34 
space. The spores retain their power of communicating disease for at 
least three years; hence the importance of cleansing and fumigating as 
described in the last chapter. 
PEBRINE. 
External symptoms.—“ The disease, pébrine, shows itself outwardly by 
the dwindling away of the worms and their inequality of size; eating 
little, they do not grow as large as when in their normal state. At the 
end of a few days black spots frequently make their appearance on 
the skin, resembling punctures or burns; the anal horn, the prolegs, 
the soft parts between the rings, are especially subject to these 
spots.”* 
Fic. 20.—Silk-worms spotted with pébrine, twice natural size (after Pa teur). 
Fig. 20 “represents, at twice the natural size, the anterior part of the 
body of sick worms covered with such spots. In one of the worms, a, 
they are just becoming visible, and the eye should be aided by a magnify- 
ing glass to render them distinct; the other, b, shows them farther ad- 
vanced, easily recognizable with the naked eye, if the worm be examined 
with a little attention. Finally, Fig. 21 shows one ring spotted with pé- 
brine, magnified to six diameters. For this cut 
was chosen a worm bearing two kinds of marks, 
one with clear-cut edges, the others surrounded 
with a halo. The first are wounds, the others 
the true spots belonging to the disease and serv- 
ing as av indication of its existence, if not al- 
ways, at least under many circumstances. The 
halos in question have generally a yellowish 
tint. They must be observed through a mag- 
Fie. 21.—Joint of a Silk-worm niying glass HO be well seen.” ? 
showing wounds and spots These spots disappear with the shedding of 
of pébrine, six times natural 4 ~ 
size (after Pasteur). the skin at each molt only to reappear again 
within a few days. Worms bearing them are figured in plate I, A, B, 
C,and D. In addition to these symptoms it is noticed that the prolegs 
do not seem to attach themselves easily to objects. In the chrysalis 
the abdomen is very much swollen and the rings stretched. In a 
highly-diseased moth the wings are wrinkled as when they emerge 
* Maillot, Lerons, etc., p. 96. + Pasteur, Etudes, ete., p. 15. 
