CHAPTER VI. A Short Explanation of the Heart and Lungs. THE framework of bone and the filling up of muscles would be nothing more than a dead mass without the constant action of the blood. This fluid circulates through artery and vein, to the most remote part of the human body, carrying away the particles that have done their work, and bringing strong, healthy ones to keep the system in repair. The blood assists the growth of every organ, and supplies the glands with materials for their products: such as tears for the eye, and saliva for the mouth. It also carries the nourishing juices to the kidneys and liver, where they are purified; and to the lungs, where the oxygen of atmospheric air takes off the carbon. The wide distribution of the vessels is shown by the fact that blood appears wherever we slightly prick or scratch the skin. Blood vessels are spread over the whole surface of the body; and within the body they run along the surface of membranes, pene trate the bones and muscles, and even find their way into every tooth through a small hole in the root. The blood from a slight scratch in the skin is of a dark colour; while that from a deeper wound is of a bright red. The former is blood which has been used on its way to be purified; and the latter purified blood which has passed through the heart, and is hastening to fulfil its work. The circulation of the blood will be dwelt on further on. The blood consists of a great number of little flat red discs, resembling pieces of money floating in a nearly colourless fluid, called the liquor of the blood. About 3,000 of these little discs (or globules, as they are sometimes called), if laid side by side, would only make up an inch of length. These discs give the red colour to the blood, and are found to contain iron, phosphorus, and potass; while the clear liquor contains several other substances necessary for building up the frame. The centre of the circulatory system is the heart, which is like a strong engine at work night and day. It contains four cavities, two of them called auricles, and two ventricles, which have walls made of muscle. The contraction of the muscles of the left ventricle forces the blood into a system of vessels called arteries; the relaxing of the muscle of the right auricle permits that cavity to receive the blood from the veins. The heart contracts or pulsates 70 times per minute, 4200 times per hour, 100,800 per day, 36,792,000 times per year; at each beat 24 oz. of blood is thrown out, 175 oz. per minute, 656 lbs. per hour, 7 tons per day. All the blood in the body passes through the heart in three or four minutes; and after traversing the system, and being purified in the lungs, passes through the heart again. The quantity of blood in an adult averages from 25 to 30 lbs. The lungs will contain about one gallon of air at their usual degree of inflation. We breathe, on an average, 1200 times per day; we inhale in the same space of time 24,000 gallons of air. th of The blood having flowed through the body, enters the lungs, where it comes into contact with the air, and is purified. The lungs are composed of very small cells, crowded as closely as possible together, and measuring, on an average, only about an inch across! They have altogether a vast extent of surface, and if collected and expanded would cover a space of fifteen square feet. To these cells the air is taken in at the mouth, and is conveyed by small tubes to the wind-pipe. These tubes or air passages may, like the arteries, be compared to a tree with its stems, boughs, branches, and twigs, the larger dividing into smaller, and these again into smaller still. They convey the air to the little cells, where it undergoes the purifying process. The air in effecting this becomes vitiated, and is unfit for further breathing. From what we have seen of God's workmanship thus far, we are prepared to find that the lungs are well protected, since in so many instances extra protection is given to parts of especial importance and delicacy of structure. In reality we find them suspended in the thorax or cavity where the heart is placed, and, like the heart, covered by a membrane in which they work with very little friction, being kept moist by a fluid manufactured on the spot, and poured over them. The circulation of blood in the some creatures is even more wonderful than in man. From the heart of a whale it gushes with the immense velocity of ten or fifteen gallons at a stroke, through a tube a foot in diameter, with a rush and roar like that of waterworks. Hamburger said that the wisdom of God was seen in nothing more glorious than in the heart. It |