36 
posed to contagion just before spinning, the chrysalis will show the par- 
asites only during its last days, while they will be abundant in the moth. 
From the mother moth the corpuscles pass into the egg and give rise 
to the diseased ‘‘seed” already remarked upon. Disease in the male 
will not, however, affect its progeny. The egg is formed while the in- 
sect is still in the chrysalis state, and it has been ascertained that 
where the corpuscles become abundant only during the last days of this 
stage they enter into the seed to a very small degree only, if at all. 
Tor this reason eggs are sometimes found to be entirely pure, though the 
issue ofa highly pébrinous parent. The development and multiplication 
of these corpuscles, though ordinarily very rapid, is insignificant in the 
egg until the formation of the larva begins. It will be easily understood 
that, though the parasite may exist in the vitellus of the egg, its detec- 
tion may be extremely difficult. But when the development of the em- 
bryo has commenced, the number of corpuscles grows also, so that just 
before, or, better still, just after the time of hatching they may be found 
by hundreds upon a casual observation. Upon a microscopical exam- 
ination at this time, Vittadini, in 1859, founded his system of selection, 
examining samples of eggs just at the time of hatching and rejecting 
those lots which showed the corpuscular disease. 
At that epoch it was believed that the corpuscles existed even in the 
healthy moth when well advanced towards its natural death. But Pas- 
teur showed this theory to be fallacious, proving, as we have said above, 
that the corpuscle is only present when the moth is diseased. He 
showed that, where the moth is free from the parasite, the egg, too, 
would be exempt, and that, as a rule, where the corpuscles exist in the 
moth, then its issue will probably be corpusculous also. There is, to be 
sure, even then a chance of its purity, as mentioned above—that is, 
where the corpuscles become abundant in the chrysalis only after the 
formation of the egg. But here, too, it is highly probable that the 
malady will have so affected the general health of the parent as to make 
her issue more apt to succumb to disease, as in the case of flaccidity. 
Therefore it is laid down as a rule, and upon this rule the Pasteur sys- 
tem of selection rests, that if, upon microscopical examination of the 
mother moth, the corpuscles of pébrine are found, then her eggs and 
issue will also be pébrineus, and should be destroyed. 
The details of the Pasteur system of selection will be given in the 
next chapter. 3 
FLACCIDITY (flacherie). 
Heternal symptoms.—When, after the worms have passed their fourth 
molt, and are eating well and regularly, they have all the appearance 
of perfect health and vigor, and the silk-raiser feels full confidence in 
the success of his crop, some will often be seen to crawl to the edges 
of the trays, and lie there languid and without motion. But for the 
loss of their wonted activity and the cessation of their naturally vora- 
