44 EGG AND SPERM SUBSTANCES 



Arbacia and Mellita were tested for their ability to fertilize jelly- 

 less ( trypsin-treated ) eggs. Evidently jellyless eggs provide a 

 more sensitive system for testing the effect of fertilizin on sperm, 

 and use of this system may resolve the conflicting data of the 

 past. 



The experimental results reviewed in this section, then, show 

 that fertilizin at the egg surface facilitates fertilization whereas 

 the same agent in solution, by virtue of its combination with 

 sperm, acts as a barrier to fertilization. The apparent inconsist- 

 ency of these observations is resolved (Tyler, 1941, 1948a, 1955; 

 Tyler and Metz, 1955) in terms of an essential role of fertilizin 

 in linking the sperm to the egg surface. According to this concept, 

 fertilizin molecules attached to or built into the egg surface com- 

 bine with antifertilizin groups of the sperm to effect the linkage. 

 Thus if the free fertilizin groups at the egg surface are reduced 

 in number by acid extraction, enzymatic digestion or blockage 

 with antifertilizin, the fertilizability of the egg is reduced. Like- 

 wise, blocking the antifertilizin groups of the sperm with univa- 

 lent fertilizin (e.g., "reversed" sperm) or univalent antisera 

 (Tyler, 1946a) reduces the number of such groups available for 

 combination with the egg surface fertilizin and correspondingly 

 lowers the fertilizing capacity of the sperm. 



It might be expected that the sperm surface would be satu- 

 rated by fertilizin during its passage through the egg jelly and 

 before the sperm reaches the egg surface fertilizin. In considering 

 this possibility Tyler (1948a) suggests that the specific reactive 

 groups of fertilizin in the gel form may be bound by cross link- 

 ages. Such linked groups would not be freely available to com- 

 bine with the sperm. Differences in the metachromatic staining 

 properties of fertilizin in the gel form and in sea water solution 

 ( Monroy et at, 1954 ) are in keeping with this view. 



Chemistry of Fertilizin 



The chemistry of fertilizin has been reviewed on several occa- 

 sions (Tyler, 1948a, 1949, 1955; Runnstrom, 1949a, 1952; Vasseur, 

 1952a ) . Therefore the present treatment will be confined largely 

 to recent work. 



