226 PHYSIOLOGICAL CHEMISTRY 



that if reduction is observed it may be due to the presence of 

 maltose or dextrose as impurities in the dextrin. In the manu- 

 facture of dextrin, small amounts of maltose and dextrose are 

 likely to be formed by complete hydrolysis of a portion of the 

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

 tion. 



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

 hol on dextrose. 



3. 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. 



i. Test glycogen solution with iodine. A red or brown color 

 develops. Warm gently by holding the test tube in a beaker of 

 water heated to about 50 C. Remove as soon as the color disap- 

 pears and cool under the tap. The color should reappear. 



ii. Test glycogen for reducing sugar with Fehling'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. 



iii. 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 Fehling 

 test. The glycogen is hydrolyzed by the acid, and the solution 

 should give a good reduction. 



