Dr. Henry R. Carter had published a paper on certain observations of his made during the epidemic of 1898 in the neighborhood of Jackson, Mississippi. It had long been known to men practically familiar with yellow fever that, in general, when you took a patient suffering from yellow fever into a house where yellow fever had not before existed, the people in that house did not at once develop the fever. We explained this by stating that it was due to the fact that the germs of yellow fever went from the patient to favorable grounds for development about the house, and there underwent some development which enabled them to produce the disease in non-immune man. We thought that the dirtier and more unhygienic were the conditions of the house, the more favorable were the conditions for the further development of the germs. Dr. Carter recorded a number of cases where the houses were isolated and the conditions favorable for making the observations, and found that the average time from the introduction of a yellow-fever patient into a house until the first case of yellow fever was contracted in that house, was about seventeen days. These observations were published to the world. Dr. Reed was greatly impressed by this publication of Dr. Carter’s. He reasoned that if it were the mosquito which transmitted the disease, this period of extrinsic incubation must be due to a period of incubation in the mosquito. He says: We were also much impressed by the valuable observations made at Orwood and Taylor, Mississippi, during the year 1898 by Surgeon Henry R. Carter, U. S. Marine Hospital Service, “A Note on the Interval between Infecting and Secondary Cases of Yellow Fever, etc.” (Reprint from _New Orleans Medical Journal_, May, 1900.) We do not believe that sufficient importance has been accorded these painstaking and valuable data. We observe that the members of the yellow-fever commission of the Liverpool School of Tropical Medicine, Doctors Surham and Meyers, to whom we had the pleasure of submitting Carter’s observations, have been equally impressed by their importance. (_British Medical Journal_, Sept. 8, 1900, pp. 656-70.) The circumstances under which Carter worked were favorable for recording with considerable accuracy the interval between the time of arrival of infecting cases in isolated farmhouses and the occurrence of secondary cases in these houses. According to Carter, “the period from the first (infecting) case to the first group of cases infected at these houses, is generally from two to three weeks.” The house having now become infected, susceptible individuals thereafter visiting the houses for a few hours, fall sick with the disease in the usual period of incubation, one to seven days.