INTRODUCTION 13 



outside this use in pathological conditions, ammonia would appear 

 to have an important function in the ordinary nutrition of the 

 body. Recent investigations by Schryver have opened up a 

 very interesting line of research, and if his results hold good, they 

 would tend to raise the status of ammonia from its present 

 position, as a mere by-product of little or no importance, to that 

 of one of the most important units in the physiological processes 

 of nutrition. 



By means of carefully carried out experiments, he has shown 

 there is no evidence that the products of tryptic digestion as 

 such can circulate in indefinite quantities in the blood-stream, 

 and that there are no such bodies present in the liver. What, 

 then, is their fate after leaving the alimentary tract ? Schryver 

 finds that the difference between the total nitrogen and the 

 nitrogen of coagulable albumin is very high in the mucous mem- 

 brane of the small intestine, a tissue most intimately connected 

 with nitrogenous metabolism. This difference is higher in the 

 carnivora than in the herbivora ; it is independent of the state 

 of nutrition, and is the same in fasting as in the fed animal ; and, 

 lastly, that the bodies represented by this nitrogen are in a state 

 of loose chemical combination with the bioplasm, such as exists 

 between an enzyme and its substrate. In this state they undergo 

 certain chemical changes like hydrolysis or oxidation ; the 

 products of the change would be eliminated and carried in the 

 blood-stream to other parts of the organism, their place being 

 taken by similar bodies, the product of tryptic digestion, which 

 in their turn would undergo a similar series of changes. 



The passage of the products of tryptic digestion through the 

 mucous membrane of the intestines would therefore be analogous 

 to a continuous chemical process. The bioplasm acts as an 

 enzyme or collection of enzymes, to specific points of which 

 side-chains are anchored ; it always keeps saturated with side- 

 chains, as is shown by the fact that the residual nitrogen is the 

 same during digestion as during a fast. 



That this saturation of the bioplasm is automatically main- 

 tained, the following considerations would make probable : 



Autolysis occurs more rapidly in the liver of a fasting animal 

 than in that of an animal during active digestion ; it is inhibited 

 by the action of ammonia and other alkalis, but accelerated by 

 the presence of acids, especially lactic acid. The acceleration 

 due to acids is a function of the absolute quantity of acid present, 



