2017届高考英语二轮专题复习精品之A breathtaking trick potentially left over from our ancestors might be found in us — the ability to sense oxygen through our skin.

　　Amphibians(两栖动物), animals such as frogs that can live both on land and in water, have long been known to be capable of breathing through their skin. In fact, the first known lungless frog that breathes only through its skin was discovered recently in the rivers of Borneo.

　　Now the same oxygen sensors found in frog skins and in the lungs of mammals have unexpectedly been discovered in the skin of mice.

　　“No one had ever looked,” explained Randall Johnson, a biologist researcher.

　　Mice and frogs are quite distant relatives, so the fact they have these molecules (分子) in common in their skin suggests they might well be found in the skin of other mammals, such as humans.

　　“We have no reason to think that they are not in the skin of people too,” Johnson said.

　　These molecules not only detect oxygen, but help increase levels of vital red blood cells, which carry oxygen around the body. Normal mice breathing in air that is 10 percent oxygen—a dangerously low level similar to conditions at the top of Mount Everest, and about half that of air at sea level. However, mice that had the oxygen sensor HIF-1 a genetically removed from their skin failed to produce this hormone (荷尔蒙) even after hours of such low oxygen.

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