“Nevertheless,” continues Hildebrandt, “the opposite is seemingly just as true and correct. I believe that hand in hand with this seclusion and isolation there can still exist the most intimate relation and connection. We may justly say that no matter what the dream offers, it finds its material in reality and in the psychic life arrayed around this reality. However strange the dream may seem, it can never detach itself from reality, and its most sublime as well as its most farcical structures must always borrow their elementary material either from what we have seen with our eyes in the outer world, or from what has previously found a place somewhere in our waking thoughts; in other words, it must be taken from what we had already experienced either objectively or subjectively.” (_b_) _The Material of the Dream.—Memory in the Dream._—That all the material composing the content of the dream in some way originates in experience, that it is reproduced in the dream, or recalled,—this at least may be taken as an indisputable truth. Yet it would be wrong to assume that such connection between dream content and reality will be readily disclosed as an obvious product of the instituted comparison. On the contrary, the connection must be carefully sought, and in many cases it succeeds in eluding discovery for a long time. The reason for this is to be found in a number of peculiarities evinced by the memory in dreams, which, though universally known, have hitherto entirely eluded explanation. It will be worth while to investigate exhaustively these characteristics. It often happens that matter appears in the dream content which one cannot recognise later in the waking state as belonging to one’s knowledge and experience. One remembers well enough having dreamed about the subject in question, but cannot recall the fact or time of the experience. The dreamer is therefore in the dark as to the source from which the dream has been drawing, and is even tempted to believe an independently productive activity on the part of the dream, until, often long afterwards, a new episode brings back to recollection a former experience given up as lost, and thus reveals the source of the dream. One is thus forced to admit that something has been known and remembered in the dream that has been withdrawn from memory during the waking state.