SENSE-PERCEPTION AND COLOUR. 2G5 



Sense-perception influenced by Colour of the Integu- 

 ments. Some very curious physiological facts bearing 

 upon the presence or absence of white colours in the 

 higher animals have lately been adduced by Dr. Ogle. 1 

 It has been found that a coloured or dark pigment in 

 the olfactory region of the nostrils is essential to perfect 

 smell, and this pigment is rarely deficient except when 

 the whole animal is pure white. In these cases the 

 creature is almost without smell or taste. This, Dr. 

 Ogle believes, explains the curious case of the pigs in 

 Virginia adduced by Mr. Darwin, white pigs being killed 

 by a poisonous root which does not affect black pigs. 

 Mr. Darwin imputed this to a constitutional difference 

 accompanying the dark colour, which rendered what was 

 poisonous to the white-coloured animals quite innocuous 

 to the black. Dr. Ogle, however, observes that there 

 is no proof that the black pigs eat the root, and he 

 believes the more probable explanation to be that it is 

 distasteful to them ; while the white pigs, being deficient 

 in smell and taste, eat it and are killed. Analogous facts 

 occur in several distinct families. White sheep are 

 killed in the Tarentino by eating Hypericum crispum, 

 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 dis- 

 tinct plants should, in the case of such widely different 

 animals, be always correlated with the same difference 

 of colour ; but the facts are readily understood if the 

 senses of smell and taste are dependent on the presence 



1 " Medico-Chirurgical Transactions," vol. liii. (1870). 



