The brain is the mass of nervous tissue within the skull. It is so tender and easily harmed that nature has walled it about by a hard, bony structure to protect it from injury. The gray substance of the nerves is where nervous impulses begin, which are conducted along the white substance. The gray matter may be compared to a telegraph office where the message is started, while the white matter is the wire along which the message travels. [Illustration: SURFACE OF THE CEREBRUM.] The spinal cord, or marrow, is a mass of soft, nervous tissue, which fills the hollow running the length of the spine or backbone. [Illustration: =NERVES OF THE FACE AND NECK=.—(a, b) _Nerve of the Face_; (d) _Nerve of the Forehead_.] From the base of the brain twelve pairs of nerves are given off to the face and head. One pair passes to the eye, and gives sight; one passes to the nose, and gives smell; one, to the mouth, tongue, and palate, and gives taste; one, to the ears, and gives hearing; and others to the face, neck, and head, and give the expressions of joy, sorrow, pain, anger, and doubt. From the spinal cord thirty-one pairs of nerves pass to the various parts and organs of the body. There could be no motion or feeling without the nerves, although they are not the true centres of either. If you obey the rules of health, as already laid down, you will be in the happy condition of those of whom it is said they do not feel that they have any nerves at all. * * * * * What move the muscles? How are the nerves in early youth? Of what are they composed? What are these parts called? What is the brain? How is it protected? Where do nervous impulses begin? To what may the gray and white matter be compared? What is the spinal cord? How many pairs of nerves are given off from the brain? From the spine? Where do they go? What is said of sensation and feeling? What if you obey the laws of health? CHAPTER XVI. SUNSTROKE AND POISONS. Don't be afraid of the sun. Its rays give life and vigor not only to men and animals, but to the vegetable world. A little tanning or browning of the skin is good for you. In summer when the rays are very strong, you should avoid them; but at other times, live in the sunlight all you can. Very rarely indeed is a child sunstruck; but it is wise to guard against it, because it is often fatal. As I have just told you, you must keep out of the direct rays of the sun when the day is very hot. It is well to carry a wet handkerchief, or several large green leaves in the crown of your hat. SYMPTOMS OF SUNSTROKE. The symptoms of sunstroke are stinging pains in the head, dizziness, weakness, confusion of sight, and in some cases, sickness at the stomach. The person becomes partly or wholly insensible and often moans or snores. Sometimes he has spasms.