CARBOHYDRATES 263 



starch. Pure dextrin is believed not to reduce Benedict's solu- 

 tion. 



44. To dextrin solution add alcohol. Recall the effect of alco- 

 hol on dextrose. 



Glycogen. 



This polysaccharide may be obtained from the liver taken from 

 an animal immediately after death, or from fresh oysters. The 

 material must be fresh, as otherwise the glycogen will have been 

 broken down to glucose by the tissue enzymes. The liver (or 

 oysters) is thrown into boiling water slightly acidulated with 

 acetic acid. After boiling a few minutes, the pieces are re- 

 moved, ground in a mortar with sand, and returned to the 

 water and boiled for several minutes. The glycogen solution is 

 then filtered while hot from the coagulated protein material. 

 45. Test glycogen solution with iodine. Warm gently by 

 holding the test tube in a beaker of water heated to about 50 C. 

 Remove as soon as the color disappears and cool under the tap. 



46. Test glycogen for reducing sugar with Benedict's solution. 

 Glycogen should not reduce, but a solution prepared as above 

 often will do so, as the result of partial hydrolysis of the 

 material. 



47. To 10 c.c. of glycogen solution add about 10 drops of con- 

 centrated hydrochloric acid and boil for about 10 minutes. 

 Neutralize carefully with sodium hydrate and repeat the Bene- 

 dict test. The glycogen is hydrolyzed by the acid. 



