122 



THE EGGS OF MAMMALS 



If oestrone in some way directly interferes with the assimila- 

 tion or metabolism of this critical nutrition then blastocysts 

 cultured with this hormone should show inhibited develop- 

 ment compared to that of controls in a normal medium. 

 Pincus and Kirsch (1936) cultured early blastocysts taken 

 from the uterus of rabbit does with varying amounts of 

 oestriol (12.5 to 25.2 y per culture) and found that control 

 blastocysts developed at the same time as those in the 

 oestriol-containing media. Oestriol was used instead of 

 oestrone because the former is much more soluble in aqueous 

 media and it also has a lethal effect upon developing blasto- 

 cysts when injected in vivo (see Table XXV). These experi- 

 ments show that the lethal effect of the hormone is not due 

 to the direct action of the hormone upon the developing 

 blastocyst. The sterilizing effects of oestriol and dihydro- 

 oestrone (Table XXV) indicate that the lethal effect is not 

 oestrone specific, and point again to the disturbance of a 

 needed nutritive condition. 



TABLE XXV 



The Effect of Various Injections of Oestriol and Dihydrooestrone 

 UPON the Implantation Ratio. (From Pincus and Kirsch, 1936) 



* Dihydrooestrone in aqueous solution, 

 t Dihydrooestrone in oily solution. 



§ Oestriol in oily solution. 



