Many mammals (39)______________ the winter through the process of hibernation (from the Latin word meaning winter). One type of hibernation is known as (40)______________ hibernation. This is brought about by the activation of a (41)___________ called H. I.T. in the animal' s blood. The temperature of the animal falls and metabolism is (42)____________ The respiratory and heart (beat) rates (43) ___________ dramatically and the temperature falls (44)__________________________________________. However, the animal will be awakened by a special control system if it is danger of freezing and may also wake for a short to excrete waste substances or to eat.

       (45)______________________________________________________________  . Energy is provided at the end of hibernation by the animal's store of brown fat. Some creatures do not actually hibernate, but enter a state of torpor. They show similar metabolic changes, (46)