INTESTINAL JUICE 721 



is distinguished by the fact that, although it has no power of digesting coagu- 

 lated 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 galactose 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, 

 coming as they do after the digestion of the starches by the am^lase 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 thickness of the 

 mucous membrane, and is probably therefore contained in the iorm 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 secretion, gives a much more active solution of entero- 

 kinaise 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. The other ferments, namely, 

 erepsin, maltase, invertase. and lactase, probably pre-exist as such in the 

 epithelial cells, especially in those lining the tubular glands of the gut, since 

 pounded mucous membrane in water yields a solution of these ferments which 

 is generally more powerful in its action than the succus entericus itself. So 

 great is the difference, in fact, that many physiologists have suggested that 

 the chief action of these ferments occurs, not in the lumen of the gut, but in 

 the passage of the food- stuffs through the epithelial cells of the small intestine 

 on their way to the blood-vessels. 



