820 THE FLAGELLATA 



In most mammals (guinea-pigs, mice, goats, rabbits, cattle, horses, etc.) 

 the trypanosome multiplies in the blood, but the course of the disease is 

 very slow and frequently ends in recovery. The presence of trypanosomes 

 in the blood is often unaccompanied by symptoms (Button and Todd). 



^Etiology. Bruce and Nabarro showed that human trypanosomiasis and 

 one of the tse-tse flies (Glossina palpalis} have a very similar distribution : 

 and they proved by actual experiment that this fly is the agent by which 

 the disease is spread. In five experiments flies fed on patients suffering 

 from sleeping sickness for 8-48 hours infected monkeys (Cercopithecus). 

 Similarly, Bruce infected three monkeys by allowing them to be bitten daily 

 over a long period by a large number of Glossina palpalis collected at Entebbe, 

 Uganda, where sleeping sickness is prevalent. 



[The fact that Glossina palpalis does in nature transmit the trypanosome 

 of sleeping sickness is now in the region of facts beyond dispute. But the 

 attention of observers is at present absorbed in determining whether other 

 species of tse-tse fly can act as carriers of the infection in nature. For a 

 while it was believed " that species other than palpalis were in this respect 

 harmless." Certain facts, however, have since been disclosed which rendered 

 a further investigation into the natural modes of transmission imperative. 

 Already Taute claims to have demonstrated that Glossina morsitans may 

 transmit T. gambiense and is of opinion that his observations show that 

 the transmission of T. gambiense by Glossina morsitans is not an exceptional 

 event. Even more recently Kinghorn is said to have been successful in 

 transmitting T. rhodesiense (infra) by means of G. morsitans. 



[The tse-tse fly is a true intermediate host of the trypanosome. Recent 

 experiments by Bruce and his collaborators have shown that after sucking 

 infected blood an incubation period of 28 days follows during which the 

 bite of the fly is non-infectious and that at the end of that period the fly may 

 become infective and may retain its infectivity for 96 days and probably for 

 as long as it lives. There is no hereditary transmission of the parasite from 

 one generation of fly to the next. 



[The source whence the fly becomes infected is still undetermined. Bruce 

 and his colleagues investigating this point in the aetiology of sleeping sickness 

 have come to the conclusion that though no antelope has up till the present 

 been found naturally infected with Trypanosoma gambiense these animals 

 living in the fly-areas are potential reservoirs of the virus of sleeping 

 sickness.] 



It is possible that there are means other than the tse-tse fly by which human 

 trypanosomiasis is spread. Martin, Leboeuf and Roubaud, for instance, consider 

 that some mosquitos (Stegomyia, Shansonia) may take a part in the propagation of 

 the disease : and certain facts observed in Uganda make it possible that the disease 

 in man may be transmitted during coitus. 



B. Trypanosoma rhodesiense. 1 



Trypanosoma rhodesiense was first observed by J. W. W. Stephens early in 

 1910 in a case of sleeping sickness in an European from Northern Rhodesia 

 who was being treated in the Royal Southern Hospital, Liverpool. The 

 trypanosome was described by Stephens and Fantham. 2 



Stephens and Fantham believe that sleeping sickness in Rhodesia, Nyasa- 

 land, and adjoining territories is due to T. rhodesiense and not to T. gambiense 

 recently introduced. They further believe that T. rhodesiense has existed in 

 the territories above mentioned from time immemorial. 



1 This section has been added. 



2 Stephens and Fantham, Proc. Roy. Soc. (1910), B, Ixxxiii p. 28. 



