This book, which is a new monograph in the well known "Bibliothèque de phtisiologie," founded by Léon Bernard, is a brief but interesting exposition, the central theme of which appears to be rationalization of BCG vaccination on the basis of immunology, and removal of the method from the field of empiricism. As such it is worth the attention of all physicians interested in this subject. An important rôle in immunity is ascribed to allergy, which, in the words of the author and Jules Bordet, if not part of immunity at least comes to its assistance. In Paraf's experience the most resistant infants and animals vaccinated with BCG are those in which a mild superinfection with virulent bacilli from without has increased the degree of allergy. Tuberculin treatment and the therapeutic use of BCG are discussed in the light of their relation to allergy.