The liquid has been in contact with the
dust-laden air outside by which it has been infected, and the
infection must be destroyed. This is done by plunging the six tubes
into a bath of heated oil and boiling the infusion. The time
requisite to destroy the infection depends wholly upon its nature. Two
minutes' boiling suffices to destroy some _contagia_, whereas two
hundred minutes' boiling fails to destroy others. After the infusion
has been sterilised, the oil-bath is withdrawn, and the liquid, whose
putrescibility has been in no way affected by the boiling, is
abandoned to the air of the chamber.

With such chambers I tested, in the autumn and winter of 1875-6,
infusions of the most various kinds, embracing natural animal liquids,
the flesh and viscera of domestic animals, game, fish, and vegetables.
More than fifty chambers, each with its series of infusions, were
tested, many of them repeatedly. There was no shade of uncertainty in
any of the results. In every instance we had, within the chamber,
perfect limpidity and sweetness, which in some cases lasted for more
than a year--without the chamber, with the same infusion, putridity
and its characteristic smells. In no instance was the least
countenance lent to the notion that an infusion deprived by heat of
its inherent life, and placed in contact with air cleansed of its
visibly suspended matter, has any power to generate life anew.

Remembering then the number and variety of the infusions employed, and
the strictness of our adherence to the rules of preparation laid down
by the heterogenists themselves; remembering that we have operated
upon the very substances recommended by them as capable of furnishing,
even in untrained hands, easy and decisive proofs of spontaneous
generation, and that we have added to their substances many others of
our own--if this pretended generative power were a reality, surely it
must have manifested itself somewhere. Speaking roundly, I should say
that in such closed chambers at least five hundred chances have been
given to it, but it has nowhere appeared.

The argument is now to be clenched by an experiment which will remove
every residue of doubt as to the ability of the infusions here
employed to sustain life. We open the back doors of our sealed
chambers, and permit the common air with its floating particles to
have access to our tubes. For three months they have remained
pellucid and sweet--flesh, fish, and vegetable e