Louis Pasteur

Silkworm disease
In 1865, Jean-Baptiste Dumas, chemist, senator and former Minister of Agriculture and Commerce, asked Pasteur to study a new disease that was decimating silkworm farms from the south of France and Europe, the pébrine, characterized on a macroscopic scale by black spots and on a microscopic scale by the "Cornalia corpuscles". Pasteur accepted and made five long stays in Alès, between 7 June 1865 and 1869.^[82]
Initial errors
Arriving in Alès, Pasteur familiarized himself with pébrine and also^[83] with another disease of the silkworm, known earlier^[84] than pebrine: flacherie or dead-flat disease. Contrary, for example, to Quatrefages, who coined the new word pébrine,^[85] Pasteur makes the mistake of believing that the two diseases were the same and even that most of the diseases of silkworms known up to that time were identical with each other and with pébrine.^[86] It was in letters of 30 April and 21 May 1867 to Dumas that he first made the distinction between pébrine and flacherie.^[87]
He made another mistake: he began by denying the "parasitic" (microbial) nature of pébrine, which several scholars (notably Antoine Béchamp)^[88] considered well established. Even a note published on 27 August 1866 by Balbiani,^[89] which Pasteur at first seemed to welcome favourably^[90] had no effect, at least immediately.^[91] "Pasteur is mistaken. He would only change his mind in the course of 1867."^[92].
Victory over pébrine
At a time where Pasteur had not yet understood the cause of the pébrine, he propagated an effective process to stop infections: a sample of chrysalises was chosen, they were crushed and the corpuscles were searched for in the crushed material; if the proportion of corpuscular pupae in the sample was very low, the chamber was considered good for reproduction.^[93] This method of sorting “seeds” (eggs) is close to a method that Osimo had proposed a few years earlier, but whose trials had not been conclusive.^[94] By this process, Pasteur curbs pébrine and saves many of the silk industry in the Cévennes.^[95][96]