SECRETION DIGESTION ABSORPTION. 



III. SALIVARY DIGESTION. 



1. Chemical Constituents of Saliva. Chew a piece of par- 

 affin gum or inhale a little ether vapor. The flow of saliva is 

 thus stimulated. Collect the secretion in a clean porcelain cap- 

 sule. Filter and divide the nitrate into five portions. 



(a) Test the first portion for its reaction with litmus paper. 

 Is it alkaline or acid ? Is the reaction very decided in either di- 

 rection ? 



(b) To the second portion add dilute acetic acid. The pres- 

 ence of mucin is indicated by the formation of a precipitate. 



(c) To a third portion add a few drops of a silver-nitrate solu- 

 tion. A precipitate of silver chlorid which is soluble in ammonia 

 and insoluble in nitric acid is indicative of the presence of 

 chlorids. 



(d) To another portion add dilute acetic acid and filter. Test 

 the filtrate with Millon's reagent. The presence of proteids is 

 shown by the production of a red coloration or precipitate. 



2. Action on Starches. (a) To some boiled starch paste add 

 a few drops of iodine. A blue coloration will occur. To some 

 powdered starch add a few drops of iodine. A blue color test will 

 also be obtained. Both cooked and raw starch respond to the 

 iodine test. 



(b) To a test-tube partly filled with a dilute Fehling's solution 

 add a little of the starch paste. Boil the mixture. There should 

 be no reduction of the copper sulphate of the Fehling's solution. 

 The copper salt is reduced by any of the reducing sugars. 



(c) To another portion of Fehling's solution add a few drops 

 of a dilute solution of dextrose. Heat to boiling and note the for- 

 mation of a copious precipitate, first yellow, and, as the heating is 

 continued, changing to a reddish color. This is the cuprous and 

 later cupric oxide formed by the reduction of the copper salt in the 

 test solution. 



(d) Repeat the test with maltose instead of dextrose. Is re- 

 duction obtained? 



