protargol
/prəʊˈtɑːɡɒl/Medicine and Biology
noun
A colloidal combination of protein and silver salts, used originally as an antiseptic and later chiefly as a stain for light and electron microscopy.
Origin
Late 19th century; earliest use found in The Lancet. From German Protargol from Prot- (in Protein) + classical Latin arg- + German -ol.