Fig. 4. The effect in African lungfish Protopterus annectens of 1 h of (A–C) acid (3 mmol kg^–1 NH₄Cl) or (D–F) base (3 mmol kg^–1 NaHCO₃) infusion (marked by the grey bar) on net excretion of acidic equivalents into the water (J_netH⁺; A,D), titratable net acid flux (J_netTA; B,E), and net ammonia excretion (J_netNH₃; C,F). J_netH⁺ was calculated as the sum of J_netTA and J_netNH₃, signs considered. Values are means ± s.e.m. for the period prior to acid or base infusion (`pre'), and for measurement periods 0–1, 2–3, 5–6 and 17–18 h post-infusion; N=11 and 8 for, respectively, acid- and base-infused lungfish. An asterisk (^*) indicates a significant difference from the pre-infusion value (one-way RM-ANOVA; P values are indicated on the figure); note that in E and F, post hoc multiple comparisons tests were unable to detect the origin of the significant differences indicated by the P values.