438 THE METABOLIC PROCESSES OF THE BODY. 



when iodine is added ; the color disappears on warming, but reappears on 

 cooling provided that not too much proteid matter has been left in the 

 solution. Treated with Fehling's fluid or other tests for sugar, the solution 

 is found to contain a small and variable, but only a small, quantity of sugar. 



If the solution be exposed, preferably in a warm room, to the action of 

 saliva or of some other amylolytic ferment, or be boiled with dilute acid, 

 the opalescence disappears ; and the now clear transparent solution gives 

 no longer the port-wine reaction with iodine. Tested, moreover, with Fehl- 

 ing's fluid or by other means it is now found to contain a considerable 

 quantity of sugar. 



If alcohol be added to the opalescent solution until the mixture con- 

 tains 60 per cent, of the alcohol (previous concentration by evaporation 

 being desirable) a white amorphous precipitate is thrown down. This pre- 

 cipitate, removed by filtration, boiled with an alcoholic solution of potash 

 in which it is insoluble, but which dissolves and destroys any proteids 

 which may be present, treated with ether to remove fatty impurities, and 

 washed with alcohol, may be obtained in a pure condition. It then appears 

 as a white amorphous powder, fairly soluble in water, but always giving 

 rise to a milky opalescent solution unless an excess of alkali be present, in 

 which case the opalescence may be slight or absent. 



The opalescent solution of this purified material gives a port-wine reac- 

 tion with iodine, but no reaction whatever with Fehling's fluid or the other 

 sugar tests. Treated with an amylolytic ferment or boiled with dilute acid, 

 the solution, like the raw decoction of liver, loses its opalescence and its 

 port-wine reaction with iodine, but now gives an abundant evidence of the 

 presence of sugar, dextrose if boiling with acid has been employed, malt- 

 ose chiefly if an amylolytic ferment has been used. If quantitative deter- 

 mination be employed it will be found that the amount of sugar obtained is 

 proportionate to the amount of the white powder acted upon ; in other 

 words the substance forming an opalescent solution is converted into sugar, 

 the solution of which is clear. Obviously the substance is a body allied to 

 the starch ; and this is confirmed by the elementary composition, which is 

 found to be C 6 H, O 5 or some multiple of this. 



Hence this body is called glycogen. And it is obvious from what has 

 been stated above that the liver of a well-fed animal at the moment of 

 death contains a considerable quantity of glycogen either in a free state or 

 in such a condition that it is set free by subjecting the liver to the action 

 of boiling water. We may add that it occurs in the liver in the hepatic 

 cells, for the reaction of a port-wine color given under certain conditions 

 by the hepatic cells is due to the presence of glycogen in them. 



374. If the liver, instead of being treated immediately upon the 

 death of the animal, is allowed to remain in the body of the dead animal 

 for several hours, especially in a warm place, before a decoction is made 

 of it, the decoction will be found to have little or no opalescence, to be 

 quite clear, to give little or no port-wine reaction with iodine, but to 

 contain a very considerable quantity of sugar. As we have said above, 

 the decoction even of a liver taken immediately after death generally con- 

 tains some little sugar, and the quantity of sugar in the liver appears, as a 

 rule, to increase steadily after death, the amount of glycogen diminishing 

 at the same time. The glycogen then present in the liver at the moment 

 of death is gradually after death by some action or other converted into 

 sugar. 



The action is that of some agency whose activity is destroyed by the tem- 

 perature of boiling water; hence the directions repeatedly given above to 

 throw the liver into boiling water. This naturally suggests the presence in 



