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DUST AND DISEASE. 311

the contrary, their author founds a defence of the doctrine
of spontaneous generation, and a general theory of sponta-
neous 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 evi-
dence of the spontaneous origin of such fungi. And he
accounts for the absence of life in .many of his experi-
ments by resorting to an hypothesis which will not bear
a moment’s consideration. But now that we know that
organic particles may pass unscathed through alkalies and
acids, the experiments of Dr. Bennett are precisely what
ought, under 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.

On anOther point also the luminous beam will cast a
light. Pasteur opened flasks upon the Mer de Glace, and,
being careful not to come between the wind and his flasks,
found the air incompetent, in the great majority of cases,
to generate life. M. Pouchet repeated Pasteur’s experiment
in the Pyrenees, adding the precaution of holding the flasks,
when they were opened, above his head. .The luminous
beam at once shows us the effect of this additional precau-
tion. Let smoking brown paper be placed at the open
mouth of a glass shade so that the smoke shall ascend and
fill the shade. A beam sent through the shade forms a
bright track through the smoke. When the closed fist is
placed underneath the shade, a vertical wind of surprising
violence, considering the small elevation of temperature,
rises from the hand, diSplacing by comparatively dark air
the illuminated smoke. Such a wind infalliny rose from
M. Pouchet’s body as he held his flasks above his head, and
thus the precaution of Pasteur of not coming between the
wind and the flask was annulled.

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