THE LIVER AND BILE 715 



During its stay in the bladder the bile is concentrated by the loss of water 

 and by the addition to it of nmcin or nucleo- albumen, derived from the 

 cells lining the bladder. Of the other constituents of bile, the pigments 

 must be regarded simply as waste products, and an index to the disintegration 

 of haemoglobin. Their mode of origin will be discussed in dealing with the 

 history of the red blood corpuscles. They pass into the intestine and are 

 there converted by the processes of bacterial reduction into stercobilin, which 

 is excreted for the most part with the faeces, a small proportion being ab- 

 sorbed into the blood-vessels and turned out in a more or less altered condi- 

 tion as the pigments of the urine. From the point of view of digestion, 

 the important constituents of bile are the bile salts, with the lecithin and 

 cholesterin held in solution by these salts. The time- relations of the secre- 

 tion, as well as of the flow of bile into the intestine in connection with the 

 processes of digestion, can be learnt from animals in which the bile is 

 conducted to the outside of the body by means of a permanent fistula. 



For this purpose Pawlow has devised the following operation : In the dog the 

 abdomen is opened, and the common bile-duct sought as it passes through the intestinal 

 wall. The orifice of the duct, with a piece of the surrounding mucous membrane 

 is cut out of the wall of the intestine, and the aperture thus made sutured. The ex- 

 cised portion of mucous membrane, with the opening of the duct, is then sewn on to the 

 surface of the duodenum, and the loop of duodenum at this point is stitched into the 

 abdominal wound. After healing, the natural orifice of the bile-duct is thus made to 

 open on the surface of the abdomen. 



In an animal treated in this way the flow of bile from the fistula is found 

 to run parallel to the pancreatic secretion. Although smaller in amount, it 

 rises and falls with the latter. Thus a meal of meat produces a large flow of 

 bile, a meal of carbohydrates only a small flow. Moreover, beginning almost 

 immediately after taking food, it attains its maximum with the pancreatic 

 juice in the third hour and then rapidly declines. 



In the production of this flow of bile two factors may be involved : (1) the 

 emptying of the gall-bladder ; (2) an increased secretion of the bile. In 

 order to determine the relative importance to be ascribed to each factor, we 

 must compare the results obtained on an animal possessing a Pawlow 

 fistula with those obtained on an animal provided with a fistulous opening 

 into the gall-bladder, the common bile-duct in the latter having been ligated 

 to ensure that the total secretion of bile passed out by the fistula. In such 

 animals we find, as we should expect, that the secretion of bile is a continuous 

 process, but that, synchronously with the great outpouring of bile into the 

 intestine during the third hour after a meal, there is an increased secretion 

 of this fluid. The passage therefore of the semi-digested food from the 

 stomach into the duodenum causes not only a slow contraction and emptying 

 of the gall-bladder but also an increased secretion of bile by the liver. 

 What is the mechanism involved in the production of these two effects ? The 

 muscular wall of the gall-bladder, as has been shown by Dale, is under the 

 control of nerves derived both from the vagus and from the sympathetic, the 

 former conveying motor and the latter inhibitory impulses. It is usual to 

 suppose that the entry of acid chyme into the duodenum provokes reflexly 



