360 IMMUNOLOGICAL STUDIES 



In the performance of the tests of inhibition of cleavage the 

 gelatinous coat ( fertilizin ) and fertilization membrane of the egg 

 are generally first removed before addition of the antiserum. The 

 antisera also act, but usually much more slowly, on eggs that have 

 not been so denuded. It appears, then, that the surface of the 

 denuded egg possesses antigenic groups similar to those of the 

 fertilizin molecule. Further discussion and evidence for the fer- 

 tilizin-like nature of the surface of the denuded egg is given in 

 the report by Tyler, Monroy, and Metz ( 1956; see also Metz, this 

 volume ) on the refertilizability of denuded fertilized eggs. 



When hatched blastulae or gastrulae are placed in antisera 

 against fertilizin they become immediately immobilized, their 

 further development is inhibited, and they presently cytolyze. 

 Evidently surface antigens of the uncleaved egg persist until 

 these stages in sufficient amount to produce cytotoxic effects upon 

 reaction with the antisera. As noted above (p. 345), there are 

 reports (Perlmann and Gustafson, 1948; Perlmann, 1953; Harding 

 et al., 1954) also of new antigens being detected at the gastrula 

 stage of sea urchins, but it is not known whether or not these are 

 surface antigens. 



Nuclear as well as cytoplasmic division is blocked by antisera 

 against fertilizin. Division is not blocked at any particular stage 

 of mitosis, and the amount of mitotic progress made depends on 

 the strength of the antiserum. In the most effective antisera (vs. 

 fertilizin) this amounts to about 15 minutes, or about one-fourth 

 to one-sixth of the first division time for L. pictiis and S. piirpura- 

 tus respectively. Treatment as short as 15 to 30 minutes in strong 

 antiserum can block cell division iireversibly. With shorter ex- 

 posures the eggs can resume development. Cleavage block is ef- 

 fected without other visible signs of damage being at first evi- 

 dent, but after several hours exposure to the antiserum cytolytic 

 changes are observed ( Fig. 2 ) . Complement is evidently not nec- 

 essary for the action since heating the antisera at 56° C for one 

 hour does not destroy the cleavage-blocking activity. A marked 

 temporary rise in respiratory rate occurs in eggs treated with 

 blocking antisera. Determinations of sodium content have been 

 made on the supposition that the treatment may have permitted 



