ENTOMOLOGY

CHAPTER XXIVDiseases Carried by Fleas 1, W. Dwight PierceFleas pass their immature stages in filth outdoors and indoors. Thelarvl!! breed in dirt and are usually to be found where animals are common,but they may breed in the dirt of kennels and stables, in the opencountry, in carpets, and closets of houses and especially in cellars. Theyare always to be found where rats or mice are common.Because of the fact that the larva imbibes filth and the adult sucksblood, we should seek other possibilities of disease transmission whichhave not hitherto been investigated. Past investigations with fleashave dealt principally with the possibility of conveying disease by thebite of the adult flea. The work which has been done on flies and whichwas quoted in a preceding lecture showed that larvIE could take up bacteriaand that these would persist into the adult stage. It is thereforeessential in the future investigations of disease transmission by fleas thataccount be taken of the possibility of the flea larvre taking up the organismfrom the filth in which they breed and retaining these organismsto be transmitted by the adult. That they may do this is demonstratedin the case of the tape worms mentioned below.Fleas do carry disease, that we know. But probably they can carrydiseases which they have never been credited with. There lies our fieldof investigation.The arrangement of organisms transmitted by fleas follows thatadopted for previous lectures.PLANT ORGANISMS TRANSMITTED BY FLEASThallophyta: Fwngi: Schizomycetes: Bacteriacet1!Bacillus pestis I{itasato, the cause of BUBONIC PLAGUE of manand rodents, is carried by fleas. Nine species of rodents, mainly rats and1 This lecture was presented on October SS, 1918. It is considerably modified forthe present edition.350