4 o8 TEXT-BOOK OF PHYSIOLOGY. 



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. The pro- 

 duction of glycogen is dependent very largely on the consumption of 

 carbohydrates, the greater the amount of sugar and starch in the 

 food, the greate? being the production of glycogen. On a pure 

 proteid diet it is still produced, though in small amounts. 



Glycogen is present also in muscles, in the placenta, in the tissues 

 of the embryo wherever, indeed, active tissue changes and growth 

 are taking place. 



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

 disposition as at present generally accepted, may be stated as follows : 

 The dextrose into which the carbohydrates are converted by the 

 action of the digestive fluids is absorbed into the blood of the portal 

 vein and carried direct into the liver, where by the action of the cells 

 it is abstracted, 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, transform the glycogen into dextrose, return it to 

 the circulation, by which it is transported to the systemic capillaries, 

 where it disappears. The blood of the hepatic vein therefore contains 

 more sugar than the blood of any other part of the body, and the 

 blood of the arteries more than the blood of the other veins. Should 

 there be a failure on the part of the liver cells to abstract the sugar, 

 it would pass through the liver into the general circulation, from which 

 it would be eliminated by the kidneys. The final fate of the sugar 

 is uncertain. It is, however, probable that after its delivery to the 

 muscles, for example, it -may be directly oxidized, or stored as 

 glycogen, or possibly utilized in the formation of living material. 

 Ultimately, however, through oxidation it yields heat, and contributes 

 to the production of muscle energy. 



In opposition to this view, Dr. Pavy, after years of accurate ex- 

 perimentation, states that the blood on' the cardiac side of the liver 

 never under normal circumstances contains a larger percentage of 

 sugar than is to be found in any part of the circulation, except in the 

 portal vein. He states that glycogen is never reconverted into sugar, 

 and denies that the liver produces sugar, to be discharged into the 

 blood; that the function of the liver is merely to arrest the passage of 

 sugar, and so to shield the general circulation from an excess; that the 

 sugar which arises in the liver after death is a postmortem product 

 and not an illustration of what takes place during life. Dr. Pavy, 

 having apparently demonstrated the glucoside constitution of proteid 

 aterial in general, accounts for the presence of glycogen in muscles 

 and other tissues on the assumption that during the cleavage of the 

 proteid molecule the carbohydrate element is set free and temporarily 



