[Illustration: FIG. 10 (Spalteholz). A view of the lower part of the trachea, dividing into the main bronchial tubes, which again branch into a tree-like form. The air-cells are built up around the terminations of the finest bronchial tubes, of which they are a sort of membranous extension.] [Illustration: FIG. 11 (Spalteholz). Shows well the relations of heart, lungs, and diaphragm. The lungs have been drawn back, otherwise the heart would be covered almost wholly by them. It will be noted that the heart-covering is attached to the diaphragm. The fact that the stomach and other important organs of the abdomen lie immediately beneath the diaphragm is a significant one for the voice-user. Manifestly, a full stomach and free, vigorous breathing are incompatible.] This misapprehension is in all probability to be traced to the dependence of the student and teacher on tradition rather than observation--on authority rather than rational judgment. If a great teacher or singer makes any announcement whatever in regard to the technique of his art, it is natural that it should be considered with attention, but it may prove a great misfortune for the individual to accept it without thoughtful consideration. The author will illustrate, from time to time, the truth of the above. In this and all other chapters of this work the student, by which term I mean every one who is seriously interested in the use of the voice, is recommended to give attention, before reading on any subject, to the illustrations employed, perusing very carefully the explanatory remarks beneath them. The author considers the summaries at the conclusion of the chapters of much importance. They not only furnish exact and condensed statements of the main facts and principles involved, but afford the reader a test of the extent to which the foregoing chapter has been comprehended. As the author has a horror of what is termed "cramming," he expresses the hope that no student will use these synopses, which have been prepared with much care, for so great a misuse of the mind as cramming implies. Breathing is essential for life. The oxygen of the air is, of all food-stuffs, the most important. Without it a mammal will perish in less than three minutes; hence there is no need of the body so urgent as that of oxygen. It is also of great moment that the waste--the carbon dioxide, or carbonic acid gas--should be got rid of rapidly; nevertheless, it is not this gas which kills when the air-passages are closed, though it is highly deleterious. The body is a sort of furnace in which combustions are continually going on, and oxygen is as essential for these as for the burning of a candle, and the products are in each case the same.