Tyrian purple the Iles Purpuraires at Mogador, in Morocco. The sea snail harvested at this western Moroccan dye production facility was "Hexaplex trunculus" (mentioned above) also known by the older name "Murex trunculus". This second species of dye murex is found today on the Mediterranean and Atlantic coasts of Europe and Africa (Spain and Portugal, Morocco, and the Canary Islands). The colour-fast (non-fading) dye was an item of luxury trade, prized by Romans, who used it to colour ceremonial robes. Used as a dye, the color shifts from blue (peak absorption at 590 nm, which is yellow-orange) to reddish-purple (peak absorption at
Sabin–Feldman dye test (negative result). The dilution of the test serum at which 50% of the tachyzoites are thin, distorted and colorless is reported as antibody titer of the test serum. The test is highly sensitive and specific with no false positives reported so far. Drawbacks of this test: 1. Difficulty in maintaining the live tachyzoites. 2. It detects immunoglobulin G(IgG) antibodies, hence cannot differentiate between recent or past infection. Sabin–Feldman dye test A Sabin–Feldman dye test is a serologic test to diagnose for toxoplasmosis. The test is based on the presence of certain antibodies that prevent methylene blue dye from entering the