The development of malignant neoplasms on dermatoses of the most varied sorts, often of many years' duration, is an occurrence too familiar to all dermatologists to admit of discussion; but to form a just estimate of the dermatoses in which such development is most frequent, to determine the proportion in each class which will probably become malignant, to ascertain the causes which lead to such degeneration — these are more difficult problems and, for the moment at least, insoluble. They are so important, however, especially as our attitude toward them must determine our treatment of many of the so-called precancerous conditions, that an attempt to formulate our present knowledge may be useful.
PRECANCEROUS DERMATOSES
Naevi.—
The naevi come first to mind, and it is about the naevi that most has been written in this connection. The vascular naevi may be dismissed at once as no assertion has been made that