Use of organic solvents for clearing (making transparent) the tissue was first mentioned more than century ago by German anatomist Werner Spalteholz.[12][13] But with some exceptions [13][14] (reviewed in [15]) was clearing techniques for whole 20th century almost forgotten. Their renaissance came in last decade, probably thank to spread of advanced techniques of fluorescence microscopy which allow optical sectioning of the specimen (confocal, multiphoton or light sheet microscopy).[15][16]