PHYSIOLOGY OF THE LIVER AND SPLEEN. 827 



into the blood as free sugar, a condition of hyperglycemia and glyco- 

 suria must evidently result, because the liver cannot be supposed 

 to handle the large amount of sugar derived from the carbohydrates 

 of an ordinary meal. We know that glycosuria does occur when 

 the carbohydrates are eaten in excess (alimentary glycosuria) for 

 this very reason. But within what we may call the normal 

 limits of a carbohydrate diet it seems most probable that the 

 contents of the portal vein never rise much above the usual level, 

 since the carbohydrate is absorbed slowly during a period of four 

 to five hours, and during this period a very large amount of blood 

 must flow through the intestines, as much perhaps -in five hours 

 as 180 to 190 liters, if one may apply to man the results of Burton- 

 Opitz, obtained for the dog, namely, a flow of 31 c.c. per minute 

 for each 100 gms. of intestine. There is, therefore, no reason to 

 suppose that the power of the liver to convert the dextrose to gly- 

 cogen is overtaxed by the amount of sugar brought to it dur- 

 ing digestion. From time to time the glycogen of the liver 

 is reconverted into sugar (dextrose) and is given off to the blood. 

 By this means the percentage of sugar in the systemic blood 

 is kept nearly constant (0.1 to 0.2 per cent.) and within limits 

 best adapted to the use of the tissues. The great importance of the 

 formation of glycogen and the consequent conservation of the sugar 

 supply of the tissues is evident when we consider the nutritive value 

 of carbohydrate food. Carbohydrates form the bulk of our usual 

 diet, and the proper regulation of the supply to the tissues is, there- 

 fore, of vital importance in the maintenance of a normal, healthy 

 condition. The second part of this theory, which holds that the 

 glycogen is reconverted to dextrose, is supported by observations 

 upon livers removed from the body. It has been found that shortly 

 after the removal of the liver the supply of glycogen begins to dis- 

 appear and a corresponding increase in dextrose occurs. Within a 

 comparatively short time all the glycogen is gone and only dextrose 

 is found. It is for this reason that in the estimation of glycogen in the 

 liver it is necessary to mince the organ and to throw it into boiling 

 water as quickly as possible, since by this means the liver cells are 

 killed and the conversion of the glycogen is stopped. How the gly- 

 cogen is changed to dextrose by the liver is a matter not fully ex- 

 plained. According to most authors, the conversion is due to an 

 enzyme produced in the liver. Extracts of liver, as of some other 

 tissues, yield an enzyme (glycogenase) that changes glycogen to dex- 

 trose.* It is probable, therefore, that the normal conversion of gly- 

 cogen to dextrose is effected by a special enzyme produced in the 

 liver cells. In this description of the origin and meaning of the liver 

 glycogen reference has been made only to the glycogen derived 

 * Tebb, "Journal of Physiology," 22, 423, 1897-98. 



