Proper identification of a pathogenic fungus isolated from a case of ringworm of the scalp is of practical importance. Certain species of fungi cause infections which commonly resist manual epilation and external medication. In such cases epilation by means of roentgen rays is the fastest and surest method of treatment. The modern classification of the ringworm fungi is not based on their clinical manifestations, nor on their morphology in the lesions, but exclusively on the gross and microscopic characteristics of their cultures. Of all the microscopic structures formed by these fungi in cultures only the large spindle-shaped macroconidia, or fuseaux, are constant enough in their morphologic characteristics to form a valid basis for classification. In accordance with the type of fuseaux they form, three genera of dermatophytes are recognized, namely, Trichophyton, Microsporum, and Epidermophyton. Ringworm of the scalp in the United States is, in the majority