LIVER. 87 



in the muscles, where it generates heat and contributes to the development 

 of muscular force. 



Glycogen, when obtained from the liver, is an amorphous, starch-like 

 substance, of a white color, tasteless and colorless, and soluble in water; by 

 boiling with dilute acids, or subjected to the action of an animal ferment, 

 it is easily converted into glucose. When an excess of sugar is generated 

 by the liver, it can be found, not only in the blood of the hepatic vein, 

 but also in other portions of the body; under these circumstances it is 

 eliminated by the kidneys, appearing in the urine, constituting the condition 

 of glycosuria. 



Formation of Urea. The liver is now regarded by many physiologists 

 to be the principal organ concerned in urea formation. The liver normally 

 contains a certain amount of urea, and if blood be passed through the 

 excised liver of an animal which has been in full digestion, a large amount 

 of urea is obtained. The clinical evidence proves that in destructive dis- 

 eases of the liver substance there is at once a falling off in urea elimination. 

 Various drugs which increase liver action increase the urea in the urine. 



Elaboration of Blood. Besides the capability of secreting bile, the 

 liver possesses the property of so acting upon and modifying the chemical 

 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 albumin, fats and salts, 

 but its sugar is increased. 



Influence of the Nervous System. The nervous system directly 

 controls the functional activity of the liver, and more especially its glyco- 

 genic function. It was discovered by Bernard that puncture of the medulla 

 oblongata is followed by such an enormous production of sugar that it is at 

 once excreted by the kidneys, giving rise to diabetic or saccharine urine. 

 This part of the medulla is, however, the vasomotor centre for the blood 

 vessels of the liver. Destruction of this centre, or injury to the vasomotor 



