Col. Gorgas first visited the Isthmus in 1904. In a little pamphlet which I have before me he then described simply the essence of the problem he had to meet. He found camped on a hill, perfectly drained and supplied with good water, 450 marines--who of course were men of exceptionally good physique, robust and vigorous. Yet in four months 170 out of the 450 were infected with malaria, and Col. Gorgas said, “if these men were our laborers, working daily in Culebra Cut, exposed to the sun and weather, many of these cases would be severe in type and at the end of the year we would be approaching the mortality of the French”. The cause for the infection was apparent. Though the marines’ camp was clean and sanitary there was at the foot of the hill, on which it was perched, a village of 400 or 500 Jamaica negroes. Examination of the people showed that all suffered from chronic malaria. The marine strolling in the village would be bitten by a mosquito--the _anopheles_ which is partial to malaria--which had already bitten an infected negro. The result was the spread of the infection among the marines. As Col. Gorgas put it, “The condition is very much the same as if these four or five hundred natives had the smallpox and our marines had never been vaccinated”. To correct this condition he proposed, “to take this village, put it under a systematic scheme of inspection, whereby we will be able to control all water barrels and deposits of water, so that no mosquitoes will be allowed to breed, look after its street cleaning and disposal of night soil, etc., so as to get it in good sanitary condition, then have the population examined and recorded, so that we will have on a card a short history of each individual and keep track of them in this way. Those suffering from malaria will be put under treatment, and watched as long as the malarial parasite is found in the blood. I hope, in this way, to decrease to the smallest limit the number of _anopheles_, the malarial-bearing mosquito, and, at the same time, to gradually eliminate the human being as a source of infection, so that at the end of a year it will be entirely safe for an unacclimated man to live in this village”. [Illustration: THE WAR ON MOSQUITOES. I. The men are oiling the surface of the streams to kill the larvae] [Illustration: THE WAR ON MOSQUITOES. II. Burning the grass that affords cover]