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SUMMARYThe cell wall of Salmolzella gallinarum, like that of other Gram-negative organisms, was found to contain a separate continuous rigid mucopolymer layer. This structure was rapidly broken down by the cell's own enzymes during wall preparation when suitable precaution against this action was not taken. Possible errors in the interpretation of cell-wall structure, deriving from this and other causes, are discussed.

In the course of our work on the biochemistry of receptor-active components of the Escherichia coli B cell wall, bacteriophages quite generally proved to be very useful and sensitive tools for helping to dissect the wall into many different, functionally intact, macro-components. For this discussion the most relevant result of these dissections is the finding that the coli wall is composed of two layers: one is lipoprotein and amounts to about 80 yo of the dry weight of the cell wall; the other layer is characterized by a large content of saccharides + lipids + a few typical amino acids which later will be considered more closely. This 2 0 % layer we have called the lipopolysaccharide layer (Weidel, Koch & Lohss, 1954).After removing the lipoprotein layer from isolated cell walls by 90 % phenol, in which it is soluble, the remaining lipopolysaccharide, when viewed under the phase-contrast microscope, appears largely in the form of extremely thinwalled transparent rods. Obviously the lipopolysaccharide layer is rod-shaped as such and forms the supporting framework of the coli wall to which it lends rigidity. The lipoprotein cannot have either of these two properties by itself because of its great plasticity which becom-directly noticeable after removing by dialysis the phenol in which it was dissolved.The relative positions of these two layers can be ascertained by using phages as indicators. Before phenol treatment the coli wall adsorbs the coliphages T2, T4 and T6. After removing the lipoprotein layer with phenol, T2 and T6 are no more adsorbed by the remainder of the wall, i.e. the lipopolysaccharide, whereas the adsorbability of T 4, as measured by rate of adsorption, is markedly increased. One is led to the conclusion that additional receptor sites for T4, which all lie in the polysaccharide layer, must have been uncovered and made accessible by removing the lipoprotein. Since the phage particles in these tests can interact with the wall from the outside only, it would follow that the outside is formed largely by the lipoprotein layer which contains the receptor sites for T2 and T6 and covers a great deal of the T4-sites actually present in the lipopolysaccharide layer.With this picture in mind we now turn to the mechanism of destruction of the double-layered coli wall by certain virulent phages. As early as 1949 we were able to show on electron micrographs that coliphage T 2, after adsorption to coli cell walls, causes structural changes within, and release of material from them (Weidel, 1951). This phenomenon seemed to indicate a specific enzymic activity of the phage particle which might well explain the more general phenomena of virus penetration and lysis 'from within' or 'from without '.