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310 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

when one-tenth per cent, sugar was present; if the amount of
sugar was increased, the reaction became acid ; if it was dimin-
ished, the reaction became alkaline.
It is equally diificult, I think, to draw a sharp line between
putrefactive and fermentative organisms, since many ferment-
organisms are capable of decomposing albuminous substances
with development of putrcfjictive products, while on the other
hand many organisms which pass as putrefactive, when brought
into saccharine solutions, give rise to fermentation without the
production of a trace of the characteristic products of putrefac-
tion. One of the mouth-bacteria which I examined in reference
to this question readily dissolved coagulated albumen with devel-
opment of bad-smelling gases, among which SHg (sulphuretted
hydrogen) and XH3 (ammonia) could be easily detected. It
also showed an inverting action, in that it converted cane-sugar
into dextrose and levulose. In the third place it split ferment-
able sugars into lactic acid, with production of CO2 (carbon
dioxide). In the fourth place it gave rise to an acid reaction in
a solution of starch, while at the same time the solution acquired
the capacity of reducing the oxide of copper ; in other words,
this bacterium showed also a diastatic action.
In these difterent fermentations there undoubtedly arise in the
later stages various secondar}- products, so that the changes
which may be brought about by this one micro-organism and
the products developed under its action make up a very large
number. This result affords an explanation of the fact that in
an open decomposing substance so many different products may
appear, and renders very doubtful the supposition that for every
new product in the process of decomposition a new organism
must be present. The twenty to thirty different compounds
which may be produced in an open decomposing solution are in
all probability not produced by one bacterium alone. It is, how-
ever, not in accordance with the facts to assume that for every
product, or indeed for every stage in the process, a new bac-
terium must be introduced.
Of the bacteria under consideration I would like to call atten-
tion to five which regularly form large gas-bubbles in the gela-
tine or tear it in pieces, as represented in Fig. 8. One of these,