1870.] BRITISH ASSOCIATION, o3T 



ID to filiiments", At the expense of the fly's substance ; and when they 

 have at last killed! the patient, they grow out of its body and give 

 off spores. Healthy flies shut np with diseased ones catch this 

 mortal disease and perish like the others. A most competent 

 observer, M. Cobn, who studied the development of the Empusa 

 in the fly very carefully, was utterly unable to discover in what 

 manner lhe smallest germs of tha Empusa got into the fly. The 

 spores could not be made to give rise to such germs by cultivation ; 

 nor were such germs discoverable in the air, or in the food of the 

 %■. It looked exceedingly like a case of Abiogenesis, or, at any 

 TViti'b, of Xeuogenesis ; and it is only quite recently that the real 

 ■course of events has been made out. It has been ascertained, that 

 when one of the spores falls upon the body of a fly, it begins to 

 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 fliaments 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 

 contagious and infectious disease called the Muscadine. Audouin 

 transmitted it by inoculation. This disease is entirely due to the 

 development of a fungus, Botrijtls Basuana, in the body of the 

 caterpillar ; and its contagiousness 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 silk worms ; 

 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 tenth of that of 

 the whole world, and represented a money value of 117,000,000 

 francs, or nearly five millions sterling. What may be the sum 

 which would represent the money-value of all the industries 

 connected with the working up of the raw silk thus produced, is 

 more than I can pretend to estimate. Suffice it to say, that the 

 City of Lyons is built upon French silk, as much as Manchester 

 ^vas upon American cotton before the civil war. 

 Vol. T. W . Xo. 3. 



