462 MEDICAL ENTOMOLOGY 



human beings is C. fells, ordinarily found on the Cat and dog. 

 P. irritans* has not been met with in the plains, while the cat flea is 

 common everywhere when domestic dogs and cats are kept. It has 

 been shown experimentally by several observers that X. cheopls will 

 attack man in the absence of its ordinary host. Many of the fleas 

 collected during the researches of the Indian Plague Commission were 

 obtained by placing guinea pigs in infected houses. 



Chick and Martin have performed some exact experiments to deter- 

 mine the readiness with which certain fleas attack man, and have 

 shown that when starved for varying periods and then placed on the 

 arm in a test tube, Ceratophyllus fasciatus feeds readily, more than 

 half the experiments proving successful even under these artificial 

 conditions. Ctenopsylla mnscitli, on the other hand, will rarely bite 

 man, while Ctenophthalmus agyrtes will not do so at all. The latter 

 flea, it should be noted, lives on field mice, not on the rats and 

 mice which frequent human habitations, and will therefore seldom 

 come into contact with human beings. Ceratophyllus acutus, the flea 

 of the Californian ground squirrel, will feed on man. 



The Indian rat flea, X. cheopis, attacks man readily, and its incli- 

 nation to do so in the absence of a sufficient number of rats for the 

 flea population is one of the factors in the role which it plays in the 

 transmission of plague. The Jigger flea has been found on a large 

 number of hosts, and Echidnophaga galllnaceus, which is normally a 

 parasite of the domestic fowl, will attack rats which frequent the hen 

 houses, and will also bite man. A certain catholicity of taste is the 

 rule among the Siphonaptera, a fact which is well brought out by the 

 lists of hosts given by Jordan and Rothschild, and by Baker, for the 

 less known fleas. 



The method of feeding can be readily observed in fleas which have 



been starved for a day or so and then placed on the arm; they can 



Method of f d" ^ e wa ^ c ^ed during the process under a hand lens. 



After the usual investigation, in which the maxillary 



palps appear to take a part, the flea settles down and presses its head 



against the skin, tilting its abdomen in the air in a way that reminds 



one forcibly of the attitude assumed by many Diptera. As the head is 



pressed to the skin the labial palps can be seen to diverge from one 



another. In a favourable light, and with a binocular microscope, one 



can see the blood passing rhythmically into the abdomen. The flea 



According to Gimlette, Ptilex irritans is unknown to the Malays of Kelatan, though 

 they recognize the dog flea. 



