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					Published November 1, 1961

                     AN ELECTRON                 MICROSCOPIC                 STUDY         OF ECCRINE                SWEAT

                     GLANDS          OF THE         CAT FOOT               AND     TOE      PADS--

                     EVIDENCE             FOR     DUCTAL           REABSORPTION                    IN THE          HUMAN

                                 BRYCE       L. M U N G E R ,    M.D., and S A U L      W. B R U S I L O W ,     M.D.

                                 From the Armed Forces Institute of Pathology, Washington, D. C., and the Department of Pedi-
                                 atrics, The Johns Hopkins Hospital, Baltimore. Dr. Munger's present address is Department of
                                 Anatomy, Washington University School of Medicine, St. Louis

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                                 The cccrinc sweat glands of the cat foot and toe pads have been studied by light and elec-
                                 tron microscopy before and after stimulation with mecholyl. The ultrastructure of these
                                 glands in thc cat is found to be entirely comparable to that in the human (13). The ultra-
                                 structure and staining properties of the secretory segment of the two species are identical.
                                 The ductal part of the feline gland is shorter and the ductal cells have only scant mito-
                                 chondria as compared with the human. Since Brusilow et al. (1) have observed that the
                                 secretion of the cat foot pad is isotonic as compared with human sweat, which is hypotonic,
                                 and since the secretory scgments of the two species are structurally identical, the striking
                                 difference in the morphology of the duct is rcgarded as being responsible for the difference
                                 in the chcmistry of the secretion of the two specics. Thus the duct in the h u m a n is capable
                                 of reabsorbing sodium and chloride.

                     Two distinct types of cells are present in the            Brusilow et al. (1) have observed that sweat
                     secretory segment of human eccrine sweat glands.       collected from foot or toe pads of the cat is isotonic
                     It has been postulated that each cell type secretes    rather than hypotonic. The sweat which is secreted
                     a different product. Mucoid (dark) cells upon          by the cat foot pad after stimulation with mecholyl
                     stimulation liberate secretory vacuoles, containing    or pilocarpine contains amounts of sodium and
                     at least an acid mucopolysaccharide, into the          chloride almost identical with those in normal
                     glandular lumen (13). Clear cells are thought to       serum. The glands which secrete this sweat have
                     deliver a predominantly watery fluid into inter-       been regarded as eccrine in type (6, 22), but
                     cellular canaliculi which convey this fluid to the     Montagna (9) believes that they are in no way
                     gland lumen. The combined secretion of these two       comparable to human eccrine sweat glands. The
                     cells traverses a long duct which presumably           present study was undertaken to examine the
                     reabsorbs sodium and chloride from the precursor       eccrine sweat glands of cat foot and toe pads by
                     sweat solution (19, 23). The resultant solution        light and electron microscopy and to try to deter-
                     delivered to the skin surface is hypotonic with        mine (a) whether these glands are comparable to
                     respect to sodium and chloride (17) and contains       those of the human, and (b) if so, why the cat
                     small amounts of other ionic and organic con-          produces an isotonic sweat whereas the human
                     stituents.                                             secretes a hypotonic sweat.

Published November 1, 1961

                    MATERIALS           AND     METHODS                        o s m i u m fixation (2) for electron microscopy. T h e
                                                                               formol-fixed tissue was embedded in paraffin,
                    T h e foot and toe pads of six adult cats of both sexes    sectioned at 5 #, and stained with hematoxylin and
                    and of two 3-month-old male kittens were studied by        eosin, the colloidal iron stain (12) and Alcian blue
                    light and electron microscopy. T h e cats were anes-       stain (11) for acid mucopolysaccharides, the PAS
                    thetized by intraperitoneal injection of Nembutal.         stain (8) for glycogen, before and after diastase
                    T h e specimens were removed by cutting with scissors      treatment, and the toluidine blue stain at p H 5.6
                    d o w n to the bone of the phalanx or metacarpal.          for basophilia and metaehromasia (10).
                    T h i n slices of tissue were cut for fixation in 10 per       Tissue for electron microscopy was fixed for 1
                    cent neutral formol or formol-Zenker solution. Small       hour in Dalton's fixative (2) dehydrated t h r o u g h a
                    cylinders, 1 m m in diameter, were cut perpendicular       graded series of alcohols, and embedded in Epon 812
                    to the skin surface and fixed in Dalton's chrome-           (Shell Chemical C o m p a n y ) according to procedures

                                            FIGURE ]
                                            Phase contrast micrograph of kitten toe pad. A portion of a secretory segment (5~) has
                                            been cut tangentially. T h e cells surrounding the lumen (L) are cuboidal, and a sugges-
                                            tion of vacuolization can be seen in the cytoplasm of some cells. A portion of eccrine
                                            duct (DU) is also cut in section, and a double layer of cuboidal cells surrounds the duct

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                                            lumen (L). The duct cells appear relatively flat, but the extent of the cytoplasm of vari-
                                            ous cells is impossible to determine at this magnification. Immediately adjacent to the
                                            duct lumen is a zone of increased contrast which represents the "cuticular b o r d e r " seen
                                            in routine preparations. N u m e r o u s capillaries (C) and fat cells (F) are present in the
                                            connective tissue which surrounds the gland. )< 900.

                                            Phase contrast micrograph of kitten toe pad secretory segment. All components of the
                                            secretory segment can be identified in this micrograph. Surrounding the lumen (L) arc
                                            two types of secretory cells. Mucoid (dark) cells (Nm) can be identified by the presence
                                            of numerous secretory vacuoles (s) present in the apical sytoplasm. Between groups of
                                            mucoid cells arc clear cells (No) which lack secretory vacuoles, and intercellular cana-
                                            liculi (IC) course bctwecn adjaccnt clear cells. All cells which can bc positively identi-
                                            fied in this micrograph arc labeled Nc for clear cells and N m for mucoid cells in thc
                                            appropriate nuclci. Myocpithclial cclls (y) can bc idcntificd as small cells of uniform
                                            contrast situated beneath the mucoid and clear cells. X 900.

                                            FIGURE .~
                                            Gallocyanin chrome alum-stained sections of secretory segment. T h e lumen (L) is sur-
                                            rounded by intensely stained nuclei indicating the presence of the various cells. T h e
                                            cytoplasm of some cells stains with the dye; these are the mucoid or dark cells (Arm).
                                            O t h e r cells lack coloration of the cytoplasm, and these are the clear cells (Me). T h e
                                            general appearance is identical with that in m a n (13). T h e apical cytoplasm of m u c o i d
                                            cells appears reticulated in this stain; the reticulation is duc to the negative staining of
                                            the secretory vacuoles as seen in Fig. 2. X 900.

                                            FIGURE 4
                                            Cross-section of secretory segment stained with the modified Hale colloidal iron stain
                                            for acid mucopolysaccharides. Areas appearing black and gray in the micrograph ap-
                                            pear blue in the microscope. In the apical cytoplasm of some cells are n u m e r o u s dis-
                                            crete, round, stained bodies (arrows) which are identical in form and distribution with
                                            the secretory vacuoles seen in Fig. 2. T h e lumen (L) also stains positively. Intercellular
                                            canaticuli cannot be identified with certainty. T h e surrounding connective tissue is also
                                            intensely colored. Cells lacking intraccllulm" mucopolysaccharide are considered to be
                                            clear cells. X 900.

Published November 1, 1961

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                             B. L. MUGGER AND S. W. BRUSILOW Eccrine Sweat Glands of Cat Foot Pads   405
Published November 1, 1961

                     devised by Luft (7). Sections of the Epon-embedded        unstained osmium-fixed tissue by phase micros-
                     material were cut with glass knives on a Porter-Blum      copy is composed of a thick epidermis, a dense,
                     microtome, mounted on Formvar-coated grids, and           discrete dermis, and a thick layer of adipose tissue
                     examined in an RCA EMU-3D electron microscope.            interlaced by bands of connective tissue. The bulk
                     Some sections were stained with saturated aqueous
                                                                               of the pad is composed of a 1 to 1.5 cm thick
                     uranyl acetate (24) to increase electron contrast.
                                                                               layer of adipose tissue which extends from the
                     Osmium-fixed tissue was also embedded in metha-
                     crylate according to routine procedures, but the          dermis to the fascia overlying the metacarpal
                     preservation was not satisfactory for electron micros-    bones. T u b u l a r structures identified as eccrine
                     copy. One micron sections of methacrylate-embedded        sweat glands extend from the epidermis, course
                     osmium-fixed tissue were cut on a Porter-Blum             through the dermis and mass of adipose tissue, and
                     microtome for light microscopy, and these sections        terminate just above the fascia that forms the base
                     were stained with gallocyanin chrome alum, PAS,           of the pad. Thus the glands are not coiled at the
                     and the Hale colloidal iron stains as described previ-    dermosubcutaneous junction as are h u m a n eccrine
                     ously (13). For phase microscopy the methacrylate         sweat glands, but rather they extend as slightly
                     was removed by soaking in xylene, and the sections        undulating tubes through the dermis and massive
                     were mounted directly in oil of refractive index
                                                                               fat pad. The duct can be identified as having a
                     1.460 (3).
                                                                               double layer of cuboidal cells lining the lumen
                        The secretion of sweat was stimulated by the
                     injection of 0.1 cc of a 0.05 per cent solution of        (Fig. 1). T h e duct extends only from the skin
                     mecholyl in normal saline into the foot and toe           surface to the zone at the base of the dermis. T h e

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                     pads. Specimens were removed 5, 15, and 30 minutes        remainder of the gland extending through the
                     after stimulation and prepared as described above.        fatty tissue of the foot pad is the secretory segment
                     Prior to injection one foot pad and one toe pad of        (Figs. 1 and 2). Toe pads differ from foot pads in
                     each animal had been removed for controls.                having less adipose tissue; as a result the sweat
                                                                               glands are more closely packed in toe pads,
                     OBSERVATIONS                                              facilitating electron microscopic study.
                                                                                  The cytology of the gland as seen by light
                     Light Microscopy
                                                                               microscopy is identical with that in the h u m a n
                       The foot pad of a mature cat as seen in cross-          (13). T h e duct is composed of a double layer of
                     sections stained with hematoxylin and ecsin or in         cuboidal cells: a layer of surface cells bordering

                                            FIGURE 5
                                            Secretory segment of adult cat foot pad. The lumen (L) of this secretory segment is
                                            present in the upper part of the micrograph. Secretory vacuoles (S) indicate the pres-
                                            ence of mucoid (dark) cells and appear to be similar to those indicated in Fig. 2. The
                                            nuclei of d e a r cells (Nc) are indistinct owing to the uniformity of density of the nucleus
                                            and cytoplasm. Between adjacent clear cells is an intercellular canaliculus (IC) which is
                                            difficult to resolve in detail at this magnification. Scattered mitochondria (M) can be
                                            seen in both cell types, but those in the clear cells blend with the background of cyto-
                                            plasmic density at this magnification. A myoepithelial cell (Y) forms a thin band sur-
                                            rounding the secretory ceils. X 7000.

                                            FIGURE 6
                                            Clear cells surrounding an intercellular canaliculus in secretory segment of cat foot pad,
                                            5 minutes after stimulation. Numerous microvilli (V) project into the intercellular
                                            canaliculus (IC). Terminal bars (T) are formed by the cell membranes of adjacent
                                            clear cells as they abut on the canaliculus. The cell membranes interdigitate as they sur-
                                            round the canaliculus, forming a lamellar system of apposed cell membranes (I).
                                            Numerous mitochondria (M) are scattered throughout the cytoplasm. Dense material
                                            thought to represent lipid (F) is also present in the cytoplasm. A portion of one clear cell
                                            nucleus (N) is present. An area of decreased density (arrow) is seen in the matrix of one
                                            mitochondrion. The background cytoplasm is predominantly granular. )< 25,000.

Published November 1, 1961

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                             B. L. MUNGER AND S. W. BRUSILOW Eccrine Sweat Glands of Cat Foot Pads   407
Published November 1, 1961

                     the lumen, and a layer of basal cells resting on the      sidered to be prosecretory vacuoles, that is,
                     basement membrane. The luminal edge of surface            secretory vacuoles in the process of formation
                     cells appears homogeneous and of dark contrast;           (Fig. 7).
                     this zone corresponds to the hyaline appearing               Clear cells are identified in electron micrographs
                     "cuticular border" seen in routine hematoxylin            as being associated with intercellular canaliculi
                     and eosin-stained preparations.                           (Figs 5 and 6). Their cytoplasm is predominantly
                        Two types of secretory cells are present in the        granular. While it is impossible to determine with
                     secretory segment surrounded by myoepithelial             accuracy the nature of the individual granules,
                     cells. As in the human, mucoid cells (dark cells of       many of them resemble glycogen units (Fig. 14).
                     Montagna (10)) have a basophilic cytoplasm                Numerous mitochondria containing occasional
                     (Fig. 3) containing the secretory vacuoles (Fig. 2)       dense granules are present in the cytoplasm of
                     in the apical part of the cell which stain selectively    clear cells. A very small Golgi apparatus is present
                     for acid mucopolysaccharide (Fig. 4) with the             in some cells, and only a few agranular mem-
                     modified Hale colloidal iron stain. These secretory      branous profiles are seen scattered throughout the
                     vacuoles are also faintly metachromatic, but are         cytoplasm.
                     PAS-negative. The other cell type of the secretory          Numerous closely packed microvilli (Fig. 6)
                     segment is the clear cell, which lacks cytoplasmic       project into the intercellular canaliculi which
                     basophilia (Fig. 3) and intracellular mucopoly-          course between adjacent clear cells. The cell
                     saccharide (Fig. 4). Between adjacent clear cells        membranes of adjacent clear cells interdigitate

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                     are intercellular canaliculi (Fig. 2) which course       with one another, producing lamellar arrays of
                     from the lumen to the base of the gland. The             membranes which radiate from the intercellular
                     contents of the intercellular canaliculi and the         canaliculi (Fig. 6). Adjacent cell membranes are
                     glandular lumen also contain mucopolysaccharide          thickened to form terminal bars as they abut on
                     (Fig. 4). The clear cells contain PAS-positive,          the canaliculi (Fig. 6).
                     diastase-digestible material presumed to be                 Surrounding both mucoid and clear cells are
                     glycogen.                                                myoepithelial cells (Fig. 13). A more detailed
                        Following stimulation the only change visible         account of the ultrastructure of myoepithelial cells
                     by light microscopy is a diminution of cytoplasmic       and the changes accompanying stimulation will
                     glycogen in clear cells.                                 be the subiect of another report.
                                                                                 In adult cats m a n y eccrine glands appear
                     Electron Microscopy of Unstimulated Secretory            dilated and have cyst-like lumens. In such a
                                                                              situation the cells surrounding the secretory lumen
                                                                              are relatively undifferentiated; only occasional
                       Mucoid (dark) cells have numerous secretory            cells contain secretory vacuoles, and intercellular
                    vacuoles in the apical cytoplasm (Fig. 5). These          canaliculi are rare. The majority of the cells are
                    vacuoles are round to oval in outline and are             cuboidal and lack cytologic specialization. Such
                    bounded by an incomplete limiting membrane as             dilated glands are seldom found in kittens, how-
                    seen in section (Fig. 7). They contain fibrillar          ever. Langley (5) noted that kittens sweat much
                    material of low electron opacity. The cytoplasm           more profusely than adult cats, and he attributed
                    of mucoid cells is predominantly granular, con-           this difference to obstruction of glands by the thick
                    sisting largely of dense 150 A granules thought to        cornified epidermis in older animals. While many
                    represent ribonucleoprotein (15). Only a few              of the eccrine glands from adult cats observed in
                    granules are associated with membrane profiles.           the present study were normal in appearance,
                    Scattered mitochondria are present throughout the         consistent observations were impossible because
                    cytoplasm (Fig. 7).                                       many were dilated. Therefore, the remaining
                       The Golgi apparatus of mucoid cells is promi-          observations were made on kittens exclusively.
                    nent, with many flattened, agranular membranous              A relatively thick basement membrane sur-
                    sacs, arranged in lamellar form, associated with          rounds the secretory segment (Fig. 13), and in
                    numerous vacuoles and vesicles. A continuity can          some areas collagen fibers appear to be inserted
                    be traced between dilatations of Golgi sacs and           into the substance of the basement membrane.
                    secretory vacuoles. The small vacuoles in intimate        Numerous small processes of fibroblasts are
                    association with the Golgi apparatus are con-             disposed circumferentially around the secretory

Published November 1, 1961

                             FIGURE 7                                                                                                                               Downloaded from on May 6, 2011
                             M u c o i d cell cytoplasm from secretory s e g m e n t of kittcn toc p a d 5 m i n u t c s after stimulation. N u m e r o u s
                             secretory vacuoles (S) arc prcscnt, s u r r o u n d c d by a distinct limiting m e m b r a n e (arrow). I n somc
                             places the limiting m e m b r a n e appears incomplete. T h c m i t o c h o n d r i a (M) d c m o n s t r a t c occasional
                             vacuolcs similar to those of the m i t o c h o n d r i a of clcar cclls following stimulation. T h e Golgi a p p a r a t u s
                             (G) is prominent, a n d n u m c r o u s small vacuoles arc intimatcly associatcd with it. Some of the vacuoles
                             in association with the Golgi a p p a r a t u s arc considered to bc prosccrctory vacuoles (P), that is, v a c u -
                             oles in the process of formation. A few crgastoplasmic m c m b r a n e s (ER) with associated granules a n d
                             isolated granulcs arc prcscnt in the b a c k g r o u n d cytoplasm. X 19,000.

                                                      B. L. MONGER AND S. W. BRUSILOW Eccrine Sweat Glands of Cat Foot Pads                                   409
Published November 1, 1961

                    segment. Occasional bundles of u n m y e l i n a t e d                    " a t t a c h m e n t plaques" is squamous epithelia
                    nerve fibers e m b e d d e d in S c h w a n n cells are present           (Fig. 11).
                    in the connective tissue surrounding the gland, b u t                         Basal cells a p p e a r similar in structure to surface
                    no nerve endings have been seen within the sub-                           cells. T h e numerous m i t o c h o n d r i a w h i c h are
                    stance of the b a s e m e n t m e m b r a n e or in contact               present in basal cells of the d u c t in h u m a n s are
                    with secretory cells or myoepithelium. M a s t cells                      conspicuously absent in the cat. I n m a n y sections
                    have not been seen in the connective tissue                               studied, only very occasional m i t o c h o n d r i a are
                    s u r r o u n d i n g the cat eccrine glands, a l t h o u g h they        present in the cytoplasm (Fig. 9), and they contain
                    are n u m e r o u s in man. Numerous capillaries are                      virtually no mitochondrial granules. T h e cell
                    e m b e d d e d in the connective tissue surrounding the                  m e m b r a n e of basal cells a b u t t i n g onto the base-
                    glands.                                                                   m e n t m e m b r a n e is focally specialized into disc-like
                                                                                              a t t a c h m e n t plates (Fig. 9). These a t t a c h m e n t
                    Electron Microscopy of Eccrine Duct                                       plates resemble half of a desmosome, consisting of
                                                                                              a thickened cell m e m b r a n e into which tonofila-
                         Surface cells of the eccrine duet have large                         ments insert, a n d a zone of density between the
                     nuclei of irregular outline a n d scant cytoplasm                        thickened cell m e m b r a n e a n d the b a s e m e n t
                     (Fig. 8). T h e luminal edge of these cells is t h r o w n               m e m b r a n e . This dense zone would a p p e a r to
                     into n u m e r o u s small, b l u n t microvilli (Figs. 8 a n d          correspond to the intermediate dense layer of the
                     10). Beneath the microvilli is a dense zone of                           a t t a c h m e n t plates between the cells of stratified

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                     filamentous and g r a n u l a r material termed the                      squamous epithelium (14). These basal attach-
                     " c u t i c u l a r b o r d e r " (Figs. 8 a n d 10). T h e "cuticular   m e n t plates are more p r o n o u n c e d in the cat t h a n
                     b o r d e r " is thin as c o m p a r e d with that in man, and           in m a n a n d resemble the basal a t t a c h m e n t plates
                     no m i t o c h o n d r i a have been observed e m b e d d e d            of stratified squamous epithelium (20).
                     in its substance, as frequently seen in man. T h e
                     general structure of the " c u t i c u l a r b o r d e r " is            Electron Microscopy of Secretory Segment after
                     identical with t h a t in the h u m a n , consisting of
                     masses of tonofilaments (terminal web) and small
                     granules (Fig. 10). T h e tonofilaments insert into                        M u c o i d cells d e m o n s t r a t e active extrusion as
                     n u m e r o u s desmosomes between adjacent duct cells                   early as 5 minutes after stimulation by the sub-
                     (Fig. 12). These desmosomes are identical with                           cutaneous injection of mecholyl. N u m e r o u s
                     pairs of structures described by O d l a n d (14) as                     secretory vacuoles bulge into the lumen, a n d o t h e r

                                                   FIGURE 8
                                                   Eccrine duct from kitten toe pad. The duct wall is composed of a double layer of ceils :
                                                   surface cells (Ns) and basal cells (Nb), labeled in the appropriate nuclei. A zone of ir-
                                                   regular density surrounding the lumen (L) is the "cuticular border" (CB) of light
                                                   microscopy. Blunt microvilli (V) project into the lumen from the cytoplasm of the sur-
                                                   face cell. Numerous desmosomes (D) are seen between adjacent cells. A distinct base-
                                                   ment membrane (BM) surrounds the duct. X 11,700.

                                                   FIGURE 9
                                                   A portion of the cytoplasm of two basal cells of the eccrine duct stained with uranyl
                                                   acetate The nuclei (N) of two adjoining basal cells are present at the extreme edges of
                                                   the micrograph. The cytoplasm contains only a few ill defined structures that could
                                                   represent mitochondria (M). Arrays of filaments that can be identified as tonofila-
                                                   ments (arrows) are scattered throughout the cytoplasm. Numerous desmosomes (D)
                                                   lie between adjacent cells. The basement membrane (BM) shows enhanced contrast
                                                   following uranyl acetate staining, as compared with Fig. 8. The cell membrane at the
                                                   base of the cell is focally differentiated into plate-like densities, resembling half of a
                                                   desmosome (A). These are dermal attachment plates which consist of a thickened cell
                                                   membrane and a dense band (toward the basement membrane) which would corre-
                                                   spond to the intermediate dense layer of the dcsmosome. X 45,600.

                     410       THE JOURNAL OF BIOPHYSICAL AND BIOCHEMICAL CYTOLOGY VOLUME 11, 1961           •
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                             B. L. MUNGER AND S. W. BRUSILOW Ecerine Sweat Glant£~ of Cat Foot Pads   411
Published November 1, 1961

                    vacuoles show fusion of their limiting m e m b r a n e s          with the glycogen mass (Fig. 14), but in these
                    with the cell m e m b r a n e (Fig. 13). Bits of cyto-            areas the mitochondrial m e m b r a n e m a y have been
                    plasmic a n d m e m b r a n o u s debris are present in           sectioned tangentially. A given cell often contains
                    the glandular lumen. T h e Golgi a p p a r a t u s is             more t h a n one such glycogen accumulation.
                    more p r o m i n e n t t h a n it is in unstimulated mucoid
                    cells, a n d prosecretory vacuoles can be easily                  DISCUSSION
                    identified (Fig. 7). Some of the m i t o c h o n d r i a are
                    vacuolated (Fig. 7) in a m a n n e r similar to t h a t           O n the basis of the above description, the sweat
                    seen in clear cell m i t o c h o n d r i a of h u m a n eccrine   glands of the cat foot a n d toe pads are found to be
                    glands following stimulation (13). After stimula-                 eccrine glands directly c o m p a r a b l e to h u m a n
                    tion the secretory vacuoles r e m a i n decreased in              eecrine sweat glands as described previously (13).
                    n u m b e r for 15 to 30 minutes.                                 I n the two species, the cytology, staining char-
                       T h e matrix of the m i t o c h o n d r i a of clear cells,    acteristics, a n d u h r a s t r u c t u r e of the secretory
                    5 minutes after stimulation, shows areas of de-                   segment are identical, b o t h in the unstimulated
                    creased density, similar to t h a t described for the             and stimulated states.
                    h u m a n (Fig. 6). This change is more pronounced                   T h e structure of the eccrine duct, however, is
                     15 minutes after stimulation (Fig. 14). I n all cells            markedly different in the two species. T h e eccrine
                    of the secretory segment, dense masses of material                d u c t of the cat is shorter a n d smaller t h a n it is in
                    resembling lipid (21) are present after stimulation               man, and the ductal cells contain far fewer

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                     (Fig. 13). Lipid droplets are only rarely seen in                mitochondria and a much thinner "cuticular
                    unstimulated cells. Masses of glycogen (Figs. 13                  b o r d e r . " T h e length of this d u c t in the cat is
                    a n d 14) are clearly d e m a r c a t e d from the general        estimated to be one-tenth the length of the gland,
                    cytoplasm in clear cells 15 a n d 30 minutes after                whereas in the h u m a n it is one-third to one-half
                    stimulation, whereas in u n s t i m u l a t e d glands the        the length of the gland (9). T h e prominence of
                    glycogen appears to be dispersed. These glycogen                  m i t o c h o n d r i a in the basal cells of the d u c t in
                     accumulations are conspicuously r i m m e d by                   h u m a n s has been emphasized (13), a n d the
                    mitochondria. I n some areas the mitochondrial                    paucity of m i t o c h o n d r i a in comparable cells in the
                    limiting m e m b r a n e c a n n o t be resolved a n d the        cat is striking by comparison.
                    substance cf the m i t o c h o n d r i o n appears to merge           Sweat secreted by the cat foot p a d is always

                                                FIGURE 10
                                               Luminal part of a surface cell of an eccrine duct stained with uranyl acetate. Micro-
                                               villi (V) project into the lumen (L). In the cytoplasm of the surface cell between the
                                               nucleus (N) and the lumen is a zone of filamentous and granular material that com-
                                               prises the "cuticular border" (CB). X 45,600.

                                                FIGURE 11
                                               A desmosome between two basal cells, at higher magnification, in the eccrine duct of
                                               kitten toc pad stained with uranyl acetate. At the desmosome the cell membranes are
                                               visibly double (a), but the upper membrane is cut tangentially and so appears as one.
                                               Between the cell membranes are three dense zones. The vague central dense b a n d (c)
                                               is the intercellular contact layer as defined by Odland (14). The other dense bands, on
                                               either side of it, are the intermediate dense layers (b). The dense regions on both sides
                                               of the desmosome represent tonofilaments cut tangentially (TF). X 130,000.

                                                FIGURE 12
                                                A desmosome between two basal cells of an eccrine duct stained with uranyl acetate.
                                                The desmosome (D) is cut in such a plane that the tonofilaments (TF) are cut in pre-
                                                dominantly longitudinal section. Similar masses of tonofilaments are also seen in the
                                                cytoplasm of the basal cells in Fig. 9. X 46,000.

                     412     THE JOURNAL OF BIOPHYSICAL AND BIOCHEMICAI~ CYTOLOGY VOLUME 11, 1961    •
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                             B. L. MUNGER AND S, W. BRUSILOW Eccrine Sweat Glands of Cat Foot Pads   413
Published November 1, 1961

                    iso-osmolar (1), whereas h u m a n eccrlne sweat is                   of the duct are u n d o u b t e d l y responsible for the
                    hypotonic with respect to sodium a n d chloride                       transport of ions from the d u c t cells to the sur-
                    (17). T h e small size a n d paucity of cell organelles               r o u n d i n g vascular supply. T h e peculiar promi-
                    of the cat eccrine d u c t is considered to be responsi-              nence of mitochondrial granules in this zone is
                    ble for the difference in the secretory product,                      consistent with the untested hypothesis of Weiss
                    since the secretory segments of the two species are                   (25) t h a t these granules represent cation exchange
                    identical in morphology. This conclusion is                           resins.
                    entirely consistent with the physiologic inter-                           Studies on the cat (4) and m a n (9) have re-
                    pretations of Thaysen and coworkers (19, 23).                         ported t h a t the a m o u n t of glycogen present in
                    Schwartz a n d T h a y s e n (19) believe t h a t the                 clear cells decreases following stimulation. I n the
                    increasing osmolarity of sweat with increasing                        present study similar changes were noted by light
                    rate of secretion is due to the limited capacity of                   microscopy; however, discrete masses of glycogen
                    ductal reabsorption. F u r t h e r m o r e , on the basis of          are present following stimulation, whereas in
                    their arguments, the initial secretion product is                     unstimulated material only dispersed glycogen is
                    most likely to be isotonic (23), a n d ductal secretion               seen. T h e discrete masses of glycogen m a y there-
                    of water is not consistent with the concentration of                  fore represent areas of confluence of previously
                    u r e a in the delivered p r o d u c t (23). T h e h u m a n          dispersed glycogen accentuated by a r i m of mito-
                    eccrine d u c t thus reabsorbs sodium and chloride                    chondria. Siekevitz a n d Palade (21) have de-
                    from an isotonic precursor solution.                                  scribed a n intimate association of m i t o c h o n d r i a

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                        T h e " c u t i c u l a r b o r d e r " of surface cells of the   and lipid droplets in pancreatic acinar cells.
                    d u c t in m a n must be capable of passive or active                 following fasting. This association was interpreted
                    transport of ions. T h e ultrastructure of this b o r d e r           as indicating t h a t the pancreatic acinar cells h a d
                    is markedly different from t h a t of other k n o w n                 converted to fatty acid metabolism. T h e i n t i m a t e
                    resorptive cell surfaces, such as those of epithelial                 association of m i t o c h o n d r i a with glycogen follow-
                    cells of the intestine (26) and renal tubules (16).                   ing stimulation in the eccrine sweat gland m i g h t
                    Since the " c u t i c u l a r b o r d e r " is birefringent (18),     in the present case represent active metabolism of
                     the masses of tonofilaments in this zone must be                     glycogen stores by secreting cells.
                    organized preferentially. Either the organization
                    of these filaments or the n a t u r e of the proteins                 Dr. Brusilow is a Research Fellow of The National
                     present in this zone (9) m a y account for the                       Foundation, Department of Pediatrics, The J o h n s
                    initial transfer of ions from the l u m e n to the cell               Hopkins Hospital.
                    interior. T h e numerous m i t o c h o n d r i a in basal cells       Receivedfor publication, January 10, 1961.

                       1. BRUSILOW, S. W., MUNGER, B. L., SHAVER, B.,                            and physiology of h u m a n and feline sweat
                            and COOKE, R. E., Comparative morphology                             glands, (abstract) Am. J. Dis. Child., in press.

                                                 FIGURE 18
                                                 Secretory segment of kitten toe pad 15 minutes after stimulation. A mucoid cell with
                                                 nucleus (Nm) and numerous apical secretory vacuoles (S) is present at the lcft. Some of
                                                 the secretory vacuoles appear to be in the process of being liberated from the cytoplasm
                                                 (arrows), in that only a delicate membrane separates the substance of the vacuole from
                                                 the lumen (L). A clear cell (No) is adjacent to the mucoid cell. The cytoplasm of both
                                                 clear and mucoid cells contains dense lipid droplets (F), which wcrc not present in the
                                                 unstimulated cells. Masses of glycogen (GL) are present in the cytoplasm of clcar cclls,
                                                 and these masses are rimmed by numerous mitochondria (M). Terminal bars (T) are
                                                 present at the luminal edges of the adjoining clear and mucoid cells. A myocpithelial
                                                 cell (Y) is present beneath the secretory cells. Surrounding the myocpithelial cell and
                                                 clear cell is a basement membrane (BM). Only the mucoid cell borders on the myoepi-
                                                 thelial cell. X 14,000.

                     414      TIlE JOURNAL OF BIOPHYSICAL AND BIOCHEMICAL CYTOLOGY ° VOLUME                         l l , 1961
Published November 1, 1961

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                             B. L. MUNGER AND S. W. BRUSILOW Eccrine Sweat Glands of Cat Foot Pads   415
Published November 1, 1961

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                             FIGURE 14
                             C y t o p l a s m of clear cell in kitten toe p a d 15 m i n u t e s after stimulation, stained with u r a n y l acetate.
                             A mass of glycogen (GL) c o m p o s e d of small discrete units is s u r r o u n d e d by n u m e r o u s m i t o c h o n d r i a
                             (M). A lipid droplet (F) is also present. At the arrows, t h e m a t r i x of the m i t o c h o n d r i a appears to be of
                             less density t h a n the s u r r o u n d i n g matrix, a consistent finding in stimulated cells. A part of a m y o -
                             epithelial cell (Y) is present in the lower part of the m i c r o g r a p h . X 27,400.

                      2. DALTON, A. J., A c h r o m e - o s m i u m fixative for                 4. KAMMAMURA, S., A cytological study of cat
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                      3. DAVXS, B. J., OgNSTXIN, L., TALEPOROS, P., a n d                             30, 81.
                           KOULIS~, S., S i m u l t a n e o u s preservation of                  5. LANGLEY, J. N., T h e secretion of sweat. Part I.
                           intracellular m o r p h o l o g y a n d e n z y m a t i c or               Supposed inhibitory nerve fibres on the
                           antigenic activities in frozen tissues for h i g h                         posterior nerve roots. Secretion after denerva-
                           resolution histochemistry, J. Histochem. and                               tion, J. Physiol., 1922, 56, 110.
                           Cytochem., 1959, 7, 291.                                              6. LOVELL,J. E., a n d GETTY, R., T h e hair follicle,

                     416        THE JOURNAL OF BIOPttYSICAL AND BIOCHEMICAL CYTOLOGY • VOLUME 11, 1961
Published November 1, 1961

                               epidermis, dermis, and skin glands of the                  Skin, Chicago, University of Chicago Press,
                               dog, Am. J. Vet. Research, 1957, 28, 873.                   1954.
                       7.    LUFT, J. H., personal communication.                 18.   SCHMIDT, W. J., Doppelbrechung und Feinbau
                       8.    McMANvS, J. F. A., Histological and histo-                   des Saumrohres (der sog. Cuticula) im
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                                Technol., 1948, 23, 99.                                   schen, Z. Zellforsch., 1959, 49, 711.
                       9.    MONTAONA,W., The Structure and Function of           19.   SCHWARTZ,I. L., and THAYSEN,J. H., Excretion
                               Skin, New York, Academic Press, Inc., 1956.                of sodium and potassium in human sweat,
                      10.    MONTAONA, W., CHASE, H. B., and LomTz,                       J. Clin. Invest., 1956, 35, 114.
                               W. C., Histology and cytochemistry of human        20.   SELBY, C. C., An electron microscopic study of
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                      11.    MOWRY, R. W., Alcian blue technics for the                   basal cell layer, J. Biophysic. and Biochem. Cytol.,
                               histochemical study of acidic carbohydrates,               1955, 1,429.
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                      12.    MowRY, R. W., Improved procedure for the                     study on the pancreas of the guinea pig. II.
                               staining of acidic polysaccharides by Mfiller's            Functional variations in the enzymatic
                               colloidal (hydrous) ferric oxide and its combi-            activity of microsomes, J. Biophysic. and Biochem.
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                               Schiff reactions, Lab. Invest., 1958, 7, 566.      22.   SPERLING, F., and KOPPANYI, T., Histophysio-
                      13.    MUNGER, B. L., The ultrastructure and histo-                 logic studies on sweating, Am. J. Anat., 1949,

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                               physiology of human eccrine sweat glands, J.               84, 335.
                               Biophysic. and Biochem. Cytol., 1961, 11, 385.     23.   THAYSaN, J. H., Handling of alkali metals by
                      14.    ODLAND, G. F., The fine structure of the inter-              exocrine glands other than the kidney, in The
                               relationship of cells in the human epidermis,              Alkali Metals in Biology, (H. H. Ussing,
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                      15.    PALADE, G. E., and SIEKEVITZ, P., Pancreatic         24.   WATSON,M. L., Staining of tissue sections for
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                      16.    RHODIN, J., Correlation of Ultrastructural
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                               Organization and Function in Normal and                    absorptive cell as studied with the electron
                               Experimentally Changed Proximal Convoluted                 microscope, J. Exp. Med., 1955, I02, 783.
                               Tubule Cells of the Mouse Kidney, Stockholm,       26.   ZETTERQVlST, H., The Ultrastructional Organi-
                               Karolinska Institute, Aktiebolaget Godvil,                 zation of the Columnar Absorbing Cells of the
                               1954.                                                      Mouse Jejunum, Stockholm, Karolinska
                      17.    ROTnMAN, S., Physiology and Biochemistry of the              Institute, Aktiebolaget Godvil, 1956.

                                                   B. L. i~VIUNGERAND S. W. BRUSILOW Eccrine Sweat Glands of Cat Foot Pad8               417

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