138 DIGESTION 



The Secretion of Bile 



The bile which pours upon the digestive mass is produced 

 partly by contraction of the gall-bladder, partly by increased 

 secretion from the liver. The unstriated muscle of the 

 gall-bladder is innervated by the vagus and sympathetic. 

 It is called into play by a nervous reflex originating in the 

 duodenum. The exact path of the reflex is unknown. 



Increased secretion of the liver has been shown by 

 BayHss and Starhng to be effected by the same mechanism 

 as secretion of the pancreas — that is, by secretin. 



THE INTESTINAL JUICE 



The succus entericus or intestinal juice is secreted from 

 the whole length of the small intestine, but in amount 

 diminishing from above downwards. 



Alkahne in reaction, it contains the following ferments : — 



1. Erepsin. — This ferment forms the third and last in 

 the series of proteolytic enzymes. Without action upon 

 proteins, it hydrolyses proteoses, peptones and polypeptides, 

 converting them into amino-acids. By its means protein 

 hydrolysis is completed, 



2. Enterokinase. — This ferment has no digestive action 

 of its own, but, as we have seen, activates trypsinogen. 



3. Maltase. — -Hydrolyses maltose to dextrose. 



4. Lactase. — Present, at any rate, in the young; hydro- 

 lyses lactose to dextrose and galactose. 



5. Invertase. — Hydrolyses cane sugar to dextrose and 

 Isevulose. 



The Secretion of Intestinal Juice 



Though some intestinal juice appears within a few 

 minutes of the taking of food, a profuse flow does not 

 occur until two hours after. The mechanism of secretion 

 is not definitely known. Attempts have been made to 

 assess the part played by the vagus and sympathetic in 

 isolated loops of intestine, but the results are largely 



