290 PKACTICAL PHYSIOLOGY 



EXPERIMENT V. Place some of the starch solution in the mouth, 

 and after a minute or so transfer it again to the test tube ; now apply 

 Trommer's or Fehling's test reduction occurs. 



Try the same experiment with some unboiled starch, and note that, 

 with Trommer's test, there is no reduction (i.e. the resistant external 

 layers have not been hydrolysed). 



The sugar produced by hydrolysing with an acid is dextrose, whereas 

 that produced by ferment action is maltose. 



Glycogen (C 6 H 10 5 ) n . Just as plants store up excess of carbo- 

 hydrate in the form of starch, so do animals store it partly in the 

 form of glycogen. The chief seats of this storage are the liver and 

 muscles. Glycogen forms a non-crystalline, white powder, the particles 

 of which have no characteristic appearance under the microscope. It 

 is soluble in water and the solution is opalescent. Solutions of glyco- 

 gen are dextro-rotatory. 



EXPERIMENT VI. A simple method for the preparation of glycogen 

 is that introduced by Frankel. It consists in grinding up fresh 

 liver or the common shell-fish, mussel, in a mortar with about three 

 times its volume of a 3 % solution of tri-chloracetic acid. This re- 

 agent coagulates the proteins The glycogen is contained in the 

 extract, and can be precipitated by alcohol. 1 After collecting on a 

 filter dissolve some of the glycogen in water and notice that the 

 solution is opalescent. Add to this a drop or two of iodine solution : 

 a port-wine colour results, which disappears on heating, and returns 

 on cooling. 



EXPERIMENT VII. Place 5 c.c of glycogen solution in a test tube 

 and add ordinary alcohol carefully until a precipitate forms. Note 

 approximately how much alcohol requires to be added to obtain this 

 (about 55 %). 



EXPERIMENT VIII. Try Trommer's test with the glycogen solution ; 

 no reduction occurs, but the Cu(OH) 2 is held in solution. 



EXPERIMENT IX. To some of the solution add a few drops of 

 25 % H 2 S0 4 and boil for about ten minutes ; dextrose is produced, 

 as can be shown by applying one of the reduction tests. 



EXPERIMENT X. Mix some glycogen solution with saliva and 

 place the test tube in water at body temperature. After about ten 

 minutes apply one of the reduction tests. It will be found that a 

 reducing sugar has been produced. 



The Dextrines (C 6 H 10 5 ) n . During the hydrolysis of starch and 

 glycogen dextrines are formed as an intermediate product. British 



1 Where not otherwise specified in these experiments, alcohol refers to the 

 commercial product containing from 92-96 % pure alcohol. 



