37 



The Importance of Flea Transmission in Epizootics. 



The following experiments, which had as their object the 

 determination of the relative importance of the Indian rat 

 flea X. cheopis, and of actual close contact in the absence 

 of fleas in the dissemination of plague from animal to 

 animal, were carried out by the Commission (Keports 1906, 

 pp. 450-67, 1907, pp. 421-36, 1910, pp. 315-35) in a series 

 of small cabins, which were built especially for this purpose. 

 In these animal houses plague-infected animals, rats or 

 guinea-pigs, were kept in close contact with healthy animals. 

 They ran about together in a confined space, and ate out of 

 the same dishes. The plague-infected animals were allowed 

 to die, and the corpses were not removed until some time 

 after death. In some instances the concentration of infec- 

 tion was very great, in one case 21 infected animals being 

 at one time in contact with 25 healthy ones. The cabins 

 were never cleaned out, so that the animals ate food con- 

 taminated with the fgeces and urine of their infected com- 

 panions. In the experiments with rats, the healthy 

 frequently ate the carcasses of the infected ones intro- 

 duced. 



Sixty-six series of experiments were carried out, each 

 involving about 40 to 70 animals. In 35 experiments fleas 

 were present and 31 were control experiments in which no 

 fleas were introduced. In all the control experiments not 

 one of the healthy animals contracted plague, whereas in 

 those cases where fleas were present an epizootic occurred, 

 varying in extent and rate of spread according to the number 

 of fleas present. 



Some interesting experiments (Reports 1906, p. 461) were 

 also carried out in the animal houses that had been used for 

 some of the previous experiments. Guinea-pigs and monkeys 

 were introduced into them for one night. Some of the 

 animals were in cages placed on the floor, and others in 

 cages covered by fine muslin gauze, or surrounded by a layer 

 of sticky fly-paper, 6 in. wide that is, the simplest precau- 

 tions were taken to exclude fleas. Of 13 unprotected 

 monkeys six died, of protected none. Of 24 unprotected 

 guinea-pigs 18 died, of protected none. The animal houses 

 remained infective three weeks after the la^t animal had died 

 from plague. This period corresponds with the maximum 

 time fleas fed on a plague rat have been shown to remain 

 infective when placed on a series of healthy animals. 



Experiments in Plague Houses. 



The Commission subsequently (Reports 1906, pp. 467-82, 

 and 1907, pp. 436-46) repeated similar experiments in 

 plague houses in Bombay. The infectivity of 142 houses 



