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Page:Popular Science Monthly Volume 72.djvu/396

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different in character from that implied by the hypothetical transformation of absorbed proteoses and peptone in the mucous membrane of the intestine. Further, there is suggested a far-reaching application of this synthetical power in the construction of tissue protein throughout the body.

Let us grant that in the intestinal walls or elsewhere the serum albumin and globulin of the blood are constructed de novo from the many simple fragments split off during the processes of digestion, what then is the origin of the many different forms of protein, nucleoprotein, etc., which characterize the various tissues and organs of the animal body? Do these result from simple transformation of the blood proteins which, as we are wont to say, nourish the active cells of the body and serve as pabulum for the hungry tissues?

No account has been commonly taken of the fact that these proteins of the blood must be taken to pieces and again put together, rearranged on a different plan, if they are to serve for the making of proteins and nucleoproteins in the cells of the muscles and other organs in which the destructive changes of life are felt. The proteins circulating in the blood are a currency which is not legal tender. And no account has been commonly taken of the familiar fact that when no food is obtainable, certain organs maintain for themselves a normal composition at the expense of the substance of other organs. When the spleen, liver, or the muscles of the limbs dissolve away in starvation, the heart feeds on what they supply. Are the proteins of these organs converted into serum albumin and globulin, or are they melted down by autolytic processes into the same cleavage products as are formed in the digestion of food, and in this form thrown into the circulating blood, which is thus in a position to supply the heart and diaphragm with just what they are accustomed to receive in the blood from the digestive organs? (Leathes.)

In attempting to answer this question, I need only call to your attention the many data collected during the past few years concerning autolysis in general; in which it has been found that practically all the organs of the body are capable under suitable conditions of undergoing auto-digestion, with formation of essentially the same cleavage products as result from the breaking down of proteins in the gastro-intestinal tract. Further, the ferments or enzymes that are responsible for these autolytic transformations have been in some measure isolated and separated from each other. When these facts were first brought to light, it was assumed that the changes in question were mainly at least the result of post-mortem conditions, but there is no justification for such an assumption. Intracellular enzymes are a part of the natural equipment of living cells, and metabolic events, nutritional changes, such as characterize the life and activity of tissues and organs in general, are undoubtedly due to the power of these agents, normally controlled, however, by a variety of conditions that must tend to balance conflicting interests. We can well imagine that in the life and death of tissue cells autolytic decompositions are constantly taking