PROPHYLAXIS. 



719 



The toxic substance appears to have a strong af- 

 finity for the parenchymatous organs, particularly 

 the liver and kidney. 



The essential principles of prophylaxis have prophylaxis. 

 been alluded to: 1, the destruction of breeding 

 places for the mosquito as described in the section 

 on malaria; 2, the isolation of patients, screened, 

 to exclude mosquitoes ; 3, the destruction of mos- 

 quitoes found in infected houses or ships; 4, the 

 individual factor of avoiding the bites of mos- 

 quitoes, which involves the screening of houses, 

 and individual care. One may go about more 

 safely in the middle of the day than before 9 a. 

 m. and after 3 p. m. For the disinfection of 

 houses, i. e., for the destruction of mosquitoes, two 

 pounds of tobacco or two pounds of pyrethrum 

 powder per 1,000 cubic feet of space may be burned 

 after the rooms are sealed. When smaller quan- 

 tities are used the insects may be only stupified, 

 and should be collected and burned (Rosenau, Par- 

 ker, Beyer and Pothier) . Sulphur dioxid is highly 

 efficient, but formaldehyd is valueless as an in- 

 secticide (Rosenau). 



The negro is less susceptible to yellow fever than 

 the white man and in him the mortality is lower. 

 Among the natives the mortality is from 7 to 10 

 per cent., among the whites from 20 to 80 per cent. 

 (Scheube). The statement that Caucasians may 

 become "acclimated" so that they are less suscep- 

 tible needs additional investigation. It seems im- 

 possible that acclimatization could mean anything 

 else than active immunization. Children and the 

 aged are attacked less frequently than those be- 

 tween the ages of ten and thirty. 



An attack of yellow fever, whether experimental 

 or natural, confers immunity of long or lasting du- 





