THE LIVING WORLD—ITS EXTENT AS REVEALED BY THE MICROSCOPE—HOW ITS REMAINS ARE DISPOSED OF WHEN LIFE HAS CEASED.  
§ 1. It has been often remarked, and with great truth, that the world abounds with life. In the remains of that which had once lived, which was at one period organic, the illustrious Cuvier and the great school to which he belonged saw the materials of life, the food, in fact, of that which exists; he held that between the inorganic and organic worlds there was an impassable gulf, or in other words, an inconvertibility or a metamorphosis, call it by what name you will. This plausible theory, with many others, is now controverted by modern chemists, who boldly assert that no organic atoms or molecules, as such, can serve as food for a plant or an animal. But be this as it may—for chemists admit that the incombustible constituents or the salts of the blood, so essential to the nourishment or support of animal life, must have passed through organic bodies27—one thing is certain, that the extent of life on the globe can scarcely be imagined. For first, as regards the vegetable kingdom, do we not observe how, as spring and summer advance, the organic beings which during winter had lain dormant at the bottom, or deeply entombed in the waters (I speak not of those to be seen at all times on the surface of the earth), rise to the surface, bringing with them countless myriads of the ova of aquatic animals and of those which haunt the surface of the water? Amongst these stand pre-eminent the infusoria or zoophytes; with these the atmosphere also becomes loaded. They form, in fact, the substratum of all animal life, constituting the food not only of animals somewhat larger than themselves, but of many much larger, as the various species of the cyprinus. Many valuable gregarious fishes, as the herring, char, and the finer species of trout, live on entomostraca; they in their turn become the food of larger and more voracious fishes. Even the whale lives on food a portion of which is almost microscopic. Now, withdraw the water by which all this life subsists, and putrescence, or fermentation and decay, must be the result upon a mass of life of which the amount may be faintly conjectured by the fact that 4,100,000,000 millions of infusoria may be found in a square inch. These insects, when dead, are found in strata extending to some acres, and many of the fossils thus discovered belong to species of genera now alive. The principles of life were at least as active in what we call the old world (though in reality the young world), as in the present; the researches of Ehrenberg, repeated by many others, have placed these opinions beyond dispute.
Now, it is by no means improbable—nay, it is almost certain—that many species of these infusoria reside in the vapour of the atmosphere.
The Austrian physicians came to the conclusion that the Asiatic cholera was of local or terrestrial origin; the facts mentioned above confirm this view to a certain extent, by disproving the general epidemic laws supposed to regulate the progress of cholera and of fever (in which cholera usually terminates), and by showing that the disease sought out, as it were, the inhabitants of certain districts favourable for the production of the deleterious influences I am now about to consider. When the epidemical influence was superadded to these, the disease appeared; its independence of changes in temperature may have been owing to other circumstances not yet investigated. Connected with this evolution of vegetable life in spring and summer, and with its effects on man, is what is called the blooming of plants. The presence of stagnant waters and of foul ditches may be discovered even at a distance by the odour of gases, especially of the sulphuretted hydrogen, they emit. Now, oxygen decomposes this gas, and thus it is not so dangerous as represented to live near waters impregnated with it; but should mud or vegetable refuse be left exposed by the drying up of the waters, this gas ascends wherever the decayed matter is renewed or turned over. Venice, Amsterdam, and other great cities similarly situated, are not unhealthy, although their canals abound with mud; but so soon as the traffic ceases or becomes trifling, a mud odour arises, originating in what the French call epuration or floraison d’eau. In every country where there are ponds, canals, or ditches, this vegetable growth takes place so soon as the temperature of the water reaches 60° Fahr. As the quickening of the plants extends from above downwards, from the leaves and stalk towards the roots, these expand, and the mud becomes loosened; the plants imbibe carbon and give out oxygen, and this circulation contributes to the loosening and to the rising of the mud along with the plant. I have witnessed several square yards of mud raised in this way from the bottom of the waters. It subsides, of course, in due time.
We have seen that the vital force has no influence upon the combination of the simple elements, as such, into chemical compounds. “No element of itself is capable of serving for the nutrition and development of any part of an animal or vegetable organization;” the vital force by its influence merely combines inferior groups of simple atoms into atoms of a higher order.
How stands it with the decomposition of animal and vegetable bodies when the influence of the vital and conservative power has been withdrawn? Let us attend to what an illustrious chemist has said on this subject:—“Universal experience teaches us, that all organized beings after death suffer a change, in consequence of which their bodies gradually vanish from the surface of the earth. The mightiest tree, after it is cut down, disappears, with the exception, perhaps, of the bark, when exposed to the action of the air for thirty or forty years. Leaves, young twigs, the straw which is added to the soil, juicy fruits, &c., disappear much more quickly. In a still much shorter time animal matters lose their cohesion; they are dissipated in the air, leaving only the mineral elements which they had derived from the soil.” “This grand natural process of the dissolution of all compounds formed in living organisms begins immediately after death, when the manifold causes no longer act, under the influence of which they were produced. The compounds formed in the bodies of animals and of plants undergo in the air, with the aid of moisture, a series of changes, the last of which are the conversion of their carbon into carbonic acid, of the hydrogen into water, of their nitrogen into ammonia, of their sulphur into sulphuric acid. Thus their elements resume the form in which they can again serve as food for a new generation of plants and animals. Those elements which had been derived from the atmosphere, take the gaseous form, and return to the air; those which the earth had yielded return to the soil. Death, followed by the dissolution of the dead generation, is the source of life for a new one. The same atom of carbon which is a constituent of a muscular fibre in the heart of a man, assists to propel the blood through his frame, was perhaps a constituent of the heart of one of his ancestors; and any atom of nitrogen in our brain has perhaps been a part of the brain of an Egyptian or of a negro. As the intellect of the men of this generation draws the food required for its development and cultivation from the products of the intellectual activity of former times, so may the constituents or elements of the bodies of a former generation pass into and become part of our own frames.” “The proximate cause of the changes which occur in organized bodies after death, is the action of the oxygen of the air on many of their constituents. This action only takes place when water—that is, moisture—is present, and a certain temperature is required for its production.”
Let us not, then, be surprised at the seemingly discordant results arrived at, and at the contradictory observations which have been made in the best faith possible, and with every regard to truth in science. The circumstances which seemed to be identical are merely analogous, but in point of fact are essentially distinct, as proved by the results. Changes inappreciable by human sense and as yet by philosophical instruments, may and no doubt do effect results, to man seemingly contradictory, simply because he comprehends them not. As chemical science makes progress, these differences are being reconciled and understood. Thus, as mere temperature exercises a truly remarkable influence over the nature of the products of fermentation, may it not be the efficient cause of the difference we observe between the malaria of the delta of the Mississippi and that floating near the muddy banks of the Scheldt? The juice of carrots, beet-root, or onions, which is rich in sugar, when allowed to ferment at ordinary temperature yields the same products as grape-sugar, but at a higher temperature the whole decomposition is changed—there is a much less evolution of gas, and no alcohol is formed.
In the fermented liquor there is no longer any sugar, and thus may it be in the great laboratory of nature; the product of the fermentation will assume in one locality a character it does not possess in another. The elements are the same; there is merely a change in temperature.
Are there facts to prove that certain states of transformation or putrefaction in a substance, are likewise propagated to parts or constituents of the living animal body? Such facts exist. On no other principle but that of assimilation can we explain the phenomena of poisoning by the puncture of the living hand in dissecting-rooms, the instrument being impregnated with a fermentescible and putrefactive substance, there undergoing a decomposition. Similar, unquestionably, must be the action of animal poisons, such as that of poisonous substances, whether animal or vegetable, of the poisons giving rise to zymo............