THE LIVER 113 



Glycogen is a carbohydrate very similar to starch, and 

 when ingested it is acted upon by the same enzymes and un- 

 dergoes 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 normal (that is, its amount on a mixed diet), but 

 is not reduced to zero, when proteids alone are taken. This 

 points to the conclusion that the source of glycogen is car- 

 bohydrates, but that it can be formed to some extent from 

 proteids. Let it be said now that practically all carbohy- 

 drates 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 carbohy- 

 drate means its conversion into dextrose (glucose, levulose). 

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

 portal vein. 



We may say that the formula for dextrose is CeH^Oe and 

 for glycogen CeHioCte, though neither of these formulae is 

 probably exactly correct. It will be seen, therefore, that the 

 abstraction of one molecule of water (HsO) from dextrose 

 will produce glycogen, 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 carbohy- 

 drates. 



It will be seen under Nutrition that the carbohydrates fur- 

 nish 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 their 

 quick consumption, but also an unfortunate lack of energy- 

 producing materials before another meal. This storing up 

 brings about a kind of conservation of energy and an eco- 

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