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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
when liberated lays. the eggs which form the starting-point
of a new cycle. N ow 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
battle 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

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