Tms volume is the outgrowth of a course of yearly lectures which have been re-written, revised and added to from time to time during the past seven years, and its publication is due to the demand of students and practicians of medicine for a small though complete volume on Hydrotherapy. The volume will fulfill its mission if it teaches in a fairly com prehensive way what hydrotherapy means and accomplishes, and succeeds in enrolling its readers into the growing fraternity of physical therapists through bringing this subject before them in a concise, clear-cut manner. The writer desires at this point to acknowledge his great indebtedness to the late Dr. J. G. Kuhn, of Hudson County, N. J with whom he spent the summer of 1897 in the study of this subject and whose in?uence has been potent in molding the author's conceptions on this therapeutic measure. Doctor Kuhn practiced hydrotherapy for over fifty years, and his tempered experience has been accepted and adopted by the author in many of the therapeutic recommendations. The writer also desires to express his thanks to the J. L. Mott Iron Works for the loan of numerous electrotypes illustrating hydro therapeutic apparatus and to Mr. H. L. Steidel for his assistance in the preparation of photographs.