After having detailed every important circumstance relative to this very peculiar organ, we have not found a single property to assist us in explaining its functions. If we examine its changes from disease, we shall find no further assistance. In maniacal persons it is found sometimes hard and dry; in idiots, soft and mucilaginous. Occasionally an abscess appears at the basis, and sometimes the pineal gland is suppurated, or filled with calculous concretions. Although we think, with some authors of high credit, that the brain is always organically affected when any violent and permanent injury of its functions has preceded, yet there is no given change, from any particular series of symptoms. Dissection does not teach us any indication to pursue; nor would the powers, which we possess, probably enable us to fulfil them, if they were pointed out.

We must, therefore, consider the brain as the material organ of an immaterial principle, intimately united with it during life, and forming with it one distinct, inseparable whole. When we speak then of the actions and functions of the brain, we speak of it only as the instrument; nor can we after this declaration be misunderstood. Though we may sometimes employ the language of materialism, we consider the materialist, in general, as a weak, uninformed philosopher, and should deprecate being confounded with the herd.

The best physiologists suppose the brain to be fibrous; and when Gall calls it a membrane, he means no more. Fibres are conspicuous at its base, and in its prolongations, the nerves. These chords convey impressions of different kinds to the brain, in a manner which has occasioned many disputes. It was for a long time supposed that the brain was a gland which secreted a fine fluid, conveyed through the minute fibres of the nerves, which conducted to their origin the impressions received at their extremities; but the great tenuity of such a fluid, its rapid motions, and, above all, the little probability of the nervous fibres being hollow, rendered this system highly improbable. Yet, that the brain was a gland appeared to be a conclusion, obvious from its structure, its large supply of blood vessels, and their very minute convolutions. These facts appeared to Dr. Cullen in so striking a light, that, while he considered the nerves as vehicles of a very fine fluid, which was the cause of sensation and motion, he supposed that the brain secreted the nutritious particles designed to repair accidental losses, either from absorption or accidents; and that these were conveyed along the surfaces of the nerves. The improvements in electricity, and more lately in Galvanism, have given a different appearance to this question, which will soon claim our attention more particularly. We shall only at present state what we consider to be the nature and properties of the nervous power.

It is probable that in each nervous fibril, an elastic fluid is inherent, forming, from the first moment of animation, a part of it; differing, however, according to the state of the constitution, in power, in mobility, and, perhaps, in other qualities. Of this fluid the nerves are conductors; and they are surrounded in their course by non-conducting membranes; while the same membrane lines every part of the brain, and is carried into the deepest cavities, guarding with particular attention the slightest aperture. In this view the sanguiferous vessels are chiefly useful in nourishing this medullary substance; and they appear to be necessary also in adapting the nerves to their office; for when the circulation is greatly increased, the sensibility is more acute; and when it languishes, or is destroyed, the nervous energy soon shares the same fate.

This fluid must be necessarily an elastic one; and impressions are apparently conveyed through it by vibrations. It does not follow from hence, that the nerves vibrate like musical chords; or that, in every the slightest motion, a portion is conveyed from the brain. The elasticity of the fluid is proved by the momentary continuance of the impression after the cause is removed; and vibration is a term employed in many branches of philosophy as a means of communicating motion, without any very distinct application. If we touch an object with a stick, or with a metallic rod, we perceive through it the impression, and, in a general way, the nature of the substance. The impression must be conveyed by something; and whatever, that something is, it may as well convey impressions through the nerves as through the rod. But, through the nerves only can it affect the brain, and produce an idea, or some change in the brain, or its fluid connected with the nature of the object, and which conveys to the mind some peculiar and discriminated impression which it afterwards retains.

We have offered these opinions, not indeed essentially different from those taught by Dr. Cullen, because it enlarges our sphere of language, and enables us more clearly to convey our own opinions. It is immaterial to the purpose whether this view be ultimately correct: it is sufficient that it meets all the phenomena already known, and carries us to the confines of immateriality; of which we can have no idea, while the organs which convey ideas are material. We know of no ideas that are innate: all are derived from sensible objects; and even in dreams, when the mind seems to sport uncontrouled, the distorted, and often apparently new, images, will be found only heterogeneous com-pounds of sensible ideas formerly received.

We can now, then, speak more fully of the functions of the brain, the seat of intellect, the receptacle of our ideas, and the scene of all the intellectual operations. Animal life, as we have said, is confined to the intercostal system, perhaps to the cerebellum; which, we own, appears to us rather an appendage to the medulla spinalis than to the cerebrum.

The most striking function of the brain is volition; and this, the great source of all our voluntary motions, is, we believe, always excited by sensation, though often by sensations wholly unperceived or unattended to. It is singular that we will the end only: the means are directed by mind, or in some cases by a necessary connection. In sneezing, in coughing, and yawning, volition appears imperfectly, if at all, exerted; and the motions excited appear to arise from a connection of nerves, though the means are directed with great precision to the end.