314 THE METABOLISM OF THE CARBOHYDRATES 



led to look to some function of the liver, for all the blood must 

 pass through this organ on its way from the intestines to the 

 tissues. We must assume that this organ is endowed with some 

 function whereby it retains the excess of sugar in the portal 

 blood and prevents its overflowing into the systemic circulation, 

 and thus creating a condition of hyperglycsemia, and consequently 

 of glycosuria. If, however, the liver be examined for sugar in a 

 perfectly fresh state, and even after a meal rich in carbohydrates, 

 it will be found to contain only a very small amount, so that the 

 excess of sugar which this organ seems to remove from the portal 

 blood cannot be retained in it as sugar. 



It must be as something else. That the liver does contain 

 some substance closely related to sugar was shown in 1855 by 

 Claude Bernard. He found that when the liver was perfused 

 through its blood-vessels with water, until the washings were 

 sugar and proteid free, and then was allowed to stand over night 

 at room temperature, a large amount of sugar reappeared in it. 

 From this result Bernard concluded that by some post-mortem 

 process sugar had been formed in the liver out of some substance 

 not sugar. 



Claude Bernard (*) in 1857 discovered this substance to be 

 glycogen, and dating from that discovery great strides have been 

 made in the subject of carbohydrate metabolism. 



At most, however, the liver contains only 10 per cent, of 

 glycogen, and, if we allow 1500 grm. for the weight of the liver of 

 a full-grown man, we can account in this way only for 150 grm. of 

 the sugar absorbed from the intestine ; and indeed, not for so 

 much as this, for the liver still contains a considerable amount 

 of glycogen after fasting, unless this be of long duration (see 

 p. 324). There must, therefore, be in the organism other places 

 besides the liver in which the excess of sugar is laid by in some 

 modified form. The muscles contain sometimes as much as 

 1 per cent, of glycogen, so that, collectively, they could probably 

 hold as much of this substance as the liver does. In these two 

 depots (liver and muscles) there might, therefore, be laid aside 

 as glycogen about 300 grm. of sugar. But our diet often contains 

 much more carbohydrate than this, so that we must conclude 

 that a considerable amount of : carbohydrate becomes con- 

 verted into, or -at least incorporated with, tissues which are 

 not carbohydrate in nature i.e. with fat or proteid. 



