The material in this book is an expansion of a lecture given at the Army Medical Center, Washington, D.C., on May 15, 1933. I have thought it best to leave it in the somewhat informal discourse of the lecture platform. References to the literature, and other annotations, are numbered consecutively and placed together at the end of the book. It should be pointed out here at the start, as it is in the text, that the author is not a medical...