INTRODUCTION. XXIX 



Worms were infected by permitting them to feed for 

 a single meal on leaves over which corpusculous 

 mattsr had been spread; they were infected by in- 

 oculation, 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. In- 

 fection 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.' l 

 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 to Alais in January 1869, for the express 

 purpose of combating the criticisms to which his 

 labours had been subjected. Pasteur is combustible, 

 and contradiction readily stirs him into flame. No 



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

 was more in favour than it is now. 



