[5] On this account the male voice should be trained by men and the female voice by women. For, as it is impossible for a man to give to a female pupil a correct perception of the tones of the head register and of the second series of the falsetto, with its peculiar female timbre, so is it impossible for a woman to sing and teach correctly the deep, sonorous chest tones of the male voice. _Frederick Wiek_, that admirable teacher, who perceives intuitively what is natural and true in instruction, has an excellent expedient. In his hours of instruction he avails himself of the aid of young women with practised voices, who sing every exercise to his female pupils until the latter are able to imitate them correctly. [6] Voices which by this overstrained and unnatural way of singing have become worn-out and useless may by correct, proper treatment recover, even at an advanced age, their former grace and power; and even those chronic inflammations of the larynx which are so difficult of treatment may be cured by a natural and moderate exercise of the voice in singing. III PHYSICAL VIEW FORMATION OF SOUNDS BY THE VOCAL ORGAN For the artistic culture of the singing voice the knowledge of the physiological processes during the formation of tones does not suffice. This knowledge brings us acquainted only with the instrument, the artistic treatment of which is to be learned. Having, therefore, in the preceding pages stated the most important points in the formation of tones, physiologically considered, we are now to consider more nearly the physical laws relating to the same, especially as the physical view of the subject, through the latest investigations and discoveries of Prof. Helmholtz, in Heidelberg, has so much importance for music in general. In order, however, to present a clear view of this branch of our subject, in so far as the recent advances of science can be practically applied to the improvement of the art of singing, we must recur to those natural laws which are doubtless well known to most of our readers.