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From 2012.igem.org

A chassis, really?

Metaphors aren't innocent

Historical praise to the frog as a martyr of science

The frog is kind-hearted…

Without it, would William Harvey discovered the blood flow? The cold-blooded animals like toads or frogs have a slow heart that is easier to analyze than mammals. It is by looking at them that Harvey made his first observations. In his work Motus Cordis, he assures that the blood is expulsed by the heart to the artery and goes by through the veins. “This is how I start to wonder if there was a circulatory move of the blood”. But, Harvey died before finding out what becomes to the blood between the arteries and the veins.

The lung devoted to Science…

Once again, we have to thank the frog for solving the enigma of the blood circulation. Observing under a microscope le lung of a frog, Marcello Malpighi noticed very thin blood vessels - the capillaries - that link the small arteries to the small veins.

In 1661, he wrote :

“Things are much easier to see with the frogs (…). The microscopic observation revealed things even more prodigious (…). I clearly saw that the blood got divided and circulated in tortuous vessels”

It is by crossing the lungs that the veins’ blood goes back to the arteries. But, to get this result, Malpighi admitted, even glorified himself:

“I have almost scarified the entire race of frogs, something that never happened before, even during the furious battle between rats and frogs described by Homer”.

… And sexual practices submit to scientists’ voyeurism.

Theories of “generation” – that is of reproduction – had aroused passionate quarrels. One of them was about fecundation: what part plays the man seed? The frog, as a very common animal, and reproducing quickly, has the merit of transparence… It reproduce by external fecundation, the eggs laid by the female are straight after recover by the mal seed.

Jan Swammerdam, Biblia naturae, Leyde, 1737-1738 [manuscript from 1679]

In the XVII th century already, Jan Swammerdam was interested by the frog’s reproduction. With a small magnifying lens, he observed the cellular division of a fecundated frog’s egg. In 1768, Lazzaro Spallanzani dressed a male frog with a little panty made of leather, not without difficulty, because the animal tried to get rid of it!

“What assure the whole, is that I’ve putted some straps to these panties. I slipped it on the harms of the male frog, under his head, between his body and the female’s one”

The females mated with these males wearing panties freed their eggs, but these ones decayed and didn’t transform in tadpole. But, inside the panties, Spallanzani found drops of transparent liquor. He took a sample of virgin eggs in a frog’s ovary, knowing by experience that they can spontaneously develop. He damped them with the collected seed and noticed a few days after that the eggs developed as well as if they were naturally fecundated by the male.

“He just came to realize the first artificial insemination in a laboratory” wrote Jean Rostand. This series of experiences – with more than 200 frogs – allowed Spallanzani to ruin the hypothesis of fecundation at distance: the direct touch of the egg and the male seed is essential.

It has nerve, and tight!

In the middle of the XVII th century, the Dutch naturalist Jan Swammerdam explored another field of life: the transmission of the nerve impulse. A frog can keep on swimming even if one’s take away its heart, while it comes to a standstill if one’s take away its heart. The blood circulation is not necessary to move (at least for the frog). In 1568 he demonstrated, in front of the Duke of Toscane, the contraction of the frog’s muscle, separated from the frog with its nerve, under the action of a simple compression of the nerve. While there’s no more links between the nerve and the spinal cord, the contraction can be repeated at will. Opposing to the most widespread hypothesis, Swammerdam concluded of his experience that the muscle contraction can’t only be explained by the action of a fluid that flowed inside of the nerve, from the spinal cord to the muscle.