1. Murr, L. E., Nature, 200, 490 (1963).
2. Murr, L. E., Proc. Penn. Acad. Sci., 37, 109 (1963).
3. Murr, L. E., Nature, 201, 1305 (1964).
4. Jorgensen, I., and Priestley, J. J., J. Agric. Sci., 6, 337 (1914).
5. Shibusawa, M., and Shibata, K., J. Elect. Eng. (Japan), 473, 1 (1927).