140 PHYSIOLOGY CHAP. 



intestine, conducted back to the liver by way of the portal vein, 

 and eliminated once more from the liver by the bile ducts. This 

 kind of entero-hepatic circulation of the bile was worked out 

 particularly by Schiff, Lussana, Baldi, Tarchanoff, and Wertheimer. 

 It is only necessary to give bile by the mouth, or to inject it 

 directly into the duodenum, of a dog with a fistula of the gall- 

 bladder, in order shortly after to see a flow from the fistula, 

 proportionate to the amount of bile administered. Again, on 

 injection by the veins, the bile is not excreted by the ureters but 

 entirely by the hepatic duct, if a moderate amount be injected. 

 On injecting ox-bile, which is green (owing to the large preponder- 

 ance of biliverdin), the secretion flowing from the biliary fistula of 

 the dog loses its orange colour (due to preponderance of bilirubin), 

 and assumes the hue of ox-bile (Baldi). This fact demonstrates the 

 specific excretory function of the hepatic cells for the constituents 

 of bile, which is of great importance, since it extends not only to 

 these but also to many other toxic and medicinal substances 

 introduced into the gastro-intestinal tube, which on reaching the 

 liver are carried back to the intestine with the bile (Lussana, 

 Moroni and Dyall, Acqua, Schiff, and others). Barbera (1898) 

 rightly insisted on a phenomenon which is not easy to explain by 

 known laws of physics and chemistry. If fasting dogs with a 

 fistula of the gall-bladder are made to ingest large quantities of 

 bile and urea together, then although both substances are taken 

 up by the portal vein, and carried to the liver, the whole of the 

 bile is constantly eliminated by the bile-ducts, while the whole of 

 the urea passes into the capillaries which lead to the central veins 

 of the lobule, and is excreted by the kidneys. To account for this 

 fact, he assumes a differentiation into two parts of the hepatic cells ; 

 the one in contact with the bile canaliculi, the other in relation with 

 the blood capillaries which lead to the central veins of the hepatic 

 lobules. These two parts must have different excretory functions, 

 due possibly to a difference in cytological structure, which we are 

 unable by our present methods to detect. But without invoking 

 any unfounded hypothesis, the fact may be explained as depending 

 on the selective attraction of the hepatic cells for biligenic sub- 

 stances (positive chemotaxis), while they repel urea (negative 

 chemotaxis). 



XX. The biliary secretion can be modified not only by the 

 composition of the blood that circulates round the hepatic cells, 

 but also by the amount of blood that flows to the liver, and the 

 vascular tonicity of the portal vein and hepatic artery. The 

 augmented secretion that occurs during digestion is partly due, no 

 doubt, to the active vascular dilatation which accompanies the 

 secretory work of all organs that function during the digestive 

 processes. 



Just as the bile secretion is promoted by a rapid and abundant 



