DUST AND DISEASE. 293 



tion. These constituted his " lot temoign," his standard of 

 comparison. On the 16th of April, 1868, he thus infected 

 thirty worms. Up to the 23d they remained quite well. 

 On the 25th they seemed well, but on that day corpuscles 

 were found in the intestines of two of them. They first 

 form in the tunic of the intestine. On the 27th, or eleven 

 days after the infected repast, two fresh worms were exam- 

 ined, and not only was the intestinal canal found in each 

 case invaded, but the silk-organ itself was found charged 

 with corpuscles. On the 28th, the twenty-six remaining 

 worms were covered by the black spots of pebrine. On the 

 30th, the difference of size between the infected and non- 

 infected worms was very striking, the sick worms being not 

 more than two-thirds of the size of the healthy ones. On 

 the 2d of May, a worm which had just finished its fourth 

 moulting was examined. Its whole body was so filled with 

 corpuscles as to excite astonishment that it could live. 

 The disease advanced, the worms died and were examined, 

 and on the llth of May only six out of the thirty remained. 

 They were the strongest of the lot, but, on being searched, 

 they also were found charged with corpuscles. Not one of 

 the thirty worms had escaped ; a single corpusculous meal 

 had poisoned them all. The standard lot, on the contrary, 

 spun their fine cocoons, and two only of their moths were 

 found to contain any trace of corpuscles, which had, doubt- 

 less, been introduced during the rearing of the worms. 



As his acquaintance with the subject increased, Pas- 

 teur's desire for precision augmented, and he finally gives 

 the growing number of corpuscles seen in the field of his 

 microscope from day to day. After a contagious 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 sometimes even to 1,000 or 1,500 for a 

 single field of his microscope. He then varied the mode 



