CH. V.] GLYCOGEN. 123 



149. Take 10 cc. of the dextrin solution in a small flask ; add 

 30 cc. of strong (95 per cent.) alcohol, place the thumb over the 

 mouth of the flask and shake vigorously for some seconds. Note 

 that a portion of the dextrin is precipitated as a gummy mass which 

 sticks to the sides of the flask. 



Pour off the alcohol, filter it and label the filtrate A. Rinse 

 the flask out with a few cc. of alcohol, shake off as much of this 

 alcohol as possible, and add 10 cc. of hot water. Shake this round 

 the flask till the whole of the gummy precipitate dissolves. Divide 

 the solution into three portions, B, C, and D. To B add a drop of 

 iodine : a purple colour is produced. Boil C with a little Fehling's 

 solution : only a slight reduction takes place. Boil D with two drops 

 of concentrated sulphuric acid for two minutes, neutralise with 

 sodium hydroxide, and boil with a little Fehling's solution : a well- 

 marked reduction occurs. 



150. To a portion of filtrate A, add a drop of iodine solution. 

 No colour is produced. To another portion of about 5 cc. add an 

 equal bulk of strong alcohol. A white precipitate of achroo-dextrin 

 is formed. 



Glycogen is a reserve polysaccharide found in the liver 

 and muscles. It forms a white amorphous powder, 

 soluble in water to form an opalescent solution. It is 

 precipitated from solution by the addition of an equal 

 volume of strong alcohol or by full saturation with am- 

 monium sulphate. It does not reduce Fehling's solution, 

 form an osazone nor ferment with yeast. It gives a reddish 

 colour with iodine. By boiling acids it is hydrolysed to 

 glucose : by most of the diastatic enzymes to maltose, but 

 by the diastase found in the liver to glucose. It is not 

 affected by boiling alkalies. It is dextro-rotatory. 



Estimation. Pfliiger's method is undoubtedly the best. 20 to 100 grams, 

 of the tissue is cut into small pieces and placed in an Erlenmeyer flask of Jena 

 glass. 100 cc. of 60 per cent, potash (" pure by alcohol " sp. gr. i. 438) is 

 added, a reflux condenser fitted, and the flask immersed for three hours in a 

 boiling water bath. The alkali destroys the proteins without attacking 

 the glycogen. 



After cooling 200 cc. of water and 800 cc. of 96 per cent, alcohol are added, 

 and the mixture left to stand over-night. The glycogen is thus precipitated 

 free from protein. The supernatant fluid is carefully decanted and filtered. 



of PHARMACY 



