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Breathing is a reflex or involuntary act. The respiratory centre, consisting of an expiratory and inspiratory division, is situated in the bulb, or medulla oblongata, the portion of the brain just above the spinal cord.
Ptisis is a substantial consumption of the humidity of the body, due to ulceration of the lungs. For when a solution of continuity occurs in the lungs, the inspiratory and expiratory forces fail. Hence the lungs do not inspire sufficient air to mitigate the innate heat of the heart, and the heart fails to purify itself of the fumosity or fumous vapors generated in itself.
Yet we have here a demonstration of the mechanical law of tone-production. Considered as a mechanical process, tone-production occurs when the energy exerted by the expiratory muscles, in their contraction, is converted into energy of motion of the vocal cords. In other words, tone-production is an example of the transformation of energy.
For several seconds the silence may be complete, while the child steadily becomes more and more cyanosed, or the body may be shaken by incomplete expiratory movements and strangled cries which are suppressed because the chest is already in a position of almost complete expiration.
It is important to realize that sounds, whether musical or the reverse, are produced by the outgoing stream of breath, by an expiratory effort.
In its practical aspect this system of breath-control is the direct opposite of the "opposed muscular" system. In one the breath is expelled powerfully, the object being to bring a strong expiratory pressure to bear on the larynx. In the other system, the air is held back, in order that the larynx be exposed to as slight a pressure as possible.
The movements of the vocal cords are so slight as to be observable only with the aid of a specially devised apparatus, the stroboscope. Can all the expiratory force expended in tone-production show such a small result? This apparent objection is found to be groundless in view of the application in this operation of Pascal's law.
The power of the expiratory blast is just what it would be if one unit of strength were exerted in an "uncontrolled" expiration. The singer exerts just nine times as much strength as is necessary to effect the same result. This is why the practice of breath-control exercises is so extremely fatiguing.
Jordan heard her bolt the door, looked anxiously before him, waited a moment or two, and then crept up to her door on his tiptoes. He placed his hands under his chin and listened. Gertrude was crying. It was an even and touching cry, not so much filled with grief as her sobs generally were, and seemed to be expiratory rather than the reverse.
The mechanical operation of tone-production comprises the following transformations of energy: First, the energy exerted in the contraction of the expiratory muscles is converted into energy of condensation or elasticity of the air in the lungs and trachea. Second, this energy of condensation of the air is converted into energy of motion of the vocal cords.
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