centre of bubbles.' The air also passed
through a Liebig's bulb containing sulphuric acid, and also through a
bulb containing gun-cotton.

It was only natural for Dr. Bennett to believe that his 'bent tubes'
entirely cut off the germs. Previous to the observations just
referred to, I also believed in their efficacy. But these
observations destroy any such notion. The gun-cotton, moreover, will
fail to arrest the whole of the floating matter, unless it is tightly
packed, and there is no indication in Dr. Bennett's memoir that it was
so packed. On the whole, I should infer, from the mere inspection of
Dr. Bennett's apparatus, the very results which he has described--a
retardation of the development of life, a total absence of it in some
cases, and its presence in others.

In his first series of experiments, eight flasks were fed with sifted
air, and five with common air. In ten or twelve days all the five had
fungi in them; whilst it required from four to nine months to develop
fungi in the others. In one of the eight, moreover, even after this
interval no fungi appeared. In a second series of experiments there
was a similar exception. In a third series the cork stoppers used in
the first and second series were abandoned, and glass stoppers
employed. Flasks containing decoctions of tea, beef, and hay were
filled with common air, and other flasks with sifted air. In every
one of the former fungi appeared and in not one of the latter. These
experiments simply ruin the doctrine that Dr. Bennett finally
espouses.

In all these negative cases, the prepared air was forced into the
infusion when it was boiling hot. Dr. Bennett made a fourth series of
experiments, in which, previous to forcing in the air, he permitted
the flasks to cool. Into four bottles thus treated he forced prepared
air, and after a time found fungi in all of them. What is his
conclusion? Not that the boiling hot liquid, employed in his first
experiments, had destroyed such germs as had run the gauntlet of his
apparatus; but that air which, previous to being sealed up, had been
exposed to a temperature of 212 deg., _is too rare to support life_. This
conclusion is so remarkable that it ought to be stated in Dr.
Bennett's own words. 'It may be easily conceived that air subjected
to a boiling temperature is so expanded as scarcely to merit the name
of air, and that it is more or less unfit for the purpose of
sustaining animal or vegetable