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tion of lesson on lesson. Of this there need be no doubt, and there we may leave the first and leading fact. But the danger of overwork is, unfortunately, not confined to the brain, it extends to the body as a whole. When the brain is overworked in the growing child, however well the child may be fed, and clothed, and cared for, there will be overwaste of substance in proportion to the overwork. There will be stunted growth and the formation of a bad physical body.

In addition to mental strain induced in the manner suggested above, there is, as I hinted at first, strain from sudden shock, leading to consequences of the most serious character. I have sometimes had to determine whether extreme shock requires to be inflicted on feeble or over-sensitive persons, in order to strike effectively, and I have been drawn to the conclusion that such is unnecessary, and that the least emotional persons may be influenced. The after effects of sudden mental shocks have, however, been unstudied by that part of medicine which I represent, and I may, therefore, be speaking from too limited experience. Nevertheless, I am clear enough in the fact that I have seen physical evils follow upon mental shock in the most obtuse men.

Special Diseases from Mental Strain. Diseases following upon mental shock or strain are divisible into two classes. There is a distinct class in which the mental shock stands out as the direct and only cause of the malady, and there is another class in which the mental shock or strain appears only to excite or to exaggerate symptoms of disease which pre-existed.

In the first class the diseases produced are the same as those which sometimes follow upon the receipt of physical injury to the nervous centres. I notice specially

I notice specially as the most perfect forms of disease of this nature, diabetes, paralysis (local or general), intermittent pulse, and arterial relaxation with arterial murmur.

Diabetes from sudden mental shock is a true type, a pure type, of a physical malady of mental origin. I have before me the notes of three cases, in which the first excretion of sugar and the profuse diuresis were symptoms as definedly sequential to severe mental strain, as when, in experiment on a lower animal, the malady is induced by inserting a needle into the brain in the region of the fourth ventricle. These cases constitute a hopeless class, the danger sudden, the course rapid, the fatal end sure.

The symptoms of paralysis from mental strain are usually less sudden in their approach, and are preceded by warnings, which, when noticed correctly, are sufficiently decisive. The most characteristic of these warnings is a sensation, on the part of the patient, of necessity during any mental effort for frequent rest and sleep; symptoms such as are described so faithfully, by Johnson, as belonging to the case of the Poet Collins. The course of these cases is usually clear; it is a progressive course towards general palsy of mind and body, and it is not unlike the decline of mental activity in the age of second childishness and mere oblivion. When this condition exists, at however early a stage, the slightest shock tells on the nervous structures, and transforms suddenly the threatening malady into the extreme reality. Sudden muscular paralysis is the most common sequence of shock, under this condition; it is in most cases, at first, a local paralysis; but it may, at once, become general in respect to all the muscular system which is under the control of the centres of volition.

Intermittent pulse is a physical symptom of cerebral and mental origin. I have never met with a case in which the disorder was not sequential to some anxiety; shock, fear, sorrow, or their similars. I have met with case upon case in which the sufferer has been able from his own perception of the intermittency to register the precise moment when the injury that caused it was inflicted. In all instances, when it is present, it is intensified by anxiety.

Arterial relaxation with murmur is the result of injury involving the emotional or organic nervous centres. I have seen it follow on direct physical injury, and I have seen it follow as distinctly on mental shock. It is a common result of intense grief, and is characterised by sudden changes of vascular tension, coldness, chills, frequent perspirations, irregular action of bowels, and, often, diuresis. But the most distressing symptom of all is the arterial murmur. This is usually heard by the patient, and is sometimes mistaken by the practitioner for aneurismal murmur. It is produced at those parts of the arterial tract where an artery runs through a rigid canal, as through the abdominal opening of the diaphagm, or the carotid canal in the base of the skull. In these rigid canals, the arteries being relaxed, the sides of the vessel press, with each impulse of the heart, on the surrounding resisting wall. Thus there is vibration and murmur, and in the case of vibration in the carotid canal the murmur is painfully audible to the patient. In these cases the symptoms are often developed in the most rapid manner, and recovery is equally as instantaneous.

It remains yet to be seen what physical change in the nervous centres is produced by sudden mental shock. The symptoms lead one to the idea that the change is identical with that which follows upon mechanical shock, or mechanical irritation ; but what the nature of the change is has all to be learned. That it is some alteration in molecular arrangement, attended with change in form of matter, is the most reasonable theory ; but experiment is still wanting to indicate precisely the modification of structure which is induced.

The class of cases where nervous shock or strain excites latent, or intensifies actual symptoms, includes some chronic eruptions on the skin (psoriasis especially), cancer, epilepsy, and insanity itself. In all these there is some preceding condition, hereditary or acquired, which, by causing primary injury to the nervous structures, leads to a chronic exhaustion, easily intensified by the slightest shock. Thus the symptoms of tertiary syphilis will recur, on venereal excess, without any introduction of new venereal poison; thus eruption on the skin will follow upon nervous shock; thus cancer so frequently shows the first signs of its presence on mental anxiety; and in two cases of persons subject to epilepsy, the earliest seizure was clearly connected with mental prostration. Respecting insanity, I doubt whether it is ever the result of simple mental over-strain; on the contrary, I take it rather to be an upshot of extreme mental inactivity; but when the tendency to it is pronounced, then mental strain excites the malady.

The psychological physician is accustomed to look at mental as evolved from physical, or social, or transmitted causes, acting on the mind through the body. I have been trying to indicate, in the present effort, physical devastations as evolved from agencies acting on the body through the mind. I think I see the reverse side of a subject which has not often been discussed, the relation of mental to physical disease, and the picture thus presented is singularly instructive. It tells me that the origin of insanity, as a concrete fact, is rather to be sought for in inactivity, hereditary and individual inactivity of brain, than in exercise of brain ; and that excessive exercise of brain is a cause not of mental, but of physical derangement. Our uneducated, cloddish populations are, in short, as I venture to assume, the breeders of our abstract insanity, while our educated, ambitious, over-straining, untiring, mental workers are the breeders and intensifiers of the worst types of physical disease.

ON RESEARCH IN MEDICINE.

DISCOURSE II.

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