with which it comes in contact, after being boiled at this temperature,
is passed through a red-hot tube, you will not get a trace of
organisms.

He then turned his attention to the mercury bath, and found on
examination that the surface of the mercury was almost always covered
with a very fine dust. He found that even the mercury itself was
positively full of organic matters; that from being constantly exposed
to the air, it had collected an immense number of these infusorial
organisms from the air. Well, under these circumstances he felt that
the case was quite clear, and that the mercury was not what it had
appeared to M. Schwann to be,--a bar to the admission of these
organisms; but that, in reality, it acted as a reservoir from which the
infusion was immediately supplied with the large quantity that had so
puzzled him.

But not content with explaining the experiments of others, M. Pasteur
went to work to satisfy himself completely. He said to himself: "If my
view is right, and if, in point of fact, all these appearances of
spontaneous generation are altogether due to the falling of minute
germs suspended in the atmosphere,--why, I ought not only to be able to
show the germs, but I ought to be able to catch and sow them, and
produce the resulting organisms." He, accordingly, constructed a very
ingenious apparatus to enable him to accomplish this trapping of this
"germ dust" in the air. He fixed in the window of his room a glass
tube, in the centre of which he had placed a ball of gun-cotton, which,
as you all know, is ordinary cotton-wool, which, from having been
steeped in strong acid, is converted into a substance of great explosive
power. It is also soluble in alcohol and ether. One end of the glass
tube was, of course, open to the external air; and at the other end of