The effect of horse serum alone, and of embryo extract alone, was compared with that of "complete medium" on the content and synthesis of ribo- and desoxyribonucleic acids and uptake of tracer P32 by chick heart cultures in vitro.

The factors mentioned are influenced by embryo extract in a manner similar to the effect in complete medium. Horse serum produced little synthesis of nucleic acids or uptake of tracer, giving only slightly more effect than Tyrode's solution alone.

Cutting the tissue into smaller pieces caused considerably greater synthetic effects, and retarded necrosis of the implant.

This content is only available as a PDF.