Page:Popular Science Monthly Volume 66.djvu/161

Rh 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 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 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 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, somewhat 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 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