WJir EYES OF ANIMALS SHINE IN THE DARK. 813 



But this doctrine has its moral aspect also. The question of duty 

 comes in at once and very obviously so soon as the actual consequences 

 of conduct have been shown to be good or bad. But it may be well 

 to show more definitely what the true line of duty is in regard to self. 

 I shall, therefore, next consider cases where self-abnegation leads 

 directly to the diminution of general happiness. — Knowledge. 



WHY THE EYES OF ANIMALS SHINE IN THE DAEK. 



By swan M. BUKNETT, M. D. 



THAT the eyes of some animals, particularly the cat, are luminous 

 when they are in the dark, is a fact established from time imme- 

 morial. It is surprising, however, to find the exact nature of the 

 phenomenon entirely misunderstood even by scientists whose lines of 

 investigation lie in the particular field to which it belongs. In con- 

 versing, not long ago, for instance, with one of the first physicists of 

 this country, who is at the same time an ardent sportsman, he gave 

 me a graphic description of a " still hunt " for deer. This method of 

 hunting, as is well known, consists in placing a bright light in the bow 

 of a boat and propelling it noiselessly through the water. The deer is 

 attracted by the light and goes toward it, but is prevented by its glare 

 from seeing his enemies who are concealed in the shadow. The 

 hunter, looking straight ahead, sees in the outer darkness — rendered 

 Egyptian by contrast with the bright light immediately in front of his 

 own eyes — two large, luminous bodies, like balls of fire. These are 

 the eyes of his victim ; and, making his calculation as to the distance 

 from the eyes down to the breast, the valiant sportsman (who proba- 

 bly is also a strong anti-vivisectionist) fires, intending to send his bul- 

 let through the heart. The eminent physicist, in speaking of this 

 luminosity, referred to it as due to the phosphorescence of the eyes, in 

 that final way in which we are accustomed to speak of things beyond 

 dispute. 



But it is hardly less surprising to read in the article " Light," in 

 the ninth edition of the " Encyclopaedia Britannica," the following 

 remarkable statement by Professor P. G. Tait, on the sources of light : 

 " 3. A third source [of light] is physiological ; fire-flies, glow-worms, 

 medusce^ dead fish (?) — the eye of a cat" (vol. xiv, p. 379). 



If these are the opinions of acknowledged authorities in optics, we 

 can hardly expect the mass of even ordinarily intelligent and informed 

 persons to have more correct ones, and should expect thorough cre- 

 dence to be given to the story of the man who claimed that he was 

 able to recognize an antagonist who struck him in the dark by means of 

 the light emitted from his own eye as the result of the blow. 



