Where the Body Does its Real Eating. When once the food has been dissolved in the food-tube and absorbed by the cells of its walls, the next problem is how it shall be sent all over the body to supply the different parts that are hungry for it; for we must remember that the real eating of the food is done by the billions upon billions of tiny living cells of which the body is made up.
The Pipe Lines of the Body. What do we do when we want to carry water, or oil, or sewage, quickly and surely from one place to another? We put down a pipe line. We are wonderfully proud of our systems of water and gas supply, and of the great pipe lines that carry oil from wells in Ohio and Indiana clear to the Atlantic coast. But the very first man that ever laid a pipe to carry water was simply imitating nature—only about ten or fifteen million years behind her. No sooner has our food passed through the cells in the wall of the food-tube, than it goes straight into a set of tiny tubes—the blood-pipes, or blood vessels—which carry it to the heart; and the heart pumps it all over the body.
Veins and Arteries. These blood-tubes running from the walls of the food-tube to the heart are called veins; and the other tubes through which the heart pumps the blood all over the body are called arteries. If you will spell this last word "air-teries," it may help you to remember why the name was given to these tubes ages ago. When the body was examined after death, they were found to be empty and hence were not unnaturally supposed to carry air throughout the body, and "air-teries" they have remained ever since. While absurd in one way, the name is not so far amiss in another, for an important part of their work is to carry all over the body swarms of tiny baskets, or sponges, of oxygen taken from the air.
Why the Blood is Red. The first and main purpose of the blood-pipes and the heart is to carry the dissolved food from the stomach and intestines to the cells all over the body. But the cells need air as well as food; and, to carry this, there are little basket-cells—the red corpuscles. Take a drop of blood and put it under a microscope, and you will see what they look like. The field will be simply crowded with tiny, rounded lozenges—the red cells of the blood, which give it its well-known color.
The White Corpuscles or Scavengers of the Blood. As the blood-tubes are not only supply-pipes but sewers and drainage canals as well, it is a good thing to have some kind of tiny animals living and moving about in them, which can act as scavengers and eat up some of the waste and scraps; and hence your microscope will show you another kind of little blood corpuscle, known, from the fact that it is not colored, as the white corpuscle. These corpuscles are little cells of the body, which in shape and behavior are almost exactly like an ameba—a tiny "bug," seen only under the microscope, that lives in ditch-water. Under the microscope the white corpuscles look like little round disks, about one-third larger than the red corpuscles, and with a large kernel, or nucleus, in their centre.
They have the same power of changing their shape, of surrounding and swallowing scraps of food, as has the ameba, and are a combination of scavengers and sanitary police. When disease germs get into the blood, they attack and endeavor to eat and digest them; and whenever inflammation, or trouble of any sort, begins in any part of the body, they hurry to the scene in thousands, clog the blood-tubes and squeeze their way out through the walls of the smallest blood-tubes to attack the invaders or repair the damage. This causes the well-known swelling and reddening which accompanies inflammation.
Blood, then, is a sticky red fluid, two-thirds of which is food-soup, and the other third, corpuscles. How tiny the blood-corpuscles are, may be guessed from the fact that there are about 5,000,000 red cells and 10,000 white cells in every cubic centimetre (fifteen drops) of our blood.
How the Blood Circulates through the Body. Now let us see how some portion of the body, say the right thumb, gets its share of food and of oxygen through the blood. We will start at the very beginning. The food, of course, is put into the mouth, chewed by the teeth, and softened and digested in the stomach and intestines. It is then taken up by the cells of the mucous coat of the intestines and passed into the network of tiny blood-pipes surrounding them, between the lining of the bowels and their muscular coat.
These tiny blood-pipes, called capillaries, run together to form larger pipes—the small veins; and the small veins from the walls of the intestine and stomach finally run together into one large pipe, or trunk-line (called the portal vein), which carries them to the liver.
In passing through the liver, the blood is purified of some irritating substances picked up from the food-tube, and the melted food which it contains is further prepared for the use of the cells of the body. The portal vein of the liver breaks up into a network of veins, and these again break up into a number of tiny capillaries, in which the blood is acted upon by the cells of the liver. These capillaries gather together again to form veins, and finally unite into two large veins at the back of the liver, which run directly into the great trunk-pipe of all the veins of the body—the vena cava (or "empty vein," so called because it is always found empty after death), about an inch from where this opens into the right side of the heart.
In the vena cava the blood from the food-tube, rich in food, but poor in oxygen, mixes with the impure, or used-up, blood brought back by the veins from all over the body and, passing into the right side of the heart, is pumped by the heart through a large blood-pipe to the lungs. This large blood-pipe divides into two branches, one for each lung; and these again break up into smaller branches, and finally into tiny capillaries, which are looped about in fine meshes, or networks, around the air-cells of the lung. Here, through the thin and delicate walls of the capillaries the blood cells give off, or breathe out, their carbon dioxid and other waste gases (which are passed out with our outgoing breath), and at the same time they breathe in oxygen which our incoming breath has drawn into the lungs.
This oxygen is picked up by, and combines with, the red coloring matter of the millions of little oxygen sponges, or baskets—the red corpuscles—and turns them a light red color, causing the blood to become bright red, such as runs in the arteries and is known as arterial blood.
The loops of tiny capillaries around the air cells of the lungs run together again to form larger pipes; and these unite, at the point of each lung nearest the heart, to form two large blood pipes—one from each lung—which pour the rich, pure blood, loaded with both food and oxygen into the left side of the heart. The left side of the heart pumps this blood out into the great main delivery-pipe for pure blood, known as the aorta, and this begins to give off branches to the different parts of the body, within a few inches of where it leaves the heart.
The Pipe Lines of the Body. What do we do when we want to carry water, or oil, or sewage, quickly and surely from one place to another? We put down a pipe line. We are wonderfully proud of our systems of water and gas supply, and of the great pipe lines that carry oil from wells in Ohio and Indiana clear to the Atlantic coast. But the very first man that ever laid a pipe to carry water was simply imitating nature—only about ten or fifteen million years behind her. No sooner has our food passed through the cells in the wall of the food-tube, than it goes straight into a set of tiny tubes—the blood-pipes, or blood vessels—which carry it to the heart; and the heart pumps it all over the body.
Veins and Arteries. These blood-tubes running from the walls of the food-tube to the heart are called veins; and the other tubes through which the heart pumps the blood all over the body are called arteries. If you will spell this last word "air-teries," it may help you to remember why the name was given to these tubes ages ago. When the body was examined after death, they were found to be empty and hence were not unnaturally supposed to carry air throughout the body, and "air-teries" they have remained ever since. While absurd in one way, the name is not so far amiss in another, for an important part of their work is to carry all over the body swarms of tiny baskets, or sponges, of oxygen taken from the air.
Why the Blood is Red. The first and main purpose of the blood-pipes and the heart is to carry the dissolved food from the stomach and intestines to the cells all over the body. But the cells need air as well as food; and, to carry this, there are little basket-cells—the red corpuscles. Take a drop of blood and put it under a microscope, and you will see what they look like. The field will be simply crowded with tiny, rounded lozenges—the red cells of the blood, which give it its well-known color.
BLOOD CORPUSCLES (Greatly magnified)
A, red blood; B, white blood.
They have the same power of changing their shape, of surrounding and swallowing scraps of food, as has the ameba, and are a combination of scavengers and sanitary police. When disease germs get into the blood, they attack and endeavor to eat and digest them; and whenever inflammation, or trouble of any sort, begins in any part of the body, they hurry to the scene in thousands, clog the blood-tubes and squeeze their way out through the walls of the smallest blood-tubes to attack the invaders or repair the damage. This causes the well-known swelling and reddening which accompanies inflammation.
Blood, then, is a sticky red fluid, two-thirds of which is food-soup, and the other third, corpuscles. How tiny the blood-corpuscles are, may be guessed from the fact that there are about 5,000,000 red cells and 10,000 white cells in every cubic centimetre (fifteen drops) of our blood.
How the Blood Circulates through the Body. Now let us see how some portion of the body, say the right thumb, gets its share of food and of oxygen through the blood. We will start at the very beginning. The food, of course, is put into the mouth, chewed by the teeth, and softened and digested in the stomach and intestines. It is then taken up by the cells of the mucous coat of the intestines and passed into the network of tiny blood-pipes surrounding them, between the lining of the bowels and their muscular coat.
These tiny blood-pipes, called capillaries, run together to form larger pipes—the small veins; and the small veins from the walls of the intestine and stomach finally run together into one large pipe, or trunk-line (called the portal vein), which carries them to the liver.
DIAGRAM OF THE CIRCULATORY SYSTEM All details are omitted. The connection between arteries and veins is shown only in the brain. Both heart and blood vessels are considerably enlarged to show clearly the course of the blood.
In the vena cava the blood from the food-tube, rich in food, but poor in oxygen, mixes with the impure, or used-up, blood brought back by the veins from all over the body and, passing into the right side of the heart, is pumped by the heart through a large blood-pipe to the lungs. This large blood-pipe divides into two branches, one for each lung; and these again break up into smaller branches, and finally into tiny capillaries, which are looped about in fine meshes, or networks, around the air-cells of the lung. Here, through the thin and delicate walls of the capillaries the blood cells give off, or breathe out, their carbon dioxid and other waste gases (which are passed out with our outgoing breath), and at the same time they breathe in oxygen which our incoming breath has drawn into the lungs.
This oxygen is picked up by, and combines with, the red coloring matter of the millions of little oxygen sponges, or baskets—the red corpuscles—and turns them a light red color, causing the blood to become bright red, such as runs in the arteries and is known as arterial blood.
The loops of tiny capillaries around the air cells of the lungs run together again to form larger pipes; and these unite, at the point of each lung nearest the heart, to form two large blood pipes—one from each lung—which pour the rich, pure blood, loaded with both food and oxygen into the left side of the heart. The left side of the heart pumps this blood out into the great main delivery-pipe for pure blood, known as the aorta, and this begins to give off branches to the different parts of the body, within a few inches of where it leaves the heart.
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