42 THE VITAMINES 



the advantage that the source of material (unpolished rice) was the 

 same in the comparison of both characteristics. We shall comment 

 upon the questions referred to, particularly the vitamines, in greater 

 detail, but at this point we wish to emphasize that the functions of 

 growth and the curative action on beriberi were tested on two dif- 

 ferent animals, the pigeon and the rat. Heated unpolished rice still 

 retained its growth promoting property, although to a somewhat 

 lesser degree, while its influence on pigeon beriberi was completely 

 destroyed. We can find many explanations for this behavior without 

 necessarily accepting the existence of two vitamines of the same type. 

 Above all, we do not know just what are the vitamine requirements 

 of these types of animals. We shall see furthermore that all the 

 known facts point to the idea that, although it shall have been demon- 

 strated that both substances differ from each other, they would 

 still be related chemically. In this connection, it might be shown 

 that various types of animals can utilize the different stages of vita- 

 mine cleavage with varying degrees of success. This could proceed, on 

 the one hand, through a difference in synthetic abilities and, on the 

 other, through certain specific symbiotic intestinal flora. 



A similar question is brought up in reference to vitamine A (anti- 

 rachitic vitamine). Mellanby (95) holds the view, that in the 

 etiology of rickets, that vitamine which according to our nomen- 

 clature must be called antirachitic vitamine (vitamine A) is of 

 importance. It is found in fats such as butter, egg-yolk, and cod 

 liver oil. Whereas Mellanby worked with young dogs, Hess (96), 

 working with rachitic children, found that milk fat had no effect, 

 while cod liver oil was found to be beneficial. From this, Hess drew 

 the conclusion that the growth-promoting vitamine found in butter 

 was different from the antirachitic vitamine. Here also, both sub- 

 stances belong to the same type, and we must bear in mind the main 

 question whether the vitamines, like other natural substances, do 

 not also deviate from each other somewhat chemically, in spite of the 

 possibility that they play the same or very nearly the same role in 

 physiology. 



Much more important and interesting are the experiments which 

 deal with the part played by milk and milk products. We are 

 sometimes almost tempted to assume that milk, aside from the vita- 

 mines already mentioned, contains still other essential substances. 

 This applies not only to milk, but also to products made from milk, 



