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.

We shall probably never attain the power of measuring the velocity of nervous action; for we have not the opportunity of comparing its propagation through immense space, as we have in the case of light.

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.

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 essential attribute of a new sense is, not the perception of external objects or influences which ordinarily do not act upon the senses, but that external causes should excite in it a new and peculiar kind of sensation different from all the sensations of our five senses.

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 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.