When cells of E. coli and Staph. aureus are dried, the efficacy of phenol is reduced but the efficacy of formaldehyde is increased. 2. A change of the aw-value by addition of salts changes the efficacy of formaldehyde as well as that of phenol. For these tests the chlorides of various alkali and alkaline earth metals were used in different concentrations. 3. The optimal efficacy of phenol and formaldehyde within the tested concentration gradientis caused by different concentrations of the ions: In low concentrations the efficacy of formaldehyde is optimally increased, the efficacy of phenol, however, attains a minimum at this concentration range. By higher concentrations of ions the efficacy of phenol is increased, that of formaldehyde is reduced. 4. The position of the cations in the periodic system also plays a role in the influence on the efficacy of the phenol and formaldehyde respectively. The cations of the lower periods from the main groups I and II favour the damage to the cells by phenol, the cations of the higher periods favour the damage by formaldehyde.
