78 HUMAN PHYSIOLOGY. 



then taken up by the delicate plexus of vessels, from which it passes into 

 the larger ducts, and finally either empties into the intestine or is regurgi- 

 tated backward into the gall bladder, in which it is stored up during the 

 intervals of digestion. 



Although the secretion of bile is constantly taking place, it is only when 

 the food passes into the intestinal canal that this fluid is discharged abund- 

 antly, under the influence of the contraction of the walls of the gall blad- 

 der ; it increases in amount during the period of active digestion, from the 

 second to the eighth hour, and then gradually diminishes. 



The Bile is both a secretion and an excretion ; it contains new constitu- 

 ents which are formed only in the substance of the liver, and are destined 

 to play an important part ultimately in nutrition ; it contains also waste 

 ingredients which are discharged into the intestinal canal and eliminated 

 from the body. 



The physical properties and functions of bile have been considered under 

 the head of digestion (see page 34). 



(2) Elaboration of Blood. Besides the capability of secreting bile, 

 the liver possesses the property of so acting upon and modifying the chemi- 

 cal composition of the products of digestion, as they traverse its substance, 

 that they readily assimilate with the blood, and are transformed into mate- 

 rials capable of being converted into the elements of the blood and solid 

 tissues. 



The albuminose particularly requires the modifying influence of the 

 liver ; for if it be removed from the portal vein and introduced into the 

 jugular vein, it is at once removed from the blood by the action of the 

 kidneys. 



The blood of the hepatic vein differs from the blood of the portal vein, 

 in being richer in blood corpuscles, both red and white ; its plasma is more 

 dense, containing a less percentage of water and a greater amount of solid 

 constituents, but no fibrin ; its serum contains less albumen, fat and salts, 

 but its sugar is increased. 



(3) Glycogenic Function. In addition to the two preceding func- 

 tions, Bernard, in 1848, demonstrated the fact that the liver, during life, 

 normally produces a sugar-forming substance, analogous in its chemical 

 composition to starch, which he termed glycogen ; also that when the liver 

 is removed from the body, and its blood vessels thoroughly washed out, 

 after a few hours sugar again makes its appearance, in abundance. 



It can be shown to exist in the blood of the hepatic vein as well as in a 

 decoction of the liver substance, by means of either Trommer's or Fehling's 



