40 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



mitochondria in form, arrangement, or, so far as is known, in function, and 

 this interpretation has been severely criticised. 



D: THE CELL IVALL OF MYXOBACTERIA 

 (54, 62, Sy, 90) 



The myxobacteria dither from most other bacteria in that they lack the 

 rigid cell wall, and are independent of flagella for motility. 



No cell wall whatever can be detected in myxobacteria by ordinary 

 staining methods, but its existence, and some of its structural characteristics, 

 can be interred from other considerations. Although the cells exhibit some 

 degree of flexibility, their structure is sufficiently rigid to enable them to 

 retain the bacillary form when immersed in fluid. Such strength would 

 unquestionably not be possessed by the improtected cell membrane. 



Myxobacteria are motile only when in contact with a surface, whether 

 a solid surface c^r the surface film of a fluid. They show a marked inclination 

 to move along the lines of physical stress in the surface, a phenomenon which 

 has been described as elasticotaxis. Their mode of progression has been 

 variously described, but appears to the author to be a worm-like action 

 analogous to peristalsis. Flexion is occasionally shown but probably is not 

 a necessary function of locomotion. 



This implies a muscular activity in the cell wall, which must be 

 capable of contracting circumferentially, to extend the cell, and also longi- 

 tudinally, to shorten and expand the cell. Muscular action in so small an 

 organ is not exceptional and is obvious in the locomotory cilia and flagella 

 of many small creatures, including bacteria. It may therefore be presumed 

 that the cell wall o{ myxobacteria comprises a longitudinal and circular system 

 of contractile fibres, which enable it to perform the flexion and the peristaltic 

 action which can be observed. It may be regarded as reasonably certain that 

 such contractile fibres are composed of protein, which serves to explain the 

 difference between the chemical reactions of the myxobacterial cell wall and 

 of the polysaccharide structure which is common to most other bacteria. 



The microcysts of myxobacteria possess a rigid cell wall which more 

 closely resembles that of eubacteria. 



