444 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



portal vein and carried to the liver. But, no. It may be 

 shown to be formed in the liver itself. The following 

 experiments show it: 



i. An animal may be fed on flesh alone (which we 

 know contains no sugar-making substance) for weeks 

 continuously, and yet sugar will be found in the hepatic 

 vein. Or else an animal may be starved for weeks, and 

 still sugar will be found in the hepatic vein. Evidently 

 it must be made in the liver. 



2. Let the liver be taken from a recently dead animal 

 and laid on the table. If now water be injected into 

 any one of the trunk vessels, the liquid running out of 

 the other two, if tested, will, of course, show sugar; con- 

 tinue the current until only pure water runs out, pure 

 both of blood and of sugar. Let the liver stand a while 

 — say an hour. If now the current be started again, the 

 issuing water will again show sugar. This may be re- 

 peated many times with similar result until finally no 

 sugar comes out. The material out of which sugar is 

 made is exhausted. The sugar, therefore, is evidently 

 made from some insoluble or nearly insoluble substance, 

 which is continually being changed into soluble sugar 

 and washed out. 



3. If a liver be kept a considerable time the sugar 

 accumulates until the liver becomes perceptibly sweetish 

 to the taste, even when cooked. 



Now, the substance from which sugar is formed has 

 been isolated and its properties and composition deter- 

 mined. It is a colorless, tasteless, odorless, nearly in- 

 soluble substance, having the composition of starch— 

 QH ]0 O 5 . It is indeed a kind of animal starch. It exists 

 in the liver in large quantities— two per cent, seven per 

 cent, and even fifteen per cent of the whole weight. 

 Like starch or dextrine, but more readily than either, it 

 is changed into sugar by enzymes. There is an enzyme 



