Contagious Diseases of Insects. 269 



attacking the cabbage worm has made its appearance in Cuba 

 at last. On the 21st I found one full-grown worm sick (head 

 downward), and in about five hours it was dead and decom- 

 posed, and several others were affected. To-day it is a difficult 

 matter to find a sound worm on the plants, while the remains 

 of dead worms are numerous." 



From Prof. G. H.French, at Carbondale, and Mr. Frank 

 Earle, at Cobden, I learned that the disease had not appeared in 

 Southern Illinois as late as October 29, nor did it occur there 

 during the season. From Champaign, east o me, Prof. Burrill 

 wrote me, October 25, that he had not yet seen any of it in his 

 small garden patch of cabbages, although watching carefully 

 for it; but that an intelligent student had described it as oc- 

 curring in fields near the town. 



In Iowa, to the westward, it seems not to have occurred 

 spontaneously that year, the only appearance of it noted by 

 Prof. Osborn, of the Agricultural College of that State, being 

 the result of an experiment, the material for which I furnished 

 him from Normal. Wherever it once occurred it continued to 

 prevail throughout the season, as far as our observations went. 



The facts clearly and positively negatived the supposition 

 that there was anything in the weather or local conditions to 

 explain either the presence or the absence of the disease, and 

 all bore out the hypothesis of a gradual progress from the east 

 westward. The same phenomena of irregular local distribution 

 were manifest the next year (1884). In certain large fields 

 almost daily observed, it was impossible to find a single diseased 

 larva at a time when, half a mile away, the cabbage worms of 

 small patches had been almost wholly destroyed, their black- 

 ened bodies, or the shriveled remnants of the same, being scat- 

 tered everywhere on the leaves. 



I may say, incidentally, that the effect of the epidemic in lim- 

 iting the ravages of the worms, was very evident last year. For 

 the first time in several seasons large fields of late cabbage were 

 brought to full maturity without the loss or serious damage of 

 a head. 



From the foregoing the conclusion is unavoidable that all 

 the circumstances of the natural occurrence and spread of the 

 disease are consistent with the hypothesis of its contagious 

 character, and wholly inconsistent with any other. 



