CHEMICAL BASIS OF THE ANIMAL BODY. 1315 



acid, or if a solution of the pigment be similarly evaporated to 

 dryness, the visual purple is comparatively resistent to the ac- 

 linn of light, although it is bleached by a sufficiently prolonged 

 exposure. 



LlPOCHROMES OR LUTEINS. 



After the rupture of the ovarian follicle which accompanies 

 the discharge of an ovum, the cavity of the follicle becomes 

 filled with a mass of cells, traversed by ingrowths of connective 

 tissue from the neighbouring stroma and frequently contains 

 blood resulting from haemorrhage at the time of rupture. 

 This is followed, most strikingly if impregnation of the dis- 

 charged ovum takes place, by a fatty degeneration of the con- 

 tained cells, resulting in the formation of a bright pigmented 

 mass of a brilliant yellow or orange colour, while at the same 

 time some of the colouring matter of the blood may be converted 

 into that crystalline substance already described under the name 

 hsematoidin (p. 1302) as being identical with bilirubin. The 

 structure which results from the above changes is known as a 

 'corpus luteum. ' The pigment at first received the name 

 lutein, under which designation as a class-name these fatty 

 pigments have usually been known. Since, however, as \\e 

 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 pig- 

 ments which while they give the reactions characteristic of the 

 group exhibit colours Qther 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 characterized 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. 

 They are characterized chemically by giving (i) a transient 

 violet colour followed by a bright blue when treated with con- 

 centrated sulphuric acid, (ii) A transient bluish-green under 

 the action of strong (yellow) nitric acid. 



1. Lutein. 



This pigment may be obtained from corpora lutea by extrac- 

 tion with chloroform. It is insoluble in water but readily 

 soluble in alcohol, ether, chloroform and benzene. These solu- 

 tions exhibit two absorption bands, one inclosing F, the other 

 about half-way between .Fand Gr. 



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

 ether, the solution slu-\vs two hands similar to those ahvadv 

 described for lipochrin or frog's fat (p. 1312), while sometimes 



