rain and wind; clothe with a view to avoiding chill; live temperately." On the Calcutta docks are painted the words: "Beware of the sun."
Tropical Diseases.—Certain diseases are so much at home in the tropics that they have come to be known as tropical diseases. This designation, however, does not mean diseases confined to the tropics, but is employed in a meteorological sense for diseases associated with, but not solely, or even necessarily directly due to, high temperatures. Sir Patrick Manson has made it clear that the difference between the diseases of tropics and extra-tropics lies in the specific cause of these diseases. For the development of certain disease germs, tropical temperatures are required; or a third organism, other than the disease germ itself and man, may be necessary. If this organism is a tropical species, as in the case of the tsetse fly, the disease is a tropical disease. "The more we learn," Dr. Manson says, "about these [tropical] diseases, the less important in its bearing on their geographic distribution, and as a direct pathogenic agency, becomes the rôle of temperature per se, and the more the influence of the tropical fauna." The fact that plague, and leprosy, and to some extent cholera as well, are practically limited to the tropics, is the result of modern sanitary precautions in the extra-tropics. The unsanitary conditions among tropical peoples favor the spread of these, and similar, diseases, and not the climate per se. Nevertheless, it is clear that these very unsanitary conditions are "more or less an indirect outcome of tropical climate."
General Conclusions: the Tropics.—All parts of the equatorial zone are not equally disagreeable or hostile to the white race. Many elderly persons, and those who are overworked, may find rest from nervous tension in the enervating climate of the tropics. Much-needed relief from the heat at sea-level may be obtained at tropical mountain stations, and many of these have become well-known health resorts. In India, the hill stations are crowded during the hot months by civilian and military officials, and it has been well said that India is governed from 7,000 feet above sea-level.
Acclimatization of the White Race in the Tropics.—The acclimatization of the white race in the tropics is a question of vast importance. Upon it depend the control, government and utilization of the tropics. It is a very complex problem, and it has been much discussed. It is complicated by race, diet, occupations, habits of life and the like. To discuss it fully is impossible at this time. The gist of the matter is this: white residents from cooler latitudes, on coming into the tropics, must adjust themselves physiologically to the new climatic conditions. During this adjustment there is more or less strain on various organs of the body. The strain may be too severe, then the individual suffers. The adjustment is usually much retarded and hindered by a persistence in habits of food, drink and general manner of living which, however well suited to the home climate, do not fit tropical conditions. Dur-
