Messrs Strickland and Swellengrebel, Trypanosoma lewisi. 531 



The development of Trypanosoma lewisi in the Rat Flea 

 (Ceratophyllus fasciatus). By C. Strickland, B.A., and Dr N. H. 

 Swellengrebel. (Communicated by Prof. Nuttall.) 



[Read 6 June 1910.] 



Little is known about the development of trypanosomes 

 outside the vertebrate host, and what is known is liable to 

 Patton's criticism, that asserts that most of the Grithidia forms 

 found in different invertebrates and considered to be develop- 

 mental forms of various trypanosomes are indeed independent 

 forms and have no connection " with trypanosomes. 



This question being of the highest importance not only 

 theoretically but also from a practical point of view in con- 

 nection with sleeping sickness, we endeavoured to trace out the 

 life-cycle of T. lewisi (provided there were any) in the rat flea 

 {Ceratophyllus fasciatus). We chose the rat flea and not the 

 louse (Haematopinus spinulosus) because it is clear from the 

 papers of Nuttall, Manteufel, Minchin and one of us (C. S.) that 

 the louse transmits the trypanosomes only mechanically, whereas 

 the flea becomes infective after 7 — 14 days and remains so for 

 a long time, which fact suggests that a true development takes 

 place. 



We infected 83 fleas out of an uninfected lot (bred in the 

 laboratory), allowing them to feed during a period of 12 hours 

 upon an infected rat (10th day of infection). The fleas were 

 then removed from the rat and were fed at intervals of three days 

 by biting non-infected rats through a gauze bag. A control series 

 of experiments was made by feeding 60 fleas (out of the same box 

 as the infected series) on a non-infected rat and by treating them 

 afterwards in the same way. Each day, for 16 days after the first 

 feeding, four to six of the infected and control fleas were dissected 

 and observations were made in vivo and in stained preparations. 



The control fleas were not always free from flagellated forms. 

 Nothing was ever seen in the living preparations ; but by making 

 stained preparations of the different parts of the gut, we were able 

 to detect flagellates in 3-3 7o o^ ^^e fleas. This fact was probably 

 due to an accidental infection, an infected rat having broken into 

 the flea box. But even if we consider the flagellates of the control 

 fleas to be natural forms, we may safely conclude that most of the 

 flagellates found in the fleas fed on infected rats are developmental 

 stages of T. lewisi, because the rate of infection was 44 ''/^ . 



VOL. XV. PT. VI. 35 



