"The acute pain of biting is first felt when the mandibles have not quite penetrated and subsequently during each distinct movement of the abdomen. The swinging of the abdomen gradually ceases as it becomes filled with blood. The sting of the biting gradually becomes duller and less sensitive as feeding progresses. The movements of the elevated abdomen grow noticeably feebler as the downward thrusts of the springy bow-like labium becomes less frequent." "As the feeding process advances one can discern through the translucent walls of the abdomen a constant flow of blood, caudally from the pharynx, accompanied by a peristaltic movement. The 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 parasite feeds ravenously." "It is interesting to note the peculiar nervous action which the rodent fleas exhibit immediately when the feeding process is completed 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while the rostrum is inserted to the fullest the parasite shakes its head spasmodically; in a twinkling the mouth is withdrawn and then the flea hops away."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 experiments 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.