This particular investigation is a beginning; It will be a partial survey of the field; for it is not the purpose of the present writer to include in this small volume an account of any work but his own, with which he feels intimately acquainted. The cases that have been under his care deeply interest him; and, by the aid of what psychological and medical studies have taught him, he now offers to conduct the reader along the path that his own steps have traced, and answer as well as he is able the questions that arise.