Those who undertake to study cutaneous mycology read but a short distance into the subject before they become acquainted with the property of pleomorphism (or better, polymorphism) which is expressed to a unique degree by the ringworm fungi. If they embark on culture studies the importance of this property will at once be borne home, because it immediately complicates the problem of determination of species, which is the very foundation for advance in this as in other parasitologic fields. Probably every dermatologist is aware that variations in cultural characteristics result from trivial alterations in the composition of the mediums, and those who have done practical work will add that even the moistness (freshly prepared or not) of the medium, the thickness o.f the layer which it constitutes and the extent to which the strain has been subcultured have more or less effect on these capricious organisms. Indeed, variations in form