''58 TRANSACTIONS OF TttE ILLINOIS 



oi the. peculiar micrococci already referred to in the alimentary canal. 

 Invariably, after death, decay was astonishingly rapid, the larvae in a 

 few hours breaking down to a grayish fluid mass. In all these par- 

 ticulars it is clear that the affection of the cabbage worm is the close 

 copy of flacherie of the silk-worm, and fully as rapid and destructive 

 in the former species as in the latter. 



We have now to deal with its roift((f//oi(s character. In my own 

 vicinity it was evidently impossible to make any experiments with the 

 cabbage-worm on this point, because all the worms in the region had 

 been so generally exposed to the contagion, that I could not find 

 healthy larvae for the purpose. I could not keep my specimens alive 

 long enough to kill them. I made, however, a few attempts to settle 

 the question through others. To Prof. Osborne, of the Iowa Agri- 

 cultural College, I sent some diseased worms with the recjuest that 

 he would place them in company with healthy worms on cabbage- 

 heads in the open air, the disease not having yet appeared in his 

 vicinity. 1 also sent him microscope slides of the blood and intes- 

 tinal fluids of sick larvae, that he might be able to recognize the dis- 

 ease if it should appear. A few days after receiving these, he wrote 

 me that the contagion had apparently taken effect, as a single worm 

 was already giving unmistakable evidence of the disease. But. 

 unfortunately, during his absence from home, the cabbages in the 

 field under observation Avere all gathered by the gardener, and the 

 experiment was thus abruptly terminated.* I also sent two boxes of 

 specimens to my friend Dr. Boardman, in Stark County, who had 

 made careful search there in a large number of fields in his vicinity, 

 in October, without finding a trace of the disease. These specimens 

 he received after several days delay, and placed others with them in the 

 boxes, twenty-five healthy larvae in each box, at the same time placing 

 as many others in a clean box, as a check lot. All were fed and 

 cared for alike, but in a few days he wrote me that every one of 

 those placed with the sick worms was dead, while the others had 

 completed their transformations in good condition. The only draw- 

 back to this result was the fact that the disease began to appear 

 spontaneously at about this time in his region, so that there was 

 a bare possibility that it was already latent in the two lots of larvie 

 which perished under experiment, while the others had escaped it. 



For further light on the contagious character of the disea:se, and 

 especially on the possibility of cultivating its virus* artificially, and 

 using it for the purposes of economic entomology, I must go back a 

 few weeks to some studies of the same affection made previously on 

 two other species of caterpillar, — the yellow-necked caterpillar of 

 the apple tree (Datana ministra), — and another species or variety of 



=■= Since the above was written. Prof. Osborne has informed me that he afterwards col- 

 lected as many worms as he could find in the debris of his cabbage field, and exposed them 

 to the remains of the diseased larvae which I had sent him, and that a number of them died 

 of the original disease under conditions such as to render it certain that they derived it by 

 contagiou irom the source mentioned. 



