“Finally, it is an observation universally made, and which may be regarded as established, ‘that the origin of epidemic diseases may often be referred to the putrefaction of great masses of animal and vegetable matters; that miasmic diseases are found epidemic, where decomposition of organic substances constantly goes on, in marshy and damp districts. These diseases also become epidemic, under the same circumstances, after inundations, and also in places where a large number of persons are crowded together with imperfect ventilation, as in ships, in prisons, and in besieged fortresses.’[40] But in no case may we so securely reckon on the occurrence of epidemic diseases, as when a marshy surface has been dried up by continued heat, or when extensive inundations are followed by intense heat.”
If we admit these facts we shall be less surprised at the ravages committed by fever, when, after great battles, the wounded are placed in the hospitals of large cities, as in Brussels after Waterloo, in Bilboa, Vienna, &c. Hospital gangrene, the scourge and terror of the wounded, soon shows itself, and cannot be arrested by any known surgical means. Much better were it for the wounded that they had been left on the field of battle. An erroneous opinion prevails, that it is to the presence of the infusoria that the evil influences are to be traced; they, on the contrary, whilst alive, act a beneficial part. The excreta of man whilst putrifying never exhibit the presence of microscopic animalculæ, whilst we find abundance of them in the same matters when in a state of decay. “A wise arrangement of nature has assigned to the infusoria the dead bodies of higher orders of beings for their nourishment, and has in these animalculæ created a means of limiting to the shortest possible period the deleterious influence which the products of dissolution and decay exercise upon the life of the higher classes of animals. The recent discoveries which have been made respecting these creatures are so extraordinary and so admirable, that they deserve to be made universally known.”
It is not to that which lives, but to that which has lived and is now dead, that we must look for the sources of those terrible fevers which destroy humanity in so many fine countries. Nor is it necessary that marshes be present, nor recently inundated lands. Egypt, annually inundated, is healthy at all times, but it is always cultivated; the desert also, which is never cultivated, and incapable of any cultivation, is also healthy. The Arabian desert which skirts the cultivated spots, converting them into so many oases, is perfectly healthy; on its soil the traveller may sleep securely; but let him cross the boundary of the water drain or stream forming the oasis, and sleep within the limits of that vegetation so delightful to look at, and violent fever is sure to overtake him on the morrow, so powerfully in this instance does nature react on man, when altering the soil, he prepares with his own hand the flowery path which leads him to the grave.
§ 2. On the Origin and Action of Humus.—To Liebig we unquestionably owe the first philosophical investigation into the history of humus. Innumerable difficulties and prejudices beset the inquiry. It was he who first showed that all vegetables and all their component parts, so soon as they cease to live, become liable to two forms of decomposition,—to putrefaction and to rottenness, that is to fermentation, and to that slow combustion to which Liebig gave the name of eremacausis, a Greek term, expressing by its original meaning the fact of slow combustion, to which the illustrious German likened that process which we commonly express by the term of pourriture, or rottenness. By this last-named process the combustible parts of bodies in decomposition combine with the oxygen of the air.
The decomposition of the rotting of the woody fibre is attended with this peculiarity—when in contact with the air, it converts the oxygen into an equal volume of carbonic acid; so soon as the supply of the oxygen ceases the rottenness stops. Now remove this carbonic acid, and add a fresh supply of oxygen, and the rotting commences, and carbonic acid reappears. The presence of water is essential to this change; the substances called antiseptic arrest it at once. Now the woody fibre in this condition of slow combustion or rottenness is precisely what we call humus or ulmine.
The functions of this humus are no doubt remarkable, and in respect of it some agricultural theories have been formed, resting on no solid basis. What seems to be tolerably well ascertained is, that in a soil permeable to air, the oxygen of the atmosphere continues to act on the humus, giving origin to carbonic acid, and thus furnishing an atmosphere for the roots of plants growing in that soil. The springing of the roots themselves seems to depend on the presence of this atmosphere; hence the labour and pains to pulverize the soil, and to give access by such processes to the atmospheric air. At this period of their growth the roots perform all the offices of their leaves which are ultimately to appear; and soon the plant has two sets of nourishing organs, the roots and the leaves. In hot summers plants derive their carbonic acid wholly from the air.
Thus gradually is formed that humus or ulmine to which agriculturists attach so much importance; that vegetable mould supposed to be the richest of all soils. But where it forms, a kind of putrefaction continually goes on; the soil is influenced deeply as a residence for man. No valetudinarian takes up his abode in the centre of a rich vegetation in hopes of recovering his health and strength, his elastic step, and freedom from lassitude and weariness; he, on the contrary, seeks other regions, where vegetation is scant, humus is not forming, and the soil is never turned over by human industry.
When vegetation is purely natural, that is when man does not interfere, the growth of plants does not in the least exhaust the soil. Look at the meadow and the virgin forest! Now chemistry explains this, or nearly so. But so soon as man interferes, he must be prepared to undertake the whole labour; if he acts on the earth, the air, and the waters, they will react on him, and sometimes with fearful effect. Beyond the processes she exhibits, and which he may read as best he can, she reveals nothing; all her secrets must be extracted from her by science, by philosophy, by the slow procedure of experiment and observation. A traveller from a distant land prepares to cross deserts of which he has had no previous experience; shortly he discovers an oasis, which to him seems a paradise, and he proposes resting for the night within its treacherous circle; but the wild Arab, the native guide, knows better, and explains to him briefly that the desert alone is healthy, and to rest a night within that seeming paradise is death. It is the Homeric tale of the syrens reduced to a reality; gorgeous decorated plants, sweet-smelling flowers, perfumes of Arabia, invite you to enter that island destined, should you unhappily accept the invitation, to prove the resting-place of all your labours.
It may seem paradoxical to maintain that by cultivation we at times render the earth insalubrious, at times comparatively the reverse, but the fact is so. It was Humboldt, as I have already remarked, who said that when Europeans first emigrated to America, the soil of certain northern states was found equal to the growth of wheat, and ague afflicted the population. With the destruction of the forests, the agues have disappeared, and wheat can no longer be grown; in the place of agues men are now afflicted with pulmonary consumption. Whoever has seen the marshy and boggy land, at times a lake, at others a black tremulous morass, and compared it with the rich drained Polder, its neat and compact farm-house, exhaustless meadows, herds of cattle, and the contented air of its well-to-do proprietor, will at once perceive that whatever might be the evil, unless it were a something truly grievous, so delightful a metamorphosis of a spot doomed by nature to eternal sterility, entailed on man, that evil was fully compensated for by the results obtained towards man’s happiness. There is, there can be, or at least there never was, any unmixed good on earth: the whole is a system of comparison and compensation; of profit or loss; of gains and drawbacks.
When the English army died off at Walcheren the inhabitants of the province were perfectly healthy, and could not comprehend the cause of the calamity. It was the same in the Crimea. Under other arrangements, those more consonant with common sense and experience, the results might have been different; still it is certain that masses of young men of immature years cannot be withdrawn from their native soil and parents’ hearths without suffering severely the consequence of the every way unnatural position they are forced to occupy; unnatural physically and morally. Barrack-rooms are not homes. No varied society is to be found there; no amusement, no employment for mind and body; it is man cut off from all human industry and enjoyment; no solace when ill, no comfort under suffering: that young men with unformed constitutions should “die off like flies,”[41] need excite no surprise.