(b. Geneva [now Switzerland]. 3 September 1710; d. Petit Sancconex, near Geneva, 12 May 1784)
Abraham Trembley’s father, Jean, was an officer in the Genevan army and rose to be its commander, the syndic of the guard. Abraham was educated at the Academy of Geneva, and in 1733 found employment as a tutor in Holland. His career was much influenced by his residence at Leiden, where he was in close touch with several distinguished scientists in the university. It was probably here that he met Count Bentinck, a curator of the university; and he became tutor to the latter’s two sons at the mansion of Sorgvliet, near The Hague. Here he carried out the researches on the hydra that gained him a fellowship in the Royal Society in 1743 and made him famous. The duke of Richmond witnessed some of his experiments at Sorgvliet. and young Trembley made a deep impression on him. On his deathbed in 1750, the duke consigned to Trembley the care and education of his son and heir, then aged fifteen. Trembley conducted the youth on an extensive tour of the Continent. When they parted in 1756, he was so generously rewarded by the young duke that it was never again necessary for him to work for a living. In 1757 he returned to Geneva, married, and bought the country house at Petit Sacconex in which he lived for the rest of his life. Trembley devoted himself mainly to the instruction of his children and to writing books on education, politics, religion, and moral philosophy. His methods of instruction were novel and anticipated many later developments in educational theory. He was deeply religious, a Christian without strictly adhering to any particular sect.
It was in June 1740 that Trembley had his first opportunity to study the hydra. He had taken into his room at Sorgvliet some ditch water containing aquatic plants. He noticed a green hydra (Chlorohydra viridissima) attached to one of the plants, and at first took it to be itself a plant. He noticed, however, that the tentacles moved, and soon found that organisms of this species could change their positions; but he still hesitated to call them animals. He decided to determine the matter by cutting one of them in two, on the supposition that if both parts survived, the organism would clearly be classifiable as a plant. The cut was made in such a way that one of the parts possessed all the tentacles. He watched the regeneration of both fragments during the following days until regeneration was complete, when both parts were tentaculate; they were indistinguishable from one another. Nevertheless, the apparent spontaneity of the hydra’s movements made it difficult for him to accept the conclusion that these were in fact plants. To obtain help in reaching a decision, he sent some specimens to Réaumer and wrote him a very long letter about his observations. The letter was read in full at two sessions of the Académie Royale des Sciences in Paris in March 1741. Living specimens were also exhibited at the Academy.
Trembley accepted Réaumur’s assurance that the organisms were unquestionably animals. A related species, probably the brown Hydra vulgaris, had in fact been discovered by Leeuwenhoek in 1702, and a note on it had been published. Professor Émile Guyénot has shrewdly remarked that if Trembley had been aware that animals of this sort were already known he would probably not have studied them so attentively; and if his first specimen had been H. vulgaris or Pelmatohydra oligactis (also brownish), he would not have been likely to think it was a plant. It would not then have occurred to him to make the experiment that resulted in the discovery of multiplication by artificial division. Trembley eventually studied all three species, but their modern names were not introduced in his time.
Réaumur checked for himself the truth of Trembley’s account, and both Bentinck and Richmond wrote to the Royal Society to confirm it. It is not easy today to recapture the sense of utter amazement caused by the realization that an animal could be multiplied by cutting it in pieces. Voltaire refused to believe it. Long afterwards he still persisted in denying the possibility and dismissed the subject contemptuously, describing the animal in print as “a kind of small rush.”
Trembley pursued his investigations on the hydra. He described the characteristics of the hydra’s living substance (afterwards named protoplasm); investigated its reactions to light and to changes in temperature; watched it capturing its prey, eating, and digesting; and he found that vulgaris and oligacits could be colored red, black, or a feeble green by supplying suitable foods. His feeding experiments led to the introduction of a particularly interesting technique. Drawing no sharp distinction between the granules of the endoderm on one hand and the nematocysts of the ectoderm on the other, he thought that the animal might perhaps be able to nourish itself if turned inside out. He succeeded in this operation, despite the almost incredible difficulty presented by the minute size of the animals. He proved that a reversed H. vulgaris can, indeed, survive and feed without re-reversal, that is, without returning to its original form. Long afterwards there were still biologists who could not believe this, but the experiment was successfully repeated by M. Nussbaum in 1887. The ectoderm cells of reversed hydras are known nowadays to be able to migrate singly or in groups to the exterior, without any re-reversal of the organism as a whole.
Trembley devoted much time to a detailed study of the budding process, regeneration, and the artificial production of monsters. He then set to work to find out whether multiplication by division could be achieved in reverse, that is, whether two hydras could be transformed into one. This operation was perhaps the most dramatic of all his experiments. He placed one hydra within another, pushing it in tail first through the mouth of the other specimen until its tail projected from near the tail of the other, while its head had still not entered the mouth. The posterior end of the internal animal was permanently grafted, and a single individual with two tails resulted, one derived from each of the two original animals. This, the first permanent graft of animal tissues, was done in October 1742. Both constituent parts of the composite organism multiplied by budding. Several modifications of the grafting process were carried out successfully.
It is noteworthy that Trembley tried on hydra nearly every possible experiment in regeneration and grafting that was likely to give interesting results. He was exploring territory that was almost entirely unknown; yet the planning of his work was so complete, and its execution so thorough, that he might almost have been performing routine experiments on a system established by the long experience of others. The only important exception is that he did not try to find out whether the polarity of a body part could be reversed so that its anterior-posterior axis could be changed.
Trembley was persuaded by Réaumur to bring together the results of his work on the hydra in a book. The result was a beautifully produced volume entitled Mémoires, pour servir à L’histoire d’un genre de polypes d’eau douce, à bras en forme de cornes (1744), with very fine illustrations by Pieter Lyonet.
Although Trembley’s study of the hydra is the best known of his works, it is arguable that some of his other researches are of equal importance. He was the first to describe multiplication and colonyformation in Protozoa and multiplication by bud-ding in Oligochaeta and Polyzoa, and he was also the first to give a full account of the anatomy of the individual in any member of the latter group. Until he discovered reproduction by budding in Oligochaeta and Polyzoa, it had never been seen in any animal other than the hydra. Some twenty years later, while living at Petit Sacconex, he was the first to witness cell division in the strict sense of the term (division of a uninucleate cell). Still, it was not possible in Trembley’s time for him or anyone else to recognize the full significance of some of his discoveries. When he discovered that Protozoa multiplied by division, for example, no one had yet suggested the separation of these animals into a distinct phylum; and when he watched cell division in Synedra, it was not known that this diatom was a single cell.
Trembley was above all a student of processes, and in this respect he led the way in zoology. It is often said that he was the father of experimental zoology, but it is doubtful whether he would have approved of this description. He used both observation and experiment freely, according to which method was most likely to serve his ends in a particular case. His only purely morphological study, however, was on the anatomy of the Lophopus (Polyzoa). G. J. Allman, in his Monograph of the Fresh-Water Polyzoa (1856), said of Trembley’s work on this animal, “The description is wonderfully accurate, and the anatomical details have been in few points surpassed by subsequent observers.” Trembley’s accuracy of observation was one of his most striking characteristics. He had a passion for demonstrable facts and perhaps an exaggerated dislike of hypothesis.
I. Original Works. Important works by Trembley are Mémories, pour servir á I’historie d’un genre de polypes d’eau douce, àbras en forme de cornes (Leiden, 1744); and Instructions d’un pére á ses enfans, sur la nature et sur la religion (Geneva, 1775).
II. Secondary Literature. Works on Trembley are J. R. Baker, Abraham Trembley of Geneva: Scientist and Philosopher, 1710–1784 (London, 1952); [Jean Trembley] Mémoire historique sur la vie et les écrits de Monsieur Abraham Trembely (Neuchâtel, 1787); and Maurice Trembley, Correspondence inédite entre Réaumur et Abraham Trembley comprenant 113 lettres recueillies et annotées par Maurice Trembley, with an introduction by É. Guyénot (Geneva, 1943).
John R. Baker
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