446 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



the large quantity of sugar carried by the portal vein to 

 the liver is detained there by dehydration into the insolu- 

 ble form of glycogen, and then slowly and continuously 

 rehydrated into the soluble form of liver sugar, and de- 

 livered little by little to the blood as the necessities of 

 combustion require. 



Observe the double change. The sugar from the in- 

 testines is afehydrated only to be rehydrated. The rea- 

 son is twofold: (i) It must be stored and delivered little 

 by little, because sugar in the blood in large quantity is 

 hurtful. Among other hurtful effects, see the cataract 

 and blindness of diabetic patients. 



(2) Liver sugar is a more easily oxidizable sugar, a 

 more combustible fuel, than glucose. Glucose will cir- 

 culate in the blood for a long time until it is finally ex- 

 creted through the kidneys in diabetic patients. But 

 liver sugar seems to burn up almost as soon as it touches 

 the oxidized blood. 



We have, then, one source of glycogen — viz., the glu- 

 cose taken up from the intestines and dehydrated in the 

 liver; but this can not be the only source, for flesh-fed 

 animals also make liver sugar. Therefore glycogen 

 must be made from albuminoids also. How it is made 

 is more uncertain. I believe it is made as follows:* 

 Remember that albuminoid food excess is split into a 

 combustible carbohydrate part and a nitrogenous incom- 

 bustible part ; the one eliminated by the lungs, the other 

 by the kidneys. Now I believe that the place of this 

 splitting is the liver, the combustible carbohydrate 

 formed is glycogen, and the incombustible part is urea.f 



But this is not yet enough. There must be still a 



* See writer's views, Am. Jour., xv, 99, 1878, and xix, 25, 

 1880. 



f Urea is proved to be formed in the liver (Nature, lvii, 395, 

 1898). 



