Some of the compounds in the active fraction of ultrafiltrates of chick embryo extract have been identified as taurine, serine, glutamic acid, xanthine, uracil, glucose-6-phosphate, glucose, ferrous iron, and inorganic phosphate.
Based on the identity of these compounds a synthetic replacement for the ultrafilterable portion of chick embryo extract has been devised. There is an additional nutritional requirement that can be met by vitamin B12. Folic acid appears to be beneficial to the system though the requirements of this or any of the above compounds except vitamin B12 remain for future research. The low nitrogen content of the isolated fraction and the synthetic mixture suggests that the main nutrition of chick cells in roller tube cultures is derived from the non-dialyzable portion of the medium.