, 249, 250, 251, - 252, 255 - in experiments on true proteid requirement, athletes, 187, 188 - in experiments on true proteid requirement, professional men, 176, - 177, 181, 185 - in experiments on true proteid requirement, soldiers, 199, 200, 201 - relation to work, 122, 123, 124 - - Nitrogen equilibrium, on low proteid diet, 176, 177, 181, 188, 200, - 201, 249, 250, 251, 252, 255 - - Nitrogen requirement, in dogs, 234–236, 245–255 - in man, 180, 184, 185, 187, 198, 227 - relation to body-weight, 184, 248 - - Nitrogenous equilibrium, 78 - - Nitrogenous metabolism, theory of Folin, 144 - theory of Pflüger, 138 - theory of Voit, 134 - - Normal diets, 155 - - Nutrition, factors in, 16, 17 - influence of chemical character of proteid on, 256 - inorganic salts, as aids in, 2 - physiological economy in, 264 - purpose of, 2 - - Nutritive balance, as affected by various factors, 117, 118 - - Nuclease, 71 - - Nucleoproteid, character of, 3 - cleavage products of, 71 - - - O - - Obesity, relation to food consumption, 270 - - Old age, metabolism in, 296 - - Osborne and Clapp, on chemistry of proteids of wheat kernel, 258 - - Osmosis, as factor in absorption, 41 - - Overeating, evil effects of, 270 - - Overfeeding, in laying on of fat, 98, 99 - - Oxidase, xanthin, 73 - - Oxidases, 64 - - Oxidation, in metabolism, 60 - nature of, in the body, 60 - older views regarding, 52 - relation to enzymes, 75 - site of, in the body, 62 - value of respiratory quotient in determination of substances - undergoing, 125 - views of Lavoisier on, 56 - views of Liebig on, 57, 120 - - Oxidative cleavage, 61 - - Oxygen, in katabolism, 62 - relation to decompositions in the body, 61 - relation to proteid decomposition, 59 - - Oxygen consumption, in climbing, 116 - in relation to work, 123 - in standing at rest, 116 - in walking, 116 - - - P - - Pancreatic digestion, of proteids, 34 - products of, 34, 67 - products of, of starch, 37 - - Pancreatic juice, composition of, 32 - condition of trypsin in, 33 - enzymes in, 32 - secretion of, 31, 32 - sodium carbonate in, 32 - - Paths of absorption, 44 - - Pawlow, on adaptation of saliva, 18 - - Pepsin, in gastric juice, 25, 26 - - Peptones, 67 - absorption of, 41 - cleavage by erepsin, 34 - effects when injected into blood, 41 - formed in gastric digestion, 26 - - Pflüger, E., theory of proteid metabolism, 138 - views on muscle work, 123 - - Phenol, 37 - - Phloridzin diabetes, 130 - - Phosphorus, excretion of, in relation to work, 123 - - Photograph, of athlete, 190 - of Fritz, 199 - - Photographs, of dogs, 248 - of soldiers, 193 - - Physical endurance, _see_ Endurance - - Physiological economy in nutrition, 264 - - Plastic foodstuffs, 58 - - Poisons, relation of body resistance to, on low proteid diet, 226 - - Polypeptid, 35 - - Portal vein, absorption of food products by, 45 - - Processes of metabolism, 51 - - Products, of cleavage of wheat kernel proteids, 259 - of gastric digestion, 26 - of pancreatic digestion, 37, 67 - of proteid cleavage, 70 - of putrefaction in intestine, 38 - of salivary digestion, 21 - - Products of digestion, absorption of, 44 - - Professional men, fuel value of food on low proteid diet, 178, 180, 185 - nitrogen equilibrium of, on low proteid diet, 176, 177, 181 - true proteid requirement of, 174 - - Progeny, influence of meat diet on, in rats, 240 - - Prosperity, relation to food consumption, 160 - - Proteid, absorption of, in dogs on low proteid diet, 233, 262 - absorption of cleavage products, 47 - amounts of food required to supply needs of body for, 272 - as food, 3 - as fuel, 6 - as glycogen former, 130 - as source of energy, 122, 123, 124, 129 - as source of energy, in fasting, 81 - availability of, 12 - body-weight on diet low in, 170–175, 181, 185, 190, 199, 245, 249, - 250, 251 - carbon moiety of, 129 - chemical basis of protoplasm, 51 - circulating, 134 - cleavage products of, 70 - composition of, 3, 69 - consumption by fruitarians, 217 - consumption by Japanese, 219, 221 - decomposition by oxygen, 59 - decomposition in work, 58 - excessive consumption of, relation to disease, 269 - effect of diet exclusively of, on rats, 239 - effect on dogs of diet low in, 233, 234, 237, 245–255 - fat absorption in dogs on diet low in, 261 - food, real need of body for, 272 - formation of carbohydrate from, 129 - fuel value of, 15 - fuel value of, metabolized during fasting, 86 - influence of chemical character of, on nutrition, 256 - diet exclusively of, upon progeny of rats, 240 - diet low in, on high proteid animals, 231, 233, 243 - on excretion of nitrogen, 59, 87, 90 - on metabolism, 83 - on metabolism of, 88 - in foodstuffs, 7 - katabolism, 75 - luxus consumption of, 59 - metabolized during fasting, 86 - minimum requirement, 59 - morphotic, 134 - need of body for, 268 - nitrogen equilibrium on diet low in, 176, 177, 181, 200, 201, 245, - 249, 250, 251, 252, 255 - overfeeding with, 98 - reconstruction of, during absorption, 42 - relation of endurance to diet low in, 210, 212 - relation of fatigue to diet low in, 208 - respiratory quotient of, 107 - resistance of body to poisons on diet low in, 226 - safety in relation to diet low in, 231 - significance of complete cleavage of, 35 - storing of, 92, 98, 99, 100 - strength tests on diet low in, 203, 206 - synthesis, 48, 49, 68 - utilization of fat in dogs on diet low in, 261 - utilization of nitrogen in dogs on diet low in, 262 - work done at expense of, 58 - - Proteid diet, experiments of Neumann on low, 286 - body-weight of dogs on low, 245, 249, 250, 251 - body-weight of men on low, 170–175, 181, 185, 190, 199 - in relation to nitrogen excretion during hard work, 123, 124 - vegetable foods in relation to, 291 - - Proteid metabolism, influence of carbohydrate on, 92, 94, 95, 96, 97 - influence of fat on, 92, 93, 96, 97 - influence of proteid on, 59, 87, 90 - Folin’s theory of, 144 - Pflüger’s theory of, 138 - significance of, 131 - Voit’s theory of, 134 - - Proteid requirement, fuel value of food in experiments on, athletes, 188 - fuel value of food in experiments on, professional men, 178, 180, 185 - fuel value of food in experiments on, soldiers, 198 - in dogs, experiments of Jägerroos, 236 - in dogs, experiments of Munk, 232 - in dogs, experiments of Rosenheim, 234 - in dogs, experiments of author, 243 - in man, 169, 170, 171, 172, 174–202 - nitrogen excretion in experiments on, athletes, 186, 187, 188 - nitrogen excretion in experiments on, in dogs, 245, 249, 250, 251, - 252, 255 - nitrogen excretion in experiments on, professional men, 177, 180, 185 - nitrogen excretion in experiments on, soldiers, 197, 200, 201 - relation to body-weight, 184, 188, 198, 227 - sample diets in experiments on, 178, 182, 189, 195 - - Proteids, as tissue formers, 58 - of wheat kernel, cleavage products of, 259 - - Proteoses, 26, 67, 69 - absorption of, 41 - cleavage by erepsin, 34 - effects when injected into blood, 41 - primary, 67, 69 - secondary, 67, 69 - - Protoplasm, 51 - - Protoproteose, 67, 69 - - Ptyalin, 20 - - Purin bases, 71, 72 - relation to uric acid, 73 - - Putrefaction, in intestine, 37 - products of, 38 - - - R - - Rats, effects of exclusive proteid diet on, 239 - effects of rice on, 240 - influence of meat diet on progeny of, 240 - - Renal activity, and diet, 297 - and inorganic salts, 298, 299, 300 - - Rennin, in gastric juice, 26 - - Resistance of body to poisons, relation to low proteid diet, 226 - - Respiration calorimeter, 102 - - Respiratory foods, 58 - - Respiratory quotient, 107 - influence of foods on, 107, 126 - influence of metabolic change on, 108 - of foodstuffs, 107 - relation to work, 125 - value of, in determination of substances oxidized, 125 - - Rest, carbon dioxide output during, 111 - influence of, on oxygen consumption, 126 - influence of, on respiratory quotient, 126 - - Rice, influence of, on growth in rats, 240 - - Rosenheim, Theodor, on proteid requirement in the dog, 234 - - - S - - Safety of low proteid standards, 231 - - Saliva, adaptation of, 18, 19 - function of, 20 - psychical secretion of, 18 - secretion of, 17, 18 - - Salivary digestion, in stomach, 23 - products of, 21 - - Salts, _see_ Inorganic salts - - Saponification of fats, 36 - - Sarcosin, 74 - - Schnyder, 115 - - Scientific research and typhoid fever, 267 - - Seasons of the year, relation to diet, 296 - - Secretin, 32 - - Secretion, of gastric juice, 24 - of pancreatic juice, 31, 32 - of saliva, 17, 18 - - Sivén, on proteid requirement, 89 - - Skatol, 38 - - Sleep, heat production during, 104, 105 - - Soaps, 36 - - Sodium carbonate, in pancreatic juice, 32 - - Soldiers, fuel value of food in experiments on proteid requirement - of, 198 - nitrogen equilibrium in experiments on proteid requirement - of, 200, 201 - photographs of, 193 - proteid requirement of, 192 - sample diet in experiments on proteid requirement of, 195 - strength tests in experiments on proteid requirement of, 203 - - Specificity of body fat, 44 - - Standard diets, 155 - - Standing at rest, oxygen consumption in, 116 - - Starch digestion, products of, 21, 37 - - Steapsin, 36 - - Stomach, absorption from the, 31 - as a reservoir, 31 - digestion in the, 25–31 - fat digestion in the, 36 - muscular movements of the, 27–30 - salivary digestion in the, 23 - time foods remain in the, 29, 30 - - Storing of proteid, 92, 98, 99, 100 - - Strength tests, on low proteid diet, athletes, 206 - on low proteid diet, soldiers, 203 - - Sugar, in blood, 45 - in blood, relation to glycogen, 46 - - Sugars, behavior when introduced into blood, 39 - selective action in absorption of, 47 - - Sulphur, excretion of, relation to work, 123 - - Synthesis, of fat, 43 - of proteid, 48, 49, 68 - - - T - - Temperance in diet, 166, 168, 270 - - Tissue formers, 58 - - Tissue metabolism, _see_ Endogenous metabolism - - Trypsin, 32 - condition in pancreatic juice, 33 - - Tryptophan, 67 - - Typhoid fever and scientific research, 267 - - Tyrosin, 34, 67, 70, 259 - - - U - - Underfeeding, dangers of, 214 - - Urea, 74 - excretion of, influence of diet on, 144 - relation of, to creatin and creatinin, 74 - - Uric acid, 73 - excretion of, as influenced by diet, 144 - relation of, to xanthin bases, 73 - - Urine, relation of diet to nitrogen distribution in the, 144 - - Utilization, of dextrose, 40 - of disaccharides, 40 - of fat in dogs on low proteid diet, 261 - of nitrogen in dogs on low proteid diet, 262 - - - V - - Variety in diet, 229, 242 - - Vegetable diet, influence upon dogs, 254, 256 - - Vegetable foods, relation to low proteid dietary, 291 - - Vegetables, cellulose in, influence on digestion, 263 - - Voit, Carl, on minimum proteid requirement, 171 - theory of proteid metabolism, 59, 134 - - - W - - Walking, oxygen consumption in, 116 - - Water in foodstuffs, 7 - - Watson and Hunter, influence of diet on growth in rats, 239 - - Wheat kernel proteids, cleavage products of, 259 - - Weight, _see_ Body-weight - - Wislicenus, _see_ Fick and Wislicenus - - Work, carbon dioxide excretion in relation to, 123 - carbon dioxide excretion during, 111, 112 - due to proteid decomposition, 58 - effect of, on energy exchange, 109, 110, 113, 115 - experiments on man, 110, 111, 112, 113, 114, 115, 116 - heat production in, 110 - influence of, on oxygen consumption, 126 - influence of, on respiratory quotient, 126 - nitrogen excretion during excessive, 127 - nitrogen excretion during fasting in, 125 - proteid decomposition in, 58 - relation of diet to, 126 - to energy exchange, 119 - fats and carbohydrates to, 58 - nitrogen excretion on proteid diet to hard, 123, 124 - nitrogen excretion to proteid diet to hard, 122, 123, 124 - relation of oxygen consumption to, 123 - phosphorus excretion to, 123 - sulphur excretion to, 123 - respiratory quotient in relation to, 125 - source of energy during fasting in, 125 - views of Argutinsky on muscle, 123 - views of Pflüger on muscle, 123 - views of Voit on muscle, 59, 134 - - - X - - Xanthin, 72 - - Xanthin oxidase, 73 - -*** END OF THE PROJECT GUTENBERG EBOOK THE NUTRITION OF MAN *** - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the -United States without permission and without paying copyright -royalties. 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