i 9 8 TEXT-BOOK OF PHYSIOLOGY 



the blood by a true act of secretion, while others, such as cholesterin and 

 lecithin, principles of waste, are merely excreted from the blood to be finally 

 eliminated from the body. The bile is thus a compound of both secretory 

 and excretory principles. 



The flow of bile from the liver is continuous but subject to considerable 

 variation during the twenty-four hours. The introduction of food into the 

 stomach at once causes a slight increase in the flow, but it is not until 

 about two hours later that the amount discharged reaches its maximum; 

 after this period it gradually decreases up to the eighth hour, but never 

 entirely ceases. During the intervals of digestion though a small quantity 

 passes into the intestine, the main portion is diverted into the gall-bladder, 

 because of the closure of the common bile-duct by the sphincter muscle near 

 its termination, where it is retained until required for digestive purposes. 

 When acidulated food passes over the surface of the duodenum, there is an 

 increase in the secretion or at least the discharge of bile, and as this takes 

 place after the nerves distributed to the liver are divided, the assumption is 

 that an agent, possibly secretin, is developed in the duodenal mucous mem- 

 brane, which, absorbed into the blood, is ultimately distributed to' the liver 

 cells and by which they are excited to activity. At the same time there is 

 excited, through reflex action, a contraction of the muscle walls of the gall- 

 bladder and ducts, a relaxation of the sphincter, and a gush of bile into the 

 intestine, the discharge continuing intermittently until digestion ceases and 

 the intestine is emptied of its contents. 



The Influence of the Nerve System. The storage and the discharge 

 of bile, brought about by the alternate contraction and relaxation of the 

 muscle walls of the gall-bladder and of the sphincter are regulated by the 

 nerve system. As the result of his experiments Doyon concludes, that dur- 

 ing the intervals of intestinal digestion the vagus nerve is carrying nerve 

 impulses which on the one hand augment the contraction of the sphincter 

 and inhibit the contraction of the walls of the gall-badder, thus establishing 

 the conditions for the storage of bile; but when intestinal digestion is in- 

 augurated the splanchnic nerve carries nerve impulses which inhibit the 

 sphincter and augment the con traction* of the walls of the gall-bladder, thus 

 establishing the condition for the discharge of the bile. 



The total quantity of bile secreted daily has been estimated to be from 

 500 to 800 grams. 



Physiologic Action of Bile. Notwithstanding our knowledge of the 

 complex composition of bile, the quantity discharged daily, and the time 

 and place of its discharge, its exact relation to the digestive process has not 

 been fully determined. No specific action can be attributed to it. It has 

 but a slight, if any, diastatic action on starch. It is without 'influence on 

 proteins or on fats directly. But indirectly and/by virtue of the bile salts it 

 contains, it plays an important part in increasing the action of the pancreatic 

 enzymes. Thus the amylolytic or amyloclastic power of the pancreatic 

 juice is almost doubled and the same is true for its proteoclastic power, 

 while its lipoclastic or fat-splitting power is tripled. 



The bile salts also dissolve insoluble soaps which may be formed during 

 digestion and thus favors the digestion of fat. If it be excluded from the 

 intestine there is found in the feces from 22 to 58 per cent, of the ingested 

 fats. At the same time the chyle, instead of presenting the usual white 



