Amies modified Stuarts original formula by replacing the glycerophosphate in the original formula for an inorganic phosphate buffer. The metabolism of glycerophosphate by coliform organisms and other Gram-negative rods, in Stuarts original formulation, resulted in proliferation of these organisms from throat, wound and fecal specimens. Amies also found that NaCl at 0.3% w/v was optimal for the preservation of Neisseria gonorrhoeae. Calcium and magnesium salts were added in the belief that these ions were of importance in controlling the permeability of the bacterial cells and contributed to their survival. Copan offers Amies transport systems as Liquid Amies Swabs, Amies Agar Gel without Charcoal, Amies Agar Gel with Charcoal, and a modified version of Amies Gel with and without Charcoal in its M40 Transystem.