rnalia; 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 practical 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 intestinal 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 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. Now Pasteur proved that
the plague-corpuscles might be incipient in the egg, and escape
detection; they might also be germinal in the worm, and still baffle
the microscope. But as the worm grows, the corpuscles 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
corpuscles infallibly appear, offering no difficulty of detection.
This was the first great point made out in 1865 by Pasteur. The
Italian naturalists, as aforesaid, recommended the examination of the
eggs before risking their incubation. Pasteur showed that both eggs
and worms might be smitten, and still pass muster, the culture of such
eggs or such worms being sure to entail disaster. He made the moth
his starting-point in seeking to regenerate the race.

Pasteur made his first communication on this subject to the Academy of
Sciences in September, 1865. It raised a cloud of criticism. Here,
forsooth, was a chemist rashly quitting his proper _metier_ and
presuming to lay down the law for the physician and biol