98 



DISINFECTANTS 



while Eggerth studied the soaps from substituted fatty 

 acids. He found that oc-brom fatty acids are more ger- 

 micidal than the unsubstituted acids (1929), that ct-hy- 

 droxy acids are highly germicidal to some species, but 

 that the substituted compounds have become even more 

 selective than the regular soaps (1930) ; a similar in- 

 crease in selectivity was observed with a-mercapto and 

 a-disulfo soaps (1931). 



Of greatest interest to the mode of action of fatty 

 acids and soaps is the etfect of pH which had been em- 

 phasized by Eggerth in 1927. Klarmann (1933) meas- 

 ured the amount of various acids required to kill Staphy- 

 lococcus aureus at 37° in 2 hours at different pH values. 

 His results are shown in Fig. 22. 



Fig. 22. ■ Concentration of various fatty acids required to kill Staphy- 

 lococci in 2 hours, at different acidities. Abscissa: pH; ordinate: per 

 cent concentration of the fatty acid, on logarithmic scale. Ce: caproic 

 acid, Ce: caprylic acid, Cio: capric acid, C12: lauric acid, C14: myris- 

 tic acid, Cis palmitic acid, Cis: stearic acid. (From data of Klarmann, 

 1933.) 



