THE LIVER 113 



after eating, and to decrease notably when eating is refrained 

 from for some time. 



Glycogen is a carbohydrate very similar to starch, and when 

 ingested it is acted upon by the same enzymes and undergoes 

 the same conversions. Furthermore, the amount of glycogen 

 in the liver is very greatly increased by restricting the diet to 

 carbohydrate foods and is lessened considerably below the nor- 

 mal (that is, its amount on a mixed diet), but is not reduced to 

 zero, when proteids alone are taken. This points to the con- 

 clusion that the source of glycogen is carbohydrates, but that it 

 can be formed to some extent from proteids. Let it be said 

 now that practically all carbohydrates are converted by digestion 

 into maltose, or maltose and dextrin and furthermore that during 

 absorption these sugars are converted into dextrose or dextrose 

 and levulose. It is customary to assume that the digestion of a 

 carbohydrate means its conversion into dextrose (glucose, levu- 

 lose). It is, then, this sugar which is carried to the liver by the 

 portal vein. 



We may say that the formula for dextrose is C 6 H ]2 O 6 and for 

 glycogen C 6 H 10 O 5 , though neither of these formulae is probably 

 exactly correct. It will be seen, therefore, that the abstraction of 

 one molecule of water (H 2 O) from dextrose will produce glyco- 

 gen, and this is the change which the liver cells are supposed to 

 effect. Again, when the conversion of dextrose into glycogen 

 has taken place, the glycogen is stored up in the liver cells, to be 

 given off continuously to the blood only in such quantities as the 

 system may demand. The liver thus becomes a warehouse for 

 the storage of all the carbohydrates. 



It will be seen under Nutrition that the carbohydrates furnish 

 the chief material to be burned up in the body for the purpose 

 of liberating heat and furnishing energy, and if they should be 

 consumed as soon as they enter the circulation, there would be 

 not only an unnecessary waste during Iheir quick consumption, 

 but also an unfortunate lack of energy-producing materials before 



