Page:Popular Science Monthly Volume 9.djvu/446

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portions of India. The severe and fatal fevers prevailing in Burdowan, Lower Bengal, during the last fifteen or twenty years, have been coincident with obstruction to the natural drainage from mills, and blockage of water-courses. The same cause has doubtless operated to a great extent in producing the fevers of Bloomingdale, Manhattanville, Yorkville, and Harlem. The establishment during the past five years of extensive subsoil drains in those portions of New York has had a visible tendency to diminish the area of malaria. A similar result on a large scale has been noticed in Lincolnshire and other parts of England, where many malarious tracts have been rendered quite healthy by similar measures, having for their object the lowering of the subsoil water-level by an increased outflow.

I have thus far confined my observations to endemic malaria. But, like other diseases dependent upon telluric or organic emanations, miasmatic fevers occasionally assume an epidemic character, and, breaking loose from their native haunts, overspread a wide extent of territory. Thus, as Hertz informs us, nearly the whole of Europe was invaded by such epidemics in 1558—in 1678−'79—from 1718 to 1722—from 1824 to 1827—and from 1845 to 1848. The cause of malaria being thus propagated is as mysterious as that of most epidemics. It is possible that such an epidemic malarial influence has been prevailing here; but we must not lose sight of the fact that sporadic cases of malarial fever appearing in non-malarial districts can frequently be traced to previous exposure in an infected locality.

Malaria, although having its ordinary habitat in low-lying regions, may under conditions favorable for its production exist at great elevations. On the Tuscan Apennines it is found at a height of 1,100 feet above the sea; on the Pyrenees and Mexican Cordilleras, 5,000 feet; on the Himalayas, 6,400 feet; on the island of Ceylon, 6,500 feet; and on the Andes, 11,000 feet. Sometimes, however, at considerable elevations it is unaccountably absent under circumstances apparently supplying every condition for its development. Thus, according to Jourdanet, close to the city of Mexico lies the lake of Tescudo, some twenty-five square miles in extent, composed partly of fresh and partly of brackish water, with a clayey bottom often laid bare over large areas as the result of evaporation under a temperature of 122° to 140° Fahr., notwithstanding which, malarial fevers seldom occur in its vicinity. At Puebla, Mexico, on the other hand, is a very malarious marsh 5,000 feet above the sea. Under ordinary circumstances, a certain altitude affords immunity from malaria, although low elevations of 200 or 300 feet above a miasmatic tract are often more dangerous than the flat lands—the poison seeming to float upward and become intensified. This was long noticeable on the heights of Bergen Hill, West Hoboken, and Weehawken, which overlook the Jersey flats. At present, the elevation