In the other building there was a screen partition dividing the space into two compartments, one containing 15 contaminated mosquitoes, the other with the same air but without mosquitoes. Controls occupying the mosquito free section remained free from yellow fever, while those exposing themselves in the mosquito-containing compartment developed yellow fever. One of these cases was bitten by mosquitoes contaminated thirty-nine days previously, a second one with fifty-one day insects and a third, who developed a severe case, was bitten by mosquitoes contaminated fifty-seven days previously. As above stated the Commission inoculated men subcutaneously with blood, taken from yellow fever patients in the first three days of the disease, with positive results. It was also found that if the blood was heated to 55°C., for ten minutes the virus was destroyed and, finally, it was found that the filtrate from a Berkefeld filter was infectious, thus showing that the virus was so minute as to pass through the pores of a filter which would hold back the smallest known bacterium (_filterable virus_). _Experiments of Guiteras._—During the summer of 1901 Doctor Guiteras, with a view to immunity production, repeated the experiments of the Army Commission and infected 8 persons, 3 of whom died. Gorgas thinks the greater severity of these infections may be explained by greater virulence of the virus developing in the mosquito during the hot season. It is known that the development of this virus requires fifteen to twenty days in winter as against the twelve days for summer. _Note._—Doctor Lazear, who had charge of the mosquito work of the Commission, tried to infect himself with experimental insects prior to his applying a twelve-day mosquito to Doctor Carroll. About three weeks later he was bitten by a mosquito which he did not at the time consider a _Stegomyia_. The attack of yellow fever which resulted from this bite ended fatally. _To summarize, the American Commission found:_ 1. That _B. icteroides_ had nothing to do with yellow fever. 2. That fomites was a negligible factor. 3. That _Stegomyia calopus_, when fed on the blood of a yellow fever patient, in the first three days of the disease, became contaminated and, after a period of twelve days, but not before, was capable of transmitting the disease to a susceptible person. Once infectious the mosquito so remained for the rest of life. [Illustration: FIG. 43.—_Aedes calopus_ (_Stegomyia calopus_), female. From P. H. Reports. FIG. 44.—_Aedes calopus_ (_Stegomyia calopus_), male. From P. H. Reports.]