Dr Esser on the Luminousness of the Eyes. 167 



Many of my friends, to whom I mentioned my experiments, 

 and the result of them, objected to me, that I could not possi- 

 bly be correct, for they themselves had observed cats' eyes 

 shining in the very darkest places, as, for example, in a cellar. 

 I have had frequent opportunities since of making observations 

 to the same effect ; but every time has, nevertheless, convinced 

 me, that, even in such places, the rays of light having passed 

 through a window or some other aperture, fell upon the eyes of 

 the animals as they turned towards the opening, and were placed 

 in a proper position in regard to the observer. Gruithuisen 

 likewise mentions a case in which he could produce light from 

 ,the eyes of a cat at pleasure ; in places absolutely dark, how- 

 ever, he never observed any light. 



To ascertain what appearance the eyes of a cat exhibit after 

 death, I cut off the head of one, placed it opposite to the win- 

 dow, at the distance of some yards, so that the rays of light 

 passing through the window might fall on the eyes. I now 

 observed, that the eyes of the dead cat shone far more vividly 

 than those of a living one. By illuminating the apartment, the 

 light was not, as in living cats, weaker but stronger, and was so 

 powerful when I completely illuminated the room, and allowed 

 the sun's rays to fall immediately on the eyes of the cat, that it 

 resembled the most beautiful green fire, which lost its intensity 

 however, and exhibited only a clear greenish brightness, when 

 the rays of the sun, as in the open air, fell on all sides. In 

 places perfectly dark, the light of the eyes, as in all my forma* 

 experiments, completely vanished. All my subsequent experi- 

 ments, in which many a cat lost its life, were uniformly followed 

 by the same result. 



The light of the. cat's eyes being brighter after death than 

 when in life, may probably be owing to this, — that after death 

 the pupil is so much dilated as almost entirely to hide the iris ; 

 and that the pupil, being now insensible to the rays of light 

 falling on it, is never closed again, and does not obstruct the 

 passage of the penetrating rays of light, as is well known to 

 be the case during hfe. 



Farther, the light of the eyes of those animals, that after 

 death were subjected to experiment, became gradually weaker 

 as the cornea grew duller. When that part of the eye was 



