Moved by the entreaty of his master, the illustrious Dumas, Pasteur took up the investigation of the diseases of silkworms at a time when the silk-husbandry of France was in a state of ruin. In doing so he did not, as might appear, entirely forsake his former line of research. Previous investigators had got so far as to discover vibratory corpuscles in the blood of the diseased worms, and with such corpuscles Pasteur had already made himself intimately acquainted. He was therefore to some extent at home in this new investigation. The calamity was appalling, all the efforts made to stay the plague having proved futile. In June 1865 Pasteur betook himself to the scene of the epidemic, and at once commenced his observations. On the evening of his arrival he had already discovered the corpuscles, and shown them to others. Acquainted as he was with the work of living ferments, his mind was prepared to see in the corpuscles the cause of the epidemic. He followed them through all the phases of the insect's life--through the eggs, through the worm, through the chrysalis, through the moth. He proved that the germ of the malady might be present in the eggs and escape detection. In the worm also it might elude microscopic examination. But in the moth it reached a development so distinct as to render its recognition immediate. From healthy moths healthy eggs were sure to spring; from healthy eggs healthy worms; from healthy worms fine cocoons: so that the problem of the restoration to France of its silk-husbandry reduced itself to the separation of the healthy from the unhealthy moths, the rejection of the latter, and the exclusive employment of the eggs of the former. M. Radot describes how this is now done on the largest scale, with the most satisfactory results. The bearing of this investigation on the parasitic theory of communicable diseases was thus illustrated: Worms were infected by permitting them to feed for a single meal on leaves over which corpusculous matter had been spread; they were infected by inoculation, and it was shown how they infected each other by the wounds and scratches of their own claws. By the association of healthy with diseased worms, the infection was communicated to the former. Infection at a distance was also produced by the wafting of the corpuscles through the air. The various modes in which communicable diseases are diffused among human populations were illustrated by Pasteur's treatment of the silkworms. 'It was no hypothetical, infected medium--no problematical pythogenic gas--that killed the worms. It was a definite organism.'[5] The disease thus far described is that called _pébrine_, which was the principal scourge at the time. Another formidable malady was also prevalent, called _flacherie_, the cause of which, and the mode of dealing with it, were also pointed out by Pasteur.