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While examining a jar filled with aquatic plants and animals, Abraham Trembley, a young tutor working for Count William Bentinck in the Netherlands, noticed tiny, green, tube-shaped organisms attached to aquatic plants. Uncertain whether they were plants or animals, he devised a brilliant series of experiments to understand their biology. He observed them contract when disturbed and take steps towards a light, gathering in front of a chevron-shaped opening in a piece of cardboard. Nearly convinced they were animals, he cut one in half expecting to see it die. Instead, it regenerated two perfectly formed bodies from the severed halves.

In this 1740 letter, Trembley reports his remarkable discoveries on this animal we now call Hydra to René-Antoine Ferchault de Réaumur, one of the greatest naturalists of his time. To describe novel phenomena where no relevant scientific terminology existed, Trembley elegantly uses analogies and common language while still being precise and systematic. Tentacles become threads, Hydra surveys its environment and regenerates like a plant growing from cuttings. Compared to modern scientific writing, Trembley’s plain language is highly accessible to a non-specialist reader.

This letter comes from the beginning of the correspondence between Trembley and Réaumur, and Trembley is concerned that he might be taking up too much of Réaumur’s time. In later letters, we see Trembley come into his own as he and Réaumur communicate as equals. Trembley and Réaumur’s correspondence led them to classify Hydra as an animal with plant-like regenerative properties. The demonstration that an animal can regenerate its entire body from a fragment, later replicated by scientists across Europe, was a challenge to the contemporary theory of emboîtement (encasement), which proposed that regeneration could only occur at specific nodes. It was also seen as a challenge to the belief that animals have a unitary, indivisible soul. Trembley’s detailed studies on Hydra regeneration, which built on his initial experiments described in this letter, were published in Mémoires pour servir à l’histoire d’un genre de polypes d’eau douce (1744).

The original text was written in 1740 and is in the public domain. The original French text was previously published in 1943 as part of the collection of Abraham Trembley’s correspondence with Réaumur by Maurice Trembley, Abraham’s great-great grandson (Publisher: Georg & Cie, Librairie de l'Université Genève).


Biography of the Author

Abraham Trembley was born in Geneva, Switzerland in 1710. In 1739 he took up residence in the household of Count William Bentinck in The Hague, as the tutor for Bentinck’s two sons. During this time, Trembley found the freshwater cnidarian Hydra attached to aquatic plants he collected on or near the Bentinck estate. This led Trembley to carry out an extraordinary series of experimental studies of Hydra biology that included the astounding demonstration that Hydra can regenerate when cut into pieces. Trembley initially communicated his work on Hydra in letters to the renowned French naturalist René Antoine Ferchault de Réaumur. Here we provide the first English translation of the letter to Réaumur in which Trembley describes for the first time his discovery of Hydra regeneration.

Biography of the Translator

Morgan McLaughlin graduated from the University of San Diego with a Bachelor of the Arts in Behavioral Neuroscience and in French with Honors. Her specific interest in neuroscience and background in 17th-18th century French have allowed her to translate this work. Her undergraduate studies led her to spend a semester in Aix-en-Provence, France where she refined her French abilities and was inspired to study abroad during her graduate studies. She completed her Maîtrise en Neurosciences at Université Laval in Quebec City, Canada and went on to work at UT Southwestern Medical Center in Dallas, Texas as a research assistant. She is currently at Universiteit van Amsterdam in Amsterdam, Netherlands pursuing her Ph.D. in esophageal cancer imaging.

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