720 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS difficulty of predicting precisely what they will do. Garratt and Brown (33) were able to produce a very simple kinetic explanation if you try to apply that to most antibacterials it just does not work. One can get a long way with mixtures within one chemical class. For example, if you are going to mix phenol and if you like chloroxylenol, and if you know the activities of the separate compounds and their concentration exponents, you can get a long way towards calculating with reasonable accuracy (q-50•o) precisely what the activity of the mixture will be. For mixtures of different classes of compounds, for example phenyl ethyl alcohol together with a paraben or similar, heaven only knows where the mathematics goes. It is not only a question of mixture of the preservatives I think Richards and McBride (34) made this point. If you have two preservatives in an ophthalmic solution you have three components in the system. Now attopine and, I think, pilocarpine will tend to enhance the activity of many of these preservatives whereas fluorescein will actimt•ro•posite direction. Until we have much more knowledge it is thus very difficult •to predicf• •Wrhat the activity of a product will be. MR. G. S¾•coes: I wonder w}i•Iher Remington (32) means a real 505/0 in the terms of mixtures in which we think of t :•:!• .,. or whether a large proportion of that 505/0 is not groups of homologues of the paralSL•,•hich can be called mixtures. DR. R. M. E. RicH^v,rs: The 505/0 do not include the parabens--these are all kinds of combinations of antibacterials probably with different modes of action and sometimes used at quite strange concentrations. THoe Loec'ruv,oev,: Many insulins contain a mixture of preservatives and, I think, this mixture is not always there for preservative reasons alone, e.g. there may be analgesic reasons. (33) Garrett, E. R. and Brown, M. R. W. The action of tetracydine and chloranphenicol alone and in admixture on the growth of E. cell. J. Pharm. Pharma½ol. 15 185T (1963). (34) Richards, R. M. E. and McBride, R. J. The preservation of ophthalmic solutions with antibacterial combinations. J. Pharm. Pharrna½ol. 23 Suppl. 235S (1971).

J. Soc. Cosmet. Chem. 23 721-737 (1972) ¸ 1972 Society of Cosmetic Chemists of Great Britain Microbiological spoilage in pharmaceuticals and cosmetics R. SMART and D. F. SPOONER* Presented on 29th September 1971 in London, at the Symposium on 'Microbial control', organized by the Pharmaceutical Society of Great Britain and the Society of Cosmetic Citemists of Great Britain. Synopsis--Manifestations of SPOILAGE by bacteria, yeasts and fungi are described. TOXIC visible, olfactory and audible effects and changes in texture and taste may be found and susceptible products are reviewed. LIQUIDS, including aqueous solutions and suspensions, syrups, emulsions and creams are particularly at risk. Spoilage of ointments and oils, solid raw materials, powders, tablets and solid COSMETICS also occurs. The involvement of PACKAGING materials and the CONTROL of MICROBIOLOGICAL spoilage is briefly discussed. INTRODUCTION A spoiled product may be described as one that has been rendered unfit for use. As pharmaceuticals and cosmetics are consumed by, or applied to, the user, manifestations of spoilage are essentially subjective, spoiled products becoming objectionable or perhaps even therapeutically inactive. Microbial spoilage can be caused by bacteria, yeasts or fungi which are all extremely versatile in their metabolic activities. This capacity for variation, whether due to mutation in genetic composition followed by selection or to changes in behaviour unaccompanied by genetic change, allows adaptation to a very broad range of environmental conditions. As a result, all classes of natural organic compounds are susceptible to * Quality Control--Microbiology, The Boots Company Ltd, Nottingham, NG2 3AA. 721