PROBLEMS OF PHYSIOLOGICAL CHEMISTRY. 157 



pounds of simple constitution formed in the gastro-intestinal tract by 

 the digestive enzymes ; if there is a complete lack of ability to construct 

 new proteid matter out of these simple decomposition products, then 

 surely we must inquire what is the real purpose of their formation ? It 

 is true that, with the limitations of our present knowledge, it is difficult 

 to see why if digestive proteolysis has for its sole object the conversion 

 of the proteid foods into forms suitable for absorption there should be 

 any considerable breaking down of proteid beyond the proteose or pep- 

 tone stage, since the latter bodies would seem to be most easily adapt- 

 able for transformation into the proteids of blood, lymph and tissue. 

 On the other hand, it is well known that the proteid of the food is 

 possessed of a physiological and chemical nature quite different from 

 that of the proteid in the blood and tissues of the feeding animal, and 

 it is quite conceivable that a synthetical process might be essential — in 

 some degree — for the manufacture of the specific proteids called for by 

 the blood and tissues of that particular species or individual. The 

 question is one that demands careful consideration and thorough in- 

 vestigation, for it touches upon a chapter in nutrition on which we have 

 at present very little satisfactory or convincing knowledge. 



In this connection we may call attention to another problem, some- 

 what far reaching, but suggested by one of the preceding paragraphs, 

 viz., the possible physiological action of the many katabolites, or decom- 

 position products resulting from tissue changes throughout the animal 

 body. In vegetable tissues, many of the nitrogenous products common 

 to these structures are endowed with marked physiological power, as 

 witness the vegetable alkaloids and the non-nitrogenous bodies like 

 salicin, digitalin, picrotoxin, etc. Years ago, physiologists recognized 

 that some of these nitrogenous bodies present in animal tissues did have 

 a distinctly toxic action when introduced directly into the circulation, 

 and hence they were frequently called animal alkaloids, but our 

 knowledge upon these points is exceedingly obscure and indefinite. 

 When we take into consideration the large number of nitrogenous 

 products formed and present in the various tissues and organs of the 

 body, products of proteolysis and of tissue changes; when we consider 

 how these products circulate through the organism, in blood and lymph ; 

 how they come in more or less immediate contact with the different 

 cells of the body prior to their decomposition or elimination, we can 

 not avoid being impressed with the part they may play in stimulating 

 and modifying tissue or other changes. 



The significance of this suggestion is made all the more potent by 

 the knowledge recently acquired concerning several of the internal 

 secretions of the body and the powerful physiological influence exerted 

 by their components. Where can be found a more active physiological 

 agent than the blood-pressure raising constituent of the adrenals, the 



