VIII. I!, (i Schobl: Plague in Manila in 1912 421 



Only a theoretical explanation can be given of the short dura- 

 tion and sudden cessation of the outbreak. One can assume 

 with great probability that the first partial disinfection drove 

 the fleas away from the primary source of infection, and that 

 they traveled as far as possible. They finally settled in those 

 guinea-pig cages which had not been molested by the first 

 disinfection. Having no new supply of plague blood (all of 

 the plague-infected guinea pigs having been removed, most 

 of them before death), the fleas soon cleared themselves of 

 plague bacilli. The peculiar feature of the outbreak; namely 

 the failure to find fleas on the animals in rooms II and V, finds 

 its explanation in the observation of the Indian Commission 

 who found that the fleas "died or disappeared very rapidly." 



The following conclusions can be drawn from these observa- 

 tions: 



1. The common rat flea {Loemopsylla cheopis) prefers the rat 

 to the guinea pig. 



2. In the absence of rats it will attack guinea pigs rather 

 than rabbits. 



3. The fleas which have sucked blood from rats or guinea pigs 

 afflicted with plague septicaemia were found to harbor virulent 

 plague bacilli inside of their bodies. 



4. The transmission of plague infection by direct or indirect 

 contact being excluded in our case, the fact that fleas of the 

 same species and harboring plague bacilli were found on the 

 rat and on the guinea pigs, the presence of flea bites on the rats 

 and on the guinea pigs with positive findings of skin lesions on 

 that part of the body where the fleas and flea bites were located, 

 together with the anatomical picture of the findings in the guinea 

 pigs, lead to but one explanation ; namely, that the plague in- 

 fection was transmitted by fleas. 



OBSERVATIONS ON ANIMALS SUSPECTED OF PLAGUE 



Out of the several tens of thousands of rodents examined 

 during the antirat campaign, we have found only two plague 

 rats which showed the typical picture of natural plague infec- 

 tion in rat; that is, cervical buboes with surrounding oedema, 

 subcutaneous injection, pleural effusion, enlarged spleen, and 

 such changes of the liver as are characteristic of natural plague 

 infection in rats. Microscopically, large numbers of plague 

 bacilli were found in these cases, and pure cultures of Bacillus 

 pestis were recovered from the spleen. Histological examina- 

 tion of internal organs, particularly that of the liver, confirmed 

 the bacteriological findings. The remainder of the plague rats 



