PREVENTION OF SLEEPING SICKNESS 107 



constantly bitten. The deadly epidemic of sleeping sickness in 

 Uganda was fostered by the fishing industry. It has been sug- 

 gested that by importing dried sea fish to trade for agricultural 

 products the natives might be induced to change their occu- 

 pation. In Congo the rubber industry is the one which is the 

 most deprecated. Personal protection against tsetse flies is dis- 

 cussed on page 501. 



Another method of protection is suggested by the researches 

 of Van den Branden who has found that a single injection into 

 the veins of salvarsan or neosalvarsan or some of their compounds 

 will sterilize the blood against trypanosomes for a period of several 

 months — in the case of salvarsan copper for 19 to 24 months. 



Infected individuals should not only be kept away scrupulously 

 from places where flies can possibly get access to them, but should 

 also be prevented from traveling to new places. Some strains 

 of trypanosomes seem to be much more virulent than others, 

 and the introduction of a virulent strain to a region where a 

 mild strain previously existed has occasionally caused a con- 

 siderable increase in the disease. The strict quarantine of in- 

 fected persons, while unquestionably worth while, is not a meas- 

 ure sufficient to stamp out the disease, since many of the wild 

 animals of Africa serve as reservoirs for the disease, harboring 

 the parasites in their blood but not succumbing to them. Tsetse 

 flies on the shores and islands of Lake Victoria, after the entire 

 population had been stringently kept away for three years so 

 that the flies could not have fed on human blood during this time, 

 were found to be still infective. The situtunga antelope and 

 other wild game undoubtedly served as a reservoir. It has been 

 suggested that a war of extermination be made on the rich and 

 interesting wild game of the countries infected with the Rho- 

 desian trypanosome in the hope of checking the rapid spread of 

 the disease (see p. 503). It has recently been shown by Taute, 

 however, that a large proportion of the wild game of Nyasa- 

 land is infected with a trypanosome indistinguishable from 

 Trypanosoma rhodesiense in all its general characters but non- 

 pathogenic to man. Taute evidently had the courage of his 

 convictions since he tried several times to infect himself with 

 this trypanosome without success. It is possible, however, that 

 a high natural immunity to the parasite may exist in many people, 

 and thus explain Taute's negative results. 



