a blow upon the head, by altering the condition of the optic lobe, will often appear to produce a flash of light; and fulness of the vessels of the sensorium will produce the effect of sound, as of singing or rushing noises in the ear. Such fallacious sensations, originating entirely in the perceptive organ itself, are termed subjective (in contradistinction to the ordinary ones, which, following upon the impression caused by some external object, are known as objective sensations), and they will hereafter be referred to as explanatory of some very curious morbid conditions.

When the ultimate change is deferred until the impression reaches the brain, it assumes a more complex character, and is made manifest in three distinct methods. The first of these is by the formation of an idea, which may be superficially described as a cerebral sensation. The second is by the disengagement of force, purely automatic or instinctive, associated with the idea, as sensorial force is with a sensation; and, like it, producing involuntary action. The third is by a force of a totally different character, and probably peculiar to the human race. This is the force of volition, or will; which has, when exerted, power to keep down the instinctive force, and to suppress all. its operations. It is, therefore, expended either in producing voluntary, or in restraining involuntary movements; and, with regard to both these modes of exercise, it will again be noticed in the proper place.

The upward course of an impression having been traced to the farthest possible point,-namely, to the working of its ultimate change in the brain,-it will

next be required to reverse the process, and to follow the change downwards, on its way to react upon the body. Passing though the sensorium, the idea is felt, and we are thus made acquainted with its existence; while the force goes on to the cord, and, acting by the instrumentality of its efferent nerves, either calls the muscles into activity, or, if it be volitional force, perhaps keeps them at rest. If the ultimate change take place in the sensorium, the motive force still has to pass to the cord in order to show itself; while the former organ feels a sensation, but does not become acquainted with an idea. If in the cord, then the development and exercise of motive force, without either an idea or a sensation, forms the sum total of the necessary result.

It will perhaps serve to render more clear the manner in which the operations dependent upon these changes are performed, if an endeavour be made to furnish some account of their rationale, and of the purposes which they respectively fulfil in the scheme of Divine Providence; so far as this can be unravelled by scientific investigations, or comprehended by finite minds. And (premising that the spinal and sensorial systems are found in a high state of development in insects; but that the brain, gradually added in ascending the animal scale, although well marked in the higher quadrupeds, attains perfection only in mankind,) it will be shown that the cord ministers mainly to the safety, and the sensorium to the pleasure, of the animal: while the brain, by acting instinctively upon ideas, gives or increases the faculty of adaptiveness to varying external circumstances; and, by furnishing

volitional power, supplies the conditions necessary to moral responsibility.

It is plainly essential to the continued existence of all animals, that they should perform certain movements: for the aeration of their circulating fluids; for the capture of their prey; for their flight or concealment from danger; and for the fulfilment of various other purposes in their economy. This necessity is perfectly provided for by the working of the spinal system; because the circumstances which require motion on the part of the animal, are those which produce an impression on the extremities of the afferent nerves, and ultimately cause the development of a force in the centre, which immediately discharges or expends itself in the accomplishment of the necessary act. Thus, the presence in the throat of food to be swallowed, and the presence of impure blood in the lungs, are the immediate and unerring excitants of the operations which such circumstances respectively demand; and the force concerned being instinctive, and not volitional, leaves no room for neglect on the part of the animal, who might otherwise be choked by forgetting to swallow, or suffocated by forgetting to breathe.

A large portion of the actions of insects, and especially their actions of progression, are, for the most part, spinal; and it is evident that the mechanism described in the last paragraph would be adequate to the accomplishment of all they do. But, if possessed only of a spinal system, although they might retain their present habits, they would have no enjoyment of existence, and would resemble machines, in every

thing but in containing a motive power within themselves. They are elevated to the condition of sentient beings by the sensorium, an organ that may be typically described as a modification of the cord, in which the changes are attended by sensation; so that a certain range of impressions produces feeling simultaneously with movement. Of necessity, this feeling must be either pleasurable or painful, and therefore the sensorium both confers the power of enjoyment, and, at the same time, entails the liability to suffering.

In this way, by the motive power of the cord, and the simple feeling of the sensorium, the habits of each insect are prompted, and its necessities are provided for. But its actions, in the absence of a brain, are blindly instinctive; being in no degree under the control of will, guided by no idea of a purpose, and incapable of being modified to meet external circumstances foreign to those in which the individual is commonly placed by nature. Hence, the range of action and the power of adaptiveness possessed by insects are both extremely limited. The bee constructs its wonderful cell, the spider of each variety weaves its characteristic web, with no knowledge of the purposes to be answered by the work; but in passive obedience to external stimuli, and by virtue of a law of its conformation which cannot be violated: these actions being performed as certainly under artificial circumstances which render them utterly unavailing, as they would be by the insects in a state of nature.

Ascending the animal scale, from insects, through fishes and reptiles, to the birds and quadrupeds, we find the brain added on to the cord and the sensorium,

and gradually enlarging as we rise. We find, also, as soon as the brain attains a size and development sufficient to endow it with functional activity, that the animal becomes possessed of a power to shape and modify its conduct according to the exigencies of its position; no longer doing always exactly the same thing, but displaying faculties seemingly analogous to the cunning or contrivance of the human species. This result is obtained by the passing on of the impression, through the sensorium, to the brain; where it excites an idea, and occasions, also, a disengagement of force, which, just as if sensorial, expends itself in producing motion. A trout, having been wounded by a hook, will shun the bait afterwards; an idea of that object, in connection with the injury it has sustained, overcoming the merely sensorial impression given by the sight of food. The resulting action is instinctive, and perfectly involuntary; but it is prompted by a kind of knowledge, and not by mere feeling. In a still higher grade of being, the impression may probably suggest a train of ideas, following each other in obedience to the law of association, and not producing movement until some final idea is arrived at. Then, as the mental process can be carried no farther, the involuntary reasoning is followed by an instinctive act, frequently very different from that which would have succeeded to the original sensation. Hence the educability of the lower animals. A perfectly untaught dog, seeing food upon a table, would have only one idea excited by the visual sensation; and the force developed with this idea would instantly expend itself in an endeavour to obtain the prize. But if the dog had been punished