CHAPTER VI.

AIR VITIATED BY ADMIXTURE WITH EFFLUVIA ARISING FROM THE DECOMPOSITION OF VEGETABLE MATTER ON THE SURFACE OF THE EARTH.

It is not only from such sources as those already treated of, that effluvia or gases arise, to contaminate the atmosphere, and to spread disease among men and beasts. Effluvia likewise spring from the putrefaction of vegetables; and, in many instances, from circumstances favourable to their development and action, they so vitiate the atmosphere, that its respiration induces some of the most virulent diseases, and, where the effects are not so serious, a state of slow sickness and great suffering is often the lot of the sufferer, during the whole course of his miserable existence. The situations of these effluvia will shortly be pointed out, along with the respective diseases incident to them.

But let us for a moment consider the changes on which these effluvia depend. Putrefaction of vegetable matter is one of the many wise provisions which the Almighty has instituted for the accomplishment of his comprehensive plan of the creation.

The surface of the earth is covered with vegetation, to supply man with food, and likewise to support the various animals placed below him in the scale of creation, so necessary to his comfort and existence. They are consumed, and, by means of digestion, become component parts of animals; and when these, in their turn, die, they go down to the earth, whence they originally sprung.

Mixed there, with other matters composing the soil, the carcasses of animals afford nourishment to vegetation again, and once more they are found as the component principles of vegetable forms. Thus the animal is constantly supplying food to the vegetable world, which, in its turn, supplies food to the other again.

In life, we found them performing functions useful to each other, and mutually correcting their unwholesome effects; in death, they are no less useful: the one is converted into the other.

All animated creation is the scene of endless changes, and is the object of successive transformations. ’Tis one mighty circle, of a thousand parts, constantly revolving,—one part occupying now this, now that place,—and each taking the place of that next it, till at length it completes the entire circle; and even then the race is not yet run, the revolution must be performed again and again, to the very end of time.

The immediate agency by which these wonderful changes are effected, is putrefaction. We have alluded to it shortly, in connection with man in health, in disease, and in death.

We have now to speak of putrefaction in connection with dead vegetable matter, in marshy situations, &c., where it is the occasion of much disease.

There is no reason to believe that it was the design of the Almighty, that the process of putrefaction, which is so essential to the great plan of successive races of animals and vegetables, should be the active engine of pestilence, which it is in many situations.

That is not the necessary consequence of putrefaction; and when it does occur, it is rather the effect of accidental circumstances. Under ordinary circumstances, where putrefaction goes on, as among vegetables moderately moist, exposed to currents of air, and mixed up with the soil, as in the various processes of agriculture, no bad results are experienced.

But when vegetation is allowed to go on year after year, without being cropped, where, as it ripens, it withers and dies; and when it dies, is allowed to accumulate and putrefy, where there is much moisture, much solar heat, and little motion of the air, where, perhaps, other circumstances are operating, favourable to rapid decomposition, effluvia are wont to ascend and vitiate the atmosphere.

Such a vitiated atmosphere has acquired various appellations, according to the place in which it has been observed, and according to the effects or diseases it produces.

But, under whatever name it passes, its origin is the same, namely, decomposing vegetable matter on the surface of the earth, perhaps, in some situations, mixed more or less with dead animal matter.

It is decomposing vegetable matter which produces the yellow fever of the West Indies, the jungle fever of India, the deadly pestilential fever of the coast of Africa, the ague in this country and in many others, the cretinism of Switzerland, the pellagra of Milan, the unwholesome condition of humanity in many parts of Italy, and especially in the country surrounding Rome, or the Campagna of Rome, as it is called. The decomposition, however, takes place under circumstances somewhat different, and hence the difference in the results of its action.

These effects are attributed to the decomposition of vegetable matter; but there is room to think that, along with that, there is combined no very insignificant proportion of matter of an animal nature.

It may safely be inferred, that wherever there is vegetation, there animals are found also; and it is well known that vast numbers of many kinds of animals live wherever decomposition is taking place, especially if the situation is warm and sheltered. The carcasses of these animals will be added to the vegetable matter, and add to the common mass of corruption.

That matter in swamps, and in unwholesome situations, said to be purely vegetable, is then a compound of animal and vegetable origin; and these effluvia arise, not from vegetable decomposition only, but from both dead animal and vegetable substances in a state of putrefaction.

There is little known of the composition of these effluvia. We are most conversant with their situations, and their effects upon health. In different situations, they produce different diseases. But no known facts entitle us positively to say that their composition is different. It is a remarkable fact, but one well ascertained, that the atmosphere, in all parts of the world, in all climates, and in all situations, is much the same in its chemical composition. It manifests the same general physical characters in all situations, whether healthy or pestilential, and the nicest investigations have detected nothing in an atmosphere known to be pestilential, that is not found in the most wholesome.

However, there is much reason to think, that this circumstance is owing, not to the absence of hurtful gases, but to the comparative insignificance of their volume beside that of the atmosphere itself, so vast in its dimensions.

Medical men have been disposed to think that effluvia which cause one disease, say the yellow fever, are not the same as that which cause another, say the fever of the coast of Africa. The only reason offered is the difference of the diseases; but that is not enough to prove that the effluvia are different in their nature. Different effects, or effects so modified as to appear very different, are the results of the same cause on many occasions. The smoke of tobacco will make one person feel comfortable, another merry, another sick, another faint, and so on; but it would be unfair, from these differences in the effects, to pronounce that tobacco-smoke was in all these cases different in its own nature.

We are satisfied that the effluvia or gases arising from marshy or unwholesome soil, are the same, generally speaking, in all situations, whatever disease is produced; and that the difference in the results is to be attributed to the varying circumstances under which they act,—for instance, the constancy or inconstancy of their operation, their greater or less intensity, the greater or less degree of concomitant moisture and heat, the greater or less amount of motion of the air,—the sheltered situation of human habitations,—the condition of the body, its predispositions from native country and the like, and the individual being accustomed or unaccustomed to the action of effluvia.

Gases are known to arise from the marshy grounds mentioned, where animal and vegetable matter is putrefying, from the fact, that the neighbourhood of swamps is most unwholesome, the inhabitants and visitors almost uniformly suffering, because unwholesome effluvia are invariably known to emanate where animal and vegetable matter is thus corrupting, and because the gases themselves may be seen rising in bubbles out of putrid water, containing dead animal and vegetable matter in a state of corruption.

These bubbles contain gases the very same as are disengaged when animal and vegetable matter are putrefying among water. They are nearly the same as proceed from merely animal matter dead and putrefying, not incorporated with the soil, viz. carburetted hydrogen, or inflammable gas, carbonic acid gas, or fixed air, and sometimes a little phosphuretted and likewise sulphuretted hydrogen.

These gases are sometimes appreciable to the organ of smell. Carburetted hydrogen is very strong, and is perceptible in many situations where there is much corruption going on; for instance, at the meadow-ground between the Dairy, on the Portobello road, and Comely Green, near Edinburgh, where the stench is so strong as to prove most offensive to passengers on the road. The source is the corrupting animal and vegetable materials, in the foul water conducted from Edinburgh, and made to overflow the ground, for the purposes of irrigation.

In such situations, it is not uncommon to observe lights floating along during the night, and superstition has not failed to make them represent evil spirits. They are known by the name of “Will o’ Wisp” and “Jack o’ Lantern;” and have, on many occasions, proved objects of no slight dread to many ignorant persons. The lights are merely ignited carburetted hydrogen gas,—the same kind of gas as that used for lighting our shops and houses.

The gas is ignited, perhaps, by the rising to the surface of the putrid water, of a bubble of phosphuretted hydrogen, which, as was before observed, burns the moment it comes in contact with the atmosphere.

Other products of an aeriform kind may be evolved also, but we have no direct evidence of their existence,—but an atmosphere, loaded with vapours of the kind mentioned, is enough to account for the production of the observed disease, in all its varied forms, when there is conjoined with it other unwholesome agencies. In some countries, the pestilential air is present throughout the year, for instance, in the country around Rome, in the fens of Lincolnshire, where ague is seldom absent; in others it is periodical, chiefly confined to the hot and rainy seasons, as in India and in the West Indies, where fevers prevail to a great extent; and in others, again, it is observed only when the wind blows from a particular direction.

These effluvia are conveyed to a distance by currents, and produce their peculiar effects, more or less, upon almost all they encounter. The malaria at Rome is carried by the wind into the city, by the channels most open to its entrance; and those parts, it is said by medical men who reside there, that are most exposed to the wind blowing off the adjacent marshy grounds, are most unhealthy. It is for that reason that the suburbs are more unwholesome than the interior of that city, where the wind does not find ready access, on account of the obstacles offered to its course by the high buildings. The high houses and streets thus act as a barrier against the entrance of the pestilence, and it is even said that the narrowest streets there, are the most healthy, as they shut out the pestilential vapour.

An obstacle of the same kind is offered by hills which interrupt the course of winds carrying with them vapours from marshy grounds. In the West Indies, where the yellow fever commits such frightful ravages, many instances are known where a town or district retains its health, from the shelter which a hill affords against the visitation of a wind that has loaded itself with deadly miasms, while sweeping over a marsh or swamp. It is the practice of those residing in those countries, not only to remove from the swamps, but also from those points to which the wind blows after passing over them.

Inattention to that consideration has led to the loss of much human life, and to the fruitless expenditure of much money in the erection of houses, barracks, and the like, which, after completion, have been found to be totally uninhabitable, from the pestilential vapours carried to them by the winds. In illustration of the influence of winds, we submit the following interesting extract from Dr Good’s Study of Medicine. He has been speaking of effluvia from animal matter. “But the foul and stinking Harmattan,” (a pestilential wind) “when it rushes from the south-east upon the Guinea coast, loaded with vegetable exhalations alone, with which it impregnates itself while sweeping over the immense uninhabitable swamps and oozy mangrove thickets of the sultry regions of Benin, triumphs in a still more rapid and wasteful destruction; so much that Dr Lind informs us, that the mortality produced by this pestilential vapour in the year 1754 or 1755 was so general, that in several negro towns, the living were not sufficient to bury the dead; and that the gates of Cape Coast Castle were shut up for want of sentinels to perform duty. Blacks and whites falling promiscuously before this fatal scourge.”

So loaded is the air on some occasions with these pestilential vapours, that they attach themselves to whatever objects they meet, houses, the sides of hills, and woods, through which they pass along with the wind, and so completely has a wood stripped the currents of their baneful accompaniments, that they have been respired after with no injury whatever.

Trees are found to give great shelter and salubrity to towns in this way, acting as they do as so many sieves retaining impurities.

It is understood that the effluvia arising from putrefying vegetable matters ascend high in the atmosphere under the influence of the solar rays, and spread far and wide, and that at night during the cold they fall with the dew to the ground again, and impart to it and to those exposed to its action, much virulence. The ground is there known to be extremely unwholesome, and those who have been compelled by want, by sickness, while travelling, overtaking them, or by being benighted, to lie down with nothing but the soil for a couch, and with no shelter from the vapours and dew that falls at night, save the sky itself, have felt this pestilential influence: on the morrow they awake distressed, parched, and affected with headach, and the usual symptoms of malignant fever.

With the close of day or the setting of the sun, the pestilential vapour falls and envelopes the country and the habitations of men with a deadly mantle—and it is then unsafe to venture into the open air in many of the finest countries of the world.

The pestilential effects of exposure to these night dews and vapours have, on many occasions, been experienced by soldiers encamping in the open grounds, and our gallant countrymen on foreign service are wont to yield in fearful numbers to a foe, merciless and unsparing.

But it is not in swampy grounds only that these vapours arise, for there is reason to think that in those places where sickness is constant, and where no such dampness of ground is observed, that decomposition of animal and vegetable matter is going on some depth below the surface, and that the extricated gases issue through the soil. This is rendered almost certain, by the fact which has sometimes been observed, that the most dangerous and sickly season is, when the ground is parched and rent with heat, permitting the exhalations generated below to ascend into the atmosphere. Instances of this occurred among our soldiers in the Peninsular war—the season, marked with the greatest prevalence of disease, the common result of vitiated air, being that when the soil was most rent with heat.

In some parts of Italy, it is remarked by that eminent physician and philosopher, Dr James Johnstone, in his admirable volume, entitled the Diary of a Philosopher, which, by the way, is a work of rare virtue, in so much as it is replete, not only with accurate medical knowledge, but with reflections in literature and the fine arts such as prove an intimacy with polite learning not always found, that fever and that general unwholesome state of body, observed in districts infested with vitiated air, prevail where inquiry has discovered no appearance of unusual dampness and corruption of the soil. He thinks that streams of putrid water, containing animal and vegetable materials, that have sunk down from the surface, in some part of their course are making their way at a little depth, and that when the soil, parched with excessive heat and drought, becomes rent, as it commonly does, the emanations previously confined rush out by the channels now presented by these fissures, and deal their deadly effects around.

Such an explanation seems to me highly probable, and deserving of more inquiry. Connected with this subject, the following facts may be interesting, and assist in forming an estimate of the probability of the truth of that explanation.

In mines, as well as on the surface of the earth, changes are constantly going on; and as in the latter situation the animal, vegetable, and mineral components of the soil are decomposing, so the minerals in the former are giving out some of their component parts and abstracting oxygen, &c. in turn from the atmosphere.

In mines some of the fossils attract oxygen from the air, but the chief process by which the atmosphere becomes vitiated there, is by the evolution of gases from the minerals. In coal pits the principal gases emitted are carbonic acid gas, commonly known as fixed air, which will support neither animal life nor combustion, as proved by the disastrous results on men having been confined in it, and by the extinction of light when immersed therein, and carburetted hydrogen gas, known as fire-damp, which cannot support respiration, and which takes fire when brought in contact with a light. These gases are the results of chemical changes going on in the minerals, in the same way as the gases before alluded to attend the decomposition of animal and vegetable substances.

These gases arise not only from the minerals exposed to view at the various surfaces, as the roof, sides, and pavement of coal pits, but issue also from the unworked minerals in the interior, by fissures or cracks in the various strata, produced by the violence used in detaching the minerals.

These fissures extend in the course of the beds, or strata, and are often scarcely visible, but are sometimes so wide as to admit the finger. It is probable that they sometimes extend a considerable way into the solid minerals.

In general, from these fissures there is constantly issuing streams of gas, of a nature varying with the character of the minerals, but for the most part they are such as have been mentioned. In the mines of Great Britain, when the atmosphere above is much agitated, as by the prevalence of southerly winds, and more especially if the violence amounts to what is termed a storm, the gases pour out in prodigious quantities, making a rushing noise, and filling the pit and excavated parts. The pit then becomes so full as to interfere with the operations of the men, who are frequently, for their safety, obliged to retire. In this case the atmosphere is lightened, and the pressure it is constantly exerting on all bodies with which it comes in contact is diminished, and the consequence is, that the gases rush out, under the circumstances already mentioned. It is known, that, during the prevalence of stormy weather, the mercury in a barometer falls; it is for a like reason, the weight upon it being less. Not only the gases issue from their caverns when the air is thus lightened, but water contained in fissures in the floor or pavement of mines rises also, sometimes to the amount of an inch or two, and it is no uncommon thing to see the extrication of vapour from a little collection of water on the floor, such as takes place when water is boiling, a movement which it very much resembles.

These facts shew that it is not improbable that pestilential vapours, ordinarily passing under the soil, may be extricated when fissures are present. It may happen that effluvia may be prevented from issuing even when fissures exist in the soil, from an increase in the weight of the atmosphere, and in this way may be explained the occasional disappearance of pestilence with a change of weather, not unfrequently remarked in some tropical countries.

During the prevalence of strong north, north-east, and north-west winds, blowing with considerable violence the currents in mines are reversed—for, instead of gases issuing from the fissures and crannies, currents of atmospheric air pour into them. These currents may be felt with the hand, and the ear can detect the rushing sound; a flame applied to a fissure is immediately drawn in, shewing the direction of the current. These facts illustrate the influence which the state of the atmosphere has upon terrestrial vapours.

As has been already observed, the exhalations from the soil obtain different names from the effects they are wont to produce. When they produce intermittent fever or ague, they are termed marsh miasms. When they produce the various forms of malignant fever, such as the yellow, the bilious fever of India, and the coast of Africa, simply pestilential effluvia—and when they induce general bad health and degeneracy of the inhabitants of a country, they are styled malaria, an Italian expression signifying bad air.

As the subject appears one which may interest the general reader, it is proposed to add a few observations on the diseases which are caused by air vitiated with effluvia from the soil.