APPLIED MICROBIOLOGY, Jan., 1966Copyright © 1966 American Society for Microbiology

Vol. 14, No. IPrinted in U.S.A.

Microbiology of DrycleaningROBERT R. BANVILLE AND ETHEL McNEIL

Clothing and Housing Research Division, Agricultural Research Service, U.S. Department of Agriculture,Washington, D.C.

Received for publication 7 May 1965

ABSTRACT

BANVILLE, ROBERT R. (Clothing and Housing Research Division, U.S. Depart-ment of Agriculture, Washington, D.C.), ANDETHELMcNEIL. Microbiology of dry-cleaning. Appl. Microbiol. 14:1-7. 1966.-An appreciable number of bacteriaon contaminated fabric survived modem drycleaning procedures. Various stagesin the process, especially steam pressing, reduced the total number of bacteria, butviable organisms were found on certain areas of garments even after pressing. Asignificant number of bacteria were redeposited on clean fabric during the washing ofordinary soiled garments in drycleaning units. These bacteria included gram-positivecocci, diphtheroid bacilli, and gram-positive sporeformers. Gram-negative bacilliwere seldom found, although some gram-negative bacilli survived drycleaning. Theredeposited organisms apparently came mainly from other garments in the sameloads, as few bacteria were isolated from the filtered solvent used for washing. Thenumber of bacteria in the drycleaning washwheel was highest shortly after the be-ginning of the wash, and decreased, with the exchange of solvent in the wheel, to alow level at the end. Although it appears that in most cases several factors combine toreduce to a low level the numbers of bacteria on articles cleaned in a well-operateddrycleaning plant, it would seem that under certain conditions pathogenic micro-organisms could be disseminated by drycleaning.

A popular impression has existed for manyyears that drycleaning is a germicidal process andcan be used as a means of disinfection of fabrics.This is exemplified by a talk given on the radio in1924, in which the New York Board of Health issaid to have authorized the statement that germscausing influenza, scarlet fever, colds, bronchitis,pneumonia, tuberculosis, diphtheria, measles,and typhus are killed by proper drycleaningmethods (4). However, research has shown thatthe antibacterial effect of drycleaning is muchmore limited than this extreme view would sug-gest.

Chassevant (2) in 1895 reported the first studyon the effect of drycleaning solvents on bacteria.He concluded that the crude benzene and petro-leum solvents then used had little value as disin-fectants. In 1917, however, Kruse [cited by Hess(6)] found that crude benzene solvents killedcocci, diphtheria bacilli, and enteric bacteriawhen detergent and moisture were present. In1922, Jackson (7) found that drycleaning in ben-zene or gasoline reduced the number of lacticbacteria on inoculated fabric by about 90%, andthat the addition of steam pressing increased the

reduction to 99.9%. He observed smaller reduc-tions on fabric inoculated with Bacillus subtilis.Connell, Lamson, and Drinker (4) inoculatedswatches with staphylococci, streptococci, andB. anthracis, and immersed them in a cleaningsolution of naphtha and soap. They pressedswatches inoculated with staphylococci and B.anthracis at a drycleaning plant. In all cases,viable cells survived.

Meanwhile, chlorinated hydrocarbon solventsbegan to be used for drycleaning. The studies ofSalkowski (10), Joachimoglu (8), and Gabbano(5) established that trichloroethylene, perchloro-ethylene, and carbon tetrachloride were bacterici-dal when mixed with water. Gabbano found, how-ever, that the dry solvents were not bactericidal.In 1931 Rimpau (9) reported that dry trichloro-ethylene required 52 hr to kill staphylococci, al-though solvent and water emulsions were stronglybactericidal. He also found many bacteria in theresidue from trichloroethylene drycleaning units,including Staphylococcus aureus, Sarcina sp.,and sporeforming bacilli. In 1939 Vierthaler (11)inoculated fabric with nonpathogenic Staphy-lococcus, Streptococcus, Corynebacterium, and

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Escherichia species, and with a sporeformer; hethen cleaned the fabric in drycleaning units withperchloroethylene, trichloroethylene, and carbontetrachloride. In all cases, cells of each strainsurvived cleaning, and the sporeformer, but notthe Streptococcus or Corynebacterium species,survived pressing. He isolated coliform organisms,as well as types similar to those found by Rimpau(9), from a drycleaning unit.The antibacterial effects of perchloroethylene

with the proportions of detergent and moistureused in modem drycleaning were investigated byHess (6). He found that immersion of inoculatedswatches in the solvent solution killed all cells ofa coliform strain within 1 hr, but that livingstaphylococci survived after 2 hr. All cells weredead after immersion for 13 hr. When similarswatches were cleaned with the same solvent in adrycleaning unit, a large proportion of both organ-isms survived. Hot-air drying, however, killedall coliform bacteria and reduced the number ofstaphylococci. Bayliss (1) studied the effect on astrain of Streptococcus faecalis of modem dry-cleaning procedures which use perchloroethyleneand white spirit (a petroleum derivative). Shefound that the reduction in the number of bacteriaon inoculated swatches brought about by cleaningand hot-air drying was relatively small, usuallyless than 10-fold. Pressing produced more sig-nificant reductions; from fabric inoculated with109 to 1012 cells per inch2 (6.5 cm2), no more than4,000 cells per inch2 were recovered after pressing,and in many trials no living cells were recovered.A laboratory study of the effect of a number ofdetergents in perchloroethylene solution onstrains of Bacillus and Staphylococcus sp. and ona coliform organism indicated that they had littlegermicidal activity. The coliform organism ap-peared least affected.

It appears well established, then, that garmentsand other articles are not generally sterilized bydrycleaning, but that various stages in the dry-cleaning process do reduce the number of bacteriaon them. There is little quantitative information,however, on the amount of the reduction, espe-cially in relation to present-day drycleaningpractices, in which the two main solvents used areStoddard solvent (a petroleum fraction) andperchloroethylene. There is even less informationon the number and types of bacteria actuallyfound in the normal drycleaning operation, andon the degree to which these may be transferredfrom one article to another during cleaning. Toobtain such information, a limited number oftests were first carried out in the laboratory on theeffect of the two solvents and of some of the de-tergents now used in this country on certainstrains of bacteria. Then, using the facilities of a

commercial drycleaning plant, the effect of actualcleaning and pressing on contaminated fabricwas studied, and tests were run to determine thepresence of bacteria in the drycleaning system andthe extent to which they would be redeposited onclean garments or other articles.

MATERIALS AND METHODSOrganisms. Four test organisms were used: Staphy-

lococcus aureus 209; a strain of Paracolobactrumaerogenoides isolated in this laboratory, M45; and twostrains isolated during this study-M667, identifiedas Pseudomonas aeruginosa, and M689, identified asStaphylococcus epidermidis. They were maintained bydaily transfer 5 days per week in AATCC bacterio-stasis broth (Difco).

Laboratory tests. Twenty-four hour broth culturesof strains 209, M45, and M667 were diluted 1: 50 inAATCC broth. Sterile 2-inch (5-cm) square swatchesof cotton print cloth were then inoculated evenly with0.1 ml of each strain and allowed to dry for 3 hr at25 C and 35% relative humidity. The dry swatcheswere immersed in solvent for periods equivalent tothe duration of normal drycleaning: 6 to 15 min inperchloroethylene, or 10 to 20 min in Stoddardsolvent. The excess solvent was then wrung out of theswatches, and they were allowed to dry at room tem-perature for 2 to 3 hr. When a detergent was used inthe solvent, the swatches were rinsed by immersionfor 15 sec in plain solvent before drying. Each of thedry swatches was macerated for 1.5 min at 15,000rev/min in a Waring Blendor. Serial dilutions of theliquid from the Blendor were prepared in peptonesolution, and plate counts were made of the originaland diluted solutions in Eugonagar (BBL). Colonieswere counted after 48 hr of incubation at 37 C.

Plant-scale trials. The greater part of this studywas conducted in a large suburban drycleaning plant.In the standard cleaning process, all articles werefirst washed with solvent and detergent in a cylinder,the washwheel, and the solvent was extracted by cen-trifugation. In most units they were then rinsed inpure solvent, and in one unit there was also a sizingbath. The articles were then tumble-dried in hot air,and in most cases were steam-finished or pressed.

Used wash solvent, after leaving the wheel, flowedin each unit through a screened enclosure, the buttontrap, to the base storage tank. From here, some solventwas drawn to the diatomaceous-earth filter and someto the still. All the solvent that was returned to thewheel for reuse was drawn directly from the filter.The rest of the filtered solvent and all of the distilledsolvent were returned to the base tank. Rinse solventwas also filtered or distilled before reuse. The sizingsolution was neither filtered nor distilled, but nor-mally was partially replaced each week by fresh solu-tion. The process is illustrated schematically in Fig. 1.

Most of the work was done with three units. Ma-chine A was a Detrex model 528-B, a 30-lb (13.6-kg)unit which was operated with a 17-min wash periodand no rinse, with the use of a 1.5% solution of anethoxylated alkanolamide detergent in perchloro-ethylene. Machine B was a Spencer Major 60-lb(27.3-kg) hot unit, which employed a 4% petroleum

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MICROBIOLOGY OF DRYCLEANING 3

3I1E SOLVENT STORAGE TANK WASH SOLVENT'STOtAGE TAN

FIG. 1. Drycleaning process. From E. R. Phillips, Drycleaning, National Institute ofDrycleaning, Silver Spring'Md., 1961. Reproduced by permission of the author and publisher.

sulfonate detergent in perchloroethylene, and was

operated with wash periods ranging from 2 to 15 minand rinse and sizing baths of 1 min each. Unit C wasa Washex 561203, which had a capacity of 100 lb(45.5 kg), and was operated with 10- to 15-min washperiods and a 5-min rinse. It used a 2.0% ethoxylatedphenol detergent in Stoddard solvent. A few sampleswere also taken from two other Stoddard solventunits. The perchloroethylene machines were usedsolely for garments; the Stoddard solvent units wereused mainly for household goods, such as draperiesand blankets, but were occasionally used for garments.

Because it appeared that mechanical removal ofbacteria would play a large role in the reduction ofbacteria on contaminated articles during washing insolvent, it was felt that the use of naturally soiled,rather than artificially inoculated, fabrics would givea more realistic picture of the antibacterial effects ofthis process. It was difficult to find soiled garmentssufficiently heavily contaminated for the reduction innumber of bacteria to be accurately measured; there-fore, much of this work was done with several piecesof terry cloth which had been used in householdcleaning and were heavily contaminated. Swatches 2inches (5 cm) square were cut from both garmentsand cleaning cloths, and were pinned in garments tobe cleaned, usually in coat sleeves. After cleaning anddrying, the swatches were removed and macerated inthe Blendor by the usual procedure.To determine the bactericidal effect of steam finish-

ing and pressing, sterile 2-inch square swatches ofwool flannel were inoculated with the usual amounts

FIG. 2. Coat sleeve with inoculated swatches sewn

in windows cut in fabric.

of each of the four test strains. They were then pinnedin garments to be finished and pressed. Since thesleeves of coats are not usually pressed, tests were

performed to determine whether the heat produced bythe passing of free steam through the sleeve duringfinishing would be sufficient to kill bacteria on theouter surface. Windows 1 inch wide and 2 inches longwere cut in the outer fabric of the sleeve of a heavywool coat, and inoculated swatches were sewn intothe opening (Fig. 2). After finishing, all swatches were

removed and macerated as usual.Cleaned blankets are normally folded double and

steamed on a steam table. To study the effects of this

treatment, 2-inch square areas of the top layer of a

blanket were inoculated with strain M45 or M689

VOL. 14, 1966

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BANVILLE AND MCNEIL

TABLE 1. Survival of bacteria oni naturally soiledswatches after cleaning inperchloroethylene units

Bacteria per inch2

FabricCleaned swatch Uncleanedcontrol swatch

Ia 42 X 103c 35 X 1032b 15 X 106d 19 X 1073b 6.8 X 106e 12 X 106

a From wool flannel garment: gram-positivebacilli (genus Bacillus) predominant.

b Terry cloth cleaning rag: gram-negative bacillipredominant.

c Average of seven trials.d Average of four trials.e Average of five trials.

before steaming; afterward, these areas were cut outand treated in the usual way.To determine the number of bacteria in the wash-

wheel during the wash, samples were taken of solventflowing from the wheel through the button trap.Samples could be taken at any time from unit A, butonly at the end of the wash from unit B. In unit C,samples were taken of solvent flowing out of the but-ton trap during the wash, and into the button trapat the end. Samples were taken from the base tanksof unit A and one Stoddard solvent unit by pipette,and filtered solvent was obtained from unit A froma valve in the line from filter to washwheel.

For isolation and enumeration of bacteria in clean-ing solvent, the membrane-filter technique describedby the Committee on Microbiological Deteriorationof Fuels of the Society for Industrial Microbiology(3) was used. From 1 to 50 ml of each sample, de-pending on the source, was passed through type HAMillipore filters. Quantities smaller than 50 ml werediluted in sterile solvent to make 50 ml before filtering.The filters were then placed on freshly poured Eu-gonagar plates and incubated at 37 C. The colonieson the filter were examined after 24 hr and againafter 48 hr under a dissecting binocular microscope.Some samples of solvent were mixed with broth

and centrifuged, and the broth was then plated inEugonagar, according to the procedure of the Com-mittee on Microbiological Deterioration of Fuels,but with a ratio of 5 ml of Trypticase Soy Broth to20 ml of solvent. Plates were incubated for 48 hr at37 C.To determine whether the bacteria in the wash-

wheel would be redeposited on clean fabric, sterile2-inch square swatches were attached to garmentsbefore cleaning, removed at the end of the drying,and macerated by the usual procedure. Wool flannelswatches were regularly used, but cotton print cloth,cotton jersey, and plain and textured nylon were usedin some trials.

RESULTS

Effect of solvents on bacteria. When swatchesinoculated with 20 X 104 to 30 X 104 cells of S.

aureus per inch2 were immersed in plain perchloro-ethylene or Stoddard solvent, 20 to 40% of thecells in the inoculum generally survived. Almostall of these were recovered from the swatches,although a few were isolated from the solvent on

Millipore filters. Even when detergents (petro-leum sulfonate or ethoxylated phenol type) were

added, together with the appropriate amounts ofmoisture, at least 10% of the original inoculumwas always recovered. A smaller proportion was

recovered, however, when the swatch was notrinsed after immersion in detergent solution.

In similar tests with strains of Paracolobactrumaerogenoides and Pseudomonas aeruginosa, im-mersion in either perchloroethylene or Stoddardsolvent produced a much greater reduction in thenumber of viable cells, although some alwayssurvived. Differences were observed in percent-ages of cells surviving immersion in preparationsof Stoddard solvent from different sources.

Effects on bacteria of washing in drycleaningunit. Many bacteria remained alive on heavilysoiled fabric after cleaning in perchloroethylene(Table 1) or in Stoddard solvent. On less heavilycontaminated swatches cut from soiled garments,a smaller proportion of the bacteria generallysurvived, reductions of 90% being common.When the most common organisms on the soiledswatches before cleaning were gram-negativebacilli, gram-negative bacilli also predominatedafter cleaning. Among the strains isolated fromsuch swatches after cleaning were Paracolobac-trum aerogenoides, Pseudomonas aeruginosa, andspecies of Alcaligenes, Achromobacter, and Flavo-bacterium.

Killing of bacteria during pressing. Except forsporeformers, most bacteria directly exposed tothe heat of the steam press were killed. Whenswatches inoculated with S. aureus 209 (Table 2)or S. epidermidis M689 were placed in the pocketsof heavy coats before pressing, an appreciablenumber of bacteria survived. The greatest numbersurvived in the outer pockets, where the swatchwas surrounded by heavy woolen fabric, but somecells survived even in the inside pockets, pro-tected from the steam on one side merely by thethin fabric of the lining.

TABLE 2. Effect of finishing and pressing onStaphylococcus aureus within inner and

outer coat pockets

No. of bacteria per inch2 remaining on swatch

TrialIn inner In outer Controlpocket pocket

1 275 9,250 180,0002 550 68,000 185,000

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When flannel swatches inoculated with S.epidermidis or P. aerogenoides were sewn into thesleeve windows, scarcely any bacteria survivedsteam finishing lasting about 20 sec. However, ontwo occasions when naturally soiled terry clothswatches were used instead of the inoculatedswatches, an appreciable number of bacteria sur-vived (1,300 to 640,000 of about 48,000,000 perinch2 at the beginning). Many of the survivorswere gram-negative bacilli.No living bacteria were isolated from areas of

wool blankets inoculated with 25,000 cells perinch2 of P. aerogenoides or 42,000 to 240,000 cellsper inch2 of S. epidermidis and steamed on theblanket table for about 10 sec.

Bacteria isolated from solvent in drycleaningunits. Most of the bacteria developing on mem-brane filters after filtration of solvent from thewashwheel belonged to the genus Bacillus,whereas most others were gram-positive cocci.The majority of the latter were species of Sarcina,but strains of Staphylococcus aureus, S. epider-midis, and Micrococcus sp. were also isolated.Other species found by this method included C.striatum, Achromobacter pestifer, Brevibacteriumfulvum, and Flavobacterium sp. That other specieswhich did not form visible colonies on membranefilters were also present in the solvent is shown bythe fact that Corynebacterium sp., which formssmall colonies, developed in large numbers insome plates inoculated with broth from centri-fuged solvent-broth mixtures.The same types of bacteria were usually found

in both Stoddard solvent and perchloroethyleneunits when the same kinds of articles were cleanedin each. Rhodotorula and Pullularia type yeastswere isolated several times from Stoddard solventunits and also from a drum of fresh, unusedStoddard solvent.

In used perchloroethylene leaving the wash-wheel, bacteria were normally most numerous inthe first few minutes of the wash, and becameprogressively fewer until the end. In eight trialswith unit A, for example, there were an average of24 bacteria per milliliter in the solvent at the be-ginning of the wash, and an average of 2 bacteriaper milliliter at the end. Samples taken of solventleaving the wheel in unit B at the end of fourwashes lasting 3 min or less had an average of 124bacteria per milliliter; in samples at the end offour washes of 6 min each, the number of bacteriaaveraged 32 per milliliter, whereas after eightwashes of 12 min each there was an average of 3per milliliter. In unit C (Stoddard solvent), somesamples taken at the end of the wash had morebacteria than samples taken at the beginning.However, limited sampling of two other Stoddardsolvent units indicated that the number of bac-

TABLE 3. Redisposition of bacteria on sterile woolflannel swatches during drycleaningI~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Unit* Length ofIwash period

A

B

C

min

17

3

4

6

10

12

10

15

Bacteria per ml insolvent leavingwashwheel atend of wash

1381

<1111

>300>15

>20

51

105

2<1

3133

5535

Bacteria per inch2on swatch aftercleaning and

drying

175<25175<2525150<25425

2,00050

140240

<25880400

40150

50<2521025

50330200

130

* In units A and B, the solvent was perchloro-ethylene; in unit C, Stoddard solvent.

teria at different stages would generally follow thesame pattern as in the perchloroethylene units.When samples from the base storage tanks were

passed through membrane filters, less than onebacterial colony per milliliter of solvent usuallydeveloped on the membrane. Even fewer bacteriawere found in solvent which had passed throughthe diatomaceous-earth filter. However, 20 to 30bacteria per milliliter were regularly isolated bythe same method from solvent in the sizing tankof unit B. Most of these were species of Bacillusor Sarcina. When the sizing tank was not drainedregularly, up to 240 bacteria per milliliter werefound in sizing solvent leaving the washwheel, al-though only a small fraction of this number wouldnormally be washed off the garments during thesizing period.

Redeposition of bacteria on fabric during clean-ing. The number of bacteria deposited on sterile

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TABLE 4. Transmission of bacteria from soiledfabric* to sterile flannel during

drycleaning in unit B

Bacteria per inch2

Length of Trial Sterile fabric Sterile fabric pinned

pinned near soiled inside back of samefabric, inside sleeve garment

min

3 1 430 X 102 30 X 1022 250 X 102 28 X 102

6 1 175 X 102 11 X 1022 395 X 102 31 X 102

* Terry cloth cleaning rag having average of 18 X107 bacteria per inch2, predominately gram-negativebacilli.

wool flannel swatches during the drycleaning ofnormal loads of garments is indicated in Table3. A similar number of bacteria were found ontextured nylon cleaned under comparable condi-tions, whereas fewer were deposited on cottonknit jersey, cotton print cloth, and plain nylon.During cleaning of household goods, fewer bac-teria were deposited on sterile swatches thanduring cleaning of garments.

Although members of the genus Bacillus pre-dominated in samples of cleaning solvent, amongthe bacteria deposited on swatches they were oftenoutnumbered by gram-positive cocci, principallyof the genus Sarcina, and by members of the genusCorynebacterium. The corynebacteria, as men-tioned above, were present in the solvent also butdid not develop on the filters. Some of the cocciin the solvent may have died during the period of2 to 3 hr between the collection and filtration ofthe solvent. The bacteria deposited on sterilefabric included strains identified as Staphylococcusepidermidis, Corynebacterium xerosis, C. pseudo-diphtheriticum, C. bovis, C. striatum, and speciesof Pseudomon. Micrococcus, Sarcina, andBrevibacterium. A strain identified biochemicallyas C. diphtheriae was isolated from a swatch cutfrom a used garment and cleaned. This strain mayhave been on the fabric originally, or have beenredeposited during cleaning.That the number of redeposited bacteria was

not larger appears to be due to the relatively smallnumber of bacteria on the articles usually dry-cleaned. When fabrics contaminated with a largenumber of bacteria were cleaned, many bacteriawere transferred to sterile swatches (Table 4).Redeposition was greatest when both sterile andsoiled swatches were attached within a few inchesof each other. However, redeposition was stillhigher than normal when the soiled and sterile

swatches were attached to different parts of thesame garment, as may be seen by comparingTables 3 and 4.

DISCUSSIONThe reduction in number of bacteria on soiled

fabric brought about by washing in solvent anddrying was generally comparable to that obtainedby Jackson (7) and by Bayliss (1) with inoculatedswatches, except that on some pieces of fabricthere was little reduction. This may be due to bac-teria being bound more tightly to some soiledfabric samples than to others, depending on themode of contamination. Differences in strainspresent may also be partly responsible.

In addition to the bactericidal action of thesolvent and the mechanical removal of cells, partof the reduction may be due to the heat of drying.This should not be relied upon as a germicidalprocess, however, as drying temperatures varygreatly. An appreciable number of gram-negativebacilli survived cleaning, even though similargram-negative bacteria were largely killed by im-mersion in solvent in the laboratory. However, inthe laboratory tests there was a longer period ofcontact between bacteria and solvent than wouldusually occur in actual practice, as the solventwas not rapidly removed by hot-air drying.Steam finishing and pressing appear to kill

more bacteria than any other stages in the clean-ing process. However, the type of steam treat-ment given to different articles varies too much tobe relied upon for disinfection. Many garmentsare not pressed at all; in other garments, certainareas, such as sleeves and the inside of pockets,receive a lower temperature than the rest of thegarment. The number of drycleaned articles usedwithout any steam pressing will be greater with theincreased use of coin-operated drycleaning. Steamfinishing or pressing may be of value in the disin-fection of articles that receive a uniform steamtreatment, such as blankets.

Although few of the strains of bacteria rede-posited on sterile fabric during cleaning were ofpathogenic species, a significant proportion be-longed to genera in which some species are patho-genic, such as Staphylococcus or Corynebacterium.It would seem, therefore, that although variousstages in cleaning combine to kill or remove themajority of bacteria present on fabric, it is stillpossible for pathogenic bacteria to be transmittedfrom one article to another during cleaning, andto survive all steps in the process under certainconditions. The extent to which this would occurwould depend on the number of bacteria on thearticles sent to be cleaned and on the proceduresfollowed by the cleaner. For example, very shortwash periods, ending before most bacteria are

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carried out of the washwheel, probably permitgreater redeposition. All data in this paper arebased on studies in one modem, well-operatedplant, in which few heavily soiled articles wereencountered. It would be desirable for furtherstudies to be carried out in other plants, under agreater variety of conditions.

ACKNOWLEDGMENTWe are indebted to Robert T. Graham of the

National Institute of Drycleaning, Silver Spring, Md.,for making available the facilities of the InstituteCleaning Plant, and for advice and assistance on manyoccasions. We also thank all members of the Institutestaff who cooperated in this study.We appreciate the technical assistance of the staff

of the clothing unit of the Clothing and HousingResearch Division, Agricultural Research Service.

LITERATURE CITED

1. BAYLISS, J. B. 1960. Investigation into the disin-fectant action of drycleaning processes anddrycleaning detergents. B.L.R.A. Rept. No.112. British Launderers' Research Association,Hendon, England.

2. CHASSEVANT, A. 1895. Action du benzene sur lesmicroorganismes. Compt. Rend. Soc. Biol.47:698-699.

3. COMMITTEE ON MICROBIOLOGICAL DETERIORATIONOF FUELS. 1963. Proposed procedures for micro-

biological examination of fuels. SIM SpecialPubl. No. 1. Society for Industrial Microbi-ology, Washington, D.C.

4. CONNELL, W. J., R. W. LAMSON, AND P. DRINKER.1924. A survey of drycleaning methods in thevicinity of Boston, Mass. J. Ind. Hyg. 6:227-244.

5. GABBANO, L. 1929. Untersuchungen uber denWirkungsmechanismus und den Desinfek-tionswert einiger Chlorderivate des Methans,Athans und Athylens. Z. Hyg. Infektions-krankh. 109:183-193.

6. HESS, R. 1960. Zur Kenntnis der desinfizierendenTrockenreinigung. Krankenhuas 52:90-98.

7. JACKSON, L. E. 1922. The bacterial action of dry-cleaning. Am. J. Public Health 12:507-509.

8. JOACHIMOGLU, G. 1921. Vergleichende Unter-suchungen uber die antiseptische wirkungeiniger Chlorderivate des Methans, Athans undAthylens. Biochem. Z. 124:130-136.

9. RIMPAU, W. 1931. Die Desinfizierende Wirkungdes zur chemischen Reinigung benutzten Tri-chlorathylens. Z. Hyg. Infektionskrankh. 112:202-221.

10. SALKOWSKI, E. 1920. Uber die antiseptischeWirkung einiger Chlorderivate des Methans,Athans und Athylens. Biochem. Z. 107:191-201.

11. VIERTHALER, R. W. 1939. Ist die chemische Reini-gund ein Desinfektionsvorgang? Z. Hyg. In-fektionskrankh. 121:447-464.

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