13. Neurons of rat spinal cord by silver stain. This staining method was first introduced by Camillo Golgi and developed by Ramón y Cajal for the study of nervous system. It is achieved by fixing black micro-crystallization of silver chromate, from reacting silver nitrate with potassium dichromate, in the neural membrane.The neurons stained in this image are likely motor neurons (not for sure), which project their axons to the muscles and transfer the signal from spinal cord to muscles to control movement.
(Image credit: Zuzanna K. Filutowska /WIKIMEDIA)