On the uptake and incorporation of thymidine by cultured chick pineal glands.

Cultured chick pineal glands showed a marked cycle in the incorporation of thymidine into DNA. They also accumulated exogenous thymidine in one, or more, endogenous thymidine pool(s). However, there was no significant variation in ability to take up thymidine during incubation with either standard medium or media of increased thymidine content. We could not eliminate the possibility of variation in size of a quantitatively minor, but metabolically extremely important, thymidine pool which "channels" precursor directly into DNA.