628 TRYPANOSOMIASIS 



Manson, has shown that sometimes the termination of a case is 

 by the onset of typical sleeping sickness. There is now practi- 

 cally no doubt that the two conditions are etiologically identical. 

 The best authorities are agreed that morphologically no difference 

 between the Tr. gambiense and the Tr. ugandense can be 

 recognised, and from considerations of priority the former term is 

 now alone employed. 



The prevalence of trypanosomes in the blood of apparently 

 healthy natives has raised the question of the possibility of 

 tolerance existing and of immunity being established. It is 

 possible that both phenomena occur, that not every infection 

 results in multiplication of the parasite in the body of the 

 victim, and that in certain cases where multiplication does occur 

 a resistance is developed which enables the body to kill the 

 parasites. The occurrence of the mononuclear reaction is here 

 significant ; it has been suggested that, when this resistance is 

 weak, the organism gains entrance to the spinal canal, and that 

 then sleeping sickness results. 



The whole of the recent work on the disease is of the highest 

 interest and importance. The strongest evidence may be said 

 to exist that the Tr. gambiense is the cause of sleeping 

 sickness, and action taken on this supposition has had a very 

 important effect in checking the ravages of the disease in Uganda, 

 where the natives have been deported from the fly areas, and the 

 brushwood in which the insects lodge has been cut down in the 

 neighbourhood of ferries. 



Not much success has attended remedial efforts in those suffer- 

 ing from infection. Here attention has been chiefly concentrated 

 on the action of organic arsenical compounds, the application of 

 which in the shape of atoxyl was first recommended by Thomas. 

 A great range of such substances and also of aniline derivatives 

 has been investigated by Ehrlich and his co-workers, and under 

 certain conditions of artificial infection in animals a complete or 

 partial destruction of the parasites has followed administration 

 of these bodies, but their application to natural infections has 

 not as yet met with decided success. Sufficient, however, is 

 known to justify further investigations of a similar kind. It 

 has been observed that a tolerance of such reagents can be 

 developed by the trypanosomes, and this fact may complicate the 

 problem at issue. 



Other Pathogenic Trypanosomes. Apart from sleeping sick- 

 ness no other important disease of man has been found to be 

 associated with trypanosomal infection, but some observations 

 on a condition observed in Brazil may be alluded to. 



