140 CAROTINOIDS AND RELATED PIGMENTS 



study of the biological origin of the egg yolk xanthophyll. In Will- 

 statter and Escher's study, however, the bulk of their carotin-like pig- 

 ment was saponifiable, so that its actual identity with carotin remains 

 doubtful. 



Xanthophyll pigmented egg yolks may not be normal for all species 

 of birds. Krukenberg (1882m) examined the yolk of the eggs from 

 two breeds of parrots. The yolk was colorless in one case, but the 

 other was weakly tinted with a pigment whose spectrum is unques- 

 tionably that of xanthophyll. 



Body tissues. It is not to be expected that animals whose eggs are 

 highly colored with carotinoid should be devoid of the pigment in 

 their body tissues. Halliburton (1886) showed that the blood serum 

 and adipose tissue of the hen, pigeon and dove contains lipochrome, 

 but the descriptions given do not make it possible to decide the char- 

 acter of the carotinoid involved. The writer has observed that the 

 pigment in pigeon serum may be extracted by shaking with ether, 

 which fact may indicate its xanthophyll nature. Schunck's (1903) 

 spectroscopic studies included the pigment of the hen's blood serum. 

 The same xanthophyll was found as in the egg yolk. The writer's 

 (1915) study of the fowl's blood also showed xanthophyll to be the 

 major pigment present in the serum, directly extractable with ether in 

 all cases in his work. 



Krukenberg's (1882b) spectroscopic drawings of the yellow skin pig- 

 ments of pigeons, hens and geese resemble very closely the known 

 spectra for xanthophyll. We now know that this pigment is xantho- 

 phyll, at least in the case of fowls, the extracts showing the phase test 

 and spectroscopic properties of this pigment. Van den Bergh and 

 Muller (1920) and van den Bergh, Muller and Broekmeyer (1920) 

 have confirmed these observations with the exception of the direct 

 extraction of the xanthophyll from fowl serum by ether. In only two 

 out of 13 cases were they able to shake the pigment out with ether. 

 The explanation of this divergence in their observations from those 

 made by the writer is not at present apparent. 



Retina. It has been known since the early observation of Hannover 

 (1840) that globules varying in color from red to greenish-yellow occur 

 in the retina of the eyes of many animals and birds. The physiolo- 

 gists were greatly interested in these pigmented globules during the 

 latter half of the 19th century, particularly as to the possibility of 

 their being related to the so-called visual pigments of the eye. These 

 colored globules interest us, however, only in so far as the character 



