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.