LEPTOMONAS CTENOCEPHALI 353 



multiply. The flagellates survive the pupal stage, and in the adult flea 

 appear in the hind-gut and Malpighian tubes. The various forms found 

 in the adult fleas are described as pre-flagellates, flagellates, and post- 

 flagellates. Certain round forms, called pre-flagellates, are described 

 from the Malpighian tubes of the flea, and to account for their presence 

 the improbable assumption is made that they have been carried there 

 by adhering to flagellate forms which have migrated from the gut. It 

 would be expected that the pre-flagellates would only exist in the larvse, 

 as it is admitted that the flagellates develop in the stomach of the larvse. 

 The pre-flagellates, it will be remembered, are the rounded forms which 

 result from the ingested encysted stages, and which develop into the full- 

 grown flagellates. If they occur in the adult flea, one must suppose that 

 they have not completed their development in the larvae which ingest 

 them, as some of them are admitted to do, and that they have passed 

 through the pupal stage of the flea. The occurrence of these forms in 

 the adult flea rather suggests that the forms pre-flagellate, flagellate, and 

 post-flagellate, which Patton describes in this and other insect flagellates, 

 do not follow one another in succession so regularly as he supposes. It 

 seems more probable that the flagellates may become rounded leishmania 

 forms, which may again develop into flagellates in the same host, without 

 necessarily passing on to the encysted stage, to be voided in the faeces. 



As already remarked, cultures of L. ctenocephali and the flagellates 

 of other fleas can readily be obtained on N.N.N, medium by receiving 

 the voided droplets of liquid faeces of fleas on sterile cover-glasses and 

 transferring them to the culture fluid. The writer (1914a) obtained such 

 cultures from dog fleas in Malta. Laveran and Franchini (1919), Chatton 

 (1919), Tyzzer and Walker (1919), and Shortt (1923) have obtained 

 cultures by washing the fleas in sterilizing fluids and dissecting them under 

 aseptic conditions. These cultures grow readily, can be maintained by 

 subculture for any length of time, and show all the forms which occur in 

 the insect gut. There is never any tendency towards the formation of 

 crithidia or trypanosome forms. Growth is very rapid, much more so 

 than in the case of the allied pathogenic leishmania. The cultures remain 

 alive for long periods, and enormous numbers of flagellates are produced. 

 In one instance in the writer's experience, active flagellates were still 

 present six months after the tube of N.N.N, medium had been inoculated, 

 and a subculture was obtained from it two months later, when active 

 flagellates had disappeared, though leishmania forms were still present. 

 In old cultures, many abnormal and evidently degenerating forms occur. 



Tyzzer and Walker (1919) made a careful comparative study of cultures 

 of Leishmania donovani (Mediterranean strain) and Leptomonas cteno- 

 cephali. The flea flagellate grew more rapidly at 21° C. than L. donovani, 



I. 23 



