TONY CRADDOCK / SCIENCE PHOTO LIBRARY TONY CRADDOCK / SCIENCE PHOTO LIBRARY
Thermometer. Multiple exposure image of a clinical thermometer with a scale in degrees celsius; the normal body temperature (37 degrees celsius) is marked by an arrow. A thermometer consists of a narrow, sealed tube with a bulb of mercury at one end (not seen here). As the mercury warms up, it expands up the tube in proportion to its temperature. The temperature can then be determined by reading off the mercury level against a scale. A patient's temperature is usually taken by inserting a thermometer into their mouth. A high or low body temperature may indicate illness, organ malfunction or exposure to extreme environmental conditions.
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