Physiological psychology / by W. McDougall.

  • William McDougall
Date:
1905
Catalogue details

Licence: In copyright

Credit: Physiological psychology / by W. McDougall. Source: Wellcome Collection.

    18/188 page 6
    been*destroyed, while the spinal cord and the trunk and limbs and their nervous connexions with the spinal cord remain in- tact, the limbs may still be excited by appropriate stimulation of the skin to execute movements that seem to be intelligently directed. Thus, if a drop of weak acid is put on the skin of the trunk of a frog whose brain has been destroyed, the hind- foot that can best reach the spot is raised and drawn across it, as though with the purpose of removing the irritation; and, if that foot is held fast, the other hind-foot makes a similar “ attempt.” Or if to the skin of the back of a dog in a similar condition an irritation somewhat similar to the bite of a flea is applied, one hind-foot will be raised towards the spot and will execute rapid scratching movements, and, though these movements are not so accurately adjusted as the similar movements of an intact animal, they are yet “ aimed ” with some precision at the spot irritated. Now such reflex movements seem to be completely deter- mined by a chain of purely physiological processes. In each case we seem to be able to trace the progress of a wave of physical change, initiated by the stimulus in the sense-organ of the skin, up the sensory nerves into the spinal cord, along certain nervous channels in the cord and out along the motor nerves that pass to the muscles whose contractions bring about the movements. There seems to be no scope for the intervention of mind as a directing agency. The whole process, from beginning to end, seems to be physically determined by the molecular structure of the nerves and by the mode of inter- connexion of sensory and motor nerves within the spinal cord, which determines that the excitement transmitted by the sensory nerves shall pass over to this or that group of motor nerves. This conclusion is borne out by the fact that similar reflex movements may be excited in our own bodies while we are in deep sleep or during the complete unconsciousness produced by such drugs as chloroform and ether. The spinal cord, in so far as it is not made up of bundles of nerves passing to and from the brain, has been shown to consist wholly of such com- plex connexions between sensory and motor nerves con-
    digitised image 1
    digitised image 2
    digitised image 3