29,6 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TABLE X Growth on agar Organism Treatment containing 0-1 Nipa 82121 , . staph. albus Washed in saline (control) -- Treated with Tween 80 Washed once after Tween 80 _ Washed twice after Tween 80 -- Washed three times after Tween 80 -- Strep. bovis Washed in saline (control) -- Treated with Tween 80 Washed once after Tween 80 _ •¾ashed twice after Tween 80 _ Washed three times after Tween 80 -- B. coli Washed in saline (control) Treated with Tween 80 Washed once after Tween 80 •Vashed twice after Tween 80 Washed three times after Tween 89 q- Pseudomo•as Washed in saline (control) -- fluorescens Treated with Tween 80 q- Washed once after Tween 80 -- Washed twice after Tween 80 -- •rashed three times after Tween 80 -- I)ISCUSSION Most of the work reported in this paper was guided by the following hypotheses regarding the possible mechanisms involved in inactivation. (a) The preservative might be effectively removed from solution by envelopment in the nonionic micelle. This might be associated with formation of complexes, possibly by linkage with hydroxyl and/or polar groups of the preservative molecule, and oxygen bridges in the nonionic compound, and also by non-polar Van der Waal forces. (b) Some effect might occur at the bacterial or fungal cell wall. This might prevent effective contact between the organisms and preservative, or alter adsorption processes. (c) Direct chemical action might result in the effective breakdown of the preservative. Parts of these hypotheses have been verified and are discussed below in the light of the experimental results. The study of the effect of nonionics of different chemical structure on preservatives showed that nonionics with strong lipophilic characteristics caused greater inactivation than similar less lipophilic compounds. This supports Arkins '9 claim that some of the preservative is preferentially soluble in the fatty part of the nonionic, leaving insufficient in aqueous solution to act against the micro-organisms. However, the experiments using tallow show that this substantially fatty material does not cause

PRESERVATION OF TOILET PREPARATIONS CONTAINING NONIONICS 227 inactivation. Thus preferential solubility of the preservative in fatty matter cannot account for the phenomenon entirely. It appears that the miceliar characteristics of nonionic surfactants are concerned in the inactivation process, because some nonionics that are not surface-active, for example, P.E.G.'s, tallow and glycerin, and which do not form micelies, do not cause inactivation. That nonionic surface-active agents might incorporate certain preservatives in their micelles could account for the inactivation of germicides of large molecular size, but the fact that compounds like formaldehyde are also slightly affected indicates that this theory does not fully explain the process of inactivation. The changes in Gram-staining characteristics of some bacteria after contact with nonionics, and the fact that some organisms are rendered more resistant to certain germicides after contact with nonionics, suggests that some change at the cell wall of the organisms may effect the degree of efficiency of the germicide. The change has not, however, been observed with all the organisms used in this series of experiments, and does not appear to be sufficiently marked or constant to account for the high degree of inactivation observed throughout the work. Because the activity of germicides of widely different molecular structure may be reduced by nonionic surfactants, it is unlikely that the phenomenon is brought about by any simple chemical incompatibility between germicides and nonionics. The concentration of preservative required to protect a toilet preparation will depend on the type of nonionic surfactant used and the amount present in the formula. Where it is proposed to use an unusually high concentration of certain types of nonionic, adequate preservation of the formula could become exceedingly expensive, and even impossible on grounds of toxicity. Highly potent germicides will probably be the best preservatives for products containing appreciable amounts of nonionic surfactant. The findings reported in this paper point to the fact that when nonionic surfactants are used in any toilet preparation the preservative will have to be considered an integral part of the formula and not merely as an ad hoc addition, as was often the case when soaps and anionic materials were used. A suitable preservative should be selected early in the development of a new formula, not only because of compatibility considerations but also because of the danger of confusing the symptoms of faulty formulation with the symptoms of microbiological attack. Bacteria, if unchecked by a preserva- tive, can cause separation of enmlsions, liquefaction of gels, the formation of gas and unpleasant odours, discoloration, cloudiness in otherwise clear products, and, in the case of pigmented products, "leaching" or aggregation of the colour. ConcLusions 1. The amount and type of nonionic surfactant present will mainly govern