352 Vitamines and Deficiency Diseases [June-September 



can be at best only very slight, since human tumors are very 

 chronic. In f owls the whole blood was drawn and analyzed ; and, 

 as the duration of the disease is only a few weeks, very much 

 more marked changes would be expected for fowl tumors than for 

 tumors of human origin. 



XIII. CONCLUDING GENERAL CONSIDERATIONS 



We see, from the present review, that the estabHshment of the 

 existence of a new group of important substances, the vitamines, 

 has stimulated a great deal of work in this connection. As the 

 numerous papers are scattered among many different Journals, only 

 a certain amount of the available data could be reviev^^ed. 



I have been severely criticized along two lines. In the first 

 place objection has been taken to the fact that a name was given to 

 these substances before they were isolated in a pure chemical con- 

 dition. To this objection I answer that, besides the fact that we 

 already know something about the vitamines from the chemical 

 point of view, it has always been customary in physiological chem- 

 istry to give names to substances which exercise definite chemical 

 influences, whether their chemical Constitution is understood or not. 

 Ferments, hormones and products of internal secretion, are among 

 "substances" the chemical nature of which has not as yet been 

 ascertained. As a matter of fact three-fourths of biological chem- 

 istry deals with this kind of " substances." As I use the term 

 " vitamines," it indicates merely a group of chemical substances 

 which possess every analogy to the already well-known class of 

 nitrogenous bases, the members of which are precipitated by phos- 

 photungstic acid or similar reagents, and which are thrown down, 

 in the mercuric chloride fraction, and by silver nitrate and baryta. 

 So far no other reagents have proved of any value for their Iso- 

 lation. Detailed knowledge of vitamines is now only a question of 

 time and improved methods. 



A second important objection to my views in this connection is 

 the fact that many diseases have been included amongst the " avi- 

 taminoses," for which there may be other etiologies than deficiency 

 of vitamines in the diet. There may be other etiologies for some 

 of these diseases, it is true, but as the followers of other ideas have 



