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[N. S. Vol. XLVII. No. 1209 



reduced to 3.15 and .89 per pair respectively. 

 This is a ratio of about 3.6 to 1 in favor of 

 the omnivorous feeders. 



The greatest number of young bom by a 

 single pair is 41 in the omnivorous group and 

 23 in the vegetarian group. The average 

 number of young for each mating is 15 for the 

 omnivorous feeders and 4 for the vegetarian. 



The number of young eaten by the parents 

 is 19.5 per cent, in the omnivorous group and 

 35.8 per cent, in the vegetarian. 



The ratio of sexes in the two groups is 113.6 

 males to 100 females in the omnivorous young 

 and 10Y.6 males to 100 females in the v^e- 

 tarian young. 



The average weight (both sexes) of the 

 omnivorous young at birth is 4.59 grams and 

 the vegetarian young is 4 grams. A much 

 heavier weight is maintained by both sexes 

 of the omnivorous rats throughout their lives 

 as shown in the curves of growth. This is 

 shown in the following table. The retarda- 

 tion of growth of the new bom vegetarians 

 appears to be due to the decreased lactation of 

 the mothers. 



was born was 169 days for the omnivorous 

 and 223 days for the vegetarian rats. 



The oldest age at which a litter was born in 

 the omnivorous group was 570 days and in 

 the vegetarian, 600 days. The average ages 

 were 330 and 334 days respectively. The 

 average duration of the period of reproductive 

 activity in the omnivorous group is thus 161 

 days and in the vegetarian group 111 days. 

 The restricted diet thus appears not only to 

 delay the period of reproductive activity, as 

 other writers have found, but also to actually 

 shorten the duration of this i)eriod. 



Matings were made to test which sex was 

 the cause of the failure to reproduce. Vege- 

 tarian pairs, when they ceased to reproduce, 

 were separated. New healthy omnivorous 

 males were mated to the vegetarian females 

 and new healthy omnivorous females were 

 mated to the vegetarian males. All these new 

 matings failed to reproduce. The conclusion 

 drawn is that a vegetarian diet produces 

 sterility in both sexes. 



It has been impossible to determine the 

 effect of a continued vegetarian diet on the 



The difference in appearance of the two 

 groups is very marked. The vegetarians are 

 smaller, have less vigor, are less active, have 

 rougher hair and a tendency to sore eyes, 

 while the omnivorous are the reverse in these 

 respects. 



The earliest ages at which the first litter 

 was thrown is 90 days for the omnivorous and 

 119 days for the vegetarian group. Since the 

 period of gestation is 21 days the age of sexual 

 maturity in each of these cases was 59 and 

 98 days respectively. 



The average age at which the first litter 



race, as only two or three successive genera- 

 tions have been reared on this diet before the 

 line of descent became extinct. We must 

 therefore conclude that a vegetarian diet not 

 only reduces the vitality, the growth, and the 

 ability to reproduce, but tends to the ex- 

 termination of the race. 



We are expecting to have the complete 

 paper ready for publication in the near future. 



J. R. Slonaker, 

 T. A. Card 

 Department of Physiology, 

 Stanford University, Calif. 



