CIRCULATION OF THE BILE. 439 



CHAPTER VII. 



THE LIVER. 



T. PHYSIOLOGICAL RELATIONS. 



THE substances which enter the liver through the portal vein 

 consist of the products of digestion in the widest sense, namely, 

 proteids including leucin and tyrosin, sugars, salts, a trace 

 of fat, and abundant water. When we parted with the proteids 

 in the duodenum, they were in the form of peptones ; when we 

 meet with them again in the vena portoe, they have been trans- 

 formed into ordinary serum albumen, apparently in the process 

 of absorption. The sugars enter the liver partly unchanged, 

 partly perhaps as derivatives lactic and butyric acid. The 

 proteids, sugars, water, salt, etc., will obviously be ' poured 

 into the liver very abundantly during digestion. At the same 

 time, there enters the liver through the hepatic artery a supply 

 of oxygen which appears to be precariously limited, if we may 

 judge by the size of the vessel. In the presence of this double 

 supply, and in proportion to it, the hepatic cells display their 

 special activity, and yield glycogen, urea, and bile. The urea 

 and bile are carried off as such, the former by the hepatic veins 

 to escape by the kidneys, the latter by the bowels. The 



glycogen has a less simple history. It accumulates in the 

 ver cells, where it appears as a form of amyloid material 

 specially adapted for storing up in an insoluble state the. sugar 

 and part of the proteids. By this arrangement the blood and 

 body generally are saved from being flushed with sugar after 

 each meal, and the sugar itself is not wasted. Under the 

 influence of a ferment the glycogen is gradually re-converted 

 into some kind of sugar ; the amount of amyloid material 

 hydrated varying with the necessities of the system. This 

 function is regulated by a nervous mechanism, having its centre 

 in the medulla, with efferent and (presumably) afferent 

 nerves. 



Another point in connection with the liver to be carefully 

 noted by the therapeutist is the circulation of the bile. The bile, 

 having entered the bowel and mixed with the chyme, is not 

 entirely evacuated by the faeces. On the contrary, its most im- 

 portant constituents, the biliary salts, are re-absorbed from the 

 bowel and carried back to the liver, again to be secreted and 

 reach the bowel. Thus the bile may be said to move in a circle, 

 comprised by the bile ducts and gall bladder, the intestine, and 

 the portal vein. 



