734 JOURNAL OF TIlE SOCIETY OF COSMETIC CHEMISTS original plant design. Pasteurization is not recommended since it is in- effective against heat-resistant bacteria or spores. Chemical sterilization is a possible alternative to heat treatment and is usually effective when it follows thorough washing to remove as much "soil" as possible this is important because spores are not always des- troyed by chemical disinfection and they may germinate in the residues. If contamination with spores is suspected, it is necessary to use strong con- centrations of chemical disinfectants maintained at elevated temperature. Chlorine is the best plant sterilizing agent in most circumstances. Cold solutions of hypochlorite yielding 200 to 250 ppm of available chlorine will sterilize glass and metal surfaces after $ min if all organic matter has been removed previously. Formaldehyde or formalin is a convenient sterilizing agent for use after plant washing but, like chlorine, its activity is greatly reduced by organic matter. Cold solutions should be used at a concentration of about 0.5% formalin (0.2% formaldehyde). This concentration will sterilize surfaces which are free from organic matter in 10 min. Cold solutions are recom- mended for both of these sterilants owing to the unpleasant or toxic effects that may result from inhalation of their fumes. Hot solutions may, however, be employed in totally-enclosed plant if proper precautions are taken. Quaternary ammonium compounds, although weight for weight less effective than chlorine and formaldehyde, have advantages such as being almost odourless, relatively non-toxic to man, and less corrosive than chlorine. They do not have a wide spectrum of antibacterial activity, being more active against gram-positive than against gram-negative bacteria they are also rendered less effective by organic matter and anionics. Since they are quite efficient surface-active agents, they can in some cases be used to clean the plant as well as to disinfect, although their detergent action would be inadequate for the removal of residues from w/o emulsions. A concentration of 0.5% of benzalkonium chloride at 60 ø will sterilize "soil"-free surfaces in less than 10 min. Residues of disinfectant solutions must be removed from the plant after sterilization in order to avoid re-contaminating the machinery, this should be done by irrigation with sterile water. The risk of recontaminating sterile machinery is high if cold water from a distilled or demineralized water storage tank is used. It is necessary, therefore, to use freshly boiled or autoclaved water, particularly if the plant is to be left idle before the next manufacturing schedule begins. The detailed advice given in the foregoing sections on plant cleaning and

HYGIENIC MANUFACTURE AND PRESERVATION 735 sterilization may well appear greatly to exaggerate the need for elaborate precautions in the manufacture of products which are not required to be truly sterile. The ultimate answer must depend on the results of micro- biological control testing if a consistently low level of contamination is already achieved, housekeeping is obviously adequate for the purpose but when high counts or potential pathogens are found, the production arrange- ments should be carefully re-examined. Important facets of this problem are whether the product tends to encourage microbial growth and whether the preservative is in danger of being overwhelmed. Quite small "pockets" of contamination, protected in one way or another from the usual cleaning or sterilizing procedures, can sometimes lead to a rapid and overwhelming increase of contamination in the bulk output constant vigilance is therefore necessary, if only to avoid such catastrophes which can be exceedingly difficult to overcome quickly. 3.9 Avoidance of contamination from human sources Personnel can play an active part in the introduction or in the preven- tion of contamination within manufacturing areas and they should be encouraged to have a continuing awareness of contamination problems. This should be done by instruction in the fundamentals of personal and factory hygiene. They should be encouraged to report minor ailments which may constitute a source of contaminating infection in the production process. Apparently healthy personnel may act as carriers for various microbial contaminants and bacteriological checks are advisable if difficulty is encountered in tracing sources of product contamination. Much can be accomplished by providing ample modern washing facilities before beginning work and after using the lavatories. Taps should not be manually operated the provision of a hand dip not exceeding 10 ppm of available chlorine may be useful. Disposable towels should be employed. Suitable clean protective clothing should be supplied including, where appropriate, caps, hair nets, gloves, and masks. It is essential to insist that such clothing should be worn and changed frequently. Personal effects should not be allowed in the washing area. Access to washing facilities should be freely available and cleanliness in changing rooms should conform to the same standard as in the working area. 4. MICROBIOLOGICAL QUALITY CONTROL Microbiological quality control serves four main purposes: