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more affected with atrophy than the other, and this cannot exist without showing itself in some corresponding inequality throughout every part of the body.

Bichat is the author who has dwelt most explicitly on the symmetry in the organs of animal life, and the effects of default in this, either from natural conformation or disease. The relation of the symmetry of double parts to unity of action and individuality of result, is so important in all the economy of life, that every deviation from it deserves careful notice; and especially where it is associated with some definite injury of the nervous system. Hitherto I have spoken principally of the effects of such disparity upon the senses and voluntary power; but must we not look to the functions of memory and association also, as probably affected in various ways by unequal or incongruous action in the two hemispheres of the brain? These faculties (if indeed we can rightly define them as separate) are manifestly dependent on organization, and only partially subject to the intellectual being. Their unity of action is as needful as that of the senses and voluntary powers, and may be presumed as closely connected with symmetry of the two sides of the brain, admitting, what may be deemed certain, that each hemisphere partakes in the organization needful to these functions. Without referring, then, to those more striking consequences of accident or disease, where the memory and associations are suddenly altered or impaired, we must admit the likelihood

sensations, but also in the texture and intimate functions of the two sides. I might name as an example (more singular from a tube being concerned), certain inflammations of the larynx and trachea, in which the vascular injection is perceived in one half only of the circumference of the tube, the other half preserving its ordinary appearance. Andral states that he has made the observation in several cases where one lung only was diseased, and this on the same side as the affection of the trachea.

of analogous effects from slower, slighter, or transient deviations from equality. It is difficult to conceive such to exist without the occurrence of some change, however obscure to observation from the complexities which surround it.

It has been supposed indeed by some, in relation to the mental faculties, that each side of the brain is separately capable of fulfilling the functions, whatever they be, in which this organ ministers to them; and this view has been applied, although somewhat vaguely, to explain the alleged fact that every portion of the brain has been found in different cases the subject of disease, without obvious disturbance of the faculties of the mind. The evidence, here, however, is insufficient in nature and amount.* And were we even to admit the assumption that a given portion of one hemisphere could minister to a certain function in all its completeness, the action being suspended of the corresponding part on the opposite side, yet is there no proof that such substitution can immediately take place; and still less any presumption that it is likely to occur where the functions. of the affected part are not suspended, but merely altered and deranged. The distinction in the latter case is manifest; and it is only partially obviated by referring to those phenomena of sensation where the organ of one side appears under certain circumstances to perform all that belongs to the entire function. The instances are as frequent of disturbance to the common action of both, from morbid changes in which one alone is originally concerned.

* One of the most remarkable cases to this effect is that recorded by Cruveilhier, where one hemisphere, throughout all its parts, was reduced by atrophy to half the dimensions of the other, yet with retention of all the mental faculties. The latter statement is obviously the doubtful part of this case; as will be well understood by all, who are accustomed carefully to look into the evidence belonging to such points.

The considerations already stated bring us immediately to the question, whether some of the aberrations of mind, which come under the name of insanity, are not due to incongruous action of this double structure, to which perfect unity of action belongs in the healthy state? When the functions which directly place us in relation to the world without, are liable to so much disorder from this source, it is to be conceived that the intellectual part also may suffer change; the result either of disturbed perceptions, of irregular associations, or of some unequal consciousness or exercise of voluntary power. The subject is very obscure, and all proof of difficult attainment; but I think it more probable than otherwise that such inequality may be a cause of some among the many forms of mental derangement. Obvious lesion or active disease are concerned in numerous cases; and these also, when affecting one side of the brain only, may produce effect by disturbing the proper correspondence, or unity of action, of the two sides. But there are presumably other cases where, without manifest injury of structure, there may be inequality enough in the actions of the two hemispheres severally, to disorder and derange the trains of thought, for longer or shorter time, and in every variety of change and degree. And the actual number and singular diversity of such mental phenomena, both in health and disease, may well warrant us in seeking explanation from any source, not incompatible with the laws of organised life.

It has been a familiar remark that in certain states of mental derangement, as well as in some cases of hysteria which border closely upon it, there appear, as it were, two minds; one tending to correct by more just perceptions, feelings, and volitions, the aberrations of the other; and the relative power of the two influences varying at different times. Admitting the general truth of this description, as attested

by many and curious examples, the fact may be explained in some cases by the co-existence before the mind of real and unreal objects of sense, each successively the subject of belief:

a phenomenon itself possibly depending on the doubleness of the brain and of the parts ministering to perception, though we cannot obtain any certain proof that such is the case. But this explanation will not adequately apply to the instances where complete trains of thought are perverted and deranged, while others are preserved in sufficiently natural course to become a sort of watch upon the former. * Here, indeed, we may still seek for explanation, by supposing the two states of mind to be never strictly coincident in time; and this view is in part sanctioned by what observation tells us of the inconceivable rapidity with which the mind actually shifts its state from one train of thought or feeling to another; a fluctuation and rapidity much greater in reality than we recognise by language, or in our common contemplation of the subject. Articulate speech, in fact, is often unable to keep pace with such changes; nor have we any means of measuring by time these momentary passages of mental existence, crowding upon each other, and withal so interwoven into one chain, that consciousness, while it makes us aware of unceasing change, tells of no breach of continuity.

It is remarkable how distinct an expression to this effect may occasionally be had from patients themselves. I have recently seen a case of which the most marked feature was a frequent and sudden outbreak of passion upon subjects, partly real, partly delusive, but generally without obvious or sufficient reason at the moment;-these excesses attended with loud screaming, execrations, and acts of violence in striking or breaking things within reach. Here the patient himself described to me the sort of separate consciousness he had when these violent moods were upon him ; his desire, but feelings of inability to resist them; his satisfaction when he felt them to be passing away. It was a painfully exaggerated picture of the struggle between good and ill. "Contra miglior voler, voler mal pugna."-Dante.

If the latter explanation be admitted, then the just mentioned cases come under the description of what has been termed double consciousness; where the mind passes by alternation from one state to another, each having the perception of external impressions and appropriate trains of thought, but not linked together by the ordinary gradations, or by mutual memory. I have seen one or two singular examples of this kind, but none so extraordinary as have been recorded elsewhere. Their relations to the phenomena of sleep, of somnambulism, reverie, and insanity, abound in conclusions, of the deepest interest to every part of the mental history of

man.

Even admitting, however, that these curiously contrasted states of mind are never strictly simultaneous, it is still a question whence their close concurrence is derived. And, in the absence of any certainty on this very obscure subject, we may reasonably, perhaps, look to that part of our constitution, in which manifest provision is made for unity of result from parts double in structure and function. This provision we know in many cases to be disturbed by accident, disease, or other less obvious cause; and though we cannot so well show this in regard to the higher faculties of mind, as in the instance of the senses and voluntary power, yet it is conceivable that there may be cases where the two sides of the brain minister differently to these functions, so as to produce incongruity, where there ought to be identity or individuality of result.

It is not easy to carry this argument beyond the form of mere question, without relinquishing that rule of inquiry which alone can rightly be admitted; but there are other points connected with this topic, of much interest to the physiology of man, and giving greater scope to research.

* One of the most remarkable cases of this nature is that narrated in Mr. Mayo's Physiology, 4th edition, p. 195.

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