THE PHYSICAL CONDITIONS OF CONSCIOUSNESS. 499 numbed and torpid nerve-centres declare their incompetence by an utter incapacity of further exertion and an ensuing irresistible inclination of the person to lie down, which, if yielded to, is followed by instant and usually fatal sleep. The inability to move a step further and the supervention of unconsciousness go along together. On entering a room we seem to see the various prominent objects in it at one glance. That is not really so ; we see them in a quick succession of glances, being unconscious of the rapid movements of the eye by which each object is successively apprehended. If the eye be fixed steadily and exclusively on one point a difficult thing to do, but which may be done by practice " the whole scene becomes more and more obscure and finally vanishes ". 1 The objects first appear dim, and then, if the almost incontrollable impulse of the eye to wander be successfully resisted, they fade away. These phenomena Sir C. Bell believed to be consequent upon the retina being subject to exhaustion. Is that the true, or at any rate the entire, cause ? Is it simply that the retina is exhausted, or is it that consciousness wanes and ceases in proportion as an impression is cut off from all its associations, sensory and motor ? The exceedingly rapid play of the very fine movements of the eyes by which we are conscious of the different objects in the room, as if we took them all in at a single glance, may help us to conceive the probably still more rapid interplays between nerve-tracts in the brain which are the apparent conditions of consciousness : move- ments of such coruscating rapidity that they might be compared perhaps to the infinitely varied and rapid play of sunlight on the sea- waves which constitutes their ' multi- tudinous laughter '. Impressions are always being made upon us by our en- vironment, many of which we are habitually unaware of, but we live and exert a certain muscular tonicity or tension, even when we do not move, in relation to them ; if we ceased entirely to react in that way we should become abso- lutely unconscious, and we should never become unconscious in the degree of sleep (which is not ever absolute insensi- bility) did we not cease to react to a great many of them. How continuous and how essential to our full personality these impressions are, even when we are habitually un- conscious of them, we never realise adequately until we find that we have lost them. A sudden deafness in one ear causes great uncertainty of position and movement, and 1 Sir Charles Bell, The Hand.
