522 BARBER. 



Of the 26 inoculated in this manner, 6 were dead the next day. 

 A femur of each of them was washed with alcohol, cut off with 

 hot scissors, and the contents pressed out at the cut surface 

 without allowing them to touch anything not sterile. From 

 these contents, hanging drops, smears, and cultures were made. 

 The hanging drops were examined at once and again after seven 

 to twenty-four hours' growth. Of the 6, two showed apparently 

 a pure culture of plague in hanging drops examined immediately 

 and in the smear, but all cultures showed in addition to plague- 

 like bacilli numerous small, actively motile bacilli. 



On the second day 5 more were dead. Four of these showed 

 apparently a pure culture of plague in hanging drops and smears, 

 and the hanging drops after growth showed apparently typical 

 plague chains. The fifth showed a mixture of plague-like bacilli 

 with the small motile bacilli mentioned above. 



On the third day 2 more were dead. One in culture showed 

 the small motile bacillus, the other Bacillus prodigiosus, both 

 apparently in pure culture. One died on the eighth day with 

 no indications of plague at necropsy, and 2 died on the thirteenth 

 and fourteenth days respectively. Therefore, 12 of the 26 sur- 

 vived twelve days or longer — all of them Rhyparobia maderse — 

 and 10 survived two weeks or longer. 



Agar-cultures were made from the four dying on the second 

 day which showed a pure culture of apparently typical plague, 

 and guinea pigs were inoculated subcutaneously with about one- 

 fifth of a 24-hour agar slant. As a control, a guinea pig was 

 inoculated with a much smaller dose of the original plague culture 

 with which the cockroaches had been inoculated. The control 

 died in nine days with typical lesions of plague ; while of the four 

 others only one showed signs of infection. This one died in 

 four days with lesions in all respects typical of bubonic plague. 



The nonmotile plague-like bacillus which failed to infect the 

 guinea pigs in the three cases has not been identified. It is very 

 improbable that it could be attenuated plague, since very large 

 doses failed to infect guinea pigs, and since cultures on agar and 

 in vaseline-covered broth were not typical of plague. 



Of the entire 26, then, only one died of unmixed plague in- 

 fection. In the case of the 10 others which died on or before 

 the second day, plague may have contributed to their death, 

 but in no case did plague bacilli occur in pure culture at necropsy. 



In all series the commonest contaminating organism found 

 alone or mixed with plague in insects after death was a small 

 actively motile bacillus, very closely resembling plague in stained 



