42 IMMUNOLOGY 



aeteristics such as morphology, fermentative powers, pigment 

 production, motilitj^, pathogenesis, etc., are constant and inherita- 

 ble and that all organisms in a colony or pure culture are alike. 

 Opposed to this are the extremely radical views of Nageli (1877) 

 who held that theie is no morphological or pliysiological constancy. 



Evidence of Heterogeneity Within a Culture. — It is now 

 quite generally kno\Mi that among bacteria constituting a pure 

 culture there is definite heterogeneity. The individuals which 

 collectively constitute the culture not only show slight variation 

 in shape, size, and staining reaction but differ in age, physiological 

 stability, pathogenicity and adaptability. Some may be avirulent 

 while others are quite virulent. 



Fluctuating Variability. — Heterogeneity in a culture may be 

 due to age, fluctuating variability, heredity, true mutation or to 

 the phenomenon of bacterial dissociation. Fluctuating variability 

 is usually illustrated by variations in size or shape which corre- 

 spond to height or weight fluctuations observed in the human being. 

 Any characteristic variation that oscillates around an average 

 type is termed "fluctuating variability." Practically all of the 

 phenomena of bacterial variation are discussed by Hadley* (1927) 

 in his excellent monograph on bacterial dissociation. Many kinds 

 of variation are quite evidently examples of either mutation or 

 fluctuating variability, but other variations are difficult to classify. 



Early Theories of Bacterial Characteristics. — According to 

 the theory of Cohn (1875), Koch (1877), Migula (1897), and 

 others that bacterial characteristics are constant, one would expect 

 all colonies obtained by plating a pure culture on agar to resemble 

 not only each other, but also the parent colony. That such is not 

 the case w^as noted by numerous workers prior to the extensive 

 study of Baerthlein (1918) in colony variation. The latter 

 investigator not only described in detail various types of colonies 

 obtained from each pure culture but he also attempted to correlate 

 colony variation with other characteristics of the organism. 

 Arkwanght (1921) is credited by Hadley (1927) with being the 

 fii-st to appreciate the significance of Baerthlein 's results. 



It would seem, however, that Bordet as early as 1909 described 

 bacterial dissociation into what are now called rough and smooth 

 colonies and found that, while both possessed a common antigenic 



*J. Infect. Dis. 40: 1, 1927. 



