r: IT A V T i; n 



Variations, Mutations, and Adaptations 



Coiicepis of Constancy of Characters 



An actinomycete culture is made uj) of an 

 extensive mass of mycelium, either of a sub- 

 strate or vegetative nature or of both sul)- 

 strate and aerial hyphae. Sooner or later, the 

 mycelium breaks up into a large number of 

 different kinds of cells and spores. These xixry 

 greatly in size and in shape, and frecjuently 

 in certain physiological properties. Largely 

 because of this, as well as under the influence 

 of different en^'ironmental and nutritional 

 factors, cultures originating from the various 

 cells and spores give rise to strains that may 

 show (juite distinct variations from the 

 original culture. These \'ariations may in- 

 volve colony structure, formation of soluble 

 and insoluble pigments, sugar utilization, 

 virulence, antibiotic production, and resist- 

 ance to antimicrobial agents. 



Following the concept of Ferdinand Cohn 

 and Robert Koch, many, if nf)t most, bac- 

 teriologists once considered the bacterial 

 cell as constant in nature and immutable or 

 monomorphic. This attitude tended to dis- 

 courage investigations of problems of varia- 

 tion and inheritance among microorganisms. 

 On the other hand, the pleomorphists were 

 inclined to consider the microbial cells as 

 undergoing considerable metamorphosis and 

 constantly giving rise to new species. The 

 history of microbiology is replete with the 

 changing influence of these two schools, one 

 concept gaining the upper hand at one time, 

 and the other at another time. 



Recently, the old problem of morphologic 



variation among bacteria has been reopened 

 to an extent that many of the modern pleo- 

 morphists tend to I'eturn to the older con- 

 cepts of Naegcli and other earlici- j)l('oinor- 

 phists that any bacterium may traiisnnite to 

 form any other bacterium. 



Enderleiii coiiied a vocabulary of nearly- 

 two hundred new words to express his ideas. 

 The life cycle of a bacterium was said to 

 consist of two simultaneous, paralk^l, and 

 coordinated processes: (a) a multiplicative 

 development through simple cell division, 

 and (b) a progressive development, \'erv slow 

 and characterized by morphologic variation. 

 It was believed that as the ontogeny of an 

 indi\idual repeats the phylogeny of the 

 race, so does the life cycle of a bacterium 

 repeat the evolution of the species; the bac- 

 teria were said to be deri\'ed from and to 

 return to an elementary unit, the mychit. 

 The life cycle of bacteria was said to begin 

 with the fusion of two haploid mychits, fol- 

 lowed by progressi\-e changes in cell com- 

 plexity; when a maximum, fixed for the 

 species, is reached, there is a final return to 

 the haploid mychit. The cycles may be in- 

 complete, shortened, or completely arrested. 



This confusion was also reflectcnl in the 

 literature on the cyclogenie of actinomycetes. 

 It is sufficient to cite the findings of Xepomn- 

 jaschy, who recognized, among the \ariants 

 of an actinomycete i.solated from the pus of 

 patients, three types of dis.sociation: 1. 

 S-type — smooth, transparent colonies, con- 

 sisting of gram-negati^'e rods, growing an- 



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