PDF - Wallace Online

390 TROPICAL NATUREpum, 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 onesescape.Now it is very improbable that a constitutionalimmunity from poisoning by so many distinct plants should,in the case of such widely different animals, be always correlatedwith the same difference of colour ;but the facts arereadily understood if the senses of smell and taste aredependent on the presence of a pigment which is deficientin wholly white animals. The explanation has, however,been carried a step further, by experiments showing that theabsorption of odours by dead matter, such as clothing, isgreatly affected by colour, black being the most powerfulabsorbent, then blue, red, yellow, and lastly white. Wehave here a physical cause for the sense-inferiority of totallywhite 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 generallyblack ;the ears and eyes are also often black ;and there isreason to believe that dark pigmentis essential to goodhearing, as it certainly is to perfect vision. We can thereforeunderstand why white cats with blue eyes are so oftendeaf, a peculiarity we notice more readily than their deficiencyof smell or taste.If, then, the prevalence of white coloration is generallyassociated with some deficiency in the acuteness of the mostimportant senses, this colour becomes doubly dangerous, forit not only renders its possessor more conspicuous to itsenemies, but at the same time makes it less ready in detectingthe presence of danger. Hence, perhaps, the reason whywhite appears more frequently in islands, where competitionis less severe and enemies less numerous and varied.Hence, also, a reason why cdbinoism, although freely occurringin captivity, never maintains itself in a wild state,while melanism does. The peculiarity of some islandsin having all their inhabitants of dusky colours (as theGalapagos) may also perhaps be explained on the sameprinciples, for poisonous 'fruitsmay there abound whichweed out all white or light -coloured varieties owing totheir deficiency of smell and taste. We can hardly believe,