Tropical Medicine and Hygiene
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IT has long been recognized that a number of diseases are peculiar to, if not confined to, warm climates. Many hypotheses in explanation of this circumstance have been advaiced, but it is only of late years-only since we have been able to recognize the germ causes of many of tllese diseases, or the media by or in which they are conveyedthat it has become possible to arrive at the true explanation. Almost without exception, tropical diseasesthat is to say, those diseases whiclh require for their successful propagation a warm climate-are caused' either by a protozoal organism or by a helminth, whichl, in their turn, in order to pass from one vertebrate host to another, demand either an animal vector peculiar to warm climates, or require a warm medium in wwhich to qualify for such passage. Hence, althouglh tropical disease once acquired can run its usual course even if the person remove to a cold or even frigid climate, that person cannot spread the disease there, nor, under natural conditions, can the disease be acquired tlhere. On the other lhand, bacterial diseases naIy be acquired and spread in any climate, as the germs in their passage from one human host to anothei do not necessarily demand any special animal intermediary, nor are they destroyed in their passage by ordinary temperatures. In the following summary relating to British contributions to tropical medicine bacterial diseases are therefore not considered. It is true