PREPARATION OF GLYCOGEN 129 



precipitated glycogen is collected and washed with a mixture 

 of one part of 1 5 per cent potash with two parts of 96 per cent 

 alcohol; if necessary, the substance may be redissolved and 

 purified in the same way. 



Glycogen may also be prepared from yeast, but not in a 

 particularly pure state, in the following manner : A quantity 

 of bakers' yeast, which has been previously well washed with 

 water, is mixed with fine well-cleaned sand and ground very 

 thoroughly in order to rupture the cells. The mixture is then 

 placed in a vessel with about thrice its volume of water and 

 heated for some time, being constantly stirred. The liquid is 

 then filtered off, cooled, and strong alcohol added to the filtrate 

 in order to precipitate the glycogen, which is filtered off. 

 The glycogen so obtained may be purified by redissolving it 

 in water, adding a little acetic acid, and boiling in order to 

 remove any proteins which may not have been removed by 

 the initial heating;, filtering, and precipitating with alcohol. 



The following method has recently bqen described by 

 Harden and Young * : The yeast is ground with an equal 

 weight of sand. It is then extracted by boiling with water, 

 and an equal volume of alcohol added to the cooled and 

 filtered liquid. The precipitate formed is collected, washed 

 with 50 per cent alcohol, and is then treated on the boiling 

 water bath with a 60 per cent solution of potassium hydroxide 

 for two hours. The liquid is cooled and poured into an equal 

 volume of water, filtered, and the filtrate precipitated by the 

 addition of two volumes of alcohol. The precipitate is col- 

 lected, and washed repeatedly with a mixture containing 

 400 c.c. of water, 100 c.c. of 50 per cent potassium hydroxide, 

 and 500 c.c. of alcohol; it is finally washed with 50 per cent 

 alcohol. 



The precipitate is then dissolved in water, and the solu- 

 tion, which is alkaline owing to the difficulty of washing away 

 all the potassium hydroxide, is neutralized with acetic acid, 

 and the glycogen precipitated by the addition of an equal 

 volume of alcohol. By repeatedly dissolving in water, and 

 reprecipitating with alcohol, a preparation may be obtained 

 free from nitrogen and ash, but it still contains yeast-gum, 



* Harden and Young : " J. Chem. Soc.," 1912, 101, 1928. 



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