644 MICROBIAL DISEASES OF INSECTS 



Causal Organism. — B. cajtB is a sKghtly oval bacillus, about i-Sn'ia length; 

 motile; Gram negative; stains deeply with crystal violet; treated by Pappenheim's 

 method it shows a characteristic bi-polar stain. 



Broth cultures develop in twelve hours at i5°-3S° with an optimum of 25°; from 

 these the odor of H2S is perceptible; in twenty-four hours broth cultures have agreen 

 fluorescence which is more marked at 25° than at 15° or at 35°- Grows rapidly on both 

 gelatin and agar showing a green fluorescence, the former is liquefied. Growth on 

 potato is meager, showing only after forty-eight hours and producing no pigment.. 



Methods of Infection. — ^Artificial. — Caterpillars of Arctia caja 

 inoculated in one of their feet by means of a fine needle dipped in viru- 

 lent blood or in a broth culture, die regularly in three days at 15°, 

 manifesting in their blood swarms of the specific bacteria. If kept at 

 25° they die in twelve to twenty-four hours. The blood of the cater- 

 pillars kept at the latter temperature appears to be the more virulent. 



Caterpillars receiving several drops of culture by means of a pip- 

 ette introduced into the pharynx, die in twelve hours at 25° with their 

 blood invaded by the bacteria. This suggests a possible practical 

 application. 



Susceptible Insects and Other Animals. — Caterpillars of Por- 

 thesia chrysorrhea are very sensitive to B. caja and die on inoculation 

 in twenty-four to forty-eight hours. 



The following Coleoptera: Hydrophilus pistaceus, Dyticus pisanus, 

 Cybister laterimarginaUs, Colymbeies fuscus are not killed by inocula* 

 tion; nor are the following Hemiptera: Notonecta glauca, Nipa cinerea, 

 Ranatra linearis. 



The white rat is not sensitive to intraperitoneal injection of i c.c. of 

 a twenty-four-hour broth culture. The tree frog, Hila arborea, dies 

 by inoculation, with the same culture, into the lymphatic sacs in 

 twenty-four to forty-eight hours with the blood invaded by numerous 

 organisms. The blood of dying caterpillars is more virulent for the 

 tree frog than broth cultures; 0.5 c.c. injected into the lymphatic 

 sacs causes the death of the batrachian in twelve hours vdth. an 

 intense bacillary septicemia. 



B. caja seems to belong to the same group as d'Herelle's B. acridio-, 

 rum. It is distinguished from it however by several characteristics, 

 both biological and pathological, being a parasite of the blood of the 

 caterpillars whereas, according to d'Herelle, the site of affection in the 

 diseased locusts is in the digestive tract. 



