344 



FOOD AND DIGESTION 



cystic duct and so passes into the gall-bladder, being probably aided in this 

 retrograde course by the peristaltic action of the ducts. The bile is discharged 

 from the gall-bladder and enters the duodenum on the introduction of food 

 into the small intestine. It is pressed on by the contraction of the coats of 

 the gall-bladder, and of the common bile-duct. Their contraction is excited 

 by the stimulus of the food in the duodenum acting through a reflex arc to 

 produce contractions, the force of which is sufficient to open the orifice of the 

 common bile-duct. 



When the discharge of the bile into the intestine is prevented by an ob- 

 struction of some kind, as by a gall-stone blocking the hepatic duct, it is reab- 



FIG. 275. Longitudinal Section of Fundus of Crypt of Lieberkiihn. b, Goblet cell showing 

 mitosis; e, epithelial cell; k, cell of Paneth; /, leucocyte in epithelium; m, mitosis in epithelial cell. 

 Surrounding the crypt is seen the stroma of the mucous membrane. X 530. (Kolliker.) 



sorbed in great excess into the blood, and, circulating with it, gives rise to 

 the well-known phenomena of jaundice. This is explained by the fact that the 

 pressure of secretion in the ducts, although normally very low, not exceeding 

 15 millimeters of mercury in the dog, is still higher than that of the portal 

 veins. If the pressure exceeds 15 mm. the secretion continues to be formed 

 but passes into the blood-vessels through the lymphatics. 



The Intestinal Secretion, or Succus Entericus. It is impossible to 

 isolate the secretion of the glands of Brunner or of the glands of Lieberkiihn, 

 but the total secretion of the intestinal mucosa can be secured by isolating a 

 loop of intestine by the operation known as the Thiry fistula. A few drops 



