248 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



fibres controlling the formation of bile. On the other hand, there are some 

 experiments, 1 although they are not perfectly conclusive, which indicate that 

 the glycogen formation within the liver-cells is influenced by a special set of 

 glyco-seerehory nerve-fibres. This fact, however, does not bear directly upon 

 the formation of bile. 



Motor Nerves of the Bile-vessels. — Doyon 2 has recently shown that the 

 gall-bladder as well as the bile-ducts is innervated by a set of nerve-fibres 

 comparable in their general action to the vaso-constrictor and vaso-dilator 

 fibres of the blood-vessels. According to this author, stimulation of the 

 peripheral end of the cut splanchnics causes a contraction of the bile-ducts 

 and gall-bladder, while stimulation of the central end of the same nerve, on 

 the contrary, brings about a reflex dilatation. Stimulation of the central end 

 of the vagus nerve causes a contraction of the gall-bladder and at the same 

 time an inhibition of the sphincter muscle closing the opening of the common 

 bile-duct into the duodenum. These facts need confirmation, perhaps, on the 

 pari of other observers, although they are in accord with what is known of 

 the actual movement of the bile-stream. The ejection of bile from the gall- 

 bladder into the duodenum is produced by a contraction of the gall-bladder, 

 and it is usually believed that this contraction is brought about reflexly from 

 some sensory stimulation of the mucous membrane of the duodenum or 

 stomach. The result of the experiments made by Doyon would indicate that 

 the afferent fibres of this reflex pass upward in the vagus, while the efferent 

 fibres to the gall-bladder run in the splanchnics and reach the liver through 

 the semilunar plexus. 



Normal Mechanism of the Bile-secretion. — Bearing in mind the tact that 

 our knowledge of the secretion of bile is in many respects incomplete, and that 

 any description of the act is therefore partly conjectural, wc might picture 

 the processes concerned in the secretion and ejection of bile as follows : The 

 bile is steadily formed by the liver-cells and turned out into the bile-capil- 

 laries ; its quantity varies with the quantity and composition of the blood 

 flowing through the liver, but the formation of the secretion depends upon 

 the activities taking place in the liver-cells, and these activities are independ- 

 ent of direct nervous control. During the act of digestion the formation of 

 bile is increased, owing probably to a greater blood-flow through the organ 

 and to the generally increased metabolic activity of the liver-cells occasioned 

 by the inflow of the absorbed products of digestion. The bile after it gets 

 into the bile-ducts is moved onward partly by the accumulation of new bile 

 from behind, the secretory force of the cells, and partly by the contractions 

 of the walls of the bile-vessels. It is stored in the gall-bladder, and at inter- 

 vals during digestion is forced into the duodenum by a contraction of the 

 muscular walls of the bladder, the process being aided by the simultaneous 

 relaxation of a sphincter-like layer of muscle that normally occludes the 

 bile-duct :it it- opening into the intestine; both these last acts are under the 

 control of a nervous reflex mechanism. 



1 Morat iiinl Dufonrt: Archives de Physiologie, 1 s 04, p. 371. 



2 Archives de Physiologic, 1894, p. 19 ; see also Oddi : Arch. tied, de Biologie, t. xxii., cvi. 



