The Midriff ([pl. III], M) is a muscular and movable partition by which the lungs are separated from the abdomen. It is arched upwards like an inverted basin, but when its muscular fibres contract it flattens and descends, thus increasing the capacity of the chest at the expense of that of the abdomen.
The Function of the Lungs is, as everybody knows, respiration, which may be considered from a mechanical or a chemical point of view. In this little work we are only concerned with the mechanical part of the subject. If we examine the lungs of a calf, which are very similar to those of a human being, we find that they are soft and elastic to the touch, giving out when pressed a peculiar whizzing sound. We may increase their volume by blowing into them through the windpipe, so as to make them double their original size, and then tie up the windpipe. On re-opening the windpipe the air escapes, and the lungs are gradually reduced to their former bulk. Now, by drawing a deep breath we produce the same result in ourselves as by blowing into the lungs of the calf; by holding the breath we produce the same result as by tying up the windpipe—that is to say, we keep the lungs in a state of expansion; and by releasing the breath we are, as it were, untying the windpipe, leaving the lungs to dwindle down gradually to their former size.
There is one very material point, however, in which the analogy ceases. It is this: we keep the air in the inflated calf's lungs by tying up the windpipe, and the corresponding act in ourselves would be to hold our breath by muscular contraction of the outlet in the throat. This is precisely what we do in straining, and in lifting heavy weights, &c.; but it should never be done in breathing for vocal purposes. Here it must, on the contrary, be our endeavour to train, to the highest possible degree, the powerful muscles of the chest and of the abdomen, instead of throwing the labour intended for them upon the comparatively weak and delicate muscles governing the outlet of the windpipe.
To make the way in which respiration is carried on clearer still, I quote the following interesting and lucid account from Huxley's "Elementary Physiology," fourth edition, p. 104. He compares the breathing apparatus to "a sort of bellows without a valve," in which the chest and the lungs represent the body of the bellows, while the windpipe is the pipe; "and the effect of the respiratory movement is just the same as that of the approximation and separation of the handles of the bellows, which drive out and draw in the air through the pipe. There is, however, one difference between the bellows and the respiratory apparatus, of great importance in the theory of respiration, though frequently overlooked, and that is, that the sides of the bellows can be brought close together so as to force out all, or nearly all, the air which they contain, while the walls of the chest, when approximated as much as possible, still enclose a very considerable cavity; so that even after the most violent expiratory effort, a very large quantity of air is left in the lungs."
Respiration, consequently, consists of two acts—namely, inspiration and expiration. Inspiration may be produced in three different ways—(1) By pushing the chest forward and flattening the midriff, so as to compel the lungs to descend and to increase in volume in order to fill the empty space created by this movement; (2) by extending the ribs sideways; and (3) by drawing up the upper parts of the chest—namely, the collar bones ([pl. III], C C) and the shoulder blades. In scientific works the first is called diaphragmatic or abdominal,[B] the second lateral or costal, and the third clavicular or scapular breathing. As, however, these terms convey no meaning to the general reader, I prefer to speak of—(1) Midriff Breathing; (2) Rib Breathing; (3) Collar-bone Breathing. In taking a full, deep inspiration, midriff breathing and rib breathing take place almost together and assist each other—that is to say, the midriff contracts and flattens, and immediately afterwards the ribs extend sideways; with this difference, however, that in men the action of the midriff takes a larger share in the work than the ribs, while in woman, on the contrary, the movement of the ribs is greater than that of the midriff.
By way of illustrating this curious difference of breathing in men and women, the following anecdote, which has the recommendation of being strictly true, may perhaps amuse the reader. Some time ago a troupe of "Female Minstrels," calling themselves, I believe, "The American Amazons," made a tour through this country. Their faces were blackened in the orthodox fashion, and they were in male attire, wearing tight-fitting garments of a peculiar kind. Two friends, both medical men, went to hear them (or perhaps to see them, I am not sure which), when Mr. A remarked that two of the performers were men. Mr. B did not see it, even when the individuals were pointed out to him, and asked his friend for the reasons for his opinion. "Why," said Mr. A, "I see it by their abdominal breathing!" And sure enough Mr. B now saw it too, and there was no mistake about it; for in the two suspected individuals the abdomen was evidently moving in respiration, while in all the others no movement was perceptible excepting that of their chests.
Plate IV.
DIAGRAMS ILLUSTRATING THE VARYING CAPACITY OF THE CHEST, ACCORDING TO THE METHOD IN WHICH THE LUNG IS INFLATED.