ion than Schwann,
though a strange attempt was made a year and a half ago to enlist him
and others equally opposed to it on the side of the doctrine.

The physical character of the agent which produces putrefaction was
further revealed by Helmholtz in 1843. By means of a membrane, he
separated a sterilised putrescible liquid from a putrefying one. The
sterilised infusion remained perfectly intact. Hence it was not the
liquid of the putrefying mass--for that could freely diffuse through
the membrane--but something contained in the liquid, and which was
stopped by the membrane, that caused the putrefaction. In 1854
Schroeder and von Dusch struck into this enquiry, which was
subsequently followed up by Schroeder alone. These able experimenters
employed plugs of cotton-wool to filter the air supplied to their
infusions. Fed with such air, in the great majority of cases the
putrescible liquids remained perfectly sweet after boiling. Milk
formed a conspicuous exception to the general rule. It putrefied
after boiling, though supplied with carefully filtered air. The
researches of Schroeder bring us up to the year 1859.

In that year a book was published which seemed to overturn some of the
best established facts of previous investigators. Its title was
Heterogenie, and its author was F. A. Pouchet, Director of the
Museum of Natural History at Rouen. Ardent, laborious, learned, full
not only of scientific but of metaphysical fervour, he threw his whole
energy into the enquiry. Never did a subject require the exercise of
the cold critical faculty more than this one--calm study in the
unravelling of complex phenomena, care in the preparation of
experiments, care in their execution, skilful variation of conditions,
and incessant questioning of results until repetition had placed them
beyond doubt or question. To a man of Pouchet's temperament the
subject was full of danger--danger not lessened by the theoretic bias
with which he approached it. This is revealed by the opening words of
his preface: 'Lorsque, par la meditation, it fut evident pour moi que
la generation spontanee etait encore Fun des moyens qu'emploie la
nature pour la reproduction des etres, je m'appliquai a decouvrir par
quell procedes on pouvait parvenir a en mettre les phenomenes en
evidence: It is needless to say that such a prepossession required a
strong curb. Pouchet repeated the experiments of Schulze and Schwann
with results diametrically