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 discover}' 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 

 igoo 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 e.xposing 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 



