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MICROSCOPICAL PHENOMENA OF DECAY. 195

determine the action on the teeth of various acids and salts, as
Avell as of fermenting albuminous substances and carbohydrates.
The fermentative substances especially showed a pronounced
action in the course of two years ; when a tooth was so protected
that the agent touched it at one point only, nothing but the
exposed place was softened and destroyed. In this way a cavity
was produced which could in no wise be distinguished from a
natural cavity of decay. Magitot ascribed this action to the acids
arising in the fermenting mixtures, overlooking the further work
of the bacteria ; he also neglected, unfortunately, to determine by
microscopical examination whether the tissue showed phenomena
identical with natural decay.
Similar experiments were afterward made by a number of
investigators, among others by Milles and Underwood. The
latter ^^^ constructed a large incubator, in which a mixture of milk,
bread, meat, saliva, and carious teeth was kept for six months
at blood temperature. Xo changes resembling caries occurred,
and this is easily conceivable from their own statements : " The
putridity of the baths was, however, so ofiensive that it was with
some relief that we decided to abandon this particular experi-
ment. . . . My health and appetite suffered from constant
exposure to all these putrid smells."
Milles and Underwood say nothing about the reaction in these
baths, but this " putridity" leads us to conclude that it most
probably was alkaline. It cannot have been acid, since we are
told that the dentine was " not a bit softened." Xow I think
that we are all pretty well agreed that there can be no caries
without acid ; hence the failure in the above experiment.
In a second experiment the same authors subjected fragments
of teeth to the action of a mixture of saliva and bread for three
months.
It is not stated whether they renewed the mixture in this
time. It would be a serious mistake not to have done so, because
many bacteria are very sensitive to the action of their own pro-
ducts, and would be devitalized long before the close of the ex-
periment. (See page 14.) Besides, a thick felt of yeast-fungi
formed on the surface of the flasks, which probably also mate-
rially interfered with the course of the experiment. In this ex-