These two factors of voice-production, the physical and the psychical, should be recognized both by the teacher and by the student in striving to develop the voice, and by the physician who seeks to restore an impaired voice to its pristine quality. The substitution by teachers of various methods, originated by themselves, for the natural physiological method to which the vocal organs become self-adjusted and for the correct processes of auto-suggestion originating within the well-taught singer himself, is the cause of most ruined voices. The physician who realizes this will, in treating an impaired voice, know how to maintain the proper balance between the two factors--between medicine and surgery on the one hand and considerations of temperament and mentality on the other. There have been written books on voice-method of which "be natural" is the slogan; books on the physiology of voice-production, in which, as far as the singer is concerned, too much importance is attached to the results of laryngoscopic examination; and books on the psychology of voice-production in which the other factors are wholly neglected. None of these three varieties of book, however, covers the ground, but each only a part of it. The three--nature, physiology and psychology--must be combined in any book that professes to offer a synthetic method of voice-production. It is possible that knowledge of the structure of the vocal organs is of more importance to the physician and to the teacher than to the singer himself, and that too constant thought of them might distract the latter's attention from the product to the machine, from the quality of voice to be produced to the vocal apparatus producing it. Nevertheless, some knowledge of the organs which he brings into play in singing cannot fail to be helpful to the vocalist himself, and surely their importance to the teacher of singing and to the physician who has an impaired voice to restore cannot be overestimated. Correct teaching, in fact, directs the mind to the end, and by taking into account the physical parts concerned in singing, imparts to them the habit of unconsciously obeying natural laws. Singing may not be a question of how a distorted throat looks in an oblique mirror, yet the knowledge that, because a note is faultily produced, the throat must be distorted, and how, will be of great service to the teacher who wishes to correct the fault, and indispensable to the physician who wishes to eradicate the results of a bad method. The very first principle of a vocal method should be, to establish so correct a use of the vocal organs that nature in this respect becomes second nature. For correct action of the voice-organs can develop into a habit so perfectly acquired that the singer acts upon it automatically; and the most disastrous result of poor teaching is that a bad habit also becomes second nature and is almost impossible to eradicate.