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GANGREXOUS TOOTH-PULPS AS CENTERS OF INFECTION. 287

dentally obtain entrance to the blood through slight wounds of
the skin, mucous membrane, etc., may enter a diseased pulp or
come in contact with a dead one. Finding here a suitable
medium, they proliferate, forming a focus of infection which
may bring about secondary disturbances at the point of the root.
This process may be illustrated by the following observation A
:
mouse having a wound at the root of the tail was inoculated
subcutaneously near the foreleg with a pure culture of a mouth-
bacterium ; twenty-four hours later this bacterium was found to
have established itself in large numbers in the old wound,
though it was not to be found in other parts of the body. If the
mouse had had a tooth with a dead pulp, I have reason to think
that the bacterium would there also have found a suitable nutri-
tive medium. The infection of the periapical tissue is usually
occasioned either by the micro-organisms working their way
into it independently from the pulp, or by the mechanical forc-
ing of infected material (remains of pulp, etc.) through the
foramen apicale. The latter may result from the pressure of
mastication when the open root is filled with soft contents, or
from the pressure of gases accumulating in the canal, or finally
from dental operations. The consequences of such an infection
depend upon the resistance offered to the advance of the bacteria
and upon the virulence and number of the latter. Putrid pro-
ducts, which may be forced through the foramen, intensify the
action of the bacteria by exerting a mechanical as well as a
toxical irritation upon the tissue. In case the decomposed pulp
contains no more living germs, particles of it may be forced
through the foramen without causing an infection. In such
cases a reaction takes places only in as far as it is produced by
mechanical or chemical irritation of the products of putrefaction,
which have been forced through the foramen.
Furthermore, apical infection with the harmless parasites of
the mouth will, cceteris paribus, be accompanied by comparatively
slight reaction.
If, on the other hand, living pathogenic bacteria are present
in the pulp, an infection will take place whose intensity depends
upon the number and virulence of the same.
Where the typically pyogenic micro-organisms, Staphylococcus