SECRETION. 407 



The same results have been shown by experiment. Thus, division 

 of the splanchnic nerves is followed by an increased discharge of 

 bile, apparently due to the dilatation of the portal vessels; stimula- 

 tion of their peripheral ends is followed by a decreased discharge of 

 bile in consequence of the contraction of the portal vessels. The 

 bile salts appear to be the most efficient stimulants to the activity of 

 the liver cells, for their administration and absorption is followed by 

 an increase not only in the amount of water and inorganic salts, but 

 of the solid constituents as well. 



The flow of bile from the bile capillaries to the main hepatic 

 duct, though primarily dependent on differences of pressure, is aided 

 by the contraction of the muscular walls of the bile-ducts and the 

 inspiratory movements of the diaphragm. Any obstacle to the dis- 

 charge of bile leads to its accumulation, a rise of pressure beyond 

 that of the capillary blood-vessels, and a reabsorption by the lymph- 

 atics of the bile constituents. After their discharge into the blood 

 from the thoracic duct these constituents are deposited in various 

 tissues, giving rise to the phenomena of jaundice. 



The Production of Glycogen. In 1857 Bernard discovered the 

 fact that the liver normally during life produces a sugar-forming 

 substance, analogous in its chemic composition to starch, to which he 

 gave the name glycogen. This substance can be obtained by the 

 following method: Small pieces of the liver of an animal recently 

 killed, preferably after a meal rich in carbohydrates, are placed in 

 acidulated boiling water for a few minutes; then rubbed up in a 

 mortar with sand, again boiled, after which the proteids are removed 

 by filtration. The filtrate thus obtained is opalescent and resembles 

 a solution of starch. The glycogen may be precipitated from this- 

 solution with alcohol as a white amorphous powder, soluble in 

 water. Chemic analysis shows that it consists of C 6 H 10 O 5 , or a 

 multiple of it. 



When either the original solution obtained by boiling or a solution 

 of this amorphous powder is treated with iodin, it strikes a port- wine 

 color. When digested with saliva, pancreatic juice, or boiled with 

 dilute acids, the solution becomes clear, and testing with Fehling's 

 solution reveals the presence of sugar. 



If the liver be allowed to remain in the body of an animal for a 

 period of twenty-four hours before the decoction is made as above 

 described, it will be found that the solution contains only a small 

 amount of glycogen but a relatively large amount of sugar. The 

 inference drawn is that after death the glycogen is transformed by 

 some agent, possibly a ferment, into sugar (dextrose). 



The presence of glycogen in the liver cells can be shown micro- 

 scopically in the form of discrete hyaline and refractive granules. 

 As they are soluble in water they can be readily dissolved out from 



