116 THE MAMMALIAN EGG 



and Dauzier infer that the egg emits an agent resembling fertilizin, 

 which, however, does not agglutinate spermatozoa but instead 

 repells or immobilizes them. Further, they consider that the female 

 genital tract contains a substance that normally neutralizes the 

 'fertilizin'. 



The relations between Bishop and Tyler's 'fertilizin' and Thibault 

 and Dauzier's 'fertilizin' have still to be elucidated. The former has 

 the characteristic effect that invertebrate fertilizin has, that of 

 agglutinating spermatozoa, but whether it can render spermatozoa 

 incapable of fertilization, as invertebrate fertilizin can, is not known. 

 Thibault and Dauzier's agent, though it does not agglutinate 

 spermatozoa, still has a right to be called 'fertilizin' for it renders 

 spermatozoa infertile, and invertebrate fertilizins are known that 

 have this effect on spermatozoa without agglutinating them (see 

 Metz, 1957). Another relation that needs to be investigated is that 

 between the strong agglutination inhibitor in vaginal washings 

 (Smith, 1949b), the female 'sperm antagglutin' (see Lindahl, i960, 

 for outline and references) and the factor in uterine secretions that 

 Thibault and Dauzier maintain opposes their 'fertilizin'. It is also 

 tempting to speculate that the acrosome reaction of mammalian 

 spermatozoa, as a feature of capacitation, may be evoked by sub- 

 stances emanating from the freshly ovulated eggs or their cumulus 

 investments (p. 96) and related in some way to the 'fertilizins' just 

 described. 



Resistance to low temperatures. When fertilized (2-cell) rabbit eggs 

 in serum were cooled slowly to o, 5 or io°C, most of those stored 

 for 24 hr, and about half of those stored for 72 hr, were able 

 to undergo apparently normal cleavage on subsequent culture. 

 Nearly 25 per cent of eggs kept at io°C for 144 hr survived, but none 

 of those kept for 168 hr. Eggs were also transferred after storage 

 to recipient animals and litters were born from eggs that had been 

 held at o°C for up to 102 hr (Chang, 1947, 1948a, b, c). Blastocysts 

 proved to be less resistant — they could grow after 1 day at o°C or 

 2 days at io°C, but the birth of young was recorded only from 

 blastocysts stored for 1 day at io°C (Chang, 1950b). Unfertilized 

 eggs recovered 2 hr after ovulation could be kept at o°C for 48 to 

 72 hr, or at io°C for up to 96 hr, and still undergo fertilization after 

 transfer, but though fertilization seemed normal, most of the 

 embryos degenerated before birth (Chang, 1952a, 1953, 1955^, d). 



