In spite of much literature, the nails remain one of the subjects about which there is very little knowledge. Histopathologic studies are manifestly difficult, and the etiology of many lesions remains as obscure now as it ever has been. It is known, of course, that fungi may attack the nails and cause lesions of various forms, that some of the generalized dermatoses are accompanied by changes in the nails, and that there are a number of congenital anomalies of the finger-nails and toe-nails. Beyond this very little is known. Among the lesions most infrequently seen is the group that presents a partial or total loss of the nails without any previous inflammatory process to which this loss may be ascribed. Various causes have been suggested for this condition, but there is no unanimity of opinion on the subject. The cases described in the literature can be divided into two