14 GENERAL HISTORY OF BIRDS. 



color. We have unfortunately no space to treat of this matter in detail at this 

 time, though a few facts deserve attention. Color is confined almost wholly to 

 the contour-feathers. Down and half-down are almost always white or yel- 

 lowish, or some shade of gray or brown, and filoplumes are gray or black. 

 Pulviplumes are generally yellowish. The color of contour-feathers is in- 

 finitely varied, but is most noticeable on the upper or outer-side of the feathers. 

 It is determined by four factors, (1) the age and worn condition of the feathers, 

 (2) the amount of air contained in the shaft and barbs, (3) pigment, and (4) 

 the microscopic structure of the surface of the feathers. New or young 

 feathers are more brightly colored than when they are old, and this is due, in 

 part at least, to the wear and tear on the surface and edge of the feather. The 

 amount of white in a feather depends upon the amount of air it contains; a 

 pure white feather lacks pigment, and is practically full of air. Our knowl- 

 edge of feather pigments is still imperfect and unsatisfactory,- — blackish, yel- 

 lowish, green and two red pigments being those which are best known. Other 

 colors, particularly blue, and the metallic luster of feathers, are caused by the 

 prismatic structure of the surface. The question whether fully grown feathers 

 can change their color other than by the wearing away of surface and edges is 

 still discussed, but the evidence accumulated in recent years seems to prove 

 that they cannot. Of course their colors may fade as they grow old, but that 

 they can in any way brighten up or undergo radical change seems to be out of 

 the question. 



Most of the colors appear to depend on optical and not chemical causes; 

 the attempts made "to extract blue, violet, and green pigments from feathers 

 so colored have as yet been unsuccessful." 



There are, however, special coloring matters developed in some birds and 

 many of these were discovered in lSSl-82 by Dr. C. W. Krukenberg. These 

 were examined both by chemical and spectroscopic analyses; especially have 

 different substances been found in the red and yellow feathers of birds. 

 The various pigments have been given the names Turacin, Titracoverdin, 

 Zoai^ubin, Zoonerythrin, Zoofuloin, Araroth, Corioniljphurin. 



Turacin has only been detected in the feathers of the Plantain-eaters or 

 Musophagidse, and more especially in their red feathers. It "gives two 

 diflferent absorption-spectra, according to whether it is in solution or not — a 

 very unusual circumstance with organic pigments. A solution-spectrum has 

 two absorption-bands, nearly coinciding in position with those of oxyhtemo- 

 globin, from which, however, Turacin differs greatly in chemical composition, 

 containing, as is well known, copper in abundance." 



Zoonerythrin "gives a continuous spectrum." 



Zoofuloin affords a spectrum "with two absorption-bands which however 

 are not those of Turacin. ' ' 



