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NUTRIENT MEDIA FOR BACTERIA IN THE ORAL CAVITY. 41

of the tongue and cheeks with sulphuric ether. If the mouth
is then held wide open over a glass or porcelain vessel, the saliva
will flow out in clear thin drops from the parotid or in long,
viscous streams from the sublingual and submaxillary glands.
Saliva thus obtained is but slightly clouded, but forms a white
precipitate when left standing. If a small quantity of this
precipitate be placed upon an object-glass in a drop of water,
covered with a cover-glass and a small drop of dilute sulpliuric
acid allowed to flow underneath, a formation of gas-bubbles will
be observed (COo), while under 20 to 40 diameters the needles
characteristic of sulphate of lime will appear. By means of
molybdate of ammonia, phosphoric acid may also be easily de-
tected in this precipitate. The latter, therefore, consists partly
of carbonates and partly of phosphates (lime-salts), and sufficiently
explains the formation of tartar. There is, consequently, no
need of having recourse to the theory, which for various reasons
is untenable, that tartar consists of the calcareous remains of
bacteria.
Pare saliva exposed to the air undergoes putrefaction, not as
rapidly, however, as is generally asserted in text-books of phys-
iology ; on the contrary, sometimes very slowly, so that no bad
smell may be detected before several days have elapsed. Only
when the saliva is mixed with organic matter from the mouth
does it soon show marked signs of putrefaction.
This may be easily understood when we take into considera-
tion the fact that human saliva contains only about 0.15 per cent,
of organic matter, and is, therefore, but a very indifterent cul-
ture medium for bacteria, since experience has taught that a
^ood culture medium must contain a much greater quantity of
organic matter. As before mentioned, if sugar is added to the
saliva no sign of putrefaction will appear, but a fermentation
takes place which engenders an acid reaction and a sour smell.
The view, entertained by many dentists, that saliva possesses
antiseptic properties, seems to me to be unfounded. Those con-
stituents of human saliva which have antiseptic properties are
present in too small quantities to be able in any way to impede
the development of bacteria. The fact that the human mouth is
so fovorable a place of liabitation for so many kinds of bacteria, is