284 Illinois State Laboratory of Natural History. 



CONTAGIOUS CHARACTER OF THE DISEASES. 



I had no opportunity to observe the progress of these 

 diseases in the silkworm, but Professor Burrill was entirely 

 confident of their contagious character as exhibited under 

 his observation. On this point he says* : "That the worms 

 came from good eggs, and were, for a considerable time, per- 

 fectly healthy and wholly free from the malady which finally 

 overtook them, we have the best of evidence. The disease 

 which carried them off was not hereditary. It was not lurking 

 unobserved during the more favorable weather in the living or 

 dying worms. Its introduction occurred about, and probably 

 at, the time of the first heavy rains spoken of, but we con- 

 fidently know -that it, could have been artificially introduced 

 without the rains or the wet weather at all. Moreover, the 

 worms continued to die after the weather cleared up, and after 

 every precaution had been taken to put them under the best 

 possible conditions. We constructed new racks in a room not 

 previously used, picked out the healthiest worms and moved 

 them to the new and clean quarters, where, afterward, the tem- 

 perature and other conditions were as favorable as could be 

 desired ; but the ravages of the disease continued with no 

 perceptible abatement. To further test the matter, other 

 apparently healthy worms, voracious feeders, growing rapidly, 

 were put out upon the open hedge, where they were watched 

 from daylight until dark to keep off the birds, and where, for 

 a time, they seemed to thrive under the favorable skies and 

 wide isolation ; but here, too, they gradually fell victims to the 

 destroyer. In each of these places about five hundred worms 

 were placed, from which, as was before said, one cocoon only 

 was secured, and this from the out-of-door lot. The latter did 

 live longer than any of the others, but at length as surely suc- 

 cumbed. Another experiment proved equally futile ; viz. that 

 of spraying the food with an aqueous solution of carbolic acid. 

 No apparent improvement followed this treatment. 



It maybe said that our disaster followed in consequence of 

 retarding too long the hatching of the eggs by keeping them in 



* Twelfth Rep. of the Board of Trustees of the Illinois Industrial 

 University, pp. 90, 91. 



