342 PHYSIOLOGICAL CHEMISTRY 



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

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

 struct new proteid matter out of these simple decomposition-products, 

 then surely we must inquire what is the real purpose of their forma- 

 tion. 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 peptone stage, since the latter bodies would seem to 

 be most easily adaptable for transformation into the proteids of blood 

 lymph and tissue. On the other hand', it is well known that the pro- 

 teid 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 con- 

 sideration and thorough investigation, 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 

 decomposition-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 con- 

 .tact with the different cells of the body prior to their decomposition 

 or elimination, we cannot 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 ex- 

 erted by their components. Where can be found a more active phy- 

 siological agent than the blood-pressure-raising constituent of the 



