INTRODUCTION
THE ETIOLOGY OF TROPICAL DISEASES
The title which I have elected to give to this work, Tropical Diseases, is more convenient than accurate. If by "tropical diseases" be meant diseases peculiar to the tropics, then half a dozen pages might have sufficed for their description; for, at most, only two or three comparatively unimportant diseases strictly deserve that title. If, on the other hand, the expression "tropical diseases" be held to include all diseases occurring in the tropics, then the work would require to cover almost the entire range of medicine; for the diseases of temperate climates are also, and in almost every instance, to be found in tropical climates.
I employ the term "tropical" in a meteorological, rather than in a geographical, sense, meaning by it sustained high atmospheric temperature; and by the term "tropical diseases" I wish to indicate diseases occurring only, or which from one circumstance or another are specially prevalent, in warm climates.
It must not be inferred from this, however, that high atmospheric temperature is the sole and direct cause of the bulk of tropical diseases. The physiological machinery of the human body is so adjusted that great variations of atmospheric temperature can be supported by man with impunity. Indeed, although temperature acts as an important pathogenic factor, it is very rarely that it does so directly. Extreme cold may cause frost-bite; exposure to the sun, sun erythema, sun headache, and symptomatic fever; a hot atmosphere, heat-exhaustion; prolonged residence in hot moist climates, vague, ill-defined conditions of debility; profuse sweating from heat of climate,
