英语时差：身体被冻时发生的变化（上）

Although Jack Frost nipping at your nose can be the subject of happy, winter songs, actual frostbite is nothing to smile about. Frostbite occurs when your body can no longer keep your skin warm, and your living tissues begin to freeze. Here’s what happens. As the air temperature starts to drop, your body conserves its heat by restricting the flow of blood to your skin, concentrating your warm blood inside. You’ll appear paler, and you’ll wrap your jacket more tightly around your shoulders. If the air temperature continues to drop below freezing, your exposed skin or extremities might become too cold. When this happens the blood vessels in the endangered areas open wide again, and blood flow increases. This extra dose of warm blood from inside your body keeps your skin from freezing, although it cools your overall body temperature.