is no exception to this law in the whole circle of nature. The microscope has lately put us in possession of some facts which render the universality of the law doubtful; in what manner, and to what extent, will be stated hereafter. In the mean time, it may still be assigned as one of the most striking characters of living beings, that they derive their origin from generation. And lastly, it is equally characteristic of them, that they terminate their existence by death. The vital energies, by which the circle of actions and reactions necessary to life is sustained, at length decline, and finally become exhausted. It has been truly said, that life is motion, superinduced in matter peculiarly arranged, and that death is the cessation of this motion. But the vital powers cease to act from cause inherent in themselves, whereas unorganized bodies would preserve their existence forever were no extrinsic force applied to them. The attraction by which their particles are held in union can be disturbed only by the intervention of such a force. Some mechanical agent must separate their particles, some chemical power must alter their composition, in order that their destruction may be effected; but, though no mechanical agent disturbs the arrangement of its particles, and no chemical power changes its composition, the living body perishes from the operation of causes that are internal and inherent. An origin by genera tion, and a termination by death, are thus distinctive characters of living beings. Such is the train of phenomena which we find associated both in on. animal and vegetable bodies, and the assemblage of which is expressed by the general term of life. It is natural to conceive that these phenomena are attached to some permanent subject, as we say that matter is the permanent subject of certain qualities, such as extension, divisibility, attraction, repulsion, and so Vital principle, or principle of life, are the terms which have been employed to denote the supposed permanent subject with which the phenomena of living beings are connected; it is convenient to have such words, but it must never be forgotten that they are used, not to express anything that has been ascertained to exist, but merely to denote our mode of conceiving of the subject, The phenomena we have stated are common both to vegetable and animal bodies: there are characters by which these two great divisions of the organized world are distinguished from each other. These characters are derived from certain properties which are possessed by the one, but of which the other is destitute. Every living being must possess the power of assimilating foreign materials into its own substance; and, since it is a law of the vital economy, that life springs from life only, it must also be endowed with the property of communicating to its descendants a nature similar to its own; otherwise every species of creatures must perish with the primitive race. The faculties of nutrition and reproduction are, therefore, properties which must be common to all living beings; and accordingly, with the exception hereafter to be mentioned, they are possessed by the most simple. The plant absorbs and assimilates nourishment; it likewise developes a germ, by the evolution of which a being is matured that possesses a similar organization and performs a similar function. But to these are limited all the functions which are exercised by this extensive class of organized bodies. To animals are superadded two other faculties, those of sensation and voluntary motion. The faculties of animals, therefore, consist of two kinds; first, of those which they possess in common with vegetables, and which are, therefore, termed vegetative, or which, because they are essential to the maintenance of life in the individual, and to the perpetuation of it in the species, are sometimes denominated vital; these are nutrition and reproduction. And secondly, of those which are peculiar to animals, and which because they belong exclusively to this division of living beings, are termed animal; these are sensation and voluntary motion. That no vegetable is really capable of sensation or voluntary motion is certain, though the sensitive plant shrinks when touched, and many curious cases are related which appear to prove that a few vegetables, under certain circumstances, possess the power of performing a kind of locomotion. But all the movements of vegetables which seem to indicate the possession of sensation and voluntary motion, may be explained on the supposition that the substance of which they are composed is endowed with the power of contracting on the application of a stimulus; a power which appears to belong to a few vegetables, which all animals pos sess, and which it is certain exists without consciousness, and therefore without volition. That all the vegetable functions are performed without consciousness we have the demonstration in ourselves: for man exercises both classes of functions, the vegetative and the animal. By observing what passes within ourselves, we know that there is no connexion between mere vegetative life and sensation. We are conscious that we exist: we are not conscious of the operation of the vegetative faculties by which we live. Of all the processes by which the aliment is converted into blood, for example, and the blood into the proper substance of the body, complicated as these processes are in the higher animals, we are wholly insensible : there can, therefore, be no reason to suppose that these functions are attended with consciousness in the vegetable in which the processes themselves are so much more simple. If in our own body a wound be made, attended with a loss of substance, this loss is speedily repaired: new fibres are formed, which arrange themselves, not only as if they were animated and intelligent, but the degree of wisdom with which they are disposed is perfect; yet all this is effected, not only without our having the least knowledge of the mode in which it is done, but even without our being sensible that it is done at all. Notwithstanding the apparent exceptions, therefore, which we shall have occasion more particularly to specify in the sequel, it may be stated as a general truth, that, since no vegetable possesses sensation and voluntary motion, and since no animal, with the ex ceptions above alluded to, is destitute of these faculties, they do afford characters peculiar to, and therefore descriptive of, animal existence. Life depends on certain conditions; these conditions depend on certain arrangements of material substances; such arrangements of material substances constitute organization; organization is thus an essential condition of life. In tracing the order of the phenomena, the first thing we observe is, a peculiar arrangement of certain textures, that is, a specific organization; the second we discover is, that the textures thus arranged exercise peculiar actions; that is, this particular organization performs a specific function. A determinate organization constitutes what is called an organ; the action of every organ constitutes what is denominated its function. Without the organ there is no function, for the plain reason, that, without the instrument by which the action is effected, there is no action in the order of the phenomena, therefore, organization, which is the primary condition of life, necessarily precedes the actions of that organization in which the functions of life consist. Organization is the antecedent; function is the sequent. The origin of the organization to which function is related as the sequent, is referrible in every case to a preexisting organization. Organization is not selfexistent, but so far back as it is possible for us to trace it, it is always preexistent. Matter neither organizes itself, nor is organized by any cause but one, a preexisting organization. : Excepting in the very lowest animals, which appear to consist of an homogeneous substance, similar in all respects to jelly, the animal body may be considered as an aggregate, formed of a number of organs; each organ is itself composed of a variety of tissues; each tissue is more or less common to all the organs. If we examine the different solids which enter into the composition of the living, or the recently dead body, in all the higher orders of animals, we find that they consist of the following substances; namely, bones, with their cartilages and ligaments, which may be considered as appendages to the bones; muscles, with their tendons; membranes of various descriptions; sacs of different structures; vessels of different kinds, and cerebral matter. There is no solid of the animal body which may not be included under one or other of these substances. All these substances, on a careful analysis, are reducible to three; namely, the cellular, the muscular, and the cerebral tissues. Of these the most simple in structure, the most abundant in quantity, and the most extensively diffused, is the first. The peculiar substance termed cellular tissue, enters as a constituent element into every other solid. It composes the main bulk of bones; it affords an external sheath to every muscle; it is interposed between the fibres of which every muscle consists; it encloses in a distinct envelope every nervous fibre; it composes almost the entire bulk of tendon, ligament, and cartilage; it enters largely into the composition of hair, nails, and other similar parts connected with the surface. The enamel of the the teeth is said to be the only solid in which it cannot be detected. It unites together all the different parts of the body, it fills up all the intervals between them. Were it possible to remove from the bones their earthy particles, and from the soft parts, the muscular fibres, the nervous matter and the fat; were it possible, at the same time, to empty the vessels and to evaporate the fluid, the body would remain nearly of the same size, and be sustained nearly of the same form by means of this substance alone. It may, therefore, be truly considered as the basis to which all the other parts of the body are attached, as the mould into which all the other kinds of matter are deposited. When examined with the naked eye, and gently distended, this substance is found to be composed of fibres or threads of extreme delicacy, finer than the finest cobweb. These fibres intersect each other in all directions, so as to leave between them minute spaces, which are termed cells. It is from this cellular appear ance, that the tissue derives its name. Its elementary structure has been the subject of much dispute it has recently been ascertained. It is chiefly to Dr. Milne Edwards, an English physician, resident in Paris, the able author of the very interesting and important papers at the head of this article, that we owe the complete establishment of the facts about to be detailed. In consequence of the opposite conclusions which the most distinguished physiologists deduced from their observations with the microscope, this instrument had been considered as valueless, and had sunk into very general neglect-a striking instance of that rashness of judg ment, founded on partial views, which is so fatal to the advancement of science. The reason why we are so imperfectly acquainted with the various objects around us, is, that our eyes are so bad; the great obstacle which opposes our successful prosecution of almost every science is, the imperfection of our senses. It is, therefore, most unreasonable to reject the aid of an instrument which increases the power of any sense a hundred or a thousand times. By adding thus prodigiously to its strength, it renders it a new sense. Without doubt the information it appears to convey must be admitted with caution, and must be corrected by the other senses and by the judgment-corrective powers to which we should be obliged to have recourse, were we endowed with a new sense. In itself it is an instrument of great value, and the labors of Prevost, Dumas, and Edwards in France, and of Bauer, of Sir Everard Home, and more recently of Captain Kater in our own country, show that its judicious employment is capable of communicating at once the most interesting and the most exact information. The cellular tissue, when in a state perfectly natural, having been subjected to no preparation capable of altering its properties, and when examined with a microscope of high magnifying power, is found to consist entirely of minute globules. These globules are arranged in irregular series, forming lines of different lengths, which take every possible direction, and intersect each other in every possible manner. From whatever part of the body the tissue be taken, both the arrange ment of the elementary globules and their diameter appear to be uniformly the same. Their diameter is estimated at about the eight thousandth part of an inch. An examination of this tissue in the four classes of vertebrated animals has led to the establishment of the curious fact, that in all the tribes of the mammalia, in birds, in reptiles, and in fishes, it is composed of globules which have precisely the same general appearance, and which are exactly of the same magnitude. Subsequently the investigation has been extended to invertebrated animals, in all of which this tissue presents the same globular structure, with this difference only, that while the greater number of the globules are of the same bulk as in the vertebrated animals, they are mixed with others of a larger volume, probably because these larger globules consist of a union of several of the elementary. The muscular tissue is arranged in two very different modes: first, in the masses properly termed muscles; and secondly, in a membranelike expansion, denominated muscular coats. There is no difference in the elementary structure of muscle, however the tissue be arranged. The proper muscles are composed of filaments, the aggregation of a number of which forms what is termed a fibre, while the fibres are collected into small bundles, which are called fasciculi. The muscle itself, the fasciculi, and the fibres, are all enveloped in a distinct cellular sheath; the ultimate filaments appear to be destitute of any cellular covering. The ultimate muscular filaments are composed of globules of the same appearance and of the same bulk as those of the cellular. In all vertebrated animals the general aspect and the magnitude of the elementary muscular globules are identical. They have recently been examined in invertebrated animals, and they present in the whole of this class the same uniform appearance. The structure of the cerebral tissue, or brain, has been examined with equal care. Whether a portion of this tissue be examined, taken from the brain, the spinal cord, or a nerve, whether from an animal belonging to the vertebrated or the invertebrated class, it is found to be composed of globules, the physical characters of which are precisely the same as those of the other tissues. The general conclusion deducible from these series of observations is, that every animal solid consists of molecules, all of which possess a primitive form and a determinate bulk; and that these constitute the elementary particles, by the various combinations of which all the tissues of animals are composed. We may say, then, that a globule of about the diameter of the eight thousandth part of an inch is the elementary organic molecule of which every solid of every animal body is composed, because the analysis of every such solid can be carried on till we come to such a globule, but by no instrument which we at present possess can we carry the analysis further. In the present state of our knowledge, therefore, this globule must be considered as the elementary organized corpuscle. The globular structure of several of these tissues had been asserted by many observers, from |