life.'

Now numerical data are attainable here, and as a matter of fact I live
and flourish for a considerable portion of each year in a medium of
less density than that which Dr. Bennett describes as scarcely
meriting the name of air. The inhabitants of the higher Alpine
chalets, with their flocks and herds, and the grasses which support
these, do the same; while the chamois rears its kids in air rarer
still. Insect life, moreover, is sometimes exhibited with monstrous
prodigality at Alpine heights.

In a fifth series of experiments sixteen bottles were filled with
infusions. Into four of them, while cold, ordinary unheated and
unsifted air was pumped. In these four bottles fungi were developed.
Into four other bottles, containing a boiling infusion, ordinary air
was also pumped--no fungi were here developed. Into four other
bottles containing an infusion which had been boiled and permitted to
cool, sifted air was pumped--no fungi were developed. Finally, into
four bottles containing a boiling infusion sifted air was pumped no
fungi were developed. Only, therefore, in the four cases where the
infusions were cold infusions, and the air ordinary air, did fungi
appear.

Dr. Bennett does not draw from his experiments the conclusion to which
they so obviously point. On them, on the contrary, he founds a
defence of the doctrine of spontaneous generation, and a general
theory of spontaneous development. So strongly was he impressed with
the idea that the germs could not possibly pass through his potash and
sulphuric acid tubes, that the appearance of fungi, even in a small
minority of cases, where the air had been sent through these tubes,
was to him conclusive evidence of the spontaneous origin of such
fungi. And he accounts for the absence of life in many of his
experiments by an hypothesis which will not bear a moment's
examination. But, knowing that organic particles may pass unscathed
through alkalies and acids, the results of Dr. Bennett are precisely
what ought wider the circumstances to be expected. Indeed, their
harmony with the conditions now revealed is a proof of the honesty and
accuracy with which they were executed.

The caution exercised by Pasteur both in the execution of his
experiments, and in the reasoning based upon them, is perfectly
evident to those who, through the practice of severe experimental
enquiry, have rendered themselves competent to judge of good
experimental work. He found