COLOUR- VARIATION 57 



domestication. Of this, horses, oxen, cats, rabbits, 

 guinea-pigs, &c., are instances. And this may be 

 explained by natural selection, at least if colour 

 is always of positive use in some way or other to 

 animals, in escaping dangers which are of daily 

 occurrence in the wild state of life, but which dis- 

 appear under domestication. Under domestication 

 colour variations, to which a more or less marked 

 tendency may always exist, are of no inconvenience, 

 unless positively repelled by artificial selection, and 

 thus such variations are often present. On this point 

 I may refer to the works of Darwin and Wallace. 



Another fact to be taken into account is that of 

 the influence of food on colour. Many bird-fanciers 

 think that by appropriate colour-feeding, as they call 

 it, they can help the production or intensification of 

 colours. For instance, they believe that canary birds 

 can be made to become of a bright yellow when fed 

 with egg, mustard seed, curcuma powder, saffron 

 water, and alcohol, in definite proportions ; they even 

 consider it useful to put yellow flowers around the 

 bird's cage. But exact experiments, scientifically 

 conducted, are yet wanting on this subject, as I 

 have but second-hand and rather untrustworthy in- 

 formation concerning the investigations conducted by 

 Dr. Sauermann, which are alluded to in the previous 

 sentence. 



