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cites various theories concerning the mode of action of marsh miasm, and finds them insufficient to account for the phenomena which they produce. He continues as follows: —

"All the aoove hypotheses failing to account for the efi "fects in question, we are naturally led" to the admission "that they are produced by the morbific influence of some u special agent; and when we take into consideration all "the circumstances attending the appearance of febrile "diseases, the circumscribed sphere of their prevalence, "the suddenness of their attack, the character of their "phenomena, etc., we may safely say that there is noth"ing left but to attribute them to the action of some "poison dissolved or suspended in the air of the infected "locality; which poison, while doubtless requiring for its "development and dissemination a certain degree of heat. "and terrestrial and atmospheric moisture, a certain u amount of nightly condensation after evaporation, and 1 the presence of fermenting or decomposing materials "cannot be produced by either of these agencies alone, "and though not indicated by the chemist, betrays its "presence by producing on those exposed to its influence "the peculiar morbid changes characterizing fever."

He quotes the following from the Researches of Dr. Chadwick: —

"In considering the circumstances external to the resi"dence, which affect the sanitary condition of the popula"tion, the importance of a general land-drainage is devel"oped by the inquiries as to the cause of the prevalent "diseases, to be of a magnitude of which no conception had "been formed at the commencement of the investigation "Its importance is manifested by the severe consequences "of its neglect in every part of the country, as well as by "its advantages in the increasing salubrity and productive"ness wherever the drainage has been skillful and effe* "tuaL"

La Roche calls attention to these facts:—That the acclimated residents of a malarious locality, while they are less subject than strangers to active fever, show, in their physical and even in their mental organization, evident indications of the ill effects of living in a poisonous atmosphere,—an evil which increases with successive generations, often resulting in a positive deterioration of the race; that the lower animals are affected, though in a less degree than man; that deposits of organic matter which are entirely covered with water, (as at the bottom of a pond,) are not productive of malaria; that this condition of saturation is infinitely preferable to imperfect drainage that swamps which are shaded from the sun's heat by trees, are not supposed to produce disease; and that marshes which are exposed to constant winds are not especially deleterious to persons living in their immediate vicinity,—while winds frequently carry the emanations of miasmatic districts to points some miles distant, where Jhey produce their worst effects. This latter statement is substantiated by the fact that houses situated some miles to the leeward of low, wet lands, have been especially insalubrious until the windows and doors on the side toward the source of the miasm were closed up, and openings made on the other side,—and thenceforth remained free from the disease, although other houses with openings on the exposed sides continued unhealthy.

The literature relating to periodical fevers contains nothing else so interesting as the very ingenious article of Dr. J. 1L Salisbury, on the "Cause of Malarious Fevers," contributed to the "American Journal of Medical Science," for January, 1866. Unfortunately, while there is no evidence to controvert the statements of this article, they do not seem to be honored with the confidence of the profession,— not being regarded as sufficiently authenticated to form a basis for scientific deductions. Dr. Salisbury claims to have discovered the cause of malarial fever in the spores of a very low order of plant, which spores he claims to have invariably detected in the saliva, and in the urine, of fever patients, and in those of no other persons, and which he collected on plates of glass suspended over all marshes and other lands of a malarious character, which he examined, and which he was never able to obtain from lands which were not malarious. Starting from this point, he proceeds, (with circumstantial statements that seem to the unprofessional mind to be sufficient,) to show that the plant producing these spores is always found, in the form of a whitish, green, or brick-colored incrustation, on the surface of fever producing lands; that the spores, when detached from the parent plant, are carried in suspension only in the moist exhalations of wet lands, never rising higher (usually from 35 to 60 feet,) nor being carried farther, than the humid air itself; that they most accumulate in the upper strata of the fogs, producing more disease on lands slightly elevated above the level of the marsh than at its very edge; that fever-and-ague are never to be found where this plant does not grow; that it may be at once introduced into the healthiest locality by transporting moist earth on which the incrustation is forming; that the plant, being introduced into the human system through the lungs, continues to grow there and causes disease; and that quinia arrests its growth, (as it checks the multiplication of yeast plants in fermentation,) and thus suspends the action of the disease.

Probably it would be impossible to prove that the foreioing theory is correct, though it is not improbable that it contains the germ from which a fuller knowledge of the disease and its causes will be obtained. It is sufficient for the purposes of this work to say that, so far as Dr. Salisbury's opinion is valuable, it is,—like the opinion of all other writers on the subject,—fully in favor of perfect drainage as the one great preventive of all malarial di»

The evidence of the effect of drainage in removing the cause of malarial diseases is complete and conclusive. Instances of such improvement in this country are not rare, but they are much less numerous and less conspicuous nere than in England, where draining has been much more extensively carried out, and where greater pains have been taken to collect testimony as to its effects.

If there is any fact well established by satisfactory experience, it is that thorough and judicious draining will entirely remove the local source of the miasm which produces these diseases.

The voluminous reports of various Committees of the English Parliament, appointed to investigate sanitary questions, are replete with information concerning experience throughout the whole country, bearing directly on this question.

Dr. Whitley, in his report to the Board of Health, (in 1864,) of an extended tour of observation, says of one town that he examined: —

"Mr. Nicholls, who has been forty years in practice "here, and whom I was unable to see at the time of my "visit, writes: Intermittent and remittent are greatly on "on the decline since the improved state of drainage of "the town and surrounding district, and more particularly "marked is this alteration, since the introduction of the "water-works in the place. Although we have occasional "outbreaks of intermittent and remittent, with neuralgia "attacks, they yield more speedily to remedies, and are "not attended by so much enlargement of the liver or "spleen as formerly, and dysentery is of rare occurrence."

Dr. Whitley sums up his case as follows: —

"It would appear from the foregoing inquiry, that in* "terraittent and remittent fevers, and their consequences, "can no longer be regarded as seriously affecting the "health of the population, in many of the districts, in which "those diseases were formerly of a formidable ctaraoter "Thus, in Norfolk, Lincolnshire, and Cambridgeshire,

"counties in which these diseases were both frequent and

"severe, all the evidence, except that furnished by the

"Peterborough Infirmary, and, in a somewhat less degree,

"in Spaulding, tends to show that they are at the present

"time, comparatively rare and mild in form

* * * *

He mentions similar results from his investigations in other parts of the kingdom, and says: —

"It may, therefore, be safely asserted as regards Eng"land generally, that:—

"The diseases which have been made the subject of the "present inquiry, have been steadily decreasing, both in "frequency and severity, for several years, and this de"crease is attributed, in nearly every case, mainly to one "cause,improved land drainage ;" again:

"The change of local circumstances, unanimously de"clared to be the most immediate in influencing the pre"valence of malarious diseases, is land drainage;" and again:

"Except in a few cases in which medical men believed "that these affections began to decline previously to the "improved drainage of the places mentioned, the decrease "in all of the districts where extensive drainage has been "carried out, was stated to have commenced about the "same time, and was unhesitatingly attributed to that "cause."

A select Committee of the House of Commons, appointed to investigate the condition and sanitary influence ol the Thames marshes, reported their minutes of evi deuce, and their deductions therefrom, in 1854. The following is extracted from their report:

"It appears from the evidence of highly intelligent and "eminent gentlemer of the medical profession, residing in "the neighborhood of the marshes on both sides of the

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