of a bird, drawn from the animal, is an excellent culture
medium for the bacteridium. Why does it resist in-
fection in the animal? Because "the living blood in
full circulation is filled with an infinite number of cor-
puscles which in order to live and perform their physio-
logical function, need free oxygen: it might be said that
the blood corpuscles are obligate aërobes. When, there-
fore, the anthrax bacteridium, enters normal blood,
it meets there an enormous number of organic indi-
vidualities ready, figuratively speaking, for what one
sometimes calls the struggle for existence, ready, in
other words, to seize for their own use the oxygen nec-
essary for the existence of the bacteridium." ¹

We see developed here the formula and the ideas of
Darwin, but in a singularly precise form. What could
be more vague than the phrase "struggle for existence?"
But "struggle for oxygen," that opens the way to ex-
perimentation, and Pasteur begins at once.

Some common bacteria sown with the anthrax bacter-
idium, in neutral or alkaline urine, prevent its developing
because they take possession of the ground more rapidly
and exhaust the oxygen. They can, in the same way,
arrest its development in an animal. "It is possible
to inject great quantities of the anthrax bacteridium
into an animal without its contracting the disease, if
some of these common bacteria have been present in
the culture used." Here we have the first example of
bacteriotherapy, to which Cantani returned later, and
which has not spoken its last word.

The interpretation of these facts has changed, and
we know now that it is less simple [than it seemed at that
time] but the idea of the struggle for existence was never-
theless then introduced into pathology, in the domain
of cellular antagonism: and it has remained there.

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