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Show 410 DR. H. G A D O W ON T H E COLOUR OF FEATHERS. [May 2, Application of the Laws of Colours to Feathers. I. P I G M E N T - C O L O U R S . 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 present about pigment in feathers is almost entirely the result of the investigations of Bogdanow and Krukenberg. Pigment may produce the following colours:- Black, resulting from the presence of zoomelanin, a colouring-matter which is probably identical with the melanin of the Chori-oidea. 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 Musophagidse. This very peculiar stuff has hitherto only been found in the Touracous. Another red pigment is the zooerythrin ; first extracted by Bogdanow from Calurus auriceps, and, as a pinkish matter, from Cotinga carulea. The same matter produces the red in the wattle round the eye of the Black Cock (hence called by Wurm, its discoverer, tetraon-erythrin). Zooerythrin has been found in very different birds, which, like Phoenicopterus, 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 Cicinnurus 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. W e 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 wliole will appear dark red. Or if we take red with a superimposed yellow layer, the result will be orange. The richness of colours will often entirely depend on the amount of pigment, e. g. grey. II. By DIFFRACTION and R E F L E C T I O N we can explain the following 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 ceratinine, is colourless, but its texture forms a fine network. 2. Simple reflection of light. The gloss of feathers, independent of |
