to the nervous system that we must turn our attention.

Although to the naked eye the nervous system is apparently made up of a
number of different kinds of material, still we see, when we turn our
microscopes upon it, that its parts are structurally the same. Reduced
to lowest terms, the nervous system is found to be composed of minute
units of structure called nerve-cells or neurones. Each of these looks
like a string frayed out at both ends, with a bulge somewhere along its
length. The nervous system is made up of millions of these little cells
packed together in various combinations and distributed throughout the
body. Some of the neurones are as long as three feet; others measure
but a fraction of an inch in length.

We do not know exactly how the mind, that part of us which feels,
reasons and wills, is connected with this mass of cells called the
nervous system. We do know, however, that every time anything occurs in
the mind, there is a change in some part of the nervous system.
Applying this fact to study, it is obvious that when you are performing
any of the operations of study, memorizing foreign vocabularies, making
arithmetical calculations, reasoning out problems in geometry, you are
making changes in your nervous system. The question before us, then,
is, What is the nature of these changes?

According to present knowledge, the action of the nervous system is
best conceived as a form of chemical change that spreads among the
nerve-cells. We call this commotion the nervous current. It is very
rapid, moving faster than one hundred feet a second, and runs along the
cells in much the same way as a "spark runs along a train of
gunpowder." It is important to note that neurones never act singly;
they always act in groups, the nervous current passing from neurone to