In the course of my work I have of late treated many persons suffering from recurrences of malaria contracted abroad, and some of these or their friends have had the curiosity to ask whether there is any likelihood of the disease becoming established once more in England where, in parts, mosquitoes capable of carrying malaria still abound. Doubtless the same thought has occurred to many others. The answer to the question is, No. It is possible, of course, that a relapsing patient favourably situated might chance to infect some of the local mosquitoes, and a few cases of malaria result; but the concentration of contagion, to use an old phrase, would fall short of the degree necessary to maintain a lasting supply of infected insects, and the imported disease accordingly would soon die out. For centuries malaria was firmly established in certain endemic centres in England, particularly the Fen country, the marshes of the Thames Estuary, the marshes of South-East Kent, and the low-lying districts around Bridgewater. In London itself, the Lambeth and Westminster marshes were notorious. But not all the malaria that developed in London was contracted on the spot. The liability of hop-pickers to the infection-which showed itself only in the following Springwas well known; and Defoe says that Londoners who go shooting in the Essex marshes, often return with an Essex ague on their backs, which they find a heavier load than the fowls they have shot. From these permanent homes, every now and again, the disease spread in epidemic form during very warm summers, especially if several such followed in succession. Since the development of parasites in the mosquito ceases when the temperature falls below 600 F., it was only during a relatively prolonged spell of hot weather that the mass infection of insects necessary to produce an epidemic could come about. The last of these extensive epidemics occurred in I858 and 59, two hot summers, and preceded by that of I857 also unusually hot. It might surprise Londoners to know that of all the patients treated at St. Thomas's Hospital during the decade i85o-6o, I in 20 was suffering from ague, and in bad years this average figure was much exceeded. At least 30 per cent of the patients treated at Gravesend Hospital about this time were cases of ague, and it is stated that nearly every person in the district suffered to a greater or less degree. After i86o there was a marked decline in.the