X'Ain ATIONS, Ml'rA'I'loNS. AND A I )Ai''rA'll( )\S 



101 



Tahi.k K) 

 Comparison of some variable properties of S. coelicolor (Stanier) 



et aL, Shimako, Saito and Ikeda, Ogins, and 

 numerous others. 



M or phological \ ariations 



Jensen (1931) obtained from single-cell 

 cultures of N. polychromogenes two different 

 variants, one a rod-shaped or K-form, and 

 the other a fihimentous or F-form. The R- 

 form produced initially a small unicellular 

 mycelium, which soon di\-ided into bacteria- 

 like bodies that multiplied by cell di\'isioii, 

 in the maimer characteristic of corynebac- 

 teria. It gave rise to two subtypes: a soft or 

 "s" and a hard or "h" type. The s-type 

 formed a soft, pasty growth of a red color; 

 the bacteria-like bodies were usually short, 

 blunt, little-branched, and partly acid-fast. 

 The h-type formed a dry, crumbly growth, 

 adhering firmly to the medium and consist- 

 ing of a longer and more slender cell, less 

 acid-fast than the s-type and with a marked 

 tendency to produce long filameiils. Th(> 

 h-type arose spontaneously in, and could 

 also be produced experimentally from, cul- 



tures of the s-type. Exposure of the h-type 

 to ultraviolet rays gave rise to a ^yellow and 

 to a white variety of the s-type. The F-form 

 was considered as a stal)ilization of the initial 

 mycelial stage of the R-form; it represented 

 an actinomycete consisting of long, delicate, 

 branching hyphae, with a well-developed 

 aerial mycelium, and without any tendency 

 to divide by septa into bacteria-like ele- 

 ments. The P'-form arose spontaneously in 

 old cultures of the s-type but not in the h- 

 type; its ai)p(>arance did not seem to be in- 

 fluenced by external factors. 



Wright obtained a similar kind of dissocia- 

 tion in se\(>ral aerobic species belonging to 

 the genus Xocardia. He observed variants 

 that were diphtheroid in nature and formed 

 a soft, highly pigmented growth. These 

 variants were believed to represent a definite 

 phase common to the members of the group 

 and pointing to the close relationship be- 

 tween the actinomycetes and the coryne- 

 Wactcria. 



Numerous other ol)ser\'ations of a similar 



