To speak, therefore, of an electric current in the nerves, is to use quite as symbolic an expression as if we compared the action of the nervous principle with light or magnetism.

It is exceedingly improbable that the identical action of the corresponding parts of the two retina is the result of a certain habituation, or of the influence of the mind.

The cooperation of the two retina in one field of vision, whatever is its cause, must rather be the source of all the ideas to which single or double vision may give rise.

A good physiological experiment like a good physical one requires that it should present anywhere, at any time, under identical conditions, the same certain and unequivocal phenomena that can always be confirmed.

To speak, therefore, of an electric current in the nerves, is to use quite as symbolic an expression as if we compared the action of the nervous principle with light or magnetism.

The sense organs experience the external light, sound, etc. with difficulty; the different sense organs only have a so-called specific receptivity for particular stimuli.

Sensation is not the conduction of a quality or state of external bodies to consciousness, but the conduction of a quality or state of our nerves to consciousness, excited by an external cause.