238 THE CANADIAN ENTOMOLOGIST. 



fed, they are found to be rapidly infected and capable of communicating 

 this pestilential disease to others with which they are associated. The 

 bacteria may be preserved in a torpid condition without loss of effective- 

 ness for at least a year, probably for several years, and that without any 

 particular care, and when required for use can be rapidly propagated in a 

 suitable fluid. 



In my address to you last year I referred to a similar form of disease 

 which had occurred among cut-worms so abundant in clover fields in the 

 Ottawa district, and in 1878 and 1879 ^^ ^ similar trouble among the 

 forest tent caterpillars at that time so abundant. Now I am glad to be 

 able to report a similar disease among the cabbage worms, and to indicate 

 to you some practical results arising from investigations regarding its na- 

 ture and mode of operation. 



Throughout most of the State of Illinois and in some parts of Michigan, 

 it was observed last autumn that a large proportion of the cabbage worms 

 sickened and died. Hundreds of their bodies were to be seen rotting on 

 the cabbage leaves or shrunken and dried to a blackened fragment. This 

 was soon brought under the notice of the State Entomologist of Illinois, 

 Prof S. A. Forbes, a most careful and indefatigable observer, who at once 

 proceeded to investigate the cause of this caterpillar plague. He found 

 the disease at first to be very unevenly distributed, some isolated fields 

 showing no trace of it, while others not far distant were fairly reeking with 

 death and decay, but as the season advanced it spread in every direction 

 until in some districts almost every worm perished. He says, "We can 

 conceive something of the significance of this disease if we imagine the 

 terror and dread which would seize mankind if such a plague should sud 

 denly assail human life. Whole towns would be depopulated and the dead 

 would rot in the streets by hundreds. There would be no escape for any, 

 because the contagion would be conveyed by the very food and drink by 

 which life was sustained." 



By dissecting specimens of the dead caterpillars, the microscope showed 

 their intestines to be full of undigested food and swarming with a 

 species of micrococcus, which appeared in the form of excessively minute , 

 spheres about one twenty-five thousandth of an inch in diameter, some- 

 times single, sometimes in pairs, and occasionally in strings of from four to 

 eight. He found that these minute organisms could be readily cultivated 

 in beef broth, and that a single drop of fluid from a diseased worm intro- 

 duced into a vessel of such broth, would in two or three days render the 



