64 THE FLEA [CH. 



ledge of the present and former distribution of this 

 species is deplorably meagre. The many books of 

 travel published in the early part of the nineteenth 

 century contain hardly any records of fleas. The 

 human flea is now cosmopolitan. Specimens identical 

 with those from Europe are found almost everywhere. 

 But it may be doubted whether this was the case 

 before the great era of travel and steam began in 

 last century. 



There is one strange and, indeed, inexplicable fact 

 in connection with the distribution of this cosmo- 

 politan species of flea. It is absent from the oases of 

 the Sahara and the Haussa countries immediately to 

 the south of the great desert. These countries have 

 long been in communication with places where Pulex 

 irritans is known to abound. There is no natural 

 barrier. The habits of the natives would encourage 

 fleas to thrive, and other forms of human vermin are 

 plentiful. There is, apparently, only one explanation 

 that is forthcoming. It is suggested that the soil 

 and climate in these regions of Africa are, for some 

 reason, unsuited to fleas. In other parts of the Dark 

 Continent, where there are European settlements, the 

 human flea seems to thrive surprisingly well and 

 to attack Europeans and natives, as well as wild 

 and domestic animals. In those parts of Asia where 

 there are European colonies and much intercourse 

 between settlers and Orientals, Pulex irritans is a 



