Robert Bentley Todd's contribution to cell theory and the neuron doctrine

Robert Bentley Todd, who is best remembered for "Todd's paralysis," made many more important contributions to neurology and neuroscience, including the concept of brain electricity and electrical discharges in epilepsy. He was also a pioneering microscopist and we here review his neurohistological studies and his contributions to the application of Schwann's (1839) cell theory to the nervous system and the later neuron doctrine, as described in his textbook The Descriptive and Physiological Anatomy of the Brain, Spinal Cord and Ganglions (Todd, 1845), his Cyclopaedia of Anatomy and Physiology (1847) and his joint textbook with William Bowman The Physiological Anatomy and Physiology of Man (1845). Writing in the mid-1840s, Todd acknowledged that the "vesicles" he observed corresponded to the earlier descriptions of "globules" or "kugeln" by Valentin and which Schwann first interpreted as cell bodies. Todd was among the first to recognize that nerve cell bodies were in continuity with axons ("axis cylinders"), sometimes associated with "the white substance of Schwann" ("tubular" fibers), or sometimes without ("gelatinous" fibers). He also described continuous nerve cell branching processes, later called dendrites. He was the first to recognize the insulating properties of Schwann's "white substance" (myelin) to facilitate conduction. Influenced by his contemporary, Faraday, Todd was also the first to develop the functional concept of dynamic polarization ("nervous polarity") to explain nerve cell conduction.