656 TRYPANOSOMIASIS 



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 ftagella 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 (-191° C.) without being killed. Minchin and 

 Thomson have shown that the rat flea, ceratophyllus fasciatus, transmits 

 the parasite by the cyclical method, infection probably occurring through 

 the fleas or their faeces being swallowed. The flea becomes infective 

 about a week after biting, and remains infective 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 {glossvna 

 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 within recent years 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 



