28 



Sir D. Bruce and others. Trypanosome 



disease in man. That the cause of the sparsity of cases in man in these 

 areas is due to the fact that man is more or less refractory to the trypano- 

 some, and that it is only rarely that the " fly " meets with a susceptible 

 subject. That this is the reason why the cases of Human trypanosome 

 disease in the Luang wa valley and in ISTyasaland do not tend to increase in 

 numbers. The disease remains stationary, as it probably has done during the 

 last thousand years. This is the working hypothesis held at present by this 

 Commission. 



These, then, are the points at issue, and it would appear at present that 

 the only way of solving the problem will be by searching and finding out 

 whether cases of T. brucei disease, or Nagaha, in man occur wherever 

 G. morsitans and this parasite are found together. Already cases have been 

 found on the Eovuma river on the borders of German and Portuguese East 

 Africa, and in the Hartley District south of the Zambesi, in Europeans and 

 natives, who certainly could only have contracted the disease in these 

 widely separated districts. 



Thanks to Mr. Garden, the Government Veterinary Officer, the Commis- 

 sion have had the opportunity of studying a trypanosome of the Nagana type 

 found in the blood of a donkey at Mzimba (lat. 1.1° 55' S., long. 33° 35' E.), 

 about 100 miles north of the northern border of the Proclaimed Area. 

 It is proposed, then, in this paper to describe this trypanosome, in pursuance 

 of the policy of describing in detail as many strains as possible of this type 

 of trypanosome, if peradventure some method of separating T. brucei from 

 T. rhodesiense may be discovered, or of proving them to be one and the same 

 species. 



Morphology of the Mzimba Strain. 



A. Living, Unstained. 



The movements of this trypanosome in the living condition are similar to 

 T. brucei and T. gambiense in being non-translatory. 



B. Fixed and Stained. 



The blood films were fixed, stained and measured as previously described 

 in the " Proceedings."* 



* 'Boy. Soc. Proc.,' B, vol. 81, pp. 16 and 17. 



