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HE terms malaria and miasm in medical phraseology include the causes of a large class of affections—what are known more particularly as zymotic diseases, which depend upon a variety of specific organic poisons whose essential nature, composition, and form, are mostly inappreciable as yet by scientific research. The general understanding, however, of these terms, is more limited; and, in conformity with the popular idea, I shall in the present paper confine their application to the cause of those wide-spread disorders, intermittent and remittent fevers—the former of which is so well known as "chills and fever" or "fever and ague."

"Time out of mind," as Watson remarks, "it had been matter of common observation that the inhabitants of wet and marshy situations were especially subject to these definite and unequivocal forms of disease." The same natural agencies which are now at work elaborating, evolving, and disseminating malaria must have been equally in operation ever since the surface of the earth assumed its present condition. Vast and remote wildernesses that have never known human presence teem, as of yore, with deadly exhalations that almost preclude the bold attempts of enterprising man to lay bare their secrets. There are some parts of India, as Bishop Heber informs us, which even monkeys and other wild animals instinctively desert between April and October of each year. The tigers go up to the hills; the antelopes and wild-hogs make incursions into the cultivated plains; and those persons, such as dâk-bearers and military people, who are obliged to venture into the marshy jungles, agree that not so much as a bird can be heard or seen in the frightful solitude.

The celebrated Pontine Marshes may be regarded as the classic home of malaria. The older historical records describe this tract as occupied with numerous towns by the Volsci. It was evidently a fertile region; for we read in Livy that the early Romans sent thither during a season of scarcity for a supply of corn. Three hundred and twelve years the Censor Appius Claudius Cæcus constructed the Appian Way across the length of the Pontine region, the soil of which must then have been sufficiently compact to support the heavy causeway. At some period of the subsequent century and a half, the country seems to have undergone great deterioration either from natural or civil causes, and to have become partially inundated; for, about 170 we find the Consul Cornelius Cethegus applying himself to draining the marshes, and restoring the land to cultivation and