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On Empusa Musce. 



By T. Charters White, M.R.C.S., &c. 



{Read October 27th, 1676.) 



About this time of the year the observer may notice flies, appar- 

 ently alive, attached to the walls, doors, or window-panes, and upon 

 attempting to capture them he will be astonished at the carelessness 

 as to the result displayed by the intended victim, but his astonish- 

 ment is not the less great when, upon examination, he finds the fly 

 dead and dry, with every abdominal ring distended, and stretched 

 apart, from its neighbour, yet simulating in its dead body every atti- 

 tude of its living state. Such a fly is the subject of an interesting 

 disease, which I have endeavoured to illustrate this evening by a 

 slide under my microscope. My bibliographical knowledge is not 

 extensive, but a careful search through several volumes of the Micro- 

 scopical Journals has served to show me that this subject has not 

 been brought under the notice of microscopists since the year 1857, 

 when it was noticed in a review of a paper by Cohn, in the fifth 

 volume of the " Quarterly Journal of Microscopical Science." As 20 

 years have elapsed since the publication of that review, I may be 

 permitted, for the benefit of our younger members, to call their atten- 

 tion to one or two facts in reference to this diseased condition of the 

 House Fly, that may afford some interest to them, should they feel 

 disposed to carry on observations for themselves. 



It appears that the disease was first observed by De Geer, in 

 1782, and was also noticed by the acute naturalist and poet, Goethe ; 

 and accurate observations were made on it in 1827, by Nees von 

 Essenbach ; but in 1835, from the careful investigations of M. 

 Dumeril, he was enabled to pronounce it a true fungus, allied to the 

 " muscardine" infesting the silkworm. In 1841 Mr Berkeley 

 determined the mould to be Sjporendonema nmscoe, but Cohn named 

 it Empusa muscce. 



The characteristic appearance of a fly affected with this disease is 

 best detected when the fly, in its last moments, settles on a window; it 



