VARIATION OF SALMONELLA PULLORUM 7 



An inagglutinable strain of the Shiga dysentery bacillus was experimentally 

 produced by Benians (1919) from an agglutinable strain, by subcutaneous inocu- 

 lation into a guinea pig of the agglutinable bacteria suspended in mucilage of 

 tragacanth. 



Dawson (1919) in an extensive study of bacterial variation induced by changes 

 in the composition of culture media observed that constituents in the medium 

 stimulated variation from the simplest to the most complex degree, which in some 

 cases practically amounted to the production of a new strain. 



Mackie (1920) reported variants obtained from B. vesiculosis when growing 

 the original type on brilliant green agar. The variants exhibited differences in 

 colonial and cellular morphology and in agglutinating ability. One variant strain 

 possessed a higher degree of agglutinability than its parent strain. 



Arkwright in 1920 introduced the terms "S" and "R" to designate so-called 

 "smooth" and "rough" colonies. He obtained from a single strain two forms, 

 one a "smooth" which formed a stable suspension in physiological saline, and the 

 other a "rough" which agglutinated in saline solution without the addition of 

 serum. These forms were derived from Bad. dysenteriae (Shiga), Bad. typhosum, 

 Bad. paratyphosum B, and Bad. dysenteriae (Flexner). Other distinguishing 

 characteristics, such as behavior in broth, and antigenic and agglutinative prop- 

 erties, were ascribed to the two forms. In 1921 Arkwright further reported that 

 "S" and "R" forms, as well as intermediate forms of Bad. dysenteriae (Shiga) 

 proved to be virulent for rabbits. It was further stated that to change one form 

 into the other, after they were apparently quite pure, was more difficult than when 

 unselected cultures were used which had shown "S" and "R" characters. 



In 1921 De Kruif reported two types of organisms as existing in a culture of 

 Past, lepiseptica, recently isolated from a spontaneous infection. The two organ- 

 isms differed greatly in their degree of virulence, as well as in other characteristics. 

 The features of each type were constant through many passages in artificial media. 



Non-specificity of agglutination with "rough" variants was reported by Schiitze 

 in 1921. He defined a substrain variant as one which contained less agglutinating 

 antigen than another of the same type. It absorbed and agglutinated the serum 

 of a superstrain, but not to the extent that the homologous strain did. On the other 

 hand, the superstrain agglutinated and absorbed the serum of the substrain to its 

 titre limit. The author also referred to "serological cosmopolitanism" among 

 rough cultures, which signified that two rough members derived from unrelated 

 sources possessed serological relationships. 



In 1922 Lohnis presented an extensive review and discussion on the subject of 

 variation and life cycles of bacteria, with special reference to the different phases 

 in the life history of microorganisms. He maintained that all the bacteria studied 

 live alternately in an organized and in an amorphous or symplastic stage, and 

 that the life cycle of each species is composed of several subcycles showing wide 

 morphological and physiological differences. 



Arkwright (1924) observed that variants sensitive to bacteriophage arose 

 spontaneously in old normal cultures from resistant strains; also, that sensitive 

 variants which were studied had always been "rough", that is, were agglutinated 

 by salt (0.85%). However, not all "rough" variants had been sensitive to phage 

 action, although all of the "smooth" cultures examined were resistant to phage. 

 The variants obtained by phage action and without the addition of phage were 

 very similar. 



In 1924 Arkwright and Goyle attempted to determine whether the "S" and 

 "R" forms correspond in any way to the "O" and "H" forms of Weil and Felix. 

 The analogies that the authors have advanced do not appear justified from the 



