Page:Popular Science Monthly Volume 46.djvu/169

Rh the eye, the ear, etc., all of which in neurology are called end organs; and thus a passage is afforded for impressions made upon these end organs by the environment to reach the cells in the cortex, and for impulses to return from the cells in the cortex to the end organs, perhaps producing, restraining, or regulating movements in them.

Now a few words as to methods of investigation. Figs. 6 and 7 are charts showing the areas in the brain presiding over certain functions as thereon indicated. Take, for instance, the leg center. A case is found with sudden, complete, and permanent paralysis of the leg; after a few months the person dies, and upon examination of the brain and spinal cord it is observed that a hæmorrhage has destroyed the cells in the part of the brain here indicated. Now, as might be expected when the body of a cell is destroyed, its processes perish; hence, when consecutive sections are made across a strand composed of these cell processes, the bodies of which have been destroyed, and the sections are placed in a solution of coloring matter, it is found that the fibers which have perished take a different color from those which have not, and thus their position may be determined. In this case, by this method, a large strand of fibers which have perished may be



traced from the brain downward very near to the lower extremity of the spinal cord. This is known as the clinical method of study. These centers have also been removed in the course of surgical procedures, with the invariable result of producing a corresponding paralysis; and similarly they have been stimulated by electrical currents directly applied to them, and movements produced in the corresponding parts. This latter method is known as the excitation method; to this, as practiced upon the brains of monkeys some thirty years ago, we are indebted for the