第三篇 Many science reports discuss medical studies that test the effect of a new drug. Usually, a large number of people is divided into two groups. Each group takes a different substance. But no one knows which group is getting which substance. One group takes the medicine being tested. Another group takes what we call an inactive substance. Medical researchers call this substance a 'placebo.' The word 'placebo' is Latin for 'I shall please.' Placebo pills(宽心丸)usually are made of sugar. Using placebos to test drugs sometimes has a surprising result. Researchers say people taking the placebo often report improvements in their health. This is known as 'the placebo effect'--pain that is eased or stopped by an inactive substance. In such testing, the drug must perform. better than the placebo to prove that it is effective. Doctors have reported that the placebo effect can be used in treatment. For example, a doctor tells a patient that a new drug will stop the pain in his leg. The pill is only sugar. But the patient does not know that. He takes the pill and says his pain is gone. Scientists are beginning to discover some physical reasons for this reaction in some people. They are learning that much of what people believe to be true comes from what the brain expects is going to happen. If the brain believes a drug will ease pain, the brain may begin physical changes in the body that can cause the expected effect. A recent examination of studies on drugs for depression found that placebos eased the depression about as well as the active drugs. Other studies have explored the power of placebos. A study in Japan involved thir people who reacted to the poison ivy (常青藤)plant. Poison-ivy causes red itchy sores(伤痕)on some people who touch it. Each person was rubbed on one arm with a harmless leaf, but was told it was poison ivy. Each person was then touched on the other arm with poison ivy, but was told it was a harmless leaf. All thir people developed a reaction on the arm where the harmless leaf touched their skin. Only two reacted to the poison ivy leaves. Doctors and scientists worry that the use of placebos may not always be harmless. They say people can become victims of false doctors and others who use placebos to claim they can cure disease. What do medical researchers usually use to make placebo pills?