468 METABOLISM, NUTRITION, AND DIET 



Dextrose is a constant constituent of the blood to the extent of about o.i 

 to 0.15 per cent. When this percentage is increased above 0.25, the 

 dextrose is either stored as glycogen, i.e., in the case of the portal blood 

 during the absorption of a carbohydrate meal, or eliminated by the 

 kidney, i.e., as in pancreatic diabetes. 



The Formation of Glycogen Glycogenesis: The important fact 

 that the liver normally forms sugar, or a substance readily convertible 

 into it, was discovered by Claude Bernard in the following way: He fed a 

 dog for seven days with food containing a large quantity of sugar and starch; 

 and, as might be expected, found sugar in both the portal and hepatic blood. 

 But when the dog was fed with meat only, to his surprise, sugar was still 

 found in the blood of the hepatic veins. Repeated experiments gave in- 

 variably the same result. No excess of sugar was found in the portal vein 

 under a meat diet, if care was taken to prevent reflux of blood from the he- 

 patic venous system. Bernard found sugar also in the substance of the liver. 

 It thus seemed to him certain that the liver formed sugar eVen when, from the 

 absence of saccharine and amyloid matters in the food, none could be brought 

 directly to it from the stomach or intestines. 



Bernard subsequently found that a liver removed from the body, and 

 from which all sugar had been completely washed away by injecting a stream 

 of water through its blood vessels, contained sugar in abundance after the 

 lapse of a few hours. This post-mortem production of sugar was a fact 

 which could be explained only on the supposition that the liver contained a 

 substance readily convertible into sugar. This theory was proved cor- 

 rect by the discovery of a substance in the liver allied to starch, termed 

 glycogen. 



Bernard's brilliant researches led him to announce the theory that the 

 carbohydrate which is periodically absorbed in large amount is stored in the 

 liver only to be reconverted to dextrose and discharged back into the blood 

 stream whenever the percentage in the blood falls below a certain level. 

 He regarded the liver as a storehouse which regulated the blood dextrose 

 to a constant level. This is the glycogenic function of the liver. 



Source of Glycogen. The greatest amount of glycogen is produced 

 by the liver upon a diet of starch or sugar, but a certain quantity is, or at 

 least may be, produced upon a protein diet. The glycogen, when stored in 

 the liver cells, may readily be demonstrated in sections of liver containing it 

 by its reaction (red or port- wine color) with iodine, and, moreover, when the 

 hardened sections are so treated that the glycogen is dissolved out, the proto- 

 plasm of the cell is so vacuolated as to appear little more than a framework. 

 There is no doubt that in the liver of a hibernating frog the amount of glyco- 

 gen stored up in the liver cells is very considerable. 



