[ 2006-11-15 12:49 ]
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.
（北京语言大学通讯员柴宇迪供稿 英语点津 Annabel 编辑）