The blot upon the brain : studies in history and psychology.

  • Ireland, William W. (William Wotherspoon), 1832-1909.
Date:
1885
Catalogue details

Licence: Public Domain Mark

Credit: The blot upon the brain : studies in history and psychology. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

    14/394 (page 2)
    rib, and looser at the edges. Some of the changes in the forces of the outer world cause modifications in the nervous system, and these, recognised by the mind, constitute what we call sensation. But the nervous system may be affected by changes within the body; for example, by an altered state of the blood ; by external injuries ; by cold or heat; or by electricity. Each nerve, when stimulated, gives its own proper and peculiar sen- sation. If one touches a nerve trunk in the leg, it will give a feeling probably referred to the foot. If one touches or stimu- lates the optic nerve, a flash of light is seen; or if one excites the auditory nerve, a sound is heard. Thus, changes within the body must be distinguished from changes without the body ; and this, in general, is easy. We soon learn the difference between what are called objective or real sounds, produced by vibration in the outer world, and subjective sounds, such as humming or buzzing in the ears, or real changes in the refrac- tion of light, and flashes of light caused by irritation of the optic nerve, or motes floating before the eyes. The nerves are more exposed to excitation at their extremities, as in their course from the surface of the body to the brain or spinal cord, they are well covered up and guarded by the other tissues, hence irritations of their trunks scarcely ever occur, save in abnormal conditions of the economy. When these do occur, we are very apt to confound the sensations arising from irritations from within the body with the ordinary stimuli derived from the contact of the outer phenomenal world. Thus, men fall into various errors. Of these, we have at present to do with illusions and hallucinations. An illusion is an erroneous interpretation of a real sensation ; that is, a sensation originat- ing from changes in the outer world acting on some part of the nervous system. Thus, a man mistakes a rock for a tower, or the play of the moonlight through the forest leaves for running M'ater, or a sheet hung up for a ghost. In these instances, the mind has been too rapid in its forecast, either by following the line of habit acquired in cases outwardl}'' similar, or by yielding to the suggestions of hope or fear, or the fallacies of a disordered mind. <^ A hallucination is a perception of a sensation arising from changes within the organism without any corresponding change