The transverse fibers of the pons Varolii unite the lobes of the cerebellum, and we may appropriately consider the functions of this organ before those of the smaller masses within the cerebral hemispheres. There is, perhaps, no subject in nerve-physiology more obscure and difficult than this one of the functions of the cerebellum. The earlier opinion, that this organ is connected with the sexual appetite, has long since been completely disproved. The special difficulty in determining the functions of the cerebellum arises from the disagreement between experiment and pathology, as also from hazard of injury to adjacent nerve-masses. Flourens was the first to investigate the functions of the cerebellum in a strictly inductive manner; his experiments have been repeatedly confirmed, and they must furnish the starting-point for all future inquiry. Flourens says: "I removed the cerebellum of a pigeon in successive slices. During the removal of the first layers there appeared only a weakness and want of harmony in its movements. On removal of the middle layers, the animal exhibited a general agitation, without true convulsions. It made brusque and irregular movements, and continued loath to see and to hear. On removal of the last layers, the animal entirely lost the power of standing, flying, leaping, or walking, which had been gradually affected by the preceding mutilation. Placed on its back, it was unable to rise. Instead of remaining quiet and immovable, like pigeons deprived of their hemispheres, it was in a continual state of restlessness and agitation, but could never make any determinate movement. It could see a threatened blow, and tried to escape, but without success. It made various efforts to recover its station when laid on its back, but utterly failed to do so. Sensation, volition, and intelligence remained, but the co-ordination of movements into regular and determinate movements of progression was entirely lost." There is no doubt that destruction of the cerebellum is frequently followed by striking disorders of equilibrium. Flourens found, however, that these disorders would, in time, be overcome by the animal, even though the lesions were deep. Upon complete destruction of the organ, the disorders were lasting. Weir Mitchell's experiment, quoted by Ferrier, would not confirm this permanency of the disorders. Weir Mitchell states that he destroyed the functional activity of the entire cerebellum in pigeons who, after some months, recovered "so far as to show only feebleness and incapacity for prolonged muscular exertion, but no real inco-ordination or unsteadiness of equilibrium." Repeated experiments have shown a decided difference of result, according to the character and location of the lesions. If these lesions are made symmetrically on both sides, or if the cerebellum be divided in the middle, from the front backward, there is no important disturbance of equilibrium. If, on the other hand, the central lobe be cut in its anterior portion, the animal tends to fall forward; if in its posterior portion, to fall backward. Lesion in one of the lateral lobes is
Page:Popular Science Monthly Volume 26.djvu/765
THE NERVOUS SYSTEM AND CONSCIOUSNESS.