Agar diffusion of ampicillin and vancomycin; inhibition zone
radii x (mm) and their squared values x2 are plotted against the logarithm of
concentration together with linear fits. Residuals are shown above each plot.
Free diffusion is described by x2 versus ln(c) plots and dissipative diffusion
by x versus ln(c). Better linear fits are obtained using the free diffusion
model. Zone sizes from a representative plate are shown.