II 



EXTERNAL DIGESTIVE SECRETIONS 



135 



have been considering. But there is one fundamental difference 

 between the biliary and the urinary secretions, i.e. the specific 

 components of bile are, as we shall see, formed exclusively by the 

 metabolism of the hepatic cells, while the constituents of the urine 

 eliminated by the kidneys are mainly pre-formed in the blood, and 

 represent the products of the metabolism of other tissues. 



The bile secretion is studied in animals by making a fistula of the gall- 

 bladder (Schwann, 1844), either leaving the bile-duct free or tying it. In 



a 



FIG. 50. Plexus of nerve fibrils within hepatic lobe of pigeon. Methylene blue method. 

 (Korolkow.) a, a, axis-cylinders of nerve-fibres passing between cell-trabeculae of the lobule ; 

 b, 6, fibrils ramifying over the cells ; c, c, hepatic lobules. 



.the first case (incomplete fistula), if the fistula of the gall-bladder is properly 

 closed, the bile can flow, as normally, into the duodenum ; in the second 

 (complete fistula), it is compelled to flow out to the exterior. In order 

 to study the process of bile secretion, it is necessary to make the fistula com- 

 plete and permanent, so as to be sure that the whole of the bile secreted 

 escapes by the orifice of the fistula. In cases of fistula of the gall-bladder 

 observed on man (Ranke, 1871, down to Noel Paton and J. M. Balfour, 

 1891), the fistula is always incomplete, and in these, cases it is seen by the 

 colour of the faeces that some of the bile secreted by the liver does not 

 pass through the opening of the fistula, but escapes by the bile duct and 

 discharges into the duodenum. 



The innumerable experiments on bile secretion by complete or 

 incomplete fistulae of the gall-bladder in man and animals have 



