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The Blood Vessels

Sources: A Handbook Of Health

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 th
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


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.

One of the first of these branches to be given off by the aorta is a

large blood pipe, or artery, to supply the shoulder and arm; this artery

runs across the chest, thence across the armpit, and down the arm to the

elbow. Here it divides into two branches, one to supply the right, and

the other the left, side of the forearm and hand. These branches have by

this time got down to about the size of a wheat straw; the one supplying

the right side is the artery which we feel throbbing in the wrist, and

which we use in counting the pulse. From it run off smaller branches to

supply the thumb and fingers. These branches break up again into still

smaller branches, and they into a multitude of tiny capillaries, which

run in every direction among all the muscle cells, delivering the food

and oxygen at their very doors, as it were. The muscle cells eagerly

suck out the food-stuffs, and breathe in the oxygen of the blood; at the

same time, they pour into it their waste stuffs of all sorts, including

carbon dioxid. These rob the blood of its bright red oxygen color and

turn it a dirty purplish, or bluish, tint.

The loops of capillaries again run together, as they did in the liver

and in the lung, to form tiny veins; and these run together at the base

of the thumb and in the wrist, to form larger ones through which the now

poor and dirty blood is carried back up the arm over much the same

course as it took in coming down it. Indeed, the veins usually run

parallel with, and often directly alongside of, the arteries. The blood

passes through the armpit, across the chest, into the great main pipe

for impure blood, the vena cava, and through this into the right side of

the heart, where it again meets the rich, but waste-laden blood from the

food tube and liver, and starts on its circuit through the lungs and

around the body again.

The blood reaches every portion of our body in precisely this same

manner, only taking a different branch of the great pure-blood delivery

pipe, the aorta, according to the part of the body which it is to reach,

and coming back by a different vein-pipe.

Why the Arteries are more deeply Placed than the Veins. In the limbs

and over the surface of the body generally, the arteries are more deeply

placed than the veins, so as to protect them from injury, because the

blood in the arteries is driven at much higher pressure than in the

veins and spurts out with dangerous rapidity, if they are cut. Some of

the veins, indeed, run quite a little distance away from any artery and

quite close to the surface of the body, so that you can see them as

bluish streaks showing through the skin, particularly upon the front and

inner side of the arms.

The Capillaries. Of course, the blood pipes into which the food is

sucked through the walls of the food tube, and those in the lung,

through which the oxygen is breathed, as well as those in the thumb

through which food is taken to the muscle-cells, have the tiniest and

thinnest walls imaginable. For once, the name given them by the wise

men--capillaries (from the Latin capilla, a little hair)--fits them

beautifully, except that the hairs in this case are hollow, and about

one-twentieth of the size of the finest hair you can see with the naked

eye. So tiny are they that they compare with the big veins near the

heart into which they finally empty much as the smallest and slenderest

twigs of an elm do with its trunk. What they lack in size, however, they

more than make up in numbers; and a network of them as fine and close as

the most delicate gauze goes completely around the food tube between its

mucous lining and muscular coat.

Though thickest and most abundant on the inner and outer surfaces of the

body, every particle of the body substance is shot through and through

with a network of these tiny tubes. So close and fine is this network in

the skin, for instance, that, as you can readily prove, it is impossible

to thrust the point of the finest needle through the skin without

piercing one of them and drawing blood, as we say, or making it bleed.

From this network of tiny, thin-walled tubes, the body-cells draw their

food from the blood.

The Meaning of Good Color. It is the red blood in this spongy network

of tiny vessels that gives a pink coloring to our lips and the flush of

health to our cheeks. Whenever for any reason the blood is less richly

supplied with food or oxygen, or more loaded with smoke and other body

dirt than it should be, we lose this good color and become pale or

sallow. If we will remember that our hearts, our livers, our brains, and

our stomachs, are at the same time often equally pale and sallow--that

is, badly supplied with blood--as our complexions, we can readily

understand why it is that we are likely to have poor appetites, poor

memories, bad tastes in our mouths, and are easily tired whenever, as we

say, our blood is out of order. The blood is the life. Starve or

poison that, and you starve or poison every bit of living stuff in the