Hæm`a*cy"a*nin (-sī"&adot;*n&ibreve;n), n. [Hæma- + Gr. ky`anos a dark blue substance.] (Physiol. Chem.) A substance found in the blood of the octopus, which gives to it its blue color.

&fist; When deprived of oxygen it is colorless, but becomes quickly blue in contact with oxygen, and is then generally called oxyhæmacyanin. A similar blue coloring matter has been detected in small quantity in the blood of other animals and in the bile.