FUNDAMENTALS OF MICROBIOLOGY IN RELATION TO CLEANSING 61 third phase may act as a powerfully adsorbing film for bacterial nutrients and a focus for bacterial clumps or colonies. Homogenization may lead to biological troubles because clusters of micro-organisms are broken up and the cells dispersed throughout the medium. Homogenizers are also difficult to clean and sterilize. Emulsions of water in oil are much more stable microbiologically than the reverse, as the organisms are confined to their own water globule. If these globules are very small (a few microns) growth appears to be halted rapidly and the organisms die out. Unsuspected reservoirs of contamination When all reasonable precautions have been taken but there still occur sporadic and serious outbreaks of infection the cause is probably an un- suspected reservoir of contamination. The following explanations have been found in factory practice: (i) poor communication between management and staff (ii) poor supervision, especially early in the morning (iii) bad hygienic design of equipment or lay-out (iv) changes in cleaning/sterilizing procedure to reduce costs (v) rapid staff turnover (vi) making assumptions without laboratory tests to check them. Filtration and clarification When a liquid product has to be cleared of suspended particles, filtration is usually adopted because clarification is expensive and may be impossible. It should be realized however that, if the product is of poor microbiological stability, filtration may do nothing to improve this, and may even worsen it because all the materiM is forced through a layer of suspended matter which may be building up a substantial bacterial population. Filter cloths or pads should be renewed frequently for this reason, and double alternating filters preceded by fine mesh strainers are to be recommended where the nature of the product makes this desirable. The size of micro-organisms One difficulty in teaching hygiene to operatives, and even to factory floor management, is to convince people of the size of bacteria. To talk about

62 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS microns is meaningless to them. A simple analogy is to point out that if a bacterium were magnified to the size of a man, then the man would have to be magnified to the size of Great Britain to maintain the proportion. No system of flitration practicable for large volumes of liquids can be relied on to remove all bacteria, although yeasts and moulds, being about 10 times the size (diameter) can usually be removed to a considerable extent. Factory water supplies The bacteriological purity of water is generally judged on the basis of the Ministry of Health Memo No. 71 which assesses potability by the pre- sumptive and faecal coli tests, supported by total colony counts at 22 and $7øC. Many years' experience has proved the validity of this method, but potability is not the same as quality for a particular industriM purpose. Defects in cosmetic and other preparations may be caused by Pseudomonas and similar Gram-negative bacteria, yeasts, moulds and other types of no public health significance. The hazards for water, which is drunk, and for cosmetics, which are applied to and remain on the skin, are quite different. The latter include Staphylococcus aureus, Pseudomonas aeruginosa, and various skin pathogens which are usually completely ignored in public health water bacteriology. A further fallacy is the assumption that water as used in the factory is as pure as water supplied to the factory. Storage in tanks and passage through pipelines, pumps, filters, softeners, etc. may easily result in gross contamination. Unless constant testing shows that the water is of adequate purity, mild chlorination (2-5 ppm) is recommended. For a survey of problems and control methods see Davis (9). Hands as a sourc• of infection Apart from obviously bad air conditions, contamination or infection of a product is always caused by contact. Of all the ways in which this can occur, there is little doubt that in practice the hands are the commonest means whereby a product becomes contaminated by a pathogenic organ- ism. Skin is impossible to sterilize and the bacterial load may vary from a few thousands to a few millions. Staphylococci and enterobacteria are nearly always found (10). Biological control of pathogens and fault-producing organisms Considerable success has been achieved in agriculture and in some