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residences of the nonimmunes. If a female adult stegomyia chanced to enter a screened house, it would have to bite a yellow fever patient within the first three days of the patient's illness. As all sick persons are removed at once to hospital wards which are kept mosquito proof, the chances of the female stegomyia getting at the patient before he is removed is very small. Then, even if the stegomyia did happen to get at the patient during the three-day period during which it can become infected, it can not transmit yellow fever until twelve days after biting the patient. Being in a screened house, and having gorged itself, it is too heavy for continued flight, and can not get out. Preparations for fumigation are always in readiness, and it is easy to see how the infected stegomyia would be killed before it could transmit yellow fever. During the yellow fever epidemic of 1905, before the residences of nonimmunes were screened, the yellow-fever wards were effectively screened, and at no time during the entire period did any of the nonimmune physicians or nurses attending the patients become infected. The value and necessity of screening the houses of nonimmunes is evident, as far as yellow fever possibilities are concerned, and the low malarial sick rate of American children and women living in screened houses in the Zone speaks for itself. (See the following table:)