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p. 205

Chapter 16

WHAT the peritonaeum is to the abdominal cavity, the pleura is to the thorax. It is the common bond of all the organs and vessels which the thorax contains; and its office is to hold each in its place with the utmost freedom of motion, and at the same time to impart to each the motions and wants of the whole; so that each may accommodate itself to the necessities of the others, and all may be combined in due proportion in the common use.

The heart and the lungs are not made independent of support through the nobleness of their office. The other parts of the body depend upon them; but there is no organ upon which these do not depend for the means of doing their use. Especially do they need the immediate and constant support of the pleura.

The heart lies between the great lobes of the [p. 206] lungs; but its action is not synchronous with that of the lungs; it expands and contracts three or four times during one respiration; and, without some means of accommodation, in dilating it would press upon air-cells when they too were in the effort to expand, and the action of both would be impeded. Again, the heart to contract freely and uniformly, must be maintained in the same relative position during all the changes and motions of the body; and still it must not be attached and bound except at the base, where it gives forth the arteries and veins. And, further, the lungs must be maintained in their proper position, and not allowed in state of collapse to fall upon the heart or to suffer displacement; and in their place they must be protected from the ribs, and provided with the means of working without friction, freely and smoothly.

Other needed uses will be mentioned hereafter; but these are plainly required, and to perform them is the duty assigned to the pleura.

One can hardly avoid a feeling of affection for [p. 207] the friendly ministry of one part of the body to another; and for none is the feeling stronger than for the modest service of the pleura, which does not pretend to be of the least importance itself, but just helps others to be important, and does for them essential service, perfectly, constantly, and without the slightest intrusion.

In itself it is composed of two membranes, one thick and fibrous, the other smooth, glossy, and moist. By its fibrous coat it applies itself closely to the lungs, covering every convolution perfectly, yet elastically, and entering between the little lobes even to the minutest air-cells, as if to be in sympathy with and give protection to its inmost thoughts. Its strong outer coat at the same time invests the lungs with an almost metallic smoothness, which is rendered more perfect by constant lubrication with delicate oils.

From the base of the lungs the pleura is reflected upon itself, and forms two membranous bags loosely enclosing again the already encased lungs. The fibrous membrane of these bags, next [p. 208] the walls of the thorax, attaches itself closely to the ribs, and extends its little fibres among the intercostal muscles, even to the fatty tissues of the chest, while the harder, smooth coat presents inwards a polished surface for the investing coat of the lungs to play upon. Thus their easy motion is secured.

On the lower wall of the thorax the pleura unites with the diaphragm, by the flexibility of which it is enabled to apply its well-oiled coat even to the hollow inner walls of the lobes of the lungs, giving them the support they need to keep them always in position, but not imposing the slightest restraint upon their free motion.

Between the great lobes the membranous walls of these bags unite, forming a partition in the chest, extending from the breast-bone to the backbone; but in this partition the two walls part, and leave space between them for a roomy closet for the heart, which is thus suspended in its place between the folds of the pleura. And in order to protect the heart and the lungs still further from [p. 209] mutual annoyance, still another fold of pleura, or, as some hold, a little pleura by itself, forms an inner bag of smoothest surface, and loosely encloses the heart; which is thus separated from the lungs by two spaces and four thicknesses of membrane.

Besides achieving this apparently impossible duty of giving to these active organs the closest and most intimate support without in the least affecting their freedom, and holding them closely related in their common work but preventing any chance of mutual irritation, the pleura through smaller chambers between its folds, behind that of the heart, furnishes safe conduct to the oesophagus on its way to the stomach, to the great aorta as it descends to distribute the life blood to the lower viscera and members, to the great ascending vein also and the chyle duct; and it imparts to them all -- and by means of the diaphragm, to the lower viscera also -- the alternate motions of the lungs -- motions of alternate reception and action, which are essential to their life and usefulness. [p. 210]   Many subordinate duties the pleura performs; but these are its chief and governing uses.

As the province of the peritonaeum is held by angels of simple quality (n. 5378), not active of themselves but readily acting from others, and above all things loving harmony, so the angels of the pleura are modest angels delighting in the harmony of the uses of the heart and the lungs. To the angels of these provinces they attach themselves closely, rendering them every support and assistance. With ready sympathy and affection for both, they interpose to receive and accommodate their strong but not coincident activities; for the impulses of affection and the thoughts of wisdom are not synchronous; they need to be accommodated to each other by intermediates who respect and love them both. They interpose also between these and the rougher, less sensitive angels, who, holding merely to the facts of the use and necessity of these vital organs, are like stony walls of protection to them, and constitute the ribs of the Greatest Man; but who would [p. 211]  grate harshly and injuriously in immediate contact with the angels who are so full of the love of doing the Lord's will that they are unwilling to think of themselves, and those who are intent upon applying the Lord's wisdom to the life of the heavens, and cannot bear to be reminded of their own importance. The support and protection of the facts they bring them, without disturbing their unselfish activity; and from full sympathy with their life, they impress it upon all comers, new and old, who pass within their domain.

Our admiration for the pleura is admiration for these modest, unselfishly useful angels; or, for the generous, devoted love for ministering to others which these receive from the Lord. Other organs of the body partake, even in a greater degree, of the spirit of mutual service; and in that service they all are images of angels' love, and of the Lord's multiform love of serving, which creates heaven and earth, and is the life of every part of them.

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