EXTERNAL SECRETIONS 487 



ja rise of pressure beyond that of the capillary blood-vessels, and a reabsorp- 

 ition by the lymph-vessels of the bile constituents. After their discharge into 

 jthe blood from the thoracic duct these constituents are deposited in part 

 i in various tissues, giving rise to the phenomena of jaundice, and in part are 

 eliminated in the urine. 



The Production of Starch (Glycogen) and Sugar (Glycose or Glucose) . 

 In 1857 Bernard discovered the fact that the liver normally during life 

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

 known as liver starch or animal starch. 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 proteins are removed by nitration. The nitrate thus obtained 

 is opalescent and resembles a solution of starch. The starch may be 

 precipitated from this solution with alcohol. It may subsequently be ob- 

 tained free by drying, when it presents itself as a white amorphous powder, 

 soluble in hot or cold 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 pres- 

 ence of sugar. 



For the reason that this starch is capable of being transformed into or of 

 generating glycose or glucose it received the name of glycogen; and inasmuch 

 as the liver continually produces glycogen it may be said to have a starch- 

 forming or an amylogenetic or a glycogenic function. 



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 starch but a 

 relatively large amount of sugar. The inference drawn is that after death 

 the starch is transformed by some agent, possibly a ferment, into sugar 

 (glucose). From this fact as well as from the results of different lines of 

 investigation, it is the generally received opinion that the same change is 

 constantly taking place in the living condition and therefore the liver is said 

 to have a sugar-forming or a glycogenetic function. The liver cells are thus 

 characterized by two processes amylogenesis zndglyco genesis. To the trans- 

 formation of glycogen into sugar the term glycogenolysis has recently been 

 applied. 



The presence of glycogen in the liver cells can be shown microscopically 

 in the form of discrete hyaline and refractive masses, which show a blue or 

 violet color with iodin. As they are soluble in water they can be readily 

 dissolved out from the cells, leaving small vacuoles separated from one 

 another by strands of cell substance. The amount of glycogen in a well 

 fed animal varies from 1.5 to 4 per cent, of the total weight of the liver. By 

 experimental methods it has been shown that the production of glycogen i< 

 dependent very largely on the consumption of carbohydrates, the greatd 

 the amount of sugar and starch in the food, the greater being the production 

 of glycogen. Nevertheless it is also certain that glycogen can be derived 

 from proteins; for if the carbohydrates are excluded from the food and the 



