But, after all, is the distribution of the sense-organs exactly that which we should expect on the Lamarckian theory? Has not Spencer taken too much for granted in this direction? The lower part of the forearm (represented by 15) we should expect to be more sensitive than the protected surface of the eyelid (11.3), but this is not the case. The forehead (22.6) is much less sensitive than the forearm, and only half as sensitive as the eyelid. The knee (36.1) is still less sensitive than any of these other parts, and this does not in the least accord with the theory, since in its constant moving forward it must be continually coming into contact with foreign bodies. The fact that the back is as insensitive as the upper arm (67.7) can hardly be accredited in favor of the theory. The great difference between the lower third of the forearm on the ulnar surface (15) and the upper arm (67.7) seems out of all proportion to what we should expect on the theory. And is it not a little odd that the end of the nose should be so highly sensitive?
There is another point that we cannot afford to neglect in this connection. It is known that in addition to touch-spots there are warm and cold spots in the skin, which produce, when touched, the sensation of warmth, or of cold, respectively, and not the sensation of touch. The degree of sensitiveness of different regions of the body throws an interesting side-light on Spencer’s argument.
The warm spots are much fewer than the cold spots. The spots are arranged in short lines radiating from centres which coincide with hairs. The number of these spots varies a good deal, even in the same region of the skin. If the sensitiveness of the skin is tested, the following results will be obtained. The list includes twelve grades of sensitiveness, beginning with the places giving the lowest maximum of intensity. About one hundred square areas were tested in each region.
COLD SENSATIONS
1. Tips of fingers and toes, malleoli, ankle.
2. Other parts of digits, tip of nose, olecranon.
3. Glabella, chin, palm, gums.
4. Occiput, patella, wrist.
5. Clavicle, neck, forehead, tongue.
6. Buttocks, upper eyelid.