on, without allowing the infusion or the cotton
ball to come into contact with any air but that which had been subjected
to a red heat, and in twenty-four hours he had the satisfaction of
finding all the indications of what had been hitherto called spontaneous
generation. He had succeeded in catching the germs and developing
organisms in the way he had anticipated.

It now struck him that the truth of his conclusions might be
demonstrated without all the apparatus he had employed. To do this, he
took some decaying animal or vegetable substance, such as urine, which
is an extremely decomposable substance, or the juice of yeast, or
perhaps some other artificial preparation, and filled a vessel having a
long tubular neck with it. He then boiled the liquid and bent that
long neck into an S shape or zig-zag, leaving it open at the end. The
infusion then gave no trace of any appearance of spontaneous generation,
however long it might be left, as all the germs in the air were
deposited in the beginning of the bent neck. He then cut the tube close
to the vessel, and allowed the ordinary air to have free and direct
access; and the result of that was the appearance of organisms in it, as
soon as the infusion had been allowed to stand long enough to allow
of the growth of those it received from the air, which was about
forty-eight hours. The result of M. Pasteur's experiments proved,
therefore, in the most conclusive manner, that all the appearances of
spontaneous generation arose from nothing more than the deposition of
the germs of organisms which were constantly floating in the air.

To this conclusion, however, the objection was made, that if that were
the cause, then the air would contain such an enormous number of these
germs, that it would be a continual fog. But M. Pasteur replied that
they are not there in anything like the number we might suppose, and
that an exaggerated view has been held on that subject; he showed that
the chances of animal or vegetable life appearing in infusions, depend
entirely on the conditions under which they are exposed. If they are
exposed to the ordinary atmosphere around us, why, of course, you may
have organisms appearing early. But, on the other hand, if they are
exposed to air from a great height, or from some very quiet cellar, you
will often not find a single trace of life.

So that M. Pasteur arrived at last at the clear and definite result,
that all these appearances are like the cas