Page:Popular Science Monthly Volume 20.djvu/603

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585
NERVO-MUSCULAR EXPRESSION.

and actual condition of the working of his brain. The educated and refined singer trains and refines his whole mind, i. e., his brain, and is well aware that his "whole soul," as he may express it, comes out in the action of the muscles concerned in producing his song and musical notes. In the infant the condition of the nervous system is best recorded in terms of nerve-muscular phenomena. It laughs, and is playful; reflex action is well marked when a finger is placed in the child's mouth. The eyes are moved and directed toward any object looked at; these are conditions of healthy action. It is well known that in the convulsive state the fists are often closed, with the thumbs turned in. All these examples of expression are nerve-muscular conditions; the movement, the attitude, the gait, result from states of the brain or spinal cord.

The normal movements of the eye are seen in the varying conditions of the pupil under the influence of light, in the changes accompanying accommodation for near and distant vision, and in the turning of the eyes in any given direction, a movement in which the parallelism of the axes of the organs is usually maintained. Each of these movements is supposed to be governed by a particular brain-center; and the convergence of the lines of the axis which takes place when the eyes are called upon to look at some very near object involves a complicated association of muscular conditions. The associated movements of the eyes may be completely lost in deep anæsthesia from chloroform, in coma from alcoholism, or in the profound sleep of infants. If, in an adult deeply under the influence of chloroform, the eyelids be gently raised, the pupils will be seen minutely contracted, often to a pin-point, the eyes having at the same time lost the parallelism of their axes. One eye may move upward or outward, while the other remains quiet, or moves in a different direction or at a different pace, thus causing a temporary and varying strabismus. Usually these movements are confined to the horizontal plane; less commonly the eyes assume a different level, one being in the horizontal plane while the other is turned downward. In these cases the coordination of the movements is restored with returning consciousness.

Loss of associated movements may sometimes be easily detected in very weakly infants while awake and sucking at the bottle, and in cases of meningitis and other conditions of coarse brain-disease; and sometimes appears to be chronic in paralyzed or partly paralyzed and idiotic persons. Many of the lower animals have the power of moving either eye separately and independently, a fact which leads to the suggestion that the brain-center that co-ordinates the movements of the two eyes may be looked upon as one more recently developed in the ascent of man.

In nystagmus, a disease in which the eyeballs oscillate rapidly, usually in an horizontal, rarely in a vertical direction, the parallelism of the axes is generally maintained. In one recorded case, the eyes were capa-