370 SOME POINTS OF GENERAL INTEREST 
for man. Rat fleas, when starved, will readily attack all 
animals, not then being particular in their choice of host. 
Such fleas, deprived of food from seventy-two to ninety-six 
hours, attack and feed on man more readily than at other 
times ; but even so, they prefer their true host to man. A 
point to be remembered is that rat fleas may be attracted to 
man, jump on him, but take some time to feed ; and thus 
a man may carry fleas from one place to another which 
when brought near a rat will attack it in preference to 
the man. 
Mode of Dispersal of Fleas . — I have already indicated one 
way in which fleas may be carried from one vicinity to another. 
Other modes are : 
(a) By means of the host in its natural wanderings. The 
flea does not stay continually on its host, but often drops 
off ; thus rats are continually shedding fleas wherever they 
go. Also remember that sick rats harbour a greater number 
of fleas than healthy ones. 
(b) When the rat is carried about in merchandise, fleas 
accompany him. 
(c) But in the absence of the rat, fleas themselves may 
travel in merchandise, grain, or clothing. However, it must 
be remembered that the adult flea, in the absence of any host, 
will rapidly die, generally in about four or five days. Still, the 
larvae, which can feed on any kind of organic rubbish, and the 
pupae, which require no food, can be carried considerable 
distances in merchandise, i.e. for periods as long as one or 
two months. 
In whatever way transported, they will select, when reaching 
their new surroundings, their true host or the next best available 
animal. 
In numbers rat fleas seem to have a distinct seasonal 
variation. Moreover, this appears to coincide with the height 
of the plague epidemic more or less closely. Also during the 
epidemic season of plague, fleas remain infective for a period 
of from ten to fifteen days ; whereas during the non-epidemic 
season they are only infective for seven days, and then not 
so highly. 
The Collection and Examination of Fleas . — How are we to 
