The general fact thus brought to light--that the mode in which a brain-centre will function depends so largely upon its initial education, but that, this education once completed, the centre can maintain its function, though deprived of sense-stimulation--is sufficiently important to merit further illustration.[17] This fact, though very clear and evident when stated from a modern point of view, has not always been recognized. So ingenious a thinker as Erasmus Darwin inferred from two cases (the one of a blind man, the other of a deaf-mute) in which the wanting senses were also absent in dreams, that the peripheral sense-organ was necessary for all perception, subjective as well as objective; and entirely neglected the age at which the sense was lost. Such noted physiologists as Reil, Rudolphi, Hartman, Wardrop (who says, "when an organ of sense is totally destroyed, the ideas which were received by that organ seem to perish along with it as well as the power of perception"), more or less distinctly favored this view; while some teachers of the blind and the physiologists Nasse and Autentreith rightly drew the distinction between those born, and those who became, blind. An experimental demonstration of the original dependence of the perceptive and emotional powers upon sense-impressions was furnished by Boffi and Schiff, who found that young dogs whose olfactory bulbs had been removed failed to develop any affection for man.
What is true of the visual, is doubtless equally true of the other perceptive centres. The dreams of the deaf-mute offer an attractive and untouched field for such study.[18] The few accounts of such dreams that I have met with, fail to give the age at which deafness set in; in one case, however, in which deafness occurred at thirty years, the pantomimic had replaced the spoken language in the dreams of thirty years later. Similarly, cripples dream of their lost limbs for many years after their loss; in such cases, however, stimulation of the cut nerves may be the suggestive cause of such dreams. A man of forty, who lost his right arm seventeen years before, still dreams of having the arm. The earliest age of losing and dreaming about a lost limb, of which I find a record, is of a boy of thirteen years who lost a leg at the age of ten; this boy still dreams of walking on his feet. Those who are born cripples must necessarily have their defects represented in their dream consciousness. Heermann cites the case of a man born without hands, forearms, feet, or lower legs. He always dreamt of walking on his knees; and all the peculiarities of his movements were present in his dream-life.