446 CURDLING FERMENTS. DESTRUCTION OF PEPSIN. [BOOK II. 



complex sugar into the simpler monosaccharides. The salivary and 

 pancreatic diastatic enzymes perform, in respect to the starches and 

 dextrins, a function of which the complement is performed chiefly 

 by the maltose-converting enzyme of the intestinal wall and, in a less 

 degree, by the lactic acid producing organisms which find a suitable 

 habitat in the small intestine. 



In reference to the digestion of fats, the pancreas seems to play 

 a part accessory, though perhaps subordinate, to that which the bile 

 discharges. By the fractional decomposition of the neutral fats which 

 it exerts, in virtue of its fat-splitting ferment, it establishes the con- 

 ditions which are favourable to the formation of a true emulsion by 

 the bile. 



Amongst the enzymes of the intestinal canal, curdling ferments 

 must not be forgotten. The mucous membrane of the small in- 

 testine, throughout its course, appears to form such a ferment, which 

 is, in all probability, also present in the pancreatic juice, although 

 so far as the Author is aware, no direct experimental evidence of the 

 fact exists. Roberts, Harris and Gow, and others, have drawn 

 attention to the fact that all extracts of the pancreas curdle milk, and 

 seem to assume that we may logically conclude that the pancreatic 

 juice exerts a similar action. But that the inference is not absolutely 

 justified results from the fact that, although the mucous membrane 

 of the stomach of all adult animals yields, on suitable treatment, 

 extracts which curdle milk, it is only in very exceptional cases (as in 

 that of man) that the gastric juice of adult animals possesses that 

 property. 



The function Attention has been drawn to the error in which 



of the lactic nearly all systematic writers have fallen in their account 

 acid fermenta- o f the reaction of the contents of the small intestine. 



testing the ln ~ If we exce P t the duodenum at the very time when 

 pancreatic juice is being most rapidly secreted, there 

 can be no doubt that the intestinal contents are acid. The acid 

 reaction is, as we have shewn, the result of the production of lactic 

 acid, at the expense of a part of the sugar formed in the alimentary 

 canal, and is effected through the agency of various organisms (see 

 p. 437). There can be no doubt that a part of the lactic acid formed 

 must at once enter into combination with the sodium carbonate 

 which is so prominent a constituent of the intestinal juice. The 

 excess must play a leading part, both in virtue of its own influence 

 and by setting free the bile acids, in preventing putrefactive processes 

 occurring in the small intestine, to the danger of the health, and to 

 the risk of the life, of the creature. 



The destruc- So long as it was believed that the contents of the 



tion of trypsin sma ii intestine presented, normally, an alkaline, and the 



enzymes^n contents of the large intestine an acid, reaction, it was 



the small believed that the pancreatic enzymes, which are all 



intestine. destroyed by digestion with dilute acids, must be 



