CAROTINOIDS IN THE VERTEBRATES 143 



cream color in fowls of the white feathered, normally yellow-shanked 

 breeds is due to deposits of xanthophyll in the feathers. 



At the same time it should be stated that Krukenberg (1881b, 

 1882a, b, m) made an extensive study of feather pigments from the 

 point of view of his lipoehromes, and inasmuch as most of his observa- 

 tions included sprct rnscopic examinations, as well as solubility and the 

 color reactions with con. H..SO, and HN0 3 , it is possible to draw some 

 inferences from his work which are of value in answering the question 

 in hand. 



Krukenberg confined his attention almost entirely to the brightly 

 colored birds, including parrots, woodpeckers, the birds of paradise, 

 the flamingo, cardinal, the tigerfinch and bullfinch and numerous 

 other individual species. His studies led him to distinguish between 

 five red pigments and five yellow pigments. Not all of these can be 

 regarded as lipoehromes, even in the sense in which Krukenberg used 

 the term, and only a few can be considered specifically as carotinoids 

 with the evidence given. There may be reasonable doubt, also, 

 whether Krukenberg was justified in considering each of the pigments 

 as separate entities. It should be stated, however, that Krukenberg, 

 himself, was aware of this. 



Of the red pigments, the most important were zoonerythrine, pre- 

 viously named by Bogdanow (1858) and rhodophane, previously 

 named by Kiihne (1878). Of the others, "araroth," found in the red, 

 orange and yellow feathers of the great red macaw, Sittace Macao, 

 and the yellow and orange feathers of Aprosmictus melanurus, is prob- 

 ably identical with zoonerythrine, as Krukenberg, himself, suggested. 

 The two remaining red pigments, zoorubin and pseudozoorubin, found 

 in the male birds, Paradwea papuana and P. rubra, are not even lipo- 

 ehromes in the broad sense. 



Krukenberg believed that zoonerythrine was a rhodophane com- 

 pound, the character of which is not stated. The properties are widely 

 different from those described by Kiihne for rhodophane, giving deep 

 orange solutions in all the fat solvents, which readily extracted the 

 pigment from the finely divided feathers, especially after several days 

 digestion with alkaline trypsin or pepsin-HCl. The blue color reac- 

 tion with con. H,S0 4 was given, but the solutions showed no spectro- 

 scopic absorption bands, only a continuous absorption beginning in 

 the green. Because of this failure to show absorption bands one is 

 perhaps justified in concluding that the pigment is a carotinoid, altered 

 either by the animal body (Krukenberg, himself, advanced the idea 



