Health Lessons, Book 1

by Alvin Davison

Fig. 87 —Side of the skull cut away to show the brain. B, backbone.

The Spinal Cord.—This is a bundle of nerve matter about as thick as your finger. It extends from the stem of the brain down the canal in the backbone. The outer layer of the spinal cord is white because it is made of the tiny threads, nerve fibers. The inner part is made of the bodies of nerve cells and therefore looks gray. The fibers are branching threads from the cells in the cord and brain.

The Message Carriers or Nerve Fibers.—In order that the managers may send messages, these fine threads, the nerve fibers, extend from them to all parts of the body. In many places from five to five hundred or more of these fibers are united in one white cord called a nerve.

Twelve pairs of nerves are joined to the under side of the brain and thirty-one pairs are connected with the spinal cord ([Fig. 86]). The nerves of the brain branch to all parts of the head and neck, and one pair goes down to the lungs, heart, and stomach. The nerves connected with the spinal cord branch to every part of the muscles, bones, and skin of the arms, trunk, and legs.

How the Nerves do their Work.—On a telephone wire we can send a message in either direction. A message can travel on a nerve in only one direction. For this reason there must be two kinds of nerves. One kind is called sending nerves because the brain and cord send orders over them to make the organs act. The other kind carries messages to the brain from the eyes, ears, skin, or other organs of sense, telling it how they feel. On this account these are named receiving nerves.

When we wish to catch a ball, the brain sends an order along the nerve threads down the spinal cord and out through the nerves of the arm to the fingers to get ready to seize a ball. The fingers are spread to grasp the ball, but they do not close until a message goes from the skin of the finger tips to the spinal cord, telling it that the ball is in the hand.

The Work of the Brain.—The brain is not only the chief manager of the body, but the home of the mind. The mind acts through the brain. The mind receives through the brain what the eye sees, the ear hears, the nose smells, and the fingers feel. All this knowledge is stored up in the mind and called memory. These facts and others learned later are worked over by the mind. This is called thought.

The mind rules and becomes good or bad according to whether it contains good thoughts or bad thoughts. It is wrong to read books and papers about robberies and murders or to tell or to listen to bad stories, because in this way evil thoughts get into the mind. The best way of keeping badness out of the mind is to fill it with goodness. It is said that Lincoln was so busy thinking how he could help others that there was no room in his mind for a bad thought. Doing some kindness every day helps much in the making of a good mind.