Performing tracing studies on fixed rather than living tissues offer significant advantages. 

• They allow scientists to study systems and structures that would otherwise be difficult or impossible to access. For example, it’s impossible to access and study structures that are located deep within the brain in the human nervous system. The only way to study these systems and structures is with partially dissected or thick-slice preparations. 
• Fixed tissues can be kept for extended periods of time without fear of deterioration. This is important because diffusion is a relatively slow process so tissues often need to be kept for longer periods to allow the movement of the dye before viewing. 
• When fixed tissues are used, the dye is not internalized by labeled cells.