390 TROPICAL NATURE 



pum, while black sheep escape ; white rhinoceroses are said to 

 perish from eating Euphorbia candelabrum ; and white horses 

 are said to suffer from poisonous food where coloured ones 

 escape. Now it is very improbable that a constitutional 

 immunity from poisoning by so many distinct plants should, 

 in the case of such widely different animals, be always corre- 

 lated with the same difference of colour ; but the facts are 

 readily understood if the senses of smell and taste are 

 dependent on the presence 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 there- 

 fore 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 detect- 

 ing the presence of danger. Hence, perhaps, the reason why 

 white appears more frequently in islands, where compe- 

 tition is less severe and enemies less numerous and varied. 

 Hence, also, a reason why cdbinoism, although freely occur- 

 ring 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 deficiency of smell and taste. We can hardly believe, 



