It is self-evident that the danger of carrying the mechanism of a register beyond its proper limit is greater if the vocal ligaments are kept together, than it would be if they were made to separate, thereby being enabled to close again under different conditions. It will be seen, therefore, that the slight inspirations after every tone are an essential part of the exercise, and must on no account be omitted. The exercise is to be taken at a convenient pitch, and then to be raised semitone by semitone in accordance with the requirements of individual voices. It may, after some time, be taken right through upon the vowel _ah_, and finally _legato_, gradually increasing the speed, to the Italian word _scala_, singing the syllable _la_ to the last note. The change from one register to another should always be made a couple of tones below the extreme limit, so that there will be at the juncture of every two registers a few "optional" tones which it is possible to take with both mechanisms. The singer will be wise, however, to avail himself of the power of producing an optional tone with the mechanism of the lower register only on rare occasions. To force the register beyond its natural limit is, of course, infinitely worse, and should never be tolerated. The practice carries its own punishment, as it invariably ruins the voice; and tones so produced always betray the effort (frequently in a most painful degree), and are consequently never beautiful. It is to be observed that the exercise given above may be varied to any extent, so long as it is based upon the principle which has been explained. The beneficial results in the development of the voice will speedily be noticed, and then sustained tones may be sung through the whole compass after the orthodox fashion. This brings me to the consideration of the "mixed voice," which is essential in bridging over the break between the "upper thick" and the "lower thin" of the tenor, and which is also frequently made use of by baritones and basses in the production of their highest tones. The "voce mista" is "mixed" in this sense, that it combines the _vibrating mechanism_ of the "lower thin" with the _position of the larynx_ of the "lower thick;" that is to say, while the vibrations are confined to the thin inner edges of the vocal ligaments, the larynx itself takes a lower position in the throat than for the "lower thin," and the result is a remarkable increase of volume without any corresponding additional effort in the production of tone. A few trials before a looking-glass will at once prove the correctness of this explanation, and, what is of more practical consequence, will enable the student with a little practice to overcome the serious difficulty of singing high tones without straining, yet with a fulness capable of being increased or diminished at pleasure.