The present volume is an expansion of a paper read at the last meeting of the International Congress of Dermatology which was held in London in 1896. On that occasion I was one of those invited to open a discussion on the question of "Ringworm and the Trichophytons." My position is the same as it was then. While holding that the plurality of the ringworm fungi is an established scientific truth, I think that the infinite series of species which M. Sabouraud asks us to accept is still nothing more than a jolie hypothèse - if I may use a famous phrase applied by another eminent Frenchman to a different matter. Till conclusive proof has been supplied it will be wise to suspend judgment.<br><br>It has been my aim in the following pages to present the reader with a concise account of recent work in the etiology of Ringworm, giving the main results and indicating the general trend of thought, without perplexing him with needless details. In dealing with treatment, I have not only described the methods which I have myself found useful but have culled freely from the experience of others; in short, I have striven rather to be practically helpful than to make a vain show of originality in a field where everything has been tried and most things have been found wanting.