138 ANTISEPTICS 



seem to have started at the same time; there was no 

 increase of the lag period. 



This very unusual effect of the dyes was explained by 

 Dubos (1929) as due to a change of the oxidation po- 

 tential of the medium by the dye. He showed that a 

 Pneumococcus R II and a Streptococcus liemolyticus 

 were inhibited only by those dyes whose oxidation poten- 

 tial was higher than that corresponding to an rH of 12.5 

 while they grew in all dyes with a lower potential. 



Ingraham (1933) verified Dubos' tentative explana- 

 tion in an extensive study of the action of gentian vio- 

 let. The relationship that she found between the length 

 of the lag phase and the logarithm of the cell concentra- 

 ,tion is rectilinear and can be expressed by 



Lagi = Lago + k log No/Ni 



where N, represents the larger and Ni the smaller inocu- 

 lum, and Lag2 and Lagi the corresponding lag phases. 

 The proportionality constant h depends upon the species 

 as well as on the medium. She furthermore showed that 

 a large inoculum may be capable of adjusting the poten- 

 tial to the optimum of cell growth so that the bacteria can 

 multiply again, while a small number of cells is not able to 

 accomplish this change. 



Hoffmann and Rahn (1944) separated the bactericidal 

 from the bacteriostatic action. In concentrations over 4 

 ppm. of crystal violet (the purest form of gentian violet 

 available), in which Streptococcus lactis was killed, the 

 order of death was logarithmic, and the deathrate con- 

 stant was practically proportional to the dye concentra- 

 tion K = 0.037 c, where c is the concentration in ppm. 

 (See Table 28). Death is probably due to the reaction 

 of the dye with some cell constituent essential for a vital 

 function such as cell division, as Stearn and Stearn 

 (1924) had claimed. It is not due to inactivation of en- 

 zymes, as Hoffmann's (1943) experiments proved. 



