ANTIBIOTIC SUBSTANCES AND DISINFECTANTS 



193 



lethal effects. The conclusion was reached that the mechanism of bac- 

 tericidal action must be considered as a separate problem for each type 

 of organism, and, one may add, for each type of compound. 



Although the major difference in the action of antibiotic substances 

 and chemical antiseptics is based upon the selective antibacterial nature 

 of the former, still an attempt may be made to correlate the two types 

 of compounds. Marshall and Hrenoff (584) constructed a disinfectant 

 spectrum for antibacterial substances with a flexible blending of differ- 

 entiated degrees of activity. The first, or ineffective, band covers a 

 range of dilutions of an agent between zero concentration and the high- 

 est dilution which still exerts no action on bacteria. The second, or stimu- 

 lative, band comprises a range of relatively high dilutions in which 

 there is a slight stimulation of bacterial multiplication j this range is 

 ordinarily narrow, but it may become broad. The third, or inhibiting, 

 and the fourth, or germicidal, bands merge indistinguishably. The 

 fifth, or impractical, band covers a range of concentrations of the dis- 

 infectant that are too great for practical purposes (Figure 19). 



By establishing the normal rate of multiplication of bacterial cells in 

 a given culture without the disinfectant, one can determine the retarda- 

 tion of that rate by the disinfectant. This rate approaches zero at com- 



DISINFECTANT "SPECTRUM' 



BACTERICIDAL 



11111111111 



HI 



Space obout I/20 totol length 



impractical 

 (insoluble, 

 too toxic, 



OR ) 



100% 



GENTIAN VIOLET 



Space just perceptible (-OOlX) 



Figure 19. Disinfectant spectrum. From Marshall and Hrenoff (584). 



