Redi (1626 – 1698)
would be vain without the confirmation of experiment” Francesco Redi, 1668
Redi, who lived in the seventeenth century, did not believe in spontaneous
generation. He explained the
presence of worms in decayed meat and plants in this way:
I feel … inclined to believe that these worms are all generated by
insemination (= breeding) and that the putrefied matter in which they are found
has no other office than that of serving as a place, or suitable nest, where
animals deposit their eggs at the
breeding season, and in which they also find nourishment: otherwise, I assert
that nothing is ever generated therein …”
I am terribly afraid … that flies may defile the
corpse of my lord Patroclus by settling on the open wounds and breeding worms in
them. Life has gone out of him and
all his flesh would rot.”
body being carried from the field of battle.
carefully observed the worms – we would call them maggots – on decaying meat
exposed to the air. About nineteen
days after they had first appeared he saw that some of them had turned into
pupae, which he collected and placed separately in glass vessels.
Eight days later he saw flies
hatch out of the pupae. Here, then,
this painstaking work Redi had recorded things which the believers in
spontaneous generation had either not seen or ignored.
Their understanding had been limited by the extent of their observations.
Redi extended his observations and thus provided support for his new
idea. This comparison bears out the
truth of the saying that we can only see as far as we look.
Possibly Redi’s persistent observations were encouraged by his beliefs
just as those of his opponents were discouraged.
to this point Redi’s work was comparable with that of van Helmont (see Background).
It consisted of observation and interpretation.
The supporters of spontaneous generation concluded their work at this
stage. Once they had produced an
explanation, they thought that nothing further was needed.
Redi, however, turned his explanation into a hypothesis and set up an
experiment to test it. Belief, he
said, would be vain without the confirmation of experiment.
briefly, Redi’s hypothesis was that the worms did not originate by spontaneous
generation but from eggs laid by the flies.
This was how he tested it:
put a snake, some fish, some eels of the
can see that what Redi had devised was a ‘controlled’ experiment. Half the
flasks were closed, half were open. This
was the single apparent difference between them.
Therefore his result could only be related to this difference.
Only in the open flasks were flies able to enter, and only in them were
the maggots produced.
realised that factors which he had not taken into account might have influenced
his results, so he continued his work.
“Not content with these experiments I tried many others at different
seasons, using different vessels. In
order to leave nothing undone, I even had pieces of meat put underground, but
though remaining buried for weeks, they never bred worms, as was always the case
when flies had been allowed to light on the meat.
One day a large number of worms, which had bred on some buffalo meat,
were killed by my order; having placed part in a closed first dish and part in
an open one, nothing appeared in the first dish but in the second worms had
hatched, which changing as usual into egg shaped balls (= pupć), finally became
flies of the common kind. In the
same experiment tried
with dead flies, I never saw anything breed in the closed vessel.”
published his findings in 1668.
will see that Redi carries out a full scientific investigation. He worked out a hypothesis,
tested it by experiment, and carefully
drew his conclusions from the results
he obtained. In contrast the work of
the supporters of spontaneous generation was only half finished.
We may well wonder how much further advanced our knowledge of nature
would be today if the exponents of spontaneous generation had adopted Redi’s
so it is interesting, and a timely reminder of how careful you have to be in
experimental work, to note that there was a flaw in Redi’s experiment.
Can you work out what it is?
Grace Monger and Richard Gliddon
eds, The Perpetuation of Life: revised
Nuffield biology text 4, Longman 1975
Roy Porter The
Greatest Benefit to Mankind, Harper Collins 1997
G. Rattray Taylor, The
Science of Life,