SALIVARY DIGESTION 57 



whereas the cleavage of several dipeptids was brought about. The 

 action is similar to that of intestinal erepsin (see Chapter XI). 'Later 

 investigations (see page 202), apparently have demonstrated that the 

 peptolytic power of saliva, at least in some cases, is due to bacteria. 



Microscopical examination of the saliva reveals salivary corpuscles, S 

 bacteria, food debris, epithelial cells, mucus, and fungi. In certain ( 

 pathological conditions of the mouth, pus cells and blood corpuscles / 

 may be found in the saliva. ^^ 



EXPERIMENTS ON SALIVA 



A satisfactory method of obtaining the saliva necessary for the ex- 

 periments which follow is to chew a small piece of pure paraffin wax, 

 thus stimulating the flow of the secretion, which may be collected in a 

 small beaker. Filtered saliva is to be used in every experiment except 

 for the microscopical examination. 



i. Microscopical Examination. Examine a drop of unfiltered saliva micro- 

 scopically, after staining with methylene blue, and compare with Fig. 20 below. 



FIG. 20. MICROSCOPICAL CONSTITUENTS OF SALIVA. 



o, Epithelial cells; b, salivary corpuscles; c, fat drops; d, leucocytes; e, f and g, bacteria; 



h, i, and k, fission-fungi. 



2. Reaction. Test the reaction to litmus, phenolphthalein and Congo red. 



3. Specific Gravity. Partially fill a urinometer cylinder with saliva, introduce 

 the urinometer, and observe the reading. 



4. Test for Mucin. To a small amount of saliva in a test-tube add 1-2 drops 

 of dilute acetic acid. Mucin is precipitated. 



5. Biuret Test. 1 Render a little saliva alkaline with an equal volume of KOH 

 and add a few drops of a very dilute (2-5 drops in a test-tube of water) copper 

 sulphate solution. The formation of a purplish-violet color is due to mucin. 



This reaction is given by protein material and simply indicates that mucin is 

 a protein. 



6. Mfflon's Reaction. 2 Add a few drops of Millon's reagent to a little saliva. 

 A light yellow precipitate formed by the mucin gradually turns red upon being 

 gently heated. 



This reaction indicates the presence of protein (mucin). 



1 The significance of this reaction is pointed out on p. 99. 



2 The significance of this reaction is pointed out on p. 97. 



