FORMATION OF SUGAR IN THE LIVER. 267 



substances themselves would be eliminated as foreign matters 

 by the kidneys. 



Then, again, it was discovered by Bernard, and the dis- 

 covery has been amply confirmed, that the liver possesses the 

 remarkable property of forming glucose or grape-sugar (C 6 H 13 

 O 6 ), or a substance readily convertible into sugar, even out of 

 principles in the blood which contain no trace of saccharine or 

 amylaceous matter. In Herbivora and in animals living on 

 mixed diet, a large part of the sugar is derived from the sac- 

 charine and amylaceous principles introduced in their food. 

 But in animals fed exclusively on flesh, and deprived therefore 

 of this source of sugar, the liver furnishes the means whereby 

 it may be obtained. Not only in Carnivora, however, but ap- 

 parently in all classes of animals, the liver is continually en- 

 gaged, during health, in forming sugar, or a substance closely 

 allied to it, in large amount. This substance may always be 

 found in the liver, even when absent from -all other parts of 

 the body. 



To demonstrate the presence of sugar in the liver, a. portion 

 of this organ, after being cut into small pieces, is bruised in a 

 mortar to a pulp with a small quantity of water, and the pulp 

 is boiled with sulphate of soda in order to precipitate albu- 

 minous and coloring matters. The decoction is then filtered 

 and may be tested for glucose. The most usual test is Trom- 

 mer's. To the filtered solution an equal quantity of liquor 

 potassse is added, with a few drops of a solution of sulphate of 

 copper. The mixture is then boiled, when the presence of 

 sugar is indicated by a reddish-brown precipitate of the sub- 

 oxide of copper. 



The researches of Bernard and others, however, have shown 

 that the sugar is not formed at once at the liver, but that this 

 organ has the power of producing a peculiar substance allied 

 to starch, which is readily convertible into glucose when in 

 contact with any animal ferment. This substance has received 

 the different names of glycogen, glycogenic substance, animal 

 starch, hepatin. 



Glycogen (C^H^C)^) is obtained by taking a portion of 

 liver from a recently^ killed animal, and, after cutting it into 

 small pieces, placing it for a short time in boiling water. It 

 is then bruised in a mortar, until it forms a pulpy mass, and 

 subsequently boiled in distilled water for about a quarter of 

 an hour. The glycogen is precipitated from the filtered decoc- 

 tion by the addition of alcohol. 



When purified, glycogen is a white, amorphous, starch-like 

 substance, odorless and tasteless, soluble in water, but insoluble 



