The movement of single cells within solid tissue masses

Individual heart and liver cells isolated from chick embryos labelled in ovo with ³H-thymidine were seeded, in culture, onto the surfaces of unlabelled, embryonic heart and liver tissue masses (both tissue fragments and cellular reaggregates). Single, labelled cells, as observed in autoradiographs, infiltrated the interiors of the tissue masses in most cases. These results might be unexpected in light of previous experiments and current notions of ‘contact inhibition of cell movement’.