In this generation, to be sure, our cephalic centres are sometimes overworked, whereas in the remote past the stress fell more on other parts; but we are rather allied to the rock-bound dead by an inherited power to respond than separated from them by a recent capacity for nerve exhaustion. As the reader will perceive, these remarks might serve to magnify the office of this book by suggesting how fundamental to the welfare of all higher animals are the powers of the nervous system, and therefore how important it will be to search out the growth changes which produce them.