CHANGE OF ACID AGGLUTINATION OPTIMUM AS INDEX 

 OF BACTERIAL MUTATION. 



By PAUL H. De KRUIF. 



{From the Laboratories of The Rockefeller Institute for Medical Research.) 

 (Received for publication, December 16, 1921.) 



INTRODUCTION. 



Two distinct varieties of microbe have been shown to exist in 

 cultures of the bacillus of rabbit septicemia (1). These have been 

 designated as Microbes D and G. Microbe D is the variety isolated 

 from rabbits dead of spontaneous infection with the rabbit septicemia 

 bacillus. It is characterized by diffuse growth in serum and plain 

 broth, forms opaque fluorescing colonies on serum agar, and is highly 

 virulent for rabbits. Microbe G, first discovered accidentally in 

 Microbe D cultures, has been proved to be a true mutant of the 

 parent D form (2). The mutant Microbe G grows in granular 

 fashion in liquid media, forms translucent bluish colonies with no 

 fluorescence, and exhibits extremely low virulence for rabbits. The 

 mutation experiments demonstrating that Microbe D, under con- 

 trollable conditions, changes into Type G were performed with D 

 strains arising from single individuals isolated by Barber's pipette. 



The granular growth of Microbe G in fluid medium is one of its 

 most striking differential characters, and has persisted throughout 

 transplants for more than 1 year. This sedimenting growth of 

 Type G in broth, compared to the evenly suspended, uniformly 

 turbid appearance of broth cultures of Type D led to an examination 

 of the acid agglutination optima of the two types. 



Methods. 



The method for the determination of the acid agglutination optimum 

 was that of Michaelis (3), later described in full by Beniasch (4). It 

 consisted in mi.xing carefully prepared suspensions of the organism 



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