How long has ice been in your bloodstream?

Birds get cold feet - why ducks and penguins don't freeze, but our tongues do

Ducks and other birds can troll around on icy ground without risk in winter and also linger on the spot. But if a person were to stand barefoot on a frozen lake, he would not be able to move from the spot in a short time. So how do birds do it, what is the difference between a duck's foot and a human foot?

Heat exchange in the duck foot

We humans also know the trick that the ducks use. In modern houses, so-called heat exchangers ensure energy savings. The residual heat from exhaust air and wastewater in buildings is used to preheat fresh water or air. Ducks have built-in heat exchangers in their legs. The cold blood from the feet flows in the veins back to the heart. The veins run parallel and closely intertwined with the arteries that bring warm, oxygen-rich blood from the heart. In this way, the venous blood pre-cools the arterial blood and the arteries warm up the blood flowing back in the veins using the counterflow principle. So the ducks always have cold feet. On the one hand, this saves energy that would otherwise be given off by the feet to the environment. On the other hand, it ensures that ducks cannot freeze onto ice surfaces. To do this, it would be necessary for the duck's feet to heat the ice and melt it, like a human foot does. This thawed ice could quickly cool down again in the cold environment and freeze the duck in the process. Nature has once again achieved an impressive development here.

Freezing a tongue on a metal rod

An effect with a similar starting position can lead to a lot of laughter but also pain in the school yard or while skiing. Many people are tempted to lick frozen metal bars with their tongues. It happens very quickly that you can no longer get away with your tongue. She is frozen! Physically, the following happens: The metal is very cold, the tongue is very warm. There is always a little spit on the tongue. If you hold your wet tongue against the cold metal, the saliva at the tongue-metal contact point can cool down very quickly. Because metal is a very good conductor of heat, it can quickly dissipate the heat of the tongue from the contact point. This freezes the saliva and acts like a cold glue. Because the tongue has many small pores into which the ice crystal extends. You can no longer get off the rack. At least not without pain. To get out of this predicament, one must try to break the contact by warming up. Good for those who happen to be carrying a warm liquid in a thermos. The others either have to warm the bar near the tongue with their hands or rely on outside help.