142 ANTISEPTICS 



cells are very young because young cells have a much 

 more active metabolism than old ones, and therefore can 

 adjust the potential more readily than old, resting cells. 



That an unfavorable oxidation-reduction potential re- 

 tards or prevents multiplication is common knowledge. 

 That it kills the bacteria fairly readily represents a new 

 experience. Ingraham (1933) made the statement that 

 bacteria are not killed by crystal violet, but Hoffmann's 

 numerous data (1943) show that even with dilute dyes, 

 99% and more of the cells are killed before multiplica- 

 tion begins. That these cells are really dead is evidenced 

 by the fact that activated charcoal, which removes all 

 crystal violet from the culture in less than a minute, did 

 not restore in them the faculty of reproduction. 



If antisepsis by dyes is due to the establishment of a 

 redox potential too high for multiplication, the species 

 with the strongest reducing power, the Clostridia, should 

 be the most tolerant to dyes, with the colon group as a 

 close second, while the strict aerobes should be more sen- 

 sitive than the streptococci. Ingraham has arranged 20 

 species in order of increasing sensitivity, and, with a few 

 exceptions, the observed order agrees with that which 

 general conceptions of ''reducing power" in these spe- 

 cies would predict. Clostridia are, in fact, the most tol- 

 erant species, while the aerobic spore-formers and the 

 aerobic yeasts Torula and Monilia are the most sensitive 

 ones. The observation of Slanetz and Eettger (1933) 

 that the fusiform bacteria can tolerate gentian violet in 

 concentrations of 500 ppm. (1:2,000 dilution) fits into 

 the picture because this group consists of strict anae- 

 robes. The highly selective action of this and other dyes 

 is probably not connected with the Gram staining reac- 

 tion, as is commonly thought, but depends upon the re- 

 ducing power of the species. Because of this selectivity, 

 some dyes have been added to special culture media to 

 suppress certain groups while permitting others to grow. 



