TROPICAL MEDICINE. As medicine advances from the status of an art to that of a science, so do the bounds which demarcate tropical medicine become more faint. Few major diseases are restricted to the lower latitudes, and tropical medi cine, as here considered, embraces all those maladies which, for some reason, prevail especially in the tropics, though not neces sarily limited thereto. Some diseases lightly regarded to-day as essentially tropical are merely commensurate with a primitive stage of civilization, and consequent unhygienic conditions. Bu bonic plague smouldered in England for centuries, every few years flaring up to epidemic degree, and ceased as an endemic infection only about 1679. Cholera was common enough in John Wesley's day to demand a paragraph in his little volume on household remedies. The Londoner of Charles II.'s time could enjoy a jest in Hudibras unintelligible to anyone not familiar with the stages of a malaria paroxysm.
The present stimulus to the special study of tropical medicine comes from the spread of commerce from causes far back in his tory and from the ever-growing complexity of modern conditions.
Special Problems of Tropical Medicine.—Liability to con tract disease in the tropics is not due in the main to inherent change in the individual, but to circumstances generally favour ing a luxuriance of animal life. The causative organisms of some diseases, e.g., malaria and yellow fever, depend for their propaga tion on insects most numerous and active in tropical conditions; warmth and humidity are essential for the development of hook worm larvae in the soil ; and in such surroundings bacterial life in general flourishes most abundantly. Though exceptions to these rules spring to the mind—typhus fever, a louse-borne disease, reaches its maximum range under cold weather conditions, and the factors governing the transmission of common colds and coughs determine the spread of pneumonic plague. The newcomer to the tropics is faced by all these potential dangers.
Preventive medicine has done him one great disservice. Born in pre-hygiene times, he would almost certainly have acquired a natural immunity to a variety of diseases which nowadays in his own country he escapes, but to which the native, surviving child hood, is relatively immune. This resistance to disease, previously believed a racial characteristic, is now generally considered a per sonal immunity gained by the individual during early life. As
regards this aspect of malaria in natives, Christopherson has shown that in hyper-endemic areas children pass through a period of acute infestation lasting for about two years. During this time manifestations of the disease are practically continuous. A stage of immune infestation is then reached which lasts through child hood into adult life. Whatever the nature of the immunity it is sufficient to enable adults, under conditions that lead to intense infection in the child, to live infected but without suffering appreciably from sickness due to malaria.
The northern sojourner in the tropics may complicate the problems of tropical medicine, already sufficiently involved, by an unwillingness to adapt his regimen and habits to new surround ings. Therefore, physiological changes, including alterations in the functioning of the endocrine glands, may result, with a con sequent train of morbid symptoms. Native customs and modes of life evolved by the empiricism of years, may repay study. A temporary adoption of the Indian fashion of wearing the shirt outside the trousers has in practice averted the threatened onset of heat stroke. The early inhabitants of Northern Africa cooled their houses by structural devices which modern architects might copy and adapt to the needs of European residents.