CHAP, iv.] METABOLIC PROCESSES OF THi: !;<>]>. 009 



ently to consider briefly the relations of the one pro. -i-ss to tin- 

 other. In the third place, as is especially indicated by tin- 

 somewhat peculiar effect on tin- hepatic cell of food -x<-lu> 

 proteid in nature, other processes, similar perhaps to the forma- 

 tion of glycogen but not resulting in the storage of my carbo- 

 hydrate material and dealing possibly with pmteid substances, 

 also take place. Hence the exact interpretation of all the 

 changes which may be observed becomes exceedingly difficult. 



Leaving the processes of the first and third kind wholly on 

 one side for the present, and confining our attention entirely to 

 the glycogen, it is obvious that the hepatic cell manufactures the 

 glycogen in some way or other, and lodges it in its own substance 

 for the time very much in the way that a secreting cell manu- 

 factures and lodges in itself for a time material for the secret ion 

 which it is about to pour forth. There is this difference, that in 

 the one case the material of the secretion, after undergoing as 

 we have seen more or less change, is cast out into the lumen of 

 the alveolus, whereas in the other case the glycogen, which must 

 undergo change since it may be made to disappear rapidly from 

 the hepatic cell, is not when changed cast out into the bile 

 passages ; it must therefore be sent back again to the blood. 



364. We say " manufactures the glycogen in some way or 

 other," and we have now to inquire what we know concerning 

 the nature and the several steps of this manufacture. 



We have already seen that the presence of glycogen in the 

 liver is especially favoured by a carbohydrate diet ; and in our 

 studies on digestion we have seen reason to think that a 

 large part at all events of the carbohydrate material of a meal is 

 absorbed as sugar by the capillaries of the intestine and carried 

 as sugar to the liver in the portal blood. Hence, it seems only 

 reasonable to conclude that the glycogen which makes its appear- 

 ance in the liver after an amylaceous meal arises from a direct 

 conversion of the sugar carried to the liver by the portal vein, the 

 su^ar becoming through some action of the hepatic cell-substance 

 dehydrated into glycogen, or animal starch as it has been culled, 

 the process being a reverse of that by which in the alimentary 

 canal starch is hydrated into sugar through the action of the 

 salivary and pancreatic ferments. Vegetable cells can undoubt- 

 edly convert both starch into sugar and sugar into starch ; and 

 there are no a priori arguments or positive facts which would 

 lead us to suppose that the activity of animal living substance 

 cannot accomplish the latter as well as the former of these changes. 

 We are quite ignorant it is true of the exact way in which either 

 the hydrationor the dehydration is effected by living substance; 

 but we are equally ignorant of the exact way in which an umy- 

 lolytic ferment effects the hydration.of starch into sugar, which 

 it carries out with so much apparent ease. It is not a 

 assumption to suppose that the continually changing living 



