LEPTOMONAS CTENOCEPHALI 351 



flagellate forms to the smallest rounded ones which have no free flagellum. 

 The clusters or rosettes of attached forms increase in size by multiplication 

 of the individual flagellates, which are able to divide longitudinally in 

 whatever form they occur. 



The small leishmania forms which arise in the hind-gut appear to 

 develop a cyst wall. The absolute proof of the existence of a cyst m 

 such minute forms is, of course, difficult to obtain, though the writer 

 (1914r/) has shown that these supposed encysted forms are protected in 

 some way against desiccation. The fseces of an infected flea, which were 

 passed while feeding, were received on to a sterile cover-glass held a short 

 distance behind it. The droplet was spread into a thin film with a sterile 

 needle and allowed to dry. The cover-glass was then placed in a dry 

 sterile test-tube for twenty-four hours, after which it was transferred to 

 N.N.N, medium, in which a culture of the flagellates was obtained. A 

 similar experiment was made by the writer (1912c) with the flagellate of 

 the human flea, Pulex irritans. This is sufficient evidence to show that in 

 the fgeces there occur forms which can withstand complete drying, and in 

 all probability these are the small apparently encysted leishmania bodies. 

 It is assumed that the flagellates and unencysted forms must be killed m 

 the process of drying. 



It is well known that the larvae of these fleas feed largely on the fseces 

 of the adults, and, as demonstrated by Noller (1914), they take up the small 

 cysts, for the same flagellates can be found in their intestine. Here, also, 

 both elongated and shorter forms occur, but the writer has never seen the 

 gut covered with attached flagellates, as in the adult. Drbohlav (1925) 

 has shown that the flagellate infection of the larvse survives in the pupse, 

 and appears as an intestinal infection in the newly-emerged adults. 



It will be seen that the infection is a simple one, which passes from 

 one insect to another by means of encysted forms voided in the faeces. 



The various types of organism from the flea's intestine are shown in 

 Fig. 164. The longest forms have a body 18 microns in length. There is 

 a distinct tendency to curvature like the blade of a curved sword. Very 

 narrow forms occur, as also much broader ones, and between the long 

 flagellate forms and the minute leishmania ones every stage can be traced. 

 The small encysted bodies which are finally produced are barely 3 microns 

 in diameter. Reproduction takes place by binary fission, and this is not 

 confined to any particular stage, flagellates of all sizes and shapes taking 

 part in the process. No stage of intracellular reproduction corresponding 

 with that of Trypanosoma lewisi in the epithelial cells of the flea's gut 

 has been seen in this flagellate or in any other leptomonas. 



There is no evidence that L. ctenocephali has any vertebrate host, in 

 spite of the claims, which appear somewhat dubious, of Laveran and 



