CAROTIN, THE PRINCIPAL YELLOW PIGMENT OF MILK FAT. 333 



spectroscopic identity of the egg yolk pigment with a xanthophyll 

 which he isolated from the yellow daffodil, the nasturtium, and green 

 leaves. Willstatter and Escher l have confirmed this with a chemical 

 analysis of the egg yolk pigment, showing it to be a true isomer 

 of the crystalline xanthophyll of green plants; they have called it 

 xanthophyll B. Escher 2 has recently published his investigation show- 

 ing that the pigment of the corpus luteum is identical in chemical 

 composition and properties with the carotin of green plants. 



These recent discoveries have opened the way for an extension 

 of such investigations to other yellow animal pigments whose isolation 

 is rendered much more difficult by their association with very large 

 quantities of fat and other substances. These discoveries have also 

 raised the question whether any relation other than chemical exists 

 between the yellow animal and plant pigments. This question has 

 never been investigated. The investigations which will be reported in 

 the succeeding papers are the first to show that there is a definite 

 relation other than chemical between the yellow plant and animal pig- 

 ments. 



1. Loc. cit. 



2. Loc. cit. 



