Abstract
It was found that such antisera are effective inhibitors of phos-phate uptake by fertilized eggs. The antisera also block cell division of these zygotes at dilutions not affecting phosphate uptake, indicating that lack of this ion doesn''t prevent cleavage. Normal serum proteins, and commercial Bovine serum albumin were also effective inhibitors of transport, though less so than the antisera. It is proposed that the inhibition is a steric phenomenon, and that antibodies against the surface compete more effectively for the essential site than other nonspecific proteins of serum.