CHEMICAL BASIS OF THE ANIMAL BODY. 267 



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

 the visual purple is comparatively resistent to the action of light 

 although it is bleached by a sufficiently prolonged exposure. 



LIPOCHROMES 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 ( 934). This is followed, most 

 strikingly if impregnation of the discharged ovum takes place, by a 

 fatty degeneration of the contained cells resulting in the formation of a 

 bright pigmented mass of a brilliant yellow or orange colour, while at 

 the same time the colouring matter of the blood may be converted into 

 that crystalline substance already described under the name hsematoidin 

 (p. 240) as being identical with bilirubin. The structure which 

 results from the above changes is known as a 'corpus luteum.' The 

 earlier (1868) examination of coloured extracts of these corpora lutea 

 led to erroneous statements of the identity of the pigment obtained 

 from them with hsematoidin, a view which was almost immediately 

 contested while the colouring matter received the name of hsemolutein. 

 A renewed investigation of the pigment led Thudichum 1 to characterise 

 it as of wide-spread occurrence in the highly-coloured fatty constituents 

 as of butter, fats, egg-yolk &c. and of some vegetable tissues, and to 

 give it the name lutein, under 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 ' lipo- 

 chrome' 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 accord- 

 ing 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. 265 may be regarded as characteristic of the 

 whole class. 



1 Centralb, f. d. med. Wiss. 1869, S. 1. 



