FATE OF GLYCOGEN IN THE ORGANISM 335 



that of a reserve carbohydrate. The sugar in the portal blood 

 which is in excess of that in the systemic blood (i.e. above 0'2 

 per cent.) is converted into glycogen in the liver, and whenever 

 the amount of sugar in the systemic blood tends to fall below its 

 normal percentage, the liver glycogen is, according to this theory, 

 reconverted into sugar, which is liberated into the blood of the 

 hepatic vein, and so keeps up the average percentage of sugar 

 in the systemic blood. At first, Bernard thought that the 

 glycogen was derived from proteids and not from carbo- 

 hydrates. 



Pavy admits that glycogen is derived from excess of sugar in 

 the portal blood, but thinks that this glycogen never again, under 

 normal conditions, becomes transformed into sugar, but is built up 

 into non-carbohydrate substances, viz. fat and proteid, which then 

 undergo metabolism along their own lines. 



We will discuss Bernard's theory first. By this theory, it is 

 easy to explain why the percentage of sugar in the systemic blood 

 should be practically constant, although there are considerable 

 variations in the sugar content of the portal blood. The amount 

 of sugar in the body depends mainly on two factors : firstly, on the 

 supply of sugar from the intestine, and secondly, on the rate of 

 oxidation of sugar in the tissues. The second factor is a fairly 

 constant one varying, of course, somewhat with the activity of 

 the muscles but the first factor varies enormously according to 

 whether digestion be in progress or not. The balance of action 

 of these two factors would therefore tend to cause, during the 

 absorption of food, an overplus of sugar in the systemic blood, and 

 during starvation, a deficit. We have, however, seen that when- 

 ever the percentage of sugar in the systemic blood rises dis- 

 tinctly above 0*2 sugar appears in the urine a condition of 

 glycosuria is established ; but glycosuria practically never occurs 

 under normal conditions ; and, on the other hand, the systemic 

 blood always contains between 0*05 and 0*2 per cent, of sugar, 

 even during starvation. To explain this, Bernard offers the above 

 theory. 



The most important facts which Bernard brought forward in 

 support of his theory are as follows : 



Firstly, the percentage of sugar in the liver is higher than in 

 any other organ or tissue. 



Secondly, after death, the glycogen in the liver gradually dis- 



