DISSOCIATION AND TRANSFORMATION 135 



Early Observations of Dissociation: 1891—1921 



Bacterial variation is not a new phenomenon. It is only the 

 study and the explanation of the underlying causes that are recent. 

 In 1891, Kruse and Pansini 763 first called attention to changes in 

 morphology, cultural characters, and virulence of pneumococci un- 

 der artificial cultivation. Pure cultures freshly isolated from pneu- 

 monic material were typical in appearance during early genera- 

 tions but, on continued cultivation on unfavorable media, the cells 

 exhibited deviations from the normal characters. The lance-shaped, 

 diplococcal forms became streptococcal or even bacillary, the cap- 

 sule rapidly vanished, and virulence waned. The degenerated cocci, 

 when passed through susceptible animals, regained their capsules 

 and virulence, and when returned to favorable media, again showed 

 normal pneumococcal morphology. Kruse and Pansini, therefore, 

 noted many of the features of dissociation and were aware of the 

 first causes of the phenomena. 



In the next year, Arkharow 17 reported changes taking place in 

 cultures cultivated in the serum of vaccinated animals. Growth 

 was slow in developing and at the end of three or four days the 

 cocci began to diminish in size, to grow in long chains, and to lose 

 virulence. Four years later, Eyre and Washbourn 373 described the 

 variations observed on continued cultivation of pneumococcal 

 strains in broth. Of one strain it was said that it differed in "mor- 

 phology, biology and pathogenic properties from the parent stock. 

 It, in fact, represented a distinct variety, possessing practically 

 no virulence, and growing luxuriantly, even at 20°C, on all the 

 usual media." The first attempts to induce this variant to revert to 

 its former state were unsuccessful. Then, by passage through a 

 rabbit, the variant reverted to its original form. 



Hiss, Borden, and Knapp (1905) 651 encountered organisms, in- 

 distinguishable in fermentative reactions from pneumococci, which 

 showed variations in morphology or agglutination, and the au- 

 thors considered that the cultures were temporarily or perma- 



