04 April 2011

Spallanzani's animalcula

Today I started reading Lazzaro Spallanzani's Tracts on the natural history of animals and vegetables*, first published probably in the late 18th century. Spallanzani was interested in some of the same animals that also excite me, including snails and microscopic aquatic creatures, or animalcules.

Spallanzani investigated the survival of animalcules in the absence of water. His subjects were the "wheel-animal" (bdelloid rotifers), the "sloth" (tardigrades) and "anguillae" (nematodes). Here is Spallanzani's drawing of a bdelloid, clearly reconizable as such.

His tardigrade, on the other hand, was less recognizable.

Certain species of bdelloid rotifers, tardigrades and nematodes indeed survive complete desiccation as well as other equally extreme physical states. Obviously, they survive if they do not die, for being alive and dead are, by definition, 2 mutually exclusive states. And death is permanent, which is a simple and fundamental rule that even gods cannot violate. Spallanzani, however, believed that his animalcules actually died when they were dried, but resurrected upon rehydration. He was a Catholic priest and his theology had perhaps biased his scientific thinking.

I will return to Spallanzani's ideas as I read more of his writings.

*English translation available at Biodiversity Heritage Library.

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