Those were mosquitoes that had bitten a yellow-fever patient within the first three days of the illness. Men were selected, partly from the Army and partly from civil life, who had expressed and signed their willingness to submit themselves to experiments. I may state that one or two of the medical men also volunteered. Into the compartment with the fifteen mosquitoes a non-immune went, in the morning, in the afternoon, and on the following morning, and submitted himself to their bite; I do not know how long, but long enough to get a number of bites. Within five days he had the disease. At the same time, in the adjacent compartment, which was simply screened from these mosquitoes by a wire netting, for twenty-one consecutive nights two non-immunes slept. They did not get the disease. Experiments of that nature were repeated on several occasions, demonstrating quite conclusively that so long as these infected mosquitoes were kept from biting, though there was only a screen between them, the individuals did not get yellow fever.

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Then, experiments were made, on a very extensive scale, to determine whether the disease was conveyed by means of fomites: that is to say, whether, as was usually supposed, the disease was carried by infected clothing, and by the excreta of the patients, and by the vomit. For that purpose, the clothing and material, soiled by the vomit, and by the blood, and by the stools of the patients, were placed in one of these rooms; and a group of non-immunes slept in contact with this clothing-in some instances between the actual sheets of the beds in which these patients had died-for twenty-one consecutive nights. That experiment was repeated with a second set of nonimmunes, sleeping, as I say, with the bed-linen and with the soiled materials of patients who had died of the disease. Not one of them took yellow fever. Then these men were

The mosquito-proof hut near Ostia, in which Sambon and Low and Terzi lived through the malaria season, 1900, without taking a grain of quinine, and without being infected with malaria. See the paper by Sir Patrick Manson, K.C.M.G., M.D., F.R.S., in the British Medical Journal, September 1900.

The mosquito hut at Camp Lazear, in which the American Commission in 1900 proved that yellow fever is conveyed, not by infected clothing, but by infected mosquitoes. See the "Life of Walter Reed," by H. A. Kelly, M.D.

subsequently experimented upon by placing them in the section of the house with the infected mosquitoes, and in each instance they took the disease.

"Altogether twenty-two soldiers submitted themselves to the experiments, and twenty-two took the disease: fortunately none of those cases proved fatal. One fatal case was a former assistant, Dr. Lazear, who had been for several years in charge of my clinical laboratory. He submitted himself to the bite of an infected mosquito, and three days subsequently developed the disease and died.

"The mosquito, to become infective, must bite the yellow-fever patient within the first three days of the patient having the disease. The mosquito itself is not infective under a period of twelve days: the mosquito may bite an individual anywhere up to the twelfth day after receiving the infection, without being infective. Then it remains infective all through the rest of its life.

"Of course, the interesting practical point comes out, that this series of experiments has already revolutionised life in those regions. Havannah within the next two years was cleared of yellow fever, the first time in the 300 years of its existence. . . . This is the kind of discovery that will revolutionise conditions of life in the Tropics. The discovery of the malarial parasite, and the discovery of the relations of yellow fever with the mosquito, will enable the Panama Canal to be built. Without those two investigations, the probability is that it could not be built it would cost an enormous sacrifice of human life, just as happened with the French. Now, there are 20,000 whites on the Isthmus at work; of course, nearly all of these are non-immune. There has been practically no yellow fever, and, what is much more important-because it was not the yellow fever that killed the French to the same extent-there is no malaria.

This chart shows the progress of yellow fever in Havana during the epidemic year ending March 1, 1901, when the sanitary authorities were putting forth every effort known to sanitary science to control the disease. This was in the "pre-mosquito period." The continuous line gives the number of cases; the dotted line gives the mortality. (From Dr. Kelly's "Life of Walter Reed." New York: McClure, Phillips & Co., 1907.)

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