ON DUST AND DISEASE. 141 



and adopted by Pasteur. Pebrine declares itself in the 

 stunted and unequal growth of the worms, in the 

 languor of their movements, in their fastidiousness as 

 regards food, and in their premature death. The course 

 of discovery as regards the epidemic is this: In 1849 

 Guerin Meneville noticed in the blood of silkworms 

 vibratory corpuscles, which he supposed from their 

 motions to be endowed with independent life. Filippi, 

 however, showed that the motion of the corpuscles was 

 the well-known Brownian motion ; but he committed 

 the error of supposing the corpuscles to be normal to 

 the life of the insect. Possessing the power of in- 

 definite self-multiplication, they are really the cause 

 of its mortality the form and substance of its 

 disease. This was well described by Cornalia ; while 

 Lebert and Frey subsequently found the corpuscles not 

 only in the blood, but in all the tissues of the insect. 

 Osimo, in 1857, discovered them in the eggs; and on 

 this observation Vittadiani founded, in 1859, a prac- 

 tical method of distinguishing healthy from diseased 

 eggs. The test often proved fallacious, and it was 

 never extensively applied. 



These living corpuscles take possession of the in- 

 testinal canal, and spread thence throughout the body 

 of the worm. They fill the silk cavities, the stricken 

 insect often going automatically through the motions 

 of spinning, without any material to work upon. Its 

 organs, instead of being filled with the clear viscous 

 liquid of the silk, are packed to distension by the 

 corpuscles. On this feature of the plague Pasteur 

 fixed his entire attention. The cycle of the silkworm's 

 life is briefly this : From the fertile egg comes the 

 little worm, which grows, and casts its skin. This 

 process of moulting is repeated two or three times 

 at intervals during the life of the insect. After 



