If veins carry dark red blood, and the vessels themselves are transparent, why is it that in the arms, hands, and legs of fair-skinned people they nonetheless look blue? After carefully studying how light travels through skin, some Canadian researchers have come up with a surprisingly simple answer to this commonly asked question.
Lothar Lilge, a physicist at the Ontario Laser and Light Wave Research Center in Toronto, and his colleagues approached the problem by setting up a simulated version of blood vessels near the skin’s surface. They filled glass tubes of varying sizes with blood and immersed them in a milk-like fatty fluid that was chemically very similar to light-colored skin in the way it transmits and reflects light. As they lowered the tubes into the fluid, the tubes gradually changed color. Right at the surface, they look red, says Lilge. But when you start lowering them down, the ...
