METABOLISM 



585 



(b) Demonstration on Fat-Soluble A. In this experiment two white rats 

 may be used as subjects. Feed them a diet similar to the one given on p. 583, 

 and after normal growth has been demonstrated (two weeks) replace the butter 



FIG. 172. RAT (No. 14) FED A DIET CONTAINING SUFFICIENT WATER-SOLUBLE "B." 



COMPARE FIG. 173. 

 (Hawk, Smith, and Bergeim: American Journal of Physiology, 56, 33, 1921.) 



by lard, leaving the diet unchanged in all other respects. The diet now contains 

 little or no "Fat-Soluble A," and the rats will consequently fail to grow. An 

 interval of two weeks is long enough to demonstrate this point. See Figs. 175 

 and 176. 



FIG. 173. RAT (No. 4) FED A DIET DEFICIENT IN WATER-SOLUBLE '"B." 



COMPARE FIG. 172. 

 (Hawk, Smith, and Bergeim: American Journal of Physiology, 56, 33, 1921.) 



(c) Demonstration on "Water-Soluble C." Feed two guinea-pigs, weighing 

 about 250 to 300 grams each, a diet of rolled oats, hay which has been heated 

 at 105 C. for several hours, and water. In addition to the above give each 



