50 PHYSIOLOGICAL CHEMISTRY 



very thoroughly digested and absorbed. The agar, because of its 

 relative indigestibility and its property of absorbing water yields a 

 bulky fecal mass which is sufficiently soft to permit of easy evacua- 

 tion. Agar has been used with good results in the treatment of con- 

 stipation in children. 1 Agar is not limited to its use in connection 

 with constipation, but may serve in other capacities as an aid to intes- 

 tinal therapeutics. 2 



EXPERIMENTS ON A PENTOSAN 



1. Solubility. Test the solubility of gum arable in hot and cold water and 

 alcohol. 



2. Iodine Test. Add a drop of dilute iodine solution to a little gum arable 

 on a test-tablet. It resembles cellulose in giving no color with iodine. 



3. Hydrolysis of Gum Arabic. Introduce a little gum arabic into a test-tube, 

 add 5-10 c.c. of strong hydrochloric acid (cone. HC1 and water i : i) and heat to 

 boiling for 5-10 minutes. Cool, neutralize with potassium hydroxide and test 

 by the Fehling or some other reduction test. A positive reaction should be ob- 

 tained indicating that the gum arabic has been hydrolyzed by the acid with the 

 production of a reducing substance. What is this reducing substance? How 

 would you identify it? 



EXPERIMENTS ON A GALACTAN 



1. Solubility. Test the solubility of agar-agar in hot and cold water. Ob- 

 serve its marked property of imbibing water (see above). 



2. Iodine Test. Add a drop of dilute iodine solution to a little agar-agar on a 

 test-tablet. It resembles cellulose in giving no color with iodine. 



3. Hydrolysis of Agar-agar. Introduce a few pieces of agar-agar into a test- 

 tube, add 5-10 c.c. of strong hydrochloric acid (cone. HC1 and water i :i) and 

 heat to boiling for 5-10 minutes. Cool, neutralize with potassium hydroxide and 

 test by the Fehling or some other reduction test. A positive reaction should be 

 obtained indicating that the agar-agar has been hydrolyzed by the acid with the 

 production of a reducing substance. What is this reducing substance? How 

 would you identify it? 



REVIEW OF CARBOHYDRATES 



In order to facilitate the student's review of the carbohydrates, the 

 preparation of a chart similar to the appended model is recommended. 

 The signs + and may be conveniently used to indicate positive 

 and negative reaction. Only those carbohydrates which are of greatest 

 importance from the standpoint of physiological chemistry have been 

 included in the chart. 



1 Morse: Journal American Medical Ass'n., 55, 934, 1910. 

 2 Einhorn: Berl. klin. Woch., 49, 113, 1912. 



