PHYSIOLOGICAL CHEMISTRY 403 



protein to be attacked by trypsin, thereby diminishing bacterial 

 growth and consequent putrefaction ; (7), and lastly, by precipitating 

 the half-digested products of chyme, so that the trypsin may the better 

 act on them. 



Intestinal Juice. Succus Entericus. This is secreted by Lieberkuhn's 

 follicles. It may be obtained pure by isolating a piece of intestine and 

 collecting the juice secreted by it. This may be accomplished by 

 cutting out a piece of intestine and stitching both ends to abdominal 

 fistulae (Vella's method), the severed ends of the intestine being sutured 

 together. Or one end of the isolated piece may be sutured, the other 

 being attached to a fistula (Thiry's method). In both these cases the 

 mesentery of the isolated portion is left intact, and the juice can be 

 removed from the loop and its action studied in vitro, or food may be 

 placed in the loop, and afterwards removed and examined. 



Extracts of the mucous membrane of the intestine, prepared by 

 scraping this off and grinding it with sand and water and then filtering 

 through muslin, usually contain large amounts of ferments. This 

 extract will contain both exoenzymes and endoenzymes. 



Succus entericus seems to contain three ferments or ferment-like 

 bodies. One of these has been known for long, and is called inverting 

 ferment, because it "inverts" (see p. 285) disaccharides. There are 

 several varieties of inverting ferment depending on the exact nature of 

 the disaccharide on which they act ; e.g. one acting on maltose (maltase), 

 one on lactose (lactase), and one on cane sugar (invertase). Lactase is 

 present in extracts of the intestinal mucosa only when the food contains 

 lactose. It is therefore absent in the intestine of herbivorous adult 

 animals (guinea pig), but is present for some time after birth, i.e. 

 when the animal is living on milk. By feeding milk to adult animals 

 lactose does not reappear in the intestine. Extracts of intestinal 

 mucosa of omnivorous animals (cat and pig) contain lactase through- 

 out life. It cannot be found in the succus entericus, and is therefore an 

 endoenzyme. 



Invertase is also stronger in extracts of the intestinal mucosa than in 

 succus entericus. 



Maltase is not confined to the intestine, being present in large 

 amount in blood serum, and in most of the organs and tissues of the 

 animal body. 



The other two ferments act on proteins. One of them, erepsin by 

 name, hydrolyses casein, proteoses and peptones into simple nitrogenous 

 crystalline products. It cannot, however, act on all native proteins. 

 It differs from trypsin in the fact that it can hydrolyse certain poly- 

 peptides, such as glycyl-glycin ; d. I. leucylglycin, etc., on which trypsin 



