The elements of the science of nutrition
i t fc 1 i s u a 1 a a g S s < M M E £> b ►4 0$ & ►J a £ g •j S > < g g 3 O O s g i < 8 s Q fc fc H O O H u u H P 1st I.80 O.06 1.86 20.0 I.I 21.0 14.9 46.5 183.6 230.1 20.0 2d I.56 O.06 1.62 22.4 1.0 234 18.0 40.4 224.6 264.6 15.2° 3d 1-52 O.06 1.58 28.2 1.0 29.1 23-9 39-5 294.7 3342 7-0° 4th I,S6 O.06 1.62 l8.9 1.0 19.9 14.5 40.5 179.0 219-5 30.0 5th-. 1.42 O.06 1.48 17.3 0.9 18.2 13-7 37-o 169.3 206.3 25.2° 1 Rubner: "Die Gesetze des Energieverbrauchs," 1902, p. 105. 86 SCIENCE OF NUTRITION. One observation was made in this experiment on the dog which was not possible in the case of the guinea-pig, and that concerned the nitrogen excretion. The nitrogen excretion for twenty-four hours is not increased by exposing the dog to a tem- perature of 7. 6°. The increased metabolism is entirely at the expense of fat. We have seen that this may also be true of work which may be accomplished at the expense of fat without raising the proteid metabolism. Reduced to terms of calories produced per kilogram of dog, the following results are obtained: Temperature. Calories per Kilo. 7.6 86.4 150° 63.0 20.0 55.9 25-o° 542 30.0 56.2 35-o° 68.5 A temperature of 20 was readily borne by this dog without any increase of his metabolism. The period of no chemical change extended over at least ten degrees between 20 .and 30 , during which time the physical regulation alone sufficed to maintain evenly the body's temperature. At 35 a decided increase of heat production set in, on account of the warming of the cells through insufficient heat loss. That the range of the physical regulation of the temperature of this small dog was due to his long hair is shown by the change in his metabolism after shaving him. Rubner shows this in the following table: Temperature. Calories per Kilo. Normal Coat of Hair. Shaved. 20° 55-9 54-2 562 82.3 61.2 52.0 25° 3O THE REGULATION OF TEMPERATURE. 87 It is clearly seen that this dog lost his power of physical regulation between 20 and 30 as soon as he lost his covering of hair. His metabolism became like that of the guinea-pig, increasing with a reduction of temperature from 30 downward, an illustration of chemical regulation. E. Voit 1 shows that the metabolism of a pigeon may be doubled after removing his feathers. Babak 2 finds that if rabbits are shaved and varnished with starch paste their metabolism rises 140 per cent., which in- crease maintains their body temperature at the normal for several weeks, although the room temperature be between 15 and 20. To determine the influence of the second factor, that of the protecting layer of fat, Rubner 8 investigated the influence of temperature on the metabolism of a fasting short-haired dog, at a time when he was emaciated, and compared it with the fast- ing metabolism after the same dog. had been fattened. The results were as follows: Dog (Thin). Same Dog (Fat). Temperature. Cal. per Kilo. Temperature. Cal. per Kilo. 5.I _ 121.3 7.3 120.5 14-4° IO °-9 15-5° 8 3° 23.3 70.7 22. o° 67.0 30.6 62.0 31.0 64.5 It appears from the above that the metabolism of the dog was the same at a low temperature in both cases, but that the minimum metabolism was almost reached at a temperature of 22 in the dog when he had a protective covering of fat, which was not the case when he was thin. The presence of adipose tissue, therefore, acts in the same way as does a warm fur to extend the range of the physical regulation, and to delay the onset of the chemical regulation of body temperature. 1 Voit: "Sitzungsber. der Ges. fiir Morph. u. Physiol.," 1904. Bd. xix, P-39- 2 Babak: "Pfliiger's Archiv," 1905, Bd. cviii, p. 389. • Rubner: Ibid., 1902, p. 137. 88 SCIENCE OF NUTRITION. The physical regulation may be increased by certain volun- tary acts, such as are observed when a dog exposed to cold lies down and curls himself up in such a way as to offer as small an exposed surface as possible. The contrast to this is offered when on a hot day the dog lies on his back and extends his limbs so as to promote the loss of heat. Rubner 1 compared the fasting metabolism of a resting dog exposed to air at about i8° with that of the same dog quietly resting suspended in a net, by which means his surface was more exposed to the influence of cold. The results were as follows: Day of Cal. from Cal. from twtat t,». Starvation. Proteid. Fat. 1OTALi 1EMP - Resting 2 33.79 430-91 464.7 175° Resting in net 3 33-79 581.50 615.2 18.2 Rubner 2 also cites an important modification of metabolism through a variation in the humidity of the atmosphere. At a medium temperature during fasting (as well as on a medium diet) the metabolism of a dog was practically unaffected by an increase of humidity in the air, as appears below: is,«™»» W t.«. o Cal. in Humidity in Temperature 20.2° 34 HoURS p ER Cent Dry day 258.4 34 Humid day 256.6 69 More on dry day 1.8 However, on a liberal diet the metabolism increases on a damp day even at a medium temperature, as for example: t-^.. .-,T»- «~ „o Cal. in Humidity in Temperature 20.2 24 HoUM p^ Cent Very dry day 249.4 13 Humid day 261.9 66 More on humid day 12.5 The increase is 5 per cent. 1 Rubner: "Energiegesetze," 1902, p. 184. 2 Rubner: Ibid., 1902, p. 188. THE REGULATION OF TEMPERATURE. 89 On a very hot day (on a moderate fat diet) the dog's metab- olism is increased by the presence of moisture in the atmos- phere. Calories per Kg. 69.28 73-54 Temperature 35°. Humidity in Per Cent. 9-1 30.0 Under these circumstances the metabolism rose 6.1 per cent, in the more humid air. There was probably an overwarming of the cells, on account of the difficulty of heat loss by evaporation of water. A cold damp climate of o° to 5° temperature also favors an increased metabolism. Rubner attributes this action of humidity to the increased conductivity of a hair covering con- taining moisture, and says that this loss may be partially bal- anced by a decreased evaporation of water from the lungs. The metabolism and the manner of heat loss may therefore be variously affected by the condition of the atmosphere as re- gards moisture. On days of ordinary dryness Rubner 1 calculates the follow- ing division of the heat loss in a starving dog under the influence of different temperatures : INFLUENCE OF TEMPERATURE ON MANNER OF HEAT LOSS. Temperature. Calories Lost by Conduction and Radiation. Calories Lost by Evaporation op Water. Total Calories op Metabolism. Humidity in per Cent. 7 78.5 55-3 45-3 41. 33-2 79 7-7 10.6 13.2 23.0 86.4 63.0 55-9 54-2 56.2 24 34 29 19 14 ic° 20° 2<C° 70° It is clear that at 7 only a little heat is lost by the evaporation of water and the greater part by conduction and radiation. As the surrounding air becomes warmer the power to lose heat by radiation and conduction diminishes and the loss through the evaporation of water increases. Rubner: "Energiegesetze," 1902, p. 189. 90 SCIENCE OF NUTRITION. Rubner has charted this experiment after making allow- ances 1 for the varying moisture conditions. The chart is here reproduced: i F* |*_*-~ \ \ ertki tmcu of t * i*. \ fa toe etd 9f m ^ 5 at \ 2 \ Mai riHi aion ■7 K* ,•■; \ %- flcti It/ si moj i 3* Jtei iuU tioi L. <• \ t* \ v* y Qcti m o f \ Chti lica* L / V \ -) Ji, \ \ te J ■* & 3 o Z \ 7 / ff > • / ff ^ » -* o H 1t S a 6 Q T ttt Fig. 4. — Rubner' s chart showing the manner of heat loss at different room temperatures in the dog. Blue, Heat loss in calories through evaporation of water. Red, Heat loss in calories through radiation and conduction. The distance between opposite points of the curved line represents the total metabolism at a particular temperature. The chart epitomizes the method of heat loss in a starving dog under the influence of varying temperatures. The discussion of the metabolism has given a foundation for the understanding of the basic requirement of an organism. The minimum requirement for energy is seen to be present when tiie fasting organism is surrounded by an atmosphere having a temperature of 30 ° to 35 °. This may be called the 1 Rubner: " Archiv fur Hygiene," 1891, Bd. xi, p. 208. THE REGULATION OF TEMPERATURE. 91 basal requirement, the minimum of energy compatible with cell life. This basal requirement is modified by temperature, by food, and by work, and it is an important factor to keep in mind (see p. 177). The principles laid down here regarding the lower animals apply equally to man. He too may come under the influence of chemical regulation, although he constantly endeavors to maintain the surface of his skin at a tropical temperature through the use of clothes. His heat loss may, like the dog's, be more difficult if he be covered with a thick layer of fat. And his metabolism is also influenced by atmospheric conditions of moisture, wind, and temperature. One of the earliest demonstrations of the action of chemical regulation was afforded by Voit, who placed a fasting man weighing 70 kilograms in the Pettenkofer-Voit respiration ap- paratus and determined the carbon dioxid and nitrogen output for six hours. The person accustomed himself to the given temperature by staying under its influence for some time previous to the commencement of the experiment. In the cold experi- ments the ventilating air was derived from the winter atmos- phere. On the very warm days the air was artificially heated. Voit 1 gives the following results: EFFECT OF TEMPERATURE ON THE METABOLISM OF A FASTING MAN. Temperature. CO a Excreted in G. N in Urine in G. 4-4° i 210.7 4.23 6.5 206.0 4.05 9.0 192.0 4.20 14-3° I55-I 3-8i 16.2 J 58.3 4.00 23.7 164.8 3.40 24-2° 166.5 3.34 26. 7 160.0 3.97 30.0 1 70.6 The nitrogen elimination remains unaffected by temperature. At the ordinary room temperature there scarcely seems to be any increase in carbon dioxid output, but at the lower temper- atures the quantity of the fat metabolism is markedly increased, 1 Voit: "Zeitschrift fur Biologie," 1878, Bd. xiv, p. 80. 92 SCIENCE OF NUTRITION. as shown by the rise of carbon dioxid elimination. The in- dividual sat quietly in a chair, but at a temperature of 4.4 could not prevent himself from shivering. The whole effect of the chemical regulation in man has been attributed by Johansson 1 to the additional metabolism due to shivering. Voit did not believe that this could be the cause, nor that the increased respiratory activity could account for the rise in metabolism. Voit believed the increase to be a reflex stimulus of cold on the skin which raised the power of the muscle cells to metabolize. Voit's views have been confirmed in Rubner' s laboratory 2 in the following series of experiments on a man: Temperature. C0 2 in Grams per Hour. 15° 32 3 20° 30.0 23° 27.9 25° 3i7 29 3 2 -4 In this experiment there was no shivering at a temperature of 1 5 and yet the metabolism increased from what it was at It has also been shown that cool baths and winds increase the metabolism, which must be effected through the chemical regulation. Lefevre 3 states that a man, who has been inured to it, may sit naked for several hours in a cold wind without loss of body temperature. Rubner 4 has measured the* effect of baths and douches last- ing three and a half to five minutes. When the water has a tem- perature of 1 6° he finds that the carbon dioxid elimination may be very largely increased, especially in the case of the douche. The effect of the douche was more marked if taken before breakfast when the intestinal tract is free from food. The results before breakfast were as follows: 1 Johansson: "Skan. Archiv. fur Physiologie," 1896, Bd. vii, p. 123. a Rubner: "Energiegesetze," 1902, p. 203. 8 LefeVre: "Comptes rendus," 1894, p. 604. 4 Rubner: "Archiv fur Hygiene," 1903, Bd. xlvi, p. 390. THE REGULATION OF TEMPERATURE. 93 INFLUENCE OF COLD BATHS ON METABOLISM IN MAN. Douche i6°. In- crease in per Cent. Bathi6°. Increase infer Cent, Volume of respiration .. Carbon dioxid excreted. Oxygen absorbed 54-5 149.5 no. 1 22.9 64.8 46.8 A cold bath, especially a douche, will therefore stimulate to a greatly increased metabolism. The respiratory quotient indicates that the increased metabolism is at the expense of the glycogen supply. There is an after-effect which lasts about one and a half hours, indicating an increased metabolism during that time. This may be the expression of the body's attempt to maintain a normal temperature after being somewhat cooled (see also p. 254). It is obvious that a cold bath will be liable to induce shiver- ing unless by mechanical effort, such as swimming, the metabolism is increased so as to supply calorific energy in another way than through chemical regulation. A bath of 35 has no effect on metabolism. Rubner finds that a bath at 44 again increases the metabo- lism, the increase being, for the volume of respiration, 18.8 per cent., for carbon dioxid 32.1 per cent., and for oxygen 17.3 per cent. This is probably due to the overwarming of the cells. Baths at this temperature find favor among the Japanese. The effect of wind is such that an imperceptible air current may have a very pronounced effect. Rubner * has shown that wind becomes perceptible when it attains a velocity of 0.4 to 0.5 meter a second, and that if a wind much below this threshold value, having a velocity of 0.18 meter per second, act upon the exposed area of the arm, there is an increased heat loss of be- tween 19 and 75 per cent., depending on the temperature of the wind, above what would be lost were the air quiet. The effect of wind of moderate humidity and different tem- peratures on the metabolism of a man clad in summer clothes, as compared with the metabolism during atmospheric calm, is shown in Wolpert's 2 experiment below: 1 Rubner: "Archivfur Hygiene," 1904, Bd. 1, p. 296. 2 Wolpert: Ibid., 1898, Bd. xxxiii, p. 206. 94 SCIENCE OF NUTRITION. INFLUENCE OF WIND ON METABOLISM IN MAN. Temperature. Calm. Grams CO a per Hour. Wind i Meter per Second. Grams COj per Hour. Wind 8 Meters per Second. Grams CO f per Hour. 2° 29.8 251 24.1 25.0 25-3 23-7 21.2 28.3 22.2 22.2 IO-I5 30.0 30. 1. 28 IC-2O 20-2* 25-30° 24.4 70-7C 35-40° According to this a breeze having a temperature of 15-20° and moving at the rate of about 15 miles per hour (8 meters per second) has a greater effect upon the metabolism of a man clad in summer clothing than a temperature of 2 would have during perfect atmospheric quiet. In all the experiments the smallest amount of carbon dioxid is eliminated between 30 and 40°. The above experiments were performed on a thin man, and it will be noticed that there was no rise in his metabolism at a temperature of between 35 and 40°. Rubner explains this as due to the sufficiency of the evaporation of perspiration on the surface for the cooling of the organism. A fat man, however, with a thick, ill-conducting layer of adipose tissue, is not so immune to the effect of high tempera- tures upon his metabolism. This is especially pronounced in a damp climate. Thus Rubner 1 obtains the following results from a fat man wearing clothes: INFLUENCE OF TEMPERATURE AND HUMIDITY ON THE ME- TABOLISM OF A FAT MAN. Humidity 30 per cent. Humidity 60 per cent. Temperature. CO2 in grams per hour. H3O evaporated per hour. C0 2 in grams per hour. H3O evaporated per hour. 20° 33-7 36.9 1 42.6 s 56 134 204 + 14 g- sweat. 3°-7. 44-5* 46.7 4 17 170+ 31 g- sweat. 186 28-30° *6— *7° ^o / •••••••••••• +255 g. sweat. 1 Body temperature rose o.i° 1 « « - 0.0 s Body temperature rose 0.4 o.o" 1 Rubner: " Energiegesetze," 1902, pp. 208, 232. THE REGULATION OF TEMPERATURE. 95 The fact that in the experiment where there was 30 per cent, humidity the metabolism largely increased at 36-3 7 without concomitant rise in body temperature, leads Rubner to theorize that there must have been an overheating of the cells where the metabolism was progressing, even though this might not have been determinable by the clinical thermometer. It appears that on a hot, humid day the metabolism of a fat individual may be fifty per cent, higher than on a day of moder- ate temperature and the same humidity. The whole of the body heat is lost through the evaporation of water which is here hindered by the humidity; and besides, there is a large excre- tion of sweat which is always accompanied by a feeling of phys- ical exhaustion. At a moderate temperature, where the greater part of the heat loss is by radiation and conduction, the ex- cretion of water is not excessive. There can be no doubt that climatic conditions modify racial characteristics. The emigrant from Northern Europe, living upon a farm in the hot and often moist climate of an Ameri- can summer, must restrict his layer of adipose tissue if he is to live comfortably. The same holds true in Italy. The difference between John Bull and Uncle Sam seems to be one of climatic adaptation On the contrary, the Eskimo cultivates a thick, fat layer to protect himself from frost. It is also interesting to note that prostrations from the heat appear in New York with 66 per cent, humidity and a temperature of 31. 5° (2.30 p.m., August 24, 1905). Rubner 1 says that a lightly clad thin man, at a temperature of 30 with humidity at 65 per cent., bore the effect so badly that he feared to raise the temperature to 35. This individual had readily tolerated 35° in dry air. The maximum mortality from "summer troubles" in chil- dren in New York coincides with the first great wave of heat accompanied by humidity which falls upon the city. Similar cli- matic conditions at later dates are not so fatal. It may be that the fatality of these intestinal affections is due to the inef- ficiency of the apparatus for the physical discharge of heat in 1 Rubner: "Energiegesetze," 1902, p. 232. 96 SCIENCE OF NUTRITION. the infant organism. It is also possible that infection may be more readily achieved under these conditions (p. 183). Another factor in the heat regulation of man is clothes. Certain savage races do without clothes, as, for example, na- tives of Terra del Fuego, who substitute a covering of oil. In such races the process of "hardening" or the development of the physical regulation must be carried to a maximum. In civilized countries man endeavors to remove all the influence of chemical regulation by keeping his skin covered. Only about 20 per cent, of his surface is normally exposed to the air. The most important constituent of clothes is the air, which is a much worse conductor of heat than is the fiber. This is especially true of furs (p. 85). Thickness of the cloth will give a greater layer of air and will prevent heat loss from the body. A densely woven cloth prevents proper ventilation and does not absorb moisture. In hot weather a porous cloth next to the skin which can absorb moisture and permit its ready evaporation is of high importance. If such a garment become thoroughly wet the evaporation of sweat at a high temperature is largely prevented, to the great discomfort of the individual, while at a lower tem- perature heat loss through conduction is greatly facilitated, with a sensation of chill. Two experiments cited by Rubner 1 in- dicate the effect of clothes on metabolism. An individual was kept at a temperature of between 11 and 12 and wore different clothes at different times. His carbon dioxid and water ex- cretion were as follows: INFLUENCE OF CLOTHES ON METABOLISM IN MAN AT A TEM- PERATURE OF 11-12. CO s in Grams per Hour. H a O in Grams per Hour. Remarks. Summer clothes. Summer clothes and win ter overcoat Summer clothes and fur coat 28.4 26.9 23.6 58 So 63 Cold, occasional shivering. Chilly part of the time. Comfortably warm. 1 Rubner: " Energiegesetze," 1902, p. 225. THE REGULATION OF TEMPERATURE. 97 When the man was comfortable the chemical regulation of tem- perature was eliminated. Rubner points out that while the radiant energy of the sun is large in quantity, he has been unable to find any influence upon a man under ordinary circumstances, but believes that it may take the place of heat produced through chemical regulation on cold days. Thus a person living in the high altitude of Davos, Switzerland, feels much more comfortable in the sun on a cold day than he does in the shade. However, Zuntz while living on the summit of Monte Rosa found that sunlight did not reduce metabolism (p. 218). In what follows it will be shown that the ingestion of food may add to the heat production of the organism and diminish the necessity of heat production through chemical regulation in cold weather. Also, it may very uncomfortably increase the pro- duction of heat and perspiration in warm weather, especially if proteid be largely taken (p. 183). From this chapter the influence of climate is seen to be note- worthy. It explains why a temperature of — 40 may be com- fortably borne in winter, in the Adirondacks, for example, if the air be dry and still; how a much warmer atmosphere which is damp and windy may "cut to the bone" with cold; how a hot, dry climate may be entirely comfortable, when air at the same temperature laden with moisture may strike down many fatally and oppress every one; and how the effect of heat may be modified by the breezes and baths at the seashore. It does not explain the effect of the dry sirocco wind which blows from the Desert of Sahara, the universal depressant action of which has been attributed to unknown cosmic influences. CHAPTER V. THE INFLUENCE OF PROTEID FOOD. It has been thought that proteid was a food which was in itself sufficient for all the requirements of the body. Pfliiger 1 was able to keep a very thin dog in good condition and doing active exercise during a period of seven months, the sole diet being meat cut as free from fat as possible. Pfliiger says that the fat and glycogen content of the meat ingested could not have yielded sufficient energy to provide for the action of the heart alone. It must be remembered, however, that meat is not pure proteid but is mixed with salts and water. The simplest diet capable of maintaining the body in condition is therefore a mix- ture of materials, or foodstuffs. Such a mixture of foodstuffs is called a food. A foodstuff is a material capable of being added to the body's substance, or one which when absorbed into the blood-stream will prevent or reduce the wasting of a neces- sary constituent of the organism. The foodstuffs are: Proteids. Gelatinoids. Carbohydrates. Fats. Salts. Water. A food is a palatable mixture of foodstuffs which is capable of maintaining the body in an equilibrium of substance, or ca- pable of bringing it to a desired condition of substance. The ideal food is a palatable mixture of foodstuffs arranged together pfliiger: "Pfliiger's Archiv," 1891, Bd. 1, p. 98. 98 THE INFLUENCE OF PROTEID FOOD. 99 in such proportion as to burden the organism with a minimum of labor. These definitions are VoitV When proteid alone is ingested by a normal adult it is very readily burned, and is only with the greatest difficulty deposited so as to form new tissue in the organism. In the early experiments of Bischoff and Voit, the fact is recorded that a dog weighing 35 kilograms may excrete 12 grams of urea in twenty-four hours, and the same dog after receiving 2500 grams of meat may excrete 184 grams, fifteen times as much. Voit 2 has shown that if that quantity of meat be admin- istered which corresponds to what is burned in starvation, nitrogen equilibrium will not be established, but some of the body's flesh will also be metabolized. This latter quantity grows steadily less if the amount of meat ingested be gradually increased until finally the point of nitrogen equilibrium is reached, at which the amount of meat ingested is equal to that destroyed in the body. To illustrate this Voit gives the following table, the results of work done on a dog: Meat Administered. Flesh Destroyed. Change in the Body. 233 —233 190 — 190 300 600 379 665 —79 -*5 900 1200 941 1 180 —41 -f- 20 1500 1446 +54 Nitrogen equilibrium was not reached until 1200 grams of meat were given, or about five times the amount of the fasting proteid metabolism. The above experiments were made in 1858. It is no longer customary to calculate the proteid metabolism in terms of flesh destroyed, but in terms of nitrogen. The old-fashioned term flesh meant meat with a nitrogen content of 3.4 per cent. It served to illuminate the significance of metabolism at a time when few were instructed in this field of work. E. Voit and Korkunoff 3 have published a research of sim- 1 Voit: Hermann's Handbuch, "Stoffwechsel," 1881, pp. 330, 344. 2 Voit: Ibid., 1881, p. 106. 8 E. Voit and Korkunoff: "Zeitschrift fur Biologie," 1895, Bd. xxxii, p. 58. IOO SCIENCE OF NUTRITION. ilar character. They fed a dog with meat which had been treated with lukewarm water to remove the extractives, and which was then squeezed in a press. This process removes most of the nitrogen containing substances other than proteid. A dog will readily eat this washed meat or " proteid." The idea was to determine the minimum quantity of proteid which it was pos- sible to ingest and still maintain nitrogen equilibrium. The different quantities of meat tabulated below were given con- tinuously for two or three days at a time. Only the results of the last day of each of these periods are quoted: Food. N in Food. N in Excreta. Difference. Starvation o 3-996 — 3-99^ ioo g. meat 4.10 5.558 — 1.458 140 g. " 5-74 6.495 — o-755 165 g. " 6.77 7.217 —o.447 185 g. " . m . 7-59 7- 8 °4 —0.214 200 g. " 8.20 8.726 — 0.526 230 g. " 10.24 10.579 —0-339 360 g. " 1 1.99 12.052 — 0.062 410 g. " 15.58 I4-3 J 4 +1.266 360 g. " 13-68 13.622 +0.058 Starvation, third day 4.026 — 4.026 The figures show that nitrogen equilibrium was reached only after supplying three and a half times the amount of proteid metabolized in starvation. The authors calculate that at this time of nitrogen equilibrium the dog was still losing 28 grams of body fat, and that not much more than fifty per cent, of the total energy liberated in the organism was furnished by the pro- teid metabolism of the time. One may thus have nitrogen equilibrium without having carbon equilibrium. Systems of diet for fat people are based on this knowledge. A loss of proteid is highly undesirable, while a gradual loss of adipose tissue may be a great relief to the obese. Bornstein 1 finds that he can add proteid to his body and burn his body fat on a mixed diet containing 1600 calories with 118 grams of proteid. Such a diet contained a fuel value less than the requirement of his organism (p. 157). If the quantity of meat ingested be steadily increased after 1 Bornstein: "Berliner klinische Wochenschrift," 1904, No. 46. THE INFLUENCE OF PROTEID FOOD. IOI nitrogenous equilibrium has been reached, the proteid metabo- lism will gradually increase, nitrogenous equilibrium will be established at higher and higher levels, and there will be a cor- responding diminution in the amount of fat burned. This was shown in the following experiment of Voit, 1 who gave different quantities of meat to a large dog weighing 30 kilograms. INFLUENCE OF INGESTING INCREASING QUANTITIES OF MEAT. Weights are in Grams. Meat Ingested. Flesh Destroyed. Gain or Loss of Body Flesh. Gain or Loss of Body Fat. Respiratory Quotient. i6 S 599 1079 1500 1757 2044 2512 -165 —99 — 79 + 43 —44 — 12 —95 —47 —19 + 4 + 1 + 58 + 57 .72 .76 •74 .81 coo 1000 icoo x o'^ w 180O 2000 .84 2 COO Nitrogen equilibrium existed after the ingestion of 1500 grams of meat and there was also no loss of body fat (carbon equilib- rium). When 2000 grams and even 2500 grams of meat were supplied it was all destroyed, as was indicated by the amount of nitrogen in the urine, but a certain quantity of carbon belonging to the ingested proteid. was not eliminated in the respiration but was retained in the body. This carbon Pettenkofer and Voit believed to have been laid up in the body in the form of fat. The respiratory quotient in the foregoing series gradually rises as would be expected from the increasing prominence of the proteid in the metabolism (p. 27). Meat alone will therefore support a dog. Rubner 2 says that a man cannot live on meat alone, not because the intestinal canal cannot digest it, but because of the physical limitations of the apparatus of mas- tication. 1 Voit: "Stoffwechsel," 1881, p. 117. 2 Rubner: Leyden's " Handbuch derErnahrungstherapie," 1903, Bd. i, p. 42. 102 SCIENCE OF NUTRITION. A subject of interest akin to the value of proteid in metabo- lism is that of the value of gelatin. Gelatin is a substance which contains very nearly the same quantity of nitrogen as proteid; it breaks up on chemical treatment into the same amino acids, except that it does not yield tyrosin, cystein and tryptophan. In the diabetic, gelatin yields the same amount of sugar as does proteid. 1 To what extent gelatin may take the place of pro- teid in the body's metabolism has long been the subject of inquiry. It was shown first by Bischoff and Voit 2 that no matter how much gelatin was ingested it was always completely burned and some of the body's proteid in addition. Therefore gelatin never builds up new tissue, although it may somewhat diminish tissue waste. Gelatin may be formed from proteid in the body, but it cannot be reconverted into proteid nor act like proteid in metabolism. Kirchmann, 3 working in the laboratory of Erwin Voit, has shown to what extent gelatin spares proteid in metabo- lism. If one takes the amount of proteid metabolism in starva- tion as one, then the ingestion of about the same quantity of gelatin reduces the body's proteid waste 23 per cent., and if eight times this amount of gelatin be given the tissue waste may be reduced 35 per cent. In other words, the ingestion of 7.5 per cent, of the total heat requirement of the organism in the form of gelatin spares 23 per cent, of the body's proteid, while the ingestion of 60 per cent, of the requirement will only cause a decrease of 35 per cent, in proteid waste. Krummacher 4 showed that the ingestion of the full heat requirement of the animal in the form of gelatin reduced the fasting proteid metab- olism by only 37.5 per cent. It is evident that no matter how much gelatin be given, tissue proteid continues to be destroyed, and it is also evident that a small quantity of gelatin has almost as great an effect as a large quantity. 1 Reilly, Nolan, and Lusk: "American Journal of Physiology," 1898, vol. i, P- 395- 2 Voit: Hermann's Handbuch, " Stoffwechsel," 1881, p. 396. 8 Kirchmann: "Zeitschrift fur Biologie," 1900, Bd. xl, p. 54. 4 Krummacher: lbid. } 1901, Bd. xlii, p. 242. THE INFLUENCE OF PROTEID FOOD. IO3 An extremely interesting experiment of Kauffmann 1 shows that when the lacking tyrosin, cystein, and tryptophan are mixed with gelatin in the proportions in which they occur in true pro- teid, and are given to a dog or to a man, nitrogen equilibrium may be established. In recent years the idea has been gaining ground that pro- teid bodies must be broken up into amino acids before absorp- tion in the intestine (p. 289). If this be true then ingestion of the cleavage products of proteid should maintain nitrogen equilibrium in the same way as the ingestion of meat. The first experiments in this direction were done by Loewi, 2 who gave a dog pancreas which had been self-digested until all the proteid had been converted into amino acids, as was indicated by the almost complete disappearance of the biuret reaction. Fat and carbohydrates were given with the digest, and nitrogen equilib- rium was obtained and even nitrogen retention accomplished. Thus, in one experiment covering a period of eleven days, pro- teolytic digestive products containing an average of 6.08 grams of nitrogen were given daily, of which only 5.19 grams were eliminated in the urine, while the balance, or 0.89 gram of nitrogen, was retained in the body of the animal. This amounted to 9.79 grams of nitrogen in eleven days. Accom- panying this nitrogen retention was one of 0.649 gram of phosphoric acid (P 2 5 ), an amount larger than was necessary for the upbuilding of new tissue from the nitrogen compounds retained. Loewi concluded that he had demonstrated the synthesis of new proteid within the organism. Lesser 8 gave a pancreatic digest of fibrin to a dog and was unable to obtain nitrogen equilibrium. Henderson and Dean 4 confirmed Loewi in finding that they could obtain nitrogen equilibrium by feeding a dog with the 1 Kauffmann: "Pfliiger's Archiv," 1905, Bd. cix, p. 440. 2 Loewi: "Archiv fur ex. Path, und Pharm.," 1902, Bd. xlviii, p. 303. 3 Lesser: "Zeitschrift fur Biologie," 1904, Bd. xlv, p. 506. 4 Henderson and Dean: "American Journal of Physiologie," 1903, vol. ix, p. 386. 104 SCIENCE OF NUTRITION. cleavage products of meat produced by treatment with sulphuric acid. Stiles and Lusk, 1 on the contrary, gave a fasting diabetic dog a pancreatic digest of meat which had undergone fourteen months of proteolytic cleavage, and observed that the nitrogen of it was completely eliminated in the urine without protecting the body from loss of proteid, which would have occurred had meat itself been administered. To reconcile these differences it seemed necessary to con- sider the differences in methods of preparing the end products of the proteid to be ingested. Indeed, Abderhalden and Rona 2 find that mice live on casein split with pancreatin as long as they do on casein alone; whereas they die much earlier if the casein has been submitted to peptic and then pancreatic digestion, or if it has been broken up by acid hydrolysis. Henriques and Hansen 3 also* find that casein broken up by acid will not main- tain nitrogen equilibrium in rats, but that if the pancreas of the ox and a small piece of the intestine of the dog (to furnish erepsin) be digested for two months at 40 , and the resulting material given to rats, nitrogen equilibrium will be maintained. The authors further find that the monoamino acid fraction (the filtrate after precipitation with phospho wolf ramie acid), and also the alco- holic extract of the last-named digest, maintains rats in nitrogen equilibrium. The residue left after alcoholic extraction will not do so. Finally Abderhalden and Rona 4 have accomplished a most interesting experiment upon a dog. The animal was given daily a constant quantity of non-nitrogenous foods which were: fat, 25 grams; starch, 50 grams; cane sugar, 10 grams; dex- trose, 5 grams. The dog was brought into nitrogen equilibrium by giving meat containing 2 grams of nitrogen. Then for this were substituted the amino cleavage products of casein, pro- 1 Stiles and Lusk: "American Journal of Physiology," 1903, vol. ix, p. 380. 2 Abderhalden and Rona: "Zeitschrift fur physiologische Chemie," 1904, Bd. xlii, p. 528. 3 Henriques and Hansen: Ibid., 1905, Bd. xliii, p. 417. 4 Abderhalden and Rona: Ibid., 1905, Bd. xliv, p. 198. THE INFLUENCE OF PROTEID FOOD. 105 duced by pancreatic digestion and also containing 2 grams of nitrogen. During sixteen days on this diet there was an average daily gain of 0.12 grams of nitrogen by the dog. Then casein hydrolized by acid and containing 2 grams of nitrogen was administered for ten days, during which time the dog lost 0.48 grams of nitrogen daily. Amino products prepared after this fashion will therefore not preserve nitrogen equilibrium. Lastly, the diet was continued without any nitrogenous food. The daily waste of body nitrogen was then 0.53 grams. The loss was the same as when the casein hydrolized by acid was in- gested, indicating that this particular array of cleavage prod- ucts had no protecting power over the body proteid. The absence of virtue in the casein hydrolized by acids is attributed by Abderhalden and Rona 1 to the complete destruc- tion of all polypeptids (p. 293) which are probably the construc- tive nuclei (Bausteine) of proteid. When the latter are present a partial reconstruction of amino acids into the proteids of blood serum is possible. It seems therefore proved that amino bodies resulting from certain proteolytic cleavages may be the equivalent in metabo- lism of ingested proteid itself. In practical dietetics these substances can have no value, as they tend to produce diarrhea, as do also albumoses and peptones when given in any quantity. 2 As illustrating this, Cohnheim 3 finds that though somatose is more digestible than meat, still over 30 grams is undesirable in the daily diet of a man. The effect of copious drinking of water upon proteid metabolism has been made the subject of various studies. A small increase in nitrogen elimination has usually been noted. This was first established by Voit, who explained it as due to an increased circulation which influenced the flow of the intra- 1 Abderhalden and Rona: "Zeitschrift fur physiol. Chemie," 1906, Bd. xlvii, p. 397. 2 Voit: "Munchener med. Wochenschrift," 1899, Nos. 6 and 7. 8 Cohnheim: "Pfluger's Archiv," 1904, Bd. cvi, p. 17. 106 SCIENCE OF NUTRITION. cellular fluids. Heilner 1 has recently shown that giving 2000 c.c. of water to a fasting dog on two successive days raises his urinary nitrogen from 3.15 grams to 4.09 and 3.58 grams on the two days of water ingestion, and then the nitrogen excretion falls to 2.22 and 2.62 on the following days. In this experi- ment the carbon dioxid excretion was very slightly increased and the temperature of the dog was not affected. The quantity of urine rose from 90 c.c to 2050 c.c. Straub 2 found that an extra ingestion of 2000 c.c. of water in a man who was in nitrogen equilibrium on a diet containing 20.56 grams of nitrogen had no effect on proteid metabolism; whereas Hawk 3 who gave less proteid nitrogen but more water, found that the ingestion of 4500 c.c. of water caused the urinary nitrogen to rise from 11.03 to 12.48 on the first day, and 11.82 on the second day, with a fall to 10.91 grams on the succeeding day when no water was given. Hawk interprets the action of copious water drink- ing as twofold, — first, to cause a removal of any accumulation of nitrogenous decomposition products from the organism, as was indicated by the greater increase of 12.8 per cent, in the nitrogen elimination of the first day; and, second, to cause a true in- crease in proteid metabolism as was indicated by the smaller increase of 6.8 per cent, on the second day of water ingestion. One of the striking characteristics of starvation metabolism was shown to be its extreme regularity from hour to hour and from day to day. What, then, is the hour-to-hour metabolism after meat ingestion? The classical experiments of Voit 4 and of Feder 5 have been more fully worked over by Gruber. Gruber 6 fed a dog with 500, 1000 and 1500 grams of meat on different days. He collected the urine every two hours after the meal and determined 1 Heilner: " Zeitschrift fur Biologie," 1906, Bd. xlvii, p. 541. 2 Straub: Ibid., 1899, Bd. xxxvii, p. 527. 8 Hawk: "University of Pennsylvania Medical Bulletin," March, 1905. 4 Voit: "Physiologische Untersuchungen," Augsburg, 1857, p. 42. 5 Feder: "Zeitschrift fur Biologie," 1881, Bd. xvii, p. 541. • Gruber: Ibid., 1902, Bd. xlii, p. 421. THE INFLUENCE OF PROTEID FOOD. 107 the nitrogen output. The curves of nitrogen elimination under these circumstances are as follows: J /.in jrams per Jgfeg 8 io iz i+ it 19 20 it Hours Fig. 5. — 1, after 500 g. meat -f- 5°g- * a * + 350 c.c. water; 2, after 1000 g. meat 4- 200 c.c. water; 3, after 1500 g. meat + 500 c.c. water. On each of these days the animal was in nitrogen equilibrium. It is evident that there is an early elimination of proteid nitrogen which here reaches a maximum between five and seven hours after feeding, and that the hour of the maximum excre- tion is delayed by increasing the quantity of meat ingested. It is apparent, therefore, that the proteid metabolism as il- lustrated by the curve of nitrogen elimination is quite different from the even metabolism of starvation. If we turn from the nitrogen elimination to that of the car- bon in the respiration, it will be found that here the elimina- tion is comparatively even. Frank and Trommsdorf l gave a dog 1 191 grams of meat which had been freed from extractives 1 Frank and Trommsdorf: "Zeitschrift fur Biologie," 1902, Bd. xliii, p. 266. io8 SCIENCE OF NUTRITION. by means of lukewarm water. The nitrogen and carbon of the urine and feces, and the carbon of the respiration were deter- mined, and from these data the proteid and fat metabolism were calculated in the usual manner. From this the heat produced was estimated. The essential results were thus tabulated: VARIATION IN METABOLISM AFTER MEAT INGESTION. No. of Hours. Per Hour. Period. N in Urine. C in Respira- tion. Calories from Metabolism. Starvation 24 4 h. 9 m. 3 h. 14 m. 5 h. 44 m. 10 h. 53 m. (night) O.1944 0.917 1-373 1.592 1.064 2.968 3.862 3.886 3.872 3493 36.72 43-94 41-53 41.00 38.46 Meat Ingested: First period after meat Second " " " Third " " " Fourth " " " It is evident that while the curve of the nitrogen elimination shows a maximum rise to nearly eight times that of fasting and varies greatly, the carbon curve is much more even and is not much above that found in starvation. The maximum rise in heat production occurs in the first four hours after the inges- tion of meat and amounts to twenty per cent. The heat pro- duction falls during the night hours. Rubner 1 has obtained similar results after giving 460 grams of washed meat to a dog weighing 24 kilograms. His calcula- tions show the following metabolism during six-hour periods: VARIATION IN METABOLISM AFTER MEAT INGESTION. First Day of Ingestion Time of Day. N in Urine. Cal. from Pro- teid. Cal. from Fat. Calories Total. Dav. q—% 5.06 6.11 4.64 2.76 18.6 I35-I 163.0 123.8 73- 6 495-5 143-9 85.2 105.4 169.5 504.O 279.O 7-Q 248.2 Nicht. 0—7 229.2 ?— n 243-1 Total 999-5 1 Rubner: "Gesetze des Energieverbrauchs," 1902, p. 365. THE INFLUENCE OF PROTEID FOOD. 109 VARIATION IN METABOLISM AFTER MEAT INGESTION (Continued). Third Day of Ingestion Time of Day. N. in Urine. Cal. from Pro- teid. Cal. from Fat. Calories Total. Day, 0— 1 5-57 8.94 5-32 2.66 22.5 148.7 238.7 142.0 71.0 600.4 130.4 33-4 763 162.4 402.5 279.1 272.1 218.3 233-4 1002.9 3-0 Night. 0— z 2-Q Total The nitrogen curve varies. The total heat production is greatest during the hours immediately following the ingestion of proteid, but is otherwise comparatively even. 