In the preceding chapters we have traced some of the elementary tendencies which prevail in the formation of dreams. These tendencies are in some respects so unlike those that rule in waking life--slight and subtle as their unlikeness often seems--that we are justified in regarding the psychic phenomena of sleeping life as constituting a world of their own. Yet when we look at the phenomena a little more deeply we realise that, however differentiated they have become, dream life is yet strictly co-ordinated with other forms of psychic life. If we pierce below the surface we seem to reach a primitive fundamental psychic stage in which the dreamer, the madman, the child, and the savage alike have their starting point, and possess a degree of community from which the waking, civilised, sane adult of to-day is shut out, so that he can only comprehend it by an intellectual effort.[243] It thus happens that the ways of thinking and feeling of the child and the savage and the lunatic each furnish a road by which we may reach a psychic world which is essentially that of the dreamer. The resemblance of insanity to dream life has, above all, impressed observers from the time when the nature of insanity was first definitely recognised. It would be outside the limits of the present book to discuss the points at which dreams resemble or differ from insanity, but it is worth while to touch on the question of their affinity. The recognition of this affinity, or at all events analogy, though it was stated by Cabanis to be due to Cullen, is as old as Aristotle, and has constantly been put forward afresh. Thus in the sixteenth century Du Laurens (A. Laurentius), in his treatise on the disease of melancholy, as insanity was then termed, compared it to dreaming.[244] The same point is still constantly brought forward by the more philosophic physician. 'Find out all about dreams,' Hughlings Jackson has said, 'and you will have found out all about insanity.' From the wider standpoint of the psychologist, Jastrow points out that not only insanity, but all the forms of delirium, including the drug-intoxications, are 'variants of dream consciousness.'