as the author’s experience, shows that the pigeon method for 
studying the vitamin B content of food, by the power of the 
substance to prevent or cure polyneuritis, yields rather irregu- 
lar results + 2% 8 8 The method of testing for vitamin B 
by measuring the acceleration of yeast growth is open to the 
question whether the culture medium is adequate in all other 
respects and whether it is safe to assume that increased yeast 
is attributable entirely to the vitamin ?**°, The nutrition re- 
quirements and rate of growth of the rat have been exten- 
sively studied by Hopkins + * 36, Osborne and Mendel **, 
McCollum &?" and others. The rat method is therefore the 
best standardized by previous work. Dr. Harriet Edge- 
worth *’, working in this laboratory, after a careful analysis 
of the yeast and rat growth methods concluded: “The rat 
growth method involves somewhat larger probable errors than 
the yeast method, but can be interpreted in terms of B vitamin 
with much greater certainty and is therefore the preferable 
method.” Skimmed milk in the form of dry powder was 
chosen as the source of vitamin B, since it furnishes the vita- 
min in a typical natural state, readily available and uniform. 
It is easily and accurately manipulated in either large or small 
quantities and is convenient for study in either the fluid or 
dry state. 
EXPERIMENTAL PROCEDURE 
Selection and Care of Animals. The rats used were twenty- 
eight or twenty-nine days old, this being the time of weaning 
adopted in this laboratory, and weighed from thirty to sixty- 
five grams when placed on the experimental diet. The experi- 
mental animals all came from mothers on a diet of two-thirds 
whole wheat, one-third whole milk and sodium. chloride, two 
per cent. of the weight of the wheat (diet 13) or this diet with 
an addition of ten grams of raw lean beef per adult rat per 
day (diet 13M). In each experiment, however, care was 
taken, that equal numbers of comparison and control rats 
came from mothers on the same diet. The lots were made up 
in the following manner. If, for example, in one experiment 
6 
