RELATIVE to the diagnosis of onychomycosis, various features have been described concerning such characteristics as the color and the shape of the nail. However, there exists no clinical feature sufficient in itself to enable one to determine mycotic causation. Microscopic examination with the observation of spores and mycelial threads and growth on culture mediums alone furnish convincing proof for this diagnosis.
In 1939, at the meeting of Polish Dermatologists held in Vilna, Poland, I read a paper on a feature, hitherto unpublished, which makes definite clinical diagnosis possible. This phenomenon does not exist in all cases but when present is pathognomonic. This phenomenon consists of a delicate white net arranged parallel to the transverse axis of the nail. It is visible through a magnifying glass, but only after a drop of cedar oil has been applied. This sign is shown in figure 1. A fragment of this nail, examined under