Contagious Diseases of Insects. 267 



of its spread, and especially to the results of experiments for 

 conveying it artificially to localities or regions where it had not 

 before appeared. 



That this affection, or one very similar to it, attacks the 

 cabbage worms of the old world, is made likely by a chance 

 remark in Curtis's "Farm Insects" (p. 96), where he says of 

 several larvae of an allied species, Pieris brassicw: U 0n the 

 20th they appeared healthy, but inclining rather to a yellow 

 color; it rained during the night, and on looking at them in the 

 afternoon of the following day, I saw they had removed to a 

 leaf, to which they stuck by four of their hinder legs, and, to 

 my surprise, they were of a dirty color, and rotten, the skins 

 being lax, and lying just as the wind blew them about. I found 

 they only contained some cream-colored fluid, a portion of 

 which was scattered upon the leaves." 



In this country the disease seems to have been first noticed 

 in the vicinity of Washington, in 1879, although little atten- 

 tion was paid to it, and its bacterial character was not then 

 ascertained. In Bulletin 3, of the United States Entomological 

 Commission, (pp. 69, 70), Dr. Riley remarks, while discussing 

 some experiments made with yeast on the cabbage worm: 



"An incident connected with these experiments which I 

 made is, however, well worthy of being mentioned, because it 

 shows how very easily single experiments may lead to false 

 hopes and conclusions. A certain proportion of the last-named 

 larvae the proportions differing in the different lots treated 

 perished before or while transforming to the chrysalis state. 

 They became flaccid and discolored, and after death were little 

 more more than a bag of black putrescent liquid. I should 

 have at once concluded that the yeast remedy was a success, 

 had I not experienced the very same kind of mortality in pre- 

 vious rearing of this larvae, and had I not, upon returning to 

 the field from which the larvae in question were obtained, found 

 a large proportion similarly dying there." 



No other notices of it have occurred in my reading, pre- 

 vious to those of its appearance in Illinois, already mentioned 

 (October 5, 1883). That it did not occur at Normal in 1882 

 is made certain by the fact that the cabbage fields there were 

 frequently visited in autumn by myself and my assistants dur- 



