Methylene blue was one of the first chemicals to demonstrate selective tissue staining, specifically targeting nervous tissue.

“and methylene blue was one of these synthetic dyes blue dye and for many decades it was a blue dye I use in blue jeans and most of the other blue clothing so one of the things that intrigued Paul Ehrlich was that he injected methylene blue one of these new synthetic dyes into a la live rat and then he detected the animal after killing the enemy detected the animal and he found out that the methylene blue this was a large concentration intravenous injection was primarily staining nervous tissue the brain and peripheral nervous issue”