128 



ANIMAL PARASITES AND MESSMATES. 



Fleas differ much in size, according to the places 

 which they inhabit. Duges, of Montpellier, gives us a 

 curious instance of this. He devoted himself to re- 

 searches on the zoological characters of this genus, 

 studying the four species which are the best known, the 

 Pulex irritans of man, Pulex canis of the dog, Pulex 

 musculus of the mouse, and Pulex vespertilionis of the bat. 



Fleas of a brown colour, almost black, and of 

 enormous size, are commonly met with on the sandy 

 shores of the Mediterranean, at least, in the neighbour- 

 hood of Cette and Montpellier ; they are more than half 

 as large as a common fly. These are human fleas, and 

 their presence on the sea- shore during the heats of 

 summer is due solely to the great number of bathers of 

 both sexes and of all classes, which lay their clothes 

 down there. If at some future day these insects were to 

 be placed in the rank of surgical species, it would be 



20. — Human Flea (Pulex irritans), after Blanchard. 



necessary to resort to those shores in order to procure 

 them ; and we might suppose that, by judicious crossing, 

 we might soon produce races that would be of real 

 service ; as yet, however, the therapeutic art has had 



