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CHAPTER II.

NUTRIENT MEDIA FOR BACTERIA IN THE ORAL CAVITY.
The organic and inorganic substances found in the mouth,
which may serve as nutriment for micro-organisms, are the fol-
lowing :
1. IS'ormal saliva.
2. Buccal mucus.
3. Dead epithelium.
4. Dental tissue softened by acids.
5. Exposed pulps.
6. Exudations of the gums, conditioned by the irritation of
tartar, etc.
7. Accumulation of particles of food.

1. Saliva.
Normal, human, mixed saliva is a colorless liquid, usually
slightly clouded by epithelium ; it is more or less slimy, slippery,
and viscous, differing with different individuals. Xormally the
submaxillary and sublingual glands furnish a viscous secretion,
whereas that of the parotid is more dilute. In healthy persons
it has a weak alkaline or neutral reaction ; its specific gravity is
1.002 to 1.006. Under the conditions mentioned in Chapter VIII,
the reaction frequently becomes acid. If kept standing, especially
at "blood temperature, it will putrefy sooner or later, according to
the amount of organic matter it contains; in the presence of
starch or sugar no real putrefaction takes place, but a process
of fermentation ensues, giving rise to an acid reaction and sour
smell, accompanied by the formation of carbonic acid.
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