PHENOMENA OF ANIMAL LIFE.

Distinction between the Kingdoms of Nature—Progress of Animal Life—Sponges—Polypes—Infusoria—Animalcula—Phosphorescent Animals—Annelidans—Myriapoda—Animal Metamorphoses—Fishes—Birds—Mammalia—Nervous System—Animal Electricity—Chemical Influences—Influence of Light on Animal Life—Animal Heat—Mechanical Action—Nervous Excitement—Man and the Animal Races, &c.

“A stone grows; plants grow and live; animals grow, live, and feel.” Such were the distinctions made by LinnÆus, between the conditions of the three kingdoms of nature. We cannot, however, but regard them as in all respects illogical. The stone—a solid mass of unorganized particles—enlarges, if placed in suitable conditions, by the accretion of other similar particles around it; but it does not, according to any meaning in which we use the word, grow. Plants and animals grow; and they differ, probably, only in the phenomena of sensation. Yet, the trembling mimosa, and several other plants, appear to possess as much feeling as sponges and some of the lower classes of animals. By this definition, however, of the celebrated Swedish naturalist, we have a popular and simple expression of a great fact.

As we have only to examine the question of the agency of the physical forces upon animal life, we must necessarily confine our attention to the more striking phenomena with which science has made us acquainted; and, having briefly traced the apparent order in which the advance of organization proceeded, we must direct our few concluding remarks to the physico-physiological influences, which we must confess to know but too imperfectly.

We learn that, during the states of progress which geology, looking into the arcana of time, has made us acquainted with, a great variety of animal forms were brought into existence. They lived their periods. The conditions of the surface of the earth, the sea, or the atmosphere, were altered; and, no longer fitted for the enjoyments of the new life, these races passed away, and others occupied their places, which, in turn, went through all the stages of growth, maturity, and decay; until at length, the earth being constituted for the abode of the highest order of animals, they were called into existence; and man, the intellectual monarch of the world, was placed supreme amongst them all. Types of nearly all those forms of life which are found in the fossil state are now in existence; and if we examine the geographical distribution of animals—the zones of elevation over the surface of the earth, and the zones of depth in the ocean,—we shall find, now existing, animal creations strikingly analogous to the primitive forms and conditions of the earth’s inhabitants. From the depths of the ocean we may even now study—as that most indefatigable naturalist, Professor Edward Forbes, has done—the varying states of organization under the circumstances of imperfect light and varying temperature.[261]

The gradual advance of animal life in the ascending strata has led to many speculations, ingenious and refined, on the progressive development of animals. That the changes of the inorganic world have impressed new conditions on the organic structures of animals, to meet the necessities of their being, must be admitted. Comparative anatomy has demonstrated that such supposed differences really existed between the creatures of secondary formations—those of the tertiary and the present periods. It has been imagined, but upon debatable foundations, that the atmosphere, during the secondary periods, was highly charged with carbonic acid; and, consequently, that though beneficial to the growth of plants, and peculiarly fitted for the conditions required by those which the fossil flora makes us acquainted with, it was not adapted to support any animals above the slow-breathing, cold-blooded fishes and reptiles. Under the action of the super-luxuriant vegetation of these periods, this carbonic acid is supposed to have been removed, an addition of oxygen furnished; and thus, consequently, the earth gradually fitted for the abode of warm-blooded and quick-breathing creatures. We do, indeed, find a very marked line between the fossil remains of the lias formations which enclose the saurians, and the wealden, in which birds make their appearance more numerously than in any previous formation.

Founded upon these facts, speculations have been put forth on the gradual development of animals from the lowest up to the highest orders. Between the polype and man a continuous series has been imagined, every link of the chain being traced into connection with the one immediately succeeding it; and, through all the divisions, zoophytes, fishes, amphibia, reptiles, birds, and mammalia are seen, according to this hypothesis, to be derived by gradual advancement from the preceding orders. The first having given rise to amphibia,—the amphibion gives birth to the reptile,—the reptile advances to the bird,—and from this class is developed the mammal. A slight investigation will convince us that this view has no foundation. Although a certain relationship may be found between some of the members of one class, and those of the other immediately joining it, yet this is equally discovered to exist towards classes more remote from each other; and in no one instance can we detect anything like the passage of an animal of one class into an animal of another. Until this is done, we cannot but regard the forms of animal life as distinct creations, each one fitted for its state of being, springing from the command of the great First Cause.[262]

But it is time to quit these speculative questions, and proceed to the examination of the general conditions of animal life at the present time.

Lowest in the scale of animals, and scarcely distinguishable from a vegetable, we find the sponge, attached to and passing its life upon a rock, exhibiting, indeed, less signs of feeling than many of the vegetable tribes. The chemical differences between vegetables and sponges are, however, very decided; and we find in the tissues of the sponge a large quantity of nitrogen, a true animal element, which exists, but in smaller quantities, in vegetables.

These creations, standing between vegetable and animal life, possess the singular power of decomposing carbonic acid, as plants do; and the water in which they live always contains an excess of free oxygen.

The polypes are a remarkably curious class. “Fixed in large arborescent masses to the rocks of tropical seas, or in our own climate attached to shells or other submarine substances, they throw but their ramifications in a thousand beautiful and plant-like forms; or, incrusting the rocks at the bottom of the ocean with calcareous earth, separated from the water which bathes them, they silently build up reefs and shoals, justly dreaded by the navigator; and sometimes giving origin, as they rise to the surface of the sea, to islands, which the lapse of ages clothes with luxuriant verdure, and peoples with appropriate inhabitants.”[263]

Most of the polypes are fixed and stationary; but the hydra and some others have the power of changing their positions, which they do in search of the light of the sun. They do not appear to have organs of sight requiring light; but still they delight in the solar influences. The most extraordinary fact connected with the hydra is its being multiplied by division. If an incision be made in the side of a hydra, a young polype soon developes itself; and if one of these creatures be divided, it quickly restores the lost portion of its structure. The varieties of the polypes are exceedingly numerous, and many of them are in the highest degree curious, and often very beautiful. The actiniÆ, like flowers, appear to grow from the rocks, unfolding their tentacula to the light; and, in the excitement due to their eagerness for prey, they exhibit a beautiful play of colours and most interesting forms. Microscopic zoophytes of the most curious shapes are found,—all of which attest, under examination, the perfection of all created things.

Infusoria and animalcula,—animals, many of them, appearing under the microscope as little more than a transparent jelly,—must be recognized as the most simple of the forms of life. They exist in all waters in uncountable myriads; and, minute creatures as they are, it has been demonstrated that many of the great limestone hills are composed entirely of their remains.

The acalephÆ, or the phosphorescent animals of the ocean, are no less curious. From creatures of the most minute size, they extend to a considerable magnitude, yet they appear to be little more than animated masses of sea-water. If any one of these sea-jellies, or jelly-fishes as they are often called (even the largest varieties of them), is cast upon the shore, it is soon, by the influence of the sun, converted into a mere fibre no thicker than a cobweb: an animal weighing seven or eight pounds is very soon reduced to as many grains. There are numerous kinds of these singular creatures, most of which are remarkable for the powerful phosphorescent light they emit. The beroes and the pulmonigrade shine with an intense white light many feet below the surface, whilst the Cestum Veneris, or girdle of Venus, gliding rapidly along, presents, on the edge of the wave, an undulating riband of flame of considerable length. There can be no doubt that this arises from the emission of phosphorescent matter of an unknown kind from the bodies of these animals.

The microscope has made us familiar with the mysteries of a minute creation which we should not otherwise have comprehended. These creatures are found inhabiting the waters and the land, and they exist in the intestinal structure of plants and animals, preying upon the nutritive juices which pass through their systems. Although these beings are so exceedingly small that even the most practised observer cannot detect them with the naked eye, they are proved, by careful examination under the microscope, to be in many cases elaborately organized. Ehrenberg has discovered in them filamentary nerves and nervous masses, and even vessels appropriated to the circulation of fluids, showing that they belong really to a high condition of existence.

Passing over many links in that curious chain which appears to bind the animal kingdom into a complete whole, we come to the articulata of Cuvier—the homogangliata of Owen.

All those creatures which we have been hitherto considering are too imperfect in the construction of their simple organizations to maintain a terrestrial existence; they are, therefore, confined to a watery medium. In the articulata, we have evidences of higher attributes, and indications of instincts developed in proportion to the increased perfection of organization. Commencing with the annelidans, all of which, except the earthworms, are inhabitants of the waters, we proceed to the myriapoda, presenting a system intermediate in every respect between that of worms and insects; we then find embraced in the same order, the class insecta, which includes flies and beetles of all kinds; and, as the fourth division of articulated beings, the arachnidans or spiders; and, lastly, the marine tribe of crustaceans.

The most remarkable phenomena connected with these animals are the metamorphoses which they undergo. The female butterfly, for instance, lays eggs, which, when hatched, produce caterpillars: these live in this state for some time, feeding upon vegetables, and, after casting their skins as they increase in size, at last assume an entirely different state, and, dormant in their oblong case, they appear like dead matter. This chrysalis, or pupa, is generally preserved from injury by being embedded in the earth, from which, after a season, a beautifully perfect insect escapes, and, floating on the breeze of summer, enjoys its sunshine, and revels amidst its flowers.

No less remarkable is the metamorphosis of the caducibranchiate amphibia, passing through the true fish condition of the tadpole to the perfect air-breathing and four-footed animal, the frog.

A metamorphosis of the crustaceans, somewhat similar to that which takes place in insects, has been of late years creating much discussion amongst naturalists: but the question appears to be now settled by the careful and long-continued observations of Mr. Thompson and Mr. R. C. Couch.

A wide line of demarcation marks the separation of the invertebrata from the four great classes of vertebrate animals—fishes, reptiles, birds, and mammalia. Every part of the globe,—the ocean and the inland lake,—the wide and far-winding river, and the babbling stream,—the mountain and the valley,—the forest with its depth of shade, and the desert with its intensity of light,—the cold regions of the frost-chained north, and the fervid clime within the tropics—presents for our study innumerable animals, each fitted for the conditions to which it is destined; and through the whole we find a gradual elevation in the scale of intelligence, until at last, separated from all by peculiar powers, we arrive at man himself.

In each of these four classes the animals are furnished with a bony skeleton, which is in the young animal little more than cartilage; but, as growth increases, lime becomes deposited, and a sufficient degree of hardness is thus produced to support the adult formation. Some anatomists have endeavoured to show that even in the mechanical structure of the bony fabrics of animals, we are enabled to trace a gradual increase in the perfection of arrangement, from the fish until the most perfect is found in man. Many of the mammalia, however, are furnished with skeletons which really surpass that of man. These belong to animals which depend for subsistence upon their muscular powers, and with whom man is, in this particular, on no equality. What is the lord of the creation, compared with the antelope for fleetness, or with the elephant and many other animals for strength?

As we ascend the scale of animal life we find a more perfectly developed nervous system; and the relative size of the brain, compared with that of the brute, is found progressively to increase, until it arrives at the utmost perfection in man. On the system of nerves depends sensation, and there can be no doubt that the more exalted the order of intelligence displayed, the more exquisitely delicate is the nervous system. Thus, in this world, refined genius must necessarily be attended with a condition of sensibility which, too frequently, to the possessor is a state of real disease.

It must be evident to every reader that but very few of the striking features of animal life have been mentioned in the rapid survey which has been taken of the progress of animal organization. The subject is so extensive that it would be quite impossible to embrace it within any reasonable limits; and it furnishes matter so curious and so instructive, that, having once entered on it, it would have been difficult to have made any selection, and we must have devoted a volume to the Æsthetics of natural science. Passing it by, therefore, with the mere outline which has been given, we must proceed to consider some of the conditions of vitality.

Bell has proved that one set of nerves is employed in conveying sensation to the brain, and another set in transferring the desires of the will to the muscles. By the separation of a main branch of one of the nerves of sensation, although all the operations of life will still proceed, the organ to which that nerve goes is dead to its particular sense. In like manner, if one of the nerves of volition is divided, the member will not obey the inclination of the brain. It is evident, therefore, although many of the great phenomena of vital force are dependent on the nervous system, and the paralysis of a member ensues upon the separation or the disease of a nerve, that the nerves are but the channels through which certain influences are carried. The vis vitÆ or vital principle—for we are compelled by the imperfection of our knowledge to associate under this one term the ultimate causes of many of the phenomena of life—is a power which, although constantly employed, has the capability of continually renewing itself by some inexplicable connection existing between it and many external influences. We know that certain conditions are necessary to the health of animals. Diseased digestion, or any interruption in the circulation of the blood, destroys the vital force, and death ensues. The processes of digestion and of the circulation are perfectly understood, yet we are no nearer the great secret of the living principle.

Animals are dependent on several external agents for the support of existence. The oxygen of the air is necessary for respiration. Animal heat, as will be shown presently, is in a great measure dependent upon it. The external heat is so regulated that animal existence is comfortably supported. Electricity is without doubt an essential element in the living processes; and, indeed, many physiologists have been inclined to refer vital force to the development of electricity by chemical action in the brain. This view has, however, no foundation in experiment beyond that afforded by the appearance of electric currents, when the brain is excited. This proves no more than that the operations of mind develope physical power in the matter with which it is mysteriously connected.

The phenomena of the Torpedo and Gymnotus we have already noticed,[264] and there are other creatures which certainly possess the power of secreting and discharging electricity. Galvani’s experiments, and those of Aldini, appear to show—and the more delicate researches of Matteucci have satisfactorily determined—that currents of electricity are always circulating in the animal frame;—that positive electricity is constantly passing from the interior to the exterior of a muscle. Matteucci, by arranging a series of muscles, has formed an electric pile of some energy.[265] These currents have been detected in man, in pigeons, fowls, eels, and frogs.

In the human body it is evident a large quantity of electricity exists in a state of equilibrium. Du Bois Raymond has shown that we may by mere muscular motion give rise to electric currents which can be measured by the galvanometer. This, however, may be said of every substance. It is perhaps more easily disturbed in the human system; indeed, the manifestation of sparks from the hair and other parts of the body by friction is not uncommon. Every chemical action, it has been already shown, gives rise to electrical manifestations; and the animal body is a laboratory, beautifully fitted with apparatus, in which nearly every chemical process is going on. It has been proved that acid and alkaline principles are constantly acting upon each other through the tissues of the animal frame; and we have the curious phenomena of endosmose and exosmose in constant effort, and catalysis or surface force, operating in a mysterious manner.[266]

With the refined physiological questions connected with the phenomena of sensation we cannot deal, nor will any argument be adduced for or against the hypothesis which would refer these phenomena to some extraordinary development of electric force in the brain. The entire subject appears to stand beyond the true limits of science, and every attempt to pass it is invariably found to lead to a confused mysticism, in which the real and the ideal are strangely confounded. Science stops short of the phenomena of vital action.

We cannot, however, but refer to the idea entertained by many that the brain is an electric battery, and the nerves a system of conductors. On this view Sir John Herschel remarks:—“If the brain be an electric pile constantly in action, it may be conceived to discharge itself at regular intervals, when the tension of the electricity reaches a certain point, along the nerves which communicate with the heart, and thus excite the pulsation of that organ.” Priestley, however, appears to have been the first to promulgate this idea.

Light is an essential element in producing the grand phenomenon of life, though its action is ill understood. Where there is light, there is life, and any deprivation of this principle is rapidly followed by disease of the animal frame, and the destruction of the mental faculties. We have proof of this in the squalor of those whose necessities compel them to labour in places to which the blessings of sunshine never penetrate, as in our coal-mines, where men having everything necessary for health, except light, exhibit a singularly unhealthy appearance. The state of fatuity and wretchedness to which those individuals have been reduced who have been subjected for years to incarceration in dark dungeons, may be referred to the same deprivation. Again, in the peculiar aspect of those people who inhabit different regions of the earth under varying influences of light, we see evidence of the powerful effects of solar action. Other forces, as yet undiscovered, may, in all probability do, exert decided influences on the animal economy; but, although we recognize many effects which we cannot refer to any known causes, we are perfectly unable to imagine the sources from which they spring.

It will be interesting now to examine the phenomena of animal heat, the consideration of which naturally leads us to consider the digestive system, the circulatory processes, and the effects of nervous excitation.

The theory, which attributes animal heat to the combination of the carbon of the food taken into the stomach with the oxygen of the air inspired through the lungs, has become a very favourite one. It must, however, be remembered that it is by no means new. The doctrines of Brown, known as the Brunonian system, and set forth in his Elementa MedicinÆ, are founded upon similar hasty generalizations. Although, without doubt, true in a certain degree, it is not so to the extent to which its advocates would have us believe. That the carbonaceous matter received into the stomach, after having undergone the process of digestion, enters into combination with the oxygen breathed through the lungs or absorbed by the skin, and is given off from the body in the form of carbonic acid, and that, during the combination, heat is produced, by a process similar to that of ordinary combustion, is an established fact; but the idea of referring animal heat entirely to this chemical source, when there are other well-known causes producing calorific effects, is an example of the errors into which an ingenious mind may be led, when eagerly seeking to establish a favourite hypothesis.

Animal and vegetable diet, which is composed largely of carbon and hydrogen, passes into the digestive system, and becomes converted into the various matters required for the support of the animal structure. The blood is the principal fluid employed in distributing over the system the necessary elements of health and vigour, and for restoring the waste of the body. This fluid, in passing through the lungs, undergoes a very remarkable change, and not merely assumes a different colour, but really acquires new properties, from its exposure to the air with which the cells of these organs are filled. By a true chemical process, the oxygen is separated from the air, that oxygen is made to combine with the carbon and hydrogen, and carbonic acid and water are formed. These are liberated and thrown off from the body either through the lungs or by the skin. In the processes of life, as far as we are enabled to trace them, we see actions going on which are referred to certain causes which we appear to explain. Thus, the combination of the oxygen of the air with the carbon of the blood is truly designated a case of chemical affinity; and we find that in endeavouring to imitate the processes of nature in the laboratory, we are, to a certain extent, successful. We can combine carbon and oxygen to produce carbonic acid; and we know that the result of that combination is the development of certain definite quantities of heat. Let us examine the conditions of this chemical phenomenon, and we shall find that in the natural and artificial processes,—for we must be allowed to make that distinction,—there are analogous circumstances. If we place a piece of pure carbon, a lump of charcoal or a diamond, in a vessel of air, or even of pure oxygen gas, no change will take place in either of these elements, and, however long they may be kept together, they will still be found as carbon or diamond, and oxygen gas. If we apply heat to the carbon until it becomes incandescent, it immediately begins to combine with the oxygen gas,—it burns;—after a little time all the carbon has disappeared, and we shall find, if the experiment has been properly made, that a gas is left behind which is distinguished by properties in every respect the reverse of those of oxygen, supporting neither life nor combustion, whereas oxygen gives increased vigour to both. We have now, indeed, carbonic acid gas formed by the union of the two principles.

A dead mass of animal matter may be placed in oxygen gas, and, unless some peculiar conditions are in some way brought about, no change will take place; but, if it were possible to apply the spark of life to it, as we light up the spark in the other case, or if, as that is beyond the power of man, we substitute a living creature, a combination between the carbon of the animal and the gas will immediately begin, and carbonic acid will be formed by the waste of animal matter, as in the other case it is by the destruction of the carbon; and, if there is not a fresh supply given, the animal must die, from the exhaustion of its fabric. Now, in both these cases, it is clear that, although this chemical union is a proximate cause of heat, there must be existing some power superior to it, as the ultimate cause thereof.

The slow combustion (eremacausis) of vegetable matter, decomposing under the influence of moisture and the air, does not present similar conditions to those of the human body, although it has been insisted upon to be in every respect analogous. That the results resemble each other is true, but we must carefully distinguish between effects and causes; and the results of chemical decomposition in inert matter differ from those in the living organism. The vegetable matter has lost the principle of organic life, and, that gone, the tendency of all things being to be resolved into their most simple forms, a disunion of the elements commences: oxygen, hydrogen, and carbon pass off either in the gaseous state or as water, whilst some carbon is liberated in a very finely-divided condition, and enters slowly into combination with oxygen supplied by the water or the air. Hydrogenous compounds are at the same time formed, and, under all these circumstances, as in all other chemical phenomena, an alteration of temperature results. Heat results from the chemical changes, and eventually true combustion begins.

The animal tissue may act in the same way as platina has already been shown to act in producing combination between gases; but of this we have no proof. We know that electricity is capable of producing the required conditions, and we also learn, from the beautiful researches of Faraday, that the quantity of electricity developed during decomposition is exactly equal to that required to effect the combination of the same elements. Thus it is quite clear that, during the combination of the carbon of the blood with the oxygen of the air, a large amount of electricity must become latent in the compound. The source of this we know not: it may be derived from some secret spring within the living structure, or it may be gathered from the matter surrounding it. There is much in nervous excitation which appears like electrical phenomena, and attempts have been frequently made to refer sensation to the agency of electricity. But these are the dreams of the ingenious, for which there is but little waking reality.

Every mechanical movement of the body occasions the development of heat; every exertion of the muscles produces sensible warmth; and, indeed, it can be shown by experiment that every expansion of muscular fibre is attended with the escape of caloric, and its contraction with the absorption of it. There are few operations of the mind which do not excite the latent caloric of the body, and frequently we find it manifested in a very remarkable manner by a suddenly-awakened feeling. The poet, in the pleasure of creation, glows with the ardour of his mind, and the blush of the innocent is but the exhibition of the phenomenon under some nervous excitation, produced by a spirit-disturbing thought. Thus we see that the processes of digestion and respiration are not the only sources of animal heat, but that many others exist to which much of the natural temperature of the body must be referred.

So much that is mysterious belongs to the phenomena of life, that superstition has had a wide scope for the exercise of its influence; and through all ages a powerful party of mankind have imagined that the spirit of human curiosity must be checked before it advances to remove the veil from any physiological causes. Hence it is that even at the present day so much that stands between what, in our ignorance, we call the real and the supernatural, remains uninvestigated. Even those men whose minds are sceptical upon any development of the truths of great natural phenomena,—who, at all events, will have proof before they admit the evidence, are ready to give credit to the grossest absurdities which may be palmed upon them by ingenious charlatans, where the subject is man and his relations to the spiritual world.

Man, and the races of animals by which he is surrounded, present a very striking group, consider them in whatever light we please. The gradual improvement of organic form, and the consequent increase of sensibility, and eventually the development of reason, are the grandest feature of animated creation.

The conditions as to number even of the various classes are not the least remarkable phenomena of life. In the lowest orders of animals, creatures of imperfect organization,—consequently those to whom the conditions of pain must be nearly unknown,—increase by countless myriads. Of the infusoria and other beings, entire mountains have been formed, although microscopes of the highest powers are required to detect an individual. Higher in the scale, even among insects, the same remarkable conditions of increase are observed. Some silkworms lay from 1,000 to 2,000 eggs; the wasp deposits 3,000; the ant from 4,000 to 5,000. The queen bee lays between 5,000 and 6,000 eggs according to Burmeister; but Kirby and Spence state that in one season the number may amount to 40,000 or 50,000. But, above all, the white ant (Termes fatalis) produces 86,400 eggs each day, which, continuing for a lunar month, gives the astonishing number of 2,419,200, a number far exceeding that produced by any known animal.

These may appear like the statements in which a fictionist might indulge, but they are the sober truths discovered by the most pains-taking and cautious observers. And it is necessary that such conditions should prevail. These insects, and all the lower tribes of the animal kingdom, furnish food for the more elevated races. Thousands are born in an hour, and millions upon millions perish in a day. For the support of organic life, like matter is required; and we find that the creatures who are destined to become the prey of others are so constituted that they pass from life with a perfect unconsciousness of suffering. As the animal creation advances in size and strength, their increase becomes limited; and thus they are prevented from maintaining by numbers that dominion over the world which they would be enabled from their powers to do, were their bands more numerous than we now find them.

The comparative strength, too, of the insect tribes has ever been a subject of wonder and of admiration to the naturalist. The strength of these minute creatures is enormous; their muscular power, in relation to their size, far exceeds that of any other animal. The grasshopper will spring two hundred times the length of its own body. The dragonfly, by its strength of wing, will sustain itself in the air for a long summer day with unabated speed. The house-fly makes six hundred strokes with its wings, which will carry it five feet, every second. The stag-beetle, were it the size of the elephant, would be able to tear up the largest mountains.

Such are the wonders of the natural world; from the zoophyte, growing like a flowering plant[267] upon an axis filled with living pith—a small remove from the conditions of vegetable life, upwards through the myriads of breathing things—to man, we see the dependence of all upon these physical powers which we have been considering.

To trace the effects of those great causes through all their mysterious phases is the work of inductive science; and the truths discovered tend to fit us for the enjoyment of the eternal state of high intelligence to which every human soul aspires.

That which the ignorant man calls the supernatural, the philosopher classes amongst natural phenomena. The ideal of the credulous man becomes the real to him who will bend his mind to the task of inquiry. Therefore to attempt to advance our knowledge of the unknown, to add to the stores of truth, is an employment worthy the high destiny of the human race. Remembering that the revelations of natural science cannot in any way injure the revelation of eternal truth, but, on the contrary, aid to establish in the minds of the doubting a firm conviction of its Divine origin and of man’s high position, we need never fear that we are proceeding too far with any inquiry, so long as we are cautious to examine the conditions of our own minds, that they be not made the dupe of the senses.

In the fairies of the hills and valleys, in the gnomes of the caverns, in the spirits of the elements, we have the attempts of the mind, when the world was young, to give form to the dim outshadowings of something which was then felt to be hidden behind external nature.

In the Oread, the Dryad, and the Nereid, we have, in like manner, an embodiment of powers which the poet-philosopher saw in his visions presiding over the mountain, the forest, and the ocean. Content with these, invested as they were with poetic beauty, man for ages held them most religiously sacred; but the progress of natural science has destroyed this class of creations. “Great Pan is dead,” but the mountains are not voiceless; they speak in a more convincing tone; and, instead of the ear catching the dying echo of an obscure truth, it is gladdened with the full, clear note of nature in the sweetest voice proclaiming secrets which were unknown to the dreams of superstition.