Vesterdal(1946), using an all-over surface-seeding technique with a sensitive
staphylococcus, also noted the extension of clear-zone edges by lysis of marginal
colonies, and recorded the diameters of outer and intermediate zone edges.
With the lowest concentrations of penicillin used the intermediate zones were
narrow and opaque. With greater concentrations these zones widened, and an
inner, translucent zone appeared, which gradually displaced the opaque zone,
and became still wider as the series was continued to the highest concentrations