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 better the progressive evolution of scientific medicine.  It is one of the oldest of known diseases.  The Greeks and Graeco-Romans knew it well.  It seems highly probable, as brought out by the studies of W.H.S.  Jones of Cambridge, that, in part at least, the physical degeneration in Greece and Rome may have been due to the great increase of this disease.  Its clinical manifestations were well known and admirably described by the older writers.  In the seventeenth century, as I have already told you, the remarkable discovery was made that the bark of the cinchona tree was a specific.  Between the date of the Countess’s recovery in Lima and the year 1880 a colossal literature on the disease had accumulated.  Literally thousands of workers had studied the various aspects of its many problems; the literature of this country, particularly of the Southern States, in the first half of the last century may be said to be predominantly malarial.  Ordinary observation carried on for long centuries had done as much as was possible.  In 1880, a young