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 young 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: 



