The condition of human internal organs is related with life itself. Then, for preventing not becoming defenceless, there is a system to notice the danger early, located far away from internal organs. This is why the skin is sensitive, especially the tips of fingers, which are most distant from internal organs, are extremely sensitive.
Fingers can be compared to antennae (feeler). Nails are kind of the skin, for protecting fingers that are too sensitive. If a nail is hurted, the finger would become sensitive, sometimes causing abnormal stimulation affecting internal organs.
*This article is translated from "Yamai hitokuchi Memo" written by Shoji Kobayashi, 2005.