1Attributive and (now rarely) in the genitive. Designating a method of fixing and staining nerve tissue to identify degenerating myelin, which is selectively stained black; especially in "Marchi method", "Marchi technique". Also: designating the combination of reagents (a solution of potassium bichromate and osmium tetroxide) employed in this method.
2Attributive Employing, or resulting from the use of, the Marchi method.
Early 20th century. From the name of Vittorio Marchi, Italian physician, who published the method in 1897.