12 RAYMOND PEARL AND ALICE M. BORING 



This development of a non-fatty pigment in the mammalian 

 lutear cells has been already described by Mulon as occuiTing in 

 atretic follicles. He speaks of the lipocholesterine as changing 

 over to an indelible pigment. This same substance certainly 

 forms in the involution of the corpus luteum of a discharged 

 follicle as shown in this present work. 



It is of especial interest to find that Blair Bell's description 

 of the corpus luteum in Ornithorhynchus, a primitive ovi- 

 parous mammal, shows it very much like that in the hen. It 

 often remains hollow, it never becomes very large. It con- 

 sists chiefly of a thickened theca interna. Sometimes it be- 

 comes a solid fibrous mass. One of Bell's figures almost exactly 

 resembles figure 4 of this paper. One would like to know 

 whether the yellow pigment is found in Ornithorhynchus thus 

 making its resemblance to the bird even more striking. 



V. BIOCHEMICAL CHARACTER OF PIGAIEx\T OF CORPUS LUTEUM 



The identity of this yellow amorphous pigment in the corpus 

 luteum remains in the ovary of the hen and of the cow has been 

 put to chemical tests as well as morphological; first of a micro- 

 chemical nature, as already partially described, and secondly by 

 various special chemical solvents. The work of Escher and of 

 Palmer and Eckles on animal pigments has been consulted in 

 selecting the reagents to use. 



The microchemical tests have been discussed in previous 

 sections, but will be summarized here. Microscopical technique 

 processes have shown the identical beha\'ior of the pigment in 

 hen and cow. It does not dissolve in alcohol or oils. It will 

 not stain with basic nuclear stains such as haematoxylin and 

 Kresylviolet, or with acid counterstains, such as eosin, methyl 

 blue, anihn blue, orange G, or with such a stain as iron haema- 

 toxyhn. Neither does it stain with the fat stain, Sudan III, 

 although there may be much fatty material in the cell in which 

 it lies. As normal secretion granules of a protein nature take 

 acid stains and secretion granules of a fatty nature take Sudan 

 III, this pigment is neither protein nor fat in composition. 



