THE VITAMINES IN THE ANIMAL KINGDOM 127 



results, and Rohmann regarded this diet as adequate only for grown 

 animals. Meat extract and dried meat powder had no particularly 

 favorable effect; egg-yolk on the contrary, was favorable but not 

 sufficient for growth, while egg-fat was not well tolerated, even in 

 older animals. In a second series of experiments, the food was 

 supplemented with yeast and baked, with the addition of egg-yolk. 

 The results were veiy good and were attributed to the yeast ; lecithin 

 was shown to be unnecessary. It may be seen that Rohmann's 

 findings coincide with those on rats. Wheeler (356) carried out some 

 experiments with mice, planned in accord with the first experiments 

 of Osborne and Mendel on rats. Here, too, protein-free milk was 

 used, and found insufficient as the sole source of vitamine; artificial 

 protein-free milk proved to be entirely inadequate. It seems that 

 mice need more protein than do rats in order to grow; yet the former 

 grow more rapidly after the addition of a milk preparation than do 

 the latter. MacArthur and Luckett (357) investigated the influence 

 of lecithin, kephalin, cerebrosides and cholesterol as additions to an 

 artificially prepared diet, and came to the conclusion that these 

 substances are superfluous. Furthermore, they studied the influence 

 of egg-yolk and found that the necessary substances (apparently 

 vitamines, as they remarked at the time) are insoluble in ether, 

 soluble in cold alcohol and thermo-stable. Butter and olive oil were 

 inactive, without any other additions. Mitchell and Nelson (358) 

 found that mice do not grow on an artificial diet till protein-free milk 

 was added. From the foregoing, it is evident that mice behave like 

 rats in their vitamine requirements. 



Guinea pigs 



Next to the pigeon and the rat, the guinea pig is one of the most 

 widely used animals for the purpose of vitamine research, especially 

 in the investigation of scurvy. It has been shown unsuited for other 

 avitaminoses, though there are no lack of investigators who propose 

 the use of the guinea pig for the study of pellagra and rickets, despite 

 its demonstrated unsuitability. This animal is likewise little used 

 for beriberi research although Schaumann (I.e. 2) reported, out of 

 65 guinea pigs fed on dry grain, two typical cases of beriberi, with 

 subsequent histological demonstrations of multiple neuritis. These 

 results have never been confirmed. On the whole, it is not easy 

 to conduct planned feeding experiments with these animals, and 



