Page:Popular Science Monthly Volume 18.djvu/617

Rh  the theorist when he applies himself to practical work with personal responsibility, and he begins to find that the means at his disposal are inadequate to the results expected from him.

 

HEN the one who listens does not comprehend, and the one who speaks understands as little, you have metaphysics," says Voltaire. Taking this as a true definition, we may say that there has been, and yet remains, much metaphysics in the treatment of the functions of the brain. But the difficulties in cerebral physiology are great. There is divergence of hypotheses, the facts themselves are not settled, and contradictions abound. The foundations of the science are yet deficient. But it does not follow that experiments are useless. For half a century important researches have been carried on; and more recently facts have been discovered to which we would here draw attention.

From an anatomical point of view the brain is composed of two symmetrical halves, right and left, united by a voluminous commissure, which probably puts into communication the homologous parts of the two hemispheres. Each hemisphere consists of a central mass, with its envelope of convolutions. The central mass, partially separated from its outer covering by the lateral ventricles, is composed of two round bodies, formed of gray nerve-cells—the active part of the nervous system. The office of these rounded ganglia seems to be to strengthen the impressions that come from without, or from stimulated parts of the brain itself, and they may take part in automatic actions. They are in relation, on the one hand, with the spinal cord, and perhaps, more or less directly, with most of the motor and sensitive fibers of the body; on the other hand, they are connected by fibers with the gray matter which is spread out in layers over the convolutions of the brain. In other words, the nerve-cells forming the periphery of the convolutions give out white fibers, which penetrate the central ganglia, probably connecting themselves with their cells. From these cells other fibers proceed toward the cord and extremities of the body. The central masses are on the line of the cerebral fibers between their origin in the gray cells of the convolutions and their termination in the cord and body generally. 