542 FAMILY: TRYPANOSOMID^ 



reason to regard it as other than T. brucei. For all practical and scientific 

 purposes, the polymorphic trypanosome, which is highly virulent for 

 small experimental animals, and which produces in these animals a varying 

 percentage of posterior nuclear forms, may be regarded as T. brucei. 

 There is, however, one difficulty in connection with T. 'pecaudi. Bouet 

 and Roubaud (1910) studied the development of a trypanosome which 

 they regarded as T. pecaudi in G. tachinoides, G. longipalpis, and G. pal- 

 palis. In the first they claim that the development commenced in 

 the stomach, and was followed by infection of the proboscis only, the 

 salivary glands not being involved. If this observation is correct, then 

 there is a definite departure from what is known to occur in the case of 

 T. brucei. Bouet and Roubaud's account of the development has not yet 

 received confirmation, and as there is a possibility that they were not 

 actually dealing with a polymorphic trypanosome, it is better to ignore 

 it at present. 



Susceptibility of Animals. — T. brucei is undoubtedly the most 

 virulent of the known pathogenic trypanosomes. It is inoculable into 

 all mammals, including monkeys, with the exception of the baboon 

 {Cynocephalus), as noted by Bruce (1903). The latter animals enjoy an 

 immunity, as do the majority of human beings. In the case of the last 

 named it has long been known that travellers who have been, constantly 

 bitten by tsetse flies {G. morsitans), and who have lost all their transport 

 animals through the ravages of these flies, have themselves remained 

 perfectly healthy. The question of the immunity of man will be referred 

 to again in connection w4th the relationship of T. brucei and T. rhodesiense. 

 Horses, mules, and donkeys are very susceptible, and die in a period 

 varying from a fortnight to three months. For camels the strain is 

 equally virulent. In the writer's experience, a convoy of over seventy 

 camels taken into the Bahr el Ghazal province of the Sudan all died of 

 the infection within a period of two months. Cattle, on the other hand, 

 are not so rapidly killed as horses, but recoveries are rare. Sheep and 

 goats are still less susceptible. Death may occur in four or five months, 

 or few symptoms may be shown. Ultimately recovery may take place, 

 with immunity to further infection. Pigs, on the other hand, quickly 

 succumb. Dogs acquire the infection easily, and die in about a fortnight 

 from the time of inoculation. Cats are slightly more tolerant. Rats and 

 mice are easily infected. The former live for about a fortnight after 

 inoculation, and mice for a shorter period. Sometimes, however, rats may 

 survive for three weeks or more. Guinea-pigs live for three or four weeks. 

 Monkeys, with the exception of the baboons, die of an intense infection 

 in three weeks or a month. Many other animals are inoculable, and acquire 

 infections similar to those indicated above. As a rule, the trypanosome 



