Page:Philosophical Review Volume 1.djvu/425

No. 4.] would overlap and slight pains or disagreeablenesses would be felt with certain sights and sounds.

If our theory be correct, the distribution of pain nerves must have much bearing upon the coexcitation of pain with other sensations. If there were no pain fibres in the optic sheath, but only in proximity to sight regions, this would explain why sensations of bodily pain do not accompany ordinary sight; only rare excitations of light, those violent enough to cause influences radiating to adjoining nerve terminals, or some mechanical disturbances upon the eye, as a blow, or some pathological irritation of the eye, would then cause optic pains. On the other hand, where the pain nerves were distributed more intimately with those of certain senses, naturally the association between pain and these senses would be proportionally more frequent and closer. In the skin the nerves of pain are found by Goldscheider to be microscopically interwoven with the nerves of touch, pressure, heat, and cold. In accordance with this is the much greater frequency of occurrence of pain sensations with pinching, pricking, bruising, burning, freezing, and so on, than with sights, sounds, and tastes.

We may go further than this and get a glimpse of why pain nerves are distributed as they are. The number and the nature of our bodily organs are determined in one way by their functions. Why our eyes are on the outside of our body follows from the nature of sight. Why we have two eyes, rather than that our skin should be covered with eyes, is because being able to see at a distance we may turn our bodies in time to use our two eyes efficiently in every direction. Two eyes are therefore sufficient. Now objects at a distance being little likely to be dangerous, it was not necessary that pain nerves should be interwoven with the rods and cones of the retina in a way to be intimately susceptible to the usual functional experiences of the retina. In contrast with this, touch being contact and the dangers of touch being immediate, touch nerves and also pain nerves were demanded from every point of the body, the one to mediate sensations of touch, and the other to warn against the dangers of contact efficiently in every direction. Similar