TRYPANOSOMA CONGOLENSE 



553 



immunity tests, but also on account of the fact that in infected animals a 

 small percentage of the trypanosomes present measure up to 25 microns 

 in length, while the remainder are small forms like T. congolense. It must 

 be admitted, however, that the trypanosome was isolated in the early 

 days of trypanosome investigations, and that the possibility of mixed 

 infections was not then considered, Yorke and Blacklock (1911), from 

 the examination of two naturally infected horses in the Gambia, came to 

 the conclusion that the original T. dimorphon strain was a mixed one of 



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Af^f*^ 



x^ 



%x 



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Fig. 227. — Trypanosoma congolense (x 2,000). (After Bruce, Hamerton, 

 Bateman, Mackie, and Lady Bruce, 1910 and 1911.) 



T. congolense and T. vivax. Whichever view may be correct, it is doubtful 

 if the exact counterpart of the original strain has been rediscovered since, 

 though French writers have frequently employed the name T. dimorpJwn for 

 the trypanosome of the T. congolense type, while others have used it for one of 

 the T. briicei type. The small pathogenic trypanosome of wide distribution 

 in Africa should therefore be known by Broden's name, T. congolense. 



Morphology.^T. congolense is the smallest of the pathogenic African 

 trypanosomes, and varies in length from 9 to 18 microns, with an average 



