Essays on pathology and therapeutics: being the substance of the course of lectures (Volume 1).

  • Dickson, Samuel Henry, 1798-1872.
Date:
1845
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Licence: Public Domain Mark

Credit: Essays on pathology and therapeutics: being the substance of the course of lectures (Volume 1). Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    height to which malaria may rise in the air. Humboldt observes that the fami of Encero, situated above Vera Cruz, is a stranger to the insalubrity that reigns over the whole coast; the elevation of this farm is 3,045 feet. Rigaud de I'Isle considers the limit to vary between 6S2 and 1,000 feet above the source of the ex- halation. In regard to this matter, however, we frequently meet with exceptions and irregularities, some of which are not easily explained, others we refer to the course and force of winds, and to the wetness or dryness of seasons. The affinity of malaria for moisture has been already spoken of I look upon this affinity to be so absolute, essential and ex- clusive in its influence, that malaria, if it were possible to prepare it in a dry state, would be totally inert and harmless. Now, as far as moisture may be carried up into the thinner regions of the atmosphere, in any notable degree of density, so far may also malaria rise upward, retaining its noxious powers ; but beyond a certain extent of diffusion, dilution or dispersion of the vapor with which it is combined, it loses that concentration which we formerly maintained to be necessary to its poisonous operation. Although I do not impugn the doctrine which attributes weight to malaria, yet this seems to me the true advantage of elevation; not that the miasm cannot reach a lofty point, but that of neces- sity it becomes, while rising, less and less concentrated, and that the chances of its dispersion are infinitely multiplied. It is also in the less dangerous hours of mid-day that the noxious vapors are carried into the upper air; they are copiously precipitated at sun-set and during the night, and then abound in the lower stra- ta near the earth's surface, in valleys and depressed situations. I have already observed that malaria seems destitute of the quality of self-repulsion, and hence argued that it is probably not a gas. In a great many instances on record, it has failed to affect persons exposed at but a short distance from its obvious source. You will find in Bancroft a collection of such examples. In the history of the Walcheren expedition it is affirmed that the crews of some ships anchored even within one-fourth of a mile of the coast, continued healthy, while every man who had gone on shore was seized with fever. The same statement is more than once repeated in the wri- tings of West Indian physicians. MacCuUoch tells us that on