~20. What the Little Brain Does.~--The little brain[B] thinks too, but
it does not do the same kind of thinking as the large brain. We may use
our arms and legs and many other parts when we wish to do so; and if we
do not care to use them we may allow them to remain quiet. This is not
the case with some other organs. It is necessary, for example, that the
heart, the lungs, and many other organs of the body should keep at work
all the time. If the large brain had to attend to all of these
different kinds of work besides thinking about what we see, hear, and
read, and other things which we do, it would have too much work to do,
and would not be able to do it all well. Besides, the large brain
sometimes falls asleep. So the large brain lets the little brain do the
kinds of work which have to be attended to all the time, and the little
brain keeps steadily at work when we are asleep as well as when we are
awake.

~21. What the Spinal Cord Does.~--If you tickle a person's foot when he
is asleep, he will pull it up just as he would if he were awake, only
not quite so quickly. What do you suppose makes the muscles of the leg
contract when the brain is asleep and does not know that the foot is
being tickled? And here is another curious fact. When you were coming to
school this morning you did not have to think about every step you took.
Perhaps you were talking or looking over your lessons; but your legs
walked right along all the time, and without your thinking about them.
Can you tell how?

~22.~ It would be too much trouble for the large brain to stop to think
every time we step, and the little brain has work enough to do in taking
care of the heart and lungs and other organs, without keeping watch of
the feet when we are asleep, so as to pull them up if some mischievous