A Practical Physiology
by
Albert F. Blaisdell
Part 5 out of 9
which may be of any shade between a light yellow and an intense black. It
is this that gives the great variety in color. Generally with old people
the pigment is absent, the cells being occupied by air; hence the hair
becomes gray or white. The thin, flat scales on the surface of the hair
overlap like shingles. Connected with the hair-follicles are small bundles
of muscular fibers, which run obliquely in the skin and which, on
shortening, may cause the hairs to become more upright, and thus are made
to "stand on end." The bristling back of an angry cat furnishes a familiar
illustration of this muscular action.
[Illustration: Fig. 100.--Hair and Hair-Follicle.
A, root of hair;
B, bulb of the hair;
C, internal root sheath;
D, external root sheath;
E, external membrane of follicle;
F, muscular fibers attached to the follicle;
H, compound sebaceous gland with its duct;
K, L, simple sebaceous gland;
M, opening of the hair-follicle.
]
Opening into each hair-follicle are usually one or more sebaceous, or
oil, glands. These consist of groups of minute pouches lined with
cells producing an oily material which serves to oil the hair and keep the
skin moist and pliant.
238. The Nails. The nails are also formed of epidermis cells
which have undergone compression, much like those forming the shaft of a
hair. In other words, a nail is simply a thick layer of horny scales built
from the outer part of the scarf skin. The nail lies upon very fine and
closely set papillæ, forming its matrix, or bed. It is covered at its
base with a fold of the true skin, called its root, from beneath
which it seems to grow.
The growth of the nail, like that of the hair and the outer skin, is
effected by the production of new cells at the root and under surface. The
growth of each hair is limited; in time it falls out and is replaced by a
new one. But the nail is kept of proper size simply by the removal of its
free edge.
239. The Sweat Glands. Deep in the substance of the true skin, or in
the fatty tissue beneath it, are the sweat glands. Each gland
consists of a single tube with a blind end, coiled in a sort of ball about
1/60 of an inch in diameter. From this coil the tube passes upwards
through the dermis in a wavy course until it reaches the cuticle, which it
penetrates with a number of spiral turns, at last opening on the surface.
The tubes consist of delicate walls of membrane lined with cells. The coil
of the gland is enveloped by minute blood-vessels. The cells of the glands
are separated from the blood only by a fine partition, and draw from it
whatever supplies they need for their special work.
[Illustration: Fig. 101.--Concave or Adherent Surface of the Nail.
A, border of the root;
B, whitish portion of semilunar shape (the lunula);
C, body of nail. The continuous line around border represents the free
edge.
]
[Illustration: Fig. 102.--Nail in Position.
A, section of cutaneous fold (B) turned back to show the root of the
nail;
B, cutaneous fold covering the root of the nail;
C, semi lunar whitish portion (lunula);
D, free border.
]
With few exceptions every portion of the skin is provided with sweat
glands, but they are not equally distributed over the body. They are
fewest in the back and neck, where it is estimated they average 400 to the
square inch. They are thickest in the palms of the hands, where they
amount to nearly 3000 to each square inch. These minute openings occur in
the ridges of the skin, and may be easily seen with a hand lens. The
length of a tube when straightened is about 1/4 of an inch. The total
number in the body is estimated at about 2,500,000, thus making the entire
length of the tubes devoted to the secretion of sweat about 10 miles.
240. Nature and Properties of Sweat. The sweat is a turbid, saltish
fluid with a feeble but characteristic odor due to certain volatile fatty
acids. Urea is always present in small quantities, and its proportion may
be largely increased when there is deficiency of elimination by the
kidneys. Thus it is often observed that the sweat is more abundant when
the kidneys are inactive, and the reverse is true. This explains the
increased excretion of the kidneys in cold weather. Of the inorganic
constituents of sweat, common salt is the largest and most important. Some
carbon dioxid passes out through the skin, but not more than 1/50 as much
as escapes by the lungs.
The sweat ordinarily passes off as vapor. If there is no obvious
perspiration we must not infer that the skin is inactive, since sweat is
continually passing from the surface, though often it may not be apparent.
On an average from 1-1/2 to 4 pounds of sweat are eliminated daily from
the skin in the form of vapor. This is double the amount excreted by the
lungs, and averages about 1/67 of the weight of the body.
The visible sweat, or sensible perspiration, becomes abundant during
active exercise, after copious drinking of cold water, on taking certain
drugs, and when the body is exposed to excessive warmth. Forming more
rapidly than it evaporates it collects in drops on the surface. The
disagreeable sensations produced by humid weather result from the fact
that the atmosphere is so loaded with vapor that the moisture of the skin
is slowly removed by evaporation.
Experiment 124. Study the openings of the sweat glands with the aid
of a strong magnifying glass. They are conveniently examined on the
palms.
A man's weight may be considerably reduced within a short time by loss
through the perspiration alone. This may explain to some extent the
weakening effect of profuse perspiration, as from night sweats of
consumption, convalescence from typhoid fever, or the artificial sweating
from taking certain drugs.
241. The Skin as a Regulator of the Temperature of the Body. We thus
learn that the skin covers and protects the more delicate structures
beneath it; and that it also serves as an important organ of excretion. By
means of the sweat the skin performs a third and a most important
function, _viz_., that of regulating the temperature of the body.
The blood-vessels of the skin, like those of other parts of the body, are
under the control of the nervous system, which regulates their diameter.
If the nervous control be relaxed, the blood-vessels dilate, more blood
flows through them, and more material is brought to the glands of the skin
to be acted upon. External warmth relaxes the skin and its blood-vessels.
There results an increased flow of blood to the skin, with increased
perspiration. External cold, on the other hand, contracts the skin and its
blood-vessels, producing a diminished supply of blood and a diminished
amount of sweat.
Now, it is a law of physics that the change from liquid to vapor involves
a loss of heat. A few drops of ether or of any volatile liquid placed on
the skin, produce a marked sense of coldness, because the heat necessary
to change the liquid into vapor has been drawn rapidly from the skin. This
principle holds good for every particle of sweat that reaches the mouth of
a sweat gland. As the sweat evaporates, it absorbs a certain amount of
heat, and cools the body to that extent.
242. How the Action of the Skin may be Modified. After profuse
sweating we feel chilly from the evaporation of a large amount of
moisture, which rapidly cools the surface. When the weather is very warm
the evaporation tends to prevent the bodily temperature from rising. On
the other hand, if the weather be cold, much less sweat is produced, the
loss of heat from the body is greatly lessened, and its temperature
prevented from falling. Thus it is plain why medicine is given and other
efforts are made to sweat the fever patient. The increased activity of the
skin helps to reduce the bodily heat.
The sweat glands are under the control of certain nerve fibers originating
in the spinal cord, and are not necessarily excited to action by an
increased flow of blood through the skin. In other words, the sweat glands
may be stimulated to increased action both by an increased flow of blood,
and also by reflex action upon the vaso-dilator nerves of the parts. These
two agencies, while working in harmony through the vaso-dilators, produce
phenomena which are essentially independent of each other. Thus a strong
emotion, like fear, may cause a profuse sweat to break out, with cold,
pallid skin. During a fever the skin may be hot, and its vessels full of
blood, and yet there may be no perspiration.
[Illustration: Fig. 103.--Papillæ of the Skin of the Palm of the Hand.
In each papilla are seen vascular loops (dark lines) running up from the
vascular network below, the tactile corpuscles with their nerve branches
(white lines) which supply the papillæ.]
The skin may have important uses with which we are not yet acquainted.
Death ensues when the heat of the body has been reduced to about 70° F.,
and suppression of the action of the skin always produces a lowering of
the temperature. Warm-blooded animals usually die when more than half of
the general surface has been varnished. Superficial burns which involve a
large part of the surface of the body, generally have a fatal result due
to shock.
If the skin be covered with some air-tight substance like a coating of
varnish, its functions are completely arrested. The bodily heat falls very
rapidly. Symptoms of blood-poisoning arise, and death soon ensues. The
reason is not clearly known, unless it be from the sudden retention of
poisonous exhalations.
243. The Skin and the Kidneys. There is a close relationship between
the skin and the kidneys, as both excrete organic and saline matter. In
hot weather, or in conditions producing great activity of the skin, the
amount of water excreted by the kidneys is diminished. This is shown in
the case of firemen, stokers, bakers, and others who are exposed to great
heat, and drink heavily and sweat profusely, but do not have a relative
increase in the functions of the kidneys. In cool weather, when the skin
is less active, a large amount of water is excreted by the kidneys, as is
shown by the experience of those who drive a long distance in severe
weather, or who have caught a sudden cold.
[Illustration: Fig. 104.--Magnified View of a Sweat Gland with its Duct.
The convoluted gland is seen surrounded with big fat-cells, and may be
traced through the dermis to its outlet in the horny layers of the
epidermis.]
244. Absorbent Powers of the Skin. The skin serves to some extent as
an organ for absorption. It is capable of absorbing certain
substances to which it is freely exposed. Ointments rubbed in, are
absorbed by the lymphatics in those parts where the skin is thin, as in
the bend of the elbow or knee, and in the armpits. Physicians use
medicated ointments in this way, when they wish to secure prompt and
efficient results. Feeble infants often grow more vigorous by having their
skin rubbed vigorously daily with olive oil.
A slight amount of water is absorbed in bathing. Sailors deprived of
fresh water have been able to allay partially their intense thirst by
soaking their clothing in salt water. The extent to which absorption
occurs through the healthy skin is, however, quite limited. If the outer
skin be removed from parts of the body, the exposed surface absorbs
rapidly. Various substances may thus be absorbed, and rapidly passed into
the blood. When the physician wishes remedies to act through the skin, he
sometimes raises a small blister, and dusts over the surface some drug, a
fine powder, like morphine.
The part played by the skin as an organ of touch will be considered
in sections 314 and 315.
Experiment 125. _To illustrate the sense of temperature_. Ask the
person to close his eyes. Use two test tubes, one filled with cold and
the other with hot water, or two spoons, one hot and one cold. Apply
each to different parts of the surface, and ask the person whether the
touching body is hot or cold. Test roughly the sensibility of different
parts of the body with cold and warm metallic-pointed rods.
Experiment 126. Touch fur, wood, and metal. The metal feels
coldest, although all the objects are at the same temperature. Why?
Experiment 127. Plunge the hand into water at about 97°F. One
experiences a feeling of heat. Then plunge it into water at about 86°F.;
at first it feels cold, because heat is abstracted from the hand. Plunge
the other hand direct into water at 86°F. without previously placing it
in water at 97°F.,--it will feel pleasantly warm.
Experiment 128. _To illustrate warm and cold spots_. With a blunt
metallic point, touch different parts of the skin. Certain points excite
the sensation of warmth, others of cold, although the temperatures of
the skin and of the instrument remain constant.
245. Necessity for Personal Cleanliness. It is evident that the skin,
with its myriads of blood-vessels, nerves, and sweat and oil glands, is an
exceedingly complicated and important structure. The surface is
continually casting off perspiration, oily material, and dead scales. By
friction and regular bathing we get rid of these waste materials. If this
be not thoroughly done, the oily secretion holds the particles of waste
substances to the surface of the body, while dust and dirt collect, and
form a layer upon the skin. When we remember that this dirt consists of a
great variety of dust particles, poisonous matters, and sometimes germs of
disease, we may well be impressed with the necessity of personal
cleanliness.
This layer of foreign matter on the skin is in several ways injurious to
health. It clogs the pores and retards perspiration, thus checking the
proper action of the skin as one of the chief means of getting rid of the
waste matters of the body. Hence additional work is thrown upon other
organs, chiefly the lungs and the kidneys, which already have enough to
do. This extra work they can do for only a short time. Sooner or later
they become disordered, and illness follows. Moreover, as this unwholesome
layer is a fertile soil in which bacteria may develop, many skin diseases
may result from this neglect. It is also highly probable that germs of
disease thus adherent to the skin may then be absorbed into the system.
Parasitic skin diseases are thus greatly favored by the presence of an
unclean skin. It is also a fact that uncleanly people are more liable to
take cold than those who bathe often.
The importance of cleanliness would thus seem too apparent to need special
mention, were it not that the habit is so much neglected. The old and
excellent definition that dirt is suitable matter, but in the wrong place,
suggests that the place should be changed. This can be done only by
regular habits of personal cleanliness, not only of the skin, the hair,
the teeth, the nails, and the clothing, but also by the rigid observance
of a proper system in daily living.
246. Baths and Bathing. In bathing we have two distinct objects in
view,--to keep the skin clean and to impart vigor. These are closely
related, for to remove from the body worn-out material, which tends to
injure it, is a direct means of giving vigor to all the tissues. Thus a
cold bath acts upon the nervous system, and calls out, in response to the
temporary abstraction of heat, a freer play of the general vital powers.
Bathing is so useful, both locally and constitutionally, that it
should be practiced to such an extent as experience proves to be
beneficial. For the general surface, the use of hot water once a week
fulfills the demands of cleanliness, unless in special occupations.
Whether we should bathe in hot or cold water depends upon circumstances.
Most persons, especially the young and vigorous, soon become accustomed to
cool, and even cold water baths, at all seasons of the year.
The hot bath should be taken at night before going to bed, as in the
morning there is usually more risk of taking cold. The body is readily
chilled, if exposed to cold when the blood-vessels of the skin have been
relaxed by heat. Hot baths, besides their use for the purposes of
cleanliness, have a sedative influence upon the nervous system, tending to
allay restlessness and weariness. They are excellent after severe physical
or mental work, and give a feeling of restful comfort like that of sleep.
[Illustration: Fig. 105.--Epithelial Cells from the Sweat Glands. The
cells are very distinct, with nuclei enclosing pigmentary granulations
(Magnified 350 times)]
Cold baths are less cleansing than hot, but serve as an excellent
tonic and stimulant to the bodily functions. The best and most convenient
time for a cold bath is in the morning, immediately after rising. To the
healthy and vigorous, it is, if taken at this time, with proper
precautions, a most agreeable and healthful luxury. The sensation of
chilliness first felt is caused by the contraction of the skin and its
blood-vessels, so that the blood is forced back, as it were, into the
deeper parts of the body. This stimulates the nervous system, the
breathing becomes quicker and deeper, the heart beats more vigorously,
and, as a consequence, the warm blood is sent back to the skin with
increased force. This is known as the stage of reaction, which is best
increased by friction with a rough towel. This should produce the pleasant
feeling of a warm glow all over the body.
A cold bath which is not followed by reaction is likely to do more harm
than good. The lack of this reaction may be due to the water being too
cold, the bath too prolonged, or to the bather being in a low condition of
health. In brief, the ruddy glow which follows a cold bath is the main
secret of its favorable influence.
The temperature of the water should be adapted to the age and strength of
the bather. The young and robust can safely endure cold baths, that would
be of no benefit but indeed an injury to those of greater age or of less
vigorous conditions of health. After taking a bath the skin should be
rapidly and vigorously rubbed dry with a rough towel, and the clothing at
once put on.
247. Rules and Precautions in Bathing. Bathing in cold water should
not be indulged in after severe exercise or great fatigue, whether we are
heated or not. Serious results have ensued from cold baths when the body
is in a state of exhaustion or of profuse perspiration. A daily cold bath
when the body is comfortably warm, is a safe tonic for almost all persons
during the summer months, and tends especially to restore the appetite.
Cold baths, taken regularly, render persons who are susceptible to
colds much less liable to them, and less likely to be disturbed by sudden
changes of temperature. Persons suffering from heart disease or from
chronic disease of an important organ should not indulge in frequent cold
bathing except by medical advice. Owing to the relaxing nature of hot
baths, persons with weak hearts or suffering from debility may faint while
taking them.
Outdoor bathing should not be taken for at least an hour after a
full meal, and except for the robust it is not prudent to bathe with the
stomach empty, especially before breakfast. It is a wise rule, in outdoor
or sea bathing, to come out of the water as soon as the glow of reaction
is felt. It is often advisable not to apply cold water very freely to the
head. Tepid or even hot water is preferable, especially by those subject
to severe mental strain. But it is often a source of great relief during
mental strain to bathe the face, neck, and chest freely at bedtime with
cold water. It often proves efficient at night in calming the
sleeplessness which results from mental labor.
Hot baths, if taken at bedtime, are often serviceable in preventing a
threatened cold or cutting it short, the patient going immediately to bed,
with extra clothing and hot drinks. The free perspiration induced helps to
break up the cold.
Salt water acts more as a stimulant to the skin than fresh water.
Salt-water bathing is refreshing and invigorating for those who are
healthy, but the bather should come out of the water the moment there is
the slightest feeling of chilliness. The practice of bathing in salt water
more than once a day is unhealthful, and even dangerous. Only the
strongest can sustain so severe a tax on their power of endurance. Sea
bathing is beneficial in many ways for children, as their skin reacts well
after it. In all cases, brisk rubbing with a rough towel should be had
afterwards.
[Illustration: Fig. 106.--Magnified Section of the Lower Portion of a Hair
and Hair-Follicle.
A, membrane of the hair-follicle, cells with nuclei and pigmentary
granules;
B, external lining of the root sheath;
C, internal lining of the root sheath;
D, cortical or fibrous portion of the hair shaft;
E, medullary portion (pith) of shaft;
F, hair-bulb, showing its development from cells from A.
]
The golden rule of all bathing is that it must never be followed by a
chill. If even a chilliness occur after bathing, it must immediately
be broken up by some appropriate methods, as lively exercise, brisk
friction, hot drinks, and the application of heat.
Swimming is a most valuable accomplishment, combining bathing and
exercise. Bathing of the feet should never be neglected. Cleanliness of
the hair is also another matter requiring strict attention, especially in
children.
248. Care of the Hair and Nails. The hair brush should not be too
stiff, as this increases the tendency towards scurfiness of the head. If,
however, the hair is brushed too long or too hard, the scalp is greatly
stimulated, and an increased production of scurf may result. If the head
be washed too often with soap its natural secretion is checked, and the
scalp becomes dry and scaly. The various hair pomades are as a rule
undesirable and unnecessary.
The nails should be kept in proper condition, else they are not only
unsightly, but may serve as carriers of germs of disease. The nails are
often injured by too much interference, and should never be trimmed to the
quick. The upper surfaces should on no account be scraped. The nail-brush
is sufficient to cleanse them without impairing their smooth and polished
surfaces.
[Illustration: Fig. 107.--Longitudinal Section of a Finger-Nail.
A, last phalanx of the fingers;
B, true skin on the dorsal surface of the finger;
C, epidermis;
D, true skin;
E, bed of the nail;
F, superficial layer of the nail;
H, true skin of the pulp of the finger.
]
249. Use of Clothing. The chief use of clothing, from a hygienic
point of view, is to assist in keeping the body at a uniform temperature.
It also serves for protection against injury, and for personal adornment.
The heat of the body, as we have learned, is normally about 98 1/2° F.
This varies but slightly in health. A rise of temperature of more than one
degree is a symptom of disturbance. The normal temperature does not vary
with the season. In summer it is kept down by the perspiration and its
rapid evaporation. In winter it is maintained by more active oxidation, by
extra clothing, and by artificial heat.
The whole matter of clothing is modified to a great extent by climatic
conditions and local environments,--topics which do not come
within the scope of this book.
250. Material Used for Clothing. It is evident that if clothing is to
do double duty in preventing the loss of heat by radiation, and in
protecting us from the hot rays of the sun, some material must be used
that will allow the passage of heat in either direction. The ideal
clothing should be both a bad conductor and a radiator of heat. At the
same time it must not interfere with the free evaporation of the
perspiration, otherwise chills may result from the accumulation of
moisture on the surface of the body.
Wool is a bad conductor, and should be worn next the skin, both in
summer and winter, especially in variable climates. It prevents, better
than any other material, the loss of heat from the body, and allows free
ventilation and evaporation. Its fibers are so lightly woven that they
make innumerable meshes enclosing air, which is one of the best of
non-conductors.
Silk ranks next to wool in warmth and porosity. It is much softer and
less irritating than flannel or merino, and is very useful for summer
wear. The practical objection to its general use is the expense. Fur
ranks with wool as a bad conductor of heat. It does not, however, like
wool, allow of free evaporation. Its use in cold countries is universal,
but in milder climates it is not much worn.
Cotton and linen are good conductors of heat, but are not
absorbents of moisture, and should not be worn next the skin. They are,
however, very durable and easily cleansed. As an intermediate clothing
they may be worn at all seasons, especially over wool or silk. Waterproof
clothing is also useful as a protection, but should not be worn a longer
time than necessary, as it shuts in the perspiration, and causes a sense
of great heat and discomfort.
The color of clothing is of some importance, especially if exposed
directly to the sun's rays. The best reflectors, such as white and light
gray clothing, absorb comparatively little heat and are the coolest, while
black or dark-colored materials, being poor reflectors and good
absorbents, become very warm.
251. Suggestions for the Use of Clothing. Prudence and good sense
should guide us in the spring, in changing winter flannels or clothing for
fabrics of lighter weight. With the fickle climate in most sections of
this country, there are great risks of severe colds, pneumonia, and other
pulmonary diseases from carelessness or neglect in this matter. A change
from heavy to lighter clothing should be made first in the outer garments,
the underclothing being changed very cautiously.
The two essentials of healthful clothing are cleanliness and
dryness. To wear garments that are daily being soiled by perspiration
and other cutaneous excretions, is a most uncleanly and unhealthful
practice. Clothing, especially woolen underclothing, should be frequently
changed. One of the objections to the use of this clothing is that it does
not show soiling to the same extent as do cotton and linen.
Infectious and contagious diseases may be conveyed by the clothing. Hence,
special care must be taken that all clothing in contact with sick people
is burned or properly disinfected. Children especially are susceptible to
scarlet fever, diphtheria, and measles, and the greatest care must be
exercised to prevent their exposure to infection through the clothing.
We should never sleep in a damp bed, or between damp sheets. The vital
powers are enfeebled during sleep, and there is always risk of pneumonia
or rheumatism. The practice of sitting with wet feet and damp clothing is
highly injurious to health. The surface of the body thus chilled may be
small, yet there is a grave risk of serious, if not of fatal, disease. No
harm may be done, even with clothing wet with water or damp with
perspiration, so long as exercise is maintained, but the failure or
inability to change into dry garments as soon as the body is at rest is
fraught with danger.
Woolen comforters, scarfs, and fur mufflers, so commonly worn around the
neck, are more likely to produce throat troubles and local chill than to
have any useful effect. Harm ensues from the fact that the extra covering
induces local perspiration, which enfeebles the natural defensive power of
the parts; and when the warmer covering is removed, the perspiring surface
is readily chilled. Those who never bundle their throats are least liable
to suffer from throat ailments.
252. Ill Effects of Wearing Tightly Fitting Clothing. The injury to
health caused by tight lacing, when carried to an extreme, is due to the
compression and displacement of various organs by the pressure exerted on
them. Thus the lungs and the heart may be compressed, causing short breath
on exertion, palpitation of the heart, and other painful and dangerous
symptoms. The stomach, the liver, and other abdominal organs are often
displaced, causing dyspepsia and all its attendant evils. The improper use
of corsets, especially by young women, is injurious, as they interfere
with the proper development of the chest and abdominal organs. The use of
tight elastics below the knee is often injurious. They obstruct the local
venous circulation and are a fruitful source of cold feet and of enlarged
or varicose veins.
Tightly fitting boots and shoes often cause corns, bunions, and ingrowing
nails; on the other hand, if too loosely worn, they cause corns from
friction. Boots too narrow in front crowd the toes together, make them
overlap, and render walking difficult and painful. High-heeled boots throw
the weight of the body forwards, so that the body rests too much on the
toes instead of on the heels, as it should, thus placing an undue strain
upon certain groups of muscles of the leg, in order to maintain the
balance, while other groups are not sufficiently exercised. Locomotion is
never easy and graceful, and a firm, even tread cannot be expected.
The compression of the scalp by a tight-fitting hat interferes with the
local circulation, and may cause headaches, neuralgia, or baldness, the
nutrition of the hair-follicles being diminished by the impaired
circulation. The compression of the chest and abdomen by a tight belt and
various binders interferes with the action of the diaphragm,--the most
important muscle of respiration.
253. Miscellaneous Hints on the Use of Clothing. Children and old
people are less able to resist the extreme changes of temperature than are
adults of an average age. Special care should be taken to provide children
with woolen underclothing, and to keep them warm and in well-ventilated
rooms. Neither the chest nor limbs of young children should be unduly
exposed, as is often done, to the cold blasts of winter or the fickle
weather of early spring. Very young children should not be taken out in
extremely cold weather, unless quite warmly clad and able to run about.
The absurd notion is often entertained that children should be hardened by
exposure to the cold. Judicious "hardening" means ample exposure of
well-fed and well-clothed children. Exposure of children not thus cared
for is simple cruelty. The many sicknesses of children, especially
diseases of the throat and lungs, may often be traced directly to gross
carelessness, ignorance, or neglect with reference to undue exposure. The
delicate feet of children should not be injured by wearing ill-fitting or
clumsy boots or shoes. Many deformities of the feet, which cause much
vexation and trouble in after years, are acquired in early life.
No one should sleep in any of the clothes worn during the day, not even in
the same underclothing. All bed clothing should be properly aired, by free
exposure to the light and air every morning. Never wear wet or damp
clothing one moment longer than necessary. After it is removed rub the
body thoroughly, put on at once dry, warm clothing, and then exercise
vigorously for a few minutes, until a genial glow is felt. Neglect of
these precautions often results in rheumatism, neuralgia, and diseases of
the chest, especially among delicate people and young women.
Pupils should not be allowed to sit in the schoolroom with any outer
garments on. A person who has become heated in a warm room should not
expose himself to cold without extra clothing. We must not be in a hurry
to put on heavy clothes for winter, but having once worn them, they must
not be left off until milder weather renders the change safe. The cheaper
articles of clothing are often dyed with lead or arsenic. Hence such
garments, like stockings and colored underclothing, worn next the skin
have been known to produce severe symptoms of poisoning. As a precaution,
all such articles should be carefully washed and thoroughly rinsed before
they are worn.
The Kidneys.
254. The Kidneys. The kidneys are two important organs in the
abdomen, one on each side of the spine. They are of a reddish-brown color,
and are enveloped by a transparent capsule made up of a fold of the
peritoneum. Embedded in fat, the kidneys lie between the upper lumbar
vertebræ, and the crest of the hip bone. The liver is above the right
kidney, and the spleen above the left, while both lie close against the
rear wall of the abdomen, with the intestines in front of them. The human
kidneys, though somewhat larger, are exactly of the same shape, color, and
general appearance as those of the sheep, so commonly seen in the markets.
The kidneys are about four inches long, two inches across, one inch thick,
and weigh from 41/2 to 51/2 ounces each. The hollow or concave side of the
kidneys is turned inwards, and the deep fissure of this side, known as the
hilus, widens out to form the pelvis. Through the hilus the
renal artery passes into each kidney, and from each hilus passes outwards
the renal vein, a branch of the inferior vena cava.
A tube, called the ureter, passes out from the concave border of each
kidney, turns downwards, and enters the bladder in the basin of the
pelvis. This tube is from 12 to 14 inches long, about as large as a goose
quill, and conveys the secretion of the kidneys to the bladder.
255. Structure of the Kidneys. The pelvis is surrounded by
reddish cones, about twelve in number, projecting into it, called the
pyramids of Malpighi. The apices of these cones, known as the
_papillæ_, are crowded with minute openings, the mouths of the
uriniferous tubules, which form the substance of the kidney. These
lie parallel in the medullary or central structure, but On reaching the
cortical or outer layer, they wind about and interlace, ending, at last,
in dilated closed sacs called Malpighian capsules.
[Illustration: Fig. 108.--Vertical Section of the Kidney.
A, pyramids of Malpighi;
B, apices, or papillæ, of the pyramids, surrounded by subdivisions of
the pelvis known as cups or calices;
C, pelvis of the kidney;
D, upper end of ureter.
]
256. Function of the Kidneys. The Malpighian capsules are really the
beginning of the tubules, for here the work of excretion begins. The thin
wall of the capillaries within each capsule separates the blood from the
cavity of the tubule. The blood-pressure on the delicate capillary walls
causes the exudation of the watery portions of the blood through the cell
walls into the capsule. The epithelial cell membrane allows the water of
the blood with certain salts in solution to pass, but rejects the albumen.
From the capsules, the excretion passes through the tubules into the
pelvis, and on through the ureters to the bladder. But the delicate
epithelial walls of the tubules through which it passes permit the inflow
of urea and other waste products from the surrounding capillaries. By this
twofold process are separated from the blood the fluid portions of the
renal secretion with soluble salts, and the urea with other waste
material.
257. How the Action of the Kidneys may be Modified. The action of the
kidneys is subject to very marked and sudden modifications, especially
those operating through the nervous system. Thus whatever raises the
blood-pressure in the capillaries of the capsules, will increase the
quantity of fluid filtering through them. That is, the watery portion of
the secretion will be increased without necessarily adding to its solids.
So anything which lowers the blood-pressure will diminish the watery
portion of the secretion, that is, the secretion will be scanty, but
concentrated.
The Renal Secretion.--The function of the kidneys is to secrete a
fluid commonly known as the urine. The average quantity passed in 24 hours
by an adult varies from 40 to 60 fluid ounces. Normal urine consists of
about 96 per cent of water and 4 per cent of solids. The latter consist
chiefly of certain nitrogenous substances known as urea and uric acid, a
considerable quantity of mineral salts, and some coloring matter. Urea,
the most important and most abundant constituent of urine, contains the
four elements, but nitrogen forms one-half its weight. While, therefore,
the lungs expel carbon dioxid chiefly, the kidneys expel nitrogen. Both of
these substances express the result of oxidations going on in the body.
The urea and uric acids represent the final result of the breaking down in
the body of nitrogenous substances, of which albumen is the type.
Unusual constituents of the urine are _albumen, sugar_, and _bile_. When
albumen is present in urine, it often indicates some disease of the
kidneys, to which the term _albuminuria_ or Bright's Disease is applied.
The presence of grape sugar or glucose indicates the disease known as
diabetes. Bile is another unusual constituent of the urine, appearing in
_jaundice_.
The bladder is situated in the pelvic cavity or in the lowest part of
the abdomen. When full, the bladder is pear-shaped; when empty, it is
collapsed and lies low in the pelvis. The functions of the bladder are to
collect and retain the urine, which has reached it drop by drop from the
kidneys through the ureters, until a certain quantity accumulates, and
then to expel it from the body.
[Illustration: Fig. 109.--Vertical Section of the Back. (Showing kidneys
_in situ_ and the relative position of adjacent organs and vessels.)
[Posterior view.]
A, 12th dorsal vertebra;
B, diaphragm;
C, receptaculum chyli;
D, small intestines
]
In the kidneys, as elsewhere, the vaso-motor nerves are distributed
to the walls of the blood-vessels, and modify the quantity and the
pressure of blood in these organs. Thus, some strong emotion, like fear or
undue anxiety, increases the blood-pressure, drives more blood to the
kidneys, and causes a larger flow of watery secretion. When the atmosphere
is hot, there is a relaxation of the vessels of the skin, with a more
than ordinary flow of blood, which is thus withdrawn from the deeper
organs. The blood-pressure in the kidneys is not only diminished, but the
total quantity passing through them in a given time is much lessened. As a
result, the secretion of the kidneys is scanty, but it contains an unusual
percentage of solids.
When the atmosphere is cold, the reverse is true. The cutaneous vessels
contract, the blood is driven to the deeper organs with increased
pressure, and there is a less amount of sweat, but an increased renal
secretion, containing a smaller proportion of solids. Certain drugs have
the power of increasing or diminishing the renal secretion. As the waste
matters eliminated by the kidneys are being constantly produced in the
tissues, the action of the renal organs is continuous, in marked contrast
with the intermittent flow of most of the secretions proper, as
distinguished from the excretions.
258. Effects of Alcoholic Drinks upon the Kidneys. The kidneys differ
from some of the other organs in this: those can rest a while without any
harm to themselves, or to the body. We can keep the eyes closed for a few
days, if necessary, without injury, and in fact often with benefit; or, we
can abstain from food for some days, if need be, and let the stomach rest.
But the kidneys cannot, with safety, cease their work. Their duty in
ridding the blood of waste products, and of any foreign or poisonous
material introduced, must be done not only faithfully, but continually, or
the whole body at once suffers from the evil effects of the retained waste
matters.
This vital fact is the key to the injurious results developed in the
kidneys by the use of alcoholic drinks. These two organs have large
blood-vessels conveying full amounts of blood to and from their
structures, and they feel very quickly the presence of alcohol. Alcoholic
liquors excite and irritate the delicate renal membranes, and speedily
disturb and eventually destroy their capacity to excrete the proper
materials from the blood.
The continued congestion of the minute structure of the kidney cuts off
the needed nutrition of the organ, and forms the primary step in the
series of disasters. Sometimes from this continued irritation, with the
resulting inflammation, and sometimes from change of structure of the
kidney by fatty degeneration, comes the failure to perform its proper
function. Then, with this two-edged sword of disaster, the urea, which
becomes a poisonous element, and should be removed, is retained in the
system, while the albumen, which is essential to healthy blood, is
filtered away through the diseased kidney.
259. Alcoholic Liquors as a Cause of Bright's Disease. The
unfortunate presence of albumen in the urine is often a symptom of that
insidious and fatal malady known as _albuminuria_ or Bright's disease,
often accompanied with dropsy and convulsions. One of the most constant
causes of this disease is the use of intoxicants. It is not at all
necessary to this fatal result that a person be a heavy drinker. Steady,
moderate drinking will often accomplish the work. Kidney diseases produced
by alcoholic drinks, are less responsive to medical treatment and more
fatal than those arising from any other known cause.[39]
Experiment 129. Obtain a sheep's kidney in good order. Observe that
its shape is something like that of a bean, and note that the concave
part (hilus), when in its normal position, is turned towards the
backbone. Notice that all the vessels leave and enter the kidney at the
hilus. Observe a small thick-walled vessel with open mouth from which
may be pressed a few drops of blood. This is the renal artery. Pass a
bristle down it. With the forceps, or even with a penknife, lift from
the kidney the fine membrane enclosing it. This is the kidney capsule.
Divide the kidney in halves by a section from its outer to near its
inner border. Do not cut directly through the hilus. Note on the cut
surfaces, on the outer side, the darker cortical portion, and on the
inner side, the smooth, pale, medullary portion. Note also the pyramids
of Malpighi.
Chapter X.
The Nervous System.
260. General View of the Nervous System. Thus far we have learned
something of the various organs and the manner in which they do their
work. Regarding our bodily structure as a kind of living machine, we have
studied its various parts, and found that each is designed to perform some
special work essential to the well-being of the whole. As yet we have
learned of no means by which these organs are enabled to adjust their
activities to the needs of other tissues and other organs. We are now
prepared to study a higher, a more wonderful and complex agency,--the
nervous system, the master tissue, which controls, regulates, and
directs every other tissue of the human body.
The nervous system, in its properties and mode of action, is distinct from
all the other systems and organs, and it shares with no other organ or
tissue the power to do its special work. It is the medium through which
all impressions are received. It connects all the parts of the body into
an organism in which each acts in harmony with every other part for the
good of the whole. It animates and governs all movements, voluntary or
involuntary,--secretion, excretion, nutrition; in fact all the processes
of organic life are subject to its regulating power. The different organs
of the body are united by a common sympathy which regulates their action:
this harmonious result is secured by means of the nervous system.
This system, in certain of its parts, receives impressions, and generates
a force peculiar to itself. We shall learn that there can be no physical
communication between or coördination of the various parts of organs, or
harmonious acts for a desire result, without the nerves. General
impressions, as in ordinary sensation, or special impressions, as in
sight, smell, taste, or hearing,--every instinct, every act of the will,
and every thought are possible only through the action of the nerve
centers.
261. Nerve Cells. However complicated the structure of nerve tissue
in man seems to be, it is found to consist of only two different elements,
nerve cells and nerve fibers. These are associated and combined
in many ways. They are arranged in distinct masses called nerve
centers, or in the form of cords known as nerves. The former are
made up of nerve fibers; the latter of both cells and fibers.
[Illustration: Fig. 110. Nerve Cells from the Spinal Cord.]
Nerve cells, which may be regarded as the central organs of the nerve
fibers, consist of masses of cell protoplasm, with a large _nucleus_ and
_nucleolus_. They bear a general resemblance to other cells, but vary much
in size and shape. Nerve cells grow, become active, and die, as do other
cells. A number of processes branch off from them, some cells giving one
or two, others many. The various kinds of nerve cells differ much in the
shape and number of processes. One of the processes is a strand which
becomes continuous with the axis cylinder of the nerve fibers; that is,
the axis cylinders of all nerve fibers are joined in one place or another
with at least one cell.
Each part of this system has its own characteristic cell. Thus we have in
the spinal cord the large, irregular cells with many processes, and in the
brain proper the three-sided cells with a process jutting out from each
corner. So characteristic are these forms of cells, that any particular
part of nerve structure may be identified by the kind of cells seen under
the microscope. Nerve cells and nerve fibers are often arranged in
groups, the various cells of the groups communicating with one another.
This clustered arrangement is called a nerve center.
262. Nerve Fibers. The nerve fibers, the essential elements of
the nerves, somewhat resemble tubes filled with a clear, jelly-like
substance. They consist of a rod, or central core, continuous throughout
the whole length of the nerve, called the axis cylinder. This core is
surrounded by the white substance of Schwann, or medullary sheath, which
gives the nerve its characteristic ivory-white appearance. The whole is
enclosed in a thin, delicate sheath, known as neurilemma.
[Illustration: Fig. 111.--Nerve Cells from the Gray Matter of the Brain.]
The axis cylinder generally passes without any break from the nerve
centers to the end of the fibers.[40] The outer sheath (neurilemma) is
also continuous throughout the length of the fibers. The medullary sheath,
on the other hand, is broken at intervals of about 1/25 of an inch, and at
the same intervals nuclei are found along the fiber, around each of
which is a minute protoplasmic mass. Between each pair of nuclei the
sheath is interrupted. This point is known as the _node of Ranvier_.
Some nerve fibers have no inner sheath (medullary), the outer alone
protecting the axis cylinder. These are known as the non-medullary fibers.
They are gray, while the ordinary medullary fibers are white in
appearance. The white nerve fibers form the white part of the brain
and of the spinal cord, and the greater part of the cerebro-spinal nerves.
The gray fibers occur chiefly in branches from the sympathetic
ganglia, though found to some extent in the nerves of the cerebro-spinal
system.
In a general way, the nerve fibers resemble an electric cable wire with
its central rod of copper, and its outer non-conducting layer of silk or
gutta percha. Like the copper rod, the axis cylinder along which the nerve
impulse travels is the essential part of a nerve fiber. In a cut nerve
this cylinder projects like the wick of a candle. It is really the
continuation of a process of a nerve cell. Thus the nerve cells and nerve
fibers are related, in that the process of one is the axis cylinder and
essential part of the other.
The separate microscopic threads or fibers, bound together in cords of
variable size, form the nerves. Each strand or cord is surrounded and
protected by its own sheath of connective tissue, made up of nerves.
According to its size a nerve may have one or many of these strands. The
whole nerve, not unlike a minute tendon in appearance, is covered by a
dense sheath of fibrous tissue, in which the blood-vessels and lymphatics
are distributed to the nerve fibers.
[Illustration: Fig. 112.--Medullated Nerve Fibers.
A, a medullated nerve fiber, showing the subdivision of the medullary
sheath into cylindrical sections imbricated with their ends, a nerve
corpuscle with an oval nucleus is seen between the neurilemma and the
medullary sheath;
B, a medullated nerve fiber at a node or constriction of Ranvier, the
axis cylinder passes uninterruptedly from one segment into the other,
but the medullary sheath is interrupted.
]
263. The Functions of the Nerve Cells and Nerve Fibers. The nerve
cells are a highly active mass of living material. They find their
nourishment in the blood, which is supplied to them in abundance. The
blood not only serves as nourishment, but also supplies new material, as
it were, for the cells to work over for their own force or energy. Thus
we may think of the nerve cells as a sort of a miniature manufactory,
deriving their material from the blood, and developing from it nervous
energy.
The nerve fibers, on the other hand, are conductors of nervous energy.
They furnish a pathway along which the nerve energy generated by the cells
may travel. Made up as they are of living nerve substance, the fibers can
also generate energy, yet it is their special function to conduct
influences to and from the cells.
[Illustration: Fig. 113.--Non-Medullated Fibers.
Two nerve fibers, showing the nodes or constrictions of Ranvier and the
axis cylinder. The medullary sheath has been dissolved away. The deeply
stained oblong nuclei indicate the nerve corpuscles within the
neurilemma.]
264. The Nervous System Compared to a Telegraphic System. In men and
other highly organized animals, nerves are found in nearly every tissue
and organ of the body. They penetrate the most minute muscular fibers;
they are closely connected with the cells of the glands, and are found in
the coats of even the smallest blood-vessels. They are among the chief
factors of the structure of the sense organs, and ramify through the skin.
Thus the nervous system is the system of organs through the functions of
which we are brought into relation with the world around us. When we hear,
our ears are bringing us into relation with the outer world. So sight
opens up to us another gateway of knowledge.
It will help us the better to understand the complicated functions of the
nervous system, if we compare it to a telegraph line. The brain is the
main office, and the multitudes of nerve fibers branching off to all parts
of the body are the wires. By means of these, nerve messages are
constantly being sent to the brain to inform it of what is going on in
various parts of the body, and asking what is to be done in each case. The
brain, on receiving the intelligence, at once sends back the required
instructions. Countless messages are sent to and fro with unerring
accuracy and marvelous rapidity.
Thus, when we accidentally pick up something hot, it is instantly
dropped. A nerve impulse passes from the nerves of touch in the fingers to
the brain, which at once hurries off its order along another set of nerves
for the hand to drop the burning object. These examples, so common in
daily life, may be multiplied to any extent. Almost every voluntary act we
perform is executed under the direction of the nervous system, although
the time occupied is so small that it is beyond our power to estimate it.
The very frequency with which the nerves act tends to make us forget their
beneficent work.
265. Divisions of the Nervous System. This system in man consists of
two great divisions. The first is the great nerve center of the body, the
cerebro-spinal system, which rules the organs of animal life. This
includes the brain, the spinal cord, and the cerebro-spinal
nerves. Nerves are given off from the brain and the cord, and form the
mediums of communication between the external parts of the body, the
muscles or the sense organs, and the brain.
The second part is the sympathetic system, which regulates the
organic life. This consists of numerous small nerve centers arranged in
oval masses varying greatly in size, called ganglia or knots. These
are either scattered irregularly through the body, or arranged in a double
chain of knots lying on the front of the spine, within the chest and
abdomen. From this chain large numbers of nerves are given off, which end
chiefly in the organs of digestion, circulation, and respiration. The
sympathetic system serves to bring all portions of the animal economy into
direct sympathy with one another.
266. The Brain as a Whole. The brain is the seat of the
intellect, the will, the affections, the emotions, the memory, and
sensation. It has also many other and complex functions. In it are
established many reflex, automatic, and coordinating centers, which are as
independent of consciousness as are those of the spinal cord.
The brain is the largest and most complex mass of nerve tissue in the
body, made up of an enormous collection of gray cells and nerve fibers.
This organ consists of a vast number of distinct ganglia, or separate
masses of nerve matter, each capable of performing separate functions, but
united through the cerebral action into a harmonious whole.
[Illustration: Fig. 114.--The Upper Surface of the Cerebrum. (Showing its
division into two hemispheres, and also the convolutions)]
The average weight of the adult human brain is about 50 ounces for men and
45 ounces for women. Other things being equal, the size and weight of the
brain bear a general relation to the mental power of the individual. As a
rule, a large, healthy brain stands for a vigorous and superior intellect.
The brains of many eminent men have been found to be 8 to 12 ounces above
the average weight, but there are notable exceptions. The brains of
idiots are small; indeed, any weight under a certain size, about 30
ounces, seems to be invariably associated with an imbecile mind.
The human brain is absolutely heavier than that of any other animal,
except the whale and elephant. Comparing the size of these animals with
that of man, it is instructive to notice how much larger in proportion to
the body is man's brain. The average proportion of the weight of the brain
to the weight of the body is greater in man than in most animals, being
about 1 to 36. In some small birds, in the smaller monkeys, and in some
rodents, the proportional weight of the brain to that of the body is even
greater than in man.
267. The Cerebrum. The three principal masses which make up the brain
when viewed as a whole are:
1. The cerebrum, or brain proper.
2. The cerebellum, or lesser brain.
3. The medulla oblongata.
The cerebrum comprises nearly seven-eighths of the entire mass, and
fills the upper part of the skull. It consists of two halves, the right
and left cerebral hemispheres. These are almost separated from each
other by a deep median fissure. The hemispheres are united at the bottom
of the fissure by a mass of white fibers passing from side to side. Each
of these hemispheres is subdivided into three lobes, so that the entire
cerebrum is made up of six distinct lobes.
The cerebrum has a peculiar convoluted appearance, its deep folds being
separated by fissures, some of them nearly an inch in depth.
It is composed of both white and gray matter. The former comprises the
greater part of the mass, while the latter is spread over the surface in a
layer of about ⅛ of an inch thick. The gray matter is the portion having
the highest functions, and its apparent quantity is largely increased by
being formed in convolutions.
The convolutions of the cerebrum are without doubt associated with all
those higher actions which distinguish man's life; but all the
convolutions are not of equal importance. Thus it is probable that only
the frontal part of the brain is the intellectual region, while certain
convolutions are devoted to the service of the senses.
The cerebrum is the chief seat of the sensations, the intellect, the will,
and the emotions. A study of cerebral injuries and diseases, and
experiments upon the lower animals, prove that the hemispheres, and more
especially the gray matter, are connected with mental states. The
convolutions in the human brain are more prominent than in that of the
higher animals, most nearly allied to man, although some species of
animals, not especially intelligent, have marked cerebral convolutions.
The higher races of men have more marked convolutions than those less
civilized.
A view of the under surface of the brain, which rests on the floor of the
skull, shows the origin of important nerves, called the cranial
nerves, the cerebellum, the structure connecting the optic
nerves (optic commissure), the bridge of nervous matter (pons
Varolii) connecting the two hemispheres of the cerebellum, and lastly
numerous and well-marked convolutions.
268. The Cerebellum. The cerebellum, or lesser brain, lies in
the back of the cranium, and is covered over in man by the posterior lobe
of the cerebrum. It is, at it were, astride of the back of the
cerebro-spinal axis, and consists of two hemispheres joined by a central
mass. On its under surface is a depression which receives the medulla
oblongata. The cerebellum is separated from the cerebrum by a
horizontal partition of membrane, a portion of the dura mater. In some
animals, as in the cat, this partition is partly bone.
The cerebellum is connected with other parts of the nervous system by
strands of white matter on each side, radiating from the center and
divided into numerous branches. Around these branches the gray matter is
arranged in a beautiful manner, suggesting the leaves of a tree: hence its
name, arbor vitæ, or the tree of life.
The functions of the cerebellum are not certainly known. It appears to
influence the muscles of the body so as to regulate their movements; that
is, it serves to bring the various muscular movements into harmonious
action. The mechanism by which it does this has not yet been clearly
explained. In an animal from which the cerebellum has been removed, the
functions of life do not appear to be destroyed, but all power of either
walking or flying straight is lost.
[Illustration: Fig. 115.--A Vertical Section of the Brain.
A, frontal lobe of the cerebrum;
B, parietal lobe;
C, parieto occipital lobe with fissure between this lobe and
D, the occipital lobe;
E, cerebellum;
F, arbor vitæ;
H, pons Varolu;
K, medulla oblongata;
L, portion of lobe on the opposite side of brain.
The white curved band above H represents the corpus callosum.]
Disease or injury of the cerebellum usually produces blindness,
giddiness, a tendency to move backwards, a staggering, irregular gait, and
a feeling of insecurity in maintaining various positions. There is no loss
of consciousness, or other disturbance of the mental functions.
269. The Membranes of the Brain. The brain and spinal cord are
protected by three important membranes, known as the meninges,--the
dura mater, the arachnoid, and the pia mater.
The outer membrane, the dura mater, is much thicker and stronger than
the others, and is composed of white fibrous and elastic connective
tissue. It closely lines the inner surface of the skull, and forms a
protective covering for the brain. Folds of it pass between the several
divisions of the brain and serve to protect them.
The arachnoid is a thin membrane which lies beneath the dura mater.
It secretes a serous fluid which keeps the inner surfaces moist.
The pia mater is a very delicate, vascular membrane which covers the
convolutions, dips into all the fissures, and even penetrates into the
interior of the brain. It is crowded with blood-vessels, which divide and
subdivide very minutely before they penetrate the brain. The membranes of
the brain are sometimes the seat of inflammation, a serious and painful
disease, commonly known as brain fever.
270. The Medulla Oblongata. This is the thick upper part of the
spinal cord, lying within the cavity of the skull. It is immediately under
the cerebellum, and forms the connecting link between the brain and the
spinal cord. It is about an inch and a quarter long, and from one-half to
three-fourths of an inch wide at its upper part. The medulla
oblongata consists, like the spinal cord, of columns of white fibers
and masses of gray matter, but differently arranged. The gray matter is
broken up into masses which serve as centers of origin for various nerves.
The functions of the medulla oblongata are closely connected with the
vital processes. It is a great nerve tract for transmitting sensory and
motor impressions, and also the seat of a number of centers for reflex
actions of the highest importance to life. Through the posterior part of
the medulla the sensory impressions pass, that is, impressions from below
upwards to the brain resulting in sensation or feeling. In the anterior
part of the medulla, pass the nerves for motor transmission, that is,
nerve influences from above downwards that shall result in muscular
contractions in some part of the body.
The medulla is also the seat of a number of reflex centers connected with
the influence of the nervous system on the blood-vessels, the movements of
the heart, of respiration, and of swallowing, and on the secretion of
saliva. This spot has been called the "vital knot." In the medulla also
are centers for coughing, vomiting, swallowing, and the dilatation of the
pupil of the eye. It is also in part the deep origin of many of the
'important cranial nerves.
[Illustration: Fig. 116.--Illustrating the General Arrangement of the
Nervous System. (Posterior view.)]
271. The Cranial Nerves. The cranial or cerebral nerves
consist of twelve pairs of nerves which pass from the brain through
different openings in the base of the skull, and are distributed over the
head and face, also to some parts of the trunk and certain internal
organs. These nerves proceed in pairs from the corresponding parts of each
side of the brain, chiefly to the organs of smell, taste, hearing, and
sight.
The cranial nerves are of three kinds: sensory, motor, and both
combined, _viz_., mixed.
Distribution and Functions of the Cranial Nerves. The cranial nerves
are thus arranged in pairs:
The first pair are the olfactory nerves, which pass down through
the ethmoid bone into the nasal cavities, and are spread over the inner
surface of the nose. They are sensory, and are the special nerves of
smell.
The second pair are the optic nerves, which, under the name of
the _optic tracts_, run down to the base of the brain, from which an optic
nerve passes to each eyeball. These are sensory nerves, and are devoted to
sight.
The third, fourth, and sixth pairs proceed to the muscles of the
eyes and control their movements. These are motor nerves, the movers of
the eye.
Each of the fifth pair of nerves is in three branches, and proceeds
mainly to the face. They are called tri-facial, and are mixed nerves,
partly sensory and partly motor. The first branch is purely sensory, and
gives sensibility to the eyeball. The second gives sensibility to the
nose, gums, and cheeks. The third (mixed) gives the special sensation of
taste on the front part of the tongue, and ordinary sensation on the inner
side of the cheek, on the teeth, and also on the scalp in front of the
ear. The motor branches supply the chewing muscles.
The seventh pair, the facial, proceed to the face, where they
spread over the facial muscles and control their movements. The
eighth pair are the auditory, or nerves of hearing, and are
distributed to the special organs of hearing.
The next three pairs of nerves all arise from the medulla, and escape
from the cavity of the skull through the same foramen. They are sometimes
described as one pair, namely, the eighth, but it is more convenient to
consider them separately.
The ninth pair, the glosso-pharyngeal, are partly sensory and
partly motor. Each nerve contains two roots: one a nerve of taste, which
spreads over the back part of the tongue; the other a motor nerve, which
controls the muscles engaged in swallowing.
The tenth pair, the pneumogastric, also known as the vagus
or wandering nerves, are the longest and most complex of all the cranial
nerves. They are both motor and sensory, and are some of the most
important nerves in the body. Passing from the medulla they descend near
the œsophagus to the stomach, sending off, on their way, branches to
the throat, the larynx, the lungs, and the heart. Some of their branches
restrain the movements of the heart, others convey impressions to the
brain, which result in quickening or slowing the movements of breathing.
Other branches pass to the stomach, and convey to the brain impressions
which inform us of the condition of that organ. These are the nerves by
which we experience the feelings of pain in the stomach, hunger, nausea,
and many other vague impressions which we often associate with that organ.
[Illustration: Fig. 117.--Anterior View of the Medulla Oblongata.
A, chiasm of the optic nerves;
B, optic tracts;
C, motor oculi communis;
D, fifth nerve;
E, motor oculi externus;
F, facial nerve;
H, auditory nerve;
I, glosso-pharyngeal nerve;
K, pneumogastric;
L, spinal accessory;
M, cervical nerves;
N, upper extremity of spinal cord;
O, decussation of the anterior pyramids;
R, anterior pyramids of the medulla oblongata;
S, pons Varolii.
]
The eleventh pair, the spinal accessory, are strictly motor, and
supply the muscles of the neck and the back.
The twelfth pair, the hypoglossal, are also motor, pass to the
muscles of the tongue, and help control the delicate movements in the act
of speech.
272. The Spinal Cord. This is a long, rod-like mass of white nerve
fibers, surrounding a central mass of gray matter. It is a continuation of
the medulla oblongata, and is lodged in the canal of the spinal column. It
extends from the base of the skull to the lower border of the first lumbar
vertebra, where it narrows off to a slender filament of gray substance.
The spinal cord is from 16 to 18 inches long, and has about the
thickness of one's little finger, weighing about 1-1/2 ounces. Like the
brain, it is enclosed in three membranes, which in fact are the
continuation of those within the skull. They protect the delicate cord,
and convey vessels for its nourishment. The space between the two inner
membranes contains a small quantity of fluid, supporting the cord, as it
were in a water-bath. It is thus guarded against shocks.
The cord is suspended and kept in position in the canal by delicate
ligaments at regular intervals between the inner and outer membranes.
Finally, between the canal, enclosed by its three membranes, and the bony
walls of the spinal canal, there is considerable fatty tissue, a sort of
packing material, imbedded in which are some large blood-vessels.
273. Structure of the Spinal Cord. The arrangement of the parts of
the spinal cord is best understood by a transverse section. Two fissures,
one behind, the other in front, penetrate deeply into the cord, very
nearly dividing it into lateral halves. In the middle of the isthmus which
joins the two halves, is a very minute opening, the _central canal_ of the
cord. This tiny channel, just visible to the naked eye, is connected with
one of the openings of the medulla oblongata, and extends, as do the
anterior and posterior fissures, the entire length of the cord.
The spinal cord, like the brain, consists of gray and white matter, but
the arrangement differs. In the brain the white matter is within, and the
gray matter is on the surface. In the cord the gray matter is arranged in
two half-moon-shaped masses, the backs of which are connected at the
central part. The white matter, consisting mainly of fibers, running for
the most part in the direction of the length of the cord, is outside of
and surrounds the gray crescents. Thus each half or side of the cord has
its own gray crescent, the horns of which point one forwards and the other
backwards, called respectively the anterior and posterior cornua or horns.
It will also be seen that the white substance itself, in each half of the
cord, is divided by the horns of the gray matter and by fibers passing
from them into three parts, which are known as the anterior,
posterior, and lateral columns.
Experiment 130. Procure at the market an uninjured piece of the
spinal cord from the loin of mutton or the sirloin or the rib of beef.
After noting its general character while fresh, put it to soak in dilute
alcohol, until it is sufficiently hard to be cut in sections.
274. The Spinal Nerves. From the gray matter on each side of the
spinal cord 31 spinal nerves are given off and distributed chiefly to
the muscles and the skin. They pass out at regular intervals on each side
of the canal, by small openings between the vertebræ. Having escaped from
the spine, they pass backwards and forwards, ramifying in the soft parts
of the body. The first pair pass out between the skull and the atlas, the
next between the atlas and the axis, and so on down the canal. The eighth
pair, called _cervical_, pass out in the region of the neck; twelve,
called _dorsal_, in the region of the ribs; five are _lumbar_, and five
_sacral_, while the last pair leave the cord near the coccyx.
Each spinal nerve has two roots, one from the anterior, the other
from the posterior portion of the cord. These unite and run side by
side, forming as they pass between the vertebræ one silvery thread, or
nerve trunk. Although bound up in one bundle, the nerve fibers of the two
roots remain quite distinct, and perform two entirely different functions.
After leaving the spinal cord, each nerve divides again and again into
finer and finer threads. These minute branches are distributed through the
muscles, and terminate on the surface of the body. The anterior roots
become motor nerves, their branches being distributed to certain
muscles of the body, to control their movements. The posterior roots
develop into sensory nerves, their branches being distributed through
the skin and over the surface of the body to become nerves of touch. In
brief, the spinal nerves divide and subdivide, to reach with their twigs
all parts of the body, and provide every tissue with a nerve center, a
station from which messages may be sent to the brain.
[Illustration: Fig. 118.--Side View of the Spinal Cord. (Showing the
fissures and columns.)
A, anterior median fissure;
B, posterior median fissure;
C, anterior lateral fissure;
D, posterior lateral fissure;
E, lateral column;
F, anterior column;
G, posterior column;
H, posterior median column;
K, anterior root;
L, posterior root;
M, ganglion of
N, a spinal nerve.
]
275. The Functions of the Spinal Nerves. The messages which pass
along the spinal nerves to and from the brain are transmitted mostly
through the gray matter of the cord, but some pass along the white matter
on the outer part. As in the brain, however, all the active powers of the
cord are confined to the gray matter. The spinal nerves themselves have
nothing to do with sensation or will. They are merely conductors to carry
messages to and fro. They neither issue commands nor feel a sensation.
Hence, they consist entirely of white matter.
276. Functions of the Spinal Cord. The spinal cord is the principal
channel through which all impulses from the trunk and extremities pass to
the brain, and all impulses to the trunk and extremities pass from the
brain. That is, the spinal cord receives from various parts of the body
by means of its sensory nerves certain impressions, and conveys them to
the brain, where they are interpreted.
The cord also transmits by means of its motor nerves the commands of the
brain to the voluntary muscles, and so causes movement. Thus, when the
cord is divided at any point, compressed, as by a tumor or broken bone, or
disorganized by disease, the result is a complete loss of sensation and
voluntary movement below the point of injury. If by accident a man has his
spinal cord injured at some point, he finds he has lost all sensation and
power of motion below that spot. The impulse to movement started in his
brain by the will does not reach the muscles he wishes to move, because
traveling _down_ the spinal cord, it cannot pass the seat of injury.
So the impression produced by pricking the leg with a pin, which, before
pain can be felt, must travel up the spinal cord to the brain, cannot
reach the brain because the injury obstructs the path. The telegraph wire
has been cut, and the current can no longer pass.
277. The Spinal Cord as a Conductor of Impulses. The identity in
structure of the spinal nerves, whether motor or sensory, and the vast
number of nerves in the cord make it impossible to trace for any distance
with the eye, even aided by the microscope and the most skillful
dissection, the course of nerve fibers. The paths by which the motor
impulses travel down the cord are fairly well known. These impulses
originate in the brain, and passing down keep to the same side of the
cord, and go out by nerves to the same side of the body.
The sensory impulses, however, soon after they enter the cord by the
nerve of one side, cross in the cord to the opposite side, up which they
travel to the brain. Thus the destruction of one lateral half of the cord
causes paralysis of motion on the _same side_ as the injury, but loss of
sensation on the _opposite side_, because the posterior portion destroyed
consists of fibers which have crossed from the opposite side.
Experiment proves that if both roots of a spinal nerve be cut, all those
parts of the body to which they send branches become paralyzed, and have
neither sense of pain nor power of voluntary movement. The parts might
even be cut or burned without pain. It is precisely like cutting a
telegraph wire and stopping the current.
[Illustration: Fig. 119.--The Base of the Brain.
A, anterior lobe of the cerebrum;
B, olfactory nerve;
C, sphenoid portion of the posterior lobe;
D, optic chiasm;
E, optic tract;
F, abducens;
H, M, hemispheres of the cerebellum;
K, occipital portion of the occipital lobe;
L, fissure separating the hemispheres;
N, medulla oblongata;
O, olivary body;
P, antenor pyramids;
R, pons Valoru;
S, section of olfactory nerve, with the trunk removed to show sulcus in
which it is lodged;
T, anterior extremity of median fissure
]
Experiment also proves that if only the posterior root of a spinal nerve
be cut, all sensation is lost in the parts to which the nerve passes, but
the power of moving these parts is retained. But if the anterior root
alone be divided, all power of motion in the parts supplied by that nerve
is lost, but sensation remains. From these and many other experiments, it
is evident that those fibers of a nerve which are derived from the
anterior root are motor, and those from the posterior root sensory,
fibers. Impulses sent _from_ the brain and spinal cord to muscles will,
therefore, pass along the anterior roots through those fibers of the
nerves which are derived from these (motor) roots. On the other hand,
impressions or sensations passing _to_ the brain will enter the spinal
cord and reach the brain through the posterior or sensory roots.
278. The Spinal Cord as a Reflex Center. Besides this function of the
spinal cord as a great nerve conductor to carry sensations to the brain,
and bring back its orders, it is also an independent center for what
is called reflex action. By means of its sensory nerves it receives
impressions from certain parts of the body, and on its own authority sends
back instructions to the muscles by its motor nerves, without consulting
the brain. This constitutes reflex action, so called because the
impulse sent to the spinal cord by certain sensory nerves is at once
reflected or sent back as a motor impulse to the muscles.
This reflex action is a most important function of the spinal cord. This
power is possessed only by the gray matter of the cord, the white
substance being simply a conductor.
The cells of gray matter are found all along the cord, but are grouped
together in certain parts, notably in the cervical and lumbar regions. The
cells of the anterior horns are in relation with the muscles by means of
nerve fibers, and are also brought into connection with the skin and other
sensory surfaces, by means of nerve fibers running in the posterior part
of the cord. Thus there is established in the spinal cord, without
reference to the brain at all, a reflex mechanism.
279. Reflex Centers. For the purpose of illustration, we might
consider the body as made up of so many segments piled one on another,
each segment presided over by a similar segment of spinal cord. Each
bodily segment would have sensory and motor nerves corresponding to its
connection with the spinal cord. The group of cells in each spinal segment
is intimately connected with the cells of the segments above and below.
Thus an impression reaching the cells of one spinal segment might be so
strong as to overflow into the cells of other segments, and thus cause
other parts of the body to be affected.
Take as an example the case of a child who has eaten improper food, which
irritates its bowels. Sensory nerves of the bowels are disturbed, and
powerful impressions are carried up to a center in the spinal cord. These
impressions may now overflow into other centers, from which spasmodic
discharges of nerve energy may be liberated, which passing to the muscles,
throw them into violent and spasmodic contraction. In other words, the
child has a fit, or convulsion. All this disturbance being the result of
reflex action (the spasmodic motions being quite involuntary, as the brain
takes no part in them), the child meanwhile is, of course, entirely
unconscious and, however it may seem to be distressed, really suffers no
pain.
Scattered along the entire length of the spinal cord, especially in the
upper part, are groups of nerve cells which preside over certain specific
functions of animal life; that is, definite collections of cells which
control definite functions. Thus there are certain centers for maintaining
the action of the heart, and the movements of breathing; and low down in
the cord, in the lumbar regions, are centers for the control of the
various abdominal organs.
Numerous other reflex centers are described by physiologists, but enough
has been said to emphasize the great importance of the spinal cord as an
independent nerve center, besides its function as a conductor of
nervous impulses to and from the brain.
280. The Brain as a Reflex Center. The brain, as we have just
stated, is the seat of consciousness and intelligence. It is also the seat
of many reflex, automatic, and coordinating centers. These give rise to
certain reflex actions which are as entirely independent of consciousness
as are those of the spinal cord. These acts take place independently of
the will, and often without the consciousness of the individual. Thus, a
sudden flash of light causes the eyes to blink, as the result of reflex
action. The optic nerves serve as the sensory, and the facial nerves as
the motor, conductors. The sudden start of the whole body at some loud
noise, the instinctive dodging a threatened blow, and the springing back
from sudden danger, are the results of reflex action. The result ensues in
these and in many other instances, without the consciousness of the
individual, and indeed beyond his power of control.
281. The Importance of Reflex Action. Reflex action is thus a
marvelous provision of nature for our comfort, health, and safety. Its
vast influence is not realized, as its numberless acts are so continually
going on without our knowledge. In fact, the greater part of nerve power
is expended to produce reflex action. The brain is thus relieved of a vast
amount of work. It would be impossible for the brain to serve as a
"thinking center" to control every act of our daily life. If we had to
plan and to will every heart-beat or every respiration, the struggle for
life would soon be given up.
The fact that the gray cells of the spinal cord can originate a countless
number of reflex and automatic activities is not only of great importance
in protecting the body from injury, but increases vastly the range of the
activities of our daily life.
Even walking, riding the bicycle, playing on a piano, and numberless other
such acts may be reflex movements. To learn how, requires, of course, the
action of the brain, but with frequent repetition the muscles become so
accustomed to certain successive movements, that they are continued by
the cord without the control of the brain. Thus we may acquire a sort of
artificial reflex action, which in time becomes in a way a part of our
organization, and is carried on without will power or even consciousness.
So, while the hands are busily doing one thing, the brain can be intently
thinking of another. In fact, any attempt to control reflex action is more
apt to hinder than to help. In coming rapidly down stairs, the descent
will be made with ease and safety if the spinal cord is allowed entire
charge of the act, but the chances of stumbling or of tripping are very
much increased if each step be taken as the result of the will power. The
reflex action of the cord may be diminished, or inhibited as it is called,
but this power is limited. Thus, we can by an effort of the will stop
breathing for a certain time, but beyond that the reflex mechanism
overcomes our will and we could not, if we would, commit suicide by
holding our breath. When we are asleep, if the palm of the hand be
tickled, it closes; when we are awake we can prevent it.
[Illustration: Fig. 120.--Dr. Waller's Diagrammatic Illustration of the
Reflex Process.
From the sentient surface (1) an afferent impulse passes along (2) to the
posterior root of the spinal cord, the nerve fibers of the posterior root
ending in minute filaments among the small cells of this part of the cord
(3). In some unknown way this impulse passes across the gray part of the
cord to the large cells of the anterior root (5), the cells of this part
being connected by their axis-cylinder with the efferent fibers (6). These
convey the stimulus to the fibers of the muscle (7), which accordingly
contract. Where the brain is concerned in the action the circuit is longer
through S and M.]
Experiment 131. _To illustrate reflex action by what is called
knee-jerk._ Sit on a chair, and cross the right leg over the left one.
With the tips of the fingers or the back of a book, strike the right
ligamentum patellæ. The right leg will be raised and thrown forward with
a jerk, owing to the contraction of the quadriceps muscles. An
appreciable time elapses between the striking of the tendon and the
jerk. The presence or absence of the knee-jerk may be a most significant
symptom to the physician.
282. The Sympathetic System. Running along each side of the spine,
from the base of the skull to the coccyx, is a chain of nerve knots, or
ganglia. These ganglia, twenty-four on each side, and their branches
form the sympathetic system, as distinguished from the cerebro-spinal
system consisting of the brain and spinal cord and the nerves springing
from them. The ganglia of the sympathetic system are connected with each
other and with the sensory roots of the spinal nerves by a network of gray
nerve fibers.
At the upper end the chain of each side passes up into the cranium and is
closely connected with the cranial nerves. In the neck, branches pass to
the lungs and the heart. From the ganglia in the chest three nerves form a
complicated network of fibers, from which branches pass to the stomach,
the liver, the intestines, the kidneys, and other abdominal organs. A
similar network of fibers is situated lower down in the pelvis, from which
branches are distributed to the pelvic organs. At the coccyx the two
chains unite into a single ganglion.
Thus, in general, the sympathetic system, while intimately connected with
the cerebro-spinal, forms a close network of nerves which specially
accompany the minute blood-vessels, and are distributed to the muscles of
the heart, the lungs, the stomach, the liver, the intestines, and the
kidneys--that is, the hollow organs of the body.
283. The Functions of the Sympathetic System. This system exercises a
superintending influence over the greater part of the internal organs of
the body, controlling to a certain extent the functions of digestion,
nutrition, circulation, and respiration. The influence thus
especially connected with the processes of organic life is generally
different from, or even opposed to, that conveyed to the same organs by
fibers running in the spinal or cranial nerves. These impulses are beyond
the control of the will.
[Illustration: Fig. 121.--The Cervical and Thoracic Portion of the
Sympathetic Nerve and its Main Branches.
A, right pneumogastric;
B, spinal accessory;
C, glosso-pharyngeal;
D, right bronchus;
E, right branch of pulmonary artery;
F, one of the intercostal nerves;
H, great splanchnic nerve;
K, solar plexus;
L, left pneumogastric;
M, stomach branches of right pneumogastric;
N, right ventricle;
O, right auricle;
P, trunk of pulmonary artery;
R, aorta; S, cardiac nerves;
T, recurrent laryngeal nerve;
U, superior laryngeal nerve;
V, submaxillary ganglion;
W, lingual branch of the 5th nerve;
X, ophthalmic ganglion;
Y, motor oculi externus.
]
Hence, all these actions of the internal organs just mentioned that are
necessary to the maintenance of the animal life, and of the harmony which
must exist between them, are controlled by the sympathetic system. But for
this control, the heart would stop beating during sleep, digestion would
cease, and breathing would be suspended. Gentle irritation of these
nerves, induced by contact of food in the stomach, causes that organ to
begin the churning motion needed for digestion. Various mental emotions
also have a reflex action upon the sympathetic system. Thus, terror
dilates the pupils, fear acts upon the nerves of the small blood-vessels
of the face to produce pallor, and the sight of an accident, or even the
emotions produced by hearing of one, may excite nausea and vomiting.
The control of the blood-vessels, as has been stated (sec. 195), is
one of the special functions of the sympathetic system. Through the nerves
distributed to the muscular coats of the arteries, the caliber of these
vessels can be varied, so that at one moment they permit a large quantity
of blood to pass, and at another will contract so as to diminish the
supply. This, too, is beyond the control of the will, and is brought about
by the vaso-motor nerves of the sympathetic system through a reflex
arrangement, the center for which is the medulla oblongata.
284. Need of Rest. The life of the body, as has been emphasized in
the preceding chapters, is subject to constant waste going on every
moment, from the first breath of infancy to the last hour of old age. We
should speedily exhaust our life from this continual loss, but for its
constant renewal with fresh material. This exhaustion of life is increased
by exertion, and the process of repair is vastly promoted by rest. Thus,
while exercise is a duty, rest is equally imperative.
The eye, when exactingly used in fine work, should have frequent intervals
of rest in a few moments of darkness by closing the lids. The brain, when
urged by strenuous study, should have occasional seasons of rest by a
dash of cold water upon the forehead, and a brief walk with slow and deep
inspirations of fresh air. The muscles, long cramped in a painful
attitude, should be rested as often as may be, by change of posture or by
a few steps around the room.
It is not entirely the amount of work done, but the continuity of
strain that wears upon the body. Even a brief rest interrupts this
strain; it unclogs the wheels of action. Our bodies are not designed for
continuous toil. An alternation of labor and rest diminishes the waste of
life. The benign process of repair cannot go on, to any extent, during
strenuous labor, but by interposing frequent though brief periods of rest,
we lessen the amount of exhaustion, refresh the jaded nerves, and the
remaining labor is more easily endured.
285. Benefits of Rest. There is too little repose in our American
nature and in our modes of life. A sense of fatigue is the mute appeal of
the body for a brief respite from labor, and the appeal should, if
possible, be heeded. If this appeal be not met, the future exertion
exhausts far more than if the body had been even slightly refreshed. If
the appeal be met, the brief mid-labor rest eases the friction of toil,
and the remaining labor is more easily borne. The feeling that a
five-minute rest is so much time lost is quite an error. It is a gain of
physical strength, of mental vigor, and of the total amount of work done.
The merchant burdened with the cares of business life, the soldier on the
long march, the ambitious student over-anxious to win success in his
studies, the housewife wearied with her many hours of exacting toil, each
would make the task lighter, and would get through it with less loss of
vital force, by occasionally devoting a few minutes to absolute rest in
entire relaxation of the strained muscles and overtaxed nerves.
286. The Sabbath as a Day of Physiological Rest. The divine
institution of a Sabbath of rest, one day in seven, is based upon the
highest needs of our nature. Rest, to be most effective, should alternate
in brief periods with labor.
It is sound physiology, as well as good morals and manners, to cease
from the usual routine of six days of mental or physical work, and rest
both the mind and the body on the seventh. Those who have succeeded best
in what they have undertaken, and who have enjoyed sound health during a
long and useful life, have studiously lived up to the mandates of this
great physiological law. It is by no means certain that the tendency
nowadays to devote the Sabbath to long trips on the bicycle, tiresome
excursions by land and sea, and sight-seeing generally, affords that real
rest from a physiological point of view which nature demands after six
days of well-directed manual or mental labor.
287. The Significance of Sleep as a Periodical Rest. Of the chief
characteristics of all living beings none is so significant as their
periodicity. Plants as well as animals exhibit this periodic
character. Thus plants have their annual as well as daily periods of
activity and inactivity. Hibernating animals pass the winter in a
condition of unconsciousness only to have their functions of activity
restored in early spring. Human beings also present many instances of a
periodic character, many of which have been mentioned in the preceding
pages. Thus we have learned that the heart has its regular alternating
periods of work and rest. After every expiration from the lungs there is a
pause before the next inspiration begins.
Now sleep is just another manifestation of this periodic and
physiological rest by which Nature refreshes us. It is during the periods
of sleep that the energy expended in the activities of the waking hours is
mainly renewed. In our waking moments the mind is kept incessantly active
by the demands made on it through the senses. There is a never-ceasing
expenditure of energy and a consequent waste which must be repaired. A
time soon comes when the brain cells fail to respond to the demand, and
sleep must supervene. However resolutely we may resist this demand,
Nature, in her relentless way, puts us to sleep, no matter what objects
are brought before the mind with a view to retain its attention.[41]
288. Effect of Sleep upon the Bodily Functions. In all the higher
animals, the central nervous system enters once at least in the
twenty-four hours into the condition of rest which we call sleep.
Inasmuch as the most important modifications of this function are observed
in connection with the cerebro-spinal system, a brief consideration of the
subject is properly studied in this chapter. In Chapter IV. we learned
that repose was as necessary as exercise to maintain muscular vigor. So
after prolonged mental exertion, or in fact any effort which involves an
expenditure of what is often called nerve-force, sleep becomes a
necessity. The need of such a rest is self-evident, and the loss of it is
a common cause of the impairment of health. While we are awake and active,
the waste of the body exceeds the repair; but when asleep, the waste is
diminished, and the cells are more actively rebuilding the structure for
to-morrow's labor. The organic functions, such as are under the direct
control of the sympathetic nervous system,--circulation, respiration, and
digestion,--are diminished in activity during sleep. The pulsations of the
heart and the respiratory movements are less frequent, and the
circulation is slower. The bodily temperature is reduced, and the cerebral
circulation is diminished. The eyes are turned upward and inward, and the
pupils are contracted.
The senses do not all fall to sleep at once, but drop off successively:
first the sight, then the smell, the taste, the hearing and lastly the
touch. The sleep ended, they awake in an inverse order, touch, hearing,
taste, smell, and sight.
289. The Amount of Sleep Required. No precise rule can be laid down
concerning the amount of sleep required. It varies with age, occupation,
temperament, and climate to a certain extent. An infant whose main
business it is to grow spends the greater part of its time in sound sleep.
Adults of average age who work hard with their hands or brain, under
perfectly normal physiological conditions, usually require at least eight
hours of sleep. Some need less, but few require more. Personal
peculiarities, and perhaps habit to a great extent, exert a marked
influence. Some of the greatest men, as Napoleon I., have been very
sparing sleepers. Throughout his long and active life, Frederick the Great
never slept more than five or six hours in the twenty-four. On the other
hand, some of the busiest brain-workers who lived to old age, as William
Cullen Bryant and Henry Ward Beecher, required and took care to secure at
least eight or nine hours of sound sleep every night.
In old age, less sleep is usually required than in adult life, while the
aged may pass much of their time in sleep. In fact, each person learns by
experience how much sleep is necessary. There is no one thing which more
unfits one for prolonged mental or physical effort than the loss of
natural rest.
290. Practical Rules about Sleep. Children should not be played with
boisterously just before the bedtime hour, nor their minds excited with
weird goblin stories, or a long time may pass before the wide-open eyes
and agitated nerves become composed to slumber. Disturbed or insufficient
sleep is a potent factor towards producing a fretful, irritable child.
At all ages the last hour before sleep should, if possible, be spent
quietly, to smooth the way towards sound and refreshing rest. The sleep
induced by medicine is very often troubled and unsatisfactory. Medicines
of this sort should not be taken except on the advice of a physician.
While a hearty meal should not usually be taken just before bedtime, it is
not well to go to bed with a sense of positive faintness and hunger.
Rather, one should take a very light lunch of quite simple food as a
support for the next eight hours.
[Illustration: Fig. 122.--Trunk of the Left Pneumogastric.
(Showing its distribution by its branches and ganglia to the larynx,
pharynx, heart, lungs, and other parts.)]
It is better, as a rule, not to engage in severe study during the hours
just before bedtime. Neither body nor mind being at its best after the
fatigues of the day, study at that time wears upon the system more, and
the progress is less than at earlier hours. One hour of morning or day
study is worth a much longer time late at night. It is, therefore, an
economy both of time and of nerve force to use the day hours and the early
evening for study.
The so-called "cat naps" should never be made to serve as a substitute for
a full night's sleep. They are largely a matter of habit, and are
detrimental to some as well as beneficial to others. Late hours are
usually associated with exposure, excitement, and various other drains
upon the nerve force, and hence are injurious.
It is better to sleep on one or other side than on the back. The head
should be somewhat raised, and a mattress is better than a feather bed.
The bedclothes should be sufficient, but not too heavy. Light tends to
prevent sleep, as do loud or abrupt sounds, but monotonous sounds aid it.
291. Alcohol and the Brain. The unfortunate effects which alcoholic
drinks produce upon the brain and nervous system differ from the
destructive results upon other parts of the body in this respect, that
elsewhere the consequences are usually both less speedy and less obvious.
The stomach, the liver, and even the heart may endure for a while the
trespass of the narcotic poison, and not betray the invasion. But the
nervous system cannot, like them, suffer in silence.
In the other parts of the body the victim may (to a certain extent)
conceal from others the suffering of which he himself is painfully
conscious. But the tortured brain instantly reveals the calamity and the
shame, while the only one who may not fully realize it is the victim
himself. Besides this, the injuries inflicted upon other organs affect
only the body, but here they drag down the mind, ruin the morals, and
destroy the character.
The brain is indeed the most important organ of the body, as it presides
over all the others. It is the lofty seat of power and authority. Here the
king is on his throne. But if, by this malignant adversary, the king
himself be dethroned, his whole empire falls to ruins.
292. How Alcohol Injures the Brain. The brain, the nerve centers,
and the nerves are all made up of nerve pulp, the softest and most
delicate tissue in the whole bodily structure. Wherever this fragile
material occurs in our bodies,--in the skull, the spine, the trunk, or the
limbs,--the all-wise Architect has carefully protected it from violence,
for a rough touch would injure it, or even tender pressure would disturb
its function.
It is a further indication of the supreme importance of the brain, that
about one-fifth of the entire blood of the body is furnished to it.
Manifestly, then, this vital organ must be tenderly cared for. It must
indeed be well nourished, and therefore the blood sent to it must be
highly nutrient, capable of supplying oxygen freely. This condition is
essential to successful brain action. But intoxicants bring to it blood
surcharged with a poisonous liquid, and bearing only a limited supply of
oxygen.
Another condition of a healthy brain is that the supply of blood to it
shall be equable and uniform. But under the influence of strong drink, the
blood pours into the paralyzed arteries a surging tide that floods the
head, and hinders and may destroy the use of the brain and the senses.
Still another requirement is that whatever is introduced into the cerebral
tissues, having first passed through the stomach walls and thence into the
blood, shall be bland, not irritating. But in the brain of the inebriate
are found not only the distinct odor but the actual presence of alcohol.
Thus we plainly see how all these three vital conditions of a healthy
brain are grossly violated by the use of intoxicants.
"I think there is a great deal of injury being done by the use of
alcohol in what is supposed by the consumer to be a most moderate
quantity, to persons who are not in the least intemperate, and to people
supposed to be fairly well. It leads to degeneration of the tissues; it
damages the health; it injures the intellect. Short of drunkenness, that
is, in those effects of it which stop short of drunkenness, I should say
from my experience that alcohol is the most destructive agent we are
aware of in this country."--Sir William Gull, the most eminent English
physician of our time.
293. Why the Brain Suffers from the Alcoholic Habit. We do not find
that the alcoholic habit has produced in the brain the same coarse
injuries that we see in other organs, as in the stomach, the liver, or the
heart. Nor should we expect to find them; for so delicate and so sensitive
is the structure of this organ, that a very slight injury here goes a
great way,--a disturbance may be overwhelming to the brain that would be
only a trifle to some of the less delicate organs.
Alcohol has different degrees of affinity for different organs of the
body, but much the strongest for the cerebral tissues. Therefore the brain
feels more keenly the presence of alcohol than does any other organ.
Almost the moment that the poison is brought into the stomach, the nerves
send up the alarm that an invading foe has come. At once there follows a
shock to the brain, and very soon its paralyzed blood-vessels are
distended with the rush of blood. This first effect is, in a certain
sense, exhilarating, and from this arousing influence alcohol has been
erroneously considered a stimulant; but the falsity of this view is
pointed out elsewhere in this book.
294. Alcohol, the Enemy of Brain Work. The healthy brain contains a
larger proportion of water than does any other organ. Now alcohol, with
its intense affinity for water, absorbs it from the brain, and thus
condenses and hardens its structure. One of the important elements of the
brain is its albumen; this also is contracted by alcohol. The nerve cells
and fibers gradually become shriveled and their activity is lowered, the
elasticity of the arteries is diminished, the membranes enveloping the
brain are thickened, and thus all proper brain nutrition is impaired. The
entire organ is slowly hardened, and becomes unfitted for the proper
performance of its delicate duties. In brief, alcohol in any and every
form is the enemy of successful and long-continued brain work.
[Illustration: Fig. 123.--Nerve Trunks of the Right Arm.]
295. Other Physical Results of Intoxicants. What are some of the
physical results observed? First, we note the failure of the vaso-motor
nerves to maintain the proper tone of the blood-vessels, as in the turgid
face and the congested cornea of the eye. Again, we observe the loss of
muscular control, as is shown by the drop of the lower lip, the thickened
speech, and the wandering eye. The spinal cord, too, is often affected and
becomes unable to respond to the demand for reflex action, as appears from
the trembling hands, the staggering legs, the swaying body, and the
general muscular uncertainty. All these are varied results of the
temporary paralysis of the great nerve centers.
Besides, the sensibility of the nerves is deadened. The inebriate may
seize a hot iron and hardly know it, or wound his hand painfully and never
feel the injury. The numbness is not of the skin, but of the brain, for
the drunken man may be frozen or burned to death without pain. The senses,
too, are invaded and dulled. Double vision is produced, the eyes not being
so controlled as to bring the image upon corresponding points of the
retina.
296. Diseases Produced by Alcohol. The diseases that follow in the
train of the alcoholic habit are numerous and fatal. It lays its
paralyzing hand upon the brain itself, and soon permanently destroys the
integrity of its functions. In some the paralysis is local only, perhaps
in one of the limbs, or on one side of the body; in others there is a
general muscular failure. The vitality of the nerve centers is so
thoroughly impaired that general paralysis often ensues. A condition of
insomnia, or sleeplessness, often follows, or when sleep does come, it is
in fragments, and is far from refreshing to the jaded body.
In time follows another and a terrible disease known as _delirium
tremens_; and this may occur in those who claim to be only moderate
drinkers, rarely if ever intoxicated. It accompanies an utter breakdown of
the nervous system. Here reason is for the time dethroned, while at some
times wild and frantic, or at others a low, mumbling delirium occurs, with
a marked trembling from terror and exhaustion.
There is still another depth of ruin in this downward course, and that is
_insanity_. In fact, every instance of complete intoxication is a case of
temporary insanity, that is, of mental unsoundness with loss of
self-control. Permanent insanity may be one of the last results of
intemperance. Alcoholism sends to our insane asylums a large proportion of
their inmates, as ample records testify.
297. Mental and Moral Ruin Caused by Alcoholism. Alcoholism, the evil
prince of destroyers, also hastens to lay waste man's mental and moral
nature. Just as the inebriate's senses, sight, hearing, and touch, fail to
report correctly of the outer world, so the mind fails to preside properly
over the inner realm. Mental perceptions are dulled. The stupefied
faculties can hardly be aroused by any appeal. Memory fails. Thus the man
is disqualified for any responsible labor. No railroad company, no
mercantile house, will employ any one addicted to drinking. The mind of
the drunkard is unable to retain a single chain of thought, but gropes
about with idle questionings. The intellect is debased. Judgment is
impossible, for the unstable mind cannot think, compare, or decide.
The once active power of the will is prostrate, and the victim can no
longer resist the feeblest impulse of temptation. The grand faculty of
self-control is lost; and as a result, the baser instincts of our lower
nature are now uppermost; greed and appetite rule unrestrained.
But the moral power is also dragged down to the lowest depths. All the
finer sensibilities of character are deadened; all pride of personal
appearance, all nice self-respect and proper regard for the good opinion
of others, every sense of decorum, and at last every pretence of decency.
Dignity of behavior yields to clownish silliness, and the person lately
respected is now an object of pity and loathing. The great central
convictions of right and wrong now find no place in his nature; conscience
is quenched, dishonesty prevails. This is true both as to the solemn
promises, which prove mere idle tales, and also as to property, for he
resorts to any form of fraud or theft to feed the consuming craving for
more drink.
298. Evil Results of Alcoholism Inherited. But the calamity does not
end with the offender. It may follow down the family line, and fasten
itself upon the unoffending children. These often inherit the craving for
drink, with the enfeebled nature that cannot resist the craving, and so
are almost inevitably doomed to follow the appalling career of their
parents before them.
Nor does this cruel taint stop with the children. Even their descendants
are often prone to become perverse. As one example, careful statistics of
a large number of families, more than two hundred descended from
drunkards, show that a very large portion of them gave undoubted proof of
well-marked degeneration. This was plain in the unusual prevalence of
infant mortality, convulsions, epilepsy, hysteria, fatal brain diseases,
and actual imbecility.[42]
It is found that the long-continued habitual user of alcoholic drinks, the
man who is never intoxicated, but who will tell you that he has drunk
whiskey all his life without being harmed by it, is more likely to
transmit the evil effects to his children than the man who has occasional
drunken outbreaks with intervals of perfect sobriety between. By his
frequently repeated small drams he keeps his tissues constantly
"alcoholized" to such an extent that they are seldom free from some of the
more or less serious consequences. His children are born with organisms
which have received a certain bias from which they cannot escape; they are
freighted with some heredity, or predisposition to particular forms of
degeneration, to some morbid tendency, to an enfeebled constitution, to
various defective conditions of mind and body. Let the children of such a
man attempt to imitate the drinking habits of the father and they quickly
show the effects. Moderate drinking brings them down.
Among other consequences of an alcoholic inheritance which have been
traced by careful observers are: Morbid changes in the nerve centers,
consisting of inflammatory lesions, which vary according to the age in
which they occur; alcoholic insanity; congenital malformations; and a much
higher infant death rate, owing to lack of vitality, than among the
children of normal parents.
Where the alcoholic inheritance does not manifest itself in some definite
disease or disorder, it can still be traced in the limitations to be found
in the drinking man's descendants. They seem to reach a level from which
they cannot ascend, and where from slight causes they deteriorate. The
parents, by alcoholic poisoning, have lowered the race stock of vitality
beyond the power of ascent or possibility to rise above or overcome the
downward tendency.
Of course these effects of alcoholics differ widely according to the
degree of intoxication. Yet, we must not forget that the real nature of
inebriety is always the same. The end differs from the beginning only in
degree. He who would avoid a life of sorrow, disgrace, and shame must
carefully shun the very first glass of intoxicants.
299. Opium. Opium is a gum-like substance, the dried juice of the
unripe capsule of the poppy. The head of the plant is slit with fine
incisions, and the exuding white juice is collected. When it thickens and
is moulded in mass, it becomes dark with exposure. _Morphine_, a white
powder, is a very condensed form of opiate; _laudanum_, an alcoholic
solution of marked strength; and _paregoric_, a diluted and flavored form
of alcoholic tincture.
300. Poisonous Effects of Opium. Some persons are drawn into the use
of opium, solely for its narcotic and intoxicating influence.
Every early consent to its use involves a lurking pledge to repeat the
poison, till soon strong cords of the intoxicant appetite bind the now
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