ACTA
`
`D EERMATO -VENEREOLOGICA
`
`VOLUME 50
`1970
`
`The Society for the
`
`Publication of Acta Dermato-Venereologica
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`Uppsala 1970
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`Acta Dermatovener (Stockholm) 50: l6l—l68, 1970
`
`BIOPHYSICAL STUDIES OF THE NORMAL NAIL
`
`Bo Forslind
`
`From the Department of Medical Physics, Karolinska Irtstitutet,
`Stockholm, Sweden
`
`Abstract. The keratin filament organization in the normal
`hum..~.;i nail has been investigated by means of micro
`X—ray diffraction. The X—ray data obtained have been
`correlated to electron microscope and light microscope
`findings concerning the structure and histology of
`the
`hard tail plate. Analyses of the calcium content in normal
`hutnan nails have also been performed. These investiga-
`tions
`show that
`the hardness of
`the nail can be ex-
`plained on the basis of cell arrangement, cell adhesion,
`and lite ultrastructural arrangement of the keratin fibrils.
`
`A thorough knowledge of normal nail histology
`and .:f the structural organization of the cell con-
`tacts as well as of the intracellular components is
`essential in explaining the functional properties of
`the nail. Such information will also provide ‘a
`basis for a better understanding of pathological
`concmions of the nail. In the past, most studies on
`the human nail have been confined to investiga-
`tions by means of
`the light microscope. The
`recei": publication by Hashimoto et al. (7) is one
`of
`the first comprehensive electron microscope
`investigations of the normal nail structure.
`In ‘ihe present report, in order to facilitate the
`interpretation,
`the findings are described in rela-
`tion -,o a coordinate system superposed on the
`nail plate. The x- and y-axes in this coordinate
`system lie in the plane of the nail plate,
`the
`Z‘3Xl1 being at
`right angles to this plane. The
`x-axis is chosen to lie in a direction parallel to the
`growth direction, the y—axis at right. angles to the
`form 1‘ axis (Fig. 2).
`The morphology of the nail plate. Macroscopi-
`C311_V, the normal nail plate has double curvatures.
`The tmgitudinal curvature lies in the (x, z)-plane,
`the transverse curvature lying in the (y, z)-plane.
`At tic light microscope level most of the details
`have been exhaustively explored (8, 9, 10, 15).
`The nail plate (Fig. 1) was earlier described as
`
`11— 702803
`
`a uniform sheet of keratinized cells originating
`from a ventral matrix in the proximal nail fold.
`This matrix was considered to terminate at
`the
`
`distal end of the lunula. The fully developed nail
`plate is supported by the part of the nail bed distal
`to the lunula (9. 15).
`The modern terminology originates from the
`work of Barton Lewis (10) who describes the nail
`as derived from three different epidermal sites.
`The dorsal nail plate (D) is formed by the dorsal
`matrix constituting the most proximal parts of the
`roof and the floor
`in the proximal nail
`fold
`(D1)/I). The intermediate nail plate (I) is formed by
`the nail matrix of the floor of the proximal nail
`fold distal
`to the dorsal nail matrix. The distal
`border of this matrix coincides with the distal
`
`border of the lunula (L). The soft ventral nail
`plate (V) is derived from the tissue lying distal to
`the lunula border. In longitudinal sections the root
`matrix of the intermediate nail plate is seen to
`overlap the matrix of the ventral nail plate at the
`lunula border. Support for Lewis’
`interpretation
`has been given by Hashimoto et al.
`(7), among
`others.
`
`Dynamic aspects of the nail growth has been
`provided by an autoradiographic study reported
`by Zaias & Alvarez (19).
`Organization of the keratin fibrils in nail cells.
`Studies on the orientation of the keratin fibrils
`
`within the nail cells have been performed by
`Astbury & Sissons (l) as well
`as by Derksen,
`Heringa & Weidinger (3) on nails comprising both
`dorsal and intermediate nail plates. The main
`bulk of keratin fibrils were found to be oriented
`
`perpendicular to the growth axis of the nail plate
`and parallel
`to -the nail surface, mainly in the
`y-axis direction.
`
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`162 B. Forslind
`
`
`
`the normal nail.
`1. Schematic representation of
`Fig.
`D, Dorsal nail plate; I, intermediate nail plate; V, ventral
`nail plate; L,
`lunula; E, eponychium;
`IM,
`intermediate
`nail plate matrix; DM, dorsal nail plate matrix; Ep,
`epidermis; De, dermis; B, bone of phalanx; Fm,
`free
`margin of nail plate; M, proximal border of nail plate
`matrix.
`
`in relation to its
`the nail
`Investigations of
`hardness. The hardness of the nail has been attri-
`
`buted to an alleged high content of calcium (8).
`No quantitative data to support this proposal have
`been published. Disulphide bridges of cystine are
`known to stabilize the fibrous keratins. The cys-
`tine content of mature nails. 9.4% by weight,
`is relatively high when compared to a value of
`1% in callus and 4.1% by Weight
`in stratum
`corneum disjunctum (14). Other biophysical stu-
`dies on the nail are rare, the exceptions being in-
`Vestigations on the indentation hardness (12) and
`on the strength of nails (18).
`So far there has been no attempt to relate re-
`sults from investigations of the morphological or-
`ganization of the cells, and /or the structural or-
`ganization of the keratin fibrils within the cells to
`the physical properties of the different parts of the
`nail plate, or to the nail plate as an entity. An
`X-ray diffraction study of the macromolecular
`organization of epidermal keratin was published
`by Swanbeck in 1959 (17).
`The present work is concerned with the normal
`nail structure in an attempt to relate the structural
`organization of keratinized tissues to their func-
`tional properties. The terminology suggested by
`Lewis (10) is used in the present communication
`and only the hard nail plate,
`i. e. the dorsal and
`the intermediate nail plates are considered in this
`report.
`
`Acta Dermatovener (Stockholm) 50
`
`METHODS AND MATERIALS
`
`and small
`Electron microscopy. Human nail clippings
`dissected tissue blocks from monkey nail
`roots (' hesus
`rnacacus) were fixed in buffered 1% osmium tetroxide
`(13) for 20 min. In an attempt to improve the c .1trast
`some clippings were fixed for 72 hours. Dehydration and
`embedding in Epon followed the principles given 1:, Luft
`(11). Sections were obtained with glass knives on an LKB
`Ultrotome set for a section thickness of 600 A. Hcgever,
`it was not possible to obtain such thin sections of this
`resistant material which displaces the zone of maaimum
`shear stress away from the knife edge. The sections were
`transferred by means of a hole grid (6)
`to a saitrated
`solution of uranyl acetate for 40 to 60 min at 60°C (2)
`for contrast enhancement. After rinsing in doubly distilled
`water the sections were mounted on carbon-coated grids
`and examined in a Zeiss EM 9 electron mici‘oscope at
`50 kV and at primary magnifications of x1700 and
`>< 7000. High
`resolution micrographs
`(X 20 00k‘.
`and
`x 40 000) were obtained in a Siemens Elmiskop I, owrated
`at 60 kV.
`X-ray diffraction. Human nail clippings from 5 P".-‘S035
`of both sexes and of different age (8 weeks to 35 years),
`with no known skin or generalized disease, as W‘l1 35
`nails from 2 monkeys (Rhesus macacus) were used as
`specimens. A Chesley micro X-ray diffraction cimefa
`(Norelco) collimated with a glass capillary having 21 difl'
`meter of 300 [um was used in the experiments. In irdef
`to record possible short spacings some specimens VVGTC
`exposed in a wide angle flat film camera with the 2211119
`collimation which had a specimen to film distance Of
`50 mm. Nickel—filtered CuKa-radiation (/‘.=l.54 A} W35
`used throughout the experiments. The nail clippings Were
`exposed with the primary X-ray beam parallel
`tr
`the
`z-axis (Fig. 2 a) or parallel
`to the y-axis (Fig. 2 (J) or
`parallel to the x—axis (Fig. 2 c), so as to give X-rag’ difl‘
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`
`Biophysical studies of the normal nail
`
`163
`
`Re|atio': between incident
`beum and nail coordinate
`system
`
`Diffraction
`plane per-
`pendicular
`to incident
`beam
`
`Planes repre-
`sented in the
`diffructogrum
`
`Chesley diffractogrom
`
`
`
`F1'8. 2. X-ray diffraction experiments on nail clippings
`with regresentation of the relation between the incident
`X‘TaY beam and the nail plate and the diffractograms.
`The latier represent patterns obtained from the interme-
`diate nail plate with the exception of pattern ed which
`
`is from the dorsal nail plate. Magnification, ><2.
`Horizontal arrows in pattern ct
`indicate 3.9 A, 4.3
`A and 5.2 A reflexions reading downwards. Vertical em
`rows indicate 27 A and 8.8—l0.8 A equatorial reflexions.
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`‘
`
`to
`resistant
`termediate nail plate. was also less
`mechanical stresses (cf. Fig. 3) since large pieces
`of this structure were easily loosened ans’
`sepa_
`rated from the dorsal nail plate at the free margin,
`In the electron micrographs little structi.ral de.
`tail except for the cell membrane were teen at
`primary magnifications at and below X 4000 due
`to the Very dense sections of the mature n..il. The
`cells of the dorsal nail plate appeared very flat
`with their smallest diameter perpendicular to the
`nail plate surface in the z-axis direction. The in-
`tercellular space between these cells was occupied 1
`by a substance. that was electron-dense and which
`filled the intercellular space completely. Some-
`times the central dense line was bisected by a
`faint
`intermediate line. The total width of this
`
`‘
`
`_
`
`164 B. Forslind
`
`Table 1. Calcium content of human nails determined
`by atomic absorption spectroscopy
`All specimens consist of finger nail clippings from both hands
`of the subject except for BF1 which contains toe nail clippings
`and GU2) which contains a mixture of finger and toe nails
`
`(Ca)
`Total
`Weight of
`fat-free
`Volume
`weight
`Specimen
`specimen
`(ml)
`%
`
`
`BF I
`BF II
`BF‘
`01
`RL
`Ll
`Si
`BN1
`BN II
`
`BF 6—8
`BF 9-10
`G15?)
`
`0.5033
`0.0586
`0.2506
`0.3168
`0.1910
`0.1361
`0.8770
`0.1953
`0.0555
`
`0.1070
`0.1789
`0.4956
`
`conc. HCI
`25
`3
`25
`25
`25
`25
`25
`25
`3
`
`cone. I-[N03
`25
`25
`25
`
`0.095
`0.184
`0.084
`0.107
`0.100
`0.081
`0.089
`0.072
`0.084
`
`0.079
`0112
`0.188
`
`three dimensions. Diffraction
`in all
`grams from the nail
`also
`obtained
`from the
`different
`registrations were
`morphological entities of the nail clippings, i.e. the dorsal
`(D) and the intermediate nail plate (I). after dissection in
`a low-powered light microscope.
`X-ray diffraction patterns obtained from porcupine
`quill tips served as identification standards for oi-keratin.
`Ca/citmt determination. Human nail
`clippings were
`collected from 7 persons of both sexes (age 11-43 years)
`with no known general or skin deseases. The collection
`period covered 8 months in order
`to reduce possible
`short—term variations. After several washings in diethyl
`ether to make specimens fat-free,
`the clippings were im-
`mersed in concentrated hydrochloric acid for 7 days or
`more in order to extract the calcium present. In two cases
`the clippings were ground into a powder before the acid
`treatment. Some of the clippings were dissolved in con-
`centrated nitric acid which also dissolved the organic por-
`tion. The determination of calcium was performed on a
`Perkin Elmer Atomic Absorption Spectrophotometer Type
`290 with reference solutions containing 40 ppm calcium
`in the form of calcium chloride in concentrated hydro-
`chloric acid or concentrated nitric acid (Table 1).
`
`RESULTS
`
`Electron. microscopic investigation. At low magni-
`fications the information obtained confirmed the
`
`results from light microscope investigations. Dur-
`ing dissection of the nail clippings under the light
`microscope it was found that the border between
`the dorsal nail plate and the intermediate nail
`plate constituted a natural cleaving plane. The in-
`
`Acta Dermatovener (Stockholm) 50
`
`In
`junction. measured up to 250 A (Fig. 4 a).
`contrast
`to the almost straight cell membranes
`of the dorsal nail plate the borders of th.
`inter-
`mediate nail plate cells had a much more incan-
`dering outline in the section. The distribution of
`.
`dense intercellular substance was more or 3 ss dis-
`continuous and the intercellular space filled by ‘
`this substance was >200 A (Fig. 4 b).
`in the
`intermediate nail plate cells, a preferred Irrienta-
`tion of the keratin filament in the y—axis direction
`was recognized at higher magnification.
`In the electron micrographs the histochemically
`demonstrated border between the dorsal and the
`
`‘
`
`intermediate nail plates (10) Was not obvi..-us but
`the differentiation characteristics between these
`
`two layers were seen to be achieved by an almost
`continuous change in the cell adhesion ‘attern.
`Juvenile and adult mature human nails as well as
`
`monkey nails were similar in nature With respect
`to the organization seen in the electron micro-
`graphs. A slightly undulating CO11ltfiClL
`line 176‘
`tween the cells of the dorsal nail plate an; ‘r1
`€10‘
`minant filament orientation in the y-axis direc-
`tion constituted the difference between the trans-
`
`verse sections and the longitudinal sectins tie‘
`scribed above.
`X-ray diffraction experiments. The X-143’ dip
`fraction experiments were performed on ui:*1'€at‘7d
`nail clippings containing the dorsal and .interme'
`diate nail plate as Well as on the untreated f.:.O13led
`constituents.
`In the experiments with the X‘”y
`beam coinciding with the z-axis
`a pattern of
`rather extended arcs or almost circular re; 67410115
`were obtained (Fig. 2 a). A somewhat higher Or’
`der of orientation was revealed with the X‘ray
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`beam coinciding with the y-axis (Fig. 2 b). How-
`ever, with the incident beam in the x-axis direc-
`tion ,. pattern of good order was obtained,
`indi-
`gating a main fiber orientation in the (y, z)-plane
`(Fig '2 c). No significant differences between nails
`from zhildren and from adults or between hu-
`man and monkey nails were found.
`It tecame apparent that the degree of orienta-
`tion ir the X-ray patterns could be related to the
`different portions of the nail plate described in
`rccen.‘ literature (7,10). The X-ray diffraction pat-
`terns from the isolated dorsal nail plate and the
`isolated intermediate nail plate had the same ge-
`neral features as had the patterns from compound
`nail glippings. However,
`in the intermediate nail
`pjate, with the X-ray beam coinciding with the
`3--zixis shorter arcs as Well as greater detail indi-
`cated an increased orientation of the keratin ma-
`terial is compared with a similar registration from
`the dorsal nail plate. This keratin pattern from
`the intermediate nail plate much resembled that
`of huzsian hair fibres in its relative Wealth of dif-
`fraction maxima (Table II).
`The diffraction patterns. contained no informa-
`tion :f a separate phase (e.g. a calcium mineral)
`in either the dorsal or the intermediate nail plate.
`The atomic absorption spcctrophotometric ana-
`lyses if the calcium Content in normal nails show
`only traces of this element. As can be seen in
`Table I, no single value exceeds 0.2% by weight.
`
`DISCUSSION AND CONCLU SIONS
`
`The electron microscope investigation demon-
`strateri that the continuous cell
`junctions in the
`dorsa‘ nail plate were similar to the tight
`junc-
`tion type of cell contact, zonula occludens, de-
`scribed. by Farquhar & Palade (4). whereas the
`somewhat wider and discontinuous junctions of
`the intermediate nail plate resembled the inter-
`rncdi .-fie junction type, zonula adhaerence.
`The mechanical properties of the nail plate are
`partly related to the properties of the cells consti-
`tuting the different nail plate units. In the dorsal
`plate it
`is
`therefore conceivable that
`the inter-
`cellular junctions permit a good interaction be-
`llW6C‘.‘
`the cells, and thus a highly rigid plate is
`formed. In the intermediate nail plate the inter-
`loekL;:g cell borders denote a large cell surface in
`comparison with the cell volyme. This part of the
`nail plate has more plastic properties than is ob-
`
`Biophysical studies of the normal nail
`
`165
`
`Table II. X-ray diffraction observation on nail
`clippings
`S : Strong, M = Medium, W = Weak
`
`Nail
`
`Intensity
`
`Porcupine quill tip
`
`Observed equatorial reflexions
`27 A
`s
`53.8-10.8 A
`s
`
`Observed meridional ref/exions
`
`23 A
`5.2 A
`4.3 A
`3.9 A
`
`M—W
`s
`M—S
`M
`
`(Q)
`27 A
`9.2.10.5 A
`
`6’)
`24.5 A
`5.18 A
`4.2 A
`3.9 A“
`
`a Data obtained from G. Swanbeck in Aspects of Protein
`Structure (ed. G. N. Ramachandran), pp. 93-101. Academic
`Press, New York, 1963.
`b Data obtained from A. Lang: An X-ray Study of or-keratin.
`II. Diffractometcr measurements of the complete diffraction
`pattern of Canadian porcupine quill. Acta Cryst 9: 446-451,
`1956.
`C Data obtained from W. T. Astbury-J. W. I-Iaggith: Pre-
`Transformation stretching of the so—called 5.1 A and 1.5 A
`spacings in oc—keratin. Biochim Biophys Acta 10: 483 490,
`I953.
`
`served in the dorsal nail plate (Fig. 3). Referring
`to the dorsal nail plate it is interesting to note that
`the intercellular coupling of the cortex cells in
`hair fibers is very similar to that of the dorsal
`nail plate in terms of widths and continuity as
`seen in electron micrographs.
`The details of the X-ray diffraction patterns
`obtained from nail clippings showed close resem-
`blance to those obtained from porcupine quill tips
`
`the preferred fibrous keratin
`which represent
`specimen for X-ray diffraction (Table II). The
`degree of fibrillar orientation is reflected in the
`X-ray pattern and a low degree of orientation is
`revealed as arcs or even complete circles. A high
`degree of orientation gives arcs reduced to dots in
`cases of perfect alignment of the fibers. Generally,
`a greater number of reflexions is then seen in
`comparison with disoriented patterns.
`In the
`X-ray diffraction photographs from nail clippings,
`the specimen possessing the highest order of
`fibrillar orientation showed a meridional 5.2 A
`reflexion characteristic of fibrous or-proteins. In
`these cases it was also possible to see the broad
`equatorial reflexions corresponding to spacings of
`25-27 A and 10 A, characteristic of oz-keratin.
`
`The equatorial arcs of the X-ray patterns were
`Acta Dermatovener (Stockholm) 50
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`
`166 B. Forslind
`
`
`
`3.
`Fig.
`Photograph of nail clipping sectioned in the
`>< 50. The lamellar
`(35.2)-plane. Oblique incident
`light,
`structure of the dorsal nail plate is suggested in the left
`hand part of the photograph. The oblique lamellae of the
`intermediate nail plate are
`artefacts
`imposed by the
`shearing forces of the scissor edge which compressed the
`plastic material of the intermediate nail plate.
`
`due to the preferred orientation of the keratin
`fibrils. However, the spread in angular distribu-
`tion,
`i.e. wider arcs, was more pronounced in the
`dorsal nail plate. This supports the concept of a
`fibril arrangement that provides for the torsional
`rigidity of the plate and a high breaking strength.
`The Water content of living cells is known to be
`about 70% by weight. Under different conditions
`of relative humidity the water content of stratum
`corneum varies significantly (16), a fact which is
`related to its
`relatively high content of water
`soluble substances (>20 % by weight). This value
`is high in comparison with that of hard keratin
`(14). No quantitative data concerning the content
`of Water-soluble substances in the isolated dorsal
`
`and/or intermediate nail plate have been pub-
`lished.
`In the hair follicle a decrease in Water
`
`content occurs at a stage where the protein syn-
`thesis appears to have ceased (5). This favours the
`concept that the final consolidation of hard kera-
`tinized cells includes water deprivation. It is con-
`ceivable that such a water deprivation can intro-
`duce a disturbance of the fibrillar orientation or-
`
`der. Complementary investigation by means of
`water substitution in not-fully-consolidated nail
`root cells as well as drying of such cells in com-
`bination with X-ray diffraction methods should
`provide information on the filament lattice defor-
`mation introduced by water deprivation.
`The information gained from the electron mic-
`rographs and the X-ray diffraction experiments
`revealed a fibril orientation in the plane of the
`A0111 Dermatovener (Stockholm) 50
`
`nail surface, the (x, y)-plane, with a pronounced
`orientation in the y-axis direction (Fig.
`Such
`an arrangement provides a reinforcement prevent-
`ing cleavage of the nail in the growth direction
`(x-axis direction) which would otherwise: easily
`damage the nail root.
`
`If calcium minerals were of importance in pro.
`ducing the hard structure of the nail, as believed
`by several authors, the mineral should be expected
`to appear in the form of apatite or calcite =":ysta1s
`as encountered in bone,
`teeth, and shells. Such
`crystals ought
`to show a preferred orientation
`within the nail plate giving a crystal patten in the
`X-ray diffraction experiments even if the mineral
`content were comparatively low. Using histo:.*’t1emi-
`cal methods, Jarret & Spearman (8) have demon-
`strated a calcium content
`in nails although no
`quantitative data are given in their report.
`.11 the
`very soft ventral nail plate a comparativelv high
`calcium content was reported, only sl.ightry less
`than that of the dorsal nail plate. This ‘ zplies
`that any calcium mineral phase present would
`hardly be of importance to the hardness
`the
`nail plate. Using calcium-EDTA to chela‘,
`and
`remove related. metals in alizarin. red stained sec-
`
`tions thosc authors have probably intror'lue...i cal-
`cium into the tissue and their result shorld be
`taken with some caution. The low calcium con-
`
`tent reported in the present study makes it un-
`likely that a calcium mineral salt
`is responsible
`for the strength of the nail. If the hardness of the
`nail plate were due to some other mineral
`lt we
`would likewise expect it to appear as a separate
`crystalline phase in the X-ray diffraction photo-
`graphs. A possible mode of interaction b=“WC€l1
`the calcium ions and the keratinized tissue is,
`
`the capacity of these ions to Lplace
`however,
`to a great extent
`irreversibly, under
`protons,
`physiological conditions. Such an exchange would
`be expected to influence the physical iproper‘."es of
`the fibrous protein and on the tissue.
`The present inVe:stigati.on indicates some func-
`tional, relationships between the cellular arr inge-
`mcnts, the cell junction types, and the structure of
`the nail plate. At the macroscopic level the cutting
`property can be ascribed to the arrangement Of
`the dorsal and the intermediate nail plates. The
`dorsal nail plate, per se,
`is rather brittle an! the
`nail plate as a whole gains in strength by the
`cooperation of the dorsal and the intermediate
`nail plates. The method employed for m2=‘;;in8
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`
`Biophysical studies of the normal nail
`
`167
`
`Fig. 4 (a). Section through
`the dorsal nail plate in the
`(x, z)-plane. (b) Section
`through the intermediate nail
`plate in the (x, Z)-Plane. Pri-
`mary magnification,
`>< 20 000.
`
`sharp razors by enclosure of a very hard and-
`brittle core between two sheets of comparatively
`plastic material
`illustrates the function of
`the
`
`composite design. In the razor the brittleness of
`the material forming the cutting edge is counter-
`acted by making the central core thin and flex-
`ible, permitting bending deformation without un-
`due stresses in the brittle material of high elastic
`modulus. The necessary rigidity of the razor is
`attained by enclosure in a non-brittle, easily de-
`formable material which can take strain under
`
`stress relaxation due to plastic flow. In the nail
`the most
`important force vector has a zpalmar—
`dorsal direction,
`ie. coinciding with the z-axis.
`Consequen-tly,
`the deformable material
`is posi-
`
`tioned on the palmar aspect of the brittle dorsal
`nail plate.
`For any plate—like structure a considerable gain
`in the load-carrying capacity is attained by the in-
`troduction of a double curvature to prevent
`la-
`teral buckling. The longitudinal curvature (in the
`(x, z)-plane) in the normal nail plate could be due
`to a difference in growth rate between the cells
`in the nail plate and / or to a pressure forming the
`curvature. Pressure-induced curvature would,
`in
`
`the present case, originate from the pressure of
`the tissue proximal
`to the eponychium, which
`constitutes the roof of the proximal nail fold and
`the opposed growth pressure. The connective
`tissue forms what could be called a “dorsal band”
`
`Acta Dermatovener (Stockholm) 50
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`
`168 B. Forslind
`
`which has ventral connections with the periosteum
`of the distant phalanx serving as an anchorage for
`the connective tissue. At the microscopic level the
`epidermis of the dorsal part of the eponychium is
`continuous with the epidermis of the roof of the
`proximal nail fold (Fig. 1). This latter epidermal
`area has a straight border towards the connective
`tissue. Such an arrangement is conceivable if it is
`recognized that the tissue of the roof of the nail
`told is exposed to the constant forces of the grow-
`ing nail plate and the pressure of the connective
`tissue “dorsal band”. Such forces are likely to
`introduce an orientation of growing cells leading
`to a lamellar shape of the cell aggregates in ver-
`tical
`sections. The dorsal nail plate originating
`from the deepest part of the proximal nail fold
`is the first part of the hard nail plate to become
`fully keratinized. The more distal
`the origin of
`the cells forming the hard nail plate the less is the
`pressure of the ‘dorsal band” and the pressure of
`growth and, consequently, the tendency to a finite
`lamellar form of the cells. The vertical section
`
`through the nail plate as seen in electron micro-
`graphs fully agrees with this interpretation. Such a
`pattern of growth will produce an apparent dif-
`ference in growth speed of the cells of the dorsal
`nail plate compared with those of the lower part
`of the intermediate nail plate. Autoradiographic
`experiments (19) give ample support to this inter-
`pretation‘. In autoradiographs of longitudinal nail
`sections obtained at a stage where the labelled
`areas of dorsal and intermediate nail plate have
`passed the lunula,
`the developed silver crystals
`appear in a rather sharp line in the intermediate
`nail plate whereas the line is broader and blurred
`in the dorsal nail plate.
`
`ACKNOWLEDGEMENT
`
`The calcium analyses were performed at the laboratory of
`Svenska BP in Stockholm through the generous courtesy
`of its director Mr Raoul Niklasson and with the able
`assistance of Mr Bo Dahl. For assistance in making‘
`electron microscopic preparations
`I
`thank Mrs
`Ingrid
`Jusinski.
`from the Swedish Association for
`Financial support
`Medical Research and from grant FG-SW—105 of
`the
`US. Department of Agriculture is gratefully acknowledged.
`
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`Acta Dermatovencr (Stockholm) 50
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`
`Received February 2, 1970
`
`B0 Forslind, M.D.
`Department of Medical Physics
`Karolinska Institutet
`S-104 01 Stockholm 60
`Sweden
`
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