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Rh many at present malaria-free and salubrious Pacific islands, malaria would become established there. And thus, though certain tropical diseases have at present a limited range, there is great probability, unless measures are speedily set on foot to prevent such a calamity, that the swift and increasing intercourse of modern times, by facilitating the intentional or accidental introduction of their subserving intermediaries, will ere long enable them to extend their present geographical range.

It is evident from what has been advanced that the student of medicine must be a naturalist before he can hope to become a scientific epidemiologist, or pathologist, or a capable practitioner. The necessity for this in all departments of medicine is yearly becoming more apparent, but especially so in that section of medicine which relates to tropical disease. This is further accentuated if we reflect that, although we do know something about a few of the tropical diseases and their germs, there must be many more tropical diseases and tropical disease germs about which we know absolutely nothing. Who can doubt that just as the fauna and flora of the tropical world are infinitely richer in species than those of colder climates, so there is a corresponding distribution in the wealth and poverty of pathogenic organisms; and that many, if not most, of the tropical diseases have yet to be differentiated? The discoveries of the last few years show this. Opportunities and appliances for original pathological study are, from circumstances, too often wanting to the tropical practitioner; but in this matter of the etiology of disease he certainly enjoys opportunities for original research and discovery far superior in novelty and interest to those at the command of his fellow-inquirer in the well-worked field of European and American research.

In the following pages I have included certain cosmopolitan diseases, such as leprosy, plague, and beri-beri, diseases which, properly speaking, do not depend in any very special way, or necessarily, on climatic conditions. They have been practically ousted from