def contract(monolayer, face, contractile_increase, multiply=False,
    contraction_column='contractility'):
    """
    Contract the face by increasing the 'contractility' parameter
    by contractile_increase
    """
    if multiply:
        monolayer.face_df.loc[face, contraction_column] *= contractile_increase
    else:
        monolayer.face_df.loc[face, contraction_column] += contractile_increase
