In Chapter 1 peptidoglycan was described as the most important component of bacterial cell walls, being vital for the normal functioning of the cell Peptidoglycan accounts for approximately 50 per cent of the weight of the wall of Gram-positive bacteria. The remaining 50 per cent is made up from a variety of accessory polymers, the most important of which are teichoic and teichuronic acids. Proteins also play an important part in the structure of the wall in some Gram-positive organisms, but in general lipids are absent. Finally some Gram-positive organisms are encapsulated; that is to say they are enveloped by a layer of material, usually polysaccharide, which adheres to the wall but is not covalently attached.