874 SOME POINTS OF GENEEAL INTEREST 
go-downs. In Nos. 1 and 2 they are abundant and regular, 
in Nos. 8 and 4 they are scanty, whereas in Nos. 5 and 6 
there should be none at all. 
Differentiation of Fleas. — The fleas which are of main, 
interest to us are those wTiich are met with in association 
with P. cheojpis on rats, and from which we might require to 
differentiate them. These are : — 
1. Pulex irritans, the human flea. 
2. Ceratophyllus fasciatus, the European rat flea. 
3. Pulex felis, the cat and dog flea. 
4. Ctenojpsylla musculi, found on mice and rats. 
5. Sarcojpsylla gallinacea, a common bird flea. 
The varieties of fleas are very numerous. Thus, 
Loemopsylla, to which genus Pulex cheopis belongs, has alone 
twenty-four known varieties. Still, as P. cheopis comprises 
98 per cent, of the flea population on rats in India, and as 
it was found to comprise 66 per cent, of them during the 
epidemic of 1909, in the Muanza district, other kinds of fleas 
on rats, though possibly capable of transmitting plague, are 
not of such practical importance. 
