154 



REVIEWS. 



Empusa Musc^, and the disease of the Common House-fly. 

 A contribution towards the knowledge of Epidemics cha- 

 racterised by the presence of parasitic Fungi. By Dr. F. 

 CoHN. Breslau, 1855 (pp. 59, with three plates). 



The subject of this paper is the well-known, curious 

 disease which prevails among common house-flies, at the 

 period when the departing warmth of autumn induces them 

 to seek shelter within doors. 



At this time innumerable dead bodies of flies may be seen 

 adhering to the windows, walls, shutters, &c., in all parts of 

 the room. The dead insect, though dry and so friable as to 

 crumble into dust upon the slightest touch, retains so far the 

 attitude of life that it is difficult, without touching, to believe 

 that it is not a li\dng fly on the point of taking flight. 

 Insects in dying usually draw up the legs and cross them 

 beneath the body, but in the case of the disease now under 

 consideration the dead body is supported upon the out- 

 stretched legs, whose feet retain their adhesive property, and 

 by the protruded proboscis, a\ ith which the fly would seem to 

 be sucking, and by which, even when the feet may happen to 

 be detached, the body is still retained in situ. The dead flies 

 in this condition are always surrounded with a halo, about an 

 inch in diameter, composed of a whitish dust, which, upon 

 examination, is found to consist of the spores of a fungus. 

 The abdomen is much distended, and the rings composing it 

 are separated from each other, the intervals being occvipied 

 by white prominent zones, constituted of a fungoid growth 

 proceeding from the interior of the body. Further ex- 

 amination will show that the whole of the contents of the 

 body of the fly have been consumed by the parasitic growth, 

 and that nothing remains but an empty shell lined with a 

 thin, felt-like layer, composed ofthe interlaced my celia of the 

 innumerable fungi. 



This disease appears to have been long noticed, though, of 

 course, in the absence of sufficient microscopic assistance, its 

 true nature was not at first known. 



First noticed, as it would seem, by De Geer in 1782, it did 

 not escape the acute eye of the illustrious Goethe, who gives 

 an accurate description of the phenomena attending it, and 

 especially of the appearance of the white dust between the 

 rings of the body, and its dispersion in a wide area around 

 the dead insect. Accurate microscopic observations upon it 



