INACTIVATION OF PRESERVATIVES BY NONIONIC AGENTS 187 Every culture was allowed to grow until it was at a convenient point in the log phase when two of the three replicates were inoculated with 0.5ml of a solution of the antibacterial agent. Simultaneously the remaining culture was inoculated with 0.5ml of the solvent as a control. The anti- bacterial solutions and the control solvents were added slowly to the cultures which were briefly shaken during the addition. This procedure eliminated temporary changes in absorbance resulting from vigorous addition of liquid to the growing cultures (9). The solvent for Dioxin and Bronopol was water, that for the phydroxybenzoates was 70% alcohol. The absorbance of each culture was measured at intervals and results with Dioxin (0.03% and 0.1%), phydroxybenzoates (0.03% and 0.1%) and Bronopol (10 [•g/ml and 100 [•g/ml) are illustrated in Figs. 1-3 respectively. 0,10 0.08 0ø06 0,0• 0,02 1A I I I I I I I i lt•O 18o 220 260 T I M E (Min,)aJ 37.5 ø RESUnTS AND D•SCUSSION Dioxin The presence of polysorbate 80 at each concentration apparently had no antagonistic effect upon the activity of Dioxin. Fig. Z shows the effects in plain broth and broth with 1% polysorbate 80. 0.03% Dioxin caused a slight inhibition of growth rate in each case and 0.1% Dioxin caused an immediate lysis, slightly greater in the culture with 1% poly- sorbate 80. The results with 0.02ø//0 polysorbate 80 (not illustrated) were substantially the same as with 1% polysorbate 80.

188 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 0.12 z z o.1 0.08 ]B o [ I t I 19o 230 270 T ! M E (Min.) at 37.5 ø Fig. I Effect of polysorbate 80 on the action of Dio •in against log phase cultures of Ps. a•'uginosa. O control. ß Dioxin 0.03% added. x Dioxin 0.1% added. A, plain broth. Diozin added after 154 min. B, broth with 1% polysorbate 80. Diozin added after 225 min. O.O8 o o 0.06 0.04 0.02 2A I I I I I 19o 230 270 T I H E ( Min. ) at 37.5 e I •1o