2014英语四级听力练习慢速4.1(2)_大学英语听力

2014英语四级听力练习慢速4.1(2)

　　Laser-Beam Scanner Tests for Malaria

　　Researchers have developed what they are calling the first non-invasive method of identifying a malaria infection in the human body. They are now using a laser beam scanner to test for the disease without opening up the body. The test is painless, does not require blood from a person, and appears to be right every time it is done.

　　Currently, medical workers study a blood sample under a microscope for evidence of the deadly parasite. The test requires a trained technician, costly equipment and time -- things that are not always available in poorer countries.

　　The new device only requires a person to place a finger on a laser device. Dr. Dmitri Lopotko is a researcher at Rice University in Houston, Texas.

　　We shine a very short light pulse through the skin. And this light pulse is absorbed only by malaria parasites because of the wavelength we use. And in response to this short light pulse, the parasite literally explodes.

　　The light comes from a low-powered laser. The device has less power than a laser pointer. It shines on a very small particle called hemozoin. The malaria parasite produces the particle after it has infected red blood cells. Hemozoin crystals are not found in normal red blood cells.

　　As the laser heats the crystals, they create small bubbles inside infected cells. Dr. Lopotko says the bubbles explode, and then make a sound that scientists can hear and count.