Nails grow at very different rates. Those on the fingers advance at about three or four times as rapidly as those on the toes. The fingernails on the longest fingers (the middle fingers) grow most quickly; those on the shortest or little fingers, most slowly. There appears to be no significant difference, with respect to growth, between the nails of the right and left hands. In summer the nails, like the hair, advance faster than in winter; the thumbnail, for instance, grows an average of one-ninth of an inch per month in the winter and one-seventh of an inch in the summer.
Beyond providing a livelihood for manicurists and nail-polish manufacturers, the function of human nails is not clear. Fingernails can be used for scratching; they also provide a mechanical support for the tips of the fingers and thus, perhaps, increase the latter's efficiency as organs of touch. But human toenails, as far as we can see, serve no useful purpose, though they may have been useful at one time.
