He is the more important, also, because he is so common.

Statistics are lacking, but possibly half of the entire human family in civilized life are visual in their type for most of the language functions.

This is due, no doubt, to the emphasis that civilization puts upon sight as the means of social acquisition generally, and to our predominantly visual methods of instruction.
The third fact mentioned is also illustrated by this type; the fact that mental instruction and derangement may come easily, through the stress laid upon vision in the person's mental economy.

I need not enlarge upon the different forms of special defect which come through impairment of sight by central lesion or degeneration of the visual centers and connections.

Suffice it to say that they are very common, and very difficult of recovery.