16 
Ohservations on British Rat-fleas 
The species of fleas, granted they are numerous enough, are only 
important if they bite hosts susceptible to plague infection, and so are 
able to transmit the disease from one to another of these hosts. 
Of the species which we found on rats all, with the exception of 
G. fasciatus and C. agyrtes, had perhaps only an accidental connection 
with the rats, and possibly never bite the rat; we cannot, however, give 
certain evidence of this. Of the species which we rarely found on the 
rat, G. musculi and S. cuniculi are the common mouse and rabbit flea 
respectively, and as the mouse and rabbit are subject to epizootics of 
plague these fleas probably serve as vectors of the bacillus. S. cuniculi 
is said to bite man, in which case plague among rabbits becomes directly 
dangerous to man. Plague among mice must be transmitted to rats or 
other hosts by the agency of a flea common to the two species in order 
to be dangerous to man. 
G. fasciatus, being parasitic on the mouse and rabbit, may sometimes 
be the cause of the transmission of the disease between these hosts. 
G. agyrtes, in view of its numbers, is the next most important 
species, but it does not bite man. The significance, therefore, is re¬ 
stricted to the possibility of its transmitting and keeping up plague 
from rat to rat. 
Other ecto-'parasites of rats. 
It is not probable that ecto-parasites of rats, other than fleas, have 
any significance in the epidemiology of plague; but we may here 
mention those which we found : 
Acarina were the most abundant of other ecto-parasites, occurring 
on about 100 rats. There were one or two Coleoptera, and a very few 
Anopleura (lice). We did not find more than five rats with lice out of 
many hundreds examiuedh 
Ticks. Three female specimens of Ixodes tenuirostris from two 
rats; found for the first time on rats, their usual hosts in this country 
beinsf small mammals (shrews, harvest mice, voles). (Determined by 
G. H. F. Nuttall.) 
Other Mites. Mostly Haemogamasits hirsictus, the common species 
found in moles’ nests; Gamasus coleoptratorum; Gamasus terrihilis; 
Gamasus sp. ? nymph. (Determined by N. D. F. Pearce.) Notoedres 
sp., the cause of ear-scabies. 
Anopleura. Haematopinus spimdosus; Haematopimis sp. ? 
1 As many of the rats were found by Drs MacAlister and Brooks to be infected with 
Trypanosoma lexoisi, it is interesting to note the scarcity of lice, as these are credited by 
some authors to be the usual carriers of the trypanosomes. 
