In exhibiting the causes, which injure the health of the mind, they will be found to be partly physical, partly intellectual, and partly moral.

The first cause of mental disease and suffering, is not unfrequently found in the want of a proper supply of duly oxygenized blood. It has been shown, that the blood, in passing through the lungs, is purified, by the oxygen of the air combining with the superabundant hydrogen and carbon of the venous blood, thus forming carbonic acid and water, which are expired into the atmosphere. Every pair of lungs is constantly withdrawing from the surrounding atmosphere its healthful principle, and returning one, which is injurious to human life.

When, by confinement, and this process, the atmosphere is deprived of its appropriate supply of oxygen, the purification of the blood is interrupted, and it passes, without being properly prepared, into the brain, producing languor, restlessness, and inability to exercise the intellect and feelings. Whenever, therefore, persons sleep in a close apartment, or remain, for a length of time, in a crowded or ill-ventilated room, a most pernicious influence is exerted on the brain, and, through this, on the mind. A person, who is often exposed to such influences, can never enjoy that elasticity and vigor of mind, which is one of the chief indications of its health. This is the reason, why all rooms for religious meetings, and all schoolrooms, and sleeping apartments, should be so contrived, as to secure a constant supply of fresh air from without. The minister, who preaches in a crowded and ill-ventilated apartment, loses much of his power to feel and to speak, while the audience are equally reduced, in their capability of attending. The teacher, who confines children in a close apartment, diminishes their ability to study, or to attend to his instructions. And the person, who habitually sleeps in a close room, impairs his mental energies, in a similar degree. It is not unfrequently the case, that depression of spirits, and stupor of intellect, are occasioned solely by inattention to this subject.

Another cause of mental disease, is, the excessive exercise of the intellect or feelings. If the eye is taxed, beyond its strength, by protracted use, its blood-vessels become gorged, and the bloodshot appearance warns of the excess and the need of rest. The brain is affected, in a similar manner, by excessive use, though the suffering and inflamed organ cannot make its appeal to the eye. But there are some indications, which ought never to be misunderstood or disregarded. In cases of pupils, at school or at college, a diseased state, from over action, is often manifested by increased clearness of mind, and ease and vigor of mental action. In one instance, known to the writer, a most exemplary and industrious pupil, anxious to improve every hour, and ignorant or unmindful of the laws of health, first manifested the diseased state of her brain and mind, by demands for more studies, and a sudden and earnest activity in planning modes of improvement for herself and others. When warned of her danger, she protested that she never was better, in her life; that she took regular exercise, in the open air, went to bed in season, slept soundly, and felt perfectly well; that her mind was never before so bright and clear, and study never so easy and delightful. And at this time, she was on the verge of derangement, from which she was saved only by an entire cessation of all her intellectual efforts.

A similar case occurred, under the eye of the writer, from over-excited feelings. It was during a time of unusual religious interest in the community, and the mental disease was first manifested, by the pupil bringing her Hymn-book or Bible to the class-room, and making it her constant resort, in every interval of school duty. It finally became impossible to convince her, that it was her duty to attend to any thing else; her conscience became morbidly sensitive, her perceptions indistinct, her deductions unreasonable, and nothing, but entire change of scene, exercise, and amusement, saved her. When the health of the brain was restored, she found that she could attend to the "one thing needful," not only without interruption of duty, or injury of health, but rather so as to promote both. Clergymen and teachers need most carefully to notice and guard against the danger here alluded to.

Any such attention to religion, as prevents the performance of daily duties and needful relaxation, is dangerous, as tending to produce such a state of the brain, as makes it impossible to feel or judge correctly. And when any morbid and unreasonable pertinacity appears, much exercise, and engagement in other interesting pursuits, should be urged, as the only mode of securing the religious benefits aimed at. And whenever any mind is oppressed with care, anxiety, or sorrow, the amount of active exercise in the fresh air should be greatly increased, that the action of the muscles may withdraw the blood, which, in such seasons, is constantly tending too much to the brain.

There has been a most appalling amount of suffering, derangement, disease, and death, occasioned by a want of attention to this subject, in teachers and parents. Uncommon precocity in children is usually the result of an unhealthy state of the brain; and, in such cases, medical men would now direct, that the wonderful child should be deprived of all books and study, and turned to play or work in the fresh air. Instead of this, parents frequently add fuel to the fever of the brain, by supplying constant mental stimulus, until the victim finds refuge in idiocy or an early grave. Where such fatal results do not occur, the brain, in many cases, is so weakened, that the prodigy of infancy sinks below the medium of intellectual powers in afterlife. In our colleges, too, many of the most promising minds sink to an early grave, or drag out a miserable existence, from this same cause. And it is an evil, as yet little alleviated by the increase of physiological knowledge. Every college and professional school, and every seminary for young ladies, needs a medical man, not only to lecture on physiology and the laws of health, but empowered, in his official capacity, to investigate the case of every pupil, and, by authority, to restrain him to such a course of study, exercise, and repose, as his physical system requires. The writer has found, by experience, that, in a large institution, there is one class of pupils who need to be restrained, by penalties, from late hours and excessive study, as much as another class need stimulus to industry.

Under the head of excessive mental action, must be placed the indulgence of the imagination in novel reading and castle building. This kind of stimulus, unless counterbalanced by physical exercise, not only wastes time and energies, but undermines the vigor of the nervous system. The imagination was designed, by our kind Creator, as the charm and stimulus to animate to benevolent activity; and its perverted exercise seldom fails to bring the appropriate penalty.

A third cause of mental disease, is, the want of the appropriate exercise of the various faculties of the mind. On this point, Dr. Combe remarks, "We have seen, that, by disuse, muscle becomes emaciated, bone softens, blood-vessels are obliterated, and nerves lose their characteristic structure. The brain is no exception to this general rule. Of it, also, the tone is impaired by permanent inactivity, and it becomes less fit to manifest the mental powers with readiness and energy." It is "the withdrawal of the stimulus necessary for its healthy exercise, which renders solitary confinement so severe a punishment, even to the most daring minds. It is a lower degree of the same cause, which renders continuous seclusion from society so injurious, to both mental and bodily health."