668 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



of sugar. Even after death, if the blood be removed from the liver by 

 injecting water through the portal vein, it will be found that after every 

 trace of sugar has disappeared, if the liver be allowed to stand for a 

 time in a warm place, the repetition of these injections will again remove 

 sugar from the liver. 



If the liver be removed from an animal immediately after death and 

 divided into two portions, if one of these is thrown immediately, after 

 rapid mincing, into a large quantity of previously prepared boiling water, 

 an opalescent decoction will be obtained which will contain barely a 

 trace of sugar. If a decoction be made of the other portion of the 

 liver, after allowing it to remain for several hours in a warm place, the 

 decoction will be clear, and not opalescent, and will contain large quan- 

 tities of reducing sugar. 



On the other hand, if to a small quantity of the opalescent decoction 

 which was free from sugar be added a few drops of saliva, or of the 

 diastatic ferments of the pancreatic juice, sugar will be abundantly 

 formed. 



It is evident, therefore, that the liver contains something which is 

 capable of being converted into sugar through the influence of some 

 ferment contained either in the liver-cells or in the blood. 



If the opalescent infusion be tested with iodine, a mahogany-red 

 color will be formed ; it is evident, therefore, that this substance is some- 

 what of the nature of dextrin or starch, and Bernard, its discoverer, 

 gave to it the name of glycogen. 



Glycogen may be obtained from such a decoction, after rapidly cooling by 

 surrounding it by a freezing mixture of snow and salt, by the alternate addition 

 of hydrochloric acid and the potasso-mercuric iodide solution* until no further 

 precipitate occurs. By this means the albuminous constituents are removed. 

 This precipitate should be filtered off, and glycogen may be precipitated from the 

 filtrate by the addition of alcohol until about 60 per cent, of absolute alcohol is 

 present in the mixture. The glycogen is then to be collected on a filter and 

 washed with 60 per cent, alcohol until the washings give no cloudiness with a 

 mixture of dilute caustic potash, ammonia, and ammonium chloride. It is then 

 to be washed with alcohol and ether. The glycogen remaining should then be 

 dried on a piece of porous earthenware at a moderate temperature. It may be 

 further purified, if necessary, by dissolving in hot water and precipitating with 

 alcohol containing a little ammonia, redissolving as before, and precipitating with 

 spirit containing a little acetic acid. 



This last precipitate should then be washed with alcohol and ether, and then 

 dried. 



As obtained by this method, glycogen is a white, amorphous, non- 

 nitrogenous substance, which, with water, forms an opalescent solution 

 and rotates the plane of polarized light strongly to the right to about 



*The potasso-mercuric iodide solution is prepared by precipitating a saturated 

 solution of potassic iodide with a saturated solution of mercuric chloride, and, after 

 washing the precipitate, making a saturated solution of it in a hot solution of potassic 

 iodide. 



