THE VITAMINES IN THE ANIMAL KINGDOM 113 



stance hitherto not utilized, it is necessary, by means of a specific 

 control, to test for the presence of vitamines. For an inorganic salt 

 mixture, that described by Osborne and Mendel, somewhat like the 

 inorganic salts of milk, or the one used by McCollum and Simmonds 

 is available. The mixtures have the following composition : 



Osborne and Mendel (314) McCollum and Simmonds (315) 



CaCO 3 134.8 NaCl 0.173 



Na 2 CO 3 34.2 NaH 2 PO 4 .H 2 O 0.347 



H 3 PO 4 103.2 K 2 HPO<. 0.954 



H 2 SO 4 9.2 CaH 4 (PO 4 ) 2 .H 2 O 0.540 



Citric acid H 2 O 111.1 Iron citrate 0. 118 



MgCO 3 24.2 Calcium lactate 1.390-1.300 



K 2 C0 3 141.3 MgSO 4 (anhydrous) 0. 266 



HC1 53.4 



Iron citrate 1.5H 2 O 6.34 



KI 0.02 



NaF 0.248 



K 2 A1 2 (SO 4 ) 2 0.0245 



The food mixture is best prepared so that it has more or less of a 

 pasty consistency, in which form it is least scattered by the rats. 

 As an example of a diet now thought to be complete, one having the 

 following composition is given : 



Substance Per cent Substance Percent 



Casein 22 Lard 20 



Cane sugar 10 Agar 3 



Starch 27 Salt mixture 3 



Butter 10 Yeast extract 6 



In older investigations, for example, in the work of Hopkins in 

 1912 (I.e. 70), or even in that of Funk and Macallum (I.e. 8.6), not 

 only was the amount of food consumed taken note of, but it was 

 estimated how much of the food intake was assimilated, by means 

 of calorimetric determinations of the food and of the excreta. In 

 the newer investigations, the tendency has been to get away from the 

 above time-consuming procedure, and to dispense with records of the 

 quantity of food ingested. The rat has become, so to speak, a 

 reagent for the testing of the value of the diet, and since many 

 thousands of experiments have been made in the last 10 years, the 

 investigators sought to simplify the experimental conditions as much 

 as possible. Nevertheless, the weighing of the food seems to us to 



