The incidence of individual chemosensitive trigeminal afferent responses to application of various agents (acetic acid at concentrations of 0.5, 0.6, 0.8, 1.0, 1.2 and 1.4%; citric acid at concentrations of 0.5, 1.0 and 2.0%; pH at 3.0, 4.0, 5.0, 6.0 and 7.0; and sodium chloride at concentrations of 0.5, 1.0, 2.0 and 5.0 mol l^–1)