XVIII] MORPHOLOGY AND TRANSMISSION 325 



and the flagellum terminates in a short free portion. The cyto- 

 plasm is coarsely granular, especially at the anterior end. 



In addition Stephens and Fantham mention the occurrence 

 of " snout " forms with an elongated posterior end. These 

 forms are present especially during the first half of the infection, 

 and although not absent from the ordinary strains of T. gam- 

 biense are much more numerous in the case of rhodesiense. 



It is important to note that the posterior position of the 

 trophonucleus has never been observed in trypanosomes in the 

 blood of man, but only in experimental animals. Wenyon and 

 Hanschell found that the percentage of posterior nuclear forms 

 varies very much, not only with the stage of infection but also 

 with the strain employed. In three strains of rhodesiense in 

 rats the percentages of these forms were found to vary in one 

 strain from o to 0-9 per cent., in the second from 3 to 7 per cent, 

 and in the third strain from 13 to 40 per cent. 



T. rhodesiense, like gambiense, is markedly dimorphic, for 

 there are long slender forms and short stumpy forms, together 

 with intermediate forms. The numerical relations between 

 these various forms are extremely variable, depending on the 

 stage of infection. The dimensions of the parasites vary from 

 13 to 39 microns in length, but the majority of them fall between 

 17 and 30 microns. 



Mode of transmission. In 1912, Kinghorn and Yorke 

 demonstrated the transmission of T. rhodesiense by Glossina 

 morsitans, the experiments being carried out at Nawalia, 

 Northern Rhodesia, on the Nyamadzi River, a tributary of the 

 Luang wa. 



About five per cent, of the flies were found to become infected 

 when fed on patients or animals containing trypanosomes. 

 The development in the fly is of the cyclical type, the insect 

 becoming infective after an incubation period of about fourteen 

 days. Once infected a fly remains infective for the remainder 

 of its life and may infect fresh animals at each successive feed. 



Temperature has a marked effect on the development of 

 rhodesiense in the intermediate host as shewn by the following 

 experiment. 



' Two batches of wild G. morsitans, batch A 95 flies, batch 



