Today surgeons can put us to sleep, cut us open, take out a bit of tissue here or there, put in another bit of tissue, metal or plastic, and sew up again. In the future they will be able to give us new arms or legs. They will be able to take out a diseased heart and put in an electric pump. This is the most important question in surgery today. Ought we to try to give people machines which will replace damaged parts of their bodies? Or ought we to try to give them “spare parts” from people who have died? We are working on both these ideas. We already have one kind of machine for the heart, a “pacemaker”. Sometimes the muscle, valves and arteries in a patient’s heart are quite healthy. But the nerves which should make it beat properly aren’t working well. The heart beats too fast or too slowly. So we put a pacemaker in the body, near the heart. It sends small regular electric shocks through the heart, at the right pace for the heart-beat. Then the heart works in the proper way. The electricity comes from a very small battery. That lasts two or three years. After that time, the surgeon has to operate again and put a new battery in. But the latest pacemakers don’t have a battery. They have a very small nuclear power station. It will work for at least ten years. 1. The most important question in surgery today is to ________.