CHOLERA, PLAGUE, TYPHOID FEVER 123 



five healthy guinea-pigs were put in : plague at 

 once broke out among them, and all died. Fleas 

 were present in great numbers throughout this 

 experiment. These fleas were transferred to a 

 room where fifty guinea-pigs had been living for 

 three weeks. Plague broke out among them, and 

 all died. 



4. Animals in cages hung above a flea's jump 

 from the floor invariably escaped plague : animals 

 in cages hung lower did not. 



5. Guinea-pigs were let run free in rooms from 

 which plague-cases had been removed to Hospital. 

 Next day, the fleas were chloroformed off the 

 guinea-pigs, and counted. It was found that nearly 

 all of them were rat-fleas, in large numbers. Many 

 of the guinea-pigs developed plague. 



6. Animals were hung in cages, in plague-infected 

 rooms ; some of the cages were made to exclude 

 fleas, some were made to admit them. None of 

 the cages touched the floor, or could be reached by 

 rats. In 122 such experiments, none of the animals 

 in the flea-proof cages got plague, but 17 in the 

 other cages did. Of 401 counted fleas, the majority 

 were rat-fleas. Of 132 dissected rat-fleas, 26 had 

 plague-germs in their stomachs. 



7. In 1907, houses under observation in Bombay 

 were divided into A, those known to be plague- 

 infected : B, those presumably plague-infected : 



