37 



FOOD AND DIGESTION 



coincident with the pancreatic flow, and then rapidly diminishes. Dale has 

 shown that the muscular fibers of the wall of the gall-bladder are supplied 

 by nerves from both the vagus and the sympathetic. The former are motor, 

 while the latter convey inhibitory impulses. The contractions of the gall- 

 bladder are provoked reflexly on the passage of the acid chyme into the 

 intestine. The gall-bladder acts as a reservoir for the bile during the intervals 



when digestion is not in progress. The 

 mechanism by which the bile passes into 

 the gall-bladder is simple. The orifice 

 through which the common bile-duct com- 

 municates with the duodenum is narrower 

 than the duct, and appears to be closed, 

 except w r hen there is sufficient pressure 

 behind to force the bile through it. The 

 pressure exercised upon the bile secreted 

 during the intervals between periods of 

 digestion appears insufficient to overcome 

 the force of the sphincter by which the orifice 

 of the duct is closed; and the bile in the 

 common duct traverses the cystic duct and 

 so passes into the gall-bladder. It is proba- 

 bly 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 com- 

 mon bile-duct. 



When the discharge of the bile into the 

 intestine is prevented by an obstruction of 

 some kind, as by a gall-stone blocking the 



hepatic duct, it is reabsorbed in great excess into the blood, and, circu- 

 lating 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 



FIG. 275. Longitudinal Sec- 

 tion of Fundus of Crypt of Lieber- 

 kiihn. b, Goblet cell showing 

 mitosis; e, epithelial cell; k, cell of 

 Paneth; /, leukocyte in epithelium; 

 m, mitosis in epithelial cell. Sur- 

 rounding the crypt is seen the 

 stroma of the mucous membrane. 

 X 530. (Kolliker.) 



