The mechanism of oxygen concentration in the swim-bladder of the eel

1. The P O 2 of venous blood from the active swim-bladder of the eel was shown to decrease with distance from the exit of the rete. This systematic change did not occur in non-secreting bladders, nor during conditions where exchange in the rete had been abolished. 2. The observed change in post-rete venous P O 2 has the same rate constant as the Root-on shift. 3. These findings modify the accepted model for counter-current multiplication of O 2 in the swim-bladder system by introducing rate constants for diffusion and action of acid in the rete. 4. The part played by the assumed impermeability to acid of the arteriovenous partition of the rete is in the modified model replaced by the slow Root-on shift. 5. The modified model contradicts the Kuhn model in that extraction of O 2 from blood is decreased at low flow and that at normal flow conditions part of the lactic acid produced can be re-used. 6. Similar modifications are indicated in the model for concentration of inert gases.