Air sac

“ But the joints of the backbone in front of the sacrum receive their air from the cervical air sac. The air cells are not limited to the bones, but ramify through the body, and in some cases extend among the muscles. ”

“ From the sac are given off tracheal tubes to the muscles of the thorax and to the walls of the stomach. Many insects have tracheal air sacs of smaller size, and the purpose of the sacs in general appears to be that of holding reserve supplies of air for respiratory pur- poses. The great size of the air sac in the cicada's abdo- men, however, suggests that it has some special function, and it is natural to suppose that it acts as a resonating chamber in connection with the sound-producing drums. Yet the sac is as well developed in the female as in the male. ”

“ Whether the air be admitted into the pleural sac, by an opening made in the side from without, or by an opening in the lung itself, the mechanical principle of the respiratory apparatus will be equally deranged. ”

“ Highly specialized air-sacs are characteristic of all birds. They are very thin-walled membranes, very poor in blood-vessels, formed by the bulged-out pleural or peritoneal covering of the lungs, through the parabronchial tubes of which they are filled with air. ”

“ The air sacs or cells communicate with the principal pulmonary tube, but a vastly smaller surface is exposed to the inhaled air, and aëration of the blood is consequently extremely imperfect and incomplete. ”

“ Cases are on record of perforation of the sac with a knife,35 and through the oesophagus by means of a sword swallowed by a juggler.36 Sometimes the perforations communicate with organs that contain gas, as the stomach or intestine or the oesophagus. Graves has recorded a case in connection with abscess of the liver. When the pericardial sac is intact, the distending gas may arise from decomposing fluid in the pericardium: it is supposed that it may even be secreted by the blood of the coronary vessels. Pure air, such as we breathe, is never developed in the sac. ”

“ When on the wing probably very little muscular effort is necessary. Their bodies contain elastic air sacs in communication with the tracheae, and at the time of flight it may be presumed that the body is comparatively empty, food being wanting, and the internal organs of reproduction, which occupy a large space when in activity, yet undeveloped, hence the sacs have full room for expansion, as explained on p. ”

“ Air sacs lie against the inner face of the membrane, furnishing the equilibrium of air pressure necessary for free vibration in response to sound waves, and a complicated sensory apparatus is attached to its inner wall. ”

“ Inasmuch as the gaseous interchange between the lungs and the blood takes place only in the terminal air sacs it follows that, at the end of each respiration, the rest of the respiratory tract is filled with air low in oxygen and high in carbon dioxide, which on inspiration is drawn back into the lungs, diluting the fresh air. ”

“ The lungs are comparatively small, but they are not the only organs of respiration (p. 242) ; for the windpipe opens also into several air-sacs, which supply nearly all parts of the body with air, and even communicate with the interior of certain bones. The bone of the pigeon’s upper-arm, for example, is hollow and contains air. By means of the system of air-sacs, the air in the lungs is completely renewed at each respiratory act, and thus the waste carbon-dioxide in the blood can be exchanged for fresh oxygen much more completely than it is in mammals. ”

“ Respiratory channels are highly developed, enabling the pigeon to fly continuously from 12 to 15 hours. Air circulates through the bronchial tubes and lungs and also through nine air sacs, from which other small, irregular cavities extend under the skin between the muscles, and even6 into the inside of the bones. These small air sacs contain a reserve of warm air which feeds the lungs during flight when the muscular apparatus consumes a large amount of oxygen. ”

“ At birth, also, the lungs are solid, so that the first air has to overcome adhesions between the collapsed walls of the bronchioles and air sacs, but after they are thus gradually unfolded, in that they are of extensible material and open to the air above, atmospheric pressure from within keeps them distended to the full extent of the chest, which is air tight. ”

“ No machine, however light and powerful, will ever fly whose travelling surfaces are not properly fashioned and properly applied to the air.
It was supposed at one time that the air sacs of birds contributed in some mysterious way to flight, but this is now known to be erroneous. The bats and some of the best-flying birds have no air sacs. Similar remarks are to be made of the heated air imprisoned within the bones of certain birds.1 Feathers even are not necessary to flight. Insects and bats have no feathers, and yet fly well. ”

“ The lungs of birds are more complex than those of batrachians and reptiles, being divided into small spaces by numerous membranous partitions. They are not lobed as in mammals, and do not lie free in the body-cavity, but are fixed to the inner dorsal region of the body. Connected with the lungs are the air-sacs already referred to, which are in turn connected with the air-spaces in the hollow bones. By this arrangement the bird can fill with air not only its lungs but all the special air-sacs and spaces and thus greatly lower its specific gravity. ”

“ Fig. 1, A pair of bellows with two separate bags, so contrived that by opening them, when applied to the nostrils or mouth of a patient, one bag will be filled with common air, and the other with the mephitic air extracted from the lungs; and, by shutting them again, pure atmospheric air will be introduced into those organs, and that drawn out, consequently discharged into the room. Thus, the artificial breathing may be continued, while the other operations on the surface of the body are carried on ”

“ It will be observed that when the sides are spread apart air flows into the bellows. When they are pressed together the air flows out. If an air-tight sack were hung in the bellows with its mouth attached to the projecting tube, the arrangement would resemble closely the general plan of the breathing organs (Fig. 41) . One respect, however, in which the bellows differs from the thorax should be noted. The thorax is never sufficiently compressed to drive out all the air. Air is always present in the lungs. This keeps them more or less distended and pressed against the thoracic walls. ”

“ Now, when we inflate a bag, as you prescribe, we do, in fact, the same thing which we do to maintain life, except that in the case of the artificial experiment our inhalation is somewhat stronger, in order that we may emit a stronger breath, so as to fill and distend the bag by compressing the air we blow into it, rather in the manner of a hard puff than of the gentle process of ordinary breathing and respiration. ”

“ When the bellows are set in action, one of the bags receives a column of atmospheric air through its valve; while the other, by means of its flexible tube and its valve, extracts a portion of air from the lungs. But, if the bellows are again shut, one of the bags parts with the impure gas drawn out of the pulmonary vessels; and the second conveys pure atmospheric air to the organs of respiration. By properly repeating this alternate process, the patient may again be enabled to exercise the important function of breathing. ”

“ Protection of the respiratory organs can to some extent be obtained by so-called respirators worn over the mouth and nose. Often they consist simply of a moist sponge or folds of cloth, or again may be complicated air-proof affairs enclosing mouth and nose, or the whole face like a mask, or even the head like a helmet ”

“ The principle of the respirator is to have a box filled with chemicals and attached by a flexible tube to a face piece or mask, which fits closely to the face. All air breathed by a man must therefore pass through the chemicals, and these are so chosen that they will absorb any and every poison that may be present in the atmosphere at the time. In order to keep the air pure in the mask and to have a double line of protection a man breathes through a special mouthpiece and has his nose clipped. ”

“ Breathing is done through a mouthpiece of rubber; the teeth close on the rubber tabs and the rubber flange lies between the teeth and the lips. The expired air finds exit through a rubber flutter valve in an angle tube just outside the mask. This arrangement furnishes a double line of protection; if the face piece is punctured or torn, gas-containing air cannot be breathed as long as the noseclip and mouthpiece are in position. ”

“ Being sack-like the sleeping bag retains the heat within and keeps the cold out. It is easy to unroll, keeps out dirt and wind and the contents may remain dry and one has full protection in any kind of weather.
The objectionable feature is that the bag cannot be drawn up closely to the body and the resulting air space is difficult to warm up. It is hard to adjust the top to keep the air from the sleeper’s shoulders and the inevitable twisting and turning of the sleeper bunches the blanket up around the limbs. ”

“ But however much the lungs vary in capacity, or the heart as to position in the respiratory motions, still the lungs are always closely applied to the thoracic walls. Between the pleura costalis and pulmonalis there occurs no interval in health. The thoracic parietes expand and contract to a certain degree; and to that same degree, and no further, do the lungs within the thorax expand and contract. By no effort of expiration can the animal expel all the air completely from its lungs, since by no effort of its own, can it contract thoracic space beyond the natural limit. ”

“ 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. ”

“ The bottle being filled with air of the density of that on the ground, and the bladder tied on in a collapsed state, the expansion of the air in the bottle would gradually fill the bladder as it rose into the rarer regions of the atmosphere. Experience would then be trusted to enable the aeronaut to judge his height from the amount of inflation noticeable in the bladder. ”

“ By the muscular action of the diaphragm and intercostal muscles, and the consequent contractions and expansion of the lungs, the alternate inspirations and expirations are produced which we call breathing. The lungs are not completely filled and emptied by each respiration, and a certain amount of air remains stationary in them. 210Were this air which remains stationary constantly in a particular portion of the lungs, the same without change, we would derive no benefit from that portion of the lungs. ”

“ The two lungs must, therefore, be alternately affected as to their capacity according as the heart occupies space on either side of the thorax. In expiration, the heart, E, is more uncovered by the shelving edges of the lungs than in inspiration. In pneumothorax of either of the pleural sacs the air compresses the lung, pushes the heart from its normal position, and the space which the air occupies in the pleura yields a clear hollow sound on percussion, whilst, by the ear or stethoscope applied to a corresponding part of the thoracic walls, we discover the absence of the respiratory murmur. ”

“ The lungs are two in number, right and left, and surround the heart, completely filling the thoracic cavity. The lungs are divided into superimposed lobes, three in the right and two in the left lung; they are composed essentially of infinitely small ramifications of the bronchi, resolving into tiny series of chambers, the pulmonary alveoli or air-cells. ”

“ In the case of specially valuable animals one may use a pneumatic cabinet the principle of which is to diminish the air pressure on the body at large by an exhaust, while pure air for breathing, at the ordinary atmospheric pressure, is introduced through a tube furnished with a face piece fitting around closely beneath the eyes. ”

“ Amongst other tests adopted by the brigade are those giving the vital lung capacity, the expiratory force, also complemental and supplemental air, the former being the measurement of the excess capacity of the lungs over a normal intake of air, the latter that quantity of air remaining in the lungs after a normal expiration.
Excess of any nature is frowned on. ”

“ It secretes a fluid which lubricates it, so that the layers glide upon each other with perfect ease. [Footnote: These pleural sacs are distinct and closed; hence, when the ribs are raised, a partial vacuum being formed in the sacs, air rushes in, and distends the pulmonary lobules.] The lungs are lined with mucous membrane, exceedingly delicate and sensitive to the presence of anything except pure air. We have all noticed this when we have breathed any thing offensive. ”

“ Lungs consist of two long membranous bags, which run the whole length of the abdomen, anteriorly to the stomach and intestines; the opening of the larynx scarcely large enough to admit a pin's head; the lungs resemble two long air-bags, more than a true pulmonary apparatus; the cartilaginous laminæ of the branchia, three in number, attached superiorly to the integuments over the cervical vertebræ, converging together beneath or anteriorly, and are attached to a cartilage answering to the os hyoides ”