176 CAROTINOIDS AND RELATED PIGMENTS 



modified in the animal body. The hypothesis was also advanced that 

 the egg yolk xanthophyll may be an individual member of the xantho- 

 phyll group of carotinoids, which the digestive and assimilative organs 

 of the hen have the ability to select from the group of carotinoids pre- 

 sented to them in the food. Considered solely from a chemical basis, 

 however, it is indeed an extraordinarily closely related isomer which 

 shows such complete correspondence in all its other properties, both 

 chemical and physical, with the single exception of the melting point. 

 Lycopin, the red isomer of carotin, found especially in the tomato, 

 has the same melting point and chemical composition as carotin, but 

 differs from it in a number of chemical properties, such as color, 

 absorption spectrum, solubilities, etc. Therefore, from this point of 

 view, also, it seems unlikely that the alleged isomerism of the egg 

 yolk xanthophyll actually exists. 



Serono and Palozzi (1911) claimed to have isolated the lutcin of 

 egg yolk by a very different method. Egg yolk was extracted with 

 95 per cent alcohol, the extract evaporated in vacuum, and the residue 

 treated with acetone. This extract is stated to have contained mostly 

 "lutein," a little cholesterol and traces of lecithin. The lutcin was 

 obtained in crystalline form from this solution by precipitation from 

 boiling acetone. The crystals thus secured are described as white to 

 pale yellow radiating clusters with a few crystalline lamella with a 

 blue fluorescence, which turn yellow almost instantly in the air and 

 become more and more colored until a deep red is reached. The 

 analyses of this lutein indicated a mixture of cholesterol,, fat and 

 cholesterol esters of oleic and palmitic acids. Egg yolk is stated to 

 contain about 4.04 to 4.17 per cent of this pigment. 



With the above observations as a basis it is not surprising that 

 Serono (1912) vigorously attacked Willstatter and Escher's work 

 showing the xanthophyll nature of the egg yolk pigment. It is obvi- 

 ous, of course, that Serono's lutein cannot be the true egg yolk pig- 

 ment. At the same time the poor correspondence of the egg yolk 

 xanthopyhll with the plant pigment with respect to the melting point 

 and elementary composition naturally offered splendid points of at- 

 tack. Accordingly Serono's assertion is quite incontrovertible that the 

 carbon content found for the egg yolk pigment by Willstatter and 

 Escher (83.58 per cent) corresponds better with the carbon content 

 of an oleic acid ester of cholesterol (83.33 per cent) than it does with 

 the carbon content of carotin dioxide (84.44 per cent). Although one 

 would hardly be tempted to accept Serono's conclusions regarding a 



