400 USES OF THE LIVER DUCTLESS GLANDS. 



is necessary to intestinal digestion, that it contains excrementitious matters 

 and that the cells constantly produce glycogen. The liver produces urea, 

 which is excreted, however, chiefly by the kidneys. It may also effect certain 

 changes in digested and foreign matters that are absorbed from the aliment- 

 ary canal. As regards its varied uses, therefore, as well as in its anatomy, it 

 has no analogue in the glandular system, and the mechanism of its action is 

 necessarily complex. 



As regards the secretion of bile, the only view that is consistent with 

 actual knowledge is that this fluid is produced by the liver-cells and is taken 

 up by the plexus of bile-ducts which surrounds these cells. The little gland- 

 ular organs that are attached to the larger branches of the duct secrete mucus 

 which gives the viscidity observed in the bile of some animals. The bile, 

 indeed, is viscid in different animals in proportion to the development of 

 these mucous glands ; and in the rabbit, in which the glands do not exist, the 

 bile has no viscidity (Sappey). The passage of excrementitious substances 

 from the blood into the bile will be discussed in connection with the action 

 of the liver as an organ of excretion, and the formation of glycogen will be 

 considered in its proper place. 



Of course the circulation of blood in the liver is a condition necessary to 

 the secretion of bile. As regards the question of the production of bile from 

 venous or arterial blood, it has been shown that the materials out of which 

 the bile is formed may be supplied by either the hepatic artery or the portal 

 vein. Bile is secreted after the hepatic artery has been tied, and also after 

 the portal vein has been gradually obliterated, the hepatic artery being intact 

 (Ore). Bile is produced in the liver from the blood distributed in its sub- 

 stance by the portal vein and the hepatic artery, and not from the blood of 

 either of these vessels exclusively ; and bile may continue to be secreted, if 

 either one of these vessels be obliterated, provided the supply of blood be 

 sufficient. 



Some of the variations in the discharge of bile have been described in 

 connection with the physiology of digestion; but although the bile is 

 poured out much more abundantly during intestinal digestion than at other 

 times, its production and discharge are constant. The bile is stored up in 

 the gall-bladder to a considerable extent during the intervals of digestion. 

 If an animal be killed at this time, the gall-bladder is always distended ; but 

 it is found empty, or nearly so, in animals killed during digestion. 



The influence of the nervous system on the secretion of bile has been 

 very little studied, and the question is one of great difficulty and obscurity. 

 The liver is supplied very abundantly with nerves, both cerebro-spinal and 

 sympathetic, and some observations have been made upon the influence of 

 the nerves upon its glycogenic action ; but with regard to the secretion of 

 bile, there is little to be said beyond what has already been stated concerning 

 the influence of the nervous system on other secretions. 



The bile is discharged through the hepatic ducts like the secretion of any 

 other gland. During digestion the fluid accumulated in the gall-bladder 

 passes into the ductus communis, in part by contractions of its walls, and in 



