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104 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

in otlier words, the acid-foriiiiiio; ferment has l)een rendered
inactive, but the unorganized, sugar-forming ferment, not.
Exp. 5. Instead of ether, enough carbolic acid is added to
make the solution one-half per cent, strong; the result is the
same. These two experiments show that the ptyaline of the
saliva (which was not injured by the presence of the ether or the
carbolic acid, as proved by the fact that it retained its diastatic
action) is not the cause of the acid reaction.
JBjXij. 6. According to Paschutin, ptyaline is devitalized by an
exposure of twenty minutes to a temperature of 67° C. Organ-
ized ferments could not be killed by the same means. AVe ac-
cordingly subject a mixture of saliva and grape-sugar to the
given temperature for twenty minutes. AVe thereby destroy
the ptyaline ; the mixture, nevertheless, l)ecomes sour if allowed
to stand in the incubator for twenty hours.
This experiment contirms the result of experiments 4 and 5,
and we begin to suspect that we have to deal with an organized
ferment. This supposition is confirmed by the following experi-
ment :
Exp. 7. A small quantity of a perfectly sterilized solution of
sugar in saliva (1-40), in a test tube with cotton cork, is infected
from the mouth, or with carious dentine, as described above ; in
twenty-four hours the solution will lie acid ; with a fraction of a
drop of this solution a second tube is infected ; it will likewise
become acid; from this a third, etc. ; each becomes acid in turn,
while the control tube (containing the same solution, not infected)
remains neutral.
The conclusion is plain that we have to do with a ferment
which is capable of reproducing itself; in other words, the agent
gi^dng rise to acid fermentations in the juices of the human
mouth exists in the form of living organisms.
I have examined twenty-two ditferent species of bacteria
which up to the year 1885 I had isolated out. of the secretions,
etc., of the human mouth, in reference to their fermentative
action; and although, as may readily l)e seen, it was impos-
sible with so large a number of ditierent organisms to carry out
the experiments to the desired degree of completion, I have
nevertheless obtained some results which may be of interest and