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The direction of hair after rotation of skin in the newborn albino ratA second experiment on hair slope.

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THE DIRECTION OF HAIR AFTER ROTATION O F
SKIN I N T H E NEWBORN ALBINO RAT: A
SECOND EXPERIMENT ON HAIR SLOPE
MILDRED TROTTER AND HELEN L. DAWSON
Department of Anatomy, Washington University, IPt. Louis, Missouri
TWO PLATES (FOURTEEN FIGURES)
The critical discussions by Landauer ( ' 2 6 a a n d b ) of the
theories of hair direction in mammals indicate that the facts
known can be understood from a uniform mechanical viewpoint. The principles of this viewpoint include certain facts
recognized in the development of the mammalian embryo,
vix., that there is a period when the rate of growth of the
skin remains behind the general body growth and consequently a gradual expansion and tension of the skin takes
place. The follicles and hairs which develop during the former period show a straight course vertically to the surface
of the skin, whereas, in the second period, the developing
follicles and their hairs follow the direction of the strain.
I n general, the direction of the hair is from head to tail, as is
also the direction of body growth in utero and for some time
after birth. The direction of the hair is indicated in the
earliest stages of development of the follicle before the hair
itself has been differentiated and this direction persists
throughout life regardless of any mechanical influence which
may have been exerted on the hair coat. Attempts to alter
the hair slope on mice (Schone, '14) and on guinea-pigs
(Trotter and Dawson, '31) have failed, but in both cases the
hair coat was established before the experiments were begun.
It would seem, therefore, that in order to alter the hair slope
the modifying influences would need to be exerted during the
developmental period of the follicles.
19
THE ANATOMIOAL RECOHD, VOL. 53, NO. 1
20
MILDRED TROTTER AND HELEN L. DAWSON
The albino rat, except for some sensory hairs about the
face, is born hairless. Fraser ('28) found that the earliest
hair follicles on the back are distinguishable in the hair germ
stage on the seventeenth day of fetal life and that the first
hairs erupted on the secorid day after birth. Schamberg and
Saleeby ('30) found that in the one-day-old rat an average
of from two to four follicles only per fold of skin were present, that in the two-day-old rat this number was doubled, and
by the third day there were ten to fifteen follicles per fold.
The greatest increase was between the third and fourth day.
On the fourth day they observed that some hairs had emerged
beyond the epidermis and by the seventh day the appearance
of hair was visible to the naked eye. A full coat of hair
was present by the sixteenth day, which was the climax of
what they consider one of the most rapid growths of hair in
animal life.
The newborn albino rat was chosen for our experimental
animal since the development of hair occurs for the most part
after birth. The problem was to alter the direction of the
hair slope in a given area on the back by rotating the skin
180°, thus bringing about an interchange in position of the
cephalic and caudal poles. Since the hair follicles and hair
develop after birth, the mechanical influences determining the
hair slope will be acting in the same direction as before with
reference to the axis of the rat, but in a reverse direction
with reference to the axis of the rotated skin. The question
then resolves itself into whether the hair slope on the rotated
skin will be directed toward the head o r toward the tail. If
the direction is toward the head, the implication would be
that either many follicles are present in the one-day-old rat
which have not been recognized or that something more than
mechanical influence is the determining factor ; if the direction is toward the tail, it would suggest that the mechanical
influence theory had stood an experimental test.
Sixty rats were subjected to the experiment, and the results of the thirty-six which survived are reported in this
paper.
SECOND EXPERIMENT O N HAIR SLOPE
21
METHOD
The procedure varied only in a few details from that reported for experiments on guinea-pigs ('31). Both of us took
part in the operations, one always working on the right side,
the other on the left. The operations were performed as
soon after birth as possible and, with one exception, always
within twenty-four hours. The rat was removed from the
nest quite unobtrusively. It was given a little ether and
on the right or left lumbar region a small arrow directed
toward the tail was drawn with India ink. With very small
scissors the area of skin on which the arrow had been placed
was cut out in the form of a square measuring from 8 to 10
111111. on a side. The cuts were made through the subcutaneous tissues down to the skeletal musculature. There was
very little hemorrhage. This square was then completely
separated from the underlying tissue and, with the arrow as
a safeguard against losing sight of the orientation, it was
rotated so that the direction of the arrow was changed from
caudad to cephalad. Thus, the position of the two poles of
the square were interchanged. Eight silk sutures were used
to fasten the square in place, one in each side and one in
each corner and drawn just tightly enough to bring into contact the cut margins. In most cases these stitches were
allowed to drop out of their own accord, which usually occurred some time before the sixteenth day. (Figure 2 shows
a stitch still in place in the ventrocaudad corner.) The surface of the square and the surrounding area were generously
smeared with warmed vaseline. ,
4 strip of cheesecloth,
trimmed so that the effect when tied around the body of the
rat was that of a signet ring, was adjusted with the broad
part superimposed on the wound. The margins of the bandage were made to adhere to the skin with collodion. The
effect proved to be lasting enough to keep the bandage in
place until it could be safely removed several days later. A
bandage was never allowed to remain on the rat longer than
five days and most were removed on the second day. Before
returning the rat to the nest its tail was tattooed with India-
22
MILDRED TROTTER AND HELEN L. DAWSON
ink dots for future identification. Ordinarily the mothers
did not seem to object to this treatment of their young and
became quite accustomed to having them removed from the
nest daily when examinations were made. Only occasionally
did a mother try to disturb the bandage or kill the young.
Healing took place by either first or second intention; in the
occasional case, when the patch sloughed, the rat was discarded. When the rats were old enough to be weaned the
males and females were placed in separate cages. Before
the imprints made by the stitches had disappeared, dots of
India ink were injected into the deeper layers of skin at the
four corners of the square. These India-ink deposits persist
throughout life and insure against the danger of losing the
square at later age periods.
The number of casualties was very much lessened during
the latter part of the operative period when we limited the
litters to not more than five or six young. I n the beginning,
litters of ten and eleven were used without elimination with
a resulting high mortality rate.
RESULTS
The direction of the hair slope was altered, but not in a
uniform manner. I n general, the directions on the rotated
areas fall into two classes, a ventrocaudad direction (figs. 5,
6, 13, 14) and a mixed direction (figs. 3, 4, i , 10, 11, and 12).
The term ‘mixed’ has been used to designate a combination
of two or more directions found on the same area of skin.
Such a combination might include both cephalad and caudad
directions with a dorsad or ventrad inclination, as well.
Other uniform directions which appeared only in single cases
include ventrad, ventrocephalad, and dorsocaudad (fig. 9)
slopes. The correlation between the kind of healing and the
direction is very marked (table 1 ) . The hairs which followed
the first intention process (fifteen cases) invariably were
directed ventrocaudally ; an equal number (fifteen cases) following second-intention healing presented a mixed direction ;
and the remainder (six cases) varied.
23
SECOND EXPERIMENT ON HAIR SLOPE
The sex of the rat and the side on which the operation was
performed could not be found to have any effect on the outcome of the experiment (table 2). Whether the healing was
by first or second intention, the most delayed cases were
completely healed within two weeks. I n a few of the cases
of second-intention healing, small necrotic areas developed
in the central portions of the square before sufficient circulation was established. The rotated area of skin, carrying the
India-ink injections as landmarks, began to increase in size
after healing had occurred and grew in proportion with the
body size of the rat. By the end of the second month the
average increase of these areas was two or two and one-half
times in length and one and one-half to two times in width.
'KIND OF REALINQ, BY INTENTION
DIRECTION
~
~
~-
First
~
I
TOTAL
______~
Second
__
Number
____
Per cent
Evidence of the greater increase in the cephalocaudad axis
over that of the dorsoventrad axis may be seen in the photographs of older rats (figs. 7, 8,13,and 14).
The development of the follicles and hair in the rotated
areas was retarded in proportion to the length of time it
took the wound to heal, whereas the hair on the undisturbed
skin was unaffected by the operation. The hair on the
squares was not visible on the surface even with the aid of
a watchmaker’s lens until the fifteenth, sixteenth, or seventeenth day. After this time its development proceeded at
the usual rate and by the thirtieth day the hairy coat, if
allowed to remain intact, appeared quite uniform. Even
though the direction of the hair on the rotated area was not
caudad, the quality of the hair on the rat permits it to blend
24
MILDRED TROTTER A N D HELEN L. DAWSON
somewhat with the surrounding hairs and a tendency to slope
in their general direction results (fig. 8). I n contrast to this,
the hair of the guinea-pig, because of its greater caliber,
TABLE 2
Details concerning the individual rats
NO. OF
RAT
SEX
SIDEOF
JPIRATION
5
M
R
8
M
L
14
16
17
19
21
23
F
M
F
F
R
26
27
M
M
L
R
28
M
M
F
R
33
34
35
37
39
40
41
42
43
44
45
46
48
49
50
51
52
53
54
55
56
57
58
59
60
R
L
L
1
DIRECTION OF
HAIR ON
KIND O F HEALING, BY I N T E N T I O N
ROTATED
I
AREAOFSKIN
1 Mixed
Second
Second
Second, with necrosis in center
First
Second, with necrosis in center
Second
IVentrocaudad
,Mixed
Mixed
elsewhere first
Secoiid
Second
Second, with necrosis in center
First
First
First
First
First
Second
'First, wit.. slight necrosis in center
First
Second
Second
Second, with necrosis in center
First
Second
First
Second, with necrosis in center
Second
First
First
Second, with necrosis i n center
Second
First
Second, with necrosis in center
First
Second
First
Wentrocaudad
Ventrocaudad
Ventrocaudad
Ventrocaudad
Ventrad
Mixed
Ventrocaudad
Mixed
Ventrocaudad
Mixed
Veil trocaudad
Ventroeaudad
Ventrocaudad
Mixed
Ventromphalad
Ventrocaudad
Mixed
Ventrocaudad
Mixed
Ventrocaudad
p::
M
F
M
P
F
M
F
R
L
L
L
L
L
R
M
F
F
M
F
F
R
M
L
L
L
L
L
R
I?
R
F
M
F
M
M
F
F
M
R
M
M
R
R
L
L
L
R
R
R
R
SECOND EXPERIMENT ON HAIR SLOPE
25
maintains the slope of the follicle throughout its shaft regardless of the slope of the surrounding hair. By clipping
the hair of the rat fairly close to the skin the true slope of
the hairs became obvious (fig. 7) or by clipping the hair in
the area immediately surrounding the rotated skin the slope
of the hair of the area in question was better shown (figs. 13
and 14). The direction of the hair was further examined
by sectioning the grafted skin of several rats; the direction
of the follicles and the portion of the shaft contained in
them invariably coincided with the direction of the free portion of the shaft. Thus, if there was a question as to the
actual slope, the area was clipped. However, no doubt as
to the direction ever arose while the hair was relatively
young and short. Since the direction of ihe follicles, once
established, does not change, an examination soon after the
hair on the rotated area appeared revealed quite the same
direction as any subsequent examination.
DISCUSSION
The aim of the experiment has been to test the theory that
the direction of hair slope is determined by mechanical influences. Areas of skin were placed in positions believed to
be ideally adapted to result in a reversal of the direction of
hair slope. If the experimental procedure had had no effect
on direction the hair would have sloped cephalad. However,
in no case did a cephalad direction occur. Therefore, it must
be agreed that the direction was altered. On the other hand,
in no case did the hair point caudad, which would have been
its direction if all the influences determining hair slope had
been unaltered. The question thus resolves itself into
whether or not the resulting directions of the hair can be
explained by mechanical influences.
I n the cases of second-intention healing and of those showing necrotic areas, scar tissue was involved and conditions
might appear not so favorable for testing the theory. However, it might be considered that the pull of a scar is a common, ordinarily unrecognized, example jn support of the
26
MILDRED TROTTER AND HELEN L. DAWSON
theory in question. The lines of strain hare been altered. It
is known that the direction of hair is toward a scar and one
of the best examples of this is afforded by the region around
the umbilicus in man. Because of the presence of the umbilical cord, the strain about the umbilical region must be present
during the fetal period when the hairs over the body are
developing. After birth when the scar heals the direction
of hair toward it persists. Other scars, the result of severe
wounds, often draw the surrounding skin so tightly that the
hairs whose direction has already been established cannot
withstand the strain and tend to converge toward the sear.
Certainly, the pull of scar tissue would be much more effective when follicles are just developing, as in these of the rat,
than on follicles already formed. The effect of the strain of
scar tissue seems to be much greater than the normal strain
due to growth, and would account for the variety of directions resulting on the areas of skin whose wounds healed
by second intention. Where the direction in these cases is
uniform and not mixed it would appear that the wound was
more severe in one part than in another and therefore the
strain was greatest in one direction. Where the injuries are
equally severe on two or more sides with or without necrosis
in the center the strain is produced in several directions, but
not necessarily in equal degrees, so that a confusion of slopes
results even on this relatively small area.
I n the cases of first-intention healing the scar was so slight
that in microscopic sections it could not be detected. The
presence of the carbon deposits from the India ink served
as a guide for the immediate vicinity of its location. Further evidence that the conditions are more nearly normal is
the fact that the directions of the hair slope on the areas
which healed by first intention are uniform, a ventrocaudad
one. I n this instance the question arises of how to account
for the ventrad inclination. A caudad direction, an exact
duplication of the direction of the undisturbed area on the
unoperated side of the rat, mi&t have been anticipated.
What influences might be present which were not acting when
SECOND EXPERIMENT O N HAIR SLOPE
27
the hairs developed at a slightly earlier period on the undisturbed skin of the opposite side? It would seem that two
factors, working together, might account for the ventrad
inclination. First, the follicles on the rotated area were
retarded in their development, and, secondly, the increased
rate of growth of the hind limbs over the other parts of the
body had set in. This faster growth on the part of the hind
limbs may tend t o swerve the strain on the skin from a cephalocauded direction to one more or less oblique, particularly
in the lateral lumbar region. The effect mould be very slight,
if at all, on the hair follicles which were already established,
but on those which were just forming (as those on the rotated
area of skin would be) it seems quite probable that the effect
would result in a ventrocaudad directioii of the hair slope.
SUMMARP
An area of skin on the lateral lumbar region of newborn
albino rats was rotated so that the positions of the caudal
and cephalic poles were interchanged. The development of
hair on the area in question was delayed for a period of
about fifteen days as a result of the operation. When the
hair did appear, the slope was either a venbrocaudad one or
a mixed one, depending on whether the healing of the wound
was by first or second intention. This finding gives support
t o the theory that the hair slope observed in the adult is
determined by the factors of tension effective at the time of
development of the hair follicle.
LITERATURE CITED
FxasER, DORISA. 1928 The development of the skin of the back of the alhiiio
rat until eruptioii of the first hairs. Anat. Rec., vol. 38, 110. 2,
pp. 203-224.
LANDAUER,
WALTER 1925 a O n thc hair direction in mammals. J. Maininalogy,
vol. 6, 110. 4, pp. 217-233.
1933 b Bemerkuiigeii zii Ludwigs Hypothese drr Morphogciiese dcs
Haarstrielis. Zoolog. Anzciger, Rd. 64, S. 235-245.
SCHAMBERG,
J. F., A N D SALEEBY,
$2. 1930 Growth in newly boru alhino rats.
Arch. Dermat. and Syph., vol. 22, pp. 34-39.
SCHONE,GEORGE 1914 Bcohachtuiigc~i iiber das Wachstum dcr Hsare. Die
1C’afur~~,isscnscliaften,
Bd. 2, R. 388-393.
THE ANATOMICAL RECORD, VOL. 5 3 , NO. 1
28
MILDRED TROTTER AND HELEN 12. DAWSOM
TROTTER,
M.,
AND DAWSON,H. L. 1931 The direction of hair a f t e r rotatioii
of skin in the guiiiea-pig: an experimeut on hair slope. Anat. Rec.,
1-01.50, 111’. 193-197.
PLATE 1
EXPLANATION O F FIGURES
Right-side operations.
1 R a t no. 27, teii days old. Shows retardcd healiiig 011 the veiitral aud
cephalic sides of the rotated area.
2 R a t 110. 27, fifteeii days old. H a i r oii rotated area not yct visible to iiakcd
eye. A stitch in veiitrocaudad coriier still in place.
3 R a t 110. 27, iiiiieteeii days old. Mixed direction.
4 R a t 110. 14, tmeiity-iiiiie days old. Mixed direction. Hair of surroriiirliug
area had beeii cut close t o skin.
5 R a t no. 16, twenty-nine days old. Vciitrocaudad direction. Hair of sur.
rouiidiiig area had been cut close t o s k h .
G R a t 110. 53, eighty-two days old. Veiitroeaudad direction. Hair of surrounding area had beeii cut close to skin.
7 R a t 110. 5, fifty-one days old. Mixed ilirectioii. Hair of rotated arca had
been cut t o about a 5-mix lriigtli; the surrounding hair was cut close to skin.
8 Rat 110. 5 , 185 days old. Aftcr cut hairs had regenerated. Shows the
teiideiicy f o r the hair of the rotated area to blend its directioii with t h a t of
geiicral body coat.
PLATE 1
SECOND EXPERIMENT ON H-ZIR SLOPE
3IILDRED TROTTER .4BD HELEN L. DAWSON
29
PLATE 2
Left-side oIwratioiis
9 Rat no. 23, eighteen days old. Dorwcaudad direction.
10 Rat no. 17, tliirtp-one days old. Mixed direction. Hair of suirouiiding
area had been eut elose t o skill.
11 Rat 1x0. 19, thirtp-one d a g s old. Mix-ed direction. Hair of surrounding
area liatl bei.11 eut close to skin.
1 2 Rat 110. 8, thirty-thrce clays old. Mixed dirrctioii Hair of surrouiidiiig
area liad been cut close t o skin.
13 R a t 110. 46, 144 days old. Shows the tcndei1c.g for the hair of the rotated
area t o blend its direction with that of general body coat.
14 Rat no. 46, 144 days old. T'rntrocaudad direction. ITair of snrrouiiding
a i c a liad lwei) cnt close t o skin.
20
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