524 BARBER. 



of unmixed plague infection, and in only one of these was the 

 culture identified by guinea-pig infections. 



Of the noninfected insects, at least one-half were living from 

 twelve to twenty-seven days after inoculation. Since all which 

 died of plague, either alone or mixed with some other bacteria, 

 died within two days after inoculation, it seems probable that 

 those surviving six days were not infected- At least 28 survived 

 two weeks or more after inoculation. 



In summary, it has been clearly shown that cockroaches may 

 be infected by large doses of virulent plague bacilli; but from 

 the fact that massive doses failed to infect a large proportion of 

 cases, it may be concluded that these insects, especially Rhyparo- 

 bia maderse, are little susceptible to plague inoculated into the 

 body cavity. 



