PRESIDENTIAL ADDRESS. 103 
(Xenopsylla, Pulex) cheopis, 4863; Ctenopsylla (Typhlop- 
sylla) musculi, 3370; Ceratophyllus fasciatus, 1380; Cteno- 
cephalus canis or felis, 61; Pulex irritans, 3. 
Ham (loc. cit., p. 147) gives a table of the information 
available at the time of writing his report (1907), as to the 
relative prevalence of the species of rat-fleas in the various 
Australian States. In Queensland, L. cheopis comprised 
90.8 to 100 per cent. of the fleas on rats; in New South 
Wales in 1902, 81 per cent.; in Sydney in 1904, 69 per 
eent.; in Neweastle in 1904, 20.5 per cent.; and in Perth, 
from December to July, 78 per cent.—but from July to 
December, 17 per cent. L. cheopis also occurs in Victoria 
and Tasmania. C. musculi composed 23 per cent. of the 
rat-fleas in Sydney in 1904, 70 per cent. in Neweastle in 
the same year, and 22 and 82.6 per cent. in Perth for the 
months respectively mentioned above. 
Of 60 rat-fieas found by me in Perth in 1906, 32 were 
L. cheopis, 27 C. musculi, and 1 C. fasciatus. . 
It is now universally recognised that L. cheopis is par 
excellence the plague flea, that is to say, that it is through 
its intermediation that the plague bacillus generally reaches 
man in bubonic and septicemic plague. As plague shows 
a pronounced seasonal prevalence, the object of this flea 
census was to ascertain not only the relative yearly preva- 
lence of fleas, but also their variations in numbers from 
week to week in order to ascertain whether there was any 
correlation between their number and the incidence of cases 
of plague in man. The accompanying table (Table V) 
will show the monthly prevalence of the various species of 
fleas on rats as met with in Sydney from 1909 to 1917. 
As regards L. cheopis, this flea is most abundant in 
February (962) and March (946), followed by April (691) 
and January (479). It will be seen, on referring to the 
summary of cases of plague in New South Wales, that these 
