Human amniotic membrane: a versatile wound dressing
JOSEPH S. GRUSS,* MB, B CH; DENNIS W. JIRSCH, MD, M SC, PH D, FRCS[C]
Human amniotic membrane proved tobe a versatile and useful temporarybiologic dressing in studies involving120 patients. Wounds, both traumaticand nontraumatic in origin, respondedto a protocol that allowed coverageof tissues as diverse as exposed bowel,pleura, pericardium, blood vessels,tendon, nerve and bone. Woundsunresponsive to usual therapeuticmeasures responded to membraneapplication. Ease of availability, negligiblecost and facilitated wound healingmake this temporary biologic dressinggenerally superior to either cadaverskin allograft or pigskin xenograft.Human amniotic membrane dressingsare therefore a useful adjunct in thecare of the complicated wound.
Dans des etudes impliquant 120 patientsla membrane amniotique humaine s'estaveree un pansement biologiquetemporaire utile et versatile. Lesblessures, traumatiques ou non, ontrepondu il un -protocole qui prevoyaitIe recouvrement de tissus aussi diversqu'un intestin, une plevre, un pericarde,des vaisseaux _sanguins, un tendon,un nerf ou un os mis il nu. Desblessures ne reagissant pas aux mesurestherapeutiques habituelles ont repondua une application de membrane. Sagrande disponibilite, son coOt negligeable et son effet benefique sur la.cicatrisation des blessures rendent cepansement biologique temporairegeneralement superieur aux allogreffesde peau d'origine cadaverique ou auxxenogreffes de peau de porc. Lespansements de membrane amniotiquehumaine constituent donc une mesured'appoint utile dans Ie traitementdes blessures compliquees.
The main goal in maJ.lagement of anopen wound is to obtain a clean andclosed wound in the. shortest time.Deleterious effects of an open woundare many and are related mainly tothe size and site of the wound. Fluid,
From the department of surgery (divisionsof plastic surgery and general surgery),University of Toronto and the departmentof surgery, St. Michael's Hospital,Toronto
*Resident at St. Michael's, St. Joseph'sand Toronto Western hospitals whilethis study was performed.
Reprint requests to: Dr. Dennis W. Jirsch,55 Queen St. E, Ste. 407, Toronto, OntoM5C lR6
heat and nutrient loss, continuingcontamination and sepsis, and associated pain and decreased mobilitymay seriously hamper patient recovery, and early coverage of a majorburn wound may be lifesaving. Thesearch for an ideal wound cover as asubstitute for the patient's skin beganmore than a century ago and continues today. In the late 1800s Girdner,1 Reverdin2 and Lee3 used cadaverand animal skin to cover burnwounds. Davis4 in 1910 reported attempts to graft pieces of amnioticsac onto granulating wound, and 3years later Sabella5 described thetreatment of a burned patient withportions of amniotic membrane.
These early attempts at substitution for the patient's skin were designed to provide permanent coverageand failed because of immunologicrejection. Years later Dog06 initiatedthe use of split-thickness cadaver skinallografts as temporary biologic dressings for large burn wounds, a procedure popularized by Brown and associates.1 Removal of such dressingsand replacement with another skinallograft or an autograft prior to rejectioa was an important factor inthe increasing rate of survival frommajor burns. The rejection reactionis unpredictable and occurs unevenly.Edema and cellular reaction produceunhealthy granulation tissue susceptible to bacterial invasion, and theconcomitant systemic response maybe severe and cause further debilitation in the burn patient.
Difficulties in obtaining adequatesupplies of cadaver skin led to asearch for substitute tissues. In 1957Rogers, Converse and Silvetti8 proposed concerted investigation into theuse of bovine embryo skin as a temporary dressing for large skin wounds.Bromberg, Song and Mohn9 laterreported the results of their laboratory and clinical investigations withpigskin xenografts, which, because oftheir commercial availability, havebecome popular in many centres.
The use of human amniotic membrane as a temporary biologic dressing has been evaluated recently, bothexperimentally and clinically, byRobson and Krizek.10 In a series of
50 rat bums infected with 108 Pseudomonas aeruginosa organisms, thisdressing was shown to be 1000 timesmore effective than split-thicknesshuman skin grafts in decreasing bacterial contamination. In another experimental model human amnioticmembrane was found to be as effective as split-thickness isograft skin butsuperior to split-thickness allograftand xenograft skin in decreasing bacterial contamination of full-thicknessskin defects created on the backs ofrats. 11 The usefulness of human amniotic membrane in the managementof open wounds was further substantiated by Robson and associates12
•13 in
a study of 150 patients, and by Colocho and colleagues14 in their use ofthe amnion layer alone as a physiologic wound dressing in 107 patientswith partial-thickness burns and splitthickness graft donor sites.
We undertook the study describedbelow to evaluate the usefulness andversatility of human amniotic membrane as a temporary biologic dressing in a wide variety of common andchallenging clinical situations, andto determine an optimal protocol forits use.
Methods
Patients
Included in the study were 120 patients in need of temporary biologicdressings. Their wounds were mainlyfull-thickness defects of diverseorigin and certain partial-thicknessdefects. Accurate clinical and photographic records were kept.
A1aterial
Fresh amniotic membranes wereobtained at the time of delivery fromwomen who were seronegative forsyphilis and had no history of premature rupture of the membranes or endometritis. Meconium-stained orfoul-smelling membranes were discarded. With aseptic technique, membranes were removed from the placenta, not separated into amnion andchorion, and washed four times withsterile normal saline, once with0.025 % sodium hypochlorite solution, then four times with normal
CMA JOURNAL/MAY 20, 1978/VOL. 118 1237
saline. With each wash the membranes were agitated thoroughly todislodge any adherent clot. Thereafter they were refrigerated in individual sterile containers at 4°C.Cultures done at repeated intervalswere uniformly sterile. No materialwas used after 6 weeks of storage.
Protocol for use of membranes
The area to be covered is cleansedwith saline, and any exudate ormedications are removed. All escharand devitalized tissue must be removed. Human amniotic membranesare placed so as to adhere closely tothe underlying wound surface without air pockets or wrinkles. Theyshould cover the entire wound surfaceand, because of their great pliabilityand adherence, can be tucked intorecesses and overhanging areas.
In full-thickness defects the chorion (dull aspect) is placed on thewound and the amnion (shiny surface) faces upwards. Membranes arechanged every 48 hours unless thereis heavy contamination or infection;then they are changed more frequently. In severely infected areas membranes should not be used while thereis a great amount of free pus. Instead, such areas should initially becleaned frequently with moist dressings (for 24 to 48 hours) and themembranes applied subsequently."Take" is evident when the membrane becomes firmly adherent tothe tissue bed without underlying accumulation of debris or pus. Thickmembranes are gently peeled off thewound surface, while thinner onesare removed by rubbing the woundsurface with dry gauze. Membraneremoval leaves underlying healthygranulation tissue. Once consistenttake has occurred the wound is readyfor permanent autogenous skin grafting or closure. Whenever possible,more superficial dressings are notused since the dry superficial layer ofamniotic membrane forms a firm andpliable wound cover, facilitating observation. Collections of serum orpurulent material beneath the membrane may be evacuated by unroofing the small blebs or changing themembrane. In mobile patients a fu:qtdressing is applied to prevent dislodgement.
In partial-thickness wounds themembrane should be applied with theamnion against the wound surface.The membrane is allowed to remain
in place undisturbed while epithelialization progresses beneath it. Spontaneous separation of the membraneoccurs when epithelialization is complete.
Clinical experience
The clinical use of human amnioticmembrane as a temporary biologicdressing is limited only by the surgeon's imagination and the availability of the membrane. Experiencederived from the management of 120patients with wounds of diverse origin has enabled us to categorizewounds into various clinical types(Table I).
Ulcers
Human amniotic membrane wasused in the management of 30 skinulcers of diverse origin, mainly ofthe leg; the underlying problems included venous stasis, arterial diseaseand diabetes. Decubitus ulcers andulcers resulting from soft-tissue infection were similarly treated. Most ofthe chronic ulcers had failed to respond to routine wound care.
In small ulcers human amnioticmembrane kept the wounds bacteriologically clean, thus allowing spontaneous closure to occur (Fig. 1). Inlarge ulcers the membranes were usedto prepare the wound for subsequentdefinitive closure. Most of these patients were treated as outpatients.
Elective surgical wounds
Certain surgical wounds may beleft open for various reasons afterelective procedures. Human amnioticmembrane can then be used to coverthe wound, preventing contamination, in preparation for definitiveclosure. Thirty wounds were thustreated. Included were wounds fromradical vulvectomy, radical mastectomy and open amputation. Following radical excision of pilonidal sinu-
Table I-Clinical types of wounds managedwith dressings of human amniotic membrane
No. ofType of wounds patients
Ulcers 30Elective surgical wounds 30Infected wounds 21Contaminated surgical wounds 12Nonhealing or poorly healing
wounds 10Burns 10Traumatic soft-tissue wounds 7
ses human amniotic membrane wassimilarly used to provide a pain-free,clean wound without the use of sitzbaths; this resulted in rapid mobilization of the patient and reduced thetime required for healing and convalescence.
Infected wounds
In 21 infected wounds human amniotic membranes were used to decrease wound bacterial counts, usually after incision and drainage of anincisional abscess. Once the countswere 1(1 bacteria or fewer per gramof tissue, as evidenced by take of themembrane, delayed wound closurewas performed. Rapid reduction ofbacterial counts permitted successfulsecondary wound closure. This treatment was particularly useful in thefollowing two cases:
Case 1: Following abdominoperinealresection of the rectum and colon,dehiscence of the abdominal woundwith exposure of small bowel loopsoccurred in a severely debilitated patient. Human amniotic membrane wasapplied to the small bowel and the openwound and was changed frequently.This resulted in coverage of the entirewound surface and small bowel withhealthy granulation tissue and facilitated successful subsequent autograftclosure.
Case 2: Human amniotic. membrane was applied directly to parietalpleura in a 58-year-old debilitated manin whom dehiscence of the thoracotomywound occurred after esophagectomyfor esophageal carcinoma. In 14 daysthe entire wound and pleura were covered with healthy granulation tissue,allowing successful closure.
Contaminated surgical wounds
In the management of 12 patientswith contaminated surgical woundshuman amniotic membrane was usedto decrease wound bacterial countsto levels that allow delayed definitivewound closure. In particular, themembranes proved extremely useful inthe management of heavily contaminated appendectomy wounds. Following closure of the peritoneum anddeep fascia the superficial woundlayers were left open and humanamniotic membrane was applied. Themembrane was changed every 24 to48 hours until take was evident. Delayed primary wound closure wasthen performed on the ward with Steri-Strips (medical products division,Minnesota Mining & Mfg. Company,
1238 CMA JOURNAL/MAY 20, 1978/VOL. 118
FIG. IA--ehronic venous stasis ulcer.
FIG. IB-Human amniotic membrane applied to ulcer.
FIG. Ie-Ulcer completely healed in 3 weeks.
FIG. 2A-Pyoderma gangrenosum of perineoscrotal area;deep, burrowing ulcers with necrotic base and underminededges witb black, "lifeless" appearance; anal stump evident.
FIG. 2B-After 6 weeks of application of human amnioticmembrane, undermined edges filled in, new epithelium atperiphery, and significan.t bealing and wound contraction.
FIG. 3-Major full-thickness burn wound after separationof eschar; large membranes used to advantage.
CMA JOURNAL/MAY 20, 1978/VOL. 118 1239
3M Center, St. Paul, Minn.) and wasuniformly successful.
Nonhealing or poorly healing wounds
I~ 10 patients with nonhealing orpoorly healing wounds of diverseorigin human amniotic membranewas applied' to stimulate healing andgranulation tissue formation. Most ofthese wounds had failed to respondto routine wound care and systemicsupport. The change in wound appearance following application of themembranes was often striking, as inthe following cases:
Case 3: A 45-year-old man underwent total proctocolectomy for Crohn'sdisease. ,Pyoderma gangrenosum of theperineum developed thereafter, withsloughing and ulceration of almost theentire perineoscrotal area, which wascompletely resistant to all forms oftreat.ment for 18 months. Frequentdressings and sitz baths necessitatednarcotic analgesia. The wound prior tothe application of human amnioticmembrane is shown in Fig. 2A. Steroidsand azathioprine were being administered for control of the Crohn'sdisease.
Pain was relieved when applicationof human amniotic membrane was begun. Every 48 hours the 'membrane wasremoved in a sitz bath and anotherapplied. No debridement or other formof wound care was used. Within 3weeks there was a remarkable transformation in appearance of the wound:the deeply undermined edges had filledin, epithelial ingrowth from the periphery was progressing rapidly, and theulcer base was replaced 'with healthy,bright-red granulation tissue. By 6weeks more than two thirds of the ulceration had healed and wound contraction and epithelialization werestriking (Fig~ 2B). Fatal cerebral hemorrhage interrupted this progression ofevents, but the near-total healing evidenced prior to death was striking.
Case 4: In a 58-year-old man achylous fistula developed after pharyngolaryngectomy and radical neck dissection for recurrent hypopharyngealradiation therapy. A large area of tissueadjacent to the tracheostoma brokedown, with deep url:dermining of thewound. edges, exposing the commoncarotid artery. After 4 weeks of application of routine dressings (sodium hypochloritel:20) 'minimal healing was evident. Human amniotic membrane wasapplied directly to the exposed carotidartery and remaining wound surfaceand tucked under the deeply undermined wound edges. Over the next 4weeks healthy granulation tissue filledthe wound, obliterating the undermined
edges and providing almost completecoverage .of the· exposed carotid artery.This allowed successful closure of thedefect with a deltopectoral flap.
In two cases human amnioticmembrane was applied directly tobone:
Case 5: Following aortocoronary bypass grafting, postoperative sternal dehiscence occurred in a 61-year-old man.The wound was resutured, but 2 dayslater dehiscence recurred, the wiresutures tearing through friable boneedges. Human amniotic membrane wasapplied to this deep wound, directlycovering the pericardium and the twolateral edges of the sternum. Frequentdressing changes were initially needed,but after 1 weeks healthy granulationtissue covered the pericardium andsternal surfaces, 'and delayed woundclosure was performed.
Case 6: In a 50-year-old man a distal tibial fracture remained ununiteddespite two attempts at open reductionand bone grafting, and osteomyelitisdeveloped at the fracture site. Following curettage and saucerization of thearea human amniotic membrane wasapplied directly to the bony cavity andadjacent exposed tendon. Healthygranulation tissue began to cover areasof exposed bone. The many remainingislands of pearly, avascular bone wereremoved on the ward and human amniotic membrane was reapplied tohealthy, bleeding bone. Four weekslater, prior to coverage with a cross-legflap, the entire bony cavity and exposed tendon were covered withhealthy, bright-red granulation tissue.Because the exact extent of devitalizedbone was accurately determined, management was facilitated.
Burns
Ten patients with full-thickness ordeep partial-thickness burns weretreated with human amniotic membrane. In full-thickness burns, oncethe eschar had been removed themembrane was applied to providecoverage and to promote the growthof healthy granulation issue prior toautografting (Fig. 3). Areas of thewound not ready for grafting (as.:;hown by failure of the membrane totake) were prepared with frequentmembrane changes until take was evident. Granulation tissue in the areasready for grafting was kept healthyuntil the entire wound was ready forgrafting. Debridement of the burnsurface by frequent changes of membrane decreased the number of grafting procedures necessary to close thewound. With massive burns and lim-
ited autograft supply the membranecovered the wound while donor sites,healed. Membrane dressings reducedpain significantly, permitting earlymobilization, es-pecially with burns ofthe hand.
Certain deep partial-thicknessburns covered with human amnioticmembrane after separation of theeschar showed accelerated healing ofthe remaining dermal elements. Coalescing epithelial' islands were seenbeneath the membrane, which separated spontaneously when epithelialization of the underlying wound wascomplete. Healthy, pliable, normalskin, without hypertrophic scar, wasproduced. Human amniotic membrane was not used in the initial treatment of partial-thickness burns sincethermal injury often results in awound with patchy areas of partialand full-thickness loss.
Traumatic soft-tissue wounds
In seven patients who had sufferedsevere soft-tissue and ,bony traumahuman amniotic membrane was usedas the immediate cover for contaminated wounds to protect exposed bone,nerves, tendons and vessels, and tomaintain tissue viability until definitive closure was ,possible. In, woundsin which the tissue viability was questionable the membranes were used todelineate areas of dead tissue andthus permit accurate debridement.
Discussion
Human amniotic membrane hasbeen used successfully as a temporarybiologic dressing in diverse clinicalsituations. Histologically the membranes consist of two loosely connected tissues, amnion and chorion.The amnion, or inner layer, is derivedfrom the epiblast and is continuouswith the embryonic ectoderm.1s Theinner surface is composed of cuboidalor flattene·d epithelial cells; the outersurface is covered with -mesenchymalconnective tissue. The chorion has amesenchymal component in contactwith the amnion, and an externalectoderm composed of transitionalepithelium. Pigeon16 has stated thatsince amniotic membrane is formedby fetal ectoderm it is really an extension of the infant's skin. Lister17
found ultrastructural and functionalsimilarities between fetal skin andamnion and chorion. Hence humanamniotic membrane can- be considered analogous to fetal skin allo-
1240 CMA JOURNAL/MAY 20, 1978/VOL. 118
graft. This may account for certainof its beneficial effects when usedas a wound dressing.
In treating this series of patientswe made no attem·pt to separate themembrane into its two layers sincethe thicker two-layered membraneprovided a more satisfactory temporary wound cover; no disintegration occurred within 48 hours whenadherence of the membrane wasmaintained. Douglas18 demonstratedinitial neovascularization of chorionapplied to experimental wounds, andRobson and Krizek13 showed decreased bacterial growth when a temporary biologic dressing took initiallyon a granulating site. Therefore weapplied the chorion to the wound surface of all full-thickness wounds. Colocho and colleagues14 showed conclusively that no vascularization occurs when the amnion is applied tothe wound. Therefore in partialthickness defects, for which vascularization is not desirable, we placed theamnion against the wound surface.This provided wound coverage, andthe membrane dessicated spontaneously when epithelialization was complete.
All biologic dressings currentlyused (cadaver skin allograft, pigskinxenograft and human amniotic membrane) serve specific functions:
• Reduction of bacterial contamination and prevention of furthercontamination.
• Reduction of fluid, protein,heat and energy loss.
• Reduction of pain.• Promotion of healing.• Protection of underlying struc
tures.• Increase in mobility.• Prediction of tissue viability
when such is initially questionable.• Preparation of full-thickness
defects and recipient sites for autografting or delayed closure.
• Psychologic improvement inthe patient.Cadaver skin allograft and pigskinxenograft have certain disadvantagescompared with human amnioticmembrane. Cadaver skin is difficultto obtain; legal problems and the exclusion of cadavers with a history ofmalignant disease, hepatitis or syphilis are further difficulties. Personnelmust be available at all times to procure the skin in a sterile manner,usually in the operating room. Baxter19 estimated that the cost of har-
vesting the skin of one cadaver was$225 and that it required, on theaverage, 6 hours of physicians' time.Pigskin is commercially available butcosts approximately $280/ms. Woodand Hale20 have estimated the costof pigskin dressings in an adult withburns of 44% of his body surfaceto be $219/d. Both allograft andxenograft skin dressings are limitedin size and shape. Human amnioticmembrane is readily available andfreely obtainable, and may be large.
One of the main benefits of woundcoverage with a biologic dressing isprevention of contamination and reduction of infection. Eade21 showedthat in burns, granulation tissue isalways heavily contaminated withorganisms; coverage with fresh viableor preserved nonviable autograft orallograft permitted granulation tissueto destroy contained organisms rapidly. Morris, Bondoc and Burkeu believed that this antibacterial effect layin the intimate closure of the openwound provided by the biologicdressing, which prevented furtherbacterial contamination and allowedthe host's defence mechanisms todeal with the infection effectively.Larson23 found that the decrease inthe count of bacteria paralleled therapid increase iIi the count of leukocytes beneath the graft. This wasconfirmed by Saymen and colleagues,24 who showed that in uncovered infected rat wounds leukocytes tended to migrate from themuscle surface to the base, and thatthis migration reversed after the application of allograft skin. They suggested that this alteration in cell migration might modify leukocyte function and result in greater bactericidalactivity. The reduction in bacterialcontamination and reversal of leukocyte migration did not occur in theabsence of wound coverage. Burlesonand EisemanlS found that the antibacterial effect of biologic dressingswas related to the adherence to theunderlying wound bed. "Skin thatstuck sterilized." They demonstratedwith pigskin that this adherence wasrelated to a fibrin-elastin biologicbond.
Experimentally human amnioticmembrane has proven equal to autograft skin and superior to allograftand xenograft skin in decreasing bacterial counts in open granulatingwounds.10JOl1 Clinically the ability ofhuman amniotic membrane to de-
crease bacterial counts was equal tothat of allograft skin and superior tothat of xenograft skin, probably because of the greater pliability andadherence of human amniotic membrane with intimate wound closureand obliteration of dead space.13 Inaddition, the mechanical debridementthat accompanies frequent membranechanges allows host resistance factorsin the granulating bed to function atpeak efficiency. The initial take ofmembrane to the granulating bedprobably contributes to this salutaryeffect since the lack of effectivenessof xenograft skin in decreasing bacterial counts has been related to itsinability to take initially on a granulating wound surface.19 The recentreduction in the neomycin content ofcommercial pigskin has further decreased this dressing's effectiveness.16JOI7
Other mechanisms have been postulated for the antibacterial propertiesof human amniotic membrane. Lysozyme, a bactericidal protein, is present in high concentration in humanamniotic membrane, and progesterone, which is bacteriostatic for certain gram-positive organisms, is alsopresent.28 Allantoin is present as well(C.W. Brigden, personal communication, 1977). Indeed, the beneficialeffect of maggots on contaminatedwounds has been considered to bedue to their excretion of allantoin.
Skin graft survival and successfulclosure of a contaminated wound bysuture or skin graft have been shownto correlate accurately with a woundconcentration of 105 or fewer bacteria per gram of tissue, except for,a-hemolytic streptococci, whose concentration must be lower for successful grafting or wound closure.19J029
Allograft take has been found to correlate accurately with a wound concentration of 105 bacteria per gramof tissue, and this forms the basis ofthe allograft test. In this way theprevious subjective evaluation ofwound readiness for grafting or delayed closure has been replaced byobjective allograft testing of thewound surface. Take of human amniotic membrane to the wound surface invariably predicts successfulautograft take or wound closure. Thishas particular application in the management of contaminated, infectedand burn wounds and chronic skinulcers. Delineation of areas of deadtissue to limit the extent of debride-
CMA JOURNAL/MAY 20, 1978/VOL. 118 1245
ment is especially important in handand face injuries, wringer injuriesand wounds caused by gunshot orother high-velocity projectiles, inwhich excessive debridement canseverely restrict function and resultin cosmetic deficiency.30
Promotion of healing followingwound coverage with a biologicdressing has been reported by manyauthors. 31
-34 In rabbits, wound heal
ing was accelerated after the application of human amniotic membrane:the repair process started earlier, themigration of fibroblasts and the development of collagen were hastenedduring the first 6 to 8 days of healing, and epithelialization occurredsooner. 35 In addition, allograft skinseems to have an organizational effect on the healing wound: 22 seconddegree burns not covered by allograftshowed edema and inflammation inthe dermis, with disorganization ofnormal maturation and loss of cellpolarity, whereas in wounds coveredby allograft the epidermis showednormal structure with a recognizablebasal layer and a normal-appearingcollagen layer in the dermis. 36 Hypertrophic scarring and keloid formationseem to be prevented in this way.
We did not use human amnioticmembrane for split-thickness skingraft donor sites, which heal rapidlywith routinely used dressings andrarely pose a problem clinically.
Conclusions
Human amniotic membrane wasused successfully as a temporary biologic dressing for various wounds in120 patients. The membrane is easilyobtained, at little or no cost. It provides excellent wound coverage andhas distinct advantages comparedwith other biologic dressings.
References
1. GIRDNER JH: Skin grafting with graftstaken from the dead subject. M ed Rec20: 119, 1881
2. REVERDIN JL: Greffe epidermique.Bull Soc Imp Chir Paris 10: 511, 1869
3. LEE EW: Zoografting in a burn case.Boston Med Surg J 103: 260, 1880
4. DAVIS JS: Skin transplantation. Witha review of 550 cases at the JohnsHopkins Hospital. Johns HopkinsHosp Rep 15: 307, 1910
5. SABELLA N: Use of fetal tnembranesin skin grafting. Med Rec NY 83: 478,1913
6. Dooo G: Survival and utilization ofcadaver skin: preliminary note. PlastReconstr Surg 10: 10, 1952
7. BROWN JB, FRYER MP, RANDALL P, etal: Postnlortem homografts as "biological dressings" for extensive burnsand denuded areas; immediate andpreserved homografts as life-savingprocedures. Ann Surg 138: 618, 1953
8. ROGERS BO, CONVERSE JM~ SILVETTIAN: Preliminary clinical studies onbovine embryo skin grafts. TransplantBull 4: 24, 1957
9. BROMBERG BE, SoNG IC, MOHN MP:The use of pig skin as a temporarybiological dressing. Plast ReconstrSurg 36: 80, 1965
10. ROBSON MC, KRIZEK TJ: The effectof human amniotic membranes on thebacterial population of infected ratburns. Ann Surg 177: 144, 1973
11. ROBSON ~lC, SAMBURG JL, KRIZEK TJ:Quantitative comparison of biologicaldressings. J Surg Res 14: 431, 1973
12. ROBSON MC, KRIZEK TJ, Koss N, etal: Amniotic membranes as a temporary wound dressing. Surg GynecolOhstet 136: 904, 1973
13. ROBSON MC, KRIZEK TJ: Clinical experiences with amniotic membranes asa temporary biologic dressing. ConnA1ed 38: 449, 1974
14. COLOCHO G, GRAHAM WP III, GREENEAE, et al: Human amniotic membraneas a physiologic wound dressing. ArchSurg 109: 370, 1974
15. BAILEY FR, MILLER AM: Textbook ojEmbryology, 2nd ed, Wood, NewYork, 1911
16. PIGEON J: Treatment of second-degreeburns with amniotic membranes. C·anA1ed Assoc J 83: 844, 1960
17. LISTER UM: Ultrastructure of the human amnion, chorion and fetal skin.J Obstet Gynaecol B,. Commonw 75:327, 1968
18. DOUGLAS B: Homografts of fetalmembranes as a covering for largewounds - especially those fromburns; experimental and clinical study(preliminary report). J Tenn A1ed Assoc 45: 230, 1952
19. BAXTER CR: Homografts and heterografts as a biological dressing in thetreatment of thermal injury. Presentedat the first annual congress of theSociety of German Plastic Surgeons,Munich, Sept 28, 1970
20. WOOD M, HALE HW JR: The use ofpigskin in the treatment of thermalburns. Am J Surg 124: 720, 1972
21. EADE GG: The relationship betweengranulation tissue, bacteria, and skingrafts in burned patients. Plast Reconst,. Surg 22: 42, 1958
22. MORRIS PJ, BONDOC C, BURKE JF:The use of frequently changed skinallografts to promote healing in thenon healing infected ulcer. Surgery60: 13, 1966
23. LARSON D: in discussion, ibid
24. SAYMEN DG, NATHAN P, HOLDER lA,et al: Control of surface wound in-
fection: skin versus synthetic grafts.Appl Environ A1icrobiol 25: 921, 1973
25. BURLESON R, EISEMAN B: Mechanisms of antibacterial effect of biologicdressings. Ann Surg 177: 181, 1973
26. HABAL MB: On the cutaneous porcineheterograft (E). Plast Reconstr Surg57: 367, 1976
27. A short note on the physiologicresponse to the cutaneous xenograftas a biologic dressing (C). J Trauma14: 94, 1974
28. GALASK RP, SYNDER IS: Antimicrobialfactors in amniotic fluid. Am J ObstetGynecol 106: 59, 1970
29. ROBSON MC, HEGGERS JP: Surgicalinfection. II. The ~-hemolytic streptococcus. J Surg Res 9: 289, 1969
30. BURKE IF, BONDOC CC: A method ofsecondary closure of heavily contaminated wounds providing "physiologic prinlary closure". J Trauma 8:228, 1968
31. ROBSON Me, HEGGERS JP: Bacterialquantification of open wounds. M ilitA1ed 134: 19, 1969
32. GILLMAN T, PENN J, BRONKS E, et al:Reactions of healing wounds andgranulation tissue in man to autothiersch, autodermal, and homodermalgrafts; with analysis of implications ofphenomena encountered for understanding of behaviour of grafted tissue and genesis of scars, keloids, skincarcinomata, and other cutaneous lesions. Br J Plast Surg 6: 153, 1953
33. ZAROFF LI, MILLS W JR, DUCKETTJW JR, et al: Multiple uses of viablecutaneous homografts in the burnedpatient. Surgery 59: 368, 1966
34. O'NEILL JA JR, GROSFELD JL, BOLESET JR: The extended use of skinhomografts. Arch Surg 99: 263, 1969
35. BAPAT CV, KOTHARY PM: Preliminaryreport on acceleration of wound healing by amnion membrane graft. Indian J Med Res 62: 1342, 1974
36. MILLER TA, SWITZER WE, FOLEY FD,et al: Early homograting of seconddegree burns. Plast Reconstr Surg 40=117, 1967
BOOKScontinued from page 1235
PROBLEM SOLVING IN IMMUNOHEMATOLOGY. Case Reports For PathologistsAnd Medical Technologists. Arthur Simmons. 204 pp. IIlust. Year Book MedicalPublishers, Inc., Chicago, 1977. $15.35,spiral bound. ISBN 0-8151-7654-6
PROTEINS OF ANIMAL CELL PLASMAMEMBRANES. Vol. 1, 1977. D.F.H. Wallach. 154 pp. Eden Press Inc., Montreal,1977. $18. ISBN 0-88831-011-0
RECENT ADVANCES IN CLINICAL BIOCHEMISTRY. No.1. Edited by D.G.M.M.Alberti. 298 pp. IIlust. Churchill Livingstone, Edinburgh; Longman Canada Limited, Don Mills. 1978. $41.60. ISBN 0-44301590-2
continued on page 1254
1246 CMA JOURNAL/MAY 20, 1978/VOL. 118