878 PATHOGENIC MICROORGANISMS 



observers, moreover, confirmed the fact that infection could be 

 experimentally produced by injections of blood or blood serum taken 

 from patients during the first three days of the disease. They 

 showed that blood taken after the fourth day was no longer in- 

 fectious: that 0.1 c.c. of serum sufficed for infection and finally 

 that no infection could take place through excoriations upon the 

 skin. They furthermore confirmed the observation of Carroll that 

 the virus of the disease could pass through the coarser Berkefcld 

 and Chamberland filters, passing through a Chamberland candle 

 "F" but held back by the finer variety known as "B." 



The fundamental factors of yellow-fever transmission thus dis- 

 covered, we are in possession of logical means of defense. The most 

 important feature of such preventive measures must naturally center 

 upon the extermination of the transmitting species of mosquito. 



Stegomyia fasciata or calopus is a member of the group of 

 ' ' Culicidae. " It is more delicately built than most of the other 

 members of the group culicidae, is of a dark gray color, and has 

 peculiar thorax-markings which serve to distinguish it from other 

 species. The more detailed points of differentiation upon which 

 an exact zoological recognition depends are too technical to be 

 entered into at this place. Briefly described, they consist of lyre-like 

 markings of the back, unspotted wings, white stripes and spots on 

 the abdomen, and bandlike 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 7 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 fatigens, 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 development of the yellow-fever 

 parasite. 



The limitation of yellow fever to tropical countries 8 is explained 

 by the fact that stegomyia develops only in places where high 

 temperatures prevail. The optimum temperature for this species 

 lies between 26 and 32 C. At 17 C. it no longer feeds, and 

 bcomes practically paralyzed at 15 C. In order to thrive, the 



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



8 Otto, in Kolle und Wassermann, "Handbuch," etc., 11, Erganzungsband. 



