1. Volta, ‘Colezione del'opere’, Tome 2, Vol. 2, p. 124.
2. Purkinje, J., ‘Beiträge zur Kenntnis des Sehens in subjektiver Hinsicht’, 50 (Prague, 1819). Purkinje excited ‘Galvanic light patterns’ (stripes and arches) with a voltaic cell of 20 V.
3. Penfield, W., and Rasmussen, T., ‘The Cerebral Cortex of Man’, 140 (New York, 1955).
4. Knoll, M., Psychol., 17, 110 (1958).