54 ANIMAL COLORATION. 



give some account of the author's (Dr. Sauermann's) experi- 

 ments, for reasons which will appear. Cayenne pepper, of 

 course, is a composite substance, from which a number of 

 distinct chemical substances can be extracted : the red colour 

 is caused by a pigment termed capsicin, which can be separated 

 from the pepper ; and it might easily be supposed that the 

 change from yellow to red in the feathers of the canary was 

 simply caused by a transference of the pigment, as in the cases 

 mentioned on p. 127; but Dr. Sauermann has shown that it is 

 not so. Yellow-coloured canaries were not in the very slightest 

 degree affected by the pigment alone; but, curiously enough, 

 parti-coloured birds did react, — the brown parts of the feathers 

 became distinctly lighter in hue. It is a fatty substance 

 (triolein) which appears to convey the pigment, and produce 

 thus a changing of the colour from yellow to red; and further 

 experiments were made with other birds, showing that it iis 

 not only canaries which are influenced by their food in this 

 way. Some white fowls, belonging to a special breed, showed 

 traces of yellow among the feathers after feeding with cayenne ; 

 but in this case there were not racial but individual differences 

 in susceptibility, for all the specimens of the birds experi- 

 mented with did not react to the stimulus. 



A similar series of experiments was made with some other 

 colours : it was found with carmine that the yellow colour was 

 destroyed and the birds became white. This unexpected effect 

 is explained by the fact that a mixture of violet and yellow 

 produces white. The proof that the fatty constituent, triolein, 

 plays the chief part in the colouring of the feathers may 

 perhaps help to explain the very singular fact that the Amazon 

 parrots change from green to yellow when fed upon the fat of 

 certain fishes. 



With regard to the white fowls referred to, the experiments 



