A clinical and histological investigation into the fate of epithelial elements buried following the...

A CLINICAL AND HISTOLOGICAL INVESTIGATION INTO THE FATE OF EPITHELIAL ELEMENTS BURIED FOLLOWING THE

GRAFTING OF "SHAVED " SKIN SURFACES

Based on a Study of the Healing of Split-skin Graft Donor Sites in Man

By NOEL THOMPSON, F.R.C.S.

From the Plastic and Jaw Department, United SheffieM Hospitals, and the Plastic Surgery and Jaw Injury Unit, Stoke Mandeville

Hospital, Aylesbury

IN 1944 Converse and Robb-Smith, following an investigation into the healing of split-skin graft donor sites, concluded that the thinner the graft the speedier the healing of the donor site, and that the quality of the repair was proportional to the rapidity of healing. Thus thin Thiersch graft donor sites healed within ten days and left merely a faintly visible scar with a soft pliable base, but thick split-skin grafts including 70 to 90 per cent. of the dermis left a donor site taking three to eight weeks to heal, and often left permanent disfigurement in the form of retracted hypertrophic scars. On microsection, the healed donor site was found to be covered by a thin atrophic epithelium incapable of providing adequate surface protection, beneath which was formed a thick layer of dense scar tissue often almost five times the thickness of normal dermis, and completely deficient in elastic tissue.

Following the introduction by Hynes (1956, 1957) of the method of" shaving" and skin grafting (whereby a cutaneous mole or scar from which the surface epithelium and immediately subjacent dermis or scar tissue has been removed, is treated by the application of a split-skin graft from another site), it seemed reasonable to apply the method to assist the healing of thick split-skin graft donor sites. By applying a thin Thiersch graft to such a site, the period required for overall healing of the graft donor site might be expected to be reduced, and the incidence of hypertrophic scarring diminished.

The technique of shaving and skin grafting usually involves the burying of those epidermal appendages--hair follicles, sebaceous and sweat glands--partially surviving in the host dermis beneath the surface graft. Despite the considerable body of evidence to the contrary--recently reviewed elsewhere (Thompson, 196o b) mprejudice based on the theoretical possibility of widespread and recurrent complications from epidermoid cyst formation under such circumstances still exists. In order, therefore, fully to determine the fate of such buried epithelial elements, serial biopsies of grafted donor sites were subjected to histological examination.

In addition, a series of patients having scars or nmvi treated by shaving and skin grafting were followed up to assess the incidence of post-operative clinical complications.

219

220 BRITISH JOURNAL OF PLASTIC SURGERY

MATERIAL AND METHODS

The investigation was conducted in four parts : - - I. Healing of Split-skin Graft Donor Sites.--In fifteen patients where

a thick split-skin graft, including approximately two-thirds of the full thickness of the dermis, had been removed from a limb, five graft donor sites were treated by the immediate application of a thin Thiersch graft (taken from an adjacent skin surface) to the whole of the donor area ; five received routine surgical dressings without the application of grafts ; and five were treated by the application of a thin Thiersch graft to the proximal half only of the donor site, before being given a routine dressing to the whole donor site.

Careful note was made of the periods required for complete healing of all donor sites, and a follow-up conducted for periods of six to eighteen months to assess subsequent progress.

2. Clinical Follow-up of Patients treated by Shaving and Skin-grafting. --Fifty-nine patients who had received the application of split-skin grafts of varying thickness to shaved skin surfaces, in the treatment of moles or scars, were subsequently followed up for periods of six to eighteen months in order to determine the incidence and nature of post-operative clinical complications.

Biopsies of Grafted Thick Split-skin Graft Donor Sites from Sixteen Patients submitted to Serial Section Histological Examination

N o .

i 2

3 4 5 6 7 8 9

IO I I I 2

I3 I4 z5 i6

Period Grafted.

7 days zx days 2 weeks 2 weeks 2 weeks 3 weeks 4 weeks 4 weeks 6 weeks 2 months 3 months 4½months 6 months

I 2 months 2o months

2o months

~e~. Age (years).

4 I 14 55 26 42 3z 55 26 55 55 64 35 47 35 2 0 18

Site. Lateral Surface of.

Thigh. Thigh. Thigh. Thigh. Arm. Thigh. Thigh. Thigh. Thigh. Thigh. Thigh. Arm. Arm. Arm. Arm. Arm.

3. Sweat Tests of Split-skin Graft Donor SiteS. lThese were conducted using the technique described by Guttmann (1947)- Quinizarin powder, dusty blue in colour, was scattered on the area to be tested, and the patient suitably heated to cause generalised sweating. The site of active sweat Fores was disclosed by a change of colour in the quinizarin dye to deep violet.

In this way grafted donor sites were tested for the clinical return of sweat-gland function in response to thermal stimulation, at two, four, ten, and twenty-four

EPITHELIAL ELEMENTS BURIED FOLLOWING GRAFTING OF " SHAVED" SKIN SURFACES 221

weeks, one year and one and a half years after operation ; in one patient an untreated donor site was tested after one and a half years.

4. Histological Examination of Grafted Donor Sites.--In sixteen patients, biopsies were taken at intervals of time varying from one week to twenty months after operation from thick split-skin graft donor sites which had been treated by the immediate application of a thin Thiersch graft, taken from an adjacent area on the same limb (see table opposite).

The age of the patients varied from 14 to 64 years, and the donor site was in all cases the thick hair-bearing skin on the lateral aspect of the thigh or upper arm.

In all biopsies serial sections were then cut and stained, using ha:matoxylin and eosin, for histological examination. Isolated sections were stained, using orcein and Van Gieson's stains, to demonstrate elastic tissue. In all, some five hundred sections were examined.

Microscopic examination using polarised light proved of considerable assistance in the identification of hair shaft material, which became doubly refractile under such conditions.

RESULTS

I. Healing of Split-skin Graft Donor Sites .--In five patients whose thick split-skin graft donor sites were allowed to heal by natural means, unassisted by grafting, the donor sites showed complete re-epithelialisation after periods of twenty-two to sixty days (average thirty-five days).

In five patients whose thick split-skin graft donor sites were treated by the immediate application of Thiersch grafts, healing was complete at the time of the first dressing on the tenth post-operative day.

In five patients where the proximal half only of the donor area had been treated by Thiersch grafting, the grafted portion had in all cases healed by the tenth day ; the ungrafted half of the donor area showed complete healing in twenty-one to ninety days (average forty-six days).

Essentially, therefore, ten grafted donor sites showed uniformly complete healing in ten days, the area remaining stably healed and the graft soft and pliable ; ten ungrafted donor sites healed in twenty-one to ninety days (average forty days) with the formation of an indurated, thickened, and contracted base which in four cases (4o per cent.) showed well-marked hypertrophic scarring (Fig. IA), and in five cases (5o per cent.) a tendency to fissure and ulcerate following minor t r a u l n a .

In all instances the donor sites of the thin Thiersch grafts healed without complications, and after some months were usually detectable only by the slight pallor and coarsening of skin texture existing at these sites.

2. Clinical Follow-up of Patients treated by Shaving and Skin Grafting. --Fifty-nine patients whose cutaneous scars or moles had been treated by shaving and skin grafting were followed up post-operatively for periods of not less than six months.

The " take" of the grafts exceeded 9o per cent. in all cases except one : a case of extensive scarring of the neck where an 8o per cent. " take" of the graft was possibly attributable, at least in some measure, to difficulties of immobilisation.


Rarely, patients developed in the grafted areas scattered " cysts" of pin-head size, disappearing spontaneously within three to six months in all but two cases

FIGS. IA and IB

A, Donor site one year after operation, o f a thick spli t-skin graft taken from the inner thigh in a girl aged i2 years. T h e arrow indicates line of junction of the proximal half of the graft donor area (treated by the immediate application of a th in Thiersch graft), with the distal half (left to heal by natural means). T h e grafted donor site is flat and pliable ; the ungraf ted donor site is in-

durated, fixed, and shows unstable hyper t rophic scars.

B, Sweat test carried out one and a half years after operat ion on the same donor site. Arrow indicates junction of grafted (proximal) with ungrafted (distal) areas. In the grafted area the sweat pores have a scattered punctate dis t r ibut ion ; in the ungrafted area sweating is largely normal, but is absent

at the site o f hyper t rophic scarring.

(3"4 per cent.). In these the cysts were of 2 to 3 mm. diameter and marginal in position, rendering their removal a simple procedure under local anaesthesia ; in both, biopsy demonstrated persistent epidermoid cysts.

Multiple localised abscesses occurred in one patient (I'7 per cent.) where deep shaving of an extensive pigmented mole had been done. The abscesses subsided uneventfully following simple incision without anaesthesia.

EPITHELIAL ELEMENTS BURIED FOLLOWING GRAFTING OF " SHAVED " SKIN SURFACES 223

All other cases (93"2 per cent.) progressed satisfactorily without untoward complication.

3. Sweat Tests of thick split-skin graft donor sites to which immediate Thiersch grafts had been applied failed to demonstrate any active sweating at two weeks or at four weeks, but disclosed positive sweating at ten weeks (Fig. 2). Even after one and a half years the active sweat pores in such grafted donor sites were - - of sparse distribution, and easily distinguish- able individually (Fig. IB). Active sweat pores were of much more frequent distribution in ungrafted donor areas, except at the sites of hypertrophic scarring where sweating was virtually absent (Fig. IB).

4. Histological Examination of Grafted Donor Areas.--Present under- standing of the normal histology of skin has been summarised by Montagna (I956).

The dermis consists of two layers : a thin superficial (" papillary ") layer, composed of delicate collagen and elastic fibres lying just beneath the epidermis, not pierced by the epidermal appendages (hair follicles, sebaceous glands, sweat glands) but forming a continuous sleeve over each of them ; and a thick, deep (" reticular ") layer composed of dense, coarse, branching collagenous and elastic fibres.

The epidermal appendages are linked to the surface epidermis, from which em- bryologically they derive. Hair follicles are cyclic organs having alternating periods of activity and rest ; the active hair follicle projects its distal extremity--the bulb, at which growth occurs--into the subcutaneous fat, but the resting hair follicle is less than

. si 91 110 FIG. 2

Sweat test at t en weeks after operat ion, on donor site o f a th ick spli t-skin graf t taken f rom the lateral t h i g h of a m a n aged 3I years, t reated by the immedia te applicat ion of a th in T h i e r s c h graft . T h e r e is scat tered punc ta t e d i s t r ibu t ion o f active sweat pores in the central graf ted area. Elsewhere (below, r ight) is ung ra f t ed donor area showing increased incidence o f active sweat pores , and (above) no rma l sk in adjacent to the donor site, showing compensa to ry hyperhidros is .

(Scale in inches.)

half this length and ends in the lower dermis without a bulb. Sebaceous glands are appendages of the hair follicles and discharge their secretion to the skin surface by way of the pilosebaceous canal. The arrectores pilorum muscles are bundles of smooth muscle fibres extending from the skin to be attached to the hair follicle just below the level of the sebaceous glands.

The eccrine sweat glands are simple tubes which extend from the epidermis to the deep surface of the dermis. Each tubule consists of a duct and a secretory coil. The duct may be divided into three segments : a spiral segment which lies within the epidermis (the " epidermal sweat duct unit " ) ; a straight or slightly undulating " dermal sweat duc t " traversing the dermis ; and a " coiled" dermal sweat duct forming with the secretory portion the basal coil found in the lowermost fibres of the dermis, or the subdermal fat.


A thick split-skin graft contains the whole of the epidermis and papillary dermis, as well as most of the reticular dermis, and includes the whole of the shorter hair follicles. The host tissues at the donor site retain only the deepest layers of the reticular dermis, containing the lower part of the longest hair follicles, and the basal coil and deepest part of the dermal excretory duct only of the sweat glands.

A Thiersch graft, however thinly and by whatever means it is cut, contains the whole of the epidermis together with the more superficial layers of the papillary dermis (Padgett and Stephenson, i948), together with the upper parts of the hair follicles and excretory sweat ducts ; the latter includes the uppermost part of the dermal sweat duct and the whole of the " epidermal sweat duct unit," opening on the surface at the sweat pore.

Comparison of the histological structure of a grafted donor site with that of one healing by natural means, in both cases at twenty months after operation (Figs. 3 A and 3B), explains many of the clinical features found in the two cases. In the grafted donor site the epidermis shows normal surface corrugations and fete peg formation, and the dermis is of relatively normal thickness and structure. In the ungrafted donor site the epidermis is without surface corrugations and the subepidermal tissue is replaced by a bulky layer of coarse-fibred scar tissue of vastly increased depth. Furthermore, when stained to show elastic tissue it is found that while the grafted specimen (Fig. 4 A) shows normal elastic tissue in host and graft dermis--as well as very marked regeneration of elastic tissue in the intermediate zone between the two--the ungrafted donor area (Fig. 4 B) shows merely bands and whorls of dense scar tissue, quite devoid of elastic fibres.

FIGS. 3A and 3 B

A, Grafted donor site, twenty months. Showing epidermis and dermis of essentially normal structure. × 2o. B, Ungrafted donor site, twenty months. Showing bulky layer of subepidermal

scar tissue. A single excretory sweat duct is seen near the surface. × 2o.

FIGS. 4 A and 4 B

A, Grafted donor site, twenty months. Stained for elastic tissue. Arrow shows plane of granulation tissue, with well-marked regeneration of elastic tissue. There is normal elastic tissue in the graft and host dermis. × 65. B, Ungrafted donor site~ twenty months. Stained for

elastic tissue. There is total lack of elastic fibres in the dense scar tissue. × 65.

FIG. 5

Grafted donor site, one week. Stained for elastic tissue. Clearly shows the three layers : Thiersch graft above, host dermis below, and intermediate layer of granulation tissue (with no elastic fibres) between. The dermis of graft and host show plentiful elastic tissue, that in the former showing

minimal degenerative changes. × 6o.

FIG. 6

Grafted donor site, one week. Excretory sweat duct in host dermis, with bulbous extremity showing spiral arrangement of luminal cells lying just below the granulation tissue layer. × 13o.

FIGS. 7A to 7 c

Grafted donor site~ one week. Three serial sections, showing : A, Excretory sweat duct in host dermis (below) approaching granulation tissue layer (above). × 12o. B, The same duct continuous with an island ofmetaplastic squamous epithelium projecting into the granulation tissue from below. x 12o. C~ The same island of metaplastic squamous epithelium undergoing early differentiation

into an epidermal sweat duct unit. The lumen can be seen. x 12o.

EPITHELIAL ELEMENTS BURIED F O L L O W I N G GRAFTING OF " SHAVED ~ SKIN SURFACES 2 2 5

,See opposite page for legends] 3 c

FIGS. 3A t o 7 c


All microsections of grafted donor sites show a clearly defined stratification into three layers. Above is the Thiersch graft with the whole thickness of epidermis and the more superficial layers of the papillary dermis; below this is an intermediate zone of granulation tissue which undergoes progressive organisation in the later biopsies; below this again is the host dermis. This layering of the tissues is especially well demonstrated in the earlier biopsies where elastic tissue stains are used ; here the granulation tissue layer intermediate between host and graft tissues forms a central unstained band, being wholly devoid of elastic tissue (Fig. 5).

The histological appearances seen at the varying time intervals, following the immediate grafting of thick split-skin graft donor sites, are described below : -

One Week.--The three layers, consisting of graft and host tissues separated by an intermediate layer of granulation tissue, were especially clearly defined (Fig. 5).

FIG. 8

Grafted donor site, one week. The surface epidermal sweat duct unit, together with its associated excretory duct in the graft papillary dermis--which has undergone squamous metap las i~for lns a bulbous process of squamous epithelial cells projecting from the surface epidermis down into the underlying granulation tissue layer. The lumen is sectioned at two points, one above and one

below, x IXO.

FIG. 9

Grafted donor site, eleven days. Showing hyperplasia of epidermal sweat duct unit of graft, which projects downwards into the underlying granulation tissue layer. The spiral lmnen is sectioned at two points, and is distended by laminated accumulations of keratin. Surface epidermis shows

hyperkeratinisation, x IXO.

FIG. IO

Grafted donor site, eleven days. Adjacent graft hair follicles have fused following epithelial proliferation ; there is evidence of early epidermoid cyst formation. × 8o.

FIG. I I

Grafted donor site, two ~eeks. Superimposition of hair follicles in graft and host, with fusion of the two at site shown by arrow. Sebaceous glands persist in the host pilosebaceous unit. x 6o.

FIG. I2

Grafted donor site, two weeks. Epidelmoid cyst formation from degenerating pilosebaceous unit in host tissues. Note arrector pill muscle (to left below), surrounding round-cell infiltration, and

keratinised debris inside the cyst. × 60.

FIG. 13

Grafted donor site, two weeks. Host excretory sweat duct (in continuity with secretory coil below), ending in the granulation tissue layer in a metaplastic island of squamous epithelium, showing evidence of differentiation into an " epidermal sweat duct unit ." The lumen is sectioned repeatedly, and is distended by an accumulation of keratinised material--an early stage of epiderrnoid cyst formation. Note the increased deposition of collagen surrounding the epithelial island, with round- cell infiltration and foreign body giant cells. A surface epidermal sweat duct unit (arrow), shows

downward proliferation. × 45-

FIG. 14

Grafted donor site, two weeks. Foreign body giant cells surrounding doubly refractile hair shaft (arrow) in granulation tissue layer. × 300.

EPITHELIAL ELEMENTS BURIED FOLLOWING GRAFTING OF " SHAVED ~ SKIN SURFACES 2 2 7

I FZGS. 8 to z4

See opposite page for legends]


The epidermis of the graft showed increased depth of fete pegs. As the result o f rapid proliferation of their constituent squamous epithelial cells, the epidermal sweat duct units formed distinct, blunt-tipped projections penetrating the underlying papillary dermis of the graft, to enter the granulation tissue layer; the spiral lumen was sectioned at multiple points in any one section (Fig. 8).

The granulation tissue layer contained frequent small islands of squamous epithelium, some of which derived from proliferating graft epidermal sweat ducts (described above), and others from host sweat ducts (described below), but many of which contained central hair shaft fragments and presumably derived from hair follicles. Though not demonstrable with certainty, it appeared possible that some of the latter may have originated in microscopic free grafts of hair follicle debris, carried into this plane during the cutting of the free graft at operation. Rapid proliferation had resulted ill the coalescence of neighbouring epithelial islands with one another and with graft hair follicles, thereby confusing the microscopic picture. Foreign body giant-cell reaction to hair shaft fragments, probably also carried into this plane by the grafting knife at the time of operation, was also evident.

The host dermis below the layer of granulation tissue was well vascularised ; capillaries containing erythrocytes were found ascending into the granulation tissue, and also from the latter into the surface graft.

Pilosebaceous units in the host dermis appeared of normal structure, but made no contact with graft tissues.

The deeply placed secretory coils of the host sweat glands appeared normal, but their associated excretory ducts showed uniformly active proliferation at their severed superficial extremities. In some cases this end of the duct showed a bulbous dilatation, just deep to the granulation tissue layer, with a spiral arrangement of the luminal cells (Fig. 6); in others, ductal proliferation and metaplasia had resulted in an island of squamous epithelium projecting into the granulation tissue from below, and showing evidence of commencing canalisation to form an " epidermal sweat duct un i t " (Fig. 7).

Eleven Days.--The graft epidermis showed parakeratosis and hyperkeratosis (Figs. 9 and IO), indicating a general increase in cellular activity. Taldng part in this, the fete pegs were increased in depth, and the epidermal sweat duct units projected down into the underlying granulation tissue layer with their spiral lumina dilated and blocked by laminated keratin (Fig. 9), as also were the surface sweat pores. Similarly, neighbouring hair follicles in the graft showed epithelial fusion, as well as indications of early epidermoid cyst formation, with keratinous and hair shaft debris in the central cavity (Fig. IO).

The intermediate layer of granulation tissue again included many islands of squamous epithelium, disclosed as having a hair follicle or sweat duct origin in most cases. Foreign body giant-cell reaction round hair shaft debris was commonly encountered.

In the host dermis the hair follicles and sweat glands appeared unchanged; frequently the host sweat ducts had proliferated into the granulation tissue layer to form metaplastic islands of squamous epithelium. The host dermis was well vascularised ; at some points capillaries could be seen ascending through the granulation tissue layer into the graft.

Two Weeks.--An enhanced degree of epithelial proliferative activity was again evident, the graft showing increased surface keratinisation (Fig. I I), increased depth

EPITHELIAL ELEMENTS BURIED FOLLOWING GRAFTING OF " SHAVED ~ SKIN SURFACES 2 2 9

of rete pegs, fusion of adjacent hair follicles, and projection of epidermal sweat duct units down into the underlying granulation tissue layer.

Foreign body giant-cell reaction to hair shaft fragments in the granulation tissue layer was again present (Fig. 14).

In the host dermis the hair follicles were undergoing early epidermoid cyst transformation (Fig. 12). At one point a fortuitous superimposition of hair follicles in graft and host tissues was followed by fusion of the two in the granulation tissue layer, yielding an apparently continuous follicle ascending from host dermis to the surface (Fig. II). Related sebaceous glands continued to survive in the host dermis (Figs. II and I2), and occasionally showed epidcrmoid cyst formation, though this was rare.

In the sweat glands of the host dermis the secretory coil persisted unchanged, but the severed upper extremity of the excretory duct showed increased proliferative and regenerative activity at its point of contact with the overlying granulation tissue layer. In most sections the duct ended at this level in an island of metaplastic squamous epithelium showing evidence of the formation of a spiral lumen, in which the aggregation of keratinised material suggested early epidermoid cyst formation (Fig. 13). In one instance the differentiation of this epithelial island into an " epidermal sweat duct unit," complete with basal cells, prickle cells, and a well-formed spiral lumen had occurred (Fig. 15). No continuity of this regenerating host sweat duct with the surface graft epidermis could be established.

The exuberant epithelial proliferation accompanying this phase of wound healing resulted in frequent aberrant fusion of the epithelial elements present. In this way had occurred fusion of cpidermoid cysts derived from graft hair follicles with epidermal sweat duct units derived from graft epidermis (Fig. 16); also, of epidermoid cysts derived from host hair follicles with the dermal sweat ducts of host sweat glands (Fig. 17). Careful examination of serial sections was often required to distinguish the latter from the cystic superficial extremities of host sweat ducts (Fig. 13).

Three Weeks.--A further instance occurred of the formation of a single continuous hair follicle from the fusion of coincidentaUy superimposed hair follicles of graft and host. In another example, however, a hair follicle in the host dermis together with its contained hair shaft appeared to have erupted successfully through the overlying graft, to become continuous with the surface epidermis ; the hair shaft and its surrounding follicle here preserved complete continuity from a level deep in the host dermis to the surface, apparently without the incorporation of an amputated graft follicle (Fig. 18).

Epidermoid cyst formation was common in the dermis of both graft and host, an origin from degenerating hair follicles at both sites being usually established by means of identifiable, contained hair shaft fragments. A further example of aberrant fusion of a host sweat duct with an epidermoid cyst deriving from a degenerating host hair follicle was found.

In one instance a host excretory sweat duct ascended through the host dermis, and the intermediate layer of organising granulation tissue, to become continuous with the surface epidermis of the graft (Fig. 19). Serial sections showed this duct to originate in the underlying basal coil of a host sweat gland, and the appearances suggested its superficial termination at the site of the sweat pore of a former epidermal sweat duct unit in the graft. This was the earliest evidence obtained of


anatomical continuity becoming established between host secretory coil and graft epidermal surface.

In another example (Fig. 20) the host sweat duct ended blindly just beneath the papillary dermis of the graft, without establishing a surface connection.

Four Weeks.--Some hair follicles of apparently normal appearance were now continuous with the surface epidermis, but for the most part the hair follicles of both host (Fig. 21) and graft (Fig. 22) had undergone transformation into epidermoid cysts, found respectively below and above the intermediate zone of now collagenised granulation tissue. Sebaceous glands survived at both sites.

Sweat gland appearances were unchanged in graft and host tissues, but no further examples of established anatomical continuity between the two were found.

Six Weeks.--Sections stained for elastic tissue disclosed its presence in the dermis of graft and host, but no elastic tissue was found in the freshly organised intermediate layer between the two.

Epidermoid cysts were especially numerous in the host dermis, at the site of decapitated and degenerative hair follicles. They contained keratinised debris and hair shaft fragments, and often had closely associated sebaceous gland elements.

An epidermal sweat duct unit of the graft epidermis formed a prominent epithelial spur projecting down into the collagenised intermediate layer, with its spiral lumen greatly distended and obstructed by laminated deposits of keratin, resulting in epidermoid cyst formation in its distal part (Fig. 24). The sweat pore was present as a grossly distended pit, filled with keratin. The appearances suggested involutionary changes in an epidermal sweat duct unit which had failed to establish a connection with any underlying host sweat gland.

FIGS. I5A and ISB

A, Grafted donor site, two weeks. An excretory sweat duct is shown sectioned repeatedly as it ascends through the host dermis from the secretory coil (below left), to the point where it enters the granulation tissue layer to differentiate into an "epidermal sweat duct unit." The latter makes no contact with the surface epidermis. Note increased deposition of collagen and round-cell infikration in the vicinity of the vigorous epithelial hyperplasia, x 6o. 13, Detail of the above, showing the regenerating "epidermal sweat duct unit." The spiral lumen has been sectioned repeatedly, and

the squamous epithelium has differentiated into basal and prickle cell types, x ix 5.

FIGS. I6A and I6B

Grafted donor site, two weeks. Serial sections, showing a downgrowing epidermal sweat duct unk (on right) from the graft surface, forming an aberrant union with an epidermoid cyst formed

from a degenerating graft hair follicle (on left), x 5o.

FIG. 17

Grafted donor site, two weeks. The mukilocular epidermoid cyst occupying the whole lower field, containing hair shaft and keratinised debris, and deriving from a host hair follicle, is linked by aberrant epithelial fusion to the surface by a degenerating graft hair follicle, as well as to underlying host excretory sweat ducts on both flanks (arrows) ; at the point of fusion the spiral lumina of the

ducts are evident, x 5 o.

FIG. i8

Grafted donor site, three weeks. A host hair follicle, with its enclosed hair shaft, has seemingly erupted through the overlying graft and granulation tissue to reach the surface. The plane of the granulation tissue is shown by the small epithelial inclusion (arrow). Where is no evidence of a point o f fusion to suggest superimposed hair follicles, and the hair shaft is continuous throughout its

course from host tissues to the surface, x 36.

EPITHELIAL ELEMENTS BURIED FOLLOWING GRAFTING OF " SHAVED " SKIN SURFACES 2 3 I

FIGS. 15A to ~8 See opposite page for legends]


Also projecting into the intermediate layer, but from below, were the terminal bulbous dilatations of host sweat ducts ending blindly at this level (Fig. 23), and presumably distended by secretion as a result of returning function in the host sweat glands.

Eight Weeks.--The intermediate layer contained hair shaft debris with surrounding foreign body giant-cell reaction and loci of round-cell infiltration.

Vascularisation of the graft was excellent. There was indirect evidence of returned sweat-gland function ; thus surface

epidermal sweat duct units appeared essentially normal, the lumen being no longer greatly dilated, or obstructed by keratin (Fig. 26). Similarly, an excretory sweat

FIG. 19 Grafted donor site, three weeks. Shows fusion of a host sweat duct with the surface epidermis of the graft at the site of a persisting sweat pore. The duct is seen to ascend from host dermis through the intermediate layer oforganising granulation tissue to reach the surface. Serial sections (not shown) establish continuity of the duct with an underlying host secretory coil. (Arrow indicates

upper border of host dermis.) x 5 o.

FIG. 20 Grafted donor site, three weeks. Dilated host sweat duct with characteristic spiral lumen sectioned at two sites, and ending blindly just below the papillary dermis of the graft. Note surrounding

round-cell infiltration. × IOO.

FIG. 21 Grafted donor site, four weeks. Epidermoid cyst arising from a degenerating hair follicle in the host dermis. An adjacent host sweat duct (below left) does not in this case unite with the cyst. x 35.

FIG. 22 Grafted donor site, four weeks. Epidermoid cyst deriving from graft hair follicle, and bulging into the underlying intermediate layer of organising granulation tissue. The cyst contains hair shaft

debris and keratinised material. × 55.

FIG. 23 Grafted donor site, six weeks. Host sweat duct, complete with papillary luminal projections, ending blindly in a cystic dilatation in the organised intermediate layer. The cyst contains a small amount of epithelial debris, and is probably distended by sweat gland secretion--the earliest indication of returning sweat gland function demonstrated. Note surrounding increased deposition of collagen

and round-cell infiltration, x 55.

FIG. 24 Grafted donor site, six weeks. Squamous epithelial spur, originating in graft epidermal sweat duct unit, projecting down through the underlying papillary dermis of the graft. The lumen is distended and obstructed by keratinised material, resulting in epidermoid cyst formation. There is surrounding round-cell infiltration. The surface sweat pore, also distended by accumulated

keratin, is seen above, x I20.

FIG. 2 5 Grafted donor site, eight weeks. Host sweat duct has penetrated the intermediate layer to enter the papillary dermis of the graft. It contains a secretion cast and is not dilated, and so probably

discharges on the surface. × I3o.

FIG. 26 Grafted donor site, eight weeks. Functional epidermal sweat duct unit. The spiral lumen is no

longer distended or obstructed by keratin, x 260.

FIG. 27 Grafted donor site, eight weeks. Grossly dilated host sweat duct with papillary luminal projections,

ending blindly at upper border of host dermis (shown by arrow), x 115.


FIGS, 19 to 2 7 See opposite page for legends]


duct above the intermediate layer was undilated and contained an apparent secretion cast in its lumen (Fig. 25) ; it might, therefore, be suspected of being of host sweat-gland origin, and of discharging to the surface, though neither assumption was concretely demonstrable in the material available.

Other host excretory sweat ducts, however, showed considerable distension and ended blindly below the level of the intermediate layer of organised granulation tissue (Fig. 27).

Twelve Weeks.--The intermediate layer contained hair shaft debris with associated foreign body giant-cell reaction, and evidence of epidermoid cyst formation, chiefly from degenerating hair follicles, persisted.

Confirmation of returned sweat-gland function was obtained, and also of the two ways in which the superficial extremities of the host excretory sweat ducts terminated. Thus serial sections (Fig. 28) demonstrated complete regeneration of apparently normal and functional sweat glands, with complete restoration of excretory duct continuity between the surface graft epidermal sweat-duct unit and the underlying host secretory coil.

Alternatively, however, a number of host sweat glands failed to reach the surface, presenting a grossly distended excretory duct with secretion casts in the lumen ending blindly below the organised intermediate layer (Fig. 29).

FIGS. 28A to 28D

Grafted donor site, twelve weeks. Serial sections illustrating continuity between the host sweat gland below and the graft epidermal surface above. In A the epidermal sweat duct unit (arrow) becomes continuous, B, with the excretory sweat duct in the graft dermis (arrow). In C the excretory duct is visible in the host dermis (arrow), and in D has become the coiled sweat duct (arrow) adjacent to the secretory coil. The sweat gland is not dilated and contains evidence of

secretion products in the lumen, x ioo.

FIG. 29

Grafted donor site, twelve weeks. Host sweat gland with its secretory coil below and its excretory duct greatly dilated and containing htminal secretion casts ending blindly at the upper border of host dermis. There is reactive fibrosis and round-cell infiltration round the dilated duct. x 120.

FIG. 30

Grafted donor site, twelve weeks. Stained for elastic tissue. The three layers are clearly shown. F, lastic tissue survives in the dermis of graft (above) and host (below). There is no evidence

of elastic fibres in the intermediate layer of collagenised granulation tissue. × 8o.

FIG. 3I

Grafted donor site, eighteen weeks. Excretory sweat duct ascending from sweat gland in host dermis, with the upper segment of the duct above, ending at the graft epidermal surface. Serial

sections demonstrated continuity between the two duct segments. × IlO.

FIG. 32

Grafted donor site, twenty-four weeks. Disintegrating epidermoid cyst deriving from hair follicle in host dermis, now undergoing replacement fibrosis. Note arrector pili muscle (lower left), surrounding round-cell infiltration, and foreign body giant cell at site of hair shaft fragment (arrow).

× IOO.

FIG. 33

Grafted donor site, twenty months. Showing excretory sweat ducts in host dermis. That on the left is sectioned four times, is undilated and is destined to open on the graft epidermal surface. That on the right, sectioned once, is dilated and contains a secretion cast ; it is destined to end blindly

at the upper border of host dermis. × 60.

]~PITHELIAL ELEMENTS BURIED FOLLOWING GRAFTING OF " SHAVED" SKIN SURFACES 235

FIGs. 28A to 33 See opposite page for legends]


No surface sweat pores or epidermal sweat-duct units, not establishing contact with underlying host sweat #ands, were discovered; it was presumed that all such had undergone involution by epidermoid cyst formation in the graft tissues.

Elastic tissue staining demonstrated elastic fibres in the dermis of graft and host, but there was no evidence of their presence in the intermediate zone separating these (Fig. 30).

Eighteen Weeks.--Pilosebaceous units appeared fully functional, the hair follicles arising in host dermis with contained hair shafts opening on the surface of the overlying graft.

Again it was confirmed that while some sweat glands formed a complete, undilated and apparently functional unit discharging to the surface (Fig. 3I), others formed a " closed" gland system with the dilated sweat duct ending blindly in the upper levels of the host dermis, below the intermediate layer.

Twenty-four Weeks.--Apparently normal pilosebaceous units were found in the host dermis ascending intact to the surface epidermis.

All true epidermoid cysts had disappeared from the sections, but scattered loci of round-cell infiltration and foreign body giant cells may have represented the sites of former cysts. At such sites (Fig. 32), all squamous epithelial cells had vanished and the cyst had undergone almost complete replacement by granulation tissue, now largely organised; persisting hair shaft fragments and the adjacent arrector pili muscle fibres indicated the original derivation from a host hair follicle.

Sweat-gland appearances were unchanged. Twelve Months.--The usual three layers, consisting of graft tissues above,

host tissues below, and the organised intermediate layer between, were still clearly demarcated. No evidence whatsoever persisted of epidermoid cyst formation, and no foreign body giant cells or loci of round-cell infiltration were present.

Sweat gland appearances confirmed the earlier findings. Where the excretory duct ended in an epidermal sweat-duct unit at the surface, the entire sweat gland presented a normal appearance; where the excretory duct ended blindly below the organised intermediate layer, the entire sweat gland showed appreciable: dilatation of both secretory coil and duct, together with some compression of the secretory cells and the presence of intraduct casts.

Twenty Months.~Elastic tissue stains showed complete elasticisation of the intermediate zone between graft and host tissues (Fig. 4A).

Pilosebaceous units of normal appearance were present. No evidence of any kind persisted to indicate the earlier presence of epidermoid

cysts; no trace was found of round-cell collections, foreign body giant cells, or doubly refractile debris.

The excellence of the blood supply to all subepidermal tissues continued to be a notable feature.

Sweat gland appearances continued to be unchanged ; thus some sweat glands of normal appearance established continuity with the surface, but many host sweat glands persisted merely as dilated, blindly ending tubules not extending beyond the host tissues (Fig. 33).

Histological Conclusions.--Within the limits of the material investigated, certain tentative conclusions may be drawn, following the histological survey of grafted donor sites reported above.

I. Elastic tissue is present in the dermis of graft and host in all biopsies~

EPITHELIAL ELEMENTS BURIED FOLLOWING GRAFTING OF " SHAVED ~ SKIN SURFACES 237

In the intermediate layer it appears late, being absent at three months (Fig. 3o), but plentiful at twenty months (Fig. 4A). In the ungrafted donor sites no regeneration of elastic fibres occurs in the subepithelial scar tissue, even as late as twenty months (Fig. 4B).

2. Hair follicles for the most part undergo epidermoid cyst formation and subsequent disintegration, whether situated in the graft (Figs. IO, 16, and 22)

or in host dermis (Figs. I2, 17, 2I, and 32). This is invariably the fate of graft follicles, except where a follicle in the graft fortuitously overlies a follicle in the host tissues ; fusion of the two may then result in the restoration of a functional pilosebaceous unit (Fig. I i). Very occasionally it may be that a large and sturdy host hair follicle successfully erupts to the surface and produces a growing hair shaft (Fig. I8).

3. Sebaceous gland cells (Figs. II and 12) are found in relation to epidermoid cysts formed from pilosebaceous units as late as six weeks after grafting. None persist after this time.

4. Sweat-gland elements must be considered in relation to their situation in either graft or host tissues. In the graft it is probable that the superficial portion of the excretory duct in the papillary dermis undergoes squamous metaplasia, and then, together with its associated surface epidermal sweat-duct unit, takes part in the vigorous epithelial proliferation accompanying the regenerative phase of wound healing. The result at seven to eleven days is a column of squamous epithelial cells descending from the surface epidermis to bulge into the underlying granulation tissue layer (Fig. 8); its central lumen is preserved and becomes increasingly distended by an accumulation of keratin (Figs. 8 and 9).

The further development of these structures would seem to depend on whether or not they become continuous with the underlying host sweat ducts. If no such link is established, then at six weeks obstruction of the lumen by accumulated keratin results in epidermoid cyst formation (Fig. 24). The fate of such cysts would appear to be that of epidermoid cysts in general, described below.

In the host dermis the secretory coils of the sweat glands appear to survive intact and, apart from dilatation in certain cases where excretion of sweat is obstructed, preserve an essentially normal appearance suggestive of continued functional capacity, even after twenty months. The associated excretory duct in the host dermis, following intense regenerative proliferation at its severed superficial extremity (Fig. 6), forms at the junction of host dermis and granulation tissue a metaplastic island of squamous epithelium (Fig. 7) which may either undergo epidermoid cyst formation (Fig. 13) or differentiation into an " epidermal sweat duct un i t " (Fig. I5) in the granulation tissue layer.

From this stage, at two weeks, the future course of sweat-gland regeneration would appear to follow one of two courses. In the first, continuity is established between the excretory sweat duct entities of host and graft tissues, enabling the host secretory coil cells ultimately to discharge their secretion to the surface. Although the sweat ducts of graft and host may become continuous as early as the third week (Fig. 19), it is probable that in most cases secretory function is not restored until the sixth or eighth week (Figs. 23, 25, and 26) ; it is certainly present by twelve weeks (Fig. 28). Sweat tests support these conclusions by demonstrating the clinical return of thermal sweating in grafted donor sites at the tenth week (Fig. 2).

It seems probable that sweat-duct continuity between host sweat gland and


graft epidermal surface results from fusion in the intermediate layer of organised granulation tissue, of the regenerating ductal elements of graft and host, in the form of localised squamous epithelial cell masses. This is supported by the apparent difficulty which proliferating sweat ducts otherwise seemingly have in penetrating granulation tissue, and by the marked attraction which rapidly proliferating squamous epithelial cell masses have for one another at this level, frequently resulting in the aberrant coalescence of hair follicles (Fig. IO), epidermoid cysts and sweat ducts (Figs. 16 and i7) ; such aberrations do not occur in normal intact skin (Holyoke and Lobitz, I952)o The less likely alternative possibility would be that where the host excretory sweat duct developed into a fully differentiated " epidermal sweat-duct un i t " in the granulation tissue layer (Fig. I5) it might ascend to fuse with the graft epidermis and so become a true epidermal sweat-duct unit.

In the second course, failure to establish continuity with graft sweat-duct elements may result in the host excretory duct forming a distension cyst in the organising intermediate layer, when sweat-gland function is restored at about the sixth to eighth week (Fig. 23). It must appear probable that most, if not all, host sweat ducts failing to establish anatomical continuity with a sweat pore at the graft surface ultimately end blindly just below the level of the intermediate layer (Fig. 27) , and persist (certainly up to twenty months and probably permanently) as a dilated diverticulum of the secretory coil, storing the secretion produced by the latter (Figs. 29 and 33).

5. Epidermoid cyst formation is common on a microscopic scale from the second week.

It is the usual fate of the pilosebaceous units of both graft and host (Figs. I2, I6, 17, 2I, and 22), except in that small minority where functional hair follicles survive (Figs. II and I8), and also of those graft sweat ducts (Fig. 24) and host sweat ducts (Fig. I3) not establishing mutual connection.

By far the commonest source of epidermoid cysts is from hair follicles ; only rarely, and in the earliest sections, is a sebaceous gland origin clearly evident.

No intact epidermoid cysts are seen after three months, and their dissolution is well advanced at six months (Fig. 32). There is no evidence whatever of their presence at one year.

The fate of such epidermoid cysts appears to be well established as terminating in spontaneous dissolution. It is a chief function of squamous epithelium to produce keratin (Montagna, 1956) ; such keratiniscd epithelial debris thrown off by the squamous epithelial walls into the lumen of the cyst so increases tension inside the cyst cavity that the epithelial wall undergoes necrosis, allowing direct contact of the products of epithelial disintegration with the dermis. As first indicated by Stewart (1912) and later confirmed by Peer and Paddock (1937) amongst others, direct contact of squamous epithelial cells or their products (desquamated stratum corneum, hair, fat, cholesterol) with the surrounding dermal stroma acts with the irritant properties of a foreign body, resulting in the replacement of the cyst by a granulation tissue rich in foreign body giant celJs (Fig. 32). When phagocytosis of these epithelial products is complete, organisation results in ultimate replacement of the lesion by fibrous tissue, and foreign body giant cells and round-cell infiltration then disappear.

6. Hair shaft fragments are disclosed by polarised light microscopy as being present up to six months at the sites of epidermoid cyst formation, and are


scattered at intervals in the intermediate layer separating graft from host tissues up to this stage, usually at the site of nodules of granulation tissue and aggregations of foreign body giant cells.

DISCUSSION

The findings of Converse and Robb-Smith (1944) on the healing of graft donor sites were in many aspects confirmed. Thus ungraffed thick split-skin graft donor sites often required prolonged periods for complete healing, and showed a high incidence of hypertrophic scarring (Fig. IA). On section these sites presented a relatively flat epidermis with a greatly increased depth of dense subepidermal scar tissue (Fig. 3B), which even after twenty months was devoid of elastic tissue (Fig. 4B). On the other hand, grafted donor sites after a similar period presented an epidermis showing normal surface corrugations and fete peg formation, beneath which delicate dermal tissue in normal amount (Fig. 3A), and of normal elastic content (Fig. 4A), existed ; in the latter connection there was evidence of advanced regeneration of elastic tissue in the organised layer intermediate between graft and host tissue.

The restoration of elastic fibres in healing wounds is slow, beginning at about thirty-six days and only well established at three to six months (yon Schroter, 1922 ). The suggestion that, as demonstrated by usual staining methods, it represents a degeneration of collagen rather than true elastic fibre regeneration (Gillman et al., I954), is not supported by more recent work (Robb-Smith, 1959).

The failure of elastic tissue regeneration in ungrafted donor areas healing after prolonged periods accounts not only for the hard, fixed base of the scarred area but also the instability of the overlying epithelium, since the adhesion of epidermis to dermis probably depends not only on the interlocking of epidermal rete pegs with dermal papillm (Brown and McDowell, 1942) but also the interlocking of epidermal cytoplasmic processes and dermal elastic fibres (Montagna, 1956).

Although Kredel and Phemister (1939) failed to demonstrate the return of sweating in Thiersch grafted areas, Conway (1939) was more successful and deduced that surface sweating returned in such cases if sweat glands survived in the bed on which the graft was placed. This was confirmed in the present investigation ; in grafted donor sites sweating was demonstrated as early as ten weeks after grafting (Fig. 2), though then and subsequently the active sweat-pore population never approached the density found in ungraffed donor sites (except at the site of hypertrophic scarring, where sweating was virtually absent) (Fig. IB).

Histological examination of grafted donor sites, however, showed in all biopsies an apparently normal distribution of sweat secretory coils, in and beneath the deep dermis of the host. This seeming anomaly was explained when it was found that those sweat glands not establishing contact with the graft epidermis yet persisted as apparently functioning units whose excretory ducts ended blindly at the upper border of the host dermis (Figs. 23, 27, 29, and 3B).

The dilated lumina of duct and secretory coil, together with the presence of luminal secretion casts and a notably well-established local capillary circulation, renders it likely that the products of secretory coil activity are resorbed from the closed duct into the adjacent blood-vessels, and possibly into the periductal interstitial fluid spaces, in much the same way as is urine in the totally obstructed hydronephrotic kidney (Hinman, 1954). This possibility is strengthened by the increasing body of indirect evidence, indicating that ductal resorption of sweat:


occurs as an established mechanism in normal sweat glands in a manner analogous to tubular resorption in the kidney (Rothman, 1954).

Although no record has been traced suggesting the survival of totally obstructed sweat glands as functioning units beneath surface skin grafts, such a concept is not without parallel : sweat glands similarly without a means of external discharge of secretion, and having identical histological appearances, have been found to survive for periods of at least five years in autogenous dermis grafts buried subcutaneously in human beings (Thompson, I96O b). No doubt can exist as to the functional capacity of these internally secreting sweat glands in the latter instance, since histochemical investigation demonstrates unimpaired intracellular enzyme activity (succinic dehydrogenase, acid phosphatase, alkaline phosphatase), as well as glycogen exhaustion following secretory stimulation (Thompson, I96O a).

Gillman et al. (1953), in an investigation into the healing of auto-Thiersch grafts replaced immediately on the graft donor site, stressed the epidermal hypertrophy and increased prominence of fete pegs evident over many weeks in the graft epidermis ; this was confirmed in the present investigation. But the curious epithelial spurs described by Gillman and his colleagues as spontaneous downgrowths from the graft epidermis in the second week, and forming " epithelial pearls " in the underlying granulations, were in the present study always identifiable as having originated in the epidermal sweat-duct unit and associated dermal sweat duct of the graft (Figs. 8, 9, I6, and 24). Since it is the primary function of all epidermal cells to produce keratin (Hartwell, I955), and since the cells of the epidermal sweat-duct unit normally undergo keratinisation (Montagna, I956), it is not strange that during a period of marked epithelial hyperplasia the lumina of the graft sweat ducts should become obstructed by keratinised masses, especially in the absence of any active flow of sweat ; indeed, during the early weeks, hyaline eosinophilic inclusions form a prominent feature in the rapidly proliferating squamous epithelium deriving from host and graft sweat ducts. Epidermoid cyst formation is the inevitable sequel, and in the deeper parts of the duct gives the appearance o f " epithelial pearls."

The appearances presented by regeneration in the host excretory sweat ducts have been described by Lobitz et al. (1954), following the removal of epidermis from normal skin, in the first week the luminal cells first swell to cause tortuosity of the lumen, then spill out of the distal cut end of the duct to form a tightly folded and spiralled tube, shaped like a cone (Fig. 6). These investigators believe the centre for such sweat duct regeneration to exist in a small zone of indifferent basal cells at the dermo-epidermal junction, but it is evident (Fig. I5) that a remarkable degree of ductal regeneration--even to the extent of forming a new " epidermal sweat-duct unit " - -may follow injury to the duct in the host reticular dermis. This is, however, the more to be expected since it is known that deep injury, even at the level of the secretory coil, may result in similar specialised ductal regeneration (Lobitz and Dobson, 1957).

The natural history of buried epithelial elements, in the context reported here, indicates that with the exception of most sweat glands and a very few hair follicles, all undergo microscopic epidermoid cyst formation and ultimate granulation tissue replacement, ending in fibrosis. There is no evidence to show that the surviving sweat glands, whether secreting internally or externally, cause late complications o f any kind.

While microscopic epidermoid cysts are common, their survival to constitute

EPITHELIAL ELEMENTS BURIED FOLLOWING GRAFTING OF " SHAVED " SKIN SURFACES 241

a clinical complication is so rare (3"4 per cent. of cases in this survey) that, having regard to the uniformly satisfactory " take" of the grafts, it can be stated that the incidence of post-operative complications following " shaving" and skin grafting is probably lower than in any other grafting procedure. It is, moreover, to be remembered that similar cyst formation occurs in naturally healing Thiersch graft donor sites (Gillman et al., I953), and comparable " sebaceous collections " have been reported by Brown and McDowell (1958) as an annoying complication of split-skin grafts in general.

It has been stated (Brown and McDowell, 1942) that epidermis is the only part of skin that regenerates, and that " t h e pad of derma that is reaUy important in giving bearing protection does not regenerate to any noticeable degree."

It has also been stressed by Peer (1955) that the cells of free autogenous skin grafts probably survive as true tissue transplants without being subjected to creeping fibrous replacement by host cells : a view supported by the seemingly permanent survival of arrector pill muscle fibres in buried dermis grafts in human subjects (Thompson, 196o b).

In these circumstances it seems probable that the most important element in autogenous free split-skin grafts is the dermis, with its delicate and irreplaceable network of collagen, reticular and elastic fibres, and its well-maintained and rich vascularisation. Such tissue provides a supple, resilient, and mobile foundation on which surface epithelium can base its nutrition and best withstand environmental trauma, thereby adequately maintaining its protective function.

Comparison of the coarse-fibred, inelastic and poorly vascularised subepithelial fibrous tissue found in late ungrafted split-skin graft donor sites, with the vascular natural dermal connective tissue present in grafted cases, serves to confirm the value of " shaving" and skin grafting as a treatment of unstable surface scars, from whatever cause.

SUMMARY

Histological and clinical evidence is submitted that : - - I. The rate and quality of healing of split-skin graft donor sites is improved

by the application of Thiersch grafts. 2. The burying of epithelial elements in the operation o f " shaving" and skin

grafting is followed routinely by the formation of microscopic epidermoid cysts, but that these undergo spontaneous dissolution within a year in the vast majority of cases. In only 3"4 per cent. of patients did clinically persistent epidermoid cysts require operative removal.

3. Following the application of Thiersch grafts to areas of partial thickness skin loss, some host sweat glands regenerate to discharge their secretion to the surface, but most do not : the latter, though continuing to survive and function, probably have their secretion internally resorbed into the local circulation. Under the same circumstances only a minimum number of hair follicles survive as functional units.

It gives great pleasure to acknowledge the assistance, direct and indirect, of many colleagues.

In Sheffield, of Mr Wilfred Hynes, from whose wards almost all the clinical material derived, and with whom association was a constant stimulus to enquiry ; Dr J. L. Edwards, Consultant Pathologist, in whose laboratories most of the microsections were cut; Dr J. Tighe,

3 D


whose scepticism enhanced many histological discussions; Dr B. F. Martin, Senior Lecturer in Anatomy in the University of Sheffield, who advised on certain aspects of histological interpretation; Mr A. McKibbins, for the main body of photomicrography.

In Stoke Mandeville Hospital, of Dr J. Harris, Consultant Pathologist, in whose laboratory the final two biopsies were sectioned.

In Oxford, of Dr A. H. T. Robb-Smith, in whose department the final photomicrographs were completed.

REFERENCES

BROWN, J. B., and McDoWELL, F. (1942). Ann. Surg., x1$, 1166. - - (1958) . " Skin Grafting." London : Pitman. CONVERSE, J. M., and ROBB-SMITH, A. H. T. (1944). Ann. Surg., I2O, 873. CONWAY, H. (1939). Surg. Gynec. Obstet., 69, 756. GILLMAN, T., PENN, J., BRONKS, D., and Roux, M. (1953). Brit .J. plast. Surg., 6, 153. - - (I954). Nature, Lond., I74 ' 789 . GUTTMANN, L. (1947). Post-grad. reed. 37., 23, 353- HARTWELL, S. W. (1955). " The Mechanisms of Healing in Human Wounds ."

Springfield, IlL : C. C. Thomas. HINMAN, F. (1954). " The Pathology of Urinary Obstruction " in " Urology,"

vol. I, ed. M. Campbell. Philadelphia : W. B. Saunders Co. HOLYOKE, J. B., and LOBITZ, W. C. (1952). 37. invest. Derm., 18, 147. HYNES, W. (1956). Brit. 37. plast. Surg., 9, 47. - - (1957). Brit. J. plast. Surg., io , I. KREDEL, F. E., and PHEMISTER, D. B. (1939). Arch. Neurol. Psychiat., 42, 4o3. LOEITZ, W. C., and DOBSON, R. L. (1957). J . invest. Derm., 28, lO5. LOBITZ, W. C., HOLYOKE, J. B., and MONTAGNA, W. (1954). ft. invest. Derm., 23, 329 • MONTAGNA, W. (1956). " The Structure and Funct ion of Skin." New York:

Academic Press Inc. PADGET% E. C., and STEPHENSON, K. L. (1948). " Plastic and Reconstructive Surgery."

Springfield, Ill. : C. C. Thomas. PEER, L. A., and PADDOCK, R. (1937). Arch. Surg., 34, 268. PEER, L. A. (1955). Plast. reconstr. Surg., 16, 16I. ROBB-SMITH, A. S . T. (1959). Personal Communication. ROTHMAN, S. (1954). " Physiology and Biochemistry of the Skin." Chicago:

University of Chicago Press. SCHROTER, F. L. H. yon (1922). Cited by Cameron, G. R., in " Pathology of the

Cell." Edinburgh : Oliver and Boyd. STEWART, M. J. (1912). J . Path. Bact., 17, 502. THOMPSON, N. (196o a). Clin. Sci., 19, 95.

(196o b). Plast. reconstr. Surg. (In the press.)

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