are some simple experiments which illustrate the vestiges of
ganglionic impressions. If on a cold, polished metal, as a new razor,
any object, such as a wafer, be laid, and the metal be then breathed
upon, and, when the moisture has had time to disappear, the wafer be
thrown off, though now the most critical inspection of the polished
surface can discover no trace of any form, if we breathe once more upon
it, a spectral image of the wafer comes plainly into view; and this may
be done again and again. Nay, more, if the polished metal be carefully
put aside where nothing can deteriorate its surface, and be so kept for
many months, on breathing again upon it the shadowy form emerges.

Such an illustration shows how trivial an impression may be thus
registered and preserved. But, if, on such an inorganic surface, an
impression may thus be indelibly marked, how much more likely in the
purposely-constructed ganglion! A shadow never falls upon a wall without
leaving thereupon a permanent trace, a trace which might be made visible
by resorting to proper processes. Photographic operations are cases in
point. The portraits of our friends, or landscape views, may be hidden
on the sensitive surface from the eye, but they are ready to make their
appearance as soon as proper developers are resorted to. A spectre is
concealed on a silver or glassy surface until, by our necromancy, we
make it come forth into the visible world. Upon the walls of our most
private apartments, where we think the eye of intrusion is altogether
shut out and our retirement can never be profaned, there exist the
vestiges of all our acts, silhouettes of whatever we have done.

If, after the eyelids have been closed for some time, as when we
first awake in the morning, we suddenly and steadfastly gaze at a
brightly-illuminated object and then quickly close the lids again, a
phantom image is perceived in the indefinite darkness beyond us. We may
satisfy ourselves that this is not a fiction, but a reality, for many
details that we had not time to identify in the momentary glance may
be contemplated at our leisure in the phantom. We may thus make out the
pattern of such an object as a lace curtain hanging in the window, or
the branches of a tree beyond. By degrees the image becomes less and
less distinct; in a minute or two it has disappeared. It seems to have a
tendency to float away in the vacancy before us. If we attempt to follow
it by moving the eyeball, it s