They are two conical-shaped organs, occupying the cavity of the chest on each side of the heart, from which they are separated by a membranous partition, the mediastinum. Their color is pinkish gray, marked with black. Each lung is divided into two lobes by a long, deep fissure. In the right lung the upper lobe is subdivided by a second fissure. The air cells in each lobe communicate with each other, but not with those of another lobe. The lungs rest on the convex surface of the diaphragm. The root of each lung comprises the pulmonary artery and veins, and bronchial tubes, with the bronchial vessels and pulmonary plexuses of nerves. They are comprised of ramifications of the bronchial tubes, terminating in intercellular passages and air cells. It is supposed that there are not less than one hundred million air cells in the lungs. The mucous membrane of the lungs presents an extent of surface of twenty-one thousand square inches; supposed to be greater than the entire surface of the skin of the body. All the air tubes, vessels, and nerves of the lungs are closely knit together into one general texture, by a delicate cellular tissue, and the whole mass, on each side, is enveloped in the serous membrane as an external coat. The pulmonary artery, which transmits the venous blood from the heart to the lungs, terminates in a minute network of capillary vessels, distributed through the walls of the air-passages and air-cells; these converge to form the pulmonary veins, which return the arterial blood to the heart.HBH 148.2

319. What is the pleura?HBH 149.1

It is the serous membrane which lines the thoracic cavity, and divides it into two chambers, by passing double across it from the breast-bone to the back-bone, thus forming a closed sack for each lung, and embracing the heart, the large blood-vessels and the meat-pipe, between the two sheets of the middle partition. If the two lungs occupied only one cavity, then any perforation of the walls of that cavity, by disease or otherwise, so that the external air could rush into it, would at once arrest the function of respiration, and immediate death would result. But now, if by any means one lung is disabled, it can lie still while the other continues faithfully to perform its functions. Such is the wisdom and goodness of our great Creator.HBH 149.2

320. How is the process of breathing accomplished by the lungs?HBH 150.1

The movement of the lungs is partly voluntary, and partly involuntary. Voluntary for the purpose of being guided by the will, and assisting speech; involuntary, that they may be acted upon by the involuntary nerves and muscles of organic life. The atmosphere presses on the surface of the body at the rate of fifteen pounds to every square inch. This pressure being the same on all parts of the body, we do not feel it. When the diaphragm is drawn down, and the breast-bone and ribs elevated, the cavity of the chest is much enlarged, and the external air rushes into the air cells, distending them in proportion to the dilation of the thorax, and keeping the surface of the lungs all the while accurately in contact with the walls of the chest in all their movements. Immediately after an inhalation of breath, all the muscles employed in expanding the cavity of the chest contract, and the ribs and diaphragm return to their natural position. By these means, and by the contraction of the muscles of the air tubes, the air is expelled from the lungs. It will be readily seen that, in the function of breathing, the lungs themselves are entirely passive, and that in order to breathe freely there should be ample room to expand the chest. When the ribs are confined by tight clothing the diaphragm is compelled to carry on the function of breathing alone, but in this case respiration is much restrained.HBH 150.2

321. What further can you say of the structure of the lungs?HBH 150.3

The sides or walls of air cells are formed of a very thin, transparent membrane, and the capillary vessels are placed between the walls of twoHBH 150.4

PICTURE AND TEXT

adjacent cells, so as to be exposed to the action of the air on both sides. It is calculated that about 266 cubic feet of air pass through the lungs of a medium-sized man in twenty-four hours. It is calculated that nearly twelve pints are ordinarily present in the lungs at one time, and that about a pint is inhaled and exhaled at one inspiration, so it would require twelve ordinary breaths to displace the air in the lungs, and supply entirely new air. This of course has reference to involuntary breathing, and not to deep and full inspirations controlled by the will.HBH 151.1

Figure XVII
PICTURE
ACTION OF THE DIAPHRAGM

322. What is Fig. XVII designed to illustrate?HBH 151.2

A side view of the chest and abdomen in respiration. 1, cavity of the chest; 2, cavity of the abdomen; 3, line of direction for the diaphragm when relaxed in expiration; 4, line of direction when contracted in inspiration; 5, 6, position of the front walls of the chest and abdomen in inspiration; 7, 8, their position in expiration.HBH 151.3

323. What is accomplished by the inhaling of air into the lungs?HBH 151.4

The air is digested, and the lungs form from it a principle convertible into the substance of the blood. They also constantly receive from the air, and transmit to the blood, a replenishing stream of that electric, magnetic, vital property, on which the nervous influence depends. The composition of one hundred parts of air is, twenty parts of oxygen, seventy-nine of nitrogen, one of carbonic-acid gas. Other gaseous matters are sometimes found in the air, but are not natural constituents. The air expired from the lungs has lost about sixteen parts of its oxygen, and gained about fourteen parts of carbon. This decarbonization and oxygenation of the blood changes it from a dark purple to a bright, florid color. The oxygen does not go into the blood as oxygen, but is converted into electricity, the same as food in its digestion is converted into chyle. The variation in the quantity of nitrogen taken up from the air in the lungs, must be regulated by the excess or deficiency of the nitrogenous principle in the food eaten. It is supposed that thirty-seven ounces of oxygen are retained from the air, and fourteen ounces of carbon thrown off by the blood through the lungs every twenty-four hours.HBH 152.1

324. What is essential in reference to the air, that it may impart vigor and length of days?HBH 152.2

It is of the utmost importance to the welfare of the body, that pure air should be supplied to the lungs at every inspiration of breath. The organ of smell is a grand sentinel to warn us of infected and impure air; happy is he who listens to the dictates of nature in this respect. It is impossible for the lungs to be fully expanded in an impure atmosphere. It irritates the lungs, and the air cells spasmodically contract to keep out suchHBH 152.3

PICTURE AND TEXT

air.. It is no wonder that those who live in the smoke and din of cities, and inhale the impurities of a hundred cess pools, and neglect to exercise their lungs by expanding them to their utmost capacity, many times a day, in pure air, should find their lungs diminishing in size, and pulmonary consumption marking them as its victims.HBH 153.1

Figure XVIII
PICTURE
PURIFICATION OF THE BLOOD

325. What is Fig. XVIII designed to illustrate?HBH 154.1

The circuit of the blood in the system, and its course into the lungs, where its purification is accomplished. From the right ventricle of the heart (2), the dark, impure blood is forced into the pulmonary artery (3), and its branches (4, 5), carry the blood to the left and right lung. In the capillary vessels (6, 6) of the lungs, the blood becomes pure, or of a red color, and is returned to the left auricle of the heart (9) by the veins (7, 8). From the left auricle the pure blood passes into the left ventricle (10). By a forcible contraction of the left ventricle of the heart, the blood is thrown into the aorta (11). Its branches (12, 13, 13,) carry the pure blood to every organ or part of the body. The divisions and sub-divisions of the aorta terminate in capillary vessels, represented by 14, 14. In these hair-like vessels the blood takes up the effete and worn-out particles of the system, which render it dark colored and impure, and it is thus returned to the right auricle of the heart (1) by the vena cava descendens (15), and vena cava ascendens (16). The tricuspid valves (17) prevent the reflow of the blood from the right ventricle to the right auricle. The semi-lunar valves (18) prevent the blood passing from the pulmonary artery to the right ventricle. The mitral valves (19) prevent the reflow of blood from the left ventricle to the left auricle. The semi-lunar valves (20) prevent the reflow of blood from the aorta to the left ventricle. The amount of air required daily in the lungs is three thousand two hundred and forty gallons, or about eight barrels per hour.HBH 154.2

326. What do we find, then, most essential to keep the lungs in a healthy condition?HBH 154.3

To emancipate them entirely from compression, so that with the greatest ease they can be filled to their utmost capacity. Just in the same ratio that the lungs are confined, and the breathing capacity of the lungs decreased, is the life shortened. It is a good exercise, especially for students, in-door mechanics, and all persons of sedentary habits, several times in a day, to fill their lungs to their utmost capacity half a dozen or a dozen times in succession, at the same time whirling their arms, or swinging them back behind them. Such exercise should be commenced carefully.HBH 155.1

327. Why is air which has been breathed considered poisonous?HBH 155.2

When the oxygen has been exhausted from the air by breathing, a person will soon expire in the air. This air is poison merely because it has no vitalizing element in it, nothing to sustain life. A fire or lamp will go out where this oxygen is consumed. In wells, or deep vaults, a lighted lamp should be lowered before a person descends into them. If the lamp is extinguished, a person could not live in the place. Carbonic-acid gas is heavier than common air, and settles to the bottom of the room or vault. In closely-crowded, illy-ventilated rooms, the purest air is in the middle of the room. A hundred persons confined in a room thirty feet in length and breadth, and the usual height, would render the whole air unfit to breathe in less than two hours. An ordinary lamp or gas-burner consumes as much air as four persons; a common stove consumes more air than fifty persons. In addition to this, a large amount of impurity is communicated to the air by the exhalations from the skin. So it will be readily seen, that the air of meeting places, crowded factories and work-shops, is in a few minutes unfit to sustain life. How important, then, that such places be well ventilated.HBH 155.3

328. What is essential to good ventilation?HBH 156.1

That the air should be pure. A lamp burning in a sick room, or a smoking lamp, requires special care that pure air is supplied to the room; but always remove, as soon as possible, the smoky lamp from the house. Light is essential to thorough ventilation. Rays of light, especially sun-light, have a wonderful, invigorating influence on the air. Those living in low cellars, or damp, shady sides of streets, or damp, dark places in cities, cannot expect to enjoy perfect health. In prevailing epidemics, as cholera, it prevails the worst in dark and damp places, and the shady sides of streets. The rooms mostly occupied in dwelling houses, should be so arranged as to have plenty of light admitted to them, and so that pure air can pass through them. It is a decided benefit, in a room where fire is burning, to keep constantly a dish of water on the stove, that the air may be moistened by the steam. It is very unhealthy to sleep in rooms in which are several house plants, or which are surrounded by, or immediately adjacent to, dense foliage. Vegetation absorbs carbon during the day, and throws off oxygen, but in the night this process is reversed, and it absorbs oxygen and throws off carbonic-acid gas. In rooms difficult of ventilation, by swinging the door back and forth rapidly several times in succession, the impure air may be pumped out of it, and pure air will rush in to fill its place.HBH 156.2

329. What is the disease to which the lungs are most liable?HBH 156.3

Inflammation of the lungs, called in its various stages and manifestations, pneumonia, pneumonitis, lung fever, pleurisy, etc. The main cause producing it is exposing the body to extremes of temperature, unequal exposure of the body, cold or wet feet, exposing the body to cold or wet, when it is exhausted either by over-exertion, or loss of sleep. The tepid wet-sheet pack is good in such cases to allay the fever on the surface of the body. Pain or oppression in breathing, or soreness in the lungs, may be relieved by the compress, made of a linen cloth of two or more thicknesses, wet and placed over the lungs, with sufficient dry flannel over it to occasion a slight perspiration. This should be wet several times a day. In a violent attack of lung complaint, if possible, immediately get the aid of some one of experience in the use of water. But it is better to studiously avoid all those causes which are liable to induce diseases of the lungs. Keep your feet warm and dry, your head cool, get a proper amount of rest every day, and labor within your strength, always avoiding exhaustion of vital power as much as possible. The thirst which attends a fever, is a demand of nature. This demand should be supplied by freely drinking of pure, soft water. The bowels should be kept regular by injections of tepid water.HBH 157.1

ORGANS OF THE THORACIC CAVITY

THE ABDOMINAL VISCERA