ive in a room
with a smoking stove. But tobacco smoke is more harmful than smoke
from a stove, for it has nicotine in it. Tobacco smoke in a room may
make a child sick.

Cigarette smoking is very harmful to the lungs, for the smoke is drawn
deeply into them, and more of the poison is likely to stay in the
body. The smoke of tobacco burns the throat and causes a cough. This
harms the voice.

WHAT WE HAVE LEARNED

1. Air is always being breathed into little sacs inside the body.
The sacs form the lungs.

2. The red blood cells pass through the lungs, and take little
loads of air. They then carry the air through the arteries
to the capillaries.

3. In the capillaries the air leaves the red blood cells, and
goes to the cells of the body.

4. The air unites with the cells, and slowly burns them to smoke
and ashes.

5. The smoke goes back to the blood, and is carried to the lungs
and given off by the breath. The ashes go back to the blood
and pass off through the skin and the kidneys.

6. The burning in the cells makes heat.

7. Some of the heat is changed to power, as it is in a steam
engine.

8. The heat also warms the body. It keeps it at the same warmth
on a cold day as on a hot day.

9. We wear clothes to keep the heat in, and so to keep us warm.

10. The air of a room needs to be changed often. It is made
stuffy by our breath.

11. The voice is made by the breath in a box in the neck.

12. Alcohol uses air belonging to the cells of the body.

13. Tobacco smoke has the same poisons as tobacco. It can poison
the whole body through the lungs.

CHAPTER XI

THE SKIN AND KIDNEYS

=122. Waste matters.=--The food is burned in the cells. As this
burning goes on, the _smoke_ goes off by the lungs and the unburned
substances, the _ashes_, go off by the skin and kidneys. The ashes are
mostly the minerals of the cells, but there are also some from the
burned albumin. All these go back to the blood and are carried to the
skin and kidneys.

[Illustration: =The skin (x100).=

_a_, _b_ and _c_ epidermis.
_d_ and _g_ tough and thick part of skin.
_e_ sweat gland.
_f_ blood tubes.
_h_ fat pockets.]

=123. The skin.=--The skin covers the whole body. It is strong and
keeps the body from being hurt.

=124. The epithe