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		8. Add 2ml culture media (2% NCS in DMEM) to wells. Split into 3 groups, 5 wells each. Group 1=face Group 2=wing bud Group 3=hind limb bud wells 1:control 2: 33 micro liters retinoic acid 3: 33 micro liters retinoic acid 4: 20 micro liters 0.1 mg/ml poly-l-lysine 5: 20 micro liters 0.5 mg/ml poly-l-lysine 9. Culture for 3 days. Discard supernatant. Fix cultures by addition of 1ml 4% paraformaldehyde. Store overnight at 4oC. 10. Wash with 2 x 1 ml PBS. Stain with 1mg/ml Alcian Blue in 0.1 M HCl overnight. De-stain with 70% EtOH. Count the number of cartilage producing nodules for each well.