#Canities.# (_Synonym:_ Grayness of the Hair.) #Describe canities.# Canities, or graying of the hair, may occur in localized areas or it may be more or less general; the blanching may be slight, scarcely amounting to slight grayness, or it may be complete. It is common to advancing years (_canities senilis_); it is seen also exceptionally in early life (_canities praematura_). The condition is usually permanent. The loss of pigment takes place, as a rule, slowly, but several apparently authentic cases have been reported in which the change occurred in the course of a night or in a few days. #What is the etiology of canities?# The causes are obscure. Heredity is usually an influential factor, and conditions which impair the general nutrition have at times an etiological bearing. Intense anxiety, fright, and other profound nervous shock are looked upon as causative in sudden graying of the hair. #Give the treatment.# Canities is without remedy. Dyeing, although not to be advised, is often practised, and the condition thus masked. #Alopecia.# (_Synonym:_ Baldness.) #What do you understand by alopecia?# By alopecia is meant loss of hair, either partial or complete. #Name the several varieties of alopecia.# The so-called varieties are based mainly upon the etiology, and are named congenital alopecia, premature alopecia and senile alopecia. #Describe congenital alopecia.# Congenital alopecia is a rare condition, in which the hair-loss is usually noted to be patchy, or the general hair-growth may simply be scanty. In rare instances the hair has been entirely wanting; in such cases there is usually defective development of other structures, such as the teeth. #Describe premature alopecia.# Loss of hair occurring in early and middle adult life is not uncommon, and may consist of a simple thinning or of more or less complete baldness of the whole or greater part of the scalp. It usually develops slowly, some months or several years passing before the condition is well established. It is often idiopathic, and without apparent cause further than probably a hereditary predisposition. It may also be symptomatic, as, for example, the loss of hair, usually rapid (_defluvium capillorum_), following systemic diseases, such as the various fevers, and syphilis; or as a result of a long-continued seborrh[oe]a or seborrh[oe]ic eczema (_alopecia furfuracea_). #Describe senile alopecia.# This is the baldness so frequently seen developing with advancing years, and may consist merely of a general thinning, or, more commonly a general thinning with a more or less complete baldness of the temporal and anterior portion or of the vertex of the scalp. #What is the prognosis in the various varieties of alopecia?#