552 TRYPANOSOMIASIS 



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 agglomer- 

 ate 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. This 

 trypanosome is very resistant to cooling, and has been exposed 

 for fifteen minutes to the temperature of liquid air ( - 191 C.) 

 without being killed. The means by which the rat becomes 

 infected naturally is not known, but probably this comes about 

 by the bite of a flea or 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, 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 



