ANTISEPTICS 135 



If another set of cultures is made Avith only 1,000 cells 

 per cc, instead of 1 million, we must add to the above 

 figures the time needed by the bacteria to multiply from 

 1,000 to 1,000,000. This corresponds to 10 generations, 

 which require 20 hours without antiseptic, but 100 hours 

 Mdth antiseptic. We must further consider that a smaller 

 inoculum demands a longer lag period, approximately 12 

 hours, in our case, instead of 3 hours. Thus, the control 

 culture without antiseptic would produce visible turbidity 

 in 6+20-|-12 = 38 hours while the culture with antiseptic 

 would need 30+100-f 12 = 142 hours = 6 days. With a 

 still smaller inoculum of only 1 cell per cc, the lag period 

 would be about 24 hours, and the total time to produce 

 turbidity would be 3 days without antiseptic and 10 to 11 

 days with antiseptic. Since experiments are often dis- 

 continued if no turbidity is noticeable after one week, an 

 antiseptic may be believed to suppress multiplication 

 completely, w^hile bacteria have been increasing contin- 

 uously, although at a very low rate. A decrease in the 

 rate of multiplication has been observed with most anti- 

 septics, e.g., with sulfanilamide, benzoic acid, SOo, peni- 

 cillin, etc. Not all of them, how^ever, cause also an in- 

 creased lag period. 



That an increased lag can give the appearance of com- 

 plete inhibition of growth, is obvious See Fig. 25). 

 Cruess and Richert (1929) found that in grape juice ad- 

 justed to pH 6.0, benzoate of soda retarded yeast devel- 

 opment greatly. With 0.6%, growth began after 12 days, 

 while with 0.8% growth started only on the 25th day. 



An interesting complication is encountered in the re- 

 sults of Lee, Epstein and Foley (1943) who studied the ef- 

 fect of urea on the development of Bacterium coli (Table 

 27). Growth was recorded by turbidity measurements. 

 (Eoughly, the turbidity is linearly related to the popula- 

 tion.) After 21 hours, the population was higher in the 

 cultures containing urea than in those without it, espe- 

 cially wdth the smaller inocula. This indicates an in- 



