His method was as follows: to demonstrate for the
septic vibrio that the return of the spore to activity
and to virulence does not depend on the obscure questions
of vital force or vital resistance, which medicine invokes
so readily, but that it is simply a question of the pres-
ence or absence of oxygen; then, when he had thus
smoothed the way, to marshal together and launch,
somewhat pell-mell, other analogous facts regarding
the ability of water- and soil microbes to become patho-
genic. Now that we know his plan of campaign let
us see how he carried it out?

In the first place let us ask if "the germ corpuscles
of the septic vibrio, although formed in a vacuum or
in pure carbonic acid gas, would not need, in order to
become active, a small quantity of oxygen. Physiology
does not know to-day of any case in which germination
is possible in the absence of air. ¹ So be it I nevertheless,
experiment has shown that the germs of the septic vibrio
are absolutely inactive in contact with oxygen, whatever
may be the proportion of this gas; but this is always
on condition that there is a certain relation between the
volume of air and the number of germs, for the first
germinations, using up the air which is in solution, may
serve as a protection for the remaining germs, and it is
thus that, actually, the septic vibrio may propagate itself
even in the presence of small quantities of air, but not
if much air is present."

That is, if, in addition to the septic vibrio, there are
present common aërobic bacteria, the latter by de-
veloping, prepare the way for the former. Thus it is
that the vibrio develops in the intestinal canal, which is
ordinarily destitute of oxygen, and Pasteur here recog-
nized once more the rôle played by associations of bac-

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