NAGANA OR TSE-TSE FLY DISEASE 655 



number. The animal usually shows no symptoms of illness. The 

 infection goes on for about two months, and then the organisms gradually 

 disappear from the blood. In the great majority of cases the rat is now 

 immune against fresh infection. If trypanosomes be introduced into its 

 peritoneum they are, according to Laveran, taken up by mononucleate 

 phagocytes and destroyed. The serum of a rat which has been infected 

 shows agglutinating capacities towards the trypanosomes, causing them to 

 agglomerate in rosettes in which the flagella are directed outwards, and 

 the serum of immune rats has a certain degree of protective action if 

 injected along with the organism into a susceptible animal. As has 

 already been noted, this trypanosome has been cultivated on artificial 

 media, on which it multiplies freely, large numbers of small forms being 

 often produced. These when injected into rats give rise to the usual 

 infection, but not so rapidly as when blood from an infected animal is 

 used. The organism multiplies at the body temperature, but a lower 

 temperature is preferable, and at 20 C. Novy and MacNeal succeeded in 

 carrying a growth through many sub-cultures. The trypanosome is very 

 resistant to cooling, and has been exposed for fifteen minutes to the 

 temperature of liquid air ( - 191C.) without being killed. With regard 

 to this infection, Minchin and Thomson have shown that the rat flea, 

 ceratophylhis fasciatus, transmits the parasite by the cyclical method 

 (mechanical infection not having been proved). The flea becomes infec- 

 tive about a week after biting, and remains infective for a long period, 

 possibly for the rest of its life. Infection may also take place through 

 another species of flea and through a louse. 



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 defined areas or belts characterised by heat and damp, sometimes 

 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. This statement may, how- 

 ever, require modification if Tr. rhodesiense (v. infra) prove to be a 

 strain of Tr. brucei. Modern knowledge on the subject dates from 

 the discovery made by Bruce in 1894 that the blood of animals suffer- 

 ing 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 



