A. TYLER 357 



of problems of fertilization and early development (of. Tyler, 

 1955a,b). One aspect of this work, which has now been reported 

 (Tyler and Brookbank, 1955; 1956a,b), will be presented here. 



Antisera prepared against extracts of developing sea urchin 

 eggs were found to block cleavage of the eggs. At first there ap- 

 peared to be a stage-specific effect, antisera against eggs in early 

 cleavage blocking early, those against later cleavage blocking 

 later. However, this was found to be illusory, the time of cleavage 

 block being dependent upon the strength of antiserum employed. 

 Antisera against eggs in early stages would block at any specific 

 later stage if appropriately diluted, and anti-late stage could 

 block early if sufficiently strong. 



Immunological literature abounds with experiments showing 

 inhibition of cell division by action of antisera against cells of 

 many kinds of organisms. In the field of cancer research this is 

 an especially active line of investigation, the efforts being di- 

 rected toward the production of antisera that act specifically on 

 the tumor cells and not on normal tissue cells. Various types of 

 material ranging from whole tissue homogenates to washed par- 

 ticulate or viral suspensions have been used as antigens, and in- 

 hibitory effects of the antisera have been described in in vitro and 

 in vivo experiments. This work cannot be reviewed here, but for 

 purpose of reference to some of the investigations in this field 

 may be cited experiments and reviews by Woglom ( 1929 ) , Lums- 

 den (1937), Phelps (1937), Sigurdsson (1942), Spencer (1942), 

 Kidd (1946), Green (1946), Dulaney and Amesen (1949), Law 

 and Malmgren (1951), Barrett (1952), Werder et al. (1952), 

 Hauschka (1952), Nungester and Fisher (1954), Imagawa et al. 

 (1954a,b), and Mountain (1955). 



A new feature of the present work is that the inhibition of cell 

 division can be obtained with an antiserum produced against a 

 chemically rather well-defined constituent, namely the substance 

 of the gelatinous coat of the egg, known as fertilizin. 



Tests of antisera produced against the various sea urchin ma- 

 terials showed that the fertilizin antisera were particularly effec- 

 tive in blocking cell division. A summary is given in Table I of 

 the number of rabbits that produced cleavage-blocking antisera 



