312 lUinois State Laboratonj of Natiirol History. 



infection, these bacterial forms became less abundant, and the 

 blood was loaded with the products of histolysis, partly, in all 

 probability, of the blood cells and partly of the fatty bodies. 

 There seems to have been in general an inverse relation between 

 the abundance of the bacteria and the abundance of these his- 

 tolysis products, the former becoming less numerous with lapse 

 of time and the latter more so. These facts have an interest- 

 ing application to those observed in the silkworm, as detailed 

 on previous pages, the condition of the later examples of the 

 zebra caterpillar being, in fact, almost precisely similar, so far 

 as microscopic appearances go, to that of silkworms supposed 

 to be suffering from jaundice. 



I have, consequently, to suggest a similar explanation of 

 these phenomena ; viz., that in the case of the latter larva the 

 bacterial affection largely lost its power, but still retained suf- 

 ficient energy to overthrow the physiological balance as the 

 larva3 approached the age of pupation, death resulting from the 

 premature histolysis of certain of the larval structures, — 

 notably the fatty bodies. 



The history of the check lot gives no evidence of serious 

 bacterial infection, but rather of that modified form of it which 

 produces premature pupal histolysis. Reviewing the entire 

 series of slides and cultures, I have no doubt that these indicate 

 the successful preservation through the winter and transference 

 to the bodies of the zebra caterpillars of certain of the forms 

 characteristic of ft ache rk in the walnut caterpillar, Datana 

 angusi. 



THE EUROPEAN CABBAGE WORM. 



(Pieris rapa\ h.) 



A second infection experiment was begun with the same 

 fluids as the foregoing upon fifty cabbage worms, twenty-five 

 of which were selected for treatment, and an equal number 

 isolated as a check. 



On the 6th August, four days after the infection, a larva 

 was found dead upon the bottom of the cage. On punctur- 

 ing the back a clear, greenish fluid exuded, which was swarm- 

 ing with a large and very active Bacillus, occurring usually in 



