Haem·a·cy·a·nin n.  Physiol. Chem. A substance found in the blood of the octopus, which gives to it its blue color.
 Note: ☞ When deprived of oxygen it is colorless, but becomes quickly blue in contact with oxygen, and is then generally called oxyhaemacyanin. A similar blue coloring matter has been detected in small quantity in the blood of other animals and in the bile.

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