Page:Popular Science Monthly Volume 24.djvu/658

640 This new material is absorbed by the cells from the blood, through the thin walls of the minute blood-vessels in their vicinity. Through the walls of the same vessels the cast-off matters pass in the opposite direction into the circulation and are washed away by its current. While the tissue is hard at work, the process of disintegration is at a maximum, and that of repair at the opposite extreme—consequently the waste is produced more rapidly than it can be carried away, and accumulates. As ashes in a stove interfere with combustion, it impedes the current of thought, and lessens its intensity. But, during repose, the opposite conditions obtain—repair is at its maximum, and waste almost or entirely suspended. The blood has been busy all night ridding itself and the tissues of all impurities, and is richly charged with oxygen. The brain, and consequently the mind, is fresh and vigorous after the night's repose; the damages have been all repaired, and the débris cleared away. It is a matter even of common observation that at no other time is the mind so sharp, clear, and strong, as in the morning.

Concrete ideas tax the mind but lightly. The more abstract ideas become, the more difficult is their comprehension, and the greater the nervous strain involved in their contemplation. For this reason, the abstruse studies should be taken up during the forenoon session, as the faculties of the mind are then in the most favorable condition to grapple with their difficulties.

Of all school-studies, mathematics requires the strongest grasp of mind, and the closest exercise of the reasoning powers and the judgment. In abstruseness and difficulty of comprehension, geometry, algebra, and arithmetic, rank in the order enumerated. Rhetoric, including grammar and composition, comes next. In every school and college, therefore, these subjects should be taken up during the morning session.

The mind learns by means of impressions made upon the gray nerve-cells, through the senses, of which sight is the most vivid and durable in its effects. Hearing ranks next, but its impressions are less vivid and more fleeting. Further, they are recalled to the memory less readily and distinctly. We all remember what we see longer than what we hear. Hence the most reliance should be placed upon the eye as an avenue of instruction, and the teacher should make use of it whenever practicable. When an impression is made upon a nerve-cell, it is said to retain it "in potency" that is, it is capable of renewing it by an exercise of the memory. Now, the clearness and permanence of a mental impression depend—(a) upon its vividness; (b) upon the frequency of its repetition; and (c) upon the inherent vigor of the nerve-cell.

To obtain vividness of impression, the teacher's language should be clear and simple; his descriptions of processes and objects sharp and vivid; he must present the same ideas again and again, in order to fix