410 DR. H. GADOW ON THE COLOUR OF FEATHERS. [May 2, 



Application of the Laws of Colours to Feathers. 



I. Pigment- COLOURS. The simplest case. It has long been a 

 matter of discussion whether or not pigment exists in feathers on 

 account of its never having been successfully extracted. Recently, 

 however, various pigments have been discovered. What we know 

 at j)resent about pigment in feathers is almost entirely the result of 

 the investigations of Bogdanow and Krukenberg. 



Pigment may produce the following colours : — 



Blade, resulting from the presence of zoomelanin, a colouring- 

 matter which is probably identical with the melanin of the Chori- 

 cidea. This is the pigment most universally found in the animal 

 kingdom, and almost every "black" feather owes its colour to this 

 pigment. 



Brown. Zooxanthin, found in brown feathers. A mixture of this 

 and the former pigment would of course give black-brown. 



Red. The best studied feather-pigment is the turacin in the red 

 quills of the Musophagidee. This very peculiar stuff has hitherto 

 only been found in the Touracous. 



Another red pigment is the zooerythrin ; first extracted by Bog- 

 danow from Calurus auriceps, and, as a pinkish matter, from Cotinffu 

 ccerulea. The same matter produces the red in the wattle round the 

 eye of the Black (^ock (hence called by Wurm, its discoverer, tetraon- 

 erythrin). Zooerythrin has been found in very different birds, 

 which, like Phcenicopterus, Cardinalis, Ibis, and Cacatua, have 

 more or less red in their plumage ; it is therefore very probable that 

 red is generally produced by this pigment. 



Allied to the zooerythrin is the zoorubin, a red-brown matter in 

 the feathers of Cicitmurus regius. 



Zoofulvin is a yellow to greenish-yellow pigment. 



Turacoverdin is found in the green feathers of the Touracous. 

 In other green feathers no green pigment has hitherto been found, 

 and the same applies to blue and violet. 



We may be almost certain that, wherever we have feathers with 

 the various shades of black, brown, red, and yellow, if these feathers 

 do not change their colour in different positions of the eye, their 

 colour is merely due to a pigment. But there may be complication ;. 

 if, for instance, the deeper strata contain a black, and the upper ones 

 superimposed red pigment, the whole will appear dark red. Or if 

 we take red with a superimposed yellow layer, the result will be 

 orange. Tlie richness of colours will often entirely depend on the 

 amount of pigment, e. g. grey. 



II. By DIFFRACTION and reflection we can explain the fol- 

 lowing phenomena in feathers : — 



1. White. There is no white pigment or white objective colour in 

 natural objects ; and wherever we have a white object, its colour is 

 due to there being an innumerable number of interstices between its 

 molecules, or air-cells in its substance. The whole substance of a 

 white feather, the ceratiniue, is colourless, but its texture forms a 

 fine network. 



2. Simple reflection of light. The ^/o5s of feathers, independent of 



