344 PHYSIOLOGICAL CHEMISTRY 



ism 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 stand- 

 ards 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 physio- 

 logically correct. 



Further, we need to know more concerning the relative decomposi- 

 tion within the body of the truly organized proteid matter of the tis- 

 sues, 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 Schondorff, 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. Schondorff drew the natural conclusion that the extent of pro- 

 teid 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 con- 

 tent 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 twofold 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 albumen, 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. 



