Viability of fibrosarcoma cells in culture. Viability of mouse NCTC 2472 fibrosarcoma cells cultured alone (Cells) or with neonatal femurs (Co-Cult) was determined by cell counts. Cell numbers are shown at initial plating (white bars), day 2 of culture (gray) and day 4 of culture (black) in serum-free (SF; graph A) and 1% horse serum (HS; graph B) media. Across three independent experiments, counts were taken from a total of 5 wells for each time point and media. Day 2 cell counts were found to be significantly different from the initial cell counts for both medias. Lowercase letters indicate comparisons between cells alone and bone-cell cocultures where (a) above each bar means no significant difference whereas (b) or (c) above each bar means a significant difference at P < 0.05 or P < 0.001 respectively.