outside world.
FIG. 5.—A Neurone from a Human Spinal Cord. The central portion represents the cell body.
N, the nucleus; P, a pigmented or colored spot; D, a dendrite, or relatively short fiber,—which
branches freely; A, an axon or long fiber, which branches but little.The Work of the Senses.—And what a problem the senses have to solve! On
the one hand the great universe of sights and sounds, of tastes and smells, of
contacts and temperatures, and whatever else may belong to the material world
in which we live; and on the other hand the little shapeless mass of gray and
white pulpy matter called the brain, incapable of sustaining its own shape, shut
away in the darkness of a bony case with no possibility of contact with the
outside world, and possessing no means of communicating with it except
through the senses. And yet this universe of external things must be brought into
communication with the seemingly insignificant but really wonderful brain, else
the mind could never be. Here we discover, then, the two great factors which
first require our study if we would understand the growth of the mind—the
material world without, and the brain within. For it is the action and interaction
of these which lie at the bottom of the mind's development. Let us first look a
little more closely at the brain and the accompanying nervous system.