BUBONIC PLAGUE 143 



ment as in the first set, and in the third pair the roof was 

 formed of corrugated iron. Under the roof in each case 

 was placed a wire diaphragm, which prevented rats or their 

 droppings having access to the hut, but which would not 

 prevent fleas falhng down on to the floor of the hut. The 

 huts were left a sufficient time to become infected with 

 rats, and then on the floor in each case healthy guinea- 

 pigs artificially infected with plague were allowed to run 

 about together. In the first two sets of huts to which 

 fleas had access the healthy guinea-pigs contracted plague, 

 while in the third set they remained unaffected, though 

 they were freely liable to contamination by contact with 

 the bodies and excreta of the diseased animals. In the 

 third set of huts no infection took place as long as fleas 

 were excluded, but when accidentally these insects obtained 

 admission, then infection of the uninoculated animals 

 commenced. Other experiments were also performed. 

 In one case healthy guinea-pigs were suspended in a cage 

 two inches above a floor on which infected and flea- 

 infested animals were running about. Infection occurred 

 in the cage, but if the latter were suspended at a distance 

 above the floor higher than a flea could jump, then no 

 infection took place. Again, in a hut in which guinea- 

 pigs had died of plague, and which contained infected 

 fleas, two cages were placed, each containing a monkey. 

 One cage was surrounded by a zone of sticky material 

 broader than the jump of a flea. The monkey in this 

 cage remained unaffected, but the other monkey con- 

 tracted plague. (Muir and Ritchie.) 



