is contused or crushed, blood is extravasated
beneath it, and the nail is usually shed, a new one growing in its
place. A splinter driven underneath the nail causes great pain, and if
organisms are carried in along with it, may give rise to infective
complications. The free edge of the nail should be clipped away to allow
of the removal of the foreign body and the necessary disinfection.

_Trophic Changes._--The growth of the nails may be interfered with in
any disturbance of the general health. In nerve lesions, such as a
divided nerve-trunk, the nails are apt to suffer, becoming curved,
brittle, or furrowed, or they may be shed.

_Onychia_ is the term applied to an infection of the soft parts around
the nail or of the matrix beneath it. The commonest form of onychia has
already been referred to with whitlow. There is a superficial variety
resulting from the extension of a purulent blister beneath the nail
lifting it up from its bed, the pus being visible through the nail. The
nail as well as the raised horny layer of the epidermis should be
removed. A deeper and more troublesome onychia results from infection at
the nail-fold; the infection spreads slowly beneath the fold until it
reaches the matrix, and a drop or two of pus forms beneath the nail,
usually in the region of the lunule. This affection entails a
disability of the finger which may last for weeks unless it is properly
treated. Treatment by hyperaemia, using a suction bell, should first be
tried, and, failing improvement, the nail-fold and lunule should be
frozen, and a considerable portion removed with the knife; if only a
small portion of the nail is removed, the opening is blocked by
granulations springing from the matrix. A new nail is formed, but it is
liable to be misshapen.

_Tuberculous onychia_ is met with in children and adolescents. It
appears as a livid or red swelling at the root of the nail and spreading
around its margins. The epidermis, which is thin and shiny, gives way,
and the nail is usually shed.

[Illustration: FIG. 107.--Subungual Exostosis growing from Distal
Phalanx of Great Toe, showing Ulceration of Skin and Displacement of
Nail.

_a._ Surface view. _b._ On section.]

_Syphilitic_ affections of the nails assume various aspects. A primary
chancre at the edge of the nail may be mistaken for a whitlow,
especially if it is attended with much pain. Other forms of onychia
occur during secondary syphilis simultaneously with the