It is one of the great services Freud rendered to psychology (and one, by the way, largely responsible for the acceptance of his doctrines by the disinterested intelligence) that he showed that a species of forgetting is nothing casual, but active and purposeful, a manifestation of the life of the unconscious.  However, though his description of the process was correct, he left it to occur in a vacuum.  As a matter of fact this forgetting consists in the inhibition of associative memory by a process in the vegetative apparatus, so as to maintain the equilibrium within itself which is reflected in consciousness as comfort.

The unconscious, in short, consists of the buried associations among the parts of the vegetative apparatus and the brain cells.  We seem to be much nearer to grasping the nature of the unconscious, when we look upon it as a historical continuum, a compound or emulsion of different and various states of intravisceral pressure and tone, in the vegetative apparatus, dependent upon the balance between the endocrines, as well as upon past experiences of the viscera in the way of stimulation or depression.  We forget that which is held down, literally, in the vegetative apparatus.  This explanation of forgetting tells, too, why the forgotten (stored in the sub-brain, the endocrine-vegetative system) continually projects itself into and interferes with the regular flow of consciousness, e.g., in slips of the tongue, mistakes of spelling, and so on:  because the energy bottled in the vegetative system tends to erupt into the consciousness into which it would ordinarily flow.

In the evolution of the mind, there have been elaborated devices to protect it against the vegetative apparatus.  Consciousness, or awareness, must be accepted as a fundamental, primal fact, like protoplasm.  Consciousness and protoplasm may be the complementary sides of the same coin.  Whatever the truth, the fact stands out that the oldest, deepest, most potent consciousness is that of the traditionally despised lowest organs, the vegetative organs, the heart and lungs, stomach and intestines, the kidneys and the liver, and so on, their nerves, e.g., the solar plexus, and the glands of internal secretion.  They invented and elaborated muscle, bone and brain to carry out their will.  Evolution has been in the direction of a greater perfection of the methods of carrying out their will.  Their consciousness, working upon the growing and multiplying brain cells, has created what we call self-conscious mind.

Mind, reacting upon its creator, has, in a sense, come to dominate them, because it has become the meeting ground of all the energy-influences seething and bubbling in the organism, and so developed into the organ of handling them as a whole, their Integrating-Executive.  But just the same and all the time, the underlying consciousness of the viscera and their accessories stand as the powers behind the throne, but as what we have now learned to speak of, in relation to the Mind, as the Unconscious.