300 BACTERIAL VARIATION 



with an alteration in the method of cell division (Nutt 1927). If normal smooth 

 strains of Salm. typhi-murium are grown in a thin layer of agar between a slide 

 and a cover-slip and watched under the microscope, it will be noted that each 

 cell division is soon followed by separation of the daughter cells, which slip past 

 each other and come to lie side by side. In rough variants derived from these 

 smooth strains, the daughter cells tend to adhere, end to end, for some time 

 after division has occurred. Short chains are formed and angular bends develop 

 at the junctions between adjacent cells. The tendency of rough bacilli to agglut- 

 inate spontaneously in normal saline appears to be due in many cases to the 

 presence, at the bacterial surface, of some lipoidal substance, since extraction 

 with alcohol at a temperature of 50-60° C. removes the salt-sensitiveness of 

 many rough strains (White 1927). It seems probable that this alcohol-soluble 

 constituent is present in the normal smooth form as well as in the rough variant, 

 but in the former it does not determine the character of the cell surface. 



In the organisms referred to above, and in many others, the S — >- R variation 

 is associated with the loss of the polysaccharide antigen that characterizes the 

 surface of the normal smooth form ; and, though the rough variant has a poly- 

 saccharide constituent of its own, there seems little doubt that the change from 

 smoothness to roughness is associated with a relative increase of lipoid as compared 

 with polysaccharide components at the cell surface, and a consequent change in 

 colloidal behaviour from hydrophile to hydrophobe. The hydrophobe qualities 

 of a suspension of rough variants is reflected by increased agglutinability by salt 

 and other non-specific agents, like the dye trypaflavine. There is not, however, 

 any dependable connection between this degree of agglutinability and roughness. 

 For example, trypaflavine agglutinates not only rough variants of bacteria in the 

 coli-typhoid group, but also Vi strains of Salm. typhi, and flagellated salmonella 

 bacilli in the group phase (Sertic and Boulgakov 1936, 1937, Hirsch 1937). There 

 would also appear to be a laying-bare of protein constituents ; since rough variants 

 of salmonella bacilli, and certain other organisms, usually give a positive Millon 

 reaction, while normal smooth strains do not (see White 19296). 



In the particular case of the pneumococcus the change from smoothness to 

 roughness is associated with the loss of the characteristic capsule, and with it of 

 the specific capsular polysaccharide that determines type-specificity. Among the 

 antigenic components that are left are a nucleo-protein antigen and a minor poly- 

 saccharide component that is common to all pneumococcal types (see Avery and 

 Heidelberger 1923, Griffith 1923, Reimann 1925, Tillett, Goebel and Avery 1930). 



A similarly associated loss of capsule and virulence has been observed in Pasteurella 

 septica (Priestley 1936) and H. influenzce (Chandler, Fothergill and Dingle 1937), which, 

 like the pneumococcus, had at the same time lost their capacity to produce specific soluble 

 substances. In bacilli with no morphologically distinguishable capsule, there is never- 

 theless a demonstrable loss of antigen characterizing the virulent form. Thus, Boivin 

 and Mesrobeanu (1936) could extract 8-9 per cent, of O antigen from smooth Salm. typhi- 

 murium but none from rough forms; and Miles and Pirie (1939) found a progressive 

 diminution in the yield of main antigen from Br. melitensis as cultures increased in agglutin- 

 ability by heat, salt, and a specific antiserum prepared against rough strains. 



It must not be supposed, however, that the mere power to synthesize large amounts 

 of polysaccharide substances, whether they appear as a capsule with a defined edge, as 

 a mucoid extra-cellular substance, or as increased cellular content, necessarily characterizes 

 the virulent smooth form. For example, Boivin, Mesrobeanu, Magheru and Magheru 

 (1936) found a high polysaccharide content in all of five smooth strains of Bad. coli, but 



