there were five variations of the diet and ten rats -for each 

 variation, then fifty rats were required. Six to eight litters of 

 from five to ten animals each would be needed to supply this 

 number of rats. Each litter was distributed over the five vari- 

 ations as far as it would go. For example, a litter of nine rats 

 would furnish two animals each for four variations and one 

 for the fifth. Then a litter of six rats would provide for one 

 rat where there were two before, and two rats where there was 

 one before, making a total of three rats for each variation of 

 the diet. The remaining thirty-five rats from the various lit- 

 ters were portioned out so that there were ten animals in each 

 lot, and in such a way that the total weight of the rats and the 

 number of males and females on each modification was prac- 

 tically the same. 



The experiments were continued for eight weeks, from 

 the begining of the fifth to the end of the twelfth week of the 

 rat's life, this being the most rapid growth period. A number 

 of experiments were continued for four weeks longer. These 

 last four weeks, however, did not show any significant differ- 

 ences which were not brought out in the growth curves from 

 the fourth through the twelfth week. 



When the milk, which was the source of vitamin B, was 

 fed separately from the rest of the diet, the animals were kept 

 in round galvanized iron wire cages, eight inches high and 

 nine inches in diameter, one rat in each cage. In addition to 

 the milk these rats received a vitamin B-free basal ration, of 

 which they ate ad libitum. In the experiments in which the 

 rats received the milk mixed with the rest of the diet, which 

 was always before them, six to eight animals were housed in 

 square iron wire cages 11" x 14" x 10". Fresh water was 

 always available. The cages were cleaned as often as seemed 

 necessary, the large cages usually every day and the small 

 round cages three times a week. Each animal was weighed 

 once a week and the food remaining weighed and subtracted 

 from the amount fed, the difference being the amount con- 

 sumed by the rat or rats during that week. 



Basal Ration and its Preparation. The basal ration used 

 was planned to contain all the essential food factors in optimum 



