he air. It is these starch grains which form many of those bright
specks that we see dancing in a ray of light sometimes. But besides
these, M. Pasteur found also an immense number of other organic
substances such as spores of fungi, which had been floating about in the
air and had got caged in this way.

He went farther, and said to himself, "If these really are the things
that give rise to the appearance of spontaneous generation, I ought to
be able to take a ball of this 'dusted' gun-cotton and put it into one
of my vessels, containing that boiled infusion which has been kept away
from the air, and in which no infusoria are at present developed, and
then, if I am right, the introduction of this gun-cotton will give rise
to organisms."

Accordingly, he took one of these vessels of infusion, which had been
kept eighteen months, without the least appearance of life, and by a
most ingenious contrivance, he managed to break it open and introduce
such a ball of gun-cotton, 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 g