158 HUMAN PHYSIOLOGY. 



by the inspiratory movements of the diaphragm, and by the contraction of 

 the muscle-fibers of the biliary ducts, as well as the vis a tergo of new-formed 

 bile. Any obstacle to the outflow of bile into the intestine leads to an accumu- 

 lation within the bile-ducts. The pressure within the ducts increasing 

 beyond that of the blood within the capillaries, a reabsorption of biliary 

 matters by the lymphatics takes place, giving rise to the phenomena of 

 jaundice. 



The bile is both a secretion and an excretion; it contains new constituents, 

 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 Production of Glycogen. In addition to the preceding function, 

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

 produces a substance analogous in its chemic composition to starch, which 

 he termed glycogen; also that, when the liver is removed from the body, and 

 its blood-vessels are thoroughly washed out, after a few hours sugar makes its 

 appearance in abundance. The sugar can also 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 test, even when the blood of the portal vein 

 does not contain a trace of sugar. 



Origin and Destination of Glycogen. Glycogen appears to be formed 

 in the liver cells, from materials derived from the food, whether the diet be 

 animal or vegetable, though a larger percentage is formed when the animal 

 is fed on starchy and saccharine than when fed on animal food. The dex- 

 trose, which is one of the products of digestion, is absorbed by the blood-vessels 

 and carried directly into the liver; as it does not appear in the urine, as it 

 would if injected at once into the general circulation, it is probable that it 

 is detained in the liver, dehydrated, and stored up as glycogen. The change 

 is shown by the following formula: 



C 6 H 12 S -H 2 = C 6 H 10 5 . 



Dextrose. Water. Glycogen. 



The glycogen thus formed is stored up in the hapatic cells for the future 

 requirements of the system. When sugar is needed for nutritive purposes, 

 the glycogen is transformed into dextrose by the agency of a ferment. 



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 dextrose. When an excess of sugar is generated 

 by the liver out of the glycogen, dextrose can be found not only in the blood of 

 the hepatic vein, but also in other portions of the body; under these circum- 



