234 HANDBOOK OF PHYSIOLOGY. 



when examined with the microscope, are found floating a number of mi- 

 nute particles, derived from the secreting ducts and vesicles of the glands. 

 In the impure or mixed saliva are found, besides these particles, numer- 

 ous epithelial scales separated from the surface of the mucous mem- 

 brane of the mouth and tongue, and the so-called salivary corpuscles, 

 discharged probably from the mucous glands of the mouth and the ton- 

 sils, which, when the saliva is collected in a deep vessel, and left at rest, 

 subside in the form of a white opaque matter, leaving the supernatant 

 salivary fluid transparent and colorless, or with a pale bluish-gray tint. 

 In reaction, the saliva, when first secreted, appears to be always alka- 

 line. During fasting, the saliva, although secreted alkaline, shortly be- 

 comes neutral; especially when it is secreted slowly and is allowed to mix 

 with the acid mucus of the mouth, by which its alkaline reaction is 

 neutralized. 



Chemical Composition of Mixed Saliva (Frerichs). 



Water, 994.10 



Solids : 



Ptyalin, 1.41 



Fat, ^ 0.07 



Epithelium and Proteids (including 

 Serum- Albumin, Globulin, Mucin, 

 etc.), 2.13 



Salts : 



Potassium Sulpho-Cyanate, . . ") 



Sodium Phosphate, . 



Calcium Phosphate. . . * I 2 29 



Magnesium Phosphate, . . j 



Sodium Chloride, . . . | 



Potassium Chloride, . . . . J 



5.9 



1000 



The presence of potassium sulphocyanate (or thiocyanate) (C N K S) 

 in saliva, may be shown by the blood-red coloration which the fluid 

 gives with a solution of ferric. chloride (Fe. 2 01. 6 ), and which is bleached 

 on the addition of a solution of mercuric chloride (Hg Cl a ), but not by 

 hydrochloric acid. 



Rate of Secretion and Quantity. The rate at which saliva is secreted 

 is subject to considerable variation. When the tongue and muscles con- 

 cerned in mastication are at rest, and the nerves of the mouth are sub- 

 ject to no unusual stimulus, the quantity secreted is not more than 

 sufficient, with the mucus, to keep the mouth moist. During actual 

 secretion the flow is much accelerated. 



The quantity secreted' in twenty-four hours varies : its average 

 amount is probably from 1 to 3 pints (1 to 2 litres). 



