TRYPANOSOMA BRUCEI 545 



measurements of T. brucei (Ziiliiland strain) in inoculated animals are 

 given by Bruce and his co-workers (1914) as follows: 



Number of 

 Species of Animal. i Trypanosomes 



Measurement in Microns. 



Measured. Average Maximum Minimum 

 Length. Length. Length. 



Monkey 



Dog \ . 

 Guinea-pig 

 Rat 



A curve showing the percentage of trypanosomes of various lengths 

 is given in Fig. 196. The percentage of posterior nuclear forms varies 

 in difEerent strains. In the case of an infection in rats of the Sudan strain, 

 thirty-six trypanosomes out of 1,138 were found by the writer (1912) to 

 show this posterior displacement of the nucleus. 



Transmission. — The transmission of T. bnicei by the tsetse fly was 

 demonstrated by Bruce (1897) in Zululand. At that time Bruce con- 

 sidered the fly to be G. niorsitans, but from observations made later, 

 Austen (1903) came to the conclusion that the fly with which Bruce 

 worked was probably G. pallidipes. It was Kleine (1909a) who first 

 demonstrated that flies did not become infective till a period of eighteen 

 to twenty days had expired from the time of feeding. The experiments 

 were made by feeding G. palpalis on sheep and a mule previously infected 

 with T. bnicei by the bites of G. morsitans. The flies were then fed each 

 day on a healthy animal, and it was found that the only animals to 

 become infected were those bitten after the long incubation period. 

 Bouet and Roubaud (1910), working w^ith the same trypanosome 

 (T. pecaudi) in West Africa, found that G. longipalpis, G. tachinoides, and 

 G. palpaJis were all capable of transmitting the trypanosome, though 

 the former was the most frequent carrier and the latter only rarely so. 

 They further found that the same trypanosome was carried by G. mor- 

 sitans. Macfie (1914) and Gallagher (1914) obtained strains of T. brucei by 

 feeding wild G. tachinoides on guinea-pigs in the Eket district of Nigeria. 

 Transmission by means of G. tachinoides has also been effected by Lloyd 

 and Johnson (1924). Bruce et al. (1913, 1913o), working in Nyasaland, 

 found that G. morsitans was the usual carrier, but they also noted (19146) 

 that G. brevipalpis could serve as a vector, both with the Nyasaland strain 

 and that from Zululand. 



Cycle in the Tsetse Fly. The developmental cycle of T. brucei in 



G. morsitans, as demonstrated by Bruce et al. (1914rt, 1914/?, 1914/), follows 



I. 35 



