160 BIO-CHEMICAL JOURNAL 



(iii) It is independent of the state of nutrition, and is the 



same in the fasting as in the fed animal. 



(iv) There is a certain amount of evidence that the bodies 

 represented by the residual nitrogen are in a state of 

 loose chemical combination with the bioplasm. 

 With these facts to guide us, the following explanation of the 

 mechanism does not seem unreasonable : 



The bodies represented by the residual nitrogen may be regarded 

 as in the same kind of chemical combination, such as exists between an 

 enzyme and its substrate (or, perhaps, between a toxin and antitoxin) ; 

 that in this state they undergo certain chemical changes like hydrolysis 

 or oxidation, such as would take place through the action of an 

 enzyme ; the products of the change would be eliminated and carried 

 in the blood-stream to other parts of the organism ; after chemical 

 change and elimination they would be replaced by other similar side 

 chains, which would, in their turn, undergo the same kind of changes. 

 The more rapid the blood-stream through the organ, the more rapid 

 will the changes be. 



According to this conception, then, the passage of the products 

 of tryptic digestion through the mucous membrane is 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 keeps, furthermore, always saturated with side-chains, as 

 is shown by the fu.t that the residual nitrogen is the same during 

 digestion as during a fast. 



The theory is analogous to that suggested by Verworn 1 to account 

 for the utilisation of carbohydrates. 



The question now arises : how does the bioplasm maintain its 

 saturation with the side-chains in the absence of ingested food-stuffs ? 

 To obtain an answer to this question, reference must be made to 

 the researches on autolysis and on the products of metabolism carried 

 from the digestive tract to the portal vein. The following sets of facts 

 are kjiown : 



(i) The autolytic enzyme acts more rapidly in the liver of a 

 fasting animal than in that of an animal during active 

 digestion. 



