Intensification of cobaltous sulphide precipitate in frog nervous tissue.

Dorsal and ventral roots of the frog's spinal cord were filled with cobaltous chloride through axonal transport. Following incubation in different buffers saturated with H2S, the resulting CoS was intensified with two kinds of physical developers, the one containing gum arabic, the other tungsto-silicic acid as protective colloid. Optimum circumstances for CoS formation were found at high pH values in model experiments. NaOH and CuSO4 pretreatments of tissues enhanced the intensification power of the physical developer containing tungsto-silicic acid. The structural integrity of tissues was best preserved when phosphate buffers saturated with H2S were employed to precipitate cobalt in histological specimens. Of the two developers the one containing gum arabic gave a finer staining of neural elements, but its intensification effect was somewhat capricious. Histological results suggested that within the range of cobalt transport (10-20 mm), neural elements filled with cobalt were quantitatively and selectively shown. At the present state of experiments neural elements with a process to the periphery are only accessible to staining with this technique.