SECRETION. 449 



liver continually produces glycogen it is said to have a starch-forming or a 

 glycogenic or an amylogenic 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 glyco- genetic Junction. 



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

 in the form of discrete hyaline and refractive masses. 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 produc- 

 tion of glycogen is dependent very largely on the consumption of carbohy- 

 drates, the greater the amount of sugar and starch in the food, the greater 

 being the production of glycogen. Nevertheless it is also certain that gly- 

 cogen can be derived from proteins; for if the carbohydrates are excluded 

 from the food and the animal fed on a pure protein diet, glycogen will con- 

 tinue to be formed in the liver though in far less amounts. 



The facts connected with the formation of glycogen, as well as with its de- 

 struction as at present generally accepted, may be stated as follows: The 

 dextrose into which the carbohydrates are mainly converted by the action 

 of the digestive fluids is absorbed into the blood of the portal vein and carried 

 directly to the liver, where a certain portion of it diffuses through the cap- 

 illary walls into the surrounding lymph spaces; by the action of the cells 

 it is then dehydrated, and temporarily deposited under the form of the non- 

 diffusible body glycogen. At a subsequent period and in proportion to the 

 needs of the system the liver cells, through the agency of a ferment, trans- 

 form the glycogen into glucose or dextrose, return it to the blood, by which 

 it is transported to the systemic capillaries, where it disappears again, diffus- 

 ing through the walls of the capillaries into the surrounding lymph spaces 

 to play a part in the general nutritive process. Though the final disposition 

 of the sugar is uncertain it is highly probable that after its delivery to the 

 muscles, for example, it may be directly oxidized or temporarily stored 

 as glycogen or possibly be used in the formation of living material. Ulti- 

 mately, however, through oxidation it yields heat and contributes to the 

 production of muscle energy. . Should there be a failure on the part of the 

 liver cells to store up its usual percentage of the absorbed sugar, 10 to 20 

 per cent, by reason of impaired nutrition, disturbance of the portal circu- 

 lation, or a larger excess of sugar in the blood of the portal vein, it would 

 pass through the liver into the blood of the general circulation and increase 

 the percentage amount of sugar above the normal (o.i to 0.2 per cent.) 

 establishing the condition of hyperglycemia. This would soon be followed 

 by its elimination from the blood by the kidneys and its appearance in 

 the urine, giving rise to a glycosuria. 

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