50 MICROBES, FERMENTS, AND MOULDS. 



VIII. MUSCARDINE, THE DISEASE OF SlLKWOEMS. 



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, hyphae 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 



