DIAPHRAGMS
As the trunk has its diaphragm, dividing thorax and abdomen, so do all dual hemispheres representing a faculty or function have their diaphragms, performing duties of an analogous nature. Every opening, in fact, has its diaphragm. Where there is none visible, it is formed by contraction, whenever needed, and but for the time being. All these various diaphragms, more particularly the one specially bearing that name, are of the greatest importance in connection with vocal utterance,—the sounds of the vessels of the abdomen being produced by an expansion of the thorax and consequent contraction of the abdomen, those of the vessels of the thorax by an expansion of the abdomen and a consequent contraction of the thorax.
For the purposes of vocal utterance, inspiration into the thorax produces an expiration from the abdomen by way of the œsophagus, accompanied by vocal sound, while an inspiration into the abdomen produces an expiration from the thorax by way of the trachea, accompanied by vocal sound; the special mode of inspiration regulating the special sound to be produced.
This proceeding has reference to outgoing sounds only. For ingoing sounds the opposite proceeding takes place; an expiration from the thorax producing an inspiration into the abdomen, and an expiration from the abdomen an inspiration into the thorax, both accompanied by sound. Every original inspiration into thorax or abdomen, of course, must have been preceded by an expiration from these parts, while every original expiration must have been preceded by an inspiration into the same. The utterance of every sound, therefore, requires at least three movements on the part of the respiratory organs. But for the action of the diaphragm, such sounds could not be produced.
All these various diaphragms fall or recede for inspiration, rise or advance for expiration; the function of a diaphragm being exercised in conformity with the manner in which it is approached. This may be done by way of the œsophagus or the trachea, i. e., from the side of the hemisphere of the abdomen, or from that of the thorax. The outward movement of the abdomen during respiration, therefore, is not caused by a pressure brought to bear on its contents by the diaphragm, but it advances and recedes in conformity with a direct process of inspiration and expiration by way of the œsophagus and the trachea; the œsophagus and trachea sustaining each other and acting reciprocally and in conjunction. This presumed pressing forward and subsequent receding of the entrails, in consequence of the descent and ascent of the diaphragm, presents a spectacle as repugnant as it is impossible of execution; the extension of the abdomen, more particularly in connection with special sounds, being so great that no pressure whatever brought to bear upon the entrails could possibly produce it.
In place of this theory, now so generally entertained, the simple fact obtains that the diaphragm descends in consequence of an influx of air into and subsequent expansion of the thorax, causing a contraction of the abdomen and an efflux of air from the same; that it ascends in consequence of an influx of air into and expansion of the abdomen, causing a contraction of the thorax and an efflux of air from the same.
