46 PHYSIOLOGICAL CHEMISTRY 



of i c.c. of the solution upon i c.c. of diluted (i : 4) Fehling's solution. Also 

 try the Resorcinol-Hydrochloric Acid reaction as given on p. 35. Explain the 

 result. 1 



GLYCOGEN, (C 6 Hi 5 )x 



(For discussion and experiments see Muscular Tissue, Chapter XX.) 

 LICHENIN, (C 6 Hio0 6 )x 



Lichenin may be obtained from Cetraria islandica (Iceland moss). 

 It forms a difficultly soluble jelly in cold water and an opalescent solu- 

 tion in hot water. It is optically inactive and gives no color with 

 iodine. Upon hydrolysis with dilute mineral acids lichenin yields dex- 

 trins and glucose. It is said to be most nearly related chemically to 

 starch. Saliva, pancreatic juice, malt diastase, and gastric juice have 

 no noticeable action on lichenin. 



DEXTRIN, (C 6 H 10 5 ) X 



The dextrins are the bodies formed midway in the stages of the 

 hydrolysis of starch by weak acids or an enzyme. They are amorphous 

 bodies which are easily soluble in water, acids, and alkalis, but are in- 

 soluble in alcohol or ether. Dextrins are dextro-rotatory and are not 

 fermentable by yeast. 



The dextrins may be hydrolyzed by dilute acids to form glucose 

 and by amylases to form maltose. With iodine one form of dextrin 

 (erythro-dextrin) gives a red color. Their power to reduce Fehling's 

 solution is questioned. The lower members of the dextrin series prob- 

 ably reduce. 



EXPERIMENTS ON DEXTRIN 



1. Solubility. Test the solubility of pulverized dextrin in hot and cold water. 

 Dextrin forms a clear solution hi hot water, distinguishing it from glycogen which 

 gives an opalescent solution. 



2. Iodine Test. Place a drop of dextrin solution in one of the depressions 

 of the test-tablet and add a dilute solution of iodine hi potassium iodide. A red 

 color results due to the formation of the red iodide of dextrin. Ordinary dextrin 

 preparations contain some starch and hi the presence of starch it is necessary to 

 have an excess of iodine present. If the reaction is not sufficiently pronounced 

 make a stronger solution from pulverized dextrin and repeat the test. The 

 solution should be slightly acid to secure the best results. 



Make proper tests to show that the red iodide of dextrin is influenced' , by 

 heat, alkali, and alcohol in a similar manner to the blue iodide of starch (see 

 page 43). 



l lt the inulifl solution gave a positive Fehling test in the last experiment it will be neces- 

 sary to check the hydrolysis experiment as follows: To 5 c.c. of the inulin solution in a test- 

 tube add one drop of concentrated hydrochloric acid, neutralize with concentrated KOH 

 solution and test the reducing action of i c.c. of the resulting solution upon i c.c. of diluted 

 (i : 4) Fehling's solution. This will show the normal reducing power of the inulin solution. 

 In case the inulin was hydrolyzed, the Fehling's test in the hydrolysis experiment should 

 show a more pronounced reduction than that observed in the check experiment. 



