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VITAL MAyiFESTATIOXS OF BACTERIA. 17

Such parasites as thrive o///// in or upon living organisms are
classed by de Bary as strictly obligatory parasites. To this class
several species occurring in the oral cavity seem to belong. Sap-
rophytes which find their conditions of existence fulfilled only
in dead substances, are called obligator}^ saprophytes. Parasites
which occur in the interior of an organism are called endophytic ;
those which vegetate only on the surface^ epiphytic. Bacteria
which on being introduced into the human or animal organism
lead to formation of pus, are designated as pyogenic.
Very careful investigations made b}' Klemperer,^^ Biondi,^-
Zuekermann,^^ and many others, have led to the conclusion that
" chemical irritants, when free from micro-organisms, cannot
produce suppuration."' Kreibohm and Rosenbach," Grawitz and
deBary^' obtained other results. According to them, certain
chemical substances, as oil of turpentine, ammonia, nitrate of
silver, etc., may under favorable conditions call forth suppura-
tion. Scheuerlen ^^ was also able to cause suppuration by the
action of an alkaloid of putrefaction (cadaverine), without the
agency of micro-organisms. Nathan ^'' repeated the experiments
of Grawitz and de Bary, and also found that suppuration took
place after injections of oil of turpentine, ammonia, and nitrate
of silver; in all cases, however, he was able by means of the
culture method to establish the presence of micro-organisms.
Nevertheless Grawitz,^* in a subsequent communication, main-
tains the correctness of his previous conclusions.
It has been suggested that these conflicting results may be ex-
plained by the fact that different investigators have made use of
diiferent animals in their experiments. While the advocates of
the theory : no suppuration without micro-organisms, have used
chiefly rabbits, guinea-pigs and rats, Kreibohm and others em-
ployed dogs.
As the matter stands at present, the burden of proof seems to
be in favor of the view that, in case of dogs at least, certain sub-
stances may, under specified conditions, produce suppuration
without the agency of micro-organisms.
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