198 TEXT-BOOK OF PHYSIOLOGY 



daily, have been approximately determined by fistulous openings either 

 in the hepatic ducts or in the gall-bladder. Although the liver presents 

 some physiologic peculiarities, there is no reason to believe that the condi- 

 tions of secretion therein are different from those in any other secretor 

 organ, or that any other structure than the cell is engaged in this process. 

 As shown by chemic analysis, the bile consists of compounds, some of which, 

 like the bile salts, are formed in the liver cells, out of material furnished by 

 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 partial 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 membrane, which, absorbed into the blood, is ultimately distri- 

 buted 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 mus- 

 cle 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. From the results of his experiments Doyon concludes that 

 with the passage of the acidulated food through the duodenum afferent 

 fibers in the trunk of the vagus are stimulated and the nerve impulses 

 thus developed, ascending to the medulla, cause reflexly an inhibition of 

 the sphincter muscle and a contraction of the muscle walls of the gall 

 bladder. The efferent fibers in this reflex, inhibitor and motor, being 

 contained in the great splanchnic nerves. With the discharge of bile and 

 the cessation of digestion the gall bladder relaxes and the sphincter con- 

 tracts, thus establishing the conditions for the storage of bile. Just how 

 this condition is brought about is uncertain though according to Doyon 

 stimulation of the central end of the divided splanchnic gives rise to an 

 inhibition of the walls of the gall bladder. 



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 



