266 LUTEINS. 



which designation as a class-name these fatty pigments have 

 usually been known. Since, however, as we have already seen 

 in the case of the chromophanes, and as will appear subsequently 

 in the case of the pigments of egg -yolk, and of the substance 

 tetronerythrin, we have to deal with pigments which, while they 

 give the reactions characteristic of the group, exhibit colours 

 other than yellow, it is perhaps advisable now to use the term 

 ' lipochrome ' as generic, and to retain lutein as specific for certain 

 yellow pigments only. The lipochromes are characterised by 

 exhibiting absorption bands which, though varying somewhat in 

 position according to the solvent employed, are usually situated 

 towards the violet end of the spectrum. From a chemical point 

 of view the reactions already described on p. 263 may be regarded 

 as characteristic of the whole class. 



1. Lutein. 1 



This pigment may be obtained from corpora lutea by extraction 

 with chloroform. If the orange-coloured solution thus obtained 

 be allowed to evaporate spontaneously, a fatty residue is left in 

 which the lutein is found in a crystalline form, as minute either 

 rhombic prisms or plates, which are pleochromatic (see p. 216). 

 They are insoluble in water, but readily soluble in alcohol, ether, 

 chloroform, and benzol. These exhibit two absorption bands, one 

 inclosing F, the other about half way between F and G. 



If egg-yolk be extracted with a little alcohol and much ether, 

 the solution shows two bands similar to those already described 

 for lipochrin or frog's fat (p. 262), while sometimes a third faint 

 band near G may be seen, especially if the residue from the 

 ethereal extract be dissolved in carbon bisulphide and examined. 

 If the residues from the ethereal extracts of egg-yolk and corpora 

 lutea be saponified and extracted with carbon bisulphide, the 

 solutions yield identical absorption spectra. 2 



Maly, 3 operating on the bright red eggs of a sea-spider (Maja 

 Squinado) considered that lutein (assuming its identity in this 

 case with that from ordinary egg-yolk) consists of two pigments, 

 vitellolutein (yellow) and vitellorubin (red). For further details 

 see the original paper. Lutein is more or less rapidly bleached 

 by the action of light. 



2. Serum lutein. 



The serum from the blood of almost all animals is usually of 

 a more or less yellow colour ; it is specially marked in the case 

 of the horse and ox, is also marked in the case of sheep and man, 

 and is but slightly present under normal conditions in the serum 



1 See Capranica, loc. cit. on p. 263. 



2 Kiihne and Ayres, Jl. qfPhi/siol. Vol. i. (1878), p. 127. Gives spectra. 



3 Monatshefle f. Chem. Bd. n. (1881), S. 18. Gives literature to date. See 

 recently Bein," Be'r. d. d. chem. Gesell. Bd. xxm. (1890), S. 421 



