不知您注意过没有，我们胳膊上、腿上的血管看起来都不是红色的，而是呈现出近似于青色、蓝色的颜色。这又是什么原因呢？原来，都是波长惹的祸。

Surprisingly, the reason why the blood in our veins looks blue only emerged in 1996 following research done by the physicist Dr. Lothor Lilge and his colleagues at the Ontario Laser and Light Wave Research Centre of Canada. They showed that when light strikes white skin, the longer, redder wavelengths penetrate deeper, and are absorbed by the blood vessels. As a result the light reflected back from the skin covering a blood vessel has a relatively higher proportion of the shorter wave lengths which gives it is blue-purple tinge. The veins of people with dark skin don't show this effect so strongly because the skin's melanin absorbs almost all wavelengths of light on the skin's surface.

The reason we go red rather than blue when we blush is because of the relative depths of the blood vessels affected. According to Dr Lilge, a vein has to be at least 0.5 mm below the skin's surface to look blue .The small capillaries that fill up with blood when we blush are much closer to the skin's surface and so look red.

capillary: 毛细管