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IMMUNITY AND St/SCfirrinfLfTY          69

fluence of the spleen was not greater than that of any
other organ in overcoming bacterial infections.

Kantlmck1 found that the removal of the spleen had
practically no influence upon the natural immunity of
animals to pyocyaneus infection.

(c) By combining two different species of bacteria, either
of which, when injected alone, would he harmless or of
-slight effect. Roger found that when animals immune
to malignant edema were simultaneously injected with
i to 2 c.cin. of a culture of Bacillus prodigiosus and the
bacillus of malignant edema, they would contract the
disease. Pawlowski found that when rabbits, which
are very susceptible to anthrax, were simultaneously in-
jected with anthrax and prodigiosus, they recovered
from the anthrax, as if the harmless microbe possessed
the power of neutralizing the products of the patho-
genic form.

Giarre found that if an adult guinea-pig, which is refrac-
tory to infection by pneumoeocci, were simultaneously in-
oculated with diphtheria, it readily died of septicemia.

Sometimes an apparent immunity depends upon the
attenuation of the culture used for inoculation, and the
erroneous results to which such a mistake may lead are
obvious. Should a culture become attenuated, its viru-
lence may sometimes be increased by inoculating it into
the most susceptible animal, then from this to a less
susceptible, and then to an immune animal. The viru-
lence of anthrax is increased by inoculation into pigeons,
and also by cultivation in an infusion of the tissues of
an animal similar to the one to be inoculated.

It must be understood that the term u immunity11 is
a relative one, and that while ua white rat is immune
against anthrax in amounts sufficiently large to kill a
rabbit, it is perhaps not immune against a quantity
sufficiently large to kill an elephant/'

It is not to be expected that such intricate phenomena
as these which have been mentioned could be observed

1 CcntralbLf. />W-A n. I\misit?nk.i 1892, xii., p. 227,