Air cells
The capillaries run in the thin walls of the air spaces. The walls of these fine blood vessels are so very thin that the air in the air cells comes in almost direct contact with the blood in the vessels. While the blood is passing through the vessels in the walls of the air spaces, something happens to both the blood and the air. The air we take into our lungs contains a great deal of oxygen and very little carbon dioxid. The air that comes out of our lungs contains a great deal of carbon dioxid and much less oxygen. In other words, the oxygen from the air goes into the blood, and the carbon dioxid from the blood goes out into the air.
Necessity of pure air
If the air we breathe is not pure and does not contain enough oxygen, the blood cannot get all the oxygen we need, and the cells of the body become sick and die. If, when we breathe, we do not fill each little air cell in our lungs with air, a great deal of the blood sent to the lungs for oxygen cannot get it. If we wear very tight clothing we cannot take a full breath and hence cannot fill all the air spaces with air. If the air spaces in the lungs are not filled, the blood does not get the oxygen it needs, as there is no other place in the body to get it.
THE EYE AND THE EAR
The eye compared to a camera
The eye is one of the most important organs in the body and also one of the most delicate. It is very much like a camera.
The cornea and the sclera
When you look at an eye you are likely to think that the front of it is blue or brown. The colored part is not the front of the eye. If you look at the eye from the side you will see that there is a curved part in front of the colored part and that the curved part is perfectly clear. This curved clear part of the eye we call the cornea. The cornea connects with the white part of the eye, and this white part extends all around the rest of the eye, except at a small point in the back where the optic nerve comes through. This white part we call the sclera.
Aqueous humor