INFLUENCE OF ACIDS AND ALKALIES ON SALIVARY DIGESTION 401 



Chlorides. Add silver nitrate to 2 cc. of saliva after first removing 

 the proteins. A white, cloudy precipitate, which disappears on adding 

 ammonia and reappears on adding nitric acid, indicates the presence of 

 chlorides. 



Proteins. Remove the mucin from a sample of saliva, as above, and test 

 by the characteristic protein reactions. A faint trace of protein can usually 

 be demonstrated. 



5. Digestive Action of Saliva on Starch. Review the tests for starch, 

 dextrin, and dextrose, as preparation for an identification of these products 

 of salivary digestion. To 10 cc. of i per cent, starch paste in the water-bath 

 at 40 C., add 2 cc. of saliva, and mix thoroughly with a glass rod. Immedi- 

 ately begin two series of tests: a, for the presence of starch; b, for the presence 

 of reducing sugar. The tests for starch can be made by adding to 3 drops 

 of solution, on a porcelain plate, an equal quantity of dilute iodine in potas- 

 sium iodide solution. Use a glass rod. Make the tests every 2 minutes 

 for 20 minutes. The tests for reducing sugar are best made by placing 2 cc. 

 of Fehling's solution in each of a series of test-tubes and adding to suc- 

 cessive tubes, at intervals of 5 minutes, i cc. portions of the digest from a 

 dropping pipet and boiling. If the tests are set away as fast as they are pre- 

 pared, a reddish-yellow cuprous oxide will settle out, and the series will give 

 a rough comparison as to the quantity of reducing sugar present. 



In the first series the deep blue of the starch reaction quickly changes 

 to a reddish-blue, a red, a reddish-brown, until finally no change in color 

 other than that produced by the mixture of the iodine occurs, showing that 

 the starch has passed the second stage of erythro-dextrin in its disappearance. 

 The indication of reducing sugar in the second series shows that this erythro- 

 dextrin has been transformed into reducing sugar, and also that the amount 

 of sugar is greatly increased during the progress of the test. 



6. The Influence of Temperature on Salivary Digestion. Prepare 

 three test-tubes, a, 6, c, containing i cc. each of saliva. Boil a, place b in a 

 water-bath at 40 C., and place c in ice water. After c has been cooled down 

 to the temperature of the ice-bath, add to each 2 cc. of i per cent, starch solu- 

 tion and mix. At intervals of 5 minutes test these three samples for the 

 disappearance of starch and appearance of reducing sugar, as in Experi- 

 ment 5. No change will take place in a; b will be quickly digested, and the 

 digestion in c will be slight or suspended. Upon placing c in a warm bath 

 digestion will quickly occur. 



7. Influence of Acids and Alkalies on Salivary Digestion. To 

 each of 5 test-tubes, a, b, c, d, e, add 2 cc. saliva and water, or the solutions 

 given in the table, so that the saliva will be uniformly diluted. Then add 

 quickly i cc. of i per cent, starch paste to each. Run parallel tests for the 



appearance of reducing sugar and disappearance of starch. 



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