Fig. 4. Effects of removal of external Ca²⁺ and Na⁺ on olfaction in Carassius auratus. (A) Typical electroencephalogram (EEG) responses from the olfactory bulb (lower traces) and their integrated activity (upper traces) to 10^-5 mol l^-1 L-serine (black horizontal bars) in AFW (open horizontal bar), to Ca²⁺-free and to Na⁺-free (shaded horizontal bars) AFW flowing over the olfactory epithelium. All three responses were recorded from the same fish. (B,C) Histograms showing pooled data (means + S.E.M.) of responses to 10^-5 mol l^-1 L-serine in Ca²⁺-free AFW (B) and Na⁺-free AFW (C) compared with their respective controls (10^-5 mol l^-1 L-serine in AFW). The number of observations is shown in parentheses. ^*P<0.05 (Student's t-test for paired data).