INTERCELLULAR SUBSTANCES AND WALLS 79 



The fundamental cell wall components are further organized 

 into systems of molecules and macromolecules. The basal structure 

 of the wall in Gram-positive forms commonly consists of: (1) 

 a hexosamine polymer derived from N-acetylglucosamine, muramic 

 acid and galactosamine ; (2) the peptides, alanine-glutamic acid- 

 -lysine or alanine-glutamic acid-diaminopimelic acid; (3) poly- 

 saccharides; (4) phosphorylated compounds; (5) antigenic proteins. 

 The hexosamine polymer chains provide an insoluble ground 

 substance to which the peptides and other components are attached 

 in an as yet uncertain manner. 



Gram-negative forms such as Escherichia coli contain similar 

 basal structures. The rigid basal structure is, however, "masked" 

 by a lipoprotein layer. Upon removal of the lipid material, the 

 characteristic Gram-positive wall can be demonstrated. 



Glucosans or aminoglucosans are evidently commonplace com- 

 ponents of the bacterial cell wall (although Corynebacterium 

 haemolyticum has no glucose in its wall) whereas the occurrence 

 of a-cellulose as a major wall substance is unusual. Acetobacter 

 xylinum when incubated with hexoses, D-fructose and D-glucose 

 especially, elaborates a wall substance which is indistinguishable 

 from natural cotton cellulose. Acetylation yields cellobiose octa- 

 -acetate; methylation and hydrolysis yields 2,3,6-trimethyl-D-glu- 

 cose; and x-ray analysis yields the usual diffraction pattern of 

 cellulose. 



Acetobacter cellulose consists of fibers 100 A in thickness, 

 5000 A in width, and 40[x in length. These fibers contain a weave 

 of fibrils 200 A in width. 



Beyond the rigid cell wall, some bacteria also produce mucil- 

 aginous encapsulating polysaccharides. The ultimate builctfng- units 

 obtained upon hydrolysis of capsular material include D-glucose, 

 D-galactose, L-rhamnose, pentoses, glucuronic acid, galacturonic 

 acid, hexosamines, and N-acetyl hexosamines. These sub- 

 stances occur in varying proportions and combinations which to- 

 gether with unusual monosaccharides serve to characterize ind- 

 ividual species or strains. Thus the capsule of Shigella dysen- 

 teriae contains L-rhamnose, a comparatively uncommon sugar, 

 together with D-galactose and hexosamine. In contrast, Corynebac- 



