152 CAROTINOIDS AND RELATED PIGMENTS 



disease, inasmuch as oxidation is undoubtedly the normal means by 

 which the animal body destroys surplus carotinoids. 



The chromolipoid pigments of birds offer many interesting physio- 

 logical problems, particularly because of their chemical difference 

 from the chromolipoids of mammals. The egg yolk pigment was 

 studied as early as 1867, and while Kiihne (1878) first recognized that 

 it is not identical with the pigment of the corpus luteum of mammals, 

 its probably chemical relation to plant xanthophyll was not suggested 

 until the work of Schunck (1903). This relation was established by 

 Willstatter and Escher (1912), and extended to include a biological 

 relation by Palmer (1915). Whether the hen's body modifies slightly 

 the plant xanthophyll or selects one of the several plant xanthophylls 

 differing in melting point from the mixed product obtained from green 

 leaves, cannot be decided at present. 



Xanthophyll also appears to be the chief, if not the sole carotinoid 

 in the blood serum, adipose tissue, nerve cells, body organs and skin 

 of fowls. Detailed studies have not been made for other birds. The 

 relation of the so-called lipochromes of the retina of the eyes of birds 

 to the carotinoids is indefinite. 



Carotinoids and related pigments are unquestionably the cause of 

 the yellow to red color of the feathers of certain birds which are 

 enumerated in the text. Although these pigments have not been 

 studied since the recent advances in our knowledge regarding animal 

 carotinoids, the evidence points to the fact that xanthophyll is one 

 of the pigments concerned in feather coloration. 



Skin coloration of fishes is similar in some respects to feather 

 coloration in birds except that the structural whites are not colloidal 

 in fishes and fish pigments are deposited in chromatophores over which 

 there is physiological control. The red chromolipoid of the skin of 

 many fishes does not appear to be identical with any of the known 

 carotinoids although it resembles carotin in many respects and appears 

 to be related to the red so-called carotinin found in many lower plants. 

 The yellow chromolipoids of fishes are no doubt true carotinoids, the 

 evidence available, based on older observations of Krukenberg and 

 MacMunn, indicating the presence of both carotin and xanthophylls. 

 MacMunn has even described a lipochrome in the skin of the gold- 

 fish Cirassius auratus, which strongly resembles lycopin. 



The chromolipoids of the blood, body tissues and organs of fishes 

 have been examined only in the case of the salmon, in which the red 



