The finger and toenails are simply modified forms of hairs, or, at any rate, are modified forms of skin, which is also what hairs are. The nail lies on a modified portion of the corium of the skin, known as the matrix, and it is by continual division of the cells of the matrix that the nail grows forward. The white crescent near the base of the nail, the lunula, is due to lessened translucency at that part. The little white spots, known as “gift spots,” in the nail, are due to the presence of small collections of air in the interior of the nail substance.
In general, the fingernails grow faster than the toenails, and those on the right hand faster than those on the left.
The rate of growth differs in different people and in different seasons. The average growth of the nail is 20i inches a year, or to put it another way, we grow a little over 11 yards of nails per year all over our bodies.
Nails are subject to all the kinds of diseases that affect the rest of the body. Diseases of the body affect the cells of the nail-bed as well as other cells of the body and, therefore, influence the growth of nails. This can be seen in transverse ridges that go straight across the nail from side to side, and were first described by Beau in 1870, and from that are named “Beau’s lines.” They have even been observed in cases of seasickness.
The nail and nail-bed are subject to infection with any organism. The commonest are the ordinary pus organisms and ringworm. These cause brittle, rough, ridged nails which are very ugly and quite troublesome to get rid of. Ringworm may affect either the fingernails or the toenails. It does not usually respond to medicinal agents. About the only method we have which is successful, aside from surgical removal of the nails, is the x-ray. Surgical removal is necessary only in a very limited number of cases.