托福考试阅读材料之Bat Spit

　　Anyone who reads gothic fiction will tell you that vampires are bad news. People who read modern medical journals, however, might disagree–in fact, they think vampires just might help save lives.

　　The kind of vampire I’m talking about is Desmodus rotundus, commonly known as the “vampire bat.” Yep, these little creatures are real; and even though they almost never turn into suave Romanian counts to drool over, they do drool a lot themselves. That’s because their saliva is an essential part of their dining habits.

　　When a vampire bat latches onto, say, a steer, it needs to keep the blood flowing from the puncture made by its teeth. That’s achieved by a natural anti-coagulant in the vampire bat’s saliva. Despite what you see in the movies, vampire bats almost never drink human blood. But people do suffer from other blood problems–a leading one being stroke.

　　Stroke is caused by a clotting in the blood which stops the flow and can starve areas of the brain of oxygen. Doctors have generally broken up clots with a compound called tPA. TPA works okay, but it has dangerous side effects, and can even hurt brain cells.

　　A better idea? Bring in the bats, says researcher Robert Medcalf, a biochemist from Australia. Vampire bat spit contains a different compound, DSPA, which does the good things tPA does with far fewer side-effects. DSPA is now being tried on patients who have suffered a stroke; the data should be in within a year. If it works, doctors might have found an unlikely friend–the vampire bat.