[The discovery by Paul-Louis Simond of the role of the flea in the transmission of the plague].

After Yersin's two fundamental discoveries of the plague bacillus and of the rat's role in its propagation, no one had sought to solve the riddle of how the bacillus itself spread and how it contaminated man. P. L. Simond was the first to realise that manipulating a rat that had recently died could be extremely dangerous whereas after a time lapse of several hours the same dead rat presented no risks to man. He was also the first to detect an insect bite as being responsible for the lesions he had observed at the beginning of bubonic plague outbreaks and called "precocious plyctenas". After having verified the presence of the bacillus in fleas of dying rats, on 2 June 1898 Simond carried out his princeps experiment on the transmission of plague to rats by fleas. From then onwards, disinsectisation was added to deratisation in plague prophylaxis.