t was not till I was a young man, at college, that I got any clew to
the significance of my dreams, and to the cause of them. Up to that time
they had been meaningless and without apparent causation. But at college
I discovered evolution and psychology, and learned the explanation of
various strange mental states and experiences. For instance, there was
the falling-through-space dream--the commonest dream experience, one
practically known, by first-hand experience, to all men.

This, my professor told me, was a racial memory. It dated back to our
remote ancestors who lived in trees. With them, being tree-dwellers, the
liability of falling was an ever-present menace. Many lost their lives
that way; all of them experienced terrible falls, saving themselves by
clutching branches as they fell toward the ground.

Now a terrible fall, averted in such fashion, was productive of shock.
Such shock was productive of molecular changes in the cerebral cells.
These molecular changes were transmitted to the cerebral cells of
progeny, became, in short, racial memories. Thus, when you and I,
asleep or dozing off to sleep, fall through space and awake to sickening
consciousness just before we strike, we are merely remembering what
happened to our arboreal ancestors, and which has been stamped by
cerebral changes into the heredity of the race.

There is nothing strange in this, any more than there is anything
strange in an instinct. An instinct is merely a habit that is stamped
into the stuff of our heredity, that is all. It will be noted, in
passing, that in this falling dream which is so familiar to you and
me and all of us, we never strike bottom. To strike bottom would be
destruction. Those of our arboreal ancestors who struck bottom died
forthwith. True, the shock of their fall was communicated to the
cerebral cells, but they died immediately, before they could have
progeny. You and I are descended from those that did not strike bottom;
that is why you and I, in our dreams, never strike bottom.

And now we come to disassociation of personality. We never have this
sense of falling when we are wide awake. Our wake-a-day personality has
no experience of it. Then--and here the argument is irresistible--it
must be another and distinct personality that falls when we are asleep,
and that has had experience of such falling--that has, in short, a
memory of past-day race experiences, just as our wake-a-day personality
has a memory of our w