The next thing in connection with the physiology of the vocal organ from which we can deduct a practical lesson is the action of the muscles governing the pitch of the voice. This process is a very complex one, and can be made clear only by _viva voce_ explanations, with the help of good models and moving diagrams, by demonstrations with the laryngoscope, and by carefully watching external signs. There is no doubt, however, that a set of muscles, described as the "Stretching and Slackening Muscles," play the most important part in this matter, and I advise the reader to study carefully the chapter on "The Movements of the Voicebox," and try the experiments mentioned in it. It will thus be seen that the flexibility of the voice depends in a great measure upon the control we have over the muscles governing the pitch; that is to say, upon the readiness and exactness with which we are able to allow them to contract or to relax. Performers upon various instruments, as for instance the piano and the violin, know that certain exercises are indispensable to brilliant execution, because they strengthen the muscles of the wrist and of the fingers, and make them obedient to the will. It has even been found that simple finger gymnastics, exercising separately different sets of muscles, and making them independent of each other, are of the greatest value, and save long hours of tedious and wearisome practising. In a similar manner we may spare ourselves much trouble and gain our end most readily by vocal gymnastics, calculated to bring into play the stretching and slackening muscles of the larynx. There is no difficulty about it. Sing F, the same tone from which we started when exercising the opening and the closing muscles, and add to it G. The alteration of the pitch is brought about by a contraction of the stretching muscles overcoming the resistance of the opposing slackening muscles, thereby _tensing_ the vocal ligaments. If you again sing F, the case is reversed, and the new alteration in pitch is brought about by a contraction of the slackening muscles overcoming the resistance of the opposing stretching muscles, thereby _relaxing_ the vocal ligaments. [Illustration: musical notation _o_ _o_ _ah_ _ah_ _ai_ _ai_ The above is an example. Take great care to render it perfectly. Sing every tone clearly and distinctly, but without jerking, at the same time _uniting_ all the tones, but without drawling. Do not try how quickly you can sing, but rather how distinctly. Commence slowly, and be in no hurry to increase the speed. Raise and lower the exercise semitone by semitone within the medium part of your voice. A variety of exercises founded upon the same principles may be introduced, and will serve to increase the flexibility of the voice in a very short time.