Page:Popular Science Monthly Volume 53.djvu/385

Rh Right Eye of the Commander, tells how a whole settlement was well-nigh ruined through its benevolent chief purchasing a staring glass eye from an astute Yankee trader. According to the narrative, this so altered the expression of the commander that even his intimates began to fear him, and it soon became rumored among the Indians that he was possessed with a devil. Possibly the uncanny effect produced by an ill-fitting glass eye is enhanced by its stony stare, resembling that of the abhorred serpent.

Emotion is largely shown in the eye—as elsewhere—through the medium of the sympathetic nerves. These are almost always outside the direct control of the will. One of their chief functions is to regulate the caliber of the blood vessels. Many people are painfully conscious that they are quite unable to keep themselves from blushing. When we blush, the sympathetic ganglia in the neck which control the facial circulation allow the small arteries to dilate, and hence the surface of the skin becomes suffused with red. Now the front surface of the eyes, although apparently non-vascular, is really filled with a network of microscopic canals containing a clear fluid. These are so minute that even the tiny red corpuscles of the blood can not enter them except under exceptional circumstances. Nevertheless, they, like the other channels of the circulation, are controlled by the sympathetic nerves, and when these give the command they become distended with lymph so as to lend to the cornea and conjunctiva a tense glistening aspect. We all know that the eyes become bright under the influence of fever, and this is obviously because the tiny lymph channels, like the larger vessels which convey the blood to the skin, are dilated and full of fluid. This, I think, is a satisfactory proof that the glistening of the eye does not wholly depend upon the muscular pressure from without. Not only do the sympathetic nerves regulate the brightness of the eyes in the manner above mentioned, but they are also the agents in bringing about changes of expression due to the enlargement or contraction of the pupil. Perhaps it may be as well to remind those of my readers who have not studied the anatomy of the eye that the pupil is a little window admitting the light to the ocular chamber, and that its diameter is regulated by the involuntary muscular fibers of the iris. Until comparatively lately there seems to have been a good deal of difference of opinion as to the action of the pupil under the influence of emotion. About five years ago I had some correspondence with Sir S. Wilkes, the distinguished president of the Royal College of Physicians, upon this very subject, and he informed me that after long inquiry he had been unable to get any trustworthy information as to how the pupil behaved in the lower animals when they were under the influence of emotion. The correspondence had