5° 
COLOUR IN NATURE 
CHAP. II 
certain birds. It is incapable of existing in states 
of oxidation and reduction, and contains copper and 
not iron, so that it is unlikely that it is closely 
related to haemoglobin. Carmine again is not 
nearly related either to turacin or haemoglobin. 
The spectrum test in this case seems to break down 
utterly. In spite of numerous difficulties of this 
kind, the literature contains numerous identifications 
of pigments based only upon the use of the spectro¬ 
scope ; thus a recent observer describes chlorophyll 
in the skin of the horse ! In the following pages 
identifications based only upon spectra have been 
almost entirely omitted, for the evidence is con¬ 
sidered insufficient. 
