Human and mammalian body temperatures are constant. For example, people, regardless of spring, summer, autumn and winter, have a normal body temperature of 36.5 ℃, while dogs also have a fixed normal temperature. However, in the hot season, people can keep their body temperature constant by sweating and fanning. There are sweat glands on the surface of human and many animals, which secrete sweat, and heat is sent out to the body through the secretion of sweat.
Although the dog should maintain a constant body temperature, it has no sweat glands on its body surface. Its sweat glands grow on the tongue. So, in the hot summer, in order to maintain normal body temperature, the dog had to stick out its long, steaming tongue, through which the whole body heat was emitted. In fact, even if it's not in summer, dogs often stick out their tongues after running and fighting, and when their bodies are hot, they can regulate their body temperature by sweating.