Some animals have parts like a man's; but
these parts are fewer. No animal has arms or hands like a man. A fish
has little fins in place of legs and arms, while a worm has not even a
head, but only a body, and yet it moves. An oyster has only a body and
cannot move. The simplest of all animals is very small. A thousand of
them would not reach an inch. Yet each is a complete animal. It is
called the _ameba_. It is only a lump of jelly. It can put out any part
of its body like an arm and take a lump of food. This same arm can eat
the food, too. It can also put out any part of its body like a leg and
move by rolling the rest of its body into the leg. It can do some things
better than a man can do them, for any part of its body can do all kinds
of work. So the ameba grows and moves and does as it likes.

[Illustration: =Different forms of an ameba (x400).=]

[Illustration: =Cells from the human body (x200).=

_a_ A colored cell from the eye.
_b_ A white blood cell.
_c_ A connective tissue cell.
_d_ A cell from the lining of the mouth.
_e_ Liver cells.
_f_ A muscle cell from the intestine.]

=2. Cells.=--A man's finger moves and grows something like a separate
animal, but it must keep with the rest of the body. A little piece of
a finger moves and grows, too. If you should look at a finger, or any
other part of your body, through a microscope, you would see that it
is composed of little lumps of jelly. Each little lump looks like an
ameba. We call each lump a cell. The cells make up the finger.

=3. What cells do.=--Each cell acts much as an ameba does. From the
blood it gets food and air and takes them in through any part of its
body. It also grows and moves. But the cells are not free to do as
they wish, for they are all tied together in armies by very fine
strings. We call these strings _connective tissue_. One army of cells
makes the skin, and other armies make the bones and flesh. Some armies
make the fingers, and some the legs. Every part of our body is made up
of armies of separate cells.

=4. The mind.=--The body is a home for the mind. The cells obey the
mind. The mind pays the cells by feeding them and taking good care
of them. When an army of cells is hurt, the body feels sick, and
then the mind tells the whole body to rest until the cells are well
again. When we study about a man's body, we learn about the separate
cells in his body.

WHAT WE HAVE LEARNED

1. Our body is made up of