188 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



the blood-vessels would be to diminish the resistance along the intestinal 

 paths, and thus lead to a greater flow of blood to that area and the portal 

 circulation. 



In all these cases one might suppose that the greater or less quantity of 

 bile formed depended only on the blood-pressure in the capillaries of the liver 

 lobules that so far at least as the water of the bile is concerned it is produced 

 by a process of filtration and rises and falls with the blood-pressure. That 

 this simple mechanical explanation is not sufficient seems to be proved by the 

 fact that the pressure of bile within the bile-ducts, although comparatively 

 low, may exceed that of the blood in the portal vein. While it is not possible, 

 therefore, to exclude entirely the factor of filtration, it is evident that the 

 quantity of secretion depends largely on the mere quantity of bjood flowing 

 by the cells in a unit of time. 



The Existence of Secretory Nerves to the Liver. The numerous 

 experiments that have been made to ascertain whether or not the secretion 

 of bile is under the direct control of secretory nerves have given unsatisfactory 

 results. The experiments are difficult, since stimulation of the nerves supply- 

 ing the liver, such as the splanchnic, is accompanied by vaso-motor changes 

 which alter the blood-flow to the organ and thus introduce a factor which in 

 itself influences the amount of the secretion. So far as our actual knowledge 

 goes, the physiological evidence is against the existence of secretory nerve- 

 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-secretory 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 

 part 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 



1 Morat and Dufourt: Archives de Physiologic, 1894, p. 371. 



2 Archives de Physwlogie, 1894, p. 19. 



