by changes in the external system which have been ignored. Also, in any fundamental sense, we shall fail to understand the retained activities. For these activities will depend upon a comparatively unchanging systematic environment.
In all discussions of Nature we must remember the differences of scale, and in particular the differences of time-span. We are apt to take modes of observable functioning of the human body as setting an absolute scale. It is extremely rash to extend conclusions derived from observation far beyond the scale of magnitude to which observation was confined. For example, to exhibit apparent absence of change within a second of time tells nothing as to the change within a thousand years. Also, no apparent change within a thousand years tells anything as to a million years; and no apparent change within a million years tells anything about a million million years. We
