Fig. 1. Active ammonia excretion across the isolated perfused gill of the shore crab Carcinus maenas. At the beginning of all experiments, the internal perfusate and the external bath contained symmetrical concentrations of 100 µmol l^-1 NH₄Cl. (A) Omission of Tris-HCl buffer in the saline. Rate of ammonia loss from the internal perfusate, rate of ammonia addition to the external bath and the calculated rate of metabolic ammonia release into the external bath are displayed (N=5). (B) Disappearance of total ammonia from the internal perfusion medium was measured as the rate of net active branchial ammonia excretion over an experimental period of 3 h (N=5). Data represent means + S.E.M.

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