Partial Replacement of CO 2 in Strain L and HeLa Cultures. ∗

Summary

Deficiency of CO₂ stopped the growth of strain L mouse fibroblasts in monolayer cultures. Cells in such cultures would recover after lengthy deficiencies upon replacement of CO₂. Ribonucleosides, deoxyribonucleosides, or extracts of normal cells would substitute partially for CO₂. A comparable level of substitution would occur with a purine and pyrimidine combination as simple as hypoxanthine and orotic acid. Combining other compounds involved in CO₂ metabolism with the ribosides did not result in more complete substitution.