There are a large number of animals that cannot maintain their body temperature. Their body temperature goes up or down according to the rise or fall of the environmental temperature. Such animals are called cold blooded or polkiothemal. Among vertebrates, fish frog and lizards are cold blooded. But higher vertebrates, i.e., birds and mammals, can regulate their body temperature so as not to allow it to fluctuate too much according to the rise and fall of environmental temperature. Those that can regulate their body temperature are called homoiothermal or warm blooded. There is a temperature controlling centre in their brain.
If the environmental temperature rises, warm blooded animals may have to resort to means whereby there can be some cooling effect. For example, when the environmental temperature rises to 41 degree Celsius, we begin to perspire, which has a cooling effect. But perspiration will lead to the loss of water for the body. Animals living in deserts cannot afford to lose water.
This is the reason why camels, instead of perspiring in the hot sun, prefer to raise their body temperature to 42 degree Celsius to bring it in tune with the environmental temperature. Otherwise, camels would have resorted to perspiration, and this would have meant loss of water from the body. On the other hand, if the environmental temperature drops, there may be shivering this sets the muscles in motion. Muscular movement generates some body heat and in this way the loss of body heat as a result for environmental cooling is countered.