ANTISEPTICS 



131 



Fig. 24. Multiplication curves of Saccharomi/ces ellipsoideus in 

 presence of various concentrations of phenol and formaldehyde. (Orig- 

 inal data.) 



creases as the concentration of the disinfectant increases, 

 and becomes zero at the inhibitive dose. 



In addition to the decreased multiphcation rate, for- 

 maldehyde causes a pronounced increase in the lag period 

 which phenol does not show. Thus three types of inter- 

 ference are possible ; extension of lag with normal growth 

 rate, decrease of growth rate with normal lag, and de- 

 crease of growth rate plus extension of lag. All three 

 types will be shown to actually occur. 



Another question arises when diluted bactericides are 

 used as antiseptics, namely, that of the ratio of inhibi- 

 tory to bactericidal concentration. On this point quite 

 extensive data have been presented by Birkhaug (1933), 

 and the ratio was found to fluctuate greatly. Table 26 

 gives a few of the reported data. AYith the last three 

 disinfectants, the inhibition of growth (without killing) 

 of Bacterium coli requires 30 to 40 times as high a con- 

 centration as the corresponding inhibition of Staphylo- 

 coccus. But the dose necessary to kill Bacterium coli is 

 only 3 to 4 times as high as that for Staphylococcus. If 

 irreversible sterility (or death) were due to the same 

 reaction as reversible sterility (or antisepsis), death 



