THE SENSES. 219 



left-hand to the right. If an opening be made in an eye at its superior 

 surface, so that the retina can be seen through the vitreous humor, this 

 reversed image of any bright object, such as the windows of the room, 

 may be perceived at the bottom of the eye. Or stiil better, if the eye of 

 any albino animal, such as a white rabbit, in which the coats, from the 

 absence of pigment, are transparent, is dissected clean, and held with the 

 cornea toward the window, a very distinct image of the window com- 

 pletely inverted is seen depicted on the posterior translucent wall of the 



FIG. 381. Diagram of the formation of the image on the retina. 



eye. Volkmann has also shown that a similar experiment may be success- 

 fully performed in a living person possessed of large prominent eyes, and 

 an unusually transparent sclerotic. 



An image formed at any point on the retina is referred to a point out- 

 side the eye, lying on a straight line drawn from the point on the retina 

 outward through the centre of the pupil. Thus an image on the left side 

 of the retina is referred by the mind to an object on the right side of the 

 eye, and vice versa. Thus all images on the- retina are mentally, as it 

 were, projected in front of the eye, and the objects are seen erect though 

 the image on the retina is reversed. Much needless confusion and diffi- 

 culty have been raised on this subject for want of remembering that when 

 we are said to see an object, the mind is merely conscious of the picture 

 on the retina, and when it refers it to the external object, or ' 'projects''' 

 it outside the eye, it necessarily reverses it and sees the object as erect, 

 though the retinal image is inverted. This is further corroborated by 

 the sense of touch. Thus an object whose picture falls on the left half 

 of the retina is reached by the right hand, and hence is said to lie to the 

 right. Or, again, an object whose image is formed on the upper part 

 of the retina is readily touched by the feet, and is therefore said to be 

 in the lower part of the field, and so on. 



Hence it is, also, that no discordance arises between the sensations of 

 inverted vision and those of touch, which perceives everything in its erect 

 position; for the images of all objects, even of our own limbs, in the 

 retina, are equally inverted, and therefore maintain the same relative 

 position. 



Even the image of our hand, while used in toitch, is seen inverted. 

 The position in which we see objects, we call, therefore, the erect posi- 



