Pasteur who believed he could never accumulate too
much proof in support of his opinion, was here not un-
mindful of the fact that the animate cause of certain
virulent diseases was still contested. He had a beautiful
argument to add to those which he had already given
on anthrax. He made it instantly in the same shrewd
way that he made an ingenious analysis.

"We should search," he says, "for proof that apart
from our vibrio there is no independent virulence pecu-
liar to liquids or solids, that, in short, the vibrio is not
simply an epiphenomenon of the disease of which it
is the obligate associate." (l.c). Here are two liquids
which are identical in the beginning, exposed to air for
the same length of time. One remains virulent, the
other does not.

They contained originally and both still contain two
kinds of substances--solids and fluids. To which does
the virulence belong? It is evident that the substances
in solution have remained the same in both cases. It
is not possible to imagine any action produced on them
by the air which would not be alike in both tubes. Only
the solids, and there are none except the vibrios, have
undergone a change, being converted into resistant spores
in one case, and harmless granules in the other. It
is, therefore, to these alone that the virulence must be
attributed.

We have not finished. We have just demonstrated
that the spore is the resistant aërobic form of the anaë-
robic vibrio. How does it return to the vibrio stage?
This is equivalent to asking, since the spore-form occurs
everywhere, under what circumstances does it again
become dangerous? We shall soon see with what bril-
liancy Pasteur answers this question.

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