ANIMAL MECHANISM. 129 



of vision, till it finally becomes totally useless : hence one 

 is doubtful, at times, which way the cross-eyed person is 

 4 looking, from a want of parallelism in the motions of the 

 eyes. When the wandering eye is exclusively attended 

 to, the vision appears unimpaired. The image is well 

 painted in the natural one, but weak in the other, solely 

 because the place of the image does not correspond with 

 the place of the image in the first. The mind, instinct- 

 ively, therefore, is devoted to the eye that gives the live- 

 liest impression, to the entire neglect of its aberrating 

 fellow. 



THE REASON WHY THE PUPILS OF AN ALBINo's EYES 

 ARE RED. 



If a person is born without the pigment um nigrum, 

 heretofore defined to be a paint to suffocate all unneces- 

 sary light, as it goes through the retina, after the image 

 is formed, the blood vessels of which the tunica choroides 

 or second coat is made, are not hidden. Consequently, 

 they show through the transparent humors, like a spark- 

 ling red gem, the size of the diameter of the pupil. If 

 a delicate brush could be inserted to give it a black coat 

 of paint, the eye would appear as others do. Such per- 

 sons can see better in a weak light than in broad day, 

 because the brightness of the sun's light dazzles, and 

 produces a tremulous motion in the whole organ. As an 

 evidence that this redness is caused by the blood in the 

 vessels, after death, when it coagulates, the redness, in a 

 great measure, disappears. White rabbits, white mice, 

 brought in cages from China, besides a vast variety of 

 birds, have no pigment on the choroides } and are there- 

 fore distinguished for red pupils. The existence of the 

 pigmentum nigrum, is a concomitant of a. day-seeing eye. 

 In man, the want of it, constituting the albino, is an 

 anomaly. 



A morbid action of the absorbents sometimes removes 

 the paint, and the pupil, to the surprise of observers, be- 

 comes scarlet. A partial absorption of it is often the 

 cause of a diminution of the original powers of vision : 

 under such circumstances, the pupil assumes a bronze 

 hue, accompanied by a debility and tremor of the globe 

 under the influence of a moderate degree of light, 



