THE YELLOW-FEVER MOSQUITO 105 



year of the last century an American Commission, 

 consisting of Drs. Walter Reed, Carroll, Agra- 

 monte, and Lazear, investigated the whole 

 subject, and, taking extraordinary risks, were 

 able to prove that the infection was not 

 conveyed by contact or through the air, or 

 from bedding or clothes soiled by the dejecta 

 of yellow-fever patients, .but by a mosquito 

 of the genus Stegomyia. Whatever the virus 

 is, it is invisible, even under the highest powers 

 of the microscope. It can be filtered through 

 a Berkefeld filter. It is destroyed by heating 

 to 55° C. If the blood of a yellow fever 

 patient, during the first three days, be inocu- 

 lated into a healthy man he gets yellow fever, 

 and it is only during the first three days that 

 the blood is infective. On the other hand, the 

 mosquito is incapable of transferring the 

 disease until the unknown organism has been 

 in its own body for at least ten or twelve days. 

 The mosquito in question belongs to the 

 species Stegomyia calopus (Blanchard), or, as 

 it is more often called in English text-books, 

 Stegomyia fasciata (Fabricius). The genus 

 Stegomyia differs from other Culicidae in having 

 a dark grey or black colour, whilst the Culicidae 

 are as a rule browner. Stegomyia also has 

 silver-white spots and silver glistening scales, 

 especially on the back of the legs and on the 

 abdomen. The grown-up mosquito is com- 



