4 88 TEXT-BOOK OF PHYSIOLOGY 



animal fed on a pure protein diet plus fat, glycogen will continue to be 

 formed in the liver though in far less amounts. 



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

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

 The dextrose or glucose 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 direct to the liver, where a certain portion of it diffuses across 

 the capillary walls into the surrounding lymph-spaces; by the action of the 

 cells or by a special enzyme 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, transform the glycogen into glucose or dextrose by the addition 

 of a molecule of water, after which it is returned to the blood, by which it 

 is transported to the systemic capillaries, where it disappears again, diffusing 

 across 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. Ultimately, how- 

 ever, through oxidation (glycolysis) 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. 



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

 states that the blood on the cardiac side of the liver never under normal circum- 

 stances 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 re- 

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

 into the blood; the function of the liver is merely to arrest the passage of sugar, 

 and so to shield the general circulation from an excess; the sugar which arises 

 in the liver after death is a post-mortem product and not an illustration of what 

 takes place during life. Dr. Pavy, having apparently demonstrated the glucosid 

 constitution of protein material in general, accounts for the presence of glycogen 

 in; muscles and other tissues on the assumption that during the cleavage of the 

 protein molecule the carbohydrate element is set free and temporarily stored as 

 glycogen. He thus accounts for the production of sugar in the body, even in the 

 absence of all sugar and starch from the food. Pavy believes that the glycogen 

 produced in the liver is utilized in the formation of fat and the synthesis of complex 

 proteins necessary to the construction of the tissues. 



The Formation of Urea. It is now generally believed that the liver 

 is the most active of all the organs which may be engaged in the production 

 of urea. This belief is based on numerous physiologic and pathologic 

 data. The compounds out of which the hepatic cells construct urea have 

 been for chemic reasons asserted to be the ammonium salts, e.g., the car- 



