Page 173 - My FlipBook

SEVENTEENTH LECTURE.

The Cause of Dental Caries.

I have now passed pretty well over the subject of bac-
teriology and caries of the teeth. There is some sketching up
that should be made, however. The cause of caries I think
you should understand pretty well, and I will not take time
to go over that this morning and sketch up the growth,
formation of plaques and the action of the caries fungus,
but will print a concise statement in connection with this
lecture that you may have it for reading and careful study.
There is but one cause of caries, and that is the caries fungus,
or micro-organisms.

Caries Fungus.

Dental caries is caused directly by micro-organisms of a
certain species, or of several species, that habitually grow in
the human mouth. The author has generally found but a
single species that seemed actively growing in the deeper por-
tions of the invasion of the dentin. This has been the strepto-
coccus media or the alpha fungus of Miller. I have frequently
found in the saliva two other varieties of streptococci, one
larger, streptococcus magnus, and one smaller, streptococcus
minor, which have maintained these characters in pure cul-
ture. These are inconstant, however, in the saliva, and often
many efforts will be required to find specimens of them. They
are similar in their characters to the streptococcus media. It
is a streptococcus averaging about five-tenths of a micron in
diameter (a micron is i-i,ooo of a millimeter) and in stale cul-
tures breaks up into single cocci, or into very short chains.
In actively growing cultures in broth it will be generally found
in chains of from four to ten individuals. It grows fairly
rapidly in beef or mutton broth, either with or without the
addition of sugar. The broth infected with these organisms
will become cloudy in from six to twelve hours, if kept at the
body temperature, and the growth will.be completed and sink
to the bottom, leaving the fluid clear in from two to four days.

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