TX 392 .S5 Copy 1 LELAND STANFORD JUNIOR UNIVERSITY PUBLICATIONS UNIVERSITY SERIES The Effect of a Strictly Vegetable Diet on the Spontaneous Activity, the Rate of Growth, and the Longevity of the Albino Rat BY JAMES ROLLIN SLONAKER ASSISTANT PROFESSOR OF PHYSIOLOGY WITH ONE PLATE AND FIFTEEN TEXT FIGURES STANFORD UNIVERSITY, CALIFORNIA PUBLISHED BY THE UNIVERSITY 1912 Monognpll UNIVERSITY SERIES Inheritance in Silkworms, I. Vernon L. Kellogg, Professor of Ento- mology. 89 pp., 4 plates. 1908. Price, $1.00. '. The Opisthobranchiate Mollusca of the Branner-Agassiz Ex- pedition TO Brazil. Frank Mace MacFarland, Professor of Histology. 105 pp., 19 plates. 1909. Price, $1.00. , A Study of the Normal Constituents of the Potable Water of the San Francisco Peninsula. John Pearce Mitchell, Assis- tant Professor of Chemistry. 70 pp., i map. 1910. Price 50c. Synopsis of the True Crabs ( Brack yura) of Monterey Bay, Cali- fornia. Frank Walter Weymouth. 64 pp., 14 plates. 1910. Price 50c. 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LELAND STANFORD JUNIOR UNIVERSITY PUBLICATIONS UNIVERSITY SERIES The Effect of a Strictly Vegetable Diet on the Spontaneous Activity, the Rate of Growth, and the Longevity of the Albino Rat BY JAMES ROLLIN SLONAKER ASSISTANT PROFESSOR OF PHYSIOLOGY WITH ONE PLATE AND FIFTEEN TEXT FIGURES STANFORD UNIVERSITY, CALIFORNIA PUBLISHED BY THE UNIVERSITY APRIL 2, I912 Stanford University Press «■ 4 THE EFFECT OF A STRICTLY VEGETABLE DIET ON THE SPONTANEOUS ACTIVITY, THE RATE OF GROWTH, AND THE LONGEVITY OF THE ALBINO RAT* INTRODUCTION. The study of dietetics today occupies one of the most important places in the field of physiological investigation. Many popular arti- cles have appeared in the past few years advocating this or that diet as best adapted to the needs of man. The argument is usually based on the personal opinion of the writer or the effects a certain diet may have had upon him. The personal idiosyncrasies which appear in these articles are too numerous to mention. Such writings are of no scientific value, and only show the trend of a certain class of people. In contrast to these popular articles appear the writing of various scientific men giving the results of their investigations. These results are based on the comparative digestibility and absorption of the diff- erent foods and upon their ability to maintain nitrogenous equilibrium in the animal experimented upon. The tendency of humanity is to go to the extremes, and nowhere is this more manifested than in dietetics. One class, vegetarians, main- tains that man should abstain exclusively from animal foods, the other class claims that the human alimentary tract is more adapted to omni- vorous food than to a strictly vegetable diet. Vegetarianism as used by most people is a misnomer. The larger proportion of the so-called vegetarians partake freely of such animal foods as milk, eggs, butter, cheese and the like. A few, the fruitarians, live wholly on nuts and fresh fruits. Another small group live on nuts, fruits, legumes and vegetables, either in the raw or cooked state. The much larger number of vegetarians (?) live on a mixed diet which dif- fers from the ordinary mixed diet in only one respect — the absence of meat. Most investigators have studied the effects of a certain diet on the animal for a limited time, which in most cases is insufficient to warrant *From the Physiological Laboratories of Stanford University. 4 EFFECT OF DIET ON THE ALBINO RAT such sweeping conclusions. Because an animal is able to maintain its weight and health for a limited time, is no argument that it could do so for its entire life. Neither has the effect on the offspring been ascertained. Such results can only be obtained by continuing the experiment during the lifetime of the animal and succeeding genera- tions. The present experiment was undertaken to determine as fully as possible the comparative effect of a strictly vegetable diet, and an omnivorous diet, upon the spontaneous energy of the animal as mani- fested by its voluntary activity, the effect on its growth, and on the length of its life. An experiment is now under way to study the effect on the progeny. No attempt has been made to study the income and outgo of nitrogen. MATERIALS AND APPARATUS. In order that such an experiment may be of value a number of similar animals must be used, and the environment of these must be the same in every respect, with the exception of diet.^ In this experiment sixteen rats were used. To secure these as nearly alike as possible, sisters were mated to the same male. After numerous trials, lasting more than a year, two sister rats of approxi- mately the same size, which had been mated to the same male, gave birth to eight each, just a day apart. Previous observations^ have shown that the young of a litter of three not only averaged heavier at birth than those of a litter of ten, but also gained more rapidly during the nursing period and had a better start at the weaning time than those of the larger litter. Also the age of the mother had an effect on the size of the litter and the average weight of the young. Very young mothers were less prolific than older females. Minot^ found in his observations on the guinea pig that the aver- age 5^oung of a litter of one weighed 85.5 grams, and the average of a litter of eight 52.2 grams. Also that the males averaged heavier (71 grams) than the females (70.2 grams). A similar condition exists between the sexes of the albino rat. This difference in weight of the two sexes becomes much more marked as the animals grow older. One should therefore have rats of the same age, of as nearly as possible the same parentage, the same number in the litter, and the same number of each sex. Owing to the fact that it is difficult to determine the sex of the young rats with accuracy, the sexes were not distributed as I would have wished. These sixteen young were arranged and designated as follows: MATERIALS AND APPARATUS 5 No. I and No. 2 from litter A, and No. 3 and No. 4 from litter B, were put into revolving cages to be used as omnivorous feeders in deter- mining their activity; No. 5 and No. 6 from litter A, and No. 7 and No. 8 from litter B, were put in revolving cages to be used in ascer- taining the amount of work the vegetarian feeders would perform; No. 9 and No. 10 from litter A, and No. 11 and No. 12 from litter B, were put in stationary cages for omnivorous controls; and No. 13 and No. 14 from litter A, and No. 15 and No. 16 from litter B, were placed in stationary cages for vegetarian controls. Thus each litter was equally and uniformly distributed. Unfortunately the sexes were not ideally grouped. The following table illustrates the manner in which the young were distributed. Omnivorous Exer- Vegetarian Exer- Omnivorous Control Vegetarian Control cised Rats cised Rats Rats Rats Litter No. I Sex Litter No. Sex Litter No. Sex Litter No. Sex A Male A 5 Male A Q Male A I,S Female " 2 " 6 Female " 10 " « 14 Male B 3 Female B 7 "■ B II Female B 15 " " 4 Male " 8 " ** 12 Male " 16 Each rat was thus confined in a cage by itself, which served as its home for its entire lifetime, and from which it was taken at inter- vals of about two weeks for a time sufficient to weigh the rat and clean its cage. The apparatus for recording the activity has already been acb- cribed,* but may be briefly given again. It consisted of a series of eight cylindrical cages which revolved on stationary axles to which were attached the nest boxes. The food and water boxes were attached to the ends of the nest boxes. The cage thus revolved about the sta- tionary nest box whenever the rat ran. Automatic devices were attach- ed to register the number of revolutions and to record them on paper kept moving by a continuous roll kymograph. The first device being read in the morning and in the evening gave the daily and nightly run of each rat through its lifetime. The second arrangement showed the distribution of the activity of each rat for each twenty-four hours during its whole life. These records were of great assistance in show- ing the peculiarities of activity which occurred at difTerent ages. This apparatus was therefore only adapted to recording the run- ning activity of the animals. Previous observations^ have shown that the running activity of the rat is proportional to the other activities. 6 EFFECT OF DIET ON THE ALBINO RAT Changes in the amount of the running activity are correct indicators of similar fluctuations in the other activities of the animal. FEEDING. No attempt was made to give a definite amount of protein food in the diet nor to try to maintain nitrogenous equilibrium. The diet was varied as much as possible, and the amount of food given was more than was eaten before the feeding time on the following day. The feed and water boxes were then cleaned and a new supply given. Cracked corn was always given. The young were weaned at the age of 28 days and placed in their respective cages, as already described. A rich mixed diet, consisting largely of bread and milk with an occasional feed of baked beans and meat hash, was given all to prevent any dis- astrous effects resulting from the sudden change in environment and methods of feeding. This mixed diet was continued for twenty-eight days. At this age (fifty-six days) all appeared perfectly healthy and normal in every respect. They had each made a normal gain. The males averaged 70.1 grams and the females 59.3 grams. The difference in the character of the food was introduced at this time, the one group being designated vegetarians, and the other, omni- vorous feeders. These two groups were fed exactly the same food each day, with the exception of meat and other animal foods which were given about three times a week to the omnivorous feeders in addi- tion to the vegetable food. The vegetable foods were as rich in protein as it was possible to obtain from this class of foods, and consisted of such articles as the following: fresh vegetables, such as lettuce, kale, cabbage, cauliflower, clover and celery; cooked vegetables, such as white, corn, brown and graham bread, biscuits, buckwheat cakes, dough- nuts, crackers, cookies, oatmeal mush, fried cornmeal mush, dumpUngs, corn, rice, baked beans, potatoes, carrots and onions; nuts, fruits and grains, such as almonds, English walnuts, apples, cracked corn, wheat, and corn meal. Occasionally, when the vegetarians seemed to be losing ground too fast, a feed of cheese, milk, or some other animal food was given. This was done only a few times soon after the vegetarians were first put on their exclusive diet. As can be readily seen, the above articles composing the vegetarian diet are either found on our tables or can readily be procurred from shops. Some of them contained small portions of animal food, i.e., graham muffins usually contain an egg and milk, bread often contains milk, doughnuts and several other articles contain animal fat. As only KIND OF FOOD 7 very small amounts of animal food were present as compared to a large quantity of vegetable food, I have called this a strictly vegetable diet, at the same time realizing it is not absolutely such a diet. The amount of food given to each rat was not weighed, but meas- ured as accurately as possible with a spoon, or by pieces of equal size. The following few days' diet taken at random will serve to show the variety of food and its frequency. April 23. Cooked corn, lettuce, cracked corn and water. April 24. Water-soaked bread, almonds, lettuce, cracked corn and water. April 25. Baked beans, lettuce, cracked com and water. Omnivorous had also meat. April 26. Graham muffins, almonds, cracked corn and water. April 27. Water-soaked bread, lettuce, cracked corn and water. April 28. Water-soaked bread, almonds, cracked corn and water. April 29. Cracked corn and water. April 30. Mashed potatoes, lettuce, cracked corn and water. Omnivorous had also meat. April 31. Water-soaked bread, buckwheat cakes, cracked corn and water. Another example at another season of the year is as follows: Nov. 14. Bread, cracked corn and water. Nov. 15. Potatoes, macaroni, cracked corn and water. Omnivorous had also meat. Nov. 16. Bread, oatmeal mush, cracked corn and water. Omnivorous had also meat and bread hash. Nov. 17. Water-soaked bread, cracked corn and water. Nov. 18. Water-soaked bread, cracked corn and water. Omnivorous had also meat and bread hash. The amount of meat given to each of the omnivorous rats was usually small, consisting of but a few grams. It was given on an aver- age two or three times each week. We have thus sixteen rats as nearly alike in regard to age, parent- age, size and tendencies as it is possible to obtain, subjected to the same environments, fed the same food with the exception that the eight omni- vorous feeders had a few grams of animal food added to their diet about three times each week. It is obvious, therefore, that whatever differ- ences may be found between these two groups of rats in regard to their activity, rate of growth, and longevity must be due wholly to the pres- ence and absence of animal food in the two diets. 8 EFFECT OF DIET ON THE ALBINO RAT ACTIVITY. In studying the characteristics of the activity one needs to refer to the kymograph records. Figures i to lo inclusive are reproductions of such records, and show the activity of each rat for twenty-four con- secutive hours at different ages. By comparing these figures a great difference is noticed in the activity at different ages. Figure i represents the activity of each rat at the age of thirty- two days, and just four days after they had been weaned and placed in the revolving cages. There is no regularity in the distribution of the activity and periods of rest. Neither is there any apparent tendency to be more active at one time in the twenty-four hours than at another. They were restless, playful and filled with a spirit of investigation. Since they were all fed at this time on the same diet, any differences in the character of the activity may be attributed to individual variation. In Figure 2. which shows the distribution of the activity at the age of six months, two important things are noticed. First, the great bulk of the activity occurs during the evening and early night time : second, the omnivorous rats (O) are more active than the vegetarians (V). There is more or less random running for an hour or so before and after the feeding time (4 p.m.), but the most is done during the night. At the age of eleven months (Figure 3) the periods of activity and rest are more sharply defined. Also the difference in the amount of vol- untary activity of the two classes is very obvious. The activity of the vegetarians is approaching closely in appearance that of old age.^ In Figure 4 the activity at the age of sixteen months is seen. Some days previous to this record the feeding time was changed to the morning to see what effect it would have on the distribution of the activity. The main bulk is seen to remain constant, but the usual ran- dom running which occurs at the feeding time has shifted to the morn- ing. At this age two of the vegetarians have died and the other two compare very unfavorably with the work of the omnivorous. Figure 5, which represents the activity at the age of twenty-one months, shows that when the feeding time is returned to the afternoon the periods of activity and rest are sharply defined. The omnivorous feeders are still quite active when compared to the remaining vege- tarians. At the age of twenty-five months all the vegetarians were dead (Figure 6). The records of the omnivorous rats show a marked ten- dency toward old age. Especially is this true in No. i and No. 4. 0{3*" BAM 9 10 (I 12 IPM2 3 4 5 6 7 8 9 10 U 12 1AM 2 3 4 5 6 7 8 Fig. I. Graphic records sliowing tlie distribution of the activity of each of the exercised rats as recorded on the kymograph paper. The rats were ;i2 days old and had been weaned and put in their cages but four days before. O and V refer to omnivorous and vegetarian rats respectively. I7 ' ' ' ' ' '" ' " ■ _ o)i u- . /5 (fi 7 _. is 8A M9 10 11 12 If Mi i 4 5 6 7 « 9 10 U 12 IAM2 3 4 S 6 7 8 Fig. 2. Graphic records of activity of omnivorous (O) and vegetarian rats (V) at the age of 6 months. "li I (8. 10 II 12 IPM 2 Fig. 3. Graphic records of activity of omnivorous (O) and vegetarian rats (V) at the age of 11 months. ( S ■ — M nif i m — L-C9 — t gagi n osa »r~i _■ 1 T . i i ifln !■ I A^rrn M ■ B — »« I ffi fi * B II 1_ 3 (5 \8 Dead ^7 Dead SAM 9 10 II 12 IPM 2 3 4 5 7 8 10 H 12 lAM 2 3 4 5 6 7 Fig. 4. Graphic records of activity of omnivorous (O) and vegetarian rats (V) at the age of i6 months. (6 Dead V? 7 Dead SAM 9 10 II 12 IPM 2 3 4 A 6 7 8 9 10 II 12 1A^3 2 3 4 5 6 7 Fig. S. Graphic records of activity of omnivorous (O) and vegetarian rats (V) at the age of 21 months. V<7 0. Dead ead (8 Dead kAM9 10 n 12 !PH 2 3 4 5 6 T « S lO U S lAM 2 3 4 S 6 1~ Fig. 6. Graphic records of activity of omnivorous (O) and vegetarian rats (V) at the age of 25 months. ,1 De« 10 II 12 IPMi 3 4 5 6 7 8 9 10 II 12 lAM 2 3 4 5 b 7 Fig. 7. Graphic records of activity of omnivorous (O) and vegetarian rats (V) at the age of 26 months. ^ I Dead {.4 Dead .a Dead , a Dead V^ 7 Dead , a De«<» •amII Io ir'""[j Ipiia 3 4 t • t • • io u la uSia s 4 9 e 7~ Fig. 8. Graphic records of activity of omnivorous (O) and vegetarian rats (V) at the age of 28 months. fl Dead 2, , „ O i 4 Dead ( S Dead ) 6 Dead 3 ^ )7 Dead ( B Dead BAMS 10 U 12 IPM2 3 4 5 6 7 8 » 10 II « IAM2 3 4 s fi 7 8 Fig. g. Graphic records of activity of omnivorous (O) and vegetarian rats (V) at the age of 31 months. 'I Dead 1 2 Dead [4 Dead V S Dead 6 Dead > 7 Dead 1 8 Dead SAM » 10 II 12 IPM 2 Fig. 10. Graphic records of activity of omnivorous (O) and vegetarian rats (V) at the age of 34 months. CHARACTERISTICS OF ACTIVITY 9 The remaining figures (7, 8, 9 and 10) represent the records for the ages twenty-six, twenty-eight, thirty-one and thirty-four months re- spectively. No. 4 in Figure 7 shows the death struggle of this rat. which ended a little before 10 p.m. In comparing these different records of activity, one notices that in the young rats the periods of activity and rest are of short duration and have no definite arrangement so far as the time of the day is con- cerned. As the rats grow older the activity becomes greater and occurs more and more during the night time, the periods of rest being confined to the daytime. This continues until the rats reach the prime of life. After some months of almost uniform activity there is a grad- ual reduction, and the distribution and amount of work done approaches that of youth. It also shows that the vegetarians are not as active, that they age more early, and that their duration of life is shorter than the omnivorous rats. Since all the animals were fed on a mixed diet for twenty-eight days after commencing the experiment, any difference in activity dur- ing this period must be considered due to individual variation. This variation is sometimes very noticeable, as seen in Table I. This table represents the average number of revolutions of five consecutive days of each rat at the ages indicated. There is not a gradual and regular increase in the amount of running done by each, but fluctuations — now greater, now less. At first this was thought to be due to making the average from too small a number of days. Therefore another table (Table II) was made, by taking the average run of each sex of each group for a whole month. The figures in the column of the omni- vorous males thus represent the average of thirty days' run of three individuals. But here again we see the lack of a uniform increase. In other words, the activity manifests itself rhythm.ically. No doubt if the number of individuals had been greater the results would have been more uniform. In a former paper I have discussed the causes of these fluctuations.- Table II is put in the form of curves in Figure 11. The rhythmical variations are very conspicuous. These fluctuations also correspond in many cases both in regard to time and appearance. For example, from the beginning to the third month there is a rapid rise in the curves, showing a great increase in the daily activity. This was, no doubt, due to the feed, for they were all fed on a strong mixed diet for almost a month, and on rich food for almost two months. The effect of this food carried them over apparently till the end of the third month, when they began to feel the effects of the lack of it. This was followed in a general reduction of amount of daily activity in all except the omnivorous lO EFFECT OF DIET ON THE ALBINO RAT OMNIVOROUS RATS VEGETARIAN RATS Age N 0. I No. 2 No. 3 ^ fo. 4 No. ; , No. 6 No. 7 No. 8 Mos. ]\ [ale Male Female I\ /lale Male Female Female Femal J I 348 1002 620 448 118 2 752 318 970 2 I 200 1 124 2118 I 336 196 4 668 716 1952 3 790 886 1956 I 832 161 8 682 1396 2238 4 5 028 5850 5782 9406 1 2150 1 542 j 2870 1468 5 I 206 3930 7280 834 42 657 1206 3496 6 540 1644 8482 540 59 6 920 I 170 1472 7 I 307 3144 IO185 3 574 108 4 I 128 3244 1904 8 2 024 3274 9518 4 276 67 6 565 2 2400 3884 9 6 002 7574 8930 2 836 83 6 656 8962 4106 ID 2 618 4398 8260 2 882 85 8 578 876 2962 II 3 620 2096 8640 2 310 100 6 340 670 882 12 2 186 4258 8902 2 616 I 144 1 528 1 898 1004 13 4 964 7066 11044 3 084 60 2 46 1 316 708 14 3 860 6374 10992 3 004 16 8 ... 524 634 15 I 428 4768 8198 2 556 9 918 96 i6 I 006 2642 13002 I 364 34 2 68 96 17 2 684 4776 5982 I 998 8 4 72 i8 744 2364 9732 I S12 8 ,8 ... 22 19 996 2476 8312 808 y 60 20 806 2056 9658 720 8 12 24 21 69c ' 1520 2210 482 = 6 .. 58 22 33^ ) 1810 5468 290 c 2 22 23 I 6gt ) 1680 3188 456 4 [O 88 24 38c > 1352 3100 220 .... 25 9A |.* 1466 4612 196 26 . 188 2538 48* 27 . 160 1968 28 180 5171 29 72 2424 30 56 2832 31 28* 1706 32 2312 33 488 34 .... 435 60* Table I. — Average daily revolutions of the omnivorous and vegetarian rats at ages indicated. female, which remained practically unchanged. Then, with the except- tion of the vegetarian female, there was another general increase up to the fifth month. Again, at the tenth month, all show an increase, except- ing the vegetarian male, which shows a slight decrease. ♦The number of revolutions during the 24 hours previous to death. DIFFERENCES IN ACTIVITY II OMNIVOROUS VEGETARIAN Age Male Female Male Female in Months (Avg. 3) (Avg. I) (Avg. I) (Avg. 3) I 73 102 68 53 2 689 724 I 169 1040 3 2455 2,944 3 542 2017 4 642 3.014 I 853 1273 5 4375 6,835 5 021 75 6 3286 8,843 845 146 7 3405 13.308 I 242 1175 8 3673 10,898 I 211 2188 9 3535 9,688 I 057 2156 lO 4717 11,643 828 2316 II 3119 10,136 998 905 12 2935 10,513 I 010 738 13 3957 9,684 826 680 14 5081 11,613 458 482 15 2285 9,110 517 519 16 2247 8,692 140 267 17 2069 9,027 179 29 18 2262 7.579 99 26 19 2212 9.357 96 7 20 1599 9.247 54 21 21 980 6,940 55 16 22 1273 7.156 37 13 23 1062 5.730 81 16 24 727 3,664 25 746 3.529 26 266 3.909 27 105 3.774 28 149 3.609 29 15 3.339 30 25 2,808 31 10 1,911 32 4 3.134 33 .... 2,033 34 320 Table II. — Average daily work as indicated by the number of revolutions computed by dividing the total run of the month previous by 30. It is especially noticeable that the curves representing the two sexes of the omnivorous feeders correspond much more closely in their fluc- tuations than those of the vegetarian feeders. In fact after the third month similarity in the character and time of these fluctuations of the 12 EFFECT OF DIET ON THE ALBINO RAT omnivorous and vegetarian feeders grows rapidly less and less. The same may be said regarding the amount of daily activity of the two classes. The omnivorous female far surpasses all others. The omni- vorous male comes next in order. Then follows the vegetarian female, Revolutions 14000 13000 12000 11000 10000 9000 8000 TOOO i\ t \ 6000 3000 AgwuiMouthit 5 fO /is ' ' 20 25 30 .% Fig. II. Curves representing the average daily activity of each sex of the exercised rats at the ages indicated. The heavy solid line (OM) is the omnivorous males, the heavy dotted line (OF) is of the omnivorous females. The light solid line (VM) is the vegetarian males. The light dotted line (VF) is the vegetarian females. closely followed by the vegetarian male. The females of each class thus surpass the males of the same group in average daily activity. When we consider the time in life at which these rats do the great- est amount of daily running we see, on consulting the curves of Figure II, that it occurs in both classes at an early age in life, usually between the seventh and twelfth month. In the omnivorous feeders it is a little later than in the vegetarians. In a former experiment^ it was ascer- tained that the greatest average daily run of the normal male and female occurred when they had reached a trifle more than one-third of their DISTRIBUTION OF ACTIVITY 13 natural lifetime. In this experiment the vegetarians seem to have done their best day's work when about one-fourth of their life had passed. This was equivalent to about one-sixth of the lifetime of the normal omni- vorous rat. Let us now consider the total amount of work, as indicated by the o bfi < I 2 3 4 5 6 7 8 9 ID II 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 OMNIVOROUS EXERCISED RATS IVEGETARIAN EXERCISED RATS Male No. I 1,200 18,850 79,750 148,460 248,990 329,900 403,070 487,130 576,360 722,880 817,000 883,120 961,360 1,068,300 1,165,990 1,206,980 1,271,700 1,309,080 1,339,080 1,382,130 1,400,500 1,429,570 1,457,500 1,469,340 1,486,250 Male No. 2 3,050 26,140 91,130 189,620 322,420 438,020 523,320 650,490 786,660 982,210 1,082,000 1,215,190 1,378,680 1,548,570 1,666,150 1,760,900 1,849,340 1,975,140 2,072,520 2,146,720 2,203,380 2,277,120 2,334,160 2,380,260 2,423,250 2,447,180 2,456,190 2,460,110 2,462,520 2,463,950 2,464,770 2,465,130 Female No. 3 Male 1,300 23,010 111,320 201,730 406,780 672,070 1,041,330 1,388,260 1,678,890 2,028,190 2,332,260 2,647,640 2,938,160 3,286,540 3,559,830 3,820,590 4,091,400 4,318,780 4,599,500 4,867,910 5,076,100 5,290,770 5,462,560 5,573,480 5,679,360 5,796,630 5,909,860 6,018,140 6,118,320 6,202,570 6,259,910 6,353,920 6,414,900 6,427,500 No. 4 2,060 23,390 118,150 248,780 409,250 508,500 656,470 777,640 870,400 952,860 1,039,650 1,104,240 1,218,620 1,399,100 1,389,440 1,455,930 1,488,930 1,529,400 1,571,080 1,588,710 1,601,920 1,613,700 1,624,420 1,631,780 1,639,060 1,642,100 1,642,580 No. 5 Male Female Female Female 2,040 37,120 143,380 198,980 249,600 276,960 314,520 350,550 382,320 407,150 437,090 467,380 492,170 505,820 511,340 515,530 520,910 523,000 525,890 527,520 529,160 530,560 533,000 No. 6 1,180 26,620 59,680 82,070 98,350 111,670 132,580 158,890 187,910 210,720 224,790 238,750 244,370 No. 7 760 22,550 76,840 133,430 180,070 238,550 290,780 374,400 450,980 555,180 581,180 604,830 634,340 651,680 686,590 704,900 No. 8 2,810 49,120 149,330 238,940 285,940 364,240 406,700 483,720 575,160 659,590 694,980 723,820 749,280 772,930 784,740 787,450 790,040 792,390 793,620 794,930 796,360 797,570 799,040 Table III. — Comparative number of revolutions made by the omnivorous and vegetarian rats at the ages indicated. The number of revolutions represents the amount of voluntary running or work of each rat. 14 EFFECT OF DIET ON THE ALBINO RAT number of revolutions which each of the exercised rats voluntarily made during its lifetime. Table III represents the total number of revolutions of each rat at the ages indicated. To give a better idea of the amount of work equivalent to these revolutions, the actual distance in miles has been computed and shown in Table IV. By consulting these tables it is OMNIVOROUS EXERCISED RATS Age ]V lale Male Mo. N 0. I No. 2 I I 2.6 2 16 22 3 68 77 4 121 160 S 211 273 6 278 373 7 341 434 8 414 551 9 487 663 10 5X2 832 II ( b9i 915 12 749 1023 13 ^il2 1155 14 ( ;)oo 1318 IS ! 586 1390 16 i( 320 1490 17 i( d8o 1560 18 I no 1665 19 I 125 1747 20 I 165 1850 21 I 188 1862 22 12 210 1920 23 i: 225 1980 24 i: 244 2025 25 i: 265 2050 26 . 2074 27 . 2090 28 . 2093 29 . 2095.6 30 . 2097 31 • 2097.7 32 . 2098 33 . 34 . Female No. 3 19 95 170 336 572 882 1181 1435 1710 1980 2230 2490 2780 3020 3230 3460 3650 3890 4125 4280 4475 4620 4720 4810 4900 5000 5100 5180 5250 5300 5350 5430 5447 Male No. 4 1-7 19.6 100 210 346 495 555 658 740 810 876 945 1036 1115 1 168 1220 1270 1298 1325 1347 1358 1362 1380 1385 1389 1391 VEGETARIAN EXERCISED RATS Male No. 5 1-7 31-5 122 168 211 234 257 297 305 345 370 396 417 428.6 433-4 436.5 440.6 444-7 445-7 447 448.5 449-7 450.9 Female Female Female No. 6 I 22.6 50.6 67.6 83-4 94-7 112.4 134-7 159 187 190.5 202 207 No. 7 19.I 65 113 153 200 246.5 317-3 382 470.5 492.6 508.3 537-7 552 581.9 592.3 No. 8 2.4 41.7 126.6 202.5 242 309 345 410 487-5 559 589 613 635 655 665 667 669.6 671-5 672.6 673-7 675 676 677.1 Table IV. — Comparative number of miles run by the omnivorous and vege- tarian rats in the revolving cages at the ages indicated. TOTAL AMOUNT OF ACTIVITY 15 readily seen that the work done by all the rats corresponds rather closely during the first three or four months. This corresponds close- ly to the average daily work shown in Figure 11. As a matter of fact the vegetarians average a trifle more at the end of the third month than Average number of revolutions Average number of miles A Omnivorous Vegetarian Omnivorous Vegetarian Age in Males Female Male Female Male Female Male j Female Mos. Avg. of 3 Avg. of I Avg. of I Avg. of 3 Avg. of 3 Avg. of I Avof I Avg. of 3 I 2,103 1,300 2,040 1,583 1.8 1.8 1-7 1-3 2 22,793 23,010 37,120 32,783 19.2 19. 31-5 27-5 3 95-343 111,320 143,380 93,283 82. 95- 122. 80.7 4 195,620 201,730 198,980 131,480 164. 170. 168. 127.7 5 326,887 406,780 249,600 133,747 277. 336. 211. 1.59-5 6 425,473 672,070 276,960 2.38,133 349- 572. 234- 201. 1 7 527,620 1,041,330 314,220 273,353 443- 882. 257- 234.6 8 638,420 1,388,260 3.50.550 339,003 .541- 1181. 297. 287.7 9 744,473 1,678,890 382,320 403,683 630. 1435- 305- 342.8 10 885,983 2,028,190 407,150 473,163 751- 1710. 345- 405-5 II 979,550 2,332,260 437,090 500,317 827. 1980. 370. 424-3 12 1,067,517 2,647,640 467,380 522,467 906. 2230. 396. 441. 13 1,186,220 2.938.160 492,170 542,663 lOOI. 2490. 417. 470- 14 1,338,657 3,286,540 505,820 556.327 iiii. 2780. 428.6 471-3 15 1,407,193 3,559-830 5II-.340 571,900 1181. 3020. 433.4 482.6 16 1,474,603 3,820,590 515,5.30 578,907 1243- 32.30. 4.36.5 488.8 17 1,536,670 4,091,400 520,910 579,770 1303- 3460. 440.6 486.6 18 1,604,540 4,318,780 523.000 .580.553 13.38. 3650. 444-7 490.3 19 1 ,660,893 4,599,500 525,890 580,763 1309. 3890. 445-7 490.6 20 1,705,853 4,867,910 527,520 581,400 1454- 4125. 447- 491. 21 1,735,267 5,076,100 529,160 581,877 1469. 4280. 448.5 491.4 22 1,773,463 5,290,770 530,560 582,280 1497- 4475- 449-7 491.8 23 1,805,327 5,462,560 533,000 582,770 1528. 4620. 450.9 492.1 24 1,827,127 5,573.480 1551. 4720. 25 1,840,520 5,679,360 1568. 4810. 26 1,858,510 5,796,630 1577- 4900. 27 1,861,673 5,909,860 1582. 5000. 28 1,862,980 6,018,140 1583- 5100. 29 1,863,450 6,118,320 1587.2 5180. 30 1,864,220 6,202,570 1587-7 5250. 31 1,864,533 6,259,910 1587.9 5300. 32 1,864,653 6,352,920 1588. 5350. 33 6,414,900 54.30. 34 6,427,500 5447- Table V. — Showing the relative amount of work done by the two classes of animals in revolving cages as indicated by the average number of revolutions and the average distance run at the different ages. i6 EFFECT OF DIET ON THE ALBINO RAT the omnivorous. This is seen by consulting Table V, which represents the averages of each sex of these two groups. From this I think one of two conclusions may be reached. Either the sudden reduction in the rich protein food of the omnivorous rats to almost a vegetarian diet (meat being given only two or three times a week) has had the effect of checking the activity of all alike, or a strictly vegetarian diet at this age is conducive to a slightly greater activity. If the latter is true it may be explained in this manner: The omnivorous rat had a satisfying diet; the vegetarians did not, and ran ^J2W •..Mte .^■^ ■ •000000 ^m'' /" /' / /' 4000000 / / / /' / / / / f / / / / f / ^ ^/"^ / / ^^ ^ TEP ::—- ^^^ , ,^ ^^''"' *«> ibiHomlu' ' i ► ■ • • ' 1 » ■ ' ' ■ i » • • • J ' « »••■■» »■■■■» Fig. 12. Curves showing the average total work and the rate it was done of each sex of exercised omnivorous and vegetarian feeders. The heavy solid line (OEM) represents the work of the omnivorous males, the heavy dotted line (OEF) the omnivorous females ; the light solid line (VEM) the vegetarian males, the light dotted line iVEF) the vegetarian females. RATIO OF TOTAL ACTIVITY 1 7 a great deal, apparently in search for what they desired. The behavior of the vegetarians strongly supports this supposition. When they were fed they ate ravenously, as if they had been starving. This was not so manifest in the omnivorous. It was true that both classes of exer- cised rats always appeared more hungry than the control rats of the same group. ( After the third month the general average of the vegetarians falls below that of the omnivorous. This is shown in the curves of Figure 12. Here we see that the omnivorous female rapidly surpasses the omni- vorous male in the amount of work done. The female vegetarian also excels the male of the same class in the distance run, but only to a small extent. The females are thus voluntarily more active than the males. We also note that the omnivorous male is much more active than either sex of the vegetarians. At the time of the death of the vegetarian rats (twenty-five months) the omnivorous female had voluntarily dome almost nine and one-half times as much work as the female vegetarian, and the omnivorous male almost three and one-half times as much as the male vegetarian. When the total amount of work voluntarily done by each class is considered, a still greater difference is observed. The omnivorous fe- male ran a total distance of 5447 miles, while the vegetarian female ran only 492.1 miles, or a ratio of about 11 : i. The omnivorous male ran 1588 miles, compared to 450.9 miles for the vegetarian male — a ratio of 3.5 : I. The average run for both sexes was, for the omnivorous rats 3517.5 miles, and for the vegetarians 471.5 miles, or a ratio of almost 7-5 : I- We thus see that when the initiative and ability to do work are considered, the result is decidedly in favor of the rats that had received animal food in their diet, and overwhelmingly against the vegetarians. The curves of Figure 12 show in a general way the rate at which the life's work was accomplished by each rat. But to show this more clearly Table VI has been constructed. The total average work for each sex in the two groups was arbitrarily divided into eight equal parts. Then the per cent of average lifetime required to do these fractional parts was computed ; also the average age in months equivalent to this per cent is given. For example, when the omnivorous male had done one-eighth of its total life's work it had lived 16.1% of its average life- time, and had reached the average age of 4.5 months. This table shows that the males of each group turn oflf their work at a relatively earlier age than the females on the same diet. As an illustration, when the omnivorous male had done one-half its life work it had lived 36.4% i8 EFFECT OF DIET ON THE ALBINO RAT of its life, while the omnivorous female had lived 41% of its life when it had accomplished a similar part of its total work. A similar rela- tion is seen to exist between the two sexes of the vegetarians. We also see that the same fractional part of total work is accomplished at an Fractional part of total amount of life's work Males (3) Female ( i ) Percentage of life re- quired to do work. . Age in months re- quired to do work . . Percentage of life re- quired to do work. . Age in months re- quired to do work. . C rt .2 Pi X Male (i). Females (3) Percentage of life re- quired to do work. . Age in months re- quired to do work. . Percentage of life re- quired to do work. . Age in months re- quired to do work. . Vs M Vs /2 Vs V4 I6.I 21.4 32.1 36.4 46.4 53-8 4-5 6. 9- 10.2 13- 15- 19.1 26.1 32.3 41. 48.8 53-8 6.5 8.9 II. I 13.8 16.6 19.9 10. 12.3 17.6 24.1 32.8 41.6 2-3 2.8 4- 5-5 7-5 9-5 15-9 22.5 31-9 42.5 49. 53-3 2.7 3-8 5-4 7.2 8.3 9.1 7/s 67.9 18. 72.6 24.7 II.8 66.1 II. 2 Table VI. — Comparison of omnivorous and doing their life's work. vegetarian rats as to the rate of earlier age in the males than in the females of the same class, with the exception of the last two items in the vegetarian group : here the male is very slightly surpassed by the female. This shows that the male ages earlier than the female. That is, when the male has begun to be inactive the female of the same age is still quite active. We further see that the vegetarians do the bulk of their work at an earlier age than the omnivorous rats. That is, they become old, decrepit, lack energy and a desire to be active at an earlier age than is true in the case of the omnivorous rats. This is true both as to per- centage of life lived and age in months. For example, when the omni- vorous rats had done seven-eighths of their total work the males had lived 67.9% of their life and the females 72.6%, the two sexes averag- ing 70%. In the case of the vegetarians the males had lived 51.7% and the females 66.1%, or an average for the two sexes of 59%. We thus see that the vegetarians had still an average of 41% of their lives to live, during which time they did only one-eighth of their work. The omnivorous had an average of 30% to live to do the remaining one- eighth of their total work. RATE OF PERFORMING ACTIVITY 19 We have already shown that the ratio of total average work done by the omnivorous rats as compared to that of the vegetarians was about as 7.5 : i. To make allowance for this, Table VII was construct- ed. This shows the percentage of lifetime of the omnivorous rats and their age in months which was required to do certain fractional parts of the total work of the vegetarians. That is, the two groups are con- sidered in respect to their ability to perform the same amount of work. The data of the vegetarians is therefore the same in this table as in Table VI. From this we see that the average ages in months of the two classes correspond rather closely until three-eighths of their work was done. After this the ages rapidly differ. When the vegetarian male died it was 22.8 months old. The omnivorous male had accom- plished the same amount of work when it was but 6.9 months old and had lived but 22.5% of its life. The female vegetarian died at the average age of 16.9 months. In contrast, the omnivorous female had done the same amount of work at the age of 5.6 months, which was equivalent to but 16.6% of its lifetime. Or the average total amount of work of both sexes of vegetarians was performed at the average age of 19.8 months, — that is, their average lifetime. Both sexes of the omnivorous feeders had done the same work at the average age of 6.2 months, which was but 20.9% of their lifetime. Fractional part of total amount of life's work 9.8 2.7 8.2 2.8 10. 2-3 15-9 2.7 13.8 3-8 10.5 3-6 12.3 2.8 22.5 3-8 Vs /. Vs 20.5 5-6 14.7 5- 41.6 9-5 53-3 9.1 Vs Vs Males (3) . . Percentage of life re- quired to do work. . Age in months re- quired to do work. . 14.6 4- 10.9 4- 17.6 4- 31-9 5-4 157 4-3 12.7 4-3 24.1 5-5 42.5 7.2 18.3 5- 13.6 4.6 32.8 7-5 49. 8.3 22.5 6.2 157 5-3 517 11.8 66.1 11.2 25.2 6.9 n X W Female (i). Percentage of life re- quired to do work. . Age in months re- quired to do work. . 16.6 5.6 Male (i)... Percentage of life re- quired to do work. . Age in months re- quired to do work. . 100. 22,8 t;.2 bo 28 5 i;? 9 285 29.2 2 !2; M ^7 288 30-5 2 !3C ) ic 7 285 31.2 2 531 le >3 285 32.2 2 Jii - 15 I 283 32.7 i5 ^5 271 33-3 1= 9 265 33-9 . 12 !8 262 34-9 . 264 35-3 . . . . 247 36.1 . 255 37-3 . . 248 37-8 244 38.6 . 237 39-2 234 40.2 231 40.8 220 41.4 218 44-5 212 454 207 T- . « T-V 01 . Table IX. — Showing the average growth of the two sexes in the groups indicated. The maximum average weight is shown in bold type. The weights are in grams. *This rat was killed because of sickness. DIFFERENCE IN GROWTH 23 Fig. 13. Curves representing the average growth of each sex of the four groups of rats. The omnivorous feeders are all shown in heavy lines and the vegetarians in light lines. Lines of the same character refer to the same sex of similar groups. OCM and VCM refer to omnivorous and vegetarian control males ; OCF and VCF represent omnivorous and vegetarian control females ; OEM and VEM, omnivorous and vegetarian exercised males; OEF and VEF, omnivorous and vegetarian exer- cised females. 24 EFFECT OF DIET ON THE ALBINO RAT A glance at Tables VIII and IX shows that, with the exception of the exercised vegetarian female, the exercised rats reach their maxi- mum weight at an older age than the control rats, regardless of the diet. In Table X these facts are in a more accessible form. It shows the individual weights and the age of each rat, and the average weights and ages of each sex in each group, at the beginning of the experiment, as the maximum weight, and at death. As already stated, the average weights of the young were about as uniform as could be gotten. When the maximum weights are considered a marked contrast is noted. In every case the average weight of each sex is decidedly in favor of the omnivorous rats. Considering the exercised rats in regard to the maximum weights and weights at death, we find the following ratios: MAXIMUM WT. AT DEATH Omnivorous male to vegetarian male 1.8 : i 2.2 : i Omnivorous females to vegetarian females 1.42 : i 1.36 : i In regard to the control rats the following ratios were found : MAXIMUM WT. AT DEATH Omnivorous male to vegetarian male 1.64 : i 1.9 : i Omnivorous female to vegetarian female . . i .22 : i -9 • i This last ratio is not reliable, as the control female had to be killed on account of sickness. There is no doubt had it been normal it would have reached a much heavier weight, since other omnivorous females did not reach their maximum weight until a much later age. In regard to growth, we must conclude that the data is decidedly in favor of the omnivorous rats and against the vegetarians. The appearance and attitude of the two groups is also in marked contrast. Figures 14, 15, 16 and 17 are photographs of eight of these rats, all being of the same age. Those on the left of each figure are omnivorous rats ; those on the right are vegetarians. Figure 14 repre- sents females. The other three figures are of males. These photographs show the marked difference in appearance and attitude referred to above. The vegetarians were emaciated and skinny. Their back arched and more or less stiffened. The fur was harsh and ruflfled, and the tail and nose inclined to be more or less covered with dry scale and sores. The attitude presented extreme lassitude and indifference. They remained in a crouched position most of the time, their legs appearing too weak to support their weight for only a short while. They lacked energy and would stay "put" when placed ready for photographing. Fio- 14 Photographs of omnivorous female (left) and vegetarian female (right) " at the age of i year 9 months 16 days. The omnivorous weighed 161 grams, the vegetarian 109 grams. Fio- 15 Photographs of omfiivorous male (left) and vegetarian male (right) at " the age of i year 9 months 16 days. The omnivorous weighed 250 grams, the vegetarian 134 grams. Fig. 16. Photographs of omnivorous male (left) and vegetarian male (right) at the age of i year 9 months 16 days. Fi.t Photographs of omnivorous male (left) and vegetarian male (right) at the age of i year 9 months 16 days. RATIO OF GROWTH 25 The omnivorous were the reverse in all these respects. They were strong, well nourished and supple. Their fur was soft and well kept. Tail and nose were clean and smooth. They appeared full of vim and energy, it being difficult to keep them quiet long enough to photograph. The photographs, though showing a great difference, fail to show the marked contrast one would see in a few minutes' observation of the two groups. Such an observation would demonstrate the great differ- ence in alertness and interest in surrounding objects, quickness and ease of movement in response to external stimuli, voluntary movement and vigor. The omnivorous appeared in the prime of life in all these respects, but in the case of the vegetarians these qualities were mani- fested as in extreme old age. Young At Maximum Weight At Death d ,fcc Q < bio > < > < E 5 _bc >. oi .s be < Male Av. Fem. Av. bO < Male Av. Fem. Av. _bf be 819 685 1222 _bfl Omnivorous Exercised Rats Vegetarian Exercised Rats Omnivorous Control Rats I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 M M F M M F F F M M F M F M M M 42 43 37 39 36 42 40 36 34 45 39 45 37 47 42 42 30 30 29 29 30 30 29 29 3C' 30 29 29 30 30 29 29 41 36 41 44 Z7 39 39 37 252 272 176 261 145 IIO 129 132 310 331 200 319 164 185 209 191 544 497 509 560 544 253 251 509 392 392 337 390 392 283 390 353 262 145 320 195 534 544 391 342 ^76 124 200 164 509 338 337 392 214 206 128 215 96 97 100 84 * 247 165 135 172 150 163 117 107 746 925 IOI4 785 685 381 463 682 1074 I361 36ot 1232 778 373 578 500 212 96 241 128 94 135 IOI4 ■508 360 Vegetarian Control Rats 129 ■484 150 778 Table X. — Showing the difference between the omnivorous and vegetarian rats in regard to the age and weight at the beginning of the experiment, the prime of life, and the death of each individual. * This weight was taken 14 days before death and is therefore heavier than it should be. fThis rat was killed because of sickness. 26 EFFECT OF DIET ON THE ALBINO RAT LENGTH OF LIFE. The various tables and curves so far given show in a general way the comparative length of life of these two groups of animals. A more detailed comparison will be necessary. In Table X the age of the death of each rat is given, also the average age of each sex comprising the various groups. When the same sex is compared it is noticed that the omnivorous feeders surpass the vegetarians in longevity by a good margin. The only exception was No. II, which should not be used in these comparisons as it was killed on account of sickness. When the averages are compared the contrast (>* ■ - «e /H V8 o» •*\r . ••{: ■ IMI 2 M 4 » • ra » K> " Hw II»» Fig. i8. Diagram representing the average age of each sex of the four groups. OE omnivorous exercised; VE, vegetarian exercised; OC, omnivorous controls; VC, vegetarian controls. M and F refer to male and female. is still more pronounced. These averages are put in diagramatic form in Figure i8. The horizontal lines represent the average age at death of each sex in the different divisions. OE, VE, OC and VC refer to omnivorous exercised, vegetarian exercised, omnivorous control, and the vegetarian rats, respectively. The relatively short duration of life of the vegetarians is very conspic- uous. If the average lifetime of all the omnivorous males is compared with the average of all the vegetarian males, we find a ratio of 1020 days to 534 days; or 1.91 : i. When the females are similarly com- O ; V Days aOO 400 600 800 lOOO 1200 Fig. 19. Diagram showing the average lifetime of all the omnivorous rats (O) and all the vegetarians (V). ♦This rat was killed at this age because of illness. LENGTH OF LIFE — APPLICATIONS 27 pared the omnivorous averaged 1014 days, and the vegetarian 574 days, or a ratio of 1.77 : i. If the average of all the omnivorous, including both sexes, is compared with the average of all vegetarian rats we have the relation of 1020 days to 555 days, or a ratio of 1.84 : i. Figure 19 shows in graphic form the total average lifetime of the omnivorous rats (O) and of the vegetarians (V). The first group lived almost twice as long as the last. This is a decided diflFerence. When we recall that all these animals were of the same age and as nearly as possible the same parentage, were subjected to similar envir- onment, and fed exactly the same food, with the exception that the omnivorous group received animal food in addition about three times a week, we must conclude that this great difference is due to the presence of this animal food and to nothing else. GENERAL APPLICATIONS AND COMPARISONS. Any attempt to make a practical application of these results to man, will no doubt be severely criticised by some on the ground that what is true of the albino rat would not hold true in man, owing to the wide difference in zoological position. Such a criticism would be based on the prevalent idea that man is a supreme being, occupying a place above animals, and with which he is not to be compared. The rat is by nature an omnivorous animal. All evidence points to the fact that man is by nature an omnivorous animal. The cftaracter 01 the teeth and the digestive tract throughout are best adapted to a mixed diet. His nearest related kin in the animal kingdom — the an- thropoid apes — are all omnivorous feeders. In his savage state he par- takes of the food most accessible, which includes animal food whenever it is possible to secure it. There is probably no animal as capable of adapting itself to so great changes in environment and in diet as man. But though he is able to adapt himself to a restricted diet, is such a diet capable of developing and maintaining his maximum mental and phy- sical energy for a long period of life? It is not a question of what food will keep the animal alive, but what diet will make it the most effi- cient machine. It is not so much a problem of determining what foods are necessary to maintain nitrogenous equilibrium in man, as it is of ascertaining what diet is necessary not only to prolong mental and physical efficiency during a long period of life, but to produce initiative in these respects. The rats fed on the mixed diet had by far the greater initiative and 28 EFFECT OF DIET ON THE ALBINO RAT ability for muscular work. The mental ability was not tested, but one would judge from their appearance and alertness that they would far surpass the vegetarians in this respect. A perusal of the literature of this subject convinces one of the fact that the results of the experiments on the rat can be applied to other animals, including man. Jaffa,® in his investigations on a family of fruitarians, says that the youngest child which had lived from infancy on nuts and fruit "was certainly undeveloped. Her bones were very small, although she had no tendency toward rhachitis. She looked fully two years younger than she was." The diet was not satisfying and the craving for other foods was occasionally satisfied by eating them. All the family were below size. Chittenden''^ fed dogs on vegetable foods and animal fat with dis- astrous result. In referring to this he says : " This is by no means an exceptional case, but we can cite many examples of like results where the animals when restricted to a purely vegetable diet, such as bread, pea-soup, bean-soup, etc., re-enforced by an animal fat, quickly passed from a condition of health into a state of utter wretchedness, with serious gastro-intestinal disturbance." Caspari,^ in studying the effect of a vegetarian diet on man, found that he could not maintain his body weight, but lost 13 K during the experiment. Milk and butter had to be added. In another person he found that he could maintain his weight on a vegetable diet. He was, however, very thin, and the amount of protein in the faeces was large. These experiments lasted for only a short time. Langworthy," in discussing food and diet in the United States, says : "In general, the food habits of the human race today are an expression of the thousands of years of experience in which man has sought to bring himself into harmony with his environment, and food habits have been determined, as regards materials selected, by avail- able supplies, man being by nature omnivorous." Man likes variety. People of the United States are well nourished compared with other races. He further says : "The acknowledged energy and achievements of the American people, together with their general good health and physical well-being, certainly indicate that we have in the main used our food resources advantageously." In regard to the digestibility of animal and vegetable foods, we find investigators pretty closely agreeing in their results. Albu,^" in metabolism experiments on a vegetarian, found that only ^Jjo of the protein and 65% of the fat of this food was digested. Snyder,^^ in GENERAL APPLICATIONS AND COMPARISONS 29 discussing the comparative digestibility of animal and vegetable pro- tein, says that 95% of the former and 85% of the latter are digested. Benedict,^- in comparing the digestibility of animal proteins and fats, found that 97% of animal protein is digested and 84% of vegetable protein. In a mixed diet he found that 92% of the protein was digested. In regard to fats he found that 95% of animal fat was absorbed and a less amount of vegetable fat. Many other investigators have found that vegetable protein is not used by the body to the same extent as animal protein.^^ ^* In regard to the effect of diet upon activity, Thompson, ^^ in his studies on dietetics, says : "Meat in general has a more stimulating effect upon the system and is more strengthening than vegetable food, and it gives rise to the sensations of energy and activity." A person^' who changed from a mixed diet to a vegetable one, in describing the effect says : " I, too, felt chilled and sleepy by day and night, so tired that I could hardly walk." This describes the general appearance of the vegetarian rats very closely. Nitti,^^ in accounting for the greater efficiency of the Italians in the United States than in Italy, attributes it to the fact that their diet here is richer in protein, containing a greater proportion of meat. In regard to the amount of protein required, most of the results again are in close accord. Caspari^^ concludes that the minimum amount of protein required varies with different individuals, and may also vary in the same individ- ual within wide limits. This is shown in the dietary study^^ of Sandow, the " Strong Man," who consumed 244 grams of protein each day. This is far above the average. Chittenden (7) has demonstrated that man can maintain his nitro- genous equilibrium on a diet containing far less protein than the average diet. He has not, however, carried this far enough to deter- mine what effect such a diet would have on the life of the individual or the race. Shutt-" found that in hogs fed on a low protein diet — corn only — the meat was inferior and soft. When additional protein was added in the form of milk, the meat was greatly improved. He also states that hogs fed on too high a protein diet had inferior meat. These results were confirmed by Skinner.'^ He adds that hogs fed on corn meal have " poor appetite, light bone, deficient development in valuable por- tions of the carcasses, and a general state of unthrift, as shown by the hair, skin, and hungry look of the animal." When one-sixth of the amount of normal ration rich in protein was added the hogs had normal growth and were in healthy condition. 30 EFFECT OF DIET ON THE ALBINO RAT Haecker^^ experimented on two groups of cows, the first group having a normal amout of protein and the second group a low amount. No difference was noticed at the end of the second year, except that the second group weighed less. Soon after this time the second group began to decline. They grew thin, hair became harsh, and their con- dition became generally poor, showing under-nutrition. The amount of protein had to be increased in order to preserve their lives. Here we see that this group did well for two years before any serious effects were manifested. A similar result was found in the rats experimented upon. The rats first showed a difference in weight. Later at the age of three or four months changes in the activity and general condition began to appear. One is not warranted, therefore, in drawing sweep- ing conclusions of the effects of certain diets on any animal from a few weeks' or months' experimentation. McCay^^ studied the effect of the native diet, low in nitrogen and rich in non-nitrogenous foods, on the physical condition, the health and the efficiency of the Bengalis, compared to European diet and Euro- peans in the University of Bengal. From the data of body weight, height and chest measurement of 2,500 Bengali students he concludes that the Bengalis "do not reach the same standard of general physique as is attained by races of European origin ; and yet from the evidence we can find no cause inherent in the Bengali as a race for this deficiency ; on the contrary, we consider that there may be a very close relationship between the lower physical development of this people and the meager protein contents of the diet on which they subsist." In comparing growth of the Bengali and European students he says : " The two classes enter college about the same age, live in the same climate and under very similar conditions . . . but the results at the end of their college career are very different. The European boys develop into strong, healthy men quite up to the average of European standards, while the Bengali students almost remain stationary as regards devel- opment." He finds that the Europeans are much more capable of en- durance. Watson and Hunter^ have shown that when young rats are fed on a diet of rice the growth is arrested and death results in two or three months. When fed on a porridge diet made by boiling together oatmeal, milk, water and salt the growth was arrested and death result- ed within four months. They were evidently not able to assimilate this food even though it was reasonably rich in protein. When fed a strict- ly flesh diet the results were disastrous in most cases when the rats were very young. When rats two or three months old were put on an GENERAL APPLICATIONS AND COMPARISONS 3I exclusively ox-flesh diet the result was favorable, growth being pro- moted, the anmials reaching a larger size than the normal control rats. In regard to races of men it is interesting to note that those whose stature is large partake freely of meat, while those of small physique live largely on a vegetable diet. Oshima^^ says in regard to the Japanese : "Among the ordinary families in the rural district the use of meat is (of necessity) restricted chiefly to festive occasions ; and among the poorer peasantry even rice is used at such times." He further says that the poorer classes of cities and country, comprising about 75% of the total population, are vegetarians from force of financial circumstances rather than from principle. They eat animal food whenever they can get it. This usually consists of fish two or three times a month, and meat two or three times a year. Boas-*^ found that the North American Indians living on the moun- tains are smaller than those living on the plains. He attributes this to greater abundance of rich food on the plains. Sill,^^ in his study of malnutrition of the school children in New York City, found that out of 210 cases, 83% practically depended on vegetable food, consisting largely of bread, tea and coffee. Albertoni and Rossi"^ found that when meat was added to the diet of the peasants of the Abruzzi region, who had been almost exclusively vegetarians for generations, there was an increase in power of assimi- lation, in body weight, and in physical power. Houssay,-" in his experiments on chickens fed exclusively on ani- mal and vegetable rations, found that the chickens fed on animal food grew much faster than those fed on vegetable rations. This corres- ponds closely to my experiments on the rats. These results correspond closely with those of Bolte.^° He fed chickens on a number of rations, and concludes : " In the absence of skim milk to mix with the grain, some other animal concentrate should be supplied. A ration containing 10% of animal meal gave a much greater gain than rations containing either no animal meal or 20% animal meal. The cost of feed per pound of gain was lessened one- third under the same condition. In regard to therapeutics, diet has a great value. Rubner,^^ in his studies on the diet of the poor who have lived largely or wholly on vegetables, concludes that this diet is the cause of lack of physical condition and ability for work; that it causes an in- crease in morbidity and mortality by lowering the ability to resist epi- demic diseases. In the treatment of tuberculosis it has been found^^ that food with a rich protein content is of great value. 32 EFFECT OF DIET ON THE ALBINO RAT McCay-^ finds that kidney disease is much more prevalent in native inhabitants of Bengal than in Europeans who live there. He attributes this to their diet, which is low in protein. Thompson/^ in regard to power of vegetarians to resist disease, says : " In regard to an exclusive or almost exclusive vegetable diet for man, the universal experience has been that while it may keep him in apparent health for some time, it eventually results in a loss of strength and general resisting power against disease, which becomes evident after some months, if not before .... Animal food in some form must be regarded as absolutely essential for all vigorous races." It is claimed that vegetarians convalesce more slowly after a period of illness.^^ That animal food makes blood richer in red corpuscles and gives firmness to muscle without excess of fat."* In 1883, when the diet consisted largely of rice, 33% of the Jap- anese marines had beri beri. In 1884 meat and bread were added to the rations, and now they hardly have three cases a year." When the effects of a restricted diet and of various diets upon the resistance of animals to certain poisons are considered, Hunt'* has found that " diet has a marked effect upon the resistance of animals to certain poisons; the resistance of some animals may be increased forty-fold by changes in diet. • Certain diets, notably dextrose, oatmeal, liver and kid- neys, greatly increase the resistance of mice to acetonitril ; their effect is similar in this respect to the adminsitration of thyroid. The experi- ments show that foods such as enter largely into the daily diet of man have most pronounced effects upon the resistance of animals to several poisons. They produce changes in metabolism which are not readily detectable by methods ordinarily used in metabolism studies. The ease and rapidity with which certain changes m function are caused by diet are in striking contrast with the essentially negative results obtained by the chemical analyses of animals fed upon different diets." Hutchison^^ claims that intellectual capacity and bodily energy are de- pendent on a mixed diet, and that " it is not without reason that the more energetic races of the world have been meat eaters." A study of the dietaries of the various races of the world con- firms this. Wherever we find advancement in civilization, great achieve- ments in the arts and sciences, maximum mental and physical ability, thrift and success, we find that animal food has formed a prominent portion of the diet. The numerous observations and experiments on man and other animals in regard to the effects of an exclusive vegetable diet, as com- GENERAL APPLICATIONS AND COMPARISONS 33 oar.d to a mixed diet, upon tlie general condition of the animal, all ag ee They show that the vegetable diet produces far -f-or results n almost every respect. Man does more work on a mixed diet than he did on a vegetable diet or almost exclusive vegetable diet. Man at ufns a griat'er stature on a mixed diet rich in protein than on veg - talk food Man has made more advancement and achieved more mtel- ectuaUy and physically on a mixed diet than on a vegetable one. He is abk to'mat'ain his 'body weight and physical well-bemg best on a ""Ihf results of the experiments on the albino rats correspond so closely with those on man and other animals that one is almost justified rconcluding that if man were subjected to the same conditions of food for h"s Ufetfme the results in regard to voluntary activity, growth and longevity would be the same. CONCLUSIONS. '^^t ThTom^c:o;s feeders are much more active -d voluntari^ do much more work during their lifetime than the vegetarians. The aver ''' f Thi ""Lpfs; the males of the same group in activity. This differenceTs greater in the omnivorous than in the vegetarian rats. '-^"'r C'tot:fwork"mplished by the vegetarians during their Ufe taJ perfo^ed by the omnivorous rats when but .0.9% of their ""^5'1hrv"eje::rian rats age much earlier in life, it r^^r^^^^ half thdr lifetime to perform the last one-eighth of their hfe s work, compared to three-tenths for the °"i"'™™f J^^^ ^^^^^j^,, The ra- \. The growth of the vegetarians w s gr a ly « -d^d^^^^^^^^^^ tio of maximum weights was as 1.62 .1 in tavor feeders. 34 EFFECT OF DIET ON THE ALBINO RAT 7. The effect on general conditions of the body was most over- whelmingly in favor of the omnivorous. The vegetarians were frail, weak, and showed extreme lassitude and indifference. The omnivorous were the reverse in all these respects. 8. The average life of the omnivorous was 1020 days, that of the vegetarian 555 days. This was a ratio of 1.84 : i. 9. The control rats in stationary cages lived longer than the exer- cised rats of the same group. 10. All of the omnivorous rats surpassed the greatest age attain- ed by the oldest vegetarian rats. 11. From numerous observations and experiments of other inves- tigators on man we would infer that similar results would obtain if he were subjected to similar conditions throughout his lifetime. REFERENCES. 1. Slonaker, J. R. : The Normal Activity of the White Rat at Different Ages. Jour. Comp. 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