Spiracle

“ It has been found in several species that there are eight pairs of abdominal spiracles, making, with the two thoracic, ten pairs in all. The first of the abdominal spiracles is larger than the others, and in the winged species may be easily detected by raising the tegmina and wings, it being more dorsal in position than those following, which are in some species exposed on the ventral surface owing to the cutting away of the hind angles of the ventral plates ”

“ But though the primary object of raising the ribs and depressing the diaphragm may be to fill the lungs, its secondary influence upon the trunk as a whole is hardly less important. The effect upon the circulation is profound. The compartments of the lungs are enveloped in innumerable capillary bloodvessels, and, as these lie around and between them in the cavity of the thorax, they must, when breath is drawn in, be subjected to a negative pressure before the lung itself, and be the first to experience a positive pressure when the air is expelled. Here, again, a diagram is the best explanation. ”

“ The numerous canal-like ducts in the lung, into which it passes, have each a blood-vessel lying alongside, so that the whole lung is thought to be full of blood. The inward passage of the air is called respiration, the outward expiration, and this double movement goes on continuously just so long as the animal lives and keeps this organ in continuous motion; it is for this reason that life is bound up with the passage of the breath outwards and inwards. ”

“ Respiration occurs by means of the skin or of gills, or, in air-breathing forms, by 'trachea,' which are small branching tubes opening on the sides of the body. But in no case has the mouth or the digestive tract any connection with the respiratory system, a condition of affairs very different from that obtaining in the vertebrates. The nervous system consists of a brain, situated above the gullet, a nerve ring round the latter, and a double nerve cord running along the body, below the digestive canal. ”

“ Can any one explain how these partial sweats should relieve the difficulty of breathing in anasarca, but by supposing that the pulmonary branch of absorbents drank up the fluid in the cavity of the thorax, or in the cells of the lungs, and threw it on the skin, by the retrograde motions of the cutaneous branch? for, if we could suppose, that the increased action of the cutaneous glands or capillaries poured upon the skin this fluid, previously absorbed from the lungs; why is not the whole surface of the body covered with sweat? why is not the skin warm? ”

“ Why air introduced into the pleural cavity through a wounded lung, should have such wholly different effects from that entering directly through a wound in the chest, was to me a complete mystery until I heard of the germ theory of putrefaction, when it at once occurred to me that it was only natural that air should be filtered of germs by the air-passages, one of whose offices is to arrest inhaled particles of dust, and prevent them from entering the air-cells. ”

“ The pulmonary tissues are endowed with great elasticity, in consequence of which the lungs collapse to about one-third of their bulk when the thorax is opened.
The root of each lung consists of bronchi, arteries, and veins, together with the nerves, lymphatic vessels, and glands, connected by areolar tissue, and inclosed in a sheath of the pleura.
Respiration consists of an expiration and an inspiration. The air passes in through the nose or [276] mouth, through the larynx, trachea, bronchi, into the lungs. ”

“ Superficial Examination of Thorax.—Observe the position, color, and degree of distention of the lungs. It should be remembered that healthy lungs, as soon as the chest is opened, owing to their inherent elasticity, will collapse, and when this normal collapse is not seen it is generally due to a loss of elasticity as occurs in emphysema, to inflammatory diseases binding the lung to the chest wall, or to the alveoli being filled with solid or fluid substances or pent-up air. Most complete distention is seen when death is due to drowning or suffocation. ”

“ The lungs are the essential organs of respiration. The tissue that forms them is light, will float in water, is elastic and somewhat rose-colored. Each lung is divided into lobes, and each lobe into a great number of lobules by the supporting connective tissue. The lobule is the smallest division of the lung and is formed by capillary bronchial tubes, air cells and blood-vessels. It is here that the external respiration or the exchange of gases between the capillaries and the air cells occurs. ”

“ And hence the absorbents of the lungs are less able to fulfil the whole of their duty. And part of the thin mucus, which is secreted into the air-cells, remains there unabsorbed, and occasions the difficult respiration, which awakes the patient. And the violent exertions of the muscles of respiration, which succeed, are excited by the pain of suffocation, for the purpose of pushing forwards the blood through the compressed capillaries, and to promote the absorption of the effused lymph. ”

“ Secretion of the Lungs.—Like the lips and mouth, the lungs are invested on their free inner surface by a delicate mucous membrane, which constantly secretes a clear viscous fluid, the mucus. The lungs, therefore, like the nose, are always moist, and just as the nose is cleared by blowing it, so the lungs are cleared by hawking or coughing. A sense of discomfort or a feeling of irritation of the windpipe induces a deep inspiration, followed by an explosive expiration, which quickly brings up the mucus, so that it can be expectorated. ”

“ As the abscess increases in size, the lung is pushed towards the spine, and that side of the chest gives a dull note on percussion. If much fluid collects the heart may be pushed out of its place, and, the lung-space being taken up, respiration is embarrassed. ”

“ Delicate, hair-like filaments, not unlike the pile on velvet, called cilia, spring from the epithelial lining of the air tubes. Their constant wavy movement is always upwards and outwards, towards the mouth. Thus any excessive secretion, as of bronchitis or catarrh, is carried upwards, and finally expelled by coughing. In this way, the lungs are kept quite free from particles of foreign matter derived from the air. Otherwise we should suffer, and often be in danger from the accumulation of mucus and dust in the air passages. ”

“ A new element of many thousand pounds weight then presses upon the surface of its body. This atmospherick fluid, adulterated in cities with innumerable impurities and feculencies is drawn into its lungs: its diaphragm and muscles of respiration then begin to act, the lungs expand, and the respiration commences. The passage between the auricles of its heart and arterial duct are gradually closed up; the sphere of the circulation is extended; the whole current of blood in its frequent revolution hourly, passes through the lungs ”

“ Minor degrees of respiration are recognized by the appearance of little groups of dilated air-vesicles, and by the fact that, although the lungs as a whole may sink in water, certain portions of them, into which respired air has penetrated, float in water even after subjection to firm pressure in the hand. ”

“ The air generated by putrefaction, and which may cause the lungs to float, is removed by pressure, but no amount of pressure, short of entirely destroying the lung tissue, will remove that which is the result of respiration or inflation ”

“ Roughly speaking, the lungs begin at the sterno-clavicular articulation above, the apex coming up above the level of the first rib, and extend downward together to the fourth cartilage, where the lower margins gradually separate, the lowest lung limit being the eleventh rib in the vertebral region. Each lung is conical. The apices extend upward and the bases, which are broad and concave, rest upon the diaphragm. The right lung is divided by a fissure into three lobes, the left into two. The root consists of a bronchus and pulmonary arteries, veins, lymphatics, and nerves. ”

“ When air has to be admitted, its fibres tighten and bring it flat again, as you and your brother brought the handkerchief flat just now by tightening it.
The whole space previously occupied by the arch of the diaphragm is thus given up to the lungs, which, being elastic, instantly stretch themselves out to it; while air, running in through the nose and mouth, fills up in proportion the empty place (vacuum) created by the extension of the lungs, exactly as in the case of the bellows. ”

“ In consumption, and to a greater extent in scrofiuska, the lungs are covered with a web-like moisture, portions of which are thrown off by the system with the perspiration.
The ordinary appearance of perspiration in a healthy state is that of an oleaginous liquid consistency resembling, say, a thin cream; but the water exuded by the lungs has the appearance of dew, and is indeed called by a term signifying "lung-dew." ”

“ The lungs follow the variations of capacity in the chest, expanding their air-cells when the latter is enlarged, and contracting when the chest is diminished. Thus, when the chest is expanded, the lungs follow, and consequently a vacuum is produced in their air-cells. The air then rushes through the mouth and nose into the trachea and its branches, and fills the vacuum as fast as it is made. ”

“ In the examination of the body-cavities and hollow organs, as well as pathologic hollow structures, the first thing to note is the escape of gas or air under pressure. Occasionally it is best to open the organ under water to note the escape of bubbles. The odor of the gas, inflammability, etc., are to be noted. The fluid or solid contents (blood, bile, urine, féces, mucus, pus, exudates and transudates, altered secretions, food-remains, concretions, foreign bodies, parasites, etc.) ”

“ When, however, respiration has been established, these organs become more voluminous, present a yielding elastic texture, and assume a florid-red colour; they, moreover, contain and transmit a larger quantity of blood, and have a specific gravity less than that of fresh water, and accordingly float in it. On cutting into the lungs, under these circumstances, the air contained in their cells will escape, and produce a peculiar crackling noise, which has been well expressed by the term 110crepitating; a bloody fluid will at the same time exude. ”

“ When diffused in the air, these noxious particles are conveyed into the system through the thin and delicate walls of the air vesicles of the lungs in the act of respiration. The mode in which the air vesicles are formed and disposed is such as to give to the human lungs an almost incredible extent of absorbing surface, while at every point of this surface there is a vascular tube ready to receive any substance imbibed by it and to carry it at once into the current of the circulation. ”

“ Exercise accelerates the rate of respiration and intensifies this sound. The vesicular murmur is heard only where the lung contains air and its function is active. The vesicular murmur is weakened as inflammatory infiltration takes place and when the lungs are compressed by fluids in the thoracic cavity, and disappears when the lung becomes solidified in pneumonia or the chest cavity filled with fluid as in hydrothorax. ”

“ For, entering by respiration into the air-cells of the lungs, divided from those of the blood but by a thin membrane, it infuses through that a stimulus into the blood, which, acting on the irritable fibres of the heart, excites mechanically the action and reaction of that muscle. ”

“ This Work is done in Its Passage thro’ the Lungs, by the repeated Compression of the Air in those Bladders upon the Arteries, with wonderful Contrivance dispers’d among ’em (160) . Herein lies the Use and Necessity of Respiration; and the sudden Mischief of Stopping it, in that the whole Mass of Blood being to pass this way, upon a Check here, there presently insues a Stagnation, that is, a Cessation of all Animal Functions, or Death; Which will be the more speedy, if not only no Air is inspired, but a Fluid of a quite different Nature from It succeeds in its Place. ”

“ At birth the lungs are pinkish-white in color but in later life they are marked with slate-colored patches, due to the deposit in the lung tissue of particles of dirt breathed in. They are light, spongy, and highly elastic, and will float in water, crepitating upon pressure owing to the air in the tissue. ”

“ And then the lungs, in respiration, are perpetually rising and falling: motions, the effect of which must needs be to open and shut the pores and vessels, precisely as in the case of a sponge, and of parts having a spongy structure, when they are alternately compressed and again are suffered to expand. ”

“ Each lung is covered, except at one point, with an elastic serous membrane in a double layer, called the pleura. One layer closely envelops the lung, at the apex of which it is reflected to the wall of the chest cavity of its own side, which it lines. ”

“ A rude apparatus to illustrate the mechanism of breathing in mammals is easily made by suspending the lungs of some small animal in a glass bell-jar closed below by an elastic membrane—a sheet of rubber, for instance—the only access for air to the interior being through the windpipe. Then the forced enlargement of the cavity, by pulling down the membrane, causes the inflation of the lungs. ”

“ The mucous membranes also, when the chemical functions of the lungs are interrupted, exemplify a similar phenomenon. The swelling of the tongue, observable in those that have been drowned or hanged, or asphyxiated by the vapour of charcoal, the lividity of the membrane of the mouth, of the intestines, and the bronchiæ which have also been remarked, depend on no other cause. ”