Page:Popular Science Monthly Volume 66.djvu/163

Rh necessary for the maintenance of health and strength are crude and inexact. We place the nitrogen requirement of the healthy man at an absurdly high level, apparently because observation has shown that man is disposed to consume an equivalent in proteid food per day. We need to ascertain by scientific experiment how far such standards are justified; to determine by definite analysis the amounts of nitrogen actually required to maintain nitrogen equilibrium and keep up bodily and mental vigor. Upon the physiological chemist of the present day rests the responsibility for the establishment of nutritive standards that will endure the test of scientific criticism, that will harmonize with daily experience, and that will prove to be physiologically correct.

Further, we need to know more concerning the relative decomposition within the body of the truly organized proteid matter of the tissues, and of the albuminous food-stuffs which, having been digested and absorbed, are in a sense a part of the tissues, but not thoroughly or completely incorporated as an integral part of the living cells. Does the urea of the daily excretion come primarily from the breaking down of the organized proteid, or does it come preferably from the disintegration of the circulating proteid? We recall the famous experiments of Schöndorff, in which blood was made to circulate through the muscles and liver of well-nourished and fasting dogs, with the result that the urea of the blood was increased only when the blood circulated through the tissues of a well-nourished animal. It made no difference with the result whether the blood employed was from a well-fed or a fasting animal; the essential factor was the condition of the muscle tissue through which the blood was made to flow. Schöndorff drew the natural conclusion that the extent of proteid metabolism was dependent upon the nutritive condition of the cells of the tissue, upon the mass of the living cell material, i. e., upon the amount of morphotic proteid present, and that the proteid content of the intermediary fluids, as blood or lymph, was of no moment in determining the rate of urea formation.

We may well doubt, however, if all the urea formed daily under ordinary conditions of life comes solely from the breaking down of the truly organized or morphotic proteid. It is more than probable that the urea has at least a two-fold origin, and, if so, it is an important matter to be able to discriminate between that which comes from the breaking down of the unorganized albumin, and that which is derived from the organized tissues. Unquestionably, the decomposition of organized proteid, the morphotic part of the living protoplasm, is quite different from that of the unorganized pabulum of the cell and surrounding media. Quite possibly, the influences controlling the two lines of metabolism are different; perhaps, there are even different kinds of nerve control.