48 PHYSIOLOGICAL CHEMISTRY 



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

 page 45). 



The color in the case of dextrin does not reappear as readily on cooling as 

 in the case of starch. 



3. Fehling's Test. See if the dextrin solution will reduce Fehling'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 make the iodine test. The power of the solution to produce 

 a color with iodine should rapidly disappear. When a negative reaction is ob- 

 tained cool the solution and neutralize it with concentrated potassium hydroxide. 

 Try Fehling's test (see page 26). This reaction is now strongly positive, due to 

 the formation of a reducing sugar. Determine the nature of the sugar by means 

 of the phenylhydrazine test (see pages 22 and 23). 



5. Precipitation by Alcohol. To about 50 c.c. of 95 per cent alcohol in a small 

 beaker add about 10 c.c. of a concentrated dextrin solution. Dextrin is thrown 

 out of solution as a gummy white precipitate. Compare the result with that 

 obtained under Glucose, 7, page 24. 



6. Influence of Tannic Acid. Add an excess of tannic acid solution to a 

 small amount of dextrin solution in a test-tube. No precipitate forms. This 

 result differs from the result of the similar experiment upon starch (see Starch, 8, 

 page 45). 



7. Diffusibility of Dextrin. (See Starch, 9, page 45.) 



CELLULOSE, (C 5 Hi O 5 ) x 



This complex polysaccharide forms a large portion of the cell wall 

 of plants. It is extremely insoluble and its molecule is much more com- 

 plex than the starch molecule. The best quality of filter paper and 

 the ordinary absorbent cotton are good types of cellulose. 



At one time there was but a single known solvent for cellulose. 

 Recent investigation has, however, revealed a long list of cellulose 

 solvents. (See Experiment 7.) 



Cellulose is not hydrolyzed by boiling with dilute mineral acids. It 

 may be hydrolyzed, however, by treating with concentrated sulphuric 

 acid then subsequently diluting the solution with water and boiling. 

 The product of this hydrolysis is glucose. 



There is some difference of opinion as to the exact extent to which 

 cellulose is utilized in the animal organism. It is no doubt, more effi- 

 ciently utilized by herbivora than by carnivora or by man. It is claimed 

 that about 25 per cent may be utilized by herbivora, less than 5 per cent 

 by dogs whereas the quantity utilized by man is " too small for it to play 

 a role of importance in the diet of a normal individual. M1 In neither 

 man nor the lower animals has there been demonstrated any formation 



1 Swartz: Transactions of the Connecticut Academy of Arts and Sciences, 16, 247, 1911. 



