The first distinct enunciation of the hypothesis that all living matter
has sprung from pre-existing living matter came from a contemporary,
though a junior, of Harvey, a native of that country, fertile in men
great in all departments of human activity, which was to intellectual
Europe, in the sixteenth and seventeenth centuries, what Germany is in
the nineteenth. It was in Italy, and from Italian teachers, that Harvey
received the most important part of his scientific education. And it
was a student trained in the same schools, Francesco Redi--a man of the
widest knowledge and most versatile abilities, distinguished alike as
scholar, poet, physician and, naturalist--who, just two hundred and
two years ago,* published his "Esperienze intorno alia Generazione
degl'Insetti," and gave to the world the idea, the growth of which it
is my purpose to trace. Redi's book went through five editions in twenty
years; and the extreme simplicity of his experiments, and the clearness
of his arguments, gained for his views and for their consequences,
almost universal acceptance.
Redi did not trouble himself much with speculative considerations,
but attacked particular cases of what was supposed to be "spontaneous
generation" experimentally. Here are dead animals, or pieces of meat,
says he; I expose them to the air in hot weather, and in a few days they
swarm with maggots. You tell me that these are generated in the dead
flesh; but if I put similar bodies, while quite fresh, into a jar, and
tie some fine gauze over the top of the jar, not a maggot makes its
appearance, while the dead substances, nevertheless, putrefy just in the
same way as before. It is obvious, therefore, that the maggots are not
generated by the corruption of the meat; and that the cause of their
formation must be a something which is kept away by gauze. But gauze
will not keep away aeriform bodies, or fluids. This something must
therefore, exist in the form of solid particles too big to get through
the gauze. Nor is one long left in doubt what these solid particles are;
for the blow-flies, attracted by the odour of the meat, swarm round the
vessel, and, urged by a powerful but in this case misleading instinct,
lay eggs out of which maggots are immediately hatched, upon the gauze.
The conclusion, therefore, is unavoidable; the maggots are not generated
by the meat, but the eggs which give rise to them are brought through
the air by the flies.
* These words were written in 1870.
These experiments seem almost childishly simple, and one wonders how
it was that no one ever thought of them before. Simple as they are,
however, they are worthy of the most careful study, for every piece of
experimental work since done, in regard to this subject, has been shaped
upon the model furnished by the Italian philosopher. As the results
of his experiments were the same, however varied the nature of the
materials he used, it is not wonderful that there arose in Redi's mind
a presumption that, in all such cases of the seeming production of life
from dead matter, the real explanation was the introduction of living
germs from without into that dead matter. And thus the hypothesis that
living matter always arises by the agency of pre-existing living matter,
took definite shape; and had, henceforward, a right to be considered and
a claim to be refuted, in each particular case, before the production of
living matter in any other way could be admitted by careful reasoners.
It will be necessary for me to refer to this hypothesis so frequently,
that, to save circumlocution, I shall call it the hypothesis of
_Biogenesis_; and I shall term the contrary doctrine--that living matter
may be produced by not living matter--the hypothesis of _Abiogenesis_.
In the seventeenth century, as I have said, the latter was the dominant
view, sanctioned alike by antiquity and by authority; and it is
interesting to observe that Redi did not escape the customary tax upon
a discoverer of having to defend himself against the charge of impugning
the authority of the Scriptures; for his adversaries declared that the
generation of bees from the carcase of a dead lion is affirmed, in the
Book of Judges, to have been the origin of the famous riddle with which
Samson perplexed the Philistines:--
"Out of the cater came forth meat,
And out of the strong came forth sweetness"