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 in a twinkling the mouth is withdrawn and then the flea hops away."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 signiflcance 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 ablfe 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. 



