THE METABOLISM OF FATS AND CARBOHYDRATES 139 



This means that a full-sized liver may hold 150 grams of 

 glycogen. 



Bernard's interpretation of his discovery was somewhat 

 as follows : The liver is the carbohydrate bank of the body. 

 Like any bank, it is subject by turns to deposit and with- 

 drawal. Its hoard is increasing when much sugar is ar- 

 riving from the intestine, for it is then diverting the surplus 

 from the blood of the portal circulation. The change by 

 which sugar is made into glycogen is clearly just the re- 

 verse of the digestive process- a dehydration and a con- 

 densation to form larger molecules as contrasted with the 

 familiar hydrolytic cleavage. The liver cells seem to be 

 stimulated to make this change by the rise of the per- 

 centage of sugar in the portal blood. When absorption 

 ceases it may be assumed that the sugar of the blood in 

 general sinks slightly in amount. This condition appears 

 to cause a reversal of the prevailing reaction in the liver, 

 the stored glycogen is gradually transformed to sugar, 

 and this passes out to renew the supply in the circulation. 

 The approximate constancy of the sugar in the blood is thus 

 accounted for in the main by the power which the liver 

 possesses to remove or return it, according to the shifting 

 conditions. 



The making of glycogen from sugars occurs only during 

 life. The converse change from glycogen to sugar takes 

 place freely after death, and is doubtless due to an enzyme. 

 It might be anticipated that a comparatively short period 

 of fasting would suffice to exhaust the glycogen of the liver. 

 As a matter of fact, there is a large reduction in the first 

 day, but the removal then proceeds slowly and is scarcely 

 ever completed. The disappearance is greatly hastened by 

 muscular activity, most effectually by the intense con- 

 vulsions produced by strychnin-poisoning. For human 

 (subjects it has been shown that glycogen is consumed 

 rapidly under the influence of iced baths. (How we are 

 able to judge of the abundance or scarcity of glycogen in 

 living men will be explained in another connection.) 



For some time after Bernard first called attention 



