DUST AND DISEASE. 15 



parasite as to excite astonishment that it could live. 

 The disease advanced, the worms died and were ex- 

 amined, and on May 11 only six out of the thirty 

 remained. They were the strongest of the lot, but on 

 being searched they also were found charged with cor- 

 puscles. Not one of the thirty worms had escaped ; a 

 single meal had poisoned them all. The standard lot, 

 on the contrary, spun their fine cocoons, two only of 

 their moths being proved to contain any trace of the 

 parasite, which had doubtless been introduced during 

 the rearing of the worms. 



As his acquaintance with the subject increased, 

 Pasteur's desire for precision augmented, and he finally 

 counted the growing number of corpuscles seen in the 

 field of his microscope from day to day. After a con- 

 tagious repast the number of worms containing the 

 parasite gradually augmented until finally it became 

 cent, per cent. The number of corpuscles would at the 

 same time rise from to 1, to 10, to 100, and some- 

 times even to 1,000 or 1,500 in the field of his micro- 

 scope. He then varied the mode of infection. He 

 inoculated healthy worms with the corpusculous matter, 

 and watched the consequent growth of the disease. He 

 proved that the worms inoculate each other by the 

 infliction of visible wounds with their claws. In various 

 cases he washed the claws, and found corpuscles in the 

 water. He demonstrated the spread of infection by the 

 simple association of healthy and diseased worms. By 

 their claws and their excrement, the diseased worms 

 spread infection. It was no hypothetical infected 

 medium—no problematical pythogenic gas — that killed 

 the worms, but a definite organism. The question of 

 infection at a distance was also examined, and its 

 occurrence demonstrated. As might be expected from 

 Pasteur's antecedents, the investigation was exhaustive. 



