14 THE FLOATING-MATTER OF THE AIR. 



his words were verified by the production of an excellent 

 crop. Other cases of prophecy still more remarkable, 

 because more circumstantial, are recorded in Pasteur's 

 work on the Diseases of Silkworms. 



Pasteur subjected the development of the corpuscles 

 to a searching investigation, and followed out with 

 admirable skill and completeness the various modes by 

 which the plague was propagated. From raothsjfix=^ 

 fectly free from corpuscles he obtained healthy worj^as,- 

 and selecting 10, 20, 30, 50, as the case might be^„he_ 

 introduced into the worms the corpusculous matter^ 

 It was first permitted to accompany the food. Let us 

 take a single example out of many. Eubbing up 

 a small corpusculous worm in water, he smeared 

 the mixture over mulberry-leaves. Assuring himself 

 that the leaves had been eaten, he watched the con- 

 sequences from day to day. Side by side with the 

 infected worms he reared their fellows, keeping them as 

 much as possible out of the way of infection. These 

 •constituted his ' lot temoin,' — his standard of com- 

 parison. On April 16, 1868, he thus infected thirty 

 worms. Up to the 23rd they remained quite well. 

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

 puscles were found in the intestines of two of them. On 

 the 27th, or eleven days after the infected repast, two 

 fresh worms were examined, and not only was the 

 intestinal canal found in each case invaded, but the silk 

 •organ itself was 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 n on- infected worms was 

 very striking, the sick worms being not more than two- 

 thirds of the bulk of the healthy ones. On May 2 a 

 worm which had just finished its fourth moulting was 

 examined. Its whole body was so filled with the 



