96 THE FLEA [OH. 



fleas put in could be recovered, and no fleas were ever 

 found alive after the fifth day. 



The European rat-flea (Ceratophyllus fasciatus) 

 seems to be quite as readily able to transmit plague 

 as the oriental insect. How far other fleas are able 

 to transfer infection we have little or no knowledge. 

 But twenty-seven experiments to transmit plague 

 from animal to animal by means of cat-fleas (Cteno- 

 cephalm felis) were once made and none of these were 

 successful. The reason for the failure we do not 

 know. 



If infected fleas are kept in captivity after they 

 have fed on septicaemic blood, it is found that, after 

 a while, they are no longer able to convey infection. 

 On being dissected no bacilli are found in them. 

 A clearing process, therefore, evidently goes on. If 

 a number of fleas be fed on a septicsemic rat and, 

 subsequently, be kept under observation and nourished 

 on healthy animals, the proportion found to be in- 

 fected steadily diminishes day by day. It is remark- 

 able that the existence of numerous plague bacilli in 

 the stomach of a flea does not seem materially to 

 affect the insect's life. Fleas, in other words, do not 

 suffer from plague though they can transmit it. 



