3l4 Illinois State Laboratory of N'attirat History. 



in the breeding cages could not be accounted for, several 

 having, apparently, been allowed to escape as the food was 

 changed. This partial experiment can, consequently, only be 

 held to verify the conclusion drawn from the one just previously 

 described, to the effect that the Bacillus used for infection may 

 be at least temporarily propagated in healthy larvae with 

 destructive effect. It is proper to add that in the remnants 

 of both the infected and check lots, the common fiacherie of 

 the cabbage worm afterwards broke out, showing that these 

 insects had been exposed to this disease before they were brought 

 to the office for the experiment. 



MuSCji-RDINE. 



This disease, long well known in the silkworm, is not a 

 bacterial affection, but is due to an invasion of the body of the 

 insect by the filaments of a "thread fungus" (Hyphomycetes), 

 whose spores germinate on the surface. These send thread- 

 like processes through the skin which at first bud off from their 

 free ends, within the body, short cells (sometimes called 

 "conidia") with which the blood of the diseased insect speedily 

 becomes loaded. These multiply by division, and finally result 

 in a thread-mycelium which makes its appearance on the 

 surface of the insect, and bears vast numbers of spores, white 

 or green, with which the body becomes covered as with a fine 

 dust. An affected larva is commonly flaccid and shrunken at 

 death, but finally, as a consequence of the post mortem develop- 

 ment of the fungus, becomes filled with threads and spores, and 

 distended to its original size, drying without shrinkage into a 

 hard and brittle mummy. 



These later stages of the development of the fungus are 

 greatly affected by the weather, a drouth preventing the con- 

 spicuous external appearance of the mycelium and the develop- 

 ment of spores, and thus limiting the spread of the disease. 



Every experienced collector finds occasional examples of 

 this disease in the field in the form of stiff and mummified 

 insects, often covered with a dense white or greenish bloom; 

 but few observations of any wholesale destruction of a super- 

 abundant species by it have been recorded, — none for America 



