136 



ANTISEPTICS 



12 3 4 5 6 DAYS eoi2J«58»a OAYS q 



Fig. 25. Effect of the amount of inoculum on the time required for 

 the development of visible turbidity in a bacterial culture, when the 

 antiseptic prolongs the lag period (left), and when it retards the 

 growth rate (right). The broken lines refer to controls, the solid 

 lines to cultures with antiseptic. Abscissa: time; ordinate: logarithm 

 of the number of bacteria per cc. 



creased growth rate. But the 5-hour measurements 

 show a decrease of growth caused by urea. The two 

 observations can be explained only by the assumption 

 that urea prolongs the lag phase, but increases the growth 

 rate. The example indicates how important it is to con- 

 sider these two phenomena separately. 



V. THE DUAL ACTION OF THE DYES 



Dyes have been employed in the treatment of wounds 

 as early as 1890, and since 1900 many attempts have been 

 made to develop dye derivatives for chemotherapeutic 

 purposes. Several such compounds have now been in 

 use for some time, but, in general, they have proved more 

 eifective against trypanosomes than against bacteria. 

 The outstanding fruits of this search for therapeutic 

 agents are rivanol and germanin (Bayer 205). 



Like many other antiseptics, dyes in high concentra- 

 tions act as disinfectants, but high concentrations are 

 rarely used. In the customarj^ w^eak solutions, their 

 effect differs from that of most antiseptics. The bacteria 



