The infected clothing building, 14 × 20 feet in size, was purposely so constructed as to exclude anything like efficient ventilation, but was thoroughly screened to prevent the entrance of mosquitoes. Into this building were brought sheets, pillow-slips, blankets, etc., contaminated by contact with cases of yellow fever and their discharges,—many of them purposely soiled with a liberal quantity of black vomit, urine, and fecal matter from patients sick with yellow fever. Nothing could better serve as the fomites which were supposed to convey the dread disease.
Three non-immunes unpacked these articles, giving each a thorough handling and shaking in order to disseminate through the air of the room the specific agent of the disease. They were then used in making up the beds which the volunteers occupied each night for a period of twenty days. The experiment was repeated three times, volunteers even sleeping in the soiled garments of yellow fever victims but in not a single case was there the slightest symptom of disease. The theory of the spread of yellow fever by fomites was completely demolished.
The infected mosquito building, equal in size to its companion, was the antithesis as far as other features were concerned. It was so constructed as to give the best possible ventilation, and bedding which was brought into it was thoroughly sterilized. Like the infected clothing building it was carefully screened, but in this case it was in order to keep mosquitoes in it as well as to prevent entrance of others. Through the middle of the room ran a mosquito-proof screen.
On December 5, 1900, a non-immune volunteer who had been in the quarantine camp for fifteen days and had had no other possible exposure, allowed himself to be bitten by five mosquitoes which had fed on yellow fever patients fifteen or more days previously. The results were fully confirmatory of the earlier experiments of the Commission—at the end of three days, nine and a half hours, the subject came down with a well marked case of yellow fever.
In all, ten cases of experimental yellow fever, caused by the bite of infected mosquitoes were developed in Camp Lazear. Throughout the period of the disease, other non-immunes slept in the little building, separated from the patient only by the mosquito-proof screen, but in no circumstances did they suffer any ill effects.
It was found that a yellow fever patient was capable of infecting mosquitoes only during the first three or four days after coming down with the disease. Moreover, after the mosquito has bitten such a patient, a period of at least twelve days must elapse before the insect is capable of transmitting the disease.
Once the organism has undergone its twelve day development, the mosquito may remain infective for weeks. In experiments of the Commission, two of the mosquitoes transmitted the disease to a volunteer fifty-seven days after their contamination. No other volunteers presenting themselves, one of these mosquitoes died the sixty-ninth and one the seventy-first day after their original contamination, without it being determined whether they were still capable of transmitting the disease.
So carefully carried out was this work and so conclusive were the results that Dr. Reed was justified in writing:
"Six months ago, when we landed on this island, absolutely nothing was known concerning the propagation and spread of yellow fever—it was all an unfathomable mystery—but today the curtain has been drawn—its mode of propagation is established and we know that a case minus mosquitoes is no more dangerous than one of chills and fever."
The conclusions of the Commission were fully substantiated by numerous workers, notably Dr. Guiteras of the Havana Board of Health, who had taken a lively interest in the work and whose results were made known in 1901, and by the Brazilian and French Commission at Sao Paulo, Brazil, in 1903.