CHAPTER III 



Surface Structures 



A: THE CELL WALL 



(i, 2, 5-12, 15-20, 24, 25, 26, 28, 29, 30, 32, 33, 35, 3<5, 40, 43-46, 49, 50, 5^, 55, 



56, 59, 61, 68, 69, 70, 71, 72, 74, 75, 77, 78, 81, 83-88, 93, 94, 95, 97, 98, 103, 



104, 105) 



BACTERIA are of such small size that the adoption, in a fluid medium, of 

 kany other form than that of a sphere, argues considerable rigidity of 

 structure. Were this rigidity absent, the forces of surface tension, 

 relatively enormous in such a case, would force the bacterium to adopt the 

 form possessing the smallest proportion of surface area to volume. While it 

 is true that some bacteria are almost perfect spheres, although these are rather 

 fewer than is often supposed, the majority are rod-shaped, usually slightly 

 spiral, and sometimes more markedly spiral so that this feature is sufficiently 

 obvious to attract attention. Their rigidity is further emphasised by the 

 absence of flexion in their movements, except in certain specialised forms 

 such as myxobacteria. An appearance of flexion is often given by the rapid 

 rotation of spiral cells, but this is almost certainly an optical illusion. Enforced 

 flexion causes fracture and distortion o( the bacterium. This rigidity is due 

 to the possession of a cell wall o( great strength. 



An understanding of the nature and behaviour of the cell wall and 

 membranes of bacteria is a necessary preliminary to studies of all kinds in 

 bacterial cytology. Neglect to acquire such an understanding has had the 

 regrettable effect of invalidating a great deal of otherwise sound and con- 

 scientious work, as well as of emphasising the defects of some to which no 

 such description can be applied. 



The most usual and indeed the most fundamental error which arises from 

 such neglect is the assumption, so frequently made, that bacteria are normally 

 unicellular, whereas in very many groups, ranging in morphology from 



