The quantity of saliva secreted in 24 hours varies. The average amount is probably from two to three pints in 24 hours.
The composition of saliva is:
| Water, | 994.10 |
| Solids, | 5.90 |
The solids are:
| Pyaline, | 1.41 | |||
| Fat, | 0.07 | |||
| Epithelium and Mucus, | 2.13 | |||
| Salts, |  | Sulphocyanide of Potassium, |  | 2.29 |
| Phosphate of Soda, | ||||
| Phosphate,, of,, Lime, | ||||
| Phosphate,, of,, Magnesia, | ||||
| Chloride of Sodium, | ||||
| Chloride,, of,, Potassium, | ||||
| 5.90 | ||||
The specific gravity varies from 1.004 to 1.008.
The rate at which saliva is secreted is subject to considerable variation. When the tongue and muscles concerned in mastication are at rest, and the nerves of the mouth are subject to no unusual stimulus, the quantity secreted is not more than sufficient, with the mucus, to keep the mouth moist.
The purposes served by saliva are of several kinds:
1. Acting mechanically in conjunction with mucus, it keeps the mouth in a due condition of moisture, and facilitates the movements of the tongue in speaking, and the mastication of the food.
2. It serves also in dissolving sapid substances and rendering them capable of exciting the nerves of taste.