262 ELEMENTARY PHYSIOLOGY less. 



of two organic acids, one called glycocholic, the other 

 taurocholic. The former consists of carbon, oxygen, 

 hydrogen, and nitrogen, while the latter contains ad- 

 ditionally a considerable quantity of sulphur. 



Bile as it is secreted by the liver is a thin fluid, but after 

 its sojourn in the gall-bladder, where it is stored in the 

 intervals between its discharge into the intestines, it 

 contains a considerable amount of mucin, secreted into 

 it by the cells which line the gall-bladder and is now 

 viscid and slimy. 



Bile has by itself no direct chemical action on food-stuffs*. 

 But it serves to neutralise the acidity of the chyme as it 

 leaves the stomach and thus prepares it for the action 

 of pancreatic juice. Further it plaj^s an important part, 

 when mixed with pancreatic juice, in leading to the 

 emulsification of fats, facilitating their subsequent absorp- 

 tion and enabling the ferments of the pancreatic juice to 

 act more rapidly and eft'ectively. It also possesses the 

 property of keeping the bowels sweet. In its absence 

 undue putrefactive changes take place. 



16. The Changes Food Undergoes in the Intestines. 

 — The only secretions, besides those of the proper intesti- 

 nal glands, which enter the intestine, are those of the 

 liver and tlie pancreas — the bile and the pancreatic juice. 

 The ducts of these organs have a common opening in the 

 middle of the bend of the duodenum ; and, since the 

 common duct passes obliciuely through the coats of the 

 intestine, its walls serve as a kind of valve, obstructing 

 the flow of the contents of the duodenum into the duct, 

 but readily permitting the passage of bile and pancreatic 

 juice into the duodenum (Figs. 67 and 76). 



The glands of Lieberkuhn are supposed to form a cer- 

 tain amount of a secretion known as succus entericus, 

 or intestinal juice, which they then discharge into the 

 intestine. 



After gastric digestion has been going on some time, 

 and the semi-digested food begins to pass on into the 



