Page:Popular Science Monthly Volume 24.djvu/657

Rh  a recurrence of the suffocating fit; but only the subsidence of the inflammation—indicated by the diminished hoarseness of the cough—gives a guarantee that the danger is past.



HE ultimate element by means of which those processes that constitute the mind are carried on, is the microscopic cell of the gray matter of the brain. These gray nerve-cells, with the delicate tissue in which they are imbedded, form a layer, from one sixth to one twelfth of an inch in thickness, on the surface of the brain. This area would be small, were it not disposed in folds or convolutions which greatly increase its extent. It is upon the number and quality of these nerve-cells, and the systematic exercise of their function, rather than upon mere size or weight of brain, that the mental capacity of the individual depends.

The activity of the nerve-cells of the brain, in other words, depends partly upon their inherent vitality or vigor of constitution, and partly upon the quantity and quality of their blood-supply. They may be stimulated into unwonted activity by an effort of the will or the spur of excited consciousness; but even in these cases, should the strain last any length of time, the blood-supply is quickly and largely increased.

Skeptics may cavil, but the solid fact remains that strength of intellect, like that of muscle, is frequently inherited. Capacities differ from the beginning. For this reason, children can not be expected to make equal progress under any system of teaching, any more than horses upon a race-course. But, by persistent and judicious training, the strength, speed, and endurance of all may be increased through a steady and gradual development.

In order that the teacher may utilize his efforts to the best advantage, he should understand the laws of the mind's development, and the influences that modify and regulate its activity. Mental philosophy deals with the former—to explain some of the latter is the object of this paper.

The brain-substance may be touched, and even cut, with little or no consciousness of sensation; yet the gray nerve-matter is very delicate in construction, and exquisitely sensitive to changes in its blood-supply. Like other organs, it is exhausted by continued activity, and needs rest in order to recuperate its vitality. All tissues wear more or less by work; that is, molecules of their cell-substance die and become foreign matter, which must be cast off and replaced by new material. 