290 FRAGMENTS OF SCIENCE. 



the well-known Brownian motion. But Filippi himself 

 committed the error of supposing' the corpuscles to be 

 normal to the life of the insect. 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 Vitta- 

 diani founded, in 1859, a practical method of distinguishing 

 healthy from diseased eggs. The test often proved falla- 

 cious, and it was never extensively applied. 



These corpuscles take possession of the intestinal canal, 

 and spread thence throughout the body of the worm. 

 They fill the silk cavities, the stricken insect often going- 

 through the motions of spinning without any material to 

 answer to the act. Its organs, instead of being filled with 

 the clear viscous liquid of the silk, are packed to disten- 

 tion by the corpuscles. On this feature of the plague Pas- 

 teur fixed his entire attention. The cycle of the silk- 

 worm's life is briefly this : From the fertile egg comes 

 the little worm, which grows, and casts its skin. This pro- 

 cess of moulting is repeated two or three times at subse- 

 quent intervals during the life of the insect. After the last 

 moulting the worm climbs the brambles placed to receive 

 it, and spins among them its cocoon. It passes thus into 

 a chrysalis ; the chrysalis becomes a moth, and the moth 

 wdien liberated lays the eggs which form the starting-point 

 of a new cycle. Now Pasteur proved that the plague-cor- 

 puscles might be incipient in the egg, and escape detec- 

 tion ; they might also be germinal in the worm, and still 

 baffle the microscope. But as the worm grows, the cor- 

 puscles grow also, becoming larger and more defined. In 

 the aged chrysalis they are more pronounced than in the 

 worm ; while in the moth, if either the egg or the worm 

 from which it comes should have been at all stricken, the 



