_A Dream, what._--What, then, is a _dream_? I reply, it is any mental action in sleep, of which, for any reason, we are afterward _conscious_. This is not the case with all, perhaps, with most mental action during sleep. Senses and the will are inactive, then, for the most part, and whatever thoughts and impressions may be wrought out in the laboratory of the mind, whatever play of forces and wondrous alchemy may there be going on, when the controlling principle that presides over and directs its operations is withdrawn, are, for the most part, never subsequently reported. Let the sensitivity be partially aroused, however, let some disturbing cause come in to prevent entire loss of sensibility, or let the conceptions of the mind present themselves with more than usual vividness and force of impression, and what we then think may afterward be remembered. This is the philosophy of dreams. What is thus remembered of our thoughts in sleep, we call a dream, more especially applying the term to such of our thoughts and conceptions in sleep, as have some degree of coherence and connection between themselves, so as to constitute a sort of unity. _Sources of our Dreams._--Our dreams take shape and character from a variety of circumstances. They are not altogether accidental nor unaccountable; and even when we cannot trace the connection, there is reason to suppose that such connection exists between the dream, and the state of the body, or of the mind, at the time, as, if known, would account for the shape and complexion of the dream. The principal sources, or, perhaps, it were more correct to say, modifying influences of our dreams are, 1, Our present bodily sensations, and especially the internal state of the physical system, and, 2, Our previous waking thoughts, dispositions, and prevalent states of mind.