9 o THE POPULAR SCIENCE MONTHLY. 



therefore, to some extent at home in this new investigation. Tbe 

 calamity was appalling, all the efforts made to stay the plague having 

 proved futile. In June, 1865, Pasteur betook himself to the scene of 

 tbe epidemic, and at once commenced his observations. On the even- 

 ing of his arrival he had already discovered the corpuscles, and 

 sbown them to others. Acquainted as he was with tbe work of living 

 ferments, bis mind was prepared to see in tbe 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 tbe 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 develop- 

 ment 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 tbe 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 bow this is now done on the largest scale, with the 

 most satisfactory results. 



The bearing of this investigation on the parasitic theory of com- 

 municable diseases was thus illustrated : Worms were infected by per- 

 mitting them to feed for a single meal on leaves over which corpuscu- 

 lous matter had been spread ; they were infected by inoculation, and 

 it was shown how they infected each other by tbe 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 dif- 

 fused among human populations were illustrated by Pasteur's treat- 

 medt of tbe silk-worms. " 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 for- 

 midable 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 labor 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 labors bad been sub- 

 jected. Pasteur is combustible, and contradiction readily stirs him 

 into flame. No scientific man now living has fought so many battles 

 as he. To enable him to render bis experiments decisive, tbe French 

 emperor placed a villa at his disposal near Trieste, Avbere silk-worm 



* These -words were uttered at a time when the pythogenic theory was niorc in favor 

 than it is now. 



