42 BIOLOGICAL PROBLEMS 



ing experiments with monkeys and very careful clini- 

 cal observations on human beings should make all 

 clear when the preliminary work on lower animals 

 has been done. Sufficient work in certain directions 

 has been carried out to justify many practical con- 

 clusions. 



With the beriberi vitamine the experimental animal 

 chiefly used has been the pigeon, an animal suffi- 

 ciently far removed from the human subject to make 

 the identification of symptoms somewhat difficult; but 

 most close observers are' convinced that the poly- 

 neuritis of pigeons, first produced by Eykman, both 

 from the similarity of its symptoms and the identity 

 of its method of production, is the same as the beri- 

 beri of man. 



The experimental work on the scurvy vitamine was 

 begun by Hoist and his colleagues in Norway, work- 

 ing with guinea-pigs; the identity of the disease 

 produced with human scurvy has likewise been 

 questioned, but is likewise accepted by the closest 

 observers. Scurvy, indistinguishable from human 

 scurvy, has been produced in monkeys by the same 

 methods which produce scurvy in guinea-pigs. 



The work on the growth factors has been carried 

 out chiefly by McCollum and his co-workers and by 

 Osborne and Mendel in America, following Hopkins 

 in Cambridge, and the experimental animal used has 

 been the rat. Of these growth factors, as has already 

 been said, the water-soluble B seems to correspond 

 with the anti-beriberi vitamine, while it is not un- 

 likely that the fat-soluble A may prove to agree in 

 distribution with the hypothetical substance which 

 prevents rickets. It is further interesting to note that 

 rickets is a disease of growth. The experimental 

 work on rickets is only in its infancy, and has been 

 conducted with yet another experimental animal the 



