512 DIGESTION. 



(Jlycogen is colored red by solution of iodine. The best 

 solution for this purpose is made by putting a little iodine in 

 water and adding potassium iodide very graduallj* to it, with 

 constant agitation, until the fluid assumes a wine-red color. If 

 caustic potash is added to a solution of glycogen, and then a 

 drop of cupric sulphate, the copper oxide is redissolved. The 

 oxide is not reduced on boiling. 



158. Influence of Food on the Amount of Glycogen 

 in the Liver. If two rabbits, one of which is fed abundantly 

 with corn, the other sparingly with green food, are kept other- 

 wise in the same conditions and killed at the same period of 

 digestion, it is found that the liver of the former contains much 

 more glycogen than that of the latter. 



** 159. Conditions which determine the Conver- 

 sion of Glycogen into Grape Sugar. Glycogen can be 

 changed into dextrin and grape sugar: 



1. By Ferments. Take a watery solution of glycogen and 

 mix some saliva with it. Put the mixture into two test-tubes 

 and place them in the water-bath at 37 to 40 C. Take out 

 one immediately after the milkiness of the solution has dis- 

 appeared. Add alcohol to it: a precipitate of dextrin is 

 formed. Filter, and wash the precipitate with alcohol. Put 

 the precipitate in water : it becomes transparent and dissolves, 

 forming a solution perfectly free from opalescence. Test a 

 lit tic of the solution with liquor potassae and cupric sulphate ; 

 no reduction takes place on boiling. To another portion add 

 iodine solution; a red color like that of glycogen appears. 

 Test the alcoholic filtrate with liquor potassae and cupric sul- 

 phate: it is reduced. This shows that the glycogen has been 

 converted partly into dextrin and partly into grape-sugar by 

 the salivary ferment. Let the other test-tube stand for some 

 time in the water-bath. Add alcohol. If it has stood long 

 enough, no precipitate is produced. Test it. On applying 

 Troinnier's test a great reduction of cupric oxide will occur. 

 This shows that the glycogen has been entirely converted into 

 sugar by the prolonged action of the salivary ferment. 



liltxtd contains a Ferment which converts Glycogen. A 

 ferment possessing the same action is contained in the blood. 

 Add a little blood to a solution of glycogen, and let it stand 

 for some time at 3Y C. Then remove the albumin and test 

 for sugar in the manner already described. 



'. /;// ,f r/,/.s._Mix a solution of glycogen with dilute hydro- 

 chloric or sulphuric acid and boil. Then add liquor potassse 

 "i excess and copper sulphate, and boil ; sugar is found. All 

 specimens of glycogen can be converted into sugar by acids, 

 they are not all alike in their behavior to ferments, some 

 specimens requiring a longer time than others. 



