Charles Bonnet

Charles Bonnet, Swiss naturalist and philosophical writer, was born at Geneva, of a French family driven into Switzerland by the religious persecution in the 16th century. The last twenty five years of his life he spent quietly in the country, at Genthod, near Geneva, where he died after a long and painful illness on 20 May 1793. His wife was Jeanne-Marie de la Rive. They had no children, but Madame Bonnet's nephew, the celebrated Horace-Bénédict de Saussure, was brought up as their son. He made law his profession, but his favourite pursuit was the study of natural science. He led a quiet life, except for 1752 through 1768, during which he was a member of the council of the Swill republic.

Charles Bonnet came up with the idea Underwater plants get bubbles of gas stuck to their leaves. This is dissolved air in the water becoming gas again and sticking to the leaves.

The account of the ant-lion in Noël-Antoine Pluche's Spectacle de la nature, which he read in his sixteenth year, turned his attention to insect life. He procured RAF de Réaumur's work on insects, and with the help of live specimens succeeded in adding many observations to those of Réaumur and Pluche. In 1740, Bonnet communicated to the Academy of Sciences a paper containing a series of experiments establishing what is now termed parthenogenesis in aphids or tree-lice, which obtained for him the honour of being admitted a corresponding member of the academy.

In 1741, he began to study reproduction by fusion and the regeneration of lost parts in the freshwater hydra and other animals; and in the following year he discovered that the respiration of caterpillars and butterflies is performed by pores, to which the name of stigmata (or spiracles) has since been given. In 1743, he was admitted a fellow of the Royal Society; and in the same year he became a doctor of laws.

In 1753, he was elected a foreign member of the Royal Swedish Academy of Sciences, and on December 15, 1769 a foreign member of the Royal Danish Academy of Sciences and Letters.

His first published work appeared in 1745, entitled Traité d'insectologie, in which were collected his various discoveries regarding insects, along with a preface on the development of germs and the scale of organized beings. Botany, particularly the leaves of plants, next attracted his attention; and after several years of diligent study, rendered irksome by the increasing weakness of his eyesight, he published in 1754 one of the most original and interesting of his works, Recherches sur l'usage des feuilles dans les plantes; in which among other things he advances many considerations tending to show (as was later done by Francis Darwin) that plants are endowed with powers of sensation and discernment.

Bonnet's eyesight, which threatened to fail altogether, caused him to turn to philosophy. In 1754 his Essai de psychologie was published anonymously in London. This was followed by the Essai analytique sur les facultés de l'âme (Copenhagen, 1760), in which he develops his views regarding the physiological conditions of mental activity.

In 1760 he described a condition now called Charles Bonnet Syndrome, in which vivid, complex visual hallucinations (fictive visual percepts) occur in psychologically normal people. (He documented it in his 87 year old grandfather, who was nearly blind from cataracts in both eyes but perceived men, women, birds, carriages, buildings, tapestries and scaffolding patterns.) Most people affected are elderly with visual impairments, however the phenomenon does not occur only in the elderly or in those with visual impairments; it can also be caused by damage elsewhere in their optic pathway or brain.