48 PHYSIOLOGICAL CHEMISTRY. 



LICHENIN, (C 6 H 10 5 )x. 



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

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

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

 with iodine. Upon hydrolysis with dilute mineral acids lichenin 

 yields dextrins and dextrose. It is said to be most nearly related 

 chemically to starch. Saliva, pancreatic juice, malt diastase and gas- 

 tric 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 amor- 

 phous bodies which are easily soluble in water, acids and alkalis 

 but are insoluble in alcohol or ether. Dextrins are dextro-rotatory 

 and are not fermentable by yeast. 



The dextrins may be hydrolyzed by dilute acids to form dextrose. 

 With iodine one form of dextrin (erythro-dextrin) gives a red 

 color. Their power to reduce Fehling's solution is questioned. 



EXPERIMENTS ON DEXTRIN. 



1. Solubility. Test the solubility of pulverized dextrin in the 

 ordinary solvents (see page 23). 



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

 depressions of the test- tablet and add a drop of a dilute solution 

 of iodine in potassium iodide. A red color results due to the forma- 

 tion of the red iodide of dextrin. 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 46). 



3. Fehling's Test. See if the dextrin solution will reduce Feh- 

 ling's solution. 



4. Hydrolysis of Dextrin. Take 25 c.c. of dextrin solution in 

 a small beaker, add 5 drops of dilute hydrochloric acid, and boil. 

 By means of a small pipette, at the end of each minute, remove a 

 drop of the solution to one of the depressions of the test-tablet and 



