Fig. 5. Antimicrobial assay shows bioactivity only in amber vesicles of Aplysia californica. Clear spots on the plate represent antibacterial activity and are seen only for spots 1, 3 and 5. Spot 1, pure ink (note that this spot is free of bacteria, but appears dark because of the purple pigment of the ink); 2, buffer control; 3, red-purple and amber vesicle extracts together; 4, opaline (note that this spot is dark because it has bacterial growth greater than the control), because opaline is a very good growth medium; 5, amber vesicle extract alone; 6, red-purple vesicle extract alone.