C. B. METZ 55 



by several workers (Frank, 1939; Tyler, 1940b, 1948a; Hartmann 

 et al, 1940; Hultin, 1947b, 1949; Rminstrom et al, 1942, 1944) 

 all of whom have reported cross reactions. Some of these reac- 

 tions were between distantly related forms clearly beyond the 

 bomids of fertilizin agglutination specificity. However, as Tyler 

 (1948a) pointed out, cross agglutination of eggs by sperm ex- 

 tracts may result from action of natural heteroagglutinins, not 

 from antifertilizin cross reactions. Natural heteroagglutinins for 

 sperm, eggs, and red cells occur widely in invertebrate bloods 

 and seminal fluids (Tyler and Metz, 1945; Tyler, 1946b; Metz, 

 1949). Another possibility is that the specificity of antifertilizin 

 is altered upon extraction from the sperm. Such loss of specificity 

 could result from alteration of the specific receptor groups or 

 from exposure of other less specific groups that are normally 

 bound. Evidently, the question of identity of the sperm surface 

 antifertilizin with the egg agglutinating agent cannot be settled 

 by the available specificity data. A thorough test of antifertilizin 

 specificity, taking the above factors into consideration, should be 

 performed. 



Role in Fertilization. If fertilizin is essential for fertilization 

 by virtue of a specific interaction with the sperm, then antiferti- 

 lizin must also be essential. However, the role of fertilizin in 

 fertilization is uncertain. Therefore, independent evidence for 

 the role of antifertilizin has been sought. Thus blocking the sperm 

 surface antifertilizin with fertilizin (Tyler, 1941; Tyler and Metz, 

 1955) or with univalent antibodies prepared from rabbits im- 

 munized with purified antifertilizin (Tyler, 1946a) reduces the 

 fertilizing capacity of sperm. Likewise partial removal of anti- 

 fertilizin from the sperm surface renders these cells less effective 

 in fertilization (Tyler and O'Melveny, 1941). Finally, treatment 

 of normal or jellyless eggs with antifertilizin solution (Tyler and 

 Metz, 1955) lowers fertilizability of eggs. This action on normal 

 eggs is evidently due to the precipitation of the egg jelly in the 

 form of a membrane, impermeable to the sperm (Tyler and 

 O'Melveny, 1941 ) . Sperm penetration of normal egg membranes 

 is considered below. 



