So they lick saliva onto their forearms where there is a network of blood vessels close to the surface of the skin and, as the saliva evaporates, their blood is cooled. This thermal image shows just how effective the process is. The blue areas on the body are the cooler parts. As the saliva dries it has to be replaced and this is a real drain on the kangaroo's body fluids. Even in the shade the earth is baking hot so the kangaroos dig away the warmed topsoil to get at the cooler ground beneath. By staying in the shade and licking to control their body temperature kangaroos manage to get through the hottest part of the day without heat stroke.


所以，它们用唾液给自己的手臂降温，因为手臂上有靠近皮肤表面的血管，唾液蒸发的同时，血液也同时得以冷却，这张热敏图，清楚显示出这个过程的效果，身体的蓝色区域温度明显降低，唾液蒸发之后必须继续补充，这构成了袋鼠体液的排放过程，即使是在树荫下地面也是灼热的，所以袋鼠刨掉地面干热的表层，以便接触到下面较凉爽的部分，躲到树荫下，舔自己的皮肤来降温，袋鼠通过这些办法，度过一天中最热的时间，而没有中暑。