giving with certainty eggs that Pasteur was content
to call healthy, but which to-day we would say were free
from parasites. It was with these eggs, the hereditary
conditions of which he knew, that he began the tentative
experiments and the large cultures of 1867.

The first thing which he had to ask himself, since he
had not yet renounced the idea of a constitutional
disease existing before the appearance of the corpuscles,
was whether the districts of silk husbandry truly consti-
tuted, as was said over and over, a deleterious center,
an infected district, in which the disease and the cor-
puscle would appear inevitably, carried by the ambi-
ent air into the healthiest broods. This doctrine spoke
too much in favor of inaction and indolence, not to have
many partisans.

To this objection Pasteur was able to respond at the
end of his preliminary experiments by showing some
lots of worms, offspring of non-corpuscular parents that
had passed through the entire metamorphosis without
being attacked, and had produced eggs which in turn
were free from corpuscles, and this too, although they
were raised not only in an infected district, but in a
silkworm nursery where by the side of them, other lots
died from the disease. Not only did the sound worms
remain sound, but their general health seemed to be
improved, and from 1865 to 1866, from 1866 to 1867,
one saw the broods improve just in proportion to the
original purity of the eggs.

Assured now of not seeing the corpuscles appear in these
sound lots, one could perform experiments on corpuscular
contagion, beginning it at different ages, could repeat
on a large scale the experiment of Gernez, and could
synthesize the results. This synthesis is most clear,
and we may summarize it very simply.

If we take sound worms and make them swallow or

-169-