大自然赋予北极熊一项防御严寒的高超本领，给了它一个奇妙的热防护系统，即使气温极低，也能够确实保证严寒不会侵入体内。这个奇妙的系统，它的基本结构其实又很简单：一层浅色透明的外皮，下面是一层深色厚实的内皮，太阳光可以透过外皮照射到内皮上，内皮能够起到吸热器的 Nature gives polar bears a superb defense against the cold, giving it a fantastic thermal protection that will ensure that cold will not invade the body, even at extremely low temperatures. This wonderful system, its basic structure is actually very simple: a light-colored transparent skin, the following is a layer of dark thick endothelium, the sun can shine through the skin to the endothelium, the endothelium can play a heat sink of