The shifting and endlessly variable character of the spontaneous luminous excitation of the retina corresponds exactly to the fitful succession of pictures presented to us in our dreams. If we attach any importance to Ladd's observations, we cannot underrate the productiveness of this subjective source of excitation for the dream; for visual pictures apparently form the principal constituent of our dreams. The share furnished from the spheres of the other senses, beside the sense of hearing, is more insignificant and inconstant.
III. Internal (Organic) Physical Excitation.—If we are disposed to seek dream sources not outside, but inside, the organism, we must remember that almost all our internal organs, which in their healthy state hardly remind us of their existence, may, in states of excitation—as we call them—or in disease, become for us a source of the most painful sensations, which must be put on an equality with the external excitants of the pain and sensory stimuli. It is on the strength of very old experience that, e.g., Strümpell66 declares that "during sleep the mind becomes far more deeply and broadly conscious of its connection with the body than in the waking state, and it is compelled to receive and be influenced by stimulating impressions originating in parts and changes of the body of which it is unconscious in the waking state." Even Aristotle1 declares it quite possible that the dream should draw our attention to incipient morbid conditions which we have not noticed at all in the waking state (owing to the exaggeration given by the dream to the impressions; and some medical authors, who were certainly far from believing in any prophetic power of the dream, have admitted this significance of the dream at least for the foretelling of disease. (Compare M. Simon, p. 31, and many older authors.)
Even in our times there seems to be no lack of authenticated examples of such diagnostic performances on the part of the dream. Thus Tissié68 cites from Artigues (Essai sur la Valeur séméiologique des Réves), the history of a woman of forty-three years, who, during several years of apparently perfect health, was troubled with anxiety dreams, and in whom medical examination later disclosed an incipient affection of the heart to which she soon succumbed.
Serious disturbances of the internal organs apparently act