the surgeon's autoclave - journal of clinical...

J. clin. Path. (1961), 14, 49.

The surgeon's autoclaveJ. W. HOWIE

From the Bacteriology Department of the University and Western Infirmary of Glasgow

This difficult, costly, and complex piece of engineer-ing occupies a central place in what is aptly describedas the aseptic ritual. The autoclave is intended toguarantee the sterility of articles which have been putinto it by exposing them to steam at a greater thanatmospheric pressure and therefore at a temperatureover 100°C. (212'F.) and usually between 121°C.(250°F.) and 134°C. (274°F.). Within the past fiveyears surgeons' autoclaves in Great Britain havebeen the subject of critical reports and investigationswhich clearly revealed that a great many of the auto-claves could not be relied upon to effect sterilizationas they were being used (see, for example, Bowie,1955; Howie and Timbury, 1956; Scott, 1957;Magee and Oakes, 1958; Nuffield Trust Report,1958; Medical Research Council Report, 1959; andWells and Whitwell, 1960). From the same work andthat of others (see Bowie, 1958a and b; Alder andGillespie, 1957; Knox and Penikett, 1958; Penikett,Rowe, and Robson, 1958; Rice, 1958; 1960; MedicalResearch Council Report, 1960) recommendationsemerged about better methods for the construction,installation, maintenance, and operation of auto-claves. These communications were received withgeneral interest, and the object of the present paperis to set down what seem to be the main points of allthis activity and to emphasize a few principles. Ifthese principles are not understood and acted uponwe shall do no more than exchange one form ofmeaningless ritual for another. The necessity is todevise and ensure the continuous exercise of an

effective process.

NEED AN AUTOCLAVE STERILIZE?

Sometimes the question is asked whether autoclavesmatter a great deal in the prevention of post-operative wound infection. An answer to this varietyof agnosticism can hardly be made in quantitativeterms from surgical practice in man as a moment'shumane reflection will surely reveal; but the answer

is not less emphatic because it cannot be expressedin figures. If an article is labelled or may credibly bepresumed to be 'sterile', a surgeon may use it witha clear conscience. But if it may be labelled only'probably sterile,' dare the surgeon accept it? What

will be the effect on his medical and nursing col-leagues if he does? Will the sister's grip of the asepticritual in her theatre remain effective? We all knowof horror stories without a moral: of the autoclavethat proved acceptable for seven years although nosteam ever entered its chamber, but only its jacket,until at last this engineering defect was discoveredduring the investigation of an outbreak of post-operative tetanus. What do we rate as significant:the seven years in a paradise of ignorance or the onecatastrophe? I know of a sterilizer which neverrevealed its defect until, challenged by unbleachedcotton wool, which was suddenly introduced as awar economy measure, it demonstrably failed to killthe tetanus spores in the cotton wool in its lowerthird. Moreover, on further tests, it also failed to killstaphylococci in the same area. These facts aboutthis particular sterilizer were discovered only afterthe majority of the patients of one morning's list haddeveloped post-operative tetanus. Its dischargechannel was ineffective. I know of another sterilizerwhich did not produce any disturbance in the mindsof those who relied on it although dressings thatcame out of it were contaminated with a variety oforganisms during the drying process. The con-taminants found were mostly aerobic Gram-positivesporing bacilli and micrococci but at different timesthey also included Clostridium welchii and Staphylo-coccus aureus, organisms not present in the dressingsbefore sterilization, so that a witty medical studentsaid of the apparatus: 'Not perhaps much of asterilizer-but a fertilizer!' Such tales are typical ofthose that abound wherever people meet who areconcerned with autoclaves; and they are not themere imaginings of enthusiasts, as is confirmed by theNuffield Report (1958) and by the writer of 'AnyOld Iron' (1959). An inefficient autoclave may notreveal its failure in terms which cause clinical mis-giving for many years. In that sense the evidencesuggests that autoclaves may not be very importantquantitatively as direct causes of hospital sepsis. Inoutbreaks of post-operative tetanus and gasgangrene, they should obviously receive morecritical study than they have often had during theinvestigation of some such reported episodes.Because they kill one packet of test spores, there is

49

on 1 June 2018 by guest. Protected by copyright.

http://jcp.bmj.com

/J C

lin Pathol: first published as 10.1136/jcp.14.1.49 on 1 January 1961. D

ownloaded from

http://jcp.bmj.com/

no guarantee that they can do so in every kind ofpackage in any part of the load or that they do notrecontaminate sterilized dressings during the dryingprocess, and what more efficient way is there of con-centrating the bacterial contamination of hospitalair in a situation where it will really matter than ofdrawing it through a defective filter into a set ofsurgical dressings? And if, as often, the defectivesterilizer also soaks the dressings and this has upsetthe surgeon, will not the sterilizer attendant makecertain that the airing process at least is thoroughlydone? I know of sterilizers where the drying process

habitually lasted an hour or longer, and of one inparticular where the process of drying was completedby placing the autoclaved drums, with open ports, ontop of a radiator. The surgeon's reaction to beinggiven a wet dressing was more predictable than thepatients' reaction to being treated with one that wasnot sterile. Lister, whose earliest concern was mainlywith airborne microorganisms, much later acknow-ledged that he was then more worried by 'grosserforms of septic mischief.' Those who so naively pre-

sumed upon their understanding of the realities ofhospital bacteriology as almost wholly to supplantLister's antiseptic methods by their aseptic ritualwere surely an unwitting source of septic mischief.We cannot measure how much. But need we? As theadvisers of surgeons surely we can stand on thedoctrine that asepsis is meaningless ritual, chargedwith hidden errors and unmeasured risks, unless allthat is labelled and regarded as sterile carries a validguarantee that it is indeed free from microorganisms.It is true that some apparatus need not be sterile,cytoscopes, for example (Francis, 1959), and deliber-ate decisions merely to decontaminate certainarticles may be accepted by those responsible pro-

vided they know exactly what they are doing. But forall that, the great majority of articles used in surgerycan and should be sterile; and the instrument mostrelied upon to effect this sterilization is the autoclave.Therefore we must see to it that our surgeons'autoclaves are effective in their design and use.

WHO IS RESPONSIBLE?

The surgeon is a busy man, skilled in his particularand difficult duties, but he has not the outlook or

experience of autoclaves possessed by a mechanicalengineer, a pharmacist, or a bacteriologist. Reason-ably, he looks for someone to see to the sterilizationof his dressings and instruments. Often the theatresister accepts this responsibility. But what does sheknow from her training of the working and main-tenance of all the different varieties and makes ofautoclaves? As much, probably, as a railway guardknows about the locomotive that pulls his train.

Sister will faithfully do what she has been taught, butautoclaves differ from each other in important detailsand sisters move around. Theatre superintendents,hospital porters, and relatively junior nurses mayalso operate autoclaves after receiving only theminimum of instruction. Often, as accidents to suchoperators have revealed, they know very little aboutthe true nature of the engineering considerations thatgovern the correct use of steam under pressure. If theengineer, usually an overworked person, is called toa faulty sterilizer he may well be content to repairobvious defects and leave it at that. If he has tomaintain and service in one hospital several differentmakes of autoclave he will need a great variety ofspare parts; and if his well meant advice is notreadily understood or willingly accepted he may bepardoned for feeling that the calorifiers for heatingthe hospital deserve more of his attention and skillthan the autoclaves; in any case the end product ofthe autoclaves is not his direct concern and he is un-likely to be unduly worried about their deficiencies un-less someone else shows real concern. If an autoclavefalls under suspicion, the bacteriologist is likely to becalled in because he is supposed to know about sporetests and because his work depends on efficientlyfunctioning autoclaves. Unfortunately, the bacterio-logist's own working experience of autoclaves maynot guide him to give the right advice about thesurgeons' autoclaves.

Bacteriologists rely on their autoclaves mainly tosterilize media, all of which are fluid during steriliza-tion, and instruments. These are easily sterilizedbecause the nature of the load offers no seriousobstruction to attainment of the steam temperaturethroughout the autoclave and the articles within it.The simple pressure-cooker type of autoclave isreadily able to meet the bacteriologist's needs, andthe danger is that he may fail to realize how differenthis instrument is from that required to steam anddry a load of packaged fabrics and other goodsrequired for use in an operating theatre or ward.Until recent reports became required reading forhospital bacteriologists, many of them revealed theirunawareness of the true mode of action of thesurgical autoclave both by the advice they offeredand by the over-simple and essentially unsatisfactorytests which they advised to check the functioning ofsurgeons' autoclaves.

Consequently, we may be forced to conclude thatone of the principal needs for efficient autoclaving isthat some member of the medical staff both educateshimself about autoclaves and undertakes theresponsibility of being answerable to his medicalcolleagues on two issues: (1) that adequate methodsand apparatus are employed and are under the day-to-day care of a person of sufficient professional

50 J. W. Howie


http://jcp.bmj.com

/J C


ownloaded from

http://jcp.bmj.com/

The surgeon's autoclave

standing to guarantee the faithful and exact per-formance of what is laid down; and (2) that regularchecks of various kinds are applied, recorded,inspected, understood, and acted upon. Both theNuffield Report (1958) and the first M.R.C. Report(1959) laid great emphasis on the need to defineresponsibility in this way.

CENTRALIZED AUTOCLAVING

Obviously both the medical man accepting suchresponsibilities and the day-to-day superviser candischarge their tasks only if the autoclaves in theircharge are not too widely dispersed in many places.In practice this means that operating theatres willrely upon a central source to supply their sterilepackaged goods but will have their own autoclavesfor unwrapped instruments and bowls. Instrumentsand bowls are easily and quickly sterilized in a verysimple type of autoclave (M.R.C. Reports, 1959 and1960), which may yet be further simplified by theoutcome ofexperiments still in progress. Such instru-ments may confidently be left to sisters and nurses,especially if their practical training and examinationcan be made to include the working of this particularpiece of apparatus. Bottled fluids will probablyremain in the charge of the pharmacist, and hereagain there is no reason to anticipate difficulty, bothbecause the problems are fundamentally straight-forward and because the training and examination ofpharmacists lays considerable emphasis on the cor-rect performance of sterilizing techniques. Currentexperiments with new designs of autoclaves forbottled fluids may be expected still further to increasethe security of this particular sterilization process.Surgical dressings and other packaged goods, in-cluding rubber gloves, thus become the main problemof the centralized autoclaving unit, and it is to thisthat the rest of this article will be directed. Theproblems of centralization and of guaranteed per-formance have been simplified in the last few yearsout of all recognition by the introduction of high-vacuum autoclaves with automatic controls. The en-hanced capacity of such apparatus was clearlydemonstrated by Wells and Whitwell (1960).

REQUIREMENTS FOR SURE AND SAFE AUTOCLAVING

A GOOD STEAM SUPPLY To guarantee the rapidkilling of resistant spores, especially in textiles, it isnecessary to have a reliable supply of steam underincreased pressure at a temperature of from 121 to134°C. (250-274-F.). If this steam is what is tech-nically known to engineers as 'just dry' it will con-dense and penetrate rapidly with lethal effect into

the substance of even the most resistant spores andit will not do more than merely dampen the dressings.However the steam is produced, direct from themains or generated in apparatus near to or actuallypart of the autoclave, it must be dry and withoutmore than 5°C. of superheat. Commonly, from in-adequate lagging and trapping, hospital mains steamsupplied to autoclaves carries more than 10% of itsweight made up of liquid water and such steam isunacceptable. Its improvement is essentially anengineering problem. Fitting adequate separatorsnear to the sterilizer is of great value, but it must beemphasized that a reliable supply of steam is the firstnecessity for efficient autoclaving, ofwhich the criteriaare the regular and rapid production of dressings thatare both sterile and dry.

REMOVAL OF AIR All parts of a load of textiles tobe sterilized must be freed of air so that the loadmay be permeated by the steam. Autoclaves of thepressure cooker type make no provision for theremoval of air during sterilization; hence they areunable to sterilize textiles. Until comparativelyrecently, this important matter was not widely under-stood by many who operated sterilizers in thiscountry, and some do not yet appear to have graspedthe point. There is little to be gained from the com-monly used practice of employing steam-eje tormechanisms to draw a vacuum, or even two vacuums,of the order of 15 in. Hg or less. These low-ordervacuums waste a great deal of steam and time andadd to the damage to sensitive fabrics, such as rubbergloves. They remove some free air from betweenpackages but they do not guarantee the almostinstantaneous penetration of steam into all parts ofthe load of dressings. Although low-order vacuumscould clearly help in marginal conditions, they arenot to be recommended in practice. Air should beremoved from the dressings either by its gradualdisplacement by steam or by drawing a high-ordervacuum, that is, a vacuum greater than 29-2 in. Hg.The small amount of air remaining in a load sub-jected to such a vacuum must be displaced by steamduring sterilization to ensure that all parts of the tex-tiles are sterilized. Simple displacement (also knownas gravity-displacement or downward-displacement)sterilizers can be very efficient, but only if theyare operated with a degree of skill and care whichcannot by any evidence of recent experience beascribed to the general group of people entrusted inthis country with the operation of surgeons' auto-claves. For success, a steam supply of the rightquality (see above) must be used upon a load lightlypacked and properly positioned in a sterilizer fittedwith a reliable automatic discharge mechanism withan adequate near-to-steam trap. The quality of the

51


http://jcp.bmj.com

/J C


ownloaded from

http://jcp.bmj.com/

steam is checked, to some extent at least, by ascertain-ing if a thermometer placed in the discharge linegives a temperature reading corresponding to thepressure.

CORRECT LOADING AND EXPOSURE The loadingof autoclaves is often done in such a way as toguarantee that, by steam displacement alone, all theair cannot be removed. Packs are more easilypenetrated than drums, but they call for more carefulstorage. Cardboard boxes have certain attractions;they appear to be more easily penetrated by steamin high-vacuum autoclaves than are drums of thekind generally employed in hospitals; converselythey are rather less satisfactory in this respect insimple displacement autoclaves. Packs have much tocommend them if the needs for their safe storage canbe met (see M.R.C. Report, 1959): they have to beprotected from dust, damp, and insects. Speciallymade metal caskets with built-in filters have a highinitial cost but many advantages which, in the longrun, may prove them to be the best form of container.Very large packs or drums or tightly packed loadswill defeat steam penetration unless a vacuum of theorder of 29-2 in. Hg can be drawn before steam isadmitted. It is hardly realized how difficult it is toget steam through the loads commonly put intosterilizers. This, perhaps more than anything else, iswhere imperfectly trained and inexperienced opera-tors fail in their understanding. High-vacuumsterilizers are justified because they overcome thisproblem and enable so great a shortening of thesterilizing cycle that few autoclaves are needed (Wellsand Whitwell, 1960) and the temptations to over-packing are reduced. Likewise if fewer autoclaves areneeded it is easier to centralize them under thecontrol of a relatively small number of more skilledattendants. Those who have to deal with oldsterilizers need not necessarily regard their task ashopeless. Some old sterilizers can be put into a stateof reasonable efficiency (for details see Scott, 1957)without too much trouble and may be worked satis-factorily if enough skill can be devoted to them. Itis with such autoclaves that care in packing andpositioning is specially important. Without this, suchsterilizers offer a poor guarantee of efficiency. Somedownward-displacement autoclaves may be success-fully upgraded to high-vacuum status either by localengineering modifications (Magee and Oakes, 1958)or by fitting conversion units which also provideautomatic control (Alder and Gillespie, 1959). Suchupgradings and conversions should not be embarkedupon without first consulting the makers and theinsurers of the sterilizer concerned.Times of exposure for a properly packed load have

been much discussed and debated. What will serve

as a minimum, e.g., for unwrapped instruments, willnot be enough for fabrics in packs or dressing drums.The M.R.C. Report (1959), which gave a reasonedstatement, recommend the following times andtemperatures as a minimum exposure after the steamhad reached the correct temperature for the pressureemployed:

3 min. at 134°C. (30 lb. per sq. in.)10 min. at 126°C. (20 lb. per sq. in.)15 min. at 121 'C. (15 lb. per sq. in.)

This short period of 3 min. at 134°C. is applicableonly to high-vacuum, high-pressure sterilizers whichare efficiently maintained and serviced and so fullycontrolled that any failure of the mechanics ofsterilization is made clear by appropriate warningsto the operator. These sterilizers obviously allow avery short time margin to cover any error, and fullattainment of the right conditions at every stagemust therefore be automatically monitored and allfailures made evident. If downward displacement isused for removal of air, and if the fabrics are cor-rectly packed and loaded into a fully efficientsterilizer, the M.R.C. Report (1959) recommendedand gave reasons for the following for temperaturesof 121 and 126°C.

min. at P21°C. min. at 126°C.(15 lb. per sq. in.) (20 lb. per sq. in.)

Instruments and utensilsFabric packsDressing drums

153045

102030

With high-vacuum equipment used under ideal con-ditions the complete cycle may be accomplished in20 minutes or less. Obviously each sterilizer manu-facturer ought to be consulted and the actual per-formance of any new sterilizer installed should becritically checked by a competent engineer andbacteriologist to ensure that whatever is laid downfor the particular sterilizer is correctly decided.

Gloves and Glove Powder One point that needsto be emphasized is that gloves should not besterilized at low pressures, for example, at 10, 7, oreven 5 lb. per square inch. If properly packed andnot over-dried, gloves may be sterilized in the sameway as other materials without being damaged. Im-perfectly sterilized gloves are a serious dangerespecially if, as all too often, they are treated withglove powder, which has not been correctly sterilized.If glass jars of glove powder with screwed-down lidsare put into autoclaves, it may be asserted thatsterilization of the contents is impossible. Glovepowder in small packets of guaranteed sterility isavailable commercially, or the powder may bespread out flat on trays and baked in a hot-air ovenat 160°C. for one hour and carefully filled, withsterile precautions, into small packets whose outside

52 J. W. Howie


http://jcp.bmj.com

/J C


ownloaded from

http://jcp.bmj.com/

The surgeon's autoclave

may be sterilized in the autoclave. Steam does notsterilize talcum powder because this substance isunwettable.

DRYING WITHOUT RECONTAMINATION Autoclaveddressings are often dried by drawing warm filteredair through them for periods that appear to rangefrom 18 minutes to several hours. With the filtra-tion methods hitherto commonly employed, oreven in the absence of any filtering mechanism, whichis not a rare situation, it is difficult or impossible toensure the sterility of the warmed air (around 56°C.)which is drawn into the sterilizer and may be passedwithout further ado directly through the open portsof unlined drums straight into the dressings. Varioustypes of filters made of cottonwool or other fabricshave served well enough if conscientiously changedand correctly fitted. Rice (1960) designed a filtrationset-up for autoclaves which greatly improved theprospects for efficient use of cottonwool filters.Work recently reported to the M.R.C. WorkingParty (M.R.C. Report, 1960) now suggests that glassfibre woven into sheet form of paper thicknessoffers the best prospects of a reliable filter which willstand up to autoclave conditions and have a workinglife of at least 12 months. The glass-fibre filterrequires the support of metal grills to prevent distor-tion and it must be set in a well-made metal canister.A critical orifice is required to ensure uniformity offlow and prevent excessive strain on the filter.Apparatus of this kind is now available from at leasttwo manufacturers in this country.' Such filtersshould be highly efficient with a methylene-bluepenetration of not more than 0 003 %.An important aspect of the problem of drying

without recontamination is to make sure that thedressings are dry at the outset, to use dry steam, andto draw a vacuum of 28 in. Hg after sterilization. Ifthis vacuum is drawn (it need not be held for evenfive minutes) and if filtered air is then used to breakthe vacuum, nothing more should be required. If thedressings are still wet after such treatment, anengineering fault needs to be found and treated.

TESTING AUTOCLAVES

Full comprehension of all the details of the principlesand practice of pressure-steam sterilization is notnormally to be expected of the bacteriologist, whowill be well advised, before tackling any autoclaveabout whose performance he is consulted, to insistthat it should first be checked by an engineer whoknows the apparatus and its function and candemonstrate the steam circuit of the particular auto-

(1) E. N. Mackley & Co., Hawks Road, Gateshead 8, Co. Durham.(2) Vokes Ltd., Henley Park, Guildford, Surrey.

clave. Such details of this kind as a bacteriologistmay require to know are emphasized and summarizedin the two M.R.C. Reports (1959; 1960). When he issatisfied that the apparatus is accepted as in workingorder by the engineer, the bacteriologist shouldinspect the recent records of temperature and pres-sure which ought to be made for every sterilizingcycle and kept for inspection. The regular inspectionof such records by someone who knows what theymean is itself probably the best single test of anyautoclave. Too often such records are made but notexamined by anyone who feels responsible for actionif they reveal some failure of the autoclave. It wouldbe a good custom if it came to be that every recordwere signed by a responsible member of the medicalstaff as well as by the sterilization attendant. A pro-perly designed and correctly instrumented autoclavethus tests itself and makes its own record. In thepast, no doubt, the form of such records has oftenbeen very hard to understand and their form hasoften been meaningless because they did not alwaysrecord the steam temperature independently of thepressure. A temperature recording instrument withits sensitive end in the discharge line is essential, aswell as a direct easily read thermometer. Recordingsmade from a dummy load in the lowest part of thesterilizer are an even better indication of per-formance. For special checks of the temperatureattained in different parts of the sterilizer, direct-reading portable thermocouples are available. Thistype of apparatus enormously enhances the ease withwhich faults may be quickly detected and localized.

Routine bacteriological checks with spores ofvarious kinds have been the subject of much con-fused thinking by bacteriologists and others. Inmany cases these tests have become as meaninglessa ritual as other forms of inadequate operation ofautoclaves. Such tests are no substitute for correctrecords of autoclave performance and scarcely neces-sary if these are properly kept and studied. As Kelsey(1958) established, many unsuitable spores have beenemployed, and intelligent use of chemical indicatorshas many advantages. Brown and Ridout (1960)made a careful and critical study of the ways of usingsuch indicators and showed both their possibilitiesand limitations. In the past, it is clear that manytests, both with spores and chemical indicators, havebeen little more than an act of self-deception andhave been welcomed mainly because they offered animpressive and apparently simple alternative tomaking sure that the autoclave was really able to dowhat was required of it. In checking new sterilizingmethods and types of sterilizer, in making sure thatrecommended times and temperatures are sufficient,in devising new types of packaging, and in reassuringthose conditioned to accepting only bacteriological

53


http://jcp.bmj.com

/J C


ownloaded from

http://jcp.bmj.com/

J. W. Howie

checks, well-standardized preparations of bacterialspores have certainly a place. Kelsey (1961) has pro-duced valuable information about the effective useand standardization of Bacillus stearothermophilusspores for this kind of work. Suitable spore prepara-tions, if strategically placed in various critical posi-tions in a sterilizer, give useful additional evidenceand corroboration of the results of other tests; butnothing valuable is established by culturing routinelya single preparation of spores of uncertain standardplaced wherever the sterilizer attendant cares to putit. A drum containing a few sterilized swabs placednear the air filter inlet may usefully be employed tocheck the efficiency of the air filter (Howie andTimbury, 1956). In spite of these generally criticalobservations, a few well-sited Browne's tubes (type IIfor high-vacuum, high-pressure sterilizers; type I fordownward-displacement sterilizers) often give earlywarning to a conscientious theatre sister that herdressings have not been adequately exposed and thatthe autoclave needs a thorough investigation. Thebacteriologist with his spores should come inonly to test new methods and as a reassurancewhen required, for example, after an autoclave hasbeen found inefficient and has been repaired. In short,it is not by some simple laboratory test that thebacteriologist will best serve the cause of efficientautoclaving and sterilization processes generally. Hecan discharge his professional duty in this matter,however, if he keeps himself up to date with newwork on the subject, assesses it critically in relationto the problems of his own clinical colleagues, acceptsmedical responsibility for the work of the sterilizingdepartment if this is so arranged as to make medicalsupervision a possible reality, and conducts a con-tinuous process of education both for those whooperate autoclaves and for those whose work dependson the guarantee of sterility which these instrumentsare intended to provide. If he can do all this andremain a good-humoured colleague he will indeed beentitled to regard himself as a worthy follower in the

succession which includes Lister and Colebrook, inhonour of whose work this article was written.

CONCLUSIONS

This article reviews much of the recent work whichhas shown that surgeons' autoclaves have been tooreadily accepted as reliable and efficient.The main principles governing the successful

operation of autoclaves are briefly stated withreferences to published works in which the necessarymatters,of detail are fully set forth.As new types of autoclaves come into use, and

while older autoclaves are being upgraded pendingre-equipment and the general establishment ofcentralized autoclaving, bacteriologists have anexacting duty to perform in gaining a full under-standing of how surgeons' autoclaves work and ofexercising a general function of education andsupervision.

REFERENCES

Alder, V. G., and Gillespie, W. A. (1957). J. clin. Path., 10, 299.. (1959). Report published by The Drayton Regulator &

Instrument Co. Ltd., West Drayton, Middlesex.'Any Old Iron.' (1959). Lancet, 2, 178.Bowie, J. H. (1955). Pharm. J., 174, 473 and 489.

(1958a). Hlth Bull. (Edinb.), 16, 36.-. (1958b). Hosp. Engr., 12, 158 and 182.Brown, W. R. L., and Ridout, C. W. (1960). Pharm. J., 184, 5.Francis, A. E. (1959). Proc. roy. Soc. Med., 52, 998.Howie, J. W., and Timbury, M. C. (1956). Lancet, 2, 669.Kelsey, J. C. (1958). Ibid., 1, 306.

. (1961). J. clin. Path., 14, 59.Knox, R., and Penikett, E. J. K. (1958). Brit. med. J., 1, 680.Magee, K. C., and Oakes, H. E. (1958). Hosp. Engr., 12, 278.Medical Research Council Report. (1959). Lancet, 1, 425.

. (1960). Ibid., 2, 1243.Nuffield Provincial Hospitals Trust (1958). The Planning and

Organization of Central Syringe Services.Penikett, E. J. K., Rowe, T. W., and Robson, E. (1958). J. appi. Bact.,

21, 282.Rice, H. M. (1958). Lancet, 2, 1275.-. (1960). Ibid., 1, 960.Scott, A. C. (1957). Ibid., 2, 633.Wells, C., and Whitwell, F. R. (1960). Ibid., 2, 643.

54


http://jcp.bmj.com

/J C


ownloaded from

http://jcp.bmj.com/

the surgeon's autoclave - journal of clinical...

Documents