DISINFESTATION 67 



these things who lives in a country where they 

 abound. Be he never so careful, sooner or later 

 he does get bitten by one of the insects, and if 

 the one that bites happens to be infected with 

 the disease he is liable to contract it. Sanitarians 

 are endeavouring to find one means or another 

 of destroying these insects, and in places with 

 marked success. For example, the work on the 

 Panama Canal was impeded and finally stopped 

 by the two mosquito-borne diseases, malaria and 

 yellow fever, until methods were adopted for 

 preventing the breeding of mosquitoes, with con- 

 sequent reduction in the incidence of the maladies. 

 The work was then resumed and successfully 

 completed. 



The control of mosquitoes is a very difficult 

 matter, involving vast schemes of drainage, and 

 treatment of water that cannot be drained. 

 The complete disappearance of this pest is never 

 to be looked for. The preventive methods must 

 be continued always, or the locality freed from 

 them will become quickly invaded again by the 

 immigration of others from neighbouring locali- 

 ties. The prophylaxis against the sleeping sick- 

 ness of Africa is even more difficult, since the 

 country involved swarms with large animals on 

 which the tsetse-flies live, and the peculiar breed- 

 ing habits of the flies make them most difficult 

 insects to attack. In this case it has been found 

 necessary to depopulate the areas where sleeping 

 sickness most prevails, pending some more satis- 



