AFRICAN TRYPANOSOMIASIS 127 



if passed through rats for many generations the rat will be killed by 

 them in two days. 



The passage of trypanosomes through dififerent species will lower 

 their virulence, e.g., some wild trypanosomes will kill monkeys in a 

 few days, but if passed first through a goat, an attempt to infect the 

 monkey fails, hence its passage through the goat lowers die virulence 

 of trypanosomes for monkeys. 



Care is necessary in adopting this as a means of differentiation. 



It has been observed that — 



T. brucei is more virulent for laboratory animals than T. gam- 

 biense. Some are deadly to horses and cattle, and are harmless to 

 dogs, monkeys and rabbits. Others show a preference for domestic 

 pigs. 



(3) Mode of Development in Tsetse Flies. 



All the trypanosomes pathogenic to man and domestic animals in 

 Africa, with the exception of two northern species, pass through a 

 specific cycle of development in the tsetse flies. The mode of develop- 

 ment in the tsetse is different for different species, and this feature may 

 be used for differentiation. North African species have not been found 

 capable of developing in tsetse. It may be that from disuse they have 

 lost the faculty, if ever they had it. 



CENTRAL AFRICAN PATHOGENIC TRYPANOSOMES. 



Group (A): Trypanosome Brucei Group. 



Synonyms : T. rhodesiense, T. ugand^e. The question of identity 

 of T. rhodesiense and T. brucei is still sub judice. 



The differentiation of the groups is according to the development 

 of the trypanosome in the tsetse. The microscope will decide to which 

 group the trypanosomes will belong. 



General features of all in this group. 



All are more or less polymorphic. 



They vary much in size and shape. 



The cytoplasm contains numerous dark-staining granules. 



The kinetonucleus is small and situated at some distance from the 

 posterior extremity. 



The undulating membrane is well developed and has bold folds. 



They affect many species of animals, including man, cattle, horses, 

 dogs, &c. 



T. brucei and T. gambiense develop in the tsetse in the same wa}-, 

 at first in the intestine, then in the salivary glands. There they com- 

 pletely develop into infective forms. No other group invades the 

 salivary glands. 



(i) Trypanosoma brucei. 



