756 STORAGE OF GLYCOGEN. [BOOK n. 



ation of glycogen but not resulting in the storage of any carbo- 

 hydrate material and dealing possibly with proteid 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 secretion 

 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 or 

 lymph. 



460. 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 very 

 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 

 sugar becoming through some action of the hepatic cell-substance 

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

 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 undoubtedly 

 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 

 hydration or the dehydration is effected by living substance; but 

 we are equally ignorant of the exact way in which an amylolytic 

 ferment effects the hydration of starch into sugar, which it carries 

 out with so much apparent ease. It is not a great assumption to 

 suppose that the continually changing living substance, which in 

 its changes is continually giving out energy, has the power of 

 acting on molecules of starch or of sugar in contact with, or even 

 only near to itself, and so of hydrating starch into the sugar or of 



