is no good reason why it may not be true, for ridicule is rather an evidence of ignorance than a test of truth; and were it not for the tables of the elasticity of vapour, the phenomena of light and radiant heat, in a word, all the actual phenomena, we might receive the doctrine, that a Torricellian vacuum may, for any thing we can affirm to the contrary, contain an individual sensitive and cogitative mind, notwithstanding the ridicule that some might be inclined to extend towards such a notion. For my own part, the opinion does not seem to me more ridiculous, than that the fixed stars should be made visible by hard particles striking off from them, travelling through space in right lines for years, and then impinging on the bottom of the eye; or even that the celestial spaces, though full of this matter of a vortex in the state of a chaos, should be regarded as a vacuum. Being thus impressed with a sense of the ridiculous in contemplating such notorious articles of modern philosophy, I must therefore be excused for refusing to reject an opinion, because it is ridiculous. All the phenomena of the Torricellian vacuum, however, are contradictory of the opinion that it has feeling or cogitation; it is therefore wholly to be abandoned. Are we, then, to suppose that nitrogen, the characteristic constituent of sentient beings, possesses a mind? Or is mind the result of a certain mixture of nitrogen, carbon, oxygen, hydrogen, and water? We cannot discover any reason why these substances should take on this phase rather than the diamond, manganese, chlorine, silica, or iron.

In fact, it must be acknowledged, that all known phenomena displayed by these and other substances, can be accounted for by a few simple laws of motion, the action of mind being excluded, and this is equivalent to the disproval of its action. If we suppose mind to be intrinsically an atomic phenomenon, we can discover no reason whatever why it should be found associated with nitrogen rather than other substances, which present no traces of mental phenomena. But if we assume that the body of an animal is a piece of mechanism contrived so as to serve the purposes of mind,

an essence distinct from atoms, then there is a most obvious reason why nitrogen and no other substance should be the characteristic constituent of animals. For nitrogen is the only undecompounded form capable of going immediately towards the constitution of contractile fibres, by which an animal's body may be moved in obedience to its will.

It cannot be denied that the whole evidence which the first blush of this inquiry affords, is adverse to the opinion that sensibility and cogitation are essential properties of atoms in any circumstances whatever; and the most probable and satisfactory hypothesis is, that mind is a third essence, whose proper action consists in feeling and cogitation, and which, when associated with atomic bodies, directs the movements of subtile matter, as that subtile matter directs the movements of atomic matter. But this is a subject in which the mind is not satisfied with conjecture, or even with strong probability, while there remains a hope of acquiring certain knowledge.

OF THE NERVOUS SYSTEM.

It is agreed on all hands, that the part of an animal on which sensibility and perception are most immediately dependent, is the nervous system; and this is evidently the characteristic of the animal nature. Its development in the ovum is analogous to the development of an embryo in a seed during maturation. It assigns the place in the scale of organized beings, which the animal to be evolved shall occupy. It is that to which all the organs are subservient. The skull and spine give it immediate protection: the ribs render possible a regular respiration, on which the state of the brain is immediately dependent: the bones of the extremities give support to muscles designed to move the body according to the suggestions of the mind, which the nervous system accommodates or manifests. In a word, the nervous system is the superior of the animal machine, in relation to which all the other organs are developed and act. The muscular sys

tem, however, has obviously an organic structure and function far more perfect, and its development constitutes the climax of atomic action. By it the animal is enabled to assume its place in creation, and the organization of a muscle seems to be the most exquisite product of matter.

The structure of the nervous system, on the other hand, seems to be extremely rudimentary and merorganic, or almost crystalline. It is even more analogous to that of the bones, than the soft parts. It contains, according to Vauquelin, only 13.35 per cent. of animal matter, and that, of the more imperfect sorts, such as fatty matter, osmasome, and albumen; of the remainder, 80 per cent. is mere water, and 6·65 per cent. consists of phosphorus, sulphur, acids, and salts. It is not to be wondered, then, that nervous matter should be destitute of decided irritability, or the power of retraction on the application of a stimulus. What chiefly excites wonder is, that a mass, composed of such elements, should be capable of assuming an organic structure at all. The texture of the brain is so very delicate, or temporary, that cerebral matter cannot be frozen and thawed again, without complete decomposition. It putrefies sooner than any other part of the animal; nay, we may justly question whether the insensibility preceding death, be not the effect of a disorganization of the cerebral tissue.

The nervous system in the most perfect animals, consists of three parts-the brain in the head, nervous filaments diffused through all parts of the body, and foliaceous or capsular expansions at the tips of the nerves. The brain consists of two parts-animal globules arranged in particular directions, and a hyaline matter, which is aqueous or gelatinous, according to circumstances. The foliaceous expansions at the extremities of the nerves, are wholly composed of this hyaline matter. Could we, then, dissect away from a human body all the parts which do not immediately form a part of the nervous system, there would remain a hyaline filmy model of the human form; and were the parts permitted to fall away into more natural positions, without their organic con

nections being destroyed, the whole would possess the form of a plant inverted, the brain being the root, the vertebral column the stem, the nerves the branches and leaf-stalks, the hyaline expansions at their extremities the leaves. The col lum or centre of the vegetative body, would be at the medulla oblongata, where the nerves of the respiratory system are attached to the symmetrical system. With regard to the atomic constitution of the brain, what chiefly demands our attention is the hyaline matter, to which the globular molecules seem evidently enough to serve as an osseous system, giving direction and support to the particles of which the hyaline matter consists. The quantity of this hyaline matter in man increases with the development of his faculties. It is more abundant in the human species than in any of the inferior animals; and it is remarked in dissections of the morbid brain, that dryness, or an increase of globular matter, is generally found associated with a deficiency of intellectual power. Every phenomenon connected with this substance, induces the belief that it is the sensorium of the animal, and that, upon its quantity and particular atomic structure, the animal's power of mind depends.

What, then, is the nature of this hyaline matter? In a recent brain it is found in a gelatinous or coagulated state: it disappears in water, and, by being congealed, is converted into water. "If a portion is cut off from a brain in a fresh state, before it has been put in water, and laid upon a dry plate of glass, and covered by a cup so as to prevent evaporation, a perfectly colourless aqucous vapour is exuded, which evaporates on exposure to the air, and hardly leaves any mark upon the glass. The cortical substance of the cerebrum contains also a fluid resembling the scrum of the human blood; it has a yellower tint than the fluids in the medullary substance, or any other part of the brain; and when dry it assumes the glassy appearance, and forms the same cracks that serum does when dried on glass *."

See Sir E. Home's Lect. on Comp. Anat. vols. iii. and v. I do not doubt but Leeuwenhoek saw the complicated structure in the brain which

This substance evidently consists of water with some particles interspersed amongst it, which cause it to form a gelatinous mass. The gelatinizing agent is expelled by congelation, and departs spontaneously when the tremulous substance has, in the progress of decomposition, become simply of an aqueous consistence; for scarcely can a drop of water be found so pure, or an atmosphere in which it may evaporate so free from foreign particles suspended in it, but some stain will be left upon a plate of glass, from which a drop of water has evaporated. It appears also, that the yellowish matter taken from the cortical substance, and which was in a liquid state when examined, contains more of the gelatinizing agent than that taken from the medullary substance examined in the tremulous state, for it left, upon evaporation, a vitreous brittle substance, and not a slight stain only.

The physical characters of this gelatinous substance are every way the same as those of the gelatinous strata and masses, which we find investing as an atmosphere, or forming a nidus, or entering into the composition of many zoophytes and imperfectly understood organic forms. When they die, it wholly vanishes in water; and when even a large mass is suffered to dry, scarcely any thing remains unevaporated. I have often known a number of Planariæ, Polypi of Sertulariæ and Flustræ, and such creatures, when they happened to die, suddenly vanish, so that, after the course of a night, not a trace of them could be detected in the vessel of water, which the day before was enlivened with them. That the constituent gelatinous matter in these cases, as well as in the brain, is connected with the highest functions of organization, is also very evident. Ova are very generally enclosed in it. An Oscillatoria rooted in it may almost be seen growing. The vital activity of gelatinous animalcules, of small Beroes, and Medusæ, is quite wonderful. Nor is it less astonishing that the large medusæ,

he describes, (Epis. Physiol. Epis. 34.); but that structure was evidently evolved by decomposition. The views given by Sir E. Home recommend themselves by their unpretending simplicity; nor is Mr Bauer a microscropic observer inferior to Leeuwenhoek.