The science of life : fully illustrated in tone and line and including many diagrams

THE HARMONY AND DIRECTION OF THE BODY-MACHINE

distinctive complexity and definiteness of his thought-processes.

We may note here, before we break off this brief first account of the working of the brain, a curious part of it lying at the back, behind and below the cerebral hemispheres and having a more closely wrinkled surface than they. This organ, the cerebellum, is a sort of private secretary to the cerebral hemispheres. It is discriminating but not conscious. Its activities may best be displayed by asingle instance. A very intricate complex of reflex actions keeps our bodies balanced. Suppose that the cerebrum intervenes and sends a command to the appropriate motor cells in the spinal cord so that the right arm is raised. The centre of gravity of the body will be shifted, and in the absence of any compensating adjustments we should sway over to the right side. But the cerebellum sees to this. It watches the acts of the superior authority and takes unobtrusive but appropriate steps so that the general equilibrium of the body may not be upset—the example chosen, it would call forth a slight compensating movement of the left arm or a slight adjustment of the position at the hip-joints. It is like the official in a Cinema studio who specializes in “ continuity,’’ it notes the actions of the directors, supplies their omissions, and, without bothering the mind in the least, sees them through.

Occasionally Mr. Everyman may afford an unpremeditated demonstration of the function of the cerebellum. It is sensitive to an excess of alcohol in the system and speedily becomes disorganized under its influence. The cerebrum itself may be even elated by this drug and may issue many bright and pleasing orders in consequence, but the cerebellum fails in its customary secretarial care. Consequently Mr. Everyman’s movements become unbalanced. He walks, but he no longer walks with grace and precision ; he may become excited by ideas and garrulous, but his larynx, lips, and mouth fail in the fine adjustments necessary for perfect articulation. He seeks to give playful slaps to his friends and misses them perplexingly. Similar results may be due to organic injury of the cerebellum, and it is sometimes difficult to distinguish the permanent from the transitory derangement.

This is as far as it is convenient to carry our account of the brain at the present time. Throughout the Books that follow this one we shall be gathering the material for a later more exhaustive attack on the mysteries of that coating of grey matter upon the outside of the cerebrum, which is the seat of Mr. Everyman’s dreams and desires, the vehicle of his imagination, the medium of his joys and sorrows, the most important stuff in the universe for every human heing.

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