Insects and Disease 
631 
organism, and that this organism is disseminated by mosquitoes, infection 
being accomplished only by the puncture of a mosquito, it is a curious fact 
that the causative germ or parasite has not yet been isolated; in other words, 
is not yet specifically known. Whether bacterium or sporozoon, whether 
inhabiting the blood solely or occurring also in other tissues, answers to 
these questions remain to be discovered. Numerous claims have been made 
by various physicians of the discovery of the parasite; the latest claim has 
been published within the last few months, but so far none of these reputed 
determinations of the yellow-fever parasite has been proved to the satisfac¬ 
tion of scientific men. That the yellow-fever germ, whatever it is, is how¬ 
ever actually carried by mosquitoes, and apparently in no other way , and that 
the dissemination of the disease thus depends upon the intervention and aid 
of mosquitoes, are facts that have been proved largely through the able and 
courageous work of American investigators. 
An early suggestion that mosquitoes might be the agents in spreading 
yellow fever came from an Havana physician, Dr. Carlos Finlay. His 
theory was based chiefly on observations of the correspondence between 
an abundance of mosquitoes and a period of increase of yellow fever. In 
1900 an Army Yellow Fever Commission, composed of Major Walter C. Reed, 
surgeon, U. S. A., and three acting assistant surgeons was appointed by 
Surgeon-General Sternberg to investigate the disease. Two members of 
the Commission, Major Reed and Dr. Lazear, lost their lives from the attacks 
of the disease they were studying. The Commission was soon able to report 
that yellow fever followed the bite of mosquitoes of the species Stegomyia 
jasciata , after the mosquitoes had first been allowed to suck blood from 
yellow-fever patients. Soon after it was able to report that yellow fever did 
not follow as a result of exposing non-immune subjects to contact with clothes 
or bedding or other belongings of patients actually suffering and dying from 
yellow fever. On the basis of these discoveries the Commission made certain 
crucial experiments whose outcome is convincing proof of the facts of the 
transmission of the disease by mosquitoes, and that it is transmitted in no 
other way. 
A small house was built, thoroughly screened against mosquitoes. In 
this house seven non-immune persons lived during sixty-three days; three 
of them occupied the room each night for twenty days, sleeping on sheets, 
pillow-cases, and blankets brought from beds occupied by yellow-fever patients 
in Havana, soiled by their discharges. Some of the bedding and clothing worn 
by the subjects in the yellow-fever house were purposely infected with the 
discharges of a fatal case of yellow fever. During all the sixty-three days the 
average temperature of the house was kept at 76.2° F., a considerable amount 
of humidity was maintained, and little sunlight or freely circulating air was 
admitted, all of these conditions being highly favorable for the development 
