166 A Manual of Veterinary Physiology. 



cent. : and in the horse, 09 per cent. (M'Kendrick). One 

 use of the liver is to regulate this amount and avoid a 

 surplus. During starvation the amount of glycogen in the 

 liver falls, and eventually disappears ; the liver has now 

 liberated to the blood the entire amount of sugar it is 

 capable of yielding. If food, particularly carbo-hydrates, 

 be now taken, the store of glycogen is replenished, and the 

 sugar-liberating function once more occurs. 



The method by which the glycogen becomes converted 

 in the liver into glucose (not maltose, as in the bowel), 

 before being issued to the blood, is generally considered to 

 be by means of a ferment (see p. 167), and this glucose, of 

 course, reaches the general circulation through the hepatic 

 veins. 



It is curious to observe that the starch must first be 

 converted into sugar before the bloodvessels of the bowel 

 can take it up, then in the liver once more converted into 

 a kind of starch, and, lastly, again into sugar before enter- 

 ing the blood. 



Glycogen differs in some respects from starch, one of its 

 principal differences being that it dissolves in cold water, 

 and is stained reddish brown by iodine. 



The total amount of glycogen obtained from a given 

 quantity of food is not wholly stored in the liver, as the 

 latter organ cannot contain more than about 10 per cent, of 

 this substance, which would represent only a small amount 

 of the soluble carbo-hydrates passing into the blood. Wo 

 know as a fact that the liver, having taken up all the sugar 

 it can from the portal vessels and converted it into stored- 

 up glycogen, allows the balance to pass through the hepatic 

 veins into the general circulation as sugar, and that it 

 is deposited in other organs (principally the muscles) as 

 glycogen for future use. The muscles of the borse contain 

 in this way a considerable quantity of glycogen. Even 

 after nine days' starvation, from I per cent, to 2'4 per cent. 

 of glycogen was found by Aldchoft'.* Blood contains no 

 glycogen. 



* Quoted by Bunge. 



