264 BIOGENESIS AND ABIOGENESIS vm 



germinate, and sends out a process which bores 

 its way through the fly's skin ; this, having 

 reached the interior cavities of its body, gives 

 off the minute floating corpuscles which are the 

 earliest stage of the Empusa. The disease is 

 " contagious," because a healthy fly coming in 

 contact with a diseased one, from which the 

 spore-bearing filaments protrude, is pretty sure 

 to carry off a spore or two. It is " infectious " 

 because the spores become scattered about all 

 sorts of matter in the neighbourhood of the slain 

 flies. 



The silkworm has long been known to be 

 subject to a very fatal and infectious disease 

 called the Muscardine. Audouin transmitted it 

 by inoculation. This disease is entirely due to 

 the development of a fungus, Botrytis Bassiana, 

 in the body of the caterpillar ; and its contagious- 

 ness and infectiousness are accounted for in the 

 same way as those of the fly-disease. But, of 

 late years, a still more serious epizootic has 

 appeared among the silkworms; and I may 

 mention a few facts which will give you some 

 conception of the gravity of the injury which it 

 has inflicted on France alone. 



The production of silk has been for centuries 

 an important branch of industry in Southern 

 France, and in the year 1853 it had attained 

 such a magnitude that the annual produce of the 

 French sericulture was estimated to amount to a 



