412 DIGESTION 



But to learn the function of bile in digestion it is more important 

 to know when and at what rate it enters the intestine. For this 

 purpose a fistula is made by cutting the natural orifice of the common 

 bile-duct with a piece of the surrounding mucous membrane out of 

 the intestine and transplanting it upon the serous coat, where it is 

 sutured. The loop of intestine, with the orifice of the duct facing 

 outwards, is then stitched into the abdominal wound, where it is 

 allowed to heal. Of course, since a circulation of the bile-acids 

 takes place i.e., an absorption from and r^ -excretion into the 

 intestine the formation of that juice cannot proceed upon abso- 

 lutely normal lines when the bile no longer enters the duodenum. 

 The only condition under which fistula bile could have the same 

 composition as normal bile would be that in which as great an 

 amount of bile-acids is introduced into the gut as escapes through 

 the fistula. A circulation of a smaller proportion of the bile-pig- 

 ments is also probable. A circulation of the biliary cholesterin is 

 denied by some observers (Stadelmann) but affirmed by others. It 

 is certain that cholesterin is of importance in the body, and if the 

 supply of sterins (p. 570) in the food is insufficient it is to be sup- 

 posed that some of the biliary cholesterin would be used over again. 



Of the direct influence of nerves, either on the secretion of bile or on 

 its expulsion, we have scarcely any knowledge, scarcely even any guess 

 which is worth mentioning here. It is true the secretion of bile may 

 be distinctly affected by the section and stimulation of nerves which 

 control the blood-supply of the stomach, intestines, and spleen, for the 

 quantity of blood passing by the portal vein to the liver depends upon 

 the quantity passing through these organs, and the rate of secretion is 

 diminished when the blood-supply is greatly lessened. In this way 

 stimulation of the medulla oblongata, the spinal cord, or the splanchnic 

 nerves stops or slows the secretion of bile by constricting the abdominal 

 vessels ; and the same effect can be reflexly produced by the excitation 

 of afferent nerves. 



The right splanchnic nerve contains inhibitory with some motor 

 fibres, and the vagi (especially the left) contain motor fibres for the 

 gall-bladder. Probably its contraction takes place naturally in 

 response to reflex impulses from the mucous membrane of the duo- 

 denum, for the application of dilute acid to the mouth of the bile- 

 duct causes a sudden flow of bile,* and the acid contents of the 

 stomach, when projected through the pylorus into the intestine, 

 have a similar effect. But, in addition, as we have seen, the secretin 

 formed will cause an increase in the rate of secretion of the bile. In 

 studying the effect of secretin it is necessary to obtain it free from 

 bile- salts, since these cause of themselves an increased secretion of 

 bile. When this is done by dissolving out with alcohol any bile-salts 

 which may be present in the extract of intestinal mucous membrane, 



* This result seems to be difficult to realize experimentally. Bainbridge 

 and Dale could not elicit reflex contraction of the gall-bladder (in anaesthetized 

 animals) in this way. 



