Blood is red to the naked eye. under a microscope, it depends.
This is not because it is not really red, but because its redness is a macroscopic feature. Human blood is red because hemoglobin, which is carried in the blood and functions to transport oxygen, is rich in iron and red in color.
Octopuses and horseshoe crabs have blue blood. This is because the protein that carries oxygen in the blood, hemocyanin, is actually blue.
A Vulcan’s blood is green, according to the story anyway, and this is presumably because the oxygen-carrying material in the Vulcan’s blood is green.
but our blood is red. it is bright red when the arteries transport it in its oxygen-rich state throughout the body. and it’s still red, but darker now, as it reaches the heart through the veins.
I bring this up because I’ve realized that there are a good number of people, some of the seventh graders my son goes to school with, some of the teachers too, who should know more, as well as a lot of people who have posted online, which say that the blood inside the body is sometimes blue.
blue?
here is some evidence that this is not true.
When I was 12 years old, I had an accident and my left wrist was torn so I could see into my arm. everything was red. blood shot out of my arteries and out of my veins. and everything was red.
here is another test. if you have blood drawn, the fluid that comes out of your vein into the vacuum-sealed container is distinctly red.
We also know why it’s red, as already noted. it is red due to red blood cells (hemoglobin). the blood changes color slightly as oxygen is absorbed and replenished. but it does not change from red to blue. changes from red to dark red.
It is true that the veins, which are sometimes visible through the skin, may appear bluish. Why is it like this? click here for the full story. but the bottom line is this: it has to do with the way the fabric absorbs, scatters and reflects light. (I think this also explains why your lips look blue when you’re cold.) but if you were to open one of your veins or cut your lip, even when you’re cold, there wouldn’t be any blue in the liquid that would gush out.
perhaps it is the fact that the veins look bluish that explains the myth that blood is blue when it flows through the veins?
or could the answer lie elsewhere? By convention, arteries are drawn in red in textbooks and veins in blue. could it be that people have taken this as a guide to its actual color?
I think this is worth understanding. it is a politically neutral example of a bit of falsehood that seems resistant to information. At a time when ignorant people openly challenge scientific knowledge on such important issues as the safety of vaccines or the dangers posed by burning fossil fuels, it seems worth trying to understand why some bad ideas are so immune. to review.
here is a hypothesis: the problem is not absolute ignorance. You can imagine children, who may never have seen an accident, cut themselves, had their blood drawn, or taken a biology class, who might gullibly believe that blood is blue, because someone told them so. even people who have been cut, or who have witnessed the scene of an accident, or who have had their blood drawn, cling to the conviction that blood is at some point blue. such conviction and confidence when everything, when all the evidence speaks against it, can only be the result of some prejudice or bias. but what? why?
It turns out that a little knowledge can be a dangerous thing. it is hard to refute a falsehood when it seems to fit so perfectly with other true, though misunderstood, propositions. that’s what’s going on here, it seems. take a little blood chemistry, textbook exposure, and the sight of your own bare arms, and you’ve got a perfect ecosystem in which to nurture a manifestly false belief.
thanks to ulysses noë for participating in this discussion.
alva noë is a philosopher at the university of california, berkeley, where she writes and teaches about perception, consciousness, and art. He is the author of several books, including his latest, Strange Tools: Art and Human Nature (Farrar, Straus, & Giroux, 2015). you can follow more of what alva is thinking on facebook and twitter: @alvanoe
