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xxiv] Nomenclature.—This is, perhaps, the most important of the several diseases covered by those loosely used terms—sun-stroke, heat-stroke, coup de soleil, insolation, heat-apoplexy, heat-asphyxia, thermic fever, and so forth. I adopt the name siriasis because, whilst distinctive, it embodies no etiological theory; it has the further merit of being the most ancient of the many names applied to the disease.

The geographical distribution of siriasis appears to be remarkably restricted. Although it is true that this type, or what passes for this type, of disease has been reported as occurring in many countries, on making careful examination it will be found that a large proportion of the reputed cases are really examples of other diseases, more especially of cerebro-spinal fever, apoplexy, tubercular meningitis, delirium tremens, pernicious malaria, or some other phase of acute disease, but not of true siriasis. According to Sambon, hyperpyrexial heat-stroke is rigidly confined to certain low-lying, sea-coast districts, and to the valleys of certain rivers. It is never found in high lands, nor above a relatively low altitude—600 feet.

It is unknown in Europe. The endemic areas are—in America, the east coast littoral of the United States, more especially in the great towns, the Mississippi valley, the coast of the Gulf of Mexico, the valleys of the Amazon and of the La Plata, and the South Atlantic coast; in Africa, the valley of the Nile, the coasts of the Red Sea, and a low-lying part of Algeria near Biskra; in Asia, Syria, the valleys of the Indus and Ganges, Lower Burma, Tonquin, and south-east China; in Australia, the Murray River district, the Queensland coast, and, possibly, the plains of Sydney. No doubt it occurs elsewhere in corresponding meteorological and telluric conditions; but many large areas in the tropical world, and especially so the interior of continents, are exempt from siriasis. It is not met with on the high seas, although it is well known on ships in the narrow, land-locked Red Sea and the Persian Gulf.