Unlike humans, dogs have no problem going barefoot in the snow. Freezing temperatures appear to have no affect. Dog mushers in the frozen north of Alaska have exploited the animals' ability for more than a hundred years but it's only now that scientists are able to explain how the dog protects its paws. 　　Gakuen University Professor Hiroyoshi Ninomiya: "Dogs exchange heat at the end of their legs, arterial blood flows to the end of their legs and then heats up venous blood before returning it to the heart. In other words, they have a heat exchange system in their feet." 　　Professor Hiroyoshi Ninomiya of Gakuen University in Tokyo says that heat exchange system is clearly visible in images of paw pad samples revealed by an electron microscope. The arteries which carry the warm blood from the heart are densely packed alongside the veins that carry oxygen-depleted blood in the opposite direction. Seals and dolphins have similiar heat exchange mechanisms and while it's common to most dogs, Professor Ninomiya says generations of breeding in some have depleted their ability to resist extreme temperatures. 　　Gakuen University Professor Hiroyoshi Ninomiya: "Dogs evolved from wolves, and so they still have some of that ancestry remaining. But that doesn't mean that one should go and drag around in the snow the entire time. There are many varieties of dogs nowadays that are not able to stand cold due to breeding." Most however are oblivious. For them, enduring the cold is no great feat. (Rob Muir/ Reuters)