PHYSIOLOGICAL CHEMISTRY 371 



CHAPTER XII. 

 DIGESTION IN THE MOUTH. 



THE salivary glands parotid, sublingual, and submaxillary along 

 with the numerous isolated gland acini scattered in the buccal mucosa, 

 pour into the mouth a secretion known as saliva. The composition of 

 this mixed saliva is as follows : 



Water, 99-42% 



Organic matter, 0*36,, 



Mucus and epithelial cells. Ptyalin and soluble protein. 

 Potassium sulphocyanide (KCNS). 



Inorganic matter, 0'22,, 



Chlorides, phosphates, and carbonates of alkalies and alkaline earths. 



It is, therefore, a very dilute secretion (specific gravity about 1005). 



The total secretion during twenty-four hours amounts to about the 

 same as that of the urine, i.e. 1500 c.c. 



The saliva secreted by the different glands varies somewhat in com- 

 position ; that from the parotid contains no mucus, and is consequently 

 a thinner fluid than that of the submaxillary, which contains much 

 mucus. The sublingual saliva also contains a certain amount of 

 mucus. 



Collect some saliva in a test tube, 1 and perform the following reactions 

 with it : 



I. To identify the various Constituents. 



EXPERIMENT I. Place a drop of saliva on red litmus paper ; a blue 

 stain results. The reaction may, however, become acid where decom- 

 position is taking place in the mouth, as is the case in decaying teeth. 



EXPERIMENT II. Place a drop of saliva on a slide, cover and examine 

 under the microscope: two kinds of cells will be seen, viz. (1) large, 

 flat, squamous cells, which have been desquamated from the surface of 

 the stratified epithelium of the mouth; (2) small round cells like 

 leucocytes, which come either from the glands themselves or from the 

 tonsils. 



EXPERIMENT III. Place some saliva in a test tube and dilute it with 

 an equal quantity of water ; now add a few drops of 10 per cent, acetic 

 acid, when a stringy precipitate of mucus will form. Filter off this pre- 

 cipitate, and note that the filtrate is watery, showing that the stringy 

 character of saliva is due to the mucus which it contains. To the 



1 The secretion of saliva may be stimulated by inhaling acetic acid through the 

 mouth, or by chewing rubber. 



