and this accounts in part for the great tenderness of corns. But the
primary and essential feature of a corn is a thickened state of the
cuticle. This is caused by too great rapidity in its formation, and
is, usually, dependent upon pressure, especially if the pressure be
combined with some friction. Hence corns are most commonly found upon
the foot, and upon the parts of the foot, where the skin is subject to
pressure and rubbing against the shoe. The drawing shows the appearance
presented by a vertical section through a corn and through a small
portion of the skin on either side. The accumulated layers of cuticle
are seen, and the enlarged papillæ shooting up into them. I need
scarcely add that it is owing to ignorance, or something worse, when
corn-cutters talk of curing the malady by taking out the _roots_; for,
corns, evidently, have no roots.
One word of advice about corn-cutting. Most persons have some
experience in this art, and some opportunity of practising it on
themselves; and many pride themselves on their skill in it. The
usual plan is to shave off layer after layer from the whole surface
of the corn; and this, by lessening the projection of the corn, may
give relief for a few days, though it does not always do that. Soon,
however, the distress returns; and the area of the corn increases
after each operation. Now, I would have you observe that it is at the
_middle_ of the corn that the papillæ are most enlarged; and it is
here that the formation of cuticle goes on most quickly, giving rise
to the little white cone or cones often seen in a corn and sometimes
wrongly called the roots. The proper mode is to confine the cutting to
this part, and to remove as much of the thickened cuticle as you can
from this spot, digging, as it were, a hole in the middle and leaving
the circumference intact. The circumference, which is not usually
tender, thus forms a wall round the excavated centre and defends it
from pressure; and great relief is experienced. Further benefit will
be found from covering the corn with some soft adhesive plaster; and
you may sometimes, with advantage, lightly apply common caustic before
putting on the plaster. If you follow these directions carefully you
may be your own chiropodists, and almost defy your bootmakers.
If, in cutting a corn, you go too deeply, you will wound the tops
of the papillæ and cause some bleeding; this is not however usually
followed by any ill consequences.
_Nails._
Almost all vegetable as well as animal surfaces are covered with some
kind of cuticle. It forms the smooth exterior of a leaf and the rind
of an apple; and the soft down of a moth or a butterfly, the scales of
fish, the feathers and claws of birds, the quills of the porcupine, the
horns of oxen and the hoofs of the horse are examples of modifications
of cuticle. NAILS and HAIR are also of this nature. They are both
continuous with the cuticle, and peel off with it when it is, by any
process, separated from the skin. Both are formed, like the cuticle, of
compressed plates or scales matted together; and these are continually
being shed or rubbed off on the one side, and supplied from the rete
mucosum on the other.
The rete mucosum, it should be stated, extends over the whole surface
of the body. In most situations, as already mentioned, it is the medium
from which the ordinary cuticle is produced; but on the upper part of
the ends of the fingers and toes it is converted into nail, and in the
hair follicles, as I will presently describe, it is transformed into
hair.
[Illustration: Figs. 75, 76, 77. Longitudinal sections of Nail.]
The drawings will help you to understand the relation of the nails to
the cuticle and the cutis. In the upper of the three (fig. 75)
the nail with the cuticle has been detached from the cutis, so that
the continuity of the two, at either end, is shown. In the middle one
(fig. 76) it is represented lying in its bed in the cutis; its
thin hinder edge being received into a furrow made for it in the cutis.
The layer of rete mucosum (_b_) extends behind and beneath it, between
it (_d_) and the cutis (_c_), and continually adds fresh material to
the nail, just as, in other parts, it adds to the substance of the
cuticle. The cuticle, or white line (_a_) is continuous with the nail
at the sides as well as at either end. The lower figure (77) shows the
bed of the cutis in which the nail reposes, the nail as well as the
adjacent cuticle and the rete having been cleared away.
Thus the addition from the rete--in other words the growth of the
nail--takes place at the hinder edge and at the under surface. In
consequence of the addition from _behind_ the nail is increased in
length and is pushed forward; and as it advances forwards it receives
accessions from _beneath_, which increase its thickness and strength.
Unless they be cut, or worn down, the nails grow to an indefinite
length; and, when they extend beyond the tips of the fingers, their
edges are bent in towards each other, and they become curved like
claws. This tendency to a convex form is shown also if the nails be
not properly supported by the pulps of the fingers. For instance, when
persons become emaciated the pulps of the fingers usually participate
in the general wasting and the nails become curved. Hence this shape
of the nails has been regarded as an indication of consumption. You
will understand, however, from what I have said that it is not really
a symptom of any one particular disease. It simply indicates that,
from some cause or other, the nutrition of the body is not properly
maintained.
The Dervishes in some parts of Asia allow the thumb-nail to grow long,
and then pare it to a point, so as to be able to write with it. Dr
Wolff, the Eastern traveller, has told me that he has repeatedly seen
this done, and that he has in his possession manuscripts written in
this way.
[Illustration: Fig. 78. Transverse section of Nail Rete and Cutis.]
Beneath the nail the cutis is disposed in a series of parallel ridges
(fig. 78) with intervening furrows. These take the same direction
as the nail, and, indeed, give rise to the fine lines that you see upon
the surface of the nail. The rete mucosum, or deep soft layer of the
nail, extends into the furrows between the ridges, just as the soft
stratum of the cuticle extends between the papillæ of the cutis. It
thus serves to keep the nail steady in its place, while it permits a
certain amount of movement, and allows the nail to slide forwards upon
the skin under the pressure caused by the growth at its hinder edge.
A little in front of the root of the nail the ridges of the cutis
suddenly become larger and more vascular. This gives a pink hue to
the nail in the greater part of its extent; while the hinder portion,
separated from the front by a crescentic line, is white, in consequence
of the subjacent cutis being there, more pale. You will, at once,
recognise the distinction between these parts by looking at your own
nails.
The ridges and furrows serve, like the papillæ in other parts of the
skin, to increase the surface of the cutis; and, by affording more
space for the distribution of the vessels and nerves, they contribute
to the sensitiveness of the part, and account for the severe pain which
is caused when any foreign body is thrust under the nail. The pulp
in the interior of a tooth, and the frog of a horse’s foot, are also
instances in which an exquisitely sensitive structure is placed beneath
a hard or horny substance. The object, in each case, is the same, viz.
to give the power of taking cognizance of impressions which are made
upon the surface.
_Hairs._
HAIRS may also be regarded as modifications of the cuticle, because,
like the nails, they are continuous with the cuticle, and are formed
from the rete mucosum. Each hair (figs. 79 and 83) is received
into a depression of the cutis, which is called a “follicle,” and which
is lined, as far as the bottom, by cuticle (_a_), and rete mucosum
(_b_). At the bottom of the follicle (_d_) the cuticle is absent, and
the hair rests, directly, upon the rete; and, at this part, the rete,
instead of being converted into cuticle, as it is at the sides of the
follicle, becomes transformed into hair, in the following way.
[Illustration: Fig. 79. Hair.]
[Illustration: Fig. 80.]
[Illustration: Fig. 81.]
[Illustration: Fig. 82.]
The cells of which the rete is composed swell out as they ascend,
and so form the soft “bulb” of the hair. The outermost cells are
gradually flattened, and assume an imbricated arrangement, overlapping
one another like the tiles upon a roof (fig. 79, _e_, and
fig. 80); and those in the interior are elongated, so as to be
converted into more or less distinct fibres. The cells nearest the
middle, or axis, of the hair remain moister and softer than those
nearer the exterior, and form what is sometimes called the “marrow” of
the hair (figs. 81 and 82).
The colour of the hair is given by the presence of minute grains of
colouring matter, like those in the cuticle of the Negro. They are
formed in the cells at the root of the hair, and pass up with them into
its structure. The quantity of colouring matter is usually slight in
infancy and childhood, and increases during adolescence. Hence the hair
becomes darker as we grow up. It is more or less deficient in the grey
hair of old age; and in the instance of Marie Antoinette, and others
whose hair is said to have turned grey in a few hours, the colouring
matter is supposed to have been destroyed by some fluid, formed from
the blood, and passing, through the pulp, into the hair.
The hairs serve to protect the skin; and, as a general rule, they
are most abundant upon the parts which are most exposed, and which,
therefore, stand most in need of such protection. They are scattered
over the back of the hand. On the palmar surface they are not required,
and they would have interfered with the sense of touch; and we do not,
accordingly, find them there, nor upon the sole of the foot, nor upon
the edges of the lips. In certain parts of some animals, however,
they serve as valuable adjuncts to the tactile organs by extending
the range within which the contact of surrounding substances is felt.
Thus the whiskers of the cat are set upon papillæ so sensitive that
the slightest touch upon any part of the hair is felt; and the animal
is thereby assisted in threading its way in the dark. This provision,
added to the mode in which their feet are muffled with soft hair and
their claws are retracted, enables the members of the feline tribe to
steal with almost absolute stillness upon their prey.
_Oil-glands._
[Illustration: Fig. 83. Hair, and Oil-glands.]
There are also in the skin a number of little GLANDS. One set of
these are called “oil-glands;” for their office is to furnish an oily,
or waxy, substance, which serves to keep the skin soft and pliable,
and defends it against too much moisture, or too great dryness of the
atmosphere. They are usually, as shown in the accompanying sketch,
(fig. 83, _g_, _g_) connected with the hairs, lying beside them; and
their ducts--the little tubes that carry off the oily matter formed in
them--open either into the hair follicles, or penetrate the cuticle at
some other part. They are not found on the palms of the hand or the
soles of the feet, because those parts are, in great measure, sheltered
from atmospheric influences, and are well moistened with perspiration.
When the dry easterly winds prevail one is disposed to wish that these
glands were more numerous on the back of the hands; for a more liberal
supply of their secretion would, probably, prevent the disagreeable
chapping to which we are subject at those times. As a substitute we
resort to some unctuous matter, such as glycerine, which if frequently
applied in small quantities performs, to some extent, the part of
the natural secretion in keeping the cuticle soft and supple, and so
preventing its cracking.
The secretion of these glands has an odour, the purpose of which,
in man, is not very obvious. It is faintest in the highest and most
civilized nations. In none is it very agreeable; and persons are
fain to conceal it by substituting some other odour, as that of
lavender or eau-de-cologne. Unfortunately the choice is not always so
refined; and one is, sometimes, disposed to think that the natural
odour must be very bad, if the substitute be preferable. The odour
varies at different parts of the body; it varies also in different
persons, sufficiently to enable the acute nose of the dog to track one
particular man among a thousand.
_Sweat-glands._
To revert to the figure (70) at page 165, the little masses at
_g_, _g_, are grains of fat lying in the meshes of the deeper strata
of the skin, or in the structure just below it. And the little balls
of twisted tube (_f_, _f_) are GLANDS that secrete the PERSPIRATION;
for, the perspiration does not ooze up from the whole surface of the
skin, but has a regular system of factories for its formation. A fine
tube (_h_) is seen passing from each of these “sweat-glands,” as they
are called. It curls in a spiral manner, like a cork-screw, where it
traverses the cuticle to open at the surface. On the palmar aspect of
the hand most of these tubes or ducts open along the tops of the fine
ridges which are there seen; and with a magnifying glass of moderate
power you can distinguish their orifices on the flattened tops of
the ridges on your own fingers. These are the “pores of the skin,”
respecting which we hear so much, and through which the Roman Bath
brings such streams from the subjacent glands.
The sweat-glands are scattered all over the body, but are especially
numerous in the palm and in the sole; and the moisture issuing from
them tends to keep the skin of these parts soft and moist, and so
fitted for the reception of tactile impressions. The quantity of fluid
furnished by them varies a good deal in different persons, and under
different circumstances. In some persons it is habitually slight; and
the hands feel dry and harsh. Or, what is equally disagreeable, it is
superabundant; and the hands are habitually damp, perhaps, cold and
clammy, staining the gloves and soiling everything they touch. In fever
the perspiration is defective; and the dryness and heat of the palm
are often the first symptoms of an accession of fever that attract the
patient’s notice.
We all know that perspiration is usually increased by exercise, or
by the application of warmth to the surface, as by the hot air in
the sudatorium of the Roman Bath; and then, by its evaporation, it
cools and relieves the body, and contributes to our comfort. We know,
too, that it is liable to be increased by any thing that produces a
depressing effect, and that it then induces an uncomfortable sensation,
chilling the surface too much, and making it cold and clammy. Most
of you have experienced the discomfort of the cold sweat caused by
fright; and some of you may have felt the cold, clammy hand of one who
was suffering under the shock of a severe accident or the prostration
caused by the sudden onset of a dangerous malady. Why perspiration
should occur under these very different conditions, producing, at one
time, so much relief, and, at another, so much additional discomfort,
it is not easy to say.
_The sense of Feeling and of Touch in the Hand._
I have mentioned three parts of the body as remarkable for the
acuteness of the sense of touch, namely, the TONGUE, the LIPS, and
the HANDS. Now in each of these the skin is richly supplied with
nerves and blood-vessels; and it is also thick and lies upon a soft
cushiony substance, so as to be yielding and to admit of being applied
accurately over any surface with which it is placed in contact, and of
again resuming its shape when the pressure is removed. For instance,
the tongue is so soft and yielding that, when it is applied to a tooth,
it dips down between the inequalities and coves accurate information of
the condition of the whole surface. The same is the case with the edges
of the lips, though not in so marked a degree as in the tongue; and
each of these parts is indebted for its great sensitiveness very much
to the delicate soft supple nature of its structure. The palmar surface
of the hand too, though, like the skin of the sole, it is strong and
tough, so as to offer considerable resistance to injury and to prove
no dainty morsel even to dogs, as we surmise from the narrative of the
death of Jezebel, is yet very soft and yielding. It is also underlaid
by a stratum of fat interwoven with strong fibres of tissue, just in
the same manner as the skin of the sole of the foot (fig. 46,
p. 99).
An accumulation of this fat and fibrous tissue under the skin forms
the “Pulps” at the ends of the fingers. The slightly conical form and
exquisite softness of the Pulps adapts them well for the examination of
the surfaces of bodies; and the sense of touch is more acute in them
than in other parts of the hand.
[Illustration: Fig. 84. Bones of Finger.]
In connection with them it is interesting to observe that the last
bone of each finger and of the thumb swells out, at the end, into a
nodulated lump, which serves the purpose both of supporting the pulp
and of giving breadth to the nail. It also, like the corresponding part
of the toe (page 99), affords a basis of attachment for the fibres
that run, from the bone, through the pad of fat, to the skin, and give
firmness and consistence to the part. The bulbous enlargement at the
ends of the phalanges of the fingers and toes is peculiar, or almost
peculiar, to man. In most Animals these bones taper to a point; in
many they are also curved. Hence the nails are, in them, comparatively
unsupported, and they become bent in at the sides and curved in their
length, that is to say, they are formed into claws. This is the case,
to a considerable extent, in the Monkey. The terminal phalanges of
the monkey’s digits are more tapering than in man; the nails are more
claw-like; and the pulps are less well-formed. This constitutes a not
unimportant feature of difference between the hand of that animal and
the human hand, in addition to those I have already mentioned.
You have experienced the sensitiveness to cold of the pulps of
the fingers and toes; and have, probably, remarked that it is more
difficult to keep them warm than any part of the body. I may add that,
notwithstanding the liberal allowance of the means of supporting life
(that is, blood and nervous influence) which they enjoy, they are very
liable to mortify from frost-bite and other causes. I have repeatedly
known that to happen when all the rest of the hand has escaped. This
must be attributed, perhaps entirely, to their exposed position as
terminal parts; and they share their susceptibility to cold with other
parts similarly circumstanced, such as the nose, the elbows, the knees
and the buttocks.
It is necessary to make a distinction between the SENSE OF TOUCH and
common FEELING or sensitiveness to pain; for they are not quite the
same. They are, it is true, very nearly alike, so nearly that we may
consider them to be modifications of one another; and it is probable
that the same nerves minister to both. Still there is a difference.
The sense of touch is the sense of contact with _ex_ternal bodies, and
enables us to take cognisance of their presence and inform ourselves of
their shape, consistence, smoothness or roughness, &c.; whereas common
sensation, or the sense of feeling, has an _in_ternal relation. It
imparts to us information respecting the condition of our own bodies or
any part of them. By the sense of touch in the tongue, for instance,
we judge of the size and hardness of the morsel in the mouth; and by
common sensation we learn that the organ is being bruised or scratched
by it. Sensation of pain commonly destroys the sense of touch. Put your
finger into a vice, and you may feel both sides of it. Screw it up, and
you have nothing but the sensation of pain. If you were to awake in
this state you would not, from the mere sensation, know that you were
_touching_ anything.
As a general rule there is a relation between the degree in which
sensation and the sense of touch are manifested in different parts of
the body. For instance, I have just been remarking on the acuteness of
the sense of touch in the Tongue; and we know that this part is very
sensitive to pain. The pain caused by a bite of the tongue is horrible;
and so effectually does it serve the good end of warning the tongue to
keep within its proper bounds, that that organ very rarely suffers from
the pressure of the teeth.
But, forasmuch as sensitiveness to pain serves a different purpose
from the sense of touch, namely, as in the instance of the tongue just
mentioned, it renders parts alive to injurious impressions, and gives
them warning to escape or protect themselves; so it is, as we might
expect, most manifested in those surfaces where a slight amount of
injury would prove most detrimental.
Thus, the membrane (the conjunctiva) which lines the eyelids and
covers the front of the eyeball is exquisitely sensitive to pain. We
are reminded of this when anything touches the eye, or when a fly
has lodged itself under the eyelid. And, when an operator wishes to
ascertain whether his patient is sufficiently under the influence of
chloroform he separates the eyelids and puts his finger gently upon
the eye, knowing that if no indication be given, by flinching, that
the impression made here is felt, it is probable that the patient will
not be conscious of the more severe impression to be made by the knife
elsewhere. Yet, this membrane is by no means pre-eminently endued with
the sense of touch. Indeed, the very acuteness of its sensitiveness to
pain quite unfits it for distinguishing the quality of the impressions
made upon it. We know very quickly that something is in contact with
the eye, but can form no idea what kind of substance it is, whether it
be hard or soft, rough or smooth.
In the hand, on the contrary, the sensitiveness to pain, though
considerable, is not proportionate to the acuteness of the sense of
touch. The sting of the rod on the palm, if my recollection serves me
right, is not so sharply felt as it is upon that other region which
shares with the hand the privilege of receiving the wrathful attentions
of the master; and, yet, that other region is by no means distinguished
for acuteness in the sense of touch.
The mode in which sensitiveness to touch and to pain are adjusted
in the hand and in the eye in relation to the functions of these two
organs is one of the admirable features of their construction. Suppose
the disposition to have been reversed--suppose the hand to have been
as tender as the eye--of what use would it have been? The contact of
a particle of dust would have caused agony; or, had the eye been no
more sentient than the hand, it would soon have been destroyed by the
chafing of foreign bodies upon its delicate surface.
How important is the sense of Feeling! more important than any of
the other senses; more so than all the others taken together. It
is almost universal in the animal kingdom. Indeed, we can scarcely
conceive animal existence without it, and are slow to admit that to be
an animal which shows no sign of it. Several of the lower animals seem
to be destitute of any of the other senses. The POLYPS, for instance,
have no sight, hearing, taste, or smell, and are dependent, therefore,
entirely, upon feeling for their communication with the external world;
and the range of this sense is extended in them by means of their
“tentacles” or “feelers” which wave about in the water, and, when they
come in contact with foreign bodies, close upon them and draw them
towards the oral opening. Thus, the tentacle of the polyp is a sort of
rudimentary hand, and, by the aid of feeling, fulfils one important
function of the hand, viz. that of the supplying the mouth with food.
The sprawling movements of an infant’s hands and the tendency which
they have to close upon anything--dress, blanket, or whatever it
be--and draw it to the mouth remind one forcibly of the feelers of a
polyp.