YELLOW FEVER 673 



All of the non-immunes taking part in these experiments were 

 American soldiers. Four of them were later shown to be susceptible 

 to yellow fever by the agencies of mosquito infection or blood-injection. 



The results obtained by the investigations of this commission may 

 be summarized, therefore, as follows: 



Yellow fever is acquired spontaneously only by the bite of the 

 Stegomyia fasciata. It is necessary that the infecting insect shall have 

 sucked the blood of a yellow-fever patient during the first four or five 

 days of the disease, and that an interval of at least twelve days shall 

 have elapsed between the sucking of blood and the reinfection of an- 

 other human being. Sucking of the blood of patients advanced beyond 

 the fifth day of the disease does not seem to render the mosquito infec- 

 tious, and at least twelve days are apparently required to allow the para- 

 site to develop within the infected mosquito to a stage at which rein- 

 fection of the human being is possible. 



The results of the American Commission were soon confirmed by 

 Guiteras ' and by Marchoux, Salimbeni, and Simond.^ These latter ob- 

 servers, moreover, confirmed the fact that infection could be experi- 

 mentally 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 infectious: 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 Berkefeld and Chamberland filters, — ^passing through a 

 Chamberland candle "F"butheld back by the finer variety known as" B." 



The fundamental factorsof yellow-fever transmission thus discovered, 

 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 " Culi- 

 cidae." It is more delicately built than most of the other members of 

 the group cuKcidae, 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 recog- 

 nition depends are too technical to be entered into at this place. 

 Briefly described, they consist of lyre-like markings of the back, 



' Guiteras, Rev. d. m^d. trop., Jan., 1901, and Am. Med., 11, 1901. 

 * Marchoux, Salimbeni. and Simond, Ann. de I'inst. Pasteur, 1908. 

 44 



