Contagious Diseases of Insects. 311 



them were 1 /^ in average diameter, slightly oval to the eye, 

 though not measurably so. 



On the morning of the 12th two other larva? were dead. 

 The blood of one contained only immense numbers of mulberry 

 granules with a moderate number of possible spherical micro- 

 cocci, — not positively distinguishable in our slides, however, 

 from the smallest mulberry granules. The blood of the other 

 larva was in a similar condition, heavily loaded with mulberry 

 cells and the results of their disintegration, but contained, like- 

 wise, a small number of various bacteria, — rarely a short, broad 

 Bacillus, apparently identical with that first used in the experi- 

 ment ; more abundantly a small spherical Micrococcus, difEering 

 in appearance from the usual form ; also a double oval Micro- 

 coccus, and an occasional patch of the true spherical so abund- 

 ant in these experiments. These last were sometimes associated 

 on the slides with patches of unsegmented cells, which evidently 

 had their origin in the fatty bodies. 



The third larva dead this day was soft, shrunken, and 

 nearly dry. The scanty fluids were full of micrococci and thick 

 with mulberry cells and granules. The effect of carbolized 

 w%ater upon the cells was, in this case, to cause separation into 

 their constituent particles. 



The results of all the above observations and experiments 

 upon the zebra caterpillar may be summarized as follows : At 

 least one of the bacillar forms occurring in the culture used 

 in this infection was conveyed to the larvas under experiment 

 with fatal effect, and probably multiplied there successfully. 

 This Bacillus almost wholly disaapeared, however, in the later 

 stages of the experiment, and so is not certainly a true patho- 

 genic form. Associated with this in the fluids of the larvae 

 treated were the usual spherical micrococci of this disease, 

 clearly identical with those applied to the food, and certainly 

 multiplying freely in the bodies of the larvae. These presented, 

 consequently, the characteristics of a pathogenic microbe. 

 A curious change was observed in the phenomena of the disease 

 in the experimental lot. Death seemed at first occasioned by 

 the immediate action of the bacteria ingested or cultivated in 

 the blood and alimentary fluids ; but at a later period after the 



