AXTI^'^EPTICS 



1:57 



TABLE 27 



Effect of size of inoculum on growth of Bacterium coli (shown by 

 turbidity measurements), in cultures containing urea. A value of 

 30 indicates 650,000,000 cells per cc. (From Lee, Epstein, and Foley, 

 1943.) 



are inactivated only for a time ; after a while they begin 

 to grow in the presence of the dye, and then multiply at a 

 normal rate, showing no trace of injury. It seems as if 

 the dye merely prolongs the lag phase without producing 

 any other effect. Churchman (1912) coined the term 

 ''bacteriostasis" for this phenomenon. 



The difference between dye bacteriostasis and the de- 

 crease of growth rate caused by most other antiseptics 

 is shown in Figure 26. The graph on the left side shows 

 the effect of rivanol (an acridine dye) on the oxygen 

 absorption of Bacterium coli. Since the oxygen absorp- 

 tion is proportional to the bacterial concentration, the 

 curves of Fig. 26 are really growth curves. The higher 

 concentrations cause a longer lag, but they do not af- 

 fect growth rates, as is indicated by the fact that the 

 growth curves remain parallel. The graph of the right 

 side represents the action of sulfa-thiazole. This com- 

 pound lowers the growth rate ; consequently the slope of 

 the growth curves decreases when the concentration in- 

 creases, and the curves spread out fan-shaped. All curves 



