All boys use jack-knives, and now and then inflict cuts upon themselves. As a rule, these do not amount to much, and only require to be washed with cold water and bound up with a clean rag; but, if a vein or artery is severed, there is great danger. [Illustration: THE HEART.—(a) _The Left Ventricle_, (m) _the Left Auricle_, (b) _the Right Ventricle_, (n) _the Right Auricle_, (g, o) _Veins to Heart_, (k) _the Pulmonary Artery_, (c) _the Great Aorta_.] HOW TO TREAT A BLEEDING ARTERY. If an artery is cut, the blood will be bright red, and will come out in jets, corresponding with the throbbing of the heart. As the arteries take the blood from the heart, the proper thing to do is to press the thumb strongly upon the artery just above the wound. Then a handkerchief should be knotted around the arm or leg, as the case may be, above the hurt; a stick placed under the bandage, and twisted about until the flow of blood is stopped. This will answer until the surgeon can be brought. CUT VEINS AND BROKEN LIMBS. The veins carry the blood back to the heart. If one is cut the blood is dark and flows steadily. It is managed more easily than an artery; all that need be done is to place some lint over the wound and bandage it firmly. This, of course, you will do as soon as possible. If you should be so unfortunate as to break or dislocate a limb, assume an easy position and calmly await the coming of the surgeon. If a finger only is fractured you can walk to his office. * * * * * What is said of this little book? To what are we liable and what should we know? What should be cultivated? What is the rule concerning a blister which may form on any part of the body? What is a good thing for boils? For the stings of insects? For slight burns? What is the remedy for continued bleeding at the nose? What is the proper course if your clothing should take fire? What should be done with a person when he faints? What is a boy apt to do when his ears or feet are frost-bitten? Give the proper course to be followed. What should be done with a slight cut? How can you know that an artery has been cut? What must be done? What is the office of the veins? What need be done if one of them is wounded? Suppose your arm or leg is broken, what is the proper course? If it is only a finger? [Illustration: THE NERVOUS SYSTEM.] CHAPTER XV. THE NERVES, BRAIN, SPINAL CORD, ETC. The muscles which move the bones are themselves moved by the nerves. The nerves are soft and pulpy in youth, but harden as you advance in years. They are composed of a gray substance, called the nerve-cell, and a white substance, known as the nerve-fibre.