THE BILE 811 



and serum globulin, includes a number of ferments, all of which are 

 adapted to complete the processes of digestion of the food -stuffs 

 commenced in the stomach and duodenum. Of these ferments two 

 are concerned in proteolysis. Enterokinase we have already studied 

 in detail. Possessing no action itself on proteins, it is a necessary 

 condition for the development of the full proteolytic powers of the 

 pancreatic juice. In addition to this ferment another ferment has 

 been described by Cohnheim under the name ' erepsin.' Erepsin 

 or some similar ferment is present in the fresh pancreatic juice and 

 in almost all tissues of the body. It is distinguished by the fact 

 that, although it has no power of digesting coagulated protein or 

 gelatin, and only slowly dissolves caseinogen and fibrin, it has a 

 rapid hydrolytic effect on the first products of proteolysis, converting 

 albumoses and peptones into amino- and diamino-acids their 

 ultimate cleavage products. 



The other ferments of the intestinal juice are connected with 

 the digestion of carbohydrates. In all mammals the intestinal juice 

 is found to contain invertase, which transforms cane sugar into glucose 

 and levulose or fructose, and maltase, which converts maltose into 

 glucose. In young mammals, as well as in those in whom the milk 

 diet is continued throughout life, the intestinal mucous membrane 

 also contains lactase, i.e. a ferment converting milk sugar into galac- 

 tose and glucose. Such a ferment can be extracted from the mucous 

 membrane of all young animals, but may be very slight or even 

 absent in the intestines of older animals, when it is no longer 

 needed for the ordinary processes of nutrition. By means of these 

 three ferments, corning as they do after the digestion of the 

 starches by the amylase of the saliva and pancreatic juice, it is 

 provided that all the carbohydrate food of the animal is transformed 

 into a hexose, in which form alone carbohydrate can be taken up 

 and assimilated by the cells of the body. The seat of origin of these 

 various ferments has been the subject of special investigations by 

 Falloise. Whereas secretin can be obtained from the whole thick- 

 ness of the mucous membrane, and is probably therefore contained 

 in the form of prosecretin in the epithelial cells covering the villi 

 as well as in those lining the follicles of Lieberkuhn, a superficial 

 scraping of the mucous membrane, which removes only the epithelial 

 cells covering the villi with the adherent mucus and intestinal secre- 

 tion, gives a much more active solution of enterokinase than a deeper 

 scraping. The most active solutions of enterokinase are, however, 

 to be obtained from the fluid found in the cavity of the intestine 

 after the injection of secretin. It seems therefore that enterokinase 

 is not present as such in the epithelial cells, but is first produced 

 in the process of secretion and formation of the intestinal juice. 



