76 



THE AMERICAN NATURALIST [Vol. LV 



the waste was easily separated from the feces and account taken, 

 of the amount. 



Sixteen mice were fed ten days on a complete diet and then 

 nine days on a diet free of vitamines and then transferred to 

 diet 401 (unlimited amount) . After one day on the later intake 

 records were begun.^ Of the 16 mice started two grew nearly 

 normally on 1 per cent, yeast/" one became sick and died, an- 

 other declined \'«ry rapidly. These four were not considered 

 in the experiment. The records of the remaining twelve are 

 shown in the table. They were of varying size and represented 

 somewhat different ages so that the results can hardly be ac- 

 counted for by the action of the normal intermittent growth 



Per Cent, Ysi 



;t), UN 



For 150 mouse days 12 mice ate an average of 1.628 grs. per 

 mouse per day and lost 2.93 grs. or 1.74 per cent. For mainte- 

 nance, then, they needed slightly more than 1.628 grs. average 

 per day. 



Figured from Period No. 1 the mice in the 187 mouse days 

 should have required a little more than 187 X 1.628 grs. and 

 gained 14.36 grs. or 8.68 per cent. 



10 In general mice require 5 per cent, of yeast in the diet for normal 



cent, require less. The individual variation for rats is, in our experience, 

 considerable though not as great as for mice. The average requirement, 



