A correlation between iodine permeability and the gram characteristic of cells

Kaplan and Kaplan demonstrated that the addition of iodine to the alcohol used as a decolorizer in the Gram procedure resulted in retardation of the rate of decolorization. If the concentration of iodine was sufficiently high, no decolorization occurred. They also found that much higher concentrations of iodine in the alcohol were necessary to prevent the decolorization of Gram-negative bacteria than for Gram-positive bacteria. In their opinion these results indicated that differences in permeability to iodine in alcoholic solution contributed to the mechanism of Gram differentiation. In confirmation of the above work, Mittwer, Bartholomew and Kallman demonstrated that iodine in alcoholic solution stained Gram-negative cells much faster than Gram-positive cells. No such difference was demonstrable for iodine in aqueous solutions. The nature of the proof presented by the above workers, however, lacked accurate and objective results, and could not be considered as conclusive. When the methods of filter paper chromatography are applied to this problem, accurate and objective results can be obtained easily