SUSCEPTIBILITY OF COCKROACHES TO PLAGUE BACILLI. 523 



preparations. Culturally its characteristics resemble those of the 

 Bacillus enteriditis group. It has occasionally appeared in mam- 

 mals inoculated with plague in this laboratory, and may persist 

 with plague through several animal passages. It is pathogenic 

 for cockroaches ; for in one series of 12, inoculated with material 

 from the lung of a monkey containing this organism probably 

 mixed with plague, all 12 died in one day. Material from one 

 of these insects carried to a new series gave a small proportion 

 of fatal infections in very small doses, and a larger proportion 

 with massive doses. A series of 5 inoculated with a pure culture 

 of this organism isolated from a cockroach gave 3 fatal infections. 



In the disappearance of plague from noninfected insects, pha- 

 gocytosis must play some part. In one insect of another series, 

 body fluid both from the leg inoculated and from a leg on the 

 opposite side of the body was removed two hours after inocula- 

 tion. Plague bacilli were found in both samples in phagocytes 

 (in one phagocyte 18 bacilli) and outside of them. 



In the series of the 26th mentioned above, the plague culture 

 was of highly virulent strain, but was the third remove from an 

 infected guinea pig and had been kept some days at refrigerator 

 temperature after the first transfer from the pig- In another 

 series, 5 large cockroaches were inoculated with material from 

 the second transfer on agar from an infected guinea pig. Two 

 days after inoculation 2 were found dead with numerous, ap- 

 parently plague, bacilli in the body fluid. Material taken from 

 the leg of one of the survivors showed no bacteria microscopically 

 or culturally. All of the 3 survivors were alive and apparently 

 well after eleven days, and 2 of them after eighteen days. 



Bacilli taken from one of the infected insects of this series 

 were grown in serum broth and this culture inoculated into 4 

 cockroaches. Of these four, 1 was sacrificed after two days, 

 but showed no infection. Of the three, 2 were alive and well 

 fourteen days after inoculation and 1 twenty-six days. 



In another series, 7 were inoculated with an emulsion of the 

 spleen of an infected guinea pig. One died in two days with 

 apparently a pure culture of plague in the body fluid. Of the 

 remaining six, 4 were alive after fourteen days, and 2 after 

 twenty-seven days. 



In all, 61 cockroaches were inoculated with virulent plague. 

 Of this number, only 9 showed at necropsy a pure culture of bacilli 

 morphologically resembling plague. Four of these cultures were 

 inoculated into guinea pigs and only one brought about a plague 

 infection. So of the entire 61, only 6 at most could have died 



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