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The surveys of Cummins & Harris (1956, 1958) established that the cell walls of Gram-positive bacteria all contain the amino sugars glucosamine and muramic acid (3-O-a.-carboxyethylglucosamine) and the amino acids alanine, glutamic acid and either lysine or aci-diaminopimelic acid. In some species either glycine or aspartic acid was also present, whereas the other amino acids found in proteins were usually absent. The component of cell-wall structure containing these compounds has been found in all bacteria so far examined and has been given the name mucopeptide (Perkins & Rogers, 1959). In addition, various non-nitrogenous sugars have been found in the cell walls of some strains, but the place of these components in the structure of the wall is not always understood. Often the complex polyol phosphate polymers known as teichoic acids (Baddiley, 1959) are present in the cell walls, and these compounds may include sugar residues glycosidically linked to the polyol. For instance, glucose occurs in the ribitol teichoic acid isolated from the cell walls of Bacillus subtilis (Armstrong, Baddiley & Buchanan, 1960). Sometimes, however, sugars are found that are not part of the teichoic acid but which are present in polymers independent of both teichoic acid and mucopeptide. Examples are the rhamnose-glucosamine polymer found in Streptococcus faecalis (Ikawa, 1961) and group A haemolytic streptococci (McCarty, 1960), and the teichuronic acid, a polymer of N-acetylgalactosamine and glucuronic acid, found in the cell walls of B. subtilis (Janczura, Perkins & Rogers, 1961). From previous work it was known that the cell walls of Micrococcus lysodeiktic contain no phosphorus (and hence no teichoic acid) and consist mainly of glucosamine, muramic acid, alanine, glutamic acid, lysine, glycine and glucose. A critical analytical study has shown that these constituents together account for 93 % of the dry weight of the walls, after allowance has been made for the uptake of water during hydrolysis (Czerkawski, Perkins & Rogers, 1963). Nevertheless, certain discrepancies were brought to light, parti-

A polymer containing glucose and aminohexuronic acid isolated from the cell walls of micrococcus lysodeikticus