FUNDAMENTALS OF MICROBIOLOGY IN RELATION TO CLEANSING T•.Bt.E III.--Continued Sterilant Circumstances where Circumstances where indicated inadvisable 59 Quaternary ammonium compounds Iodophors Ortho-phenyl-phenol Nitric acid Hexachlorophene Chlorhexidine Amphoterics Where odour, taste and toxicity to be avoided. Where safety in use im- portant. Where gram- positive organisms chief danger. Where alkaline detergent desired. Where calcium scale a problem For equipment not coming into contact with food Where calcium scale a problem Where contact with hands, etc. possible.-In toilet pre- parations, etc. As 'antiseptic'. Where neutral conditions required Where low cost important. Where gram-negative organisms a likely danger. Where rinsing difficult (e.g. rough surfaces) With galvanized iron Where equipment not all stainless steel. Where strong acid dangerous. Where fat-protein films a special problem Not for food equipment Where cost important- Detergent-sterilants and their use A detergent-sterilant is required to carry out the following operations: (i) Remove all soil. (ii) Remove or kill all pathogens and potential pathogens. (iii) Remove or kill all fault-producing organisms (FPO). (iv) Reduce bacteria to 1 per sq cm surface area or per ml cubic capacity. The main fields of application for detergent-sterilants are given in Table IV. Table IV. Applications of detergent-sterilants for sanitizing equipment 1. In general for all cleansing purposes where heat cannot be used, e.g. walls, floors, wooden and plastic table tops, refrigerators, cold stores, etc. 2. The food industries, particularly for equipment for perishable foods such as milk and the more vulnerable foods such as meat, poultry, fish and eggs. 3. Medical and surgical activities: hospitals, clinics, surgeries, etc. 4. Sanitary aspects of communal activities: schools, colleges, catering, swimming and shower baths, public lavatories, public transport and all equipment communally used. 5. Institution maintenance cleaning. 6. Domestic: dishwashing, babies' and children's items particularly in nurseries, etc. 7. Cleaning or washing operations where heat cannot be employed: manual operations, delicate fabrics, plastics, etc. 8. Agriculture: particularly dairy farms, animal pens and all equipment wherever animals are involved. 9. Sanitation generally: wherever potentially dangerous material is handled as in slaughter houses, disposal of offal and refuse, etc. 10. Sewage disposal and all operations involving obnoxious material.

60 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS In general, detergent-sterilants, like chemical sterilants, are particularly useful where for any reason heat cannot be used, or is expensive or incon- venient. The value of changing methods and sterilants Particular methods, and particular chemical formulations are often specially good for certain purposes and against particular types of organ- ism. The consistent use of one method and/or one formulation may lead to a weakness in the overall system because of a slow film build-up (too slight to be noticed) or acclimatization by a particular organism, e.g. coif, spore- former or yeast. The types of organism surviving on equipment depend on the nature o! the soil and the sanitizing method used. It is therefore strongly recom- mended that at intervals, say once weekly, a different method should be used. For in-place cleaning systems it may not be convenient or economic to change the system drastically, e.g. use steam or hot water instead of hypochlorite, but it is usually possible to change the type of detergent and/ or sterilant. In-place or circulation cleaning The scale of operations in factories today and the shortage and cost of manpower have revolutionized our attitude to cleaning and sterilizing. The classical idealist methods would be impossible today, and all rdevant industries have gone, or are rapidly going over to in-place cleaning. Pro- vided all the equipment is suitably designed for this purpose, the method can be entirely successful. The usual system is a closed circuit with spray devices for tanks. A minimum velocity to give turbulent flow in pipdines, and properly formulated detergents and sterilants are essential. Permanent tanks for these solutions, regular laboratory control and automation allow such systems to operate with very little man-power although capital cost may be high. The problem of emulsions In addition to the purdy physical and chemical problems associated with the formulation of emulsions there will often be microbiological problems. Three phases may be involved--the continuous phase (usually aqueous), the discontinuous phase (usually fatty) and possibly an adsorbed layer phase which may have considerable significance for organisms. This