STRUCTURE OF LOBULES. 63 



independent course, and finally form the large veins which 

 join the abdominal vena cava just behind the diaphragm. 

 When a portal canal, however minute, is cut across, it is ob- 

 served to contain a twig of the hepatic artery, a larger twig 

 of the portal vein, and a minute branch of the hepatic duct 

 the hepatic artery especially ramifies on the ducts and, finally, 

 from its capillaries arise a minute set of branches correspond- 

 ing to veins, which communicate with the ramifications of the 

 portal vein. These ramifications of the portal vein proceed 

 between the pin-head lobules, and at last penetrate the lobules, 

 and end in capillaries from which the minute vein already 

 spoken of returns the residue of the blood after secretion to 

 the small trunk of the hepatic vein on which the pin-head 

 lobule rests. Minute branches of the hepatic duct arise from 

 each pin-head lobule, conveying away the secretion. The pin- 

 head lobules are filled with hepatic cells, which are of the kind 

 called nucleated cells, the medium diameter of which does not 

 exceed the thousandth part of an inch. The mode in which 

 these cells are concerned in the production of the secretion 

 is still far from being agreed on. 



It does not appear that the bile in the horse has been made 

 a special subject of investigation. Yet it does not seem that 

 there is any very essential difference in the bile of mammals 

 in general. This secretion may be regarded as a species of 

 soap, formed by the combination of two peculiar resinoid acids 

 with soda. Both these acids namely, the glycocholic and 

 taurocholic contain nitrogen. The taurocholic also contains 

 sulphur, from which the glycocholic is free. In bile, also, 

 there is a peculiar colouring matter known usually as biliverdine. 

 There are also found cholesterine and a small amount of 

 stearic, oleic, and lactic acids, united with potash and ammonia. 

 There is no saccharine matter in the bile, nevertheless the 

 liver appears to have the power to convert some other proxi- 



