406 TEXT-BOOK OF PHYSIOLOGY. 



liarities of the liver would indicate that it has a variety of relations to 

 the general processes of the body. Experimental investigation has 

 brought some of these relations to light. Though its physiologic 

 actions are not yet wholly understood, it may be said that it 



1. Secretes bile. 



2. Produces and stores glycogen. 



3. Assists in the formation of urea. 



Secretion of Bile. The physical properties and chemic com- 

 position of the bile have already been considered (page 203). 

 The characteristic salts of the bile, sodium glycocholate and tauro- 

 cholate, do not pre-exist in the blood, and therefore must be formed 

 by the liver cells out of materials derived from the blood of the 

 intralobular capillaries. The antecedents of the bile salts, glycocoll 

 and taurin, are crystallizable nitrogenized compounds, and known 

 chemically as amido-acetic and amido-ethylsulphonic acids. Their 

 chemic composition indicates that they are derivatives of the proteids 

 or the albuminoids, though the intermediate stages in their produc- 

 tion are unknown. The origin of the cholalic acid with which they 

 are combined is equally obscure. The bile salts as they are found 

 in the bile are produced in the liver cells by metabolic activity. 



The primary coloring-matter of the bile, bilirubin, has been shown 

 to be a derivative of hematin, a product of the disintegration of hemo- 

 globin. It is supposed that the liver cells bring about this change 

 by combining water with hematin, with the abstraction of iron. The 

 product thus formed is bilirubin, which is excreted, while the iron is 

 for the most part retained. 



^Cholesterin is a waste product derived largely from the nerve- 

 tissue^kvlt is brought to the liver and simply excreted by the cells. 

 The remaining constituents of the bile, water and inorganic salts, are 

 secreted here as in all other glands. 



When once formed, the liver cells discharge these various com- 

 pounds into the channels by which they are surrounded; they then 

 pass into the open mouths of the bile-ducts at the periphery of the 

 lobules. Under the increasing pressure which arises from the secre- 

 tion and accumulation of bile, this fluid flows from the smaller into the 

 larger bile-ducts, and finally is emptied either directly into the in- 

 testine or into the gall-bladder, where it is stored until required for 

 digestive purposes. The secretion of bile, as observed by means of 

 a biliary fistula, is continuous and not intermittent, though the rate 

 of flow is subject to considerable variation. 



The liver cells,asfar as the secretion of 



* b f JnjfiRe^nTTrfTEe nenrejgstemT^Their activity, however, 

 is stimulaecTT)3^4ke^nc which arises during 



digestion in consequence of the dilatation of the intestinal vessels, 

 since it is at this period that the rate of discharge is the greatest. 



