The author and the publishers acknowledge with gratitude the following permissions to make use of copyright material in this work: Messrs. D. C. Heath & Company, for permission to quote from “Unified Mathematics,” by Louis C. Karpinski, Harry Y. Benedict and John W. Calhoun. Messrs. G. P. Putnam's Sons, New York and London, for permission to quote from “Organism as a Whole” and “Physiology of the Brain,” by Jacques Loeb. Messrs. Harper & Brothers, for permission to quote from “From the Life, Imaginary Portraits of Some Distinguished Americans,” by Harvey O'Higgins. Messrs. D. Appleton & Company, for permission to.