884 PATHOGENIC MICROORGANISMS 



surface waters. Its flying radius is apparently not very large. 

 Unlike the Anopheles, its habits are diurnal, instead of nocturnal. 

 Rosenau states that experience of the epidemic in New Orleans in 

 1905 showed that this mosquito docs not fly far from its place of 

 birth. We take from the same writer the statement that, in order 

 to hold back the small mosquito, a mesh must be used containing 

 at least twenty strands to the inch. 



Prevention may, therefore, be summed up as consisting in screen- 

 ing of patients, screening of houses, destruction of mosquitoes within 

 houses by insecticides and fumigation and the painstaking removal 

 of all stagnant waters in the neighborhood of human habitations 

 with especial care to the screening of drinking water cisterns in 

 places where, as in Bermuda, drinking water is collected in rain 

 water receptacles. In places like Bermuda, the Stegomyia fasciata 

 is common, and yet there has been no case of yellow fever, we 

 understand, since 1869. 



Immunity. Natural immunity against yellow fever was formerly 

 assumed to exist in the negro race. More recent investigations have 

 not borne out this assumption. The negro soldiers of the American 

 army in Cuba were afflicted equally with the white troops. The 

 relative immunity of dark-skinned races, however, is explained pos- 

 sibly by the fact that the stegomyia prefers to attack light-colored 

 surfaces. 



A single attack seems to protect against subsequent infection 

 throughout life. 



Relative immunity was produced by Marchoux, Salimbeni, and 

 Simond, 22 by injections of the serum of convalescents, serum heated 

 to 55 C., and of defibrinated blood preserved for eight days in 

 vessels sealed with vaseline. 



Experimental work is being carried out by Noguchi on both 

 active and passive immunization by the use of his pure cultures 

 of the Leptospira icteroides. These experiments are being actively 

 carried out at the present time, but final results have not yet been 

 achieved. On the whole, however, the promise of this work is great 

 and extremely encouraging. It is especially encouraging in con- 

 sideration of the great similarity between this Leptospira and the 

 one of Weil's disease with which immunization experiments are also 

 full of promise. 



22 Marchoux, Salimbeni, and Simond, Ann. <le 1'mst. Pnsteur, -190.3. 



