188 LOUIS PASTEUR, 



diate. 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 resto- 

 ration 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 employ- 

 ment of the eo-o-s of the former. M. Radot describes 



oo 



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 asso- 

 ciation of healthy with diseased worms, the infection 

 was communicated to the former. Infection at a dis- 

 tance was also produced by the wafting of the corpus- 

 cles through the air. The various modes in which 

 communicable diseases are diffused among human popu- 

 lations 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.' ] The disease 

 thus far described is that called pebrine, 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. 



Overstrained by years of labour in this field, Pasteur 

 was smitten with paralysis in October 1868. But this 

 calamity did not prevent him from making a journey 



1 These words were uttered at a time when the pythogenic theory 

 was more in favour than it is now. 



