6 1 8 TRYPANOSOMI ASIS 



Nagana or Tse-tse Fly Disease. This is a disease affecting 

 under natural conditions chiefly horses, cattle, and dogs; it is 

 prevalent especially in certain regions of South Africa, though 

 it probably may occur elsewhere. In the horse the chief 

 symptoms are the following : The animal is observed to be 

 out of condition, its coat stares, it has a watery discharge 

 from the eyes and nose, and the temperature is elevated ; 

 swellings appear on the under surface of the abdomen and in 

 the legs; it gradually becomes extremely emaciated and 

 anaemic, and dies after an illness of from two or three weeks to 

 two or three months. In other animals the symptoms are of 

 the same order, though the duration of the disease varies much ; 

 thus in the dog the illness does not last more than one or two 

 weeks, while in cattle it may continue for six months. It is 

 doubtful whether a domestic animal attacked by the disease 

 ever recovers. The popular idea regarding the etiology of the 

 disease was that it was contracted by animals passing through 

 certain rather restricted and sharply denned areas or belts 

 characterised by heat and damp, usually lying beside rivers, 

 and always infested by the tse-tse fly (glossina morsitans), to the 

 bite of which the disease was attributed ; in this connection it 

 is important to note that though man is frequently bitten by 

 the tse-tse fly he does not contract nagana. Modern know- 

 ledge on the subject dates from the discovery made by Bruce 

 in 1894 that the blood of animals suffering from nagana 

 swarmed with a trypanosome now known as the Tr. Brucei, 

 and in 1895 he was instructed by the Governor of Natal to 

 undertake the investigation which led him to work out the true 

 etiology of the disease. It may be said that this research 

 forms the starting-point of the important work done during 

 the last decade with regard to infections by trypanosomes. 

 In his earlier work Bruce found that the parasite was present 

 in the blood of every animal suffering from nagana and absent 

 from the blood of healthy animals in the affected districts; 

 further, that the fever which marks the onset of the disease was 

 accompanied by the appearance of the trypanosome in the 

 blood ; and finally, that the transference of the smallest 

 quantity of blood from an affected to a healthy animal origin- 

 ated the disease. He then proceeded to investigate the part 

 played by the tse-tse fly in the condition. He found that if 

 flies taken from the fly belt were transported to a place where 

 nagana did not occur, kept for a few days, and then allowed to 

 bite susceptible animals, the latter did not contract the disease 

 this result showing that it was not, as had been supposed by 



