A. TYLER 363 



are directed against the particular molecular sites that are con- 

 cerned in the fertilization reaction. The presence of antibody on 

 the surface, due to reaction with determinants at neighboring 

 sites, could suffice to prevent effective interaction between the 

 fertilizin of the egg surface and antifertilizin of the sperm. 



The fact that, in sea urchins, a cell division-blocking antiseiimi 

 can be produced by immunization with a surface constituent of 

 the cell suggests that this may be possible with various types of 

 cells of other animals. Some recent experiments of Billingham and 

 Sparrow ( 1955 ) may be interpreted as pointing in this direction. 

 These investigators injected saline washings of dissociated epi- 

 dermal cells from one rabbit intradermally into another. When 

 skin grafts were subsequently attempted from the former to the 

 latter, the accelerated incompatibility reaction, typical of an im- 

 munized animal, was exhibited. It seems likely that the washings 

 contained prinjarily, or solely, surface constituents of the cells, 

 and that these served as the effective antigens. In the cited ex- 

 periments no in vitro tests were made of j)Ossible cytotoxic action 

 of the serum of the immunized animal on donor cells, but earlier 

 experiments by Billingham and Sparrow ( 1954 ) showed that 

 treatment of the dissociated cells with the seiTun of an animal 

 that had been immunized by attempted skin graft can completely 

 or partially prevent the cells from giving rise to epithelium upon 

 grafting. They hesitate to term this cytotoxic action since no cyto- 

 lytic effects were observed on the serum-treated cells. However, 

 there was evidently a specific effect of the antibodies that ren- 

 dered the cells susceptible to early disintegration upon trans- 

 plantation. 



It seems reasonable to expect, then, that antigens effective in 

 engendering the production of specific cytopathogenic sera may 

 be prepared from various kinds of tissues, normal and neoplastic, 

 by extraction of surface constituents. Such extracts, obtained by 

 mild extraction methods, would contain a less complex mixture 

 of substances than obtained by the usual homogenization proce- 

 dures that are employed. Possibly in some cases preparations con- 

 taining a single chemical constituent could be readily obtained, 

 as is the case with sea urchin eggs. The current trend, particularly 



