92 DISSOCIATIVE ASPECTS OF BACTERIAL BEHAVIOR 



It is doubtful if Baerthlein appreciated the full significance of his observations. 

 For some time at least he believed that his various culture types represented merely 

 "mutations," such as had been described earlier (especially in secondary colony forma- 

 tion) by Neisser,' Massini,^ Miiller,^ Tenfold,^ Thaysen/ Burri/ Eisenberg/ Leding- 

 ham," and many others. It thus remained for Arkwright/ in 1921, to grasp more fully 

 the significance of Baerthlein's work. Among members of the colon-typhoid-dysentery 

 group Arkwright noted particularly two colony forms which occurred in each species 

 with marked persistency. One was round, regular, opacjue, and characterized by a 

 smooth, glistening surface; the other was flat, irregular, translucent, and showed a 

 rough or sandpaper-like surface. The former was termed the "S" type (smooth), the 

 latter the "R" type (rough). The S type culture, on aging, transformed readily into 

 the R. The latter, however, held to its new characteristics with considerable tenacity. 

 While the S type culture grew in broth with a homogeneous clouding, the R type gave 

 an agglutinative or sedimentary form of growth. These two culture forms were ob- 

 served by Arkwright in B. coli, B. typhosus, and B. dysenteriae. His splendid and far- 

 seeing work marks the beginning of a new epoch in the study of bacterial variation. 



In 1921 De Kruifs also made, independently, a contribution of fundamental im- 

 portance dealing with dissociation in the rabbit Pasteurella type. Bad. lepisepticum. 

 In this species he observed two forms of culture, differing from each other in colony 

 form, manner of growth in broth, serological and immunological reactions, and par- 

 ticularly in virulence. De Kruif designated these two types "D" and "G," respectively. 

 As we can now see, his D form was analogous to Arkwright's S, while his G form was 

 analogous to Arkwright's R. In De Kruif's experience, while the D type culture was 

 highly virulent for rabbits, the G form possessed little, if any, virulence. Moreover, 

 while the D form in the killed state was of little value as an immunizing agent, the G 

 form, living, when injected into rabbits even in small doses, produced immunity to 

 large amounts of virulent culture. Even one dose secured these results. 



Since the important works of Arkwright and De Kruif in 1921, the same line of study 

 has been carried into many other fields: to the streptococci by Cowan*; to the pneumococcus 

 by Griffith^, also later by Reimann^ and by Amoss^; to B. typhosus and B. enteritidis b\' Ark- 

 wright and Goyle,9 and by Goyle'" alone; to the Salmonella forms by White," and by Topley 

 and Ayrton"; to B. cholerae suis by Orcutt"; to the cholera vibrio by Balteanu'^; to FriedLind- 

 er's bacillus by Julianelle'^ ; and to B. coli quite recently by Dulaney.'^ De Kruif's work has 



' Neisser, M.: loc. cit. ^ Massini, R.: loc. cit. ^ Hadley, Philip: loc. cit. 



'> Arkwright, J. A.: /. Path. &° Bad., 24, 36. 1921. 

 sde Kruif, P.: J. E.xper. Med., 33, 773. 1921; also 35, 631. 1922. 

 ' Cowan, Mary: Brit. J . Exper. Path., 3, 187. 1922. 



^ Griffith, F.: Public Health and Medical Subjects, Ministry of Health, Rep. 18. London, 1923. 

 * See Hadley, Philip: loc. cit. 



' Arkwright, J. A., and Goyle, A. N.: Brit. J. Exper. Path., 5, 104. 1924. 

 '0 Goyle, A. N.: /. Path, c^ Bact., 29, 149. 1926. 



" White, P. B.: Special Rep., Med. Research Council, No. 91. London, 1925. 

 " Balteanu, I.: /. Path, b' Bact., 29, 251. 1926. 

 ■3 Julianelle, L. A.: /. Exper. Med., 44, 683. 1926; also p. 735. 

 '■* Personal communication. 



