Fig. 4. Root-effect of red blood cell (RBC) suspensions. (A) Haemoglobin-bound oxygen concentration vs pH. pH values at `Root on' of 90%, 50% and 10% are indicated. RBC suspensions utilized for in vitro perfusion of isolated eyes: red circles (trout) and blue diamonds (human). Correlation coefficient of fitted line: r=0.962. (B) P_O2 vs pH of anaerobically acidified samples of trout (red circles) and human (blue diamonds) RBC suspensions. The pH value at 50% Root-effect is indicated by broken lines. Correlation coefficients of fitted lines: r=0.949 (trout RBC samples) and r=0.055 (human RBC samples). Confidence intervals (95%) to the fitted sigmoidal curves are indicated by broken lines.