Chapter IX · ON POISONS, MIASMS AND CONTAGIONS.

§ 1. Although the amount of disease and mortality traceable to accidents, to the ordinary atmospheric changes of which the thermometer gives us due information, to the habits of life and the effects of hereditary influence, be sufficiently great, it yet seems nothing when compared with the terrible inflictions occasionally and at uncertain periods visiting man, whether shut up, as it were, within the confined haunts of cities, or living apart in the open country, in situations where it might be reasonably imagined no such influences could reach him. The poison of typhus, for example, if it be a poison, spares none: in certain epidemics the citizen and the peasant suffer alike: the strong robust man in the prime of life is its special victim; cholera attacked the inhabitants of the remote and isolated cottage as certainly as the careful wealthy citizen, and with the same results. No mode of life, nor sex, nor age was security against it; no race, no locality.45 An inquiry into the origin of such influences is the most important to which man’s attention can be directed. These terrible epidemics appear under various forms; sometimes it is by typhus or influenza, cholera or plague; even those diseases which seem to be endemic, or confined to a locality, assume the form of epidemical raging pestilences, and then disappear for a time. Thus the remittents and yellow fevers of tropical climates do not always put out their whole strength; there is a lull, a season of repose, when man, deluded by the security of a few years, hopes that at last the evil influence has disappeared for ever. Vain hope! It moves in cycles, like the typhus of temperate climates, falsifying all predictions. Thus, in Jamaica, the grave of so many noble English regiments, the fever, sometimes called remittent, sometimes yellow fever, exhibited its fitful attacks during eighteen years, in the following capricious manner, at a station called Port Antonio, about eighty miles from Kingston. At Stoney Hill Barracks, the disease was still more capricious.46 As the poison producing intermittents and remittents must be presumed to be always present, it is incomprehensible how it should at times cease its attacks on man, showing that another influence or element requires to be present to render its attack successful. Again, we find that within a limited range, a long residence in a land unhealthy to the stranger seems by acclimation to diminish if not entirely to eradicate the susceptibility to disease on the part of the latter; but this opinion must be received cautiously and with reserve, for the phenomenon may be partly due to the difference in race, respecting which we as yet know but little. The banks of the Scheldt, the Polders of Holland, and the mouths of the Rhine, the Danube, and the Indus, are healthy to the natives of these districts; graves to foreigners. In all inquiries of this kind, these well-established facts must not be overlooked.

§ 2. When a chemical substance is applied externally or internally to the living tissues of an animal sufficiently strong to dissolve the affinity between them and the vital force, and to substitute for it other stronger affinities, the explanation of the phenomena is easy, and the coarsest chemistry offers a solution. The action of caustic potass, of concentrated sulphuric acid, present the examples of this kind of dissolution. Other substances alone poisonous when given in concentrated doses, are known to pass, when sufficiently diluted, through the blood, and be eliminated by secretion and excretion from the body: after causing disturbances more or less grave, more or less important, the combinations they form, if any, with the living organic molecules are overcome by the vital force, which then resumes its usual influence. Of such substances some pass off unaltered, others are decomposed, and the bases only appear in the secretions or excretions. Whilst passing through the lungs, certain of these vegetable salts combine with the oxygen of the air, and the respiration in consequence becomes slower, or in other terms, they diminish the production of arterial blood.47

Now, these salts48 when placed in contact with animal and vegetable substances, perform the same function as in the lungs: they take a part in the combustion going on, and, as in the living body, are converted into carbonates. Left to themselves for a time, from their aqueous solution, the acids composing them finally completely disappear.

Mineral acids and nonvolatile vegetable acids, as well as mineral salts with an alkaline base, have the property, when sufficiently concentrated, to arrest the whole process of this slow combustion;49 common salt, as is well-known, arrests putrefaction: so does alcohol.

The chemical action of certain other mineral salts is different, such as the salts of the peroxide of iron, of lead, bismuth, copper, and mercury. These are inorganic poisons. They combine with the tissues of the organs, and so destroy life. The mode of action of the poisons of prussic acid, strychnine, morphine, &c., is as yet unknown.

“But there exists a class of substances no less fatal than the preceding, originating in certain decompositions. In a preceding Chapter (III.) we have inquired into the origin of these poisons, and shown them to originate in fermentation and putrefaction. Let us apply the chemical principles regulating these processes to organic matters, to the products of the animal economy; all the elements of these matters are derived from the blood, the most complex of all existing substances. In decomposing, a poison is occasionally produced speedily mortal when it comes in contact with the blood of the living animal. The venomous principle produced by decomposing animal bodies is not always the same: that originating in certain German sausages is quite peculiar; the person who partakes of this fatal dish dies mummified; he does not rot or fall to pieces like those who perish from wounds received in dissecting-rooms; on the contrary, he dries up and withers, but does not putrify.50 Liebig, the discoverer of this poison and its effects on man, states that the venom is destroyed by boiling-water and alcohol, but that these do not absorb it.

Similar in the mode of action on the economy are the poisons of small-pox, plague, &c. The substances which arrest fermentation and putrefaction, also neutralize the power of these poisons; but the essence of these poisons has not yet been obtained in an isolated form, and thus nothing positive is known of its real nature. One thing seems certain; contagions, poisons and miasms are not living beings nor animalcules, any more than yeast. They may be, and probably are, produced by fermentation, but this is neither caused by nor terminates in the formation of living animalcules, to which all or any of these phenomena might be attributed.

A nice distinction has been drawn by a distinguished chemist between a contagion properly so-called and a miasm. When the disease-producing matter is the product of a disease, it is a contagion; if it be the product of putrefaction or of eremacausis of any substance, animal or vegetable,—does it act by virtue of its chemical character, and not of its condition (etat), in forming a combination, or in causing a decomposition, it is then a miasm.

The history of diseases so originating scarcely supports this view. Typhus, which at times seems to originate in a miasm, at times seems to assume a contagious character. The same may be said of yellow fever. But however this may be, the distinction applies to such diseases as intermittent and remittent fevers, which originating in a miasm, itself springing from the putrescence of animal or vegetable bodies, gives rise to disease which does not reproduce the miasm. Now, between diseases so produced and those arising from contagion properly so called, there is this remarkable distinction: the blood once altered is no longer susceptible of the same contagion, whereas against miasms there is no such security.51

In every contagious disease, and perhaps even in those simply arising from miasms, there is an odour which fills the chambers of the sick, and is recognisable at once. Ammonia is very generally present, as it is wherever animal decompositions are going on, that is, putrefaction. The foul airs emanating from stagnant and neglected ditches is composed, as has been long known to chemists, of carbonic acid and sulphuretted hydrogen gases, and these are viewed by some as amongst the most dangerous of miasms. These gases may be destroyed by acid vapours now in common use.52 From chemistry we also derive another valuable lesson in respect of substances directly destroying human life. The materials ready to undergo putrefaction, and thus to generate miasms, may all be present, and yet no miasms are given out, and man escapes; this security depends upon the absence of that third principle requisite to bring the others into activity.

Thus it happens that in his extensive and elaborate inquiries, Major Tulloch was continually met by difficulties which overthrew at once all existing medical theories, rendering it even probable that the supposed relation of cause and effect between marshes and miasms, and miasm and fever, was merely accidental. In what that third element consists, that immediately exciting power which urges on the decomposition to an extent it had not before attained, rendering that miasm mortal, or at least most dangerous, which heretofore the vital force was able to resist, has not yet been discovered.

Is it electricity? is it ozone?53 or does it depend on some unknown principle in the elements of the atmosphere, for the detection of which we have no instrument? Does security in such cases depend on the presence in the atmosphere of some such principle as ozone? Whatever be the cause, the fact is certain; epidemics follow cycles of increase and decrease; like comets, they come and disappear at long intervals. Our business in the mean time lies with what is constantly present, in a more or less aggravated form—the malaria continually reproduced, always efficient in certain regions of the earth; in the overcoming of which, as I have endeavoured to show, well-directed human industry is far from unavailing.54