ELEMENTARY PHYSIOLOGICAL CHEMISTRY 217 



DIGESTION IN THE MOUTH. 



The salivary glands parotid, sublingual, and subm axillary along 

 with the numerous isolated gland acini scattered over the mucosa, pour 

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

 mixed saliva is as follows : 



Water, 99 -42 per cent. 



Organic Matter, 0'36 ,, 



Mucus and epithelial cells. Ptyalin and soluble proteid. KCNS 



Inorganic Matter, '22 per cent. 



Chlorides, phosphates, and carbonate of alkalies and alkaline earth. 



It is, therefore, a very dilute secretion, its specific gravity being only 

 about 1005, ordinary water being taken as 1000. 



The total secretion during 24 hours amounts to about the same as 

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



The saliva excreted by the different glands differs somewhat in com- 

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

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

 mucus, or than the sublingual saliva, which also contains a certain 

 amount of that substance. 



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

 with it : 



I. To Identify the Various Constituents. 



EXPERIMENT I. A drop placed on red litmus paper produces a blue 

 stain. The reaction may, however, become acid where decomposition 

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



EXPERIMENT II. If a drop of saliva be placed on a slide, covered 

 and examined 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 occur. Filter off this 

 precipitate, and note that the filtrate is watery, the stringy character 

 of saliva being due to the mucus which it contains. To the filtrate add 

 a few drops of Millon's reagent and boil. The result shows the presence 

 of proteid. 



1 The secretion of saliva may be stimulated by inhaling, through the mouth, 

 -some acetic acid. 



