THE SKIN OF THE DOMESTIC PIG* WILLIAM MONTAGNA, Pn.D. AND JEUNG S. YEN, M.S. Little is known about the anatomy or thehematoxylin and eosin, 0.05% toluidine blue physiology of porcine skin; the only pertinent(buffered at pH 4.5), the PAS technic, Verhoeff's stain, Giemsa stain, PTAH, HIll, Mallory's Azan modern studies are those of Schaffer (1) andtechnique and the DD reaction for —Sil and Kitamura (2), and Kurasumi and Kitamura (3)—S—S groups (l3arrnett and Seligman, 1952 (4)). on the glands of the so-called carpal organs. ThereAlkaline phosphatase, alpha naphthol esterase, is, furthermore, practically no data that sub-naphthol AS esterase (see Gomori (5)), tween esterase (Stowell and Lee, 1950 (6)) and eholines- stantiates the often repeated statement that theterases (Montagna and Ellis, 1957 (7)), were dem- skin of the pig is similar to that of man. Thisonstrated in frozen sections of tissues fixed in brief survey of the histology and histochemistry10% formalin. of the skin of the pig, therefore, should be a useful Succinic dehydrogenase (Farber and Louvierel, reference for those who plan to do further work1956 (5)), monoamino oxidase (Glenner, et at, 1957 (9)), and phosphorylase (Takeuchi and Kuri- on this animal. The pig, a highly specialized mam-aki, 1955 (10)) were studied in frozen sections of mal, with highly specialized habits, has manyunfixed tissues. local, topographic anatomical differentiations in its skin, which are beyond the scope of this study. GENERAL DESCRIPTION We have been more interested here in analyzing the general body skin, to allow us to draw some The skin of the pig has a remarkable number of focal specializations, some of these being asso- generalizations. The skin has a gross resemblance to that ofciated with rich glandular fields. The most signifi- man, particularly after the bristles have beencant specialization has occurred in the rhinarium, removed. Like man, the pig has a sparse cover ofor snout, which has become flattened and ex- hair; the epidermis has a well-differentiated under- panded, and used to good advantage for routing. sculpture, the dermis has a thick papillary bodyThe snout has the only surface that is compara- and a rich population of elastic fibers. These areble to the friction areas of most non-hooved mam- mals (palms and soles); it is different, however, in specious similarities, however, and it is apparent that in other respects the skin is very differenthaving over its surface widely spaced, short from that of man. vibrissac (Fig. 1). The snout has undergone ad- mirable adaptations: it has a very thick epidermis under which are many tactile nerve endings, end- MATERIALS AND METhODS organs, and sinus hair follicles. Like the friction Specimeus of skin were taken from 6 adult sows surface of other mammals, the surface of the immediately after they had been slaughtered.snout is kept moist by the secretion of special Pieces were removed from the scalp, ear, eyelid,scrous glands deep in the dermis. Midway be- lip, gular region, the entire snout, back, chest and carpal organs and mental organs. Small pieces oftween the bases of mandibles, is a round, raised tissue were fixed in Helly's fluid and T.C.A. andnevus-like structure called mandibular or mental embedded in paraffin. Sections were stained withorgan, which is composed of sebaceous and *Fromthe University of Oregon Medicalapocrine glands, and very coarse vibrissae. Proxi- School, Portland, Oregon, and the Oregon Re-mally on the ventral surface of the carpus, and gional Primate Research Center, Beaverton,extending to just between the two hind toes Oregon. This work was supported in part by grants from(numbers 2 and 3) is a row of large pores into the United States Public Health Service (RG-which open the duets of special serous glands 2125-Cl2), Colgate-Palmolive Co., and Revlon, Inc. clustered around the pores. Together, the glands Publication No. 24, Oregon Regional Primatecomprise the carpal organ. Schaffer (1) (1940), Research Center, Beaverton, Oregon, establishedKitamura (2) (1957) and Kurosumi and Kita- 1960 by grants FR 00163 (formerly R-5129-R-1) and FR 00170 (formerly RD 5690) from the Na-mura (3) (1958) have already described the tional Institutes of Health, U. S. Public Healthglands of the earpal organs, but we have some Service, Department of Health, Education anddetails to add to their observations. Welfare. Received for publication August 1, 1963. The surface of the skin of the pig is creased by 11 12 THE JOURNAL OF INVESTIGATIVE DERMATOLOGY , :-—-v P 'I. Fiu. 1. A whole snout from a freshly killed animal FIG. 2. Epidermis from the back, stained with hematoxylin and eosin THE SKIN OF THE DOMESTIC PIG 13 delicate intersecting sulci, which when shavedtum granulosum and the cells immediately above attain a superficial resemblance to the skin ofthem. The stratum corneum of the snout, the lips man. Though breeds vary in the profusion ofand between the toes abounds in enzymie activ- their hairs, pigs have a moderate to sparse coat ofity. AS esterase activity, present in the malpighian hair, longer and coarser on the back than on thelayer, is absent from the stratum corneum. The belly. The hairs are shorter and more crowdedmost striking feature of the epidermis is the together in those areas where the expansion of thepresence of alkaline phosphatase in the lower skin surface is minimal, such as between theportion of the malpighian layer; the reaction toes, at the base of the ears, on the head, thefades in the upper cells of the spinous layer and is axillary and inguinal regions, etc. Short, coarseabsent from the stratum eorneum (Fig. 3). There vibrissae are widespread over the snout, theis some acetyleholinesterase but no butyryleho- muzzle, and on the upper and lower lips; theylinesterase in the malpighian layer. are much longer on the mental organ. The only outstanding feature of the melano- cytes, when these are present, is their very large The Epidermis size and the conspicuousness of their dendrites. Relatively thick everywhere, the epidermis has a conspicuous undersculpture of more or less The Dermis regularly alternating large and small ridges (Figs. A substantial papillary body consisting of fine 2, 3). It is thickest, and with a correspondinglycollagen fibers rests under the tortuous epidermis. more elaborate understructure, on the glabrousIn the thick reticular layer are woven coarse surface of the lips, on the snout and between thebundles of collagen fibers oriented largely hori- toes. A granular layer, better differentiated in thezontally. The cell population is sparse, and there epidermis between the toes, on the snout and theare no melanotie dermal melanocytes. Elastic glabrous surfaces of the lips, is occasionally dis-fibers are numerous everywhere. In the papillary continuous over the trunk. The stratum eorneumlayer delicate fibers branch toward the epidermis is deep and compact everywhere, and somewhatas they do in the skin of man. In the snout, where resembles that of the friction surfaces of the skinthe dermal ridges are extremely long, many elastic of other mammals. In preparations treated forfibers extend along with capillaries up to the —SR groups the entire lower two-thirds of thepapillary bed. Fine elastic fibers are wound stratum eorneum is reactive. Often even thearound the hair follicles. upper part shows some reactivity. On the snout The dermis has a moderate number of super- and lips the entire layer is intensely colored. Whenficial capillaries which form a plexus inside the treated for —S-—S groups, the entire eornealdermal ridges. The endothelium of these vessels, layer is consistently colored. however, has no alkaline phosphatase activity. The whole malpighian layer, but particularlyIn fact, the only alkaline phosphatase activity in the basal layer, stains well with basic dyes. Ex-capillaries is in those around the apocrine sweat cept in occasional isolatedfoei, there is no glyeo-gland, and occasionally some of those around the gen in the malpighian layer. There is always ahair follicles. In contrast, all capillaries have band of glyeogen in the upper cells of the mal-strong ATPase activity. pighian layer in the epidermis of the snout. The Only a few nerves that contain acetyleholin- malpighian layer has pronounced suecinie de-esterase are present in the general body skin. In hydrogenase reactivity; a color reaction in thethe snout, eyelid, lower lip and gular region, stratum corneum may indicate the presence ofthere are numerous free nerve endings and end abundant —SH groups. A thin band of colororgans. Sausage-shaped and bead-shaped end immediately above the stratum granulosum re-organs in the snout rest under the epidermal minds one of the sulfhydryl-rieh keratogenous zoneridges. In the snout, fine, free nerve-endings also in the epidermis of man (11). MAO reactivity,run against the long epidermal ridges, and seem weak in the malpighian layer, is strong in theto penetrate them (Fig. 4). stratum granulosum. Phosphorylase activity is In the gular skin and in the eyelids, skeletal barely detectable. Nowhere strong, alpha naph-muscle fibers rise to the papillary body from be- thol esterase activity extends throughout the mal-neath; these are encrusted by conspicuous end- pighian layer, with the best reaction in the stra-buttons that are strongly reactive for both buty- 4: p 'ii! 741 /4 N FIG. 3. Epidermis Gf the snout with abundant alkaline phosphatase activity in the lower part of the malpighian layer. FIG. 4. Pleomorphic end organs just under the epidermis of the snout, and intraepidermal nerve fibers, both showing acetylcholinesterase activity. FIG. 5. Portion of a large hair follicle cut longitudinally to show the prolongations of the dermal papilla into the bulb, and the dendritic melanocytes in the matrix. FIG. 6. Hair follicle cut longitudinally to show the aggregates of melanocytes in the matrix 14 THE SKIN OF THE DOMESTIC PIG 15 ryleholinesterase and acetyleholinesterase.