SECRETION. 'JIT 



secretion of bile. Of these substances the < >m- whose action is most undoubted 

 is bile itself or the bile acids. When given as dried bile, in the form of 

 pills, a marked increase in the flow is observed.' 



Relation of the Secretion of Bile to the Blood-flow in the Liver. — 

 Numerous experiments have shown that the quantity of bile formed by the 

 liver varies more or less directly with the quantity of blood flowing through 

 the organ. The liver-cells receive blood from two sources, the portal vein 

 and the hepatic artery. The supply from both these sources is probably essen- 

 tial to the perfectly normal activity of the cells, but it has been shown that bile 

 continues to be formed, for a time at least, when either the portal or the arterial 

 supply is occluded. However, there can be little doubt that the material actually 

 utilized by the liver-cells in the formation of their external and internal secre- 

 tions is brought to them mainly by the portal vein, and that variations in the 

 quantity of this supply influences directly the amount of bile produced. Thus, 

 occlusion of some of the branches of the portal vein diminishes the secretion; 

 stimulation of the spinal cord diminishes the secretion, since, owing to the large 

 vascular constriction produced thereby in the abdominal viscera, the quantity of 

 blood in the portal circulation is reduced ; section of the spinal cord also dimin- 

 ishes the flow of bile or may even stop it altogether, since the result of such an 

 operation is a general paralysis of vascular tone and a general fall of blood- 

 pressure and velocity ; stimulation of the cut splanchnic nerves diminishes the 

 secretion because of the strong constriction of the blood-vessels of the abdom- 

 inal viscera and the resulting diminution of the quantity of the blood in the 

 portal circulation ; section of the splanchnics alone, however, is said to increase 

 the quantity of bile, in dogs, since in this case the paralysis of vascular tone 

 is localized in the abdominal viscera. The effect of such a local dilatation of 

 the blood-vessels would be to diminish the resistance alono- 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. 



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 that in 

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

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

 1 Journal of Experimented Medicine, 1897, vol. ii. p. 4'.'. 



