160 SPECIAL PHYSIOLOGY 



indefinitely in pure glycerin. For use one needs only to wash out 

 the glycerin thoroughly. 



3. Experiments and Observations. (1) Subject saliva (a) and 

 (b) to the Fehling test. It will be found that neither the extract 

 nor the secretion will reduce the CuSO 4 . 



(2) Subject starch paste to the same test. The result is negative. 



(3) Mix equal volumes of starch paste and salivary extract in a 

 beaker. Place the mixture in the incubator, which is kept at a 

 temperature of 35 to 40 C. After ten or fifteen minutes subject 

 the mixture to a test with Fehling's solution. If the conditions are 

 normal a copious precipitate of CuO indicates that a change has 

 been wrought in the mixture. The starch has been changed to a 

 reducing sugar by the ptyalin of the salivary extract. 



(4) Mix equal volumes of starch paste and salivary secretion in 

 a beaker; place the mixture in the incubator for ten or fifteen minutes; 

 test with Fehling's solution. The presence of a reducing sugar 

 shows that the secretion of the human salivary glands has the power 

 to change starch to sugar; to change an insoluble diffusible foodstuff 

 to a soluble diffusible one. 



(5) Put a few crumbs of bread in a test-tube; add dilute iodine. 

 Starch is an important constituent of bread. 



(6) Put a few crumbs of bread in a beaker; add salivary extract; 

 place in the incubator twenty minutes. Disintegration of the pieces 

 and a marked increase of the amount of reducing sugar indicates 

 the digestive action of saliva upon bread. 



(7) Put a bit of fibrin into salivary extract; place in the incubator. 

 An hour or a day will show no apparent change in the fibrin. Had 

 one used any other proteid the result would have been the same. 

 We are justified in the conclusion that saliva contains no ferment 

 capable of changing proteids. 



(8) Put a bit of fat or a drop of oil into a few cubic centimetres 

 of salivary extract, shake vigorously; place in incubator. After an 

 hour or a day one can see no change in the fat or oil, and is justified 

 in the conclusion that saliva contains no ferment which acts upon fats. 



(9) To a small amount of raw starch add salivary extract; place 

 the mixture in the incubator; shake frequently; after fifteen minutes 

 test for reducing sugar. There will probably be a relatively small 

 amount of reducing sugar. If one watches the progress of digestion 

 for several hours he will be convinced that the cooking of starch 

 very greatly facilitates its digestion by saliva. 



(10) Boil a few cubic centimetres of saliva; add starch paste; place 

 in the incubator for ten minutes; test for reducing sugar. What is 

 the verdict? 



(11) Test the salivary secretion with neutral litmus. Determine 

 whether its faint alkaline reaction is essential to its action as a 

 digestive fluid. 



