50 MICROBES, FERMENTS, AND MOULDS. 
VIII. MuscarpIne, THE DisEAsE oF SILKWORMS. 
Muscardine, which is caused by a true fungus, 
Botrytis bassiana, must not be confounded with other 
diseases which attack the silkworm, such, for instance, 
as pebrin, which, as Pasteur asserts, is caused by a 
bacterium, or, strictly speaking, a microbe, and, accord- 
ing to the recent researches of Balbiani, by Psoro- 
spermia. We shall presently revert to this disease. 
Botrytis bassiana is a true mould, belonging to 
the group of Oomycetes, and allied to the potato- 
fungus, Peronospora. It is propagated by spores, 
which, when falling on a silkworm, germinate and 
penetrate its body. A mycelium is then developed, 
which may take possession of the whole caterpillar 
without appearing externally. The germination is 
rapid in proportion to the age of the silkworm. 
When death has been caused by the develop- 
ment of the mycelium, hyphz appear through the 
animal’s skin; these soon bear white, chalky spores, 
which are readily detached and float in the air in im- 
palpable dust like smoke. The silkworms on which 
the dust falls do not appear to be diseased, and eat 
with avidity, but they die suddenly. It takes from 
70 to 140 hours to develop the spores and spread 
the contagion. It is difficult to free the breeding- 
houses from all the silkworms which die in this 
manner; those which die after having crawled up 
to the heather to prepare for their transformation 
