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swering; and until more of the mysteries connected with this part of our nature shall be cleared up, we must be content to regard the truth as an ultimate fact. That some positive and permanent change is effected, both in the organization and in the spirit, there can be no doubt. But concerning its character, we would not venture even a conjecture. Nor would we dare to say that in the case of our bodily habits, the tie which connects the successive acts of which they consist, or more properly through which they are manifested, may not lie back in the spirit. This, it is well known, has other modes of acting upon the organization besides that of will. Of one of these, indeed, we have a striking example in the influence of enotion over the muscles of the countenance, and when particularly vivid, of the body generally, even when opposed by the most strenuous exertion of our voluntary powers. From recent anatomical and physiological investigations, there is reason to believe that this influence is exerted through an entirely distinct set of nerves, having a different origin and different properties from those which transmit the commands of the willnerves especially appropriated to that office, and wholly incapable of ministering to either sensation or voluntary motion. Now it may be that in the repetition of those actions, which have been chained to one another by habit, so that the direct agency of the will is no longer required for their performance, an indirect influence is exerted through the mind voluntarily placing itself in special relation to the parts of the organization upon which the actions are immediately dependent, and retaining the meanwhile a certain latent consciousness of the general purpose to be accomplished by them. Indeed, something of this kind, we think every one is sensible of even when engaged in those occupations which custom has rendered most familiar to him.

Pursuing our investigation in the order which would seem to be indicated by the nature of the subject, we shall next consider the phenomena of conception. These do not, like those of sensation and perception, depend upon the action of any outward organs. Whether relating to the objects of sight, hearing, or smell, neither the eye, the ear, or the nose has any part in their production. Nay, their manifestation is clearest and steadiest when these organs have been put completely at rest, by the entire exclusion of the media which act upon them. Even the destruction of the organs, after they have once supplied the mind with ideas, does not impair the powers of conception.

But while there is abundant proof that this faculty is wholly independent of the outward parts of the bodily frame, there is equally strong evidence that in the present state, it cannot be exercised ex

1849.] Connection between the Brain and Conception.

545 cept through the brain. In diseases of that

organ

the powers of conception are commonly disturbed sooner and also more seriously than those of sensation and perception. It is moreover well known that a moderate degree of pressure, applied to certain parts of the brain suspends, during its continuance, the exercise of all the mental faculties. And what is perhaps equally satisfactory on this point, in the ordinary and healthy condition of the organ, unusual or prolonged activity of any of the intellectual powers, occasions an increased tendency of the circulation towards it.

The question then arises, in what way and to what extent does the brain minister to conception ? We answer, in the same way and to the same extent that it ministers to perception. The idea of an object we believe to be awakened by the spontaneous action of the cerebral extremities of the same nerves which, under the stiinulus of impressions received through the senses, originally presented the object itself; the chief difference between the two cases being, that in the former, the action, though not originating in the will, is subject to its influence, while in the latter,it is wholly beyond the control of our voluntary powers. The reasons by which we are led to the adoption of this opinion, are,

1. The very close resemblance of our conceptions to our perceptions. This is seen not only by direct comparison of the two classes of phenomena, but from the fact that the former are continually mistaken by us for the latter. As we have already noticed, what are usually denominated acquired perceptions are only conceptions connected by the ties of association with the object which serves to introduce them. And yet so perfectly similar are they to the perceptions for which they pass, that it is only by the most careful attention, that we are able to distinguish them. In sleep too, when the senses are at rest and the power of the will over the cerebral organs is suspended, the ideas awakened by their spontaneous action, no longer under our control, assume the independent character of external existences, and while the state continues, are actually regarded by us as such. Indeed, it would seem, that whenever we lose the power of voluntarily shaping our conceptions and of banishing and recalling them at pleasure, whether it be through sleep, reverie, or insanity, we uniformly mistake them for perceptions, and our ideas, as they succeed one another in the mental train, appear to us as actual and outward realities. We are then in a state similar to that which the advocates of the wild scheme of idealism would have us believe to be our habitual and normal condition. Now we say it is contrary to the analogy of every other part of the human structure and therefore a priori improbable, that in framing the special organism of the mind the Divine Being shou!d have constituted one extremely delicate and complex set of nerves for awakening our perceptions, and another equally delicate and complex apparatus for evolving our conceptions, when these two classes of phe-, nomena are so nearly alike, that during our waking as well as our sleeping hours, and in health no less than under the influence of disease, we are continually confounding them with one another. It is far more in harmony with that beautiful simplicity, and that strict economy in regard to means which are so conspicuous in all the Creator's works, to suppose that both are produced by the same organs, and that the difference between them arises from these organs acting in the two cases, either in different ways, or what is perhaps more probable, with different degrees of intensity.

2. The association of our conceptions, through the corresponding perceptions. Whenever two objects have been repeatedly seen together, the idea of one in any manner awakened, immediately calls ap that of the other. Whenever two sounds have been heard many times in connection with each other, the thought of one, however

suggested, introduces that of the other. In like inanner the recollection of a friend's countenance brings with it not only his general appearance, but the tones of his voice, the peculiarities of his manner, together with numerous circumstances connected with him, by virtue of associations established among these several ideas, through the perceptions which originally awakened them. Indeed it would seem that our conceptions are both more readily and more permanently linked to one another, by the simultaneous or successive repetition of the corresponding perceptions, than by a similar repetition of the conceptions themselves, owing, it is probable, to the organs evolving them acting with greater intensity in the former case than in the latter. Now all this is readily explained from the universal and all-pervading law of habit, if we suppose the two classes of phenomena to be dependent upon the same portions of the brain, but wholly inexplicable on any known principle of the human constitution, if we suppose them to be dependent upon different portions. 3. The apparent absence in the brain of

any
other
organs

besides those which minister, on the one hand to sensation and perception, and on the other, to automatic and voluntary motion. In order to have a just conception of this fact, and of its bearing upon the present inquiry, it will be necessary to consider somewhat more in detail than we have hitherto done, the structure and functions of the several parts of the nervous system-a circumstance which we are the less inclined to regret, as such a consideration will disclose new proofs of the wisdom and goodness of the Creator. It will moreover, show that even

1849.]

Systems of Nerves.

547

in the most mysterious and inscrutable operations of life, there is no direct interposition of the divine agency, but that in this, as well as in every other department of nature, ends are brought about by means skilfully adapted to produce them.

Until within a comparatively late period, all the different nerves were supposed by physiologists to have the same office. They were believed to be the channels, through which impressions are transmitted from the outward organs to the brain, and from the brain to the outward organs. They were regarded as together constituting but a single system, which having its centre within the cranial cavity and radiating thence to every part of the body, regulates and controls all the living phenomena. From recent anatomical and physiological investigations, however, it is in ferred, that instead of one, there are no less than five different systems of nerves, having as many separate and distinct centres and performing as many separate and distinct functions. These different systems are not isolated, it is true. On the contrary, they are connected with one another by numerous affiliations, whereby entire harmony of action is secured as well as the most perfect unity of result. Each system, however, is complete within itself, and may continue to act-a case which in certain diseases actually happens—after the others have ceased to perform their respective offices.

Two kinds of matter, and so far as can be ascertained from microscopic examination, only two, enter into the composition of each of these systems the white and the gray. The white matter consists of a great number of exceedingly minute, fibres, which together with the sheaths embracing and protecting them, make up the entire substance of the nerves. Its office is believed to be simply that of conduction, each tubulated fibre being in fact a separate channel along which impressions received at one of its extremities are transmitted to the other. Two distinct sets of nerves are connected with each system, the one afferent and the other efferent-the former serving to convey impressions from the circumference of the system to the centre, and the latter from the centre to the circumference.

The gray matter is very unlike the white. Its structure instead of being fibrous is glandular. It is moreover traversed by innumerable veins and arteries, which supply it abundantly with blood; while the white matter receives but a comparatively small quantity of this fluid. From these circumstances, as well as from the position which it occupies in the several systems, it is believed to perform the office of separating from the blood, the peculiar agent or fluid, whatever it may be, by which the trasmission of impressions along the nerves is effected. It is collected into masses of varying dimensions, which either singly or in groups, constitute the centres of the respective systems. All the afferent nerves terminate in them; all the efferent originate from thein. Indeed it is only through these central masses of gray matter, that the two sets of nerves are connected with each other, and the circle of which they form parts, completed. Minute portions of the same substance are also found about the external extremities of the nerves of sensation, having for their office, it is thought, the secretion of the peculiar fluid or principle by which these nerves are excited to action. The mere mechanical impression made upon the outward senses is not, it would seem, their proper stimulus, but only the means of disengaging and applying it. It is not improbable that the extremities of all the other afferent nerves, are in like manner enveloped by the gray matter, although its existence about them has not as yet been demonstrated.

These observations are of a general character and apply equally to all the different systems of nerves belonging to the human frame. For the further elucidation of the subject, we add a few brief remarks upon the situation, structure, and offices of each.

1. Of the sympathetic system. This has no connection with either the brain or the spinal marrow, but is situated wholly without the cavity containing those organs. It was first separated by physiologists from the rest of the nerves, and received its name from the supposition that a peculiar sympathy is established through it, among the several parts which minister to nutrition and secretion. The concatenated masses of gray matter which form its centre, are lodged principally within the general cavity of the trunk, and the nerves proceeding from them are distributed mainly to the thoracic and abdominal viscera. Branches from this system also accompany the arteries throughout all their ramifications. Connected exclusively with the organs concerned in the maintenance of life, it is believed to preside over their action, and to regulate and barmonize their closely related and often mutually dependent functions. Hence it is frequently called the visceral system or the system of organic life. The nerves belonging to it are incapable of ministering to either sensation or voluntary motion, nor do they in any manner or at any point come into relation with the spirit. The connection between the latter and the parts to which they are distributed, is established solely through the medium of twigs and branches which come from other systems.

2. Of the excito-motary system. This has its origin in a series of ganglia occupying the axis of the spinal marrow, the exterior or fibrous portion of that body only serving to connect the sensory and voluntary nerves with the brain. Emerging at different points from this axial

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