Nothing illustrates more clearly the interdependence of the sciences than the reciprocal impulse given to new researches in pathology and entomology by the discovery of the part played by insects in the transmission of disease. The flea, the louse, the bedbug, the house fly, the mosquito, the tick, have all within a few years taken their places as important transmitters of disease. The fly population may be taken as the sanitary index of a place. The discovery, too, that insects are porters of disease has led to a great extension of our knowledge of their life history. Early in the nineties, when Dr. Thayer and I were busy with the study of malaria in Baltimore, we began experiments on the possible transmission of the parasites, and a tramp, who had been a medical student, offered himself as a subject. Before we began, Dr. Thayer sought information as to the varieties of mosquitoes known in America, but sought in vain: there had at that time been no systematic study. The fundamental study which set us on the track was a demonstration by Patrick Manson,(3) in 1879, of the association of filarian disease with the mosquito. Many observations had already been made, and were made subsequently, on the importance of insects as intermediary hosts in the animal parasites, but the first really great scientific demonstration of a widespread infection through insects was by Theobald Smith, now of Harvard University, in 1889, in a study of Texas fever of cattle.(4) I well remember the deep impression made upon me by his original communication, which in completeness, in accuracy of detail, in Harveian precision and in practical results remains one of the most brilliant pieces of experimental work ever undertaken. It is difficult to draw comparisons in pathology; but I think, if a census were taken among the world's workers on disease, the judgment to be based on the damage to health and direct mortality, the votes would be given to malaria as the greatest single destroyer of the human race. Cholera kills its thousands, plague, in its bad years, its hundreds of thousands, yellow fever, hookworm disease, pneumonia, tuberculosis, are all terribly destructive, some only in the tropics, others in more temperate regions: but malaria is today, as it ever was, a disease to which the word pandemic is specially applicable. In this country and in Europe, its ravages have lessened enormously during the past century, but in the tropics it is everywhere and always present, the greatest single foe of the white man, and at times and places it assumes the proportions of a terrible epidemic. In one district of India alone, during the last four months of 1908, one quarter of the total population suffered from the disease and there were 400,000 deaths--practically all from malaria. Today, the control of this terrible scourge is in our hands, and, as I shall tell you in a few minutes, largely because of this control, the Panama Canal is being built. No disease illustrates