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118 in May 1900. These observations showed that between the occurrence of the first cases at isolated farmhouses and of the first succeeding groups of cases at the same houses there was a lapse of 2 or 3 weeks, while subsequent cases developed in a shorter period of incubation of from 1 to 7 days. To Dr. Carter, this indicated that there was in a life cycle of the infecting organism an intermediate host, such as the mosquito, which harbored the cause of the disease for a period before passing it on. 17

To the work of Ross and of Carter, Reed added a perspicacious observation of his own at Pinar del Rio, 100 miles west of Havana, where yellow fever broke out in the American garrison. One of the victims was a general prisoner, under confinement in the guardhouse since 6 June 1900, who fell sick on 12 July and died on the 18th, and was autopsied by Dr. Agramonte on the 19th. The fact that this guardhouse prisoner, effectively in quarantine insofar as yellow fever exposure by ordinary means was concerned, should sicken and die of yellow fever, led to the conjecture "that, perhaps, some insect capable of conveying the infection, such as the mosquito, had entered through the cell window, bitten this particular prisoner, and then passed out again." This, Dr. Reed added, was only a supposition, but it was a supposition no doubt strengthened by the reflection that iron bars at the windows and armed guards at the door could keep the prisoner from visiting places of infection, but would not keep infected mosquitoes from visiting the prisoner. 18

And then there was Dr. Finlay and his long-held mosquito theory which he had "ingeniously discussed," as Reed put it, as early as 1881 and had repeated since, notably in papers published in 1891, 1894, 1895, and as recently as 1899. Although the Cuban doctor had "no results in support of his theory" Reed wrote, * * * the argument in favor of an intermediate host seemed so strong * * * that investigation along this line was determined upon." 19

Already, around the 1st of July, members of the Yellow Fever Board had called upon Dr. Finlay and had received his most cordial cooperation, for which Reed expressed "sincere thanks." The doctor turned over larvae and eggs of the suspected species of mosquito, which became the foundation of the breeding stock used in the experiments. Dr. Lazear, who had had entomologic training and experience with mosquitoes in Italy, was placed in charge of the work of