Cell cannot remain alive outide certain limit of temperature and much narrower limit mark the boundarie of effective functioning. Enzyme ytem of mammal and bird are mot efficient only within a narrow range around 37C;a departure of a few degree from thi value eriouly impair their functioning. Even though cell can urvive wider fluctuation the integrated action of bodily ytem are impaired. Other animal have a wider tolerance for change of bodily temperature.
For centurie it ha been recognized that mammal and bird differ from other animal in the way they regulate body temperature. Way of characterizing the difference have become more accurate and meaningful over time, but popular terminology till reflect the old piion into warm-blooded and cold-blooded pecie; warm-blooded included mammal and bird wherea all other creature were conidered cold- blooded.
A more pecie were tudied, it became evident that thi claification wa inadequate. A fence lizard or a deert iguana-each cold-blooded----uually ha a body temperature only a degree or two below that of human and o i not cold. Therefore the next ditinction wa made between animal that maintain a contant body temperature, called home0therm, and thoe whoe body temperature varie with their environment, called poikilotherm. But thi claification alo proved inadequate, becaue among mammal there are many that vary their body temperature during hibernation.[由wWw.HaozuoWen.com整理]