[Footnote 85: This indeed seems to have been recognised by Wundt, who regards a 'functional rest of the sensory centres and of the apperception centre,' resulting in heightened latent energy which lends unusual strength to excitations, as a secondary condition of the dream state. Külpe (_Outline of Psychology_, p. 212) argues that the existence of vivid dreams shows that fatigue with its diminished associability fails to affect the central sensations themselves; this increased excitability resulting from dissociation may itself, however, be regarded as a symptom of fatigue; hyperaesthesia and anaesthesia are alike signs of exhaustion.] [Footnote 86: The exhaustion sometimes felt on awaking from a dream perhaps testifies to its emotional potency. Delboeuf states that a friend of his experienced a dream so terrible in its emotional strain that on awaking his black hair was found to have turned completely white.] [Footnote 87: The fundamental character of emotion in dreams has been more or less clearly recognised by various investigators. Thus C. L. Herrick, who studied his own dreams for many months, found that the essential element is the emotional, and not the ideational, and that, indeed, when recalled _at once_, with closed eyes and before moving, they were nearly devoid of intellectual content (_Journal of Comparative Neurology_, vol. iii. p. 17, 1893). R. MacDougall considers that dreaming is 'a succession of intense states of feeling supported by a minimum of ideational content,' or, as he says again, more accurately, 'the feeling is primary; the idea-content is the inferred thing' (_Psychological Review_, vol. v. p. 2). Grace Andrews, who kept a record of her dreams (_American Journal of Psychology_, October 1900), found that dream emotions are often stronger and more vivid than those of waking life; 'the dream emotion seems to me the most real element of the dream life.' P. Meunier, again ('Des Rêves Stéreotypés,' _Journal de Psychologie Normale et Pathologique_, September-October 1905), states that 'the substratum of a dream consists of a cœnæsthesia or an emotional state. The intellectual operation which translates to the sleeper's consciousness, while he is asleep, this cœnæsthesia or emotional state is what we call a dream.']