I take shelter behind the inadequacy of the English
language. And now to the explanation of my use, or
misuse, of the phrase.

It 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