XVIII] GENERAL ACCOUNT 323 



suffering from trypanosomiasis, parasites oeing found in his 

 blood on November ijih, 1909. 



The patient subsequently returned to England and in 1910 

 was admitted into the Royal Southern Hospital. 



The same year Stephens whilst examining a stained speci- 

 men of the blood of a rat infected with this race of trypanosomes 

 observed a marked peculiarity in its morphology, and in 

 November, 1910, Stephens and Fantham gave a full description 

 of this new species of human trypanosome under the name of 

 T. rhodesiense. 



The announcement of the discovery of a new species of 

 human trypanosome has given rise to a great deal of discussion 

 as to the nature of T. rhodesiense and its relation to pre-existing 

 species of trypanosomes. Whereas some authors tend to regard 

 it as merely a variety of T. gambiense, hardly distinct, others 

 consider it to be a form of T. brucei that has acquired patho- 

 genic properties for man. The latter view seems rather unlikely, 

 for on two or three occasions man has been shewn to be 

 immune against experimental infection with T. brucei, and, 

 moreover, human serum has a curative action on nagana in 

 experimental infections. 



By means of cross-immunity reactions Laveran and Mesnil 

 have shewn that rhodesiense is distinct from both gambiense 

 and brucei, and therefore it must be regarded as a new species 

 of human trypanosome. 



There can be little doubt that T. rhodesiense has arisen 

 within the last few years and that it is an interesting example 

 of the origin of a new species at the present time. As the 

 transmitting agent G. morsitans is widely distributed through- 

 out Rhodesia and East Africa, there is no reason why this 

 disease, had it previously existed, should not also have had 

 a wide range of distribution, instead of being restricted to one 

 or two valleys in Nyasaland and Rhodesia, and the symptoms 

 are so characteristic that the disease could hardly have re- 

 mained unnoticed. 



Since the discovery of the trypanosome, however, its range 

 of distribution has increased considerably and already cases 

 have occurred south of the Zambesi. The sudden appearance 



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