Page:Popular Science Monthly Volume 35.djvu/399

This page has been proofread, but needs to be validated.

the extent of appropriating the food placed at its lips; yet, for the effective use of the arms and legs, mouths of training are necessary; while definite movements of the trunk, as in dancing, bowing, etc., are acquired much later in life. It is also a most significant fact that the center for the control of the various and complex movements concerned in speech is limited to the left side of the brain in right-handed persons—a few cases having been recorded in which disease of the corresponding locality on the right side of the brain has been followed by loss of speech in the left-handed[1]—implying that the more frequent and intelligent use of the muscles of the right hand and arm has had some connection with the development of the faculty of speech. This is corroborated by the fact that, among the lower animals, there is little if any difference in the use of the anterior limbs, as there is also absence of the faculty of speech—a factor of the highest importance in mental development.

Although the doctrine of localization has distinguished opponents, Prof. Goltz denying that either sensations or movements have any special centers in the brain, and the late George Henry Lewes opposing the idea to the extent of saying, "It is the whole man who feels and thinks," nevertheless the doctrine is gaining ground. At least two cases have been recorded of otherwise normal individuals in whom a congenital absence of the left hand and a part of the arm was accompanied by a rudimentary condition of the corresponding convolution on the right side of the brain, showing that the building up of these motor areas in the brain is largely dependent on muscular exercise during the period of growth. That the maintenance of their nutrition in the adult is also to some extent dependent on muscular exercise is made probable by the fact that wasting of the corresponding convolution has been found in a few instances after amputation of a limb. Removal of the brain, slice by slice, in the lower animals is followed by a corresponding reduction both of intelligence and of power of voluntary movements which disappear together in about an equal degree; and every observer knows that in many cases of brain disease intelligence and the power of voluntary movement alike suffer in proportion to the extent of degradation of brain substance. There is also no more conspicuous feature of idiocy than its accompanying feeble, irregular, and uncoordinated movements. Just what relations exist between the motor areas of the brain and general intelligence is not a matter for dogmatic assertion; but that these centers form a part of the intellectual machinery is undoubted, and the facts cited, without reference to theories, may be regarded as proving my second thesis, viz., that the systematic and regular use of the voluntary muscles of the body

  1. Küssmaul.