THE LIVER. 139 



is colored wine-red by iodine. It may hold copper oxyhydrate in 

 solution in alkaline liquids, but does not reduce it. A solution of 

 glycogen in water is not precipitated by potassium-mercuric iodide 

 and hydrochloric acid, but is precipitated by alcohol or ammoniacal 

 lead acetate. Glycogen seems to be changed somewhat by prolonged 

 boiling with dilute caustic potash (VINTSCHGAU and DIETL). It is 

 converted into glucose by diastatic enzymes and also by being boiled 

 with dilute mineral acids. 



The preparation of pure glycogen (simplest from the liver) is 

 generally performed by the method suggested by BRUCKE, of which 

 the main points are the following: Immediately after the death of 

 the animal the liver is thrown into boiling water, then finely divided 

 and boiled several times with fresh water. The filtered extract is 

 now sufficiently concentrated, allowed to cool, and the albumin 

 removed by alternately adding potassium-mercuric iodide and 

 hydrochloric acid. The glycogen is precipitated from the filtered 

 liquid by the addition of alcohol until the liquid contains 60 vols. 

 per cent. The glycogen is first washed on the filter with 60$ and 

 then with 95$ alcohol, then treated with ether and dried over 

 sulphuric acid. It is always contaminated with mineral substances. 

 To be able to extract the glycogen from the liver or especially from 

 muscles and other tissues completely, which is essential in a quanti- 

 tative estimation, these parts must first be boiled for a few hours 

 with a dilute solution of caustic potash, say 4 gms. KOH to 100 gms. 

 liver (KtJLz). 



The quantitative determination is ordinarily performed accord- 

 ing to the above method of BRUCKE, fyit care must be taken that 

 the precipitate obtained by the potassium-mercuric iodide and hydro- 

 chloric acid is removed at least four times from the filter and stirred 

 with water to which has been added a few drops of hydrochloric 

 acid and potassium-mercuric chloride, and refiltered so as to be cer- 

 tain that all the glycogen is obtained in the filtrate (KiJLz). The 

 quantity of glycogen may also be determined by the polariscope or 

 by titration after first converting the glycogen into glucose by boil- 

 ing with an acid. 



Numerous investigators have endeavored to determine the origin 

 of glycogen in the body. The quantity of glycogen in the liver is 

 increased after partaking of many substances, in the first place by 

 the varieties of sugar and several other carbohydrates (PAVY and 

 others), also by glycerin (VAN BEEN, WEISS, LUCHSINGER), gelatin 

 (WOROSCHILOFF), and the glucoside arbutin. Inosit (KuLz) and 

 mannit (LUCHSINGER) have, on the contrary, no action. Fat is 



