124 
Parasitic Arthropoda 
end of the meal is signified in an abrupt manner. The flea shakes 
its entire body, and gradually withdraws its proboscis by lowering 
the abdomen and legs and violently twisting the head.” 
‘‘When starved for several days the feeding of the rat fleas is 
conducted in a rather vigorous manner. As soon as the proboscis 
is buried to the full length the abdomen is raised and there ensues a 
gradual lateral swaying motion, increasing the altitude of the raised 
end of the abdomen until it assumes the perpendicular. The flea is 
observed at this point to gain a better foothold by advancing the 
fore tarsi, and then, gradually doubling back the abdomen, it turns 
with extreme agility, nearly touching with its dorsal side the skin 
of the hand upon which it is feeding. Meanwhile, the hungry para¬ 
site feeds ravenously.” 
‘‘It is interesting to note the peculiar nervous action which the 
rodent fleas exhibit immediately when the feeding process is com¬ 
pleted or when disturbed during the biting. Even while the rostrum 
is inserted to the fullest the parasite shakes its head spasmodically; 
in a twinkling the mouth is withdrawn and then the flea hops away.” 
A habit of fleas which we shall see is of significance in considering 
their agency in the spread of bubonic plague, is that of ejecting blood 
from the anus as they feed. 
Fleas are famous for their jumping powers, and in control measures 
it is of importance to determine their ability along this line. It is 
often stated that they can jump about four inches, or, according to 
the Indian Plague Commission Xenopsylla cheopis cannot hop farther 
than five inches. Mitzmain (1910) conducted some careful experi¬ 
ments in which he found that the human flea, Pulex irritans, was 
able to jump as far as thirteen inches on a horizontal plane. The 
mean average of five specimens permitted to jump at will was seven 
and three-tenths inches. The same species was observed to jump 
perpendicularly to a height of at least seven and three-fourths inches. 
Other species were not able to equal this record. 
The effect of the bite of fleas on man varies considerably accord¬ 
ing to the individual susceptibility. According to Patton and Cragg, 
this was borne out in a curious manner by the experiments of Chick 
and Martin. ‘‘In these, eight human hosts were tried; in seven, 
little or no irritation was produced, while in one quite severe inflam¬ 
mation was set up around each bite.” Of two individuals, equally 
accustomed to the insects, going into an infested room, one may be 
literally tormented by them while the other will not notice them. 
