Page:Mind (Old Series) Volume 9.djvu/105



The problem of the relation of right- and left-sidedness to the more general law of bilateral symmetry has not yet been studied with the method or comprehensiveness which it requires and which is now possible. The vast clinical, physiological, popular, and historical literature upon the subject (of which we are preparing a bibliography), presents so much interesting material that before recounting our own studies, we must first briefly resume some of the more important results now claimed.

It has been said, on a basis of more or less careful and averaged measurements or other observations, that the right and left eyes often have slightly different near and far points and different powers of accommodation and discrimination, both of form and colour; that the bulbi have different degrees of rotary mobility and the pupils unlike apertures; that it makes a difference in apparent projection-distance whether an object be seen with the right or left eye, so that we ought not to say identical points with reference to an object, but coincident points, as if the retinae were laid one within the other like two cups; that if we point at an object with both eyes open we shall find, on closing each eye alternately, that we have instinctively pointed in the line of the right eye, or vice versa, if we are left-handed; that the outer angle which a vertical makes with a horizontal line in monocular vision seems greater by about half a degree for the left than for the right eye; that the error in putting the finger through a ring is greater when the right than when the left eye is closed, so that a true, mean, cyclopean eye would be slightly to the right of the median line; that in short the right eye is commonly the best for microscopic or macroscopic work, and is less liable to many forms of disease and congenital defects. And yet, though an expert stereoscopist does not usually mistake patterns a part of which is presented to each eye for those that are monocular (with only a tabula rasa before the other), the two eyes are of course so intimately connected that they probably act from one root and practically as one organ, and only disease or artifice can make their axes diverge or move asymmetrically up or down. Their motor seem regulated by their retinal functions, so that, according to Ludwig, if the retinae are