PROBLEMS OF PHYSIOLOGICAL CHEMISTRY. 159 



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 decomposi- 

 tion 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 com- 

 pletely 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 proteid metabolism was depend- 

 ent 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. 



