heated dry was fed in two ways: (1) mixed with the rest of 

 the diet, replacing 25 per cent, of the starch in diet 94. This 

 ration was always available and the rats ate ad libitum. (2) In 

 another series of experiments the milk, which was heated dry, 

 was reconstructed before feeding by making 25 grams up to a 

 volume of 250 cc. with water. This was fed in doses of 8 cc. 

 per rat per day. The advantage here is that all the rats re- 

 ceived exactly the same amount of vitamin per day. Positive 

 controls, animals receiving in the one case the diet containing 

 25 per cent, of unheated milk and in the other case 8 cc. per 

 day of the reconstructed unheated milk, were run in every case 

 in comparison with the rats receiving the heated food. Nega- 

 tive controls, receiving only the vitamin-free diet were run in 

 almost all but not every experiment. This was done in order 

 to make sure that the basal diet did not vary. 



THE ADEQUACY OF THE BASAL DIET 



In order to prove that the basal ration contained the 

 optimum amounts of the various constituents, it was fed 

 to a series of rats in comparison with diets in which 

 each ingredient of the basal ration, the casein, butter 

 fat and salt mixture, were in turn used in larger amounts. 

 It was thought that perhaps another protein such as ex- 

 tracted meat might prove to be a more adequate protein, 

 or the meat might be more palatable and that therefore the 

 rats would eat more of the basal ration. Consequently diet 94 

 was also compared with a diet in which extracted meat residue 

 replaced the casein. Commercial extracted meat residue was 

 purified according to the method described for casein (page 7). 



TABLE I. 

 The following diets were used in the comparison : 



Diet 94 102 103 105 104 



% % % % % 



Casein 18 18 -23 18 18* 



Butter fat 10 15 10 10 10 



Starch 68 63 63 67 68 



vSalt mixture (O. &M.) 40 .... 44454 

 * Meat residue. 



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