52 Things not generally Known. 



window, sparkled brilliantly; but in other positions the light 

 suddenly vanished. On causing the cat to be held so as to ex- 

 hibit the light, and then gradually darkening the room, the 

 light disappeared by the time the room was made quite dark. 



In another experiment, a cat was placed opposite the win- 

 dow in a darkened room. A few rays were permitted to enter, 

 and by adjusting the light, one or both of the cat's eyes were 

 made to shine. In proportion as the pupil was dilated, the eyes 

 were brilliant. By suddenly admitting a strong glare of light 

 into the room, the pupil contracted ; and then suddenly dark- 

 ening the room, the eye exhibited a small round luminous point, 

 which enlarged as the pupil dilated. 



The eyes of the cat sparkle most when the animal is in a 

 lurking position, or in a state of irritation. Indeed, the eyes 

 of all animals, as well as of man, appear brighter when in rage 

 than in a quiescent state, which Collins has commemorated in 

 his Ode on the Passions : 



" Next Anger rushed, his eyes on fire." 



This brilliancy is said to arise from an increased secretion of the 

 lachrymal fluid on the surface of the eye, by which the re- 

 flection of the light is increased. Dr. Esser, in places absolutely 

 dark, never discovered the slightest trace of light in the eye 

 of the cat ; and he has no doubt that in all cases where cats' 

 eyes have been seen to shine in dark places, such as a cellar, 

 light penetrated through some window or aperture, and fell 

 upon the eyes of the animal as it turned towards the opening, 

 while the observer was favourably situated to obtain a view of 

 the reflection. 



To prove more clearly that this light does not depend upon 

 the will of the animal, nor upon its angry passions, experiments 

 were made upon the head of a dead cat. The sun's rays were 

 admitted through a small aperture ; and falling immediately 

 upon the eyes, caused them to glow with a beautiful green light 

 more vivid even than in the case of a living animal, on account 

 of the increased dilatation of the pupil. It was also remarked 

 that black and fox-coloured cats gave a brighter light than 

 gray and white cats. 



To ascertain the cause of this luminous appearance Dr. Es- 

 ser dissected the eyes of cats, and exposed them to a small re- 

 gulated amount of light after having removed different por- 

 tions. The light was not diminished by the removal of the 

 cornea, but only changed in colour. The light still continued 

 after the iris was displaced ; but on taking away the crystalline 

 lens it greatly diminished both in intensity and colour. Dr. 

 Esser then conjectured that the tapetum in the hinder part of 

 the eye must form a spot which caused the reflection of the 



