THE CHEMISTRY OF THE DIGESTIVE JUICES 373 



extract is at once active. The trypsinogen can therefore be activated 

 within the pancreatic cells, gradually when the pancreas is simply 

 allowed to stand after excision, more rapidly in presence of the dilute 

 acid. The ordinary tests for ferment action (destruction by boiling, 

 activity in very small amounts, etc.) have shown that this property 

 of the intestinal juice is due to a ferment, although it differs in 

 certain respects from most ferments -for instance, in requiring a 

 relatively high temperature to inactivate it. The smallest trace 

 of enterokinase will convert a large quantity of trypsinogen into 

 trypsin if time be given. At the same time, although to a much 

 smaller extent, the fat-splitting and starch-digesting activity of the 

 pancreatic juice is increased. The secretion of the duodenum causes 

 a greater increase in the proteolytic power than that of the other 

 portions of the small intestine, while no such difference has been 

 made out in the case of the amylolytic and lipolytic functions. It is 

 probable that the enterokinase, which is secreted mainly in the upper 

 two -sevenths of the small intestine, and solely by the intestinal 

 epithelium, acts only on the trypsinogen, and that the amylopsin 

 and steapsin are aided in some other way. Enterokinase is only 

 found in the intestinal juice when pancreatic juice is present in the 

 gut. It is therefore secreted in response to the presence of tryp- 

 sinogen or of some other constituent of the pancreatic juice. 



Delezenne has attempted to explain the interaction of enterokinase 

 and trypsinogen as an adaptive phenomenon of the same kind as the 

 formation of antitoxins and hsemolysins (p. 31). According to him, 

 enterokinase acts like a complement in haemolysis, while trypsinogen 

 plays the part of an intermediary body or amboceptor which enables 

 the enterokinase to attack the protein molecule. He asserts that 

 enterokinase, or a substance which produces a similar effect on tryp- 

 sinogen, is contained not only in the mucous membrane of the intestine, 

 but also in leucocytes, in fibrin (one of whose properties it is to pick 

 out ferments from liquids containing them), in lymph-glands, in snake 

 venom, and even in certain anaerobic bacteria. On this view trypsin 

 would not be a definite substance produced by the interaction of 

 enterokinase and trypsinogen, but only an expression for these two 

 bodies acting together. Strong evidence against this view, and in 

 favour of the independent existence of trypsin, haj been brought forward 

 by Bayliss and Starling, and it does not seem to merit further con- 

 sideration. According to Mellanby, enterokinase is really a proteolytic 

 ferment, and trypsinogen contains a protein moiety with which trypsin 

 is firmly combined. The conversion of trypsinogen into trypsin 

 depends on the digestion of this protein moiety, and the consequent 

 liberation of trypsin. Vernon has put forward the view that, while 

 enterokinase starts the activation of trypsinogen in the intestine,- and 

 can no doubt in time complete it, the .trypsin a.s it is formed aids in the 

 activation of more trypsinogen to trypsin, and so on by a process of 

 so-called auto-catalysis of the trypsinogen. This idea can be har- 

 monized with Mellanby's conception by assuming that the trypsin 

 formed from trypsinogen can itself digest the protein moiety of a further 

 portion of trypsinogen. 



