Class “> Book Copyright N°_ COPYRIGHT DEPOSIT: - P< re Nee ft eS ee 7 ee _— re ae, ea Lae ee ‘ts (a een r= as ah rim ia a.« s —% a ae tes] ah ae wer -« . ih PRUNCIPLES OF SNE MATL NUTRITION. WITH SPECIAL REFERENCE TO THE NUTRITION OF FARM ANIMALS. BY HENRY PRENTISS ARMSBY, Pu.D., LL.D., " Director of the Institute of Animal Nutrition of The Pennsylvania State College; Expert in Animal Nutrition, United States Department of Agriculture. THIRD EDITION, REVISED. FIRST THOUSAND. NEW YORK: JOHN WILEY & SONS. Lonpon: CHAPMAN & HALL, LiMiTED. 1908. eer TY LIBRARY of CONGRESS Two Copies Received DEC 29 1908 Copyrignt entry Copyright, 1903, 1908, BY HENRY P. ARMSBY. The Scientific Presa Bobert Brummond and Company Nem Dork i PREFACE. THE past two decades have not only witnessed great activity in the study of the various problems of animal nutrition, but they are especially distinguished by the new point of view from which these problems have come to be regarded. Speaking broadly, it may be said that to an increasing knowledge of the chemistry of nutrition has been added a clear and fairly definite general conception of the vital activities as transformations of energy and of the food as essentially the vehicle for supplying that energy to the organism. This conception of the function of nutrition has been a fruitful one, and in particular has tended to introduce greater simplicity and unity into thought and discussion. Much exceedingly valuable work has been done under its guidance, while it points the way toward even more important results in the future. The following pages are not a treatise upon stock-feeding, but are an attempt to present in systematic form to students of that subject a summary of our present knowledge of some of the fundamental principles of ani- mal nutrition, particularly from the standpoint of energy relations, with special reference to their bearings upon the nutrition of farm animals. Should the attempt at systematization appear in some instances premature or ill-advised, the writer can only plead that even a temporary or tentative system, if clearly recognized as such, may be preferable to unorganized knowledge. The scaffolding has its uses, even though it form no part of the completed building. The attentive reader, should there be such. will not fail to note that the work is limited to those aspects of the subject included under the more technical term of ‘The Statistics of Nutrition,” and that even in this restricted field some important branches of the cubject have been omitted on account of what has seemed to ili iv PREFACE. the writer a lack of sufficient accurate scientific data for their profit- able discussion. Moreover, many principles which are already familiar have been considered rather cursorily in order to allow a more full treatment of less well-known aspects of the subject, even at the expense of literary proportion. The substance of this volume was given in the form of lectures before the Graduate Summer School of Agriculture at the Ohio State University in 1902, and has been prepared for publication at the request of instructors and students of that school. In thus presenting it to a somewhat larger public the author ventures to hope that it may tend in some degree to promote the rational study of stock-feeding and to aid and stimulate systematic investigation into both its principles and practice. STATE COLLEGE, Pa., November, 1902. CONTENTS. PAGE IntTRopuctTion ee eee ecoeosnseeeeeeeeeee00208080 eeeeeveeeeoeeveveeeee ee een ee 1 The Statistics of Nutrition eee eeveee ee eee eeeevoeoeoeeeeoeoeeeeee eo eeeee 3 PART i: THE INCOME AND EXPENDITURE OF MATTER. ® CHAPTER I. THE Foop eevee eeee eeeeeveveeer ee eereereee eee ee eeeeceoeaoeceoeceoeoeoeaeeeeeeeoee8 5 CHARTER TU: METABOLISM.........- Re pa) Rel 0c R ag LGN Hh eR chetasaveretee 14 § 1. Carbohydrate Metabolism... . 20.0... ps2sseceesnces “ids (0a 17 § 2. Fat Metabolism........ Beare tenon ois lcjore.ls osu na orrevels Mestenavevehe 29 Sr ArOpercMetaDOlISIs. aera la/elorareiele a's a ale" aie ajo #atm 2 are eheranel at 38 JASaEE) OVO KL a othe Auta Ren ls, OSI ARCTIC ERIS Oeics as a etc 38 Gata Olisraeney. oc ectemiancl oval ecets a eiaieleserouatey lemweneaerercar eee iene 41 ihe NOm=proteids:. <2 sci. cess.a, .ccies secre cece seth e crete 114 The- Minimum) of WerOvelasi. crise vecpereeicis te erere eta 133 Effects on Total Metabolism... #i:ciou inte e oeniellssttvieaet 144 Mutual Replacement of Nutrients.............ese00- 148 Utilization of Excess—Sources of Fat..........ee- 162 CHAPTER VI. THE INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM.......2.- 185 § 1. General Features of Muscular Activity.............ccccceece 185 Muscular’ Contraction’. tance eran ch enee 185 Secondary Effects of Muscular Exertion..............+. 191 $2. Jifiects upon Metabolism. <(.:.,). 2). . smo c pe cee eee entelci Bias 193 Upon the Proteid Metabolism..............0000008- Sees 104 Upon the Carbon Metabolism.............. e406 eon PART LI. THE INCOME AND EXPENDITURE OF ENERGY. CHAPTER VII. PORCH AND HNERGY ceraecioere | 2d cloiteieeeiclele sine eb d.cieelee sloth basen CHAPTER VIII. Mrrrops Or INVESTIGATION: «42 .)c/ecciciieil ee ee nic tees atciore efosersinte Biso eanuree CHAPTER IX. Tur CONSERVATION OF ENERGY IN THE ANIMAL Bopy...... OStetcete A sis) CHAPTER X. Tue Foop as a Source or ENerGyY—METABOLIZABLE ENERGY.......-. 269 § 1. Experiments on ‘Carnivora, ’.’;.\./c.5 cones. ceiat ye See eee 272 $2. Experiments on Man... «iced oi's.0s sin ane F' sie ae ae 277 § 3. Experiments on Herbivora.................: okie ors Sisiantaly Rae 281 Metabolizable Energy of Organic Matter................ 284 Total Organic: Matteris (uk so.. 2 eee eine eee 285 Digestible Organic. Matter... :....)..0rtae«ecesaneumetan 200 Energy of Digestible Nutrients... ....1sesses uenase een 302 GTOSS HNerey.s,. wale ns oheheisieatarete: aleveteyaneletsta tien Saat ni eter 302 Metabolizable Energy..... evens uesauna eseccees --. 310 CONTENTS. vil CHAPTER XI. PAGE ING ISESINGA CIMA VV, ORR ators ayora tei a teeeseve cose one cid stone, gins) cue ol wie’ Slareteie oid @erminlemlele 336 § 1. The Expenditure of ae Ve DY Me MOU Y w-0 a ete a) heise shone atta 2 cos 336 Ror Ener Masuime NTETA DONS. 5 W m'x\chos tya'ae'e engl sja ave lafers sieleceyee so 340 Nature of Memands for Fmergy. \,./2s. cmictbve oo aes acess eigen 340 LCA TPE LO CU CHL OME Sec Sets oc ratle etic cee ta eatin ters oratoncuaiate 344 Influence of Thermal Environment ...............- 347 Iniiiuenecel ot Sizelor Aminnalice\: es atiercle ls seas susie toes 359 § 3. The Expenditure of Energy in Digestion and Assimilation..... 372 CHAPTER XII. Nev AVAILABLE HNERGY—MAINTENANCE........ccccccccccccceccsecs 394 Solem Ree mlerceumemtie VANES 2.2/0) Flencpohstelacdaleis wrelalthaie sim steveie/eiaw ¥is_a sick 396 § 2. Modified Conception of Replacement Values.............220:. 405 Seka h NS Aleve AAU. 2 cy. hs wre ata elans,petee apc 21s caie le sole n siabe mola sPalenavaile aie 412 Determinations of Net ALVA INTD ye cya. dlrefetete, wloieiiarenate «6 413 DISCUSSIOMMOIMEESULESIE aren aie aren cee erste cheat eta 430 Infiiencevof Amount of Hood’. .25 62... csecesiiceens 430 Character Ofehoodearer teecis fescue ne he aie ale 431 *hemMaintenamcerhwtlOn sto. sucie cloice © eleieielsieversccoierere 432 CHAPTER XIII. PRE) URLIZABUON, ORO LUNEIR GY. 5: occ «4/0: oliciiovele'sia isis, bieleveeie.@ a8) cueve 'ssalsie 444 SPS iilizaionslonMicsie tis Ui) im osepete teri rca ate elelete etavorelevere a ieie ere 448 Paepenimental ueculbs 1.!acinacye tere nivite is ern; eie)ier, ofarsteraiel alete ae 448 DISC UBSIONOF mELESULGS) fs Nive reeit ef eie Sa sialon aia) svetalale atevers 465 Influence ot Amount of MOO... j\a\0 s/c cue scien os 466 Influence of Thermal Environment................. 471 Influence oi Character (of Moody. si o.iesisieislag lees 472 The Expenditure of Energy in Digestion, eslapied cholo Ibis sien) Biuule havens e Sate don wa moa eae risen nae c 491 So. Uiulizatron morn Muscular Work 5. ome dec ee eile tiettjo nce 494 Utilization of Net Available Energy.................62- 497 The Efficiency of the Animal as a Motor............ 498 Conditions determining Efficiency.................. Blt Utilization of Metabolizable Energy.................... 525 WY Oli SMe SHIP ALIOUSS exec ava eis epecele csiciers ia ¢ ate. aiuis ene 528 Lia — ; ‘ik ya ; $s ” ¥s, we" Tota Por ee + ie pe THE PRINCIPLES OF ANIMAL NUTRITION. INTRODUCTION. TuE body of an animal, regarded from a chemical point of view, consists of an aggregate of a great variety of substances, of which water, protein, and the fats, with smaller amounts of certain carbohydrates, largely predominate. By far the greater portion of the substance of the body, aside from its water, consists of so- called “ organic” compounds; i.e., compounds of carbon with hydro- gen, oxygen, nitrogen, and, to a smaller extent, with sulphur and phosphorus. These compounds are in many cases very complex, and all of them have this in common, that they contain a con- siderable store of potential energy. It is through these complex “ organic”? compounds that the phe- nomena of life are manifested. All forms of life with which we are acquainted are intimately associated with the conversion of com- plex into simpler compounds by a series of changes which, regarded as a whole, partake of the nature of oxidations. During this break- ing down and oxidation more or less of the potential energy of these compounds is liberated, and it is this liberation of energy which is the essential end and object of the whole process and which, if not synonymous with life itself, is the objective manifestation of life. This is equally true of the plant and the animal, although masked in the case of green plants by the synthetic activity of the chloro- phyl in the presence of light. The process is most manifest in the animal, however, both on account of the inability of the latter to utilize the radiant energy of the sun and on account of the greater intensity of the process itself. Setting aside for the moment any storing up of material, and I . PRINCIPLES OF ANIMAL NUTRITION. therefore of potential energy, in the body for the future use of the -animal itself or of its offspring as being, from a physiological point of view, temporary and incidental, the sole useful product of the animal is energy. All the physical effect which we can produce, either through our own bodies or those of our domestic animals, is simply to move something, and moving something is equivalent to the exertion of energy. This motion may be the motion of visible masses of matter in the performance of useful work or the invisible molecular motion of heat, which is economically a waste product, but in either case the animal is a source of energy which is imparted to its surroundings. From this point of view, then, we may look upon the animal as a mechanism for transforming the stored-up energy of the sun’s rays, contained in its tissues, into the active or “kinetic” forms of heat and motion. The various cells and tissues of the living animal body, in the performance of their several func- tions, break down and oxidize the proteids, fats, carbohydrates, and other materials of which they are composed or which are con- tained in them, seizing, as it were, upon the energy thus liberated and converting it, here into heat, there into motion, again into the energy of chemical change, as the needs of the organism demand. The very definition of physical life, then, implies that the living animal is constantly consuming its own substance, rejecting the simpler compounds which result and giving off energy in the various forms characteristic of living beings. Obviously, this process, if unchecked, would soon lead to the destruction of the organism and the dissipation of its store of potential energy. To prevent this catastrophe is the object of the great function of nutrition. This function, in its broader outlines, is familiar to us all through daily experience and observation. The living animal requires to be frequently supplied with certain substances which collectively constitute its food. This food contains a great variety of chemical ingredients, but much the larger part of it consists of “organic” compounds belonging to the three great groups already noted as making up the larger share of the organic matter of the body, viz., the proteids, the fats, and especially the carbohydrates, and while the individual members of these groups differ in the two cases, the ingredients of the food, like those of the body, contain a large store of potential energy. These and other “organic” substances, INTRODUCTION. 3 together with more or less mineral matter, are separated by the organism, in the processes of digestion and resorption, from the un- essential or unavailable matters of the food. The latter are rejected from the body, while the former are used by it to take the place of the material broken down and excreted by its vital activities, and thus serve to maintain its capital of matter and of potential energy. In other words, the food may be regarded as the vehicle by means of which a little portion of the “infinite and eternal energy * from which all things proceed ” is put for the time being at the service of the individual ; as being not so much a supply of matter to make good the waste of tissue as a supply of energy for the mani- festations of life. The animal body, then, from our present standpoint, consists of a certain amount of matter which has been temporarily segregated from the rest of the universe and which represents a certain store or capital of potential energy. This aggregate of matter and energy is in a constant state of change or flux. On the one hand, its vital activities are continually drawing upon its capital. By the very act of living it expends matter and energy, On the other hand, by means of the function of nutrition, it is continually receiv- ing supplies of matter and energy from its environment and adding them to its capital. Plainly, then, the growth, the maintenance, or the decay of the bedy depends upon the relation which it is able to maintain between the income and the expenditure of matter and energy. If the two are equal], the animal is simply maintained without increase or decrease; if the inecme is greater than the expenditure, the body adds to its capital of matter and energy, if the income is less than the expenditure, the necessary result is a diminution in the accumulated capital which, if continued, must ultimately result in death. We thus reach an essentially statistical standpoint, and this aspect of the subject of nutrition. which has been designated by some writers as “The Statistics of Nutrition,’’ forms the subject. of the succeeding pages. The topic naturally divides itself into two distinct although closely related parts, viz.: 1. The income and expenditure of matter. 2. The income and expenditure of energy. 4 PRINCIPLES OF ANIMAL NUTRITION. These topics will be considered in the above order, it being assumed that the reader is already familiar with the general nature of the nutritive processes included under the general heads of digestion, resorption, circulation, respiration, and excretion. PARE -l THE INCOME AND EXPENDITURE OF MATTER. CHAPTER I. THE FOOD. THE supply of matter to the body is, of course, contained in the food, including water and the oxygen taken up from the air. In a more limited and familiar sense, the term food is employed to signify the supply of solid matter, or dry matter, to the animal. It is proposed here simply to recall certain familiar facts relative to the composition and digestibility of the food in this narrower sense, taking up the subject in the barest outline. Composition.—While a vast number of individual chemical compounds are found in common feeding-stuffs, the conventional scheme for their analysis unites these substances into groups and - regards feeding-stuffs as composed, aside from water and mineral matter, essentially of protein, carbohydrates and related bodies, and fats. Or, setting aside the mineral ingredients, the “organic” ingredients may be divided into the nitrogenous, comprised under the term protein, and the non-nitrogenous, including the fats and carbohydrates. ProteIn.—The name “protein” originated with Mulder, who used it to designate what he supposed to be a common ingredient of all the various proteids, but it has since come to be employed as a group name for the nitrogenous ingredients both of feeding-stuffs and of the animal body. The amount of protein in feeding-stuffs we have at present no 5 6 PRINCIPLES OF ANIMAL NUTRITION. means of determining directly, but it is commonly estimated from the amount of nitrogen upon two assumptions: first, that all the substances of the protein group contain 16 per cent. of nitrogen, and second, that all the nitrogen of feeding-stuffs exists in the proteid form. On the basis .of these assumptions, protein is, of course, equal to total nitrogen X 6.25. Although it was never claimed that this method of estimating protein was strictly accurate, it was for a long time assumed that the two sources of error involved were not serious. Later investi- gations, however, have dispelled this pleasing illusion. Further investigations of the true proteids, notably those of Ritthausen and of Osborne, have shown a very considerable variation in the per- centage of nitrogen contained in them, while, on the other hand, the researches of Scheibler, E. Schulze, Kellner, and others have shown the presence in many feeding-stuffs of relatively large amounts of nitrogenous matters of non-proteid nature. The results of these latter investigations have made it necessary to subdivide the total nitrogenous matter of feeding-stuffs into two groups, called respec- tively “proteids” and “non-proteids,”’ while the name “protein” has been retained in the sense of total nitrogen X 6.25 or other con- ventional factor. Jor various classes of human foods, Atwater and Bryant * propose the following factors, based on the results in- dicated in the next two paragraphs, for the computation of protein from nitrogen: FAGNITIVAN TOOUS! .. 2,2 eke ake ook Ache ieee eae gpa ee 34 6.25 Wheat, rye, barley, and their manufactured products 5.70 Maize, oats, buckwheat and rice, and their manufactured PT OUUCTS la. sce aie tems oh ones ol etwas ELE te eee 6.00 Dried: seeds of Leotmes .). es cs sis vatieuetnr at hate nite eee 6.25 VERET ALES. 2 'S'. 5 '% sccrurcldicla: sy Scenyena to ape hoeeak on eee eae 5.65 | ht a a a SL Ale ere Oe IR Bee Sci RT 5.80 Proteids.—In the absence of any adequate knowledge regarding the very complex molecular structure of the proteids, both the classification and the terminology of these bodies are in a very con- fused state. For convenience, however, we may adopt here those * Storrs (Conn.) Ag. Ex. St., Rep. 12, 79. THE FOOD. | tentatively recommended by the Association of American Agri- cultural Colleges and Experiment Stations,* viz.: Albumins, { Simple Globulins, Albuminoids +{ and allies. Protein. Total - : Derived. nitrogen com- [ Proteids (Modifies } Compound. pounds Collagens or gelatinoids Extractives, | : L Non-proteids Aimides, amido-acids, ete. It is not necessary for our present purpose to enter into any dis- cussion either of the properties of the proteids as a whole or of the differences between the different classes of proteids. One point, however, is of particular importance, namely, the elementary com- position of these bodies. As noted above, this has been found to be more variable than was supposed earlier. In particular the per- centage of nitrogen has been found to have a somewhat wide range. “Recent investigations with perfected methods show percentages of nitrogen in the numerous single proteid substances found in the grains ranging from 15.25 to 18.78. These are largest in certain oil seeds and lupines and smallest in some of the winter grains. Ritthausen,f a prominent German authority, concedes that the factor 6.25 should be discarded, and suggests the use of 5.7 for the majority of cereal grains and leguminous seeds, 5.5 for the oil and lupine seeds, and 6.00 for barley, maize, buckwheat, soja-bean, and white bean (Phaseolus) rape, and other brassicas. Nothing short of inability to secure greater accuracy justifies the longer contin- uance of a method of calculation which is apparently so greatly erroneous.” (Jordan.) Non-proteids—This term is used as a convenient designation for all the nitrogenous materials of feeding-stuffs which are not proteid in their nature. It is an abbreviated form of non-proteid nitrogenous bodies. The substances of this class found in plants are chiefly the organic bases, amides, amido-acids, and similar bodies which are produced by the cleavage of the proteid molecule under the action of digestive and other ferments or of hydrating agents. They appear to exist in the plant partly as intermediate stages in the synthesis of the proteids and partly as products of *U.S. Dept. Agr., Office of Experiment Station, Bul., 65, p. 117, { Landw. Vers. Stat., 47, 391. . 8 PRINCIPLES OF ANIMAL NUTRITION. their subsequent cleavage in the metabolism of the plant. They are chiefly soluble, crystalline bodies. The most common of them is asparagin, which has been, to a certain extent, regarded as typical of the group. The non-proteids are commonly determined by determining as accurately as possible the non-proteid nitrogen and multiplying the latter by the factor 6.25. In the case of asparagin, however, which contains 21.2 per cent. of nitrogen, the proper factor obviously should be 4.7, while the factor would vary for the different forms of non-proteids which have been observed in plants. It is no simple matter, therefore, either to determine directly the amount of non- proteids or to decide upon the proper nitrogen factor in any partic- ular case. For the present, however, the factor 4.7 would seem to be at least a closer approximation to the truth than 6.25. In the animal body the group of non-proteids is represented by the so-called “extractives” or “flesh bases’’ of the muscle, chiefly creatin and creatinin. Fats.—The fats of the plant, like those of the animal, consist chiefly of glycerin compounds of the so-called “fatty acids,” or of similar bodies. These are accompanied in the plant, however, by other materials—wax, chlorophyl, ete.—which are extracted along with the fat by the common method of determination and consti- tute part of the “crude fat” or “ether-extract.” The results, therefore, which have been obtained in feeding experiments with pure fats cannot be used with safety as a basis for estimating the nutritive value of the so-called “fat” of feeding-stuffs, particularly in the case of coarse fodders. CARBOHYDRATES. — The well-characterized group of carbo- hydrates makes up a large proportion of the organic matter of our more common feeding-stuffs. Those members of this group occur- ring in any considerable quantities in feeding-stuffs may be sub- divided on the basis of molecular structure into the hexoses, on the one hand, whose molecules contain six atoms of carbon or a mul- tiple of that number, and the pentoses, or five carbon series, on the other. In the grains and other common concentrated feeding-stufis, and particularly in the food of man, the hexose group largely pre- dominates, including starch, dextrin, the common sugars, and more or less cellulose. In the coarse fodders consumed by our domestic THE FOOD. 9 herbivorous animals, while the hexose group is also largely repre- sented it is accompanied by no inconsiderable quantities of carbo- hydrates belonging to the pentose group. The individual members of this latter group are both less abundant and less well known chemically than the hexoses, and at present our knowledge of their actual nutritive value is somewhat scanty. Since the methods for their determination are based upon the fact that they yield furfural upon boiling with dilute hydrochloric acid, some recent analysts have proposed the term “furfuroids” as a more appropriate desig- nation of these substances as determined by present methods. In the conventional scheme for the analysis of feeding-stuffs, the carbohydrates are subdivided, not upon the basis of their chemical structure but upon the basis of their solubility. Those members of the group which can be brought into solution by boiling dilute acids and alkalies under certain conventional conditions are grouped together as ‘“Nitrogen-free extract,’ while those ingredients which resist solution under these conditions are designated as “Crude fiber.”? The more common hexose carbohydrates, such as starch, sugars, etc., are included in the nitrogen-free extract, while the larger part, although not all, of the cellulose is included under the crude fiber. At the same time, more or less of the pentose carbo- hydrates or “furfuroids” are found in both these groups, while the crude fiber of coarse fodders contains also a variety of other ill- known compounds, somewhat roughly grouped together under the general designation of ligneous material. Digestibility.—A part of nearly all common food materials is incapable of digestion and is rejected in the feces. In the food of man and that of carnivorous animals this indigestible portion is usually small and may disappear entirely. In the food of herbivora, on the other hand, there are contained relatively large amounts of substances which are incapable of solution in the digestive tract, while varying proportions of materials which in themselves are capable of being digested may escape actual digestion under some circumstances. In the latter animals, therefore, it becomes par- ticulary important to determine the digestible portion of the food. The digestibility of a feeding-stuff is estimated indirectly by deter- mining as accurately as possible the undigested matter eliminated from the body in the feces and subtracting it from the total amount se) PRINCIPLES OF ANIMAL NUTRITION. contained in the food. This method may of course be applied either to the dry matter or the organic matter of the food asa whole or to any single determinable ingredient. Meranouic Propucts.—The digestive tract of an animal, how- ever, not only serves as a mechanism for the digestion of food but has excretory functions as well, and the rejected matter contains, besides the undigested portion of the food, these excreta and the metabolic products of intestinal action. In the case of food largely or completely digestible, these substances may make up the larger portion or even the whole of the feces, while, on the other hand, they constitute but a small proportion of the bulky excreta of herbivora. It is obvious that these products must be taken account of if it is desired to learn the actual digestibility of the food. Unfortunately, however, we have at present no trustworthy method for their deter- mination. In the past it has been customary to designate the difference between food and feces as digestible and, in the case of domestic animals at least, to assume that the error involved is not serious. Apparent Digestibility—Availability—Even with herbivo- rous animals, however, the presence of the so-called metabolic products in the feces may give rise to serious errors in the deter- mination of the real digestibility of some ingredients of the food, notably fat and protein. “With carnivora, or with the’ human subject, the case is for obvious reasons still worse, and it is scarcely possible to determine the digestibility of the food in the strict sense of the word. The difference between food and feces does represent, however, the net gain of matter to the organism resulting from the digestion of the food. To express this conception, the use of the word avail- able has been proposed by Atwater.* The “available nutrients” of a food, according to him, are the actually digestible nutrients minus the metabolic products contained in the feces and which may be regarded as representing the expenditure of matter, in the form of residues of digestive fluids, intestinal mucus, epithelium, etc., necessarily incident to the digestion of the food. The term has been * Storrs (Conn.) Agr’] Expt. St., Rep., 12, 69. THE FOOD. II used chiefly in connection with human nutrition. In discussions of animal nutrition the terms digestible and digestibility have become so firmly established that it may be questioned whether the intro- duction now of a new term would not create more confusion than it would prevent, and whether it is not preferable, when strict accuracy of expression is required, to attach a modifying word. and designate the difference between food and feces as apparently digestible, in distinction from the real digestibility, which we cannot as yet deter- mine. DETERMINATION OF APPARENT DiGESTIBILITY.—The determi- nation of the apparent digestibility of the nutrients of a feeding- stuff in the above sense, or of their “ digestibility ” in the older sense, consists simply in determining the amount of the feces or of their separate ingredients and comparing them with the correspond- ing amounts in the food. Aside from ordinary analytical precautions, the chief condition of accurate results is that the feces correspond to the food consumed. In animals with a comparatively simple digestive canal, like man and the carnivora, this is readily brought about by the ingestion of a small amount of some substance like powdered charcoal or infu- sorial earth, which is in itself indigestible and which serves to sepa- rate the feces of two successive periods. In the case of herbivora, on the other hand, the undigested residues of the food become mixed to a large extent with those of the previous period. In this case, therefore, it is essential that a preliminary feeding be continued for a sufficient length of time to remove the residues of previous foods from the digestive organs, and further that the experiment itself -extend through a number of days in order to eliminate the influence of irregularity of excretion. SIGNIFICANCE OF Resuuts.—It is plain from what has just been said that what the results of such an experinient actually show is that a certain amount of material has disappeared from the food during its transit through the alimentary canal. This fact of itself. however, does not necessarily show that the missing material has been digested in any true sense. In the case of animals possessing a relatively short and simple digestive apparatus. we are probably justified in assuming that the difference between food and undigested matter represents material that has actually been m2 PRINCIPLES OF ANIMAL NUTRITION. digested. In the long and complicated digestive apparatus of herbivora, however, there is the possibility that a variety of proc- esses may go on aside from a simple solution of nutrients by the digestive fluids. In particular, it has been shown, as will appear in greater detail later, that extensive fermentations, particularly of the carbohydrates, occur, and that relatively large amounts of these bodies may be destroyed in this way. Furthermore, with our present conventional scheme for fodder analysis, we have to take account of the possibility of the conversion of members of one group of nutrients into those of another. For example, it seems not improbable that a portion of the crude fiber of feeding-stuffs may be so modified in the digestive tract, without being actually dissolved, that, in the feces, it is determined as nitrogen-free extract, thus diminishing the apparent digestibility of the latter group and increasing that of the crude fiber.* Composition OF Diaestep Foop.—The proleids during the process of digestion are largely converted into proteoses and pep- tones, while the trypsin of the pancreatic Juice, at least outside the body, carries the cleavage of the proteid molecule still further and gives rise to comparatively simple, crystalline bodies. It is not altogether clear to what extent this degradation of the proteids occurs in natural digestion, but the probability appears to be that it does not play a large part, and it has been generally believed that the proteids are resorbed chiefly as proteoses and peptones.f The non-proteids being largely crystalline bodies and readily soluble, we may presume that they are resorbed without material change except so far as they may serve as nitrogenous food for the micro-organisms of the digestive tract. The fat of the food does not undergo any profound change in digestion, but is claimed to be resorbed largely in the form of an emulsion. -A part of it, however, is undoubtedly saponified by the bile, although the extent to which this process takes place is a disputed point, while in some cases at least a cleavage into glycerin and free fatty acids appears to take place. The carbohydrates, particularly the easily soluble members of the hexose group, are in the case of man and the carnivora, and * Cf, Fraps, Jour. Am, Chem. Soc., 22, 543. t See note, p. 58. THE “FOOD: 13 probably also to a large extent in the swine and horse, converted into sugars and resorbed in that form. Fermentations.—Reference has already been made to the fermen- tations taking place in the digestive tract. In the herbivora, and especially in ruminants, these fermentations play an important part in the solution of the carbohydrates which make up so large a portion of the food of these animals. These bodies undergo a fermentation which was first studied by Tappeiner * in the case of cellulose, but which has since been shown by G. Kiihn 7 to extend also to the more soluble carbohydrates. The products of this fermentation appear to be methane, carbon dioxide, and organic acids, chiefly, according to Tappeiner, acetic and butyric. Of these products, only the organic acids at best can be supposed to be of any value to the animal organism, and obviously it makes a very serious difference in our estimate of the nutritive value of starch, for example, whether it is resorbed chiefly or entirely in the form of sugar or whether in a ruminant more than half of it, as in some of Kiihn’s experiments, is fermented. * Zeit. f. Biol., 20, 52. + Landw. Vers. Stat., 44, 569. CHAPTER II. METABOLISM. General Conception.—By the various processes of digestion and resorption the epithelium of the alimentary canal extracts from the crude materials eaten those ingredients which are fitted to nourish the animal and transmits them more or less directly to the general circulation which carries them to all the tissues of the body. While these ingredients are many in number and diverse in charac- ter, yet the vast mass of them, aside from the water in which most of them are dissolved, may be grouped under six heads, viz., ash ingredients, albuminoids or bodies related to the albuminoids, amides and other crystalline nitrogenous substances, fats, carbo- hydrates, and organic acids, and these, together with relatively small amounts of other materials, may be regarded as constituting the real food of the organism. As was pointed out in the Introduction, the cells of which the living tissues of the animal body are composed are the seat of con- tinual chemical change. On the one hand, the digested ingredients of the food which are brought to them by the circulation are being built up into the structure of the body. On the other hand, the material of the cells is undergoing a continual process of breaking down and oxidation, uniting with the oxygen supplied by the blood to form the waste products which are removed from the body through the organs of excretion. These excretory products are substantially carbon dioxide, water, and urea and similar nitroge- nous substances. The general term Metabolism is commonly used to designate the totality of the chemical and physical changes which the materials of the resorbed food, or of the tissues formed from them, undergo in being converted into the excretory products. Similarly, we may speak in a more restricted sense of the metabolism of a single ingre- 14 METABOLISM. 15 dient of the food, as of the proteids, carbohydrates, or fats. Thus proteid metabolism signifies the chemical changes undergone by the proteids of the food in their conversion into the corresponding excretory products. In ordinary usage the chemical reactions undergone by the ash ingredients of the food are not included, the word metabolism being practically used to designate the chemical changes in the organic matter of food or tissue. METABOLISM A PROCESS OF OxIDATION.—The process of met- abolism as a whole is one of oxidation. While we must beware of being misled by analogy into regarding as a simple burning of food-materials that which is in reality a highly complex action of the living cells of the organism, still the final result is much the same in both cases. Starting with more or less complex organic substances and oxygen, we end either with the completely oxidized compounds carbon dioxide and water or with nitrogenous sub- stances like urea more highly oxidized than the protein from which they are derived. The oxidative character of the total metabolism is most simply illustrated by a comparison of the percentage of oxygen contained in the most prominent ingredients of the food, on the one hand, and in the chief excretory products, on the other hand, as in the follow- ing statement: Percentage of Oxygen. In food: POLI PAV eTARE) | we tote wa sialahsln mies soos 23.00 iS omer. se se). Pan iad ois wih Lens. al tere nsey i 11.50 IDES 70 Siete Dey ae Ae ree PALE 5O..Oo In excreta: Wine te ee tainbsrs nd eek Ua aa | ae ae 26.67 Curbom clomidert 1s 3's aoe sha aie aes ee G22 A REYNE ARR atte te cs Yat ainant eo ate See oT had as 88.89 Merasouism AN ANALYTIC PRocess.—From a slightly different point of view, metabolism may be described as an analytic process. The molecules of the food constituents are highly complex. The molecule of dextrose or levulose, the forms in which the carbo- hydrates are chiefly resorbed, contains 24 atoms; the molecules of 16 PRINCIPLES OF ANIMAL NUTRITION. the three most common fats, respectively 155, 167, and 173 atoms. The molecular structure of the proteids has not yet been made out, but it is highly complex.* The molecules of the excretory prod- ucts, on the contrary, are comparatively simple, those of carbon dioxide and water containing but three atoms each, that of urea eight, and even that of hippuric acid but twenty-two. In metabolism, in other words, the complex molecules of the . carbohydrates, fats, proteids, ete., which have been built up in the plant, by means of the energy contained in the sun’s rays, out of carbon dioxide, water, and nitric acid or ammonia, gradually break down again into simpler compounds, their atoms reuniting with the oxygen from which they were separated in the plant. MeTABOLISM A GRADUAL PRocESS.—The chemical changes in- cluded under the term metabolism take place gradually. As has already been indicated, metabolism is not a simple oxidation of nutrients, like the burning of fuel in a stove, but the nutrients enter, to a large extent at least, into the structure of the cells of which the various tissues are composed. Metabolism is really the sum of the chemical actions through which the nutrition and life of these cells is manifested. These actions, however, differ from tissue to tissue and from cell to cell, and even in the same cell from time to time, and the resulting metabolic products are correspondingly varied. Between the nutrients supplied to the cells by the blood and the final products of metabolism as excreted from the body there are innumerable intermediate products, a few of which we know but concerning most of which we are still ignorant. We know the first and last terms of the series and thus are able to measure, as it were, the algebraic sum of the changes, but of the single factors making up this sum. as well as of the specific tissues concerned in the changes, we are largely ignorant, although we know that they are numerous. ANABOLISM AND KatasBotisM.—While the process of metab- olism as a whole is one of analysis and oxidation, with liberation of energy, it must not be supposed that each single step in the process is of this nature. As has been already pointed out, the chemical activities of the tissues possess a dual character. By the * Osborne (Zeit. physiol. Chem., 38, 240) has recently obtained the number 14,500 as the approximate molecular weight of edestin, METABOLISM. 17 various processes of nutrition, ingredients of the food are first incor- porated into the tissues of the body, to be subsequently broken down and oxidized. In this building-up process changes undoubt- edly occur in the direction of greater complexity of molecular struc- ture, involving the temporary absorption of energy. Thus it is known that fats may be formed from carbohydrates in the body. Many physiologists hold that the metabolism in the quiescent muscle results in the building up of a complex “contractile substance, ” whose breaking down furnishes the energy for muscular work. In general, we may regard it as highly probable that the molecules of the living substance of the body are much more complex than those of the nutrients of the food, and that the former are built up out of the latter by synthetic processes, carried on at the expense of energy derived from the breaking down of other molecules. Such changes as this are called anabolic and the process anabolism, while the changes in the direction of greater simplicity of molecular structure are called katabolic, and the process katabolism. The metabolism of the living body, then, consists of both anabolism and katabolism. By the former the food nutrients are built up into body material; by the latter they are broken down, yielding finally the compara- tively simple excretory products. On the whole, however, the katabolism prevails over the anabolism, so that metabolism as a whole is, as already stated, an analytic and oxidative process. Neither the anabolism of tissue production nor the minor anabolic changes which seem to occur in various tissues alter the main direc- tion of the metabolic changes in the body, but, from the standpoint of the statistics of nutrition, are simply eddies in the main current § 1. Carbohydrate Metabolism. HEXOSE CARBOHYDRATES. The hexose carbohydrates of the food appear to be resorbed chiefly by the capillary blood-vessels of the intestines. For the most part, they reach the blood in the form of dextrose, with smaller amounts of levulose and galactose, and with greater or less quantities of acetic, butyric, lactic, and other acids derived chiefly from the fermentation of the carbohydrates in the digestive tract. 18 PRINCIPLES OF ANIMAL NUTRITION. The percentage of dextrose in the blood is small, but remarkably constant, the limits of variation being from about 0.11 to about 0.20 per cent., and the average about 0.15 per cent. Its amount varies but slightly in different regions of the body, and in different classes of animals, and is searcely at all affected by the nature or amount of the food. Not only so, but any excess of dextrose in the blood is promptly gotten rid of. It is a striking fact that if any con- siderable amount of this substance, which forms so large a part of the resorbed nutriment, be injected directly into the blood it is treated as an intruder and at once excreted through the kidneys. Evidently it is of the greatest importance to the organism that the supply of this substance to the tissues shall be constant. Under ordinary conditions, however, the influx of sugar from the digestive tract is more or less intermittent. After a meal rich in easily digestible carbohydrates, an abundant supply of it is taken up by the intestinal capillaries, while on a diet poor in carbohydrates or in prolonged fasting, the supply sinks to a minimum. This is, of course, especially true of animals like man and the carnivora in which the process of digestion is comparatively rapid, but even in herbivorous animals, with their more complicated digestive appara- tus, the rate of resorption of dextrose, and still more its absolute amount, must be more or less fluctuating. Evidently there must be some regulative apparatus which holds back from the general circu- ation any excess of dextrose, on the one hand, and prevents its being excreted unused, and on the other, supplements any lack resulting from a deficiency of the food in carbohydrates. This regulation is accomplished by the liver. Functions of the Liver. The functions of the liver in this regard appear to be twofold: First, it manufactures dextrose and supplies it to the general cireu- \ation; and second, it serves as a reservoir, or a place of deposit, for any excess of carbohydrates supplied by the digestive apparatus. . Tur Liver As A Source or Dextrrose.—The blood as it comes from the intestinal capillaries, bearing the digested carbo- hydrates and proteids, enters the liver through the portal vein and is distributed by means of the capillary blood-vessels into which this vein divides through all parts of that organ, reaching the general METABOLISM. — 19 circulation again through the hepatic vein. In its passage through the capillaries of the liver, the blood is subjected to the action of the cells of the liver (hepatic cells). Our knowledge of the exact nature of this action is still more or less conjectural, in spite of a vast -amount of experimental investigation, but certain general facts are pretty clearly established. In the first place, the hepatic cells appear to serve as a source of dextrose when no carbohydrates are supplied in the food. If a carnivorous animal be given a diet as free as possible from carbo- hydrates, as, for instance, prepared lean meat, consisting substan- tially of proteids, its blood still contains a normal amount of dex- trose and the blood in the hepatic vein is found to be richer in dextrose than that of the portal vein, showing that this substance is being formed in the liver. Moreover, while the percentage of dextrose in the blood is small, the total amount thus manufactured is very considerable. Seegen * estimates it at about one per cent. of the weight of the body in twenty-four hours. This is regarded by many physiologists as an overestimate, the considerable differ- ences in sugar content between the portal and hepatic blood found by Seegen being regarded as in part the -effect of the necessary operation. Indeed, it is questioned by some whether any actual difference in sugar content between the portal and hepatic blood under normal conditions has been satisfactorily established analyti- cally, but the indirect evidence at least seems strongly in its favor. In the second place, the same outflow of dextrose from the liver appears to take place when the animal consumes a mixed diet con- taining carbohydrates. In this case also, except shortly after a meal containing much carbohydrates, the blood of the hepatic vein shows an excess of dextrose over that of the portal vein. The amount of dextrose thus introduced into the circulation is sub- stantially the same as in the first case, and its percentage in the blood is not perceptibly altered. The source of this dextrose, how- ever, is not so simple a question, since it is possible that all or a considerable portion of it may be supplied directly or indirectly by the dextrose resorbed by the intestinal capillaries. Granting the continual production of sugar by the liver, sub- * Die Zuckerbildung im Thierkérper, p. 115. 20 PRINCIPLES OF ANIMAL NUTRITION. stantially two suppositions are open: On the one hand, we may consider that the resorbed carbohydrates of the food, after being temporarily stored up in the liver, as described below, are given off again without radical change and that the sugar-forming power of the hepatic cells is limited to the transformation of the proteids and perhaps the fats of the food. Or, on the other hand, we may sup- pose that the nutrients brought to the liver by the portal blood enter into the constitution of the protoplasm of the hepatic cells, and that the vital activity of this protoplasm gives rise to the dex- trose found in the blood, to the glycogen found in the liver, and to other products of whose nature we are largely ignorant. The evidence at hand is doubtless insufficient for a final decision between these alternatives, but the latter hypothesis would seem more in accord with our general knowledge of cell activity. As relates to the carbohydrates, it is supported by the fact that while various sugars besides dextrose (lzvulose, mannose, galactose, sorbinose, and, as Miinch * has shown, certain artificial hexoses) may be con- verted into glycogen, the resulting glycogen is always the same and the product of its hydration is always dextrose.t In other words, the molecular structure of these sugars is altered in a manner sug- gesting an assimilation by the hepatic cells rather than anything resembling an enzyme action. The subject can be more intelli- gently considered, however, in the light of a discussion of the second function of the liver. Tue Liver AS A RESERVOIR OF CARBOHYDRATES.—When the food is rich in carbohydrates, the supply of dextrose to the blood through the intestinal capillaries is more or less intermittent. As a means of regulating this intermittent supply, the hepatic cells have the power of arresting the dextrose brought to them by the portal vein and converting it into a polysaccharide called “ slycogen” or “animal starch” which is stored up in the liver. On the other hand, when the supply of carbohydrate food is cut off, and especially if all food be withdrawn, the glycogen of the liver rapidly diminishes, being apparently reconverted into dextrose. This latter phenomenon may be readily observed in the liver of a freshly killed animal. If the fresh liver, after removal from the * Zeit. physiol. Chem . 29, 493. +Compare Neumeister, Physiologische Chemie, p. 326 METABOLISM. 21 body, be washed out by water injected through the portal vein till all sugar is removed, and if then, after standing for a time, the wash- ing be renewed, the first portions of water that pass contain sugar. The same process may be repeated several times. What is known as the glycogenic function of the liver was dis- covered by Claude Bernard in 1853, and has been the subject of a bewildering amount of discussion and controversy, both as to the origin of glycogen, its final fate, and its relations to the production of dextrose by the liver. Certain facts, however, may be regarded as established with at least a high degree of probability: First—The liver produces glycogen from dextrose and other (not all) carbohydrates, as above described. Second—The liver seems also to form glycogen from proteids, since this substance is found in considerable quantity in the livers of animals fed exclusively on meat. Third—Glycogen largely disappears from the liver during fast- ing, and to a considerable degree also in the absence of carbo- hydrates from the food. Fourth—The liver produces dextrose at an approximately con- stant rate, largely independent of the food-supply or the variations in the store of glycogen. These facts seem to point unmistakably to the sugar-producing fanction of the liver. as the primary factor in the whole matter. The general metabolism of the body requires a constant proportion of dextrose in the blood, and as this dextrose is consumed the liver furnishes a fresh supply. This supply it manufactures from the materials brought to it by the blood of the portal vein. When carbohydrates are lacking in this blood, it apparently has the power of breaking down the proteids and perhaps the fats, thus supplying the needful dextrose. Some authorities claim that the same process goes on when carbohydrates are present, and it seems not unlikely that this is true, but when the food-supply consists so largely of carbohydrates as it does in the case of our domestic herbivorous animals, the conclusion seems unavoidable that at least a consider- able part of the dextrose consumed in the body must be derived from these substances. As already suggested, a very plausible view of the matter is to regard the resorbed nutrients of the portal blood as serving to feed the protoplasm of the hepatic cells and to look 22 PRINCIPLES OF ANIMAL NUTRITION. upon the dextrose as one of the products of the metabolism of those cells. Since, however, the demands of the organism for dextrose and the supply of it, or of the materials for its manufacture, in the food do not keep pace with each other, sometimes one and sometimes the other being in excess, the liver has a second function. When the food-supply, of whatever kind, is in excess, instead of continuing to produce dextrose the metabolism in the liver takes a slightly differ- ent form and produces the insoluble glycogen, or perhaps the dex- trose of the portal blood is simply converted into glycogen without entering into the structure of the hepatic vrotaplasm. When, on the other hand, the food-supply is deficient, the stored-up glyco- gen is converted into dextrose; whether by some sort of enzyme action or by again serving as food for the hepatic protoplasm is uncertain. Fate of the Dextrose of the Blood, The fact that the proportion of dextrose in the blood is approxi- mately constant, notwithstanding the continual supply which is received from the liver, shows that there must be a continual abstrac- tion of dextrose from the blood, which is as continually made good by the activity of the hepatic cells. In fact, the dextrose of the blood appears to play a very prominent part in the animal economy, and the function of the liver in preparing it from other ingredients. of the food is a most important one. CONSUMPTION IN THE MuscLtes.—From the point where it leaves the liver, our knowledge of the metabolism of the dextrose of the blood is scanty, but a large proportion of it undoubtedly takes place in the muscles. It was early shown by Chauveau that the proportion of dextrose in the blood diminishes in its passage through the capillaries of the body, so that the arterial blood con- tains more of this substance than the venous. In conjunction with Kaufmann * he has subsequently shown more specifically that in its passage through the muscular capillaries and through those of the parotid gland the blood is impoverished in dextrose, and to a much greater extent in the active than in’ the quiescent muscle. Coin- * Comptes rend., 103, 974 and 1057; 104, 1126 and 1352. METABOLISM. 23 cident with this disappearance of dextrose, there is an increase in the carbon dioxide of the blood and a decrease of its oxygen. The relations of the dextrose of the blood to the evolution of heat and work in the muscles and other tissues, so far as they are at present understood, will be considered in a subsequent chapter. For our present purpose it suffices to note the fact that it disappears in the capillaries with the ultimate production of carbon dioxide and water. That the dextrose is immediately oxidized to carbon dioxide and water, however, is extremely unlikely. It has been suggested that the lactic acid which is found in the muscle after muscular contraction is one of the intermediate products of the oxidation. Several considerations, however, seem to render it more probable that the dextrose first enters in some way into the constitution of the muscles, or in other words, that a synthetic or anabolic process precedes the katabolic one. MuscuLaR GuycoGEN.—Another fact, of much interest in this connection, is that the muscles (and other tissues also), as well as the liver, contain glycogen. Moreover, the muscular glycogen diminishes or disappears during work and reappears again after rest. It would appear, then, that the muscular tissue shares with the liver the ability to form glycogen. As in the case of the former organ, the simplest supposition is that this glycogen is produced from the dextrose supplied in the blood, and Kiiltz * and others have shown that subcutaneous injections of sugar give rise to a formation of muscular glycogen in frogs whose livers have been removed. On the other hand, of course, the considerations pre- sented above relative to the sources of the liver glycogen apply, ceteris paribus, to the formation of glycogen in the muscles. Neither the source nor the exact functions of the muscular glycogen are yet beyond controversy, but the facts just stated strongly suggest a storing up of reserve carbohydrates during rest to be drawn upon when there is a sudden demand for rapid metabolism. Far Propuction.—In addition to its important relation to the muscles, the dextrose of the blood likewise supplies nourishment for the fat tissues of the body. Hitherto we have spoken as if the supply of dextrose to the blood were determined substantially by * Neumeister, Physiologische Chemie, p. 322. 24 PRINCIPLES OF ANIMAL NUTRITION. the demands of the general metabolism for material to produce heat and motion. Plainly, however, the capacity of the muscles and the liver to store up carbohydrates is limited, and if the food-supply is permanently greater than the demands of the organism, some other provision must be made for the excess. Under these cireum- stances the superfluous dextrose which finds its way into the blood gives rise to a production of fat, which is stored up as a reserve in special tissues and apparently does not enter again into the general metabolism until a permanent deficiency in the food-supply occurs. The experimental evidence of the production of fat from carbo- hydrates, as well as the quantitative relations of the process so far as they are known, will be considered subsequently. In its relations to the economy of the organism the process is analogous to the formation of glycogen in the liver, except that the storage capacity of the fat tissues is vastly greater, but as compared with the forma- tion of glycogen it is distinctively an anabolic process, the fat molecule being more complex and containing more potential energy than that of dextrose. Hanriot,* assuming the formation of olein, stearin, and palmitin in molecular proportions, represents the process by the equation: 13C,H,,0, = CzsH,.,0, + 23CO, + 26H,0. PENTOSE CARBOHYDRATES. ~The facts of the foregoing paragraphs relate primarily to the hexose carbohydrates, particularly starch and sugar, and to a con- siderable extent to the metabolism of carnivorous animals. The food of herbivora, however, contains a great variety of carbohy- drates and especially considerable quantities of the pentose or five- carbon carbohydrates. That these substances are in part digest- ible, or that at least a considerable proportion of them disappears from the food during its transit through the alimentary canal, was first shown by Stone,t+ and has sinee been fully confirmed by the investigations of Stone & Jones t and of Lindsey & Holland,§ but of their further fate in the body relatively little is known. * Archives de Physiol., 1893, 248. t Agricultural Science, 5, 6. {+ Amer. Chem. Jour., 14, 9. § Ibid., 8, 172. METABOLISM. 25 Ebstein,* who was the first to investigate this subject, showed qualitatively the presence of pentose carbohydrates in the urine of man after the ingestion of arabinose and xylose even in very small doses, and concluded that these sugars are not assimilable. Salkowski ¢ shortly afterward observed the appearance of pen- toses in the urine of rabbits given arabinose after five or six days of fasting. He found in the urine, however, only about one-fifth of the amount ingested, together with small amounts in the blood and larger ones in the muscles, but there was a considerable increase of the glycogen of the liver. From the latter fact Salkowski con- cludes that arabinose may be, either directly or indirectly, a source of glycogen. The glycogen found in his experiment was the ordi- nary six-carbon glycogen. Subsequent investigations-by Cremer,} Munk,§ Frentzel,|| Linde- mann & May,§ Fr. Voit,** Jacksch,t> Mitinch,{{ Salkowski,§$§ and others have been directed largely to two questions, viz., whether the pentose carbohydrates are oxidized in the body and whether they serve as a source of glycogen. PENTOSES OXIDIZED IN THE Bopy.—As the general result of these investigations, it may be stated that pentoses (in particular arabinose and xylose), whether administered by the stomach or injected into the blood, are at least partially oxidized in the body. In the human organism the power of oxidizing the pentoses, which do not normally constitute any considerable portion of its food, appears to be quite limited, and even when they are given in small quantities a portion (no% all) is excreted in the urine. In the rabbit the pentoses seem to be more vigorously oxidized, only about twenty per cent. being excreted unaltered, even when compara- tively large doses are given. In these experiments the pentose sugars were administered in considerable amounts at once, and the excretion of a portion unal- tered would seem to be a phenomenon similar to the temporary * Virchow’s Archiv, 129, 401; 132, 368. J Arch. klin. Med., 56, 283. + Centralbl. med. Wiss., 1893, p. 193. **Ibid., 58, 524. t Zeit. f. Biol., 29, 536; 42, 428. ++ Zeit. f. Heilk., 20, 195. § Centralbl. med. Wiss., 1894, p. 83. tt Zeit. physiol. Chem., 29, 493. | Arch. ges. Physiol., 56, 273. 8§ Ibid., 32, 393. 26 PRINCIPLES OF ANIMAL NUTRITION. glycosuria caused by large doses of the common sugars. The pen- tose carbohydrates in the ordinary food of herbivora, however, are largely or entirely the comparatively insoluble pentosans. As already stated, these bodies are partially digested—that is, they do not reappear in the feces. As to the manner of their digestion we are ignorant. If we are justified in assuming that the digested portion is converted, wholly or partially, into pentoses, then the conditions differ from those of the experiments above mentioned in that the production and assimilation of the pentoses is gradual. Under these circumstances we might be justified in anticipating a more complete oxidation of these bodies. To what extent this is true it is at present impossible to say. Weiske,* in connection with his investigations upon the digestibility of the pentosans, states that the urine of the sheep and rabbits experimented upon gave only a slight reaction for pentoses. The writer has not been able to find any records of other tests of the urine of domestic animals for pentoses. PENTOSES AS A SOURCE OF GLycoGEN.—Most, although not all, investigators have found an increase in the glycogen of the liver consequent upon the ingestion of pentoses, but in every case it has been the ordinary six-carbon glycogen. This has been commonly and most naturally interpreted as showing that the pentoses are not themselves converted into glycogen in the body, but are simply oxidized in the place of some other material which is the true source of the observed gain of glycogen. In the light of known facts regarding the apparent power of the liver to produce glycogen from _ very diverse hexoses (see p. 20) it would seem, however, that the possibility of an actual assimilation of the pentoses by the hepatic cells should at least be borne in mind. THE ORGANIC ACIDS. Tn addition to such quantities of the organic acids, free and com- bined, as are contained in their food, relatively large amounts of these substances are, in the case of herbivorous animals and par- ticularly of ruminants, produced by the fermentation of the carbo- hydrates in the alimentary canal. For this reason their meta- * Zeit. physiol. Chem., 20, 489. METABOLISM. 27 bolism may properly be considered in connection with that of the carbohydrates themselves. But little is known of the metabolism of the organic acids, how- ever, beyond the fact that they are oxidized in the body, a portion of the resulting carbon dioxide appearing in the urine, in combina- tion with sodium and potassium, rendering that fluid alkaline. Wilsing * and v. Knieriem + have shown that organic acids such as result from the fermentation of carbohydrates are not found to any appreciable extent in the excreta, while the researches of Munk f and Mallevre,§ which will be considered more particularly in another connection, have shown that the sodium salts of butyric and acetic acids when injected into the blood are promptly oxi- dized, and Nencki & Sieber || have shown that lactic acid is readily oxidized, even by a diabetic patient. NON-NITROGENOUS MATTER OF THE URINE. 6 It has been implied in the foregoing pages that the digested carbohydrates of the food, whatever the intermediate stages through which they may pass, are ultimately oxidized to carbon dioxide and water. Of the ordinary hexose carbohydrates this is doubtless true, but with some of the large variety of substances ordinarily grouped together, by the conventional scheme of feeding-stuffs analy- sis, as “carbohydrates and related bodies,” or as “crude fiber’’ and “nitrogen-free extract,” the case appears to be otherwise. It has been shown that the urine, in addition to the nitrogenous products of proteid metabolism which will be considered in a subsequent section, contains also non-nitrogenous materials, pre- sumably metabolic in their nature. In the urine of man and of the carnivora these non-nitrogenous substances are chiefly or wholly such as might be derived from the metabolism of proteids (phenols and other compounds of the aromatic series), and their amount is comparatively small. In the urine of herbivora, particularly of ruminants, however, their quantity is relatively very considerable, and it seems impossible to regard any large portion of them as derived from the proteid metabolism. * Zeit. f. Biol., 21, 625. t Arch. ges. Physiol., 46, 322. + Ibid., 21, 139. & Tbid., 49, 460. || Jour. pr. Chem., N. F., 26, 32. 28 PRINCIPLES OF ANIMAL NUTRITION. Henneberg * found that from 26.7 to 30.0 per cent. of the organic matter of sheep urine was neither urea nor hippuric acid, while from 95 to 100 per cent. of the total nitrogen was contained in these two substances. G. Kiihn in his extensive respiration experiments on oxen, as reported by Kellner,+ assuming that all the nitrogen of the urine was in the form either of hippuric acid or urea, found that from 40.05 to 67.64 per cent. of the total carbon of the urine was present in non-nitrogenous substances. The more recent investi- gations of Kellner,{ as well as those of Jordan § and of the writer,| have fully confirmed this fact. Apparently these non-nitrogenous organic substances are de- rived in some way largely from the coarse fodders. Their propor- tion in the urine is relatively large when the ration consists exclu- sively of coarse fodder, and the addition of such fodders to a basal ration causes a marked increase in their amount, while, on the @ther hand, such concentrated feeding-stuffs as have been inves- tigated do not produce this effect in any very marked degree. Furthermore, their amount seems to bear no fixed relation to the protein of the coarse fodder. When the amount of the latter ingredient is small, the total organic matter of the urine has in some cases exceeded the maximum amount that could have been derived from the protein of the food, thus demonstrating that a portion at least of the non-nitrogenous urinary constituents must have had some other source. As the proportion of protein in the food increases, the amount of nitrogenous products in the urine likewise increases, while that of the non-nitrogenous products appears to be more constant, so that the ratio of urinary nitrogen to carbon increases. The most plausible explanation of these facts seen.s to be that the substances in question are derived from some of the non-nitrogenous ingredients of the coarse fodders, but from what ones, or what is the nature of the products, we are still ignorant. * Neue Beitriige, etc., p. 119. + Landw. Vers. Stat., 44, 348, 404, 474, 529, tIbid., 47, 275; 50, 245; 53, 1. § New York State Expt. Station, Bull. 197, p. 27. || Penna. Expt. Station, Bull. 42, p. 150. {A further discussion of this subject in its relations to the energy of the food will be found in Part II. METABOLISM. 29 § 2. Fat Metabolism. Scarcely a tissue or portion of the animal body can be named in which more or less fat is not found. The muscular fibers, the epithelium, the nerves and ganglia, etc., all contain cells in which globules of fat may be recognized, so that the capacity to produce or store up fat seems to be common to almost all the cells of the ‘body. It is particularly in certain cells of the connective tissue, however, that the large accumulations of visible fat in the body take place. At the outset these cells present no special characters, but in a well-nourished animal globules of fat begin to accumulate in them, the cells enlarge, the globules of fat coalesce into larger ones, and finally the cell substance is reduced to a mere envelope, the nucleus being pushed to one side and almost the whole volume of the cell occupied by fat. Masses of connective tissue thus loaded with fat constitute what is called adipose tissue. Large deposits of adipose tissue are met with surrounding various organs, particu- larly the kidneys, but the largest deposit of fat is usually in the connective tissue underlying the skin. In milk production, too, large amounts of fat appear in the epithelial cells of the milk glands. Fat Manufactured in the Body.—The older physiologists held that all the ingredients of the body pre-existed in the food. Specifi- cally, animal fat was regarded as simply vegetable fat which had escaped oxidation in the body and been deposited in the tissues. But while there is no doubt that the fat of the food can contribute to the fat supply of the body, the food of herbivorous animals usually contains a relatively small quantity of fat and the amount produced by a rapidly fattening animal or by a good dairy cow is usually much greater than that consumed in the food. Deferring to subsequent pages a discussion of the sources of animal fat,* we may content ourselves here with anticipating the general results of the great amount of experimental inquiry which has been expended upon this question. These results may be briefly summarized in the following statements: * For avery complete review of the literature of fat production up to 1894, see Soskin, Journ. f. Landw., 42, 157. 30 PRINCIPLES OF ANIMAL NUTRITION. 1. The animal body produces fat from other ingredients of its food. 2. The carbohydrates and related bodies of the food serve as sources of fat. 3. It is probable that the proteids also serve as sources of fat. So far, then, as that portion of the fat which is actually pro- duced in the body from other substances is concerned, we may most readily conceive of its formation as consisting essentially of a manufacture of fat by the protoplasm of the fat cells, which are nourished by the carbohydrates, proteids, and other materials brought to them by the circulation. Functions of the Food Fat.—The fat which is manufactured in the body from other ingredients of the food, however, often con- stitutes the larger portion of the total fat production, while but a relatively small proportion at most can be derived from the fat of the food. The question naturally arises whether this smaller portion contained in the food is simply deposited mechanically, so to speak, in the fat cells, or whether it too, like the carbohydrates and proteids, serves to nourish the fat cells and supply raw material out of which they may manufacture fat. At first thought the former alternative might seem more prob- able. The fat of the food, so far as we are able to trace it, does not undergo any considerable chemical changes, such as the proteids do, e.g., in the process of digestion, but is largely resorbed in the form of only slightly altered fat. | Moreover, resorption of fat takes place largely through the lacteals and the resorbed fat reaches the general circulation without, being subjected like the carbohydrates to the action of the liver. Deposition oF Foreign Fats.—The view just indicated is supported to a considerable extent by the results of experiments upon the fate of foreign fats introduced into the body. Experiments by Radziejewsky * and Subbotin + were indecisive, but Lebedeff { was later successful in obtaining positive re- sults. Two dogs, after prolonged fasting, received smal! amounts of almost fat-free meat together with, in the one case, linseed oil, *Virchow’s Archiv., 56, 211; 48, 268. + Zeit. f. Biol.. 6, 73. { Thier. Chem. Ber., 12, 425; Zeit. Physiol. Chem.. 6, 149: Centralbl. med. Wiss., 1882. 129. METABOLISM. 3t and in the other, mutton tallow. After three weeks, during which the animals recovered their original weights, the adipose tissue was found to contain, in the one case, fat fluid at 0° C. and agreeing very closely with linseed oil in its chemical behavior, while in the other ease the fat had a melting-point of over 50° C., and was almost identical with mutton fat. On the other hand, the same author in experiments with tributyrine failed to obtain any noteworthy deposition. of this substance. Munk * fed large amounts of rape oil to a previously fasted dog for seventeen days and found in the body considerable amounts of fat differing markedly in appearance and properties and in the proportion of olein to solid fats from normal dog fat. He likewise succeeded in isolating from the fat eruic acid, the characteristic ingredient of rape oil. In a second experiment + the fatty acids prepared from mutton tallow were fed with similar results, the proportion of stearin and palmitin to olein being approximately reversed as compared with normal dog fat. The latter experiment is also of interest as showing that the fatty acids may be synthesized to fat in the body, the change taking place, according to Munk, in the process of resorption. More recently Winternitz { has experimented with the iodine addition products of fats. He observed the retention of a con- siderable proportion of iodine in the body (of hens and dogs) in organic form and also found iodine in the fat of the body at the close of the experiment. Similar experiments on a milking goat § showed that at least 6 per cent. of the fat fed passed into the milk. Henriques and Hansen || fed two three-months-old pigs for about nine months with ground barley, to which was added, in one case linseed oil and in the other cocoanut oil, while in the succeeding three months the rations were exchanged. Samples of the sub- cutaneous fat of the back were taken (with the aid of cocaine) at four different times and the fat of the carcasses at the close of the experiment was also examined. The results showed an abundant deposition of the linseed oil (and cocoanut oil?). On the other * Thier. Chem. Ber., 14, 411; Virchow’s Archiv., 95, 407. + Archiv. f. (Anat. u.) Physiol., 1883, p. 278. t Zeit. physiol. Chem , 24, 425. § Thier. Chem. Ber., 27, 293. | Ibid., 29. 68. 32 PRINCIPLES OF ANIMAL NUTRITION. hand, experiments with cows failed to show any passage of linseed oil as such into the milk. Leube * made subcutaneous injections of melted butter on two dogs and found an abundant deposit of butter fat especially under the skin of the abdomen, the Reichert-Meissl number of the fat being 20.46 in the first case and 15.3 in the second. Rosenfelt + fed fasted dogs with mutton fat and observed a large deposit of this fat in all parts of the body. INFLUENCE OF FEEDING ON CoMPOSITION OF F aT. —In addition to the more purely physiological experiments just cited, there are on record a not inconsiderable number of feeding experiments, especially upon swine, in which the feeding appears to have sensibly influenced the appearance, firmness, melting-point, or composition of the body fat. , While it is not impossible, however, that in some cases the peculiar fats of the food (e.g., the fat of maize or of the oil-meals) may have been deposited in the adipose tissue unchanged, it must be borne in mind that these experiments were made on mixed rations and that undoubtedly there was a considerable production of fat in the body from other ingredients of the food. This being the case, we are left in doubt as to whether the effect observed is due directly to the fat of the food or is to be explained as an effect of the food as a whole, or of some unknown ingredients of it, in modifying the nature of the metabolism in the fat cells. That such an explana- tion is at least possible would seem to be indicated by the well- established fact that marked changes of food do modify the metabolism in the milk gland sufficiently to materially affect the proportion of volatile fatty acids in butter fat. . A striking example of the possibility of such an effect upon the metabolism of the fat cells is afforded by the recent investigations of Shutt { into the causes of “soft”? pork. _On the average of a con- siderable number of animals, he finds that the shoulder and loin fat of pigs fed exclusively on maize shows a very low melting-point and a high iodine absorption number, indicating a large percentage of olein, and inclines to attribute this effect to the oil of the maize. When, however, he fed skim milk with the maize, he obtained pork * Thier. Chem. Ber., 25, 45. + Ibid., 25, 44. ¢t Canada: Dominion Experiment Station, Bull. 38. METABOLISM. 33 of good quality, the fat having a melting-point and iodine number not widely different from those obtained with the most approved rations. While it is possible that part of this effect was due to a reduced consumption of maize oil, so that more fat was produced from the other ingredients of the food, the conclusion seems justified that the principal factor was the influence of the skim milk upon the nutrition of the fat cells. This influence may with some degree of probability be ascribed to its protein, and it is worthy of notice that in Shutt’s experiments the rations which produced the highest grade of pork were composed of materials rich in protein. Another fact warns us to be cautious in our interpretation of the results of this class of feeding experiments. Such experiments in most cases involve a comparison of the composition of the fat from animals differently fed. Albert * has found that both with swine and sheep the composition of the body fat is subject to very considerable individual variations as to melting-point, refractive index, and iodine number, the differences being, in his experiments, greater than the average differences which could be ascribed to the feeding. Moreover, the fat of the same individual has not the same com- ‘ position in different parts of the body. This point has recently been the subject of an elaborate investigation by Henriques & Hansen,} whose results show a higher melting-point and a lower iodine number in the inner as compared with the outer layers of fat. This difference they ascribe to the difference in the tempera- ture of the tissues and support this view by an experiment with three pigs. One animal was kept in a stall heated to about 30° C. for two months, while the others were exposed to a temperature of 0° C., one unprotected and the other partially enveloped in a sheep- pelt. At the close of the experiment the fat immediately under the skin gave the following figures: Todine Solidifying Number. Point. Keptiatro0r—oo Cie. o 2 Sake 69.4 24.6° C. Kept at 0°, in sheep pelt: Part under the pelt........ 67.0 25.4° C. Par hie x POSE or we 's:.,' poate nes 69.4 24.1° C. Kept at 0°, unprotected.......:. (ORS 23.3° C. * Landw. Jahrb., 28, 961, 986. + Bied. Centr. Blatt. Ag. Ch., 30, 182. 34 PRINCIPLES OF ANIMAL NUTRITION. Towards the interior of the body the differences became grad- ually less. It is evident, then, that the sources of possible error in ex- periments upon the influence of food on the composition of body fat are considerable, and that not only is great care necessary to secure representative samples of fat for examination, but the effect of individuality must be eliminated so far as possible by the use of a considerable number of animals. When we add to this the other fact that the fat production of herbivorous animals is largely at the expense of other nutrients than fat, we shall hardly incline to give the results of such investigations much weight as regards the question of the functions of food fat. QUANTITATIVE RELATIONS.—Some further light upon the point under discussion may perhaps be obtained from a consideration of the quantitative relations of food fat to fat production shown by respiration experiments and which will be considered more fully on subsequent pages (compare Chapter V). In scarcely any of these experiments has the food fat been deposited quantitatively in the tissue. In three out of five experiments by Rubner in which fat was given to a previously fasting animal, from 65.82 to 91.89 per cent. of the fat supplied in excess of the amount metabolized during fasting was stored up in the body. Similarly, in the ex- periments of Pettenkofer & Voit, in which the fat was added to a ration already more than sufficient for maintenance, on the average 87.86 per cent. of the fat of the food was deposited in the tissues. Kellner,* among his extensive respiration experiments upon cattle, reports the results of three in which peanut oil was added to a basal ration more than sufficient for maintenance. The amounts of fat consumed in excess of the basal ration and the resulting gains by the animals were as follows, the slight variations in the amounts of the other nutrients being neglected: Gain by Animal. < Additional Fat Gain of Fat Animal, Digested, in Per Cent. of Fat Grams. Protein, Fat, Digested. Grams. Grams. D 677 8 239 35.30 F 542 86 205 387.83 G 458 44 27 60.91 * Landw. Vers. Stat., 53, 112, 124, 199, 214. METABOLISM. 25 Computations of the proportion of the energy of the added fat which was recovered in the total gain of flesh and fat (compare Chapter XIII, § 1) showed, according to the method of computa- tion employed, a loss of from 31 to 48 per cent. The comparatively small losses observed in Rubner’s and in Pettenkofer & Voit’s experiments may well be ascribed to a con- sumption of energy in the work of digestion (compare Chapter XJ), but it hardly seems possible to account in this way for the large losses observed by Kellner. Apparently the peanut oil in these experiments, after its digestion and resorption, must have been subjected to extensive molecular changes involving a considerable expenditure of potential energy, and if this be true, the suggestion of an assimilation by the fat cells and a construction of animal fat from the oil is obvious. ConsTANcy OF ComposITION OF F'ats.—The relatively constant and characteristic composition of the fat of the same species of animal, notwithstanding differences in the food, has been urged in favor of the view that the fat of the animal is a product of the protoplasmic activity of the fat cells. “The fat of a man differs from the fat of a dog, even if both feed on the same food, fatty or otherwise” (M. Foster). The steer produces beef fat and the sheep mutton fat on identical rations. Unless, however, we are prepared to discredit the experimental results above cited, it would appear that this general and approximate uniformity of composition is largely due to a general uniformity of food, and that marked changes in the nature of the latter may result in altering the former. To this must be added, as already insisted upon, the fact that much of the fat found in the body, especially in the herbivora, is undoubtedly produced in the organism. We may fairly presume that this fat will be the characteristic fat of the species. If we may suppose further that a considerable share of the food fat is oxidized directly, and if we take into consideration the general uniformity of diet of our domestic animals and the relatively small total amount of fat which it often contains, we have at least a plausible explanation of the observed facts and one which does not preclude a direct deposi- tion of food fat in the body and a consequent effect upon the com- position of the body fat. The Katabolism of Fat.—The proportion of the food fat which 36 PRINCIPLES OF ANIMAL NUTRITION. serves to increase the store of fat in the body depends largely upon the total food-supply. When the latter is more than sufficient to balance the total metabolism of the organism, the excess may give rise to a storage of fat, and under these circumstances the food fat or a part of it may, as we have seen, contribute to the increase of adipose tissue. On the other hand, when the food-supply is in- sufficient, not only is its fat in common with its, other ingredients in effect consumed to support the vital processes, but the fat pre- viously stored in the adipose tissue is drawn upon to make up the deficiency. Under these circumstances the fat disappears more or less rapidly from the fat cells, passing away gradually either into the lymphatics or the blood-vessels in some manner not as yet fully understood. Fat, then, whether derived immediately from the food or drawn in the first instance from the adipose tissue of the body, passes into the circulation and serves to supply the demands of the body for oxidizable material and energy, the final products of its oxida- tion being carbon dioxide and water. Of the intermediate steps in this katabolic process we are comparatively ignorant, but one hypothesis regarding it has acquired so much importance in its bearings on the availability of the potential energy of the food as to require mention here. ForMATION OF Dextrose FRoM Fat.—This hypothesis is, in brief, that the first step in the katabolism of fat takes place in the liver and consists in its conversion into sugar. In other words, it is held that the fat of the food or that drawn from the adipose tissue of the body supplies the liver with part of the material for its fune- tion of sugar production described in the previous section. This hypothesis is advocated especially by those physiologists who, like Seegen in Vienna and Chauveau and his associates in Paris, look upon the.carbohydrates, and particularly dextrose, as the im- mediate source of the energy exerted in muscular contraction or in the’various other forms of physiological work. The evidence upon which this view is based will be considered in subsequent chapters. For the present it suffices to point out that, if we admit its truth, then the general metabolism of the body is essentially a carbohydrate metabolism. Whether we consider the case of a fasting animal, living upon its store of protein and fat, or that of an METABOLISM. SY | animal receiving food, the liver breaks down the proteids and fat supplied to the blood either by the food or from the tissues, pro- ducing dextrose. This dextrose, like that derived from the carbo- hydrates of the food, is then, as indicated in the previous section, oxidized in the tissues either directly or with previous conversion into glycogen. As regards the katabolism of fat, in particular, Nasse * has brought forward reasons for believing that the liver is concerned in it. Seegen + submitted fat to the action of finely chopped, freshly excised liver suspended in defibrinated blood at a temperature of 35—40° C., in a current of air and observed a considerable formation of sugar in five to six hours as compared with a control experiment without the fat. He likewise found { in experiments upon dogs fed on fat with little or no meat that the blood of the hepatic vein was much richer in sugar than that of the portal vein. On the basis of the probable amount of blood circulating through the liver, he computes that the total amount of sugar thus produced was much greater than could have been supplied by the glycogen stored in the liver and the amount of proteids metabolized (as measured by the urinary nitrogen), and hence concludes that at least the difference was produced from fat. As was pointed out in the preceding section, however, many physiologists regard the large differences between the dextrose content of the portal and the hepatic blood observed by Seegen as being in large part the result of the necessary operation and thus abnormal, and the production of glycogen or dextrose from fat is not regarded as proven by the majority of physiologists. Thus Girard |] and Panormow § found the post-mortem formation of sugar in the liver to be strictly pro- portional to the disappearance of glycogen, and similar results were obtained by Cavazzani and Butte.** Kaufmann,}{} who has developed this hypothesis in considerable * vy. Noorden, Pathologie des Stoffwechsels, p. 85. + Die Zuckerbildung im Thierkorper, p. 151. Slbia. ape liv § Cf. Neumeister, Physiologische Chemie, p. 368. || Arch. ges. Physiol., 41, 294. - “] Thier. Chem. Ber., 17, 304. ** Tbhid., 24, 391 and 394. t+ Archives de Physiol., 1896, p. 331. 38 PRINCIPLES OF ANIMAL NUTRITION. detail, represents the two supposed stages in the katabolism of fat by the two following equations, proposed by Chauveau:* First Stage: 2(C;,Hy490,) +670, = 16(C,H,,0,) + 18CO,+ 14H,0. Second Stage: 16(C,H,,0,) +960,=96CO,+ 96H,O. Even, however, if we admit the formation of dextrose from fat in the body, it may fairly be doubted whether the process is as simple as these equations, even if regarded as simply schematic, would imply. § 3. Proteid Metabolism. ANABOLISM. : Digestive Cleavage.—The digestion of the proteids is essen- tially a process of cleavage and hydration under the influence of certain enzyms. By this process the complex proteid molecules are partially broken up into simpler ones. By the action of pepsin in acid solution we obtain albumoses and peptones, while the trypsin of the pancreatic juice, at least outside the body, carries the cleavage still further, producing crystalline nitrogenous bodies of comparatively simple constitution. Opinions are still more or less divided as to how far these processes of cleavage and hydration are carried in the actual process of digestion, where the products of the action are constantly being resorbed, but there are not wanting in- dications that it is both less extensive and less rapid than in arti- ficial digestion. It likewise seems to have been demonstrated that some soluble proteids are capable of direct resorption without change, while others are not and some, notably casein, are promptly coagulated by the rennet ferment, apparently expressly in order that they may be subjected to the action of the digestive ferments. In a general way, the statement appears to be justified that the larger share of the proteid material of the food is resorbed as albumoses and peptones. (See note, p. 58.) Purposr or THE CLEAVAGE.—The fact just mentioned that, on the one hand, some soluble proteids appear capable of direct re- sorption, while, on the other hand, some, like casein, are at once rendered insoluble as the first step in digestion, plainly necessitates a material modification of the old view that the object of the cleay- age and hydration of the proteids in digestion is to render them * La Vie et |’Energie chez |’Animale. METABOLISM. 39 soluble. Undoubtedly this is an important function of the digestive fluids, but the fundamental object lies deeper and is found in the constitution of the proteids themselves. Constitution of the Proteids.—When acted upon by the various digestive ferments, or by strong acids or alkalies, the proteids readily undergo hydrolysis and yield a series of products of decreasing molecular complexity and increasing solubility, rang- ing from very slightly modified proteids through the so-called proteoses and peptones to still simpler substances. When the hydrolysis, especially acid hydrolysis, is pushed as far as possible there result a number of comparatively simple crystalline products, which are qualitatively the same for all the simple proteids, with a few exceptions. The known primary cleavage products of the simple proteids are all amino-acids. One of the first of these to be isolated was glycocol or amino-acetic acid. The other cleavage products of the simple proteids may be regarded as derived from glycocol by the replacement of one atom of hydrogen by various atomic groupings. In all of them, the amino group occupies the same position in the molecule relatively to the carboxyl group as in glycocol, viz., the so-called alpha position. The amino-acids derived from the proteids may be sub- divided into mon-amino and di-amino acids, the larger number of those at present identified belonging to the first of these groups. Some of them are derived from the simple fatty acids, others contain aromatic and other radicals, and a few the element sulphur. Altogether, some seventeen different cleavage products of this sort have been identified. These amino-acids account for from 60 to 70 per cent. of the proteid molecule and appear to be its characteristic ingredients, the constitution of the rest of the prcteid molecule being unknown. The amino-acids which are obtained by the hydrolysis of proteids may be caused to combine with each other, the amino- group of one uniting with the carboxyl group of the next, with the elimination of one molecule of water, forming the so-called peptids. As many as seven amino-acids have been thus linked up into peptids, the more complex of which resemble in many respects the proteids. The latter are, indeed, believed to be substantially very complex “polypeptids,”’ which are split up by 40 PRINCIPLES OF ANIMAL NUTRITION. the action of the digestive ferments into the comparatively simple atomic groupings of which they are composed—the so-called ‘“‘building-stones”’ of the proteids. Differences in Proteids.—In a few proteids, certain of these atcmic groupings are not found at all. For example, no glycocol — is produced by the hydrolysis of casein or albumin and no lysin from gliadin or zein. Furthermore, while most of the simple proteids yield qualitatively the same cleavage products, the relative proportions of these several. products vary widely in proteids from different sources. One of the most striking in- stances of this is glutaminic acid, which ranges from about 30 per cent. on the average of the wheat proteids to 9 per cent. on the average of the four common animal proteids, casein, egg albumin, serum albumin, and serum globulin. Food Proteids and Body Proteids——What is especially to be noted in this connection is that the food proteids are not identical with the body proteids. This is especially true of the vegetable proteids in the food of the herbivora, and of the casein of milk, but is measurably true in all cases. A simple resorption of unaltered proteid, therefore, would not serve the purposes of the organism. The food proteids must be changed to body proteids. This means, however, that the proportions of those molecular groupings which have just been spoken of must be changed—that is, the molecules of the food proteid must be so far broken down into their constituent atomic groupings as to permit of a rearrangement and repropor- tioning of the latter into molecules of body proteid. Such a partial breaking down of proteid material takes place i in digestion. The products of proteid digestion, as they are pre- sented to the resorbent organs of the digestive tract, are no longer proteids, but the constituent atomic groupings out of which body proteids may be built up. Rebuilding of Proteids.—The simple proteids are resorbed, as we have just seen, in the form of comparatively simple cleavage products, in part as amino-acids and in part probably as more or less complex polypeptids. Out of these substances the body builds up the great variety of proteids peculiar to itself and which differ in chemical structure and properties from those of the vegetable world. Since it has not been possible to identify any of the amino- = METABOLISM. 41 acids in the blood, the current view has been that these “‘building- stones”? of the proteids are synthesized in the epithelial cells of the resorbent organs, and that the resulting proteids—in par- ticular serum albumin—are passed on to the blood to serve as nourishment to the proteid tissues of the body. If this be the case, however, it is evident that the blood proteids must sub- sequently undergo an extensive hydrolysis and that their con- stituent atomic groupings must be rearranged on a different plan to produce the various tissue proteids. In other words, if the molecular débris of the food proteids is promptly recon- verted into blood proteids in the epithelial cells, the splitting up effected in digestion must be to a considerable extent repeated in the nutrition of each tissue and even, perhaps, of each cell. This fact has led to the belief that the real seat of the synthesis is not, or at least not exclusively, the epithelial cells of the intes- tine, but that every living cell, each in its own measure, builds up its own proteids from the fragments supplied by the digestive process. The failure to detect individual cleavage products in the blood is plausibly explained by the relatively small amounts resorbed in ordinary cases and by the fact that when not synthe- sized to proteids they seem to undergo rapid katabolism. Whatever may finally prove to be the case in this respect, however, there is no dispute as to the general facts that the food proteids undergo more or less complete cleavage in the digestive process and that the resulting fragments are subsequently built up again into body proteids and that, therefore, the first step in proteid metabolism is an anabolic process. KATABOLISM. Final Products.—The anabolic processes which have just been indicated might be characterized in general terms as a preparation of the food proteids for their diverse functions in the body. In the performance of those functions they, like all the organic ingredients of the body, undergo katabolic changes, liberating the energy which was originally contained in them or which may have been tem- porarily added in the preliminary anabolic changes. We have every reason to believe that the katabolism of proteids is a gradual process, passing through many intermediate stages, but we have very little actual knowledge of the steps which intervene between 42 PRINCIPLES OF ANIMAL NUTRITION. the proteids and bodies which are either excretory products themselves or closely related to them. Such information as has thus far been acquired upon this subject has resulted chiefly from attempts to trace back the excretory products to their antecedents. The products of the complete breaking down and oxidation of proteids in the body are carbon dioxide and water, excreted through the lungs, skin, and kidneys, and urea and a number of other com- paratively simple crystalline nitrogenous compounds found in the urine. To these are to be added the nitrogenous metabolic prod- ucts of the feces, the sulphuric and phosphoric acids resulting from the oxidation of the sulphur of the proteids and the phosphorus of the nucleo-proteids, and the relatively minute amounts of nitroge- nous matter found in the perspiration. EXcRETION OF FREE NirroGEN.—The question whether any portion of the nitrogen of the proteids is excreted as free gaseous nitrogen is one which has been the subject of no little investigation and controversy in the past, the especial champions being, on the affirmative, Seegen in Vienna and, on the negative, Voit in Munich. It would lead us too far aside from our present purpose, however, to attempt even to outline the evidence, and it must suffice to say that the great majority of physiologists regard it as established that there is no excretion of gaseous nitrogen as a result of the katabolism of proteids, but that all the proteid nitrogen is excreted in the urine and feces with the exception of small amounts in the perspiration. In accordance with this view, we shall assume in subsequent pages that the urinary nitrogen (together with, strictly speaking, the metabolic nitrogen of the feces and perspiration) furnishes a meas- ure of the total proteid katabolism of the body. A brief consideration of some of the principal nitrogenous products of proteid katabolism will serve to indicate some of the main features of the process, so far as they have been made out. Urea.—Urea, or dicarbamid, CON,H,, is the chief nitrogenous product of proteid metabolism in the carnivora and omnivora. In the urine of man, e.g., from 82 to 86 per cent. of the nitrogen is in the form of urea.* Antecedents of Urea.—A vast amount of study has been expended upon this question without as yet leading to any general unanimity of views. It appears, however, to be fairly well made out that at * vy. Noorden, Pathologie des Stoffwechsels, p. 45. METABOLISM. 43 least a considerable part if not all of the urea is formed in the liver, and that its immediate antecedent is ammonium carbonate, to which it is closely related chemically. This theory of Schmiede- berg’s is supported by the facts: Ist. That ammonium salts, and also the amid radicle NH, in the amino acids of the fatty series, when administered in the food are converted into urea. 2d. That ammonium carbonate or formiate injected into the portal vein is converted in the liver into urea which appears in the blood of the hepatic vein. 3d. That the administration of inorganic acids to the dog and to man results in the excretion of ammonium salts in the urine, it being supposed that the acid displaces the weaker carbonic acid and that the resulting ammonium salt is incapable of conversion into urea in the liver. 4th. Severe disease of the liver has been observed to result in a decreased production of urea and an excretion of ammonium salts in the urine. Later investigations by Minkowski * and others have followed the process of the formation of urea one step further back and ren- dered it highly probable that the ammonium salts out of which urca is formed reach the liver in the form of ammonium lactate. It has been shown that sareolactic acid is one of the products of the meta- bolism of the muscles. It would appear that this acid unites with the ammonium radicle derived from the proteids to form ammonium lactate, and that the latter on reaching the liver is first oxidized to the carbonate, which is then converted into urea. If, by disease or surgical interference, this action of the liver is prevented, ammo- nium lactate appears in the urine, and the same effect may even be produced by excessive stimulation of the proteid metabolism, so that the production of ammonium lactate exeeeds the capacity of the liver to convert it. Uric Actp.—Urie acid is contained in small amounts in the urine of mammals. With birds it constitutes the chief nitrogenous product of the proteid metabolism. In mammals it must be regarded as essentially a product of the katabolism of the nucleo- proteids of the food or of the body tissue, although a portion of * Cf. Neumeister, Physiologische Chemie, pp. 313-318. 44 PRINCIPLES OF ANIMAL NUTRITION. the urie acid thus produced is further katabolized and yields urea. In birds there is an extensive synthetic production of uric acid from simpler katabolic products. Hippuric Actb.—This substance is a normal ingredient of the urine of mammals, but in that of man and the carnivora is found in but very small amounts. In the urine of herbivora, on the other hand, it occurs abundantly. Light was thrown upon its origin by the well-known discovery by Wohler, in 1824, that it is also found in large amount in the urine of man or of carnivora after the administration of benzoic acid. Chemically, hippuric acid is benzamido-acetic acid, or benzoyl glycocol. When the food contains benzoic acid the latter unites with glycocol resulting from the metabolism of the proteids and forms hippuric acid, while otherwise the glycocol would be further oxidized to simpler nitrogenous products. The synthesis of hip- purice acid has been shown to occur only in the kidneys in the dog, but in the case of the rabbit and frog they appear to share this capacity with other organs. In this action of benzoic acid we have the most familiar demon- stration of the formation of metabolic products intermediate be- tween the proteids and the comparatively simple nitrogenous sub- stances found in the urine. Glycocol has never been detected in the body, obviously because as fast as it is formed it 1s again decom- posed. Benzoic acid reveals its presence by seizing upon it and converting it into a compound which is incapable of further oxida- tion, and is therefore excreted. Other less familiar examples of the same fact might be cited did space permit. The normal presence of small quantities of hippuric acid in the urine, even when no benzoic acid is contained in the food, arises from the fact that the putrefaction of the proteids in the intestines yields aromatic compounds, containing the benzoyl radicle, which are resorbed and combine with glycocol to form hippuric acid. The origin of the large quantities of hippuric acid ordinarily ex- erected by herbivora, however, or rather of its benzoyl radicle, is still more or less of a puzzle, notwithstanding the consider- able amount of investigation which has been devoted to its study. The most natural supposition would be that the food of adi METABOLISM. 45 these animals contains substances of the aromatic series capable of yielding benzoic acid or its equivalent in the body, but in none of the feeding-stuffs known to be efficient in causing an excretion of hippuric acid have such compounds been discovered in quantity even remotely sufficient to account for the hippurie acid produced. On the other hand, the hypothesis that the benzoyl! radicle of the hippuric acid is derived to any large extent from the proteids of the food appears to be decisively negatived by several facts: First, the quantity of proteids in the ordinary rations of herbivora is relatively small, and even if it all underwent putrefaction the amount of aromatic products which could be formed, on any reason- able estimate, would account for only a small fraction of the hip- puric acid actually found.* Second, in several instances it has been observed that variations in the extent of the putrefactive processes in the intestines, as measured by the amount of con- jugated sulphuric acid in the urine (compare p. 46), bore no rela- tion to the variations in the production of hippuric acid. Third, the addition of pure proteids or of foods very rich in proteids to a ration does not increase the production of hippuric acid, and in at least one case + was found to diminish it and even stop it alto- gether. Apparently we must regard the non-nitrogenous ingredients of feeding-stuffs as the chief source of hippuric acid formation, but be- yond this our knowledge is rather vague. It is well established that the coarse fodders are the chief producers of hippuric acid, while the concentrated feeding-stuffs give rise to little or none, and may even reduce the amount previously produced on coarse fodder, as may also starch. Among the coarse fodders, the graminex: give rise to a markedly greater production of hippuric acid than the leguminose. ‘This effect of the coarse fodders naturally led to the suspicion that the crude fiber contained in. them in large amounts might be the source of the hippuric acid, and in fact numerous experiments seem to show that some relation exists between the two, although the results of various investigators are far from con- cordant. Finally, the investigations of Goetze & Pfeiffer, t and of * Compare Salkowski, Zeit. physiol. Chem., 9, 234. + Henneberg and Pfeiffer, Jour. f. Landw., 38, 239. t Landw. Vers. Stat., 47, 59. 46 PRINCIPLES OF ANIMAL NUTRITION. Pfeiffer & Eber,* have shown with a high degree of probability that the pentose carbohydrates of the feed have some connection with the production of hippuric acid.t The former investigators observed a marked increase in the production of hippuric acid by a sheep after the administration of cherry gum (impure araban) and of arabinose, and the latter obtained the same effect, although in a less marked degree, by feeding cherry gum to a horse. They also call attention to the differences in the behavior of the pentose carbo- hydrates in the organism of the herbivora and in that of man and the earnivora, but do not attempt to give a final solution of the problem of the origin of the hippuric acid in the former case, while they freely admit that it is difficult, if not impossible, to explain some of the facts already on record on the hypothesis that the pen- toses are the chief source of hippuric acid. CREATIN AND CREATININ.—Among other nitrogenous constit- uents of the urine of man and the carnivora may be mentioned creatinin. This body is the anhydride of creatin, and the two together constitute the principal part of the so-called flesh bases which are contained in considerable quantity in muscular tissue. When meat is consumed, its creatin is converted into creatinin and excreted quantitatively in the urine, the creatinin content of which may be thus considerably increased. As to the physiological signifi- cance of the creatin of muscular tissue opinions are divided, but good authorities are inclined to regard it as an intermediate product of the metabolism of the proteids which is ultimately con- verted into urea, and to urge that the fate of creatin taken into the stomach is not necessarily the same as that of the creatin produced in the muscles. Aromatic Compounps.—Besides the benzol radicle of hippuric acid, small amounts of other aromatic compounds are also found in the urine. These bodies, belonging chiefly to the phenol and indol groups, owe their origin exclusively to the putrefactive processes already mentioned as taking place in the intestines, and are found in the urine almost entirely in combination with sulphuric acid as the so-called conjugated sulphurie acids, so that the amount of the latter is employed as a measure of the extent of these putrefactive processes. * Landw. Vers. Stat., 49, 97. + Later results by the same authors, however, throw doubt on this con- clusion. METABOLISM. 47 MerTapouic Propucts in FEcrs.—As already stated in Chapter I, the feces contain, in addition to undigested residues of the food, certain materials derived from the body of the animal. This fact was early recognized as true of both carnivora* and herbivora.t Of more recent investigations may be noted especially those of Miller,{ Rieder,§ and Tsuboi || on carnivora, those of Prausnitz™ and his associates on man, and those of Kellner,** Stutzer,+} Pfeiffer, |t and Jordan §§ on herbivora. These “metabolic products” appear to consist of unresorbed or altered residues of the digestive fluids and of mucus and other materials excreted or otherwise thrown off by the walls of the intes- tines. Their production goes on even when the digestive tract is void of food, producing the so-called fasting feces which constitute a true excretory product. The consumption of highly digestible food—e.g., lean meat—does not seem to materially increase their amount, but when food containing indigestible matter is eaten it is believed that they increase in quantity. It is presumed that these substances are largely nitrogenous in character, and it is known at any rate that not inconsiderable amounts of nitrogen may leave the body by this channel. In other words, these nitrogenous substances, derived from the proteids of the body, instead of undergoing complete conversion into the ordinary crystalline products have their katabolism interrupted as it were at an intermediate stage. Many attempts have been made to determine the amount of these metabolic products, or of their nitrogen, in the feces, but without much success, and it may fairly be said that at present we have no method which can be depended upon to distinguish sharply between the nitrogen of undigested-food residues and that of metabolic products. ” * Bischoff and Voit, Die Ernihrung des Fleischfressers, p. 292. + Henneberg, Beitriige, etc., 1864, p. 7. t Zeit. f. Biol., 20, 327. § Ibid., 20, 378. || Jbid., 35, 68. q{ Ibid., 35, 287; 39, 277; 42, 377. ** Landw. Vers. Stat., 24, 434; Bied. Centralbl., 9, 763. +} Zeit. physiol. Chem., 9, 211. ttJour. f. Landw., 31, 221; 33, 149; Zeit. physiol. Chem., 10, 561. §$ Maine Expt. Station Rep., 1888, p. 196. 48 PRINCIPLES OF ANIMAL NUTRITION. NITROGEN IN PERSPIRATION.—The perspiration of such animals as secrete this fluid must be regarded as one of the minor channels by which nitrogen is excreted. In human perspiration there have been found, in addition to small amounts of proteids, urea, uric acid, creatinin, and other nitrogenous products of the proteid meta- bolism. In a recent investigation, Camerer * found about 34 per cent. of the total nitrogen of human perspiration to be in the form of urea, about 7.5 per cent. existed as ammonium salts, and the remainder in undetermined forms, including uric acid and traces of albumen. The total quantity of nitrogen excreted in the insensible perspi- ration appears to be insignificant. Atwater & Benedict + found it to amount to 0.048 gram per day for an adult man in a state of rest. Rubner & Heubner { obtained from the clothing of an infant 2.83 mers. of ammonia and 0.0205 mgr. of urea per day and estimated the total nitrogen of the perspiration at 39 mers. When the secretion of sweat is stimulated by work or a high external temperature the amount of nitrogen excreted may be con- siderably increased as compared with a state of rest, although its absolute amount is still small. Atwater & Benedict,§ in a work ex- periment, observed an excretion of 0.220 gram of nitrogen per day in the perspiration of man. The Non-nitrogenous Residue of the Proteids.—The various nitrogenous products found in the urine and other excreta, the most important of which have been noticed above, are believed to con- tain all the nitrogen of the metabolized proteids. This does not imply, however, that a quantity of proteids equivalent to this nitro- gen, or even to that of the urine, has been completely oxidized to the final products of metabolism, viz., carbon dioxide, water, and urea and its congeners. A comparison of the ultimate composition of the proteids with that of the nitrogenous products of their metabolism reveals the fact that an amount of the latter sufficient to account for all the nitrogen of the proteids contain but a relatively small part of their carbon, hydrogen, and oxygen. Taking urea as the chief and + Zeit. f. Biol., 41, 271. U.S. Dept. Agr., Office of Expt. Stations, Bull. 69, 73. + Zeit. f. Biol., 36, 34. § Loc. cit., p. 53. METABOLISM. 49 typical metabolic product, and using average figures for the com- position of animal proteids, we have, omitting the sulphur of the proteids, the following: Proteids, Urea. Residue. Or OGG salt ee A area ae 53.0 6.86 46.14 iy ro mene ashe wee) eheO 2.29 4.71 One ta One ion 24.0 9.14 14.86 INDEPEN G8. os ests 16.0 16.00 100.0 34.29 65.71 After abstracting the elements of urea, we have left considerably over half the hydrogen and oxygen of the proteid and the larger part of its carbon. A substantially similar result is reached in case of the other nitrogenous metabolic products. The splitting off of these products from the proteids leaves a non-nitrogenous residue. Fate OF THE NON-NITROGENOUS ReEsipUE.—The foregoing statements and comparison must not be understood to mean that the proteids split up in the body into two parts, viz., urea, ete., on the one hand, and an unknown non-nitrogenous substance or sub- stances on the other. As we have already seen, the processes of proteid metabolism are far more complicated than such a simple cleavage. Neither are we to assume that any substance or group of substances corresponding in composition to the “residue” of the above computation exists. The figures mean simply that while the nitrogenous bodies of the urine contain all the nitrogen of the proteids they do not account for all of the other elements, but that part of the latter must be sought elsewhere. Ultimately, of course, the elements of this non-nitrogenous residue are converted into carbon dioxide and water. The conver- sion into these final products, however, is necessarily a process of oxidation, presumably yielding energy to the organism. It is a matter of some interest, then, to trace the steps of the transforma- tion so far as this is at present possible. Formation of Sugar.—in discussing the functions of the liver in § 1 of this chapter, we have seen reason to believe that this organ continues to produce sugar when the diet consists largely or exclu- sively of proteids. In this case we are forced to the conclusion that this sugar is manufactured from the elements of the non-nitrogenous residue. 5° PRINCIPLES OF ANIMAL NUTRITION. This conclusion, based on what appears to be the normal func- tion of the liver, is further strengthened by a large number of ex- periments and observations upon the metabolism in diabetes. This disease, whether arising spontaneously or provoked artificially, is characterized by the presence of large amounts of sugar in the urine. It has been shown that this production of sugar continues when all carbohydrates are withdrawn from the diet, and further- more, that the amount of sugar excreted bears a quite constant relation to the amount of proteids metabolized, thus clearly in- dicating the latter as the source of the sugar. It is true that the formation of sugar from proteids is denied by some physiologists,* but by the majority it seems to be accepted as a well-established fact that sugar is one of the intermediate products of proteid metabolism. Of the steps of the process, as well as of its quantitative rela- tions, we are ignorant. In effect, it is a process of oxidation and hydration, since a residue of the composition computed above would require the addition of both hydrogen and oxygen to con- vert it into sugar, but that it is as simple a process as this state- ment would make it appear, or that the conversion is a quantitative one, may well be doubted. In conclusion it may be stated that while recent investigations have shown the presence of a carbohydrate radiele in numerous (although by no means all) proteids, it does not appear that this fact stands in any direct relation to the physiological production of sugar from these substances. In the first place, the carbohydrate radicle constitutes a much smaller proportion of these proteids than corresponds to the amount of sugar which they are apparently capable of yielding in the body, and in the second place it appears to be a well-established (although not undisputed) fact that the organism can produce sugar from proteids which do not contain the carbohydrate radicle. Formation of F'at—Whether fat is formed from the elements of proteids in the animal body is at present a subject of controversy, but this question will be more profitably considered in a subsequent chapter. It is sufficient to remark here that while much of the earlier evidence bearing upon this point has been shown to be * Cf. Schéndorf, Arch. ges. Physiol., 82, 60. METABOLISM. 51 A inconclusive, the formation of fat from proteids has not yet been disproved and has weighty direct evidence in its favor, while the facts that sugar may be formed from proteids, and that carbohy- drates are certainly a source of fat to the animal organism are strong additional arguments in favor of its possibility. Schematic Equations—Chauveau and his associates * whose views regarding the functions of the carbohydrates in the body have already been mentioned, regard the katabolism of the proteids as taking place in three stages. The first consists of the splitting off of urea with production of carbon dioxide, water, and fat, accord- ing to the equation: 4(C7oH12N 1302.5) + 1 390, (Stearin) = 2(CgrHi4,05) + 36CON,H, + 13800, + 42H,0 + 28,. The resulting fat is then, according to Chauveau, further oxi- dized in the liver, yielding dextrose, in accordance with the equation already given on p. 38, viz., 20 57H, 90g + 670, = 16C,H,,.0,+ 18CO,+ 14H,0, and the dextrose is finally oxidized to carbon dioxide and water. Another equation representing the katabolism of proteids is that proposed by Gautier, which regards the first step in the process as a combined hydration and cleavage with the production of urea, fat, dextrose, and carbon dioxide, as follows: PCr elia Nao) + 28H,O (T ‘ anit; ) ripalmitin —18CON;H,+2C.,H5.0.+ CeH,,0,+ 18CO,+S). It may be assumed that these authors regard the above equa- tions simply as schematic representations of the general course of proteid metabolism and do not intend to imply that there are no intermediate stages in the process. Interpreting them in this sense, we have good reasons for believing that the facts which they represent are qualitatively true. A chemical equation. however, expresses not merely qualitative but quantitative results. If the above equations have any significance beyond that of the mere verbal statement that fat and sugar are products of proteid meta- * Cf. Kaufmann, Archives de Physiol., 1896, p. 341. 52 . PRINCIPLES OF ANIMAL NUTRITION. bolism, they mean that from 100 grams of proteids there is pro- duced, according to the first scheme, 27.61 grams of fat, and that from this, by the addition of oxygen, 44.67 grams of sugar are formed. Some of the evidence by which these equations are sup- ported will be considered in another connection, but may be antici- pated here in the statement that, in the judgment of the writer, it is far from sufficient to establish them as quantitative statements. THE NON-PROTEIDS. Under this comprehensive but somewhat vague term have been grouped all those numerous nitrogenous constituents of the food which are not proteid in their nature, the name being a contraction of non-proteid nitrogenous substances. It includes the extractives of meat, and in vegetable foods several groups of substances, of which, however, the amides and amido-acids are most abundant. Various substances of this class are produced by the splitting up of the reserve proteids in the germination of seeds and apparently also to some extent in the translocation of proteids in the growing plant, while some at least of them appear to be produced syntheti- eally from inorganic materials and to be the forerunners of pro- teids. In young plants a considerable proportion of the so-called crude protein (N X 6.25) often consists of these non-proteids, and considerable interest, therefore, attaches to their transformations in the body. AMIDES OXIDIZED IN THE Bopy.—It has been shown by numer- ous investigators that various amides and amido-acids when added to the food are oxidized, giving rise to a production of urea. Shultzen & Nencki* found that glycocol, leucin, and tyrosin were thus oxidized, while acetamid apparently was not. So far as glycocol is concerned, this result is what would have been expected, since, as we have seen (p. 44), this body appears to be normally formed in the body as an intermediate product of proteid meta- bolism. Similar results were obtained by v. Knieriem + from trials with asparagin, aspartic acid, glycocol, and leucin. Munk f likewise found that the ingestion of asparagin increased the pro- * Zeit. f., Biol,, ‘8; 124: Faoid., 20,2772 sudok ¢ Virchow’s Archiv. f. path. Anat., 94, 441. METABOLISM. 53 duction of urea in the dog, all the nitrogen of the asparagin together with an excess over that previously found in the urine being ex- ereted. The sulphur in the urine also increased. Hagemann * has more recently fully confirmed this result. Salkowski + found that glycocol, sarkosin, and alanin were oxidized to urea and caused no gain of proteids. Apparently, then, this class of bodies, like ammonia, furnish material out of which the organism can con- struct urea. . Can AmipEsS REPLACE PRoTEIDS?—Since the amides yield the ame end products of metabolism as the proteids, it is natural to inquire whether they can perform any of the functions of those substances. Amides not Synthesized to Proteids—We have already seen that the albumoses and peptones resulting from the cleavage of the proteids during digestion are built up again into proteids in the process of resorption. The amides commonly found in vegetable feeding-stuffs are likewise simpler cleavage products of the proteids, ' and some of them are also formed in digestion by the proteolytic action of trypsin. . Can proteids be regenerated from these simpler cleavage products? ° If this is the case, then it should be possible, under suitable con- ditions, to cause a gain of proteids, or at least to maintain the stock of proteids in the tissues, on a food free from proteids but containing amides. Up to the present time, however, all attempts of this sort have failed. With the most abundant supply of non- nitrogenous nutrients and ash, the animals perished when supplied with amides (asparagin) but not with proteids.{ What has thus been found to be true of asparagin we may regard as probably true of other amides and say that there is no evidence that the animal body ean build proteids from amides. Partial Replacement of Proteids—But even if the amides can- not serve as a source of proteids to the animal, it seems not impos- sible that they may by their oxidation perform a part of the fune- tions of the proteids, thus protecting a portion of the latter from oxidation and rendering it available for tissue production. * Landw. Jahrb., 20, 264. + Zeit. physiol. Chem., 4, 55, tCompare Politis, Zeit. f. Biol., 28, 492,and Gabriel, /b., 29, 115. 54 PRINCIPLES OF ANIMAL NUTRITION. The earliest investigations upon this point are those of Weiske * and his associates upon the nutritive value of asparagin. The experiments were made upon rabbits, hens, geese, sheep, and goats, and in the case of the two latter species included experiments on milk production. While the experiments are open to criticism in some respects, as a whole they seemed to show that asparagin, especially when added to a ration poor in proteids, caused a gain of proteids by the body. Weiske accordingly concluded that aspara- gin, while not capable of conversion into proteids, was capable of partially performing their functions and thus acting indirectly as a source of proteids, and this view has been somewhat generally accepted. Subsequent experiments by Bahlmann,} Schrodt,t{ Potthast,$ Meyer,|| and Chomsky {| upon milch-cows, rabbits, and sheep gave results which tended to confirm Weiske’s conclusions. Not all of Weiske’s experiments, however, gave positive results in favor of asparagin, and experiments upon carnivorous and omniv- orous animals have failed to show any such effect. In addition to the experiments of Politis and of Gabriel, referred to above, Mauthner,** Munk,++ and Hagemann ff have failed to observe any gain of proteids by the body as a result of the ingestion of asparagin, but found simply an increase in the apparent proteid’ metabolism as measured by the urinary nitrogen. Influence on Digestion.—It can hardly be assumed that the actual processes of metabolism in the body tissues are fundamen- tally different in different species of mammals, and investigators have therefore been led to seek an explanation of the striking differ- ence in the effects of asparagin on herbivora and carnivora in the differences in the digestive processes of the two classes of animals. Digestion in herbivora is a relatively slow process and, as pointed out in Chapter I, is accompanied by extensive fermentations par- * Zeit. f. Biol., 15, 261- 17, 415; 30, 254. + Reported by Zuntz, Arch. f. (Anat. u.) Physiol., 1882, 424, tJahresb. Agr. Chem., 26, 426. § Arch. ges. Physiol., 32, 288. || Cf. Kellner, Zeit. f. Biol., 89, 324. { Ber. physiol. Lab. Landw. Inst. Halle, 1898, Heft 13, p. 1. ** Zeit. f. Biol., 28, 507. ++ Virchow’s Arch. f. path. Anat., 94, 441. tt Landw. Jahrb., 20, 264. METABOLISM. D3 ticularly of the carbohydrates of the food, as is shown by the large amounts of gaseous hydrocarbons produced by these animals. In carnivora, on the contrary, digestion is relatively rapid and the dog, as a representative of this class, excretes, according to Voit & Pettenkofer,* but traces of hydrocarbons, and according to Tap- peiner,} none. Zuntz { has therefore suggested that soluble amides introduced into the digestive canal of herbivora may be used as nitrogenous food by the micro-organisms there present in preference to the less soluble proteids, so that the latter are to a certain extent protected, and that it is even possible that the amides are synthesized to proteids by the organisms. Hagemann § has added the suggestion thaf the proteids possibly thus formed may be digested in another part of the alimentary canal and thus actually increase the pro- teid supply of the body. : If this explanation is correct, we should expect the effect of asparagin to be more marked when the proportion of proteids in the food is small, and precisely this appears to be the case. In Weiske’s first experiments, which gave the most decided results, the nutritive ratio of the ration without asparagin was 1:19-20, while a later experiment with a nutritive ratio of 1:9.4 showed no effect of the asparagin upon the gain of protein. Chomsky’s results, too, were obtained with rations poor in protein and rich in carbo- hydrates. Later experiments on lambs by Kellner || have fully confirmed this anticipation. In his first experiment two yearling lambs were fed with a mixture of hay, starch, and cane-sugar, having a nutri- tive ratio of 1:28, until nitrogen equilibrium was reached, when fifty grams of the starch was replaced by asparagin. The result was a gain of protein by both animals as compared with a loss in the first period. In the third experiment asparagin was substi- tuted for starch in a ration having a nutritive ratio of 1 :7.9, and caused with one animal a slight gain and with the other a slight loss of protein. In the fourth experiment it was added to a ration * Zeit. f. Biol., 7, 433; 9, 2 and 438. + Ibid., 19, 318. ft Arch. ges. Physiol., 49, 483. § Landw. Jahrb., 20, 264. || Zeit. f. Biol., 39, 313. 56 PRINCIPLES OF ANIMAL NUTRITION. having a nutritive ratio of 1:7.7, and caused neither a gain nor a loss of any consequence. Particular interest attaches to Kellner’s second experiment in _ which ammonium acetate was added to a ration poor in protein (1:19), followed in a third period by a quantity of asparagin ‘con- taining the same amount of nitrogen. The average amounts of protein (N X 6.25) gained per day and head by the two lambs were as follows: Basaltranion’:)* . wor. tis- seme he os ee 4.12 grms. | ~ “« + ammonium acetate...... 15.56 “ ‘ re REE SDAP OSL. < ohe eine wots pe TDADOAS s Although it is impossible to suppose that the ammonium acetate is capable of performing any of the functions of proteids in the body, it nevertheless caused as great a gain of protein by the body as did the asparagin. The only obvious explanation is that both these substances acted in the manner suggested by Zuntz to protect the small amount of protein in the food from the attacks of the organized ferments of the digestive tract. Accepting this explana- tion, we must suppose that when the contents of the alimentary canal contain a normal amount of proteids the micro-organisms find an abundant supply of nitrogenous food in their cleavage products and reach their normal development, so that an addition of soluble nitrogenous substances is a matter of indifference. When, on the other hand, the amount of protein present is abnormally low, as in Weiske’s and Kellner’s experiments, the organisms are limited in their food-supply and attack the food proteids them- selves. Kellner’s results stand in apparent contradiction to the earlier ones of Weiske and Flechsig,* who report no gain of proteids as re- sulting from the addition on three days of a mixture of ammonium carbonate and acetate to a ration poor in protein. The excretion of sulphur in the urine was likewise unaffected. They assume, however, a long-continued after effect of the ammonium salts on the nitrogen excretion. If the comparison be limited to the three days on which the ammonium salts were given and the next following day, a gain of 1.15 grams of nitrogen per day results, but, as just stated, there was no corresponding gain of sulphur. * Journ. f. Landw., 38, 137. —— METABOLISM. 5) 7 Keliner’s experiments afford indirect evidence that both the asparagin and the ammonium acetate actually did stimulate the development of the ferment organisms, in the fact that the apparent digestibility of the carbohydrates of the food was increased. On the basal rations starch could be readily recognized in the feces, but under the influence of the two substances mentioned it dis- appeared. In the second experiment the increase in the amounts of crude fiber and of nitrogen-free extract digested was as follows: - Nitrogen-free Crude Fiber. Extract. - With ammonium acetate... 10.7 grms. 20.4 grms. With asparacim. 5.26 sn tO/0r,! ZOO Since we know that large amounts of the nitrogen-free extract are attacked and decomposed by organized ferments in the her- bivora, and that this is the chief if not the only method by which crude fiber is digested, we are justified in interpreting the above figures as demonstrating an increased activity of these organisms as a result of the more abundant supply of nitrogenous food. The bearing of this result upon the so-called depression of digestibility by starch and other carbohydrates is obvious, but is aside from our present discussion. Tryniszewsky * experimented upon a calf weighing about 175 kgs., using in the second and fourth periods (the first period being preliminary) a ration of barley straw, sesame cake, starch and sugar, containing a minimum of non-proteids. In the third period one- third of the sesame cake was replaced by a mixture of asparagin, starch and sesame oil, computed to contain an equivalent amount of nitrogen, carbohydrates, and fat. Owing to differences in digest- ibility, however, the amounts of digested nutrients, and particu- larly of nitrogen, varied more or less. The results of the nitrogen balance per 100 kgs. live weight were: Nitrogen Digested. Nitrogen Gain of Metabolism, | Nitrogen, Proteid, Non-proteid, Total, Grms. Grmis. Grms. Grms. Grms, Jeter Wiscobonc TAG, oeeebsacar 72.16 56.86 15.3 ir (NU eee ie 67.05 23.68 90.73 78.43 12.3 SON INS Garces DOSS Gia vactsce's ecoste 90.86 76.36 14.5 * Jahresb. Ag. Ch., 43, 513. 58 PRINCIPLES OF ANIMAL NUTRITION. From the smaller gain in Period III, the conclusion is drawn that the asparagin has a lower nutritive value than the proteids. In this period the percentage digestibility of the crude fiber of the ration was found to be 64.88, as compared with 43.96 and 33.33 In the second and fourth periods, an effect corresponding to that observed by Kellner, and which Tryniszewsky also ascribes to an increase in the micro-organisms of the digestive tract. The results of the experiments which have been cited are, of course, valid, in-the first instance, only for the particular non- proteids experimented with. If, however, the above interpretation of the results is correct, it is to be anticipated that other soluble nitrogenous substances in the food will be found to produce similar effects. If this anticipation proves to be correct, then we shall reach the following conclusions regarding the amides and similar bodies in feeding-stuffs. 1. That they do not serve as sources of proteids. ; 2. That in rations very poor in protein they have, in the her- bivora, an indirect effect in protecting part of the food protein from fermentation in the digestive tract. 3. That in carnivora, and in herbivora on normal rations, they probably have no effect on the production of nitrogenous tissue. Nortr.—Since the foregoing lines were put in type the investiga- tions of Cohnheim,* Loewi,t Kutscher & Seemann,{ Abderhalden,$ Strusiewicz,|| and others, seem to have shown that the proteid cleavage in digestion is more complete than had been previously believed. Cohnheim finds an enzym, erepsin, in the small intestine which acts energetically upon the peptones, forming crystalline cleavage products, while Loewi and others state that the mixture of “amides” thus produced is synthesized to proteids in the intes- tinal epithelium and may completely replace proteids in the food. The negative results of earlier experiments are ascribed to the fact that usually a single amide was experimented upon and that con- sequently but one out of the several molecular groupings necessary for the reconstruction of the proteid molecule was present. * Zeit. physiol. Chem., 83, 451. § Ibid, , 44, 199. + Centbl. f. Physiol., 15, 590. | Zeit. f. Biol., 47,143. t Zeit. physiol. Chem., 34, 528. CHAPTER III. METHODS OF INVESTIGATION. AN essential prerequisite for an intelligent study of the income and expenditure of matter by the animal body is a knowledge of the general nature of the current methods of investigation and of the significance of the results attained by means of them. It is not the purpose here to enter into technical details; this is not a treatise upon analytical or physiological methods. The present chapter will be confined to outlining the general principles upon which those methods are based and to pointing out the logical value of their results. It will be confined, moreover, mainly to those general methods by which the balance of income and ex- penditure of matter is determined. Tissue.—The animal body has already been characterized as consisting, from the chemical point of view, of an aggregate of various substances, chiefly organic, representing a certain capital of matter and energy. These various substances are grouped together in the body to form the organized structures known as tissues. For the sake of brevity, then, it may be permissible to use the word tissue as a convenient general designation for the aggre- gate of all the organic matter contained in the tissues: of the body, including both their organized elements and any materials present in the fluids of the body or in solution in the protoplasm of the -cells. In this sense tissue is equivalent to the whole capital or store of organic matter in the body. GAINS AND LossEs.—The tissue of the body; as thus defined, is in a constant state of flux, the processes through which the vital - functions are carried on constantly breaking it down and oxidizing it (katabolism), while the processes of nutrition are as constantly building it up again (anabolism). If the activity of nutrition 59 60 PRINCIPLES OF ANIMAL NUTRITION. exceeds that of destruction, material of one sort or another is stored up in the body, and such an addition to its capital of matter and energy we may speak of as a gain of tissue. Conversely, if the katabolic processes consume more material than the processes of nutrition can supply, the store of matter and energy in the body is diminished and a loss of tissue occurs. A simple comparison of the amount of matter supplied in the food (including, of course, the oxygen of the air) with that given off in the solid, liquid and gaseous excreta, therefore, will show whether the body is gaining or losing tissue. The mere fact of a gain or loss of matter by the body, however, conveys but little useful information unless we know the nature of the material gained or lost. This we have no means of determining directly. The processes of growth or decrease are not accessible to immediate observation, while changes in the weight of the animal (even aside from the great uncertainties introduced, especially in the herbivora, by variations in the contents of the alimentary canal) represent simply the algebraic sum of the gains and losses of water, ash protein, fats, and other materials, and so give but a very slight clue if any to the real nature of the tissue-building. We are compelled, therefore, to have recourse to indirect methods, and to base our conclusions as to tissue-building upon a comparison of the income and outgo of the chemical elements of which the body is composed, particularly of nitrogen and carbon. The Schematic Body.—The basis of this method of compari- son is the conception of the schematic body, first introduced by Henneberg.* This conception regards the dry matter of the body of the animal as composed essentially of three groups of substances, viz., ash, fat, and protein, with at most comparatively small amounts of carbohydrates (glycogen), and assumes that the vast number of other compounds which it actually contains are present in such small and relatively constant proportions as not to materially affect the truth of this view. A knowledge of the ultimate compo- sition of these three groups then affords the basis for a computation of the gain or loss of each from the income and outgo of their ele- ments. Asu.—The ash ingredients of the body form a well-defined * Neue Beitriige, ete., p. vii. METHODS OF INVESTIGATION. 61 group, and the determination of the gain or loss of each ingredient from a comparison of income and outgo is in principle a relatively simple matter and calls for no special consideration here. Fatr.—The elementary composition of the fat of the body has been shown to be remarkably similar not only in different animals of the same species, but likewise in different species. The classic investigations of Schulze & Reinecke * upon the composition of animal fat gave the following results: Carbon. Hydrogen. Oxygen. No. of i Sam- | Aver- | Maxi-| Mini- | Aver- | Maxi-| Mini- | Aver-| Maxi-} Mini- ples. | age |mum}]mum| age |mum|mum| age | mum] mum Bers |e her | keri) ber’ | Pers || Per i rert| Per Per Cent. | Cent. | Cent. | Cent. | Cent. | Cent. |-Cent. | Cent. | Cent. SCCh tata ctacteletel sc 10 |76.50\76.74,76.27 11 -91/12.11/11.7611.59 11.86,11.15 On kehatp ote, a tereiere 6 |76.54/76.'78/76.29:11.94/12.07|11. 86/11 .52/11.83)11.15 Mortton) fat... 1 12 |76.61/76. 85/76. 27 12.03/12.16)11.87111.36)/11.56/ 11.00 Average...... 28 |16.50 12.00 11.50 WYOY os ok oondace 76.63 12.05 11.32 atte ccitoicts cteicce 76.56 11.90 11.44 EliGrselaettesiacct a: Wiad 11.69 111.24 WIGNER Sci tecctars ss 76.62 11.94 ial 44 Benedict and Osterberg + obtained the following results for the composition of human fat: Carbon, Hydrogen, Per Ceut. | Per Cent. Sample ING 21 ner. ci- 76.29 11.80 OG Se a care 76.36 11,72 ee SEO Bais tals ei 75.85 11.87 ss se av: bs cele ee 75.95 11.85 e¢ TS ocr Ae oe 75.94 11.74 ss SOG eee e eet oe 76.97 11.69 eo Be ies wtatares 76.18 11 84 zs UP 3) Sane Ceara 76.05 11.81 Average 76.08 11.78 The fat of the body has been commonly regarded as containing 76.5 per cent. of carbon. A gain of 100 parts of fat by the body * Landw. Vers. Stat., 9, 97. + Amer. Jour. Physiol., 4, 69. 62 PRINCIPLES OF ANIMAL NUTRITION. is accordingly equivalent to a gain of 76.5 parts of carbon, and con- versely, if it be shown that the body has gained one part of carbon in the form of fat, this is equivalent to a gain of 1+0.765=1.307, or, in round numbers, 1.3 parts of fat. Benedict & Osterberg’s average corresponds to the factor 1.314. Prorern.—As in the case of the food, the term protein is used to signify the whole mass of nitrogenous material in the body, in- cluding, besides the true albuminoids, the collagens or gelatinoids, the keratin-like bodies, the nitrogenous extractives, ete. Neumeister * gives the following figures for the elementary composition of the simple albuminoids: Minimum, Maximum, Average, Per Cent. Per Cent. Per Cent. QAEDON ion tere ae alee 50 55 52 Hydrogen: os 02.02% 6.5 7.3 7 INIETOPER . sy ‘ THE FASTING METABOLISM. 89 animal is explained by Voit to be due to an increasing difficulty in transferring the reserve fat from the adipose tissues, thus resulting in a diminution of the amount of fat (or its cleavage products?) circulating in the organism. If the body is well supplied with fat at the outset this phenomenon does not at first appear, and the ratio of proteid to total metabolism remains nearly constant for a time. With continued fasting the store of body fat is, as has just been shown, drawn upon much more rapidly than that of protein, while at the same time the total amount of the former present at the beginning of fasting is often less than that of the latter. Asa necessary result, the ratio of fat to protein in the body decreases. When this decrease passes a certain point, the fat of the adipose tissue is drawn upon with more and more difficulty for material to supply the demand for energy, and as a result additional protein is metabolized to make good the deficiency of available fat. From this time on, the ratio of proteid to total metabolism shows a con- tinually accelerated increase. The time when the increase in the proteid metabolism becomes marked depends upon the original condition of the body. If the animal is well nourished, and espe- cially if it contains large reserves of fat, the increase may be long deferred or even fail to appear at all. If, on the other hand, it is poorly nourished and eontains little fat, an increase of the proteid metabolism may take place almost from the outset. The following three examples, cited by E. Voit from Rubner’s experiments, may serve to illustrate these three types of fasting metabolism: Guinea Pig. Dog. Rabbit. Proteid Proteid Proteid Day of Metabolism Day of Metabolism Day of Metabolism Fasting. in % of Total Fasting, in % of Total Fasting. in % of Total Metabolism. sd Metabolism. Metabolism. ae 10.4 2-4 16.3 3 16.5 as cere Vat sil 10-11 ToL 5-7 23.6 eh eee aN 11.0 12 Ta) 9-12 26.5 Dereieredatersr< 11.9 13 17.4 13-15 29.8 Greasicct.: 11.8 14 20.0 16 50.1 cS RAeOe 17-18 96.4 go PRINCIPLES OF ANIMAL NUTRITION. Schulze * claims that this increase in the proteid metabolism of the fasting animal is not, in all cases at least, due to lack of fat or other non-nitrogenous material to protect the protein from destruc- tion. He advances the hypothesis that the loss of protein incident to the fasting so injures the cells that finally many of them die and the protein of their protoplasm becomes part of the circula- tory protein of the body and is rapidly decomposed, thus giving rise to an increased excretion of nitrogen. While it is not impossible that this ingenious hypothesis has some basis of fact, Kaufmann,} in a quite full review of the litera- ture of the subject, together with original experiments, shows that it can by no means supplant Voit’s explanation. He points out in particular that the time when the increase in the proteid metabolism begins seems to bear no relation to the loss of protein which the body has sustained, while, on the other hand, it coin- cides quite closely with the time when the supply of visible fat is nearly exhausted. Summary.—In the light of the facts set forth in the foregoing paragraphs we may sketch the general outlines of the fasting meta- bolism somewhat as follows: In the early stages of fasting, particularly if the previous food has contained an abundance of proteids, the proteid metabolism may be considerable. As the effect of the previous food disappears, however, and the store of “circulatory protein” in the body is ex- hausted, the proteid metabolism speedily falls to the minimum amount required for the vital activities of the protoplasm, and the remaining demands of the body for energy are supplied by the metabolism of the stored-up fat. If the latter is fairly abundant, this stage may last several days, the total metabolism remaining nearly constant and the proteids supplying a nearly constant pro- portion of the necessary energy (according to E. Voit about 15-16 per cent.). Sooner or later, however (unless in a very fat animal), the supply of fat from the adipose tissue begins to flag. The de- mand for energy, however, remains unabated, and as the fat-supply falls off, more and more protein is metabolized in its place, until at * Arch. ges. Physiol., 76, 379. + Zeit. f. Biol., 41, 75. {Compare also E. Voit’s critique of Schulze’s investigations. (Zeit. f. Biol., 41, 550.) re ) THE FASTING METABOLISM. gt last the metabolism may even become almost entirely proteid in its character. We have in these facts the first of the numerous illustrations which we shall meet in the course of this discussion of the plasticity of the organism in adapting itself to differences in the food-supply, and of the controlling influence exerted upon the course of its metabolism by the demand for energy. Tue INTERMEDIARY MeETABOLISM.—The prime object of the metabolism of the quiescent fasting animal is, as already pointed out, to supply energy for the performance of the vital functions. Mention has already been made in Chapter II of the hypothesis that the immediate source of energy to the cells of both muscles and glands is the metabolism of carbohydrate material. This hypothesis in effect regards the metabolism of the fasting animal as divisible into three processes: first, the splitting up of the proteids, yielding urea and fat; second, the partial oxidation of fat, whether derived from the proteids or from the adipose tissue, yielding dex- trose; third, the oxidation of the resulting dextrose in the tissues. So far as the kind and amount of excretory products are con- cerned, it of course makes no difference whether the metabolism takes place in accordance with this hypothesis or whether the proteids and fat» are oxidized directly in the tissues. In either case the fasting animal iives upon its store of proteids and fat, and the resulting excretory products, as well as the amount of heat produced, are qualitatively and quantitatively the same, so that the coincidence observed by Kaufmann * between the observed results and those computed from his equations is without special significance in this case. There is, nevertheless, an important and essential difference in the two views. If we regard the proteids and fat as yielding up their energy directly for the vital activities, then all the energy thus liberated is available for this purpose. If, on the contrary, we suppose these substances to be first partially metabolized in the liver or elsewhere in the organism, then only that portion of their potential energy which is contained in the resulting dextrose is available directly for the general purposes of the body. The re- mainder of their energy is liberated as heat during the preliminary *Archives de Physiologie, 1896, pp. 329 and 352. 92 PRINCIPLES O# ANIMAL NUTRITION. metabolism, and while contributing its quota towards maintaining the normal temperature of the body is not directly available for other purposes. In other words, the question is not one as to the total energy liberated, but as to its form and distribution. As regards the fasting animal itself, the question is of minor impor- tance; but, as will appear in subsequent chapters, it materially affects our views as to the relative values of the several nutrients of the food. GHAPTER V. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. THE metabolism of the fasting animal was regarded in the pre- ceding chapter as representing the essential demands of the vital. functions for a supply of matter as a vehicle of potential energy. Under these conditions, as we have seen, the total metabolism bears a close relation to the mass of active tissue, while the qualitative character of the metabolism, that is the ratio of proteid to non- proteid matter consumed, appears to be likewise constant for any given condition of the body, depending upon the relative supply of proteids and non-nitrogenous matters to the active cells. When food is given to such an animal the conditions are modified in essen- tially three ways: First, to the metabolism incident to the fasting state is added that required to supply the energy consumed in the digestion and assimilation of the food. Second, the food-supply may alter the proportions in which the various nutrients are supplied to the active cells, and thus affect the metabolism qualitatively, giving rise to a relatively greater or less metabolism of proteids, fats, carbohydrates, ete. Third, the food-supply may be in excess of the requirements of the body and lead to a storage of matter of one sort or another. The quantitative relations of the food-supply to the total metabolism and to the storage of matter and energy in the body may be most satisfactorily considered upon the basis of the amounts of energy involved. Accordingly we may content ourselves here with a simple mention of this side of the question, deferring a dis- cussion of it to Part II and confining the present chapter largely to a study of.the qualitative changes in the metabolism brought about by variations in the food-supply. As in the previous chapter, it will be convenient to consider the relations of the proteids of the 93 94 PRINCIPLES OF ANIMAL NUTRITION. food and of the body separately from those of the non-nitrogenous nutrients. § 1. The Proteid Supply. The effects of the proteid supply upon metabolism may be most readily and clearly traced in experiments in which the food consists solely, or nearly so, of proteids, deferring to the next section a consideration of the modifications introduced by the presence of non-nitrogenous- nutrients in the food. Effects on Proteid Metabolism. Our knowledge of the relations between proteid supply and proteid metabolism in the animal body is based upon the funda- mental investigations of Bischoff & Voit,* Carl Voit,t and Petten- kofer & Voit,f at Munich. The results of these researches have been so fully confirmed by subsequent investigators and have become so much the common property of science that it is unneces- sary to do more than summarize them here, with the addition of such examples as may seem best adapted to illustrate them. Amount ReEquirRED TO ReEacH NirroGeN EquiLisrium.—As we have seen, the proteid metabolism of a fasting animal speedily reaches a minimum which we may probably regard as representing, at least approximately, the amount of proteids necessarily broken down and oxidized in the vital activities of the tissues of the body. If we supply proteid food to such an animal, we might naturally be inclined to expect that the first use to which the proteids of the food would be put would be to stop the loss of proteid tissue, and that if as much proteid was supplied in the food as was being metabolized in the body, nitrogen equilibrium would be reached. Experiment shows, however, that this is very far from being the case. Even the least amount of proteids causes a prompt increase in the urinary nitrogen, and each successive addition of proteids results in a further increase, so that itis not until the food proteids largely exceed the amount metabolized during fasting that nitrogen equilibrium is reached. Thus Bischoff & Voit, * Gesetze der Erniihrung des Fleischfressers, 1860. + Published chiefly in the Annalen der Chemie und Pharmacie and the Zeitschrift fiir Biologie. See also Voit, “Physiologie des Stoffwechsels,’’ in Herman’s Handbuch der Physiologie. t Zeit. f. Biol., 3, 29 and 33. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 95 in a series of experiments upon a dog fed exclusively on lean meat, obtained the results shown in the following table, the proteid metabolism being expressed in terms of flesh with its normal water content (N X 29.4) instead of dry proteids: Date. Meat Fed. Meee. cae fa 1858. JAN TRAD Us A ang Bee Bon ae ee 0) 223 — 223 a ON ey Ae neta tee aeMe ge 0 190 —190 Pe TP eAIL CLE Shae cup vres sts op bases 300 379 — 79 UBS UPADES Sy ora al laa are Als a a 600 665 — 65 EMU EAN CL Oye wis seen nail. 900 941 — 4l PA me Mr Sacer? bean. ete MAb Leis ae ~1200 1180 + 20 BM OI ee NEE rama eer ter eres te 1500 1446 + 54 TNO pty IOs Wie Ml ANA cas are 1800 1764 + 36 Ee eel sun See rings ote eb uote. 1500 1510 — 10 LSD yom O Nr ea ete te 1200 1234 — 34 EP A OMe ener Soe Ty acy eer 900 945 — 45 pia E RRS ayaa Saber hay ine. 600 682 — 82 ete Eade Os neat tay se ities else 300 453 —153 CO NEN OTS “OAT, TEA ae irene Siren ne 176 368 —192 Ho IST) Dey ag lc a A ean ee Be ie a 0) 226 — 226 A much later series by E. Voit & Korkunoff,* in which the results were determined in terms of nitrogen, may ve cited to illus- trate the same point. The food was lean meat from which the extractives had been removed by treatment with cold water. It contained 1.25 to 1.96 per cent. of fat. Nitrogen in Food. Food, Feces and Urine,| Gain or Loss, Grms. Grms. ms. ON olan orate ste eee ease ey oitaleusccye 0 3.996 —3.996 100 grms. extracted meat........ 4.10 5.558 —1.458 140 SS COIN, in aN Seen 5.74 6.495 —0.755 G5y aa e Ey an iy ate at 6.77 (heres —0.447 St, aa * Sete ee Oona 7.59 7.804 —0.214 200K. Be Citeg Ra Hi | 8.20 8.726 —0.526 230) <5 a CIES Sak gt, Se Be 10.24 10.579 —0.339 SOOM se “s NS ES Rae 11.99 12.052 —0.062 ANI) oe Met ie vat, er aes tek 15.58 14.314 +1.266 AGO) mews “ ak a SEES 13.68 G22 +0.058 * Zeit. f..Biol., 32, 67. 96 PRINCIPLES OF ANIMAL NUTRITION. The proteid supply gradually overtakes the proteid metabolism, but when only proteids are fed the supply must largely exceed the fasting metabolism in order to attain nitrogen equilibrium. E. Voit has endeavored to obtain a numerical expression for this relation by taking as the basis of comparison the fasting meta- bolism. He estimates (loc. cit., p. 101) that of the total nitro- gen excretion of a fasting animal 81.55 per cent. is derived from true proteids and 18.45 per cent. from the extractives of the muscles. Since the food in his experiments consisted substan- tially of true proteids, he compares its nitrogen with 81.55 per cent. of the nitrogen of the excreta and thus finds that the mini- mum supply of proteid nitrogen required to reach nitrogen equi- librium was between 3.67 and 4.18 times that metabolized during fasting, the true value being estimated at 3.68. Five other less exact experiments gave confirmatory results and similar confirma- tion is found in the experimental results of C. Voit. Errect oF Excess oF Protrips.—lIf the supply of proteids to a mature animal be still further increased after nitrogen equilib- rium is reached, the excess of proteids is promptly metabolized, its nitrogen reappearing in the excreta. In other words, the ex- cretory nitrogen keeps pace with the supply of nitrogen in the food. The experiments by Bischoff & Voit just cited serve to illustrate this fact also. Approximate nitrogen equilibrium was reached on 1200-1500 grams of meat, but in other trials even double this supply caused but a slight apparent gain of nitrogen, and it is probable that if the total urinary nitrogen had been determined instead of the urea, and account taken of the nitrogen of the feces, even this small difference would have disappeared. It is needless to multiply examples of this perfectly well-estab- lished fact. The animal body puts itself very promptly into equi- librium with its nitrogen supply and no considerable or long-con- tinued gain of proteid tissue can be produced in the mature animal by even the most liberal supply of proteid food. TRANSITORY STORAGE OF PRotTEIDs.—But while no continued gain of protein by the body can be brought about by additions to the proteid food, nevertheless, during the first few days following such an increase in the proteid supply a transitory storage of nitro- gen takes place. Conversely, too, a decrease in the proteid supply THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 97 causes at first a loss of nitrogen from the body, which, however, unless the new supply of proteids falls below a certain minimum is as transitory as the gain in the other case. In other words, while the nitrogen excretion of the mature animal is in the long run equal to the supply in the food, when the amount of the latter is changed the full effect on the excretion is not realized at once. This fact is well illustrated by the following selection from C. Voit’s investigations upon the dog,* the results being expressed in terms of “ flesh’’: “* Flesh’? Metabolized per Day. Previous) New N : Ration. | Ration. On VE ey Boe Grms. | Grms. | Previous Meat. Meat. | Ration. |1st Day./2d Day. 3d Day.|4th Day.|5th Day./6th Day.|7th Day. Grms. Grms. | Grms. | Grms. | Grms. | Grms. | Grms. | Grms. 1800 | 2500 1800 | 2153 | 2480 | 2532 500 | 1500 047 | 1222 | 1310 | 1390 | 1410 | 1440 | 1450} 1500 0 | 1500 | 176 | 1267 | 1393 | 1404 2500 | 2000 | 2500 | 2229 | 1970 1500 | 1000 1500 | 1153 | 1086 | 1088 ; 1080 | 1027 1000 500 1000 706 610 | 623 560 An example of the same fact is found in the experiments cited on p. 81, in which a:. proteid food was withdrawn, the nitrogen excretion falling rapidly, but reaching its minimum only after three or four days. Voit explained the facts just adduced as the consequence of the difference between organized and circulatory proteids already noted on p. 82. According to this hypothesis, the amount of the proteid metabolism is chiefly determined by the store of circu- latory proteids in the body. The ingestion of additional proteids increases the amount of these circulatory proteids in the body, and as a consequence the proteid metabolism increases until the nitrogen excretion overtakes the supply. Similarly, a decrease in the pro- teid food has the converse effect. PROTEID METABOLISM AND NITROGEN EXcrEeTION.—Up to this point, following common usage, the terms nitrogen excretion and proteid metabolism have been employed as practically synony- mous. In one sense this usage is correct, but it is liable to give * EK. v. Wolff, Erniihrung Landw. Nutzthiere, p. 271. 98 PRINCIPLES OF ANIMAL NUTRITION. rise to a misconception. It is perfectly true that the presence of one gram, e.g., of nitrogen in the urine, implies that about six grams of protein have yielded up their nitrogen in the form of urea or other metabolic products and therefore have ceased to exist as pro- tein. It by no means follows from this, however, that this protein has been completely oxidized to carbon dioxide and water. We have already seen (Chapter II, p.48) that the abstraction of the elements of urea from protein leaves a non-nitrogenous residue equal to nearly two-thirds of the protein, and that there is reason to believe that this residue may, according to circumstances, be oxidized to supply energy or give rise to a production of glycogen or of fat. In other words, the separation of its nitrogen from pro- tein and the complete oxidation of its carbon and hydrogen are two distinct things. When, therefore, we assert, on the basis of the evidence noted above, that the proteid metabolism of the mature animal is determined by the supply of proteids in the food, what we really mean is that the cleavage of proteids and the excretion of their nitrogen is so determined. Rate or NITROGEN Excretion.—A consideration of the course of the nitrogen excretion after a meal of proteids is calculated to throw light upon the relations of nitrogen cleavage to the total metabolism of the proteids. The early investigations of Becher, Voit, Panum, Forster, and Falck showed that when proteids are given to a fasting animal the rate of nitrogen excretion shows a rapid increase, reaching a maximum within a few hours. Feder * observed the maximum rate of nitrogen excretion by dogs in different experiments between the fifth and eighth hour after a meal of meat. From this point the rate of excretion de- creased less rapidly than it had increased and continued to decrease until about thirty-six hours after the meal. Graffenberger,t experimenting upon himself, obtained similar results after the consumption of fibrin, gelatin, and asparagin, while the results with a commercial “meat peptone” were markedly different; and Rosemann,f{ in studies upon the rate of nitrogen excretion by man, traces clearly a similar influence of the ingestion of nitrogenous food, while Krummacher’s§ results on dogs fully * Zeit. f. Biol., 17,531; Thier. Chem. Ber., 12, 402. } Zeit. f. Biol., 28, 318. t Arch. ges. Physiol., 65, 343. § Zeit. f. Biol., 35, 481, THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 99 confirm those of Feder. Sherman and Hawk * have likewise found the curve of nitrogen excretion by man after the ingestion of lean meat to show the same general form observed by Feder and by Graf- fenberger. NITROGEN CLEAVAGE INDEPENDENT OF ToTaL METABOLISM.— Kaufmann,t by the method outlined in Chapter VIII, has made’ a series of determinations of the nitrogen excretion, respiratory exchange, and heat production of dogs during the time when nitro- gen cleavage is most active, i.e., from the second to the seventh hour after a full meal of meat. From his theoretical equations for the complete metabolism of proteids (pp. 51 & 75) he computes the respiratory exchange and heat production corresponding to the observed excretion of urinary nitrogen and compares them with the actual results per hour as follows: Proteid Computed. Observed. EL TSN REGGAE Lh Le al ed oie aie crete: Gone aoe: eee dak oie: Saint Liters. Liters. Cals. Liters. Liters. Cals. INos, dis: 9.329 8.132 9.745 45.0 5.953 6.767 30.6 oe. Dr 9.926 8.565 | 10.373 48.0 7.064 7.972 34.6 on oie 9.350 8.153 Qe 45 .4 (LG 8.236 34.0 ea: ae 9.540 8.231 9.864 45.8 7.398 8.673 34.0 Ree Dit 6.632 5.783 6.9380 32.0 5.228 6.596 Dilenll meee Oiy 9.491 8.276 9.918 46.1 6.393 7.813 29.7 SAT Re 8.685 7.503 9.075 42.2 6.325 7.730 29.0 So ito ha 9.958 8.683 | 10.406 48 .4 6.702 7.903 33.6 Sy SUED 8.928 Uo 9.235 43.0 6.062 7.916 35.3 Sm Oppel @lLOs 500 9.202 | 11.027 51.0 The liPas 8.589 32.7 But a glance is needed to show that the total metabolism, whether measured by the gaseous exchange or by the heat produc- tion, is much less than that computed, which is equivalent to saying that the non-nitrogenous residue of the proteids was not completely oxidized. Gruber,$ whose experimental results upon the rate of nitrogen excretion fully confirm those above cited, has shown very clearly the bearing of these facts. He points out that if we * Amer. Jour. Physiol., 4, 25. + Archives de Physiologie, 1896, pp. 346 and 768. $+ Kaufmann’s factor for proteids, derived from the formula C,,H,,,N,,03)S, is 6.39. § Zeit. f. Biol., 42, 407. 100 PRINCIPLES OF ANIMAL NUTRITION. regard the nitrogen excretion as denoting the complete metabo- lism to carbon dioxide, water, urea, etc., of a corresponding amount of proteids, we get figures for the total evolution of energy (heat) in the organism which are entirely incompatible with those derived from other considerations. For example, a daily diet of 1500 grams of lean meat given to a dog not only suf- ficed to supply the demands for energy but produced a storage of fat in the body. The total daily production of heat, computed from the results of respiration experiments (see Chapter VIII), was 1060.2 Cals., equivalent to 88.3 Cals. in two hours, which must have been derived essentially from the metabolism of proteids. If, how- ever, we compute the evolution of energy from the results of the nitrogen excretion as determined in two-hour periods, we get strik- ingly variable results. Elon Unies SURE RE ee, Hquiveley ; ere OPN ie Pe state oe tee one: Se 3.11 80.6 PSD eh RRS PN ohh, rel Stet Neri 148.2 LO atige when ieee tea anieiene ees 6.62 171.6 DO lake NORTE einai leeks one 6.98 181.2 RE aR Oca DA A te AC 6.35 165.1 ES PR ee crete he as ee 6.04 156.0 Qa A reed ce elenese teeta 5.08 132.6 11S CAVETELE) le. tian joe. 2.65 68.9 Ta Oue Crae et Meee tenetee | 1.24 32.5 The heat production as thus computed varies from over twice the average two-hour rate to an amount equal to scarcely more than one half of the average fasting metabolism of the same animal (62 Cals. per two hours). Such fluctuations are entirely inconsistent with all data as to the heat production of the body, which, as we shall see later, appears to go on with a remarkable degree of uni- formity under uniform conditions. The only reasonable conclu- sion, then, appears to be that the nitrogen cleavage and the total oxidation of the proteids are distinct and at least largely inde- pendent processes. Gruber’s explanation of these facts is substantially as follows: It is well established that a relatively constant composition of the blood and of the fluids of the body generally is an essential condi- * One gram N equivalent to 26 Cals. See Chapter VIII. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 101 tion of normal physiological activity. It has been repeatedly demonstrated, however, that when the period of growth is past, the animal body has not the ability to produce any material amount of proteid tissue. A large supply of proteid food, then, necessarily tends to alter the composition of the blood and other fluids of the body,.and the nitrogen cleavage is evidently an effort on the part of the organism to counteract this effect by splitting off from the proteids a nitrogenous group which can be rapidly excreted, leav- ing a non-nitrogenous residue which, so far as it is not immediately needed to supply energy, is capable of storage in the relatively inert and insoluble forms of glycogen and of fat. According to Rosemann,* the rapid increase in the nitrogen ex- cretion after a meal arises from two concurrent causes: first, a direct stimulus to the proteid metabolism, due to the rapid increase of proteids and their digestion products in the blood, which is somewhat transitory in character; and, second, the effect of a larger relative supply of proteids in causing, according to well- known physico-chemical laws, a relatively larger number of mole- cules of these substances to enter into reactions with the cell proto- plasm. The accompanying graphic representation by Gruber + of the course of the nitrogen excretion of a dog on the second day of, GRMs. N 5 0 2 4 6 8 1012141618 202224 2 4 6 8 10121416 18202224 2 4 6 8 10121416 19 2022 24 2 4 6 8 1012 1416 18 20 22 26 HOURS RATE OF NITROGEN EXCRETION PER TWO HOURS, feeding with 1000 grams of lean meat and on the three following fasting days shows plainly the sudden stimulation of the excretion * Loe. cit. ft Loe. cit., p. 421. 102 _ PRINCIPLES OF ANIMAL NUTRITION. at first and the fall, rapid at first, and then very gradual, until the minimum of the fasting excretion is reached about the third day. On the other hand, Rjasantzeff * and Shepski + ascribe the in- crease in the nitrogen cleavage after a meal to the increase in the. digestive work rather than to the proteids as such. They find it possible, by stimulating the activity of the digestive organs without introducing food, to considerably increase the nitrogen excretion in the urine, while, on the other hand, the introduction of proteid food through a gastric fistula produced little or no effect. They also find the increase with the same amount of food nitrogen to be proportional to the (estimated?) amount of digestive work, but seem to offer no explanation of the equality of nitrogen cleavage and nitrogen supply. Cause oF TRANSITORY STORAGE.—-As already noted (p. 96), any change in the rate of proteid supply in the food, while resulting ultimately in a corresponding change in the rate of nitrogen excre- tion, gives rise to a transitory gain or loss of nitrogen by the body, which was interpreted by Voit as consisting in a corresponding change in the stock of “circulatory protein” in the body. The facts which we have just been considering permit us to trace some- what more fully the details of the phenomenon. Gruber points out that while the larger part of the nitrogen cleavage consequent upon a single meal of proteids takes place within a few hours, the remainder is prolonged over two or three days, as in the ease illus- trated above, while he likewise shows experimentally that this effect is not due to a retention of the nitrogenous metabolic prod- ucts, but represents the actual course of nitrogen cleavage. Such being the case, the transitory gain or loss incident to a change in the rate of proteid supply is most simply explained as the result of a superpogition of the daily curves. Let it be assumed, for example, that 80 per cent. of the nitrogen cleavage incident to’ a single meal of proteids takes place on the first day, 15 per cent. on the second, 5 per cent. on the third, and 2 per cent. on the fourth. Then if we give to a fasting animal an amount of proteids contain- ing 100 grams of nitrogen for five successive days and then with- draw the food, the food nitrogen will be excreted as follows on the several days: * Jahr. Thier Chem., 26, 349. { Ibid, 30, 711. —— THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 103 Feeding. Fasting. 1st 2d 3d 4th | 5th | 1st | 2d 3d Day.| Day.|Day.| Day. | Day.| Day.|Day.| Day. From food of 1st day of feeding....| 80 | 13] 5] 2 o Serpe Sis mare ON SON hel ee POL | Fe hy oe we cto been al uae te oth OUP tLe: [op hae or cha) OVER a1 TY Se a Re ly la (ree Ue ig eS La a re I UES AL (Koy eeaeey Wr Manes Nee ee OT CEBU ce WOtA He eee: 80 | 93 | 98 |100 |100 | 20 | 7} 2 e On the above assumptions, there remained in the body at the end of the first day 20 grams of nitrogen in the form of unmeta- bolized proteids. At the end of the second day this had increased to 27 grams, and at the end of the third day had reached the maxi- mum of 29 grams. At the end of the first day’s fasting it had fallen to 9 grams, at the end of the second day to 2 grams, and at the end of the third day to zero. In other words, the transitory storage of proteids observed by Voit and others is explained by Gruber as due to the fact that the nitrogen cleavage extends over more than a single day. In reality, of course, the excretion does not take place with any such mathematical exactness as in this schematic example, and after long fasting in particular a certain rebuilding of proteid tissue may occur, but the assumed figures may serve to give a general notion of the relations of food-supply and excretion. In brief, then, we may suppose that when proteid food is given to afasting animal the stimulating effect upon the nitrogen cleavage anticipates the use of the proteids for constructive purposes and that a large proportion of them is thus destroyed as proteids before it can be used to make good the loss of proteids by the organized tissues. In other words, the proteids actually available for the tissues are much less than the amount supplied in the food. In this view of the matter we can readily see why the proteid supply overtakes the nitrogen excretion so slowly and why two or three times the amount metabolized in fasting is necessary to make good the loss from the body and ensure nitrogen equilibrium. 104 PRINCIPLES OF ANIMAL NUTRITION. Effects on Total Metabolism. In the preceding paragraphs the effects of an exclusive proteid diet upon the proteid metabolism have been discussed. There remain to be considered its effects upon the metabolism of fat. PROTEIDS SUBSTITUTED FOR Bopy Far.—When proteids are given to a fasting animal the proteid metabolism is increased, as we have seen, but at the same time the loss of body fat is diminished. Pettenkofer & Voit * fed a dog with varying amounts of lean meat, which may be regarded as consisting chiefly of proteids together with small amounts of fat, with the following average results in terms of nitrogen: Meat ed, |. Mitvogen | eutroren ||, Gale er Los | Gan : Grms. Grms. Grms. Grms, 0+ 0 5.6 +5.6 —95 500 1A) 20.4 —3.4 —47 1000 34.0 36.7 —2.7 —19 1500 + 51.0 51.0 0) + 4 Rubner § has obtained a similar result by the use of the proteid mixture resulting from the extraction of lean meat with water, and which still contained some fat. As compared with the fasting state, the consumption of 740 grams of the moist material (containing 72.2 per cent. of water) produced the following effect: : Nit Fat trogen of Food, Metabolized, Metabolized, wettst Grms. Grms. ASIN Gas od 2 as ceis senior 0 5.25 84.39 1 Cec Ree ease mane me RAL VN A Soeee 26.37 28 .37 Difference...... hehe’ 421.12 — 56.02 The increased nitrogen cleavage resulting from an increase in the proteid supply liberates a certain amount of energy for the vital activities of the body, while the non-nitrogenous residue of the cleav- * Zeit f. Biol., 7, 489. + Average of first two experiments, p. 84, Chapter IV. t Series I only. The others showed a greater gain of fat and of nitrogen § Zeit. f. Biol., 22, 51. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 105 age becomes available also as a source of energy to the organism, and the metabolism of fat is correspondingly diminished. In effect, then, the proteids are simply substituted for more or less of the body fat asa source of energy, and Rubner, in a series of experi- ments which will be considered in Part IT, has shown that the sub- stitution takes place, under the condition of these experiments, ap- proximately in proportion to the amount of available potential energy contained in the proteids and fats respectively. That is, if the extra proteids metabolized can supply a certain amount, 100 Cals., e.g., of energy to the organism, the fat metabolism is diminished by a corresponding amount, so that the total expend- iture of energy by the body remains unchanged, being simply drawn from different sources in the two cases. AmouNT ReEQuiIRED TO PRopuUcE CarBon EQuiLiBprium.—In the experiments by Pettenkofer & Voit cited above, the quantity of food proteids which resulted on the average in nitrogen equili- brium produced substantially an equilibrium also between the supply and excretion of carbon. The earlier experiments of Bidder & Schmidt * gave similar results. Later experiments, however, have given divergent results, nitrogen equilibrium appearing to be reached with an amount of proteids which is far from supplying sufficient energy for the organism, so that while the stock of pro- teids in the body is maintained, its store of fat is still drawn upon. We have seen that the proteid metabolism in the normal fast- ing animal amounts to 10-14 per cent. of the total metabolism, while according to E. Voit (p. 96) the food proteids required for nitrogen equilibrium are, roughly, 24 to 3 times the fasting proteid metabolism. It follows, then, that an amount of proteids con- taining from 25 to 42 per cent. of the total available energy expended by the fasting organism will maintain its store of proteids, and this being so, the remaining 58-75 per cent. must necessarily be sup- plied by the metabolism of body fat. Thus with the dog on which E. Voit’s main experiment was made, nitrogen equilibrium was approximately reached with 12.05 grams of nitrogen in the food,t equivalent to 75.31 grams of protein (NX6.25) and containing * Compare Atwater & Langworthy; Digest of Metabolism Experiments; U.S. Dept. of Agr., Office of Experiment Stations, Bul. 45, 388. i OGnelb., - 09. 106 PRINCIPLES OF ANIMAL NUTRITION. approximately, according to Rubner (see Chapter X), 321 Cals. of available energy. The actual expenditure of energy by the animal was not determined, but is estimated by the author on the basis of Rubner’s investigations at about 1280 Cals. Several experiments by Rubner * lead to the same conclusion. In these experiments the carbon and nitrogen of the excreta were determined and the nitrogen of the food estimated from average figures. The proteid metabolism having been computed from the total excretory nitrogen, the corresponding amount of carbon is computed from the average composition of the proteids and any ex- cess in the excreta is assumed to be derived from the metabolism of fat. (Compare p. 78.) The following are the results in brief, including the one cited above (p. 104): : Nitrogen} Fat Food. Ni ia oa of Metab- Romarke: GT Excreta, | olized, 3 Grms. Grms, INOUHIAG fy. as tea ence ae gre a 4.38 | 49.33 415 grms. lean meat ...| 14.11 | 13.72 | 25.44 | Average of several days. INGthine (i. sack eis clot hook 2.80 | 79.94 740 grms. lean meat .../ 25.16 | 20.63 | 30.73 | 1st two days of feeding. DOR DII EE Sin cme eeiees ese he eee ag 5.25 | 84.36 740 grms. extracted lean’ 1021221 He oe PT 35.22 | 26.37 | 28.37 | Ist to 4th day of feeding. Nothing tie 55 seme ence ete 1.08 | 22.88 390 grms. lean meat ...| 13.26 | 8.53 | 11.42 | 1st day of feeding. No Ghimp: 20%) i iae seen eae 1.08 | 22.88 350 grms. lean meat ...; 11.90 | 10.10 , 11.79 | 3d to 6th day of feeding. POMINUNE Fts Vera's sates eee ees 3.50 | 37.24 , 580 grms. lean meat ..| 19.72 | 18.47 | 21.45 | Ist to 7th day of feeding. While some of the experiments were hardly continued long enough to absolutely establish the sufficiency of the proteid supply, nevertheless we see in all cases a material loss of fat on rations which apparently are sufficient to prevent a loss of nitrogen from the body. It should perhaps be noted that in Pettenkofer & Voit’s ex- periments 1000 grams of meat nearly prevented a loss of nitrogen * Zeit. f. Biol., 22, 43-48; 30, 122-134, THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 107 from the body. It appears possible, then, that nitrogen equilib- rium might have been reached with a less amount than 1500 grams, and that with this less amount there might still have been a loss of fat from the body. Whether this possibility is sufficient to explain the apparent discrepancy between these and later results must, however, remain a matter of conjecture. UTILIZATION OF Excess or ProTEIpS.—We have seen that no very considerable or long-continued storage of protein takes place in the body of the mature animal. However large the supply of food proteids, the body very soon reaches the condition of nitrogen equilibrium, the outgo of this element in the excreta equaling the supply in the food. This fact, as has been pointed out, does not necessarily prove that the elements of the food proteids are com- pletely oxidized in the organism. As was shown in Chapter II, ‘the abstraction from proteid matter of the elements of urea (or, more strictly speaking, of the elements found in the urine) leaves a very considerable non-nitrogenous residue available for the pur- poses of the organism. It was there stated that this residue could serve as a source of energy, and likewise that there was good reason to believe that sugar was formed from it, while finally the question of its ability to serve as a source of fat was reserved for discussion in the present connection. Formation of Fat from Proteids. Mention has already been made in Chapter IT (p. 29) of the fact, first asserted by Liebig,* that the animal body manufactures fat from other ingredients of its food. As a result of the investiga- tions incited by the publication of his views regarding the origin of animal fat, Liebig’s classification of the nutrients into “ plastic” and “respiratory” was generally accepted. The proteids were regarded as the material for the growth and repair of the muscles and the force exerted by the latter was considered to arise from their oxidation, while the non-nitrogenous ingredients of the food, especially the carbohydrates, were the source of the animal heat, and when present in exeess gave rise to a production of fat. As time went on, however, observations began to accumulate * Compare p. 163. 108 PRINCIPLES OF ANIMAL NUTRITION. tending to show that the proteids were not without influence on fat-production. As early as 1745 R. Thomson,* in experiments on ,nilch cows, noted an apparent connection between the supply of proteids in the food and the production of butter. Hoppe + in 1856 interpreted the results of an experiment in which a dog was fed lean meat with and without the addition of sugar as showing a formation of fat from proteids. The same author ¢ in 1859 claimed to have shown a slight formation of fat from casein in milk exposed to the air, and this was confirmed later by Szubotin.§ The latter author, and also Kemmerich,|| and later Voit, experimented upon the production of milk-fat by dogs. Their results, while indicating the possibility of a formation of fat from proteids, were indecisive. Prrrenkorer & Vorr’s EXPpERIMENTS.—Carl Voit, however, was the first to distinctly champion the new theory, and aside from certain confirmatory facts,** such as the formation of fatty acids in the oxidation of proteids, the formation of adipocere, the alleged formation of fat from proteids in the ripening of cheese and in the fatty degeneration of muscular tissue, especially in cases of phos- phorous poisoning,—facts not all of which are fully established and whose importance in this connection has probably been over- estimated,—the evidence bearing on the question of the formation of fat from proteids has been until recently largely that supplied by the famous researches of Pettenkofer & Voit {ft at Munich. In these experiments a dog weighing about 30 kgs. was fed varying amounts of prepared lean meat from which fat, connective tissue, etc., had been removed as completely as was possible by mechanical means. The material thus prepared, while still con- taining small amounts of fat, ete., was as near an approach to an exclusively proteid diet as was practicable, it having been found impossible to successfully carry out feeding experiments with pure * Ann. Chem. Pharm., 61, 228. t Virchow’s Archiv, 17, 417. + Virchow’s Archiv, 10, 144 § Ibid., 36, 561. || Wolff, Erniihrung Landw. Nutzthiere, p. 351. “{ Zeit. f. Biol., 5, 136. ** Compare Voit’s summary in 1869, Zeit. f. Biol., 5, 79-169. ++Am. Chem. Pharm., II, Suppl. Bd., pp. 52 and 361; Zeit. f. Biol., 5, 106; 7, 433. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 109 proteids. The experiments were conducted with the aid of a respi- ration apparatus, the gain or loss of proteids and fat being com- puted from the nitrogen and carbon balance in the manner described in Chapter III. The following is a condensed summary of the average resuits of these experiments, as given by the authors,* but includes also the average of all the experiments with 1500 grams of meat. On Gain (+) or Loss (—) by Animal. Number of Meat Eaten per Day, Experiments. Gris. | Flesh. . Fat. Grms. Grms. 0 —165 —95 500 — 99 —A7 1000 — 79 —19 3t 1500 0 4+ 4 22 1500 + 18 ae 1 1800 + 43 + 1 2 2000 — 44 +58 1 * 2500 — 12 +57 the smaller rations, which were obviously insufficient for main- tenance, the animal lost both flesh and fat. A ration of 1500 grams of meat per day sufficed approximately to maintain the ani- mal as regards flesh and to cause a small gain of fat. On the heavier rations the excretion of nitrogen kept pace with the supply in the food in the manner illustrated on pp. 94—96 but the excretion of carbon fell considerably below the supply, indicating a produc- tion of fat. It is to be noted that only the last three experiments in the above table actually show any very considerable production of fat. The insufficient rations naturally do not, and while among the twenty- two trials with 1500 grams of meat the majority appear to show a formation of fat, the amount is usually comparatively smail, and in two cases a loss was observed. On the whole, however, the evi- dence of this series of experiments has been generally aceepted as conclusive in favor of the formation of fat from proteids. PFLUGER’S RECALCULATIONS.—One very important point, how- ever, has until recently been overlooked. The evidence is based on * Zeitschr. f. Biol., 7, 489. + Series 1 only. IIo PRINCIPLES OF ANIMAL NUTRITION. a comparison of the income and outgo of carbon and nitrogen. Pfliiger,* however, has called attention to the fact that while Pet- tenkofer & Voit made direct determinations of the outgo of these elements, or at least of the principal factors of it, the income is not computed from actual analyses of the meat used, but upon the assumption of average composition. According to Pfliiger, not only are the possible variations from the average in individual experiments a serious source of error, but the average itself is erroneous, the percentage of carbon assumed in the meat being too high. Pettenkofer & Voit estimate the ratio of nitrogen to carbon in lean meat } as 1 : 3.684, while according to Pfliiger it is not higher than 1 :3.28, and probably lower. Moreover, Petten- kofer & Voit failed to take due account of the fact that a part of the gain of carbon which they observed could be ascribed to the fat still contained in the prepared “lean” meat. Another, although slight, source of error, according to Pfliiger, lies in the fact that the carbon in the urine was estimated from the amount of nitrogen f6und by analysis on the assumption of a ratio of 1:0.60, while it should be 1:0.67. | Using the above corrections, Pfliiger has recalculated twenty- four of the experiments by Pettenkofer & Voit, which have been generally accepted as demonstrating the formation of fat from pro- teids, with the results shown on the opposite page.{ In the great majority of cases the experiments as recalculated show a loss instead of a gain of fat, and in three of the four cases in which a gain still appears it is small in amount, and, as Pfliiger believes, within the limits of experimental error. Naturally such calculations as the above can neither prove nor disprove the hypoth- esis that the proteids serve as a source of fat. They simply show that the experiments which have served as the principal support for that hypothesis do not demonstrate what they were supposed to. The question turns largely upon the elementary composition of the meat used by Pettenkofer & Voit, which they failed to determine. It is manifestly impossible to repair this error now, * Arch. ges. Physiol., 51, 229. + Including such fat as cannot be removed by mechanical means. t Loc. cit., p. 267. The experiments which showed a loss of fat as origi- nally computed are omitted. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. III Gain (+) or Loss (—) of Fat. Meat Eaten SANA STE Rh Seer e es Biaecies erect 5 Aes a According to Pet- According to tenkofer & Voit. Pfliiger: Grms. Grms. Gael OS PSO aa aitie ss paces 1800 + 1.4 —35.8 Jat USES ye OC i ye eee eee 2500 +56.7 + 3.93 Miche 45 USG25 co tendecaciceas 1500 + 3.4 —29.3 ete niece otras els feats ois 1500 + 7.3 —23.4 Cah SE Sy CREE Gomer 1500 +34.4 + 3.7 Se Pe cs ae Lary: 1500 O07 ier CO PO rs Se cee aerated 1500 +35.9 + 3.8 EG 11S ar co Ret erie 1500 +22.9 — 8.4 RIS GR te aie: caro wal a sie 1500 + 8.7 —13.5 Fe OES OS ora ep tet aen eet ween 1500 +17.4 — 8.3 Hebu2OveUSGSnk- i cone oes 1500 0.0 —31.6 Bee Ot Et nae. Sei chee ce 1500 + 9.9 —22.1 See fame gee are ciate estes 1500 + 2.1 —24.4 Mee teen ares ee Le, 1500 4403 —16.9 {: (Dip Ely 8 Rea na eee 1500 0.0 —31.8 Te ting aR pp paket eat oe 1500 oa eeABES =175 ee LO Aoi getiicr tomy aGtec eeteisis 1500 + 9.0 —22.0 -) fiw aXe Py a Ue a epee Bae 1500 SEI). 7/ —13.0 SE EXS ORS) ce eoea ere amen 1500 +26.3 — 5.4 Sea Ly emerwac. ciate tear wea eucis 1500 +29.1 — 2.9 Sm Morar de Aa tet to eh 2000 +55.9 +13.6 SO OU LMCAN. whl etre br inett Sh 2000 +58.5 -- 136 SIMUL Veet chy hc PNG O's aise c Shavaks cee s 1500 +11.9 —20.6 BRERA he rine ee 1500 + 9.4 25307 and since Pfliiger’s estimates seem to be at least as trustworthy as Pettenkofer & Voit’s, and lead to exactly the opposite results, the only verdict possible, so far as these experiments are concerned, is “Not proven.” LATER EXpERIMENTS.—Shortly after the publication of Pfliiger’s critique, E. Voit, in a preliminary communication, presented the results of investigations upon this question undertaken in the Munich laboratory. So far as the writer is aware, no complete account of these experiments has yet appeared, but the data given by Voit in the preliminary account show a retention in the body of 8 to 10 per cent. of the carbon of the metabolized proteids, and to this extent confirm the earlier results obtained by his father. He believes the observed gain of carbon to be too great to,be accounted for by the storage of glycogen and interprets it as showing a production of fat from proteids. *Includes a correction of Pettenkofer & Voit’s figures for the urinary nitrogen. Loc. cit. p. 263. + Thier. Chem. Ber., 22, 34. LIZ PRINCIPLES OF ANIMAL NUTRITION. Kaufmann likewise interprets the results of the respiration ex- periments cited in another connection on p. 99 as demonstrating the production of fat from proteids, but in view of the brevity of the experiments (five hours), and the fact that they covered the period of most active nitrogen cleavage, this conclusion seems hardly justified. Cremer * has reported the results of an experiment upon a cat which he regards as showing a formation of fat from proteids. The animal, weighing 3.7 kgs., passed eight days continuously in the respiration apparatus and received per day 450 grams of lean meat. No complete nitrogen and carbon balance is reported. The average daily excretion of nitrogen was 13 grams. Assuming the ratio of nitrogen to carbon in fat and glycogen-free flesh to be 1 :3.2, this corresponds to 41.6 grams of carbon in the form of proteids, while the total excretion of this element was only 34.3 grams, thus showing a retention by the organism of 7.3 grams per day. The body of the animal at the close of the experiment was found to con- tain not more than 35 grams of glycogen and sugar, while the ob- served gain of carbon during the eight days was equivalent to about 130 grams of glycogen. It is therefore concluded that fat was formed from proteids. In three other experiments, with an abundant meat diet, it is computed that from 12.6 to 17.0 per cent. of the carbon of the metabolized proteids was stored in the body. Gruber { has recently reported two experiments, dating from the year 1882, in which a dog was fed 1500 grams per day of lean meat. The nitrogen of feces and urine were determined daily for six and eight days respectively and the carbon dioxide of the respiration on five days in each experiment; the carbon of urine and feces and of the metabolized proteids was computed from the nitrogen, using for the carbon of the proteids the factor 3.28. The excretion of nitrogen approximately equaled the supply, especially on the Jater days of the experiments, but from 10 to 15 per cent. of the carbon was unaccounted for in the exereta. The total reten- tion of carbon during the experiments, together with the equivalent quantities of glycogen, were: * Jahresb. Agr. Chem., 40, 538; Zeit. f. Biol., 38, 309. + Kohler (Zeit. f physiol. Chem., 31, 479) found an average of 1:3.16 for the fat-free flesh of cattle, swine, sheep, rabbits, and hens. See p. 64. t Zeit f Biol., 42, 409. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 113 | Carbon. | Equivalent Glycogen. Experiment 1, seven days........ 113.9 Grms. 256.3 Grms, be RI by, Mi es seface 9.325 IOS EOE AAT Oe 13% These amounts of glycogen are much greater than have ever been found in the body of a dog of this weight (about 20 kgs.), and the larger part of the storage of carbon must therefore have been in the form of fat. In addition to the above results on normal animals, Polimanti * has reported experiments apparently showing a formation of fat from proteids in phosphorous poisoning. The latter investigation, as well as those of Cremer and of E. Voit, have been the subjects of searching criticism by Pfltiger,f who claims to have shown the in- sufficiency of the experimental evidence adduced, but it is impos- sible here to enter into the details of these controversial articles. Negative results have also been reported by Kumagawa & Kaneda.{ Rosenfelt,$ Taylor, Athanasiu,§{ and Lindemann,** but in a matter of this sort negative evidence naturally carries much less weight than positive, and on the whole there would appear to be good reason for still regarding the proteids as a possible source of fat. DIFFICULTY OF PRooF.—A serious difficulty in the way of an unquestionable demonstration of this possibility lies in the limited amount of proteids which an animal can consume. As we have seen, a relatively large supply of them is necessary even to produce nitrogen equilibrium, and a still further large addition is required to supply the demands of the organism for energy. Only the proteids supplied in excess of this latter amount are available for fat produc- tion, and thus it comes about that the limit of consumption and digestion by the animal is reached before any very large produc- tion of fat can take place. On the other hand, if non-nitrogenous nutrients (carbohydrates * Arch. ges. Physiol., 70, 349. } Ibid, 68, 176; 71, 318. tU.S. Dept. Agr., Expt. Station Record, 8, 71. § Jahresb. Physiol., 6, 260. | Jbid.. 8, 249, Jour Exper. Medicine, 4, 399. { Arch. ges. Physiol., 74, 511. ** Zeit. f. Biol., 39, 1. 114 PRINCIPLES OF ANIMAL. NUTRITION. for example) are employed to supply a part of the necessary energy, a more abundant fat production may be caused but the results are ambiguous, since it is possible that the non-nitrogenous residue of the proteids may be metabolized to furnish energy otherwise supplied by the non-nitrogenous nutrients and that the actual material for the formation of fat may come from the latter. That proteids added to a mixed ration may give rise to a large amount of fat has been strikingly shown by Kellner * in experi- ments on oxen in which wheat gluten was added to a fattening ration. Approximately 198 grams of fat were produced for each kilogram of protein fed, but to the writer the reasoning by which Kellner seeks to prove that this fat must have been derived directly from the proteids seems inconclusive. Finally, as was indicated in Chapter II (p. 50), the apparently well-established fact that the metabolism of proteids in the body gives rise to the formation of carbohydrates (or at least may do so), together with the further fact that fat is undoubtedly formed from carbohydrates, renders it difficult to assign any reason why the non- nitrogenous residue of the proteids should not supply material to the cells of the adipose tissue for the production of fat. § 2. The Non-nitrogenous Nutrients. Effects on the Proteid Metabolism. The relations between proteid metabolism and proteid supply which have been outlined in the preceding section, while deduced mainly from experiments in which the food consisted substantially of proteids only, are of general applicability, yet are subject to im- portant modifications in the presence of non-nitrogenous nutrients. Tend to Diminish Proteid Metabolism.—As was first shown by C. Voit, the addition of non-nitrogenous nutrients to a ration consisting of proteids tends to render the proteid metabolism less than it otherwise would be. The effect is common to the fats and carbohydrates, although with some differences in details. Fats.—The following example, taken from Voit’s experiments, t illustrates in a somewhat marked way the influence of the addition of fat to proteid food upon the excretion of nitrogen. A dog con- suming daily 1000 grams of lean meat received in addition on two days 100 and 300 grams of fat, with the following results: * Landw. Vers. Stat., 58, 456. + Zeit. f. Biol., 5, 334. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 115 $$ eS Food per Day. Urea per Day, Maat, Fat, Grms. Grms. Grms. ity tava veered «ce eek 1000 0 Bl 7 rapeoer Maen gta cee: bos 1000 100 74.5 Boe Ba Noah va tbeae web o 1000 300 69.3 PR PAD aE a ws rviare a wide 1000 0 81.2 In the whole series of eight experiments with varying amounts of meat and fat the decrease in the excretion of urea ranged from 1 per cent. to 15 per cent. of the amount supplied in the food, averag- ing about 7 per cent. . With the same amount of fat in the food the decrease in the excretion of urea was not, as a rule, greater with large than with moderate rations of meat. On the other hand, with a small proteid supply in the food the production of urea was sometimes increased slightly by the addition of much fat, and the same result was observed to a more marked extent when fat alone was given to fasting animals. With medium rations of meat, in- creasing the fat supply had usually little effect, but with heavy meat rations it tended to further diminish the excretion of urea. Subsequent investigation has fully established this tendency of fat to diminish the proteid metabolism, and the fact is too well known to require extended illustration here. As a recent instance may be cited the following results obtained by Kellner * in experi- ments upon oxen, in which oil was added to a basal ration: Nitrogen Digested. Nitrogen in Urine. Basal Ration, |Basal Ration + Oil,| Basal Ration, |Basal Ration + Oil, Grms. Grms. Grims. Grms. Osc B ecatnaie eit ee 135.30 134.55 122.54 120.38 Oserline ¥en se les: 111.67 109/17 106.03 89.27 OxtGeaeorne ren 86.27 87.08 86.30 79.83 CARBOHYDRATES.—The effects of the readily soluble hexose carbohydrates (starch and the sugars) have been quite fully inves- tigated, while as to-those of the less soluble carbohydrates, particu- larly of the five-carbon series, considerable diversity of opinion still prevails. * Landw. Vers. Stat., 58, 121 and 210. 116 PRINCIPLES OF ANIMAL NUTRITION. Starch and Sugars.—The investigations of C. Voit * show that starch or sugar added to a proteid diet causes, as does fat, a decrease in the elimination of urea. Voit found an average decrease of about 9 per cent. in the proteid metabolism, the extremes being 5 and 15 per cent. with varying amounts of carbohydrates. An in- crease in the carbohydrates, the proteid food remaining the same, tended to further diminish the excretion of urea. The following examples illustrate this effect of the carbohydrates. When given to a fasting animal, carbohydrates did not, as in the case of fatty cause an increase in the proteid metabolism. ~ _ Food. Urea per Day, Meat, | Carbohydrates, | Grms. Grms. Grms. June 23-—July 2, 1859 Ne Snidisie-s Nam tarehtoeran 500 300-100 35.4 ARIEL "Dna, tye) Aas Wate a tere ON eee kA ee 500 0 39.9 Sully, (ARNO. AIS64 eo ee eee ak ene 800 0) 59.1 o Oe eee ea S leeds ane Sera a onare 800 100-400 54.5 = QE Oc aed pe cage stae eccrine 800 0 63.8 JibyePS— 20 MGOA ees eatr ae «cab Rave tee 1000 0 73.5 TE EZO AG sie, 8 RPI He horns eas eee 1000 100-400 64.4 SP OS ANE La Gat oe a rimteta Neat ec pad ee 1000 0 79.6 a Se ee ee VINE. 29—IiulyrSs USGS peer eter ieee 1500 0 114.9 July 8-13, SPAM crt AN nett 1500 200 103.3 Dent. 1G) SSO crc een ke iene tenet 2000 0 143.7 seme (oon Hl eae) 2 35)° Se TRS hd seh ke 2000 200-300 131.0 —- This effect of the carbohydrates, like that of fat, has been abun- dantly confirmed by later investigators and is one of the well-estab- lished facts of physiology. Weiske + in particular has investigated the effect of the non-nitrogenous nutrients upon the metabolism of sheep, while Miura { and Lusk $ have shown that the abstraction of carbohydrates from the diet of a man results in a marked increase in the proteid metabolism. The following data, taken from Kell- ner’s extensive respiration experiments at Mdéckern, illustrate the same effect of starch in the case of cattle: * Zeit. f. Biol., 5, 434. + Zeit. physiol. Chem. 21, 42; 22, 137 and 265. t v. Noorden, Pathologie des Stoffwechsels, p. 117. § Zeit. f. Biol., 27, 459. ° — THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 117 | Nitrogen Digested. Nitrogen in Urine. : Basal Ration ; Basal Ration B 1 Ration, Sis B 1 Rat ayes Grines ee ane psyco rae tee Oxo ee Meeps cit Sco teases 135.30 118.40 122.54 | 104.69 OMB os: Seals, cleus: ek teie 67 107.55 106.03 81.18 OAC el oeea rete te ciate acters 86.27 80.92 86.30 63.83 Ores Eee aetonera:c tnislisintss 116.51 94.66 109.28 81.71 (Oicid Dacha Sake SF eetaua eyaicene 128.11 118.18 122 .62 103.13 Since the addition of starch to the basal ration diminished the apparent digestibility of the protein, the effect is most clearly seen by comparing the daily gains of nitrogen by the animals on the two rations, as follows: On See eT ici Difference. 3 F Grms. CONFIDE a rcgctaetin teins. Sasuke ooh WA SG) i374 + 0.95 Oxe yes aseicaciaa tie heals 5.64 26.37 +20.73 OsAG Her setae eens —0.03 17.09 +17.12 (OB) 8 [eat ete Vt aan eee amet Tl ee 12.95 + 5.72 Ox pae re, Saja. eee yh oe 5.49 15.05 + 9.56 Cellulose—The peculiar position occupied by cellulose, as the essential constituent of the “crude fiber” of feeding-stuffs, in the nutrition of domestic animals causes much interest to attach to the study of its effects upon metabolism. We shall consider here only its effects upon the proteid metabolism. The first to take up this subject appears to have been v. Knie- riem,* who experimented upon rabbits. In a preliminary experi- ment the addition of prepared “crude fiber” to a basal fiber-free ration in which the necessary bulk was obtained by the use of horn- dust + gave the following results for the urinary nitrogen per day: Tey Witham ber aac. Sse up elees 0.9034 grams II. With 9.284 grams fiber......... OC. 7O1S Ti Wathoutriber voce. te 2k. OR Z5000 tar The low figure for the third period is ascribed to the effect of the crude fiber still remaining in the digestive tract. In a follow- ing series, in which respiration experiments were also made, the following results per day were obtained for the nitrogen: * Zeit. f. Biol., 21, 67. + Shown to have been entirely indigestible. 118 PRINCIPLES OF ANIMAL NUTRITION, Nitrogen | Nitrogen | Gain of Period. Food per Day. of Food, *|of Excreta *; Nitrogen, Qrms. Grms. Grms, I. 9days. | Milk and horn dust ........... 2.75 3.35 —0.60 II. 10 days. | Same + 22 grms. crude fiber ...| 2.75 2.65 +0.10 III. 5days. | Milk and horn dust ........... 2.70 3.03 —0.33 TV. 4days. | Same + 11 grms. cane sugar ...| 2.70 3.02 —0.32 Vio Sidays.f- 02 Saga TE 3 * 2.70 2.73 —0.03 Weiske { disputes v. Knieriem’s conclusion that cellulose dimin- ishes the proteid metabolism. He experimented upon a sheep, which was fed in a first period exclusively on beans. In succeeding periods the effect upon the proteid metabolism of adding to this ration, first, inferior oat straw, and second, starch was tested, the bean ration being diminished slightly in these periods in order to keep the total digestible protein of the ration as nearly uniform as possible. On the basis of a preliminary digestion trial with the straw, the quantity of starch was so adjusted as to supply, in Period III, according to computation, an amount of digestible carbohy- drates equal to the digested fiber and nitrogen-free extract of the straw of Period II, while in Period V it equalled the digested nitrogen-free extract only. Actual determinations of the digesti- bility of the mixed rations showed that this equality was approxi- mately, although not exactly, reached, the amount of digested starch being rather less than the computed amount. The results as regards the proteid metabolism as originally re- ported by Weiske are given in the first portion of the table on the opposite page. v. Knieriem,§ having criticised the results on the ground that the metabolic nitrogen of the feces was not taken into account, and that when this was done the experiments made a more favorable showing for the digested crude fiber, Weiske || has recalculated his results on the assumption that the feces contained 0.4 grams of metabolic nitrogen for each 100 grams of dry matter digested, with the results shown in the second half of the table. * Not including that of the horn dust. + Results regarded by the author as of doubtful value t Zeit. f. Biol., 22, 373. § Ibid., 24, 293. \| Ibid., 24, 553. {Compare Kellner, Landw. Vers. Stat., 24, 434; and Pfeiffer, Jour. f. Landw., 33, 149. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 119 Uncorrected. Corrected. 8 Nit C 5 Ration. cent Nitro- puted Nitro- appar | mee | ain, | NU | 8 | Gain Di- Urine Di Urine gested. gested, Grms. | Grms. | Grms. | Grms. Grms. | Gims. HE 500 grms. beans....| 20.51] 20.93 |—0.42| 22.02} 20.93 |+1.09 me 7{ a0), beeps 19.58| 16.82 |+2.76| 21.78] 16.82 | +4.96 515 “ce sy e . . . . . AOU ss a eans IV. at = oe 18.81] 17.26 |+1.55) 21.09) 17.26 |+3.83 Average of II. and IV. +2.16 +4.40 510 grms_ beans Oi fs } 180 «starch }..] 20.03] 14.94 |+5.09| 22.16; 14.94 |+7.22 20 “ sugar 500 * beans Vv 90 “ starch ;..| 20.64] 17.75 |4+2.89| 22.43] 17.75 |+4.68 10 7 GO. csugar It will be seen that the experiments make substantially the same showing for the relative effects of cellulose and starch whether we take the uncorrected results or eliminate so far as possible the effects of the greater amount of food in the later periods upon the excretion of metabolic products in the feces. The addition of starch and sugar in Period III produced about twice as great an effect in reducing the proteid metabolism as did a somewhat larger amount of digestible fiber and nitrogen-free extract from straw in Periods II and IV. In Period V the starch added was only equal to the digested nitrogen-free extract of the straw in Periods II and IV. Since the effect upon the proteid metabolism is substantially the same, Weiske concludes that the nitrogen-free extract of the straw, which has the elementary composition of starch, is equal to it in its effect upon the proteid metabolism, and that the digested crude fiber is valueless in this respect. It must be said, however, that this latter conclusion is not warranted by the facts, since it rests upon the unproved assumption of equality of nutritive value (in respect of the proteid metabolism, at least) of starch and the nitrogen-free extract of the straw. Weiske also experimented with rabbits, finding in one case no effect upon the proteid metab- olism and in the second an increase of it, as a result of adding crude fiber to a fiber-free ration. 120 PRINCIPLES OF ANIMAL NUTRITION. Lehmann * experimented upon a sheep by adding respectively crude fiber, prepared from wheat straw, and starch to a basal ration. The results were not entirely sharp but showed plainly a decrease of the proteid metabolism on the crude fiber ration which was equal approximately to 61 per cent. of that secured by the use of starch. In a second series of experiments, Lehmann and Vogel + compared the effects upon the proteid metabolism of sheep of cane- sugar and of the digestible non-nitrogenous matters of oat straw. On the basis of a very careful discussion of the experimental errors, they show that the latter substances have a marked effect in diminish- ing the proteid metabolism, and in particular that if we ascribe this effect exclusively to the digested nitrogen-free extract, as Weiske does, we must admit that the latter produced an effect from two to nine times as great as that of cane-sugar. They therefore con- clude that their results show qualitatively an effect of the digested cellulose upon the proteid metabolism. Reckoning the digested nitrogen-free extract of the straw as equivalent to sugar, they com- pute from the average of all their experiments that the cellulose produced 75.7 per cent. as great an effect as the sugar, but they do not regard this quantitative result as well established. Holdefleiss { experimented upon two sheep, feeding in a first period meadow hay exclusively. In the second period one half of the hay was replaced by a mixture of peanut cake, starch, and a little sugar, while in the third period the starch was replaced by paper pulp. In one case a fourth period was added in which the paper pulp and sugar were simply omitted from the ration. The digested nutrients and the proteid metabolism per day are tabulated on p.121. Converting the small differences in the amount of crude fat digested into their equivalent in nitrogen-free extract by multipli- cation by the factor 2.5, Holdefleiss computes from a comparison of the second and third periods that the digested crude fiber pro- duced on the first animal’80.1 per cent. and on the second animal 84.2 per cent. of the effect of the starch. A somewhat higher value would be obtained from a comparison of the first and second periods in the case of Sheep II, avhile on the other hand a comparison of the corresponding periods with Sheep I gives a much lower value, and is * Jour. f. Landw., 37, 267. t Ibid., 37, 281. } Bied. Centr. Bl. Ag. Chem., 25, 372. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 121 Apparently Digested. cVisieee: Gain f en of] +; petlone Crude| Crude |_N. tr. | Nitro-| Urine, ag Fat, | Fiber, |Extract,) gen, | Grms. Gis Grms.| Grms. | Grms, | Grms. Sheep I. Pernod t Hay only \n... 2 Sansa 13 .55|315 . 72/470 .85/15 .02|13..83) 1 19 «<2 | Hay, peanut cake, sugar, aAndsstarchi-e eee \15.27|134.11/560.71)13.55)11.31) 2.24 “ .3 | Hay, peanut cake, sugar, and paper pulp........ 113 .67/439 . 32/320 .21/13 76/11 .26| 2.50 “<4 | Hay and peanut cake..... 18 .57)171 .12)345 .92)16.25)14.45) 1.80 Sheep II. | erie Ay | Play Oly... ieb isle) acre el os 11 .76)171 .92/276 .42'10.88| 8.45] 2.48 “2 | Hay, peanut cake, sugar,| enoestancine yeas seed, 13.07| 77.48)/336.62| 9.54) 7.85) 1.69 “3 | Hay, peanut cake, sugar, and paper pulp........ 15.14/235 .31|198.46) 8.82) 7.62) 1.20 even consistent with the view that cellulose has no effect upon the proteid metabolism. In other words, the results on Sheep I, in the first period, appear inconsistent with the other results. Kellner * has experimented with rye straw extracted with an alkaline liquid under pressure in the same manner as in paper- making and containing 76.78 per cent. of “crude fiber” and 19.96 per cent. of nitrogen-free extract. The results as regards the pro- teid metabolism, compared with those on starch, are given in the upper table of p. 122. Taking the figures as they stand, and attempting no correction for the marked depression in the apparent digestibility of the nitro- gen resulting from the addition of the extracted straw or starch, they show a considerable effect by both in diminishing the proteid metabolism relatively to the supply in the food and thus causing an increased gain of nitrogen by the body. Any correction for the metabolic nitrogen of the feces, as in Weiske’s experiments, would, of course, tend to make the effect appear still greater. With the first animal, after taking account as well as possible of the slight differences in the fat digested in both periods and of the slight effect of the starch upon the digestibility of the fiber of the basal ration, the digestible matter of the extracted straw, five sixths of which was cellulose, appears to have produced more than twice as great an effect as an equal amount of starch. With the second * Landw. Vers. Stat., 53, 278. 122 PRINCIPLES OF ANIMAL NUTRITION. eee ee ee Apparently Digested. Nitrogen | Gain of par al ane of Orne, Nitrogen rude} Crude Ae A rms. Grms. Fat, |Fiber, |Extract, nee, Grms.|/Grms.| Grms. 2 Ox H. MSU ieee Rar. ee Period 5| Extracted straw..} 116 | 3129) 3351 | 102.47 76.31 | 26-16 <¢ 4) Basal ration. ..... 101 | 1083] 2912 | 116.51 | 109.28 7.23 Difference... .... 15 | 2047| 439 |—14.04 |—32.97 | 18.93 Cros | uarChelsa (ena 92 | 1057} 4773 94.66 81.71. } 12.95 “4) Basaliration:: . 2. 101 | 1083) 2912 | 116.51 | 109.28 1.28 Difference...... —9 | —26) 1861 |—21.85 |—27.57 aye. Ont. Period 5| Extracted straw..} 110 | 3101) 3344 | 112.19 95.80 | 16.39 | A4| Basaliration» 42): 107° |) 1114) 2895 |) 128.11 | 122,62 5.49 Difference. ..... 3 | 1987} 449 !|—15.92 |—26.82 | 10.90 APES SO tArCh es ate. ot 85 | 1105} 4396 | 118.18 | 103.13 | 15.05 «< 4! Basal ration.... .. 107 | 1114} 2895 | 128.11 | 122.62 5.49 Difference... . .| —22 eI 1501 | —9.93 |—19.49 9.56 animal, on the contrary, the effect of the digested matter of the ex- tracted straw was but little more than two thirds that of the starch. Ustjantzen * has recently reported the results of an experiment upon a sheep substantially like those of Weiske (p. 118), a basal ration of beans receiving, in succeeding periods, additions of meadow hay, rice, or sugar, the two latter being computed to supply an amount of digestible carbohydrates equal to the digestible nitrogen- free extract supplied by the hay. The increased amounts of crude fiber and nitrogen-free extract digested and the resulting increases in the gain of nitrogen by the animal were as follows: Crude river, | Sitgorentree | Gain of Grms. Grms. Grms. From ay ration 2. 6. 62s es 108 .60 1 E95).05 Sido A POLIC Otte dW dy. Lich ev se nee ae —2.53 107.15 2.90 sag i <2) a AS OS eR 5.07 109.20 2.59 It appears that, as in Weiske’s experiments, the carbohydrates of the rice and sugar produced nearly as great an effect upon the * Landw. Vers. Stat., 56, 463. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 123 gain of nitrogen as the total non-nitrogenous matter digested from the hay, and the author follows Weiske in concluding that the digested crude fiber produced but little effect on the proteid metabolism. The same author also reports experiments upon a rabbit similar to those of v. Knieriem, crude fiber prepared from hay being added to a basal ration of peas, with the following results, which show practically no effect of the crude fiber upon the proteid metabolism: Niiroeer Nitrogen Excreted. Guinan Food. OL OO a Guamon nan enn aIe Ee MT SU LRORen. Grms. | Urine, | Feces, | Total, | Grms. Grms. Grms. Grms. IEBEGE 38 Sia Hin Sey SC Se eS 0.845 | 0.855 | 0.016 | 0.871 |—0.026 “and 5 grams. crude fiber....| 0.857 | 0.821 | 0.120 | 0.941 |—0.084 ee Derek SUDALAL EL IS 5,5Fk: ).845 | 0.701 | 0.080 | 0.781 |+0.064 meh ubtesiat ‘Ooo crude fiber... 7 0.860 | 0.899 | 0.170 | 1.069 |—0.209 While it is obviously unsafe to draw any positive conclusions regarding the relative effect of cellulose and the more soluble carbo- hydrates from the various experiments cited above, the balance of evidence seems clearly to show that their influence upon the pro- teid metabolism is qualitatively the same, while it appears on the whole probable that digested cellulose is at least not greatly in- ferior quantitatively to digested starch. Organic Acids—Certain methods of preparing or preserving fodder, notably ensilage, result in the formation of not inconsider- able amounts of organic acids. Moreover, it appears that these acids are normally produced in considerable quantities in the herbivora by the fermentation of cellulose and other carbohydrates, and that fact naturally leads to a consideration of their effects upon meta- bolism as compared with the latter substances. We have seen (p. 27) that the organic acids are oxidized in the body, and it therefore seems natural to suppose that they may influence the proteid metabolism. This question has been investi- gated by Weiske & Flechsig.* After some only partially success- ful experiments on a rabbit, they fed a sheep with a basal ration (of hay, starch, cane-sugar and peanut cake) containing a liberal supply of protein and having a nutritive ratio of 1:3.4. To this ration there was added in succeeding periods lactic acid as calctum lactate, acetic acid as sodium acetate, and for comparison dextrose. * Jour. f. Landw., 37, 199. “T24 PRINCIPLES OF ANIMAL NUTRITION. Disregarding for our present purpose the slight effect of these sub- stances upon the digestibility of the non-nitrogenous ingredients of the ration the results were: Nitrogen Nitrogen Gain of Digested, | of Urine, | Nitrogen, Grms., Grms. Grms, Basal TALLODN bse eee a Oe ee OO EES 18.06 17.56 0.50 “+ 60 grms. lactic acid a ety bac 17.83 15.60 2.23 “cc “ee + 120 “ec Gane ee t gens Me 18.03 | 15.72 | 2.31 TSE VCEW lin fst 0) 0 atime game iene MTA Pint rene Saba coe ele 18.69 16.85 1.84 "+ 60 grms. dextrose See Raedeist 17.69 15.29 2.40 “ ‘“ 4 120 “ (Three days only. ) ai wapi'e lote.te xa i7/ ° 93 12 86 2 07 Basal ration: 2s is take bet ees eee ere 18.70 16.54 2.16 pr “+60 grms. acetic acid ites doa t an HSI [18.70*]| 17.04 | 1.66 The smaller amount of lactic acid seems to have produced as great an effect in reducing the proteid metabolism as an equal weight of dextrose, but no further effect was noted from an increase in its amount, as was the case with the dextrose. The acetic acid, on the contrary, seems to have had a tendency to increase rather than to diminish the proteid metabolism, and the same effect was indicated in one of the experiments on a rabbit. It is to be re- marked, however, that the sodium acetate appeared to be particu- larly obnoxious to the animals. In the case of the sheep it was in- troduced into the stomach in solution by means of a funnel, and besides causing the animal considerable discomfort had a very marked diuretic action. It may perhaps be questioned whether the results obtained under such conditions represent the normal effects of acetic acid. Pentose Carbohydrates.—While the fate of the pentose carbo- hydrates in the body has been the subject of considerable research (compare Chapter II, p. 24), their effect upon the proteid meta- bolism does not seem to have been specifically investigated, although Pfeiffer & Eber, in the course of experiments upon the origin of hippurie acid, observed that after the consumption of 500 grams of * Assumed to be the same as with the basal ration. ‘The actual nitrogen of the feces for these three days was 4.78 grms., making the apparently dirested nitrogen 19.33 grms. | Landw. Vers, Stat., 49, 137. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 125 cherry gum, containing 41.98 per cent. of pentose carbohydrates, the urinary nitrogen of a horse decreased by over 6 per cent. They leave it uncertain, however, whether the effect was due to the pentosans or to other ingredients of the gum. Among the early experiments of Grouven * are also four in which gum arabic, added to an exclusive straw ration, materially reduced the proteid metabolism, but the methods of these early experiments were naturally somewhat defective. On the other hand, Cremer’s experiments | with rhammose on rabbits showed no marked effect of this substance upon the proteid metabolism. Total Non-nitrogenous Matter of Feeding-stuffs—The digestible non-nitrogenous matters of feeding-stuffs, aside from a small pro- portion of fat, are commonly although loosely grouped together as carbohydrates. They include both hexose and pentose carbohy- drates, such organic acids as may be present or as are formed during digestion, and a variety of other less well-known substances. As has already appeared in discussing the effeet of crude fiber, the mixture of material included in the digestible crude fiber and nitro- gen-free extract shows the same tendency as starch and sugar to diminish the proteid metabolism. In other words, while the com- mon designation of digestible carbohydrates may be of questionable accuracy from a chemical point of view, nevertheless the some- what heterogeneous mixture to which it is applied behaves, in this respect at least, qualitatively like the pure hexose carbohydrates. ' Numerous instances of this are cited by v. Wolff { in his discus- sion of the data prior to 1876. Of more recent results, attention may be specially called to those of Kellner, some of which have been cited above. The results upon coarse fodders are those which are of particular interest, since it is these whose ingredients are least known chemically. They are presented on the following page in the same form as those upon extracted straw above. Although the addition of hay or straw to the basal ration in- creased the supply of digestible nitrogenous matter, the proteid metabolism was not proportionately increased, but in every instance * Wolff, Erniihrung Landw. Nutzthiere, p. 289. ft Zeit. f. Biol., 42, 451. { Ernihrung Landw. Nutzthiere, pp. 288-309. PRINCIPLES OF ANIMAL NUTRITION. . 126 ae 6|% ow | | Meadow Hay. F | 1 Basal ration + hay.. he S| eds igo Dea Pathe | Difference ........ G 2 Basal ration + hay.. G | : oe chs sratantie QQ ey bey jeofee 3 ‘ He bo wT ee) ~e Rh ro) a ie © ae Ko) =) ait = i) << Difference ........ | Basal ration + hay.. ‘ “ | ‘ He bo Difference Oat Straw. Basal ration + straw “ igs w bo Difference 1! Basal ration + straw 3 “ce igs Differecne ee eee eee Wheat Straw, 1| Basal ration + straw 4 Ng AMT TAA Difference ........ 1} Basal ration + straw ye one Het ee eee eee Crude Fat. Grms. Ze 90 33 58 20 38 Appar Crude Fiber. Grms. 1553 1007 546 1675 1137 538 1786) 1083 139 90 | 49 86 20 66 115 101 14 111 107 4 703 1822 1083 739 1797 1114 683, 1701 1007 694 1732 1137 595 1904 1083 821 1943 1114 829 ently Digested. } of Nitrogen- Pentosans in Fiber and Extract, Nitrogen. Gris.|Grms.| Grms. | 3850] 1383 133.84) 97 3014) 1069 111.67, 106 836 | 1498 108.96 91 1143 86.27, 86 4006 3120 4037| 1487 145.94 122 2912) 1071,116.51| 109 1125} 416) 29.43 ! 12 4148) 1531 146.84 2912) 1071 116.51 1236] 460, 30.33 130. 109 21 4108] 1542 163.37) 2895] 1059 128.11. 137 122 1213) 483, 35.26 15 3735| 1553 119.15 3014! 1069 111.67 721| 484) 7.48 3804) 1574) 91.77) 3120} 1143, 86.27) 684| 431 5.50 110.80 116.51 3436) 1485 2912) 1071 he 414 —5.71 3511) 1555)128 .94 2895, 1059128 .11 616 496) 0.83 —2 886 5a 22.69} 5 Nitrogen Urine. Grms. 19 ‘03 314 me ~8.84| .30 .30 .00 19 .28 ao 78 .28 .50 ao 62 .30 40 03 63 36 .30 94 .32 28 .96 119.89 122.62 .73 Gain of Nitro- gen. Grms. 36.65 | 5.64 31.01 17.66 —0.03 17.69 23.75 7.23 16.52 16.06 7.23 8.83 | 25.40 5.49 19.91 5.64 14.11 20.41 —0.03 20.44 4.48 |. 7.28 —2.75 9,05 5.49 3.56 19.75. a THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 127 save one the gain of nitrogen by the body showed a marked increase, and this, it is to be noted, after the feeding had been continued for a considerable time. The one exceptional case, on wheat straw, is readily explained by the obvious effect of this material in increas- ing the metabolic nitrogen of the feces and thus diminishing the apparent digestibility of the protein of the ration. Had account been taken of these metabolic products, the increased gain of nitrogen by the animals would doubtless have been more marked ‘inall cases. This gain, it would seem, may fairly be ascribed to the large additions of digestible non-nitrogenous matter derived from the hay or straw added. — CoMPARATIVE EFFEcts OF FaT AND CARBOHYDRATES.—C. Voit * found the hexose carbohydrates to be superior to fat in diminishing the proteid metabolism. He gives the following comparisons: ; Food per Day. Urea Date. Soe | Peper Day. Meat, Carbohydrates or Fat, Grms. Grms. Grms. IN OWAEIIG—2 2" OSH Tt. oto vie lons Slope stays 150 150-350 sugar 13.4 Te ECL SO Ie sh .ieless aver one 150 250 fat 15.6 Oct: 28—Nov- 8, 1857... 2.2.52... 176 100-364 starch 1 ae Nov. 8-15, ura rig ile ga 2 176 250 fat 16.2 Rebea25-25) USO ec eaererors ers ore 400 200 fat 31.9 CS 6 ee CO i tee ee 400 250 starch 30.5 ees MCh wo lebih tr. & fers ah 400 250 sugar 30.3 A fiitsyey CEB} mie tae ee eee ics Aree 500 250 fat 38.5 p ADRs oe 1 ae one pe ee 500 300 sugar 32.7 eb OO en cin Phe eet attics sino 500 200° * 35.6 SO INL eye SOO! a0 cisy cate ls:ah as 500 LOOM ;s" 37.9 Wel = 22, VSO cate ars ors syapeyetel ohens 800 250 starch 52.8 “Oy [i ga UR a a 800 200 fat 54.7 DMs o-2Os LS OLE ye /< 0 tale esis 1000 0 i 73.5 oO. hs ae Pay AGA 8 URS 1000 100 starch 68.5 “ 97 aN DR vee lA iat 1000 400 “ 60.2 PT Rie el ARGL ©. ee ok 1000 0 79.6 ae IRD 2 ve ee Sop ey wd 1000 100 fat 74.5 Ne Geet kA Shia sid ane shale bia ae 1000 300 “ 69.3. SRC Ngee eet oe ier 1000 Or, 80.2 PAM Lae LOO eis stchcids atepe tei eaters 2000 200-300 starch 128.4 NC Rr Sa ia Sige et Ca eles 2000 250 fat 135.9 * Zeit. f. Biol., 5, 447. 128 PRINCIPLES OF ANIMAL NUTRITION. Subsequent investigations have substantially confirmed this conclusion. Thus Kayser * in an experiment upon himself found that the replacements of the carbohydrates of his diet by an amount of fat equivalent to them in heat value caused a marked increase in the urinary nitrogen, resulting in a loss of this element by the body in place of the previous small gain. The possible effect upon the apparent digestibility of the proteids of the food does not appear to have been considered. Wicke & Weiske ¢ report two series of experiments upon sheep in which equivalent (“isodynamic’’) quantities of fat and of starch were added to a basal ration. In the first series the basal ration was comparatively poor in proteids and fat, having a nutritive ratio of about 1:8.3 ; in the second series it was richer in both these substances and had a nutritive ratio of 1:5.1 and 1:6.3 for the two animals respectively. As is usually the case, the starch dimin- ished the apparent digestibility of the protein of the basal ration, while the fat produced but a slight effect in this direction. Not- withstanding this complication, however, the effect of the starch in diminishing the proteid metabolism was clearly greater than that of the fat, and if the results were corrected for the increase in the nitrogenous metabolic products in the feces they would be still more decisive. The investigations of E. Voit & Korkunoff upon the minimum of proteids, which will be considered in a subsequent paragraph, also show a superiority in this respect of the carbohydrates over the fats which these authors ascribe to the greater lability of their molecular structure which enables them to enter into reactions in the body more readily than the fats. Magnitude and Duration of the Effect.—The pre-eminent position of the proteids in nutrition has perhaps led investigators to attach undue importance to this power of the non-nitrogenous nutrients to diminish the proteid metabolism. It is well to note that it is relatively small. C. Voit, as already stated, found an average decrease of about 7 per cent. with fats and about 9 per cent. with carbohydrates, and subsequent investigators have ob- tained results entirely comparable with these. ProrEerD METABOLISM DETERMINED By SuppPLy.—lIn the presence * y, Noorden, Pathologie des Stoffwechsels, p. 117. +Zeit. physiol. Chem., 21, 42; 22, 137. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 129 ot non-nitrogenous nutrients it is still true that the proteid meta- bolism, or more exactly the excretion of nitrogen, is mainly deter- mined by the supply of it in the food just as it is uponian exclusive proteid diet. Fat or carbohydrates simply produce a relatively small, and probably more or less transitory, diminution of it with- out affecting the substantial truth of the above statement. Lawes & Gilbert,* in discussing the results of their fattening experiments upon sheep and pigs, called attention to the very wide variations in the amount of protein consumed, both per unit of weight and especially per unit of gain, and concluded that the ap- parent excess of protein in some cases must have served substan- tially for respiratory purposes. The subsequent investigations of Bischoff, Voit, and v. Pettenkofer upon the proteid metabolism of carnivora showed clearly that the dependence of the latter upon the proteid supply, which is so marked upon a purely proteid diet, is equally evident upon a mixed diet, and thus supplied a scientific explanation of the facts observed by Lawes & Gilbert. The effect. of the proteid supply upon the nitrogen excretion is clearly shown by the following summary of Voit’s experiments: + Food. Urea Excreted, Grms. Fat. Lean Meat, Grms. Grms. > 250 150 | 17.0 300 176 18.9 250 250 19.7 200 500 36.6 200 800 56.7 250 1500 100.7 Since Voit’s researches, very many experiments, among the earliest of which were those of Henneberg & Stohmann ¢ upon cattle, have confirmed his results, both for earnivora, herbivora and omnivora. A somewhat striking example is afforded by Stoh- mann’s § experiments upon milch goats which are summarized in the following table: * Rep. Brit Asso. Adv. Sci., 1852; Rothamsted Memoirs, Vol. II. + Zeit. f. Biol , 5, 329. t Beitriige, etc., Heft 2, p 412. § Biologische Studien, 121. 130 PRINCIPLES OF ANIMAL NUTRITION. p Eaten peruey: Protein Protein E Digested Metabolized o Date. Tinseed per Day, per Day,* a Hay, Meal Grms. Grms. = Grme. Grms. | May *Sazpay tt OM 1500 | 100 111.6 66.6 2) SuMe MONS A. ise sta 1450 150 125.0 79.4 3 ered Cle Cro sty baad 1400 200 132.2 90.6 ey) SLY ERO eRe? oe os ee 1350 250 150.9 90.1 5 Ds oped ad mae elt! 1250 350 170.5 101.6 Gy) Atte (Sau 1100 500 193.8 117.9 fh Beara oa a 950 650 221.4 143.1 Bid) et) aa 7 Leap tra 800 800 257 .2 173.7 9 para br Len Se ene ce 1600 0 92.9 56.3 LO WPOGhT SHO ves. a co eiee 1600 0 | 74.1 41.9 A full compilation of these earlier results has been made by v. Wolff,+ and the fact is now so well established that further cita- tions would be superfluous. Rate or NirroGEN Excretion.—Some interesting hints as to the manner in which the non-nitrogenous nutrients produce the effect upon the proteid metabolism which has just been described are afforded by a consideration of the rate of nitrogen excretion under their influence. It was shown in the preceding section that the effect of a meal of proteids was a sudden, almost explosive, increase in the nitrogen cleavage and excretion, reaching its maximum within a few hours after the meal. If, however, non-nitrogenous nutrients are given along with the proteids, the character of the curve is essentially altered, the maximum rate of excretion being less and being reached somewhat later, while the fall from this maximum is less rapid. In other words, the rate of excretion becomes more uniform—the curve is flattened out. The influence of fat in this respect is clearly shown in the experiments of Panum { and of Feder { cited pre- viously, and appears evident also in those of Graffenberger.§ In the latter experiments the nitrogenous substances to be tested were added to a mixed diet. The results show a distinct maximum, but the rate of decrease after the maximum was reached was not rapid, * Exclusive of the protein of the milk. { Erniihrung Landw. Nutzthiere, pp. 285-309 t Thier. Chem. Ber., 12, 402. § Zeit. f. Biol., 28, 318. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 131! and only a part of the nitrogen appeared during the twenty-four hours following its ingestion, viz.: WALTERS BA oy sele detente e wie. sera Sine 49.2 per cent. Vee ele. (2) eas aNe ts ea cme cae ss Orie ioe WAGES EOHE:. 2 RR Aes Ae Oe CHO aS WES ET ACIN .S GMeita iS ace ese s. 8: COO EO ee see Rosemann’s * results upon the rate of nitrogen excretion by man, likewise cited above, indicate a similar effect of the non- nitrogenous nutrients, the fluctuations due to the ingestion of mixed food being much less sharp than those found by other experi- menters with proteids alone. If we accept Rosemann’s view (p. 101), that the sudden increase in the nitrogen cleavage is due, in part at least, to a direct stimulus to the metabolic activity of the cells, arising from the presence in the fluids of the body of an increased percentage of proteids, we may perhaps suppose that the simultaneous resorption of non- nitrogenous matter renders this stimulus less and so reduces the maximum rate of nitrogen cleavage. This conjecture possibly receives some support also from the results of Krummacher,+ who, contrary to Adrian and Munk, finds that the division of the proteid ration into several meals not only renders the rate of nitro- gen excretion more uniform, but reduces somewhat the total amount excreted. Gebhardt { has also obtained similiar results. There is also the possibility, however, that the non-nitrogenous nutrients may modify the rate at which the proteids are resorbed, or perhaps, as has been suggested by various investigators, the extent to which the proteids are converted into amide-like bodies by the pancreatic juice or the extent of proteid putrefaction in the intestines. Suggestive in this regard is the fact found by Gruber § that common salt, which acts as a stimulant to thesecretion of hydro- chloric acid by the stomach, and would thus tend to favor gastric as compared with intestinal digestion of the proteids, produces an effect on the nitrogen excretion similar to that of the non-nitroge- nous nutrients. *Arch. ges. Physiol., 65, 343. + Zeit. f. Biol., 35, 481. t Arch. ges. Physiol., 65, 611. § Zeit. f. Biol., 42, 425. 132 PRINCIPLES OF ANIMAL NUTRITION. EXTENT OF PROTEIN STORAGE.—Whatever may be the expla- nation of the action of the non-nitrogenous nutrients, its effect is obvious. Attention has already been called (p. 102) to Gruber’s hypothesis that the transitory storage of nitrogen following an increase in the proteid supply is the result of a superposition of the daily curves of nitrogen excretion. The effect of the non-nitroge- nous nutrients appears to be to diminish the rate of nitrogen cleavage and to protract it, in the case of a single meal of proteids, over a longer time. Evidently, then, an increase of the proteid supply in a mixed diet, or the addition of non-nitrogenous nutrients to a pro- teid diet, will extend its effect over a considerably longer period than in case of an exclusive proteid diet—that is, nitrogen equi- librium will be reached more slowly, and there will be a longer or shorter time after the change during which the nitrogen excretion will be less than in the absence of the non-nitrogenous matters. This explanation also implies, however, that the storage of nitrogenous matter in the body of the mature animal is of limited duration and that no long-continued gain of protein can occur; in other words, that it is impossible to materially increase the proteid tissue (lean meat) of a mature animal. Numerous comparative fattening experiments with domestic animals, notably those of Henneberg, Kern, & Wattenberg * upon sheep, fully sustain this conclusion. On the other hand, metabo- lism experiments with domestic animals rarely show an equality between the income of nitrogen and its outgo in feces and urine, but almost always indicate a gain of nitrogenous matter by the body. As regards the significance of this fact, however, several considerations must be borne in mind. First, the normal growth of the epidermal tissues—hair or wool, hoofs, horns, ete.—as pointed out in Chapter III, consumes a por- tion of the nitrogen of the food and contributes its share to the storage of nitrogen in the body. Second, the adipose tissue itself contains a small percentage of proteid matter, and a storage of fat in considerable amounts in- volves the production of new adipose tissue in which to store it. Third, in many cases the metabolism experiments which show astorage of nitrogen have been made within a rather short time * Jour. f. Landw., 26, 549. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 133 after a change in the ration, and can therefore be interpreted as showing simply that sufficient time had not elapsed to reach nitro- gen equilibrium. If we consider also the somewhat indefinite nature of the term mature, and likewise the possibilities of error due to mechanical losses of excreta and to escape of nitrogen from the latter by fermen- tation and decomposition, we can readily see why the results of a short metabolism experiment may not agree with those of a long fattening experiment; yet, nevertheless, it must be confessed that the impression left by a comparison of the whole mass of evidence is that the discrepancy is as yet but partially explained. In conclusion, we may anticipate a discussion in Chapter VI, and call attention to the fact that muscular exertion may, to a limited extent at least, stimulate those constructive processes which result in a storage of protein in the body. The Minimum of Proteids.—In the preceding section it ap- peared that the administration of proteid food.to a previously fast- ing animal caused a prompt and large increase in the nitrogen cleavage and excretion, while but a comparatively small portion of the proteids was applied to constructive purposes, the result being that two to three times as much proteids must be given as are metabolized during fasting before nitrogen equilibrium is reached. This effect was there ascribed to the stimulating effect of the rapid digestion and resorption of the proteids upon the nitro- gen cleavaye, much of the proteids being apparently destroyed as such before they can serve for tissue-building. We have just seen that the effect of the non-nitrogenous nutri- ents is to diminish somewhat the nitrogen cleavage, apparently by moderating this stimulating effect. The necessary result is that, as the nitrogen supply is increased, it and the nitrogen excretion will start more nearly together and approach each other more rapidly upon a mixed diet than upon one consisting of proteids only. Conse- quently, while the percentage decrease in the proteid metabolism is, as we have seen, relatively small, nitrogen equilibrium may be reached with a much smaller supply of proteids than is the case in the absence of the non-nitrogenous nutrients. Indeed, it is con- ceivable that a sufficient supply of carbohydrates or fats in the diet should practically destroy the stimulative effects of the proteids. in 134 PRINCIPLES OF ANIMAL NUTRITION. which case we might expect a proteid supply equal to the fasting proteid metabolism to be sufficient to produce nitrogen equilibrium. Seen in this light, the apparently insignificant effect of the non- nitrogenous nutrients becomes a very important factor in nutrition. The effect of the non-nitrogenous nutrients in largely diminish- ing the necessary proteid supply was pointed out by C. Voit * and appears clearly in many of his experimental results. Thus from the summary on p. 95 it appears that from 1200 to 1500 grams of lean meat per day was required to maintain the animal experimented upon in nitrogen equilibrium. When fat or carbohydrates were added to the ration, however, strikingly different results were reached, as appears from the following comparative statement, the results being expressed as “flesh” with 3.4 per cent. of nitrogen: Food. Heck Gain of Meat. | Fat or Carbo-| bolized. a “ hydrates. BOOK an ee 416 —116 GOD oc Ba teene 674 — 74 Meat only (average of both series). i200) ee ae 943 — 43 DAOO SA Cee Bee 1207 ie L5OO Etec ae 1478 + 22 500 250 Add + 56 Meat and fatty. xi: cu Bies 0% coo 800 200 720 + 80 1000 250 875 +125 500 300-100 502 — 2 Meat i Neon a nati (compare 300 100400 763 4 37 p- © et.ele wvellemiiee felehes aes («| «eters 1000 100-400 902 ab 88 In the presence of non-nitrogenous nutrients, nitrogen equi- librium was reached with quantities of proteids from one third to one half as great as the amount required when fed alone. In other words, the non-nitrogenous nutrients materially reduced the mini- mum of food proteids required to maintain the proteid tissues of the body. In view of the peculiar importance of the proteids in nutri- tion, as well as of their relative scarcity and high cost, particu- larly in the food of our domestic animals, great interest attaches to a determination of the least amount required to sustain a mature * Zeit. f. Biol., 5. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 135 animal. The results obtained by. E. Voit & Korkunoff * regard- ing the minimum requirement upon an exclusive proteid diet have already been stated in the first section of this chapter (p. 95). The same investigators have also studied the more interesting question of how far the necessary proteid supply can be reduced in the presence of non-nitrogenous nutrients. ProTeIpS AND Fat.—The experiments were upon the same general plan as those just referred to on proteids alone. Beginning with an insufficient quantity of proteids, the amount was gradually increased, that of the fat remaining constant, until nitrogen equi- librium was reached. As in those experiments, too, the nitrogen of the food was practically all in the proteid form, and its amount is compared with the proteid nitrogen excreted, it being assumed that 18.45 per cent. of the urinary nitrogen was derived from the extractives of the flesh metabolized in the body. To the writer it would seem that a more suitable unit would be the total excretory nitrogen, since the proteids’ of the food had to make good the loss of extractives as well as of true proteids from the body, and the former loss is as unavoidable as the latter. Accordingly, the results have been stated in the table below in both ways. Two series of experiments were made: one in which the total food-supply was less than was required to supply the estimated demands of the body for energy, and one in which it considerably exceeded that demand, with the following results: Per Cent. of Energy Minimum of Food Nitrogen. Total Demand Supplied by Aperseee Per Cent of Fasting Petue Ee een Andie Metabolism, Gis: | PerCent.| percent] p-Total, | Proteia. Series I: i Experiment 1 ....); 4.85 72 90 a3 157 193 as Disa Ae Dy 73 30) al D6 133). | > 163 Series IT: Experiment 3 ....| 4.98 116 12850) > 6 6R | 133 > > 162 $e 4....| 4.01 127 140 Dee 128 157 «“ Bil Aa ASSESS 137 | 150 | 5.07 | 131 161 The authors also compute from experiments by C. Voit and by Rubner percentages lying between 162 and 207, and state as their * Zeit. f. Biol., 32, 58. 136 PRINCIPLES OF ANIMAL NUTRITION. final result that the minimum of.proteid nitrogen on a diet of pro- teids and fat lies between 160 and 200 per cent. of the proteid nitro- gen excreted during fasting. These figures when computed on the total excretory nitrogen would become 131 per cent. and 163 per cent. respectively. PROTEIDS AND CARBOHYDRATES.—We have seen (p. 127) that the carbohydrates diminish the proteid metabolism to a greater extent than the fats. The results which have been reached as to their effect in lowering the minimum demand for proteids are on the whole in accord with this fact. With a liberal supply of carbo- hydrates in the food, a much smaller quantity of proteids would seem to suffice to maintain nitrogen equilibrium than when the non-nitrogenous matter of the ration consists of fat. Indeed, ac- cording to some investigators, the proteid metabolism may ever be thus reduced much below that during fasting. Munk * appears to have been the first to advance the view last mentioned. In an investigation upon the formation of fat from carbohydrates a dog was fasted for thirty-one days and then re- ceived a diet consisting of a little meat with large amounts of carbohydrates (starch and sugar) and also, during the first twelve days, gelatin. Omitting these twelve days and also the earlier days of the fasting period, the average daily excretion of nitrogen in the urine was Twelfth to thirty-first days of fasting........... 5.38 grams Thirteenth to twenty-fourth days of feeding (200 grams meat, 500 grams carbohydrates)..... 5.79 “ On the seventeenth day of the feeding the urinary nitrogen reached the minimum of 4.133 grams, and Munk regards this as showing the possibility of a reduction of the proteid metabolism considerable below the fasting level. It is to be noted, however, that the nitrogen excretion varied considerably from day to day, and a selection of a single day for comparison seems hardly justified. Hirschfeld + and Kumagawa { found that the nitrogen equili- * Arch. path. Anat. u. Physiol., 101, 91. } Ibid., 114, 301. t Ibid., 116, 370. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 137 brium of man could be maintained on a diet containing little nitro- gen but abundance of non-nitrogenous nutrients. Under these conditions the urinary nitrogen was reduced to 5.87 grams and 6.07 grams per day respectively, and the total nitrogen excretion to 7.45 grams and 8.10 grams, amounts much lower than have been observed for fasting men. ‘Thus in the extensive investigations by Lehmann, Miller, Munk, Senator, & Zuntz * of the metabolism of two fasting men, much higher figures than the above were ob- tained for the urinary nitrogen, and Munk (loc. cit., p. 225) calls attention to the fact that in one case the urinary nitrogen on the second day succeeding the fasting period was materially less than on the last day of the fasting, viz., 8.26 grams as compared with 9.88 grams. In a subsequent series of experiments upon dogs, Munk + showed that by very liberal feeding with food poor in proteids (rice with small amounts of meat) the nitrogen balance could be maintained for a considerable time at an amount very much lower than pre- vious observers had found for the proteid metabolism of fasting dogs of similar weight. Length Avera; e AGEN PL Urinary of Exper- te ; | Nitro- iment, eight, 4 éo gen os uh Fat, | Starch, | Nitrogen, | G°™, Daye.) See Gime. | Gems, | Gems, |, C% Ser a, 5 11.20 55 116 2.63 2.61 § ; it ee ees 5 10.21 38 96 2.48 2.40 So i Cae 4 9.88 | 53 | 108 | 2.66 | 2.67 RVs bak 4 8.25 47 100 2.60 2.62 Aye (MULE «8 ea aye. f oF 14.4 3.65 Fasting: jWalck....... e 8.9 5.10 Munk also cites in support of his conclusions Rubner’s results on a dog fed exclusively on carbohydrates. A reference to these results as tabulated on a subsequent page does in fact show in most cases a decrease in the proteid metabolism as compared with the fasting values, but how much of this is due to the normal decrease during the first few. days of abstinence from proteid food it is dif- * Arch, path. Anat. u. Physiol., 181, Supp. t Ibid., 182, 91. 138 PRINCIPLES OF ANIMAL NUTRITION. ficult to decide. Munk also cites results obtained by Salkowski,* who observed the nitrogen excretion of a dog on a light ration con- taining but little proteids to be scarcely greater than in the absence of all food. E. Voit & Korkunoff (loc. cit.) also included the carbohydrates in their investigation upon this subject, following the same general method as in the experiments with fat. The following are their results compared with the fasting proteid metabolism exactly as in the former case: Per Cent. of Minimum of Food Nitrogen. Total | Energy Demand | ——————_——— —s Live | Nitrogen| Supplied by Per Cent.of Fasting Weieht, | Exere- Metabolism. Kgs. Ractive Carbo Seay Grms. hydrates, eee ne Total, | Proteid, Per Cent.| Gent. Per Cent. Per Cent. Series I: | | Experiment 3a) 24.0 | 4.93 TS) OLS S 5.438 aS Wel eebae sf 2 24.6 4.94 19 92 5.00 101 124 Series IT: Experiment 5 Dies al 4 OS: 111 | 122 5.11 103 126 a 1 24.1 5.20 115 | 126 | >4.91 >94 | >123 es 2 24.7 4.94 iiss | desk 082260) % 0. 2050“ OPISS Wort, G Korkunonhrcic i os 25. sah esas a > 0), 204s & :eouRBysqns snoueZo1}INN Cae Ol aaa esvarout ut dn paroyg | a) Tal -ui'9)] 8,6 6! (ere): 8) pile a, pooy uL peurnsuoy } ‘ej 0) She) |ey\e- 698, owe veliene 6.0» le) iw **(poonpoad) peurso; Apo JON ©) [s\ sv. ia_.e © eva)! 0) 0 levels pe eee Se aU ur peutoy Apeayy YB iT er aie cae acme ee ae esa Tas 8°90 j8°96 j0O'248 |F'98 6°79 |e'Ig |6°s9 [2°69 |F:s8 eee Tater tel Paleo mle OrOmiaOucak Great One 1 Gecseni aie is at 18-9209 8098 IT GEL IZ-9LL io 10ck 8°c— 9° OI—|I'8— |Z 8— 6° 241-6 SI—|9 zZI+\6'9+ |b 2+ ase. |G Te 210" GS. eer 2a Cl Fe O° eo> I Sr On Pr Onip-ilocy | Sr. 122672 82S 950% 058% Sizeir |929¢ Race 110.908 ||P GL 1GseL G27 sete eset |600L\¢ ¢6 Cie Osseo Oa) a Gli CKO ee Wy ope 0: Sa) 0°28 |0O'F4 |0O 18 [0°18 |0'+9 |o'2ZE [O’SET |0°Z0T '0'00T Ceo 12 FS. 10 99 IZ-99 SI8°8G" |L-Ze Passe le-ee iG yy Oem eran 1605 Gry a Ie Gk le 9G IG bbe |Pi0Ge. 19° ST 669 |0°29 \6°89 It F9 Ia TZ |o'62 |9°69 (6°22 |T'E9 6 8 LZ 9 g 14 € G ft ps7 PRINCIPLES OF ANIMAL NUTRITION. Even on the most extreme assumptions it is only possible to regard the fat produced as derived wholly from the proteids of the food in three eases in which an excessive proportion of the latter was fed. If the probable digestibility of the foods used be considered, and Henneberg’s factor (51.4 per cent.) for the possible production of fat from proteids be used, the results show even more decidedly a formation of fat from carbohydrates. In a later paper,* in reply to criticisms, the authors state that they have reviewed and recal- culated many of their experiments with the result that, while the experiments with ruminants (sheep and oxen) failed to furnish con- clusive evidence of the formation of fat from carbohydrates, a large number of those with pigs unquestionably showed such for- mation. In view of their historical interest it has seemed desirable to give the results of Lawes & Gilbert’s experiments in some detail, although at the time they hardly secured the recognition which was due them and Voit’s views became the generally accepted theory for the next twenty-five years. | Notwithstanding the latter fact, however, results of experiments on herbivorous animals speed- ily began to accumulate which were difficult to reconcile with Voit’s hypothesis. Experiments on Ruminants.—Experiments on milch cows were made by Voit himself, as already noted. G. Kithn & Fleischer + a little later discussed the results of two of their extensive feeding experiments on milch cows in their bearing on this point, and M. Fleischer { did the same with the results of similar experiments made by Wolff and himself.§ Their results are tabulated on the opposite page. Neither Voit’s nor Fleischer’s results are such as to require the assumption of a formation of fat from carbohydrates. Those of Kiihn & Fleischer show a small excess of fat in the milk over that producible from the fat and proteids of the food, but the authors * Jour. Anat. and Physiol., 9, 577; Rothamsted Memoirs, Vol. IV. + Landw. Vers. Stat., 10, 418; 12, 451. : t Virchow’s Archiv, 51, 30. § Jour. f. Landw., 19, 371, and 20, 395. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY.° ‘171 Fat of | Fat from Fat of Fodder, Protein, teh the Mille, Guns |) (Gimmes? s EES Grms. Voit.) Experiment a.............../ 318.8 | 401.8 | 720.6 | 577.5 sr HL Bee nate et 276.0, |, 308.5), 584.5. '887°3 a= ee vf Bexperiment Fo7./° 2183-57 |e) e79e 5. | 92682 0) 16 27 6b Henna Ge BeISeDeD 9) sa "4e I..| 183.5 | 69.5 | 253.0] 292.0 : S jeleperiment: L.i.2% at. of 170.5 | 158.5') 329:0 | 303.5 Fleischer: 1 0 abs Sa 166.5 | 170.0 | 336.5 | 290.5 regard the differences as within the limits of error in such experi- ments. ‘ Studies of the results of fattening experiments with ruminants give similar results. On the basis of Lawes & Gilbert’s determi- nations of the composition of the increase of live weight in fattening, the amount of fat produced in such an experiment may be approxi- mately computed and compared with the amounts of proteids and fat in the food. Such a comparison by the writer * in seventy-seven experiments on sheep showed that, with one or two possible excep- tions, the fat and proteids of the food were sufficient to account for the amount of fat formed, although in some of the experiments little margin was left. Experiments on Swine.—Experiments with swine, on the other hand, as Wolff ¢ has shown, have almost without exception given results which can scarcely be explained except upon the hypothesis of a formation of fat from carbohydrates. These animals, as Lawes & Gilbert pointed out in their early papers, are especially adapted to experiments of this sort, simce they consume a relatively large amount of easily digestible food, have a small proportion of offal to carcass, and are by nature inclined to lay on fat readily. It was therefore to be expected that experiments upon swine would show a production of fat from carbohydrates, if such took place, more decisively than those upon ruminants. Experiments on pigs by Weiske & Wildt,{ it is true, on the same plan as those by Lawes & Gilbert, yielded results consistent with Voit’s theory, showing a formation of 5565 grams of fat in the * Manual of Cattle Feeding, p. 177. { Ernihrung Landw. Nutzth., pp. 354-356 t Zeitschrift f. Biol., 10, 1. 172 PRINCIPLES OF ANIMAL NUTRITION. body as compared with a possible 6724 grams from the fat and proteids of the food. The feeds used, however, were not well suited to young animals and the gain was abnormally small in proportion to the food consumed, so that the results could not be expected to be decisive. Moreover, the presence of non-proteid nitrogen in the food is not considered in the computation. (See the next paragraph.) Sources of Uncertainty.—Up to this point the results of experi- ments on herbivorous and omnivorous animals had been somewhat conflicting. Before taking up the later investigations it is desir- able to point out some of the uncertainties attaching to experiments such as those above enumerated. These relate, first, to the amount of fat actually produced, and second, to the possible sources of supply in the food. The basis for estimating the amount of fat actually produced by a fattening animal was in two cases a comparison with the amount in a supposedly similar animal at the beginning of the fattening, the fattened animal being actually analyzed. In the remainder the increase in live weight was assumed to have the composition found by Lawes & Gilbert. It need scarcely be pointed out that the results of such comparisons can be only approximate and are sub- ject to a considerable range of error. Only the most decided results one way or the other can be accepted as at all conclusive. In experiments on milch cows the production of milk fat can of course be determined, but the variations in the weight of such an animal often render any conclusions as to gain or loss of body fat so difficult that the results as a whole are less satisfactory than those on fattening. The possible sources of fat in the food, aside from the carbohy- drates, are the ether extract and the proteids. As regards the first, it is certain that not all the digestible ether extract of stock foods is true fat. | With the proteids the case is still worse. In particu- lar we now know that a portion, and in some cases a considerable portion, of the total nitrogenous matter of feeding-stuffs consists of non-proteid material, which so far as we know contributes little if anything directly to fat production. This is a very important source of error. Thus the writer * has shown, as has also Soxhlet,f that if * Manual of Cattle Feeding, p. 182. + Compare Soskin, Jour. f. Landw., 42, 203. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 173 account be taken of this fact the teachings of Weiske & Wildt’s experiment cited above are exactly reversed and show a formation of fat from carbohydrates. 471 ( 110 55 20: 75 269 Chamiewskiis< se ele ee Geese 203 105 32 137 640 100 51 9 60 445 (59 days 15,109 | 7,766 | 1,490 | 9,256 | 17,585 Jordan: +74 “ Cows 34,661 | 17,816 | 2,211 | 20,027 | 37,637 ‘ | Anis 2,209 | 1,131 | 1,504 | 2,635 | 3,289 - In view of the extreme assumptions made in these computations as to the possible contribution by the proteids and fat of the food * Digested protein of food less gain of protein by the animal. + In original 2572 grms. t Computed on a different basis wee oie other experiments loc. cit ,.p 84. : Compare 176 PRINCIPLES OF ANIMAL NUTRITION. to fat production, and of the very large differences between this amount and the fat computed to have been actually formed, the possible errors of the method are relatively insignificant, and these investigations, together with the earlier ones, must be regarded as establishing the fact of a formation of fat from carbohydrates. The earliest experiment to be published in full demonstrating the production of fat from carbohydrates in the body of the dog, was by Munk.* The animal was deprived of food long enough to render it certain that but traces of fat remained in the body. It was then fed for twenty-four days on a diet consisting of small amounts of meat, with some gelatine, and large quantities of starch and sugar. In the body of the animal at the close of the experiment 1070 grams of fat were found, of which Munk estimates that at least 960 grams must have been produced during the experi- ment, while the proteids fed could have produced as a maximum only 415.3 gramis and the meat itself contained but 75 grams of fat. Even if a formation of fat from gelatine be admitted, a considerable excess of fat remains unaccounted for except by the carbohydrates of the food. Respiration Exrperiments.—There are not wanting, however, for final demonstration, experiments with the respiration apparatus, in which the total income and outgo of nitrogen and carbon has been determined. Meissl, Strohmer, & Lorenz,+ in very carefully conducted respi- ration experiments upon swine, using a wide, a medium, and a narrow nutritive ratio, obtained the following results: Food, Proteid | Equivalent | Fat of dane Pere bolism, Fat, ; : y. Gum, barca Grms. ao euueecreises Pree RIGO ees ean cas oe 65.4 33.6 7.9 41.5 353.9 Meg ANE Ahr a Ss aa be 64.1 33.0 16.4 49.4 413.2 BAMlevice tee ons ohancin 88.0 “alisy 174 lee) 60.4 208.7 Flesh meal, rice, and WHEVas cite tia ¢0:3 381.6 196.1 48.6 244.7 256.3 Almost simultaneously C. Voit { gave a preliminary account of * Virchow’s Archiv, 101, 91. + Zeit. f. Biol., 22, 63. ¢Sitzungsber bayr. Acad d. Wiss.; Math. Phys, Classe, 1885, p. 288. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 177 respiration experiments made in his laboratory by Lehmann & E. Voit with geese and by Rubner with a dog which demonstrated a production of fat from carbohydrates. Rubner’s experiment was shortly afterward published in full.* It was a respiration experi- ment covering four days immediately following a fortnight’s heavy feeding with meat. On the first two days of the experiment the animal fasted and on the second two received only starch and cane- sugar. The results for the last two days were: Proteid: metabolismy 2 2.405. ccs oes 15.94 grams, Equivalent fat, according to Rubner.. 7.65 “ POM OOUNH tre. ee se Suis eats ee AO te Maximum from fat and proteids...... iy Oate os Fanactuallyproduecd..302 5.6.0... ILG2b Even after making all possible deductions for the fact that some carbon may have been retained in the body in the form of glycogen instead of fat, and also for a possible residue of undigested starch in the alimentary canal at the close of the experiments, Rubner still computes that at least 40.7 grams of fat must have had its origin in carbohydrates. Lehmann & E. Voit’s experiments have only recently ap- peared.+ In their introduction they report also the results of ex- periments on fattening geese made by C. Voit several years previous to 1883, which likewise show a production of fat from carbohydrates. G. ixtthn and his associates,{ at the Méckern Experiment Station, have demonstrated, by means of respiration experiments in which starch was added to rations but slightly exceeding the maintenance requirement, a formation of fat from carbohydrates by ruminants (oxen). In view of the possibility (see p. 27) that part of the car- bon of the urine may be derived from the non-nitrogenous matter of the food, and in order to be on the safe side, the authors assume as possible that all the carbon of the proteids metabolized may have been stored up in the body in the form of fat. On this extreme and improbable assumption their results were as shown on the following page: * Zeit. f. Biol., 22, 272. + Ibid., 42, 619. t Reported by Kellner; Landw. Vers. Stat., 44, 257. 178 PRINCIPLES OF ANIMAL NUTRITION. . . Maximum | Fat Proteid Ppigaen Fat of feng Rat ‘Ashe imal. Period. | Metabolism, d, . ae oC Grms. cee rane P reese I 2a SYBIAN 259 86 345 423 i 2b 382.0 265 81 346 332 If 2, 297 .4 206 77 283 434 Ill 2 104.4 72 60 132 281 IV Z 126.9 88 60 148 160 III 3 506.9 351 69 420 375 IV 3 548.8 380 74 454 388 III 4 980 679 84 763 526 V 2a 232. 161 ; 42 203 396 V 2b 268 186 42 228 407 V 3 149 103 39 + 142 703 VI 2a PAR Se Maite ks | Pree Nfl Dela ac) ba 191 304 VI 2b 232 161 545) 196 381 VI 3 186 129 43 172 507 In most of these experiments the rations were purposely made poor in proteids and fat, and in all such cases, with one exception, a formation of fat from carbohydrates is clearly demonstrated. In three cases in which large amounts of proteids were fed, as well as in some similar experiments not included in the above table, it was possible to account for-the fat production otherwise, but such nega- tive results in no degree weaken the positive teaching of the remain- ing trials. The more recent investigations of Kellner et al.* at the same Station, in which starch was added to a basal ration, although under- taken primarily for other purposes, likewise show the formation of an amount of fat inconsistent with the hypothesis of its production from the fat and proteids of the ration only. The failure of Pettenkofer & Voit to obtain affirmative results in their earlier experiments appears to be largely explicable, in the light of more recent knowledge, from the conditions of the experi- ments themselves. Pfliiger ¢ has recalculated their experiments on the same basis as those upon the formation of fat from proteids (see p. 109), and has pointed out that in the majority of cases the total food was, according to his computations, scarcely more than sufficient for the maintenance of the organism, thus leaving no excess of any kind for fat production. Moreover, out of those ex- * Landw, Vers. Stat , 53, 1. + Arch, ges. Physiol , 52, 239. ° 7 THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 179 periments in which the conditions were favorable for a production of fat from carbohydrates, some actually do show that result, al- though they were classed by Voit as “exceptional cases,” while its failure to appear in others is explained, according to Pfliiger, by the increased metabolism due to maltreatment of the animal and the overloading of its digestive organs with starch. Whether we admit all of Pfliiger’s criticism or not, it is now uni- versally conceded that the carbohydrates are an important source of fat. If we are to go further and deny with Pfliiger the production of fat from proteids, we are brought back, by a curious reversal of views, substantially to Liebig’s classification of the nutrients into 4 plastic” and “respiratory,” but, as already pointed out, it ap- pears altogether probable that the proteids also contribute to fat production. However this may be, it is clear that in the case of herbivorous animals, which ordinarily consume relatively little proteids and fat and large amounts of carbohydrates, the latter are ‘the most important factors in fattening, and the results of Lawes & Gilbert (p. 167), according to which the gain of fattening ani- mals is largely determined by the supply of non-nitrogenous matters in the food, are seen to be in full accord with the most careful physi- ological investigation. Evidence from Respiratory Quotient.—The formation of fat from carbohydrates is a process of reduction. If we suppose all the ecar- bon of 100 parts of dextrose, together with the necessary hydrogen and oxygen, to be united to form fat of the average composition stated on p. 61, we have the foilowing: Dextrose. Bauivalent, Residue. Aguivalens; E Cet Warloneer sys del oats 40 .00 Ze Oly (OKO) eed RY Se Ot aa be eh Senge core ene ME AW a BE Ww GrOreD i. a. ss. os 3 6.67 6.28 0.39 ORSON Oe eteccal Oxygen eat Ghicte tal susie loka ath 53.33 6.01 47.32 ay 44 .20 100.00 52.29 47.71 See 44.20 | The excess of oxygen we may further suppose to unite with the carbon of 41.44 additional parts of dextrose, producing 60.78 parts of earbon dioxide and’ 24.86 parts of water. The process would be an intra-molecular combustion analogous to a fermentation, pro- 180 PRINCIPLES OF ANIMAL NUTRITION. ducing carbon dioxide without the intervention of oxygen from out- side. The latter fact, of course, is equally true whatever substance combines with the excess of oxygen of the carbohydrate. The tendency, therefore, will be to increase the respiratory quotient and, if large amounts of carbohydrates are thus transformed, to even raise it above unity. Numerous such instances are on record. Thus Regnault & Reiset * report a quotient of 1.024 in case of a hen, and Reiset + ob- tained quotients of 1.004 and 1.054 with a ewe and a boar. Han- riot & Richet,{ in studies on the respiration of man, found that the ingestion of carbohydrates caused the respiratory quotient to rise markedly and sometimes to exceed unity. Later Hanriot § studied the transformations of glucose in the organism of man and obtained similar but more marked results, the quotient reaching as high a value as 1.28. Magnus-Levy || has likewise observed quotients greater than unity in the case of a dog fed large quantities of carbohydrates, and Bleibtreu,{/ in experiments on fattening geese in a form of Regnault respiration apparatus, also verified this fact, as have Kaufmann ** and Laulanié t+ in experiments upon dogs with sugar. The exten- sive respiration experiments of Zuntz & Hagemann {tf on the horse also afford numerous instances of respiratory quotients greater than unity. The evidence of the respiratory quotient, then, is entirely in accord with the conclusions reached by other methods as to the formation of fat from carbohydrates. NON-NITROGENOUS NUTRIENTS OF FEEDING-STUFFS.—It has become customary to regard the digestible non-nitrogenous ingre- dients of feeding-stuffs, aside from the ether extract, as consisting essentially of carbohydrates. As has several times been urged on * Ann. de Chim. et de Phys. [3], 26, 45. ft Ibid. [3], 69, 145. t Comptes rend., 106, 419 and 496. § Archives de Physiol., 1893, p. 248. |} Arch. ges. Physiol., 55, 1. “| Ibid., 56, 464; 85, 366. ** Archives de Physiol., 1896, 341. tt Ibid., 1896, 791. t{ Landw. Jahrb., 27, Supp. III. THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 181 preceding pages, however, this is far from being the case as regards the materials actually resorbed from the digestive tract of our common domestic animals, particularly the ruminants. A demon- stration of the production of fat from carbohydrates, therefore, does not necessarily show that the chemically diverse materials resorbed from coarse fodders, e.g., are available for fat produc- tion. As a matter of fact, however, what a large proportion of the experiments just cited actually show, under a strict interpretation, is that fat was produced from the non-nitrogenous nutrients of the rations other than fat. In many of the experiments, it is true, nota- bly those with swine and with geese, the ration consisted of concen- trated feeding-stuffs whose “nitrogen-free extract” consisted to a large extent of hexose carbohydrates. Similarly, in G. Kiihn’s ex- periments the fat production was secured by the addition of starch to rations slightly above the maintenance requirement. In these eases, therefore, at least the larger part of the fat production in excess of that possible from proteids and food fat must be ascribed to the hexose carbohydrates. In experiments like those of Henne- berg, Kern & Wattenberg, and of Jordan, on the other hand, a not inconsiderable proportion of the non-nitrogenous nutrients was necessarily derived from coarse fodders and was, therefore, largely of undetermined nature. In such cases it is obviously im- possible to say whether the fat production was at the expense of the hexose carbohydrates only or whether the other non-nitrog- enous ingredients participated in it. Other considerations, however, seem to render a participation of these substances in fat production, directly or indirectly, at least highly probable if not certain. Crude Fiber.—The experiments of v. Knieriem (p. 161), as we have seen, seem to show that digested cellulose may be as efficient as other carbohydrates in protecting the body fat,—that is, as part of a maintenance ration. The numerous experiments cited on pp. 117-123 likewise indicate that it has an effect similar to that of other carbohydrates in diminishing the proteid metabolism. Kell- ner * has also investigated its value in a fattening ration, using for this purpose the material resulting from the treatment of rye straw * Landw. Vers. Stat., 53, 278. 182 PRINCIPLES OF ANIMAL NUTRITION. with an alkaline solution under pressure and containing 76.78 pei cent. of “crude fiber.” This material was added to a basal ration somewhat more than sufficient for maintenance. The results as regards the proteid metabolism have already been considered (p. 121); the following table shows the effects also upon the fat production : Apparently Digested. Gain. Crude Crude | N.-free a“ : 5 3 a Protein, P Jt) eee Gat, | Hier, | exdract, iggein Fggtein| Fate On Hs Period 5 | Extracted straw..| 116 | 3129 3351 654 157 735 (o>) As Basalsrationeern ae 101 | 1083 2912 749 43 191 Difference...... 15 | 2047 439 | —95 | 114] 544 Period’) |istarchice oe cee k cs. 92 | 1057 4773 629 78 565 eed ||Basalirationag.. .2 101 | 1083 2912 749 43 191 Difference...... —9 | —26 | .1861 |—120 35 374 Ox J: Period 5 | Extracted straw...| 110 | 3101 3344 747 98 693 ee 4a\.Basalérationtace. LOT") Lg 2895 836 33 223 Difference...... 3 | 1987 449 | —89 65 470 Period @iqiotarch. \. A2.sher. ais 85 | 1105 | 4396 | 764 91 | 472 oe (Am Basal rapliOns secs. 107 | 1114 2895 836 | 33 223 Difference...... —22 —9 1501 249 The varying quantities of nutrients digested stand in the way of a direct comparison of the results. If, however, we reckon 1 gram of digested fat equivalent to 2.25 grams of digested crude fiber or nitrogen-free extract or protein (isodynamic quantities according to the usual method of computation), and if we further convert the gain of proteids into its equivalent amount of fat, on the same principle, by multiplication by 5.7 and division by 9.4, we have the results shown in the table on the opposite page. While no great quantitative accuracy attaches to such a com- putation, it is sufficient to show that the effect produced in this case THE RELATIONS OF METABOLISM TO FOOD-SUPPLY’. 183 Total ‘ Carbohydrate Se eee Gain per Equivalent | Equiva ent Kilogram GE NumEntG of Gain, Nutrients, Guage Grms. Grms. Ouew ike Extracted straw, period 5-4......2.". 2425 613 252.8 Starch, Bt) Sarstedt ee fa 1695 395 233.0 Ox J: Extracted straw, period 5-4......... 2334 509 218.1 Starch, iss oes OPE ie ee 1370 284 20773 by the addition to the basal ration of digestible matter five sixths of which was derived from crude fiber, was not inferior to that produced by the addition of an equal amount of pure starch. It would seem that these results may fairly be taken as showing that the products of the digestion of cellulose by ruminants are substantially of equal value with those of the digestion of starch. This, however, by no means warrants the conclusion that starch and cellulose are of equal value in ordinary feeding-stuffs. The mate- rial used in these experiments had been so altered mechanically and freed from incrusting materials by the treatment to which it had been subjected that 88.3 per cent. of its organic matter and 95.8 per cent. of its-erude fiber was digested. The same animals digested but 52.5 per cent. of the crude fiber of wheat straw, and the digestible organic matter of the latter proved far less efficient than that of either starch or extracted straw. A full discussion of these facts may be more profitably undertaken in connection with a consideration of the energy relations of feeding-stuffs in Part I]; for the present it may suffice to point out that the difference just noted appears to depend on physical rather than chemical causes. _ Pentose Carbohydrates.—We have already (p. 156) seen reason to believe that the pentose carbohydrates may serve as a source of energy to the organism and protect other materials from oxidation. This, of course, is equivalent to an indirect production of fat. In the same connection, however, the experiments of Kellner, just mentioned, were referred to as indicating a direct participation by these bodies in fat production. About one third of the digested matter of the extracted rye straw was found to consist of bodies 184 PRINCIPLES OF ANIMAL NUTRITION. yielding furfural, presumably pentosans, as appears from the follow- ing modified form of the last table: Total Carbohydrate Equivalent of Nutrients. Total Fat Equivalent of Gain, Pentosans, | Other Substances, Grms. Grms. rms. Oni: Extracted straw, period Oe i teks 809 1616 6138 Starch, 3-4....6% —34 1729 395 Og: Ss Extracted straw, period Ow ete 834 1500 509 Starch, 3-4. —89 1459 284 If we regard the furfuroids as not contributing to the fat pro- duction, then we must assign to the other nutrients of the extracted straw a value from 66 to 74 per cent. greater than that of the digested matter of the starch, a result which is hardly conceivable. Apparently we must admit that the furfuroids in this case pro- duced approximately the same effect as the other non-nitrogenous nutrients and were at least indirectly if not directly a source of fat. CHAPTER VI. THE INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. Ir is a matter of common experience that muscular exertion results in a very marked increase in the vital activities of the body. The rate of circulation and respiration is greatly quickened and the increased metabolism in the organism ‘is shown by the loss of weight and by the increased demand for food to make good the destruction of tissue. Indeed, no other factor even approaches muscular exer- tion in the extent to which it increases the metabolic activities of the body. We have now to.consider in some detail the nature of muscular exertion and the precise character of its effects upon metabolism. § 1. General Features of Muscular Activity. Muscular Contraction. The work of the muscles is accomplished by contracting, and a brief consideration of some of the more prominent general features of muscular contraction will conduce to an intelligent study of the main subject of the chapter. It will be possible here to consider this phase of the subject only in its most general outline, and the reader is referred to works on physiology for details. When a suitable stimulus, which in the living animal is usually a nerve stimulus, is applied to a muscle it contracts; that is, it tends to grow shorter and thicker. This change is brought about by a shortening and thickening of the individual fibers of which the muscle is built up. A single stimulus, such, for example, as that caused by the making or breaking of an electric circuit, gives rise to what is known as a simple muscular contraction. If such a stimulus is repeated with sufficient frequency it produces a 185 186 PRINCIPLES OF ANIMAL NUTRITION. series of simple contractions which fuse together, resulting in a state of contraction which continues, subject to the effects of fatigue, as long as the stimulus acts. This form of muscular contraction has received the name of “tetanus.”’ In the living animal the ordinary contractions of the muscles brought about through the nervous system, even those that seem but momentary, are essen- tially tetanic in their character. Chemical Changes during Contraction.—Under the influence of a stimulus sufficient to produce a muscular contraction there occurs a sudden and large increase in the chemical changes which are continually going on even in the quiescent muscle. More mate- rial is metabolized in the muscle during contraction and energy is thus liberated for the performance of work. Our knowledge of the nature of these chemical changes in the contracting muscle is comparatively meager, but three main features appear well established: First, during contraction the neutral or slightly alkaline reac- tion of the quiescent muscle c anges to an acid reaction, probably through the formation of sarcolactie acid. Second, there is a large increase in the amount of oxygen taken up by the muscle from the blood and a still greater increase in the amount of carbon dioxide given off by it.* Third, under normal circumstances, Judging from the amount of the urinary nitrogen, there appears to be no considerable increase in the nitrogenous products of metabolism. From the increase in oxygen consumed and carbon dioxide given off we might be led at first thought to suppose that the increased activity in the muscle during contraction was of the nature of a simple oxidation. Certain other facts, however, seem to show that this view of the matter is inadequate. OxipaTions INcompLeTE.—That the increas i metabolism in the con‘racting muscle is not a simple oxidation of some material t carbon dioxide and water is indicated by the fact of the produc- tion of lactic or other acid in the muscle. Plainly, if the energy for muscular contraction is produced by oxidation the oxidation is at least incomplete. * Some good authorities doubt whether the carbon dioxide resulting from muscular exertion actually leaves the muscle in that form. Compare Schiffer, Text-book of Physiology, 1898, Vol. I, p. 911. A INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 187 ReEsPirRATORY QuorieNT.—By analogy with investigations upon respiration we may designate the ratio between the oxygen con- sumed and the carbon dioxide given off by the muscle as the respi- ratory quotient of the muscle. Numerous investigations upon this point have shown that during contraction much more carbon diox- ide is given off than corresponds to the oxygen consumed, or, in other words, the respiratory quotient of the active muscle is con- siderably greater than unity. As early as 1862 Sczelkow * determined the gaseous exchange ° between the blood and the muscles of the posterior extremities of a dog, tetanus being produced by an electric current. He found that during rest more oxygen disappeared from the blood than corresponded to the carbon dioxide taken up by it, while during tetanus, on the contrary, the carbon dioxide considerably exceeded the oxygen. His results, calculated for the posterior extremities alone, were as follows: ~ Per Minute. ¥ ; Respiratory Experiment. Carbon Oxygen Quotient. Dioxide c.c c.c. 1 ES trae ohare ee Sees 1.60 4.10 0.41 Bem gee LLeTANUSHeer ee ete ae re | aod 3.92 2.65 2 JEM ESL A rn Sco ROLE SORE rs 2.62 4.25 0.62 a ee INES Si aOStes® Geawe ase Ret See eta sacle Wendtotc) 10.52 1.18 3 TEMES Hic, ea, ORC TEE Boeing cae Tete 3} .24) 0.54 Search sal psAcas METAS ot tere eerie |e LOZ, (DD 1.41 : SEM Rte yn Ri fe Paes 4.71 0.75 i eee Metamurs’: se hie dre eee ey eG 9.38 1.30 5 PRR Sales ioe ct cyatets Sukie aphi e B83 5.82 0.40 a. pe a 1) ARCS VEEN aU ec aS SRE were rece ard beans P53 18.7F 0.80 In the above experiments, with a single exception, the quantity of oxygen consumed by the active muscles was more than that taken up in a state of rest, but the increase in the amount of carbon dioxide given off was still greater, so that the respiratory quotient was largely increased, exceeding unity in every instance but one. * Sitzungsber. Wiener Akad. d. Wiss., Math-Naturwiss. Klasse, 45, IT, 171. 188 PRINCIPLES OF ANIMAL NUTRITION. Chauveau & Kaufmann * have more recently obtained simi- lar results. Their experiments were made upon the Levator labii superioris of the horse, both in a state of rest and in a state of activ- ity consequent upon the consumption of food. From the amount and composition of blood entering-and leaving this muscle the following results were obtained for the oxygen consumed and carbon dioxide given off per kilogram of muscle in one minute. On the average of the three experiments, in round numbers, twenty-one times as much oxygen was consumed during work as during rest and twenty-nine times as much carbon dioxide was given off. Oxygen Consumed. Carbon Dioxide Given Off. Experiment. Rest, Work. Work = Rest, Work. Work + Grms. Grms. Rest. Grms. Grms. Rest. 7d SARS Ree Sa sae .00479 | .07148 14.9 .00365 | .12534 34.3 Sy aise Sel ceca .01167 | .20190 Mviac .01168 | .35488 30.4 Anke ptm el .00419 | .14899 35.6 .00518 | .25709 49.6 Average........| .00688 | .14079 2025 00864 | .24577 28.5 These facts show plainly that the increased metabolism of the active muscle cannot consist wholly of a direct oxidation, since the carbon dioxide given off from the muscle contains more oxygen than direct experiment shows to have been taken up by the muscle during the same time. OxyGEN NoT EssentiAL.—A further and still more striking proof of the above assertion is found in the fact that the living muscle can execute a considerable number of contractions in the entire absence of oxygen. Setschenow is quoted by Ludwig & Schmidt ¢ as having found that muscles would contract freely when supplied with oxygen-free blood, while L. Hermann { has shown that an excised muscle may continue to contract ina vacuum. The well-known investigations of Pfliiger § show that frogs may continue to live and execute more or less extensive motions in an atmosphere of pure nitrogen for * Comptes rend., 104, 1126, 1352, 1409. + Verhandl. Siichs Akad. d. Wiss., Math-Phys. Klasse, 20, 12. t Unters. u. Stoffw. der Muskeln. § Arch. ges. Physiol., 10, 313. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 189 several hours, giving out considerable amounts of carbon dioxide, and Bunge * has made similar observations upon the movements of certain intestinal worms (Ascaris) in one per cent. salt solution made as nearly oxygen-free as possible. Weinland + has shown that in the latter case the energy is derived chiefly from the cleavage of glycogen with the production of carbon dioxide and lower fatty acids. SumMaAry.—The three classes of facts just adduced justify the conclusion that the chemical changes by which energy is liberated in a muscular contraction are not simply oxidations, but are of the nature of a cleavage of some complex substance or substances with evolution of carbon dioxide. There is, in other words, a sudden “explosive”? decomposition of substances elaborated in the muscle during rest. Of the nature of the material thus broken down we have littie definite knowledge. We can say, however, that if it is nitrogenous matter its nitrogen is ordinarily retained in the muscle in some form and that in effect the metabolized material is non- nitrogenous. The increase in the consumption of oxygen during work appears to be to a certain extent a secondary process, accOm- plishing the further oxidation of the primary products of metabolism. At the same time, the fact that the amount of oxygen consumed - responds very promptly to work and also to rts cessation shows that these primary products, whatever they may be, are very speedily oxidized, either in the muscle or elsewhere in the organism. Thermal Changes during Contraction.—A considerable por- tion of the energy set free during muscular exertion always takes ultimately the form of heat. When the muscle acts without shorten- ing, as when supporting a weight (isometric contraction) — that is, when no external work is done—all the metabolized energy takes the form of heat. If, on the other hand, the weight be lifted (iso- tonic contraction) —if external work is done—a portion of the energy takes the form of motion. The interesting question of the relation between the external work performed and the total amount of energy metabolized will be considered later. For the present it is sufficient to state that muscular action always produces heat and that a very considerable share of the metabolized energy ultimately takes this form. * Zeit physiol. Chem, 8, 48. f Zeit. f. Biol., 42,55; 45, 113. toe 6=COo6RS til Sa: 190 PRINCIPLES OF ANIMAL NUTRITION. Muscular Tonus.—The chemical and thermal changes just enumerated as characterizing the muscle during contraction are taking place in it to a less extent at all times. Even at rest the muscle respires and produces heat, as is well illustrated by Sezel- kow’s and Chauveau & Kaufmann’s experiments quoted above. The living muscles of the body are elastic and may be said to be always slightly on the stretch, as is shown by the fact that when cut they gape open and that they shorten when their attachments to the bones are severed. This slight degree of contraction of the resting muscles has been called muscular tonus, and it is at least a plausible conclusion that the chemical changes taking place in a quiescent muscle furnish the energy to maintain this tonus. According to Chauveau * we may regard the essence of muscular contraction as a sudden increase in the elasticity of the muscle. He holds that all the energy liberated by muscular metabolism is converted first into the elastic force of the muscle and only secondarily into heat. Ac- cording to this view the slight degree of elasticity of the quiescent muscle is produced by the constant metabolism going on within it. In active muscular contraction this process is greatly exaggerated and the katabolie processes exceed the anabolic, thus giving rise to a great increase in muscular elasticity which in turn may be con- verted into work. In repose following work, we may assume that the substances broken down during contraction are built up again, while in prolonged repose the two processes must substantially balance each other. | Muscular tonus is most noticeable during the waking hours, under the influence of external stimuli to the central nervous sys- tem, and consequently the rate of metabolism and the heat produc- tion tend to be greater than during sleep. To this is to be added, as a further cause of greater metabolic activity during the waking hours, those continual slight movements of the body which usually take place even in what is commonly spoken of as a state of rest and which may be designated as incidental movements. That the total amount of metabolism required for the mainte- nance of muscular tonus is considerable seems to be indicated by the observations of Rohrig & Zuntz,t and of Colasanti,t who * Le Travail Musculaire et l'Energie qu'il Represente. Paris, 1891. + Arch. ges. Physiol., 4, 57; 12, 522. t Ibid., 16, 157. 5 INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM: Ig! found that when the motor nerves of the rabbit are paralyzed by curari the rate of metabolism, as measured by the respiratory ex- change, falls to about one half the amount during rest and does not react to changes of external temperature. Pfliiger * computes from his experiments a similar reduction of about 35 per cent. Under these conditions the heat production of an animal is insuffi- cient to maintain its normal temperature, and unless the loss of. leat from the body is hindered by coverings or otherwise it soon perishes. Frank & F. Voit,+ on the contrary, found that curarized dogs excreted no less carbon dioxide than in the normal state, pro- vided the body temperature was kept normal. Secondary Effects of Muscular Exertion. The greater activity of the muscular metabolism during the performance of work gives rise to important secondary effects, par- ticularly upon the circulation and respiration. It is a familiar fact that in active exercise the action of the heart is largely increased and the breathing becomes deeper and more rapid, and that ordi- narily the limit of muscular exertion is set, not by the power of the muscles themselves, but by the ability of the heart and lungs to keep pace with the demands upon them. CrrcuLaTion.—The circulating blood is the medium by which oxygen is conveyed to the muscles and carbon dioxide and other products of their metabolism removed. The latter function is of special importance, since an accumulation in the muscle of the products of its own metabolism speedily reduces and ultimately suspends its power to contract. In active muscular exercise, there- fore, an increase in the rate of circulation is essential to the con- tinued activity of the muscles. This increase appears to be brought about by the accumulation in the blood of the products of metab- olism, which act as a stimulus to the vaso-motor center. The result is a dilation of the peripheral blood-vessels, which is aided by the mechanical effects of muscular contraction. To offset this and prevent a fall of arterial blood pressure, the visceral capillaries are probably constricted, while the rapidity and strength of the heart- beats are largely increased. The rapidity of the circulation as a * Arch, ges. Physiol., 18, 247. + Zeit. f. Biol., 42, 349. 192 PRINCIPLES OF ANIMAL NUTRITION. whole is thus greatly augmented, while at the same time a larger percentage of the total blood passes through the muscles. For example, in the experiments of Chauveau & Kaufmann, cited above, the ratio between the circulation in the resting as compared with the active muscle varied from 1:3.35 to 1:6.60. Zuntz & Hagemann,* in their investigations upon the work of the heart, found the average amount of blood passing through the heart of a horse per minute to be during rest 29.16 liters and during work 53.03 liters. By this increase in the rate of circulation through the muscles the carbon dioxide and other injurious products of muscular metabolism are rapidly removed and an abundant supply of oxygen is ensured. In fact it is usually true that during work which is not excessive the venous blood contains less carbon diox- ide and more oxygen than during rest. Since the heart is a muscular organ, it is obvious that this in- crease in the circulatory activity must add materially to its metab- olism. In the performance of work, therefore, there is an expend- iture of matter and energy, not only for the work of the skeletal muscles but likewise for the additional work of the heart. Zuntz & Hagemann in their experiments upon the horse just mentioned compute that during moderate work the metabolism due to the work of the heart amounts to 3.8 per cent. of the total metabolism of the body. RespiratTion.—The greater activity of the circulation conse- quent upon muscular exertion would be futile were not provision made for more efficient aeration of the blood in the lungs through an increased activity of the respiration. The latter appears to be brought about, like the increase in the circulatory activity, by the effect of the greater amount of metabolic products in the blood, acting in this case upon the respiratory center. It has been shown that an accumulation of carbon dioxide in the blood does not have this effect, but that a lack of oxygen, such as occurs, for example, in asphyxiation, provokes powerful movements of the respiratory organs. In ordinary work, however, whatever may be the case in excessive muscular exertion, the effect is not caused by a lack of oxygen, for the blood, as already noted, is usually more arterialized * Landw. Jahrb., 27, Supp. ITI, 405. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM: 193 than during rest. Apparently the stimulation of the respiratory center is brought about by the other products of muscular metab- olism, whatever they may be, which find their way into the blood. Under the influence of this stimulus the respiratory movements increase in frequency or depth or both, thus making possible a more active gaseous exchange between the blood and the air in the lungs. This action is usually so efficient that the expired air dur- ing work contains a smaller proportion of carbon dioxide than it does during rest, notwithstanding the fact that the total quantity eliminated is much greater. Since respiration, like circulation, is maintained by muscular action, it is true in the former case as in the latter that a greater activity of the function necessitates a greater metabolism for that purpose. Zuntz & Hagemann * have recently investigated the work of respiration in the horse, the augmented respiratory activ- ity being brought about by an admixture of carbon dioxide to the > inspired air, this resulting in a marked increase in the depth of the respiratory movements. With the animal upon which most of the experiments were made they found an increment of from 2.02 c.c. to 5.23 ¢.c. of oxygen consumed for each increment of one liter in the volume of airrespired. In general, although with some exceptions, the work of respiration as thus measured increased with the in- creased depth of the respiratory movements. The results upon other horses were somewhat variable. It was observed, however, that in the performance of ordinary work by the horse the effect was chiefly upon the frequency of respiration rather than its depth. The former effect the authors believe to involve less work than the latter and moreover an amount largely independent of the total volume of air respired. § 2. Effects upon Metabolism. It is obvious from the foregoing paragraphs that the production of external work is a complex phenomenon. As regards its effects upon the total metabolism, the main features involved seem to be: 1. An explosive decomposition of some unknown “ contractile substance” in the muscles. * Landw. Jahrb., 27, Supp. III, 361. 194 PRINCIPLES OF ANIMAL NUTRITION. 2. The oxidation somewhere in the organism of the immediate products of this decomposition to the final excretory products. 3. Since the state of contraction appears to be only an exagger- ation of the muscular condition during rest, we may reasonably suppose that there is a continual re-formation of the “contractile substance’ going on. 4. As secondary effects there is a marked increase in the activ- ity of circulation and respiration, thus involving supplementary muscular exertion. It is plain that however interesting and important to the physi- ologist may be studies of the changes in the muscle itself, from the point of view of the statistics of nutrition the important thing is the total effect upon the expenditure of matter and energy by the organism under varying conditions of work. The energy relations of the subject will be discussed subsequently in Part II. Here we are concerned more particularly with the nature of the material expended in the production of work, and as a matter of convenience we may, as in the two preceding chapters, take up first the effect upon the proteid metabolism and second that upon the metabolism of the non-nitrogenous substances. 3 Effects upon Proteid Metabolism. Earuier INVESTIGATIONS.—Since the muscles, which are the instruments by means of which work is produced, are composed essentially of proteid material, it was natural to regard the proteids as the source of muscular power and to assume that the energy developed during work was supplied by an increased metabolism of these substances. This view was supported by the authority of Liebig, who, however, does not appear to have based it upon any actual experiments, and it was quite generally, although not universally, accepted. C. Voit * appears to have been the first to subject this idea to investigation. His experiments were made upon a dog weighing about 32 kilograms. The work performed, by running in a tread- mill, was considerable, being estimated to average 1.7 kgm. per second for the whole twenty-four hours. Experiments were made * Untersuchungen iiber den Einfluss des Kochsalzes, des Wassers, und der Muskelbewegungen auf den Stoffwechsel. 1860. Compare the summary by E. v. Wolff in Die Ernihrung der landw. Nutzthiere, pp. 386-388. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM: 195 both during fasting and with a daily ration of 1500 grams of lean meat. The results obtained were as follows: Meat Water Urine Urea mbper Experiment. | ater cow lhc ae oa I 05 Rest 258 186 14.3 ee / Work 872 518 16.6 Rest 123 145 11.9 Pee Bere de elas athe ooo 0 Work 527° 186 1203 Rest 125 143 10.9 Rest 182 1060 109.8 PE Rees ar Aas ate dos 1500 Work 657 1330 WAN Rest 140 1081 109.9 { Work 412 1164 114.1 IV eo 1500 Rest 63 1040 110.6 | The average increase of the proteid metabolism, as measured by the urea excreted, was in the fasting experiments 11.8 per cent. and in the experiments with food 4.95 per cent. The absolute difference in grams, however, was materially less in the fasting experiments, although approximately the same amount of work was performed in both cases. A similar experiment upon an older and quite fat dog while fasting showed an increase of only 6 per cent. in the proteid metabolism. Subsequently Pettenkofer & Voit * made similar experiments upon a man, the work consisting in turning a heavy wheel provided with a brake. The work was performed in the respiration appara- tus. The results showed a large increase in the carbon dioxide excreted, but scarcely any effect was noted upon the excretion of nitrogen, as will be seen from the following table: e Water Excreted. Nitrogen | Carbon ; Oxygen | Number of Urine, Dioxide Taken Up. of | Grms. Excreted, Tn Evapo- Gums. Experi- Grms. Urine, rated, ments. Grimms. Grms. Fasting : CStiy pile cee 12-4 716 1006 §21 762 Z, Winker. Ae ss o/5'e eS 1187 746 1777 1072 1 Average diet ESI aes. cs ee els 10) 928 1218 931 832 3 Wiorkees sao ck sr 1733 1209 LSS 1727 981 2 * Zeit. f. Biol., 2, 478. 196 PRINCIPLES OF ANIMAL NUTRITION. Pettenkofer & Voit regard the slight increase in the proteid metabolism which they observed in most cases as a secondary effect of muscular exertion. They have shown, as we have seen, that when the cells of the body are abundantly supplied with non-nitroge- nous nutrients, either in the form of food or of body fat, there is a tendency to diminish the proteid metabolism. In work, on the con- trary, large amounts of non-nitrogenous material are oxidized, as their respiration experiments show. The supply of these nutrients to the cells is thus diminished, and it is to this that they attribute the increase in proteid metabolism. Results like those just given can hardly be interpreted other- wise than as showing that the non-nitrogenous constituents of the body or of the food, rather than the proteids, are the source of the energy expended in muscular work, but the first attempt to com- pare the amount of work performed with the energy available from the proteids metabolized was the famous experiment of Fick & Wislicenus * in 1866. These observers made an ascent of the Faulhorn and found that the amount of proteids metabolized ~ during and after the ascent, as measured by the urea excreted, was insufficient, according to their computations, to account for more than one third of the energy required to raise their bodies to the height of the mountain, making no allowance for the work of the internal organs, nor for those muscular exertions which did not contribute directly to the work done. Fick & Wislicenus found no considerable increase in the uri- nary nitrogen in their experiment. Subsequent investigators, among whom may be mentioned Parkes,t Noyes,{ Haughton,$ Meissner,|| Schenk,4{ and Engelmann,** have reported appar- ently conflicting results regarding the influence of work on the proteid metabolism. Im some cases an increase was observed, while in other cases no material effect was apparent. The increase when observed was never large except in the experiments of Engel- * Vrtljschr. Naturf. Gesell. Ziirich , 10, 317. tT Phil. Mag., 4th ser., 32, 182. t Amer. Jour. Med. Sci., Oct., 1867. § Brit. Med. Jour., 15, 22. || Virchow’s Jahresber., 1868, p. 72. 4 Centralb. Med. Wiss., 1874. p. 377. ** Archiv f. (Anat. u.) Physiol., 1871, p. 14. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 197 mann, and was entirely insufficient to account for the energy ex- pended. Oppenheim made the interesting observation that work pushed to the point of producing dyspncea caused a marked increase in the proteid metabolism. INFLUENCE OF ToTaL AMouNT OF Foop—KELLNER’s INVEs- TIGATIONS.-—Doubtless the conflicting results of earlier experiments are due in part to defective technique, but they arise in part also, as it would seem, from another cause to which attention was first called by Kellner in 1879-80. Kellner’s experiments were made upon the horse. ‘They differed from most earlier experiments, first, in that the comparison was made between different amounts of work instead of between work and rest, and second, that the individual periods instead of covering only a few days were extended over two or three weeks. Series I.—Kellner’s first series * was made primarily for the purpose of testing the influence of work upon the digestibility of the food, but the total nitrogen of the urine was also determined. The methods employed for this purpose were somewhat imperfect, there being some mechanical loss and probably also a loss of ammonia from the urine, but the author believes the results of the several periods to be fairly comparable. The amount of work performed was measured by a dynamometer. The numerical results of the measurement have since been shown to be too high, but the relative amount in the several periods is not thought to be materially affected by this error. The results of the several periods are briefly summarized in the following table: Nitrogen. Live Weight 5 Work, at Close Period. Kem. of Period, Digested, In Urine, Kgs. rms. Grms. f (Se ee ae Se ee ote iat 625,000 134.41 99.0 534.1 LIS Am ever ins Saat enor notts Seer 1,250,000 128 .32 109.3 529.5 1 Ue a tee 1,875,000 W272 116.8 S225, TINY) a bgeeceaei eens Brees epee vcactee 1,100,000 126.40 LOR? 508.8 AVE rarities wetted cue age 625,000 129.41 98.3 518.0 While the above figures show a considerable nitrogen deficit, the urinary nitrogen increased and decreased with the amount of * Landw. Jahrb., 8, 701. 198 PRINCIPLES OF ANIMAL NUTRITION. work performed in a manner which can searcely be explained other- wise than as a result of the changes in the latter. The ration con- sumed was amply sufficient for the light work of the first and fifth periods. When, however, more work was demanded from the animal, the live weight promptly fell off, showing that the total ration was insufficient. This insufficiency of the total ration Kellner believes to be the cause of the increase in the proteid metabolism. A consideration of the daily results confirms this view. In passing from periods of lighter to those of heavier work the increase followed promptly upon the change. In Period III, with the most severe work, the proteid metabolism continued to increase through- out the period and apparently had not reached its limit at the close. Conversely, when the work was diminished in Periods IV and V it decreased as promptly as it had increased. Finally, it should be noted that the additional amount of proteids metab- olized was entirely insufficient to furnish an amount of energy equivalent to the increase in the work. In four succeeding series of experiments Kellner * has investi- gated this phenomenon more fully, some of the sources of error noted above having been avoided in the later researches. The results, as will appear, still show a deficit of nitrogen. Kellner estimates that about 6 grams of nitrogen per day were required for the growth of hoofs, hair, epidermis, ete., and believes that there was some loss of urinary nitrogen mechanically and chemically. Series IT.—In this series of experiments the ration, consisting of 7.5 kilograms of hay and 4 kilograms of beans. was purposely made rich in protein. In spite of this liberal supply of protein, however, the same result as in the first experiment was noted to an even more marked extent. As in the first series, too, the increase in the excretion of nftrogen promptly disappeared when the amount of work was diminished. Series IJJ.—In this series the animal was brought as nearly as possible into equilibrium with his food upon rather light work. The work was then trebled, while at the same time an addition was made to the non-nitrogenous ingredients of the ration by substitut- ing for a portion of the beans an amount of oats containing the same absolute quantity of protein. In this second period there was a slight increase in the digestibility of the protein and, therefore, a * Landw. Jahrb., 9, 651. - INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 199 corresponding increase in the urinary nitrogen (compare Chapter V), but this was small compared with the much greater amount of work performed. Moreover, it did not, as in the first series of experiments, augment from day to day during the period of severe work. The following table shows the principal results of this series, the figures for urinary nitrogen and for live weight being given for the first and second halves of each period: : | Nitrogen. = Period. ioe | Weight : A Digested, In Urine, Kg. Grms. Grms. PS ( 158.9 560.3 i ein ia: ae Sena ae cw eh a pt a4 oie ape) wae) Te: 810,000 IV Giae ] 164.1 556.8 ae 174.0 541.3 TL Cee an ot ee em ee 2,430,000 | 178.8 i i718 Page Tiles Ae ae aaa eee 810,000 | 178.8 eed ores Series IV.—Upon the basis of the foregoing facts Kellner deter- mined the maximum amount of work which his horse could perform on a fixed medium ration without causing an increase in the proteid metabolism. One kilogram of starch was then added to the ration and the maximum amount of work that could be performed upon this new ration without causing such an increase was determined. In the nature of the case this determination could not be of the highest accuracy, but it 1s amply sufficient for our present purpose. The principal results are given in the following table, the amount of work being expressed by the number of revolutions of the dyna- mometer, since relative results are all that are required: | . Nitrogen. | ss ive Period. ae ee Me Digested, In Urine, | Kg. Grms. Grms. | Is eter | (;. 300° |) 107.2 | 540.0 die ova? ease 1 ie GOO" || 110.2 | 538.3 Ilb. Loe me tmm0Ne Ch iat tt) | Ais.6 | 583.1 10 GC Cpseceeneeecane a mage Ta | 109.4 532.5 eee rs oceteton S400" oh) 109.6 530.7 eee oe 4 = {With 91) 800.1). gop = ft. 15.5 517.1 i hs eae (2s starch) ~ i 600. «/') ‘ : 109.6 515.4 200 PRINCIPLES OF ANIMAL NUTRITION. Kellner estimates that the maximum amount of work which could be performed on the ration containing starch was 700 rey- olutions as compared with a maximum of 500 revolutions without starch. Even if this estimate of Kellner’s be regarded as high, it is evident from the figures given that the addition of the starch enabled materially more work to be performed without an increase in the proteid metabolism. ‘The results obtained in this and the subse- quent series have been made the basis of interesting computations regarding the utilization of the potential energy of the food which will be considered in Part II. Series V.—This series was precisely similar to the preceding one, except that the addition of non-nitrogenous matter to the ration was made in the form of oil by substituting flaxseed for linseed meal. The protein of the ration remained unchanged, while the fat was increased by 203 grams. The results were entirely similar to those with starch, as the following table shows: Nitrogen. ti Period. Were a = Weight, Digested, In Urine, Kg. Grms. } Grms. lec a ee (| 500 |) (| 148.9 | 496.5 Hi ae et See i Pate L yso0 4] 149-2 | 49328 ey, coke aan allan 59. | 147.5 | 485.8 Miter ress BG esta || 550 153.0 479.4 Tee ae: 700 148.1 | 476.0 16h, fi ee | Ay | 700 ‘as 153.9 | 469.0 ANG afar ase A ess aie 650 145.6 | 466.4 ret epee ae | offat {| 650 145.0 | 460.8 While Kellner’s method of investigation may be regarded as somewhat imperfect and necessarily giving but approximate results, yet it suffices to bring out in a very striking manner the intimate ° relation existing between the supply of non-nitrogenous nutrients in the food of a working animal and the effect of the work upon the proteid metabolism. In conelusion, it should be noted that in all Kellner’s experiments there was a fairly abundant supply of protein. Whether the same result would be obtained on a ration containing the minimum amount of proteids required by the organ- ism is not shown. In no case was the increase in the proteid metab- olism, when observed, sufficient to supply energy equivalent to the additional work done. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM, 201 Later INvesTiGATions.—In 1882 North * made experiments upon himself in which a considerable amount of work, mainly walk- ing from 30 to 47 miles while carrying a load of about 27 pounds, was performed on one day of each experiment. The account of the experiments does not give sufficient data for computing the total amount of work performed, but it was evidently very considerable and resulted in a marked increase in the excretion of nitrogen. It is not possible, however, to determine whether the total food was adequate for the work days, but it was no greater then than during the periods of rest. Argutinsky,} in experiments upon himself, observed as a result of rather severe work a very marked increase in urinary nitrogen which continued at least three days after the cessation of the work. Munk { subsequently criticised Argutinsky’s results on the ground that the supply of non-nitrogenous nutrients in his diet was insuffi- cient. Krummacher § obtained results quite similar to those of Argutinsky, but his experiments are open to the same criticism as those of his predecessor, namely, an insufficient supply of non- nitrogenous nutrients, as he himself points out in a later paper. Hirschfeldt || failed to observe any material increase in the nitrogen excretion as the result of work upon a diet containing a-considera- ble excess of food over the amount required for maintenance. This was true both upon a diet containing little protein and one abun- dantly supplied with this nutrient. Pfliiger, like Liebig, regards protein as the sole source of mus- cular energy. As yet only a preliminary sketch of his investiga- tions has been published. He fed a lean dog upon prepared lean meat, that is, upon a nearly pure proteid diet, for seven months. The animal remained apparently in perfect health and was able to perform a large amount of work. Under the influence of the work the excretion of nitrogen was observed to increase somewhat, but not sufficiently to account for the energy expended in the work. This phenomenon Pfliiger explains by supposing that during work * Proc. Roy. Soc., 36, 14. } Arch. ges. Physiol., 46, 552. t Arch. f. (Anat. u.) Physiol., 1890, p. 552. § Arch. ges. Physiol., 47, 454. || Virchow’s Archiv., 121, 501. 4] Arch. ges. Physiol., 50, 98. 202 PRINCIPLES OF ANIMAL NUTRITION. the organism economizes in its demands for proteids elsewhere than in the muscles. The further interesting observation was made that with continuous work the proteid metabolism, which at first showed an increase, diminished again and even reached its original value. With aration containing but little protein and much non-nitrogenous material, a small increase of the proteid metabolism was observed as the result of work. The preliminary account of the experi- ments affords no adequate data for computing the sufficiency of the total food. Krummacher,* in his second investigation, made three separate experiments. In the first of these the total food was estimated to be approximately sufficient for maintenance (38 Cals. per kilogram), while in the other two it was much in excess of this. The following table shows the total amount of food per kilogram, expressed as Calories of metabolizable energy,t the amount of work performed, and the percentage increase of the proteid metabolism: Energy of Food. J Work |. of Proteid Measured, | Metabclsm, Total. Per Kg. Kgm. Per Cent. Cals Weight. Cals. Experiment 9 iJ e 2459 38 153,070 21 ss 1 Dee aes Poa 5034 64 324,540 22 a 18 fl Conga eet Cape 5701 72 401,965 iz The work done consisted in turning an ergostat. It has been shown by subsequent investigators that not over 30 per cent. of the energy of the body material metabolized in the performance of work in this way can be recovered in the work actually done. Assuming this high figure, and further that Krummacher’s esti- mate of the maintenance requirements is accurate, it appears that the food in these experiments was insufficient to supply the energy required for the amount of work actually done. It was observed, as in other experiments of this nature, that the increased exeretion of nitrogen continued for a day or two after the cessation of the work. Only in the first experiment, however, was even the total proteid metabolism during the periods of work, to- gether with the excess above the rest value observed on succeeding * Zeit. f. Biol., 38, 108: + See Chapter X. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 203 days, sufficient to supply an amount of energy equal to that actually measured on the ergostat, so that at least the larger share of the energy must have been derived from non- nitrogenous materials. Zuntz & Schumburg,* in investigations upon soldiers, observed an increase of the proteid metabolism as the result of marching, carrying a considerable weight. The increase, however, seemed to bear no direct relation to the amount of work performed, but rather to the conditions under which it was done. Thus excessive heat or sultriness of the atmosphere, resulting in unusual fatigue, was ac- companied by an increased excretion of nitrogen. The increase continued during the two days following the work. Frentzel — experimented upon dogs. In the first series the ani- mals were fed pure fat, while in the second series no food was given. The work, which was done upon a tread power, was considerable. In the first series there was an increase of 9.25 per cent. in the nitro- gen excretion in the work experiments, while in the second series a maximum increase of 44.26 per cent. was computed, which, how- ever, is believed by the author to be too high. A method of com- putation which he considers more nearly correct makes the increase in the second period 13.31 per cent. In the first series of experi- ments the food consisted of 150 grams of fat per day except upon one of the work days, when only 80 grams were consumed. No data are given regarding the sufficiency of this ration, but according to kK. Voit’s compilation ¢ it would appear hardly adequate for the maintenance of a dog of the weight used (36 kilograms). The work, therefore, even in the first series, was probably done upon insuf- ficient food. In neither case was the increase in the amount of protein metabolized equivalent in energy content to the actual amount of external work done, and in the first series even the total proteid metabolism was not, while if we allow for the consumption of energy in internal work, heat production, etc., it was not suf- ficient in either series. Atwater & Sherman § have reported observations upon the * Arch. f. (Anat. u.) Physiol., 1895, p. 378. ft Arch. ges. Physiol., 68, 212. t Zeit. f. Biol., 41, 115 § U.S. Dept. Agr., Office of Experiment Stations, Bull. 98. 204 PRINCIPLES OF ANIMAL NUTRITION. food consumption, digestion, and metabolism of three bicyclers during a six-day contest. They find that, in spite of an apparently liberal diet containing large amounts of protein, all three riders lost considerable proteid tissue during the race. The conditions of the investigation were not such as to permit of a determination of the sufficiency of the food consumed, but the computations by Carpenter of the actual amount of work done seem to render it very probable that the body fat must have been drawn upon to a con- siderable extent. RECAPITULATION.—The investigations above cited seem to show beyond a doubt that when work is performed upon food less than sufficient to maintain the body and supply the amount of energy required for the work the proteid metabolism is somewhat increased. Whether the converse of this is true, namely, that when the food is sufficient such an increase in the proteid metabolism does not occur, is not so clear, for the reason that in most, if not all, of the cases we have no adequate data as to the sufficiency of the food. It is plain, however, that the question is not so easily inves- tigated as might appear at first sight, and that the final solution of the relations of work to proteid metabolism can only be reached by means of investigations in which the total metabolism both of matter and energy is determined. GAIN OF PROTEIDS DURING WorK.—Caspari and Bornstein have recently made further investigations into the possibility of a gain of protein as a result of work which was mentioned above in con- nection with Pfliiger’s experiments. Caspari * experimented upon a dog which received an amount of food computed to have been fully sufficient for its maintenance and to supply energy for the work done. Furthermore, a consider- able portion of the non-nitrogenous nutrients of the ration, consist-. ing largely of carbohydrates, was given shortly before the work was done, while in some cases additional sugar or fat was given at that time. In the first experiment, work was performed upon three successive days. Upon the second of these there was a consider- able increase of the urinary nitrogen, but upon the third its amount fell below that of the rest period. The average for the three days of work was almost exactly equal to the value found for the last * Arch. ges. Physiol., 88, 509. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 205 day of the rest period and less than the average for the four pre- vious rest days. In the second experiment the work was continued for four days, then a rest day intervened, and then the work was continued for five more days. At the outset there was a slight increase of the proteid metabolism, but in the second period of five days it showed a marked decrease resulting in a progressive gain of nitrogen by the body, as is shown in the following tabular statement of the daily average results: Extern : “ i i Daye more |e Nemoeen IP eee erotica tte of Done, Cnmaie of Feces, Grms. Nitrogen, Cals. Grms. Grms. Hrs, meetks che ees: 0 Dealt 1.89 23.68 —0.46 Dae Amer ae arr aick kee 0 Dyan: 1.89 22.00 +1.22 SUSE beet at ine 0 Dye alt 1.89 21.98 +1.24 See Perera ey si 597 PASS Aha 1.78 24.72 (2) —1.39 Eee ree als baat: 467 P45) AML 1.78 Daan +0.01 TOS STR aears et Bae see 2h ek 597 PAS, Wal eS me +0.10 1 Ue a Ae 596 PIS) WAL 1.78 1.83 +1.50 MLS ec ao ee @) PAR eal Maree) 22.06 +1.27 a (le aie An ees 595 25a 1.78 20.82 +2.51 MeO re tek sara ence 590 Dey Al 1.78 19.64 6 NGS VON ee tn, SL eee a aa 178 20 a nS ar HOS oo Bo. 588 Pe Tye I 1.78 19.87 +3.46 NSU I pels sect RR 586 Zyeilelt WS 7s) 19.79 +3.54 This gain Caspari ascribes to an actual growth of the muscles as the effect of exercise, this growth according to him taking the form of a hypertrophy of the fibers. No determinations of the gain or loss of carbon were made. Bornstein,* who had previously investigated the possibility of increasing the store of proteids in the body by the.addition of pro~ teids to the food, has also contributed to the investigation of this phase of the question. His experiments were made upon himself. For seven days he consumed a uniform ration containing a moder- ate amount of protein and sufficient non-nitrogenous nutrients, according to previous experience, to maintain his body. The latter was in equilibrium with the food as regards nitrogen from the first day. Then the proteid supply was increased by approximately 50 per cent. by the ingestion of pure proteids and light work (17,000 * Arch. ges. Physiol., 83, 540. 206 PRINCIPLES OF ANIMAL NUTRITION. kgm. per day) done by turning an ergostat. As a result of the in- ereased supply of proteids in the food the proteid metabolism in- creased promptly, reaching its maximum upon the fifth day, when it very slightly exceeded the supply. From that time, however, it decreased gradually during the remaining thirteen days of the experiment, so that a gain of proteids by the body resulted, which was still in active progress when the experiment was discontinued. Counting from the time when the proteid metabolism reached its maximum the average gain of nitrogen per day was Wirgensve: Gaye. os. ahisckes sere sem cere 1.28 grams hast wiive days txt tut on eee pee Be Vt AVOrace Ol Bll, ese. wiiys sa Serbs Sea Ore e: The author computes that 22 per cent. of the proteids added to the food was stored up in the body. In a previous similar experi- ment without work it was found that only 16 per cent. was thus stored. ; Two respiration experiments with the Zuntz apparatus were made during the work. The difference between their results and those of similar experiments during rest was used as the basis for computing the actual amount of energy metabolized in the body for the performance of work. This was found to be equal to 0.0100875 Cal. per kgm. external work, which is equivalent to 171.5 Cals. for the whole daily work of 17,000 kgm. Assuming the original ration to have been a maintenance ration, Bornstein computes that the portion of the added proteids which was actually metabolized was insufficient to supply the energy necessary for the work done and that some of the fat of the body was drawn upon. The loss in live weight was found to agree with this assumption. The above investigations seem to show, not only that work may be done without increasing the proteid metabolism but that it may actually result in diminishing it, a fact which appears in harmony with the common observation that the tendency of exercise is to build up the muscular tissue. Summary.—While the results which have been cited are not in — all respects conclusive, and while further investigation is required to fully elucidate the relations of muscular exertion to proteid metab- olism, the following general conclusions seem to be justified by the evidence now available: INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 207 1. The non-nitrogenous ingredients of the food or of the tissues are the chief source of muscular energy. In by far the greater number, if not all, of the experiments upon this subject the amount of protein metabolized, as measured by the nitrogen excretion, was insufficient to furnish energy equivalent to the work done, the de- ficiency being in many cases very great. This statement, it will be observed, does not assert that the proteids are not concerned in the production of this energy. We may regard it as very probable that the non-nitrogenous matter metabolized has first entered into the structure of the muscular protoplasm, which, as we know, consists largely of proteids, but in a contraction it is largely, if not wholly, the non-nitrogenous groups contained in the protoplasm which are metabolized rather than the nitrogenous groups. 2. With insufficient food there may be a considerable increase in the proteid metabolism as a result of muscular exertion, espe- cially when pushed to exhaustion. 3. This increase is far from sufficient to supply energy for the work actually done, is not usually proportional to it, and seems cevendent to a considerable degree upon accompanying conditions. 4. With sufficient food the increase of the total proteid metab- olism consequent upon muscular exertion is at the most slight and possibly equal to zero. 5. In some cases a storage of proteids has been observed to result from the performance of work. FUNCTIONS OF Prorerps.—If the above conclusions are admitted, it is possible to suppose that in a muscular contraction under favor- able conditions—that is, when there is an abundant supply of non- nitrogenous material—there is no increased metabolism of the proteids. This view of the subject would regard the question as being simply one of the relative supply of nutrients, the energy being evolved from non-nitrogenous nutrients when these. are in abundance, while in default of them the proteids are drawn upon. Another view of the subject, however, is possible, and perhaps more probable. It would appear that muscular exertion tends to produce two opposite effects upon the proteid metabolism: first, to break down additional protein, as is shown when work is done upon insufficient food; and second, to build up proteid tissue when 208 PRINCIPLES OF ANIMAL NUTRITION. the food is sufficient, as is illustrated in the experiments of Caspari and Bornstein. As a basis for a tentative hypothesis, it seems allowable to sup- pose that both these processes—that of anabolism and katabolism of proteids—are continually taking place in the muscle and that both are exaggerated by exercise. In other words, we may imagine that the performance of work by a normally developed muscle requires an increased proteid katabolism, which is balanced, at least in the course of the twenty-four hours, by a corresponding increase in the proteid anabolism. With a liberal supply of food proteids, then, a part of the latter would, during rest, simply undergo nitro- gen cleavage and be used virtually as “fuel,’’ but when work was done they (or part of them) would be used to replace the proteids katabolized in the muscles. Upon this hypothesis, the proteids might play a not unimportant part in the production of muscular work without any evidence of it appearing in an increased nitrogen excretion. It is to be remarked, however, that even on this suppo- sition the proteids could not be regarded as furnishing all, or even, in many cases, a large share, of the energy liberated. On insuffi- cient food, the hypothesis would assume that the energy supply is deficient and that proteids which would otherwise be ‘used for muscular anabolism are diverted to use as “fuel,” probably under- going a preliminary. nitrogen cleavage and furnishing their non- nitrogenous residue to the muscles as a source of energy. The above tentative hypothesis implies that if work were per- formed upon a ration containing only the minimum amount of proteids required during rest, it would cause an increase of the proteid metabolism, no matter how much non-nitrogenous mate- rial was supplied, because there would be no proteids available which could be diverted to repair the waste assumed to be occa- sioned by muscular activity. Up to the present time, however, we possess no experimental investigation of this phase of the ques- tion. However this may be, we know that the performance of work requires a well-developed muscular system. To produce and de- velop such a system, a liberal supply of protein is essential, while we may reasonably suppose that to maintain it involves a larger proteid supply in the food than is required to maintain the proteid INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 209 tissue on a lower level. This fact alone would indicate the need of a reasonably liberal supply of protein in the food of working animals. If the hypothesis above outlined be approximately correct, it is necessary that the food also contain protein which during rest may be simply a source of heat, but which during work may be diverted to repair the increased waste of nitrogenous tissues caused by ex- ertion. This accords with the well-established fact that the dieta- ries selected by athletes and others who undertake severe physical exertion are almost invariably rich in protein.* It is of course difficult to say how far the large amount of proteids in the dietaries of athletes represents a real physiological demand and how far it is a matter of tradition or of taste, but it hardly seems likely that so universal an opinion should be lacking in some considerable basis of fact. Effects upon the Carbon Metabolism. In the foregoing paragraphs we have seen that as a rule the total proteid metabolism is not much affected by muscular exertion. While proteids undoubtedly have important functions in connection with the production of work, it is nevertheless true that normally the energy liberated in muscular contraction is derived chiefly or wholly from the breaking down of non-nitrogenous material. Moreover, even in those cases in which a considerable increase of the proteid metabolism has been observed, its amount has been entirely insufficient to account for the extra evolution of energy. It therefore becomes of especial importance to consider the effects of work upon the carbon balance. The Gaseous Exchange.—Since the influence of muscular ex- ertion upon the proteid metabolism is at most small, it is possible to compare the carbon metabolism during work and rest without material error upon the basis of the.gaseous exchange simply, and as a matter of fact a large share of our knowledge of the subject rests upon determinations of the respiratory exchange. Is Larcety [ycreasep.—The fact that muscular work largely increases the evolution of carbon dioxide and water and the con- sumption of oxygen by the organism is too familiar from ordinary * For a summary of American experiments bearing upon this point see Atwater & Benedict, Boston Medical and Surgical Journal, 144, 601 and 629 + Compare, however, Chittenden, Physiological Economy in Nutrition, New York, Stokes Co., 1904. 210. & PRINCIPLES OF ANIMAL NUTRITION. experience and too well established scientifically to require more than illustration. The fact of such an increase was shown in the researches of Lavoisier. Scharling,* who as early as 1843 con- structed an apparatus somewhat like the Pettenkofer respiration apparatus (see p. 70), states in his account of his experiments that moderate work increases the excretion of carbon dioxide and that it is also greater shortly after a meal. Of other early researches upon this point may be mentioned those of Hirn + in 1857, and especially those of Smith { in 1859. The investigations of Petten- kofer & Voit § in 1866 appear to have been the first to be executed in accordance with modern methods. Their results have already been cited in their bearing upon the influence of work on proteid metabolism, but may be repeated here: ane Water Excreted. 6 | T1 Lore arbDo xyze y aTreeen Dinxile = Taken | Number. Grms. | | Exereted, In Evapo- Up. | oe Grms. Catania mater Grms. Mens. ; Grms, Grms. Fasting: RESP tcote ecreheness 12.4 716 1006 821 | 762 2 Work accep cts 12.3 1187 746 Vit LOT 1 Average diet: | ReStigcr ros ae yeceiexe LAO 928 1218 93 | 832 3 WV Shaiya iat Mijares 1209 1155 I Zia LOS 2 Subsequent investigators such as Speck, || Hanriot & Richet,4 Katzenstein,** Loewy,;+ and many others have fully confirmed the results of the early experimenters. The increase in the oxygen taken up was not actually demonstrated in all of these experiments, but it was in some and may be reasonably inferred in the remainder- * Ann Chem Pharm , 45, 214 + Comptes rend Soc. de Phy sique de Gaines 1857; Revue Scientifique, ler Semestre, 1887. t Phil. Trans., 1859, p 681. § Zeit f Biol., 2. 478 | Schriften der Gesell.der ges Naturwiss zu Marburg, 1871; Arch. klin Med, 45, 461. { Comptes rend., 104, 435 and 1865; 105, 76; Ann. de Chim et de Phys., (6), 22, 485. ** Arch ges Physiol., 49, 330. +7 Lbid , 49, 405. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 211 Errrects ARE IMMEDIATE.—Experiments like those of Petten- kofer & Voit, extending over twenty-four hours, give simply the total effect of the performance of work upon the carbon balance. By the use of the Zuntz type of apparatus, however, it is possible to follow the gaseous exchange in its details through successive short periods as well as to determine the amount of oxygen con- sumed. The data thus obtained give a clear picture of the imme- diate effects of work upon metabolism and have led to the extensive use of this type of apparatus in experiments of this nature. The results of these experiments agree with common experience in showing that these effects appear very promptly and soon reach their maximum, disappearing as promptly after the work ceases. In other words, the increase in the carbon metabolism is very closely confined to the time during which the work is actually performed. The Respiratory Quotient.—The ratio between carbon dioxide produced and oxygen consumed, commonly known as the respira- tory quotient, as has been pointed out in Chapter III, enables us to form a fairly clear idea as to the general nature of the total mate- rial metabolized, and hence much study has been bestowed upon the relation between these two quantities, Is VARIABLE.—We have already seen that the respiratory quo- tient may vary considerably during repose, being largely deter- mined by the nature of the food. The same thing is true of the respiratory quotient during work. Zuntz,* in experiments on a fasting dog, obtained the follow- ing values for this quotient: Number of Average Experi- Respiratory ments. Quotient. PESO ap CRRA INT cts 2B a(n) -5 ow nes Se ecaaye anche etakeueee etocal amos 2 0.69 Pe AETV AIL RRS se Nase 9s gree a's oy 0a wieCsor a eyes ie 6 0.71 Horizontal ocomotione tyes ee cine ecient stars 8 0.73 oe Como tics pr ball eras, ol oes sical avs olatavetare.cte oho-alece 5 0.77 Ori zontalvdrsihtgete ce cise iss eine hee Pacistohecets os 10 0.77 In Zuntz & Hagemann’s + experiments upon the horse the respi- ratory quotient in the single work periods ranged from 0.729 upon a * Arch. ges. Physiol., 68, 191. ¢ Landw. Jahrb., 27, Supp. III, 296-331. 212 PRINCIPLES OF ANIMAL NUTRITION. ration of grecn alfalfa to 0.996 upon hay, straw, and oats. The averages obtained for different forms of work were as follows: Walking, nearly horizontal. ss... .e.6e +. 0.865 " up & slight inclne’s seo ACE aes 0.847 4 ni SUCCDEL ACUMES 15h ost eae See ote OS Oe Dratt, nearly horizontal: ok oie eee 0.890 Walking with load, horizontal.............. 0.840 yi cS ediyeini cine. ~ sets eat See 0.893 Trot, nearly horizontal.w-- cs xe we tee eee we 0.882 * with load, nearly horizontal............. 0.873 ee MhOrizou tal Gpalcs cts seth. a ea tee 0.927 The total range of the respiratory quotient in these experiments was 0.84 to 0.93. It is thus seen to be higher with herbivorous animals, subsisting largely upon carbohydrates, than with the dog. Cuancr Causep py Work.—Chauveau states as the result of his investigations upon the origin of muscular power that the per- formance of work always increases the respiratory quotient. His first experiments * were made upon a man who had fasted for sixteen hours. The work consisted in the alternate ascent and descent of a staircase, the work of ascending being equal to about 29,000 kgms. in the seventy minutes of the experiment. Samples of the expired air were taken by the Tissot apparatus } for five minutes at a time at intervals during the work and the respiratory quotient determined by a comparison of its composition with that of the normal atmosphere. The following were the results for the respiratory quotient: Immediately before work..............0-. 0.75 Hirsh: to filth mine. 2 SY ee peta es Tenth to fifteenth minute... ccic.cssastacsss OL8T Fortieth to forty-fifth minute................ 0.9 Sixty-fifth to seventieth minute............ 0.74 * Comptes rend., 122, 1163. 7 Archives de Physiol., 1896, p. 563, The apparatus is of the Zuntz type. INFLUENCE OCF MUSCULAR EXERTION UPON METABOLISM: 213 é A second experiment,* begun after fifteen hours’ fasting, was divided into two periods. The first was similar to the previous experiment, but lasted for thirty minutes only, the work of ascent equaling in that time about 30,000 kgms. « The subject then rested for a time during which he consumed 105 grams of butter. Two hours after the ingestion of the butter the experiment was repeated, samples of the expired air being taken for three minutes at a time. The results as regards the respiratory quotient were as follows: Fasting. Three minutes before beginning work........ 0.706 Twelfth to fifteenth minute............/...... 0.804 Twenty-seventh to thirtieth minute.......... 0.812 RS Ota Ee te em akc Ae aia ni eigen oem Osos Two Hours ajter Ingestion of Butter. Three minutes before beginning work......... 0.666 Twelfth to fifteenth minute................... 0.7838 Twenty-seventh to thirtieth minute.......... 0.809 In conjunction with Laulanié + he has also experimented on dogs and rabbits, the muscular contractions being caused by electric shocks. The method of determining the respiratory exchange, as described by Laulanié, consisted in using a Pettenkofer type of apparatus with a small but constant known rate of ventilation. The outgoing air passed through a small gasometer, but the current could be shunted and the sample of air contained in the gasometer analyzed. No details of the experiments or of the methods of cal- culation are given. The first table on the following page contains Laulanié’s summary of the results. § An even greater increase in the respiratory quotient has been sbserved by other investigators. Thus Hanriot & Richet || found * Comptes rend., 122, 1169 ft Ibid., 122, 1244, 1303: Archives de Physiol. 1896, p. 572. t Archives de physiol . 1896, pp. 619 and 636. § Energetique Musculaire, p. 70. || Comptes rend., 104, 435 and 1865: 105, 76. 214 PRINCIPLES OF ANIMAL NUTRITION. ° . Respiratory Quotient. Animal. , Food. noe | Before | During After Work. | Work. Work. . | = Rabbit. ..\Ad lain. ook be sake Clee i 7 | 0.880 | 0.970 | 0.799 Dog .... Fasting from 1 to 7 days.. 5 | 0.776 | 0.849 | 0.733 Dog ....|Abundantly fed with milk porr idge. 2 | 1.016 | 1.027 | 1.033 in the increments of carbon dioxide and oxygen over the rest values quotients much greater than unity and reaching in one case 3.5 (?). Speck * likewise found an increase in the respiratory quotient as the result of work. Although he observed numerous exceptions, he regards it as the rule that it increases with the severity of the work. On the other hand, Katzenstein,+ in experiments on men, found in some cases no considerable increase in the respiratory quotient during work. He gives the following average results, of which those in the first table do not relate to exactly the same subjects in the three cases: Turning Ergostat. PACE WIVIK. nls saci eattabes Ue ares tetarie wre een 0.824 Henvy ‘work: oo. dete ae keoeheaec ene lees Walking. Subject Subject Subject Subject No. 1. No. 2. NO. \3.%) | Nowe Repouer te sik sf. asees Geet 0/801 +): (0178 fy 0. Vi) Os Horizontal locomotion .......... 0.805 O77 > 4 O82 | 0.895 Locomotion up: hill... 2.0.4... 0.799 0.79 | 0.865 0.86 In all cases, the determinations of the respiratory exchange covered only a few minutes soon after the work began, and * Arch, klin. Med., 45, 461. + Arch. ges. Physiol., 49, 330. t A very corpulent individual, INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 215 no mention is made of the nature of the diet except in one case (fasting). The individual results were rather variable, but most weight is given to those on Subject No. 1, with whom most of the experiments were made. Katzenstein believes Speck’s results to be due in part to a change in the rate of respiration, causing the excretion of carbon dioxide to exceed its actual production (p. 73), and in part to a deficiency of oxygen in the tissue of the contracting muscles. Loewy,* like Katzenstein, found that work pushed to the point of producing a considerable degree of fatigue raised the respiratory quotient, while moderate work did not. Rapid turning of the wheel of the ergostat, preventing full breathing, or compression of the upper arm by means of a rubber band, produced the same effect, which he attributes to a lack of oxygen. The most marked results seem to be those for the first few minutes of work, although in one case work continued for ten to twenty minutes an producing fatigue raised the respiratory quotient. Probably the most extensive and carefully conducted investiga- tions of this nature are those of Zuntz and his associates upon the dog, and particularly on the horse. Some data from the latter investigations have already been given on p. 212. The following table adds to the averages there quoted those for the corre- sponding rest periods. In these experiments there was a distinct lowering of the respiratory quotient instead of an increase. In Respiratory Quotient. Kind of Work. Periods. Ms Repose. Work Walking nearly horizontal. .......... MD ea Oh 0.943 0.865 up stent POAC era, sei) suse fe Ae a, "db, e, 0 0.940 0.847 ‘* ‘stee per gr ACER Anolon setae a, b, Cnt 0.953 0.900 Draft, nearly 4h6is TAMU we at oreo eae (oh Ge Yn 0.956 0.890 Walking with load, nearly horizontal. . €,1,0 0.915 0.840 a WTOP OMA eree cys pat ctall «are eieos €, 2, 0, 0 0.915 0.893 Trot, nearly horizontal............... a, €, f, 0 0.943 0.882 oe n with load...... €, 1, 0 0.915 0.873 * horizontal wath) drafts... .0)=.... Oana 0.943 0.927 * Arch. ges. Physiol., 49, 405. 216 PRINCIPLES OF ANIMAL NUTRITION. all cases the animal was liberally fed, usually with oats, hay, and cut straw. VARIATION DURING Worxk.—In their experiments cited above, Chauveau & Laulanié find that the rise of the respiratory quotient which they regard as the invariable result of muscular exertion occurs promptly upon the beginning of the work, and the same thing is shown by the earlier results of Chauveau. As the work is con- tinued, however, the quotient shows a tendency to fall again, some- time even going below its original rest value, while in a period of rest following work a still further decrease is observed. The results of their experiments * are contained in the table on the opposite page. Zuntz & Hagemann j also report a number of experiments on the horse in which the respiratory exchange was determined in suc- cessive periods of work. The following are their results for the respiratory quotient: Successive Values of Respiratory Quotient. Aggregate Length No. of Ee eS ia eS ae of Work Periods, Experiment. Mint 1 2 3 By de Gente AS 917 .865 80 seen ot he 913 806 1214 rs LT bee hain rs 929 .889 102 AOR atenc one 925s, .948 897 100 ogee oa etotele oar 920 931 875 924 CN en ahe ene 865 .868 911 54 AG Ieee eked 928 .921 34 Pree et a at, 910 .926 48 DS ean 974 .905 837 65 Goceeriiocniwoane 863 .820 73 Boe Mee : 911 922 ty 71 OTe stats coe 949 .934 “380 124 Wes tenors eine eae 936 .909 878 78 CBT Soret ite 931 904 883 75 The results cited in the foregoing paragraphs would appear to justify the general conclusion that in the case of fasting animals or * Comptes rend., 122, 1244, ft Loc. cit., pp. 290-292. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 217 ce8° &&8" 168° OFL* LITO" E |@80°1 6c0'T 189° | 189° 802° |08L° OLL" |OLL 9S." 489° 681° 066 | 01% ot 09 cP 08° "HIOAA 19}JB YSoY JO saqnuryy “UOAIS JOU QUIT) JOVXT » G18° 263° | F66" 090° 1)000°T 686" | C8s° | 686 «008° |x0F8" 800°T PPO T Git” | 803° 998" | 998° 006" | 006° 9F8° |006° OOE | OLE | OG | OSL | OBT 06 686° 86° 826° +098" FO T 061° 08.1" 968° OFS" S06" 09 “UOI{VUIULIGJE Surpada.g YAO A, JO saynury ‘sjuetj}ON* £107 v11dseyy 000°T L10°T GP 000°T 000°T [terse £0 T sores UNaIgH py —"'*" Zursey sep Z “dulpaay [B19QIT Joye sanoiy g POUO SLOW LI [oh for ren” [B1eql] 19}JB sinoy ¢ Ses ” ” € rss » ~stBepz ta Sure F » 8,48p | 77" Zunysey sAvp 9 “- ZUl4svy SInoy FZ “poo ” qrqquy | ” ” *‘jeMIUy “oN 218 PRINCIPLES OF ANIMAL NUTRITION. of those insufficiently fed the respiratory quotient is increased by the performance of work, while with well-fed animals, especially those receiving an abundance of carbohydrates, this effect is not apparent. As the work is continued, there appears in many cases to be a tendency toward a diminution of the quotient, while in rest following work a still further decrease may occur. Nature of Non-nitrogenous Material Metabolized.—As already pointed out, a comparative study of the final products of metab- olism during rest and work does not itself afford direct evidence as to the nature of the material actually metabolized in a muscu- lar contraction, but simply shows the total effect of the contraction itself and of the secondary activities resulting from it upon the make-up of the schematic body. When we attempt to go further than this, other methods of investigation are requisite, although experiments like those already cited may afford important con- firmatory evidence. CONCLUSIONS FROM RESPIRATORY QUOTIENT.—The significance of the respiratory quotient in experiments upon work has already been illustrated in Chapter III (p. 76). Neglecting any slight error due to small changes in the proteid metabolism, the variations in the respiratory quotient as outlined in the foregoing paragraphs enable us to trace the corresponding changes in the nature of the earbon metabolism. The metabolism of a fasting animal at rest is, as was shown in Chapter IV, largely a metabolism of fat. Corresponding to this, the respiratory quotient of such an animal approaches the value 0.7 for pure fat, although never quite reaching it, since some pro- tein is always metabolized. Numerous instances of this fact are seen in the experiments already cited. When such an animal per- forms work, the respiratory quotient has been found to increase materially, thus showing that, in addition to the fat, carbohydrate material is being metabolized. This is entirely in accord with the well-established fact that muscular exertion causes the glycogen, both of the muscles and of the liver, to decrease and even disappear entirely. With an animal at rest and liberally supplied with car- bohydrate food, on the other hand, the respiratory quotient ap- proaches or even reaches unity, showing that the metabolism is essentially carbohydrate in character. When work is required of INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 219 such a subject, little change is noted at first in the respiratory quo- tient. The cells of the body being richly supplied with carbohy- drates apparently utilize these as the most readily available source of energy. In either case, however, continued work makes large demands upon the non-nitrogenous materials available, the store of carbohydrates in the body is rapidly depleted, and the fat of the body is drawn upon to an increasing extent as a source of energy, the necessary result being a diminution in the respiratory quotient. ' In the experiments of Chauveau & Laulanié only the respira- tory quotients corresponding to the total metabolism are given, and consequently the changes in the character of the metabolism indi- cated above can only be traced qualitatively. In Zuntz & Hage- mann’s investigations the increments of the carbon dioxide and oxygen over theeest values are given, and from them the propor- tion of oxygen applied respeetively to the oxidation of fat and of carbohydrates is computed. The following average results for the various forms of work show clearly that the ratio of fat to carbo- hydrates metabolized may vary through a very wide range. Oxygen per Minute applied to the Oxida- tion of _ Kind of Work. Periods. Fat, Carbohy- Gc: drates, ¢.c. Walking nearly horizontal........... Qn bei. 2,0 4.3638 2.9962 sf up a slight grade............ a, b, e, o 10.433 7.465 “e eet RLCE DEL PLAGE: Gh. sc jstes @, ONE fain 8.665 ISS Pals Draft, nearly horizontal... .........'.. bie f,2 8.882 12.992 Walking with load, nearly horizontal... é, 2; 0 5.962 3.317 Seay Up ay BU AGE, res aor aterssis cate cy é, 1, 0, 0 8.525 14.892 Trotemnearly horizomtalen. vic la s.a5 os Og @ 7.852 14.201 «with load, nearly horizontal..... €, 1,0 Pe clS” 416023 es eterna Ori ZOnualesy svete coe Gi fine 14.007 45.050 Tue InTeRMEDIARY Metrasouism.—As stated, the conclusions drawn from the respiratory quotient relate, strictly speaking, to the total effect of muscular exertion upon the store of matter in the body. The results of such experiments show that, as a consequence of a given amount of work, a certain quantity of fat and of carbo- hydrates has been oxidized somewhere in the organism. . 220 PRINCIPLES OF ANIMAL NUTRITION. Many eminent physiologists, however, netabiy Zuntz and his pupils, go further and regard both the fat and the carbohydrates of food or body tissue as immediate sources of muscular energy.and as of value for this purpose in proportion to their content of potential energy—that is, to their heats of combustion. In other words, they hold that either fat or carbohydrates may be in effect directly metabolized by the muscular tissue and that each under like condi- tions yields substantially the same proportion of its potential energy in the form of mechanical work. On the other hand, Chauveau * and Seegen + and their followers, as has already been indicated, regard the carbohydrates as the im- mediate source of energy for all the vital activities and hold that fat (or proteids) must first be converted into dextrose by the liver before it can be utilized. It is particularly with regardeto muscular exer- tion that this theory has been elaborated, the conclusions as to other forms of vital activity being to a considerable extent based upon analogy with the former. Funetions of the Liver.—According to this theory the material which is actually metabolized in a muscular contraction is a carbo- hydrate, viz., either the dextrose carried to the muscle by the blood or the glycogen which is stored up in it. Muscular activity is thus brought into intimate relations with the sugar-forming function of the liver, and a chief office of that organ is considered to be the preparation of the necessary carbohydrate material from the various ingredients of the food. The main facts which have been estab- lished may be summarized as follows (compare Chapter II, §$1 and 2): 1. Dextrose is being constantly formed by the liver, which not only modifies the carbohydrates of the food but likewise appears to produce dextrose from proteids and particularly, according to this school of physiologists, from fat. 2. Dextrose is as constantly being abstracted from the blood by the tissues, particularly the muscular tissues, as is shown by the constancy of the proportion of dextrose in the blood. 3. The dextrose content of the blood is, according to Chauveau, , * La Vie et l’Energie chez l’ Animale. t Die Zuckerbildung im Thierk6rper. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 221 maintained during fasting until the very last stages of inanition. When it finally disappears there is a rapid fall in the body temper- ature and death speedily follows. 4. Both the production of dextrose by the liver and its con- sumption in the tissues appear to be augmented by muscular exer- tion. The latter fact is shown by the well-known experiments of Chauveau & Kaufmann * upon the masseter muscle of the horse. Comparing the amount of blood passing through the muscle and the decrease in its percentage of dextrose in rest and in work they found that the consumption of dextrose in the two cases was in the proportion of 1:3.3872. Subsequent experiments + upon the Leva- tor labwi superioris of the horse, the results of which as to the gaseous exchange have already been cited (p. 188), gave the following figures for the dextrose abstracted from the blood per kilogram of muscle in one minute: Rest, Grms. Work, Grms. | Work + Rest. a J Dec oe\ip 10 618) nea ae Ree ed A nar 0.00598 (?)} 0.07026 (?) 1S es SVSAVER Were ieee cee da 0.06358 0.22303 Sroll “ AN See paste are A eo Bae oie 0.03976 (?)| 0.12852 oEee AV CAG Crmcmre tits ciaganee la lee see 0.03644 0.14027 3.85 The authors also call attention to the fact that in these two series of experiments the arterial blood supplied to the active muscle contained a higher percentage of dextrose than that supplying the same muscle in a state of repose, notwithstanding the consumption of this substance by the muscle, and conclude that muscular activ- ity stimulates the production of dextrose by the liver. .. The observa- tion of Kiilz,{ that prolonged muscular exertion may cause the dis- appearance of glycogen from the liver, may perhaps be interpreted as sustaining this conclusion. * Comptes rend., 103, 974, 1057, 1153. + Ibid., 104, 1126, 1352, 1409. t Arch. ges. Physiol., 24, 41. 222). 1. PRINCIPLES OF ANIMAL NUTRITION. Muscular Glycogen.—KEspecial interest attaches in this connec- tion to the behavior of the glycogen of the muscles. Nasse * appears to have been the first to show that the muscular glycogen is consumed during contraction. This result has been abundantly confirmed by other investigators, notably by Weiss,7 while, as just stated, Kiilz has shown that the same thing is true of the glycogen of the liver. It has also been shown that glycogen accumulates in muscles whose activity has been suspended by section of their nerves or other- wise. An early statement to this effect, unaccompanied by experi- mental proof, is by MacDonnel.{° Chandelon § investigated the influence upon the glycogen content of the hind leg of a rabbit of, first, ligature of the arteries, and second, section of the motor nerves. The first treatment caused a large loss and the second a large gain of glycogen. Morat & Dufourt || confirmed these results and also found that the formation of muscular glycogen was more rapid in a fatigued quiescent muscle than in a normal one, while Aldehoff 4 has shown that in a fasting animal glycogen persists longer in the muscles than in the liver and reappears first in the former when food is given. In view of these facts it can hardly be doubted that the muscu- lar glycogen is in some way a source of energy to the muscles, being destroyed during contraction and stored up again during rest. Chauveau’s Interpretation.—By a comparison of their results for dextrose just cited on p. 221 with those for the gaseous exchange of the muscle as given on p. 188, Chauveau & Kaufmann show that during rest there was a storage of dextrose and of oxygen in the muscle. During work, on the contrary, more carbon dioxide was produced by the muscle than corresponded to the amount of dex- trose which was abstracted from the blood, and this carbon dioxide contained more oxygen than was supplied to the muscle by the * Arch. ges. Physiol., 2, 97; 14, 482. - e + Sitzungsber. Wiener Akad der Wiss., Math-Nat. Klasse, 64, II, 284. t Proc. Roy. Irish Acad., Ser. I, 7, 271. © Arch. ges. Physiol , 18, 626. || Archives de Physiol , 1892, 327 and 457. { Zeit. f. Biol., 25, 137. INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 223 blood during the same time. The average results, computed in ' milligrams per minute, were: : During Rest, | During Work, Merms. Megrms. Caen MeO lOO sf. nalts ol Mis tass Lieve s leat 0.11803 2.48490 i (Le GON pEOCUGeU nih em seers 2 ss cone ee 0.08424 3.15052 «required to oxidize dextrose taken up from JEL OYA ie elk ay APS ROU ane San Oo RN 0.58305 2.35055 WAR OHON GOs MEOMUCEE G hii. <.o.cs): 2 to as Salas ote 0.03160 1.18128 bi PPOCkErosettakenmmiap. £).9te em sti waded 0.21862 0.88118 During rest the muscle was storing up both carbohydrate (gly- cogen) and oxygen, thus supplying itself with a reserve of potential energy. During activity this reserve, as well as the supply brought by the blood, was drawn upon for the performance of work. The fluctuations of the respiratory quotient resulting from mus= cular exertion are explained by Chauveau in outline as follows: At first there is a rapid oxidation of the stored glycogen of the muscles and of the dextrose of the blood, resulting in a respiratory quotient approaching unity. As the work progresses the store of carbohydrate material in the organism becomes relatively exhausted, unless there is a large supply of it in the food, and to meet the demands of the muscles an increased production of dextrose from the fat of the food or of the body takes place in the liver. This change, however, according to the equation proposed on p. 38, con- sumes 67 molecules of oxygen for each 18 molecules of carbon diox- . ide produced. This process, superadded to the combustion of carbohydrates in the muscles, results in the observed lowering of the respiratory quotient. The further lowering of the quotient during a succeeding rest period results from the great diminution in the amount of carbohydrates oxidized in the muscles, the for- mation of carbohydrates from fat in the liver still continuing for a time in order to replenish the exhausted store of muscular glycogen. Fat as a Source of Muscular Energy.—According to the above theory, fat is only indirectly a source of muscular energy, in that it serves for the production of dextrose in the liver, and the 224 PRINCIPLES OF ANIMAL NUTRITION. same thing is held to be true of protein so far as it contributes energy for muscular exertion. As we have seen in Chapter II, however, the formation of dex- trose from fat in the liver is by no means universally admitted, and Chauveau’s ingenious theory as to the immediate source of muscu- lar energy has not lacked opponents. If it is true, fat has a much lower value for that purpose than corresponds to its potential energy as measured by its heat of combustion. If it be assumed to be converted into dextrose in accordance with the equation on p- 38, it is easy to compute that about 36 per cent. of its potential energy will be liberated as heat in the process and that consequently only the 64 per cent. remaining in the resulting dextrose will be available to the muscles. Consequently the relative values of fat and dextrose for the production of work will be as 162 to 100 and not as 253 to 100. While the evidence of the respiratory quotient is not incon- sistent with Chauveau’s theory, it is also not inconsistent with the view which supposes fat to be directly metabolized for the produc- tion of mechanical work. The difference lies, not in the amounts of carbon dioxide and oxygen evolved but in the place where and the form in which the energy is liberated, and the question can therefore be satisfactorily discussed only on the side of its energy relations. Postponing that discussion for the present, it may be remarked here that while it appears to be true, as already stated, that the muscular glycogen and the dextrose of the blood are a source of muscular energy, and perhaps the most readily available one, it by no means follows that they are the only source. The muscle contains other non-nitrogenous reserve materials besides glycogen, and notably a not inconsiderable amount of fat and of lecithin. Moreover, recent investigations (see pp. 63 to 65) have shown that the amount of the muscular fat is greater than was formerly sup- posed, and that some of it cannot be extracted with ether and behaves almost as if in chemical combination. Indeed, it appears not improbable that both fat and carbohydrate molecular groupings, as well as proteids, enter into the structure of living protoplasm. Finally, not only the muscle but the blood which nourishes it contains fat as well as carbohyhrates, the former indeed being more INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 225 abundant than the latter. There would seem to be no inherent difficulty, then, in supposing that the fat of the muscle and of the blood serves directly as a source of energy, although the writer is not aware of any investigations upon the influence of the contraction of a muscle upon its fat-content. PART II. THE INCOME AND EXPENDITURE OF ENERGY. CHAPTER VII. FORCE AND ENERGY. Force is defined as whatever is capable of changing the rate of motion of a mass of matter. When a force acts upon a mass, im- parting to it a certain velocity, it does work, the amount of work being measured by the product of the force into the distance through which it acts. Energy may be defined as the capacity to do work. Any mass of matter which can act upon another mass in such a way as to change its rate of motion is said to possess energy. KINETIC AND PoTenTIAL ENERGY.—In studying energy we distinguish between kinetic energy, or the energy due to motion, and potential energy, or the energy due to position. The falling weight of a pile-driver at the instant it strikes the pile possesses a certain amount of kinetic energy and does a corresponding amount of work on the pile. When it is raised again a certain amount of work is done on it, and when it comes to rest at the top of the ma- chine a corresponding amount of energy is stored up in it as poten- tial energy. As long as the weight is supported at this point it does no work, but simply possesses the possibility of doing work. When it is allowed to fall again, this potential energy due to its position is converted into the actual or kinetic energy of motion, and when it reaches the point from which it was raised and strikes the pile it does work upon the latter exactly equal to that formerly 226 FORCE AND ENERGY. 227 stored up in the weight as potential energy, which again was equal to the energy expended in raising it. An even simpler example of the conversion of potential into kinetic energy and vice versa is a swinging pendulum. When at rest for an instant at the end of a vibration it possesses a certain amount of potential energy, corresponding to its vertical height above the lowest point of its are. When it reaches this lowest point, so far as the mechanism of which it forms part is concerned it has no more potential energy because it cannot fall any farther. In place of this, however, neglecting mechanical resistances, it con- tains an exactly equivalent amount of kinetic energy, due to its motion. During the second half of the swing this kinetic energy is expended in again raising the pendulum, and when it has all been expended the pendulum will (in the absence of external resistance) have been raised to exactly the same height as before above its lowest point. In other words, its kinetic energy will have been re- converted into an equivalent amount of potential energy and so the alternate conversion and re-conversion goes on as long as the pendulum continues to swing. The same facts which have been illustrated above in the case of the motion of visible masses of matter are likewise true of molecular and atomic motions. When molecules of carbon dioxide and water are converted into starch in the green leaves of the plant, work is done upon them by the energy of the sun’s rays. Their constituent atoms are forced apart and compelled to assume new groupings. In this process a certain amount of kinetic energy has disappeared and the resulting svstem of starch molecules and oxygen molecules contains a corresponding amount of potential energy. Under suitable conditions the reverse process may also take place. The atoms may, so to speak, fall together and resume their old positions, producing the original amounts of carbon dioxide and water and giving off in the process the exact amount of kinetic energy which was originally absorbed. This energy may appear in the form of heat, as ip ordinary combustion, or in any other of the various forms of energy, according to circumstances. The last example is but an illustration of the general fact that in every chemical reaction there occurs a transformation of energy which most commonly takes the form of an evolution or absorption 228 PRINCIPLES OF ANIMAL NUTRITION. of heat. That branch of science which deals with the connection between chemical and thermal processes is known as thermo-chem- istry. Since kinetic energy in the animal is derived from chemical processes, and since it largely takes the form of heat, we may regard the study of the transformations of energy in the organism as con- stituting a branch of thermo-chemistry and proceed to a consider- ation of the fundamental laws upon which the latter subject is based. THE CONSERVATION OF ENERGY.—In any system of bodies not acted on by external forces the sum of the potential and kinetic energy is constant. In other words, while the ratio of potential to kinetic energy may vary, and while each may take various forms, as mass-motion, heat, electric stress, etc., there is no loss of energy in these conversions. Energy, like matter, is indestructible. This great law of the conservation of energy was first clearly enunciated by Mayer, and forms the foundation of all modern conceptions of physical processes. In the case of the swinging pendulum used above as an illustration the total energy of the system composed of the earth and the pendulum is constant, a portion of it simply alternating between the potential and kinetic states. So, too, in the system of atoms of carbon, hydrogen, and oxygen, the potential energy contained in the system before the starch is burned is simply converted into the kinetic energy of heat, while the total energy of the system remains the same. INITIAL AND Finan Srates.—An important consequence of the law of the conservation of energy, which was first deduced and demonstrated experimentally by Hess in 1840, is known as the law of initial and final states. This law is that in any independent system the amount of energy transformed from the potential to the kinetic form, or vice versa, during any change in the system, depends solely upon the initial and final states of the system and not at all upon the rapidity of the transformation or upon the kind or number of the intermediate stages through which it passes. Although this law is true in the general form here sta&ed, it was originally propounded as related to chemical reactions and forms the basis of the science of thermo-chemistry. If we start with starch and oxygen and end with the corresponding quantities of carbon dioxide and water, the amount of kinetic energy evolved is a sel FORCE AND ENERGY. 229 the same, no matter whether the starch be burned almost instanta- neously in pure oxygen or whether it be subjected to slow oxidation in the tissues of a plant buried in the soil; whether carbon dioxide and water are the immediate products of the action or whether the starch be previously transformed into maltose, glycogen, dextrose, lactic acid, ete., etc., as in the body of the animal. We have simply to determine the potential energy of the system in its initial and in its final state, and the difference is equal to the amount of kinetic energy evolved during the change. The truth of this law, as ap- plied to chemical processes, has been fully demonstrated by the researches of Berthelot and Thomsen. That the same law applies to the processes taking place in the body of the animal is exceed- ingly probable, a priori, and has been demonstrated experimentally by the researches of Rubner and of Atwater and his associates. Heats oF CompusTIon.—We have no means of determining the total amount of potential energy contained in a system, but can only measure that portion which is manifested by the change to the kinetic or the potential form during some change in the system. Tn other words, we may assume the potential energy of the system in some particular state as zero and obtain a numerical expression for its potential energy in some other state as compared with this standard state. For the latter we shall naturally sclect that one in which no further conversion of potential into kinetic energy can, according to our experience, take place. In the case of organic substances, such as those entering into the metabolism of the animal, the system consists of the substance itself and oxygen, and the state of complete oxidation is the one in which experience shows that no further evolution of kinetic energy is possible by chemical means. Thus, to recur to the example of starch, if one gram be oxidized in accordance with the equation C,H,,0;+60,—6CO,+5H,0, the amount of heat evolved will be 4183 cals.,* this being the amount of energy converted from the potential to the kinetic form. From the system represented by the second member of the above equa- tion we can get no further evolution of heat. We therefore repre- * For the units of measurement see the following paragraph. 230 PRINCIPLES OF ANIMAL NUTRITION. sent its potential energy by 0 and accordingly that of the system starch + oxygen by 4183 cals. for each gram of starch. This value is called the heat of combustion of starch, and shows how much energy can be liberated from this substance by its conversion into CO, and H,O. It is common to speak of this as the potential energy of the starch, and the expression has the advantage of brevity, but it should not be forgotten that it is really the potential energy of the system C,H,,O,; + 60, as compared with the system 6CO, + 5H,0. In like manner the heat of combustion of any organic com- pound, or of any mixture of compounds such as a feeding-stuff, represents the amount of energy which a given weight of it evolves in the form of heat when completely oxidized. In the case of nitrogenous ‘bodies the final products are.CO,, H,O, N,, and in case of proteids SOs. Heats of combustion may be determined at constant pressure or at constant volume. When the substance is burned under ordi- nary atmospheric pressure the amount of heat evolved may include, besides that due to the difference in the chemical energy of the substance before and after burning, a mechanical component due to the fact that the volume of the products is not the same as that of the original substances. If it is greater, work is done in overcoming atmospheric pressure and the heat production is diminished by a corresponding amount. In the contrary case, work is done by the atmosphere upon the products of combustion and heat is evolved. When the substance is burned in a confined volume of oxygen, as in the bomb-calorimeter, the possibility of such mechanical action is eliminated and we obtain a quantity of - heat representing solely the difference in chemical energy. The heats of combustion at constant volume are therefore, from a theoretical point of view, the more correct. On the other hand, however, all ordinary processes of combustion, including those occurring in the animal organism, take place under atmospheric pressure, which is practically constant, and therefore the actual heat value of a sub- stance oxidized in the body is measured by its heat of combustion at constant pressure. If there is no change in volume during the combustion, then the two heats of combustion are, of course, iden- tical. This is the case, for example, with the carbohydrates, which FORCE AND ENERGY. 231 form so large a part of the food of herbivorous animals. Further- more, the difference in the case of the other common nutrients is so slight that the heats of combustion as determined with the bomb- calorimeter may be used without appreciable error in computing the metabolism of energy in the body. The only substance involved in such computations for which the correction needs to be made is methane, CH,, the heat of combustion of which is at constant volume 13,246 cals. per gram and at constant pressure 13,344 cals. Units oF MEASUREMENT.—The unit of force is the dyne, which is defined as the amount of force required to produce in a mass of one gram, in one second, an acceleration of one centimeter per second. When a .orce acts upon a mass, the amount of work done is measured by the product of the force into the distance (measured along the direction of the force) through which it acts. The unit of work is the erg, which is defined as the work done by a force of one dyne acting through one centimeter. Energy has been defined as the power of doing work, and is measured by the amount of work done, that is, in ergs. Since, however, the erg is a very small quantity, it is often more con- venient in practice ‘to use a multiple of it. For this purpose the quantity 10 erg=1 Kilojoule (J) is a convenient unit. Energy is also frequently expressed in units based on weight instead of mass, the most common being the gram-meter, the kilogram-meter, and the foot-pound. The gram-meter is the work done against gravity in raising a weight of 1 gram through 1 meter. Since, however, the force of gravity, and consequently the weight of a given mass, varies at different points on the earth’s surface, it 1s necessary to state also where the weight is taken. At the level of the sea, in temperate latitudes, the force of gravity equals 980.5 dynes. Under these conditions, then, doing 1 gram-meter of work would be equivalent to exerting a force of 980.5 dynes through 100 cm., which equals 98,050 ergs. The kilogram-meter (kgm.) is the work done against gravity in raising | kilogram through 1 meter, and is accordingly 1000 times the gram-meter or 98,050,000 ergs. The foot-pound is the work done against gravity in raising 1 pound through 1 foot and accordingly equals 13,550,000 ergs. In addition to mechanical energy the animal produces heat. 232 PRINCIPLES OF ANIMAL NUTRITION. For the measurement of heat various units are in use, but the ones most commonly employed in physiology are the small and the large calorie. The small calorie (cal.) is defined as the amount of heat required to raise the temperature of 1 gram of water through 1° C. Since, however, the specific heat of water varies somewhat with the temperature, it is necessary to specify the average temperature of the water. The temperature of 18° C. has been quite commonly used for this purpose, the resulting unit being indicated by the abbreviation cal,,. Atwater & Rosa,* however, in their work with the respiration-calorimeter, have employed the temperature of 20° C., designating their unit by cal,,. The difference between the two is very slight, 1 cal,, equaling 1.0002 cal,,. The large calorie (Cal.) is the amount of heat required to raise the tempera- ture of one kilogram of water through 1° C., or is equal to 1000 small calories. The temperature at which the large calorie is measured may be indicated as in case of the small calorie. The calorie, however, while commonly used, and while in some respects a convenient unit, is in a sense not a rational one. Since heat is one form of energy, and since, in accordance with the law of the conservation of energy, there is a fixed relation between it and other forms of energy, a rational unit would be one bearing a simple numerical relation to the units employed to measure other forms of energy, or in other words, the erg or some simple multiple of it. As already noted, the Kilojoule (J) is a convenient unit for this purpose. It has two advantages over the Calorie: first, it permits of a direct comparison of heat with other forms of energy (expressed, of course, in units of the same system); and second, it is an “abso- lute” unit, that is, it is based on the fundamental units of space, mass, and time, and has a perfectly definite magnitude, while the Calorie has not unless the temperature at which it is measured is stated. To this may be added that in discussing physiological relations it avoids the sometimes confusing implication that the quantities of energy dealt with actually exist in all cases as heat. The relation between the Calorie and the Kilojoule is as follows: 1 Cal,,=4.183 J =41,830,000,000 ergs; 1J =0.2391 Cal,,=10,000,000,000 ergs. * U.S. Dept. Agr., office of Expt. Stats., Bull. 63, p. 55. FORCE AND ENERGY. 233 Since, however, most of the results of investigations upon the physiological relations of energy are expressed in calories (often without any statement of temperature) it will be more convenient in the following pages to empioy this unit rather than the more rational Kilojoule. Finally, since measurements of mechanical energy (as in experi- ments with working animals) have been commonly made in weight units, it 1s necessary to know the relation of these to the calorie. These relations are included in the following table, the force of gravity being taken as 980.5 dynes: EQUIVALENCE OF UNITS OF ENERGY. Ergs.* Valojoules.)) iy Cu atas 5 fi Scere. 1 Kilojoule t= 4 Fo set. fee Oi ree ||) chee act ee 101989 i gram-=meter = ......- 980 75> 107 * || 980.5 =108S a eee 0.001 1 kilogram-meter =.... 980.510° | 980.5+10° 1000 { foot-pound = 25.4... .. 135.54 10° | 135.5108 138.2 0.1382 Wealiginn aches i aes 4.183 X10! 0.004183 | 426.6 0.4266 PRGalnies 2, ape tagccne ea ee 4.183 10"° 4.183 426600 | 426.6 Le calys Calis i Kaloyouley =) 25 a 738 .1 239 .1 0.2391 SCAM IME LOTS an sroite asthe els r=y el -bel= 0.007236 0.002344 | 0.2344+10° I kilosram=meter = —-)).5..--.... 7.236 2.344 0.002344 Pease WOUMG P= TATA halo co ichdle © [wn nes Sere ah ols. 0.3239 0.000324 etentirne dye eeAaus. sho wie fsesis Pelz ve Me's SUOSE 4 SOG erate alate 0.001 Me Meee aro ice iaek shart gu Sasha! 3087. 1000 : * From Ostwald, Grundriss der allgemeinen Chemie. CHAPTER VIII. METHODS OF INVESTIGATION: THE food is the sole known source of energy as well as of matter to the body of the warm-blooded animal, and the total income of potential energy, according to the principles Jaid down in the pre- ceding chapter, is represented by the heat of combustion of the food. A portion of this food, as we have seen in Part I, is metabolized in the body, while part of it escapes complete oxidation and is re- jected as undigested matter in the feces, as metabolic products in feces, urine, and perspiration, and as combustible intestinal gases. All these substances still contain more or less of their original store of potential energy and collectively constitute one main division of the outgo of energy. We may call it, for brevity, the outgo of potential energy. A portion of the food may also be applied to the production and storage of tissue (protein and fat) in the body, and this, from our present point of view, is to be classed with the outgo of potential energy. The potential energy of the remaining portion of the food, viz., that which is completely oxidized, may take various transitory forms in the organism, but ultimately it leaves it in one of two forms of kinetic energy, viz., as mechanical work or as heat. Here we have the second main division of the outgo of energy, viz., the outgo of kinetie energy. These relations may be briefly expressed in tabular form, as shown at the head of the opposite page. As in the corresponding chapter of Part I, it is proposed to con- sider here simply the general principles of the more important methods available for determining the income and outgo of poten- tial and kinetic energy, without entering into technical details. 234 METHODS OF INVESTIGATION. 235 Income: Food Outgo: Feces Urine Perspiration Combustible gases Storage of tissue Work Heat Kinetic energy. | | Potential energy. Determination of Potential Energy. The Energy of the Food.—-The potential energy of the food is conveniently measured by converting it into the kinetic form of heat; that is, by determining its heat of combustion. This determina- tion is effected by means of an instrument known as a calorimeter, in which the heat produced by the complete combustion of a known weight of the substance under examination is absorbed by some calorimetric substance and its amount measured by the change of temperature or of physical state of the latter. The calorimetric substance ordinarily employed is water, the increase in tempera- ture of a known weight of this substance giving directly the amount of heat in calories. It is, of course, essential either that all the heat produced shall be transferred to the calorimetric substance or that it shall be possibie to correct the observed results for any heat that may escape absorption. Another essential is that the oxidation shall be complete, a condition whose fulfillment it is by no means easy to secure. Two general methods have been employed for this purpose. The first was that of Thompson,* as used by Frankland and subsequently modified by Stohmann,t in which the oxidation is effected by means of pure potassium chlorate, corrections being made for the heat evolved in the decomposition of the latter substance. The second method, which has aimost entirely replaced the first, con- * Described by Frankland, Proc. Roy. Inst. of Great Britain, June 8, 1866, and Phil. Mag. (4), 32, 182. { Jour. pr. Chem., 127, 115; Landw. Jahrb., 18, 513. 236 PRINCIPLES OF ANIMAL NUTRITION. sists in burning the substance without any admixture in highly compressed oxygen contained in a lined steel bomb as first devised by Berthelot * and subsequently modified by Mahler, Hempel, and Atwater. With this type of calorimeter very accurate and com- paratively rapid work may be done. Frankland was the first to undertake determinations of the heats of combustion of foods and food ingredients, using the origi- nal form of the Thompson calorimeter. Subsequent investigators, of whom may be especially mentioned Stohmann, v. Rechenberg and Danilewski, Berthelot and his associates, Rubner, and Atwater, Gibson & Woods, have continued these investigations with im- proved apparatus and more refined methods,{ and we now possess a considerable mass of data as to the heats of combustion of the more important ingredients of animals and plants and of the prod- ucts of métabolism. Atwater § gives the following summary of the results on record up to July, 1894 (see pp. 237-9). In the course of recent investigations into the energy relations of the food of man and of domestic animals a considerable amount of data has also been secured regarding the heats of combus- tion of foods and feeding-stuffs. A summary of the results of such determinations on 276 samples of human foods of various kinds has been published by Atwater & Bryant.|| No similar compilation of heats of combustion of feeding-stuffs is as yet avail- able. It need hardly be pointed out that, taken by themselves, such results furnish no measure of the relative values of the various feeding-stuffs. Like a chemical analysis, they supply but a single factor, albeit an important one, for such a com- * Ann. de Chim. et de Phys., (5), 28, 160. + For the technical details of the method reference may be had to the published descriptions of the apparatus or to Wiley’s Principles and Prac- tice of Agricultural Chemical Analysis, Vol. ITI, p. 569. t For a historical sketch of the development of calorimetry, as applied to food substances, compare Atwater, ‘Chemistry and Economy of Iood,” U.S. Department of Agriculture, Office of Experiment Stations, Bull. 21, pp. 116-126. § Ibid., pp. 127 and 128. Compare also Rep. Storrs Expt. Station, 1899, p. 73. || Rep. Conn, Storrs Expt. Station, 1899, p. 97. METHODS OF INVESTIGATION. 237 , HEATS OF COMBUSTION OF ORGANIC SUBSTANCES. Berthelot Thompson-Stohmann Method. Method. Stoh- Stoh- apite: Berthe-| mann | mann By Rub- lot and} and and Dani- ner, | Gibson. Asso- | Lang- | Asso- | lewski. ; ciates. | bein. | ciates. ALBUMINOIDS, ETC. Gluten Marsan satan hors eeke DOIO TS wdc = ae tees 6141 MST GAM iene tcl Seay sas) eval ernst ateeteg kel Ms cr 5961.3 J PIED AVES 71 oh 9 en ENE oie PRP 5832 .3/5941.6]...... 6231 SON lope einen Ae tee egal genome 5917.8 TS AAGUOTOIIET aye SPiN ta, Cen Saree Dae Ise 5907 .8 eine ko] SE ORAM ocabioee Gee SOMO Nate sa acl dcaoe 5950 IMRIKECASCIME tat etarcrs Scbsneeieeeets, e1 5626 . 4/5867 5717 | 5785 e SOEs is RCS Cero Ce Oro 5849 .6 Molo CGO ee seit hae Sebo 8112.4 5840.9 Geo UMA Ra eo pier a eavsuere ee. oll tne a) HB obese 5573 sViaitiee irae UN otees ce, bye ese shoes 5780 .6'5745 .1 igovallloumimyse ee cee termite rye 5687 415735 .2| 5579 Muscle, extractives and fat re- TMOG Saray weirs crore rele’ tees Dees CAV SDIlc.0 6 oe bllouee ae 5778* Crystalhzed albumin 76/2 2 ess 2 |e 0. s01: 5672 5598 Muscle, fat removed.) toe Tests os = 3662.6) 5324 |...... 5656* Ho ee En yah Une eer cee ey | 5640.9 JEU oveyol inlowohaNs ibk-ais Gao onees oe 5529 .1/5637.1) 5511 | 5709 arnack! sralloumentijersces jet ie wet 5553 WiOOlGERiE ye On inten Re hae a, 5564 . 2/5510 .2 Wanelitem Seat ce ve eos sels Peet ans 5479 5362 HifomMWOtEs kang seeaey hanes oes ees | Arcata 5355.1 PeMLOMGL erry oro he einstein nee DIS Sills eae 5069 TEV Sa) fea LOTS ea oaks caer Beye oe cae Aen ge ed | Pace 5493 @hondriney shee eas tee eet a 5342 .4/5130.6]...... 4909 OsSeiniAeneNs geist aiteo Gres ba. 5410.4)5039 .9 ilo OU ar era ASS cero tycin Oa'does 5095 .7|4979 .6 (Ghipimtats oa, vareye cteas Sate oh oles 4655 [4650.3 TDG CTIOY Ae ene Ratchet ure ARICA tallies 4146.8 PArAolObUlitbss = Ao stcy oe Grave feelers ales =i ae 5637 AMIDS, ETC. [UE AA AD A SOM a 2530.112541.9) 2465 | 2537 | 2523 CriycOCOllye! tara ha hari Gets 3133 .6/3129.1| 3053 2 NIE eye ttee A Ure Nga fer coset ok Ui Weg eee ae 4370.7|4355 .5 Wet caminch Os abe aise suk tees teats ak ona 6536 .5)6525.1 AEKOSIM ns, soci cm stey ewer heen 5 Merl erate cree 4505 .9 FU pUnIG ACK Jos kaa ott wit 5659.3 5668.2) 5642 FANS} OF MEMEO OL, es enemy as eee ecco 2911 .1\2899 PV EOSM I £5 tsa cans nie Boreas a 5915.9 VS PARAC UN 5 5 ike ene etna te 3396 .8 3514 3428 IRREA GIN) (CEVAEUE) kas oidnene sonata ccs. ler flee lle ae (3206) gE Cwater-free)i iyi ee. We et Shale 4275.4 [WhirKoeeV or Le Sine Sopa Aimer ceniege OA 2754 |2749.9| 2621 GAIN Ss © asso tcl eres) ehys rot ecen er 3891.7 SORSEUL SS Ip Nt aoe, ca ee ee [5231 .4| * Calculated ash-free. 238 PRINCIPLES OF ANIMAL NUTRITION. HEATS OF COMBUSTION OF ORGANIC SUBSTANCES (Continued). Berthelot Method. Berthe- Rieke wd and! and so- eaten. rane: Fats. 1 Animal: Hist OF, BWANC sensor. atic cles eee telheneelsye 9476.9 St OLOXED seit kiss etree ,o eraoie ee 9485.7 Bat of sheep’ tance ts coher mcr 9493 .6 Rt; OF NOTSes ae tos ohio RE OS eee Hatt? OF COR Tet eerie mea ogee lloneras ted? Mats Ol TOOSE ES. tec a cco cvehor: al eteper ral lee ators Raton ducks anyse Pelco ee el mera eee ee FSG OF TAM eyes sce ake citer alate creme lye ete be Bitbersteee vetey hae eee sie hoe eee 9215.8) Spero Gile' Mn hen mee Regain tal ea BAL 2. Vegetable: | Olive oil (expressed) ........ Aim elaeeeees Poppy-seed oil (expressed)...)......|...--. Rape-seed “ lia bet beh sah ena Ether extract of various seeds.}......)...... | CARBOHYDRATES, ETC. | | 1. Pentoses: | ATAIDIIMNIOSOS a tisuseahel o aikhhas bese cceats |3714 (3722 eV LOSerz eee ce eee ete (3739 .9)3746 IHNIGOSEe Pr Arete wicks choos ciel arte eee 4340.9 Rhamnose (water-free) ......}...... 4379 .3 as COnyStt) Ut An. So alerts 3909 .2 2. Hexoses: SOLDIMOSEH .. He eer dec bees lle ee ee 3114.5 CG ACLOSE Ye hea. Fea coe slo ics leva S21 5 ESETTOSEL hin heel e Hie cette 3762 |3742.6 IETUCEOSE: ye Cisteveis, oe) cis el oe ell otearerenes 3755 3. Heptoses: Glucoheptose.-!'e.-% 22 eee 3732.8 4, Disaccharids: Cane SUGAaN tinct. detec yrsccteul: 3961 . 7/8955 .2 NT yee The treoketec si ecmicge eset ba oat 3951.5 a el MODY SUS) berets ats las 3777 .1|3736.8 MAGORG pees erits Svcinns Abels mie ote 3949.3 # (OGVSUS) Mere Meare islet sta lcs ieee 3721.8 Prehalosericisicrsaisiaareticaarkeo arene lie cess eee 3947 Ai oS A(CEYVRUs) pate tern bret she’s Wil atetou see 3550.3 5. Trisaccharids: Meletriose to fucka ee eile «2 4020 |4020.8 oY (eryiit.) isos amscm 0] We're 3400 .2 Melezitose ah vatctions Maherohe Rie neee ated Unease 3913.7 Thompson-Stohmann Method. Stoh- mann and Asso- ciates. By Dani- lewski. Rub- ner, | Gibson. 9423 | 9515 9380| 9686 wige, ©., 06. © fe Pies wat ‘a’ je. ey ew) BL oS e wre e)|/e ee owe 9489) 9619 9130 9467 oe 3695 a eles) © eee eeeleweeee METHODS OF INVESTIGATION. 239 HEATS OF COMBUSTION OF ORGANIC SUBSTANCES (Continued). Beck Thompson-Stohmann Method. Berthe- Eee ea B. Rub- | lot and} and and Dani-| jer, | Gibson. Asso- | Lang- | Asso- | lewski. ; ciates. | bein. | ciates. 6. Polysaccharids: Giiap embins seit sectn it srenseec etl sree sted 4190.6 (We lhMLOSeh wea s il edhe sect Meercne 4200 /4185.4! 4146 PS USUEC LPS huh ohidee tans ete te gL ane AD oa ea ceo Alera tal eee acealiette a elas 4164 UD TEsg et gsi Olgeymee ae eae ae 4180 .4/4112.3 iraiypi irate eS peek Se Sheree ce eet oti 4187.1|41383.5| 4070 ALCOHOLS. Hpi aleoholi se. 5.2 9 .)0'6 o-0 9 7068 Merl Geuimiekere weamnees ahs Ws len ataeck el Seeestiataes 4112.4] 4317 IMPS be yes vice Punt Wetereht a, click tre AQOG 2 | 399728 PSOOST we eae 3959 IFAW OYS}H EANA RSE 0 Eee eee 3676 .8/3679 .6 ACIDS. PNG HC ae See Pane Ramee nd 3490.4 IPE an nko aia oleae Rec eee ec eck cl EREN ee 9352 .9| 9226 PLUG CHMM EIN oi eaten tte here asker weet aes (tee aca 9429 (ONT era OE ae aes ale Cabana eS Sere Fe a 9494 .9 AVE OT Gia eaeh ened cies a econ seher cus LOO BRAN E s imine 1960 SUG UIC Peds creee thane sea aeons S006 22 terre: 3019 UDSSSUESIT NO), COO SNS EG op SR tae aL eeu et ee fe RL 1745 Oriente es AU eS eR RP oh ae DAT OIE he ee 2397 parison. Just as the chemical analysis shows the total amounts of various substances or classes of substances present, so the heat of combustion shows the total amount of potential energy which has been stored up in the feeding-stuff. In both cases the knowl- edge thus acquired must be combined with data, secured in an entirely different way, as to the availability of these ingredients or this energy before we can form a judgment as to the relative values to the animal. CoMPUTATION OF Huats or Compustion.—The heat of com- bustion of a mixture of various organic substances, such as are contained in ordinary foods and feeding-stuffs, is equal to the sum of the heats of combustion of the single ingredients. If the latter are known we may obtain the heat of combustion of the material in question either by a direct calorimetric determination or by deter- mining chemically the proportions of the several ingredients and multiplying the amount of each into its known heat of combustion. 240 PRINCIPLES OF ANIMAL NUTRITION. The first method, when available, is obviously to be preferred, and is to be regarded as indispensable in all exact investigations into the energy relations of the food of man or of animals. With materials whose proximate composition is fairly well known, how- ever, the agreement between the computed and the actual heat of combustion is very close, as has been shown by Wiley & Bigelow * and Slosson + for hulled cereals and cereal products. Atwater & Bryant, in their publication just referred to, have discussed this question very fully in relation to human foods and have proposed a series of factors for the ingredients of the various classes of foods by whose use they obtain a most satisfactory agreement with the calorimetric results. On the other hand, in case of vegetable products containing much woody and fibrous material the actual heat of combustion is higher than that computed under the ordinary interpretation of the results of chemical analysis. Thus the actual heat of combus- tion of unhulled oats was found by Wiley & Bigelow to be about 4.5 per cent. higher than the computed value, and Merrill { has obtained similar results for wheat middlings and bran and for hay and silage. This obviously arises from the presence among the ill-known bodies constituting the so-called lignin and incrusting substances of compounds having higher heats of combustion than the common carbohydrates. It is not impossible that a series of factors similar to those of Atwater & Bryant might be worked out for different classes of stock foods, so that their heats of combustion might be computed from their chemical composition. In view, however, of the comparative case and rapidity with which direct calorimetric results can be accumulated it may be doubted whether such an undertaking would repay the labor involved. Methods have also been proposed and somewhat extensively used for computing the heat of combustion of the digested portion of the food. This phase of the subject, however, can be more profitably considered later. The Energy of the Excreta.—For the visible excreta (feces and urine) substantially the same method is available as for the food, * Jour. Am. Chem. Soc., 20, 304. + Wyoming Expt. Station, Bull. 33. t Maine Expt. Station, Bull. 67, p. 169. METHODS OF INVESTIGATION. 241 viz., a determination of the heat of combustion. An element of uncertainty, however, which is ordinarily not met with in the case of the food, arises from the ready decomposability of the excretory products, which is liabie to result in a loss of energy during the drying necessary to prepare them for combustion. The urea of the urine, in particular, is very readily converted into the volatile ammonium carbonate. Comparative determinations of nitrogen in the fresh and in the dried urine will show the amount of nitrogen lost in drying, and on the assumption that only urea is decomposed the loss of energy can be readily computed from the known heat of combustion of that substance. Atwater & Benedict * have found this assumption to be substantially correct for human urine, and the same may be presumed to be the case with the urine of carniv- ora. It has usually been assumed to be applicable also to the more complex urine of herbivora, although without, so far as the writer is aware, any experimental proof. A greater or less loss of nitrogen has also been observed in the drying of the feces of domestic animals, particularly of horses and sheep, but the nature of the material decomposed has not yet been investigated, and the same is true of the possible decomposition of non-nitrogenous materials in both urine and feces. Atwater & Benedict (loc. cit.) found the loss of nitrogen from human feces to be insignificant. CoMPUTATION OF ENNERGY.—The computation of the energy of the visible excreta is much less satisfactory than in the case of the food on account of our inferior knowledge of the proportions and chemical nature of their ingredients. The Urine.—Formerly the urine was assumed to be substan- tially an aqueous solution of urea, and numerous computations of its energy content were made on this basis, particularly in connec- tion with estimates of the metabolizable energy of the proteids, while the same method has been applied also in estimating the metabolizable energy of feeding-stuffs. Rubner + was the first to demonstrate the serious nature of the error involved in this assump- tion and to show that the energy of the urine is materially greater than the amount thus.computed. In the urine of the dog he found * U.S. Dept. Agr., Office of Experiment Stations, Bull. 69, p. 22. + Zeit. f. Biol., 20, 265; 21, 250 and 337; 42,302. Compare Chapter X. “ 242 PRINCIPLES OF ANIMAL NUTRITION. the energy content to be from 6.7 to 8.5 Cals. per gram of nitrogen in place of 5.4 Cals. as computed on the assumption that only urea was present, while for human urine he has obtained values ranging from 6.42 Cals. to 8.87 Cals. per gram of nitrogen, and Tangl * has reported even higher figures. Kellner + has shown that the difference is still greater in the urine of an ox receiving only coarse fodder, the actuai energy being about six times that computed on the above assumption and nearly 175 per cent. of that computed after allowing for the hippuric acid present. In subsequent investigations { he finds that the energy content of the urine of cattle is much more nearly proportional to its carbon than to its nitrogen, being approximately 10 Cals. per gram of carbon. In six cases reported by Atwater & Benedict § in the course of their investigations with the respiration-calorimeter, the amount of energy found in human urine from a mixed diet as compared with that computed from the nitrogen reckoned as urea was: Total Nitrogen, x Grms. Actual, | Computed, Cals. Cals. Sx merimenh NO. ois wie teeste eitetere tclebene ee Verde 511 392 I . ey AUR VA Oued is: a wan eye eerie abt a 64.29 504 348 < OMY Gin the ORE Eh ee dees Fay at, aes 70.60 569 382 F or AVeS hd rire ete A hee at tw ter 77.90 | 658 421 sé SEO CO! Uae aw ESS Seen eee meal (alr 597 388 ae SAECO Meramec ere Regn ott eet 8 STE CTO 589 421 Here, too, it is evident that a computation on the basis of the urea yields results much below the truth, and later experiments by the same authors have fully confirmed this result. The Feces.—Our knowledge of the proximate principles con- tained in the feces is so small that no satisfactory computation of their energy content is possible, except perhaps in the case of car- nivora on a purely meat diet, where the total amount of feces is * Arch. f. (Anat. u.) Physiol., 1899, p. 261. + Landw. Vers. Stat., 47, 275. t Ibid., 53, 437. § U. S. Dept. Agr., Office of Experiment Stations, Bull. 63. METHODS OF INVESTIGATION. 243 small. On a mixed diet containing any considerable proportion of vegctable matter, and particularly in the case of herbivorous ani- mals consuming large amounts of coarse fodders, only an actual determination of the heat of combustion can be depended upon. Since the feces of these animals contain a larger proportion of the indigestible lignin, etc., than does their food, the heat of combustion of the feces is correspondingly higher, but its actual value must obviously depend to a considerable degree on the character of the food. Combustible Gases.—Since it is impracticable to collect sepa- rately the combustible intestinal gases, we must of necessity com- pute the amount of potential energy carried off in these substances. This computation has been based on the arhount of carbon con- tained in these gases, determined in the manner indicated on p. 72, upon the assumpticn that only methane (CH,) was present. It has been shown that this gas exists in considerable amounts in the digestive tract. of herbivora, and it is probable that the above assumption is substantially accurate, although a small amount. of hydrogen has been found by some observers. In experiments by Fries,* at the Pennsylvania Experiment Station, in which both the carbon and hydrogen of the combustible gases excreted by a steer consuming chiefly timothy hay were determined, the follow- ing ratios of hydrogen to carbon were obtained: Period A. First day, 132.900 Second day, 1:22916 Period B. First day, 1:2.978 Second day, 1:2.947 Period C. First day, 1:2.899' Second day, 22-95) Period D. First day, 1:3.051 Second day, 1:3.096 Average, 132964 Computed for CH,, 1:2.976 * Proc. Soc. Prom. Ag. Sci., 1902. 244 PRINCIPLES OF ANIMAL NUTRITION. These results tend strongly to substantiate the belief that the combustible gases practically consist of methane only. Perspiration.—In view of the relatively minute amounts of organic matter contained in the perspiration it has generally been regarded as a negligible quantity. The data given on p. 48 for the nitrogen of the sensible perspiration would afford some approxi- mate data for computing the amount of energy contained in it. The Energy of Tissue Gained.—The amount of potential energy stored up in a gain of tissue, or the amount liberated in the kinetic form in case the gain is negative, cannot, of course, be made the subject of a direct determination. The amounts of protein and of fat gained or lost can, however, be determined by the methods described in Chapter III, and their energy content computed from average figures. The errors involved are those incident to the method of computation from the carbon and nitrogen balance, which have already been considered in the chapter cited, and those arising from uncertainty as to the exact energy content of the material gained by the body. PROTEIN.—Just as computations of the gain or loss of protein by the body have been based upon the average composition of the proteids, so computations of its energy content have been based upon the average heat of combustion of these substanees. The compilation by Atwater on pp. 237-9 contains the available data up to 1894. For approximate computations the value 5.7 Cals. per gram has been commonly used, while in more exact computations it has been assumed that the gain of protein by the animal has substan- tially the heat value as well as the chemical composition of fat-free muscular tissue (see p. 63), and the average of Stohmann’s two determinations, viz., 5.652 Cals. per gram, has been employed. Kxohler’s investigation * of the composition of fat and ash-free muscular tissue (p. 64) included determinations of the heats of combustion which are reproduced on the opposite page. Fat.—Rubner, in his computations, employs the round number 9.4 Cals. per gram for fat, while Kellner uses the value 9.5 Cals. Benedict & Osterberg,t whose determinations of the composition of * Zeit. physiol. Chem., 31, 479. t+ Amer. Jour. Physiol., 4, 69, METHODS OF INVESTIGATION. 245 No. of Heat of Combus- Samples. tion per Gram, Cals. (CHIR A ear oe Sits Sb OIE HO OIE Oo AO RZ tes aie 4 5.6776 SS HULECETO epee ot = eet) NNEC ACO" gS See Rear eee ae 2 5.6387 SONU Cael PMMA Patercieee) scare seat ice ocular eof ss Dy 5.6758 HOTS Mea Oe PSOE RERR other cheats, hol oars ind ahgiovons eveions ates eo 5.5990* TRA SIONS eS ans cid GORGE NGL eet cars, eons eee 2 5.6166 7 5.6173 human fat are given on p. 61, found for the heat of combustion of the same twelve samples values ranging from 9.474 Cals. to 9.561 ‘Cals. per gram, the average being 9.523 Cals. Other results are noted in the table on pp. 237-9. Determination of Kinetic Energy. Mechanical Work.—The energy of the mechanical work done by the animal upon its surroundings is derived, as was seen in Part I, immediately from body materials and mediately from the food, and is one of the two forms in which kinetic energy leaves the body. The energy of the mechanical work done by the animal may be measured in various ways, the consideration of which belongs to the domain of mechanics and lies outside the scope of the present work. In general two classes of appliances have been used: First, dynamometers proper, in which the work is expended in overcoming a known resistance, produced either by friction or by a magnetic field, the work done being measured by the tension of a spring or by the amount of electric energy produced. Second, the tread power, in which the work, aside from that of locomotion, consists in lifting the body vertically and is propor- tional to the product of the mass of the body into the distance through which it is raised. Heat.—The second form in which kinetic energy leaves the body is heat. In an animal doing no work all the energy arising from the metabolism in the body ultimately takes this form, and even when mechanical work is done the larger share of the outgo of kinetic energy consists of heat. Part of this heat is imparted to the surroundings of the animal by conduction and radiation and a * Contained an average of 3.65 per cent. glycogen. 246 PRINCIPLES OF ANIMAL NUTRITION. part is expended in the evaporation of water from skin and lungs and takes the form of the latent heat of water vapor. ANIMAL CALORIMETERS.—The direct determination of the heat produced by an animal, especially a large animal, is not an easy task. It requires in the first place a calorimeter large enough to contain the animal and in the second place, for experiments of any length, the maintenance of a sufficient ventilating current of air under such conditions as shall not affect the accuracy of the calori- metric determination, while the latent heat of the water vapor carried out in the air-current must also be taken account of. In other words, such an apparatus must be at once a respiration appa- ratus and a calorimeter, and hence the name respiration-calorimeter has come to be applied to it. Various forms of animal calorimeters have been devised, some of which may be briefly mentioned. Lavoisier & Laplace,* in their investigations upon the origin of animal heat, employed an ice-calorimeter, in which the heat is measured by the amount of ice melted. Crawford {+ investigated the same subject using a water-calorimeter, as did, later, Dulong f and Despretz,§ while more recently Wood,| and still later Reichert,{ have also employed the water-calorimeter. The ice-calorimeter, however, necessarily subjects the animal to an abnormally low temperature, while with the water-calorim- eter it has been found very difficult to secure a uniform heating of the different strata of water. These facts led to the employment of air as the calorimetric substance, the heat being measured either by the increase in the volume of a confined body of air at a constant pressure or the increase in the pressure at constant volume, and until quite recently the most exact methods have been based on this principle. Scharling,** Vogel,t} and Hirn,{{ between 1849 and 1864, used * Hist. Acad. Roy. d. Sc., 1780, 355. + Experiments and Observations on Animal Heat. London, 1788. ~ Ann. de Chim. et de Phys. (3), 1, 440. § Ibid., (2), 26, 337. || Smithsonian Contributions, 1880. 4 Univ. Med. Mag., Phila., 2, 178. ** Jour. pr. Chem., 48, 435. +t Arch. d. Ver. f. Wiss. Heilk., 1864, p. 442. tt Recherches sur l’équivalent méchanique de la chaleur. Paris, 1858. METHODS OF INVESTIGATION. 247 crude forms of the air-calorimeter. In 1885 Richet * described an air-calorimeter for small animals, the heat being measured by the increase in the volume of a confined portion of air at constant press- ure. His experiments were of short duration (1 to 14 hours) and no specific statement is made regarding ventilation and no mention of any determinations of the latent heat of the water vapor. _ In 1886 d’Arsonval + described a differential air-calorimeter, and in 1890 ¢{ two other forms of animal calorimeter, the first being a water-calorimeter of constant temperature with automatic regu- lation of the flow of water, for which a high degree of accuracy is claimed, and the second an air-calorimeter, but he reports no ex- periments with either form. In the same year Laulanié § (see p. 70) described briefly a Regnault respiration apparatus which was also used as a calorimeter, and has subsequently reported some resuits obtained by its use. One of the best known forms of animal calorimeter is that of Rubner.|| This is essentially a Pettenkofer respiration apparatus, the walls of the chamber being double and the whole surrounded by an air space which in its turn is surrounded by a jacket con- taining water kept at a constant temperature. The amount of heat given off to the calorimeter is measured by the expansion under constant pressure of the confined volume of air between the two walls of the respiration chamber, while from comparative de- terminations of moisture in the ingoing and outcoming air the heat removed in the latent form is computed. Rosenthal 4 has constructed a somewhat similar instrument in which the respiratory portion is a Regnault apparatus, while the heat is measured by the increase in pressure of the air at constant volume, instead of by the increase in its volume as in Rubner’s apparatus. Both instruments are therefore air-calorimeters, and the numerical values of their readings must be determined experimen- tally for each instrument. These two forms of apparatus are of a size sufficient for experiments with small animals (rabbits or small dogs). * Archives de Physiol , 1885, II, 237. 7 Jour. de ]’Anat. et Physiol., 1886. t Archives de Physiol., 1890, pp. 610 and 781. § Ibid., p. 571. || Calormetrische Methodik, Marburg, 1891; Zeit. f. Biol., 30, 91. q Arch. f. (Anat. u.) Physiol., 1894, p. 223. 248 PRINCIPLES OF ANIMAL NUTRITION. In 1894 Haldane, White & Washbourne * described a form of air- calorimeter in which the expansion caused by the heat produced by the animal in one chamber is balanced by that. produced by a flame of hydrogen burning in a‘second similar chamber. The calorimeter is essentially one of constant volume, but the heat is computed from the amount of hydrogen burned. Laulanié + in 1895 described a Pettenkofer apparatus with small _ventilation (see p. 71) which served also as an air-calorimeter, and still later { has described a differential water-calorimeter. Kauf- -mann,§ as mentioned on p. 69, has determined the respiratory -exchange of animals during short periods in a confined volume of air. The apparatus consisted simply of a zine receptacle which served also as a radiation calorimeter. The internal temperature and that of the surrounding air were measured by recording ther- mometers and the loss of heat calculated according to Newton’s law. The atmosphere in the apparatus was saturated with water- vapor at the start, so that the moisture excreted by the animal was condensed and no correction for the heat of vaporization was neces- sary. By far the most important form of respiration-calorimeter yet devised, however, not only as regards accuracy but particularly in view of the range of work of which it is capable, is that of Atwater & Rosa,|| the respiratory part of which has already been mentioned (pp. 72 and 79). In this apparatus water is used as the calori- metric substance, but in the form of a constant current instead of a large stationary mass. As described by the authors the appara- tus consists of a Pettenkofer respiration apparatus provided with special devices for the accurate measurement, Sampling, and analy- sis of the air-current. A current of cold water is led through copper- absorbing pipes near the top of the respiration chamber and takes up the heat given off by the subject. The volume of the water used being measured, and its temperature when entering and leaving being taken at frequent intervals, the amount of heat brought out * Jour. Physiol., 16, 123. 5s + Archives de Physiol., 1895, p. 619. t Ibid., 1898, pp. 538 and 613. § Ibid., 1896, p. 329. | U. S. Dept. Agr., office of Experiment Stations, Bulletins 63 and 69, METHODS OF INVESTIGATION. 249 in the water-current is readily calculated. To this is added the latent heat of the water-vapor brought out in the ventilating air- current. By means of ingenious electrical devices, a description of which would occupy too much space here, the temperature of the interior of the apparatus is kept constant, and any loss of heat by radiation through the walls or in the air-current is prevented. In test experiments the apparatus has given extremely accurate re- sults. An especial advantage of this apparatus is that it is practicable to make it of large size, and also to continue the experiments for an indefinite length of time. The original apparatus was of a size sufficient for experiments on man, while all previous forms were restricted to experiments on small animals. Recently a modified Atwater-Rosa apparatus has been completed under the writer’s direction at the Pennsylvania Experiment Station, with the co- operation of the Bureau of Animal Industry of the United States Department of Agriculture, of a size sufficient for investigations with cattle, and still larger ones are in process of construction. Computation oF Hrat Propuctrion.—The respiration-calorim- eter, in its more perfected forms, is a camplicated and costly appara- tus both in construction and use, and, moreover, is a rather recent development. It was natural, therefore, that attempts should be made to determine the heat production indirectly by computations based on the kind and amount of matter oxidized in the body. We may conveniently distinguish three distinet although closely related methods of attacking the problem, all of which assume as a fundamental postulate that the oxidation of a given substance in the body liberates the same amount of energy as does its oxidation outside the organism. In the next chapter we shall examine into the correctness of this postulate; for the present we are con- cerned simply with the methods of computation based on it. Computation from Gaseous Exchange.—From a knowledge of the ultimate composition and heat of combustion of a substance it is easy to compute the amount of heat which will be produced by the oxidation of an amount of it sufficient to yield a unit of carbon dioxide or to consume a unit of oxygen. Conversely, then, we can compute from the carbon dioxide evolved or the oxygen consumed in a given time the corresponding amount of energy liberated. 250 PRINCIPLES OF ANIMAL NUTRITION. Such computations have been made by different authors for the three principal classes of nutrients, viz., the proteids, carbohydrates, and fats, the results of a few of which are as follows: eee Zuntz.t | Kaufmann. | Laulanié.§ Per. Per || Per* |) Per. | Per |). Per |) Pers) sPer Liter | Liter | Liter ; Liter | Liter | Liter | Liter | Liter Oy |. GOs |) OF | COgel 205 COs eae Cals. | Cals. | Cals. | Cals. | Cals. | Cals. | Cals. Cals. Protelds)|liesn< che eae eae 5.464/4.289/5 .644/4.476 5.569|/4.647 ..... 4.6 at aw ie ees arene orate 6 .586/4 .676)\6.628/4.686 6.648/4.650 6.571/4.6 Dextrose: 62/00. heweoca A OUSIALONG! sed tian 5.056|5.056 bareh ete hers eas 3 Br 4.976/4.976)|5.047/5.047 Wane-surare Rie se eel 5.090'5.090 “Carbobydratens:. so oh I BNIB aD) (0) iL Bt rein dhs tate ae yuahed weal) +182) 2067} 2079) + 12/+0.6 POUL we |. bancie tue a ee +3525) 47387] 47552) +165 +0.35 Work Experiments : ROR MO Rate SEB aah. coats as —415) 3829) 3726; —103)/—2.7 | 250 FL ALE SR ne 18 78 Ae oan —391; 3901) 3932) + 31/+0.8 186 Epes ee ee eee e yee eas aid hese —308) 3922; 3927) + 5)+0.1 | 200 Te ee pact eee NTN Re re —255| 3515) 3589} + 74/4+2.1 255 aS | 8 SPR A Ae re Rn caer —234| 3479) 3470) — 9!—0.3 249 “LP -T Se eaemieengtle: ON « BAR yr —164| 3439 ae — 19)/—0.6 249 os een ie SARS a he Se ghee Tm —347| § 3573) 3565, — 8/—0.2 196 as ai eae Stay | eae —451| 3669) 3632) — 37/—1.0 197 he a aT A —388) 3629) 3487] —142)—1.2 | 250 BE GtAE oC oaievortcis ch nee, cme —2953| 32956] 32748] —208|/—0.63 2032 Totals, rest and work.......... + 572) 80343} 80300} — 43)—0.05 —— 268 PRINCIPLES OF ANIMAL NUTRITION. In the former case the observed heat production includes the heat into which the work was converted. The total of all the experiments shows an almost absolute agree- ment between the computed and the observed results. To a trifling extent, however, this arises from a compensation between the rest and work experiments, the computed heat tending to be slightly too small in the former and slightly too great in the latter, but the agreement in each series is so close as to amount to a demonstra- tion of the applicability of the law of the conservation of energy to the metabolism of the animal organism. CHAPTER X. THE FOOD AS A SOURCE OF ENERGY—METABOLIZABLE ENERGY. Wirn the establishment of the law of the conservation of energy in its application to the animal body, and with the development of the methods of calorimetric research briefly out- lined in Chapter VIII, it has become possible to study success- fully the problems of animal nutrition from a new standpoint, re- garding the food as primarily a source of energy to the body and tracing, to some extent at least, the transformations which that energy undergoes in the organism and particularly the extent to which the latter utilizes it for various purposes. Some data regarding the total energy of foods and their constitu- ents have already been givenin Chapter VIII. It was there pointed out, however, that the total energy, taken by itself, does not fur- nish a measure of the nutritive value of a substance. It is now necessary to enter upon the question of the availability of this energy to the organism. ToTaL AND METABOLIZABLE Enrrcy.—The heat of combustion of the food represents to us its total store of potential energy. By no means all of this potential energy, however, is accessible to the organism. cy oc, Seer > 8.447 “ ti Cis GR e'9 a SE RR 8.020 4)" vs | (sh RM Ay ores. ose LEO.) The same authors report ¢ the average of 46 determinations as 7.9 Cals. per gram of nitrogen. Tangl { has reported materially higher figures, especially for diets containing large amounts of carbohydrates and fat. In the case of a mixed diet more or less of the potential energy of the feces may be derived from the non-nitrogenous nutrients of the food, and we should hardly be justified in making for these experiments a computation like that made for the meat diet. The rather small range of the figures in most cases, however, would seem to show that the metabolizable energy of the proteids of ordi- nary mixed dietaries is substantially the same as that found by Rubner for carnivora. Tangl’s results perhaps suggest the possi- bility of the occasional presence in human urine of non-nitrogenous matters similar to those found so abundantly in that of ruminants. RuBNeEr’s ComputTations.—Rubner’s earlier researches did not include experiments upon man, but from the results given in the foregoing section he endeavored to compute approximate factors for the metabolizable energy of the mixed diet of man.§ For this purpose he estimates that, on the average, 60 per cent. of the pro- tein of the diet is derived from animal sources and 40 per cent. from vegetable. Jor the animal protein he uses the value found above for lean meat, and for vegetable protein the average of the values for syntonin and fibrin (since these have an ultimate composition * U.S. Dept. Agr., Office of Experiment Stations, Bull. 69, + Report Storrs Expt. Station, 1899, p. 100. t Arch. f. (Anat. u.) Physiol., 1899, 261. § Loc. cit., p. 370. THE FCOD AS A SOURCE OF ENERGY. 279 similar to that of the proteids of the grains). Correcting these values for the error involved in the usual computation of protein from nitrogen, he obtains as the average metabolizable energy of the protein (N X 6.25) of a mixed diet 4.1 Cals. per gram. For the fat and carbohydrates it is assumed that all their poten- tial energy is metabolizable, but an allowance is made in the latter case for the error due to the ordinary computation of the carbo- hydrates by difference and for some minor sources of uncertainty. Rubner’s final averages are— Protein (NX6.25)......... 4.1 Cals. per gram. BED ie eieste easiest Peay aa is by Oi TELLS he vet Carbohydrates: .°2)052..:0% AVE sees arena Ge The value for protein, by the method of computation, includes an allowance for the metabolic products contained in the feces, but neither it nor the values for the other nutrients include any estimate for the loss through imperfect digestion. In other words, they refer to the digested nutrients. These figures were designed expressly for computing the metab- olizable energy of human dietaries, and even for that purpose are confessedly only approximations. In the absence of more exac, figures, however, they have been somewhat extensively used for computing the metabolizable energy of the digested portion of the food of domestic animals. For purposes of approximate estimates such a use of them was perhaps justifiable, but in too many cases their origin seems to have been forgotten and a degree of accuracy ascribed to them which they do not possess. As will be shown presently, later investigations have yielded materially different results for the metabolizable energy of the several classes of nutri- ents in the fuod of herbivorous animals. Later Experiments.—Quite recently Rubner * has published the results of some experimental investigations into the validity of the averages or “standard figures” given above. In these experiments the weights and heats of combustion of food, feces, and urine were determined calorimetrically and the metabolizable energy as ob- tained from these data was compared with that computed by the use of the above factors. In making the latter calculation an allowance + Zeit. f. Biol., 42, 261. / 280 PRINCIPLES OF ANIMAL NUTRITION. was made for the percentage loss in the feces equal to that observed in the actual experiment. The results for the metabolizable energy per day were— Cc oe i Cc d : t ted, Diet. oe "Cals. Cals. Potatoes only 255). 212 i.t.caie cele vepecdme ts ena Oe 1911.4 1911.5 Rive‘bread: bolted Hours... 22 ees o.oo 2060.4 2079.3 ok Sunbalted hors cles ter sere al 1773.1 1758.6 Mixed diet, poor in:fab sic. icer «cic ce ee Meise 2400.5 2376.0 Peg Ge, ARO a pale ave Wes ere nae ee one 2698 .8 2600.0 ‘ ‘ ‘ ‘ , I 2574.1 2608 .0 («4 « # and carbohyd’s }t7] 3519°6 2610.0 Mixed diet—growing boys............ i = ie sets As above noted, the computed results include a deduction for the energy of the undigested matter in the feces. Rubner finds that the heat of combustion of the organic matter of the latter varies but little even on extremes of diet, so that the loss through this channel is approximately proportional to the amount of the ex- cretion. In the experiments on mixed diet the percentage loss of energy in the feces varied from 4.3 per cent. to 7.9 per cent. of the energy of the food. ATWATER’S INVESTIGATIONS.—By far the most extensive data as to the metabolizable energy of human foods and dietaries are those derived from the investigations upon human nutrition made under Atwater’s direction by the United States Department of Agriculture with the coédperation of Wesleyan University, the Storrs Experiment Station, and various other experiment. sta- tions. Atwater & Bryant* have summarized these results in a preliminary report of which the essential features are given in the following paragraphs. From the best data available, the heats of combustion of the protein, carbohydrates, and fats of various classes of foods are esti- mated. In these estimates account is taken as fully as possible of the proportion of nitrogen in proteid and non-proteid forms, and of the varying percentage of nitrogen in different proteids, the nitro- gen factors used being those quoted on p. 6. The accuracy of * Report Storrs Agr. Expt Station, 1899, p. 73. THE FOOD: AS, AS SOURCE, OF “ENERGY. 281 these estimates is checked by a comparison of the computed with the actual heats of combustion of 276 different samples of food, the average results showing a close agreement. Assuming the potential - energy of the urine to be all derived from the proteids, the average of 7.9 Cals. per gram nitrogen given above (p. 278) corresponds to 1.25 Cals. per gram of protein (N X6.25) metabolized. The loss of energy in the feces is estimated from a number of digestion experi- ments upon single foods, the results being checked by a comparison of the actual and computed apparent digestibility in 93 digestion experiments on mixed diet. Finally, the proportions of the several nutrients which are derived from different classes of foods in average mixed diets are computed from the results of 185 dietary studies. The final results thus obtained for the metabolizable energy or “fuel value” of the nutrients are shown in the table on page 282. The average results for the ordinary mixed diet of man were— PFOUEIe ceiie te sores else aces 420Cals pereram (Gambolydinahesse se sila Vpn tbe ZNO PIN a ge 7 ATE g ues Nate te ate aes chs ae ble ected. oy fry thy eeu hE These factors are smaller than those proposed by Rubner, largely because they relate to the total and not to the digested nutrients. Comparisons of the computed with the actual metabolizable energy of mixed dietaries, using the factors of the above table, gave con- cordant results. § 3. Experiments on Herbivora. THE M6ckERN INvesticatTions.—The larger share of our present knowledge regarding the metabolizable energy of the food of her- bivora is due to the investigations upon mature cattle which have been made by Kellner * since 1894 at the Méckern Experiment Station. In the earlier series of experiments (including those by G. Kithn, reported by Kellner +) additions of commercial wheat gluten and of starch were made to a basal ration consisting exclu- sively of coarse fodder (hay or straw). In the later series of ex- periments additions of the same substances and of oil and beet molasses on the one hand, and of coarse fodders on the other hand, were made to a mixed basal ration. * Landw. Vers. Stat., 47, 275; 50, 245; 58, 1. t Ibid., 44, 257. 282 PRINCIPLES OF ANIMAL NUTRITION. Nutrients a aor Total Fuel Value. Kind of Food “ oo ae ee of | Tot a mgecd d t Material. peur wae aed iticerche fi Avail Per Grm. P Tr eo 100 Grms. Grm. enced able Nu- rr Sette Total. | abic: trients. utrients. pbs es Protein: | Grms. Cals. |Per Cent.| Cals. Cals. Cals. Meats, fish, ete ...| 438.0 5.65 97 5.50 4.40 4.25 dN ora: er ety WAR xe 6.0 thay A) 97 5.60 | 4.50 4.35 Dairy products ...; 12.0 5.65 97 5.50 4.40 4.25 Animal food....| 61.0 5.65 | 97 | 5.50 | 4.40 | 4.25 Gereals Sagi hea ee 3 31.0 5.80 | 85 4.95 4.55 3.70 Gerumes... <\. See: 2.0 O20 78 4.45 4.45 3.20 Vegetables ....... 5.5 5.00 83 4.15 3.75 2.90 NS eeacek Choon O25 5.20 85 4.40 3.95 pels Vegetable food .| 39.0 5.65 85 4.80 4.40 3.55 Rotalerood .o.e)<5 100.0 5.65 92 5.20 4.40 4.00 Fat : Meat and eggs....} 60.0 9.50 95 9.00 9.50 9.00 Dairy products ...| 32.0 9.25 95 8.80 9.25 8.80 Animal food....| 92.0 9.40 95 8.95 9.40 8.95 Vegetable food . 8.0 9.30 90 Seon iP eoeoO 8.35 Total-tacds..ee 100.0 9.40 95 8.90 9.40 8.90 Carbohydrotes : Animal food.... 5.0 3.90 98 3.80 3.90 3.80 Gerealses 2. sinh. 55.0 4.20 98 4.10 4.20 4.10 Ibemumies scores. cil) oh BO 4.20 97 4.05 4.20 4.05 Vegetables .......} 13.0 4.20 95 4.00 4.20 4.00 5 EPULGSs Aen te yee ters 5.0 4.00 90 3.60 4.00 3.60 DHIBARS es, nike els 21.0 3.95 98 3.85 | 3.95 3.85 Vegetable food .| 95.0 4.15 97 4.00 4.15 4.00 Total foods < ... | 100.0 4.15 97 4.00 4.15 4.00 | \ In each experiment the digestibility of the ration was deter- mined in the usual manner, and also the carbon of food, feces, urine, and respiration (including methane, etc.), and the nitrogen and heats of combustion. of food, feces, and urine. The experiments were made with every precaution and extended over a sufficient length of time to ensure normal results. In each experiment the respiratory products were determined in four or five separate periods of twenty-four hours each. No such complete experiments with THE FOOD AS A SOURCE OF ENERGY. 283 other classes of herbivorous animals have been reported, although partial data are available from experiments on horses and swine. MetHop oF Statinc Resuits.—The determination of the metabolizable energy of a given ration by experiments like the above is, in principle, very simple, although requirmg many appli- ances and much technical skill. When, however, we attempt to generalize the results much greater difficulties are encountered than in the cases previously considered. In investigations upon carnivora and upon man the metaboliz- able energy, as we have just seen, is usually computed upon the total nutrients of the food—that is, upon the total amounts of protein, carbohydrates, and fat—the deduction for the loss of energy in the feces being included in the factors employed. This is possible because the amount of potential energy thus removed is small in itself and subject to relatively small variations on ordi- nary diet and also because the crude nutrients composing the food are largely chemical compounds which are at least fairly well known. The food of herbivora, on the contrary, is both more complex and less well known chemically and contains a much larger and very varying proportion of indigestible matter. As a consequence the feces, instead of being chiefly an excretory product, consist mainly of undigested food residues with but a small proportion of meta- bolic products, and contain a large and variable part of the total potential energy of the food. For all these reasons it seems likely that any attempt to compute general factors for the metab- olizable energy of the crude nutrients of feeding-stuffs similar to those of Rubner or Atwater for the nutrients of human foods would be confronted by almost insuperable difficulties. It was natural, then, to attempt to eliminate these difficulties by computing the results upon the digestible nutrients of the feed- ing-stuffs, but even here considerable difficulties arise. The di- gested nutrients, particularly in the case of coarse fodders, are far from being the pure protein, carbohydrates, and fats which our ordinary statements of compdsition and digestibility assume them to be. Furthermore, a considerable and a variable proportion of the waste of proteid metabolism in the herbivora takes the form of hippuric acid, a body less completely oxidized than urea, and ac- 284 PRINCIPLES OF ANIMAL NUTRITION. cordingly containing more potential energy, while the urine of sheep and cattle also contains not a little non-nitrogenous matter of some sort. Finally, the slow and complicated process of diges- tion in the herbivora is accompanied by fermentations and the evolution of gaseous hydrocarbons (methane), and perhaps of hydrogen, both of which carry off a more or less variable propor- tion of the potential energy of the food. By means of experiments with approximately pure nutrients it is possible td secure factors for the metabolizable energy of the digested nutrients of con- centrated feeding-stuffs, but in the case of coarse fodders about all that is practicable in this direction is to compute the results of experiments upon the total digestible matter. There is possible, however, a third method, viz., to compute the metabolizable energy upon the total organic matter of the feeding- stuff, expressing it either as Calories per gram or pound of organic matter or as a percentage of the gross energy. In the latter form the result would be analogous to a digestion coefficient and would show what proportion of the total energy of the material, as: deter- mined by combustion in the calorimeter, was capable of being met- abolized in the body. This method of expressing the results has certain advantages in directness and simplicity, and especially in putting the whole matter on the basis of energy values. In the sueceeding paragraphs the available data will be considered from both the standpoints last named. METABOLIZABLE ENERGY OF ORGANIC MATTER. For a discussion of the matter from this standpoint we have to rely almost entirely upon the Méckern investigations already men- tioned.* In the case of those earlier experiments in which the ration consisted exclusively of a single coarse fodder the computation of the metabolizable energy of the latter is, of course, readily made. In the experiments in which the food under investigation was added to a basal ration the computation is somewhat less simple. The details of both methods will be best explained by illustration. * For later results on timothy hay, clover hay, maize meal, broom corn, and oats, see Armsby & Fries: U.S. Dept. of Agriculture, Bureau of Animal Industry, Bulletins 51 and 74; and Tangl: Landw. Jahrb., 34, 1. THE FOOD AS A SOURCE OF ENERGY. 285 Total Organic Matter. Coarse Fodders. FED ALtone.—For Ox H, fed exclusively on meadow hay, Kellner obtained the following results * per day and head: Ingesta. 7,263} grams meadow hay......... 32,177.3 Cals. Excreta. 2,547 + grams feces....... 11,750.3 Cals. 13,675 me Te: aera, onda. Oi) ke isso re metwane ne 2a eS Guaexcretatiy peat coins oN Pos 15,809.00 POU TEMES ree era Paeh shale, Nettie he aden aie 16,368.3 “ Had the ration exactly sufficed for the maintenance of the ani- mal, the difference of 16,368.3 Cals. would represent exactly its metabolizable energy. In reality, however, the nitrogen and car- bon balance indicated a gain by the animal of 37.2 grams of protein (N X6.00 {) and 140.8 grams of fat, equivalent to 1548.8 Cals., so that the amount of energy actually converted into the kinetic form was 16,368.3 — 1548.8 =14,819.5 Cals. The potential energy of the 140.8 grams of fat, however, while it was not actually rendered kinetic, might have been had the needs of the organism required it. Its retention in the potential form was, in a sense, temporary and accidental, and its energy should properly be considered as a part of the metabolizable energy of the food. With the gain of protein, however, the case is different. Its total potential energy equals 211.2 Cals., but not all of this is capable of conversion into kinetic energy. According to Rubner’s results (p. 275) each gram of urinary nitrogen derived from the met- abolism of the protein of lean meat corresponds to 7.45 Cals. If this result is applicable to the forms of protein consumed by her- bivora (and we shall see later that there is good reason to believe that such is approximately the case), then the metabolism of the 37.2 grams of protein gained would have added 46.2 Cals. to the observed potential energy of the urine, while the remaining 165 Cals. would have taken the kinetic form and should, therefore, be regarded as part of the metabolizable energy of the food. * Toc. cit., 58, 9. + Dry matter. t{ Compare pp. 67, 68. 256 PRINCIPLES OF ANIMAL NUTRITION. In other words, to get at the actual metabolizable energy of the ration in this experiment we must add to the observed potential energy of the urine the amount of 46.2 Cals. by which it would have been increased had all the protein of the food been metabolized, or, what is the same thing, must subtract this amount.from the ob- served difference between food and excreta., This leaves 16,322.1 Cals. as the metabolizable energy of 7263 grams of dry matter or 6750 grams of organic matter in meadow hay, and the metabolizable energy per gram of organic matter is therefore 2.418 Cals. Computed in the above manner, the several experiments of this category gave per day and head the following results: | di : Metabolizable 2 Energy of Energy. 5 —— Ani a Per mal. Ration. ag . Grm. Hs Urine | Meth- O o<5| Food, | Feces. | (Cor- |*, 71, | Total, sf ‘A Cals. Cals. | rected). Cals Cals. ae s Cals a | Mat- 50 ; ter, ‘@) | Cals. ae a ae a a AG PVC ACL OWA dnc sierra) ete 6750)32177 .3)11750.3)1991 .2 2113.7,16322.1 2.418 Ii Ms pT EIR et cee ..|7816/36975.1/15524.1)1925 .7*|/3137 .2)16288.1 2.097 V va WES eae eet daieaka Roe 7199)34211 .5}15312 .2)1559 .3*|2268 .5/15071.5 2.093 Vi + Teh On het raia te Stent oheys 7125/33855 .4|13765 .2|1737 .9*/2480 .6/15871.7/2.228 XX N gph Oe a ier ae? 7809 /37167 .3'13880 .7 3224.6 '2646.1|/17415.9,2.230 I - a) HCA, Roe Sn rR 6815)32252 .2|14669 .0'1686.9 |2092.3)13804.0 2.026 A VETS 20st needa e A Sechelt ipa ech] eR ba (areas eee |: eae B | Meadow hay and oat straw... 7107|33794.4/14576 .1)1440.3 (|2331.2)15446.8)/2.173 lil Clover ; _ . . |7328|34603 . 2 15505 .1)1549.6* 2670. 1 14878.4 2.031 IV -) : Se “,. .|/7074|33405 .1)15250. 6)1481 .o* 2491 io iach .7\2.004 * Energy of urine computed from its carbon content. It should be noted that the figures for the energy of the feces in these and in all the succeeding experiments include that of the met- abolie products contained in them. While the latter are not derived directly from the food they are a part of the expenditure made by the body in the digestion of the food, and there is, therefore, the same reason for ineluding their energy as for including that of the organic matter of the urine. Both contain a eertain amount of potential energy, derived ultimately from the food, which has escaped being metabolized in THE FOOD AS A SOURCE OF ENERGY. 287 the body and so is to be deducted from the total energy of the food to obtain its metabolizable energy. ' Experiments on timothy hay made by the writer,* in which the amount of methane exereted was estimated from the amount of non- nitrogenous nutrients digested, gave the following results, the cor- rection for the gain or loss of nitrogen being computed in a slightly different way from that expiained above: ENERGY PER GRAM ORGANIC MATTER. Experiment I. Experiment II. |Experiment VI. Cals Cals. Cals. ASUCECE) ev DS ity eR Nari Aes 8 Me ar 2.104 1.8388 2.139 BO pS) A bk AES LaLa Feeds irae © NAR 2.007 2.164 2 olino Re eee: Mey AMS pens wth eek ates ce 1.904 1.824 2. LY6 PNVETAD CR eet mee rarererageh. ee tye 2.005 1,.942 Res Bwerce Of alee. by. «ees 2.037 It should be noted that the above figures are, as already stated, approximate only. The energy of the methane was estimated, while the determinations of the energy of the urine were not, in all cases, satisfactory. We are probably Justified, however, in regarding the results as a close approximation to the truth. Coarse FoppErs Apprep To BASAL Ratrion.—As an example of this ‘class of experiments we may take Periods 4 and 7 with Ox H.+ The rations in the two periods were as follows: Total Weight. Containing Organic Matter. Period 4, | Period 7, | Period 4, | Period 7, | Difference, Kgs. I Ses. Grms. Grms. Grms. Meadow hay RR Soames Whee ahs 4 8 3198 6495 3297 Molasses-beet pulp ........ 3 3 2386 2413 27 Pedmub, Mealy isk etielee ea 1 1 818 | 835 17 8 \P2 6402 9743 3341 * Penna State Experiment Station, Bull 42, p. 153. t Loc cit., 58, 278-335. 288 PRINCIPLES OF ANIMAL NUTRITION. The potential energy of food and excreta (that of the urine cor- rected to nitrogen equilibrium) and by difference the amounts of metabolizable energy were: Urine Metaboliz- Food, F : Met! . . cant. | Teg | Corresteay,| Methane | able Energy. IPETIOdG7 sece kee 46,275.0 | 14,104.8 2,593.0 3,564.2 | 26,013.0 See A a eee 30,338. 1 8,574.9 1,795.0 2,579.4 | 17,388.8 Difference ....| 15,936.9 5,529 .9 798.0 984.8 8,624 .2 The metabolizable energy of the additional 3341 grams of or- ganic matter eaten in Period 7 was therefore 8624.2 Cals. This added food was intended to consist of hay, but the unavoidable variations in the moisture content of the feeding-stuffs resulted in a slightly greater consumption of the other ingredients of the ration also. Of the 3341 grams of additional organic matter, 3297 grams, as the previous table shows, were from the hay and 44 grams from the basal ration. If, then, we would ascertain the metabolizable- energy of the added hay only, we must subtract from the difference of 8624.2 Cals. between the two rations the metabolizable energy of this 44 grams of organic matter from the other feeding-stuffs. But while the gross energy of the latter is known, its metabo- lizable energy cannot be computed exactly, since it is impossible to determine what part of the energy of the excreta was derived from this particular portion of the ration. By assuming, however, that the same percentage of its gross energy was metabolizable as was the case with the basal ration, and that its non-metabolizable energy was similarly distributed between the various excreta, we may compute a correction which, although not strictly accurate, will not, in view of the small quantities involved, introduce any serious error. In this case the gross energy of the 3297 grams of organic matter in the added hay was 15,728.6 Cals., and the table takes the form shown on the opposite page. As thus computed, the metabolizable energy of the 3297 grams of organic matter added to the basal ration in the form of hay was 8504.8 Cals., equal to 2.580 Cals. per gram. The total correction amounts to 119.4 Cals., and even a considerable relative error in it would not materially change the final results. . THE FOOD AS A SOURCE OF ENERGY. 289 Uri Metaboliz- aoe: Becks, (Gomecred), eae able Hoey : | Cals. oH Cals. jetvalore h7/ lan 8 seer 46,275.0 | 14,104.8 | 2,593 .0 3,064.2 | 26,013.0 $e Arcata tia 30,338 .1 8,574.9 1,795.0 2,579.4 | 17,388.8 Difference....| 15,936.9 5,529 .9 798 .0 984.8 8,624.2 Correction ....| —208.3 —58.9 1171.3} —17.7 —119.4 15,728 .6 5,471.0 785.7 967.1 8,504.8 Percentages... 100.0 34.78 5.00 6.15 54.07 In these computations it is assumed that the increased metabo- lizable energy of the ration is derived entirely from the added feed- ing-stuff, or, in other words, that the latter exerted no influence either upon the digestibility of the basal ration or upon the propor- tion of its energy lost in urine and in hydrocarbons. That such is the case we have no means of proving, and it is, indeed, unlikely that it is exactly true. The metabolizable energy of the added feeding-stuff as above computed includes any such effects—that is, it represents the net result to the organism of the added coarse fodder. Table I of the Appendix contains the results of all the experi- ments of this sort, computed in the manner illustrated above. It will be noted that in all but two cases the correction is less than in the above example. In each ease the table shows also the per- centage of the gross energy of the feeding-stuff which was found to be metabolizable and the percentage carried off in each of the excreta. Summary.—The results of the foregoing determinations of the metabolizable energy of the organic matter of coarse fodders are summarized in the table on page 290, which shows the gross and inetabolizable energy per gram of organic matter and also the percentage of gross energy found to be metabolizable. Concentrated Feeding-stuffs.—The metabolizable energy of the organic matter of a concentrated feeding-stuff when added to a basal ration can, of course, be computed by the same method as in the case of added coarse fodders, but, as we shall see, some special difficulties arise in its application. The only commercial concentrated feeding-stuff upon which such experiments have been reported is beet molasses, although 290 PRINCIPLES OF ANIMAL NUTRITION. Per Gram Organic latter. Metaboliz- | Metabolts ee veble me a 5 - Cals. SRerey, pee 4.767 | 2.418 | 50.72 AID ILO dole vivian tee are co eiahs wa Mi got se : : : wh ede ena Oat Abe lols osive atchanahe (inae teheneire ares 4.731 2.097 44 .32 Reh MES CSV oc bats. einia hie Siete Be 4.7592 2.093 44.06 SPN © ae a i Tsk Ae ape GOR els a a Seas 2.228 46.88 PT A TR UV OL ARIE! s.2 Nanak eas tolern Touma = staal ficce Sa eee 2.161 45.47 Peas Me oi oc ac solely pi vat gs glade atte ekie 4.760 2.230 46.86 OE fe CE Smt ade tS Hat ob hc worms etna oie ee ae 4.734 2.026 42.80 Soh ENS LORE Nie eho a Eh aoe able a 4.743 5| 1.938 40.75 oy DTN SG IY SRE UR eee ee 2.087 | 44.00 tf) (Se AVERARO Ce. Po ay SR Sie cet i kite. Dues 2.010 | 42.38 re WG VRS ARE, MECTIOG COS 5p ptelev as oes l 2.520 52.82 Ee Ras LAAg Noe, edhe ei Se ee 4.771 2.580 54.07 Ere mre prei gia ge oe ec, Mansa tiles ) 2.540 | 53.24 Ee Wey Val VCE OWN J ts tovecets a cpert steel seat ay nM eRe eS 2.547 53.38 Average of seven samples ............ 4.751 2.213 46.56 Timothy Hay (approximate) .............. 4.670 2.037 43.62 Oat Straw : (OO abl Dees tee Sty ay Mets Sars airy rch a ain 1.760 36.54 LR CRG TRE Se Dilla) Guia ERAT ta 816 {| 16s | 35.05 WA META DCL. iz his ioy-lstsvahe clemeloravartyatesstarscche clare eet ere tees 1.724 35.80 Wheat Straw: 0) ail 5 eae oer oey 9.0 ee HBS on A aN SEs 1.411 29.75 Peete rien.) atk anc 08 butte 6g ane 4 748 | 1.540 | 32.47 AV ETAL C2. 25 3) 7 oleae ielsiers: Tale MISES SG EEN 1.475 SHES Extracted Rye Straw: Sk PARR INU MeN ATAN YT CONTIG Fa 00 Avenbvei yl Pans Ue etiaas Meals Latent es 8.213 | 75.588 experiments were also made by Kellner with wheat gluten, starch, oil, and extracted straw, the aim of which was to determine the metabolizable energy of the various digestible nutrients. As an illustration of this class of experiments we may take one upon molasses with Ox F’,* comparing Period 3, on the basal ration, * Loc. cit., 58, 172-227. THE FOOD AS A SOURCE OF ENERGY. 291 with Period 6, on the same ration with the addition of molasses. Comparing, first, the organic matter of the two rations we have the following: Total Organic Organic Matter in Matter Fed, Molasses, 2 Grms. Grms. dBevatete WG 50's Bc ears eaCeLore Cra ae 8262 1702 MeMe esti Ae a ious ot she Soh cTatee Wicia aesthetic 6630 0) 1632 1702 In the period with molasses 70 grams less of the basal ration was consumed than in the period without, and a correction must accordingly be made for this in the way explained on page 288. The energy of food and excreta in the two experiments (that of the urine being corrected to nitrogen equilibrium), together with the correction for the 70 grams of organic matter, is shown in the following table: . Metaboliz- Gee) | ovamen Cane a | cane (BRIE mnetey, als. Beriod 6.7.2.4. 37,946.2 | 11,365.8 | 1,786.1 | 2,397.9 | 22,396.4 CORRAL Tt a Bij 327.8) 9S 599i 24) 1530700) ) 2.56027. 7.63709 6,618.4 | 1,766.6 256 116 QPS ales 7585 Correction .... +330.8 +101.3 +16.2 + 27.0 +186.3 6,949.2 1,867.9 Zao —135.8 4,944.8 ‘Dividing the metabolizable energy of the molasses, 4944.8 Cals., by the number of grams consumed, 1702, gives the metabolizable energy of 1 gram of organic matter as 2.905 Cals. REAL AND APPARENT METABOLIZABLE ENERGy.—The above figures, however, demand more critical discussion. While the addi- tion of molasses to the basal ration increased the amount of poten- tial energy carried off in the feces and urine, it diminished that in the methane; that is, it acted in some way to check the fermen- tation in the digestive tract to which this gas owes its origin. In other words, under the influence of the molasses the loss of energy by fermentation of the basal ration was diminished by 135.8 Cals., and this amount, by the method of computation, is added to the metabolizable energy of the molasses. 2092 PRINCIPLES OF ANIMAL NUTRITION. Moreover, the loss of energy in the feces is a complex of sey- eral factors. The amounts of organie matter and of the several nutrients excreted in the feces in the two periods (not corrected for the 70 grams difference in organic matter consumed) were as follows: Organic | protein Crude Reragene | Crude Gens | Grme.” | Giver | wxtract, |" Guew rms. Perigd Oi tere aok sek eee 2132 403 595 1068 | 66 AIRES I Gee ae 8 to Oe 1797 284 527 924 | 62 Differences sb tok as 2: | 335 119 68 144 | 4 ‘ In addition to protein and nitrogen-free extract, which may possibly represent indigestible material in the molasses, the feces contained 68 grams more crude fiber and 4 grams more fat in Period 6 than in Period 8. These cannot have been derived from the molasses, since the latter does not contain these ingredients. This feeding-stuff, in other words, diminished the apparent digestibility of the fiber and fat of the basal ration. As a matter of fact, the ingredients of molasses being practically all soluble in water, it is probable that nearly all the difference in the amount digested is due to the diminished apparent digestibility of the basal ration under the influence of the molasses. The figure above given for the metabolizable energy includes all these effects; that is, it shows the net result as regards energy ob- tained from molasses fed under the conditions of these experiments, the nutritive ratio of the basal ration being 1 : 5.8 and that of the molasses ration 1:6.4. To get at the actual amount of energy set free from the molasses itself we should need to subtract from the metabolizable energy as calculated above the energy corresponding to the decreased excretion of methane and to add to it the metabo- lizable energy corresponding to the decrease in the amounts of crude fiber and ether extract digested, assuming that all the excess of protein and nitrogen-free extract in the feces was derived from the molasses. Computed in this way * the real metabolizable energy * One gram of crude fiber = 3.3 Cals., and one gram of ether extract = 8.3 Cals. See p. 332. THE FOOD-AS A SOURCE OF ENERGY. 293 of the organic matter is 2.977 Cals. per gram. This would be a mini- mum figure, while if we assume, as suggested above, that the mo- lasses is entirely digestible, this figure is still too low and should be increased to equal the gross energy of the organic matter. If, however, either one of these latter values were used in com- puting the metabolizable energy of rations, the results would obvi- ously be too high unless corrections were made for the effect upon the apparent digestibility of the other feeding-stuffs in the ration. The figure first computed, while including several different effects, nevertheless seems better adapted for use in actual computations under average conditions, while the second gives the more accurate idea of the store of metabolizable energy contained in the feeding- stuff regarded by itself. The distinction is analogous to that between apparent and real digestibility, and we may accordingly speak of the apparent and the real metabolizable energy of feeding- stuffs. The whole of our present discussion of the metabolizable energy of the organic matter (total or digestible) of food materials relates to the apparent metabolizable energy. This is obvious as regards the concentrated feeds from the above example, and logic- ally applies also to those cases in which coarse fodders were added to the basal ration, while in the case of the coarse fodders used alone the distinction vanishes or is reduced to one between apparent and real digestibility. The experiment with beet molasses well illus- trates the difficulties in the way of determining the actual metabo- lizable energy of feeding-stuffs which cannot be used alone. Bret Mo.asses.—In two later experiments the addition of molasses increased instead of diminishing the excretion of methane. The results of the three experiments upon molasses, computed in the same manner as the experiments upon coarse fodders, are con- tained in Table II of the Appendix. In the last two experiments 10 to 12 per cent. of the energy of the molasses was lost in the products of intestinal fermentation, but this was more than counterbalanced by its less effect upon the digestibility of the rations, so that the final result is a higher figure for the apparently metabolizable energy than in the first experi- ment. Summarizing the results per gram as in the case of the coarse fodders we have: 204 PRINCIPLES OF ANIMAL NUTRITION. ; Apparently Gross : Metabolizabl Per Cent epee: | Meupotaml | EE ” als. RRS ie rare «sen iacs Mistuys alerts 4.084 2.905 TUG : TiO BD yar cade rin os 4.188 3.308 79.00 ci PO akc be tM x A ; i 3.044 72.70 Average, ample L202) 08 een hs heist. ees 3.176 75 .85 Srarcu.—In a considerable number of the trials commerci:] starch was added to the basal ration. The earlier experiments by Kiihn were intended primarily to throw light on the possible for- mation of fat from carbohydrates (compare p. 177). In them, starch was added to a ration of coarse fodder only and the nutritive ratio was purposely made very wide, the result being that more or less of the starch escaped digestion.” In the later experiments by Kellner the starch was added to a mixed ration. Except in the first two experiments the nutritive ratio was a medium one and but traces of starch escaped digestion. It will be convenient, therefore, to tabulate these two classes of experiments separately, as has been done in Tables III and IV of the Appendix, the com- putations being made as in the p*evious cases. The same remarks which were made on p. 291 concerning the distinction between real and apparent metabolizable energy apply to these results. As computed they represent the net gain to the organism from the consumption of starch aud are the algebraic sum of several factors. In particular, there was a considerable loss of energy in the feces, even in the later experiments in which but traces of the starch itself escaped digestion. In other words, the starch either lowered the digestibility of the basal ration or in- creased the formation of fecal metabolic products or both. The method of computation adopted virtually looks upon this as part of the necessary expenditure in the digestion of the starch. On the other hand, there are several cases in which there was a de- crease in the outgo of potential energy in the urine, even after the results are corrected to nitrogen equilibrium. This, from our pres- ent point of view, is credited to the starch and increases its apparent metabolizable energy. THE FOOD AS A SOURCE OF ENERGY. 295 The results on starch, expressed in Calories per gram of organic matter, may be summarized as follows: Apparent Gross Metaboliz- | Per Cent. Energy, able Metaboliz- Cals. Energy, able. Cals. Kiithn’s Experiments : pnponyolkey Ih. Ope INU lesen eae attic. 6 eh Pe aiers 4.249 3.029 uel ASS Nasa Ge Ni a iy Ce ee a 4.249 205 63.71 PAN CLAD ON Ryle zireie Mefensraen retest nhs 4.249 2.867 67 .46 SanaplemulenOxaVew beriode2auanty erecta - 4.236 3.347 78.95 e MO erate tas Dp) ES aeRO ee 4.236 3.161 74.68 a oh a) 10 Be ALRINDEINY.17) a Ri oS ae | 4.236 3.018 71.26 * Soe okay /iieiers, Seu Jt ae Ae Ae Pee ee 4.236 2.964 69.98 ANT CT AD CUMS titer cule ctar epee tare oitleraue Sk Le 4.236 Sele 73.72 Anetacetot Ivamdltlee rch. seen 4.243 | 2.995 | 70.59 Keliner’s Experiments : Sarples Weands (ls@)et Be Ate ees ets 4.165 2.027 48 .62 Ste eta Ostet cae he a ees Se 5 4.165 2.028 48.68 HAW CTA: Clie Usk det ensehiard sc auates cottaba aha. etter: 4.165 2.028 48.65 Sartell Oxayateite «tinue ta.amfaustte a A's 4.156 2.792 67.20 ie SHES be dhs Cee eed Eas en Ip ae 4.156 2.969 | 71.44 a OES COPIA NO aan eg Hog URE 4.156 3.214 71.32 IAVICT AL Cea wares eeetajelssrchscuetsipelaieralavelnye 4.151 2.992 71.99 recent age 2S Ob. al Cage Mane eh Ae 4.180 3.3013 79.22 ss ese Rate fell Sees A eee Sh Rt een 4.180 3. 017 72.16 PAWVEFAD ORG SIA Ne tks Ae opeapeyseomcte. Ste neala ohsites 4.180 SLO ae oROo Average som aman DV 25 foe-t.n0u save ove 4.168 3.079 73.84 Wueat GLUuTEN.—Seven experiments upon commercial wheat gluten are reported. three by Kihn and four by Kellner. The chemical composition of the dry matter of the three samples of gluten employed is shown in the first table on the next page. In Kiihn’s experiments the gluten caused a marked increase in the apparent digestibility of the basal ration. which by our method of computation augments the apparent metabolizable energy of the gluten, so that in one case it amounts to over 101 per cent. of the gross energy. The correction for organic matter is also rela- 296 Kiihn’s Experiments, |~ Per Cent. Oxen B and C, Oxs} Per Cent. | Per Cent. PNR, Wine Oe neti. Mckee eect 1367 2186. 7 2.80 RIEGLe Proven. cM ve too ose een ene 87.88 83.45 | 82.67 UU EMI OT fae al. ercpeciciee echoes 0.47 0-08.) 0.43 Nitrogen-free extract............ 8.07 po ae il 13.38 Bither extract’ Oe. s.at waa es os 2 0.26 | 0.72 100.00 100.00 100.00 tively large. great. the Appendix. PRINCIPLES OF ANIMAL NUTRITION. Kellner’s Experiments. more accurate, we have per gram of organic matter— In Kellner’s experiments the variations are not so Computed as before, the results are as shown in Table V of Summarizing Iellner’s figures, as probably the Apparent Gross Energy Metabolizable Per Cent Cats. Energy. Metabolizable. Cals. Sample I, Ox B, Period 1.... 5.675 3.019 53.18 < tee Rae ) Des 5.675 Delfi) 65.55 pas iP UIE OF ghee eat he Sit ey 5.679 4.062 TLL SEMA GG: cos sisi ha sleet he ok: 5.675 3.600 63.45 Sturdy 0) feud O IG Oo <8) B hae Rae 5.808 4.061 69.90 Average of land II ......... 5.742 3.831 66.68 The wheat gluten was by no means pure protein and the above figures of course apply to the feeding-stuff as a whole, including its fat and carbohydrates as well as its protein. The question of the metabolizable energy of the latter wil] be considered subsequently. Pranut Oi_.—Three experiments with this substance are re- ported by Kellner, In the first the oi! was given in the form of an emulsion, prepared by saponifying a small portion of the oil with sodium hydrate, and was completely digested. In the second and third experiments it was emulsified with lime-water. In this form it was less well digested. and in one ease (Ox F’) affected the digesti- bility of the basal ration unfavorably. The results per gram of organie matter, computed as before, constitute Table VI of the Appendix and are summarized in the following table: THE FOOD @S A SOURCE OF ENERGY. 297 Metabolizable | G E ; Per Cent. Cals Enerey, Metabolizable. SampleT;. Ox), 5.4...2. 9.493 7.382 WG SoS ie se SO 5 ee 4.973 52.52 ERTIES Chee cic! = 5.623 59.39 Aver nice nslle vacua tone | SPSS RRNAIe a oHONS ees ais 5.298 55.96 SuMMARY.—The foregoing results may be conveniently sum- marized in the table below, which shows the average gross energy per gram of organic matter, the percentage of this gross energy earried off unmetabolized in the various excreta, and the apparent metabolizable energy expressed both per gram of total organic matter and as a percentage of the gross energy: Apparent Gross Percentage Loss in Metabolizable En'gy Energy. per Grm Or Per ganic Grm Per Mat Or- | Cent ter, | Feces.| Urine. | Methane. | ganic of Cals at- | Gross ter, |En’gy. Cals Meadow sHAY. 1. 2\stalese sate aise Lis is 4.751/40.96] 5.71) 6.77 |2.213146.56 Bithaba Neve ties set Sela erence ctte 4.670|47.27) 2.61 6.50*|2 .037|43 .62 OS GES ta ieteers ie Ae chc ne cucto yc 4.816/56.80) 2.08 5.32 |1.724/385.80 WW teate SUnawepst acs tsctantarsteisr. AAO Doe 22), 203i 8.30 |1.475/31.11 Fispnacteds inyensunciwe cu aries see 4.251)12.75|—0.79| 12.46 |3.213/75.58 Beet molasses, Sample II....... .|4.188| 9.93} 2.91) 11.31 |3.174/75.85 Starch, Kiihn’s experiments. ..... 4.243/19.59|—0.92| 10.74 |2.995/70.59 ‘¢” "Kellner’s xpenmicats LETC aavaye mai OM Shes cya reaps iiss seers ee 4.165|/55.91)/—2.07| —2.49 |2.028/48.65 Medium rations............... 4.168|17.61|—0.66 9.21 |8.079|73.84 Wheat gluten, Kellner’s experi- MME TUGS Rey Ace amcreydaretarsverersiemeienle 5.742)/20.16] 13.08 0.08 |3.831|66.68 Peanut oil, Oxalate 9.493)24.34/—1.08} —1.02 |7.382|77.76 ESM Ly arohdeeamer reer: 2 9.464|64.77|—1.19)/—16.10 |4.973/52.52 a BEGUN Oooh fem meat ee ae 9.464/41.00) 1.37) —1.76 |5.623/59.39 e * Estimated. Digestible Organic Matter. As appears especially from the figures of the last table, the loss of energy in the feces is the one which is subject to the greatest vari- ation. In other words, the digestibility of a feeding-stuff is the 298 PRINCIPLES OF ANIMAL, NUTRITION. most important single factor in determining its content of metabo- lizable energy. We may eliminate this factor by computing, on the basis of the determinations of digestibility, the energy of the digested organic matter and the proportion of this energy which was lost in urine and methane or was metabolizable. In this way we may secure figures which will be useful as a basis for estimat- ing the energy values of rations in experiments in which it has not been determined, and which will also afford, from some points of view, a better idea of the relative extent of the losses other than those in the feces. Coarse Foppers ALONE.—In the cases in which coarse fodder constituted the exclusive ration the computation from the data given on p. 286 and the amounts of organic matter apparently digested in the several experiments is very simple and yields the following results per gram digested organic matter: Tho sans Metabolizable Energy. Ani-| Feed. Gross mal. | Energy. U ye = hane Per aS G ait Gent Cent. Cals A | Meadow hay I.........:.-- 4.509 9.75 | 10.35 | 79.90 | 3.603 Ju y Pe AURIS CaM Aye des | 4.408 8.98 | 14.62 | 76.40 | 3.368 if a gd Sy ems eee tect 4.317 S25) WeL22 00) 79 7oN lh eee VI v4 Chel Ea lidbey sa veys ce cae atioal teases oe 8.65 ; 12.35 | 79.00 | 3.474 XX | a ied > Viiaehsrstcs teeters | 4.452) 13.85 | 11:36 | 74.79 | 3.3380 I | << OPP! i Cer Se aed 4.371 O59.) TSI 7S LoL Nee | AN OT ADO ce ci terse tr taae ete rele 4.409 9.85 | 12.09 | 78.06 | 3.442 | Average for timothy hay .| 4.377 4.95 | 12.33 | 82.72 | 3.620 Coarse Fopprrs AppED To BasaL Ratrion.—From the re- sults contained in Table I of the Appendix we may compute in sub- stantially the same manner the total and metabolizable energy of the digestible organic matter of the coarse fodders which were added to the basal rations. In the table referred to, a correction was introduced for the small differences fn the amount of the basal rations consumed in the periods compared. In the present com- putations it has been assumed that the organic matter of these small differences possessed the same digestibility as the total organic matter of the basal ration. For example, in the case of Ox H, THE FOOD VAS A SOURCE OF ENERGY. 299 Periods 4 and 7, the amounts of digestible organic matter in the two rations were: TRIES OTCL, 7 ARM > SPR aR eA 7106 grams (PGA Aare te Aa eimecsiecese woe sys aie Sat 4845 “ iiteremee: isso sels.) 25). eaten: v1 a The table shows, however, that in Period 7 the animal received, 44 grams more of total organic matter in the basal ration than in Period 4. In the latter period the digestibility of the organic matter was found to be 75.7 per cent. Consequently, of the excess of 2261 grams of digestible organic matter in Period 7 440.757 =33 grams may be regarded as derived from the basal ration and 2261—33=2228 grams from the meadow hay added. The corresponding corrected amounts of energy as given in the same table are— Total Cals. a eae Pieced Cals. Energy of added hay (corrected)......... 15728 .6 w FUCORrESPONC Ing FECES LA. a. ess ae 5471.0 ce = digested) matter. .1.1.ln seecsat ot 10257 .6 4.604 Metabolizablevenergys 2025 ec-2s ee sts ci 8504.8 3.817 The table on the next page contains the results of these com- putations expressed per gram of digested organic matter. ell- ner * has made the same comparison in a slightly different man- ner. His results for the gross energy of the digested matter are given subsequently (p. 310). Those for metabolizable energy do not differ materially from those here given. CONCENTRATED FEEDING-STUFFS.—The results of experiments upon concentrated feeding-stuffs may of course be computed in the same manner as those upon coarse fodders Just considered. In the case of materials like starch, oil, and gluten, however, which differ widely from ordinary feeding-stuffs and which produce material and readily traceable effects upon the digestibility of the basal ration. relatively little value attaches to computations of the appar- ent metabolizable energy, and only the average results with these materials have been included in the summary on page 301 for the * Loc. cit., 53, 414 and 447. 300 PRINCIPLES OF ANIMAL NUTRITION. Apparent Loss in Metabolizable : Total Energy. i ee} Energy, A: 2 als. | <| a Per Cent, | Per Cent, | Per Cent. | Out Meadow Hay - 1 EO) pe Sample V. ......| 4.356 8.61 10.20 81.19 3 0au G | 2 | * We staveraie 4.496 7.42 12.58 79.70 | 3.583 Average ...... 4.4296] 8.17| 11.39] 80.44 | 3.560 neo Sample VI.......| 4.531 8.32 7.74 | 83.94 | 3.803 ED Miss 6/4604 7.66 9.43 82.91 3.817 fea SOE Vibe Soba athe (06 9.64 9.33 | 81.03 3.651 Average ...... 4.547 | 8.54| 8.83] 82.63 | 3.757 Oat Straw : Bale Sample wie ese. 4.441 5.30 LOT 84.53 3.754 Gaol PA So We Sod 4.586 4.32 14.42 81.26 3. ¢26 Average ...... 4.514| 4.81| 12.30] 82.89 | 3.740 | Wheat Straw: * H!1{ Samplel........ 4.488) (4.75 | 20.11 | “75.141 3°87 . "* * Loc. cul., 58, 407. THE FOOD AS (A SOURCE OF ENERGY. 397 A slightly less amount of the basal ration was eaten in Period 3 than in Period’4. The difference in crude nutrients and in esti- mated digestible nutrients was as follows: . Estimated Digestible. Total, Grms. Stas Gass 5 aaerey Wala, IBrOvelMNe a ceo etc oie 4 2 ifitea! Crude fiberts i. .2 eaten 13 Nitrogen-free extract.... 23 t _ oe 111.8 This amount of 112 Cals. should be added to the energy of the digested matter of Period 3 or subtracted from that of Period 4 in order-to render them comparable, thus making the real difference due to the starch 7067 Cals. Still further, the starch diminished the digestibility of the other nutrients of the ration by the following amounts: | ‘ Equivalent SRE Bnarey iCalsi JENS NEMA ad Ans wo aloe 118 673.8 Crude fiber. 2.2.0... 17 oles Ether extract...... 9 74.9 819.8 Had these amounts been digested in Period 3 as in Period 4, the energy of the digested matter of the ration would have been 820 Cals. greater, and the difference between the two periods would have been 7887 Cals. The digestible nitrogen-free ‘extract was 1876 grams more in Period 3 than in Period 4. Assuming all of this to be derived from the starch, we have for the energy of each eram of digested nitrogen-free extract 7887+ 1876 = 4.204 Cals. The following table* contains the results of all the starch experiments computed in the manner just outlined: * Toc. cit., 58, 412. 308 PRINCIPLES OF ANIMAL NUTRITION. ENERGY OF DIGESTED NITROGEN-FREE EXTRACT OF STARCH, TLL iatinonctus toate Re ens tee Alenbteee 4.283 Cals. Oa TIN eta athe ei a inepen tt Ae eine at alae 4.202 “ Ox VeCPertods 20) eee os ots ote 4.380 “ Oe (Pera rab n tac bs ue ee ee es ee ee Or WINGPenoGgs2b) chy ae. o/s een A159” Geir stn eerie eee pines tue ete ae 4.050 “ COM te Leen i pereatet cick eae 4.000 ‘“ OS aes Dae kg tps SA WN ibs Seen 4.099 “ Ox AIR eek Gran cue eee eer ees EL roe 4.219 ‘“ OMG Fe etc ce Pea Rone enone = 2 eA be OF ol Re ey eens Se era a BA 4.204 “ Gch FE RA Bets Seva ee at Ree Yl 6 4.095 < WA OR AR Oooo ie ticte'd sited Mark a bait A ABS CARBOHYDRATES OF EXTRACTED STrRAw.—Computed in the same manner as the experiments upon starch, the two experiments upon this substance gave the followimg results: * Fe WA Soak noi oe nite eb ee Benes 4.278 Cals. Ua Mire oat er anet cea aba conned erat A216.) & AVETASR) tats Gs unas Be oe ae ee 4.247. * This average is slightly higher than woulu be computed on the assumption that the digested erude fiber and nitrogen-free extract had the heat values respectively of the digested crude fiber of hay and the digested nitrogen-free extract of starch. Peanut O1n.—Four experiments upon this substance similarly computed give the following results. * 3 6) a B DSM Tit. Ura SP PPh Moria 8 508 Cals. CUR ay bo oer alc: cle Sete es eee S.s45. 0 ib >A ac ee eh CL et” CR eat Jt Bear 1G) dl CRS Gay ee Bila tees Pe oe PPS SRR! Jes [i ria AWEDRDE N.S x ge, oso Nie ena waren S SZ * Loc cit, 58 413 and 414 THE FOOD AS A SOURCE OF ENERGY. 309 As in the case of the ether extract of hay, the energy of the digested fat is less than that of the original material, which was 9.478 Cals. per gram. PROTEIN OF WHEAT GLUTEN.—Comparing the experiments with and without this material exactly as in the case of the starch, we have the following results * for the energy of the digested protein: Gy COTO rian hes oe Sc cores 5.728 Cals. Ox Br (Penodis) ee ce yee... . om etiee Deco WY ama CO CNCHETIOGU SE tere tare smo acy soe Deus. Oh SGP enon eta isch arnaee Gira 6.040 “ Ue) ba) ig CL GL 5) Lao 9) Ae ie a Ge 0092-2 OxQU (Perel S)sruiues..5 bite oeleau i xe CPenmodr aye ih oa ose Caz ROM LCP CEIOG? Oeresaporkes eek have a aks 6.061% PNVCT ACRE ou amet Darel vcs sM nth oni De OiGa © In these trials three different kinds of gluten were used which were prepared by somewhat different processes. The averages for the three sorts separately were as follows: INOESE cee erie e eruees p ip ty pen Ray 5vifa2 Cals ES Oe SE AE ee EO RGR bE ot aE 5 (92790 Bin HOS ahd Cae a Ae Cae Sal Eo ae 6.1684 ¢* a OTa:) sf The above figures refer to the so-called crude protein, that is, to nitrogen X 6.25. The proteins of wheat, however, contain con- siderably over 16 per cent. of nitrogen. Using Ritthausen’s factor, namely, 5.7, for the computation of protein from nitrogen reduces the amount of protein in the gluten and increases that of the nitrogen-free extract by the same amount. The energy of the digested protein when computed on this basis equals 6.148 Cals. per gram. Orcanic Marrer of Coarse Fopprrs.—For the total digested organic matter of hay and straw the following heat values per gram were computed: * * Loc. cit., 58, 412 and 414. 310 PRINCIPLES OF ANIMAL NUTRITION. Meadow hay Iz. Ok Ayer ve. re eee 4509 Cals. sf Ae a ee ae ae rea ASR Lee 4408 ‘ = eae ee ERE 4317 Cals. fe * pate) ted SER stn eed 4398 ‘“ ae . Ba ONES SRE DUNE Se ie a eae 4452 “ Hi pred 0 Or iar [Es aye UME Sane Ara 4371 “ M yaa ise Tere nel CMAP i 4355 Cals. ) ae Renters MOAR Ss Se eds m2 dagen eee sere * a i a nn a 4534. * oF pit oh Watley se 2000. 4535‘ : opts) RMR [Saat Ist ead ABOD. ie AVETEPE Of IDS: y'\5 cance ones aoe 4437“ Gat straw Ox Fo fe ie ee eee 4443 Cals. Ct 6 Pees Mea APE Ae ot eee hr 4584 ‘“ PAVEV ADE Se M2 Sg) ue Seek oh ae en 4513 = Wihedtemaw, Ox te ole ee ie ye oe 4553 Cals. . A (05. att MADERA YOR Ta eam heae, ois Vi AOS. a, A WON AIEG: oie chon ti a5 nthe scan olen eae tah chiar 4470“ The digestible matter of the straw has apparently about the same heat value as that of hay. Metabolizable Energy. Protein.—A portion of the gross energy of the digested protein is removed in the urea and other nitrogenous products of metabo- lism, and in addition to this there is to be considered the possibility - of a loss of energy by fermentation in the digestive tract. Lossrs IN Metuanr.—lIn nine of the Mockern experiments in which wheat gluten or flesh-meal was added to the basal ration, the amount of carbon excreted in the form of hydrocarbons per day and head was as tabulated on the opposite page. The differences between the excretion with and without gluten are small in amount and are sometimes positive and sometimes negative, the averages being probably within the limit of experi- mental error. The percentage losses of energy in methane as DHE VFOOD ASA’ SOURCE “OF ‘ENERGY... * 311 Carbon in Form of Hydrocarbons. Petied:| jAnded: eriod. dded, With Grms. Prom Bee Addition of Differences, Grms. A Guten: Grms, Kithn: ° COxen TER ee tee tora: 3 680 186.4 205.7 +19.3 me UN eh le ees 4 1360 186.4 207.6 +21.2 HOA TAY Saleh oy eee 3 680 187.7 187.6 — 0.1 BON TOO. CAGE Oe Sk pee 2a 1000 * 148.7 162.9 +14.2 TE SCD Cnr iy nea a 2b 1000 * 148.7 157.4 + 8.7 Average......... 171.6 184.2 +12.6 Kellner rer spay. cheek sae ont 1 1700 208.9 211.0 + 2.1 S01 3) ee A 3 1700 208 .9 200.9 — 8.0 AN OE AES aS Ceara 3 1700 183 .0 GTi —15.9 a) D epee eee ae 4 1600 166.1 WADE + 4.6 Average......... WH 7 187.4 — 4.3 * Flesh-meal. computed in Table V of the Appendix, like the figures just given for the carbon of the methane, lead to the conclusion that the pro- tein of the food does not participate in the methane fermentation. Those figures were: Carb Peniod. tye its tee suet: 10.81 per cent. par SUE Trait 4 eels ene eta Ads es a hey HaUSiasaw tar PERS tah eck Meets cise AP SEHR Ne? eS e2Guac dt ee aed 8 SNL EB Laie caste dbe Migs ti On0S i rae eas} Pu CAC aM co AAO MeN Olt fn AAS ra Bh oe SS eee Ne a OBO TC i EL SOP AR eed punt tates, ee bas raed BOM eee i FAVELA OG Wee idly fu ode rr ete enna oa Kellner * reaches the same conclusion by comparing the ratio of the methane carbon to the amount of digested carbohydrates (nitrogen-free extract+crude fiber) in the several periods. The former amounted to the following per cent. of the latter in his experiments: * Loc. cit., 58, 420. 312 PRINCIPLES OF ANIMAL NUTRITION. Basal Ration Basal Ration, + Gluten, Per Cent. Per Cent. 2.94 2.96 2.94 2.82 S71 2.41 2.75 2.71 2.87 3.19 2.84 2.82 Had the large quantities of digestible protein added to the basal rations produced any material amount of methane, that fact must have been reflected in the above percentages. This method of comparison takes into account the probable effect of the carbo- hydrates of the wheat gluten in increasing the production of methane, and the substantial agreement of the results with and without protein leads to the same conclusion as the preceding data. It seems fair to presume that this conclusion applies to protein in general, although a strict demonstration of it, especially for coarse fodders, would have its difficulties. Losses IN Urtne.—While the assumption that the urine is essentially an aqueous solution of urea leads to grave errors in the case of the carnivora, this is still more emphatically true of the urine of herbivora, particularly of ruminants. The presence in the urine of herbivora of hippuric acid and other nitrogenous compounds less highly oxidized than urea has of course long been known, while, as stated on p. 27, the presence of considerable amounts of non- nitrogenous organic matter was subsequently demonstrated by Henneberg and by G. Kihn in the urine of ruminants. ‘It follows from these facts that the energy content of the urine of these animals must be higher in proportion to its nitrogen than is the case with carnivora or with man, but the experimental dem- onstration of this fact and the realization of the extent and im- portance of the difference are of comparatively recent date. Cattle-—It is to Kellner * that we owe the first direct determi- nations of the potential energy of the urine of cattle. The two animals used in the experiment were fed, the one (A) on meadow hay, and the other (B) on meadow hay and oat straw. The results as regards the urine were as follows, per day and head: * Loc, cit., 47, 275. THEY FOODSAS \A-SOURCE.- OF ENERGY. 313 Ox A. Ox B ‘Notalenitrogenty-rs- .-. sete 61.28 grams. 46.63 grams, o M@ANDOM Etatata: O2ee* Wheat straw, corn meal, and linseed meal |11.24 “ |10.77 “ |10.95 “ The methods employed to prepare the urine for combustion were not altogether satisfactory, and the range of possible error is rather large. In but two cases, however, was the energy of the urine less than twice that corresponding to its nitrogen calculated as urea (5.434 Cals.), while in one case it reached over seven times. that amount. Neither carbon nor hippuric acid having been deter- mined, ‘no computations can be made as to the amount of non- nitrogenous matter present. Jordan * has reached similar results on the urine of cows, the average energy content per gram of nitrogen being as follows: Total Nitrogen, Hetennet enarey, Energy per Grm. Grms. Cal Nitrogen, Cals. Cow No. 12: erode cere 87.0 1658.3 - 19.06 LU PAM Eee seers 6 Gero 78.8 1547 .2 19.63 Sat eoeme tt cual Megas a 42.8 1323.5 30.93 CowalNon Oras sac ecsmele oct 65.5 1452.5 22.18 As in the writer’s experiments, the energy per gram of nitrogen varies within wide limits, being greatest when the total nitrogen of the urine is least. In other words, it would appear that the non-nitrogenous ingredients of the urine of cattle are sant to less fluctuation than the nitrogenous ingredients. Kellner’s later experiments have fully confirmed his earlier results, as will appear in greater detail in subsequent paragraphs. He finds that the carbon rather than the nitrogen of the urine is the measure of its potential energy, and that an estimate of 10 Cals. per gram of carbon gave for his experiments results closely approximating the truth.t * New York State Experiment Station, Bull. 197, p. 28. + Loc. cit., 58, 437. THE FOOD AS A SOURCE OF ENERGY. 315 Other Species—We may probably assume without serious error that the results obtained with cattle apply in general to sheep and other ruminants. No direct determinations of the energy of the urine of the horse or the hog have yet been reported, but Zuntz & Hagemann * have made some estimates of it in the case of the horse on a mixed ration of hay, oats, and straw. They determined the total carbon and total nitrogen of the urine and, on the assump- tion that only urea and hippuric acid are present, compute the proportion of each of these, and thence the energy of the urine. They thus find the potential energy of the latter, per gram of nitro- gen, equal to 15.521 Cals. Neither hippuric acid nor energy having been determined directly, it is impossible to check the above com- putation or to ascertain whether any non-nitrogenous organic matter was present. It is to be noted, however, that the ratio of carbon to nitrogen in the urine was much lower than in Kellner’s experiments on cattle, viz.: Auntie er thaeemanme i ars. ja ace os 1.526 :1 Feline ty oAC iron 4 Ue ti. ahs ob es 3.015 31 Ge Cas) SUPE Aue nay i, RS Apa 3.458 :1 This fact clearly indicates that at least there was very much less non-nitrogenous matter present in the former case. Meissl, Strohmer & Lorenz f in their respiration experiments on swine likewise determined carbon and nitrogen in the urine. Computed by the method of Zuntz & Hagemann the energy of the urine averaged 9.55 Cals. per gram of nitrogen, while the average ratio of carbon to nitrogen was 0.745:1. These results would seem to indicate that the loss of energy in the urine of the hog is not very much greater than in ‘that of the carnivora. METABOLIZABLE ENERGY OF PROTEIN OF CONCENTRATED FEEDS. —Accepting it as demonstrated that there is no material loss of potential energy in the form of fermentation products of protein, the data regarding the energy of the urine just considered afford the basis for an approximate estimate of the metabolizable energy of the digested protein. Catile—Kellner’s experiments upon cattle afford data for com- puting the metabolizable energy of the digested protein of wheat * Landw. Jahrb., 27, Supp. III, 239. { Zeit. f. Biol., 22, 63. 316 PRINCIPLES OF ANIMAL NUTRITION. gluten and of beet molasses. The method of computation is pre- cisely similar to that already employed for calculating the metabo- lizable energy of the total organic matter; that is, the results upon the basal ration are subtracted from those upon the ration con- taining the material under experiment. Taking as an example the results upon wheat gluten with Ox C in Periods 1 and 3 we have the following comparison: Digested. Guile ef - Rare Nit oaet : of Urine, y Protein, Crude pp ae ga Ether Cals. Animal, Grms. Fiber, Extract. | Extract. Grms. Grms. (Geis Grms. emOdes wn Ao 1694 1279 5648 34 2592.8 20.31 Fa a8 Sanaa 598 1289 5464 40 1666.4 16.01 Difference. ..... 1096 —10 184 —6 926.4 4.30 The difference of 4.3 grams in the amount of nitrogen gained by the animal is equivalent to 32 Cals. which would otherwise have appeared in the urine. This added to the 926.4 Cals. actually found makes a total of 958.4 Cals. for the increase in the potential energy of the urine due to the 1096 grams of protein digested. There are also differences in the amount of non-nitrogenous matters digested, particularly of the nitrogen-free extract. As Tables I, III and IV of the Appendix show, both starch and crude fiber, as repre- sented by the extracted straw, tend to diminish the amount of energy carried off in the urine. These differences were observed when from 2 to 2.5 kilograms of these substances were added to the basal ration. If the differences are proportional to the amount fed, the energy corresponding to the small difference observed in this ex- periment would not exceed 15 or 20 Cals., and may be neglected, while the maximum difference in any experiment of the series would probably not exceed 70 to 75 Cals. Assuming that all the additional protein digested came from the wheat gluten, we have for the corresponding energy of the urine 958 .4 +1096 =0.874 Cals. per gram protein digested. Subtracting this from the total energy of the digested protein as found on p. 309, viz., 5.975 Cals., we have 5.101 Cals. as the metabo- THE FOOD AS. A_SOURCE (OF ENERGY: 387. lizable energy of one gram of digested protein of wheat gluten in this experiment. For the four experiments upon this substance, computed as in the above example, the results were as follows: y Difference in Protein Energy of Urine.* digested Ghat Per G f x en, 5 Gri, ree Bepteuie y Cals. Ox ds Periods atid: d2/.. 5. crease otdersie, a: 2185 2547 .3 1.166 Pom OPC ORION ot cRet hs soe Ook ake Cae 1096 958.4 0.874 OSI) EES LT St ae a Ne 1056 1061.1 1.005 Coad] Ot SUT Ze) at EDA a A at a 1148 1362.1 1.186 PDNICV RO 55 fore eterrcho! sas a chis¥a\tal n/a ade oneia oC army « 1371 1482.2 1.081 * Corrected to nitrogen equilibrium. Subtracting from the total energy of the digested protein the potential energy carried off in the urine we have for the metab- olizable energy of one gram of protein 5.975 Cals. —1.081 Cals. =4.894 Cals. « If we use Ritthausen’s factor, 5.7, for proteids, the average digested protein becomes 1250 grams and the loss of energy in the urine 1.190 Cals. per gram of protein. Subtracting this from 6.148 Cals., the gross energy of one gram of NX5.7 (p. 309), we have for the metabolizable energy of the latter 4.958 Cals. per gram. The average increase in the energy of the urine for each addi- tional gram of nitrogen excreted in these experiments (6.756 Cals.) was almost exactly the same as Rubner found in his experiment on extracted lean meat (6.695 Cals.). This may be taken as indi- cating that the process of proteid metabolism is substantially the same in both classes of animals, while the fact that the result is notably greater than the energy of urea shows that in the herbivora as in the carnivora other waste products than urea result from the proteid metabolism. In three other experiments beet molasses was added to the basal ration, resulting in the digestion of an increased amount of nitrogenous matter. Computing the results as in the case of the 318 PRINCIPLES OF ANIMAL NUTRITION. wheat gluten, and assuming that the large amounts of soluble carbohydrates digested had no effect on the potential energy of the urine, the results were as follows: Aree Di i ine.* Protein bidekicd ifference in Energy of Urine from Molasses, Grms. Total, Cais. Per Ba Ra Tere) ok tre Coe apa 117 256.1 2.189 te» Leases Cr fy EE 160 240.3 . 1.502 We a Rie eo oc oe 122 192.6 1.579 ASVOERLOR 0c yikins oo mee 133 229.7 Le 2 * Corrected to nitrogen equilibrium, It will be seen that the loss of energy in the urine is much greater than in the case of the gluten or than in Rubner’s experi- ments with carnivora. Since it is improbable that the soluble carbohydrates of the molasses escape oxidation, it would appear that some of the nitrogenous material of the latter must have passed through the system unmetabolized. Kellner suspects that it is made up in part at least of xanthin bases. If we consider the nitrogen of the molasses to represent crude protein (N X6.25) with a heat value of 5.711 Cals. per gram, the metabolizable energy per gram would be 3.984 Cals. In view, however, of the fact that only a very small proportion of the nitro- gen of the molasses is in the proteid form, such a calculation seems of doubtful value. Swine.—In the investigations of Meissl, Strohmer and Lorenz* upon the production of fat from carbohydrates (p. 176) the carbon and nitrogen of the urine were determined in six experiments. Applying to the results Zuntz & Hagemann’s method of computation (p. 315) we obtain the following estimates for the energy per gram of nitrogen in the urine of the hog in these experiments and for the corresponding metabolizabie energy of the digested protein: * Zeit. f. Biol., 22, 63. THE FOOD AS A SOURCE OF ENERGY. Bw) Nitrogen Total Energy Aistao- Experi- Nitrogen) as Hip- E otal | per Grm. BPEG, ment Feed. as Urea,| puric of tine of per No. Grms. Acid, eae Nitrogen,| Grm Grms. ° Cais. |Pretein als 1 FRAC Coe ia tise fae aw oe a tcp Ee 9.58 0.88 | 115.7 | 11.06 | 3.941 Ps Re SVE Rien a 9.22 LOAM D2 DUG el Deez Sos 3 PORES stig © how a2) a hoe yes 13.04 1.04 | 146.5 | 10.40 | 4.048 4 Whey, rice, and flesh meal.| 59.89 1.17 | 410.0 |- 6.72 | 4.636 5 MOM eer siejeivas ge cets se 9.35 0.45 83.7 8.54 | 4.344 6 OP na Fate ah ae eA ey On 6.48 0.29 56.4 8.33 | 4.379 Ixornauth & Arche * report the following results on the urine of swine fed chiefly upon cockle: Experiment Nitrogen, Carbon, Ratio, No. Grms. Grms. CiaNe Hee Wie n. 10.56 |: 10.30 | 0.975:1 PD a RE LE Bec eee Cone a 10.30 9.53 0.926: 1 ee ee le eM 10.41 9.96 02957 21 Averages ncieia s LOA2 9293 0.953 i 1 The results, computed as in the previous case, make the average energy content of the urine 10.27 Cals. per gram of nitrogen, equivalent to a metabolizable energy of 4.067 Cals. per gram of protein. In the two fasting experiments of Meissl, Strohmer & Lorenz the ratios of carbon to nitrogen and of computed energy to nitro- gen are similar to those obtained with fasting carnivora. The abundant supply of proteids in the diet in the fourth experiment seems to have had the effect of reducing these ratios to values comparable with those obtained by Rubner for extracted meat and by Kellner for the digested protein of wheat gluten. These facts seem to indicate clearly that the nature of the proteid meta- bolism in all these animals is substantially the same. In the ex- periments in which ordinary grains were used, the computed energy content of the urine is notably greater relatively to its nitrogen. How far the excess of carbon found in these cases was due to an * Landw. Vers. Stat., 40, 177. 320 PRINCIPLES OF ANIMAL NUTRITION. increased formation of hippuric acid and what part of it, if any, is” to be ascribed to the presence of non-nitrogenous matter in the urine, the experiments afford no means of estimating. : The Horse—Zuntz & Hagemann’s results on the horse, p. 315, although the result of feeding mixed rations, may be conveniently considered here. The cemputed energy of the urine was 15.521 Cals. per gram of nitrogen, equivalent to 2.483 Cals. per gram of protein. Assuming for the latter, as before, a value of 5.711 Cals., there remains for the metabolizable energy 3.228 Cals. per gram. ProtTetn oF Coarse Fopprers.—Almost the only dats on this point are those afforded by Kellner’s experiments upon cattle. In those in which coarse fodders were used alone we can of course compute the metabolizable energy of the protein directly from the amount digested and from the energy of the urine. In those experiments in which coarse fodders were added to a basal ration we can compare the two experiments in the same manner as those upon gluten. neglecting, as in that case, the differences in the non- nitrogenous nutrients digested. Passing over the details of the computation, the final results, including the metabolizable energy of the digested protein com- puted upon the assumption that its gross energy equals 5.711 Cals. per gram, are as given in the table on the opposite page.* The writer’s experiments on timothy hay, the results of which as regards the energy of the urine have already been given on p. 314, when computed in the same manner as the above experiments give the following results for the metabolizable energy of the digested protein: Sen Seo ete Ce heen hee 2.625 Cals a Fie eae RE et ig ne PEN 2.830 ‘“ Me as cen hes EA a oe a ee a:116-** Avera sis (isa ce eawae ees S08 Influence of Non-nitrogenous Matter of Urine.—In the previous paragraphs there appeared reasons for supposing that the processes of proteid metabolism are essentially the same in all domestic * The figures given in this table for digested protein, energy, etc., refer solely to that derived from the coarse fodder and not to that of the total ration. THE FOOD AS A SOURCE OF ENERGY. 321 Difference in : f Energy of Urine.* Metaboliz- Protein ed Nelle Bapey (N X6.25) er Grm. Digested, Per Grm. of igestible Grms. Total, Protein Protein, Cals. Digested, Cals. als. Meadow Hay : NOE ed ae ae 440 1991.3 4.526 1.185 ian a eb ee eee 342 1686.9 4.933 0.778 Pe ae ee Be Pe Ss a 137 583 .2 4.257 1.454 til my ES 146 556.5 3.812 1.399 “Vi, * Hh Peed 1... 193 781.4 4.049 1.662 ‘gap i PRs: i eo 220 798.0 3.632 2.079 ast. “eagle Ferree 213 9390.5 4.368 1.343 goth. Ae Ts | ae oe 413 1925.7 4.662 1.049 < LS Soy el a ne 451 1559.3 ; 2.255 Ke HS oe dE ee ees 458 1737.9 1.517 in ies + SaaS 540 3224.6 —0.262 0 ee pe 323 1434.1 1.272 Oat Straw : eth F..... 35 354.2 —4.409 oo SL wed | REA ee ee 48 274.0 —0.001 {> ae ae pe ee ee 42 314.1 —1.767 Wheat Straw : ee. Te a oa eee —11 289 .7 ?) ? so Bi os hs gy! ee ape ae amie 14 413.2 | 29 .520 —23.809 OS Behe EE 2 | 351.5 | (2) (2) * Corrected to nitrogen equilibrium: animals and consequently that the metabolizable energy of the proteids cannot be widely different. In these results upon coarse fodders we meet an apparent contradiction of this conclusion, the metabolizable energy of the digestible protein as above computed being quite variable and much lower than the values found for pure proteids, while in the straw we get large negative values. These latter results, however, while appearing at first sight para- doxical, furnish the clue to the apparent contradiction. In the case of the straws it is evident that a very considerable part of the potential energy of the urine must have been contained in non- nitrogenous substances, and that the latter must have been derived largely from the non-nitrogenous matter of the food. We have already seen, however, that these non-nitrogenous excretory prod- 322 PRINCIPLES OF ANIMAL NUTRITION. ucts are a normal constituent of the urine of cattle both on hay and on mixed rations. Their effect on the computation becomes more obvious in the case of the straws, simply because of the relatively small amount of protein in the latter feeding-stuffs. In these cases we get impossible results when we assume that all the potential energy of the urine is derived from the proteids metabolized, but it is clear that the results on the hays must be affected by the same error, and there is little question that the low and variable results noted in the table are to be explained in part in this way. We know no essential difference between the real proteids of the differ- ent coarse fodders, nor between those of coarse fodders and grain, nor any reason why they should not be metabolized in substantially the same way in the body and possess approximately the same metabolizable energy. It would seem more reasonable, then, to assume that the proteids of coarse fodders are metabolized sub- stantially like those of concentrated fodders, and to take provision- ally the results obtained for the protein of wheat gluten as repre- senting approximately the metabolizable energy of the digested protein of the total ration, while we regard the remaining energy of the urine as derived largely from the non-nitrogenous nutrients of the food. Hippuric Acid.—The statement last made, however, requires some modification. Nota little of the potential energy of the urine of cattle is contained in the hippurie acid which these animals excrete so abundantly. This being a nitrogenous product, it is natural to look upon it as derived from the proteids of the food, but it must not be forgotten that this is only partially true. Its glycocol portion origmates in the proteids, but its phenyl radicle appears to be derived in these animals largely, if not wholly, from the non-nitrogenous ingredients of the food (compare p. 45). If the metabolism of one gram of protein is arrested at the glycocol stage by the presence in the organism of benzoic acid, there has already been liberated from it about 3 Cals. of energy, while about 2.7 Cals. remainin the glyeocol. The resulting hippuric acid, however, contains about 11.6 Cals. of potential energy, or more than the original protein. In this case, then, the larger share of the energy of the excretory product (8.9 Cals. out of 11.6 Cals.), although con- tained in a nitrogenous substance, is derived ultimately from the THE FOOD AS A SOURCGE..OF ENERGY. 323 non-nitrogenous matter of the food. It is clear, then, that the non-nitrogenous radicle of the hippuric acid and the non-nitrogen- ous organic matter of the urine together represent a large share of the potential energy of the latter, and that it is quite as in- correct to compute the metabolizable energy of the protein on the assumption that all the energy of the urine is derived from it as it is, on the other hand, to simply deduct from its gross energy the _ energy of the equivalent amount of urea. Ether Extract.—Our only data upon this ingredient are fur- nished by the four experiments upon steers by Kellner. in which peanut oil was added to the ration. In the first two experiments this oil was emulsified by means of a small quantity of soap made from the same oil. The result was a milky fluid which was readily digestible and which caused no considerable decrease in the digesti- “bility of the basal ration. In the second two experiments the oil was emulsified with lime-water, giving a thickish mass which was not very well digested and which, in the case of Ox F particularly, caused a considerable decrease in the digestibility of the crude fiber and nitrogen-free extract of the basal ration. It should be noted that in the experiment with Ox E the oil was not added to a basal ration, but was substituted for a part of the bran. From Table VI of the Appendix we obtain the summary tabulated on the next page, showing the effects of the oil upon the loss of energy in the gaseous hydrocarbons and in the urine, the results of the experi- ment on Ox E being included. Upon the evidence of these four experiments, bearing in mind that the one with Ox E was upon the substitution of oil for bran, we should not be inclined to ascribe to the fat of the food any con- siderable effect either upon the formation of hydrocarbons or upon the amount of potential energy carried off in the urme. As regards the hydrocarbons, the differences in the cases of Oxen D and G are insignificant. In the case of Ox F, on the contrary, the production of hydrocarbons was reduced nearly one half; this it may be noted was the case in which there was a considerable effect upon the digestibility of the basal ration. As regards the energy of the urine, the differences, except in the case of Ox E, are relatively small and are in both directions. Provisionally, therefore, we are probably justified in assuming 324 PRINCIPLES OF ANIMAL NUTRITION. Ani- . E f Uri D Ani-| Period. | (Sacre oe |g Sea D a: win eee ee 2851.2 2909.0 D 1 Basal aration’. oceeias os 2407 .0 2957 .0 Differences;:,.¢ 2. 2.0 —55.8 ear —48 0 es E 3 Withisolls eae teen: 2026.2 2640.8 E 1 Basalerabionseeis feo ene 2312.9 2950.4 Differences: 25..1-.<06 slow sc —286.7 —309 6 Pie F 5 Withvol et sasecearacee 1455.0 1369.1 F 3 Basal) ersaitlone ene keds 1530.0 2560.7 DifferenCes- 8 s.ich. 2 ses —75.0 —1191.6 G 5 With outs etoccee rot hae 1452.1 PRY ALL G 3 Basaly rationale 1359.6 2524 .7 Differences)... eos 92.5 —153.5 as Kellner does that none of the energy of the fat was lost either in the hydrocarbons or in the urine, and that consequently the metab- olizable energy of the digested fat was the same as its gross energy, namely, 8.821 Cals. per gram, as given on p. 308. If we assume that the ether extract of hay behaves like the peanut oil, taking no part either in the production of methane or in the loss of energy through the urine, its metabolizable energy would likewise be the same as its gross energy, namely,8.322 Cals. per gram, as computed on p. 305. No results upon the metabolizable energy of the ether extract are available in the ease of other species of herbivorous animals. Carbohydrates.—Those of Kellner’s experiments in which starch, as a representative of the readily digestible carbohydrates. and extracted straw, consisting largely of “crude fiber,’’ were added to the basal ration afford data for an approximate computation of the metabolizable energy of this group of nutrients in the ox, and experiments by Lehmann, Hagemann & Zuntz afford partial data for the horse. Srarcu.—tThe results of the Méckern experiments, as recorded in Tables III and IV of the Appendix, show that the starch had but a slight effect upon the amount of potential energy carried off in the urine of the ox, although the general tendency was to THE FOOD AS A.SOURCE OF ENERGY. 325 diminish it slightly. On the other hand, the formation of hydro- carbons was markedly increased except in two cases. It has al- ready been shown that the proteids of the food do not take part in the production of these gases, and that the same is probably true of the fat under normal conditions. Neglecting the small effects upon the urine, therefore, we may compare directly the increase in the digested carbohydrates with the increase in the gaseous hydro- carbons, using for this purpose the differences between the two rations uncorrected for the slight variations in the consumption of dry matter. Taking first the last five of Kellner’s experiments.* which seem to represent the most normal conditions, we have the following: Difference in Carbohydrates Digested. Difference in Energy of Nit f eae Chile Biber: itrogen-free als. pe te Extract, Ox7 DR enodi2 . Hae. Santer: —64 +1388 +424 .4 (SR Sa ah Te oe, ce GER ae —64 +1609 +822 .0 .G eS A Oe A ae —50 +1598 +645.8 Me oles By PAG) Fes ae ate a eee —26 +1861 +604.5 oe | Bo COS aan ae pie.og Wen — 9 +1501 +769 .9 “RLY EEE ES} Ae Bia cons ey Re —213 +7957 3266.6 Assuming that the same proportion of hydrocarbons is pro- duced in the fermentation of crude fiber as in that of starch, we may compare the algebraic sum of the two with the energy of the methane as follows: 3266.6 Cals. + (7957 — 213) =0.422 Cals. per gram. Subtracting the latter result from the gross energy of the digested nitrogen-free extract of starch, we have for the metabolizable energy of the latter 4.185 Cals. —0.422 Cals. = 3.763 Cals. per gram. In the experiments on Oxen B and C the basal ration was a heavy one, with a rather wide nutritive ratio, and already con- tained large amounts of digestible carbohydrates. Under these cir- cumstances the added starch was very imperfectly digested, while * Loc. cit., 58, 422. 326 PRINCIPLES OF ANIMAL NUTRITION. the production of hydrocarbons was diminished. ‘Kellner suggests that the latter effect may have been due to a partial suppression of the organisms causing the methane fermentation by other species, and suspects that the presence of large amounts of carbohydrates along with little protein favors this result. At any rate, the con- ditions are evidently unusual if not abnormal. In Kiihn’s experiments the starch was added to a ration of coarse fodder. The nutritive ratio was wide, but the absolute amount of carbohydrates was much less than in the two experiments by Kellner just mentioned, less starch appeared to escape diges- tion, and the production of hydrocarbons was increased in every ease. The following are Kithn’s * results: Difference in Carbohydrates Digested. Difference in Energy of d een tant ar ah ana Sinner ma fe iieidlat hate) Crude Fiber, Nitrogen-free Cals, Grms. Extragt, Grms. COs eriOde inten rere crete ote te chore —220 1529 706.2 rea), y Pep se pet St ae as aR, —180 1408 856.7 Sas ue IU Seine tretescnia oe —195 1537 752.6 aie Tad Dh ecktea nO Pieced re einvare eicvcuchoncie —130 1539 665.5 wv Vi; es Shieh chabrastevcns evs: ekepievaele —176 2619 1181.0 sont Vale e PATA MARA, PED e ac RE ORIN OTA —146 . 1468 729.5 Sa. Vil, L PA VEU AN Rae ha ENC fs 9 Fd — 8&8 1554 649.9 ss 2100 fe SE hire ue Bae” Saori Sesto —156 2587 1407.0 ARO GAS Soca eke. « cite et Oe Bic ee Lee —1291 14241 6948 .4 Assuming as before the equivalence of crude fiber and nitrogen- free extract as regards the production of hydrocarbons we have 6948 .4 Cals. + (14241 — 1291) =0.5387 Cals. per gram, 4.185 Cals. —0.587 Cals. =3.648 Cals. per gram. Determinations by Lehmann, Hagemann «& Zuntz7{ of the amount of methane produced by the horse will be considered in connection with the metabolizable energy of crude fiber. Zuntz f has pointed out that the fermentation of the food in the horse takes place largely in the ccecum and after the more digestible carbo- hydrates have been resorbed. Accordingly he regards the metabo- * Toc, cit., 44, 570. + Landw. Jahrb., 23, 125. t Arch. ges. Physiol., 49, 477. THE FOOD AS A SOURCE OF ENERGY. 327 lizable energy of starch and similar bodies in this animal as equal to their gross energy, viz., 4.185 Cals. per gram in the case of starch. EXTRACTED Straw.—The two experiments in which extracted straw was added to the basal ration, when computed as in the case of the starch experiments, give the following results: Difference in Carbohydrates Digested. Difference in : Energy of te ; eae. : itrogen-free als. cute en, | St Oa ERE ERIOGLO a eileto ie WPackelree 2046 439 1425.1 heck a ae gy Stay anters 1987 449 1425.2 PROT ALS Ree tac aferenuetetenct RA ee ars 4033 888 2850.3 The loss of energy in the hydrocarbons equals 0.579 Cals. per gram of total digestible carbohydrates (of which 82 per cent. was crude fiber), and the corresponding metabolizable energy of the carbohydrates is 3.668 Cals. per gram. This is a materially lower figure than Kellner found for starch and indicates that the loss of energy in the gaseous products of fermentation is greater in the case of crude fiber than in that of the more soluble carbohydrates, an indication which, as we shall see, is confirmed by the results of other experiments. CARBOHYDRATES OF COARSE Fopprrs.—Upon the same two assumptions, viz., that the carbohydrates are the sole source of the gaseous hydrocarbons, and that the latter represent the entire loss of energy from the digested carbohydrates, we may compute the metabolizable energy of the total digestible carbohydrates of the various coarse fodders exactly as in the case of the extracted straw, the results being tabulated on the next page. If we average the results for each feeding-stuff and compute them as in the foregoing cases, our findings are as given on p. 329, where the rations are arranged in the order of their crude fiber content. In computing the metabolizable energy, the gross energy of the digested carbohydrates has been assumed to be the average 328 PRINCIPLES OF ANIMAL NUTRITION. COARSE FODDERS ALONE. Digested Carbohydrates. Energy of Animal. Crude Fiber, Nitrogen- petnane : Extract Grms A Meadow: hay al s.trenysmicrrerie ot 1262 2713 PAG Wepre 1 me os PARAL I Caee Sa NT Ps 1765 2610 S13722 V Oe Pata CRY PE ME WIM pI yt a ee 1572 2315 2268 .5 VI S A. UPB she cuba eae Pes 1642 2420 2480.6 Xe ee Mae eee 1560 2999 2646.1 I LOPES U fie Se a nn 1266 2348 2092.3 B me “* and oat straw.... 1702 2357 230l.2 III Clover - Gy See oe ghee 1676 2226 2670.1 IV J ou eG ef 1565 2145 2491.3 * COARSE FODDER ADDED TO BASAL RATION. Difference in Carbohydrates Digested. Energy of Animal. | Period. 5 Methane, Crude Fiber, ee Sos Grms. Extract, Grms. F if Meadow hay V....... 546 836 689.9 G 2 4 Pea mV tes 538 886 907 .4 H 2 of SOO VAI, hoe 703 1129 phere H 7 f SN dl UNE ete ed 739 1236 898 .0 4 Dy ee Gea LB eee 683 1213 984.8 F Dey | (Oatystrawe Wl saes eee 694 721 679.2 G 1 af SET | Cl ike esate Stl 595 684 923 .4 H 1 Wheat straw I........ 821 524 1213.0 a} 1 as i ABT) Roeder: 829 616 1281.0 of the results given on pp. 304 and 306 for the digested crude fiber and nitrogen-free extract of coarse fodders, viz., 4.226 Cals. per gram. As a whole, the figures given on p. 329 show a_ tendency toward an increased production of methane with an increase in the proportion of crude fiber, but considerable variations are found in individual eases. It is evident, therefore, from these results, as well as from those already cited in connection with the experiments upon starch and upon molasses, that a variety of factors influence the extent of this fermentation. THE FOOD AS A SOURCE OF ENERGY. 329 100 Parts Digested Carbohydrates Metaboline Contain Energy of lable Energy ————| Methane of Total per Grm. | Digested ‘Cates || Carbo Crude Nitrogen- Redeata: ydrates fibers | pee | eae | Peg INEM OW DAY polis oait see's kin Sin ete Oli 68.3 0.532 3.694 es Gor PIV US es A Bae Ae Re Cg 34.2 65.8 0.580 3.646 fs Cart JUNE see ees, Shades ie foe ae 35.0 65.0 0.579 3.647 gs OE CAN Eh An Dae a ran onan 537) ob) 62a 0.458 3.768 oo ia ANG oe Ste RO ny UR nea tee 38.6 61.4 0.569 3.629 ss Seema Mnyay Wt te dh bone se Wats, AMD 40.4 59.6 0.597 3.657 as Oo cue OEnd Nene doa ae aoul Ile) 58.1 0.574 83 4(6tayY Glovers ues nie oo EATEN 42.6 De: 0.678 3.548 Oatestraw alle aye k eet en. 47.8 5) Pe 0.595 3.631 WWihea straw: Votes. c.f hee os ee: 59.1 40.9 0.894 | 3.332 A comparison of the methane production with the digestibility of the feeding-stuffs shows in general that the former is greatest when the latter is least, that is, with the feeding-stuffs which tend to remain longest in the digestive tract. Here too, however, excep- tions occur, and it would appear that the physical condition of the feeding-stuff is not without its influence. The exceedingly com- plicated nature of digestion in ruminants, and the fact that it is a chemical rather than a physiological process, and is therefore sub- ject to considerable variations according to the nature and amount of the food, render it difficult, if not impossible, with our present knowledge to compute very trustworthy averages for the amount of energy carried off in this way. CrubeE Finer. Ruminants.—Both the ultimate composition and the heat of combustion of the digested nitrogen-free extract have been shown to agree quite closely with those of starch, and the nutritive value of the former has commonly been assumed to be the same as that of the latter. If we are justified in somewhat extending this, and assuming that the nitrogen-free extract of coarse fodders suffers the same loss by the methane fermentation as does starch, the figures of the preceding paragraphs supply data for computing the corresponding loss suffered by the crude fiber. ‘330 PRINCIPLES OF ANIMAL .NUTRITION. In the case of the extracted straw, for example, there was digested in the total of the two experiments : CLUE GEL IY: totes tats ects e's ane Bae 4033 grams Nitrogen-free extract....3........-.> 888“ Assuming the loss of energy in the methane to have been 0.422 Cal. per gram of nitrogen-free extract digested (the same as that found by Kellner for starch, p. 325), the 888 grams of these sub- stances correspond to a loss of 374.7 Cals. Subtracting this from the total loss of 2850.2 Cals., we have 2475.5 Cals. as the energy of the methane produced from 4033 grams of crude fiber, which is equal to 0.614 Cal. per gram. The total energy of the digested crude fiber was shown on p. 304 to be approximately 4.220 Cals. per gram. Subtracting the loss in the methane, 0.614 Cal., leaves 3.606 Cals. as the metabolizable energy of one gram of digested crude fiber. A similar computation of the average results upon the other coarse fodders affords the figures of the following table for the metabo- lizable energy of one gram of digestible crude fiber: Digestible Crude Fiber of Loss a —— pas ss : Cals. HELA COCCLISEEAW. ts /acceiohey tere lops eros ele tee vet toes 0.614 3.606 ELS TER MIOMO rs a nah s,s) «che lela tele apa efeeke 0.909 3.311 {ead deghtompasalunciilOne. | cies aie seen 0.614 3.606 Oat straw added to basal ration .......... 0.783 3.437 Wheat straw added to basal ration......... 1.219 3.001 The loss of energy in methane, as thus computed, is in all instances greater than in the case of starch. Owing, however, to the slightly higher value obtained for the gross energy of the digested crude fiber, the difference in metabolizable energy between starch and crude fiber is somewhat less marked, and is hardly sufficient of itself to justify assigning a materially lower nutritive value to the latter. It is worthy of note also that the loss in the methane appears to be a very variable one, justifying the conclusion already reached that other factors than the proximate composition of the food ma- terially affect the extent of the methane fermentation. The Horse.-—The production of methane by the horse appears to be much less copious than that by ruminants. Lehmann, Hage- THE FOOD AS A SOURCE OF ENERGY. 331 mann & Zuntz* in eight respiration experiments obtained the following results, the hydrocarbons being computed as methane: Crude Fiber Digested. Methane Excreted. 698.5 grams 26.8 grams His Oh SOR | Seat rae 13.0 ras cc “ce DOE O ce ce (a9 16.4 (a9 cc ce 31 0 (a9 (as (a3 a9 il ce ia (79 23.0 (as As already noted on p. 326, Zuntz + has pointed out that the fermentation of the food in the horse takes place largely in the ececum and after the more digestible carbohydrates have been resorbed. The authors consequently compute the excretion of methane entirely upon the crude fiber of the food. On the average . of the eight somewhat discordant experiments, in which the food consisted of oats, hay, and cut straw, 100 grams of digested crude fiber yielded 4.7 grams of methane, which corresponds exactly with the results reported by Tappeiner { for the artificial fermenta-~ tion of cellulose. In the same experiments an excretion of approxi- mately 0.203 gram of hydrogen per 100 grams digested crude fiber was observed. Deducting the corresponding amounts of energy from the energy of the apparently digested cellulose we have— Womibenmercy Ob feram..i..o 2.5004 4,220 Cals. Energy of CH, (0.047 gram). 0.627 Cal. Energy of H (0.002 gram)... 0.070 “ 0.697 Cal. Metabolizable energy of 1 gram............. 3.523 Cals.§ While less methane is apparently produced by the horse than by the ox, the assumption that it all arises from the fermentation of the crude fiber gives.the latter a metabolizable energy not greatly different from that found in the case of the ox. It is of course * Landw. Jahrb., 28, 125. + Arch. ges. Physiol., 49, 477. t Zeit. f. Biol., 20, 88. € As computed by the authors, 3.487 Cals. on the basis of 4.185 Cals. total energy per gram of crude fiber. 332 PRINCIPLES OF ANIMAL NUTRITION. implied in this that the metabolizable energy of the digested nitro- gen-free extract is the same as its gross energy. Summary.—The results recorded in the preceding paragraphs regarding the metabolizable energy of the several classes of digesti- ble nutrients are summarized in the following table: METABOLIZABLE ENERGY OF DIGESTIBLE NUTRIENTS. Cattle, Horse, Swine, Cals. per Cals. per Cals. per Grm. Grm. Grm. Protein (N X 6.25): . Brom :wheat gluten: 25s ok one eicae 4.894 a ie Se ENE a7 0 hase iasicke? Sonic 4.958 Pe beetamolasses #2 huens oe ene ee cia 3.984 ge TATKOU. PPR ol. cca. penne heel: Shia el eee 4.083 oe «ration of oats, hay, and straw 3.228 eee VTE AGO W) WA okisce ccc ces ee ae 13272 moiet eUMIMIOURIY SION Rein cies Srcatore ieee ease 3.057(?) BY PUG crcksey ys atatecnele Sere bus Myre oe oboe (?) Fat : From, peanut iil. ))ci. sane cee ai eee eee 8.821 chay (etheriextract) itis ..i7 0562. Ge 8.322 Carbohydrates : Starch, Kellner’s experiments ........... 3.763 SP kainnis Aiea yen Cra ee 3.648 Nitrogen-free extract (assumed) .........]......... 4.185 Crude fiber, of extracted straw .......... 3.606 . Shes, “Ran Tem alone.) gh. a0 gl saat 3.311 cs eo“ «* added to basal ration .| 3.606 # (lo a OMLISULAW: UR Cctahycceeiren 3.437 HJ tte ee WEA SULA Wie scien cone 3.001 ss ee Hibs v0.20 hap) 810) Meade Aa nema eG os Ae 3.523 Perhaps the most striking thing about these figures is the wide range of the results upon the same class of nutrients. For reasons already stated, this is most noticeable with the protein, but it is sufficiently marked also with the other two groups. Moreover, such meager data as we possess regarding other animals than the ox indicate that the results vary with the species of animal, a fact which should not surprise us, but which, nevertheless, adds mate- rially to the complexity of the subject and greatly widens the range of necessary investigation. It is obvious, therefore, that at present our knowledge is too imperfect to allow of the assignment of average values for the metabolizable energy of the different classes of THE FOOD AS A SOURCE OF ENERGY. 333 nutrients (as ordinarily determined) even for a single species of animal. The results tabulated above, however, are amply sufficient to justify the statement on p. 279 that Rubner’s averages are not appli- cable to herbivorous animals, and that the metabolizable energy as computed with their aid is hkely to vary widely from the truth. Indeed, since Rubner’s factor for fat (9.38 Cals. per gram) is 2.27 times that for carbohydrates and protein (4.1 Cals. per gram) a computation of the metabolizable energy of feeding-stuffs or rations as it has not uncommonly been made simply gives a series of figures about 4.1 times as great as that obtained for total digestible matter when the digestible fat is reduced to its starch equivalent by multi- plication by 24. So far, then, as a comparison of one feeding-stuff or ration with another is concerned, this process adds no whit to our knowledege. It does, it is true, give some idea, albeit an inade- quate one, of the total amount of metabolizable energy present. As yet, however, our accurate knowledge of the energy requirements of domestic animals for various purposes is comparatively meager. If we base our computations on the feeding standards now current, we simply repeat with them the useless multiplication performed on the feeding-stuffs. On the other hand, if we take the results of such exact experiments on the metabolism of energy as are available, then, as the above results show, we shall be computing the energy requirements upon one basis and the energy supply upon a mate- rially different one. Significance of the Results.—A much more fundamental prob- lem than that raised in the foregoing paragraph confronts us when we come to reflect upon the general method by which it has been attempted to compute the metabolizable energy of nutrients, and to consider the real significance of the results. In so doing we may properly confine ourselves to the results upon cattle, those for horses and for swine being more or less fragmentary and uncertain. By far the larger proportion of the results above tabulated, as well as the most’ important of them, are based on experiments in which additions were made to a basal ration, the computation being by difference. As was pointed out in discussing the apparent metabolizable energy of the organic matter on previous pages, and as was specifically illustrated in the case of one experiment on 334 PRINCIPLES OF ANIMAL NUTRITION. molasses (p. 291), the difference in the metabolizable energy of the excreta is the algebraic sum of the differences in the energy of methane, urine, and the several proximate ingredients of the feces, and some of these differences may be positive and others negative. The computations of the metabolizable energy of the organic matter as made in the. earlier paragraphs give the net result to the animal under the condition of the experiment and include all the secondary effects upon digestion, etc. In the computations here considered Kellner’s methods have been followed. In the first place the influence of the added feed upon the digestibility of the basal ration has been eliminated by basing the computation upon the digested matter. Still further, such effects as the decrease of the methane excretion in certain of the experiments with molasses, oil, and starch, and the diminished export of energy in the urine under the influence of starch and ex- tracted straw, have not entered into the computation. In other words, the endeavor has been to determine the actual amount of energy liberated by the breaking down of the molecules of the di- gested starch or protein or fat in the organism without regard to these various incidental effects; that is, to determine the real and not the apparent metabolizable energy. Either method of computation would seem to be entirely defensi- ble, and our choice between them will be largely determined by the point of view. For the purposes of the physiologist, desirous of tracing the details of the chemistry and physics of metabolism, the results obtained by the latter method will be of more interest. On the other hand, the student of nutrition who is especially in- terested in the problems of feeding will not fail to note that the results thus reached represent, from his standpoint, only a part of the truth. They show (barring errors of detail) how much energy is liberated in the body from the several nutrients, but the loss or saving of energy in the incidental processes constitutes just as real a part of the balance of energy which he wishes to determine as the energy liberated from the nutrients themselves, and must be taken account of in his calculations. Whether this can best be done by using some such factors as those just tabulated and then making a correction for these incidental gains and losses, or whether the method followed in the earlier paragraphs is to be preferred, it THE FOOD, ASA SOURCE OF ENERGY. 335 would probably be premature to attempt to decide at present. Pending further investigation and experience, however, it should be remembered that the figures on p. 332 will give, in most cases, too high results for the metabolizable energy of mixed rations, while the same thing is still more emphatically true of Rubner’s factors. One additional point requires mention. In discussing the metabolizable energy of protein it was pointed out (p. 320) that it is at least a plausible hypothesis that the proteids are metabo- lized in the herbivora substantially as in carnivora, and that the excess of energy in the urine is derived from the non-nitrogenous ingredients of the food. If we accept this hypothesis, however, and assume the metabolizable energy of protein (N X 6.25) to be in the neighborhood of 4.9 Cals. per gram, then the figures for the non-nitrogenous nutrients are subject to a still further deduction, especially in the case of coarse fodders. If we were to assign to the fat its full value as given, it would not be difficult to compute the metabolizable energy of the carbohydrates on this basis, and probably a set of factors could be worked out which would correspond to the actual results obtained with mixed rations. These, however, if successfully obtained, would be substantially identical with the results given on previous pages for the apparent metabolizable energy of total or of digestible organic matter, and it does not appear that the former would offer sufficient advantages over the latter to justify the labor involved in their computation. CHAPTER XI. INTERNAL WORK. § 1. The Expenditure of Energy by the Body. Havine considered the food in the light of a supply of energy to the animal, it now becomes desirable to take a more general view of the subject and inquire into the uses to which the energy of the food is applied in the organism. We have already distinguished between that portion of the potential energy of the food which is convertible into kinetic energy in the body, and which we have here called metabolizable energy, and that portion of it which is rejected for one reason or enother in the potential form in the various excreta. This latter portion we may dismiss from consideration for the present. The former portion—the metabolizable energy—as common experience informs us, is applied to two main purposes. First, it supplies the energy for carrying on the various activities of the body. Second, if the supply is in excess of the requirements of the body a portion of it may temporarily escape conversion into the kinetic form and he stored up as gain of tissue, notably of fat. We may say briefly, then, that the metabolizable energy of the food is used, first, for the production of “physiological work” and second, for the storage of energy. Physiological Work.—The term “physiological work” in the previous sentence is employed in a somewhat loose and general sense to designate all those activities in the body which are sus- tained by the metabolizable energy of the food and whose ultimate result is the production of heat or motion. A more definite idea of what the term includes may be gained by a consideration of the chief factors. which go to make up the physiological work of the body. 336 INTERNAL WORK. 337% Work oF THE VoLuNTARY MuscLes.—The most obvious form of physiological work is that performed by the contraction of the voluntary muscles, either in the performance of useful work or in the various incidental movements made during the waking hours. In a sense the production of muscular work may be said to be the chief end of the metabolizable energy of the food, inasmuch as all the other activities of the body (apart from the reproductive functions and, of course, from mental activities) are accessory to this. In amount, however, the energy of muscular work is much less than the energy expended in other forms of physiological work and consumes a comparatively small percentage of the metaboliz- able energy of the food. TyrerRNAL Worx.—The body of an animal in what we commonly speak of as a state of rest is still performing a large amount of work. The most evident forms of this are the work of circulation and res- piration. In addition to these, however, there are less obvious kinds of work whose total is probably very considerable. The body is an ageregate of living cells. The living cell, however, is constantly carrying on activities of various sorts, and these’ activities require a supply of energy, although how much of the energy of the food is consumed in the various processes of secretion, osmosis, karyoki- nesis, etc., it is difficult to say. In the numerous varieties of internal work the energy involved passes through various forms. Ultimately, however, since it accomplishes no work upon the surroundings of the animal, it is converted into heat and leaves the body either by radiation and conduction, as the latent heat of water vapor or as the sensible heat of the excreta. Work or DIGESTION AND ASSIMILATION.—Logically the work of digestion and assimilation would be classed as part of the internal work of the body, but motives of convenience make it desirable to consider it separately. In a fasting animal, with the digestive tract empty, the various forms of internal work indicated above go on with a considerable degree of constancy, and the resulting heat production is quite uniform under like conditions. If food be given to such an animal there results very promptly an increase in the excretion of carbon 338 PRINCIPLES OF ANIMAL NUTRITION. dioxide and the absorption of oxygen and in the amount of heat produced. In general terms this is brought about in four ways: First, the muscular work required for masticating and swallow- ing the food and moving it through the digestive apparatus involves an expenditure of energy which finally gives rise to the evolution of heat. Second, the activity of the various secreting glands of the diges- tive tract is stimulated, again making a demand for energy and giving rise to an increased heat production. Third, the work of the resorbing cells likewise makes demand . for energy. Fourth, the various fermentations, cleavages, hydrations, and syntheses which the food ingredients undergo in the course of diges- tion, resorption, and assimilation may occasion in individual cases either an evolution or an absorption of energy, but taken as a whole result in the production of a greater or less amount of heat and con- sume a corresponding amount of the metabolizable energy of the food. Propuction or Hrat.—The body temperature of the healthy warm-blooded animal is practically constant, any considerable variation from the average indicating some serious disturbance of the animal economy. Since this temperature is ordinarily higher than that of the environment, a continual production of heat is necessary to maintain it. As stated above, the various forms of internal work, including the work of digestion and assimilation, give rise in the aggregate to the evolution of a large amount of heat, and this heat is of course available for the maintenance of the body temperature. Whether its amount is sufficient for this purpose, or whether under any or all circumstances there is a production of heat for its own sake, simply to keep the animal warm, is still a debatable question. Many eminent physiologists, notably Chauveau and his associates, hold that the primary function of metabolisrn is to furnish energy for the physiological processes going on in the body. They hold that the potential energy of the food is converted imme- diately into some form of physiological energy, which in its turn, in fulfilling its functions, is converted into’ heat which serves inci- dentally to maintain the body temperature. In other words, they regard heat as substantially an excretion and would consider that INTERNAL WORK. 399 in the course of organic evolution those forms have survived in which the incidental heat production was sufficient to meet the demand of the environment. Other physiologists no less eminent hold that at least an ex- ceptional demand for heat (low external temperature) may be met by a direct combustion of food or body material for that purpose. - We shall have occasion later to give further consideration to these divergent views. SummMary.—The following scheme may serve to summarize what has been said above regarding the uses to which the energy of the food is put in the body, the possible direct heat production being considered, for convenience, as part of the physiological work of the body in order to include it among the other forms of the expenditure of energy : Energy of excreta. Work of voluntary muscles. Gross energy Physiological | Internal work. Metabolizable work energy Work of digestion and assimilation. Heat production. Storage of energy. For the sake of directness of statement, language has been used above which seems to imply that the food is directly oxidized some- what like the fuel in a locomotive. While statistically the effect is the same as if this were the case, it must not be forgotten that the body itself constitutes a reservoir of potential energy and that the energy liberated in its various activities comes primarily from the potential energy stored up in its various tissues, while the func- tion of the food is to make good the Joss this occasioned. The metabolism of matter and energy in the body might be compared to the exchange of water in a mill-pond. The water in the pond may represent the materials of the body itself, while the water running in at the upper end represents the supply of matter and energy in the food, and that going down the flume to the mill- wheel the metabolism required for the production of physiological work as above defined. The water flowing into the pond does not immediately turn the wheel, but becomes part of the pond and ‘loses its identity. Part of it may be drawn into the main current | 340 PRINCIPLES OF ANIMAL NUTRITION. and enter the flume comparatively soon, while another part may remain in the pond for a long time. Pursuing the comparison still further, as but a small proportion of the energy liberated in the de- scent of the water in the flume takes the form of mechanical energy, most of it being converted into heat, so in the body but a small proportion of the energy expended in physiological work takes ultimately the form of mechanical energy. Finally, if we compare the flow of water in the stream below the dam to the heat produc- tion of the body, that flow may be increased, in case of need, in two ways, viz., by opening the gate wider and letting more water pass through the flume (increase of physiological work) or by lowering the dam and allowing more water to flow over, corresponding to a heat production for its own sake, if such takes place. The succeeding sections of this chapter will be devoted to a con- sideration of the expenditure of energy in the various forms of in- ternal work, including that of digestion and assimilation, while the subjects of the production of external work and of, the storage of energy may be more appropriately considered in subsequent chap- ters. § 2. The Fasting Metabolism. If an animal be deprived of food for a sufficient length of time to empty the digestive tract, and kept in a state of rest as regards muscular exertion, the expenditure of energy in external work and in the work of digestion and assimilation are both eliminated, while there can be, of course, no storage of energy. Under these condi- tions the metabolism of energy in the organism is confined to the maintenance of those essential vital activities which were grouped above under the term “internal work” in the narrower sense, to- gether with any direct production of heat for its own sake. The fasting animal, then, affords the most favorable opportunity to study the laws governing the expenditure of energy for the internal work of the body. The fasting metabolism has already been con- sidered in Part I from the side of the matter involved; here we are concerned with its energy relations. Nature of Demands for Energy. Without attempting to enter into details, it may be said that the internal work of the fasting organism may be roughly classified INTERNAL WORK. 341 as muscular, glandular, and cellular. To the demand for energy for these purposes we have probably to add, at least in some cases, a direct demand for heat production. MuscuLtar Work.—The more obvious forms of muscular work in the quiescent animal are circulation and respiration. To these are to be added as minor factors any movements of other in- ternal organs, and especially the general tonus of the muscular system, while finally, the various incidental movements made by such an animal, although not logically belonging in the category of internal work, practically have to be classed there in actual experimentation. It would be aside from the purpose of this volume to enter into any detailed consideration of these forms of internal work, but a few general statements regarding their amount may be of interest. Circulation.—The work performed by the heart is determined by two factors, viz., the weight of the blood moved and the mean arterial pressure overcome. Quite divergent results have been ob- tained by various investigators for the former factor, while the latter is more readily determinable. Zuntz & Hagemann * estimate the output of blood by the heart of the horse from a comparison between the blood gases and the respiratory exchange, and compute the expenditure of. energy in circulation to be 5.01 per cent. of the total metabolism of the horse in a state of rest and 3.77 per cent. during moderate work. Hill 7 estimates the average work of the heart in man at about 24,000 kilogram-meters in twenty-four hours. As the velocity of the circulation increases, the friction in the pe- ripheral blood-vessels, and consequently the arterial pressure, rap- idly augments, so that in case of severe muscular exertion, for ex- ample, the work of the heart may readily become excessive. Respiration.—The work of respiration consists essentially of an expansion of the thorax against the resistance caused by the atmospheric pressure and the elasticity of the lungs and the rib cartilages. Zuntz & Hagemann { estimate its amount in the horse at about 4.7 per cent. of the total metabolism. Muscular Tonus.—As was pointed out in Chapter VI, the living * Landw. Jahrb., 27, Supp. III, 371. t Schiiffer’s Text-book of Physiology, II, 43. t Loc. cit. 342 PRINCIPLES OF ANIMAL NUTRITION. muscle is in a constant state of slight tension or tonus, and is con- stantly the seat of metabolic activities which we may presume serve, in part at least, to maintain that tonus. This is, of course, equivalent to saying that there is a continual liberation of kinetic energy in the resting muscle, which temporarily takes the form of muscular elasticity but ultimately appears as heat. As to the amount of energy thus liberated exact information seems to be lack- ing, but in view of the relatively large mass of the muscles as com- pared with that of the other active tissues we may assume that it is not inconsiderable. The same thing would seem to be indicated also, as noted in Chapter VI (p. 191), by the great decrease in the metabolism and heat production ordinarily observed as the result of paralysis of the motor nerves by curari. Incidental Muscular Work.—It is rare that an animal, even when at rest in the ordinary sense, does not execute more or less motions of various parts of the body, all of which involve a conver- sion of potential energy into the kinetic form. Even apparently insignificant movements may materially increase the amount of metabolism. Zuntz & Hagemann,* for example, report a respira- tion experiment upon a horse in which the uneasiness caused by the presence of a few flies in the chamber of the apparatus caused an increase of over 10 per cent. in the metabolism. Johanson, Lan- dergren, Sonden & Tigerstedt,f in two-hour periods, found the fol- lowing average and’ minimum values per day and kilogram weight for the excretion of carbon dioxide by a fasting man during sleep, the results plainly showing the increased metabolism due to rest- lessness: Average, Minimum, Grms. Grms. Third day (first day of fasting) ......... Eone 7.296 6.744 POUNEIAY “ASS Fac che biscotti iav ane eta ce amt te 7.704 6.768 Pitty yee GVery: TESULESS) ie Tr nh otlstererastend eit 8.136 7.524 Sree e pce cn Gras rchcve MCE Te wile atta ecereaetoeete 7.488 6.684 Gey Crile isk. ani | She lees Serer oel tia ei ok CP ar mere 7.212 6.564 Subsequently Johanson {| compared the excretion of carbon dioxide by a fasting man when simply lying in bed (awake) with * Landw. Jahrb., 28, 161. + Skand. Arch. f. Physiol., 7, 29. t Ibid., 8, 85. " INTERNAL. WORK. 343 that obtained when all the muscles were as perfectly relaxed as possible. The results per hour were: U5 Sana al 6) 276 (a lt ae 24.94 grams Complete muscular relaxation..... AOSTA. Furthermore, there is more or less muscular exertion involved during the waking hours in maintaining the relative position of the different members of the body. This is notably true of the effort of standing. In experiments with the respiration-calorimeter under the writer’s direction* the heat production of a steer per minute while standing and lying was found to be approximately as follows: | Lying, | Standing, Ratio, Lying to Cals. Cals. Standing. WPETIOCMAGE any ate Scicreane oes 5 BRR, We0al 13 1 Beal Oho! EBSA os ae ie aie ene 5.781 7.700 il 2 1 aay AO UN CAR es asa aera 6.310 8.177 1 : 1.296 SCP RT) ear ee VANE cin fe A ers al 6.605 8.495 le 286) Zuntz + found an even greater difference in the case of the dog, the average oxygen consumption per minute being— LC yigh aN twa eet ceo EMSA hg am Pa ee ran Aa CLC: UAC eR Rest atas atte MeN OR tl 245.6 “ In experiments of any considerable duration on normal animals it is impossible to avoid more or less expenditure of energy in this incidental muscular work, while it is often a matter of difficulty to make the different periods of an experiment comparable in this respect. GLANDULAR Work.—The activity of the various secretory, ab- sorptive, and excretory organs may be conveniently summarized under this head. While the purpose of the glandular metabolism is, in the majority of cases, primarily a chemical one, the accom- ‘plishment of this purpose involves an expenditure of energy which, * Proc. Soc Prom. Agr. Sci, 1902. t+ Arch. ges. Physiol , 68, 191. 344 PRINCIPLES OF ANIMAL NUTRITION. so far as it is not removed from the body in the potential form in the secretions or excretions, ultimately takes the form of heat. Moreover, the fundamental features of glandular metabolism appear to be indentical with those of muscular metabolism. Thus Henderson * has shown that the active submaxillary gland of the dog does not lose nitrogen as compared with the inactive gland, but does lose weight, evidently from the metabolism of non- nitrogenous matter. Similarly, Bancroft ¢ found the respiratory exchange of the same gland during activity to be three or four times that during rest. If we may accept these results as typical, we must conclude that glandular, like muscular metabolism is largely at the expense of non-nitrogenous matter, and shallnot hesitate to summarize the two together as parts of the internal work of the body. CrELLULAR Work.—While both muscular and glandular work are forms of cell activity, a passing mention may be made for the sake of completeness of such processes as imbibition, filtration, osmosis, protoplasmic motion, karyokinesis, ete., which, while taking place in the various organs, are so general in their nature and form so essential a part of our conception of cell life that it seems proper to speak of them collectively as cellular work. As to the quantitative importance of these activities, so far as they can be differentiated from the special functions of the various organs, we lack the data for forming any definite conception, although it would appear that it must be small. Heat Production and Regulation. As we have just seen, the forms of internal work are numerous and some of them are not readily accessible to measurement. All of them, however, have this in common, that the energy used in their performance ultimately assumes the form of heat. This being the case, while the single factors making up the internal work are not readily determined, a determination of the total heat produced by a fasting animal in a state of rest (either directly or by computation from the amount and kind of matter metabolized) will show the total! amount of energy consumed in the * Am. Jour. Physiol., 3, 19. t Journal of Physiol , 27, 31. INTERNAL WORK. 345 performance of the internal work and how it varies under varying conditions. Carnivorous animals, with their short and relatively simply digestive canal, lend themselves most readily to experiments of this sort although rabbits and guinea-pigs have been employed to some extent, as well as, for short periods, men. Constancy Under Uniform Conditions. — Attention has al- ready been called in Chapter IV to the relative constancy of the total metabolism of the fasting animal, particularly as compared with the total mass of active tissue in the body. This constancy has been especially emphasized by Rubner,* and forms the basis of his determinations of the replacement values of the several nutrients wnich will be considered in the following chapter. With a rabbit the following daily averages, computed per 100 parts of nitrogen in the body, were obtained: Day of Experiment. eee a Rata clined. bind storeichithiemp er eevee sees Pi AK, 16.2 NintebOManheentaeek seis yee es 2.19 13.8 Since the ratio of proteids to fat metabolized did not vary greatly in these trials, the total amount of carbon dioxide ex- creted may be taken as an approximately accurate measure of the total metabolism. For the several days of the experiment, this was as follows: Carbon Dioxide Excreted. a SVereee Live ay. eight, cou! Per Head, Live Wocht, Grms. Grms. Tenn ie Oy een Is sate in a ea ec el aN ot 2091 36.1 17.26 SSVENulys we torsion eae eye k 2002 all 3S 15.90 EN Giratina ene edocs naan BN PAS er 1907 SUze 15.90 Aenitheysyeneen au hire cee ie ee 1864 29.2 UGE (05) MaWelititry mare iecome rt cr toe 1764 30.2 Thea aS piimrbeent hye ee kee Aeney arora IFS 27.4 15.81 Hourtecnthie. steer ee eso 1716 27.4 15.95 HRELEGTIEN, s wea tea cath eee nehncs ier. 1697 2000 15.90 * Zeit. f. Biol., 17, 214; 19, 312. 346 PRINCIPLES OF ANIMAL NUTRITION. With a dog the following results were obtained: Carbon Dioxide ; ; Fat Excreted. Live Nitrogen NMatab= Paks ey Day. Weight, in Urine, ab at ee Grms. Grms. Guns’ Per Head Per Kg. Grins. Weinht, Grms. IIPS HE ls otcie artne felete seco ators 9190 4.23 51.74 187.4 20.70 SECON Kieren acer sielerete 8920 2.89 45.94 L570 17.838 Mount siseen cles sek sas 8620 3.65 42.90 146.9 17.99 Trait Fe hye etre er encucneys 8190 2.59 45.55 Koy Rr 18.70 JU year aeerdicn 8030 2.41 41.83 140.4 17.86 Utweltithy sr. cict.e eis ever orer- 7890 2.53 36.48 127.9 16.13 SPHITGSEMUEM Meyers etevetane sos 7970 2.98 37.45 134.8 17.06 THOUPLCEMDIK. citer sus tis ois 7830 3.02 33.80 125.0 16.12 Rubner also quotes the following results by Kuckein on a cock: Carbon Dioxide per Day. ’ “Ke. Live Weight. ALE 6 CRAG red eee ae aS bE be 21.73 grams. APU. ean RE ie eM consonants 2 oh Seventh. nsod cece cee ah eS aes Rubner’s experiments on a guinea-pig * show a similar constancy, the heat production being computed from the total metabolism: Heat Production Day. per Kilogram. Baarertiches |) ALA RBAN, 0, Sa rshares nee tate aa hoe 149.9 Cals. SECOMC. a hk sce aeee seen ee 162° 6% A bl coune Imag ten yaar ne wanes ak aes ag brye8 TS yet 3 Vie ek PROT Ess Mies te wane ade) ok eee me eta a 1402504 Prisha foo x. os tyeeetay Oeste ee hartge cathe. LSA hes Oa SSL UET:, ei weirs Si cee te al navel ramen eaerici Ss T5096" ute Senpenthiti «soy pte ok oleate ak el eee ee TUL ERTAONY S35 wend Ssh Sree sk Ales can a eee ae L550 wee Nambhik. (eat a utes etn tah eenses 162..67".- Concerning this point Rubner says: + “The uniformity of the fasting metabolism proves that, in spite of the undoubted limita- tation of all the voluntary functions which can cause a consump- tion of matter, no further reduction of the metabolism is possible, * Biologische Gesetze, p. 15. + Loc! cit., 19, 326. INTERNAL WORK. 347 and we recognize from this that we have to do here with a constant metabolism which is indissolubly connected with life itself. The animal in the fasting state adjusts itselj to the minimum metabolism.’ In other words, the metabolism and consequent heat production of the fasting, quiescent animal speedily reaches a minimum which represents the aggregate demands of the vital activities of the organism for energy; that is, which represents the internal work of the body in the sense in which the words are here used, plus the metabolism required for any direct production of heat which may be necessary to maintain the normal temperature of the animal. The relative importance of the internal work in the narrower sense and of the direct heat production as regards their demands for a supply of energy will appear more clearly when we consider, in the following paragraphs, the effects of varying conditions, and particularly of the thermal environment, upon the heat produc- tion of the fasting animal. Influence of Thermal Environment on Heat Production.*—An animal, particularly in the temperate zones, is subject to consider- able variations of external conditions, particularly of temperature, which, in the first place, tend to affect the rate at which it emits heat, and secondarily, within certain limits to modify the amount of heat produced in the body. Bopy TrEMPERATURE.—AS regards their body temperature, animals have been divided into two great classes: the cold-blooded (poikilothermic), whose temperature as a rule differs but slightly from that of their surroundings, and the warm-blooded (homoio- thermic), whose temperature remains approximately constant dur- ing health whatever be that of their surroundings. Since all our domestic animals, as well as man himself, belong to the second group, it alone will be considered in the following paragraphs. Since the animal is constantly producing heat in the various ways already indicated, it is obvious that in order to maintain a constant body temperature it must be able to give off this heat at the same average rate at which it is produced. Janke illustrates this necessity in a striking manner by computing that if the * The discussion of this subject follows to a considerabie extent that of Ranke in the introduction to his ‘‘EKinwirkung des Tropenklimas aui die Erniihrung des Menschen,’’ Berlin, 1900. 348 PRINCIPLES OF ANIMAL NUTRITION. body of a man were unable to give off the heat which it pro- duces, a single day would suffice to raise it to a pasteurizing temperature, while in the course of a year, at the same rate, a temperature of over 17,000° C. would be reached. Furthermore, since the external conditions of temperature are subject to frequent and sudden changes, it is obvious that the balance between heat production and emission must be capable of prompt adjustment to varying circumstances. Tuermic Rance.—tThe ability of the animal body to adapt itself to changes of temperature has, however, often been ex- aggerated. Asa matter of fact this adaptation is possible only within a comparatively narrow range, and unless we hold fast to this fundamental idea we are in danger of reaching fallacious and absurd conclusions. Man has considerably extended the range of climate within which he can exist by means of clothing, shelter, artificial heat, and even to a slight extent artificial refrigeration, and this fact often leads unconsciously to an overestimate of the . possible thermic range. These means of artificial protection re- sult essentially in modifying the temperature to which the body is actually exposed, and the same is true in a less degree of the differ- ences in the summer and winter coats of animals. The fact still remains that the actual thermic range of any species is and must be strictly limited. All life implies a certain amount of metabclism, and consequently of heat production. With rising temperature a point must sooner or later be reached at which the animal is unable to impart this heat to its surroundings as fast as it is produced, and in which the rise in temperature ne¢essarily resulting will prove fatal. With falling temperature a point will be reached at which the greatest possible amount of metabolism in the body will be unable to equal the rate at which heat is lost to the surroundings and the animal will perish from cold. Both the maximum and minimum points and the extent of the thermic range will vary for different species and varieties of animals, but at best the range is relatively small. Means or RecuiatTion.—Within the thermic range of a given animal the adjustment to its thermal environment may be effected in one or both of two ways, viz., by a regulation of the rate of emis- sion of heat or by a variation in the heat production. INTERNAL WORK. 349 Regulation of Rate of Emission.—Heat is given off by the body in four principal ways: (1) by. conduction; (2) by radiation; (3) by evaporation of water; (4) as the sensible heat of the excreta. By conduction, heat is transferred directly from the body to its surroundings, including such solid objects as it may be in con- tact with and particularly the air. The rate of loss in this way will depend upon the relative temperature and conductivity of the surface of the body and of the substances with which it is in contact, and in case of the air will be also influenced by the rate of motion of the latter relatively to that of the body. By radiation, a constant exchange of heat goes on between the body and objects not in immediate contact with it. Since the body is usually warmer than its surroundings, the net result of this ex- change is a loss of heat by the body, the amount of which depends upon the specific radiating power of the surface of the body and upon the difference in temperature between the latter and sur- rounding objects. By evaporation of water from the skin, and to a less degree from the mucous membrane of the air-passages, a large amount of heat may be removed as latent heat of vaporization. The amount of water evaporated from the skin, and, consequently the rate at which heat is carried off, will depend in part on the amount transpired by the skin, but when this is abundant, chiefly upon the relative humidity of the air and upon its rate of movement. Finally, the heat removed in the excreta is relatively small, and in the case of the fasting animal in particular is insignificant as compared with the losses through the other three channels. In general we may say that the rate of emission of heat in all of the first three ways named is determined by two sets of condi- tions, viz., those relating to the environment of the animal (tem- perature, relative humidity, movement of air) and those relating to the animal itself and particularly to its surface. The conditions of the first set, of course, are beyond the control of the organism. Their tendency is to produce the same effect upon the rate of emission of heat that they would upon that of a lifeless body, viz., to increase it as the temperature of the surroundings is lowered and their conducting power increased. In the case of the 350 PRINCIPLES OF ANIMAL NUTRITION. living animal this tendency is offset by the regulative mechanism acting upon the second set of conditions, so that, e.g., a fall in the temperature of its surroundings within certain limits instead of increasing the rate of emission, as in the case of a lifeless body, has no effect upon it. This regulation of the rate of emission is effected chiefly by means of changes in the temperature and state of moisture of the skin, brought about on the one hand through the vaso-motor mechanism ‘and on the other through the special nerves of perspiration. Variations of external temperature acting. upon the peripheral nerves influence by reflex action the activity of the vaso-motor nerves which regulate the caliber of the minute blood-vessels. Exposure to cold causes a contraction of the capillaries of the skin and a relaxation of those of the viscera. As a result more blood passes through the latter, while the flow through the skin is diminished, the latter becomes paler, and since the heat, given off is not fully replaced by the blood current, its temperature falls. Exposure to heat has the contrary effect. The capillaries of the skin relax, more blood flows through them, the skin becomes flushed and its temperature rises, while the flow of blood to the viscera is checked. A fall in the temperature of the skin, however, tends to diminish the rate of emission of heat both by conduction and radia- tion, while a rise in its temperature has the opposite effect, thus counteracting the tendency of changes of external temperature. In other words, the “emission constant” of the skin ehanges to meet changes in external conditions. So exactly are these mech- anisms adjusted in health that within certain rather narrow limits they maintain the rate of emission of heat, and consequently the average temperature of the body, very nearly constant. Obviously, however, there must be a limit above which the temperature and radiating power of the skin cannot be increased to compensate for a rise in external temperature. The second method of regulation then comes more markedly into play through the familiar act of perspiration, or sweating. At high temperatures the activity of the sweat-glands is greatly stimulated, in part doubtless by the more abundant supply of blood to the skin, but chiefly by reflex stimulation of the special nerves which control the secretion of sweat. The evaporation of the relatively large amount INTERNAL K’ORK. 351 of water thus supplied to the surface of the skin is a powerful means of refrigeration, as we know no less from common experience than from scientific determinations, the evaporation of a single gram of water requiring approximately 0.592 Cal. of heat. With very high temperatures, especially in a humid atmosphere, however, even this method of disposing of the heat becomes insufficient and the extreme upper limit of the thermal range is passed. These two methods of regulation of the body temperature are often spoken of collectively as “physical” regulation. Variations in Amount of Heat Produced.—Just as there is a superior limit beyond which the regulation of the body tempera- ture by the means above described cannot be carried, so it is obvious that there must be a lower limit of regulation. However niuch the cutaneous circulation may be reduced, the skin will always lose heat to a sufficiently cold environment faster than it is being generated by the internal work of the body. Under these circumstances the only method by which the temperature of the animal can be main- tained is an increase in the rate of generation of heat. That changes of external temperature affect the amount of heat generated was shown by the experiments of Lavoisier and the observations of Liebig, but Liebermeister* appears to have been the first'to clearly enunciate the theory of regulation by variations in the rate of production. The fact of such regulation has been fully demonstrated by numerous subsequent investigators. As a typical example we may take the well-known experiments of Theo- dor + on a cat, some of the results of which are as follows: 2 Temperature, CarbonDioxide Oxygen Temperature. CarbonDioxide. Oxygen Deg. xcreted, Taken Up, Deg. Excreted, Taken Up, Cent. Grms. Grms. Cent. Grms. Grms. —5.5 19.83 17.48 Wes 17.63 Ff yl —3.0 18.42 18.26 16.3 113 97/53 14.74 O22 18.24 19.95 2 (eal 14.34 12.78 35.0 17.90 14.82 29.6 1sel2 10.87 Numerous other investigators have obtained similar results, but the effect of low temperature in stimulating the heat produc-. tion of warm-blooded animals is too well established to require an * Arch f. (Anat. u.) Physiol., 1860, pp. 520 and 589; 1861, p. 661. t Zeit. f. Biol., 14, 51. Sb ks PRINCIPLES OF ANIMAL NUTRITION. extended citation of authorities here. Some of Rubner’s * more recent results, however, are of interest as showing the delicacy of the reaction. The experiments were made on fasting dogs in a state of complete rest, the heat production being computed from the total metabolism of carbon and nitrogen: Tempera- Heat Production per ture, Deg. C. Kg. in 24 Hours. IS Ee ane hip BEES yh Tea aed 8 78.68 Cals. ve wc Pt Osher dre rRtol ate, s1are fo. (CC See Ui RE bat nega 2 eal Neen 69.78 ik UR hare ea A 67:06“ ee Sib ea ge aeeoas aoe 40; 60.0% L220 Fas EE Re ae ae B92138 i" 7 15.9 dic li Me ...5 85.99“ DOD Ariss Se Aca rn Se ny USA she aig eeeta ey oem 39°00 =" Ill Mee onl On Oe ee age g Soul TIAL ene WR RA ees “coe: = This method of regulation of the body temperature is often briefly designated as “chemical” regulation. Just how the additional generation of heat is effected is not so clear. From the fact that the muscles are the seat of a very large part of the heat production of the body we should naturally be inclined to look to them as the source of the increase. In quite a number of experiments on man, of which those of A. Loewy + and of Johansson { may be especially mentioned, a stimulation of the heat production with falling temperature was only observed when there was visible muscular action, such as shivering, while in the other cases only the “physical” regulation occurred. Any contrac- tion of the muscles would of course be a source of heat, but the in- crease with falling external temperature has been repeatedly observed with animals in the absence of this obvious cause. Whether in such eases there is an increase in the tonus of the muscles, involv- ing an increase in their metabolism, or whether, through some form of reflex stimulation, the rate of oxidation is accelerated * Biologische Gesetze, p. 10. + Arch. ges. Physiol., 46, 189. tf Skand. Arch. f. Physiol., 7, 123. INTERNAL WORK. 395 simply for the sake of the heat produced is still an unsettled ques- tion and one which, for our present purpose, we need not pause to_consider. As to the fact of the increase there is no question. CriTicAL TEMPERATURE.—In early writings upon this subject the influence of external temperature in increasing or diminishing the heat production of the body was frequently spoken of as if it were of unlimited application, and the same idea has passed more or less fully into the popular literature of the subject. But little reflection is necessary, however, to show that this cannot be the case. Common observation teaches us that neither our own metab- olism nor that of our domestic animals, as roughly measured by the consumption of food, is affected, for example, by the difference between winter and summer to any such extent as would correspond to the difference in average temperature. Moreover, if every rise in external temperature diminished the heat production, there would be a temperature at which no heat production at all would occur and at which, therefore, life could exist without metabolism, which is a contradiction in terms. ‘This extreme case renders clear the fundamental error of this view, viz., that of regarding the heat production as an end in itself and not as, substantially, an incident of the general metabolism. Carl Voit* was the first to demonstrate by exact scientific experiments the limits within which the influence of temperature upon metabolism (the so-called chemical regulation) is confined. His experiments were a continuation of those of Theodor (p. 351), and were made upon a man weighing about 70 kgs. and wearing ordinary clothing. After exposure for some time to the tempera- ture to be tested he passed six hours in the chamber of the respira- tion apparatus, fasting and in complete rest. During the six hours the excretion of carbon dioxide and nitrogen was as follows: Temperature. yaa | Nitrosey Heo ee cea uly Naoeee Grms. Grms. eg. C. Grms. Grms. 4.4 210.7 4.23 234.5 01 164.8 3.40 6.5 206.0 4.05 24.2: 166.5 3.34 9.0 192.0 4.20 267 160.0 3.97 14.3 ifs}5). 11 3.81 30.0 170.6 : 16.2 158.3 4.00 * Zeit. f. Biol., 14, 57. 354 PRINCIPLES OF ANIMAL NUTRITION. Later and more comprehensive experiments with animals by Rubner have given corresponding results. Thus with two guinea- pigs the following figures were obtained in 24-hour experi- ments: * Mature Animal. Young Animal. Temperature | Temperature | CO, per Kg. ||Temperature | Temperature | CO, per Kg. of Air, of Animal, and Hour, of Air, of Animal, and Hour, Deg. C. Deg. C. Grms. Deg. C. Deg. C. Grms. 0) 3/510) 2.905 0) 38.7 4.500 Teel BY a2 PAC SL 10 38.6 3.433 20.8 37.4 1.766 20 38.6 2.283 PA eof 37.0 1.540 30 38.7 1.778 30.3 BAe aka 35 39.2 2.266 34.9 38.2 15273 40.0 39.5 1.454 A later experiment by Rubner ¢ upon a dog, in which the heat production was measured by a calorimeter, gave the following results: Temperature of Air. Heat Production per Kg. Fe oe OMe RARE. ee eth hasih SEC Sea R ET 83.5 Cals. Lee GAR Ricks. satiate Ween ee Nectte REE 6320 BOD ER eve eremn ew rato yena mes #2 On Mactan me tate Dow a Oe eee i eT acne Sagat eh samCNe taht So ceeen ei ie SOI) aaa dele By ro) SMe Rogue caylee EAE hy | DO NZ wits The uniform testimony of these various experiments is that for each species there is a certain external temperature at which the metabolism and consequent heat production reach a minimum. With man in ordinary clothing it would appear to lie at about 15° C.,f with the dog at about 20° C., and with the guinea-pig at about 30°-35° C. Below this point the heat production rises or falls with changes of external temperature; or, in other words, the constancy of the body temperature is secured, in part at least, by * Biologische Gesetze, p. 13. + Archiv f. Hygiene, 11, 285. ¢ Rubner (Biol. Gesetze, p. 30) says that for naked man it is about 37° C. INTERNAL WORK. 355 means of the so-called “chemical” regulation, that is, by variations in the production of heat. Above this point the heat production, instead of a further de- crease, shows an increase, which, however, is slight as compared with the differences observed as a result of the “chemical” regu- lation. Here we are obviously in the domain of the “ physical” regulation—the regulation by changes in the emission constant of the skin. This temperature at which the chemical regulation ceases, and which presumably varies for different species of animals, Ranke calls the critical temperature. Below it the regulation is chiefly “chemical,” above it chiefly “physical.’”” The slight in- crease in the metabolism above the critical point is plausibly ex- plained as due to the greater activity of the organs of circulation, respiration, and perspiration required for the “physical” regula- tion. Rubner’s experiments also show that the portion of the thermic range lying above the critical temperature falls into two distinct subdivisions. For a certain distance above that point, the factors chiefly concerned in the regulation of the body temperature are conduction and radiation, which keep pace with the rising tem- perature in the manner already explained. At the same time, there is a small increase in the rate of evaporation of water, approxi- mately equivalent to the slight increase in the metabolism above the critical temperature to which attention has just been called. Matters go on in this way through a certain range of temperature until the regulative capacity of the vaso-motor mechanism is utilized to its maximum. If the external temperature still rises, the emission of heat by conduction and radiation begins to decrease as it would in a lifeless object, and the deficit thus occasioned is made up by a sudden increase in the exhalation of water vapor, coinciding, in man, with the production of visible perspiration. This sudden increase in the activity of the sweat-glands is accom- panied, as we should expect, by an increase in the total metabolism and consequent heat production. These phenomena are well illustrated by Rubner’s experiments with a fasting dog, already partially cited on the opposite page. The following table shows the amount of heat carried off by con- duction and radiation and as latent heat of water-vapor at the 356 PRiNCIPLES OF ANIMAL NUTRITION. several temperatures, and the same facts are also shown graphically in the accompanying diagram. (| Disposed of by | Temperature Total Heat of Air. Production, Conduction As Latent Deg. C. Cals. and Heat of Water Radiation, Vapor, Cals. Cals. ke 83.5 Wee 11.8 15.0 63.0 49.0 14.0 20.0 dono ote 16.2 25.0 54.2 31.3 16.9 30.0 56.2 30.0 26.2 HEAT OF WATER VAPOR 76°C 15°C 20 C 25°C 80°C It appears, then, that a certain minimum heat production, corresponding to the metabolism at the critical temperature, is inseparably connected with the life of the animal. The very fact that the heat production at this temperature is a minimum shows that its amount is not determined by the-needs of the organism for heat. If the latter were the controlling condition, a rise of exter- nal temperature should still further reduce the generation of heat, while as a matter of fact it is accompanied by a slight increase up to the point where the amount of heat produced overpasses the ability of the organism to dispose of it and death results. The natural conclusion is that the metabolism at the critical tem- perature is that which is necessary for the performance of the various functions of the organism, and that the heat production at this temperature, therefore, represents the amount of energy necessarily consumed in the internal work of the body. This is, of course, Rubner’s conclusion (p. 346) in a slightly altered form. The case is not unlike that of a room in which a fire must be kept burning for some purpose—a kitchen, for example. In winter, changes in external temperature may be met by burning more or INTERNAL WORK. 357 less fuel. As spring advances, the fire is reduced until it is just sufficient for the necessary work. If the weather still continues to grow warmer, since the fire cannot be further reduced the excess of heat is gotten rid of by opening the windows more or less, while, to carry out the analogy, in very hot weather we may sprinkle the floor or wet the walls to secure relief from heat through the evapora- tion of water. MopiFICcATION OF CONCEPTION OF CRITICAL TEMPERATURE.— In our discussion thus far we have considered chiefly the influence of external temperature on metabolism and heat production. This is, however, by no means. the only condition affecting the heat balance of the body. Of the other meteorological factors, three call for special mention, viz., wind, insolation, and in particular relative humidity. Wind.—In a perfectly still atmosphere, the layer of air next to the skin becomes warmed and loaded with water vapor and con- stitutes to a certain degree a protective envelope which is removed with comparative slowness by gaseous diffusion. A current of air, by removing this protecting layer and bringing fresh portions of air in contact with the body, increases the emission of heat both by conduction and by evaporation of water. This is in accord with the common experience that a degree of cold which can readily be borne when the air is still becomes intolerable in a brisk wind, while, on the other hand, the oppressiveness of a very hot day is sensibly relieved by even a slight breeze. The effect of wind, then, is to transpose the thermic range of the animal to a higher place in the thermometric scale, and to correspondingly raise the critical tem- perature. Insolation.—The direct rays of the sun impart a considerable amount of heat to the body. The effect of insolation, therefore, is the reverse of that of wind, viz., to transpose the thermal range and the critical temperature downward. A similar effect js pro- duced, of course, by the sun’s heat when reflected from surrounding objects, or by the radiant heat from hot. objects, the earth, for ex- ample. On the other hand, the radiation from the body into space during the night, especially at high altitudes and through a dry, clear atmosphere, may have a very considerable effect in the con- trary direction. 358 PRINCIPLES OF ANIMAL NUTRITION. Relative Humidity.—The relative humidity of the air affects the emission of heat in two principal ways. At Jow temperatures, where the evaporation of water plays a subordinate rdéle, it increases the rate of emission by increasing the conductivity and specific heat of the air, and also the conductivity of the skin and the body covering (hair, fleece, clothing), these effects outweighing its in- fluence in diminishing the relatively small amount of evaporation Moist cold is, therefore, more trying than dry cold. At high temperatures, on the other hand, where a large pro- portion of the heat is removed by evaporation, a high relative humidity, by checking this evaporation, hinders the emission of heat, this effect overbalancing any slight increase in conductivity. Moist heat is accordingly more oppressive than dry heat. An increase in the relative humidity, then, abbreviates the thermal range at both ends, while at moderate temperatures it appears to have but little effect, a diminution of the loss by evap- oration being compensated for by an increase in radiation and conduction. CriticAL THERMAL ENyIRONMENT.—From the above it is obvious that the so-called critical temperature is not a constant, even for the same species or the same individual, but that other factors than the temperature of the air materially affect it. What is constant (relatively at least) is the rate at which heat is produced in the body by the metabolism necessary to sustain its various physiological activities, that is, by its internal work. In order to maintain the normal body temperature, the total outflow of heat through its various channe]s must, at its minimum, be equal to the amount thus liberated in the organism. The outflow of heat, as we have seen. is affected directly or indirectly by the external conditions, and Jargely by the three just mentioned. In- numerable combinations of these conditions are possible, and any one of them whose combined effeet upon the animal is to make the outflow of heat equal to the rate of evolution due to the internal work will constitute a critical point in the above sense. Any change in such a set of conditions which tends to increase the outflow of heat will. like a fall in temperature, be met chiefly by an increased heat production, Any change tending in the opposite direction will be compensated for by the effects upon the organ- INTERNAL WORK. 359 ism whch have already been described and which result in maintain- ing the rate of emission of heat at a point enough higher than before to provide for carrying off the extra heat arising from the physio- logical work of the regulative mechanism itself. In other words, instead of a critical temperature, we get the conception of a critical thermal environment, which may be reached under a variety of conditions, and below which we have the domain of “chemical” regulation, while above it is the region of “physical” regulation. Influence of Size of Animal on Heat Production.—The total metabolism of a large animal is necessarily greater than that of a small one of the same species, but it is not proportional to the weight, being relatively greater in the smaller animal under com- parable conditions. RELATION OF HEAT PRopUCTION TO SuRFAcE.—Bergmann * appears to have been the first to connect the fact just stated with the relatively greater surface of the smaller animal, but we are in- debted to Rubner + for the first quantitative investigation of this phase of the subject. His experiments were made on six dogs whose weights varied from 3 to 24 kilograms each. The total metabolism (proteids and fat) of each of these animals in the fasting state was determined in from two to thirteen experiments, and from their results the average heat production of each animal was computed. The table on page 360 { shows the air temperature and the computed heat production per kilogram live weight in each experiment, and also the same corrected to the uniform tempera- ture of 15° C. This correction is made on the basis of Theodor’s experiments (see p. 351), according to which a difference of 1° Centigrade caused the amount of oxygen taken up by the cat to vary 1.11 per cent. The first series consists of a selection from Pettenkofer & Voit’s experiments. Whether we consider the observed or the corrected heat pro- duction we find that with the single exception of the corrected result for No. VI the amount per unit of live weight increases as the weight itsclf decreases. * Cited by Rubner. + Zeit. f. Biol , 19, 5385 t The figures of the table are computed from those given by Rubner in loc. cit, p 540, and differ in some cases from the summary given in loc. cit., p 542. L VI 4 X VII ¢ | PRINCIPLES OF ANIMAL NUTRITION. Date. Pettenkofer & Voit’s experiments Average “cc PAINE ce 23, Average “ec 14, Average 22, ce 25% | Average i 3, | Feb i Average une gO PISS Sees sarc ‘ “ce i mlppeliey.« (0) 0) 6, 0) esa a Bebei24: 18820 take. els ‘ > piule isi wl le; wi hi is. a “ce Janel 2s Ss) see es ee “ b¥sj (ea) Piieie'e ie) ole Dec pola USS nee cea “cc “cc falda $30, BBO ces Cale cers ‘ ce Heat Production per Kg. Live Air Tem- d Weight, Beet, gs. eg. C. Observed, Corrected Cals. Cals.’ 30.96 ize 38.99 39.90 29.87 Nite 7 31.82 BPAET, 31.44 16.2 37.39 37.89 30.38 13.9 36. 54 36.09 30.66 TGR2 36.18 36.66 24.11 | 15.0 | 41.40 | 41.40 PABA Ta) 1b 5y5(0) 40.22 40.22 PBI 1N55e,(0) 41.10 41.10 Py, 15.0 40.91 40.91 19.80 16.9 47.95 48.91 19.01 14.5 ANG) Tf! 45.48 18.79 16.0 42.79 43 .22 19.20 15.8 45.48 45.87 18.20 13.9 50.72 50.11 17.20 16.6 41.54 42.29 Lead 15-83 46.13 46.20 9.05 19.2 66.32 69.10 8.83 20.9 60.28 64.19 8.68 20.2 64.88 68 .58 8.53 NAO) 60.66 64.66 iit sil 18.4 61.16 63.42 10.87 20.0 57.86 61.04 9.51 19.95 61.86 65.16 6.84 15.8 65.01 Goan 6.36 23 .6 63.65 69.70 6.14 2067 58.13 61.79 6.83 18.2 FAURE 73.56 6.69 18.0 76.85 79.39 6.56 1550 71.60 71.60 6.40: 16.5 75.03 76.23 6.66 14.6 61.55 6heat 6.50 16.4 54.91 55.73 6.36 L6vs 53.64 54.39 6.21 15.9 52.57 53.09 6.15 18.4 61.06 63.22 5.98 19.2 54.24 56.73 6.44 17.6 63.02 64.79 3.34 15.0 84.45 84.45 3.05 ib Aker g 97 .S6 95.41 2.91 20.6 80.00 84.88 3.10 | 16.1 87.44 25 INTERNAL WORK. 301 SUMMARY. Heat Production per Kg. Shae uae No. of voage Tiva Production Animal. c y Corrected (Corrected) ie. Obeewed, to 15°, als. ESL Cals. LES ee Renae oie 30.66 36.18 36.66 100 1H Re Ree aiterie ts PB (ll 40.91 40.91 112 NEES Poh ansietcors 19.20. 45.48 45.87 125 AVEC Pet pe yt We, FAO) 46.13 46.20 126 IV eA sere cites, © 9.51 61.86 65.16 178 VATA eRe cen es 6.44 63 .02 64.79 77 AVA ees a eee 33, IO) 87.44 88 .25 241 Rubner also determined approximately the surface exposed by his animals, in part by direct measurement and in part by calcu- lation, and computed the heat production per square meter of sur- face, with the following results: Heat No. of Animal. roy ilranuaee cies : i Cals. 13 Ua ne oe 10750 1046 dO oie, Bee encanta 8805 len 1 Caer eee ara Po 7500 1207 IVS a sicrdche sicene 7662 1097 = Wee ayer tokiss 5286 1183 AVES 7 hg Boe ee 3724 1120 6 ee 2423 1214 He also cites * the results of experiments by Senator on the heat production of fasting dogs, and a respiration experiment by Reg- nault & Reiset, as follows: Heat Production. Live Weight Calculated No. Kegs. : Surface, Seb ee Tenens tl Morr creas ; Cals. face, Cals. VATU x See re 10.80 5423 52.31 1035 Oe aaa thetee 1.82 4285 53.76 944 Bee ae tiers 6.09 Stae) . 63 .04 1031 3,4) CARR Nees 5.68 3534 68 .40 1101 EXOD. 2b te eets 5.40 3462 74.16 UIUS/ CI Ceased Seo aie 4.24 2924 69.12 1003 BALI GR cd) ies aes Nes 5.59 3508 12.82 1154 * Loc. cit., p. 551. 362 PRINCIPLES OF ANIMAL NUTRITION. With one exception, the results per square meter agree very well with those of Rubner, both absolutely and relatively. Rubner has also shown in later experiments * that the same thing is substantially true of guinea-pigs, both at zero and at the temperature of about 30 degrees, at which the heat production is at its mimimum (critical temperature). He likewise points out ft that the well-known rapid metabolism of children as compared with adults is, so far as the available data show, quite closely pro- portional to their relative surface, and observations on the diet of a dwarf t gave a like result. Richet,§ working with an air-calorimeter of constant pressure, in which the heat production was measured by the amount of water displaced by the expansion of the air, obtained the following results on rabbits, and similar results upon guinea-pigs are also reported: ; ; reat Total Heat The & Number of Live Weight. ie Expressed in | Gat oF Experiments. Kgs. PCs ie c.c. of Water | Per Unit o als. Displaced. Surface. ae hth Bake a OPN, 4.730 119 NR nel steve sol cRete tiem 2.2-2.4 3.985 110 130 1 DARTS eR ic RS 2 2.42.6 3.820 115 129 Ah EF he Os ae U8 ee 2.6-2.8 3.650 119 abe / (SMe aetna Sharebee 2.8-3.0 3.570 125 128 Se EN ot eh, a ow aa 3.0-3.2 3.320 130 127 It would appear from the description of the experiments that only the heat given off by radiation and conduction was measured, no specific statements being made as to ventilation or as to the loss of heat as latent heat of water-vapor. The experiments were also of short duration, ranging from sixty to ninety minutes. The same author in later experiments || determined the respi- ratory exchange™ of rabbits of different weights. Computing the * Biologische Gesetze, pp. 17-18. + Zeit. f. Biol., 21, 390. t Biologische Gesetze, p: 9. § Archives de Physiol , 1885, II, 237. \| Ibid., 1890, pp. 17 and 483; 1891, p. 74; Comptes rend , 109, 190. 4| By means of an apparatus described briefly in Comptes rend., 104, 435 INTERNAL }/ORK. 363 results per square centimeter of surface by the use of Meeh’s for- mula (p. 364) he obtained the following figures, while similar results are also reported on guinea-pigs, rats, and birds. Carbon Dioxide Number of Average Live | per Square Cm. Experiments. Weight, Kegs. of Surface, Mers. AYRE Doses | Wee: 24.0 2.65 15h oy hop ene cer P35 2.60 Hote enemee pet RS 2S 71) rts Sefer ee, 9.0 2.81 DoE ea 6.5 2.69 TN an Ade 5.0 PA OY Ober cre ros cele Brel Pail Aba eeh ones. 3 ete 2.35 2.70 EK. Voit * has recently published an extended compilation of results bearing upon this point, including experiments on man, dogs, rabbits, swine, geese, and hens, the heat production being in most cases computed from the metabolism of carbon and nitrogen. The results when computed per square meter of surface, while they show not inconsiderable variations in some individual cases, never- theless as a whole substantially confirm the conclusion that the fasting metabolism is in general proportional to the surface. Still more recently Oppenheimer + has shown that the law also holds good for infants. Causes of Variations.—In comparing experiments made upon different animals by different observers at different times some variation in the results would naturally be expected. The experi- ments compiled by Voit were not all made at the same temperature, but the range in most cases is relatively small and can hardly have exerted any considerable influence. Differences between the differ- ent animals as to their normal rate of emission of heat (thickness of coat, quality of skin) may perhaps have also had an effect, although probably a small one. A more important source of error seems to lie, as Voit points out, in the computation of the results to unit surface, what is actually measured, of course. being the total heat production cf the animal. In solids which are of the same shape, that is, which + Zeit. f. Liol., £1, 113. + Ibid., 42, 147. 364 PRINCIPLES OF ANIMAL NUTRITION. are geometrically similar figures, the: surface is proportional to the two-thirds power of the volume. If we let S=surface and V=volume, then S=kV3, in which k is a constant for any given form. Putting W=weight, if the bodies have the same specific gravity we may substitute W for V in the above equation, and we then have Shwe On the assumption that the bodies of animals of the same species constitute similar figures and have the same specific gravity, the value of k has been determined for several species, as follows (the weight being expressed in kilograms and the surface in square centimeters) : Man. a ose ones 12.9 Meeh (Zeit. f. Biol., 15, 425). Dog ene wees 11.2 Rubner (Jbid., 19, 548). IRAN NS oc5e Se 12.9 Rubner (/bid., 19, 553). 1 Ca) c= et 9.02 Heaker (Zeit. f. Veterinark., 1894). Henise: aoe 10.45 Rubner (Zeit. f. Biol., 19, 553). Guinea-pig.... 8.89 Rubner (Biol. Gesetze, p. 17). vide : hae t Rubner (Zeit. f. Biol., 19, 553). The heat production per unit of surface in most of the foregoing experiments is computed by the use of these factors. The results of such computations, however, are necessarily approximations only. While animals of the same species are of the same general shape, we can by no means regard them as being exactly similar figures in the geometrical sense, nor can we safely assume them to be of exactly the same specific gravity, since changes in the amount of contents of stomach and intestines, and particularly in the quantity of fat in the body, would cause greater or less variations, Moreover, the state of fatness has, as Voit points out, still another effect. As an animal grows fat, the increase in size is mainly transverse and not longitudinal, the effect being like that of in- creasing the diameter of a cylinder of fixed length.* In such a case, however, the increase in the surface is not proportional to the two-thirds power of the volume, nor to the square root of the vol- * In the case of an animal, of course, we have the additional fact that the deposit of fat is not of uniform thickness over the whole surface of the body. INTERNAL WORK. 365 ume, as Voit states. The curved surface of the cylinder will be proportional to the square root of its volume, while the surface of the two ends will be proportional to the volume, and the ratio of total surface to volume will depend upon the ratio of length to diameter, being greater as the latter becomes less. Obviously, the calculation of the surface of an animal from its weight is a more or less uncertain one, and it is not surprising that the results should be somewhat fluctuating. It seems very doubt- ful, however, whether the larger differences found in Voit’s com- pilation can be explained in this way, and Voit shows that there is another factor to be considered, viz., the mass of active cells in the body, which has a material bearing on the results. Before proceeding to a discussion of this point, however, it is desirable to consider briefly the significance of the general fact of the close relation between heat production and surface. Significance of Results—Let us imagine an animal exposed to its “critical thermal environment” (p. 358) to gradually shrink in size while the external conditions remain the same. Under such circumstances the loss of heat to its surroundings will tend to in- crease relatively to its mass—that is, the body, like an inanimate object, will tend to cool more rapidly. This tendency can be met and the body temperature maintained in only two ways, viz., either by some modification of its surface—e.g., thicker hair—which will lower what we may call its emission constant, or by a relative in- crease in its rate of heat production. The results which we have been hgneetay show that in general the emission constant, i.e. the rate of heat emission per unit of surface, is substantially the same in small and large animals, and that the greater loss of heat in the former case is met by an increased production. In this aspect the effect is simply an ex- tension of the influence of falling temperature, the increased de- mand for heat being met by an increased supply, so that the extent of surface appears as the determining factor of the amount of met- abolism. In the case of an animal exposed to a temperature below the critical point, however, the increased demand for heat appears to be met largely by a stimulation of those processes of metabolism which do not result in any visible form of work, while the internal work, 366 PRINCIPLES OF ANIMAL NUTRITION. in the more restricted sense of the ordinary functions of the internal organs, does not seem to be materially affected. Are we justified in assuming the same thing to be true in our imagined shrinkage of an animal? In other words, is the work of the internal organs proportional to the mass of the body and is the increased heat production in the smaller animal due to the same cause as that observed when an animal is exposed to a falling temperature? It appears quite clear that this question must be answered in the negative. It is a well-known fact that the circulation, respira- ticn, and other functions are as a rule more active in small t!an in large animals, and this greater activity must necessarily result in the evolution of relatively more heat. If we raise the temperature of the surroundings to a point corresponding to the critical thermal environment, we may, as we have seen, regard the heat production as representing the internal work in the narrower sense. Rubner * reports experiments of this sort upon four guinea- pigs at 0° C. and at 30° C., which gave the following results for the production of carbon dioxide: CO, per Hour at 0° C. CO, per Hour at 30° C. Weight of jee eel Animal, Grms. Per Kg. Per Square Per Kg. Per Square Weight, Meter Surface, | Weight, Meter Surface, Grims. Grms. | Grms. ‘GQrms. 617 2.905 20280 1.289 1235 568 3.249 30.30 1.129 LORS 223 * 4,462 30.47 1.778 12.14 206 4.738 31.56 1.961 13.16 With the first and third of these animals direct experiment showed that the minimum production of carbon dioxide (critical point) was reached at about 30°-35°, and we may fairly assume this to be true of the other two. At 30° C., then, we may assume that the “chemical” regulation was practically eliminated and that the observed metabolism was that due to the work of the internal organs. Under these conditions, as the figures show, the metab- olism was still approximately proportional to the surface of the animal, and consequently greater per unit of weight in the smaller than in the larger animals. * Biologische Gesetze, pp. 12-18. INTERN.1L WORK. 267 Strong confirmation of this conclusion is afforded by the exper- iments previously cited. In many of them, notably in Rubner’s, the range of size is so great that to regard the differences in heat production as arising from a direct stimulation of the metab- olism, as in the case of a fall in the external temperature, leads to improbable consequences. Thus a comparison of the largest with the smallest dog in Rubner’s experiments (p. 361) shows that if we regard the heat production of the former as represent- ing simply the work of the internal organs, over 56 per cent. of the heat production of the smaller animal must, on the supposition that the internal work is proportional to the mass of the body, have arisen from some other source. Such an enormous increase in the metabolism of the body simply for the sake of heat production can hardly be regarded as probable. Still further, if we assume (compare p. 354) a temperature of about 20° C. to represent the critical point for the dog, then, on the hypothesis that the necessary internal work per unit of weight is the same, we find that a fall of one degree in temperature must have produced about six times the effect upon the metabolism of the smallest dog that it did on that of the largest one, while if we take the other alternative and seek to explain the results on the assumption of a higher critical tempera- ture for the smallest dog, we find for the latter about 364° C. Taking these considerations along with the results of Rubner’s trials with the four guinea-pigs, 1t seems most reasonable to assume, in default of more extensive investigations directed to this specific point, that the critical temperature is substantially the same for large and small animals of the same species and that the work of the internal organs is approximately proportional to the surface of the animal. Substantially the same conclusion has been reached by v. Héss- lin * from a quite different point of view. He points out that the increased production of heat below the critical temperature is not proportional to the difference in temperature between the body and its surroundings, as it should be, according to Newton’s law, if the emission constant of the surface remained the same. Taking as an example Theodor’s experiments (p. 351) he makes the following comparisons: * Arch. f. (Anat. u.) Physiol., 1888, p. 323. 368 PRINCIPLES OF ANIMAL NUTRITION. | Diff Betw Body 1 a et bat x Potécnal Temperate > Carbon Dioxide in 12 Hours. eee egrees. Dees Relative. Ee Relative. 30.8 ne 18.0) 12.03 1.00 PAD 17.9 Zao 14.34 1.19 1178} PAT 3.6 17.76 1.48 0.2 37.8 oB2D 18.24 152 —5.5 43.5 6.0 19.83 1.65 It would appear from these figures that even below the critical temperature the “physical” regulation plays a large part in the regulation of the body temperature, being simply supplemented by the “chemical” regulation, and that therefore the demand for heat has not the determining influence upon the heat production which Rubner supposes. According to v. Hdésslin the apparent dependence of the total metabolism upon the surface is only a par- ticular case of a general morphological law and he points out: First, that since, according to him, the velocity of the circula- tion does not vary greatly in large and small animals, the average amount of blood passing through the organs, and consequently their supply of oxygen, will be proportional to the total cross- section of the blood-vessels, which again, similar form being assumed, will be proportional to the two-thirds power of the volume (or weight) of the body. Second, that the capacity of the alimentary canal to digest and resorb food and thus to supply material for metabolism is limited in the same proportion. Third, that the work of locomotion—substantially the only form of external work in the wild state—at a given speed is pro- portional to the two-thirds power of the weight. In short, v. Hésslin claims 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. According to this view, then, the heat production of the fasting animal at the criti- cal temperature represents the internal work, which is proportional INTERNAL WORK. 369 to the two-thirds power of the volume of the body, while below this point there is superadded a stimulating effect upon the heat production, which, since it acts through the surface, we may assume to be proportional to the latter. Comparison of Species.—In the foregoing discussion compari- sons have been made between large and small animals of the same species, with the result that both their internal work and their total fasting metabolism appear to be closely proportional to their : surface. Going a step further and comparing the average results of the several species with each other, E. Voit * reaches the inter- esting and striking result that the same relation of total fasting metabolism to surface is substantially true as between different species. The following table contains the averages, with the addi- tion of the fasting metabolism of the horse as computed by Zuntz & Hagemann, which Voit believes with good reason to be too low: Fasting Metabolism. Average Tem- Average perature, Weight, Kgs. Deg. C. Per Kg., Per Square Cals. Meter, Cals. IORSe es fed a legen: Opal G2) 441 ils) > 948 INVIUTIC UR fe Aho Suysel ZO | 128 19.1 1078 iaaesee rn = ox ben 14.3 | 64.3 Bye il 1042 |DYoyee Sah) Maes eae 18.0 ee, LE ot 1039 LR] 0) on Oe cere tae 18.2 PB onl 776 CGOSe Head: haat 15.0 3.5 66.7 967 DERE Siete ee yo bata 18.5 2.0 AO 943 With the exception of the rabbit, the average heat production of these various animals per unit of surface does not show any ereater variations than have been observed between different animals of the same species, more or less of which, as we have seen, can probably be accounted for by errors in the estimate of the surface of the body. Accepting the fact of the general proportionality of heat pro- duction to surface, and passing over for the moment the excep- tional case of the rabbit, it is plain that the considerations which have been adduced in discussing the results upon the same socucut., p= 120: 370 PRINCIPLES CF ANIMAL NUTRITION. species will in the main apply to a comparison of different species. It is true that what data we have indicate that there may be more or less difference between the critical temperatures for different species, but in view of the enormous range in the size of the animals experimented on this cannot largely modify the results. Any reasonable assumptions as to critical temperatures and as to rates of variation per degree in heat production would still leave the corrected results substantially proportional to the surface. Appar- ently we must conclude that in all these different species, as well as in larger and smaller animals of the same species, the internal work, as measured by the total metabolism at the critical tem- perature, is substantially proportional to the surface. How generally this may be true we have at present no means of judging. It is clear, however, that in the process of organic evolution one of the very important factors has been the demand for heat exerted by the environment upon the animal. This has been met to some extent by modifications in the coat of the animal, but to a very large degree by changes in the rate of heat produc- tion, with the result that, other things being equal, those forms have survived whose normal heat production, resulting from internal work alone, was sufficient to maintain their temperature under the average conditions surrounding them without, on the one hand, calling largely into play the processes of “chemical” regulation, nor, on the other hand, producing so much heat as to render it difficult for the body to get rid of it. RELATION OF Herat Propuction To Mass or Tissur.—As already indicated, E. Voit. in his article cited above, has shown that while the heat production js in general proportional to the sur- face, there is also another determining factor, viz., the mass of the active cells in the organism, a rough measure of which is the total nitrogen of the body exclusive of that of the bones and the skin. This conclusion is based chiefly on experiments with fasting animals. As the weight of such an animal decreases, its relative surface must increase, and, as was shown on p. 364, probably more rapidly than in proportion to the two-thirds power of the weight. Under these circumstances we should naturally expect that the relative heat production would increase, but as a matter of fact it rather shows a tendency to decrease. EE. Voit, in discussing the results of Rubner s INTERNAL WORK. 371 and others, computes the heat production per unit of surface, and also compares it with the amount of nitrogen computed to be present in the organs of the animal on the several days of the ex- periment. The following results of one of Rubner’s experiments with rabbits are typical of those obtained in this way: Heat Production per Day. aeyeraee Day of Fasting. WeEne. i! Sra Per 100 Grms. Total, Per Kg.. | Meter of | Nitrogen, Cals. Cals. Surface, Cals. Cals. AUGUEROL Hoek Cho cl Bea el eRe eM te rest lama sta" 155 TARO) 730 310 GUTH mi Ga eh CR A a ae i pa 2093 117 55.9 556 243 WEVEMULMM ey semris eeeye fa eunk sete 2007 102 50.8 499 220 JNM ST EG fas OE BD oe re Re a 1923 97 SONS 488 221 Penthwand: tweltthy ... 62. 2). . 1841 95 al 8} 494 227 Thirteenth and fourteenth .. Wise 88 SOT 463 222, Fifteenth and sixteenth ....| 1646 81 49.2 ANSE uly | PASS Seventeenth and eighteenth) 1507 72 47.8 428 | 219 The heat production per unit of surface is seen to decrease at first rapidly and later more slowly, while the heat production per unit of weight shows but a slight decrease and that per unit of nitrogen scarcely any. From these and other similar results, Voit concludes that the law of the proportionality of heat production to surface as enunciated by Rubner and as extended by himself must be limited in its application to animals in like bodily condition, and that an animal with a low stock of nitrogenous tissue will, under the same conditions, show a lower heat production per unit of surface than a well-nourished animal. The exceptionally low average for the rabbit noted on p. 369 he explains on this hypoth- esis as resulting from the frequent use for such experiments of animals in a poorly nourished and “degenerate” condition re- sulting from long confinement. The result has an interesting bearing in another direction. Most of the experiments cited by Voit were probably made at tem- peratures below the critical points for the several animals. In our previous discussion we have assumed that under these cireum- stances the heat regulation is accomplished largely by “chemical” means—by variations in the rate of production. In these experi- 372 PRINCIPLES OF ANIMAL NUTRITION. ments, on the contrary, since the heat production decreased along with the decrease of nitrogenous tissue, we see the regulation of body temperature effected by a diminution in the rate of emission of heat, which, however, was in most cases less marked than in the instance just cited. Either we must conclude that the abnormal condition arising from fasting enables the animal to diminish the rate of emission of heat to an extent not possible to the well- nourished one, or we may suppose that in the latter case the stimu- lation of the metabolism by the abstraction of heat begins before the possibilities of “physical” regulation have been exhausted; that, in other words, the domains of “chemical” and “ physical” regulation overlap. Obviously the latter conclusion is entirely in harmony with v. Hésslin’s views as stated on pp. 367-8. § 3. The Expenditure of Energy in Digestion and Assimilation. General Conception. Foop Incrnases MretanorismM.—That the consumption of food increases the metabolism and consequent heat production in the body has been known since the time of Lavoisier, who observed the oxygen consumption of man to increase materially (about 37 per cent.) after a meal. Regnault & Reiset * also, among their respiration experiments on animals, report the following results for the oxygen consumption of two rabbits while fasting and after eating: . Fasting, After Eating, Animal. Grms. Grms. Aa GR Epa 2.018 3.124 Bye WEA Sic iere Ceo 3.590 Subsequent investigations by Vierodt, Smith, Speck, Fredericq, v. Mehring & Zuntz, Wolfers, Potthast, Hanriot & Richet,} Magnus- Levy, Zuntz & Hagemann, Laulanié, and others, some of which will be considered more specifically in subsequent paragraphs, have fully confirmed these earlier results, so that the fact of an increased met- abolism consequent upon the ingestion of food is undisputed, * Ann. de Chim. et de Phys. (3), 26, 414. + Ibid. (6), 22, 520. INTERNAL WORK. 373 CAUSE OF THE INCREASE.—Two possible explanations of the above fact naturally suggest themselves, viz., that, on the one hand, the more abundant supply of food material to the cells of the body may act as a direct stimulus to the metabolic processes, or, on the other hand, that the increased metabolism may arise from the greater activity of the organs of digestion, or finally, that both causes may act simultaneously. The results obtained by Speck,* who found that the increase began very promptly (within thirty minutes) after a meal, would indicate that it can hardly be due to a stimulating action of the resorbed food upon the general metabolism, but must arise, in large part at least, from the activity of the digestive organs. Specific investigations upon this point were undertaken by Zuntz & v. Mehring.t They found that glycerin, sugar, egg-albumin, puri- fied peptones, and the sodium salts of lactic and butyric acids { when injected into the circulation caused no material increase in the amount of oxygen consumed as determined in successive short periods by the Zuntz form of respiration apparatus. It is well estab- lished that some of these substances do increase the metabolism when given by the mouth, and the authors verified this fact for sugar and for sodium lactate and likewise showed that substances like sodium sulphate, which are not metabolized in the body, caused a similar rise in the metabolism when introduced into the digestive tract. They therefore conclude that the effect of the ingestion of food upon the metabolism is due chiefly to the expenditure of energy required in its digestion. Wolfers § and Potthast, || in experiments sup- plementary to those just mentioned, obtained confirmatory results. ~ On the other hand, Laulanié,{ in the experiments mentioned on p. 180 in their bearings upon the formation of fat from carbo- hydrates, obtained almost as marked an increase in the oxygen consumption subsequent to the injection of sugar into the circula- tion as after its administration by the mouth. * Arch. exper. Pathol. and Pharm., II, 1874, p. 405. + Arch. ges. Physiol., 15, 634; 32, 173. t The results of their experiments upon organic acids have already been cited in Chapter V, p. 157, in another connection. § Arch. ges. Physiol., 32, 222. || Ibid., 32, 280. 4] Archives de Physiol., 1896, p. 791. 374 PRINCIPLES OF ANIMAL NUTRITION. On the whole, however, and in view of the patent fact that the activity of the digestive apparatus consequent upon the consump- tion of food must lead to an expenditure of energy, the results of Zuntz & v. Mehring appear to have been generally accepted as proof that it is this influence rather than any direct effect of the resorbed food upon the metabolism to which the increase of the latter after a meal is to be ascribed. This increased expenditure is often, although rather loosely, spoken of as the “work of digestion.” Factors or Work oF Dicrestion.—lIn the process of digestion we are probably safe in assuming that the muscular work of pre- hension, mastication, deglutition, rumination, peristalsis, ete., con- stitutes an important source of heat production. A secondary source of heat production, which we may designate as glandular metabolism, is the activity of the various secretory glands which provide the digestive juices, to which may be added also the work of the resorptive mechanisms. Jl urthermore, the various processes of solution, hydration, cleavage, ete., which the nutrients undergo during digestion contribute their share to the general thermic effect. Fermentations.—To the above general sources of heat produc- tion during the digestive process, there is to be added as a very important one in the case of ruminating animals the extensive fer- mentation which the carbohydrates of the food undergo. We have already seen that a considerable fraction of the gross energy of these bodies is carried off in the potential form in the combustible gases produced. Dd Oe ee Fide all TO RAo +853 1951 63.4 BOO) AO CP arbenb hc ciety dao Sus hugs 442 —554 500 “ meat; 200 grms. starch} 1316 Se S7 691 79.1 500 grms. meat; 200 grms. dextrose} 1180 +108 662 89.7 Rubner’s Experiments : IN OGDIN Pars eis oede amen tems yoeicis tease 0 —436 76.12 grms. cane- sugar.......-- 305 Salil 320 104.9 TOS OW rns She we Tae ce ta 420 —22 414 98.6 Nothimare aie crc sais ols 2 pam Naoe 0) —451 97.3 grms. cane-sugar......./).--+ 389 — 87 364 93.6 |W A 9 Res Bh bie ead. eRe 68 By! 77 113.2 143.0 “ tn Rees ue Nee One hee 572 +1907 641 112.0 INOtHING Es ath tre eee aN oletee 0) —302 42.96 grms. starch (digested)...... 177 —138 164 92.6 INO) Tula Ae, Ren ar Bab Seen Ee Buns at are 0 —354 57.38 grms. starch (digested)...... 244 == 11240) 214 87.8 INOGDIN OAS. ot teeter haat eaten nee rie 0 —302 94.36 grms. cane-sugar; 67.96 grms. starch; 4.7 erms. fate o20 9% 2 9d). en 702 +365t| 667 95.0 300 grms. meat; 63.7 grms. dextrose 500 —126 ; 300 “ eens Reenter 559 —84 42 iit 300. * gaia ates a 691 +34 160 83.7 Magnus-Levy’s Experiments : iy 2121 +850 | 1890 89. ORICA Y TRCE ER othe ice esti ee ~| 2226 +934 | 2066 92. 999 —81 910 91. OO * Fasting metabolism estimated from previous experiments. + Gain of carbon assumed to be all in the form of fat. { Of dextrose added. Experiments on Herbivora.—Comparatively few experiments have been reported from which the net availability of the food of herbivorous animals can be computed, and as regards the common farm animals in particular there is an almost entire lack of data, although numerous experiments upon the relative value of various NET AVAILABLE ENERGY—MAINTENANCE. 419 materials for productive feeding have been reported and will be considered in the following chapter. Far.—Rubner’s experiments include one * in which fat was fed to a rabbit with the following results: Fasting. Fed BO anes: Metabolizable energy of food ............. 0 Cals. 227 Cals. TNOXIEM aM, Leo OR ic a rac Pen eee ae —101. * al tal PN Gamniover casting metabolism. joi. cs: 2 4cvils oh. dotaneeee PB} AE USELESS YCIIIE O61 3 93 ane Mo las cee Se See Bae gh | IP aL re 98 .2% In connection with his investigations upon cellulose, v. Knie- riem } also experimented upon the influence of fat on the metabo- lism of the rabbit. The basal ration consisted of milk, to which was added in the second period 3.94 grams of dry butter fat per day. Computing the amounts of energy by the use of Rubner’s factors the results were: Metabolizable Meteen Gate Gain, Gals. Net Availability, , S. H er Cent. Milk and butter fat .......... PAO 8 —19.5 IN GHIS 5 EE ee 2 sg a : 169.8 —55.2 IDIMEreNCe). «4.0 hy sede ak Bit ad) By), 7 95.2 CaRBOHYDRATES.—Rubner { reports three experiments with cane-sugar on a cock from which the following results are com- puted: Metaboliz- ian oo Food. ght pcrey Availability, ‘ Cals. | Total, en: Per Cent. Cals. olism, Cals. igehnines a cred Ruta es Gig whe 2990 34 grms. cane-sugar.../.... 136 —121 118 86.8 DNF VE III Oras 2 Sars ce enchant yeh 0 —258 45 grms. cane-sugar ........ 180 |e a 157 87.2 BO PD aor Aha, exe 200 — 53 205 102.5 * Zeit. f. Biol., 19, 333. + Ibid., 21,119. — ¢ Ibid., 19, 366. 420 PRINCIPLES OF ANIMAL NUTRITION, From the comparisons of cellulose and cane-sugar made by v. Knieriem (loc. cit.) and cited on p. 161, the’ following figures for the net availability of the energy of the latter substance may be com- puted: on a Gain. zB | & Metab- Net olizable ae A A Food per Day. Energy Over abiney z : of Food, Total, Basal | Per Cent. * c) als. Cals. Ration, ea) Za Cals. PITH Cee a MilkcAd | BS) 22 Schnee ke |, 85014 37 IV| 4 | “ +11 grms. cane-sugar..| 393.7 | —15.9 | 22.0 50.5 Ve! 3 | ees see s ro sl 48087) | 69-9] 10728 82.5 A series of experiments by May * upon the effect of fever on metabolism affords incidentally a few data bearing on the availa- bility of the energy of dextrose. In his experiment No. 5 (loc. cit., p- 23) the ingestion of 30 grams of grape-sugar, an amount approxi- mately equivalent to the fasting metabolism, caused no increase in the computed heat production as compared with that during fasting. In this experiment there was no fever. In Experiment No. 6 (p. 25), with fever, the ingestion of the same amount of grape-sugar pro- duced a computed gain of 2.88 grams carbon as fat, but caused no increase in the computed heat production. [Experiment No. 7 (p. 26) was similar to No. 6, but showed a decrease in the computed heat production, which, however, coincided with a decrease in the fever. On the whole, Mey’s results appear in accord with Rubner’s hypothesis of a substitution of the heat resulting from digestive work for that arising from the metabolism of tissue. Pentoses.—Cremer’s experiments + with rhamnose upon rabbits, cited in Part I, p. 157, afford data for computing the net availa- bility of this representative of the pentoses. For this purpose Cremer computes from the excretion of nitrogen and carbon (neg- lecting the feces), in the manner described in Chapter VIII, p. 253, the amount of energy liberated by the metabolism of protein and fat in the body, assuming that the rhamnose, after deducting the small amounts in feces and urine, was completely oxidized. The following are the results for each day of the four experiments: * Zeit. f. Biol., 30, 1. } Ibid.; 42, 451. NET AVAILABLE ENERGY—MAINTENANCE. 421 ee amps Se Ee ee he te ee Metabolizable Food, Grms. Energy of Food, Hows by Body, Experiment I : Ba SRR ry ee es 0 147.4 Rhamnose, 11.584 grms.... 45.3 114.0 INOUE acd soe «. 0: afaielsie-0'e's 2 0 113.3 Experiment II : TARO) ai agg ee oe a 0 180.7 Rhamnose, 17.09 grms..... 66.8 111.6 INUIT 52S ee oe aes 0 184.8 Experiment III : GUT SMe ae AES 0 129.1 Rhamnose, 18.96 grms..... 74.1 54.3 INGoltineree Oe era Net} 0 113.1 . (av’ge of two days) 0 113.4 Experiment IV : IOC 0S sche ciate Sees 0) 146.0 is EAR ra ee PE a 0 141.4 Rhamnose, 18.66 grms....... 72.9 53.3 22.0 98 .1 - S20 ea Da Sth ene * The total amount of rhamnose (24.3 grms.) was given on the first day, but it is estimated from the results for the carbon excretion that this amount of it was not metabolized until the second day. The results as to net availability obtained by comparison with the several fasting days vary considerably, as the following state- ment shows, several of them exceeding 100 per cent.: Experiment I. Compared.wathy first dayin ia iiekloe aces cs 74 per cent. % see ME MUEGIE CLE Weis teeta ag Sd Cae Negative Experiment IT. Compared with firstodaye ss An ie Seis els: 103 per cent. r Vo SAUMMIMGI Ceti aasaniateRietc rect o%ccase eS Sie Experiment IIT. Compared with first daily te eo Ue ees ee. 101 per cent. Be Pa eRHITOY Cai ee nsetale wee 5 25 a! See OMe Sle oe Second and third with fourth and fifth days. 80 “ “ Experiment IV’. Third compared with second day. ......... 121 per cent. " sh LOUDLY ea 9 812) of. ni OS ea 422 PRINCIPLES OF ANIMAL NUTRITION. The great variations in the results, as well as the large propor- tion of cases in which the availability appears to exceed 100 per cent., show that little value attaches to them as quantitative deter- minations, although they undoubtedly show that rhamnose pos- sesses a comparatively high nutritive value. Crude Fiber—The experiments of v. Knieriem have already been cited in Chapter V in their general bearings upon the metabo- lism of matter. As was there noted, certain corrections were neces- sary on account of the residue of undigested cellulose remaining in the digestive canal at the close of the experiment. The results given below are based on those computed by- the author, as sum- marized on p. 161, on the assumption that the resorption of the remaining digestible crude fiber was complete after two days. ra Gain. : (ogee onzable . ro = Food per Day. Energy Over oe one of Food, | ‘Total, | Basal | Per Cent. a) 2 So) Sere toxias Ty sts IMENTS Fa Ai cio ala tade foie hee a stetoke 341.7 |—46.8 shies wt ae Il| 10} “ + 22grms. crude fiber ee | 39.9 | 121.3* for eighit days y..u. 374.6 |— 6.99) 31'0 | 196.5¢ MUTA Psy | OTIC Se Sopa bras coeycqnts era cua 350.1 |—37.9 , ee * Compared with Period I. + Compared with Period III. It is evident from the above figures that while the experiments show qualitatively a nutritive value for the cellulose, they are in- sufficient for a quantitative determination of its amount. In striking contrast with these results are the conclusions drawn by Zuntz & Hagemann from their experiments upon the horse which have already been considered in the previous chapter (pp. 389-391). As was there explained in detail, these investigators have estimated the expenditure of energy in the digestion of crude fiber from a comparison of the computed heat production in two sets of experiments in which the proportion of coarse fodder eaten differed considerably, it being assumed that 9 per cent. of the metab- olizable energy of the nutrients other than crude fiber was consumed in their digestion. On this basis the digestive work caused by the crude fiber is computed at 2.086 Cals. per gram, or rather more than NET AVAILABLE ENERGY—MAINTENANCE. 423 its average metabolizable energy. In other words, it is computed that under the conditions of these experiments, with a ration more than sufficient for maintenance, the net availability of the energy of the crude fiber was practically zero. The authors report no experiments upon rations below the maintenance requirement, but appear to regard the metabolizable energy of the crude fiber as being indirectly available, under such conditions, substantially in the manner assumed by Rubner and already explained. As has been noted, Zuntz & Hagemann’s conclusions as to the value of crude fiber for work production are in apparent harmony with those of Wolff, which will be discussed in the next chapter, but on the other hand they contrast sharply with the results of Kellner (see Chapter XIII, § 1), who observed a high percentage utilization of the energy of one form of crude fiber ‘in the ration of fatten- ing cattle. On previous pages some reasons were presented for questioning the quantitative accuracy of Zuntz & Hagemann’s computations, but even aside from these their conclusions as re- gards the value of crude fiber are difficult to reconcile with obvious facts. Thus they compute (loc. cit., p. 280) that the expenditure of energy in the mastication and digestion of average straw is greater than its metabolizable energy, so that for the horse this material has a negative value. When forming part of a mainte- nance ration we mcy probably assume that below the critical amount of food (p. 408) the heat generated during the digestion of the straw would be of use to maintain the body temperature, but this could not possibly suspend the expenditure of energy in the various forms of internal work, such as respiration and circulation. Since, however, by hypothesis, the straw can contribute no energy directly for these purposes, it follows that the consumption of this material alone cannot reduce the loss of tissue below the amount requisite to supply energy for the internal work, while on an exclusive straw ration above the critical amount of food the more straw the animal consumed the sooner it would starve. Orcanic Actps.—The results of a considerable number of ex- periments in which salts of organic acids were ‘*njected into the blood have already been presented in Chapter V (p. 157). The general result was that lactic and butyric acids caused little or no increase in the heat production of the animal—in other words 424 PRINCIPLES OF ANIMAL NUTRITION. that practically all their potential energy was available to prevent loss of tissue. In such experiments, of course, there is no digestive work in the proper sense. What they indicate is that what we have called rather loosely the work of assimilation for these sub- stances is practically zero. Acetic acid, on the other hand, was found by Mallévre to increase the consumption of oxygen by from 10 to 17 per cent., indicating a considerable waste of energy directly or indirectly. TimotHy Hay.—The experiments described in the foregoing paragraphs relate to pure or nearly pure nutrients. Experiments upon a steer have been made by the writer in conjunction with Fries in which the availability of the apparent metabolizable energy of timothy hay has been determined. To a basal ration consider- ably below the maintenance requirement, consisting of 3250 grams of hay and 400 grams of linseed meal, three different additions of timothy hay were made, the digestibility of the ration in each period being determined, and likewise the total balance of nitrogen, carbon, and energy by means of the respiration-calorimeter. The results as to energy, uncorrected for the very small differences in the organic matter of the basal ration consumed and for the changes in the live weight of the animal, were as follows: * Period A. | Period B. Period C. Period D. Outgo, weed Outgo, incor! Outgo, |Income, Outgo, |Income, Cals. Cals. Cals. | Cals. Cals. Cals. Cals. Cals. A eyeto as epee oon eae hae sre 1 he oY Vere ae ZO 29 Tie ees 745 fy Ao) 3) | 29,647 Excreta: | | Bess ee or tn (ROO eee Wes) eee ae andy a Cakes | 14,276 Urine stacey: BES] enh le | Oral nes Tae | 1,220 Methane...... 996|...... Reiger oer era ee | 1,896 Metabolizable ...| 6,618]...... |: Qi4RBS aoe | WAP DOS oe cae | 12,255 14,923) 14,923) 20,297 20,297) 25,198} 25,198) 29,647| 29,647 Metabolizable ...]...... GiGiILS hacer DASD | mtr ie eae 12,255 Heat produced ..| 9,067|...... (AOPAO Ss 4 LOLGOG sees 111,183 Carer ioss.).te see PAO rc se ei oe) Ne ke] [eae | 1072 | | = 9,067| 9,067; 10,206 10,206} Lie2ee 11,222) 12,255! 12,255 | | * Proc. Soe. Prom. Agr. Sci,, 1902. For a full discussion of the revised figures and for later results on cover hay and maize meal, see U. 8. Dept. Agr , Bureau of Animal Industry, Bul- letins 51 and 74. NET AVAILABLE ENERGY—MAINTENANCE. 425 Subtracting the results on the basal ration of Period A from those of the other periods, as in previous cases, we have the following: there, Gain of Tissue, |NetAvailability, emo ayo Seis Goo ee eA S 9,482 —724 GAUL N (NA Aba SRO 6,618 —2,449 Difference.......... heh 2,864 1,725 60.24 IRS SOCIO con Sa cee tere E222 616 OTS TES AA ea a 6,618 —2.449 DIMEN! 25 ysoustentecnerareey- 4,604 3,065 66.57 J2tey Yoyo Ul DY 2 iy Paneer Rn 12,255 1,072 OS IRE ISIN iar SED 6,618 —2.249 Wilerence se sena ss os oe 5,637 3,521 62.46 PAW CTU CUtaaN a: Bem nue yete [ge eee cath Ce ccksa opel Sia aleleens et elias 63 .09 Strictly speaking, only the first of the above percentages repre- sents the net availability for maintenance, since the other two include some gain. From the difference observed between the metabolism of the animal standing and lying, however, it was computed approximately what the gains would have been had the same position been maintained for the whole twenty-four hours, with the following results: Metabolizable Gain, Standing, | Net Availability, Energy, Cals. Cals. Per Cent. Weriodue reser ccs a 9,482 —1,606 GWA: Seema s Sener a aeee avete 6,618 —3,507 Witterence! ii. )aleterecsist=.2, 3y< 2,864 1,901 66.37 12 rerarers bed Oye Cian cess eee pleases 11,222 — 550 SrA Ent, fore cia Sinisa teers 6,618 —3,507 WiikenenCe: ok ste s- 32 4,604 2,957 64.23 ReniOde Daecmaemiekinccen.: 12,255 23 Coe oe Near RN Sas od rare a ts 6,618 — 3,507 DiffeTenCe: .feretecis's ooo elo 5,637 3,539 62.62 TNNEIG IOS Sy Sobran recht ach ERGO GIRS CIty CHET ONION HITCIERERCREa B E 64.41 426 PRINCIPLES OF ANIMAL NUTRITION. Metabolizable Gain, Lying, Net Availability, Energy, Cals. Cals. Per Cent. °. BEIIOG de -1tee Cae EY. 9,482 easy Fae AD REA Ss oN han ls uae a 6,618 —1,046 Difference ...... rate ge 2,864 2,203 76.92 Period We vba ay. Gee 11,222 2,136 tO RANG. A iar ee ee) ety 6,618 —1,046 IMiHerence Ws akes ws ene 4,604 3,182 69.12 Perigds Dye dan ee! 12,255 2.743 SEs CAS Aa Res eeu ks WOR te 6,618 —1,046 Difference} nok ae 5,637 3,789 67.22 INNGEASE 2 oxo ttn shyt: Firs) | Ace ea aa Sate ba bee ae 71.08 The results are likewise shown graphically on the accompanying diagram, in which the full line represents the average availability 8000 7000 8000 9000 10000 11000 12000 METABOLIZABLE ENERGY, CALS, NET AVAILABLE ENERGY—MAINTENANCE. observed and the broken lines that computed respectively for standing and lying, while the points indicate the results for each neriod. As computed standing, the results are all practically at or below the maintenance point, and their fairly close agreement with each other and with those actually observed indicates that the net availability of the metabolizable energy of this sample of timothy hay was between 63 and 65 per cent. Summary.—The. foregoing data as to availability are sum- marized in the following table, those experiments in which the total ration was less than the maintenance requirement being separated 427 from those in which more or less gain by the body took place: EXPERIMENTS ON CARNIVORA. Below Maintenance. Proteids : Pettenkofer & Voit Magnus-Levy ..... Fat: Pettenkofer & Voit PRT Mer RN ae cise ete Starch : Pettenkofer & Voit. Magnus-Levy (rice). Dextrose : Cane-sugar : Jenbleyates aya AS wie ais Ke) aa NPR WOONN & a le oce) Fe St non HO 0 104.9 [ 98.6 6 2 Starch and Cane-sugar -: Teoma Psa o5 Oe os ool EXPERIMENTS ON HERBIVORA. Below Maintenance. - Fat: Per Cent. VAM ETVCTIA ane eee Beet eee 95.2 Cane-sugar : i) 86.8 ilo Grete yey e eeeeval. ruth ceete 87.2 102.5 Vall sGoraalsstns Goer aie atae SOLS 428 PRINCIPLES OF ANIMAL. NUTRITION. Above Maintenance. Proteids: Per Cent. Pettenkofer & Voit ....... 81.5 j Parle eee eee. Bias cence 79.0 Magnus-Levy .......:...- 84.0 Fat: ( 59.6 Pettenkofer & Voit..%.... / 93.7 73.8 98.6 RI TMeT cs sere ere sito ratote 94.9 89.1 98.5 Maarieleyy ates | agnus-Levy 97.0 Starch : T280 Pettenkofer & Voit....... 63.4 79.1 f 89.1 Oa eae agnus-Levy (rice) 92 8 Dextrose : Pettenkofer & Voit........ 89.7 RIDDEN Y ./s eit we Mineo es 83.7 Cane-sugar : MUD NERS fer; ae a ichete et taeseetels 112.0 Cane-sugar and Starch : RAUDNEI se eisai ciae tae tees Pentoses : 74.0 (?) 103.0 110.0 Cremer 2520. ieee 101.0 79.0 80.0 a PAL 88.0 Crude Fiber: ihay ove 12123 FAASMIETIEMN DS 4s serio vy. Knieriem i 126.5 Timothy Hay: Armsby & Fries.......... 63-65 Above Maintenance. Fat: Per Cent. Rubner’ 52:53. ston eee aoe 98.2 Cane-sugar : Ws KmMeriem.. Vv. ccs c cents rosea NET AVAILABLE ENERGY—MAINTENANCE. 429 It scarcely seems possible to draw any well-founded conclusions regarding the net availability of the several nutrients from such widely divergent results as those tabulated above, even if the ex- treme and obviously incorrect figures be discarded. Two things, however, seem worthy of remark. First, in but few cases does the net availability of the food reach 100 per cent., and most of those results relate to cane-sugar or rham- nose; that is, to cases in which some of the gain of carbon which is computed as fat may have been in the form of a carbohydrate. It would seem fairly safe to conclude, therefore, that no such complete substitution of the heat resulting from digestive work for that rc- sulting from the general metabolism took place as Rubner’s hypoth- esis supposes. Apparently, under the conditions of these experi- ments, there was, in most cases at least, a material loss of energy in digestive work. Second, there is no clear indication of a smaller loss of energy below than above the maintenance ration, although the wide range of the results renders a definite conclusion upon this point hazardous. This question, however, may be more properly considered in con- nection with a study of the utilization of the net available energy of the food. Finally, it is to be said that if the validity of the conception of a critical amount of food, as developed on p. 409, be admitted— that is, of an amount-of food below which the heat resulting from the work of digestion and assimilation is substituted for that pro- duced by the general metabolism, while above it no such suksttu- tion takes place—a very important element is lacking for the interpretation of the above experiments, except, perhaps, those on timothy hay, in which the uniformity of the results with varying amounts seems to show clearly that all the rations supplied more than the critical amount of food. If that conception is correct, to determine the real availability of the energy cf a food it is necessary to compare the effects of two quantities both of which are greater than the critical amount. On the other hand, the complete substitution of energy supposed by Rubner could only be demonstrated by comparing quantities less than the critical amount, while a comparison of quantities below the latter amount (including, of course, fasting) with those exceeding it 430 PRINCIPLES OF ANIMAL NUTRITION. can give only mixed results varying with the quantities com- pared.* It seems tolerably clear, then, that the whole subject of the net availability of foods and nutrients needs reinvestigation by more rigorous methods and with due regard to the amounts of the food materials compared and to the thermal environment of the animals experimented upon. Discussion of Results. For the reasons just stated, any strict quantitative discussion of the above results seems impossible. At the same time, certain general conclusions may be at least tentatively deduced from them which, even though to a considerable extent speculative, may at least serve provisionally as a connecting thread between the known facts. Influence of Amount of Food on Availability.—In the fore- going paragraphs it has been tacitly assumed that, the amount of food eaten has no influence on its availability, or, to state it in another way, that the expenditure of energy in digestion and assimi- lation is proportional to the quantity of food. To express the same thing in mathematical terms, we have assumed, in constructing the diagram on p. 410, that the net available energy is a linear function of the metabolizable energy. While it seems highly probable that such is the case the only ex- periments bearing specifically upon this question of which the writer is aware are those upon timothy hay just cited. An examination of the graphic representation of the results strongly supports the hypothesis that the net availability of the food is independent of its amount, but the evidence of so few experiments must naturally be accepted with some reserve. The other recorded results, as computed above, apart from the possible source of uncertainty pointed out on p. 429, show such considerable variations in indi- vidual cases that it scarcely seems possible to reach any definite conclusions from them regarding the influence of quantity of food. As will appear in the next chapter, the extensive respiration exper- iments made in recent years at the Méckern Experiment Station by G. Kithn and O. Kellner upon fattening cattle indicate that the * Rubner, in his latest publication (Gesetze des Energieverbrauchs bei cer Erniihrung, Leipsie and Vienna, 1902) has also adopted this view. NET AVAILABLE ENERGY—MAINTENANCE. 431 _actual gain obtained (expressed in terms of energy), at least within certain limits, is proportional to the amount of metabolizable energy supplied in excess of maintenance. This would mean that above the maintenance ration the energy required for digestion and assimilation plus that consumed in the chemical changes incident to the formation of new tissue (compare p. 396) is proportional to the amount of food. If this be true it seems more reasonable to conclude that each of these forms of work separately is propor- tional to the amount of food than to assume a compensation between the two, and granting this, we should have every reason to suppose that the same proportionality would hold good for the work of digestion and assimilation below the maintenance requirement. Character of Food.—The investigations of Zuntz & Hagemann (pp. 3885-393) have shown that, in the case of the horse at least and doubtless with other animals also, the work of digestion and assimilation varies with the kind of food, a result which is entirely in accordance with what we should expect.. For reasons stated in describing their experiments, their results are to be regarded as qualitative rather than quantitative, but they suffice to demon- strate the.very marked difference as regards availability which exists between the relatively pure nutrients employed in the exper- iments of Pettenkofer & Voit, Magnus-Levy, Rubner, and others and the feeding-stuffs consumed by our herbivorous domestic animals, and to show the fallacy involved in applying the results of the former experiments directly to the latter case. The same conclusion is also indicated by the few results upen timothy hay on p. 424. Unfortunately no other direct determinations of the availability of the food of herbivorous animals in amounts below the mainte- nance ration are on record, so that we are unable to compare either different feeding-stuffs or different species of animals in this respect. The extensive investigations of the Méckern Experiment Station mentioned in the previous paragraph show how large a proportion of the metabolizable energy of the food of fattening animals becomes economically waste energy, thus fully confirming the conclusions drawn from Zuntz & Hagemann’s experiments upon the horse, but they afford no means of distinguishing between the work of diges+ 432 PRINCIPLES OF ANIMAL NUTRITION. tion and assimilation and the energy expended in converting the resorbed material into permanent tissue. The Maintenance Ration.—As already defined, net available energy is that portion of the metabolizable energy of the food which serves to make good the losses of potential energy arising from the internal work plus the work of digestion and assimilation, or, in other words, which contributes towards the maintenance of the stored-up capital of energy. We may, therefore, appropriately consider the bearings of the known facts regarding availability upon the amount of food required for maintenance. RELATIONS TO AVAILABILITY.—Not a little effort has been expended in determining the maintenance requirements of farm animals on the more or less tacit assumption that this quantity is a constant for the same animal, and the same assumption has even more largely controlled in computations based on the experimental data obtained. ; By the maintenance ration, of course, we understand a ration just sufficient to prevent any loss of tissue—that is, of potential energy—by the animal. To accomplish this we must give a ration containing net available energy equal in amount to the potential energy lost when no food is given. Expressed thus in terms of net available energy, the maintenance requirement under given condi- tions is a constant and is equal to the energy of the fasting metabo- lism. The maintenance requirement, however, particularly in the case of farm animals, has not usually been expressed thus, since the necessary data are lacking, but in terms of total digestible matter or of real or supposed metabolizable energy. When thus expressed, however, it is apparent in the light of the foregoing discussion that the maintenance requirement must be a variable, depending upon the availability of the metabolizable energy of the food. Referring again to the graphic representation on p. 410, it is evident that, under the conditions there represented, with an availability ex- pressed by tan DAC, the amount of metabolizable energy required for maintenance will be equal to OS. Furthermore, it is equally evident that as the availability decreases and the angle DAC con- sequently becomes more acute OS will increase. Only when the critical amount of food, OM, is greater than the fasting metabolism NET AVAILABLE ENERGY—MAINTENANCE. 433 and the point K falls above the axis OX will there be an apparent exception to this law. In that case, since the energy expended in digestion and assimilation seems to be indirectly utilized, the ap- parent availability will be 100 per cent. and the metabolizable energy required for maintenance will be constant and equal to the energy of the fasting metabolism. This case might and perhaps does occur with animals whose food consumes little energy in digestion, such as the carnivora. As was pointed out on p. 412, however, an increase in the work of digestion tends to reduce the critical amount of food and there would appear to be good reason for believing that, in ruminants at least if not in the horse, it lies considerably below the point of maintenance. RELATIVE VALUE OF GRAIN AND Coarse FoppER.—We know from the investigations of Zuntz & Hagemann (pp. 385-393) that the work expended in the digestion of coarse fodders is, in the horse and presumably therefore in other animals, materially greater than that caused by grain. It follows, then, that a unit of digestible matter or of metabolizable energy should have more value for maintenance in the latter than in the former. That such is the case with cattle is rendered probable by experi- ments by the writer.* In the absence of a respiration apparatus the nutritive effect of the rations was judged of from the live weight and the proteid metabolism during relatively long periods and the methane production was computed from the carbohydrates digested. A ration in which only about 24 per cent. of the digested organic matter was derived from coarse fodder, as compared with rations consisting exclusively of coarse fodder, gave the following results for the metabolizable energy of the maintenance ration per day and 500 kegs. live weight: Exclusive coarse fodder, 12 experiments.... 12,771 Cals. Earselyserain, os Cxperments: 504 ac cis. . 115023" Such determinations of the maintenance requirements of the horse as have been made tend to confirm the results obtained with ruminants. Wolff, in his investigations upon work production described in the following chapter, has computed the maintenance requirements of the horse in the manner there explained both from e * Penna. Expt. Station, Bull. 42, p. 159. 434 PRINCIPLES OF ANIMAL NUTRITION. his own experiments and from those of Grandeau and LeClere, with the following results per 500 kgs. live weight: Total Digestible Nutrients,* Grms. Osshay sloneip.: sata ledicieeris ahi dei ed 4586 About equal parts hay ies DANEEL tod ceeaaaete 4190 About $ grain and + hay (Grandeau) ........ 3626 Zuntz & Hagemann,} from the results of a respiration experi- ment with the horse, make a still lower estimate of the maintenance requirement, viz., 3265 grams total nutrients per 500 kgs. live weight on a ration of which about four sevenths was grain, but after allowing for the differences in crude fiber content compute a satisfactory agreement between their results and Wolfi’s. Since their estimate for the work of digestion of crude fiber is really based on the difference in digestive work required by coarse fodder and by grain this is equivalent to showing that the latter 1s more valuable for maintenance than the former. On the other hand, Grandeau and LeClere { in later experiments on exclusive hay feeding found that the live weight was almost exactly maintained for a month on 8 kgs. of hay per day, the total digested nutrients being as follows: Total Digestible Nutrients. Animal. ae ee: ial Per Head, Per 500 Kgs., | Grms. | Grms. INGOs ML arumercieis Sas 395 2892 3660 Pk WED ayia ¥o yates 419 3036 3622 MANA Va ee ee teehee ae 413 3058 3701 These figures do not materially exceed the average computed by Wolff from their previous experiments on heavy grain rations. The horses had a half-hour’s walking exercise daily, so that the ration seems to have been amply sufficient for maintenance, and no reason for the divergent result is obvious. While none of these comparisons have the conclusiveness of * Including fat * 2.4. + Loc. cit., pp. 422-4. e { L’alimentation du Cheval du Trait, 3d memoir, pp. 23-31. NET AVAILABLE ENERGY—MAINTENANCE. 435 complete metabolism experiments, their results as a whole indicate clearly that the metabolizable energy of the grains is more valu- able for maintenance than that of the coarse fodders, a fact un- doubtedly due to the greater expenditure of energy in the digestion and assimilation of the latter. The maintenance ration of horses, cattle, and sheep, then, as ordinarily expressed (i.e., in units of digestible matter or of metabo- lizable energy) is not a constant but a variable, depending on the availability of the metabolizable energy, and such a statement of it, to be definite, must be accompanied by a statement of the kind of feed used. No similar experiments upon swine appear to have been made. The ordinary feed of this animal, however, probably varies less in availability than that of ruminants, and it may be presumed that no such striking differences would be found. VALUE OF CRUDE Fiser.—As a result of Wolff’s conclusions con- cerning the apparent worthlessness of crude fiber for work production, as discussed in the succeeding chapter, and of Zuntz & Hagemann’s estimates regarding its digestive work (p. 389), there has been a tendency to ascribe the difference between grain and coarse fodders to the greater amount of crude fiber in the latter, forgetting that what these investigators have actually shown is simply the lower value of the digestible matter from coarse fodders, and that their conclusions regarding crude fiber are deductions from the observed facts. Kellner’s more recent experiments (see p. 182 and Chapter XIII, §1) have demonstrated that at least one form of crude fiber is nearly as efficient in producing a gain of fat by cattle as is starch. A fortiori, therefore, it should be equally valuable for maintenance. We have as yet no sufficient evidence to justify us in ascribing the difference between grain and coarse fodder to the crude fiber as such aside from its influence on the mechanical structure of the material. INFLUENCE OF THERMAL ENvIRONMENT.—It has been not uncommonly assumed that the maintenance requirement of an animal is affected by changes in the temperature and other external factors which combine to determine the refrigerating effect of the environment; in other words, the heat produetion of the animal has been looked upon more or less distinctly as an end in itself. ~~ 436 PRINCIPLES OF ANIMAL NUTRITION. We have already seen reason to believe that this is the case to a very limited extent only, even in the fasting animal, and to a still less degree in one consuming food. If we are justified in thinking that the critical amount of food for herbivorous animals is ordinarily less than the maintenance requirement, it follows that the heat production on a maintenance ration is in excess of the actual needs of the organism for heat by an amount depending upon the avail- ability of the metabolizable energy of the food, and that this excess of heat is disposed of by “physical” regulation. That such is the case appears to be clearly indicated by the writer’s experiments upon timothy hay (p. 424), since there was obviously no such in- direct utilization of the heat resulting from the work of digestion and assimilation as takes place, according to Rubner’s theory, below the critical amount of food. If, now, the temperature to which such an animal is exposed falls, it is in accord with all that we know regarding the regulative processes in the body to suppose that the additional draft on it for heat will be compensated for by a fall in the emission constant rather than by an increased produc- tion of heat, or, to put it in another way, that some of the heat resulting from digestive work will be utilized to maintain the tem- perature of the animal instead of being at once dissipated. No exact experiments upon the influence of external tempera- ture on the maintenance requirement appear to have been made, but Kern, Wattenberg & Pfeiffer * have investigated the influence of the greater exposure to cold caused by shearing upon the metabo- lism of sheep consuming a maintenance ration. A slight decrease in the proteid metabolism was found to result, due, as Pfeiffer con- jectures, to a more rapid growth of wool after shearing, but the corresponding difference in the metabolism of energy is insignificant. The removal of a nine-months fleece appears to have caused at first an increased excretion of carbon dioxide, but this practically dis- appeared within four or five days and is probably to be attributed to greater muscular activity on the part of the shorn animals. Comparing the results before shearing with those obtained from five to sixteen days after, we have the following averages, the amount of water-vapor given off being only an approximate esti- mate: * Jour. f. Landw., 39, 1. NET AVAILABLE ENERGY—MAINTENANCE. 437 Estimated Carbon dioxide | Water-vapor per Day, per Day, Grms. Grms. Before shearing (4 experiments)... 719.6 1939 After Be (4 ee Neer t2ond 434 The total metabolism, as indicated by the excretion of carbon dioxide, shows scarcely any increase as a result of the shearing, and if we accept Pfeiffer’s suggestion that the result for the first of the four days (736 grams) may have been slightly affected by the stimu- lation of movement above noted, the difference becomes still less. On the other hand, the difference in the amount of water-vapor given off is very striking and apparently admits of but one con- clusion, viz., that drawn by Pfeiffer, that the unshorn animals upon a maintenance ration produced an excess of heat which was gotten rid of by evaporation of water, while the shorn animals, instead of meeting the greater refrigerating effect of their surroundings by an increased metabolism, stmply evaporated less water and thus com- pensated for the increased loss of heat by radiation and conduction. Even in the case of man, where the digestive work is much less than in the herbivora, the heat production on a mainte- nance ration may be in excess, and even largely in excess, of the minimum requirement, it being simply a question of clothing, temperature, etc. This has been most strikingly demonstrated by Ranke,* who shows that with relatively high temperature angl humidity the heat production on a maintenance ration may be so ereat as to even produce pathological effects and that under such circumstances the consumption of food is instinctively reduced below the maintenance requirement. Sanborn, in experiments upon the maintenance ration of swine, found the amount of middlings required, per hundred pounds of live weight, to be as tabulated on the next page. The second summer experiment is not comparable with the others, since the smaller animal would require a relatively greater maintenance ration. The remaining experiments seem to show a lower requirement for maintenance in winter than in summer. * Kinfluss des Tropenklimas auf die Erniihrung des Menschen, and Zeit. f. Biol., 40, 288. + Mo. State Agr. Coll., Bull. 28, pp. 5 and 6. 438 PRINCIPLES OF ANIMAL NUTRITION. Maintenance, | Live Weight, Requirement, | bs. per 100 PORE 40S. rs , { 173.5 5 Winter (temp. about 40° F.) .... 4 17] ‘. 1.89 : aye , oa \ 173.6 2.02 Summer ( SORE) maces 1 48 3 2 07 « On the other hand, Cooke,* in a series of experiments cn swine at the Colorado Station, found the following amounts of computed digestible matter required for maintenance per hundred pounds live weight of animals weighing from 85 to 182 pounds per head: Ta HOG weathers t Pes eet een Ate a eae 0.93 Ibs. Imoamoderate weather i. 0% wi: Skid ih.o ogo bees Laer Peiecold Weather ce Qi) Covell ae Akane ae 1e4de Consumption of Water.—A not inconsiderable amount of energy is usually required to raise the ingesta to the temperature of the body. ‘This is particularly true of the water consumed, especially in case of the herbivora, both by reason of its relatively large amount as compared with the dry matter of the food and on account of its high specific heat. At first thought it might seem that the warming of the ingesta is part of the work of digestion, since it is an expendi- ture of energy in preparing the food for assimilation. This same matter or its equivalent, however, finally leaves the body, in the form of various excreta, at body temperature, thus carrying off as sensible heat substantially the same amount of energy which was imparted to it when its temperature was raised, and this heat it imparts in cooling to the environment of the animal. . It would seem, then, that the warming of the ingesta may be more logically regarded as a part of the general draft for heat which the surround- ings make upon the animal, the process being simply a little less direct than the loss of heat by radiation and conduction through the skin. From this point of view the influence of the consumption of cold food and particularly of cold water will be subject to the same general laws as the other forms of the demand for heat. On a ration supplying less than the critical amount of metabolizable * Private communication. NET AVAILABLE ENERGY—MAINTENANCE. 439 energy any iticrease in the consumption of water (taking this as the typical case) will increase the metabolism by an amount sufficient to warm the water to the body temperature. Above the critical amount of food the excess of heat arising from the digestive work will, we may reasonably suppose, be applied to the warming of the additional water consumed, and only when this is insufficient will an increased metabolism be required to make up the deficit. In case of farm animals, however, it would appear that the waste heat even on a maintenance ration is ordinarily sufficient, and more than sufficient, to supply all the energy needed for warming the ingesta. The Time Element.—One important factor in modifying the results of the demand for heat, particularly with relation to the water consumption, is what we may call the time element. Hitherto it has been tacitly assumed that all the factors making up the demand for heat act at a uniform rate. Asa matter of fact this is at best only partially true. Ordinarily a farm animal is watered but once or twice per day and then consumes a relatively large amount in a few minutes. A sudden demand for heat is thus set up, since this water must be raised to body temperature within a compara- tively short time. It is quite conceivable, therefore, that the demand for heat may temporarily exceed the supply, requiring the deficit to be made up by an increased metabolism, while if the same water consumption were distributed uniformly over the twelve or twenty- four hours no such effect would be produced. Such a temporary increase in the heat production, however, cannot be made up for later when the heat production is in excess, but is a permanent loss. Once converted into heat, tue enezgy of food or ‘tissue has, so to speak, escaped from the grasp of the organism, which appears to have no power to reconvert it into any other form of energy. We may plausibly suppose that these considerations constitute a partial explanation of the advantages observed in practice from the warm- ing of drinking-water and the installation of self-watering devices in the stable. What is true in regard to the consumption of water is of course equally true of other forms of the demand for heat.. The time ele- ment is an important factor. Thus an exposure of an hour or two in a cold yard or to a cold rain may cause an increased metabolism 440 PRINCIPLES OF ANIMAL NUTRITION. — and heat production although the average conditions for the twenty- four hours may be such that the necessary production of heat by the internal work and the work of digestion and assimilation would be more than sufficient for the needs of the animal. INFLUENCE OF Size or ANrMAL.—The discussion of the heat production of the fasting animal in Chapter XI led us to the con- clusion that under comparable conditions, at least for the same species of animal, the internal work is probably approximately proportional to the surface of the body. This, however, is equiva- lent to saying that the quantity of net available energy required for maintenance is proportional to the body surface. Furthermore, if we are right in supposing that the available energy is a linear function of the metabolizable energy, the amount of the latter required for maintenance will also be proportional to the surface of the body. Referring once more to the diagram on p. 410, if OA is proportional to the body surface, then OS, which for a given food bears a fixed ratio to OA, must also be proportional to the surface. If the critical point, K, lies above the maintenance requirement, then the metabolizable energy required for maintenance will equal the fasting metabolism, and this, as shown on pp. 359-363, is pro- portional to the surface. Apparently, then, we are justified in concluding that the mainte- nance requirements of different normal animals of the same species are proportional to their body surface, or, for approximate computa- tions, to the two-thirds power of their live weights. It must not be overlooked, however, that the results upon which this conclusion is based were obtained largely with the dog, an animal which when at rest lies down, and which, therefore, in these experiments was in a state of almost complete muscular relaxation. Our common farm animals, on the contrary, pass a considerable portion of their time standing, which involves an expenditure of energy in muscular work. This expenditure we should naturally assume to be pro- portional to the mass to be sustained rather than to its surface, and if this be true we have here a second determining factor in the maintenance requirement. How important this factor is it is diffi- cult to say, although the writer’s results with a steer (p. 343) in- dicate that it is a large one. Its tendency would be to make the maintenance requirement increase more rapidly than the surface. NET AVAILABLE ENERGY—MAINTENANCE. 441 Moreover, so far as we can judge from the accounts of Rubner’s experiments, it would seem likely that what were designated on p. 342 as incidental muscular movements are a more important factor in determining the maintenance requirements of farm ani- mals than they are in fixing that of the dog. While, therefore, we are probably justified in retaining pro- visionally the computation of the maintenance requirement in proportion to the real or estimated surface, it should be with a clear understanding that it is at present a deduction from experiments on other species and under more or less different conditions. Effect of Fattening on Maintenance Requirement.—An interesting question,,and one of practical importance, is what effect the pro- gressive change in weight of the same animal as it is fattened has upon its maintenance requirement. We can hardly suppose that the internal work of the body will be materially increased by such a gain. The increased mass of tissue must involve, of course, some increase in metabolism, but all that we know of metabolism of adi- pose tissue indicates that it is very sluggish. The most important effect might be anticipated to be an increase in the muscular ex- ertion required in standing, perhaps counterbalanced to a greater or less extent by the tendency of the fat animal to pass more of its time in a recumbent position. Zuntz & Hagemann * have investigated the effect of a load carried on the back upon the metabolism of the horse, and have found the latter to be proportional to the total mass (horse plus load), but the applicability of this result to another species of ani- mal and to an increase of weight caused by fattening may perhaps be questioned. The only experiments upon cattle bearing on this point are those of Kellner,t who has compared the maintenance requirements of fattened and unfattened cattle. It being impossible to hit upon exactly the maintenance ration, it is computed from the actual results. In case there was a loss of tissue the maintenance requirement of the animal is computed by subtracting the poten- tial energy of the excreta from the potential energy of food plus tissue lost; in other words, the replacement of energy claimed by Rubner is assumed to occur. When there was a gain of tissue, on * Landw. Jahrb., 27, Supp. III, 269. ¢ Landw. Vers. Stat., 50, 245; 53, 14. 442 PRINCIPLES OF ANIMAL NUTRITION. the other hand, the amount of metabolizable energy required to produce it is computed on the basis of the results upon utilization obtained in other experiments, this larger amount being added to the energy of the excreta and the sum of the two subtracted from the potential energy of the food; that is the energy of digestion and assimilation above the maintenance ration is assumed to be waste energy. Computed in this way, and assuming further that the mainte- nance requirements of different animals are substantially propor- tional to the two-thirds powers of their live weights, the results are as follows: : Main- Live Stable No. of rat t Accents Wren ? Pie "i Require- Deg. C. | Gals.’ Observed : Wintatbemey' tye ete seevast eit sole enererels if 632 15.2 13,470 Msp bemed astberess ah kono ercteet kere shat oie 3 785 WSs 19,671 Computed to same live weight : Wathattemed eee e-8 a sae oe insets a 800 Lon2 15,760 HEE Koya TCT De cba ean staNey cict c Me NTS ear Oe 3 800 5) 371 19,920 Kellner concludes from these figures that the maintenance re- quirements of fattened animals are greater per unit of surface than those of unfattened ones. These experiments, it is true, were on different animals and the individuality of the animal is an important factor in determining the maintenance requirement. The results on the seven unfattened animals, when computed to 600 kgs. live weight, show a range of 1760 Cals., or 13.54 per cent. of the average, while the three results on fattened animals, computed to 800 kgs. live weight, show a range of 2420 Cals., or 12.16 per cent. of the average. Moreover, in making up the average of the unfattened animals, one animal was excluded on the ground that the results were prokably abnor- mally high, but the same animal is subsequently included among the three fattened animals the results on which are averaged. Even after making all allowances for these facts, however, the results for the fattened animals are decidedly higher relatively NET AVAILABLE ENERGY—MAINTENANCE. 443 than for the unfattened, but how much higher can hardly be deter- mined from such averages. Comparing the results on the one animal common to the two series of experiments we have— ive WOERY Maintenance, req | Excess ; Per- Metab-| Rnergy paved Food, | Gain, | centage olism. Gent ¥ als. Cals. | Utiliza- Cals. | Food, Me cmeral tion, Cals. i Proteids (meat): | Pettenkofer & Voit.......... 1041 | 1325 | 1225 100 38 38.0 (| 261 347 307 40 13 By h 5) ! 944 | 1549 | 1169 380 418 | 110.0 FROMMER isete tere, ate l'siaters ores 4 944 | 1463 | 1169 | 294 | 332 | 112.9 || 944 | 2181 | 1169 | 1012 805 79.6 Coaher (48) 1325 920 405 250 Gllaa Sanat iahG wdc cy olcd 743 | 1325 920 405 296 Toi Fat: | ( 1086 | 3298 |} 1108 | 2190 878 40.1 Pettenhoter & Volt... ...- 554*, 942 565 377 329 87.3 | 554*, 1884 565 | 1319 837 63.5 {| 658 | 1738 671 | 1067 | 1016 95.2 466 942 476 466 428 91.8 ARITTIOMET ate Brats oropesnroke- eral eas | 261 348 266 39 49 59.8 944 | 1549 963 586 540 92.1 Starch : ( 1098 | 2015 | 1220 795 353 44.4 Pettenkofer & Voit........ 1098 | 3076 | 1220 | 1856 853 46.0 554*| 874 616 258 ie Y/ bom Rubner (“ carbohydrates”’, as- sumed to be starch)........| 944 | 1549 | 1049 500 509 ! 101.8 Cane-sugar : } BOT sd aR 6 oan teria 451) 572 | 470'|, 102 | 190 | 186.3 Cane-sugar and Starch (93 per cent. availability) : iubnemery-iseupacitascines sees c 302 702 325 377 365 96.8 While as a whole the results of the computation would seem to indicate that the percentage utilization for tissue building is less than the percentage availability, the remarkable range of the figures and the uncertain basis upon which they are computed do not encourage any attempt at a critical discussion. Experiments on Man.—The only respiration experiments upon man which the writer has been able to find in which any large amount of excess food was given are those of Johansson, Lander- gren, Sondén & Tigerstedt + already cited on p. 383 in their bearing on the subject of digestive work. If we assume, on the basis of * Loss on basal ration. + Skand. Arch. f. Physiol., 7, 29. 452 PRINCIPLES OF ANIMAL NUTRITION. Magnus-Levy’s results, that the work of digestion in man equals about 9 per cent. of the metabolizable energy of the food, the average results of the experiments are as follows: Pasting metabolism) y2s-2 ee meets oe sees 2022.4 Cals. Metabolizable energy of food............... 4193.4 “ Computed maintenance requirement....... 2222.5. CESS TOO, 58 te Noe een ars cree a eae 1970, 9.0 4 (TEIN Rh ial ce eet alee NR Cre ee ake ee 1676.0) Percentage wtilizations Jukes + seis oe & 85.0 per cent. The computation gives a somewhat lower percentage for the utilization of the excess food than that assumed for the availability of the maintenance food. Experiments on Swine.—Meissl, Strohmer & Lorenz * in their investigation upon the sources of animal fat made six respiration experiments with swine, the results of which afford some data as to the utilization of their food by these animals. In Experiments V and VI, made on two different animals, no food was given, and the following results were. obtained, the energy equivalent to the loss of tissue being computed as in Rubner’s experiments in the pre- vious chapter: Metab- Experi- | Tempera- eiouts Live Loss of Loss of ee 00 ee ment. ture. ash Weight, | Nitrogen,| Carbon, Glism live Deg. C. Feeding. Kgs. Grms. Grms. Gals Weight,t | als. WWibsacabae 20 24 140 9.80 224 51 2607 2083 VI | 20 12 120 9.55 375.78 SA 20.4 72 120 Onin 194.93 2291 2029 { The experiment begun only twelve hours after the last feeding obviously gave too high results, owing to the presence of food in the digestive canal. That this source of error was substantially eliminated after twenty-four: hours appears probable from the close agreement of the results with those obtained after seventy-two hours. The average fasting metabolism per 100 kgs. live weight is 2056 Cals. and this average has been made the basis of the com- putations which follow, except in Experiment I. This experiment * Zeit. f. Biol., 22, 63. + Assumed to be proportional to the two-thirds power of the weight. THE UTILIZATION OF ENERGY. 453 having been made on the same individual as Experiment V, the result of the latter is used directly. In Experiments I and II the ration consisted of rice, in Experi- ment III of barley, and in Experiment IV of rice, flesh-meal, and whey. In all cases large amounts of food were consumed and a rapid production of fat was observed. The digestibility of the food was determined. Its metabolizable energy has been computed by the writer from the results of the digestion experiments by the use of the following factors: * ! gram digestible proteins. .*.. i. 2.224 .<) Onan Oe ee 40.4 16.5 0.780 GTA ME RESON. Pe oe 36.2 15.9 0.756 Wyerrere ts Sn aa lk | 808 16.2 0.768 Sample VI, Ox H, Period 7 tne, Ser ae 50.4 26:35": 1.266 Wil Ay EL as ee 48.4 26.1): 1.247 ag VL MU toscroystenaeene, ot PYe cox seon cas 34.8 18.55: 0.883 DNS CNN REE 8 1 SOO AO IE CIC RNS) SCS 44.5 Dane i132 Megerage NV and) Wiles tk sa ts 5 41.4 20.0° 0.950 Oat Straw: CaS ee els au Par Rarele alae & Bix e's 38.8 14.2 0.682 a Corset cred Me erate (ace Thre steer cata ovay Sha canon 33.4 i a ay, 0.564 WAV ETAD Osyera turer cdstorsiors feel oie erage fs 36.1 _ 12.9 0.623 Wheat Straw: Ox Fes. 3 Stnicnstear ties wah see scPoy ch epeeeve 10.8 3.2 0.153 pia) trees steps ae pate rma a atisl iaha palin pte ece. crac 24.0 738 0.373 AVETASC. oe sen 3 o's WER OooU SC onOReE 17.4 Bebra nd 0.263 Extracted Rye Straw: OPEL ae cL ie aVapcice iare aredorshivecciarous yer aeras 67.3 516 2.194 Send Soma ae CL SHEE Sich ate & helion diel stenvecsr ous 58 .6 43.6 1.854 PAVETA SS PAN o Sinisa cafe We Shievaerccas 63.0 47.6 2.024 eet Molasses : Sample ESO Ga OAR PRS Aare oem ie 58.5 41.6 1.700 We CORNED 2's clap seateraiere neds ee ERO 65:9 | 2.760 sf Mh clone isc sche cticnerecpaers.: 50.2 36.5 1.529 ASST asta din ae oe eee Ae PAlEG Le TG bine 2.145 Starch—Kithn’s Experiments : eae ee PRs Gen eee Sample I. Ox A Nes Sos tape slash cone Sait aueil mind Q GO 73076 7! 1.514 ESSA RILN Arch oie ave ik en Ga a | ee ge rcs opt Mrernee tenia) Sem ee er 49..G.. L183... gadey hk Ao8 Sample If, Ox V, Period 2a ~. 5 ll Hep 2e) reac lank neo) ga (i be Adc Pe ah 1 as eae | ae 53.7 40.1 1.699 SOW allan VE WiLL SNe oA rineRemer ares 59.7 He ese CV ETS esate DDR Hen es 48.1 34.3 1,452 HORS SERS EU em aes cee ea 46.6 32.6 1.380 PAV CRAG Crean A Gniah relist kcora dct 50.4 Bl sa 1.578 PAN era pe Wiss Gell, S cyaneeierovsi ei cltiareiehcte 50.0 35.4 150 ~ 462 PRINCIPLES OF ANIMAL NUTRITION. ENERGY UTILIZED (Continued). Per Cent. of Pre Cent ak Per Grm Metabo- otal F Gros : | gnerme, | Enerey. | Sreanie Starch—Kellner’s Expervments : Sample 1. aud TE, Ox Bos. cic sekes> 65.4 31.8 1.325 EL Ss BU CO Caen ee eats 57.6 28.0 1.168 AWOL ARO Eis cis ki frist arn Se aetsieabtanis ine 61.5 29.9 1.247 Sample UE Ox D...|.cid ¢ Peateoaae beh € 53.7 36.1 1.500 Bi) SEES MORN ois da ro tieotes Dee ee 64.8 46 .2 1.922 ERIE) SEL, Fs eters ok eaten 65.8 50.9 2.116 AV ETAB OC eiche Ward. crsiefaela Ses cistatlagtve oyelle 61.4 44.4 1.846 PamplesLVs Ox Hes. ce ains bye siers 56.0 44.4 1.855 gry ees Se Lh eee ee eee, 54.8 39.5 1.652 PAVET ARC feicloncrer otc los Saceyels ook cone onesie 55.4 42.0 1.754 Aovernge-ITE and TV... 5'5..2 sakes sone 58.4 43.2 1.800 Wheat Gluten—Kiihn’s Experiments : Cy EDT, PIGS atta fas bre metas eth eee ae se 45.3 37.0 2.289 BP ANDI i arte Bn Ae cttw Oat olannsee tp tae te ta le 48.0 35.8 2.213 INVETAG OS 2 ciareieis!eiore hasta eyelets atale tarde 46.7 36.4 2.251 Om MVR, Face salen hee saremrs ee a Oeinee 58.2 58.9 3.645 Wheat Gluten—Kellner’s Experiments : Saniple J, Ox By Periods a... bc. dias 36.9 19.6 pa a hiss Bnet AM hes cE SA ays "OY ans Mind Pee cas bacays 49.7 32.6 1.849 Ae rs ees: FAD. Sahay a exw Sts os mitshe oe 43.2 30.9 1.850 PAN EPARO rte chet ahels Gniaw mia we prea rere 43.3 27.7 1.605 Sample TT Ox Dat. cite eeaelaesie eae 37.3 26.1 1.516 Avetage of I andy 3.520 s,: sc as 40.3 26.9 1.561 Peanut Oil. Pampa. 1. Ox Dy, cutive waar sist eae tee 51.6 40.1 3.811 fe > aa ie Ala gu hrrines wayside ane 65.1 34.2 3.238 Be DS ET ata ape Mas olen 66 oa ae 69.4 41.2 3.903 A.VETARO.)c's'e.cihin wiewide ek on'acw is Som. 67.3 37.7 3.571 THE UTILIZATION OF ENERGY. 463 moved, but the experiments were upon maintenance feeding only and afford no data for a computation of utilization. A series of respiration experiments on sheep was made by Kern & Wattenberg at the Gottingen-Weende Experiment Station in 1879, the results of which were reported after Kern’s death by Henneberg & Pfeiffer.* Varying quantities of nearly pure proteids (conglutin or flesh-meal) were added to a basal ration of hay and barley meal, the amount of proteids in the ration being regularly increased by about 50 grams in each of four successive periods and then similarly diminished through three more periods. The experiments suffered from some defects in technique which later experience has remedied, the results most strikingly affected being those for the amount of methane excreted. For the first two periods no results are reported; for the remaining periods they are quite variable, and those on different days of the same period differ widely. The authors consider that their figures represent the minimum amount present, and in their final computations usc the average of all the five periods as the basis for estimating the quantity of carbon excreted in this form. The amounts as actually determined showed a considerable diminution in the periods in which most proteids were fed, contrary to Kiihn’s results, but it is worthy of note that the average proportion of carbon dioxide to methane was not much different from that found by the latter. The determinations of carbon dioxide in the respiratory products likewise showed considerable fluctuations from day to day, but as the results are mostly the average of three or four trials of twenty- four hours each it may be assumed that these variations are more or less compensated for. The respiratory products were determined for both animals together, although ail the other data were secured for each individual. The results given on the following pages, therefore, are the totals for both animals. It is stated that addition of proteids to the ration resulted in the diminution, and final disappearance in the middle period, of the hippuric acid of the urine, but the actual amounts present are re- ported only for the first and last periods. It is not possible, there- fore, to make any satisfactory computation of the energy of the urine or of the proper factor for the metabolizable energy of the digested proteids of the total ration. Py another method of com- * Jour. f. Landw., 88, 215. 464 PRINCIPLES OF ANIMAL NUTRITION. putation, however, it seems possible to secure an approximate idea _of the relation of added food to gain. By subtracting from the food digested in Periods II-VI the average amount digested in Periods I and VII, on the basal ration, we find the amounts of added food, consisting chiefly of proteids. Reckoning the metabolizable energy of the added pro- teids at 4.958 Cals. per gram (compare p. 317), that of the crude fiber and nitrogen-free extract at 3.674 Cals., and that of the ether extract at 8.322 Cals., we get the approximate metabolizable energy of the added food, and can compare it with the energy of the corre- sponding gain. Thus for Period II we have the following: DIGESTED. Nitrogen- z . Crude Ether Protein,* a free y Fiber, z Extract Grms. | Gms: | Extract, | “Grins, Period silane ot le trcchas cre ctae } PAUIRSB? 280.77 643 .22 20.88 Periods Land WIS, 3) 452 101.05 277.91 633.12 21.60 DOIMEVERE Es 2 262s Ac. 5 bw cme’ 110.28 2.86 10.10 —0.72 12.96 Equivalent metabolizable Cals. Cals. Cals. CNET OV Aal tie PR ae 546.8 BO ae esvesuat cree —6 * Protein of basal ration and of feces equals N X 6.25; that of conglutin or flesh-meal equals its total organic matter. GAIN, 1 Protein Grms. Fat, Grms. : Periods ls .n 2. sacs 15.00 69.27 , Periods Iand VII... : 6.85 19.66 Difference ........ hte foe eae 49.61 Cals. Cals. Equivalent energy | 46.3 °471.5 _ The figures for the gain are those given by the authors, based on the assumption of a uniform excretion of methane throughout the experiments; the gain of protein includes that contained in the wool produced. The animals gained slightly in weight. in addition to the growth of wool. Computed on this basis, the percentage of the energy of the added food which was utilized was as follows: THE UTILIZATION OF ENERGY. Metabolizable 465 E f Period. Added Food, | Resulting Gain. | Rice als. ‘ pe ee 588.4 517.8 88.00 Conglutwor = -"SN sR. R.eak eas 1100.3 741.8 67.42 l eee 1639.2 1106.8 67.51 Pe eer horas eae A 1131.7 672.5 59.41 Flesh-meal:) yy0 77777777! 454.9 315.7 69.39 A computation based on the observed amounts of methane would affect the above figures in two ways. First, if the added proteids diminished the production of methane, this was equivalent to an increase in the apparent metabolizable energy of the food, and the figures for the latter must be correspondingly increased. Second, the gain of fat will also appear relatively greater in the intermediate periods, II-VI, and the figures for the energy of the gain must also be increased. Computed on this basis the results are: E f E f Period. Added’ Pood, Resulting Gain. ea \ | a Cae ee 715.4 605.7 84.68 Conglutin: TELE Gees ae Set Rar 1245.8 842 .4 67 .63 | TIN MORN So ANE a 1902.3 1288.8 67.76 , si Cm E Meera raee De rel: 1288 .2 780.7 60.59 Flesh-meal:) yy 77777707 582.1 403.6 69.33 No obvious explanation of the exceptionally high results ob- tained in Period IL presents itself. Those of the remaining periods do not seem to indicate any considerable differences in the utilization of different quantities. The figures are notably higher than those computed from the Méckern experiments, but in view of the uncertainties attaching to them too much stress should not be laid on this fact. Discussion of Results. As was pointed out at the beginning of this section, and as was further apparent in considering the results of experiments upon carnivora, our knowledge of the net availability of the energy of feeding-stuffs and nutrients is too imperfect to permit the experi- 466 PRINCIPLES OF ANIMAL NUTRITION. mental results above detailed to be discussed from the standpoint of the percentage utilization of the net available energy. I'urthermore, even confining ourselves to a consideration of the utilization of the metabolizable energy of the food, we have already seen that the recorded results upon carnivorous animals show such wide divergencics as to render it difficult if not impossible to draw any quantitative conclusions from them. For the present, accordingly, our discussion of the utilization of energy must be confined chiefly to the results which have been reached with herbivora, and in the main to the Mockern experi- ments, and we must content ourselves with an attempt to trace the relations between metabolizable enetgy and energy utilized. or, to look at the subject from the other point of view, with determining the proportion of the metabolizable energy of the food which is expended in the combined work of digestion, assimilation, and tissue building. Irom the practical standpoint this is of course the important thing, since either form of expenditure of energy constitutes, in the economic aspect of the matter, a waste, but it is nevertheless to be regretted that it is at present impossible to further analyze this waste. Influence of Amount of Food.—As in the discussion of net availability in Chapter XII. we have thus far assumed the energy utilized to be a linear function of the net available or of the metabo- lizable energy of the food. Before proceeding further it becomes important to consider how far this assumption is justified by the facts on record. CarNnivora.—Of the experiments upon ecarnivora recorded on preceding pages, those of Rubner with different amounts of meat, when computed by his methed (that is, assuming an availability of 100 per cent. below the maintenance point, as on p. 450). appear to indicate that the utilization above that point is constant. If, how- ever, a lower percentage of availability is assumed, as on p. 451, this constancy disappears. . None of the other results there sum- marized seem suitable for diseussion.from this point of view. SwiNe.—If in the experiments of Meissl, Strohmer & Lorenz, as computed on p. 454, we express the estimated metabolizable energy of the excess food as a percentage of the fasting metabolism, we have the following comparison of the percentage utilization with THE UTILIZATION OF ENERGY. 4607 the relative amount of excess food, to which may be added Kor- nauth & Arche’s results similarly computed: Excess Over Fasting Percentage Metabolism, | Utilization. Per Cent. Meissl : Experiment: >To 5.4.68 5. 133 80.7 . iS Lee paths 250 WO Ca METS: eS 74 70.9 us VRE tee 180 67.1 Kornauth & Arche: Experiment, UNE. oe... 3: 126 TA iS 1 LAY saa es on 129 65.3 While there is some variation in the percentage utilization, as would naturally be expected in experiments with different animals, the range in the relative amount of excess food is much greater and there is no indication of a connection between the two. Ruminants.—the earlier Méckern experiments by G. Kiithn include one upon wheat gluten and two upon starch in which two different quantities were added to the basal ration of the same animal. The final results were as follows: ‘ Percentage Added t pesmi Animal. Period Basal eatin ne a ao Kgs able Energy. “ Ill 3 0.68 45.3 Wheat gluten.... { lll 4 1 36 48.0 ( V 2a P40) 53.2 | V 2b 2.0 53.7 Starchenccsevloce- V 3 Seo) 59.7 1 VI 2b 220) 48.1 t VI 3 3.5 46.6 These results do not indicate that any material effect is exerted upon the utilization of the metabolizable energy of the food by the amount consumed, since the differences are small in themselves and in both directions. ? The results, reported by Pfeiffer, of experiments upon the addi- tion of varying amounts of proteids to a basal ration, as computed by the writer (p. 465), likewise show a fairly constant percentage 468 PRINCIPLES OF ANIMAL NUTRITION. utilization of the energy of the proteids used, with the exception of the strikingly higher result of the first period. A similar conclusion may be drawn from a study of the Méckern results as a whole, as recorded in Table VII of the Appendix. While the computed percentages in each series vary more or less in the different experiments, the differences are in most cases not large and appear to bear no relation either to the total quantity of food given or to the amount of the particular food under experi- ment which was added to the basal ration, but to be due rather to individual differences in the animals. This is strikingly shown in the following table, in which the results upon hay, wheat gluten, and starch are arranged in the order of the percentage utilization: Metaboliz- | Total Excess} Percentage able Energy | Over Com- | Utilization Feeding-stuff. Animal.| Period.! of Added | puted Main-| of Metabo- Food, tenance, lizable . ‘als. als nergy J 2 7875 12,192 34.8 G 2 5726 9,780 36.2 Meadow hay ..:......; F 1 5506 10,184 40.4 l H 7 8505 11,905 48.4 H 2 7875 11.275 50.4 (ive 1 4483 15,129 36.9 D a 5713 17,373 37.3 C 3 6033 19,635 43.2 Wheat gluten ......... IAD! 3 2913 8,982 45.3 Il 4 5332 11,401 48.0 B 3 5507 16,153 49.7 Kel LY 3 3645 7,132 58.2 VI 3 $264 12,364 46.6 VI 2b 5088 9,138 48.1 racy ee gk IV 2 4350 3411 49.2 Starch—Kiihn's expts. . TI 2 4998 6 592 50.0 V 2a 5425 8,821 53.2 Vv 3 9658 13,054 59.7 Hie 2 4420 16,080 53.7 J 3 4826 9,142 54.8 H 3 6668 10,068 56.0 Starch—Kellner’s expts {| C 2 3027 16,829 57.6 F A 5009 9,686 64.8 | B | 2 3291 13,937 65.4 eet: A 53887 9,441 65.8 But while this is true of each series by itself, a comparison of the two series upon starch leads to a different conclusion. In Icihn’s experiments the basal rations consisted largely or exclu- sively of coarse fodder. In Kellner’s experiments the starch was ee THE UTILIZATION OF ENERGY. 469 added to a materially heavier basal ration containing considerable erain and therefore already tolerably rich in starch and other carbo- hydrates. In spite of the smaller average amounts of starch added, then, Kellner’s results in a sense represent the percentage utiliza- tion of larger quantities of starch than do Kithn’s; that is, they represent the utilization of starch at a greater distance above the maintenance ration. The average utilization (pp. 461-2) was— Gin SOX PETUMEMES 5 i 92 G8 Sects ww 5 ape vee eye 50.0 per cent. Kellner’s experiments, moderate rations... 58.4 “ “ ys ok heavy rations...... Olor ts ack, It would appear, then, from these figures that the metaboliz- able energy of starch was more fully utilized in rations containing a relatively large quantity of it. At least a partial explanation of this seems to be afforded by the variations in the production of hydrocarbons (methane). As was mentioned in discussing the metabolizable energy of starch, the conditions in Kiihn’s experi- ments were such as to permit a considerable proportion of the starch to undergo the methane fermentation, while the more abun- dant supply of it in Kellner’s experiments resulted in reducing, or in some cases wholly suppressing. this fermentation of the starch. The effect of this, as there pointed out, was to make the metaboliz- able energy per gram greater in Kellner’s than in Kithn’s experi- ments, but it has also another result. As we have seen, the methane fermentation constitutes part of the work of digestion, in the general sense in which that term is here employed, the amount of the latter being measured by the heat evolved. This amount being less in Kellner’s than in Kihn’s experiments, the net availability of the metabolizable energy of the starch should be greater, and, other things being equal, the storage of energy (gain of tissue) should also be greater. Kellner * computes that for each 100 grams of starch digested there was produced, on the average, methane corresponding to the following amounts of carbon: Ini Kian, Fexperimentsw gee Sk dso. s 3.0 grams in Kellner’s experiments 20. 25202. naw. hs * Loc. cit., p. 423. 47° PRINCIPLES OF ANIMAL NUTRITION. An approximate computation of the probable differences in the — heat evolved by the fermentation, based on such data as are avail- able, gives as a result 0.159 Cal. per gram of starch, or somewhat more than one-half the difference in average utilized energy, viz., 0.265 Cal. per gram. The data on which the computation is based, however, are too uncertain to allow us to attach very much value to the results, except perhaps as an indication that the supposed cause of the difference in the utilization of the energy is insuffi- cient to fully account for the effect. ConcLusions.—It cannot be claimed that the above results are sufficiently extensive or exact to permit final conclusions to b2 drawn, but their general tendency seems to be in favor of the hy- pothesis that the proportion of energy utilized is substantially inde- pendent of the quantity of food, provided that the changes in the latter are not so great as to modify the course of the fermentations in the digestive tract. The results upon starch just considered seem to indicate that if the variations in quantity or make-up of the ration are pushed beyond that point, a difference in the pro- portion of the energy utilized may be caused by a difference in the digestive work; in other words, that it is the availability that is modified rather than the proportion of the available energy which is recovered as gain. While not denying that the latter function may be also modified, either directly as the effect of varying amounts of food, or indirectly by changes in the chemical nature of the sub- stances resorbed from the digestive tract under varying conditions of fermentation, it seems probable that the main effect is that upon availability. It is to be observed that the rations used in these experiments, while not heavy fattening rations, still produced very fair gains. The experimental periods were comparatively short and hence the testimony of the live weight itself is liable to be misleading. Taking the actual gains of fat and proteids as shown by the respi- ration experiments, however, and comparing them with the compo- sition of the increase of live weight in fattening as determined by Lawes «& Gilbert, it appears that the total gain per day was equiva- lent to from 0.9 to 2.5 pounds gain in live weight per day in the ex- periments on coarse fodder, while in those upon concentrated feeds the corresponding range is from 1 to 3 pounds. Pee, THE UTILIZATION OF ENERGY. 471 It may be remarked further that the rations in Kiihn’s experi- ments differed materially from those ordinarily used in practice, both as to their make-up and their very wide nutritive ratio, so that the conditions may fairly be regarded as in a sense abnormal. Kellner’s rations represent more nearly normal conditions, and they fail, as we have seen, to give any clear indications of an in- fluence of amount of food upon the proportion of energy utilized. Whether other feeding materials show a behavior analogous to that of starch, future investigations must decide. In the meantime we are apparently justified in discussing such results as are now on record upon the provisional hypothesis that, within reasonable limits, the utilization of energy is independent of the amount of food, or, in other words, is a linear function. Influence of Thermal Environment.— The influence of the thermal environment of the animal upon its heat production and upon the net availability of the energy of the food has already been fully discussed in previous pages and needs only a brief consider-* ation here. RuMINANTS.—We have already found reason to think that in ruminants the heat production on the ordinary maintenance ration is in excess of the needs of the body. JKitihn’s and Kellner’s results show us that from 25 to 72 per cent. of the metabolizable energy of the food supplied in excess of the maintenance requirement was converted into heat, so that the heat production was frequently increased 40 or 50 per cent. above that which was observed on the maintenance ration. Under these circumstances we can hardly suppose that any moderate changes in the thermal environment would sensibly affect either the availability of the food energy or its percentage utilization. The writer is not aware of any exact determinations of the influence of the thermal environment upon the heat production of fattening ruminants, but the above conclusion is in harmony with the practical experience of many feeders that moderate exposure to cold is no disadvantage, but rather an advantage in maintaining the health and appetite of the animals, and it appears also to have the support of not a few practical feeding trials.* * Compare Henry, ‘Feeds and Feeding,” second edition, p. 364, and Waters, Bulletin Mo. Bd. Agr., September, 1901, p. 23. 472 PRINCIPLES OF ANIMAL NUTRITION. Naturally this can be true only within limits, and exposure to very low temperatures, especially in a damp climate, and particu- larly to cold rains, causing a large expenditure of heat in the evapo- ration of water from the surface of the body, may very well pass the limit and cause an increase in the metabolism simply to main- tain the temperature of the body. Finally, the time element, as pointed out on p. 439, is one to be taken into consideration. Swingn.—As was remarked on p. 435, the work of digestion is doubtless less with the swine than in ruminants, on account of the more concentrated nature of his food, and as was shown on p. 438, the maintenance requirement appears to be affected by the thermal environment. The same reason would tend to make fattening swine more susceptible to this influence than fattening ruminants. This conclusion is borne out by the experiments of Shelton * at the Kansas Agricultural College, who found that swine kept in an open yard during rather severe weather required 25 per cent. more corn to make a given gain than those sheltered from*extreme cold. Influence of Character of Food.—Attention was called in the previous chapter to the fact that the expenditure of energy in the digestion and assimilation of the food is largely dependent upon the nature of that food, but as was there pointed out, we have few quantitative determinations of the differences. Experiments of the class now under consideration show marked variations in the proportion of the metabolizable energy of different foods which is utilized, and we should naturally be inclined to ascribe these variations to differences in the work of digestion and assimilation rather than to differences in the physiological processes involved in tissue production. The data recorded in the foregoing pages constitute only a beginning of the study of the utilization of the energy of feeding- stuffs, but a brief consideration of the main results will prove at least suggestive. : CONCENTRATED FEEDING-STUFFS.—AS we saw in connection with the discussion of the metabolizable energy of feeding-stuffs in Chapter X, the Méckern experiments, to which we owe the larger share of our present knowledge regarding the metabolism of energy in farm animals, were made for the purpose of comparing the * Rep. Prof. of Agriculture, 1883. THE UTILIZATION OF ENERGY. 473 principal classes of nutrients rather than commercial feeding-stuffs. Accordingly such representative materials as starch, oil, and glu- ten were largely used, and we have as yet but few determinations either of the metabolizable energy of ordinary concentrated feeding- stuffs or of its percentage utilization. We have already considered to some extent the advantages and disadvantages resulting from making the pure nutrients, on the one hand, or actual feeding-stuffs, on the other, the starting-point for investigations. Passing over this question for the present, we may conveniently group together here such results as are on record for materials other than coarse fodders. Starch.—Starch, as a representative of the readily digested car- bohydrates, has, as we have seen, received a large share of atten- tion. The results obtained are tabulated in the Appendix, and _ have already been partially considered in their bearings upon the influence of amount of food. It was there noted that the earlier series of experiments by Kiihn, in which the starch was added to a ration. of coarse fodder only, gave results differing decidedly from those obtained later by Kellner from the addition of starch to a mixed fattening ration. Among the latter experiments, more- over, were two (animals B and C) which were exceptional in that very large total amounts of starch were contained in the ration, relatively large amounts escaping digestion, while none of the added starch underwent the methane fermentation. A clear image of the fate of the total potential energy supplied to the organism in the starch is best obtained by a study of its per- centage distribution among the several excreta, the work of digestion, assimilation, and tissue building, and the gain secured, as in the table on page 474, in which each of the three sets of experiments indicated above is given separately. The figures for the work of digestion, ete., are, of course, obtained by difference. As pointed out in the discussion of metabolizable energy, the percentage of the gross energy carried off in the feces includes, as here computed, not only the energy of the undigested portion of the starch itself, but also that of the portion of the basal ration which escaped digestion under the influence of the starch. This is espe- cially true of Kellner’s experiments with moderate rations, in which little or no starch could be detected in the feces. Similarly, the 474 — PRINCIPLES OF ANIMAL NUTRITION. PERCENTAGE DISTRIBUTION OF GROSS ENERGY OF STARCH. Work of Diges- tion, Assimi- In In lation, Feces. | Urine. In Methane. p 3 f =| | 9 | : ro ae ees ee 1] V| 2a] 8.82] 1.03} 11.20} 36.95] 42.00 ee er tt || v | 26 |15.73| —0.27| 9.86] 34.581 40.10 VI | 20 | 22.49! —2.61| 8.86) 36.96) 34.30 Vilies 19.03; —0.88| 11.87| 37 38) 32.60 (| D| 2 |29.99| —3.27| 6.08] 31.10! 36.10 Kellner’s experiments: |) Fl 4. |16.42| 0.73) 11.41| 25.24) 46/20 Moderate rations....... 4 G| 4 1335 0.35) 8.98! 26.42) 50.90 || H| 3 |15.72| —2.32! 7.38] 34.82] 44.40 lL} J|3 114.85] 1.14, 11.85) 32.66) 39.50 Kellner’s experiments: . Bi 2 59 .60| —3.25|—4.96| 16.82} 31.80 pn REGUS (URE br 2 C | 2 | 52.22} —0.89|—0.01| 26.68| 28.00 Averages: Kithn’s experiments ..... ....[...-] 19.59] —0.92| 10.74) 35.19) 35.40 Kellner’s experiments: Moderate rations....... see tise] L621 | —0:66). 9.21) 30: 64943520 LCA ys TADIONS i.e us ...-|....| 55.91 | —2.07|— 2.49] 18.75] 29.90 negative losses in the urine and, in two cases, in the methane mean, of course, that under the influence of starch the metabolic or other processes were so modified that less of the potential energy of the basal ration was lost through these channels. The starch, so to speak, borrowed energy from the basal ration. In brief, the figures of the table give us a picture of the aggregate net results of supplying 100 units of additional potential energy in the form of starch, or in other words, of the “apparent” utilization. As between Iiithn’s results and those of Kellner upon moderate rations, the chief difference, as already noted, is the less evolution of methane in the latter and, apparently as, in part, a consequence of this, the smaller expenditure of energy in the work of digestion, ete. Combined with the slightly smaller loss in the feces, this results in making the energy utilized a much larger percentage of the gross energy. Apparently Kellner’s figures correspond most nearly to normal conditions of feeding and may be taken to repre- sent the average utilization of starch under these circumstances, THE UTILIZATION OF ENERGY. 475 In Kellner’s two experiments on heavy rations the enormous losses in the feces cut- down the percentage utilization to a very low figure and thus render difficult a direct comparison with the other averages. While the above form of stating the results appears the simplest and most direct, it is of interest also to eliminate the influence of varying digestibility by computing the percentage distribution of the gross energy of the apparently digested portion of the starch. This is particularly the case since Kellner’s computations of his experiments are made in a somewhat similar way. Combining the data given on p. 461, regarding the percentages of metaboliz- able energy utilized, with those on p. 301 for the energy of the . apparently digested matter, we have the following: DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED STARCH. “Work of Digestion, In Urine. | In Methane. |Assimilation,| In Gain. Per Cent. Per Cent. and Tissue Per Cent. Building. Per Cent. Kithn’s experiments .......- Soilien ket 13.42 43.89 43.88 Kellner’s experiments: Moderate rations......... —0.92 Le, 2 3/38 52.44 Heavy rations <......234: —4.95 —6.15 42.77 68 .33 Kellner’s computations are made in a different manner.* Omit- ting in the computation of metabolizable energy the correction for nitrogen gained or lost, he compares the period in which starch was fed with that on the basal ration substantially as has been done above. He then, however, introduces a correction for the influence of the starch upon the digestibility of the basal ration. For ex- ample, comparing Periods 3 and 4 on Ox H, he finds in the manner shown on p. 307, Chapter X, that the equivalent of 820 Cals. less of the basal ration was digested in the period in which starch was added to it, while there is a further correction of 112 Cals. to be made for the less amount of organic matter of the basal ration con- sumed in Period 3, making a total difference of 952 Cals. Of the gross energy of the basal ration, 79.9 per cent. was found to be met- * Compare Landw. Vers. Stat., 58, 450. 476 PRINCIPLES OF ANIMAL NUTRITION. abolizable, so that the above difference in gross energy would corre- spond to 745 Cals. of metabolizable energy. Of the metabolizable energy of the basal ration in excess of maintenance, 59.6 per cent. was recovered in the gain. If, then, the differences in organic matter consumed and in the digestibility of the basal ration had not offset some of the effect of the starch in Period 3, there would have been 745 Cals. more of metabolizable energy disposable from the basal ration, and presumably the gain resulting from this would have been 59.6 per cent. of 745 Cals., or 444 Cals. We have, then, by this method the following: Metabolizable < Energy of Energy Above Gan Maintenance, Gals / Cals. ' 7 Period Simms (Perio dAl ea i 5 uacys ahs epensw-u eee | 6667 3752 Gorrection Tor Jivenweimbin; areas suc ake torte ae 67 40 6600 - 3712 Correction for organic matter and for decreased | ie eSMDUTEV A ot. 5, 2! e se ee ye oie g ieee mt eerie 745 444 7345 4156 Percentage wWiilizeecOn classe sc = oa ke iattacte al eee eet ieee oe 56.6% Kellner’s results, then, assuming that the corrections are accu- rate, represent respectively the metabolizable and the utilizable energy of the digested matter of the starch itself, while the results as computed on the preceding pages represent, as was there pointed out, a balance between the various negative and positive effects of the addition of starch. In other words, Kellner attempts to com- pute the real as distinguished from the apparent utilization of the enerey of the starch. The comparison on the opposite page of the percentages obtained in this way with those computed on p. 461 will therefore be of interest. Kellner also computes by his method the distribution of the cross energy of the digested starch in Kithn’s experiments and in his own experiments on moderate rations. As calculated im Chapter a pp. 325-6, the average loss of potential energy in methane was 12.7 ner cent. in Kiihn’s experiments, and 10.11 per cent. in Kellner’s, while none of the potential energy of the digested starch passed , i j ; i THE UTILIZATION OF ENERGY. 477 UTILIZATION OF METABOLIZABLE ENERGY OF STARCH. Real Utiliza- Anparent tion as Utilization as Animal.| Period.| Computed by | Computed on Kellner. p. 461. =r Cent. Per Cent. feiPsaeiult 2 46.2 50.0 || IV 2 49 .0 49 .2 ear aN lve eee V 2a 51.3 53.2 Kiihn’s experiments .........: ! Vv ob 52 6 537 Heda 2b 48 .0 48.1 Gye at 3 46.8 46.6 Kellner’s experiments: ( D 2 54.2 53.7 | iF 4 63 .2 64.8 Moderate rations........... | G + 65.2 65.8 | H 3 56 .6 56.0 L J 3 OMe 54.8 Lea Navan a ONS recta clasts e 5 ores aie Averages. RG SPER POTIMEMUS ss se sols gly Saree fe 2 he set 49.0 50.0 Ixellner’s experiments: Moderahe pret On sics seats 24 cipal neneks tse a ae: 58.9 58.4 MORIN TUDO 6 NV tve. oy ages cident shee ek eile ore 58.9 61.5 into the urine. In the two eases, then, 87.30 per cent. and 89.89 per cent. respectively of the potential energy of the digested starch was metabolizable. Of this metabolizable energy 49.0 per cent. and 58.9 per cent. respectively was recovered in the gain. Com- bining these figures we have— DISTRIBUTION OF ENERGY OF DIGESTED STARCH. Work of ° In Urine |In Methane, esate ies In Gain Per Cent. | Per Cent and Tissue | Pen Cent. Building Per Cent. Kiihn’s experiments........... 0 12270 4452 42.78 Kellner’s experiments: Moderate rations........... 0 TO. LE 36.95 52.94 The final results for the energy recovered in the gain of tissue, whether expressed as a percentage of metabolizable energy or of energy of digested matter, are substantially the same numer- ically as those reached by the former method of computation, but this agreement is purely accidental, and the significance of the 478 PRINCIPLES OF ANIMAL NUTRITION. figures is essentially different, as already explained. From the re- sults last given, assuming the gain of energy to have been entirely in the form of fat, Kellner * computes that the conversion of starch into fat in cattle takes place according to the following scheme: LARCH. a stack be ie 100.00 grams +Oxygen........ eeOe ye! ee Yield: MGERANG 4: tik warpath hae 3.17 grams Weiter A lien: come ren 23.40 “ Carboni diomde: tink. ek S375" ot AGC Oost so eehtn ww ictan Bias eeu eD 23.34 “ 138.69 grams fS5c00) pak Ovl.—Applying to Kellner’s three experiments upon the addition of oil to a basal ration the same method of computation which was used for the stareh—that is. computing the apparent utilization— we have the results shown in the two following tables: DISTRIBUTION OF GROSS ENERGY OF OIL. Work of | In Digesignn, ‘a | ¢ | In Feces. | In Urine. eae | 22 Gains E | & | Per Cent. | Per Cent. | Par Gent, | 898 204 | Per Cent. Fe Building. 4\ ae Saniple’ 1.77 s.504 D| 3] 24.34 | —1.08 |— 1.02 | 37.66] 40.10 o-oT FF} 5| 64.77 | —1.19 |—16.10 | 18.32 | 34.20 pe), tele G| 5 |. 41.00 1.37 |— 1.76 | 18.19 | 41.20 Average of Sample 1J}.../... 52.89 0.09 |— 8.93 |] 18.25 | 387.70 $ e DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED OIL. Sample I “ce II 5: | In Urine. 2 Animal. Period. Per re Mosk reed ieneWoraitee «Actes D 3 —1.42 |— 1.34 { ik 5 —3.38 |—45.69 > Db ad © O1PXO56 Bi 0 G 5 2 : 82 aa 3 , Ol for Sample Tf) 04. 2a). faa —0.53 |—24.35 * Loc. cit., 58, 452. Work of | Digestion Assimila- Tn'Gain: Hom mane Per Cent. Building | Per Cent. 49.76 | 53.00 52.01 | 97.06 30.83 | 69.86 41.42 | 83.46 THE UTILIZATION OF ENERGY. 479 As was noted in the discussion of metabolizable energy in Chapter X, the results on Ox I appear to be exceptional, but those upon the other two show considerable differences, and it is evident that further investigation will be necessary to obtain satisfactory data upon the effect of oil fed in this way. Kellnev’s method of computation. based upon the provisional conclusion on p. 323, Chapter X, that oi] has substantially no effect upon the loss of energy in urme and methane under normal condi- tions, gives the following results: PERCENTAGE OF METABOLIZABLE ENERGY UTILIZED, As Computed As Computed by Kellner. on p. 462. OxGD oor. Ag Se 51.6 CS I sae COP HEE Ae be ieee 65.1 ECan (EES Ae 59.4 69.4 DISTRIBUTION OF ENERGY OF DIGESTED OIL. Work of Digestion, Ani- Rano In Urine,| In Methane, | Assimilation | In Gain, mal. er10C. |Per Cent.| Per Cent. and Tissue | Per Cent. Building, Per Cent. Sean alkew ese qamane D 3 0 0 47.8 92.2 e JEAN lakes: G 5 0) 0) 40 6 59.4 IAN CTAG@E cies. 12 Sa sfetteia lieu ckararal ie iC) 0) 44.2 55.8 Average computed DSTO Deel Ail Sioere-\olslisl-|| (ss vieteohs 0.5 —2.2 40.3 61.4 The numerical results of these experiments show more clearly than was the case with the starch the difference in the two methods of computation. Both methods agree, however in showing that the combined expenditure of energy in the digestion and assimilation of the oil and in tissue building is very considerable. We have already seen that the expenditure of energy in the digestion of fat by ecar- nivora and by man is comparatively small. If we are justified in assuming that the same thing is true of ruminants, the result just reached signifies that the digested fat undeigoes extensive trans- formations before being finally deposited in the adipose tissue, 480 PRINCIPLES OF ANIMAL NUTRITION. Until, however, we have satisfactory determinations of the per- centage utilization of fat by carnivora, or of its net availability in ruminants, or both, no final conclusion on this point is possible. Wheat Gluten.—Yhe three samples of this feeding-stuff experi- mented upon contained respectively 87.88, 83.45, and 82.67 per cent. of crude protein in the dry matter, the remainder being chiefly starch, with the exception of 2.22 per cent. of ether extract in the first lot. A reference to the results obtained for the metabolizable energy will show that they were variable and also that, especially in the earlier experiments, the incidental effects were large. Tabulating the results as in case of starch and oil we have the results contained in the tables on this and the opposite pages. P DISTRIBUTION OF GROSS ENERGY OF WHEAT GLUTEN. | Work of } Diges- In In tion. ia Wie Feces. | Urine, |Methane.| Assimila-| In Gain. | 5 | Per Cent. |pey Cent.|Per Cent.| tion. and/ Per Cent. 2 iB Tissue clas Building. | Per Cent.| (| TIT | 3 |—10.38 17.85 10.81 | 44.72 | 37.00 Ps , , |} WL) 4.i;— 1.28) 21.71) 5.08 |-38.69 ) 35280 Kiihn’s experiments. . 4 1 J ite Ay.'...|— 5.83 | 19:78 | 7.95 | 41.70 | 36:40 1V | 3 |—16.17 | 16.18 ;—1.26 | 42.35 | 58.90 Kellner’s experiments fil edsacie al SOR 165) 9162 58 0.08 | 38.58 ! 19.60 a || B| 3 | 22.55 | 13.52 |—1.62 |.32.95 | 32.60 Sample I..........- J) C| 3] 20.89 | 11.19 |—3.69 | 40.71 | 30.90 || Av.|...| 24.53 | 13.76 |—-1.74 | 35.75 | 27.70 Sample Lbs cecceauru: D|4 | 15.80] 12.39 | 1.91 | 43.80 | 26.10 Average of land II.|....|...| 20.16 | 13.08 0.08 | 39.78 | 26.90 The exceptionally small loss of energy in the urine in the case of Ox IV, Period 3, and the total suppression of the methane fer- mentation, as well as the fact that the metabolizable energy was apparently greater than the gross energy, seem to justify exclud- ing this experiment from the average, although there was appar- ently nothing abnormal in the ration fed.” In the experiment with Ox D, Period 4, the nutritive ratio was very narrow (13.3), and Kellner considers this a probable explanation of the THE UTILIZATION OF ENERGY. 481 DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED MATTER. Work of ; pesnen: =a . : sslmua- . 2 | © | Per Cont, | Methane. | tion, and | £2 Gain. oe Per Cent. pupae 7 = 7 Per Cone {| III | 3 Koy AlZ 9.79 40.50 33.54 ig fw Ge 21.44 5.02 38.24 35.30 Kiihn’s experiments ...... { SIAR y ocr ia ie ae 7.39 39.38 34.42 ti IV 3 13.92 | —1.07 36.44 AOR Al Kellner’s experiments: ines einen t 23.74 OMe 48 .06 28.09 | Biles 17.46 | —2.10 42.57 42.07 Samp ewiy sivas cede shel { Giirs 14.15 | —4.67 51.46 39.06 } | [| Av }...] 18.45 | =—2.22 47.35 36.42 PM LeU te. sr balsa eure oats Di). o4 |e 172 227 \ra2 Oly | 3t 00 Average ot Mand (22 5\2 slo... 16259 0.02 49 .68 Sail relatively small utilization of the protein as computed by method. (See below.) An unexpected result is that while earlier sample of gluten seems to have increased the methane fermentation, the later samples, although containing more starch, caused a decrease in the methane production except in case of Ox}. his the Digestible Protein.—Kellner does not attempt to compute the energy utilized from the wheat gluten as a whole by his method, but uses the results as a basis for computing the utilization of the energy of the digested protein. He finds that of the metabolizable energy of the latter, computed in the manner described in Chapter X (p. 316), the following percentages were recovered in the gain: (52 1B ay HUME ea Pe se rote EAM 45.0 per cent. >. Satis ee URN BMPS Boneh Bia (eV Goo AD Mle et (2 5c) NH TOE ce ee AO Ree ae STO On fe Sh (Oe BY Ga se RAN ee Tats ties po Coe im ASS en fF PETAR Eas hic ee INR Cie ew AOR ED ye! tort CAD aa eye Hare Lemmas AP a Saat aA ae The average loss of energy in the urine was found (p. 19.3 per cent. of the gross energy of the digested protein. 317) to be Applying 482 PRINCIPLES OF ANIMAL NUTRITION. this average to the above figures, and assuming with Kellner that the protein does not take part in the methane fermentation, we have the following: DISTRIBUTION OF ENERGY OF DIGESTED PROTEIN, Work of oe PA ets Peet St : ' ssim c eels Per Cont, ‘Ter Cane: and. Trees. Pec Cont : Building. Per Cent 1 BAR ae rope tee ae 44.38 36.32 ‘Raat, gene ar 46.24 | 34.46 1 eee ey ee ate 44 .30 36.40 SAV SS Scie eee 19.30 0 41.32 39.28 Average 44.07 36.63 ie bas ee 54.15 | 26.55 There is a wide discrepancy between these results and those computed on p. 465 from the experiments of Kern & Wattenberg upon sheep with conglutin and flesh-meal. Omitting the apparently exceptional result of Period II, we have the following as the per- centages of the (computed) metabolizable energy of the digested proteids which was utilized in those experiments: | Period. Fer Cert ; i Hil 67 .63 Conplutine ss «4% 1V 67.76 INVOTAV CN. diet srcrs alicia; svbista ieee 67 70 V 60.59 Flesh-meal......... / VI 69 33 PAMELAU Ee cvercunle te gstall aisle islets 64.96 While the gain in these cases includes a considerable growth of wool, it seems difficult to suppose that this alone can have made the conditions so much more favorable for the storing up of the added protein as to account for the great difference between these results and Kellner’s, and it must apparently 0 left to further investigation to clear up the matter. ie tb tee THE UTILIZATION OF ENERGY. 483 It need hardly be added that none of these results are directly comparable with those computed above, after another method, for the wheat gluten as a whole. Beet Molasses.—The results of the three experiments upon beet molasses show such great differences, as was noted in Chapter X and as is further apparent from the following table, that any dis- cussion of them would evidently be premature: DISTRIBUTION OF GROSS ENERGY OF BEET MOLASSES, | Work of Silo3 In Digestion, & | .© | In Feces. | In Urine. | Methane. | Assimilation,) In Gain. ‘a | & | Per Cent. | Per Cent. | Per Cent.) and Tissue | Per Cent. a! A Building. Per Cent. Sample I.... |) Ee: 26.87 3.92 == Le 29.56 41.60 we TT Ayes Ulimte, 5.40 | 3.16 12.44 13.10 65.90 ea Se (| J} 6 14.45 2.67 10.18 36.20 36.50 JAN OEIC ae eisicnol [a Glol arc oe PA N72) BP 11.31 24.65 51.20 Rice.—The two experiments upon swine by Meissl, Strohmer & Lorenz, when computed as on p. 454, show that of the (estimated) metabolizable energy of the food approximately the following per- centages were recovered in the gain: LECSTCTOY ONS Se Rel gua AYRE OR Beg Oi a SM arte 80.7 per cent. CFA 2) Nn 2 ac Tad, Layee > PREMADE ei pdie oh hate late Se oice oe, 5 BOAO Koby These results are notably higher than any obtained in experi- ments on ruminants. Like the results on barley and cockle below they are the expression in another form of the well-known supe- riority of the swine as an economical producer of meat. Barley—For the utilization of the energy of this grain the single experiment by Meissl, Strohmer & Lorenz gives 70.9 per cent. of the (estimated) metabolizable energy. Mixed Grains.—For mixed grains Kornauth & Arche’s results on swine give figures which do not differ materially from the result just computed for barley, viz.: Prcperinentt. Ti vosi stom vere oe aiclese 0 vier~ » (is per cents te EEE Wa. Sea New ate tele uey’ Mesa te bos 40.4 Hay V eh ca Chea | ECC ne AU aes | Bia 36.2 fea 5 \ilmAtversce Seite erie 40.2 38.3 (elpOscoEl xRerrod) 2.2 /2.i0) { 50.4 Nii, Sacer Come Ry iiss Ah Sie es Ale aay ten a Lai oe a a a IPR cap atuel ara che Mee cca 35.8 34.8 | ee eee (Gl PA WenraA@e ya acc: 42.8 44.5 AVERAGE OL Ve ams Vili a We, ot so See SE —— ‘ 2 x : 4 THE UTILIZATION OF ENERGY. 487 Wheat Straw.—Tabulating the results upon wheat straw in the same manner as those for oat straw we have DISTRIBUTION OF GROSS ENERGY OF WHEAT STRAW. Work of | Direction j In ssimila- | : Animal. Period. | ue eee eae, Methane. | tion, and | LN aeard Per Cent. Tissue Building. Per Cent. tp areal Sect ss £3}. GO sad 1.88 7.96 26.55 3.20 iz 1 | 56.03 2.85 8.65 | 24 67 7.80 AMEPaGe <. \cuns. : | 58:21 237 8.31 25561). ¥5.50 DISTRIBUTION OF ENERGY OF APPARENTLY DIGESTED MATTER. Work of coe} Digestion, ‘ Animal | |\Period) | Bet Guee))| Bee Coan’ | ead Tissue °| Per Cont. | Building. Per Cent. 1c. 2 ees Parone ere 1 4.75 20.11 67 .03 8.11 Rr, fe ea ea 1 6.49 19.67 SO m2, Wi Wrerige..c..elen wa. 5.62 19.89 61.57 12.92 PERCENTAGE OF METABOLIZABLE ENERGY RECOVERED. Computed by Computed by the I 3 98 3.42 0.861 2.0 1 5.6 Ss o)ih io ees ee Catto 4.06 4.04 0.997 Se 5" 3 2.0 BAe ts thescis el scre™ 4.11 3 86 0.940 4.7 1 bs ASG stot ciacaeiacsrectoe ALY ieee) 3.63 0.933 2.0 1 Ay) AGO ook Sia 3.44 0.929 9.0 3 A les) Average .:..... 3.94 Sere 0.950 25 | 1.4 2.8 Corrected *..... 4.04 3.86 | In the same period eight experiments were made in which the ~-sad-power was set as nearly horizontal as possible and driven by the steam-engine, the animal being simply required to maintain his place on the power. The results for oxygen were as shown in the first portion of the following table: * A comparison of Zuntz’s method with the results obtained in the Pet- tenkofer respiration apparatus showed that the gaseous exchange through the skin and intestines amounted to about 24 per cent. of the pulmonary respiration in case of the oxygen and 3 per cent in case of the carbon di- oxide. These additions are accordingly made to the figures of the respira- tion experiments and the results designated as “ corrected.”’ ee ie i Bt ee THE UTILIZATION OF ENERGY. 5°05 WALKING WITHOUT LOAD OR DRAFT. PERIOD a. Per Kg. Live Weight. Observed. Oxygen Equivalent E | to Work. No. of Live Per Minute. u Experiment. | Weight . Werk ics ' i= = Distance | Work of Per Meter| Per | Per Meter Oxygen | Traveled | Ascent, | Traveled. |Minute, Traveled. c.¢. Meters. Kgm. | Gr.-m. ¢.¢. )\|) (G.imm. | H NOOR eee A ree ee 429 9.0 57 (Obs Sie AO) Ps yp ie) Cab ayes aie a Gates 434 eS 87 OF SAW Alo: 7.3 | 84 LOPE tt arene 428 LDR? | 94 0.89 9 IEP Aes 4) testes “1S a ee ee 428 PATE 95 0.87 9 8:7) 92 AGOLEM sed hog? 430 10.8 92 0.70 8 6.9 | 7A BLOC y eae. eo: 430 WLay 99 0.74 8 ees) 79 A DEN GE a se a 434 Pes} 98 0.79 § 8.4 86 CR aN ee ee 434 ela, 93 0.76 8 Tian vies Average ...| 480.9 | 11.405 | 89.338 | 0.764 8.643 | 7.463) 83.793 (Croveseere (Here AY 5, Sa RE eye le 2 le | Ad Petes, Lede oe 85.888 If from the oxygen consumption in each of the above experiments we subtract the average rest value for the same period (3.94 c.c.) the remainder will represent the increase due to the work, as shown in the seventh column, and this divided by the distance traveled gives the figures of the eighth column. The average respiratory quotient of that part of the respiration due to the work in these eight experiments was 0.894. On the very probable assumption that the work caused no material change in the metabolism of either proteids * or crude fiber, or in other words, that the energy for work was derived substantially from solu- ble carbohydrates and fat, the calorifie equivalent of 1 ¢.c. of oxygen is computed and the following calculation of energy made for the average of the eight experiments (compare pp. 76 and 251). These results are not corrected for cutaneous and intestinal respiration. Per Kg. Live Weight per Minute. Oxyoencombmed withwiat ues sc sesh ks 3.4415 c.e. Oxygen combined with starch............. 4.0215 “ Brora lata erie te eM tee SS Saye dete 7.4630. “ Mictuiv len tieMmene vane) rey tad ms ti ays, as 260 36.420 cals. * The authors show that even a considerably increased proteid meta- bolism would not materially affeet the computation of energy. 506 PRINCIPLES OF ANIMAL NUTRITION. Energy per Meter Traveled (Including Work of Ascent). Per ke. total mass .2-6 2595 as rrr 0.3948 cal. A as od Male rr 0.4077 “ Perikg. live weighty. jas) tiegeins armies oh 10. 1733 kem. Wiathio1 siseemte a. 1 lp Sas Sane ik ee ee 8.643 gr.-m. Determinations of the work of locomotion were made in six different periods, or thirty-five experiments in all. The average for each period, computed in terms of energy as in the above example, is given in Table VIII of the Appendix. It is to be noted that these results still include the small amount of work expended in-ascending the slight incline. This factor is determined in the manner shown in the following paragraph. Work of Ascent.—In four periods experiments were made (thir- teen in all) upon the work of ascending a moderate grade at a walk. The average results, computed on the same basis as before, are contained in Table IX of the Appendix. By comparing the average results of these two series of experi- ments in the manner explained on p. 500, letting x equal the oxygen or energy required per kilogram live weight for locomotion through 1 meter horizontally and y the corresponding quantities for the performance of 1 gram-meter of work of ascent we have the follow- ing equations: For Oxygen. z+ 4.395y= 83.480 c.mm. x+107.041y=222.941 c.mm. For Energy. z+ 4.395y=0.4035 cal. x+107.041y=1.0795 cals. Solving these we obtain the following values respectively for the work of locomotion per meter and for the energy expended in Energy. Oxygen ec mm. fp es | zi cals. Kgm. Locomotion per meter: Per kg: live weight............. 77.509 0.3746 0.1592 ofr ics, POL aS es eters. | 75.048 | 0.3618 0.15388 Ascent, per kilogram-meter...... 1359.00 | 6.5858 2.7990 * Weight of animal plus weight of apparatus carried. THE UTILIZATION OF ENERGY. 597 doing 1 kgm. of work of ascent, and the utilization of the available energy in the latter case is 35.73 per cent. Work of Draft.—Fer the work of draft at a aie up a shght incline, the results tabulated in Table \ of the Appendix were obtained. Giving x and y the same significance as before, and letting 2 represent the oxygen or energy corresponding to one gram-meter of work of draft, we have the following equation, based on the results per kilogram live weight and meter traveled: x+5.115y+ 153 .127z= 306.561 cmm.=1.5021 cals. Substituting in this the average values of x and y obtained as in- dicated in the previous paragraph, but from a larger number of experiments, we have z2=1.4504 c.mm.= .007143 cal. per gram-meter. The above details of a few of the experiments may serve to illus- trate the methods of computation employed. Similar determina- tions were made upon various forms of work under differing condi- tions, the results of which will be given later. Correction for Speed.—Before final data could be obtained, however, it was found necessary to take account of the speed of the animal, since comparisons of the various periods showed that the metabolism due to the work of locomotion at a walk increased materially as the velocity increased. To compute the necessary correction, the authors divide the thirty-five experiments of Table VIII into three groups according to the speed. For each group the oxygen and energy correspond- ing to the work of ascent are computed, using the values of y given on the previous page (1359 c.mm.; 6.5858 cals.), and subtracted from the total, leaving the following as the amounts per kilogram live weight due to horizontal locomotion: Oxygen : Oxygen Re- | Increase of | Heat Value No. of Velocity Consumed Respira- | calculated to| Oxygen per | of Oxygen Experi- per Minute, per Kg. tory Respiratory Meter per Meter ments. Meters. and Meter, | Quotient. | Quotient of Velocity, (Corrected), c.mm. 0.86, ¢.mm e.mm, eals. 6 78.00 66.69 0.896 Giese 0.697 0.3363 20 90.16 76.04 0.848 Cea ast) 0.683 0.3787 9 98.11 SOURS ORS TS Sea. ire eee 0.4058 508 PRINCIPLES OF ANIMAL NUTRITION. On the average, an increase of 1 meter per minute in the speed was found to cause an increased metabolism corresponding to— ORV RRD: 5 oie pots att etn ge eee I 0.692 ¢.mm. BIST yiec. iery cteid Stan le eyes > het ekg 0.00345 cal. A similar computation for the experiments on ascending a con- siderable grade without load or draft showed a similar difference, which, however, seemed to be chiefly or entirely due to variations in the work of locomotion. When the amount of the latter was computed with the correction for speed just given, the metabolism due to the actual work of ascent seemed to be independent of the speed, the only exception being two experiments at a rapid walk in which over exertion of the animal was suspected. In the thirteen experiments on the work of ascending a moderate grade contained in Table IX, the average speed was $1.95 meters per minute, while in the thirty-five experiments with which they are compared (Table VIII) the average speed was 90.16 meters. From the table on p. 506 we compute that the consumption of oxygen (R.Q.=0.86) and the corresponding energy values per kilo- gram and meter at these speeds would be | Oxygen Energy, ¢.mm. cals. At 90.16 M. velocity....... 75.80 0.3746 81 .955M. Sar ea Be 70.05 0.3462 \ Substituting this corrected value of x in the equations on p. 506, we have as the corrected value of y per kilogram-meter for ascending a moderate grade . 6.851 cals. =2.912 kgm.=34.3 per cent. In brief, a correction for the value of x is computed. using the first value of y, and then this corrected value of x is used to com- pute the corrected value of y. In other words, the method is one of approximation, but the errors of the corrected values are pre- sumably less than the unavoidable errors of experiment. Effect of Load.—In a number of experiments the horse carried on the saddle a load, consisting of lead plates, corresponding to that of arider. The mere sustaining of such a weight at rest was found THE UTILIZATION OF ENERGY. | 509 to increase the gaseous exchange, the total metabolism being sub- stantially proportional to the total mass (horse+load), but in com- puting the work experiments the same rest values are used as for the preceding experiments; that is, the results include the wor required to simply sustain the weight as well as that required move it. Computing the results in the same manner as before | authors obtain for an average speed of 90.18 meters per mi the following results: Locomotion per Meter. Per kg. live weight ......... 0.5004 cal. = 0.2126 kgm. te ee OLELAMASSS. wna. cae OeoO LA” “ire = Oe1 66a)" Ascent. Per kilogram-meter ........ 6.502 cals. = 2.7640 “ = 36.192 A comparison of these figures with those on p. 506 shows that for this animal a load of 127 kes. caused about 8 per cent. increase in the energy expended, per keg. of total mass, in horizon- tal locomotion, but no increase in that expended per kilogram- meter in ascent. Work of Descent—In descending a vrade the force of gravity acts with instead of against the animal and tends therefore to diminish the metabolism. On the other hand, however, as the steepness of the grade increases the animal is obliged to put forth muscular exertions to prevent too rapid a descent, and this tends to increase the metabolism. It was found that an inclination of 2° 52’ caused the maximum decrease in the metabolism. At 5° 45’ the metabolism was the same as at 0°, while on steeper grades it was greater than on a level surface. Work at A Tror.—A smaller number of experiments were made upon work at a trot under varying conditions. In trotting, the up and down motion of the body is much greater than in walking, while but a small part of the muscular energy thus expended is available for propulsion. It was therefore to be expected that the enercy required for horizontal locomotion would be greater at a trot tha at a walk, and the results of the experiments corresponded fully with this expectation, the computed energy per meter being foun | to be Per kg. live weight.......... Si cara eee 0.5660 cal. Se og Ties (HORSE =} AOAC )py wiee.c 6 Se a5, 00:0 OLO4T De 510 PRINCIPLES OF ANIMAL NUTRITION. at a speed of 195 meters per minute. The fact of such an increased expenditure of energy in trotting as compaged with walking has also been confirmed by the results of Grandeau, which will be con- sidered in another connection. It was also found that in trotting, unlike walking, the work of locomotion was independent of the speed within the limits experimented upon (up to a speed of 206 meters per minute, or about 7} miles per hour). A load of 127.2kgs. increased the work of locomotion per kg. of mass by about 10 per cent. as compared with the increase of 8 per cent. at a walk. One experiment on work of ascent and one on horizontal draft, both without load, showed a utilization of, respectively, 31.96 per cent. and 31.70 per cent., but two other experiments on horizontal draft, in which the work was thought to have been excessive, gave an average of only 235.35 per cent. Summary.—The final results of the experiments upon the horse may be summarized as follows: Work at a Walk. Work at a Slow Trot. Available Energy ates Available Energy | Utiljza- Expended tion. Expended. fant Pers a an CS ee Cent. Cent. cals. Kgm. cals. Kgm For 1 kgm. work of ascent, without load : VOT Cipradew Ae are eee 6.8508'2.9116 34.3 | 7.3647*/3.1300*|31 .96* DBA BP ELAR Cot crt aia < iin le 6.97872 .9660 33.7 For 1 kgm. work of ascent, with load : LS WI QTACES oo dis seine eras 6.502 |2.7634 36.2 For 1 kgm. work of drajt: *) Oswerdes << tas 7.51903, 1960.31 .3 } ioaren: a oeaareea BB PIPUAOE 05.4 shal bool 10.3360 4.3930 22.7 Locomotion per kg mass per meter without load : Speed of 78 00 M. per min.| 0.3256) PE OO 1G 6 Fe AIOE BEG Ke, ast ves 0.5478t « «“ogir® « & | 93929) J The same with load : | Speed of 90.18 M_ per min | O32) Wage (PEAR We So 0.6007t * Single experiment | Two experiments. Work probably excessive. ¢ Independent of speed. (oe THE UTILIZATION OF ENERGY. SII Conditions Determining Efficiency. From the results recorded in the preceding paragraphs it appears that, as we were led to expect from a consideration of the efficiency of the single muscle, the efficiency of the animal as a converter of potential energy into mechanical work varies with the nature of the work and the conditions under which it is performed, although the variations ure perhaps hardly as great as might have been expected. In general, we may say that in the neighborhood of one third of the potential energy directly consumed in muscular exertion is recoy- ered as mechanical work. This appears to be a high degree of effi- ciency as compared with that of any artificial transformer of poten- tial energy yet constructed. The steam-engine, the chief example of such transformers, even in its most highly perfected forms, rarely utilizes over 15 per cent. of the potential energy of the fuel, while in ordinary practice one half of this efficiency is considered a good result. The comparison is misleading. however, for three reasons: First, the figures given in the preceding pages relate to the utilization of the net available energy of the food. As we have seen, however, a certain expenditure of energy in digestion and assimilation is required to render the food energy available, while still another portion of the latter is lost in the potential energy of the excreta. In the case of herbivorous animals. these two sources of loss very materially reduce the percentage utilization when computed upon the gross energy of the food. Second, the comparison takes no account of the large amount of energy consumed continually throughout the twenty-four hours for the internal work of the body of the animal, and which continues irrespective of whether the animal is used as a motor or not. Third, the expenditure of energy in locomotion is not considered in computing’ the efficiency of one third. When these three points are allowed for but little remains of the apparent superiority of the animal as a prime motor, even omitting from consideration the greater cost of his fuel (food). It remains now to consider somewhat more specifically the in- fluence upon the efficiency of the animal machine of some of the more important conditions. " 512 PRINCIPLES OF ANIMAL NUTRITION. Kinp or Worx.—Of the forms of work investigated, that of ascent, that is, of raising the weight of the body (with or without load), appears to be the one which is performed most economically. The horse in ascending a moderate grade without load showed an efficiency of 34.3 per cent., while with a load of 127 kgs. a slightly higher efficiency was obtained, viz., 36.2 per cent. (The latter figure, however, includes some estimated corrections for speed.) For the dog (p. 502) the average result was 30.7 per cent. For man the figures of the table on p. 503 correspond to from 28.1 to 36.6 per cent. The efficiency, however, was found to decrease with the steep- ness of the grade. Thus with the horse it fell from 34.3 to 33.7 per cent., with an increase of the grade from 10.7 to 18.1 per cent. The experiments of Loewy on man, averaged on p. 503, show the same result in a more striking manner. ‘Taking separately the experiments on each subject we have the following: Efficiency. Grade Per Cent. AUL eae & auc Per Cent. Per Cent. Per Cent 23 34+ 3 BOs) 36.6 30.5 343 32 6 36 6 36.6 29.0 S2ro By yay The work of horizontal locomotion consists largely of successive liftings of the weight of the body., It might therefore be expected from the above results that this work would be performed even more economically than that of ascent, since it is obviously the form of muscular activity for which animals like the horse and dog are specially adapted. In the case of the walking horse, Kellner * has proposed a formula. based on mechanical considerations, for com- puting the work of locomotion. Zuntz f has applied this formula to the animal used in his experiments and computed the mechanical work of locomotion at the three speeds for which the total metabo- lism was also determined (p. 507). Landw. Jahrb., 9 658. } Ibid , 27, Supp IIL. p 314 THE UTILIZATION OF ENERGY. 513 A comparison of these figures, expressing the total metabolism in its mechanical equivalent, is as follows: Per Kg. Mass and Meter. Speed Mee per ae : Minute. ota Computec Metabolism Work ee aee Gram-meters. | Gram-meters. Clen Cy: 78.00 138.4 | 49/14 eae 5) 90.16 155.8 54.54 35.00 98.11 167.0 58.40 34.97 This computation gives an efficiency slightly greater than that obtained for the ascent of a grade without load, and in so far tends to confirm our conjecture, but the basis on which the work of loco- motion is computed can hardiy be regarded as sufficiently accurate to give this result the force of a demonstration. The work of draft appears to be performed considerably less economically than that of ascent or locomotion. Thus, for the horse, the efficiency for nearly horizontal draft was found to be 31.3 per cent. at a wall, and in one experiment at a trot 31.7 per cent., as against 34-36 per cent. for ascent. In two other experiments at a trot, in which the work may have been excessive, a much lower efficiency was found, viz., 25.4 per cent. Tor draft up a grade of 8.5 per cent. at a walk the efficiency was greatly reduced, viz., to 22.7 per cent. The above figures refer to the work of draft only, after deducting the energy required for locomotion and ascent. A similar difference was likewise observed with the dog (p. 502), the efficiency in nearly horizontal draft being 28.8 per cent. as compared with 30.7 per cent. for work of ascent. Experiments on man, not cited in the above pages, in which the work was performed by turning a crank, have shown decidedly lower figures for the percentage utilization. SPEED AND Gait.—The energy expended by the horse in loco- motion at a walk was found to increase with the speed at the rate of 0.00334 cal. per meter and kilogram mass for each in- crease of 1 meter in the speed per minute. Kellner’s mechanical analysis of the work of locomotion mentioned above divides it into two parts, viz., that expended in lifting the body of the 514 PRINCIPLES OF ANIMAL NUTRITION. animal and that expended in imparting motion to the legs. The former portion is regarded as constant, while the latter portion would increase with the speed. The very close proportionality between the work thus computed and the total metabolism, as shown by the table on the preceding page, is a strong confirma- tion of the correctness of both methods and places the conclusion as to the influence of speed upon metabolism beyond reasonable doubt. It is to be remembered, however, that it is the total metabolism per kilogram and meter which increases with the speed. The percentage utilization of the energy, so far as the data at our commiand enable us to determine, apparently remains constant. Practically, however, it is the former fact which interests us, since the expenditure of energy in locomotion is comparable to that in internal work and has only an indirect economic value. A similar effect of speed on the metabolism in horizontal locomotion was observed by Zuntz* in experiments on man. In those with the dog, on the other hand, the variations in speed were between 64.2 and 85.9 meters per minute, but no material difference in the metabo- lism due to locomotion was observed. In trotting, a horse expends much more energy per unit of hori- zontal distance than in walking. Thus, trotting at an average speed of 195 meters per minute (a little over 7 miles per hour), as compared with walking at an average speed of 90.16 meters per minute, gave the following results for the metabolism per kilo- gram mass and meter distance. Tropung. 65 <5. Ween AEN gs he oT 0.5478 eal. VV eM VE TS os ate ks [Elacoceng eos ante ete teks hee 0.3666 “ On the other hand, speed is, so to speak, obtained more econom- ically at the trot than at the walk. In the averages just given the speed was increased by 116 per cent., while the metabolism was in- creased by only 49 per cent. The same result is reached in another ‘way by computing, by means of the factor given at the beginning of this paragraph (0.00334 cal.), the theoretical walking speed which would give a metabolism equal to the average metabolism in trot- ting. We find this to be 147 meters per second, as compared with 195 meters ata trot. Moreover, it was found that at the trot the metab- olism did not increase with the speed, within the limits of the ex- * Arch. ges. Physiol., 68, 198. 4 | | THE UTILIZATION OF ENERGY. 515 periments. These, however, did not include speeds above 206 meters per minute (about 74 miles per hour), and the work was done on a tread-power, so that there was no air resistance. At this moderate speed it is not probable that the latter factor would be a large one, but it is one which increases as the square of the velocity, so that at high speeds it constitutes the larger portion of the resistance. At high speeds, too, the muscles contract to a greater degree, thus decreasing their efficiency, and additional auxil- lary muscles are called into play, both directly and to aid the in- creased respiration. It is a matter of common experience that while a horse is able to travel for a number of miles consecutively at 6 to 7 miles per hour, drawing a considerable load, he can maintain his highest speed for only a short time even without load, and does this only at the cost of largely increased metabolism. It is evident then that there is a limit beyond which an increase of trotting speed must increase the metabolism with comparative rapidity. Loap.—Supporting a load on the back while standing was found to increase the metabolism of the horse No. III approximately in proportion to the load—that is, the metabolism computed per unit of mass (horse+load) increased but very slightly. In locomotion with a load the metabolism is, of course, increased, since the load as well as the body of the animal must be lifted at each step. The increase over the metabolism at rest and without load, both walking and trotting, was found in the case of Horse III to be somewhat greater (8-10 per cent.) than the increase in the mass moved (horse + load). After making allowance for this increase in the work of locomo- tion, the efficiency in ascent with a load was found to be unaffected by the latter; that is, the energy expended in lifting a unit of mass (horse+load) through a unit of distance remained substantially the same. Indeed the figure obtained (36.2 per cent.) is slightly higher than that without load (34.3 per cent). Interesting indi- vidual differences in the above particulars were, however, observed between Horse No. III and some of the other animals experimented upon, particularly Nos. II and XIII, which form the subject of a sueceeding paragraph. SpEcIms AND Size or ANtMAL.—In ascending a moderate grade, the efficiency seems to be about the same in the ‘horse and in 516 PRINCIPLES OF ANIMML NUTRITION. man, while in the dog it is apparently somewhat less, as is seen from the following comparison: Grade, Efficiency, Per Cent. Per Cent. MADR ta chttieae Nate 23 Byes IOTBGR ry Arete orice 1OK7 34.3 a ad Ae Sa RES Ms As Oo 18.1 Sot iB fe ere SRE eae 17.2 30.7 The energy expended in horizontal locomotion, on the other hand, showed more marked differences, viz.: Energy Expended per Kg. Mass per Meter, Kgm. Speed, Meters per Minute. Doreen Ase (fseoye 0.501 Maris eae say ce 42 .32-74.48 0..211-0.334 IGrse see os Be are 78.00 0.138 The relatively high figure for the dog is perhaps due in part to the considerable muscular effort apparently required (p. 499) to main- tain the erect posture. It has been shown by v. Hésslin,* however, by a mechanical analysis of the work of locomotion, that the latter does not increase as rapidly as the weight of the animal, but in proportion to its two-thirds power, or, in other words, approximately in proportion to the surface. If we compare the experiments upon different species of animals on this basis—that is, if we divide the total energy expended by the animal for locomotion by the product of the distance traversed into the two-thirds power of the weight —we obtain the following figures: | | Door ames Meat We utd sk hes 1.501 kgm. Mann fisteritsec baa sne var aca ae 0.861-1.274 kgm. IOTSS Nivins sak ees kc sk eR ees 1.058 kem. . Computed in this way, the figures for the horse and those for man at a comparable speed (74.48 M. per min.) do not differ greatly, and v. Hésslin’s conclusions are to this extent confirmed. The figures for the dog still remain higher than the others. If, in the case of * Archiv f. (Anatomie u.) Physiol., 1888, p. 340. THE UTILIZATION OF ENERGY. 517 this animal, we compare the total metabolism in locomotion with that during standing instead of lying, as was done in the case of the horse, the figure is reduced to 1.803 kgm., or not much higher than in the case of man. It must be remembered, however, that the figures above given for man include the metabolism due to standing. InpivipuaLity.—Zuntz & Hagemann’s investigations show that the efficiency of the horse is affected toa considerable degree by the individual differences in animals. The experiments whose results are summarized on p. 510 were upon a single animal (No. III). In addition to these a small number of experiments were made with several other animals, mostly old and more or less worthless ones, besides the considerable number upon Horse No. II previously reported by Lehmann & Zuntz.* The results are com- puted by the authors in terms of energy and corrected for speed upon the basis of the results obtained with Horse No. III. In a single case the work of ascent required slightly less expen- diture of energy than with Horse No. III, and in another case the work of horizontal locomotion, computed to the same live weight in proportion to the two-thirds power of the latter (see the oppo- site page) was also less than for Horse No. ITI, but as a rule these old, defective horses gave higher results. For ascent, omitting one exceptional case, the range was as follows: Per-Kgm. of Work. Minimum....... 5.906 cals. = 39.84 per cent. efficiency DPM tee Oo AO at a OOS oy y “ etse NomihWe Or sok oir (234030) es cit “ With one very lame horse (string-halt) the figures reached the maximum of 12.343 cals., or an efficiency of only 16.6 per cent. A similar range was observed in the results on horizontal loco- motion. Reduced to a speed of 78 M. per minute and to the live weight of No. III, the range was as follows: Per Meter and Kilogram Live Weight. IATA LERES (a scope eed cach et, eRe eS Se 1) 284 eal. Recital ias a eis doa Cre neni ene. 'S he ORAier<° jie rcecen ii ica Wa OW et Ue i ee aN ene AR O2336R 5 * Landw. Jahrb., 18, 1. A. a A : ee eee ~ 518 PRINCIPLES OF ANIMAL NUTRITION. The very lame horse mentioned above gave a still higher figure, viz., 0.566 cal. A somewhat larger number of experiments with Horse No. XITL brought out the interesting fact that the increase in the metabo- lism caused by carrying a load on the back was markedly less than in the case of No. III, both at rest and in motion. PER KILOGRAM MASS (HORSE + LOAD). Without Load, With Load, eals. per Minute. cals. per Minute. Standing : Horse Ge ae 15.990 14.670 TEAL | ALDI Coane see 18.311 18.389 Walking horizontally : cals. per Meter. | cals. per Meter. Elorse 2 DEL eee 0.389 0.388 CS al Wl Wptean ae i oe 0.367 0.391 Trotting Horizontally : Horses iie see 0.553 0.488 ST ba Dae ree ee 0.548 0.601 While, without load, Horse No. XIII showed a greater metabo- lism, both while walking and trotting than did Horse No. III, the additional effort required for carrying a load was relatively less, so that in every case the metabolism per unit of mass, instead of increasing, remained unchanged or even diminished. The percent- age efficiency of the animal in ascending a grade was also not materially affected by the load, while with Horse No. III it ap+ peared to increase slightly. The experiments with Horse No. II previously reported,* when recalculated + in the same manner as the later ones, likewise show interesting individual differences. For horizontal locomotion, after correcting for varying speeds, we have per kilogram mass (horse + load) the following: Horse No. IT, Horse No. ITI, cals. per Meter. | cals. per Meter. Walking without load........ 0.415 0.367 i Willa LOR Gisele rte eye 0.385 0.391 Trotting without load........ 0.499 0.548 4; With loads te es, cst 0.415 0.601 + Landw. Jahrb., 18, 1. + Ibid., 27, Supp. III, 355 THE UTILIZATION OF ENERGY. 519 As these figures show, No. II was decidedly inferior to No. III in walking without load. In trotting, on the other hand, he was somewhat the superior of No. III, or in other words the change from walking to trotting caused much less increase in his metabo- lism. Like No. XIII, he carried a load with decidedly less expendi- ture of energy than did No. II. For the forms of work in which the percentage efficiency could be measured the results were as follows, the grades, however being not exactly the same for No. II as for No. III: Horse No. II, Horse No. III, Per Cent. Per Cent. Ascending, moderate grade... 33.2 34.3 sé heavier grade..... 31.7 33.7 Draft, nearly horizontal...... 29.0 31.3 PO WAS AP ETACLE) hn. Veatch 22.4 22.7 It seems a fair presumption that such individual differences as those above instanced are caused, in large part at least, by differences in the conformation of the animals resulting from heredity or ‘‘spontaneous” variation. A strain of horses which has been bred and trained especially for the saddle through a number of generations might very naturally be expected to be more efficient in carrying a load than a strain which has been bred for speed in harness or strength in draft, while the latter might as naturally excel the former in efficiency at the trot or in draft. Similarly, a race of horses developed in a hilly country might be. expected to be more efficient in ascending a grade than one in- habiting a flat region. It would seem, too, that these differences may be not inconsiderable. The results cited suggest an interest- ing line of thought and investigation for the student of breeding. TRAINING AND F'aticuE.—It is a familiar experience that any unaccustomed form of work is much more fatiguing at first than it is later. This is due in part to the fact that in making unfamiliar motions more accessory groups of muscles are called into activity than are necessary later when more skill has been acquired. The experience of a learner on the bicycle is an excellent example of this. In the second place, however, simple exercise of a group of 520 PRINCIPLES OF ANIMAL NUTRITION. muscles in a particular way seems to increase their average mechan= — ical efficiency. Gruber,* in two series of experiments upon himself, obtained — the following figures for the excretion of carbon dioxide during rest, horizontal locomotion, and hill climbing, all the trials being made about the same length of time (four to five hours) after the last meal: Work of Carbon Dioxide Ascent, Excreted in 20 Kgm. Minutes, Grms. Series I; EROSTPAN ers trae Svea Tone ted Rece tere ap ah ca eRe oc Rea Ge) |e, eT ae sales tes er eee 9. 706* Horizontal lOoCOMOtlOM.j.ysm syciete see ke ole oieus one Ore ree 19 .390* Hill climbing without practice BUN ote ler e 5892 40.982 “< after 12 days’ practice.. 6076 32.217 Series II (2 months later): DUES tecicthaeie cre thet atgce Oye clea aye 1s Sur Saoearoratte, AE wh aie ae ee 12.833 Honzontalllocomonion.cs cece 5 + nak ae iaaye sore eae 22.418 Hill climbing without practice RESO eRe Re 7376 38 .832T ‘« after 14 days’ practice.. 7539 31.001 * Some carbon dioxide may have escaped absorption. + Some carbon dioxide lost. Schnyder + has confirmed and extended Gruber’s results. In experiments in a treadmill upon two different subjects he ob- tained the following figures for the work performed per gram of carbon dioxide excreted in excess of that given off during rest: Kgm. hae ( Without ‘trainimg..5 ste saves oe te Se 218.13 Mama aad et, Bar H After 2 months’ training... 0.5. be eee 253.18 Without training...... Fe ie ea es 243.93 NOR gies tet cote hon ta MRA Menon iact Mieentalantels Wendie vAcASdnty Sho a om 285.52 / pap Mees Gy alin Uy acosm peste! ae a ae 349.40 Fx Nh) WVU LOUIG LAUD: 46 ar uth iene ave chee ane Syren 302.76 Ire Kee COR EME) 5 Sper dave: tneienne oan tee ec 404.39 . . . . ‘ That the greater efficiency after training is not due solely to a diminished use of accessory muscles is shown by Schnyder’s experi- _ ments on convalescents. His results were as follows: * Zeit. f. Biol., 28, 466 + Ibid., $8, 289. THE UTILIZATION OF ENERGY. 521 Work per Gram, Car- bon Dioxide 2s Months eeibermnrst tidal seeyereseyaleiee + ore 441.17 yehils1 he bate ee ee Ae nae ear Aiea en A eS Er 231.24 No. 3—lTreadmill.... } AOA Vey AnveL WES CEA ca diet leka mets tales 231.24 etc os GOON, UR Meare ers enclepeiene eee natasha 2 286 .25 In walking the same distance (468 M.) No. 1 excreted the following excess of carbon dioxide over the rest value: RIES Gy Ghee rar aos Od. neha ee tate 5 4.505 grams pNeenui ler oly tAii Need Sy ra Rs hod rl ede 3090): * omrotii oy lester eit lo lke eS ng Se Zrlouey sig It appears from these results that the gradual strengthening of the muscles during convalescence results in a more economical per- formance of their work, largely independent of any special training for a particular kind of work. It seems a justifiable conclusion, therefore, that a part of the gain due to training arises from its direct effect in strengthening the muscles, as well as from the in- creased skill acquired in their use. Conversely, the effect of fatigue in increasing the relative metabolism, as shown by Loewy,* would seem to be in part a direct effect. Schnyder summarizes the matter in the statement that it is not the work itself, but the muscular effort required, which determines the amount of metabolism. In the case of domestic animals kept chiefly for work, however, we may safely assume that they are constantly in a state of training, and that the results obtained by Zuntz and his associates on the horse are applicable to work done by normal animals within the limits of the experimental conditions. * Arch. ges. Physiol., 49, 405. 522 PRINCIPLES OF ANIMAL NUTRITION. ReLaAtTive VALUES OF Nutrrients.—In the foregoing discussion it has been tacitly assumed that the stored-up energy of the pro- teids, fats, and carbohydrates of the body is all net available energy, ready to be utilized directly for the production of mechanical work. As we have seen, however, on previous pages, a school of physiolo- gists, of which Chauveau may stand as the representative, denies this, and holds that the fat in particular must be converted into a carbohydrate before it can become directly available. In discussing the source of muscular energy in Chapter VI it was shown that the recorded results as regards the nature of the material metabolized were insuffi¢ient to decide the question, since the final excretory products are qualitatively and quantitatively the same whether the fat is directly metabolized in the muscle or undergoes a preliminary cleavage in the liver or elsewhere in the body. The results as to energy, however, would be materially different in the two cases. The dextrose resulting from the cleavage of fat, according to Chauveau’s schematic equation (p. 38), would contain but about 64 per cent. of the potential energy of the fat, the remainder being liberated as heat. We cannot, however, suppose that the energy of this dextrose can be utilized by the muscle any more completely than that of dextrose derived directly from the food. It follows, then, that the percentage utilization of the total energy metabolized during muscular work should be materially ereater when the metabolized material consists largely or wholly of carbohydrates than when it consists chiefly of fat. By supplying food consisting largely of one or the other of these materials, it is possible to bring about these conditions, and a determination of the respiratory exchange and the nitrogen excretion will then afford a check upon the nature of the material metabolized and the means of computing the utilization of its potential energy. Investigations of this sort have been reported from Zuntz’s laboratory. The earliest of these were by Zuntz & Loeb * upon a dog, the method being substantially the same as that with which the preceding pages have made us familiar. Their final results for the energy metabolized per kilogram and meter traveled ( including the work of ascent) were: * Arch. f. (Anat. u.) Physiol., 1894, p. 541. THE UTILIZATION OF ENERGY. 523 ~ Diet. Hgspeatery | Energy, cals. APO LALO S ROMs se lee rs cd eh os tA cee dere Ae us iolens A Degitss 2.58 Chiefly fat Focts Ab at Moses oo Ea IN ce ee ae = 0.74 2.43 ro ‘ (body freed from carbohydrates by PLOT NED foie Pees okie = pase Seausynit oS elke Steve’ 0.71 aye Much BURA TWIGDNPEOUCICS 3.000... os ols daca siete s 0.83 2.58 «and little PEOUIG say NA ene 0.88 2.63 The differences are quite small, while, as Zuntz points out, if 2.6 cals. represent the demand for energy per unit of work when carbohydrates are the source it should, according to Chauveau’s theory, rise to about 3.68 cals. when the energy is derived exclu- sively from fat. Altogether similar results have been recently reported from Zuntz’s laboratory by Heimeman,* and by Frentzel & Reach, in experiments on mane In Heineman’s experiments the work, which was never exces- sive, consisted in turning an ergostat, the respiratory exchange being determined by means of the Zuntz apparatus and the total urinary nitrogen being also determined. I'rom these data, reckon- ing 1 gram of urinary nitrogen equivalent to 6.064 liters of oxygen,{ the average amount of energy metabolized on the vari- ous diets, and the proportion derived respectively from proteids, fats, and carbohydrates, is computed. Py comparison with rest experiments the increments of oxygen and carbon dioxide due to the work were determined, and from these the energy consumed per kilogram-meter of work was calculated upon three -different assumptions: first, that the proteid metabolism was not increased by the work; second, that it increased proportionally to the oxy- gen consumption; third, that as large a proportion of the energy for the work was furnished by the proteids as is consistent with the observed respiratory exchange. The results are summarized in the following table: * Arch. ges. Physiol., 83, 441. } Ibid., 83, 477. t Zuntz, Arch. ges. Physiol., 68, 204. 524 PRINCIPLES OF ANIMAL NUTRITION. Total Energy Energy-per Kgm. Supplied by of Work. Respira- - — - a Ss A te Z | 3 Predominant Nutrient. Quo. a c ar- | ata 2 Receus = i aus ae Y- | teids, | sump- | sump- | sump- Cals. | drates, Cals. tion, tion, tion, Cals cals. cals. cals. ae. ja...| 0.783 | 3829 | 1379 | 18:1 40.68. eee 10.35 ge aes ire ) b....| 0.724 | 4422 246 163 | 9.39 9.35 9.27 . (a...| 0.805 | 3414 | 1823 TIE 48 i ir ia sje fe 10.46 Carbohydrates. 5°" "| 9 901 | 1543 | 3374 | 139 | 10.67 | 10.63 | 10.87 As much’ proteids as POSSIDIGE eae veneers 0.796 | 3381 | 1620 Oli 4) LIAO 27 eae The subject was not able to consume even approximately enough proteids to supply the demands for energy, so that the experiments are virtually a comparison of the utilization of fat and carbohydrates in different proportions. With the exception of the third group, the results seem to show thatethe energy of the fat metabolized was utilized, if anything, rather more fully than that of the carbohydrates. Frentzel & Reach experimented upon themselves, the work being done by walking in a tread-power; otherwise the methods were similar to those of Heineman. In computing the results of the experiments on a carbohydrate and a fat diet they assume that there was no increase in the proteid metabolism as a consequence of the work. For the experiments on a proteid diet they com- pute the results both on this assumption and also on the assump- tion of a maximum participation of the proteids in work produc- tion. Calculated in this way the total evolution of energy per kilo- eram weight and meter traveled was as given in the table on p. 525. The results show a slight advantage on the side of the carbo- hydrates, which in the case of Frentzel is regarded by the authors as exceeding the errors of experiment. They compute, however, that it is far too small to afford any support to Chauveau’s theory. Zuntz * has recalculated Heineman’s results, using slightly different data but reaching substantially the same result. He shows, however, that they are affected by the influence of train- ing already discussed on p..519. Arranging the experiments in chronological order, it becomes evident that the work was done * Arch. ges. Physiol., 83, 557. a THE UTILIZATION OF ENERGY. 525 Respiratory Energy per Kg. Quotient. and Meter, cals. Frentze.—fat diet: [Enunehinan KOLec eh nes oleae EOC ean mean 0.766 2.088 BECONGL WEEK en cits Ses sie aed 0.778 2.049 RYE Reie td bo 00 ORC aa Oe 0.773 2.066 Frentzel—carbohydrate diet: Eis nee eae ema cine etiam wc craters eis 0.896 1.932 SE COMGe WEE Kas serersior tie cies tinier arontts 0.880 2203 PAN ET LEC emcee pena A stct oh, cilanoeee 0.889 1.980 Frentzel—proteid diet: PAS Ges UNMNO LOW eye vene «© oiceaye) ii ) (0.799 { 1.933 Second assumption. ............. y ik ( 1.824 Reach—fat diet: SUES UMW EE Koes, 3. fle Scere ale Aoi be 4 whe’ 0.805 2.259 DEGOMC Wesker rae coe ls cole sisis ete 0.766 2.034 PACT AMC: cede pies tte arated fared eee 0.781 PASAY) Reach—carbohydrate diet: BS Gewyee lores ttarmy ctor trap t te tine ae 0.899 2.202 SECON GV CO KU aan Aree ite a eiaeue c 0.901 2.005 VELA OS eet? RON OMe Nero. oi 0.900 2.086 with increasing efficiency, largely independent of the food, and the fact that most of the experiments with fat came later in the series than those with carbohydrates largely, although perhaps not en- tirely, accounts for the observed difference in efficiency, while the low figure for proteids is accounted for by the fact that these were among the earliest experiments. A similar effect appears in the experiments of Frentzel & Reach, although it is less marked, since walking is a more accustomed form of work than turning a crank. On the whole, Zuntz concludes that these experiments warrant the conclusion that in work production the materials metabolized in the body replace each other in proportion to their heats of combus- tion—that is, in isodynamic and not isoglycosic proportions. THE UTILIZATION OF METABOLIZABLE ENERGY. the investigations just discussed give us fairly full data as to the utilization of the stored-up energy of the body in the produc- tion of external work, and this, as we have seen (p. 497), is sub- stantially equivalent to a knowledge of the utilization of the net 526 PRINCIPLES OF ANIMAL NUTRITION. available energy of the food. These determinations by Zuntz and his co-workers, however, do not bring the energy recovered as mechanical work into direct relation with the energy of the food; that is to say (aside from such computations of available energy as those made by Zuntz & Hagemann* for the food of the horse), they do not tell us how much of the energy contained in a given feeding-stuff we may expect to recover in the form of mechanical work, but only what proportion of the stored-up energy resulting from the use of this feeding-stuff is so recoverable. It is the former question rather than the latter, however, which is of direct and immediate interest to the feeder of working animals. The feeding-stuffs which he employs are comparable to the fuel of an engine, and the practical question is how much of the energy which he pays for in this form he ean get back as useful work. Meruops oF DETERMINATION.—I wo general methods are open for the determination of the percentage utilization of the energy of the food. It is obvious that if we know the net availability of the energy gross or metabolizable) of a given food material we can compute its percentage utilization in work production from the data of the foregoing paragraphs, with a degree of accuracy depending upon that of the factors used. For example, if we know that the net available energy of a sample of oats is 60 per cent. of its gross energy, then if the oats are fed to a draft horse utilizing, according to Zuntz & Hagemann, 31.3 per cent. of the net available energy, it is obvious that the utilization of the gross energy of the oats is 600.313 = 18.78 per cent. An entirely similar computation could of course be made of the percentage utilization of the metabolizable energy of the oats. Unfortunately, however, as we have already seen, our present knowledge of the net availability of the energy of feeding-stuffs and nutrients for different classes of animals is extremely defective, and extensive investigations in this direction are an essential first step in the determination of the percentage utilization of the energy of feeding-stuffs in work production by this method. Until trust- worthy data of this sort are supplied, results like those of Zuntz & Hagemann can be applied to practical conditions only on the basis * Landw. Jahrb., 27, Supp. III, 279 and 429. THE UTILIZATION OF ENERGY. ow of more or less uncertain estimates and assumptions regarding the expenditure of energy in digestion and assimilation such as those discussed in Chapter XI, § 3. The second possible general method for the determination of the percentage utilization of the energy of the food in work pro- duction is that employed in the determination of the utilization in tissue production. Having brought the animal into equilibrium as regards gain or loss of tissue and amount of work done with a suit- able basal ration, the material to be tested is added and the work increased until equilibrium is again reached. The increase in the work performed compared with the energy of the material added would then give the percentage utilization of the latter. The accurate execution of this method would require the em- ployment of a respiration apparatus or a respiration-calorimeter for the exact determination of the equilibrium between food and work, while the skill of the experimenter would doubtless be taxed in the endeavor to so adjust food and work as to secure either no gain or loss of tissue or equality of gain or loss in the two periods to be compared. Indeed, it may safely be said that exact equality would, as a matter of fact, be reached rarely and by accident, and that as a rule it would be necessary to correct the observed results for small differences in this respect. To make such corrections accurately, however, requires, as we have seen in § 1 of this chapter, a knowledge of the net availability and percentage utili- zation of the food, and we are thus brought back to the necessity for more accurate knowledge upon fundamental points. The extensive investigations of Atwater & Benedict * upon man appear to be the only ones yet upon record in which the actual balance of matter and energy during rest has been quantitatively compared with that during the performance of a measured amount of work. Unfortunately, however, the gains and losses of energy by the bodies of the subjects in these experiments were relatively considerable, while the experiments thus far reported seem to afford no sufficient data for computing the net availability of the food for maintenance or its percentage utilization for the production of gain. Moreover, the authors appear to regard the measurements * U.S. Department Agr., Office of Experiment Stations, Bull. 10°; Mem- oirs Nat. Acad. Sci., 8, 231. 528 PRINCIPLES OF ANIMAL NUTRITION. of the work done as not altogether satisfactory. In a preliminary paper * Atwater & Rosa compute a utilization of 21 per cent. Inasmuch as they have not further discussed the question of the utilization of the food energy for work production it would seem premature to attempt to do so here. It may be remarked, however, that the figures given seem to indicate a rather low degree of effi- ciency for the particular form of work investigated (riding a station- ary bicycle). Wolff's Investigations. The horse, being par excellence the working animal, has natu- rally been the subject of experiments upon the relation of food to work. While as yet the respiration apparatus or calorimeter has not been applied to the study of this phase of the subject, two ex- tensive and important series of investigations have been made upon the work horse, viz., by Wolff and his associates in Hohen- heim and by Grandeau, LeClere, and others { in Paris, in which the attempt has been made to judge approximately of the equilibrium between food and work from the live weight and the urinary nitro- gen. Grandeau’s experiments were made for the Compagnie générale des Voitures in Paris, and were directed specifically toward a scientific investigation of the rations already in use by the company and to a study of the most suitable rations for the different kinds of ser- vice required of the horses. They were, therefore, while executed with the greatest care and exactness, largely “practical” in their aim. Wolff’s experiments were made at the Experiment Station at Hohenheim and were broader in their scope, being directed largely to a determination of the ratio of (digested) food te work. The following paragraphs are devoted chiefly to an outline of Wolff’s experiments, but with more or less reference also to Grandeau’s results. ; Methods.—In discussing the effects of muscular exertion on metabolism in Chapter VI, mention was made of the interesting * Phys. Rev., 9, 248; U.S. Dept. Agr., Office of Experiment Station, Bull. 98, p. 17. + L’alimentation du Cheval de Trait, Vols. I, II, II, and IV, and Annales de la Science Agronomique, 1892, I, p. 1; 1893, I, p. 1; and 1896, II, p. 113 . @ conpivina ie a THE UTILIZATION OF ENERGY. 529 results obtained by Kellner regarding the influence of excessive work upon the proteid metabolism of the horse. It was there shown that when the work was increased beyond a certain amount there resulted a prompt increase of the urinary nitrogen and at the same time a steady falling off in the live weight. The method employed in Wolff’s experiments, and which originated with Kellner, is based upon this fact. It may perhaps be best illustrated by one of Kellier’s earliest experiments,* in which starch was added to a basal ration, the results of which have already been referred to in Chapter VI (p. 199). In the first period the daily ration consisted of 6 kgs. of oats and 6 kgs. of hay, while in the second period 1 kg. of rice starch was added. Digestion trials showed that there was digested from these rations the following: Period I, Period IT, Increase. Grms. Grms. Grms. Grude protem gf. 02.0). ek 757 .07 750.53 — 6.54 OO Rial ols alae OEE Pe eG eae 636.10 713.40 + 77.30 Nitrogen-free extract ........... 3874 .36 4488.15 +613 .79 EVGherextracthonts cat. s reece ta ante 279.45 275.43 — 4.02 5546.98 6227.51 + 680.53 The work was performed in a special sweep-power which was so constructed as to act as a dynamometer. With a uniform draft of 76 kgs., the daily work in the four subdivisions of the first period consisted of 300, 600, 500, and 400 revolutions respectively, while in the two subdivisions of the second period it was 800 and - 600 respectively. From the daily results for live weight and urinary nitrogen and from a comparison with another period in which 1.5 kes. of starch was fed, Kellner concludes that the maximum amounts of work which the animal could perform without causing an increase in its proteid metabolism and a decrease in its live weight were for the first period 500 revolutions and for the second period 700 revo- lutions. The difference of 200 revolutions, then, represents the additional work derived from the added starch. Two hundred revolutions with a draft of 76 kgs. equaled 438,712 kgm., to which is to be added the work of locomotion, estimated by Kellner (com- * Landw. Jahrb., 9, 670. 530 PRINCIPLES OF ANIMAL NUTRITION. pare p. 539) at 100,000 kem., making the total additional work 538,712 kgm. Kellner compares this difference with the increased amount of nitrogen-free extract digested, 613.79 grams, neglecting the small differences in the other nutrients. As corrected in a later publication,* the results are as follows: 613.79 grms. starch = 2527.601 Cals. = 1,071,698 kgm. 538,712 + 1,071,698 = 50.27 per cent. If we base the calculation upon the difference in total organic matter digested, the percentage will of course be somewhat smaller. It was discovered later that the indications of the dynamometer used in these experiments and many subsequent ones were untrust- worthy, so that no value attaches to the percentage computed above, but it serves just as well to illustrate the method employed, and which was followed in the whole series of experiments. In brief, the attempt is to find in the indications of live weight and urinary nitrogen a partial substitute for the determination of the respira- tory products. As Kellner and Wolff do not fail to point out, the results are but approximations, and in any single experiment may vary considerably from the truth, but on the average of a large number of experiments it was hoped that satisfactory results might be reached. In later experiments rather more importance seems to be attached to the effects upon live weight than to those upon urinary nitrogen, but it should be noted that the live weight showed remarkably small variations from day to day, under the carefully regulated conditions of the experiments, and was quite sensitive . to changes in the amount of work done. The experiments may be conveniently divided into three groups. The first of these | includes the years 1877 to 1886, inclusive, in which the work done was compared with the total digested food. The second { covers the experiments of 1886-1891, in which the digested crude fiber was, omitted in East: the work-equivalent of the food, while the third group § includes the experiments of 1891-1894 with a new and more accurate form of dynamometer. * Wolff, Grundlagen, ete., p. 89. + Grundlagen fiir die rationelle Fiitterung des Pferdes, 1886, 66-155; Neue Beit triige, Landw. Jahrb., 16, Supp. III, 1-48. { Landw. Jahrb , 16, Supp. III, 49-131, and 24, 125-192. g Ibid., 24, 193-271. —sow~ es —. THE UTILIZATION OF ENERGY. 531 Experiments of 1877—1886.—During the years named, in addi- tion to the preliminary investigations necessary in working out the method, a large number of experiments were made on three different animals. The rations consisted largely of hay and oats in some- what varied proportions, together with smaller amounts of other feeding-stuffs. In three experiments on starch and four on oats a comparison of the increase in digested nutrients * with the in- creased work which could be done gave the following results: + Increase in Digested! |Increase in Work Done) Nutrients Equivalent Nutrients, at 76 Kg. Draft, to 100 Revolutions, Grms. Revolutions. Grms. sO SHIRE Ge Wariner 677.3 PA S12 RTS san ees TES: 175 318 PME eon ole py Mtoe et & Anats aes S Ac gina t wicite 315 | | THE MAINTENANCE REQUIREMENT.—As already stated, it was discovered later that the dynamometer used was unreliable and gave too high readings, so that the above result cannot be em- ployed to compute the utilization of the energy of the added food. It does, however, in its present form, enable us to compute the maintenance requirements of the horse by subtracting from the total digested food the nutrients equivalent to the work performed (i.e., 3.15 grams the number of revolutions). ‘The results of such a computation made by Wolff ft are given on p. 532. The actual live weights in these experiments were somewhat below the normal weights, which were regarded as being about 533 kgs. for No. I, 500 kgs. for No. II, and 475 kgs. for No. III. Wolff considers the maintenance requirements to be independent of minor changes in weight, and on the basis of the above “normal ” weights computes the maintenance requirements per 500 kgs. live weight as follows: Le Si eet Sid Devoe MEI RMR They al ae A 4143 grams Be ME: ei vo ae A Stet Pena wc 2 ad 4260 “ Ekg 0 Gl oO Ag AE hae Stet ova Aon PASS St HUE EMRIs ie ae ALQO: * The algebraic sum of the differences in the single nutrients is used, and in this and the succeeding comparisons the digested fat 1s multiplied by 2.44, 7 Loc. cit., pp. 125-129. ¢ Loc cit., pp. 99 and 132. 532 PRINCIPLES OF ANIMAL NUTRITION. No. of | Total reward Live | No. of | Equiva- For Bxperi-lWuerenta: eras Pitahatrt, (Raewolu. Nu ments. Grms. 4 Kgs. tions. peste 8, Gainel Rrorse [es . YS. 4 | 6305.6 asm! 521 €00 1890 4416 Horse IT: 1881-82.... if 5831.1 1:6.64 | . 477 546 1720 4111 1882-83... . 4 6748.3 1:6.37 | 486 662 2085 | 4663 1883-84. ... 6 5920 .2 e720 |) e457. 567 1786 4134 Average...| 17 6078.4 | ,1:6.80 473 577 1818 4260 Horse IIT: | 1881-82.... 6 Doles LG 454 ; 404 1273 4041 1882-83....; 6 | 6061.3 | 1:6.88 | 469 | 683 | 152 3909 1883-84 5 5734.8 bi feha ty |) brs} 580 1827 3908 SOD one ery 4 5761.2 i Teor 4ars 575 1811 o200) Average.. | 21 | 5717.8 Lene 329 467 | oul 1766 | 3952 By means of a comparison of the results by groups * Wolff shows that the maintenance requirement as thus computed is appar- ently independent of the amount of work done and of the nutritive ratio, and from this uniformity concludes that the relative efficiency of the food for work production is unaffected by these factors, within the range of his experiments. A series of similar experiments on Horse No. III in 1885-86,7 computed in substantially the same way, gave results for the main- tenance ration agreeing well with those of earlier years, viz., Period. Se er AUR. soe eee 3934 grams total nutrients Sai Bt aes ee Ne eh eg ae 3984 “ oe «< ’ 9 obi Deand Vaiia ee ee AOOT eh « © te WO? ater sca ee te 4094 “ 66 «“ “ pf 0) Fe gear ey SCV at 4094 i ee ‘ AVeTAGE: OF. wiriise seeks 4021. “ & «“ with an average live weight of 475 kgs., equivalent to 4230 grams per 500 kgs. In a succeeding period (IX), however, in which hay alone was fed, a decidedly higher result was obtained, viz., 4357 grams per head, or 4586 grams per 500 kgs. * Loc. cit., pp. 135 and 137. { Landw. Jahrb., 16, Supp. III, 32. ire. » THE UTILIZATION OF ENERGY. 533 Experiments of 1886-91.—In the experiments thus far de- seribed, with the exception of the last, the proportions of grain and coarse fodder in the rations were not widely different, the latter furnishing on the average fully one half of the dry matter fed. Consequently the experiments were not calculated to bring out any difference in the nutritive value of the two such as is indicated by the results of the one trial with hay alone. GRAIN vs. Coarse FopprR FoR MAINTENANCE.—The results obtained by Grandeau & LeClere upon the maintenance ration of the horse when fed a mixture containing about 75 per cent. of grain fully confirm the indications of Wolff’s trial with hay. Their experiments have been very fully discussed, and in part recalculated, by Wolff * in their bearing on this question. The three horses experimented on were fed two different amounts of the same mixture in several different thirty-day periods, eighteen such periods in all being available for comparison. In all of them the animals were led daily, at a walk, over a distance of about four kilometers. Wolff estimates the amount of work of locomotion by 2 amount of nutrients from the total digested obtains the amount re- quired for maintenance. The results are as follows: WwW. ‘ means of the formula s(—) v and by subtracting the equivalent Nutrients! For Maintenance. No. of Live Digested Equiva- Experi- Weight, | Nutrients,} lent to ments. Kgs. Grms. Work, Per Per Grms. Head, 500 Kgs., Grms. Grms. Heavier Ration - Horses l= ws. 3 416.6 3553 110 3443 4132 i) UGS ee a bs 405.9 3432 108 3324 4078 a i EG) aa 4 439.0 3625 119 3506 3994 HAVCEA SC eeu a |2 ie eee 420.5 3537 112 3425 4068 Lighter Ration : Horse pul eee 2 411.0 3060 108 2952 3636 be TANTS eee ‘4 441.2 3310 119 3191 3617 Average......[..0000: 426.1 | 3185 114 | 3071 | 3626 The results, and particularly those on the lighter ration, which appeared ample for maintenance, are much lower than those com- * Landw. Jahrb., 16, Supp. iII, 73-81. . 534 PRINCIPLES OF ANIMAL NUTRITION. puted in the previous paragraph. ‘The difference is too great to be ascribed to experimental errors in estimating the small amount of work done, and can most reasonably be ascribed to the difference in the character of the ration. Apparently the horse, like cattle (p. 433), requires less digestible food for maintenance when the latter consists largely of grain than when it is chiefly or wholly coarse fodder. Direct experiments by Wolff * likewise show that the digestible nutrients of concentrated feed (oats) are more valuable for work production than those of coarse feed (hay). The experiments were made in the manner already described, the draft being uni- formly 60 kgs. Although the measurements of the work actually done are probably incorrect, it may be assumed to have been substantially proportional to the number of revolutions of the dynamometer. A ration of 3 kgs. of hay and 5.5 kes. of oats served as the basal ration, to which was added in one case 4 kgs. of hay and in another 14 kgs. of oats. The nutrients digested in each case and the equivalent amount of work secured were: Digested. ns e - 52 | Ration Nitrogen Ether Total Ea 2 = ; = 2 Protein, Tone free Ex- (Fat X 35 o Grms. Cris Extract, tract, 2.4), ge Py | 3 Grms. Grms.)| Grms. } | | I-III | 7 kgs. hay, 5.5 kgs. oats| 822.58 | 816.68 | 3889.64 | 186.7: 5973.62 | 750 WS eclro) pode im OO : 2 “| 626.46 | 422.74 | 3068.46 | 184.78 | 4561.13 350 Avisog wna) ances ss 196.12 | 393.94 | 821.18 1.94 | 1412.49 400 Per sLOO WS VOMUONE cise cote Rieke wile altos erate otekall eae 353.12 VI. 3 kgs. hay, 7 kgs. oats...) 754.52 | 355.24 | 3719.24 | 252.17 | 5484.21 700 View thes BS Biya ey 626.46 | 393.94 | 3068.46 | 184.78 | 4561.13 350 Lb ikgsoats. yi es 128.06 |—67.50 650.78 67.39 873.08 350 Per 100 revolutions ..|........ | Ra vem coaieil ite gan tue tte oe Rei oe 249.45 The relative value of the digested matter of hay and of oats for work production in these trials was thus approximately as 5:7. In the earlier experiments (p. 531) it was found,that when oats or starch were added to a basal ration, approximately 315 grams of digested nutrients were required to produce the amount of work represented by 100 revolutions at 76 kgs. draft. Converting this result and the one just given for oats into kilogram-meters, Wolff computes that 100 grams of digested nutrients was equivalent, * Loc. cit., pp. 84-95. THE UTILIZATION OF ENERGY. 535 in round numbers, to 85,400 kilogram-meters in the earlier experi- ments and to 90,480 in the one just cited. While these figures are not correct absolutely, they are probably comparable, being ob- tained with the same apparatus. In the later experiment the work of locomotion is computed by Wolff’s formula, which gives higher results than Kellner’s. ‘Taking this into account we may regard the agreement of the two equivalents as satisfactory. VaLurE oF Crupe Fiser.—In all the experiments with con- centrated feeds the additional nutrients digested from the added food contained no crude fiber, the apparent difference, indeed, being in most cases, as in the above experiment, negative. When hay was added, on the other hand, over one fourth of the addi- tional nutrients digested consisted of. crude fiber. If, now, we negiect this crude fiber and compare the work and the fiber-free nutrients we have 1018.55 + 4.00 = 254.64 grams of fiber-free nutri- ents per 100 revolutions, or a figure corresponding almost exactly with that obtained for the fiber-free nutrients added in oats or starch. In other words, it would appear from this result that the digested crude fiber of hay is as valueless for work production as it appears to be for maintenance. If, however, the crude fiber is valueless both for maintenance and work, then by omitting it altogether from our computations we ought to get results for the maintenance ration and for the ratio of nutrients to work which are independent of the proportion of grain to coarse fodder in the ration. Confirmatory evidence of this sort is abundantly furnished by Wolff’s experiments and likewise by the results of Grandeau on maintenance. Taking first the averages of the experiments of 1877-1886 (p. 532) we have— Fiber-free Nutrients for Maintenance. Nutrients Digested. No. of Equiva- Revolu- lent Without | tions at | Nutrients, Crude 76 Kgs. Grms. | Per Head, Per 500 Total, Crude ; Fib : Grms Gunde. | pipes Grms. eae bs Horsey o/s 2. 6306 | 815 | 5491 600 1890 3601 3378 pa Le 6078 | 978 ; 0100 a7 1818 3282 3282 arid LET 5718 809 | 4909 561 1766 143 3306 DASHES eens lhe ecto Koaceey Oe saeco | Boge er aecnetee, eee Sea tcicanscws 2 3322 | 536 The results of the series made in 1885-86 on Horse No. III (p. 532), computed in the same way, give the following as the “ PRINCIPLES OF ANIMAL NUTRITION. amounts of fiber-free nutrients required for maintenance: Per 500 Kgs. oye Hes, | Live Weight, Period: ie + ts actuks.c eee 3270 3442 ella Cl Lares, Salty ora i O 3186 3353 Ae) a eamelVianie a ee 3242 3413 ret WEL Se a 3342 3549 Jebimea\ SM Sk ta eal > 3316 3490 ie yl Be Sa nies 8 3170 3335 AVerawe -b cio kas as os 3254 3430 From Grandeau’s experiments (p. 533), by the same method, we have for the lighter ration the following: Per 500 Kgs. Fen Heed, Live Weight, rorse dye ee te se 2732 3324 oh *ird td Bl peat, Famed ear 2935 3328 INVETRED 0) G CVs ian cite omni eae 3326 Finally, for the series of experiments by Wolff, just discussed, upon the relative value of the digested matter of oats and of hay, and from which the conclusion as to the lack of value of the crude « fiber was drawn, by computing backwards, we get figures for the fiber-free nutrients required for maintenance which not only agree with each other, as they necessarily must, but also with those of the earlier experiments. The results are: Bertier Per 500 Kgs Live Weight. Grms Period I-III .......... 3175 3342 of LY 2.5 ae ie ers 3275 3429 fe Vas aus Seen 3180 3329 «f Va ee oko 3196 3364 AV ORERE cir. tented ieee fale cicioe Siete ote eee a 3366 THE UTILIZATION OF ENERGY. Sov Wolff’s conclusions from these results * are— 1. The digested crude fiber is apparently valueless, both for maintenance and for work production. 2. The remaining nutrients may be regarded as of equal value whether derived from grain or coarse fodder. 3. The maintenance of a 500-kg. horse requires approximately 3350 grams per day of fiber-free nutrients. Wolff’s subsequent experiments up to 1891 + gave results con- firmatory in general of the above conclusions. Particularly was this the case when the work of locomotion was computed by Kell- T ner’s formula and not by the formula 2 (— Jv The work done ~ (expressed in number of revolutions of the dynamometer) per 100 grams of fiber-free nutrients was reasonably uniform and agreed well with the results previously obtained, while the fiber-free nutrients required for maintenance likewise agreed with the results given above. On the other hand, the inclusion of the digested erude fiber in the computations gave in many cases strikingly discordant results. In view of the unreliability of the measurement of the work no conclusions can be drawn as to the percentage utilization of the energy of the food, and it seems unnecessary to describe the individual experiments. A discussion by Wolff t of the results of some of the experi- ments by Grandeau in which work was done, although rendered uncertain by the difficulty in estimating the work of locomotion at varying velocities, and by the changes in live weight of the animals, seems to indicate that they also confirm Wolff’s conclusions. SIGNIFICANCE OF THE Resuutts.—In drawing his conclusions Wolff is careful to say that the digested crude fiber is apparently valueless, and while calling attention to Tappeiner’s then recent results on the fermentation of cellulose in the digestive tract as probably explaining its low nutritive value he points out that other ingredients of the food may also undergo fermentation. He therefore holds fast to the fact actually observed, viz., the lower nutritive value of the digested matter of coarse fodder compared _ * Loc. cit:, p. 95. + Landw. Jahrb., 24, 125-192. t Ibid., 16, Supp. ILI, 110-126. 538 PRINCIPLES OF ANIMAL NUTRITION. with that of grain, and virtually regards the amount of crude fiber as furnishing a convenient empirical measure of the difference. In the light of our present knowledge this reserve seems amply justified. The difference in the value of coarse fodder and grain we should now regard as arising largely from the difference in the amounts of energy consumed in digestion and assimilation. Kell- ner’s experiments on extracted straw discussed in the previous section have shown, however, that with cattle this difference is by no means determined by the simple presence of more or less crude fiber, but is related rather to the physical properties of the feeding-stuff, while Zuntz (see p. 392) has shown that the same factor largely affects the work of mastication in the horse. That the nutritive value of the rations in Wolff’s experiments was pro- portional to the amount of fiber-free nutrients which they contained, or, in other words, that thé energy expended in digestion, ete., was proportional to the digested crude fiber, is explained by the limited variety of feeding-stuffs employed. The coarse fodder was meadow hay with, in some cases, an addition (usually relatively small) of straw, while the grain was commonly oats, part of which was in some instances replaced by maize, beans, barley, flaxseed, or oil-meal, while starch was added to the ration in a number of trials. The larger part of the work of digestion, under these circumstances, was probably caused by the coarse fodders, viz., hay and straw, while the digested crude fiber was likewise derived chiefly or entirely from these substances. Such being the case, it follows that the loss of energy through digestive work would be in general proportional to the amount of crude fiber in the ration. The essential point in Wolff’s experiments is that the omission of crude fiber renders the results concordant, and this is as well explained in the manner just indicated as by the estimate of Zuntz & Hagemann that the work of digesting and assimilating crude fiber consumes the equivalent of its metabolizable energy. Experiments of 1891-94.—In the dynamometer employed by Wolff the resistance was produced by the friction of metallie sur- faces. A copy of his dynamometer was employed by Grandeau & LeClere in their investigations at Paris, and these experimenters found* that the measurement of the work was subject to large errors, * Fourth Memoir, p. 49. THE UTILIZATION OF ENERGY.. 539 particularly in experiments at a trot, owing to the continual changes in the friction. Wolff believes that in his experiments, all made at a rather slow walk, the errors are less, but admits that they are sufficient to deprive his computations of utilization of all val e. Grandeau & LeClerc, however, were successful in improving the dynamometer, by the addition of an integrating apparatus,* so that its measurements of the total work were satisfactory, and this apparatus was added to Wolff’s dynamometer in 1891. Before that date, therefore, Wolff’s experiments, while of great value in many other respects, afford no trustworthy direct data as to the utili- zation of the energy of the food for work production, although, as we have just seen, they afford some information on subsidiary points. From 1891, however, we may regard the measurements of the work done on the dynamometer as reasonably accurate. Corrections. — Unfortunately, in the light of subsequent investigation, the same is not true of some of the other factors entering into the comparison, particularly the work of locomotion and the metabolizable energy of the food. In all his later experiments Wolff computes the work of hori- a : 1 /W zontal locomotion per second by means of the formula = ce )e in which W equals the weight of the animal, g the force of gravity, and v the velocity per second. Zuntz’s experiments, however, appear to show that this formula gives too high results, the error increasing with the velocity, and Wolff + himself recognizes the truth of this for higher speeds. According to Zuntz’s determinations (p. 512), Kellner’s method of computation gives results agree- ing quite closely with those computed from his respiration experi- ments. Under the conditions of Wolff’s experiments this corre- sponds quite closely to 50,000 kgm. per 100 revolutions of the dynamometer, and in the comparisons which follow this amount has been substituted for that computed by Wolff, thus reducing materially the figures for the total work performed. Wolff estimates the metabolizable energy of the food, on the basis of Rubner’s results, by multiplying the digested fat by 2.4, adding the remaining digested nutrients, and reckoning the total * Ann. Sci. Agron., 1881, I, 464. { Landw. Jahrb., 16, Supp. II, 119. 540 PRINCIPLES OF ANIMAL NUTRITION. at 4.1 Cals. per gram. As we have seen, however (Chapter X), this figure is‘probably too high for herbivora, although exact figures for the horse are not yet fully available. Approximately, however, we may estimate the metabolizable energy of the several digested nutrients as follows (p. 332): Proves... css Meee oes oe oe 3.228 Cals per gram Cride fiberesi.) eV case 8. SIR: Se oe Nitrogen-free extract.......... TON Ta ee pics ae Ether extracts Assets oe wii BD eee Zuntz * estimates the metabolizable energy of the total nutri- ents (including fat X 2.4) at 3.96 Cals. per gram. This figure is probably somewhat high, especially for rations containing much crude fiber or ether extract, but may serve the purpose of approxi- mate calculations. - EXPERIMENTS ON SINGLE FEEDING-STUFFS.—Comparatively few of the experiments admit of a direct computation of the utiliza- tion for a single feeding-stuff, since in most cases the amounts of two or more feeding-stuffs were varied simultaneously. As an example of the former class we may take Periods I and II of the experiments of 1892-93. In Period I the ration consisted of 7.5 kgs. of hay and 4 kgs. of oats per day, while in Period II the oats were increased to 5.5 kes. The quantities of nutrients digested and the metabolizable energy of the difference between the two rations (computed by the use of the factors just given) were— - Crude Nitrogen- Ether Total Protein, : f t Grms. | “Qe || extract, | Gach | Ge ‘Berioaslly wees 1022.4 849 .6 4152.8 175.8 6446.6 pate Lk ce es 847.8 819.9 3598 .4 Siew 5595.3 Difference .... 174.6 29.7 554.4 38.7 851.3 Cals. Cals. Cals. Cals. Cals. Equiv. energy... 564 105 2320 332 3321 In Period I (20 days) the daily work consisted of 300 revolutions of the dynamometer. With this amount of work the live weight of the horse underwent very little change, but there was a material * Landw. Jahrb., 27, Supp. III, 418. > oS oe THE UTILIZATION OF ENERGY. 541 gain of nitrogen, so that Wolff estimates that the work might have been increased to 350 revolutions. In Period II (23 days) the daily work was increased to 450 revolutions and the same behavior was observed, while a further increase to 500 revolutions during the last ten days checked the gain of nitrogen without causing a decrease in live weight. Taking 350 and 500 revolutions respec- tively as representing the maximum amount of work that could be done on the two rations, the equivalent of the oats added may be computed as follows: Equivalent Revolutions. Work, Kgm. FR ETIOUplilie Aen ey ween ee o hahe olds oakslo tee abe 500 1,030,687 sv EN Se CES RD SR CRS eat AS re ea 350 722,678 ND REET COR eerste tees yea hie Pouca caeies Sus le eae 150 ~ 308,009 Wiorkot locomotion for 50 revolutions. =... ..)..s8\..s.4.4+-.: 75,000 otaltciiterence mem sone ee - Sp oienecehaar ecco Gad Soe sean 383,009 Bice Oe eres Sameer ees hr, tree a Me arora, Nc ni aeie, ah Sees 903 Cals. The percentage utilization was therefore 903 + 3321 = 27.2 per cent. The above figures serve to exemplify the general method of computation and likewise to illustrate the weak points in Wolff’s experiments, viz., the uncertainty in the determination of the work of locomotion and the impossibility of demonstrating the equilib- rium of food and work without the use of the respiration apparatus or calorimeter. Out of the whole number of experiments between,1891 and 1894, seven admit of a comparison of this sort, viz., four on oats, two on ' straw, and one on beans. Upon making the computations, how- ever, the results are found to be so exceedingly variable (the range for oats, e.g., being from 16.89 to 63.96 per cent.) as to demonstrate that the data of Wolff’s experiments are not sufficiently exact to be used in this way, and that the apparently reasonable result just computed is purely accidental. UTILIZATION OF FIBER-FREE NUTRIENTS.—But although Wolff’s results do not enable us to compute the percentage utilization of single feeding-stuffs, if we accept provisionally his conclusions re- garding the non-availability of the crude fiber they afford data for numerous computations of the utilization of the fiber-free nutrients, 542 PRINCIPLES OF ANIMAL NUTRITION. and these computations in turn supply a check upon the hypoth- esis of the non-availability of crude fiber. Wolff makes the comparison by deducting from the total fiber- free nutrients 3300 grams per 500 kgs. live weight for maintenance and comparing the energy of the remainder with the amount of work done. In the following tabulation of his results this method’ has been pursued. For the energy of the fiber-free nutrients, Zuntz’s figure (3.96 Cals. per gram) has been used and the work of locomotion has been estimated at 50,000 kgm. per 100 revolutions of the dynamometer (compare p. 539). ete aie utrients a i .. Minus 3300 Work Done. = 5 Period. Ration. Grms. ps —————— = 0 =A Grms.| Cals. | Kgm. |Cals.| ~ 1891. We ss. | sHay.7 20) kes:: oats, 4.5 kgs Se: ee aes 1424] 5,639] 931,676 2.197|38.95 Teta Alger we aOr SiO ee Tee Se oer 1,990} 7,881]1,.129,568 2,663)33.79 TYE. CO ee O rT eR Se NN ees 2,259] 8,945}1,094,328 2,581/28.86 AV ELA DC veces tae Ricks rae Eaoetetein aie te BS | tetegs ogaetdse | caste eet oll ete een oes 1892. Ta-d Hay, 7.5 kgs.; oats, 4.0 {fs op fe ERR AT 1,775| 7,026)1,074,802 2,535/36.07 Rb 25: es 1: a ae De De oe straw, 1 kg....| 1.8/3] 7.416]1, 153,813 2.720|36.68 Ts AL Loe eeeram5-Oilkes-= 9) mlepikess Sori Gs0s0 912 454 2,152/35.73 IV. cone ANDY ate oe OPE “1.5 “ .| 1,860} 7,365/1,186 ,577|2,799138.00 Ve. Oo ED oe MMOntS hbk gy oem Aeon ate 1.903) 7,537|1,188 ,388)2,803|/37.18 ANCTALO oe. bycteis cae e descent ee Renan | ea 2 |. ote OO nme 1892-93. ‘ies BSc Esai Dakeas: Onbse 40 ix pse 5 seer ae 1,475] 5.841] 897,678/2,116 36.24 th 1 Aras & Sr AO ot BAO Ona oon SRE ne eee ea te 2,297! 9.095/1,280,687/3,024 33.20 Ill ea On Olan TPIS DG Pts en, gai SA MBRT 1,670] 6.613} 905,568/2,135 32.28 IVb De AG AO!. ies “6.5 “ 3 straw, 1 ke... .|\ 2,036). 8:063)1 167 127|2.752 s4- 14 Vex Pay Oe te te St des yam Be IES os NDS 77 TOZION 42) 2851s Sho ee Vic SFA e AiaQ), SAA (eG eas tees. 2 2632/1 10,660) 1,549 ,620/3,655 34.28 PSCC). VORA RETO ENE Oe PAE OE ee OL Te ole vate eent as 1893-94. | Dees Hay, 6.5 kgs. ; oats. 4.0 kgs.; straw, 1.0 kg.| 1,607) 6,362) 900,267/2.122 33.36 1 eee 30 abe: 2.5kgs.| 2,580,10,220 1,549 ,262|3.653 35.76 Vest: oO eae SP Taina cOMone, pe Ah s\n 2.560) 10.140 1,545 ,702/3,645 35.95 MIs foe os Ulai; 14 BORD aye Fa Ok ihe 2'880'11,420 1,673,786 3,948 34.61 DAV OLAPS: Satan cists SMe at rg rere ose aoreabcMe neve, axel eee we er Fs ey as 05 In every instance but one the utilization as thus computed exceeds 31.3 per cent. In other words, the energy of the body material which, according to Zuntz & Hagemann’s results, must have been metabolized to produce the amount of work done exceeds considerably the amount computed to be available from the food. There being no reason to question the substantial accuracy of Zuntz & Hagemann’s factor, this means, of course, that if the food and work were in equilibrium our estimates of the energy available from i, THE UTILIZATION OF ENERGY. 543 the food are too low. Either 3300 grams of fiber-free nutrients (13,063 Cals.) is too large an allowance for maintenance, or the assumption that the energy of the digested crude fiber is substan- tially equivalent to the work of digestion and assimilation is erro- neous, or, finally, the figure of 3.96 Cals. per gram of digested nutri- ents is too small. As regards the latter possibility, while it may be conceded that the energy per gram of digested matter will vary somewhat in different experiments, the difference will be too small to materially affect the result. The uncertainty regarding the maintenance requirement may be readily eliminated by a computa- tion based on the differences between the several periods, thus afford- ing, to a degree at least, a test of the correctness of Wolff’s hypothe- sis regarding the crude fiber. The following table contains the results of such comparisons. In each series the period with the least amount of digested food (fiber-free) has been compared with _ the other periods of the same series. Meteo nergy (a) Wo k, Utili ti 3 Rees Cals. Pant, Cals. 1891. Penlod@ Whereas Soares 20,949 2663 SMI Gant ths, arsine cng iors -18,707 2197 2,242 466 20.79 Renodeivit Ache cuece ones 22,013 2581 Se Gee Ayatn ea ose e 18,707 2197 3,306 384 LG 1892 (Period Va=as sah soak eis cs 20,094 2535 CE 18 I ieee A omer 19,091 2152 1,003 383 38.19 PERO Mlbw me teieereres ots 20,484 2720 aaa SLUR ate cass ex Neveeeveiore 19,091 2152 1,393 568 40.77 PP SmOd Veet access 20 433 2799 GND ER Pa tae RE 19,091 2152 1,342 647 48.21 544 PRINCIPLES OF ANIMAL NUTRITION. phen asm es Mbeete Work, Utilization, ae Cals, Per Cent. Cals. 1892. | IRETIOGIP VS. + teers satin aot 20,605 280 Bee: PST ee tate 19,091 | 2152 1,514 651 43.00 1892-93. IRGriods Vie Render. cnvebtcaccvart 22,163 3024 SOS Mean alleen see oes 19,295 2126 2,868 898 31.31 IPEriO Gg LV Or Stetck ts eredcks 21,131 2752 go" geet AUP ae. oe 19,295 2126 1,836 626 24.10 Period: V 2220.0. ee. ose 23,278 3352 eee a CATT MR estar: 19,295 2126 3,983 1226 30.78 PenodeVier cee see 23,728 3655 eek baland Cae ea 19,295 2126 4,433 1529 34.48 1893-94 Reniods lie cee. eenn 2a: 23,288 3653 TES ig ie Rae Cet ere 19,430 2122 3,898 1531 39.68 Peniagd VM, cameieens 23,208 3645 OP ITE 2 astictta, Sede. MERE 19,430 2122 3,778 1523 “0.31 Pernod! Vie see vee 24,488 3948 fe | Fee Sr RE etmek & 19,480 i 2122 5,058 1826 36.10 Totals and averages, ex- cluding 1891-92...... 31,066 11,408 36.73 With the exception of the experiments of 1891-92, which were the first with the new form of dynamometer and which Wolff con- siders unsatisfactory, we have but two cases in which the apparent utilization does not exceed 31.3 per cent. Having eliminated. the uncertainty as to the maintenance ration, and the figures for the energy of the food being regarded as substantially correct, this can THE UTILIZATION OF ENERGY. 545 mean only one of two things, viz., that the figures for the work done are too high or that the deduction on account of the crude fiber is too great. That a determination of the equivalence of food and work by Wolff's method is subject to considerable uncertainty in an indi- vidual case is obvious, but there seems to be no apparent reason why it should be uniformly overestimated. The measurement of the work was made with great care, and while the work of locomo- tion is an estimate, its close agreement with the results of Zuntz & Hagemann (p. 539) renders it unlikely that it is seriously in error. It would appear, then, that with the rations used in these ex- periments the energy required for digestion and assimilation was less than the energy of the digested crude fiber. How much less it was, however, unfortunately does not appear, and we are obliged to content ourselves for the present with this negative conclusion. ZuNTZ & HAGEMANN’S ComPpuTATIONS.—These investigators * ‘have recalculated Wolff’s results in a still different manner. In- stead of taking for the amount of work equivalent to the ration the figures given by Wolff, which, as already explained, are to a certain extent estimates, they take the amount of work actually performed in each case and correct for the observed gain or loss of live weight. This method is in conception more scientific than Wolff’s, pro- vided the requisite correction can be accurately.estimated. As the basis for such an estimate, Zuntz & Hagemann take an early experi- ment by Wolff,; from which they compute that one gram loss of live weight is equivalent to one half revolution of the dynamometer (at 76 kgs. draft). From the same experiment they compute the mechanical equivalent of one revolution as 2694 kgm. This, how- ever, aside from the fact that it is the result of a single series of experiments, was obtained with the old form of dynamometer, whose indications, as we have seen, were too high, but the later experiments unfortunately are not reported in a way to permit of an estimate of the difference. Taking the correction, then, as estimated, Zuntz & Hagemann divide Wolff’s experiments into two groups, viz., those in which the work was 400 or less revolutions and those in which it was more * Loc. cit., pp. 412-422. t Grundlagen, etc., p. 80. 546 PRINCIPLES OF ANIMAL NUTRITION, than 400 revolutions. Comparing the averages of these two groups, they obtain the following: Total Loss of Nutrents,| Work, Kem. | wots, Grms. | Grms. Heavier work (18 experiments)........... | 6236 | 1,415,755 | 179.5 Lighter “ (13 zo Wie dette igettanenenndes 5851 995,225 7.3 Differene AMG chats. eee chee ae 385 420,530 172.2 Correction for loss.of weight.........006..0|..0.008. 231,922 188,608 According to this computation, the 385 grams of added nutrients enabled 188,608 kgm. of work to be performed. At 3.96 Cals. per gram the metabolizable energy of the added nutrients equals 1524 Cals. From this, according to Zuntz & Hagemann, is to be de- ducted 9 per cent. for the work of digestion and also 2.65 Cals. for each gram of total crude fiber in the added food. On this basis we have the following: Weight, Energy Grms. als Digested nutrients.............. 385 1524 Average crude fiber fed: Heawier work i.7-esaecekas see 2338 Lighter work, .; 2.22.2 2.asannee 2356 Differenceyic, Ade Bec cies ok —18 ! Equivalent energy... 2: .y... oc). 0cates see | —48 Work of digestion (1524 x 0.9)..|.......... { 337 Deduction... ek eae ca deu oe ta tae a | 89 A-vailableienerprys {26% Se. pusrelcts shel adda te ee eae 1435 Work done (188,608 + 424)......].......... | 445 The work done is 31 per cent. of the computed available energy of the food, a figure corresponding very closely with the 31.3 per cent. found by Zuntz & Hagemann. The difference in the average amount of crude fiber fed in the two groups of experiments is so small that the estimate for the - THE UTILIZATION OF ENERGY. 547 energy required by its digestion hardly affects the computation. What the result appears to show is that the estimate of 9 per cent. for the digestion and assimilation of the fiber-free nutrients is approximately correct. The difference in the amount of digested crude fiber was some- what greater than that in the totalamount. Ifwe make the com- parison of the two averages on the basis of the fiber-free nutrients in the same manner as in previous cases we have— Fiber-free nutrients: IRMCMWAET WOT Ea g0. sea eye haces Oe 5524 grams RAMEY VOTES Sareea saree Se atone ees 5086“ IDGienemee. fs sont see es eee ees 438 “ quivelentvenetey s20 245... sec. Dawa dhe 1735 Cals. Binet oy Obs WOFee... 0-2. oe ia thes aceiche. soy v4 © 445 “ MUTI ar GIT ect, ci Warts oat winds cesie hers 25.65 per cent. Apparently a considerable amount of energy was required for the work of digestion and assimilation in addition to that equiva- lent to the digested crude fiber, a result which seems to conflict with the conclusions drawn from a discussion of the same experi- ments in the preceding paragraph. The apparent discrepancy lies in the determination of the amount of external work equivalent to the added nutrients. Wolff, as we have seen, after securing an approximate constancy of live weight, corrects the measured amount of work in accordance with his judgment of the amount which would have been equivalent to the ration given and relies on the ‘‘might of averages” to overcome the inherent uncertainties of his method. Zuntz & Hagemann, on the other hand, reckon with the measured amount of work, but are then compelled to correct their final result for the loss of live weight, and unfortunately this correction is relatively a very large one (over 50 per cent.) and rests upon a rather uncertain basis. While it would perhaps be pre- sumptuous to attempt to decide the relative value of the two methods and the probability of the divergent conclusions based on them, one can hardly avoid feeling that the trained judgment of the actual experimenter is a safer reliance than such a relatively large cor- rection computed by a critic. 548 PRINCIPLES OF ANIMAL NUTRITION. In any case it is obvious that while the extensive researches of Zuntz and his associates afford very reliable data as to the ratio between the energy liberated in muscular work and the amount of external work accomplished, or, in other words, as to the utilization of the net available energy of the food, we have as yet, notwithstanding the vast amount of work done by Wolff and his co-laborers and others, but very fragmentary and uncertain data as to the utilization of the metabolizable energy of the food for work production. Yaa me labs BYD.G TABLE I. METABOLIZABLE ENERGY OF COARSE FODDERS. Feed Added. Animal. Meadow hay V { Difference... . Correction.... Percentage... QQ Meadow hay V ; Difference.... Correction.... Percentage... jeojee Meadow hayVI | Difference... . Correction... . Percentage... mo Meadow hayVI | Difference.... Correction.... Percentage... Co | Period. wh Organic ; Metabolizable aes Energy of , Energy. os 3 | Per g = +; Urine Gem: © |@¢g| Food, Feces, (Cor- |Methane,| Total, cS sey |ieeit2 | POXKCENE, Cals. | rected), | Cals. CalsSa SAMS a @) Mat- =» |< Cals o q ter, ar Cals. 9475)6024/44821.2 |16323.7 | 2113.3 | 3250.6 |23133.6 6630/3175|31327.8 | 9599.2 | 1530.0 | 2560.7 |17637.9 2845/2849|13493.4 | 6724.5 583.3 689.9 | 5495.7 +19.0 +5.9 +0.9 +1.5 | +10.7 13512.4 | 6730.4 584.2 691.4 | 5506.4 |1.933 100.00 49.81 4.32 5.12 40.75 9405/5950/43811.3 |15336.3 | 1916.1 | 3432.1 |23126.8 6651/3206/30750.7 | 9491.5 | 1359.6 , 2524.7 |17374.9 2754|2744/13060.6 | 5844.8 556.5 907.4 | 5751.9 —45.4 | —14.0 —2.0 —3.7 | —25.7 13015.2 | 5830.8 554.5 903.7 | 5726.2 |2.087 100.00 44.80 4.26) 6.94 44.00 19527 |3323/45255.8 |14103.7 | 2576.3 |! 3306.6 |25269.2 6402) 3198/30338.1 | 8574.9 | 1795.0 | 2579.4 |17388.8 3125|/3125|14917.7 | 5528.8 781.3 727.2 | 7880.4 —8.9 —2.5 —0.5 —0.8 — Oeil: 14908.8 | 5526.3 780.8 726.4 | 7875.3 |2.520 100.00 37.07 5.24) 4.87 52.82 = \9743 6495/46275.0 |14104.8 | 2593.0 | 3564.2./26013.0 6402/3198/30338.1 | 8574.9 | 1795.0 | 2579.4 |17388.8 3341|3297/|15936.9 | 5529.9 798.0 | 984.8 | 8624.2 —208.3 | —58.9 | —12.3 | —17.7 119.4 15728.6 | 5471.0 785.7 967.1 | 8504.8 |2.580 © 100.00 34.78 5.00 6.15 54.07 549 55° Feed Added. Meadow hay VI { Difference... . Correction.... Percentage... Oat straw II.. Difference ... Correction... . Percentage ... Oat straw II.. Difference... . Correction... . Percentage. . . Wheat straw I ; Difference.... Correction.... Percentage... Wheat straw I ; Difference.... Correction... . Percentage ... Extracted rye § ~ straw Difference ...| Correction ... Percentage... Extracted rye § straw Difference... . Correction... . Percentage .. .| Animal. he] QA seis) Organic Matter Energy of Eaten. | n 6 | ; Blog Urine 2x Oo} oe §| Food, Feces, (Cor- |Methane, Ss ig || (Cale: Cals. | rected),| Cals. "| aU Cals. on 2 9539/6340 45239.6 |13218.1 | 2755.1 | 3620.2 4 |6458/3239 30548.5 | 8171.2 | 1824.6 | 2722.2 3081|3101 14691.1 | 5046.9 | 930.5 | 898.0 | 101.8 | +27.2 6.1 9.1 114792.9 | 5074.1 | 936.6 | 907.1 100.00; 34.30 6.33 13 2 9819/3170 46690.1 |18296.3 | 1884.2 | 3239.9 3 \6630/ 031327.8 | 9599.2 | 1529.8 | 2560.7 3189/3170 15362.3 | 8697.1 | 354.4 | 679.2 —94.3 | —28.9| —4.6| —7.7 15268.0 | 8668.2 | 349.8 | 671.5 100.00] . 56.77 2.29 4.40 1 |9740/3115 45626.1 |17983.1 | 1633.6 | 3448.1 3 6651] 0 30750.7 | $491.5 | 1359.6 | 2524.7 3089/3115 14875.4 | 8491.6 | 274.0 | 923.4 +126.5|+39.0| +5.6 | +10.4 a '15001.9 | 8530.6 | 279.6 | 933.8 | ; 100.00) 56.86 1.86 6.23 1 '9611/3195 45570.1 |17751.7 | 2084.7 | 3792.4 4 6402) 0 30338.1 | 8574.9 | 1795.0 | 2579.4 '3909/3195 15232.0 | 9176.8 | 289.7 | 1213.0 | | Sus ee, i Pace TES | 115155.4 | 9155.1 | 285.2 | 1206.5 | 100.00) 60.41) 1.88 7.96 1 95833188 45365.9 |16562.1 | 2237.8 | 4003.2 4 '6458| 030548.5 | 8171.2 | 1824.6 | 2722.2 3125/3188 14817.4 | 8390.9 | 413.2 / 1281.0 is |+302.4 | + 80.9 | +18.1 | +26.9 | 15119.8 | 8471.8 | 431.3 | 1307.9 100.00) 56.03) 2.85) 8.65 5 9114!2665 41900.7 | 9926.4 | 1756.5 | 4004.5 a 6402, 0 30338.1 | 8574.9 | 1795.0 | 2579.4 2712 2665 11562.6 | 1351.5 | —38.5 | 1425.1 | = 990) Tall Conse: —19.8 |11329.9 1285.7 | —52.3 | 1405. 100.00, 11.35) —0.46, 12.40 5 9142/2659 41962.6 | 9799.0 | 1705.8 | 4147.4 4 6458) 030548.5 | 8171.2 | 1824.6 | 2722.2 —-—|—- | SV ——————— 2684/2659 11414.1 | 1627.8 |—118.8 | 1425.2 |—113.3 | —30.3 | —6.8 | — 10.1 11300.8 | 1597.5 |—125.6 | 1415.1 100.00) 14.44) —1. 11] 12:62 APPENDIX. TABLE I (Continued), Metabolizable Energy. Total, Cals. 1.688 8691.2 |3.261 (Ostk }26310.4 117830.5 8479.9 —66.1 | 8413.8 |3.164 74.45 a APPENDIX. 551 TABLE II. METABOLIZABLE ENERGY OF BEET MOLASSES. | Organic Apparent Matter Energy of Metabolizable Eaten. Energy. ae P 5 er Feed Added. q & Trt Gram ae pe Urine O = ie Re Ne q Food, Feces, (Cor- |Methane,| Total, re z Fox aa lec es Cals: Cals. | rected),| Cals. Cals. Mee Acer! SSO Cals. nee a o | le} } a er, “ ] o ~ qo s may 3 | 9311! 576 44025.3 |16041.5 8839 0. 40964.5 16615.5 472) 576| 3060.8 |—574.0 +502.9 |+204.0 3563.7 |—370.0 100. —10.38 10037 | 1157 48293.6 |16593.3 8839) 0 40964.5 |16615.5 1198/1157} 7329.1 | —22.2 =—171.2 | —69.4 7157.9 | —91. 100.00) =i 9483) 582 44860.3 16845. 8787| 0.40725.6 117202. 696] 582) 4134.7 |—356. |— 534.4 |— 225. 3600.3 |—582.2 100.00) —16.1 11636,1746 54939.3 |14514.7 10067| 261 46129.1 |11874.4 15691485 8810.2 | 2640.3 SRO) |) Sey ee) 8429.7 | 2542.4 100.00; 30.16 11533, [742 54469.0 |13753.4 ee 261 46129.1 |11874.4 14661481) 8339.9 | 1879.0 462.3 | +16.0 8402.2 | 1895.0 100.00} 22.5 11994'1746 56293.6 |17643.2 10407| 261 47458.0 |15746.8 eS) Se 1587)1485 8835 1896.4 ‘4 4 /— 136.5 8424.2 | 1759.9 100.00, 20.8 11578 1407/56053.6 17322.9 9974, 0/46945.4 |15718.3 1604 1407} 9108.2 | 1604.6 —934.1 ; —312.7 8174.1 | 1291/5 a6 Apparent Metabolizable inergy. Per Meth re: | 2 anc + | r- Total, | P Cals. ac ig. anie Cals. | ‘Mat- ter, | Cals | 3669.6 |22965.4 | 3326.3 |19593.4 344.3 | 2672.0 +40.8 |+240.5 385.1 | 2912.5 5.057 10.81] 81.72 3703.0 25006.9 3325.3 |19593.4 377.7 | 5413.5 ; =13.9 | =shg 363.8 | 5331.6 4.608 5.08) 74.49 3346.7. |22631.7 | 3348.0 |18740.6 a —1.3 | 3891.1 “7 —43.9 |—246.0 —45.2 | 3645.1 |6.263 —1.26 101.25 F 3753.7 |33298.6 3716.3 |28579.9 fe J 37.4 | 4718.7 r —30.7 |—235.7 6.7.| 4483.0 |3.019 © 0.08) 53.18 3574.9 |34048.6 3716.3 |28579.9 —141.4 | 5468.7 SeCN | SSE}. —136.4 | 5507.4 |3.719 | —1.62| 65.55 2973.0 |32933.3 3255.9 |26669.6 —282 6263.7 dj = 25D" =o : —311.1 | 6032.5 |4.062 = 71.61 3171.9 32090.8 2957.0 |25863. 1 214.9 | 6227.7 —58.8 |—514.7 156. 1 | 5713.0 |4.061 | 1.91! 69.90 —— es APPENDIX. 555 TABLE VI. METABOLIZABLE ENERGY OF PEANUT OIL. Organic Apparent Matter Energy of Metabolizable Eaten. Energy. 4 z Per Feed Added. a le. Urine oi f rs Zs Food, Feces, (Cor- |Methane, Total, ae | se = roto) Cals. Cals. | rected),| Cals. Cals. Ries Feta oul ior To Cals. ae rales hacen ae i ec el As als. p | 3 10752] 709/54007-3 [17467 5 | 2351.2 | 2909.0 |31279.6 | _ Peso l- i D| 1/9974] 0/46945.4 |15718.3 | 2407.0 | 2957.0 |25863.1 Difference... 778| 709| 7061.9 | 1749.2 | —55.8 | —48.0 | 5416.5 Correction... soley (— TORO: |i 0) | 20585) se | —- 6730.8 | 1638.3 —72.8 —68.8 | 5234.1 |7.382 Percentage .. : 100.00 24.34 —1.08} —1.02 77.76 . §| F | 5 | 7491] 798/39185.9 |14585.7 | 1455.0 | 1369.1 |21776.1 Peanut oil IT. 4 | +) 3 | 6630| \ 0/31327.8 | 9599.2 | 1530.0 | 2560.7 |17637.9 Difference... 861] 798} 7858.1 | 4986.5 —75.0 |—1191.6) 4138.2 Correction.. . —302.0 | —92.5 | —14.8 | —24.7 |—170.0 7556.1 | 4894.0 —89.8 | 1216.3 | 3968.2 |4.973 Percentage .. 100.00 64.77) —1.19} —16.10 52.52 §| G@| 5 | 7396] 798/38057.3 |12512.9 | 1452.1 | 2371.2 |21721.1 Peanut oil II.) | G@ | 3 | 6651| 0130750.7 | 9491.5 | 1359.6 | 2524-7 |17374.9 Difference. ye 745) 798) 7306.6 | 3021.4 92.5 |—153.5 | 4346.2 Correction... +249.5 | +77.0 | +11.0 |] +20.5 |4+141.0 7556.1 | 3098.4 103.5 |—133.0 | 4487.2 |5.623 Percentage .. : 100.00 41.00 Iersig||e aby PAS) 59.39 APPENDIX. © w w ——T,lC Cc an al —_ 4 4 F'0¢ €°'266E £°o1s°2 i e982 - ea ae en eT, 6°89 | Z:€00'% | 2668's | T'686'ET | S's8e‘LT | 6°899 i ERG Seine hoy cee st ee ae ET G'096S | U'GLZIT GAC I AiO hae ae eae ae hte **qySTIOM 9ATT IOj UOl}D91I0O/) ¥'820'9 | T'SLZF'IT T'F9%'SS_ Ons I¢- Tha Geral si cy eet Ee et | er tee hl ce eas “** 7907) Bur OTUBS.0 IO} UOTI9I10/) P1809 | Z'OSFIT | 0'68z‘ET | 2 69'S% | 9° FS9 Z : pea OE ABY + UOlVBI [esBg “TA vy nopvayy Zz°9e 9°SL0°C __ S9SL'S bei 9at'o es eee ee As) plea ul sie a.m see! wie, é.6/e 6 aouala YT Beh | SLL1 | p'SsO'y | GS TZe'el | 6 PAE'LT | 9'IZD | & Ws Fe a ee ee ae te ae oes UOIPBI [BSB 6° 2Ss's | 9° 622'6 G° 1S a Ca I€1 am [Fete ame ltl ees esl tence del a coll AD (erp meme Niches ae see rie eg TS are qySIOM OATT Ioj WOT}IILIO/) £'S6L'S | $'8F9'6 T1018 oe TI- L°St— JL Og — a) eee tet ie OTC UL ome S10 IOf TWOTDAIIO“N) L908 | T° F496 | 2°eSF‘ET | 8 9zL‘e% | 8089 z ey a i a oe PASE A> UOT TeRuE “A ivy nopvayy FOF 3° COS £°90¢°¢ _ F90¢‘¢ oe eee oe Usk Ne Ble) 6) ee!» . * 0UaIO ICT Ter | 2:910% | FP LL9F | G'O96CI | 6 LE9.ZT | G96 g 1 RAE he Pe EE ae uoryed [eseg G 6&3 Fr | 8 S8r‘OT 9° F8— € 961— sr tss sess qUBSTOM BAT LO} WOT]IALIO[ Tree'r | 1'0se‘or Sr ea" 9° F+ L°01+ PLied (bi Tract mea A | Niet ety ad wD |b seams ore prey eye es as * 19})8UI o1uBBIO IO} WOT}DIIIO|D G'6Ish | F 69EOL | 2° F9L‘ZI | 9 EET‘Es | 0'E8g T ulin tn Sie atau Avy + uoljes Teseg “4 fivyy nopvayy *SSOOXT] >) 1@) > 79) “SsTBO BS 0) “SBI jo uo ‘(peqoes1109) ‘gouBudy ‘aouBuey ‘AS IOUT FOSIM ore y craw -Bz110) urer) jo -ULB IN JIAO “ULB 9[4BZI| VATT I seta! 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"i ’ ; ‘ 1 : INDEX. PAGE Acid, acetic, effect of, on proteid metabolism. ......... Se RORSIOIID eens 123 bots MmMEetADOlistn Fi otes enc cagneie Pekcauyass. acboxeisions 160 Mes RA GE MCI AUS OL ay afeces chsh oicpiarelaia acevaisyemniartiercuers oie ueiare inks 160 aspartic. formed fron prOterds ic. soe ai. sis eeiee via0,e a0 8 0 /aie da, ane aie 39 COR GURITPASCG 1 T4201 08 Ya, le bo eRe ee en ere SR 52 benzoic; formation of hippuric acid from), 222)... 4.4.4.5. 0-6 44 butyzic, effect of, on total metabolismi...5. s.5 5 codec owas « 158 REP ACCME Meg NMS Clases, oy ster tic ts siaier Seles pacalor tis 4a! utc 158 SiBEaMAles LOTIMEd alrOMPEOLCIOSH, 22 4-cis yeti 0 «oad oe a telaser one 39 hippuric, effect of proteids on formation of..................... 463 NOBIMETFOVM Ores WONT SIMADNO EAC, cook aaooe secs ee socnone 44 CAIRO Oat peering ie etree SK Bee for Hen 44 pV CTY LeU i he CON a PRE SR oe CMR 28 SRR Phen at ce 44 LOSEIOMENELO-VANIN 5, 3 avs chapel aloe RL aay real 313, 322 non-nitrogenous nutrients as source of................. 45 COUSTEAU ECO) Dt Bin cha ceca a ots Eee OEE Re ats Pa eee 44 pentose carbohydrates as source Of... 06 6. ds eis ee o ofers 46 Howmees Orr loeuvAonell TeveNClS Ores sae dong dkusodns Saace 44, 45 lactic, effect of, onproteid- metabolism... 06. ..6 cesses eenssee- 123 Lege Span SIS a tas at of op screayss ork ak eoatoe geeks arate. oho 158 production of, in metabolism of carbohydrates............ 25 EC PISGCMICMER EIU VONs tom vet tn ern. Paint staha aes, Ae ode slate « 158 Neigs, OLZAMIG pHOSENEM TONNE XCTALA faayrteae picts 2 oe oe esscidie 6 0a a3 Oo toca’ a7 effect of -ouproteid metabolism). 245.055 sce stick 123 totalametab lista iste Lele. gatek (od sto oa cake 157 MU tied WaT Oy. Ol pct s ofrcsdio, acl ehuy beta oy heateheens 425 AOR CLANDESTINE Oko, tient bts teh «ofl dienatay, tarars havo a) o« 2% endweee ol 26 PSPC Z RIA UN Ret etean lepea ofact Sw, nat aber Sf dlrs hes i produced by fermentation of carbohydrates.......... 13, 26 Pe placenienh VWalnestGte ws Ae cre wc co Soala oh ae ee Sip wade wets Gy) NCI, MNIG HII WEL SIG MUO. aailta ey chopeaaeree akeraive/cisfersteei aye eielersleys oa.ce.ave.2 48 WRN UTEING a seein ietorad avn ein Miwininis fod 6s de wlauabee teens Marots 43 TUM Orr: ore iors rake ee roiata Oe ner olets dw sire Sid ee ha auaia'w Sherk Marans 43 574 INDEX. PAGE Activity, muscular, general features of.............005 Gs Sea Avan Pee Algae tISSUS, «4's a avs nite kinly 9 eiestmate utes ohare PO PET eT 29 Alanine. Oxidi Zed <1; DOG yr5365 st sare) soo Sa pto.c7s eis s hekoroitntere Ee teaget eee ana 53 PATERAINONGS, | 5 «0:55 vie dsc bw ae ie gaat ee ae ee a Salt oheheadtersantets compound... ..°s Soanee ei eae a a swnes melee Uwe one 7 COMPOREION.GE. sais < os cine ea we oes eee 62 LERUGECS 3h, sare wocin ie wtoh ate mata Reeth Sw yaa eee oe eae 7 WOME So cic 5: Fake, inveinseye ocetsqguatesiese etalon otal eee eee keene 7 AMPLE ss. |. vl dk bee See aes Bape ose eo leeen nie iin eee v simple; compdésition, Of: . ...1... 506i. es a Sa ht bo Spies meee 62 Albumins: \.2<.:. RAR cate te Re a Se IWR ae ete MR sic ae if Albumioses' formed: fromi protetas.j lose cn ewe oi we Ole sins era 38, 39 PANTINEO-YCHIS, Nt Se hea lola varatote bois wie lehe nip ale et cettis a ele eva alta et en ae cee if PAYG A ioe rae oi ow So pn teeta ete ae CS Blain, © he ROLE acer ahaa eee Z formed from. PrOreldsiscs eran iat ae wee eee ee este 7, 39, 52 imiuenceof, on digestibility. 73.5 162 ae 2 = bs fa. oe ele Be ae ee 54 ocarbobydratess 4.224. eck eta 57 erude fiber: pee eee 57, 58 nitrogen-free extract........... 57 fermentation of carbohydrates................ 55 in dicestive wractr sis. cn cane 54 METADOMSIMIM OL. ees eee coe eee oie ols Teneo ats eae) oer one ee 52 not-Kynthesized -tosproteids. Vil es Gere ac iee vi cteinte eps tee oe 53 oxigized in body; 2i..n20 sate eee dae ake ols ee Ok ae ee 52 replacement or proteids by ..% 5.92. oe setae eee «he aie ree 53 UREA COLNE HOM $te25 Pe feters oS Salas sete Nile ettele See eran ends a ec 39 Ammonium acetate, influence of, on digestibility of carbohydrates... . 57, 58 crude‘tibers;.. & «cat 57 nitrogen-free extract. 57 Carbonate. as antecedentryor Urea... <2 ee abe aya seers 54 PNLEAMOL MOM -KOLCNO Ses, caet key apcieesich-ocis 2 aye) vue vais oar ssevec lan ao 8 PR NArvLe Aco formed MOM PNOCCl sa Ss vas. ais cso ine slew bes esto vere weiss 39 ERD 22s ST) OF 00 INA eae See ra ya a 52 Assimilation, expenditure of energy in digestion and.- ............ 372, 275 tissue building and. .... 491 Gis OSS GHOTET OV Aner ee oso eros ae « Srearetelen orto 5 6S. gases 35 WiOL Ka Oleg tereiticy epee Pe tcte isos a one akan ek ores 337, 372,375 USC SOLON Aopen ce oan Sara she. 6 ce wie) oreo sia 80, 93, 406 above critical pomt..:js30 0.0056 407 MRE GaP are notes oe cate «ante, oa e-toekele 381 carbohydrates. ........ 379, 382, 384 1-2) Each gre: a 378, 382. 384, 385 MAPRECY ICU ste ay sists oa e aie 382, 384 PEGUCTOS stn, tat cha pee 381, 382, 384 indirect utilization of heat from.... 406 576 INDEX PAGE Assimilation, work of, digestion and, in dog... ......e.escecccvevcsees 378 DIOTSO: 55 nse eels bs = er 385 621 a erent teh Sti Bengtanoey pt —— methods of determining........... 377 relation of, to surface............ 408 Avallability of nergy, PYOSKS 4.% .) 417, 419, 427, 428 CIUde bere tae ea eaten. ee ee 422, 428 feed aoe soe ee eae 416, 419, 427, 428 OPLAMICACIOS, 4 iy ob Ven tee ot oe 423 DERLOSES Ceres. cerca eet te eee 420, 428 AROMGIEIS.Vayeisen ae otis fcr eee RRO -. 414, 427, 428 famaor hry dave tes pear egies poe sleet a 424, 428 influence of amount of food on............. 430 character/of-Tooud:on:2 .. dase oe 431 relation of maintenance ration to............ 432 Danley, wtilizatiom OF Enenry. Ob... sv tas. wes 20s ae ose cre sete 483, 491 Beet molasses, metabolizable energy of ........4..........- 293, 297. 301 . digestible protein of......... 318, 332 WMV ARNO INOTA ONE Ya kwiae Doeobe os nce oace 483. 490. 491 Benzoie acid, formation of hippumcacidiirom, «ascents se ieee 44 Benzoyl radicle of hippuric acid;source Of 22t4.. 2p eee eee 44, 45 Blood, consumption of dextrose of. in muscles. ................+02000- 22 parotid gland, ..0.2.. few ap bcos peewee on Oe Ce 9 food, replacement of proteids by............+.ee08. 149 nitrogen-free Oxtract: 2. cil «panacea hee ete Sa 9 oxidized, computation of, from respiratory quotient 76 PENTOSE. 7; ars veo eteinly ve Wine Fk =k vice aed ole 8,9 assimilabulitys Of; sgk.i-ister ceccste Mena re tere eee 25 as:source-of hippuric acid. ...<.-: > swan ee wee 46 determinatlon*al 5; ::/5).1;icaresce pen ss ss aoe 9 GigestiP Uy, Ol - 2s. «oak waives one = ole oe 24 effects of, on proteid metabolism.............. 124 total metabolism: .....0... /2.tedeme 156 formation af fatirom.3.\:0s cests~ bs s/o ee ee 183 glycocen fromece. prac see caries 25, 26 metabolism of. See Metabolism............... of erude fibers, ifsc. 6 ee 84 metabolism. cs. etna cide ee 14,15 of carbohydrates......... 23, 27 PAL ois fs <1 Ska ee 36 PIOtelGs 5. 2. c's ae 42 equilibrium, amount of proteids required to produce............ 105 factor Lor COMpUtAblOM OL Labs Onl sea ner eee ee ciao 62, 78 income And OULZO/OL cs eee en oe etcemtae coe alse hale Sree eee 69 Gebermina tron Of s. : fr Peak ou tes hileleri 44 metabolizable energy of food of............cececceceecees 272 INDEX. 579 PAGE WAGE /ORCreRMOM OL MMCUMANE [DY 2, 22 cc's < «= age go == eRe 12 cleavage ‘of fabian 2. tA asero te vegas che cea Steals tai eae eee 12 DIOLEIAS ID. 5s sespask ~ yn see Ciao See 12, 38 PULPOSS Clo nso sis eas asd oe ae 38 expenditure of energy in assimilation and............... 337, 372 tissue building and. 491 influence of amides On» 25 ....3 9 ss -Gacw ness oa on 6s <6 oe 54 ASPALAPINGON A c/s. saci pyarteate eres 6 eiclele eee 54 NON=PYOtEIGS. ONees< fs vasa c eee Spl miata oie 54 peptones produced. duringy . 5,022.3 «sms fen mia eee 12 proteases produced durmmgs. cia. <:< nccn0 5 ox aud ane neds 90h 12 saponification Of fat In. ecg. 5.5 ws ws cereiemcinn ae ae 2 WOLKS OLS. biz, Sacra tents Ces eae eae A ee ee: 337, 372, 493 assimilation and..s seine bee 80, 93, 337, 372, 376, 406 above critical point. (=... 5 «cram 407 below critical point... ...:....<5e: 405 indirect utilization of heat from.... 406 ini thei dog 5: hae oe eo ee 378 the ors. sey 0s wo oe se ee 385 WA ois 2a yeaa nen heats ee 382 methods of determining........... 377 Of DOHE! es). 12 nick aie tals ee 384 carbohydrates......... 379, 382, 384 ERSTE ee Se 378, 382, 384, 385 mixed dietri ae. .8 2 eee *,.. 382, 384 PrOReIGS or co eet wee 381, 382, 384 relation Of, tosuriace... . ccm 408 factors Olercigt Joe shea recep os me Oe ee ee 374 POLICIES HORS is sccnielens te haers, Tate erie iis «eine ree 389 Digestive tract, functions.of jinsexerevion.-... 22. se. sah wine «= co nee 10 Dog, consumption of oxygén by, in locomotion. .............e.e0 00 eee 500 works of ‘ascenit; 499 Work Of SSCONbs ii ws.. 6+. . 2, 226, 336, 339 in digestion and assimilation. ......... 312,319; 500 and tissue building. 491 method of deter- IMM Se yes os 2 377 Pucey. expencdinure Ol, 11 lOEOMONMON es. 16d.) 5)-00c)-'> Soc eee ween se 510 DA CLO Rae pparche dpcrehces) hotahcieye Seah os 502 584 INDEX. PAGE Energy, expenditure of, in locomotion, by horse, at a walk 504, 506, 508, 510 533, 539 TINEA. Sactarere face eal atatfeis Pens astiesl «ee 503 influence of gait on. .......:.... 513 individuality on..... 517 load'on. (7... 509, 510; 515 size of animal on.... 516 Species on. 7 Gy tae 516 Bpeed oni 2) 3°. 2 7s 513 SUS CIN eee a re ne eas ie toca 499 SUSTAIN OAC ieee se ee ae eee 508, 515 influence of individuality on.. 518 TOOD AS/SOUTCO’OL 5 oe ee hse eae ane 0) oe Or cee a eee 2, 289 eTOss, Of divestible crude hibert vis. settee sees ncetels sss eee 303 ether eExtrache vi st ac cdc enusic se fain eee eee 304 nubrientstc ek see PAE eee 302, 306 Organic MAter= HAA. Sass aec eee ee eae 309 income and expenditure ots 77) 05 4.ten 4o5,o oe ee ee 3, 226 ISSINCUNG, A rep nA te Sanne hE RS. t OReE icre eee Oe 226 déterminationy Gis "567 ors aps tate a Site ahe late 245 liberation of, in animal body....... ws Bice an id tata Bale x iatee eee 1 Joss'olsimyassimllation oletats « nc: crise siceert ere aes eneeeiee ene 35 fermentations.) Jc 521 ake ee onc eie oir ere onan e 374 DIPPURIC REG. nS ccnte Bt ole & pheiatetie etaet tees eee ane 313, 322 MCtMANE. o-f cisco tee awe are eae 310, 325, 330, 335 TISSTE MALTON Ay eo cia oe eke one Beatie canto negete eee eee 444, 447 WALI OHNOCSUAS. crepe seeeteshel secre rete castorate Ree 374 MHETADOLZADIEH IN eh ENG Sa Oe ote See atone er teueteney Woyehe tei eter eae 269, 270 ApPparents.d.06 b Nesiaee svsie-crs Miakeevers epevershsppianet caste 291 factorstomes ee. PG et (UE eon ae 279, 281, 333 FAC WHBEL’ Sin n55, a cir wre 5 sss ae 281 Rubber Sie Fos soars atest eee 279, 333 of coarse fodders. 285, 286,287, 290, 297, 298, 300, 301 concentrated feeding-stuffs......... 289, 297, 299 digestible carbohydrates. ............... 324, 332 Crudediber: trey eco setens 329, 332 etherextract:): Csacn cet ee cee 323, 332 MUUCIEDUSs | ee ees ae ster 310, 332, 333 Organic Matter... ae wes 297, 307 protein .310, 315, 317, 318, 320, 327, 332 fiber-free nutrients, utilization of, in work pro- GUCHONY Ae oes hea wieie eee 541, 548, 547 food OlCarniVoOraccis crcreicie Gress e ewe eee 272 NEN DIV-OLA sos ose, vik wes eine ee 281 INDEX. 585 PAGE Energy, metabolizable, of nutrients, utilization of, in work production... 545 PROCCIOSA: Ae he Bate are ts acs ees 272, 276, 277 total orzamie- matters =. to... oe 284, 285 MURS ote rayon ete Sec ua Oe te ee Sree Been 291 utilization of, in work production.......... 525, 540 methods of de- termina- tion. ... 526, 528 Wolt’s investi- gations..... 528 muscular Tatas Source Of)... 02. 56 sae hole ee Seek See 200, 223 IBEGULIGS Fs SOULCE Ob. vas skool en ee 6 18s erie 201, 207 SOUUCCHOL AG rN avai oueers tenner Mente ree cial nator ORE ks al 196 Sanehioad SOMECEIOLS 4 5 25, oa) oe siete steer c.b.e wie ise alars 199 mabureroidemlandstotyessy. Ae icles os cee hacia e kesh on 2.22 340 PAVE, NE NIETO (Syst Gok aliens eran ear rere Cate eR ERE eae ae 394 GEterminaionlolaeme nme eraser. aoe 413, 427, 428 for maintenance.......... 396, 406, 410, 413, 427, 497 VOLS RT A onic Sere ue rameter cnstalcimite sist elas 497 olrcarbohydraless -cs.c «sc ee ce 417, 419, 427, 428 CLUE Grom esa nN eee eoce ate carey sae 422, 428 TET Uke cooks ht Sse pare eter ROR Aceh RI Sh eae 416, 419, 427, 428 OLSAMICACIUS ates ee ie ane oe 423 OCWILOSES Ss agetevaede ie ence © ter ehotevess she ore tellshs 420, 428 OLOUCLOS eels erent tena Ae 414, 427, 428 GLI O Lhiyalia ye mere ne ta share et Nate aes erstaet eens 424, 428 Wializaitvonvot piminw Orkewte cee so corse sey araree see os 497 ELE Da le pe BS AR tet eR och AO Re ay oP 2 provein, losses ol, im maethAMes, oe o..%-2)s fas oc) ste ess aie sale ere es wel * 310 NIEIING Sere ey carer ere Mace ens) sy ies oaaa ena ate ee ec 312 PCO i pe ete cele ele arcs ehetate SG peas a's! ea aka ale eee ees 226 GeteEmiMatylOUROlee tense esi Py eisieleietacre sete see em 235 Olfcombustiblecasesie. smectite stele stoic ranscen se sates 16 243 EXCLela ACOMpULAOMLOle aceasta ees «ee 8 241 etermimatrom Ola ty ew snaec celeste ete «see 240 feces (COMMpUtALIOM: Clear. < scsi ae cclu.sie'e els es + wie 242 Hood Acetermln atom Ofte a... -c15steee se eeces eters 3) Sane 235 THiIMsO Leah mer ee orca see le. evens icvaece, suetocw eee 244 POEOREMI DN ee pension x atss oo2 vib cheeve tp oes 244 HASSUC MeN eet lates scsler ei Siete tails lee Senate bait 244 [S SLRSS CPPS ON Sate 8 A Ne A ee eee ae 244 MUTLING peepee eee oh Mate rece ea, 5/8. pve es 27¢2, 275, 278, 312 COMIMUEAIOMMOE ore cs es oes ee ales) 241. 277, 312 SPOKE AA AIT WOU Se Penta a a sf oars 2 Wiedd -rs Sunde oe eeie a oe i aranstormation Gi im animal DOGY.. 22). F.)2%).1. 6c 6 a wreels ole dle os 2 556 INDEX. PAGE Energy, transformation of, in muscular contraction................00+ 495 units: of measurement: of 7.5. .e 8 eae een ese eee ee 231, 233 utilization of, in tissue building. ................ 444, 447, 448, 461 by carmivena, << \5 e008 fos 448, 466 50012) 01S hae MRAP RRR Pica ihe oc... 451 PUMIMaNts. sce eee 455, 461, 467 Swine,’2s.. "jee swe he ke 452, 466 earlier experiments on......... 460 effect of amount of foodon..... 466 character of fecodon ... 472 differences in live weight On =).2* Yam 457 thermal environment on 471 WORK: 3 EEGs aun ae eee pases 444, 447, 494 ° by Gog. iis...’ oic2 dalasawe's ache eee 494 OVS) «5 45 Seen ee wat eee 502 atria UO beet. eet eee se 509 walks. S247 oe) ofS ele 504 INVA: ~s.,. ccl0e iofaiayte. se duet obet opel ee A eee 502 influence of fatigue on...........20.-008 519 individuality on:'...:3 729 sane 517 kandjofiworkion= =<) ee 512. LORGUODY fer io Jee nto 508 size of animalion=. +... sae 515 Species ON... ..2 2. ee 515 SPECH OB... iia nee 507, 513, 514 traiming ion... 2.92) fod... eee 519 Ofvdscenthic tise ase oe oe 502, 503, 506, 510 by.dogs fac cname tations eee 502 OVSCs\. So fisece wdiere ee ee 506 500): 11 RIE ISN SIS El 503 effectiofierade.on: ... 5. Ja. . ame 012 loadon ..... 509, 510, 515 COS) eee CRE St Rr, ata 502, 510, 513 by dogs aed 56« sv ees 502, NOTSC on4o Aa te cers leek 507 locomotion, computed. .............. 513 olibamley: . orthtgih inte asic atrors ce tte eee 483, 491 beetunolasses) cei Ae ec eer heteaereetere 483, 490, 491 carbohvdratessen: scree ae 461, 462, 473, 490, 491 coarse fodderss. eee See 484, 490, 491 concentrated feeding-stuffs.......... 472, 490, 491 digestible carbohydrates. ........ 475, 477, 490, 491 DTOVEI,; 5 Sonic d mk eisai ee 481,491 extracted straw. hanes whic scetah ikin aire 488, 490, 491 a INDEX. 557 PAGE Energy, utilization of, of meadow hay............cccceceeoes 484, 490, 491 MAPS OMAN S 304651 Are RLS aay Me Ew cic ecole 483, 491 oat straw......¢+-.. ETE Ws) RES 485, 490, 491 “Ol od epee eee Te ne eg ee 478, 490, 491 J ORRO HEIN IS ass erate a ee 463, 482, 491 Beet cra. dns edi’, Mes eohy ates a. ey Mae ehe 483, 491 SCRE cay ee akties £ takes cnn ancy deta tin we hee mee 51 later experiments) >c4-7,,5tav eee ee 111 Pettenkofer and Voit’s experiments. ... 108 Pfliiger’s recalculations.............. 109 functions of foodiiv sew ose dee Oe Boece edo 30 gain.or loss of, determination Of ¢ totn-% pec ae wy oe oe ne oii 69, 77 influence of glycogen on computation of........ . .66, 78 potential. enemy job...) hier tier csie= ee eee 244 influence of, on minimumiol protetds.... 5. yni: issn oop nee + eee 135 intrimuscular tissues... ° Secs ecianisne<, teas peckelaasedne tee steer nae eee 63, 64 Icataloolismioty sss. 2 nace ven cise Sotane ous home elo Fonc aaa Reger si ene eae 35 lossiof energy in assimilation, Of). ...00/s)sienincry. shereleaee ete ee 35 THAT CLUE CCl SLI OCLY es a anehe nate lees ks ticles siisaete tench oii) voce lero easie 29, 30, 163 metabolism of. See Metabolism. mutual replacement of carbohydrates and........ 5 = halige oeus a ee 151 net availability of .enerey Ofi:2ctig neti .,.0'd.sis ve ee wae ats = ol eae 372 ingredients, heats of combustion of... .......020+nc00cesceenoaps 236 metabolizable energy of. See Energy. DEGUBC OL. 5 x i\cic vin Fete, « Sopsie Meso cians erm Dae wel ee a ee ee 2 potential energy of, determination of...........0c.c0sscccecces 235 purposes:to which applied. 3)... ..¢s.: seas « sla eieaeoes + tone ene 80 Foods; heats of combustion of .\ 25.22.05. wee ex oot ee eae ee 236, 237 Food-supply, relation..of metabolism to. . 0.06 5... .eecesaens sk eee as oo wilas saree eens Ge 69, 77 influence of glycogen on computation of................. 66, 78 potential energy ofe.c:0. «chia ooecdee soe a. eo eee 244 nitrogen DY DOGY .. .vadie oli oom tne tee weak oe ee Skee ee 66, 67 protem iby body:.+,/..%- = ssc. %as oe seulcare idl atta. os ose oes eevee 20 INDEX. 593 PAGE Glycogen, identical, from hexoses and pentoses.............0eeeeeeeeee 26 influence of, on computation of gain or loss of fat.......... 66, 78 MA VIMISGIM AMAIA IO ie 2 xe meee anata Nokes Nee ade koala cus 64 muscular, disappearance of, in work..............2..8e0005 23 MINEMOMS OL Arte oh ees eet la: neck CARS whe See 222, 223 > Teappearance Orin Testy OSH ys SEN ec ee do 23 reconversion Off intodextrose? 0) oO. ee ere. 20; 22; 34 Grade, influence of, on efficiency of animal. :.......200.000 05 .00c00 cee 512 utilization of energy in work of ascent.......... 512 Wer OKCESCENb Se . os vu!s aca ets I IO. ee 26 proberdsy.. Coors 509, 515 non-nitrogenous ingredients of feeding-stufis OU Wrest eee rapen Melek Se ate 154 MPNFL TNE OM5 54 ooo Gane 144, 154 organic acidS ON... . 6.2.66. ee eee eee eee 157 pentose carbohydrates on.......--++++++++- 156 proteid supply on......-. 62. eee ee ee eee eee 104 MINAIMITAOSCROMEp reste, saya jevet alle ener s cloiet ie Tel ah-l stent efiol= 156 Ti Ses rae eae ae eh oe aye rdels oy; - 202s 01 8 ele) a) 83, 90 proportional to active tissue............ 86, 93 nitrogen cleavage of proteids independent of......... 99 ratio of, to proteid, in fasting...........--- 86, 88, 89, SO urea produced in. ... 1.1.01 - ee eect ene teen eceenes 14,15 water produced in..........-- sere cence cee meee eeeees 14,15 Methane, excretion of, by cattle... .. cs eee eee eect eee eee eeeee SCRA 243 600 INDEX. PAGE Methane in excreta, determination of... .......ccceccccccccccscccees 69, 72 losses of: energy in o.55 tet tone eke pees 310, 325, 328, 330, 335 produced by fermentation of carbohydrates................. 13 Methods of investigation:. S50> choi ee toc ei oben ee a ei 234 Milk fat, formation of, from carbohydrates: . 2.0.2. ca... sc cwneesiee 174 Minimum demands of-vital funetions:,.')/ ¢i's275 5 Sis 3 sew Pe awa eee 80 of proteids: 5's 3N FOS ee ioe a ot cae eae ee amount of non-nitrogenous nutrients required to TRACI. USS ot cea See Rena ani has ON aie een 139 effect-of carboydrates onl< 5.04.2 cic cmeeeeee ne 136 fat on 2. Feet stdin so ee 6 ei. < Oe meee 135 non-nitrogenous nutrients on............ 134 on DGS Ss, cc acktaetabed ssc pan 143 forherbivoras? 5 Sac. de. ae eas eel ewe aoe 140 Wag F Bie, at ea is ai a Siyabs, GAS Me 82, 83, 90, 94 ; less than fasting metabolism: <0... su. «snes cane 136 Mixed diet, work of digestion and assimilation of... .. Risse Oe esate see 382, 384 grains; utilization Of EnerryiOl fs Noes od oe ca ets Mepis Salata 483, 491 Mockermexperimentia oo) eee ee ete Le oe ea Wate ae eee 281, 455 Motor, efficiency: of animalias 02.22 st 22s Sr te ee ae ee eee 498 Mucins, composition of......... ai cin Sod abe Gi oie p alsl gieiete ay ee eh) oh ouby acgs eee eee 62 Muscle; consimption or dextrosein >.) sos bon woe ee a ee ee ee 22, 221 contractile substance of i: k 2e eae ee po oe eee ae Cee eee 17 efficieney of single a. 7202 fo es cies Lede Ce ee eee 495 CXtPACH VES OF... ces cele oe ne © A eae One ae ee 8 formation: of glycogen:in 32.22 DY 25,005 Cas Pees ce eee eee 23 Fespiratory- quotient:ar, 62st wiles were ed wie ee eee a aeeisee 187 Pesuing: storare of: dextrose in), 4a beso. Ce ee Sa eae 222 OXYEERAGR.. fe toe So ee ese aa ee 222 voluritary,; WORK Of: 2255 Soe ecco Hed eb aees o We 1 Smee 337 Nails; composition of2123). S505 S65 Set sae Seems aaee ais nee Cee - 63 Nitrogen-free extract, apparent digestibility of..............0ccc cece 12 influence of amides on.... 57 ammonium acetate on. 57 asparagin on. 57 non-proteids GUiNss «vias 57 carbohydrates of. \.ciisie ee co ane bee ae 9 digestible, gross energy of..........cseeeeees 305, 306 ‘Sfarburoids Of, 2 5.5.45, oes « oot oon eae ee 9 pentose carbohydrates Of. 55.0.5 6.405 was Cae eine 9 Nitrogen balance, computation of heat production from carbon and..... 255 cleavage of. protendgs ss isi53icdisven samaeesnee Ok Cues Reeee 98 INDEX. 601 PAGE Nitrogen cleavage of proteids, effects of non-nitrogenous nutrients on.... 151 independent of total metabolism......... 99 COMUENILIOL PrObeldSs., ashlee aces Sree nie See kt Ria eile ers 39 equilibrium, amount of proteids required to reach............ 94 EStinmaiongolproteimMromi tes: nc kigees cs oe soe ee eee ok cus 5, 6 exerction. enectolproveidsron. <2 02! 23. oS aiees eee eee wine 94,95 IGE Ph OS AAAS e Pe es ee eee ae ene e 42 PIBBHELU MISHA OONSMOT ANC. ..x .-.5, sas’ dsoin don as dee Wedd, Bares al 40 formation of dextrose from, in liver................. 19, 21, 49, 50 if) Ha) 0 0 or Oe ae edna ae eine Pics Ot 30, 50, 98, 101 difficulty Of PrOOL OL - 45h ethene ge oedehe ee 113 SQUALIONS TOR ..< ..c3- p pueuelv ek Beemer ss 51 later experiments 2\.ty. Sen lee wie mite ae Pettenkofer and Voit’s experiments.... 108 Pfliiger’s recalenlasiens. «5 pene ber = ae 109 Gly COmen TOMI 1 catty teres coer erie fee ese 21,98 SUPT TOUR ays, sieges ome sone ea eel 19, 21, 49, 50 functiionsob. IM wMUsSeUlAmeent1ONs: se ci. ett crepes penne ote 207 Patt of; QUIN WOE. = jie? .o.22.s.5 oie bids ev ete te Se 204 glutaminic acid formed frome. <.'s »\s8,23aisoin a nate bes oar 39 IN PETSPITALION. or 6.55. sty o-oo amar is eb WONTON Sp epee See a 48 intermediary metabolism of. 3°. icc \\. aes ak Meee sie oe 91 Keatabouisna of. sis. 5 in atts a tome wheter cht ke vi ates o-oo reg Sai dee ete a 41 excretory nitrogen measure of..............-- 42 final products Ol. ! .). 2 uss 4h oe en or ae 41 lewem formed front. A cauohod «005.08 asee hoes Vidhan Rie eee 39 metapolizable Gnerpy Olen a. .ebske «ie hee teens 272, 276, 277 metabolism of. See Metabolism. MINTURN OF 5, 2:08 aes eaecae eats Shale crtuet chacstahel aire ie eu cgeienstcrcieae oad Meni 133 amount of non-nitrogenous nutrients required to TEAC ohoerscaiec. 6 sista oie, s aheote pata oiaes Gea REN eT Bs 139 effect of non-nitrogenous nutrients on........... 134 effectsrofonibhealth’: 4% ¢.<)16 skein. sateen er 143 INDEX. 605 PAGE Proveidasmimimum: of for herbivera cic. ecict-s Bek Wie ew Soe ke 140 IN TAS LEME were reiney sa HN) RRR eS caD, 82, 83, 90, 94 influence of carbohydrates on.................. 136 Bee COMER NN IR SR a Sin RON go ancy 3 135 less than proteid metabolism in fasting.......... 136 Teel ue Wel ee oes 5 sas cee MMAR ORL IS or oe Sebi te 15 CEST 8 RR Od AR SA SE Ce Bg an kee kL a 39 net availability of energy of ::2)..02 40 lnc egies e 414, 427, 428 MGTOM EMCO V APC Ol cy ose n5:ih-a ays as 19 omar eT a Pe we 98 Cause OIE) Wa a Ae e.. PL st 100, 101, 103 effects of non-nitrogenous nutrients on.... 131 independent of total metabolism. ........ oO COMPEMU Ol ce anaes SAlinn Sorry oe Ey 6, 7,39 NGU-TMCLOSSNGUS LESTE Oto... 2.3. Hes eye ae a ese 48,98 LATCLOL Wee ae RAR Cero aon oe 49, 98 formation of sugar from......49, 50, 98 HOM-Proverds NOt synpMesized LOn, i wees chan Mae Se aloes os 53 PEHLONeSMORIMEC OMe aa RA eee Lee es ate 12, 38, 39 PELCCNLARE On MIPLOMEM UM arpa c/gek aoses o Abie Hee tte Se lek ae 6,7 (PEOLCOSES LOLMEM MOU cy dc cycenaruersycre7 eS cA Pe ek oe ee 12, 39 Puirelaction of Mm intestines: «2.4, ds.25 asa ee ete wnikite eos 44, 46 DLOMUCIS LOL | ot SI eo, ok 44, 46 rebuilding of, from. cleavage productiasste cn hich ies ee ee 40 Teplncemention ob yyanil doc... Samar aioe toes ater sa a Meee ere bowl 53 BSAA Se anes ts ora rahe tee ooh PRESS LIS 54 Laichn ines eer eerh).creevon Na ae wobec etna e 149 fats and carbohydrates of food............ 149 RGN PRQuevester ohh AE st eG Te oon Sas 53 TESORO TOM Olt seehiast ea Sms ee Ua ORS an he Shaheen a ee 12 LES WIPACOL VOM OWMeMItsOle: corres atdets shes vase taechctersaia Rus oie: 74, 75 Syiichestsrot peptqnes lO 8 Ase a oieeiathe aso Sains ae le 40 Bubsthubed tor backwaters ee AR Malncnci ke sad wen ci ae Sree 104 Proteid supply, etfects of,;.on metabolism :wies.... 5 oss. oa Se cs 94, 104 proterdimetaloligmi a isoki os oe ws ads ays 94 POuaL MC LA OMSMAA Ne eral «5 erie 2.8 aie os ayers 104 PCOLGIOS BEC MMII ONO Ole es me ahi ted Ua wala oti avis odie bie s « dala wee 5,7 FRITS GIA RC TETEAe9 (0 | ernest ENE > ee a ae 96 Dy POSUM MGR NAC O Mer comieate ws MyuPPeUAE IS). 5.) <6 ote es so Sef opw G0.ae Scion e ahs 39 MMI ZAONGO! EMETE Olina. wwe me ste ANS. xia oes ahe sel 482, 491 PCE eat se ae ei ie eA gsiace ciel 2 a jaiedie secure 107 work of digestion and assimilation of................ 381, 382, 384 Lay SUI ROU re ESS FET aR es See dR ae es ce ee 82 (Fe) Ta SY OSLO TE ERS Take Mier aaa Hey iy OI ES NRE a Rarer a txstehotees 62 dices tililitvaetemeall se ses ac betes witcnt\ens Ste See uete vet oc dcctaateceueneystols olor 10 digestible, gross energy Riera 9 cgatsy > copa Sa SIRI c RUNG fol Seats 309 606 INDEX . PAGE Protein, digestible, metabolizable energy of .. 310, 315, 317, 318, 320, 327, 332 NEiZAtion Of enerey Oleweas eee eee ene eae 481, 491 estimation of, errare!iniins i: 9.. este wee son Reine 6 from Mitropens APA steek iccctircss tence: hee ianchr eee 5, 6 factor for computation of, from nitrogen.............. 6, 67, 68, 77 in WiirMaN LOOMS Ack. cava seccs rates’ ees eee eee ee eee 6 eain‘or loss of, by. bOdyy «6.7.25 4 cas! oh b= Sie ere 66 potential enerpyrols, 4 5 aos eee oh eee 244 infeeding-stullis: 13 2so:s.cG sb ae ee ee ee ee ee 5 loss of, in fasting, effect of, on metabolism.................... 90 ehersy) of mn Miethee eI) ie Fee eae oan cee ae 310 AUDIT Gh PEs a aa sche REPOS Cte Pred 312 MatUre’ OL ss 5. sets, aN can. erercte lated Saks atte ME eeapace. REE eet 5 al bedy, sompositionsof. i: eee ee aoe Me ene ee 62, 65, 66 percentage-of nitropen-in.. ... 0s suw yoke ae oe 62, 65 OLEADLZSA GT eyes eee eee aes a Foie sore la eee wa tee cave eR ere 82 nercentage of nitrogen incl eote . hgeke tc ee ee ee 6, 62, 65 TAbLOOb favo IM DOC Wal Las lI Ore ese a eae ee 88, 89, 90 real digestibilityol <:.a: 2: .aces due Geel foe ee es eae 10 Stoke tau) Of. Seen cn Goes ces selec cn eee 102 extent Ob Sk ecckucset Beetle oe ee ene 132 terminology Ols-< Reet ais Oe OR Gee a Te hare eI ieee 6,7 iProteoses, formed trom proterds sent meen ice ee eect tees 8, 12, 39 produced during:digestion\: pee et ee ee oe ee ee 12 Putrefaction. of proteids in intestineés:.¢ 227 2010. fa. Sab tds we eee we 44, 46 productw@on 4 h2.2 os Seas 44, 46 Ohiotient; Vespiratoryahe onecki: Wile Oe Se bales esas. ea ee 74 change) Cased biyaworke > ocr seterer ats ceneee eters 212 computation from, of carbohydrates oxidized... .. 76 faboxidioed. Crews none 76 deductions from; 42 #7 eas, he tee ee ee 75 ° during work, conclusions tromie. - eet. eteanes 75 effects of muscularexertion om. 5.2025.. 5124. pees 211 in fat-formation from carbohydrates............. 179 ofscarbobydratesNacn ace noe hoe hae oaem open 74 PEGs Pe Mae ie Gas cave 6 ord aco een RpO ENS Sue Mae ae 74 MIVIBELGS 6 Ge ess xia xcs he gi CRORE ae 187 influence of contraction on............ 187 PIONS. 5.05, Chg. se Ve eed Ce eee ate 74,75 VAPIAUONSIOL, .. cringe eee es Lees ee eee 211 during works 80% fale tae kee 216 Fea], CHGTIUIIG. 6. os: oscapavn’c hate erkiahe taney aiane (oer Rode so sane Sree ee re 348 Rate of nitrozensexcrevion 47, Ww Geaciatere ptccelearsistetesn erate wie amere ete Cele ta are 98 Ration, maintenance. See Muinlenance. Regulation of body temperature. «...0ceeesescccesenccsvccsceses 347, 348 INDEX. 607 PAGE Regulation of body temperature, chemical... ............0seeceeeeee 352 TC AMNO rs. vs AS oh Fea atege ales: exe ace 348 PliySICAls cra Sk eae ean Sa eee wiels's 2 351 emi Sslonloilaeabesyenecmoee cas nt coe eee ee eens ave wae 349 ennet ferment shUNElLOMS) Ola. eteisc lect oe) ates ye. ges ee the etawes sig eis « 40, 41 Replacement, isodynamies law Gh tis. sii. eis Sai bedi ews Says easels 152, 399 isoolvcosicmlawiOlnee t.,c- + koe sec cee enn ae eee 153, 399 mutualsohstatiandicarbohydratess<4e- ss sees es os coe 151 non-nitrogenous ingredients of feeding-stuffs... 154 PUGS TIUUS 17-4 sey aseyd, Sees aa ae wes eee ee 148 GhimEOUeIds; Dy amancless Ns chs b/S UE hs eecta cee tiene Se alee 6 53 ASP aka Cine Ae ee ee gaate users sores oe tl aes 6p 54 od yaar tek te cen 2 pare cta nc aeers, fol Sater’ 149 carbohydrates and fat of food............. 149 NOME LOLCIGS aeyerrectrte ts paos aver mene aa Oe a ae onus 53 VATE OL ACCEIC TCL mr erct sen tess lic zysiet ee wit cae cis a shetrein 160 Lo untiyanl Grae dieanae ce stcsertee ci cetera peas oe ontuie ore 158 Garp oly clinebesarneny tte mee. sore wae exch tae aise he arereiete 152 cellulose meer. Sens or clotatte bavsigia vavcte's dis o4 162 CHUL pi by Cree Me eto tee Eee Peness, horace) a aeaa et erste 161 IER KOpEN EHV [es ele ee ua carer A aan he ted RS Gare oe eR 158 non-nitrogenous ingredients of feeding-stuffs..... 154 TNULUIL SINUS eee Oe ew ee the ac oh oxie ates aera hans coretiele 152 ORGAMIUCE ACL Seater ree wk tows aoe cease Onis Let 157 pentose carbohiydratess 720 Woes Sea ewes wees 156 FAAMMOSC eae aces tea eo Ma wee a the ee ee ena ns ote 156 este. NEN=MiLrogenous, OlpPEOLEIUS se cides facil 6 gales eas ae es 48, 98 PAG CROLaRae Sta Nass Salle Sos Sis 49,98 formation of sugarfrom..... 49, 50, 98 FLESOEMOMOl CArNOMy Glave: sion > chase! sical ceeee ac thn Wes G orate Sstckaw iste 12 NEN @SCy, View na tae Gent iain s Sh es WPA I%/ TAUCK larder treet Ae aes eee cies 18 GeXtrosesrabelOliaase stan 6 avis ot aide Petes wipe wdog ae sole 18 LAP ALAM extrarenal nl a Sus VAN AAS desde se Soe we 12, 30 TROT O LOLS a trap reas th Ayes cepa eet vere a sic) et she] Svaca van suay okeit 12 TOPE O KEIO Fly co Oe a beware oy nA eo Rar a sar eae 12 Res pibarlon ap Paras. cats SiMe tees bas .'ae Sielsdere cwlaileteroww.s Males aele 2 69 Geterminatlonson- water Dy... cscs... ss os ee sie 79 IRetteniorerttyjpenOlvnc + s!scieleie ds eyacier mots Ales eee 70 veomannlitatyperoimers sin aoc 20 cle clas « ov shale ele us 69 PMMGAAGY OE Glew wordt ctl ne saree oles es ivleews Oates 72 PES PILL LOM=CALOTIMMEDON coh. pee erMEE = siset sos) ofa dae oe aie swe ele wae 246, 248 Respiration, determination) of products/of: ... 2... 2... eee eee eee 69, 73 eliecis'ot musculanexention Ones; trlecies see dere dee ena: 192 TOL Olin Biwi oid & 6, Bk cccco.tie LOGIE E.On EOD ci ecie ae I ae 193, 341 608 INDEX. PAGR Respiratory exchange, determination of...........cccccccccccccccees 73 in intermediary metabolism.................08- 405 Rest, reappearance of muscular glycogen im.........0..ccccceccceeees 23 Rhamnose, effect of, on total metabolism................0..+ececeeee 156 replacem@it WallleiGl~ i aw eas creole eel, Ath aaee e 156 Riceputilizationvof Cnerey Ol. oii y Saawavsste pee aeia Gee ere ee 483, 491 Ruminants, utilization Gt enercy-1m. 22-5 2. ok coe eee cienie 455, 461, 467 Sarkosin oxidized un bodys. aws .) ¢ ck eee eo eet eee Pera 63, 64 glycogen aa engs Ob L eeee es seen 64 heat of combustioniol.. ne cee eee ee eee 63, 64 ‘onus, muscular’. 22... sn. chaeies = cok mio Maeiea st Satine: Cena 190 influence of, on heat production................e20e. 191 metabolism: sie ok eee hes ae ee ere eee 190 WOLKE: OFF jo. 's1s, aoe ote Beate ones Wie i esos eects arc Paget ete 341 Training, influence of, on utilization of energy in work................ 519 ‘Transformation of energy in body 2:52... once ee eee 2 musculancontractlone ascii. aceite es SS 495 Trot, expenditure of energy in locomotion at................. 509, 510, 514 Utilization ohenerr yim workabe ae. seis iii ete tere ieee 509, 510 ‘Tyrosin, formed from protetds:.;iai0iigit.oet ne sua ces cule hee Se eee 39 Oxidized im bod yin scien cies clare «sn toie tenets rete ee entero 52 Wnts of, heates sx.c5 ei cscs 2 ua Sree eet Sess os ee ee roe heer oe 232 measiirementol- energy. eee aw. hist Se sbeehcieiarcns ee eer 231, 233 | U3: RE AR Stoke Tae ris thee Sie tS AAC REE OE TOA CRG OY 2 Fan ooo Ole 42 antecedent OL. sco is..fe,acdes tan S10 Sista anc !cpet & « uchanshatisteine chat Retane nea 42 AMMONIUM CarbOMALe ASs- 4. «cece meee ate ete eee 43 lactate BS «.):), 4 Ae ee 43 as measure of proteid metaboliam ii sur)... 250 on soa 38 eve 68 im perspiration, «7. £1, Gee vee tee ae k SSR Oe Oeil S a eee 48 production of; from amides, = .. eel kutaretsie sis eerane ate ellos so terete 52 In IMeE GA OUST ar ols hte cies s:-vekepale Get gpehNsnei ove 14,15 of proteids ic. Gila ee 42 LES etcit: 1c (0 Aa ROD peers 5) SU Oe eee amen rR OOO A AGG uhicsr hou cc 43 OTIPINKOLe. 2 eyeehereerereys sors HS UNE eas Stee eat fc voter ad ne ene 43 Itt PETSPITATLOD ice ios» win vee Wiehe gee Oe Se he) ere 48 Thy lenis ot) Sara RP Ror Mori Cen sto kOl te Loe cue 43 Drine,aromatic compoumdaini ic: F755 «5 c'hs ea navs ss At a ee a 46 computation of potential energy Of..........0ceeeeceeeees 241, 313 conjugated sulphuric acid in: ..:.. 3 sy ceW ees ak senescent ee eee 46 INDEX. 611 PAGE Miia, er EAGT AR bore sare wv a wg Pt slter els Se Ck a eae Sede ae awele 44 FECT A Se Beg ROE ae 2 ei ar, 8 een Ba a 46 Peered OL CNELEN OF HOLEUI Mia, oh. Sucre ww btws eran OE De eR eS alle non-nitrogeneus matter Of. 4...8.25 ioe ee. ce eee nee 27, 312, 320 BRB OUME OR unica ce oe UP CE 28 derived from coarse f sede Wana eS oict 28 non-nitrogenous matter.. 321 APPETITE OL Saas iar. ge” coc cee ve hee tos as ak 320 SOUTCE Of 4 PRIA ee 27, 321 MEMLOSCR IN erred eis ase iene cee eee 226 Colbie ooo. fc kld vedy Loe ee OO ee Rae el, 2 a 344 change in respiratory quotient caused by.................4. ys es coefiicient..of atilizationein .%. i. sa22% a. ss eeeine oe cole eee 498 disappearance of muscular glycogen in..............00.e2e00- 23 gain, ols proteids during + Aiea t ac acs. dc eyed See ee 204 glandular, «oso. 0: 5 aioe: Siecle od sale eae aroladiahay sara Zinc as ot angie Ue 343 Breanna 3 TN hs son ad Arg SRE aun velts eve RETR AV esas we tctinca 2 oe 336, 337 fasting heat production a measure of................4.- 344 DOAUSCULAT, oad, 2). Sic eh SRR ATS COs de ae os eee ee 341 relation‘of; to surace’:.4c-.-lorcerstavio ee eee eee 366 kind of, influence of, on efficiency of animal.................... 512 mechanical, determinabion Of--.. +e ciex cris clemson 245 muscular, disappearance of glycogen in.............2.02deeceee 23 incidental. vic es. Sik dyn a ee ae ee Ne 342 net available energy. for). «0 ei Sree eee AO soe ol ei ee 497 of ascent, consumption of oxygen in, by dog................... 500 COTPECTED. (05.5 ps cine Gs BRA eee ee 508 utilization of energy int 25.308 2. Hee 502, 503, 510 by dog. erie ate 502 horses: 2. vPro 505 MOV 0 ab a teal erie i 5, 5 503 effect of grade on............. 512 loadionse Ree eer. 509, 510 PIP C UL BELOID cas OS Ghia ‘wien em, 1d ad crane ere i aa eee 191, 341 escent. s.c. 53 hindi eo GARG oc a. Saeco acces ae 509 iMfluence.Of PTAdeON hace ae cee ie eee eee 509 digestion and assimilation. .......... 80, 93, 337, 372, 376, 406, 493 above critical point; :. 0.24... see 407 below: critical pomt 0 ..7%.-. eee 406 indirect utilization of heat from.... 406 LOM ASE Reve ate eae tae 378 NOSE. 25.0, Sea deen nae 385 NLA STAC ae eters tape cereie) siateeneane 382 methods of determining........... 377 Of: OMEN Tsao ha. hee ees eee 381 carbohydrates... ....... 379, 382, 384 Seales ee xe See 378, 382, 384, 385 mMiKedidiGiveiemetreseh cores 382. 384 proteidsyiytiek. eee 381, 382, 384 relation of, tosurface.............. 408 INDEX. 613 PAGE Werk: of Giceaiimm eeebore Obs 1.20). treet atlas odratay. wea euield bs 374 TG} (CVV LEN] OFS) a ee ee erly en, ce ee ee 389 drait, consumption of oxygen in, by dog....................- 501 DAM AT MOM Cl Casters ooes aa mcleGortos Soeen e 502, 507, 513 bynGope ee iene sel. cris aceite: « 502 INOKSE Nees Heyes eh eee 507, 513 JaVEATCUOE, Bisco ee ERRAND Ech eee hg La a a 192, 341 LOcoMobloneCoOMpUbaLOMtO lege aa. es ys oe sons vse) s seis) ee weer’ 512 consumption of oxygen in, by dog.........-....-. 500 horseeieroe ieee hee 20CO Sorreciion for speedsinos! csi... s sien. es 2 507, 508 expenditure of energy in, by dog. ................ 500 horse. ... 504, 506, 508, 509 510, 514, 533, 539 utilization of energy in, computed................ 513 TITAS GI Caltil OL mops ates crete ore teacnonener acces c re) elistene eerie. © te Serciel ay wlsheyaereca) ots 391 TITUS LIL EM OTIS Ae oettei-c5 95 seared cue anaire Loh ewe) oPPer avaie aclis) evctievieveve of ches) sy oll « 341 ee OD eae en een ts abc otis obey cow are ters we obo SSE Melee eles, sie 192, 341 $5 GeetTD CILIA Ore arretr oye SOS she aasie fevsare, Sven AE eucie lara) leyenavais qyalle: sini tleuelayeralis 343 VOM AINVA INNIS CLES awetse Mrs sea these nce cecvnjepe Siamvareeisics Sener. Siere ope 337 PAG ORTH eT e e, Seae sors ec wal ise toie So oe erm wie sree aul ee oie 5 ag 336 Broduction, TuMCHON Of TiVer IMs «cis Ads 6 ks. sng 0s sis desieis veo, 08s 206 nelapive VAlUeOLMUMtTeMts Ile. crc. side escola = §22 coarse fodder and grain LOTS, Santen oe ege e 533 Wale lOlecrud Cail erehOL years. oijesctela s aie ons etecstatertes SByn, a7/ Pe LOL ares sons ware alensrote eo esas ravers etaneee'e = 522 millizationlol energy ess. ae cee ea e's sed woes ees 444, 447, 494 Pye ODers hucr ccna aitcacvareverniaree Sele cach eroseey = 499 INOLSE tera elerc olor sree i essvecelsie) sre. susi's silane, o:'4) abe) 502 Aue LEO Userete etsters Gem ais) siadeveveyeeusi~ 509 2 a aR ae ae RP aR Pe a 504 TAME a ccs cue snesanesa vs) erencke hei severe Sees ares 502 INHMENCE OF FALIPUEC ON. . . secs yccs obec ess 519 individuality on............. 517 Kandvoh work OMy-).cec ee oo 512 Oa OM. AGicdc oak 3 ves oe aiee 508 size.ot animal! Ons... ce. ose 515 BMOCIES OU chai; sys is aim ote mae sale 515 SWEEGION N24. lccre soiete 507, 513, 514 GAME ON. 0). sccitix Gisicee cei’ 519 metabolizable Cnere yy IN ae os we ce wees ciebe nos « 525 methods of determina- ION Ey setae cieeereere aes 526, 528 AE Ve GTN Ae oe J ra AS Ph ent” | 7 i . ye ae om ; Ta) Oo es “A o “ 1 ; vi i eis as - . / - pani ’ ee . ¢ 4 = ‘ Pa ORN Kp Sone a) re Ps * * re . a 614 INDEX. Work, utilization of metabolizable energy in, Wolff’s investigations. . of feeding-stuffs in. satan Wee 34 re, ad, i om Ges +4 -~* 4 ‘+ =) Mis “2 os A): es a Ce a Phi oe < e 7 PI > WVU