KATABOLISM. 445 



for this purpose in the liver cells. The process of 

 change is, of course, a hydration, exactly like that which 

 saccharizes starch — viz., C 6 H 10 O 5 -|- H 2 = C 6 H 18 6 . 

 This substance is called glycogen, or the sugar-maker. 

 It has the same equivalent composition as starch and dex- 

 trine, but almost certainly a different molecular structure, 

 and therefore slightly different properties. For exam- 

 ple, it is more easily changed into sugar, and it gives a 

 different reaction with iodine. The sugar formed from 

 it, though it has the same equivalent composition as 

 glucose or intestinal sugar, has also probably a differ- 

 ent molecular structure, and therefore also slightly dif- 

 erent properties. It is apparently more easily oxidized 

 into CO a and H 2 0. It is better, therefore, to call it 

 liver sugar or hepatose. 



The formation of this sugar is a pure chemical not a 

 vital process, for it takes place in the dead as well as in 

 the living liver. The true vital process is the formation 

 of the glycogen, not the sugar. 



Such are the undoubted facts. But the question oc- 

 curs, Whence comes the, glycogen and what is its pur- 

 pose? There are certain other facts which throw light 

 on this question. 



1. The amount of amyloid food — say,. potatoes and 

 rice — which is consumed by a man in a day, or even at a 

 single meal, may be two pounds. The whole of this is 

 changed into sugar, and, if carried at once into the blood, 

 would make that liquid as sweet as sirup. But, on the 

 contrary, the quantity of sugar in the general circula- 

 tion is very small— only a trace. What becomes of it ? 



2. It will be remembered that the whole of the sugar 

 is taken up by the capillaries of the portal vein, and car- 

 ried to be distributed through the liver before reaching 

 the general circulation. 



Now, putting these facts together, it is evident that 



