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country, and that most of its views have been rather confirmed than weakened by subsequent inquiries. At present, we shall bestow less attention on the leading idea than on the subordinate but no less important principles from which chiefly that is supposed to derive its support. In illustrating and explaining them, we shall not confine ourselves strictly to the author's text, his work being intended for a class of readers somewhat familiar with the subject.
Physiologists have been fond of considering life as a state maintained by the action of certain forces, mysteriously attached to the organic structure, against the perpetual influences around it that tend to impair its vigor and drive it from the material form which it serves to animate. It appears, too, that particular parts of the structure are subjected, not only to the general operation of this law, but, each in its peculiar way, to some special adverse influence tending to deteriorate and destroy them. The lungs, the liver, the bladder, the glands, are thus exposed to mortific agencies in the earth or atmosphere; and in this respect the brain differs from them only in the kind of agencies that deteriorate its quality and prepare it for fatal disease. Though not so easily examined and described as many of the agencies of nature, yet we may be none the less able to mark the general character of these, the mode of their operation, the extremes of their activity, and the means of prevention.
To ascertain the initial movement of disease, we must consider the brain reduced to its simplest elements. These, as now understood, consist of a cell, with connecting filaments, and blood vessel. Within the former, which is nourished by the latter, is generated the nerve-force on which the mental phenomena depend. By means of this simple apparatus are evolved all those primitive forces which, in one way or another, are essential to the mental phenomena. The various combinations of cell and vessel furnish the requisite variety of particular results. The vital force which keeps them in activity, and thus secures the fulfilment of their appropriate function, is called excitability, and, of course, supposes an exciting agent. In the healthy state, this activity of the one and the other is exactly balanced, and the function is perfectly executed. Let
this excitation be increased, as it is by adverse influences, and then this nice relation is disturbed, and the ultimate result is marred. Here we have the starting-point of all morbid movements, all abnormal conditions. The ultimate morbid condition is determined by the location, the extent, and the manner of progress of the morbid activity. Its existence is announced by one or more of various affections, ranging from a simple exaltation of the normal sensibility to the most demonstrative affections of the mental or nervous power. Considering the local extent of the morbid action, the rapidity of its progress, and the diverse functions of the various parts of the brain, we cannot be surprised at the almost infinite variety in the final issue, while the initial morbid movement, the essential condition, is the same in all. Consequently, we may have, in one case, a disorder of sensibility, such as the neuralgias ; in another, a disorder of motility, such as chorea ; in another, a neurosis, such as hysteria, catalepsy, eclampsy, epilepsy; or the disorder may be chiefly a mental one, such as eccentricity or mania. By a law of morbid nervous action, these various disorders often supplant or accompany one another in the course of their progress, and assume protean shapes without end. Change is the characteristic feature of all forms of nervous disease.
A word or two more as to the primordial fact of mental disorder, before we turn to its ultimate results. These results, varying as they may in apparent intensity abstractly considered, convey no certain indication of the intensity of the morbid movement on which they depend. Something, however, may be learned on this point from the order of their succession. In one case, for instance, epilepsy may be the first appreciable sign of a morbid condition, while in another it may be the last in a long series of pathological events. At first only what may be called a dynamic lesion, it may end, if life continue long enough, in lesions of structure visible to the eye. These mark only the duration of the morbid action, but indicate nothing as to the initiatory stage. Hence it is that dissection, in the case of persons who have died insane, often reveals to the eye, even though assisted by the most ingenious instruments, no change of structure, - a fact which has given rise to the idea, entertained by a few, that the brain is not
the seat of insanity. The point of material interest is, that, between the first and the last member, in this series of morbid actions, there may intervene a period measured in most cases by years or generations. This curious fact, the full significance of which has been but recently learned, furnishes us with a key to many of the mysteries of mental derangement. The phenomena attending it cannot be too carefully considered, and, therefore, no apology is needed for presenting them with some degree of minuteness.
The adverse influences that vitiate the health of the brain seldom do more at first than produce that abnormal movement already mentioned, called superexcitation. Its effect on the mind, when it has any effect at all, is chiefly manifested by some slight deviation from the ordinary routine of human conduct, and from an average propriety of thought and feeling. The person may exhibit some phase of exaltation or depression, some eccentricity of manner, some extravagant notions, some disregard of the common conventions of society, some domestic estrangements, some strange and impulsive movements, a fondness for drink, or some other debasing habit, and often only an unreasonable manner of dealing with practical matters, not easily described, but obvious enough to the practised eye. Oftener, however, the effect is witnessed scarcely at all in the . psychological condition, but is manifested solely in anomalous sensations, - in pain or aching of the head, or some other neuropathy, in a sense of weariness, or in some form of nervous disease. Nothing more than this may be exhibited during the life of the individual. He dies and gives no other sign of cerebral disorder, but the disorder may not die with him. It passes along to successive generations in accordance with the laws of hereditary transmission, and makes its appearance in a variety of forms. The existence of this law was known to the earliest observers, but the full range of its operation, especially in regard to morbid and abnormal conditions, began to be discerned only within a very recent period. Already investigation has made us acquainted with many of the conditions by which this curious physiological process is governed, and has thrown a flood of light on one of the obscurest problems in the science of life. Our limits will allow us to discuss this subject only so far as seems necessary for a clear understanding of the points more particularly before us.
It is an ordinance of nature that in the process of generation like produces like. Not that the beings thus produced are exactly alike. Diversity there always is. It is for the scientific inquirer to ascertain the limits to which this may extend. In a rude general way they have already been determined by the common observation of mankind. The likeness is something closer than that which prevails between the members of a common order or genus. It is not the likeness of a lion to a tiger, or of a horse to an ass, but the likeness of a lion to a lion, and of a horse to a horse. On the other hand, this kind of likeness does not exclude a certain amount of difference ; and we are no less strongly impressed with this fact of diversity, as existing between individuals, than we are with the essential similarity of all the individuals of a species. Here, then, are two orders of hereditary transmission, or heredity, if we may Anglicize the French term, viz. one embracing the traits that characterize the species, the other the traits peculiar to individuals. With the latter only we have to do in this inquiry.
The transmission of the bodily features by the parent to the offspring has been more thoroughly investigated, especially in the case of some of the domesticated animals, during the last fifty or sixty years, than ever before ; and the result has been to demonstrate a degree of exactness and uniformity in the operation of the laws that govern it that reminds us of the phenomena of brute matter. Not only is the existence of the general law proved, but, what is equally important, the apparent exceptions to it are proved to be subject to laws no less inflexible. But at the very threshold of the subject, we meet with an order of facts liable to mislead the hasty observer. We are in the habit of saying that the features of the parent are transmitted to the offspring, but we must bear in mind that, of necessity, the features of both parents cannot coexist in the child. He cannot inherit the aquiline nose of the one and the snub nose of the other, the black eyes of the one and the blue eyes of the other, the vigor and hardihood of the one and the
fragility of the other; but on the contrary, will have perhaps the eyes of the one and the nose of the other, the hands of the one and the feet of the other. In place of this combination of traits derived some from the one parent and some from the other, there is usually a mixture, often obvious, but amounting occasionally to a complete fusion where no trait of either parent can be discerned marked by its original character. Let us observe, in passing, that traits implying considerable deviation from the normal type, - such as supernumerary toes or fingers, or dwarfish limbs, - which have arisen from some inexplicable play of organic affinities, are not transmitted with the same uniformity. In many of the offspring they do not appear at all, and unless particular pains are taken by pairing those only in which these peculiarities exist, they sooner or later disappear altogether. Indeed, no remarkable trait of recent origin is easily perpetuated. Of this fact stock-breeders are perfectly aware, for not until the desired trait has descended through several generations are they sure that it is firmly fixed in the blood and not liable at every remove to disappear. Thus steadily nature adheres to prevailing forms, and shrinks from a perpetuation of any considerable deviation from them.
There is another reason why the features of neither parent should be very exactly reproduced in the offspring. Every individual carries within him the mingled blood of two other individuals, in both of whom are to be found traces of innumerable streams flowing from distant sources as into a common reservoir, which are often interrupted, probably, and may disappear from view, but which preserve to the last their distinctive qualities. It is not necessarily from his immediate predecessors alone that the individual derives his physical and mental qualities. In him may reappear the tokens of some distant ancestor, which have been transmitted from one generation to another in a latent state. The natural tendency of mingling various bloods is to neutralize the activity of one or another, or to reduce the sphere of their influence within the narrowest limits; and the more remote they are, the stronger their tendency to be absorbed and confounded in the nearer and stronger streams of the immediate parentage. Accordingly,