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MOUTH-BACTERIA AS EXCITERS OF FERMENTATION. 115

B. Action of the Mouth-Bacteria on Albuminous Substances.

By far the majority of moiitli-baeteria, in fact of all bacteria,
possess an action similar to pepsine, in converting (peptonizing)
coagulated albumen into soluble moditications. The essential
diiference, however, consists in this : that, while pepsine exerts
its peptonizing action only in the presence of acids (especially
muriatic), bacteria exert it in neutral or alkaline media also.
The albuminous substances, therefore, even when insolulde, offer
an excellent nutrient medium for bacteria. The products arising
from the development of mouth-bacteria in albuminous media are
the same as those arising fnmi putrefaction of organic substances
in general. These are chiefly bad-smelling gases, sulphuretted
hydrogen (SH^), ammonia (XH3) ; further, CO^, II,X, sulphide
of ammonia and the products mentioned on page 28. The re-
sultant reaction of all the products of any process of putrefaction
is, ;is far as my ol)servations go, invariably alkaline.
In my experiments the albumen was so congealed in the test
tubes as to expose the largest possible surface, ?.r., the tubes were
prepared in the same way as tubes of beef-ldood serum. K
kept in a damp chamber to prevent drying up, the material may
be held ready for use for any desired length of time. Four of
the bacteria examined would not grow on this medium, six
exhibited Init limited growth, while the others developed com-
paratively well, in some cases completely liquetying the albumen.
Whether these bacteria produce more peptone than is necessary
for their own nutrition, and whether and to what extent they
might thereby benefit the human body, is a very difficult prob-
lem. In a large quantity of coagulated white of egg inoculated
with a bacillus from the mouth, which showed intense putrefac-
tive properties, I was able on the third day to detect traces of
peptone by means of the biuret test.
In the presence of small quantities of sugar the characteristic
phenomena of putrefaction are much less pronounced, or are
altogether wanting. Xo bad-smelling products are formed, or,
if formed, they immediately undergo further clianges, and an
acid reaction takes the place of the alkaline. I found that a bac-
terium, tested particularly in reference to this point, occasioned
a neutral reaction in the presence of -^^ per cent, of sugar when