142 CAROTINOIDS AND RELATED PIGMENTS 



the carotin which is present in traces in fowls. Some basis for this 

 is given by the fact that its CS 2 solution was orange colored. On the 

 other hand, the spectrum of this pigment, both in ether and CS 2 , as 

 shown by Kiihne, resembles xanthophyll rather than carotin. Kiihne's 

 xanthophane would seem to be the usual xanthophyll met with in 

 fowls, in spite of the one-banded spectrum pictured for it. The rhodo- 

 phane is obviously not a carotinoid in the sense in which this term is 

 now applied. Whether it is a decomposition product, which, in fact, 

 AYaelchi (1881) believed to be the case for all of Kiihne's pigments, or 

 another type of pigment, related perhaps to the carotinoids, cannot be 

 decided from the meager evidence at hand. Perhaps this is the same 

 pigment which Wurm (1871) extracted with chloroform from the 

 wattles and "roses" (red warty spots over the eyes) of pheasants, and 

 called tetronerythrine. 



It might be mentioned in concluding the reference to Kiihne's work 

 that he was unable to observe similarly colored globules in the retinal 

 epithelium of man, cow, pig or snakes, but he did observe that the 

 same three pigments appear in the pigeon retina as in the fowl. Cer- 

 tain observations respecting the eye pigments of frogs will be referred 

 to presently, in connection with the carotinoids in amphibia. 



Feathers. Nowhere among the vertebrates does pigmentation and 

 color attain the brilliancy and variety that is seen in the feathers of 

 birds. Lovers of bird life, in general, as well as ornithologists, have 

 long been interested in the phenomena. The whole range of brilliant 

 as well as less conspicuous colors seems to be due to pigments of three 

 colors, namely, red, yellow and black, together with the structural 

 colors blue * and white. Various combinations of these pigments and 

 colors appear to be entirely responsible for the effects observed. It is 

 true that Gadow (1882) speaks of structural yellow in birds' feathers, 

 but the absence of yellow pigment in these cases does not seem to be 

 proved. Besides, the colloidal theory of optical or structural color 

 seems to preclude yellow among such colors. Of the three common 

 pigments involved, black is undoubtedly melanin. Since the two re- 

 maining colors due to pigment are those met with among carotinoids, 

 interest is at once aroused as to the possibility of the carotinoids being 

 involved. Unfortunately no modern investigation has been made of 

 these pigments with this point in mind, with the exception of the 

 observations of Palmer and Kempster (1919b, c) showing that the 



* That blue color in feathers is an optical and not a pigmented color seems to have 

 been recognized first by Bogdanow (1858). 



