BILATERAL ASYMMETRY OF FUNCTION. 101 that some of the phenomena of insanity sinning against know- ledge and conviction, rapidly contrasting states of mind, &c. might be explained by disparity, incoordination or disturbed equi- librium between the hemispheres. Even Lotze and Friedrichs conjecture that one half of the brain may be conscious of psychic disease in the other, while Pick thinks it is through the functions of the sane parts of the brain that it is possible to become con- scious of disturbed sanity. Hoppert and Jensen believe double thinking, or illusions of memory, when a new impression or experience brings with it a sense of familiarity, is due to the dual function rather than, as Buccola and others before him prefer to think, to a recrudescence of forgotten dreams and reveries. Flechsig thinks the hemispheres may function alternately. The morbid impulse to write mirror-script may be due to centres on the weaker side suddenly becoming the dominant ones. A normal differentiation of function, culminating perhaps in or near the island of Reil and the cortical centres above, may perhaps be assumed. Several observers now hold that the motor area is larger in the left hemisphere, which Hughlings Jackson calls the leading side. The voluntary power to speak words has been located here, and the automatic power of speaking in the corres- ponding centres of the right of the brain. Strieker compares the two hemispheres to two coachmen, each with a pair of lines, driving the same horses ; the right coachman is strong and trusty, but the left one is more skilful in fancy evolutions. The human infant, hi making synchronous movements with both arms, makes at first many more symmetrical than con- gruent movements, i.e., more movements involving corresponding muscles of both arms than those in the same direction with non- corresponding muscles. These latter movements appear to be learned later, then one hand learns to act, the other remaining at rest, and finally both hands learn to act independently at the same time. An expert " will-virtuoso " is even able to write a Hebrew sentence from the Old Testament in one direction with one hand, while the other is writing a French madrigal, alternate lines backwards perhaps, and both with extreme rapidity. A thorough and psychological piano-teacher lays far less stress at first on the running scales involving congruent motions, than upon exercises which early and completely dualise the action of the two hands, both in tempo and in direction. These phenomena involve no such " division of the attention " as has been inferred, but one hand learns to act more automatically, and the focus of attention to alternate rapidly from right to left. Life is not, how- ever, as has been seen, an even struggle for a monopoly of func- tio7i between the two halves of dual man. Nurses cany children on their own right arm, leaving the child's right arm a freer field of motion. They hug them on the right side, disturbing the equi- librium of blood-pressure. Early in history the right hand became Associated with the south, with the sun, faced in worship, with
