1. If the concentration of choline esterase is determined at different sections from the head to the caudal end of the electric organ of Electrophorus electricus (Linneaus) S-like curves are obtained. These curves are essentially the same as those which show the number of electric discs per centimeter and the E.M.F. per centimeter.
2. In the organ of Hunter the concentration of the enzyme does not differ from that in the adjacent parts in the main organ. This again coincides with the observations on the number of plates per centimeter in this organ.
3. The concentration of the enzyme was determined in different parts of the brain and the spinal cord and compared with that in a gold fish. The concentrations here are of the same order, but in the spinal cord of the eel the concentration is even lower than in the gold fish. As the cell bodies of the nerves innervating the electric organ in the spinal cord, these results do not lend support to the assumption of a special concentration of the enzyme in these nerves.
4. In the muscles adjacent to the electric organ an enzyme concentration has been found which is of the order of that in the electric tissue itself and much higher than in ordinary striated muscles.
5. The suitability of the organ for the preparation of enzyme solutions has been investigated and compared with that of the organ of Torpedo.