ins of the lake,
and rushing with audible patter into deeper water at the approach of
danger. The origin of this periodic crowd of living things is by no
means obvious. For years I had never noticed in the lake either an
adult frog, or the smallest fragment of frog spawn; so that were I not
otherwise informed, I should have found the conclusion of Mathiole a
natural one, namely, that tadpoles are generated in lake mud by the
vivifying action of the sun.

The checks which experience alone can furnish being absent, the
spontaneous generation of creatures quite as high as the frog in the
scale of being was assumed for ages to be a fact. Here, as elsewhere,
the dominant mind of Aristotle stamped its notions on the world at
large. For nearly twenty centuries after him men found no difficulty
in believing in cases of spontaneous generation which would now be
rejected as monstrous by the most fanatical supporter of the doctrine.
Shell-fish of all kinds were considered to be without parental origin.
Eels were supposed to spring spontaneously from the fat ooze of the
Nile. Caterpillars were the spontaneous products of the leaves on
which they fed; while winged insects, serpents, rats, and mice were
all thought capable of being generated without sexual intervention.

The most copious source of this life without an ancestry was
putrefying flesh; and, lacking the checks imposed by fuller
investigation, the conclusion that flesh possesses and exerts this
generative power is a natural one. I well remember when a child of
ten or twelve seeing a joint of imperfectly salted beef cut into, and
coils of maggots laid bare within the mass. Without a moment's
hesitation I jumped to the conclusion that these maggots had been
spontaneously generated in the meat. I had no knowledge which could
qualify or oppose this conclusion, and for the time it was
irresistible. The childhood of the individual typifies that of the
race, and the belief here enunciated was that of the world for nearly
two thousand years.

To the examination of this very point the celebrated Francesco Redi,
physician to the Grand Dukes Ferdinand II. and Cosmo III. of
Tuscany, and a member of the Academy del Cimento, addressed himself in
1668. He had seen the maggots of putrefying flesh, and reflected on
their possible origin. But he was not content with mere reflection,
nor with the theoretic guesswork which his predecessors had founded
upon their imperfect obser