Printed in Great Britain 223 The Relationship Between the Nature of the Cell Wall and the Gram Stain-

None of the classes of major chemical constituents of the walls of bacteria and yeasts is exclusive to organisms which give a Gram-positive reaction. Walls of Gram-positive bacteria are richer in mucopeptide than are those of Gram-negative bacteria. The latter are characterized by high lipid contents. Yeast walls are rich in polysaccharide complexes. There appears to be a broad correlation between the Gram reaction and the decreased leakage of 32P compounds from labelled cells on exposure to increasing ethanol concentrations in the range 50-100 yo (v/v) ethanol. The data on the release of 32P compounds are in accord with the cell-wall ‘ permeability ’ mechanism for the Gram reaction and imply quantitative rather than all or none differences in Gram behaviour. Mechanical rupture of the cell wall or digestion of the wall with lysozyme rendered organisms which had been previously Gram stained in suspension by the technique of Wensinck & BoevC (1957), susceptible to decolorization with 96 yo (v/v) ethanol in water