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 
‘jnhine 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 seemea 
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 
7 
