266 TROPICAL NATURE, AND OTHER ESSAYS. 



of a pigment which is deficient in wholly white animals. 

 The explanation has, however, been carried a step further, 

 by experiments showing that the absorption of odours 

 by dead matter, such as clothing, is greatly affected by 

 colour ; black being the most powerful absorbent ; then 

 blue, red, yellow, and lastly white. We have here a 

 physical cause for the sense-inferiority of totally white 

 animals which may account for their rarity in nature ; 

 for few, if any, wild animals are wholly white. The head, 

 the face, or at least the muzzle or the nose, are generally 

 black ; the ears and eyes are also often black ; and there 

 is reason to believe that dark pigment is essential to 

 good hearing, as it certainly is to perfect vision. We 

 can therefore understand why white cats with blue eyes 

 are so often deaf, a peculiarity we notice more readily 

 than their deficiency of smell or taste. 



If, then, the prevalence of white coloration is generally 

 associated with some deficiency in .the acuteness of the 

 most important senses, this colour becomes doubly 

 dangerous ; for it not only renders its possessor more 

 conspicuous to its enemies, but at the same time makes 

 it less ready in detecting the presence of danger. Hence, 

 perhaps, the reason why white appears more frequently 

 in islands, where competition is less severe and enemies 

 less numerous and varied. Hence, also, a reason why 

 albinoism, although freely occurring in captivity, never 

 maintains itself in a wild state, while melanism does. 

 The peculiarity of some islands in having all their 

 inhabitants of dusky colours (as the Galapagos) may 

 also perhaps be explained on the same principles ; for 

 poisonous fruits may there abound which weed out 

 all white- or light-coloured varieties, owing to their 



