Improved methods for cobalt filling and silver intensification of insect motor neurons

A Parafilm disk floating on saline and bearing a drop of cobalt solution in which the nerve stump is bathed provides a convenient and versatile method for in vitro or in vivo filling of neurons for cobalt sulfide staining. Silicone grease around the edge of the disk provides an effective seal around the nerve as it passes between the two solutions. Using a modified developer, silver intensification of cobalt sulfide stained neurons may be done in the light at room temperature, and the time of optimum intensification may be observed under a dissecting microscope.