94 THE FLEA [CH. 



or of a virulent culture of plague bacillus, were 

 lightly spread over the part. Many successful in- 

 fections were obtained in this way. 



Similar experiments were made in which the 

 plague culture was first spread on the skin, and, 

 afterwards, healthy fleas were allowed to feed on the 

 same spot. Successful infections were also obtained 

 by this means. 



Two facts then seem to be demonstrated beyond 

 doubt : first, that the puncture made by a flea will 

 allow the bacillus to gain access to an animal's body 

 and to infect it ; secondly, that there is a possibility 

 of infection by the fseces of fleas. 



As to whether this is the usual process the highest 

 authorities are not ready to express any opinion. 

 The safest course appears to be to kill fleas but to 

 avoid rubbing them in. 



Good work was done during the recent outbreak 

 of plague in San Francisco when the energies of an 

 army of men were directed to controlling and de- 

 stroying the rat population. Enormous numbers of 

 rats were killed, their breeding places were destroyed 

 and everything was made as uncomfortable for them 

 as possible. Men of science were at the same time 

 engaged in collecting and examining the fleas from 

 many thousands of rats. The great success of the 

 work confirmed the soundness of the theory on which 

 it was based. The spread of the most terrible of 



