Chapter VI 



Clu'iiiical Relations between Plant and Animal 



Carotinoids 



It is a chemical axiom, so to speak, that the final proof of the 

 identity of like chemical compounds must be furnished by a chemi- 

 cal analysis of the purified substances, together with complete cor- 

 respondence in all known chemical and physical properties. It has 

 been stated repeatedly in the preceding chapters that evidence has 

 been presented which shows the character of the chemical relationship 

 between plant and animal carotinoids. It is desired to consider this 

 evidence in more detail in this chapter. 



Egg yolk xanthophyll. It is not necessary to present again the 

 observations showing the close relationship between the pigment of 

 the yolk of the hen's egg and the plant chromolipoids, which was 

 known to numerous workers through the macroscopic examination of 

 the pigment. Reference may be made, however, to the spectroscopic 

 studies of Schunck (1903) who first showed the correspondence be- 

 tween the egg yolk pigment and one of the groups of plant carotinoids. 

 Schunk's results, secured largely by a photographic study of the 

 absorption spectra of the pigments separated by inadequate, and 

 unfortunately by inaccurate means, were obtained before carotin and 

 xanthophylls were established as chemical entities. This method was 

 described in Chapter II. It could not have insured the freedom of 

 the "xanthophylls" from admixture with carotin. Nevertheless 

 Schunck was careful to distinguish between xanthophylls and "chry- 

 sophyll," which he recognized as probably identical with carotin. 

 The spectrophotographs show this very clearly so that the spectro- 

 scopic relations between one of Schunck's flower xanthophylls (his 

 so-called L. xanthophyll) and the egg yolk pigment rightly deserve 

 credit for being the first to show the xanthophyll character of this 

 animal chromolipoid. 



Crystals of egg yolk pigment are stated by Willstatter and Escher 

 (1912) to have been observed first by Kiihne (1882). It was stated 



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