THE CARBOHYDRATES 209 



GLYCOGBN. 



Glycogen is present as reserve food material in the organs of 

 animals, but is also found in plants. In plants it is present in largest 

 amount in yeast, as much as 30 per cent, of the dry weight having 

 been recorded. In animals glycogen exists in greatest amount in the 

 liver, usually from 1-4 per cent, but 12-16 per cent, have been 

 obtained and 20 per cent, from frog's liver. Glycogen is found in 

 other organs of animals, especially muscle. Heart muscle always 

 seems to contain a quantity of glycogen. Oysters and other molluscs 

 contain considerable quantities of glycogen. 



Preparation. 

 From Liver. 



In order to obtain as large an amount of glycogen as possible the animal 

 should be fed on a diet containing carbohydrate. The livers of rabbits con- 

 tain a considerable quantity if they have been fed on carrots 5 or 6 hours 

 previously. The animal is killed by bleeding, the liver removed and washed 

 out with saline solution. It is broken up into small pieces and thrown into 

 boiling water acidified with acetic acid. The proteins of the liver are thus 

 coagulated and the enzyme which converts glycogen into glucose is destroyed. 

 The pieces of liver are ground up finely in a mortar and extracted with 

 boiling water. The extracts are combined (the remainder of the proteins 

 precipitated by adding an equal volume of 10 per cent, trichloracetic acid), 

 and the opalescent solution precipitated by adding an equal volume of alcohol. 

 The precipitate is redissolved in water and reprecipitated with alcohol. The 

 precipitate is dried by treating with alcohol several times, then with ether and 

 placing in a desiccator over sulphuric acid. 

 . Pfluger's method of preparing glycogen yields a purer preparation : 



The finely broken up liver is stirred up with water and 60 per cent, 

 potassium hydroxide so that it contains 15 percent. KOH and heated for 

 2 hours on the water-bath. The solution is filtered and mixed with an equal 

 volume of alcohol. The glycogen is precipitated and washed with a mixture 

 of i part of 1 5 per cent. KOH and 2 parts of alcohol. It may be redissolved 

 and reprecipitated by alcohol. It is then washed with alcohol and ether and 

 dried. 



From Yeast. 



Yeast is ground up with sand to rupture the cells, extracted with boiling 

 water, and the filtered solution precipitated by adding an equal volume of 

 alcohol. The precipitate is collected, washed with 50 per cent, alcohol and 

 heated for 2 hours on a boiling water-bath with a solution of 60 per cent, 

 potassium hydroxide to dissolve proteins. The liquid is cooled, poured into 

 an equal volume of water, filtered and precipitated by adding two volumes of 

 alcohol. The precipitate of glycogen is washed with alcohol containing KOH 

 and then with alcohol. It is purified by solution in water, neutralisation of 

 the alkali with acetic acid, and precipitation with an equal volume of alcohol. 

 This procedure is carried out several times. The product contains yeast gum. 

 This is removed by dissolving in water and saturating the solution with am- 

 monium sulphate. The glycogen is precipitated and washed with ammonium 



