SALIVARY DIGESTION 59 



7. Preparation of Mucin. Pour 25 c.c. of saliva into 100 c.c. of 95 per cent 

 alcohol, stirring constantly. Cover the vessel and allow the precipitate to stand 

 at least 12 hours. Pour off the supernatant liquid, collect the precipitate on a 

 filter and wash it, in turn, with alcohol and ether. Finally dry the precipitate, 

 remove it from the paper and make the following tests on the mucin : (a) Test 

 its solubility in the ordinary solvents (see page 21); (b) Millon's reaction; (c) 

 dissolve a small amount in KOH, and try the biuret test on the solution ; (d) boil 

 the remainder, with 10-25 c.c. of water to which 5 c.c. of dilute HC1 has been 

 added, until the solution becomes brownish. Cool, render alkaline with solid 

 KOH, and test by Fehling's solution. A reduction should take place. 



Mucin is what is known as a conjugated protein or glycoprotein 

 (see page 112) and upon boiling with the acid the carbohydrate group 

 in the molecule has been split off from the protein portion and its 

 presence is indicated by the reduction of Fehling's solution. 



8. Inorganic Matter. Test for chlorides, phosphates, sulphates, and cal- 

 cium. For chlorides, acidify with HNOs and add AgNOa. For phosphates, 

 acidify with HNOs, heat and add molybdate solution. 1 For sulphates, acidify 

 with HC1 and add BaCl 2 and warm. For calcium, acidify with acetic acid, CH 3 - 

 COOH, and add ammonium oxalate, (NH 4 )2C 2 O4. 



9. Viscosity Test. Place filter papers in two funnels, and to each add an equal 

 quantity of starch paste (5 c.c.). Add a few drops of saliva to one lot of paste and 

 an equivalent amount of water to the other. Note the progress of filtration in 

 each case. Why does one solution filter more rapidly than the other? 



10. Test for Nitrites. Add 1-2 drops of dilute H 2 SO 4 to a little saliva and 

 thoroughly stir. Now add a few drops of a potassium iodide solution and some 

 starch paste. Nitrous acid is formed which liberates iodine, causing the formation 

 of the blue iodide of starch. 



n. Thiocyanate Tests. (a) Ferric Chloride Test. To a little saliva in a 

 small porcelain crucible, or dish, add a few drops of dilute ferric chloride and 

 acidify slightly with HC1. Red ferric thiocyanate Fe(SCN) 3 forms. To show 

 that the red coloration is not due to iron phosphate add a drop of HgCl 2 when 

 colorless mercuric thiocyanate forms. 



(6) Solera's Reaction. This test depends upon the liberation of iodine through 

 the action of thiocyanate upon iodic acid. Moisten a strip of starch paste-iodic acid 

 test paper 2 with a little saliva. If thiocyanate be present the test paper will assume 

 a blue color, due to the liberation of iodine and the subsequent formation of the so- 

 called iodide of starch. 



12. Digestion of Starch Paste. To 25 c.c. of starch paste in a small beaker, 

 add 5 drops of saliva and stir thoroughly. At intervals of a minute remove a 

 drop of the solution to one of the depressions in a test-tablet and test by the io- 

 dine test. If the blue color with iodine still forms after five minutes, add another 

 5 drops of saliva. The opalescence of the starch solution should soon disappear, 

 indicating the formation of soluble starch which gives a blue color with iodine. 



1 See "Reagents and Solutions." 



2 This test paper is prepared as follows: Saturate a good quality of filter paper with 0.5 

 per cent starch paste to which has been added sufficient iodic acid to make a i per cent 

 solution of iodic acid and allow the paper to dry in the air. Cut it in strips of suitable size 

 and preserve for use. 



