That light is capable of acting on muscular fibres, independently
of the influence of the nerves, was mentioned by several of the old
anatomists, but repudiated by later authorities. M. Brown Séquard has,
however, proved to the Royal Society that some portions of muscular
fibre--the iris of the eye, for example--are affected by light
independently of any reflex action of the nerves, thereby confirming
former experiences. The effect is produced by the illuminating rays
only, the chemical and heat rays remaining neutral. And not least
remarkable is the fact, that the iris of an eel showed itself
susceptible of the excitement _sixteen days after the eyes were removed
from the creature’s head_. So far as is yet known, this muscle is the
only one on which light thus takes effect.--_Phil. Trans. 1857._