390 TROPICAL NATURE v 
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 albinoism, 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, 
