t if you took the same vessel and exposed
the infusion to the air, then you would get animalcules. Furthermore, it
was found that if you connected the mouth of the vessel with a red-hot
tube in such a way that the air would have to pass through the tube
before reaching the infusion, that then you would get no animalcules.
Yet another thing was noticed: if you took two flasks containing the
same kind of infusion, and left one entirely exposed to the air, and
in the mouth of the other placed a ball of cotton wool, so that the air
would have to filter itself through it before reaching the infusion,
that then, although you might have plenty of animalcules in the first
flask, you would certainly obtain none from the second.

These experiments, you see, all tended towards one conclusion--that the
infusoria were developed from little minute spores or eggs which
were constantly floating in the atmosphere, which lose their power of
germination if subjected to heat. But one observer now made another
experiment which seemed to go entirely the other way, and puzzled
him altogether. He took some of this boiled infusion that I have been
speaking of, and by the use of a mercurial bath--a kind of trough used
in laboratories--he deftly inverted a vessel containing the infusion
into the mercury, so that the latter reached a little beyond the level
of the mouth of the 'inverted' vessel. You see that he thus had a
quantity of the infusion shut off from any possible communication with
the outer air by being inverted upon a bed of mercury.

He then prepared some pure oxygen and nitrogen gases, and passed them
by means of a tube going from the outside of the vessel, up through the
mercury into the infusion; so that he thus had it exposed to a perfectly
pure atmosphere of the same constituents as the external air. Of course,
he expected he would get no infusorial animalcules at all in that
infusion; but, to his great dismay and discomfiture, he found he almost
always did get them.

Furthermore, it has been found that experiments made in the manner
described above answer well with most infusions; but that if you fill
the vessel with boiled milk, and then stop the neck with cotton-wool,
you 'will' have infusoria. So that you see there were two experiments
that brought you to one kind of conclusion, and three to another; which
was a most unsatisfactory state of things to arrive at in a scientific
inquiry.

Some few years after this, the quest