I will take leave of this part of my subject by warning my readers against the mistake, which may be caused by a superficial perusal of these pages, that it is the chief aim of the above breathing exercises to enable the singer or speaker to cram as much air as possible into the lungs. I have pointed out some of the evils which are likely to arise from exaggerated breathing efforts; yet I wish to say again, most emphatically, that it is quite possible to _overcrowd_ the lungs with air. This is a matter of every-day occurrence, which is not, however, on that account any the less reprehensible; for, as I have already mentioned, it is sure to lead, sooner or later, to forcing and inequality of voice, and to congestion of the vessels and tissues of the throat and of the lungs. Now we come to the question of the production and cultivation of the voice, including the nature and the proper treatment of the registers. In this connection I shall endeavour to explain a series of exercises based upon physiological facts, which will enable the reader to strike out a safe and direct path, avoiding much useless drudgery, and leading to eminently satisfactory results. As it is not my object to supply a singing manual, but simply to point out the way of treating the voice upon scientific principles, I shall not attempt to deal separately with the different classes of voices, or to go into minute details; but it will rather be my aim to lay down general principles, leaving my readers to carry them into practice, and to elaborate them according to individual circumstances. It must also be borne in mind that the exercises I am going to recommend will here be taken as they suggest themselves, while passing in review the various parts which unitedly form the mechanism of the human voice. Therefore, in the actual process of training a voice, they will have to be taken in a different order from that in which they are discussed here, in accordance with the general plan of this book. The movements of the pyramids with the vocal ligaments attached to them are governed by two sets of muscles pulling them either together or away from each other. These have been fully described under the names of the "Closing Muscles" and the "Opening Muscles;" and the reader will at once see the importance of devising a set of exercises which shall call these opening and closing muscles into play, thereby making them powerful, and bringing them under the control of the will.