SCURF is a material composed of minute portions of the dry external scales of the cuticle. These are, in moderate quantity, con tinually separated by the friction to which the surface of the body is subject, and are in duo proportion replaced by others deposited on the inner surface of the cuticle. Sometimes, however, they separate in unnatural quantities, and this constitutes the disease called Pity Pityriasis (from wirupov, bran) is a disease of the akin in which irre gular patches of the cuticle appear covered with thin bran-like scales, or with particles of a fine white powder, which, as fast as they fall oll; are succeeded by others. It may be regarded as a morbid excess of the natural process of desquamation which is constantly going on, and by which the old cuticle is removed from the surface of the body to axe replaced by that of more recent formation. The commonest form of this disease is that called Pit yriosis capitis, or dandrif£ It affects chiefly the scalp and eye-brows, and is most frequent in children, in whom it originates either from generally disordered health or from mere neglect of cleanliness. It occurs also on the face and sometimes on other parts of the body in adults and old persons after exposure to the sun or a cutting wind, and it usually accompanies the commence ment of baldness. The only local treatment which is necessary or
useful is frequent washing, and the application of some mild and simple ointment.
In the other forms of pityriasis the discoloration of the cuticle is a more prominent sign than its desquemation in fine scales. P,rersicolar occurs in the form of irregular yellow or light brown patches, which are chiefly situated on the front of the chest and abdomen, and aro commonly called liver-spots or tan-spots. The extent and form which such spots present are infinitely various ; but though they sometimes exist unaltered for several years, they rarely produce any inconvenieneo beyond a slight itching. P. rare is an aggravated form of the pre ceding; the spots are more or less brightly red, and are the seats of considerable irritation. In P, niqra the essential part of the disease, which is of very rare occurrence, is the production of a cuticle of nearly a black colour.