124 THE CARBOHYDRATES. [CH. V. 



The precipitate is washed with ten times its volume of 66 per cent, alcohol, 

 containing i cc. per litre of saturated sodium chloride. After settling, the 

 fluid is filtered through the original filter paper. This process is repeated once 

 more, and then the precipitate is shaken with ten times its volume of 96 per 

 cent, alcohol and filtered through the same paper. The precipitate is washed 

 with ether, dissolved in boiling water and the solution made up to one litre. 

 200 cc. of this are treated with 10 cc. of concentrated HC1 and heated in a 

 flask on a boiling water bath for three hours, to convert the glycogen into 

 glucose. After cooling, the solution is neutralised with 20 per cent, potash 

 and filtered through a small paper into a 250 cc. measuring flask. The wash- 

 ings from the flask used for inversion are filtered through the same paper to 

 remove the last traces of glucose, and the solution brought up to 250 cc. The 

 percentage of glucose in the solution is determined by analysis. This multi- 

 plied by -927 gives the amount of glycogen in the 200 cc. of the solution used 

 for inversion, and so the percentage in the tissue can be readily calculated. 



Preparation. A rabbit, which has had a full meal of carrots some five 

 or six hours previously, is killed by decapitation. The liver is cut out as 

 quickly as possible, and the gall-bladder removed. The liver is rapidly 

 chopped into small pieces, a small portion being reserved for Ex. 156, and the 

 remainder immediately thrown into boiling water. After about two minutes 

 boiling the larger morsels are strained off, pounded to a paste with sand in a 

 mortar, and replaced in the boiling water. The proteins in solution are then 

 coagulated by making the boiling fluid just acid with acetic acid. The fluid 

 is filtered through coarse filter paper. In this way a crude solution of glycogen 

 is obtained. 



151. Boil 5 cc. in a test-tube. The characteristic opalescence 

 does not disappear. (Distinction from erythro-dextrin.) 



152. To a small amount of the cooled solution add iodine, 

 drop by drop. A red colour is formed, which disappears on shaking, 

 until with a certain amount of iodine added it is permanent. Now 

 heat the solution. The colour disappears, to reappear on cooling. 



NOTE. If much protein is present in solution the colour will not re- 

 appear on cooling unless a considerable amount of iodine be added. This is 

 due to the fact that proteins combine with iodine to form an iodo-protein. 



153. Saturate 10 cc. of the solution with finely-powdered 

 ammonium sulphate. The glycogen is precipitated. Filter, and 

 add a drop or two of iodine to the nitrate. No red colour is pro- 

 duced. Scrape the precipitate off the paper, boil with a small 

 amount of water. The solution is markedly opalescent. Cool the 

 solution, and add iodine. A port-wine red colour is obtained. 



154. Boil 5 cc. of the solution with a little Fehling's fluid. A 

 very slight or no reduction is obtained. 



NOTE. If the liver has been rapidly boiled, no sugar will be present. If 

 delay has occurred during the initial stages of the preparation, some of the 

 glycogen will have been converted into glucose. (See Ex. 156.) 



