86 



plague rats, and that the faeces of such fleas contained the 

 B.pestis for about the same time. He succeeded in infecting 

 rats with fleas from diseased rats 15 times in 76 experi- 

 ments. In each experiment 10 possibly infected fleas were 

 allowed to feed on the rat. Verjbitski also made experiments 

 similar to those of Gauthier and Eaybaud described above, 

 and out of 40 experiments, using 10 fleas apiece, infection 

 was conveyed in 4. 



Listen (1905) pointed out that the common flea infesting 

 rats in India was not Ceratophyllus fasciatus or Typhlopsylla 

 musculi, as in Europe, but a non-pectinated flea identified by 

 Eothschild as X. cheopis. Listen observed multiplication of 

 the plague bacillus in the stomach of this flea. Although his 

 experiments on transmission, which were made by allowing 

 fleas to bite first an animal suffering from plague and subse- 

 quently a healthy animal, were not successful, he brought 

 forward much interesting and valuable circumstantial evidence 

 in favour of the view that plague is epidemiologically thus 

 spread. He showed that X. cheopis takes readily to another 

 host e,g. , guinea-pigs and man when rats are not 

 available. 



The possibility of the rat flea carrying plague from one rat 

 to another was demonstrated in a considerable series of 

 experiments by the Commission for the Investigation of 

 Plague in India (Reports, 1906, pp. 435-50). A glass case 

 was used containing two wire cages side by side, each 

 standing in a tin tray which collected the urine. Both trays 

 were filled with sand, in order to provide dryness and 

 shelter for the fleas. Each cage was furnished with a lid 

 through which the rats were introduced, and food and water 

 given to them, and the whole apparatus was covered in with 

 fine muslin to prevent the escape of the fleas. A rat placed 

 in one of these wire cages could not come in contact with a 

 rat in the other cage, nor with its urine or fasces. 



The method of experiment is as follows. A plague- 

 infected rat and a number of rat fleas were placed in one of 

 the wire cages. After the rat died a fresh healthy rat was 

 put into the other cage, the corpse of the infected rat being 

 left in for 24 hours longer. Sixty-six experiments with 

 English white rats and with Bombay wild rats were done in 

 this way, with the result that 30 healthy rats contracted 

 plague ; fleas formed the only apparent means of trans- 

 mission of the bacilli from rat to rat. 



In order to exclude aerial infection a second series of 

 experiments was carried out, in which fleas were taken from 

 a rat which had died from plague and placed on a fresh rat 

 in a clean flea-proof cage of similar construction to that 

 already described, but containing only one wire cage. Out of 

 38 experiments 21 successful transmissions were obtained in. 

 this way. 



