EXAMINATION OF THE LIVER. 133 



Reactions of Glycogen. 



1. Heat a small portion of the substance on platinum-foil 

 until all the carbon is burned: only a very small amount of 

 .ash should remain. 



2. Dissolve 0.25 g. by warming with 50 cc. of water or 

 0.5 g. in 100 cc. 



(a) Determination of the rotation: If the dextrorotation is 

 not distinctly apparent, add some sodium hydroxide solution. 



(6) Add to a small portion of the solution a very small 

 quantity of iodine potassium iodide solution saturated with 

 sodium chloride. The solution turns reddish-brown; con- 

 tinue to add the iodine as long as the intensity of the color 

 perceptibly increases, then divide the mixture into two parts. 

 Heat one part gently: the color disappears, but returns on 

 cooling. The addition of sodium hydroxide decolorizes the 

 solution at once, sodium carbonate acts more slowly (com- 

 bination with the iodine), acids gradually decolorize the solu- 

 tion (forming sugar). 



According to Hoppe-Seyler, in order to determine the 

 presence of glycogen in neutral solutions, place equal por- 

 tions of dilute iodine solution in two test-tubes of the same 

 diameter, to one add some of the solution to be tested, to the 

 other the same quantity of water, and compare the colors. 



(c) Dissolve some commercial peptone in a few cubic 

 centimeters of the glycogen solution and make the test with 

 iodine: the reaction only appears after the addition of 

 considerable iodine and may not appear at all when the 

 quantity of the peptone exceeds that of the glycogen. The 

 color formed frequently disappears on standing from the 

 gradual combination of the iodine. Impure, dilute solutions 

 of glycogen, therefore, give a poor iodine reaction. 



(d) Boil a few cubic centimeters of the glycogen solution 

 a short time with about one-third of its volume of hydrochloric 



