674 DISEASES OF UNKNOWN ETIOLOGY 



unspotted wings, white stripes and spots on the abdomen, and band- 

 like white markings about the metatarsi and tarsi of the third pair 

 of legs. The peculiar power of transmitting yellow fever possessed 

 by this species is explained by Marchoux and Simond ^ by the fact 

 that Stegomyia fasciata is unique among culicidae in that the female 

 lives for prolonged periods after sucking blood. Among other species 

 — Culex fatigans, Culex confirmatus, and most others — the female lays 

 its eggs within from two to eight days after feeding on blood and rarely 

 lives longer than the twelfth day — the time necessary for the develop- 

 ment of the yellow-fever parasite. 



The limitation of yellow fever to tropical countries ^ is explained by 

 the fact that stegomyia develops only in places where high tempera- 

 tures prevail. The optimum temperature for this species lies between 

 26° and 32° C. At 17° C. it no longer feeds, and becomes practically 

 paralyzed at 15° C. In order to thrive, the species requires a temperature 

 never going below 22° C. at night and rising regularly above 25° C. 

 during the day. The females only are dangerous as sources of infection. 

 The insect, like Anopheles, has the peculiarity of feeding chiefly at night. 



Experiments done by Reed, Carroll, Agramonte, and Lazear,' to 

 ascertain whether the power of infecting was hereditarily transmissible 

 from the mosquito to following generations, were negative. A positive 

 result, however, has been reported by Marchoux and Simond.* This 

 question must still await more extensive research. 



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 rela- 

 tive immunity of dark-skinned races, however, is explained possibly 

 by the fact that the stegomyia prefers to attack light-colored surfaces. 



A single attack seems to protect against subsequent infection 

 throughout life. 



Artificial immunization has, so far, been unsuccessful. Relative 

 immunity was produced, however, by Marchoux, Salimbeni, and 

 Simond, 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. 



1 Marchoux and Simond, Ann. de I'inst. Pasteur, 1906. 



2 Otto, in KoUe und Wassermann, "Handbuch," etc., 11, Erganzungsband. 

 « Loc. cit. 



» Marchoux and Simond, Comptes rend, de la soc. de biol., 59, J905. 



