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Diversity of cell types in epidermis of the mouse under normal conditions and following topical application of estrogen.

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DIVERSITY O F CELL TYPES I N EPIDERMIS O F THE
MOUSE UNDER NORMAL CONDITIONS AND
FOLLOWIPU'G TOPICAL APPLICATION
O F ESTROGEN1y2
CHARLES E. McCREIGHT AND WARREN ANDREW
Bowman Gray School of Medicine,
Winston-Salem, N . C.
EIGHT FIGURES
INTRODUCTION
Various investigators have observed cells in the epidermis
other than the types usually described for the several strata.
Lymphocytes appear frequently in epithelial tissues, having
migrated there as motile cells from the blood or connective
tissues. Kondo ('22) first reported these cells in epidermis.
Clear cells along the deep border of the epidermis were
observed by Masson ( '26)' who believed them to have a role
in pigment distribution. Pigmentary cells were observed by
Bloch ('27) and investigated at length by Billingham ('48,
'49), Billingham and Medawar ( '53)' and Reynolds ( '54).
MacCardle, Engman and Engman ('41) studied clear cells
in both pigmented and non-pigmented epidermis. Andrew
and Andrew ( '49, '54) found considerable proportions of
lymphocytes and clear cells in epidermis of the rat and of
man, as well as cells intermediate in morphology between these
types, and they suggested the replacement of Malpighian
cells of epidermis by transformation of lymphocytes via clear
I n p a r t f r o m a thesis prepared by the senior author as a partial requirement
f o r the Doctor of Philosophy degree a t The George Washington University.
Aided bg a contract between the Office of Naval Research of the Department of
tho Xavy and The Rownian Gray School of Medirinc, XR 102 024.
iG1
762
C. E. MCCBEIOHT A N D W. ANDREW
cells. Similar proportions of lymphocytes and clear cells for
the epidermis of the mouse were reported by Andreasen ( '52).
Mitotic figures have been observed among the Malpighian
cells of the epidermis in a number of species, although clearlydefined figures are rare under normal conditions (Thuringer,
'28; Andrew and Andrew, '49). Mitotic rliythin in epidermis
has been investigated by Ortiz-Picon ( '34), Blurncnfclc\ ( '39),
Cooper and Schiff ( '38)' Cooper ( '39), and Cooper and
Franklin ( '40). Little evidence of amitotic division of epidermal cells has been seen.
The principal objective of this study was to investigate the
cellular constitution of the epidermis of the mouse, including
the appearance and relative numbers of the various types
of cells and of mitotic figures that might be encountered. I n
addition, it was thought worthwhile to employ some treatment
to stimulate proliferation, a procedure which might be expected to affect the various cell types in different ways. It
was decided to use estrogenic ointment, with the hope of
clarifying in some degree the effects of this agent on the
epidermis. I n most instances estrogenic treatment of various
mammals has resulted in at least a n initial proliferation of
the epidermis (ICun, '37 ; Qoldzieher, '46 ; Bullough, '47 ; Eller
and Eller, '49 ; Dunaif and Finerty, '50). Prolonged treatment
results in thinning of the epidermis (Hooker and Pfeiffer, '43;
Sabella, Bern and Kahn, '51). Pincus ( '50) states that the
skin and integumentary system are clear target organs for
ovarian hormones, and this has been established in large
part by experiments with topical application.
MATERIALS AND METHODS
Skin specimens from 24 Swiss AlS-1 Albino and six C57
Black 'mice, 14 to 16 weeks old, were included in this study.
All of the albino animals were males. Seven of these received
no treatment. The black mice were of both sexes, and none
received treatment.
Nine male albino mice were given daily topical applications of small portions of estrogenic hormone cream, contain-
CELL TYPES I N EPIDER.MIS O F MOUSE
763
ing 10,000 I. U. of natural estrogen and estradiol per ounce.
This cream was rubbed gently for 5 minutes over the previously-clipped dorsal scapular area. Three animals were
sacrificed after one week and three others after two weeks
of this treatment. Meantime, one mouse died of unexplained
causes, and the two remaining animals were sacrificed after
three weeks of treatment. Lanolin was employed in identical
manner with 9 other male albino Cmice, three of which were
sacrificed at the end of each week for the three-week interval.
Thus there are 8 groups of animals to be considered (tables 1
and 2 ) .
All animals were sacrificed a t approximately 3 : 00 P.M.
Specimens of skin from the dorsal scapular region approximately 1em2 were fixed in 10% formalin, and paraffin sections
were cut at 6 .u. Harris' hematoxylin and eosin stain proved
adequate.
For each animal 1,000 cells in the epidermis were observed
and classified. Cell counts were limited to the basal and
spinous layers. Furthermore, it was decided to consider only
the portions of the epidermis lying between hair follicles,
where the surface epithelium is of more or less uniform thickness and uncomplicated by accessory organs, I n addition to
counts of ordinary resting Malpighian cells, records were
made of numbers and relative positions of lympliocytes, clear
cells, cells intermediate in morphology between these two
types, and mitoses of the several phases. An integral counter
proved of great benefit in recording these observations. Means
of cells of each category f o r animals in each group were calculated, and the differences of means for each category between groups of animals were examined mathematically for
significance, according to the methods of Hill ( '39). With an
ocular micrometer several measurements of thickness of the
epidermis of each animal were made, and mean epidermal
thicknesses for normal mice of each strain and f o r animals
which had received identical treatment were calculated. For
these determinations the stratum corneum was omitted, since
varying amounts of it may adhere in different instances. Ob-
764
C. E. MCCREIGHT AND W. ANDREW
servations were made with oil immersion light microscopy.
Photomicrographs were taken at identical magnification and
may be compared directly with one another.
OBSERVATIONS
The epidermis of untreated albino mice exhibits, at least
to some extent, all of the strata usually described for mammalian epidermis (fig. 1).As a rule the stratum germinativum
is two to three cells in thickness, while the stratum granulosum
is one or two cells thick. The width of the stratum lucidum,
where present, is negligible, and the stratum corneum of
the dorsal scapular region is a thin layer. The regular
epidermal cells of the Malpighian layer are polyhedral in
shape, and often they are somewhat flattened parallel to the
dermal surface. Their nuclei are vesicular, with one or more
prominent nucleoli. The stratum granulosum is present consistently, and the cytoplasmic granules, though distinct, are
small. Average epidermal thickness is 17.7 p (table 1). Lymphocytes constitute 4.26% of cells of the stratum germinativum
(table 2). They are located primarily in the basal layer and
vary in size and shape. The majority are spheroid, but
elongated lymphocytes are not rare. Clear cells make up
2.91%, and approximately two thirds are in the basal layer.
The cytoplasm of a clear cell usually forms a halo around the
nucleus, taking virtually no stain, and appears similar to
that seen in lymphocytes, though much more abundant. Sometimes the nuclei are eccentrically placed. Nuclei of clear cells
differ little from those of regular Malpighian cells in size and
staining characteristics. Certain cells, comprising 2.64% of
those of the germinal layer, exhibit characteristics that vary
between those of lymphocytes and clear cells. Following the
classification of Andrew and Andrew ( ’49, ’54), these have
been placed in a category termed “intermediate cells’’ (table
2). The nuclei are much darker than the vesicular type, but
not sufficientlychromatic to be classified as lymphocytes. The
cytoplasm is usually pale and ranges from slightly to much
765
CELL TYPES I N EPIDERMIS O F MOUSE
more abundant than in lymphocytes. An average of three
mitotic figures per 1,000 cells was observed (table 2). Almost
invariably they are located in the basal layer, and prophase
figures predominate. Evidence of amitotic cell division was
not seen.
TABLE 1
Epidermal thicknrss in mice of two strains and in animals treated as indicated.
Measurements included only t h e basal, spinou.9, and granular layers. An average
of three represrntative mea.stirenients f o r each animal was taken, and t h e m e a n f o r
cnch group is given here.
~
NO. OF
ANIMALS
THICKNESS OF EPIDERMIS
STRAIN
TRIGATMEN"
Microns
Cell layers
albino
none
17.7
3-4
C57 Black
ll0llC
12.0
2-3
albino
cstrogen
1 werk
30.0
6-8
albino
c s t rogcii
43.0
7-9
2 weeks
albino
cstrogc.11
3 weeks
25.0
4-5
albino
laiiolin
1 week
20.0
4-5
albino
1:uioliii
2 weeks
22.0
4-6
albino
laiioliii
3 weeks
20.0
3-5
The epidermis of the untreated black mice is considerably
thinner than that of the albinos (fig. 2). The average measurement is 12.0 p, and in some places the Malpighian layer consists
of a single layer of cells (table 1). The stratum granulosum
is present consistently as a thin layer. However, it is quite
distinct, and often the cyotplasmic granules are very large.
The granular appearance of the cytoplasm of Malpighian
cells is more pronounced in epidermis of these mice than in that
of albinos (compare figs. 1 and 2). Occasionally a narrow
766
C . E. MCCREIGHT A K D W. ANDREW
stratum lucidum is seen. Little or no pigment is noted within
the epidermal cells, but a segmental arrangement of dense
aggregations of very dark pigment granules, corresponding
to the “shingle arrangement” of the cuticle of the hairs, is
seen within the hair shafts. I n the female this pigment seldom
appears below the skin surface, but in the male it reaches
down almost to the bulbs of the hair follicles. No other sex
differences were observed. Lymphocytes in the epidermis
of the black mice are in proportions quite similar to those
for the albinos, while clear cells and intermediate cells are
slightly more numerous. Only 0.12% of the epidermal cells
of the C57 Black strain appeared to be in process of mitosis
(table 2).
The most obvious change in the epidermis of the male albino
mice following topical estrogenic applications is a marked
thickening of both the stratum germinativum and the stratum
granulosum. After one week of treatment the epidermis
measured 30.0 p in thickness and contained approximately
twice the number of cell layers seen f o r untreated animals
(table 1 and fig. 3 ) . Kuclei were slightly larger on the whole.
Granules, or aggregates of the same, were large and conspicuous in the cytoplasm of cells of the granular layer. Increases in lymphocytes, clear cells, and intermediate cells all
proved significant statistically. Mitotic figures were 9 times
as frequent as in untreated specimens (table 2 ) . After estrogenic treatment for two weeks nearly all the changes seen
after one week were accentuated. The epidermis was two and
a half times as thick as that of untreated animals and contained numerous cell layers (table 1). Nuclei of the stratum
germinat ivum were greatly hypertrophied. The st ratuni
granulosum contained dense masses of granules, which practically obscured cellular detail, and scattered granules were
seen in adjacent cells of the Malpigliian layc’t (fig. 5). Lymphocytes a i d the intermediate typcs of cells were even morc
numerous than after one week of estrogenic treatment, but
clear cells were in proportions only slightly greater than in
untreated specimens. Cells in mitosis had increascd to 3.53%
767
CELL TYPES I N EPIDER.MIS O F MOUSE
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768
C. E. MCCREIGHT A N D W. A N D l l E W
of the total cell population, or over 10 tinies as ireyucrit as iii
untreated epidermis (table 2). Three weeks of estrogenic applications resulted in an epidermis thinner than that of the
animals treated for one week (fig. 7 and table 1). Howcvei-, all
categories of the special cell types under consideration were
more numerous than in epidermis of untreated animals, ~ h i l e
clear cells reached the greatest proportion seen during estrogen administration, and mitoses were approximately as
numerous as after two weeks of applications (table 2).
Applications of lanolin resulted in epidermal thickening of
only moderate degree, but here also the efect was greatest
after two weeks of treatment (figs. 4, 6, 8, and table 1).
Specimens at the end of each of the three weeks of the
procedure contained greater proportions of lymphocytes and
intermediate cells than did the epidermis of untreated mice,
and clear cells were in even greater porportions than following
estrogenic treatment. However, mitotic figures were fewer
than in epidermis of untreated mice (table 2).
DISCIJSSION
The epidermis of the mouse is quite thin when compared to
that of the human with its many layers of cells. I n spite of this
fact the epithelium contains all the strata commonly described
for the mammalian epidermis (Cowdry, '32 ; Maximow and
Bloom, '52). Furthermore, the cells of the individual strata
appear to possess no outstanding cytological differences from
those of human epidermis. However, they differ in shape,
and in the epidermis of the mouse a basal layer of cylindrical
cells is not common. Usually the cells of this layer are polyhedral in shape, and they may be elongated in the direction
parallel t o the dermal surface. The epidermis of the C57
Black mice is considerably thinner than that of the albinos,
and a single layer of cells may compose the entire stratum
germinativum.
I n a study of age changes in the skin of albino rats, Andrew
('51) found no stratum granulosnm in the epidermis of the
CELL TYPES I N EPIDERMIS O F MOUSE
769
ear, abdomen, or back in young and middle-aged rats, but this
stratum was conspicuous in the epidermis of the same areas
in the senile animals. I n all of the young adult mice of the
present study the stratum granulosum was present consistently in the dorsal scapular region.
The percentages of lymphocytes in epidermis of mice of both
strains compare closely and are only slightly greater than
those recorded for the same animal by Andreasen ( '52) and for
the rat and man by Andrew and Andrew ('49, '54). Also,
the occurrence of these cells in the basal layer and deeper
portion of the spinous layer agrees with the findings of these
investigators. We cannot agree with Billingham and Medawar
( ' 5 3 ) that there is any possibility that the cells in question
are not lymphocytes. Andreasen ('52) stated that he had seen
evidence of degeneration of lymphocytes in the epidermis,
but this could not be confirmed from our observations. No
evidence of karyorrhexis, karyolysis, or pycnosis was seen.
I n spite of the deeply chromatic nuclei of lymphocytes, the
presence of some internal structure in them generally was
recognizable. The proportion of clear cells in epidermis of
the mouse compares closely with the findings of Andrew and
Andrew ( '49, '54) for the human, but is less than their average
findings for the rat. The intermediate types of cells are two
to three times more numerous in the epidermis of the mouse
than reported by Andrew and Andrew ( '49, '54) for the rat and
man. Nevertheless, individual interpretations as to the categories into which many of the cells should be placed necessarily would vary considerably with different observers.
The significant difference in percentages of mitotic figures
in the epidermis of the untreated albino and black mice is unexplained, Identificaion of mitotic figures, especially early
prophases, often is difficult, and there is considerable chance
of error. Although the proportion of cells of the Malpighian
stratum seen in mitosis appears to be small for these animals,
it is larger than that reported by Andrew and Andrew ('49,
'54) for the rat and the human and many times greater than
that observed by Thuringer ('28) in human epidermis. The
770
C. E. M C C R E I G H T A N D W. ANDREW
mouse is a iiocturnal animal, and the time of day at which
sacrifice was made represents a portion of the daily cycle
during which epidermal mitosis occurs more frequently than
during night hours (Ortiz-Picon, '34 ; Blumcnfeld, '39 ; Cooper
and Franklin, '40). It appears reasonable to assume that
even though mitosis may not be the only means of replacement of cells of the epidermis of the mouse, it well may be the
principal mechanism. The various cell types and intermediate
forms observed by Andrew and Andrew ( '49, '54) in epidermis
of the rat and man were seen in that of the mouse and indicate
that a transformation of lymphocytes to regular Malpighian
cells in this species is at least another possible means of
replacement.
The initial increase in epidermal thickness following estrogenic treatment is in accord with most of the earlier investigations. The decrease at the end of the third week of
the applications is somewhat in conformity with the findings
of Hooker and Pfeiffer ('43) for the rat, except for the time
element, which was longer, actually months, before thinning
was noted by these workers. Dunaif and Finerty ('50) obtained similar thinning for rats after dosage with high levels
of estrogen. The presence of excessive amounts of mitotic
activity in the stratum germinativum of the mice following
topical estrogenic applications indicates that mitosis must
be the major factor responsble for the large increase in numbers of cells. However, the fact that mitotic activity had
decreased very little in epidermis of animals treated for
three weeks from that noted in specimens after two weeks of
treatment, in spite of the decrease in cell population, indicates
that mitosis may not be the sole factor responsible for the
hyperplasia seen with the shorter periods of treatment.
Butcher ('51) reported little o r no effect froni applications
of lanolin on the skin of rats. Proliferation of moderate degree occurs in the epidermis of albino mice in our inaterial.
However, mitosis is depressed below normal proportions, and
the method of increase of cell population mas not determined.
The relatively great proportions of clear cells in all stages
C E L L TYPES I N E P I D E R M I S O F MOUSE
771
of lanolin treatment of the epidermis are outstanding in the
present series.
SUMMARY
1. The dorsal scapular epidermis of young adult albino and
C57 Black mice contains all strata typical of mammalian
epidermis. However, the epithelium is thin, especially that
of the black animals. The stratum germinativum contains in
places only a single layer of cells. The stratum granulosum is
present consistently.
2. Approximately 90% of the cells of the stratum germinativum of both strains are of the regularly described
Malpighian type. The remaining 10% consist of over 4%
of lymphocytes, approximately three per cent of clear cells,
and three per cent of cells intermediate in morphology between
lymphocytes and clear cells. Mitotic figures are rare in epidermis of both strains, but over twice as numerous for the white
as for the black mice.
3. Marked thickening of the epidermis of male albino
mice following daily topical applications of estrogenic cream
reaches a peak at the end of the second week. Cell population
of the stratum germinativum is increased greatly, and percentages of lymphocytes, clear cells, and intermediate cells in
this stratum are significantly greater than in untreated specimens. Mitotic figures are 10 times as numerous.
4. Thickening and hyperplasia of lesser degree and large
percentages of clear cells are seen after lanolin applications,
but mitotic figures are fewer than in untreated epidermis.
5. The hyperplasia following estrogen applications is assumed to be related primarily to the greatly increased incidence of mitosis, but that in epidermis treated with lanolin
is not accounted for in this study.
LITERATURE CITED
E. 1952 o n the occurrence of the lymphocytes in the normal
epidermis. Acta derm. vener. Suppl., Stockh., 32: 17-21.
ANDREW,W. 1951 Age changes in the skin of Wistar Institute rats with
particular reference to epidermis. Am. J. Anat., 89: 283-320.
ANDREASEN,
772
C. E. MCCREIGHT AND W. ANDREW
ANDREW,w . , AND N. v. ANDREW 1949 Lymphocytes i n the normal epidermis of
the rat and of man. Anat. Rec., 1 0 4 : 217-241.
1954 Lymphocytes i n normal epidermis of young, older middleaged, and senile rats. J. Gerontol., 9: 412-420.
BILLINGHAM,R. E. 1948 Dendritic cells. J. Anat., 86: 93-109.
1949 Dendritic cells in pigmented human skin. J. Anat., 83:
109-1 15.
BILLINGHAM,
R. E., A N D P. B. MEDAWAR 1953 A study of the braiichccl cells of
the mammalian epidermis with special reference to the f a t e of their
division products. Phil. Trans. B., 837 : 151-171.
BLOCH,B. 1927 Das Pigment. In : Handbuch der Haut- urid Geschlechtskrankheiten, 1, Springer, Berlin.
BLUMENFELD,
C. 11. 1939 Periodic mitotic activity i n the epidermis of the
albino rat. Science, 90: 446-447.
BULLOUGH,H. F. 1947 Epidermal thickness following oestrone iiijections in
the mouse. Nature, 15.9: 101-102.
BUTCHER,E. 0. 1951 Effects of applications of various substances on epidermis
of rat. J. Invest. Dermat., 1 6 : 85-90.
COOPER,Z. K. 1939 Mitotic rhythm in human epidermis. J. Invest. Dermat.,
2 : 289-300.
1940 Mitotic rhythm in the epidermis of
COOPER,2. K., AND H . C. FRANKLIN
the mouse. Anat. Rec., 78: 1-8.
COOPER,Z. K., AND A. SCHIFF 1938 Mitotic rhythm in human epidermis. Proc.
Soc. Exp. Biol. and Med., 33: 323-324.
COWDRY,E. V. 1932 “The Skin,” i n Cowdry’s Special Cytology, 2nd ed.,
1: 1-38,
Paul B. Hoeber, Inc., New York.
DUNAIF,c. B., AND J. C. FINERTY
1950 The effects of estrogen adminstration
upon epidermal proliferation. J. Invest. Dermat., 15: 363-371.
ELLER,J. J., AND w. D. ELLER 1949 Estrogenic oiiitinents. Cutaneous rffeets
of topical application of natural estrogens, with report of threc
hundred and twenty-onc biopsies. Arch. Dermat. and Syph., 59 :
449-464.
GOLDZIEHER, M. A. 1946 The effects of estrogens on the senile skin. J.
Gerontol., 1 : 196-201.
HILL, A. B. 1939 Principles of Medical Statistics, 2nd od., The Lancet Limited,
London.
HOOKER,
C. W., AND C. A. PFEIFFER1943 Effcets of sex hormones upon body
growth, skin, hair, and scbaceous glands i n the rat. Endocrinol.,
9%’: 69-76.
KONDO,K. 1925 (1922) Studien iiber die Wanderzellen i n der Haut. I. Mitt.
Uber die Wanderzcllen in der Epiderinisschiclit 8on Menschen und
Kaninchen. J a p . Jour. Med. Sciences, 2 : 59-60 (abstracted in German
from thc Japanese i n Kyoto Ig. Z., 19: 386-407).
KUN, H. 1937 Wirkungen des Follikelhormons auf die H a u t hie Yerkutaner
Verabreichung. Histologische Untersucliungen an Infantilen und
Senilen Ratin. Wien. Klin. Wchnschr., 50: 408-41 1.
CELL TYPES IN EPIDERMIS O F MOUSE
773
MACCARDLE,
It. C., M. F. ENGMAN,
JR.,AND M. F. ENGMAN,
SR. 1941 Histology
of neurodermatitis. Arch. Dermat. and Syph., 44 : 161-189.
MASSON, P. 1926 Les naevi pigmentaires, tumeurs nerveuses. Ann. d ’anat.
path., 3: 417-453.
MAXINOW,A. A., AND W. BLOOM 1952 A Textbook of Histology, 6th ed., W.
€3. Saunders Co., Philadelphia.
J. 112. 1934 Uber Zellteiluiigsf requenz und Zellteilungsrhythmus
ORTIZ-PICON,
in der Epidermis der Maus. Ztschr. f . Zellforsch. u. mikr. Anat., Bd.,
1 9 : 488-509.
PINCUS,
G. 1950 “The Physiology of Ovarian Hormones,” in Pincus and
Thimann’s The Hormones, 1st ed., 2 : 1--31.
REYNOLDS,J. 1954 The epidermal melanocytes of mice. J . Anat. Lond., 88:
45-58.
SABELLA,
J. D., H. A. BERN AND R. H. KAHN 1951 Effect of locally applied
vitamin A and estrogen o n r a t epidermis. Proc. Sor. Exp. Biol. and
Med., 7G: 499-503.
J. M. 1928 Studies on cell division i n the human epidermis. 11.
THURINGER,
A. Rate of cell division i n the prepuce. B. Influence of various factors on cell division. Anat. Rec., 40: 1-13.
PLATE 1
EXPLANATION OF FIGURES
Magnification of all the photomicrographs is X 675, and the stain is Harris’
hematoxylin and eosin.
Epidermis of untreated male albino mouse. Note the stratum germinativurn
of two to three cell layers i n thickness and the distinct stratum granulosum.
There is a lymphocyte in the basal layer a t the right and another near the
basal layer a t the left. These may be compared with the lymphocytes i n
the dermis benrath and their similarity is observed.
Epidermis of untreated female C57 Black mouse. This epidermis is thinner
according t o actual measurements and i n cell layers than t h a t of the albino
mouse. Three heavily stained lymphocyte nuclei are seen in the epidermis.
Epidermis of male albino mouse a f t e r one week of applications of estrogenic
ointment. The stratum gerrninativum is 4-6 cells in thickness and the stratum
graiiulosum is two or iiiore rrlla thick. The granules of the latter 1:tyer are
large and form aggregates.
Epidermis of male albino mouse a f t e r oue week of applicntions of lanolin.
The Malpighian layer is threr to four cells thick and the stratum granulosum
is prominent. Note ari intermediate type of cell i n the bnsal layer near the
left side of the picture. It has a small halo of cytoplasm, and the nucleus
shows characteristics of both lymphocyte and regular Malpighian cell. To
the l e f t of this cell is a n irregular nucleus of a lymphocyte. A mitotic
figure in metaphasc coiifiguration lies just above the basal layer and slightly
to the right of the center of the photomicrograph.
Epidermis of male albino mause a f t e r two weeks of applications of rstrogenic.
ointment. Marked thickening of the stratum germinativum and many hyper
chromatic nuclei in and iiear the basal layer are outstanding. Several clear
cells a r e seen scattered throughout the Malpigliian stratum. Observe the great
enlargement of individual nuclei compared with those of the epidermis of
the untreated albino animal shown above.
Epidermis of male albino mouse after two weeks of applications of lanolin.
Little difference in thickiiess either of the stratum germinativum or of the
stratum granulosum from t h a t of the animal treated oiily one week and
shown above is seen. Several lpiphocytes lie along the bnsal layer.
Epidermis of male albino mouse a f t e r three weeks of applications of estrogenic
ointment. The epidermis is much thinner than t h a t of the animals t h a t received like treatment f o r one or two weeks, and the nuclei of the Malpighian
cells are little larger than those of the untreated specimens. A prominent
lymphocyte is seen about the center of the photomicrograph niid slightly superficial to the nuclei of the basal cells.
Epidermis of male albino mouse after three weeks of applications of lanolin.
THe epidermis at this stage is somewhat thinner than a f t e r two weeks of the
treatments and comparable with t h a t of the animals which were treated with
lanolin for oiily one week. Note the prominent lymphocytes a t the left side
of the picture and the clear cell in the basal layer j u s t to the right of ceut,er.
774
CELL T Y P E S I N E P I D E R M I S O F MOUSE
C.
E. MCCRICIGHT AND W. ANDREW
PLATE 1
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