BY DR. LAUDER BRUNTON. 511 



order to get the gtycogen pure. This is best done by precipi- 

 tating them with potassio-mercuric iodide, as recommended by 

 Briicke. This solution is made by precipitating a solution of 

 mercuric chloride with potassium iodide, washing the precipi- 

 tate and adding it to a boiling solution of potassium iodide till 

 the latter is saturated. 



When the filtrate from the liver is cool, add hydrochloric acid 

 and potassio-mercuric iodide solution to it alternatel}*, as long 

 as they cause any precipitate. Stir the mixture, let it stand 

 about five minutes, and then filter. Add alcohol to the filtrate 

 till glycogen begins to be copiously precipitated, taking care 

 not to add an excess of alcohol, lest other substances be also 

 precipitated. The glycogen is best precipitated when the mix- 

 ture contains 60 per cent, of absolute alcohol. Collect the gly- 

 cogen in a filter, wash it, first with dilute alcohol, then with 

 strong alcohol of 90 per cent. (sp. gr. 822), which makes it more 

 easy to separate from the filter. Extract it- with ether and dry 

 it rapidly on a flat plate. Instead of separating the albumin 

 from the glycogen by potassio-mercuric iodide, the boiling solu- 

 tion of glycogen may be slightly acidulated with acetic acid 

 and filtered. The filtrate is then quickly evaporated to half its 

 bulk and mixed with its own volume of strong alcohol of 90 

 per cent. The glycogen is precipitated along with a little glu- 

 tin. To separate it from this it is boiled with liquor potassae 

 for an hour or more, neutralized with acetic acid, precipitated 

 with alcohol, collected on a filter, washed first with strong alco- 

 hol and then with absolute alcohol till all traces of water have 

 been removed, and then the alcohol displaced by absolute ether. 

 The glycogen remains as a white powder. It is to be quickly 

 dried by spreading it in a thin layer on a warm porcelain plate 

 and passing a current of air over it. If the glutin has not been 

 perfectly removed, or if the water has been incompletely dis- 

 placed by the alcohol and ether, the glycogen in drying becomes 

 converted into a gummy mass, instead of forming, as it ought 

 to do, a white powder. 



* 157. Properties of Glycogen. Glycogen is amorphous, 

 colorless, and tasteless. In water it is readily soluble. The 

 solutions are strongly opalescent, and when concentrated are 

 quite milky. They are, apparently, true solutions, as they pass 

 unchanged through filters and through animal charcoal, and no 

 particles can be observed in them by the microscope. Briicke, 

 however, considers that they are not true solutions, but merely 

 suspensions of particles of glycogen swollen up in the fluid. The 

 opalescence disappears on the addition of caustic alkalies, 

 although the alkali does not destroy the glycogen. In alcohol 

 and in ether it is insoluble. It contains no nitrogen. When 

 burnt on platinum foil, it does not give off the peculiar smell 

 of nitrogenous bodies, nor does it leave any ash. 



