vn] FLEAS AND PLAGUE 89 



any scientific journal. But his ingenious and careful 

 experiments showed that fleas could transmit plague 

 from animal to animal. He found that the commonest 

 flea captured off rats at Cronstadt was Leptopsylla 

 musculi, the usual host of which in other places is the 

 mouse. Now this flea does not, except very rarely, 

 bite human beings, and the real significance of the 

 facts discovered was not appreciated. 



The common rat-flea in most parts of Europe is 

 Ceratophyllus fasciatus and in India and sub-tropical 

 countries Xenopsylla cheopis. This last species has 

 acquired the title of "the plague flea/' or, more 

 accurately, the oriental rat-flea. 



During the plague investigations in India many 

 careful experiments have been made proving beyond 

 doubt that the disease may be transferred from rat to 

 rat by the transference of fleas from a septicsemic to 

 a healthy animal. It was first shown that when fleas 

 were present the plague could be transferred from 

 rat to rat, kept in proximity, but carefully screened 

 so as to avoid any possibility of contact. Next, fleas 

 were collected from rats dead or dying of septicsemic 

 plague and transferred to healthy rats living in flea- 

 proof cages. More than half of the healthy rats 

 contracted plague. It was shown that if fleas are 

 present, the disease once started spreads from animal 

 to animal ; and it would seem that the rate of progress 

 was in direct proportion to the number of fleas present. 



