ABSTRACT
Records were made from the hind-brain of 15-cm tench (Tinea tinea, Osteichthyes) by the use of capillary micro-electrodes. At the completion of recording the electrodes were left in position and the site of recording was marked by the following method. The Ringer bathing the brain was replaced by a mixture of equal parts of 110 mM FeCl3 and Ringer. After 4 h, ferrocyanide ions were released electrolytically from the micro-electrode. The electrolyte in the micro-electrodes was 2·5 M KCl+0·5 M Na4Fe(CN)6. The optimum quantity of electricity for the electrolysis was found to be 2× 10-4 coulombs. The brain was then fixed overnight in 90% alcohol, sectioned at 20 μ, and stained with eosin.
Precipitates of Prussian blue about 20 μ, in diameter were found at the site of the electrode tip.
