Contagious Diseases of Insects. 377 



THE SILKWORM (Bomhyx man, L.) 



Late in July, 1884, I heard from Professor Burrill, of the 

 State Industrial University, that a lot of silkworms which 

 were being reared under his direction for experimental purposes 

 were dying rapidly from an apparently contagious disease 

 resembling the flacherie of the old world, and wishing to im- 

 prove the opportunity thus afforded to determine the possibility 

 of conveying this affection to our native Lepidoptera, I had, 

 July 30, some of the dead and dying larvae sent me by mail 

 from Champaign. From our correspondence at the time and 

 from an account of the experiment by Prof. Burrill, published 

 in the Twelfth Report of the Board of Trustees of the Illinois 

 Industrial University, 1884, we learn that the lot of worms 

 (about 80,000 in number) in which this disease broke forth 

 were Raised from eggs derived from a perfectly healthy brood 

 of the preceding year ; that they commenced to hatch June 21 ; 

 that they were kept in a clean and thoroughly ventilated build- 

 ing set aside for their use on the University grounds ; that they 

 began to spin July 25 ; that between this date and the 29th 

 183 cocoons were produced, but that in consequence of the out- 

 break of this disease among them only a single additional 

 cocoon was made during the season. The entire remainder of 

 the 80,000 worms perished, — commencing to die July 23, and 

 continuing until the latter part of August. 



Desceiption of the Disease. 



In a note of July 23, Prof. Burrill says of the affected 

 larvae that they " become yellow, shorten up; the skins become 

 very tender so that they can hardly be picked up without burst- 

 ing; body flaccid; the blood loses its clearness and becomes 

 thick with a dirty yellowish color.'' Again, July 26, he writes: 

 " They first refuse food and uneasily creep around, then become 

 yellowish and flabby." 



In the article above cited. Prof. Burrill distinguishes two 

 forms of disease among the larvge, as follows: 



" In one case the affected larvae became restless, ceased 

 eating, the skin assumed a decidedly yellowish tint and ulti- 



