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20 Confirmation and extension of Ross's work.—Ross's observations were quickly confirmed and elaborated by the Italians, by Daniels, and by Koch. Grassi has shown that several species belonging to the genus Anopheles, more particularly—at all events as regards Italy—Anopheles maculipennis, are the special mosquito-hosts of the malaria parasites of man. Step by step he traced the crescent-forming and the non-crescent-forming malaria parasites through their mosquito hosts, finding that in their evolution they closely resembled that which Ross had so successfully demonstrated for the avian plasmodium, and had so clearly foreshadowed and partly demonstrated for the malaria parasite of man. In conjunction with Bignami he repeated successfully in man Ross's experiment of conferring malarial disease by mosquito bite. Bastianelli, Celli, Dionisi, Buchanan, and many others have confirmed Ross's statements, and have added to our knowledge of the extracorporeal cycle of the malaria parasite.

Finally, on behalf of the Colonial Office and the London School of Tropical Medicine, with the assistance of Drs. Sambon and Low, I instituted two experiments which dispose for good and all of any objections that otherwise might have been advanced against the theory. Drs. Sambon and Low, Mr. Terzi, their servants and visitors, lived for the three most malarial months of 1900 in one of the most malarial localities of the Roman Campagna—Ostia—in a hut from which mosquitoes were excluded by a simple arrangement of wire gauze on the doors and windows. They moved freely about in the neighbourhood during the day, exposed themselves in all weathers, drank the water of the place, often did hard manual work, and beyond retiring from sunset to sunrise to their mosquito-protected hut observed no precautions whatever against malaria. They took no quinine. Although their neighbours, the Italian peasants, were each and all of them attacked with malaria, the dwellers in the mosquito-proof hut enjoyed an absolute immunity from the disease. Whilst this experiment was in progress, mosquitoes