554 FAMILY: TRYPANOSOMIDyE 



of 14 microns (Fig. 227, Plate V., h, p. 456). Its breadth is under 3 microns. 

 There are no forms with a fiagellum, though sometimes in certain indi- 

 viduals there may be difficulty in deciding whether a short one is present 

 or not. The nucleus is central in position, while the kinetoplast often 

 projects over the border of the parasite. According to Laveran and 

 Mesnil (1912), T. dimorphon occasionally shows much larger forms up to 

 20 or even 25 microns in length, but the majority of the trypanosomes in 

 any pure infection of T. congolense fall within the dimensions given above. 



The trypanosome occurs naturally in horses, donkeys, oxen, goats, 

 sheep, pigs, and dogs, in which it produces a rather chronic wasting disease 

 associated with fever and progressive ansemia. Rats may sometimes be 

 inoculated, but, as pointed out by Bruce and his co-workers (19136), many 

 strains have no effect on rats. 



Working with what was undoubtedly this trypanosome in the Sudan, 

 the writer produced an infection in tw^o dogs which he had inoculated 

 from cattle. 



Transmission and Reservoir. — The wild game of Nyasaland were shown by 

 Bruce et al. (1913e) to be reservoirs of T. congolense, as many as 14'4 per 

 cent, of those examined in the "fly country" being found infected 

 (see p. 509). It was further shown (1914c) that the strain with which 

 they worked (T. pecorutn) was conveyed by Glossina morsitans. Bouet 

 and Roubaud (1910), with the trypanosome they called T. dimorpJion, 

 found that G. longipalpis was the chief carrier, but that G. tachinoides and 

 G. palpalis could also act as vectors. Bruce et al. (1910a) and Fraser and 

 Duke (1912c) in Uganda found that the strain (T. pecorum) was carried 

 by G. palpalis, while Bruce et al. (19146) found that G. hrevipalpis could 

 transmit the trypanosome in Nyasaland. Croveri (1919) showed that in 

 Somaliland G. pallidipes was the vector of this trypanosome, which was 

 referred to as T. somaliense. Duke (1923c) has again effected the trans- 

 mission of T. congolense by G. palpalis in Uganda. 



Cycle in the Tsetse Fly. — The mode of development in the tsetse 

 fly, which differs from that of T. gambiense, was studied by Robertson 

 (1913) and Bruce et al. (1914c). There is at first an intestinal development, 

 followed by migration forwards of long narrow trypanosomes to the 

 hypopharynx, where a change into attached crithidia forms and then 

 into trypanosomes of the blood type takes place, after which the flies 

 are infective (Fig. 218). There is no invasion of the salivary glands, as 

 there is with T. gatnbiense. Duke (1912) in Uganda found that the part 

 of the proboscis which became most heavily infected was the labrum, 

 while in only one instance were trypanosomes observed in small numbers 

 in the hypopharynx. After the forward migration of the intestinal forms, 



