216 ELEMENTARY PHYSIOLOGY less. 



agents into grape sugar, or dextrose, as it should be 

 called ; and this glycogen is similarly converted with ease 

 into dextrose. Indeed, if the liver of such an animal as 

 the above, instead of being examined immediately after 

 death, be left in the body, or be placed on one side after 

 removal from the body for some hours before it is 

 examined, a great deal of the glycogen will have dis- 

 appeared, a quantity of dextrose having taken its place. 

 There seems to be present in the liver some agent capable 

 of converting the glycogen into a special sort of sugar 

 called dextrose and this change is particularly apt to 

 take place if the liver is kept at blood-heat or near that 

 temperature. 



Now if, instead of the liver of a well-fed animal, the liver 

 of an animal which has been starved for several days be ex- 

 amined in the same way, very little glycogen indeed will be 

 found in it, and when this liver is left exposed to warmth 

 for some time very little dextrose is found. That is to 

 say, the liver has, in the first case, formed the glycogen 

 and stored it up in itself, out of the food brought to it by 

 the portal blood : in the second case, no food has been 

 brought to the liver from the alimentary canal, no glyco- 

 gen has been formed, and none stored up. If the liver 

 in the first case be examined microscopically with certain 

 precautions, the glycogen may be seen stored up in the 

 hepatic cells ; in the second case little or none can be seen. 



The kind of food which best promotes the storing up 

 of glycogen in the liver is one containing starch or sugar ; 

 but some glycogen will make its appearance even when an 

 animal is fed on an exclusively protein diet, though not 

 nearly so much as when starch or sugar is given. 



It would appear, tlien, tliat the hepatic cells can manu- 

 facture and store up in themselves the substance glycogen, 

 being able to make it out of even protein matter, but more 

 easil}^ making it out of sugar ; for, as we shall see, all the 

 starch which is eaten as food is converted into sugar in the 

 alimentary caual, and reaches the liver as sugar. 



