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44 THE MICRO-ORGASISMS OF THE HUMAN MOUTH.

ticularly favorable conditions of nutrition for certain species of
bacteria. The apparently strictly oblig-atorv parasitic bacteria of
the mouth, Spirochete dentium and Spirillum sputigenum, find
here the peculiar conditions essential to their deyelopment. It
is a yery interesting fact, and one showing what a powerful
influence the nature of the culture medium may haye upon the
growth of bacteria, that though numberless attempts have been
made to construct a culture medium adapted to the wants of
these bacteria, they have all signally failed, so exactly must the
natural conditions be imitated before they can be induced to
grow.

7. Accumulation of Particles of Food.
The chief source of nutrition for the oral bacteria is, however,
furnished by the particles of food collecting between the teeth,
or in fissures, depressions, cavities of decay, etc., or adhering
even to their free surfaces. These, consisting chiefly of albu-
minous substances and carbohydrates, mixed with the other
nutrient matter mentioned under 1 to 6, present an almost per-
fect culture medium for bacteria.

After these introductory remarks, we shall now proceed to
the study of the bacteria of the human mouth, a subject which
has justly attracted a vast deal of attention in dental, as well as
in medical circles, within the 'last few years.