But when, as in sleep, the pressure on the limits of consciousness is relieved by the inactivity of some of the higher cerebral centres, the "critical point" of consciousness is lowered, various new elements rise above the threshold, and elements hitherto subordinate acquire greater prominence. Of the throng of images present to the mind during sleep, the most part are so evanescent as to fade from the memory shortly after waking. The common run of dreams, no doubt, are comparable in intensity to the feebler reverberations accompanying the main movement of our waking thoughts, and assume temporary importance only because they do not come into competition with more vivid impressions. Thus sensations of organic processes are frequently predominant during sleep, just as the Clank and clash of shunting trains, the gross machinery which underlies our social life, forms an unregarded element in the complex mass of sound which fills our ears in the daylight hours, but attains to solitary distinctness in the quiet of the night.
We thus sometimes obtain in dreams knowledge of latent illness of which no sign could be discerned in our waking hours. Again, in sleep we frequently revert to forgotten memories of our earlier years, and our dreams are constantly coloured by the emotional tone which prevailed in childhood. Our consciousness in dreams is thus still a compound, but it is a compound which includes different elements. Further, in dreams there may be spon-
