156 COHN, ON EMPUSA MUSC.E. 



1. In tlie autumn the common house-fly is subject to a 

 fatal disease, which occurs epidemically, and disappears in 

 the course of the following winter. 



2. This disease is characterised by the development of a 

 microscopic fungus — Emjmsa muscce — in the interior of the 

 body of the fly ; the death of the insect is caused by the 

 vegetation of this parasitic growth. 



3. The disease is manifested externally, at first by a de- 

 gree of slowness in the motions of the flies ; at this stage, 

 the fluid (blood) which occupies the interspaces between the 

 viscera increases greatly in amount, and is found to contain 

 innumerable fat-drops, which give it a milky appearance. 



4. Innumerable very minute free cells make their appear- 

 ance in the blood, having a very delicate, at first indistin- 

 guishable membrane, and granular contents. 



5. These cells rapidly attain to a very considerable size, 

 and when uniformly noui'ished retain their original spherical 

 or ovoid form ; but usually, owing to the unequal supply of 

 nutriment, probably referable to the circulation of the blood, 

 they assume the form of longer or shorter tubes. 



6. The globular or tubular forms exhibit towards water 

 and other reagents, precisely the same reaction as do cells 

 originating in free cell-development. When placed in 

 water they swell out considerably, and even the most elon- 

 gated tubes soon acquire a globular figure, their contents at 

 the same time coagulating and exhibiting large oil-drops ; 

 the membrane, in the younger stages, is dissolved altogether 

 in the water ; older cells merely burst at one end, through 

 which the contents escape. 



7. A few hours before death the fly ceases to exhibit any 

 spontaneous movement ; the abdomen becomes much dis- 

 tended by the increased quantity of blood-fluid, and in con- 

 sequence of the innumerable, free, occasionally very large 

 fungus- cells floating in it. 



8. At this time all the ftmgus-cells have regained the 

 ovoid form, probably owing to the uniform nutrition Avhich 

 they receive when the circulation of the blood ceases; at 

 one, more rarely at two points of these cells, ciecal processes 

 are formed, which elongate in a root-like manner, interlace 

 with each other, and throw out branches. Many thousands 

 of them in this condition surround the viscera without pene- 

 trating into their substance ; nevertheless, it is soon appa- 

 rent that the parasitic fungi are nourished at the expense 

 of the tissues. 



9. After death, the body of the fly exhibits peculiar con- 

 tortions and extensions of the legs, wings and abdomen ; 



