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. Throughout the work of the Army Commission and down to the present time many fruitless efforts have been made to discover the specific organism of yellow fever. It was clearly established that the claims of Sanarelli for _Bacillus icteroides_ were without foundation. It was found, too, that whatever the infective agent might be it was capable of passing through a Berkefeld filter and thus belongs to the puzzling group of "filterable viruses." It was further found that the virus was destroyed by heating up to 55° C for ten minutes. It is generally believed that the organism is a Protozoan. The question of the hereditary transmission of the yellow fever organism within the mosquito was left unsettled by the Army Commission, though, as we have seen, it was raised by Finlay. Marchoux and Simond, of the French Commission devoted much attention to this phase of the problem and basing their conclusions on one apparently positive case, they decided that the disease could be transmitted through the egg of an infected _Aëdes calopus_ to the second generation and thence to man. The conclusion, which is of very great importance in the control of yellow fever, has not been verified by other workers. Once clearly established that yellow fever was transmitted solely by mosquitoes, the question of the characteristics, habits, and geographical distribution of the insect carrier became of vital importance.