Page:American Journal of Psychology Volume 21.djvu/557

Rh with a corresponding effect upon co-ordination. Head's cases on the other hand clearly illustrate that the loss of tactile sensations alone in man has little or no effect upon voluntary movement.

2. Physiological Experiments.

In order to determine the effect of the loss of "resident sensation upon movement, Mott and Sherrington working on the monkey severed the dorsal roots on one side of the cord supplying the arm and leg with sensory innervation, viz., the 4th cervical to the 4th thoracic inclusive, and the 2d to the loth post-thoracic inclusive. The results are described in their own language as follows: "From the time of performance of the section onward as long as the animal may be kept [they kept them about four months] the movements of the hand and foot are practically abolished. On the other hand, the movements of the elbow and knee, and especially the movements at the shoulder and hip, are much less impaired. If the feeding time be deferred, and an animal, in which the apæsthete limb is an arm, be tested by offering it fruit after the sound arm has been secured behind the back, there is no attempt to use the apæsthete limb for reaching the food, but the neck is thrust forward in order for the mouth to seize it." One monkey tried to take food with the apæsthete foot but failed,–"the digits were not moved." "The defect in motility increases from the attached base to the free apex of the limb; so that, for instance, while comparatively slight at the hip, it is successively greater at the knee and ankle, and greatest (amounting as regards volition, to absolute loss) in the digits." The authors conclude that volition "has been absolutely abolished by the local loss of all forms of sensibility." (Proc. Roy. Soc., Vol. 57, pp. 481 ff.)

Bastian, on the other hand, while accepting these facts criticises Mott and Sherrington's interpretations. Brain, Vol. 18, pp. 609 and 615. Bastian argues that limb movements may be paralyzed or rendered defective in two ways: (a) by organic lesions (b) by functional defects. These functional defects are of two sorts: in the one case the "seat" is cerebral, in the other, spinal. He says that "in cases of complete hemianæsthesia due to lesions or functional defects in the posterior part of the internal capsule, there is not only no paralysis, but little or no impairment in the ability to perform, under visual guidance, even the most delicate movements with the apæsthete limbs." As is well known, Bastian holds that there are no motor centres strictly speaking, that what we call motor centres are essentially kinaesthetic centres and that impulses have to pass through these centres before a movement can be made, but that these impulses may originate in the auditory centre –3