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Hygienic Physiology

J >> Joel Dorman Steele >> Hygienic Physiology




The plasma also contains fibrin, [Footnote: it is usual to say that fibrin
is contained in the blood. It probably does not exist as such, but there
are present in the blood certain substances known as _paraglobulin_
and _fibrinogen_, which by the action of a third substance, _fibrin
ferment_ under certain circumstances, form fibrin and so cause
coagulation. The exact nature of the process by which fibrin is produced
by these three factors is not understood--See Foster's _Text Book of
Physiology_, p 22.] albumin--which is found nearly pure in the white of
an egg--and various mineral substances, as iron, [Footnote: Enough iron
has been found in the ashes of a burned body to form a mourning ring.]
lime, magnesia, phosphorus, potash, etc.

FIG. 36.

[Illustration: _Blood Crystals_]

USES OF THE BLOOD.--The blood has been called "liquid flesh"; but it is
more than that, since it contains the materials for making every organ.
The plasma is rich in mineral matter for the bones, and in albumen for the
muscles. The red disks are the air cells of the blood. They contain the
oxygen so essential to every operation of life. Wherever there is work to
be done or repairs to be made, there the oxygen is needed. It stimulates
to action, and tears down all that is worn out. In this process, it
combines with and actually burns out parts of the muscles and other
tissues, as wood is burned in the stove. [Footnote: For the sake of
simplicity, perhaps to conceal our own ignorance, we call this process
"burning." The simile of a fire is good so far as it goes. But as to the
real nature of the change which the physiologist briefly terms
"oxidation," we know nothing. This much only can be asserted positively. A
stream of oxygen is carried by the blood to the muscles (in fact to every
tissue in the body), while, from the muscles the blood carries away a
stream of carbonic acid and water. But what takes place in the muscles,
when and what chemical change occurs, no one can tell. We see the first
and the last stage. We know that contraction of the muscles somehow comes
about, oxygen disappears, carbonic acid appears, energy is released, and
force is exhibited as motion, heat, and electricity. But the intermediate
step is hidden.

There are certain theories advanced, however, that are worth considering.
Some physiologists hold that the muscle has the power of taking up the
oxygen from the _hemoglobin_ (a body that comprises ninety per cent
of the red corpuscles when dried, and is the oxygen carrier of the blood),
and fixing it, as well as the raw material (food) furnished by the blood,
thus forming a true contractile substance. The breaking down or
decomposition of this contractile substance in the muscle, sets free its
potential energy. The process is gentle so long as the muscle is at rest,
but becomes excessive and violent when contraction occurs. (See "Foster's
Physiology," p. 118.) It is also believed by some that the chemical change
in the muscle partakes of a fermentive character; that, under the
influence of the proper ferments, the substances break up into other and
simpler products, thus setting free heat and force; and that this chemical
change is followed by a secondary oxidation by the oxygen in the arterial
blood, thereby forming carbonic acid and water, as in all putrefactive
processes. But these and other views are not as yet fully understood;
while they utterly fail to tell us how a collection of simple cells,
filled merely with a semifluid mass of matter, can contract and set free
muscular power. The commonness of this act hides from us its wonderful
nature. But here, hidden in the cell--Nature's tiny laboratory--lies the
mystery of life. Before its closed door we ponder in vain, confessing the
unskillfulness of our labor, and fearing all the while lest the _Secret
of the Cell_ will always elude our search.] The blood, now foul with
the burned matter, the refuse of this fire, is caught up by the
circulation, and whirled back to the lungs, where it is purified, and
again sent bounding on its way.

There are then two different kinds of the blood in the body: the red or
arterial, and the dark or venous.

TRANSFUSION.--As the blood is really the "vital fluid" it would seem that
feeble persons might be restored to vigor by infusing healthy blood into
their veins. This hypothesis, so valuable in its possible results in
prolonging human life, has been carefully tested. Animals which have
ceased to breathe have thus had their vitality recalled. In the
seventeenth century the theory became a subject of special investigation.
A maniac was restored to reason by the blood of a calf, and the most
extravagant hopes were entertained. But many fatal accidents occurring,
experiments upon human beings were forbidden by law, and transfusion soon
fell into disuse. It has, however, been successfully practiced in several
cases within the last few years, and is a method still in repute for
saving lives.

COAGULATION.--When blood is exposed to the air, it coagulates. This is
caused by the solidifying of the fibrin, which entangling the disks, forms
the "clot." The remaining clear, yellow liquid is the _serum_. The
value of this peculiar property of the blood can hardly be overestimated.
The coagulation soon checks all ordinary cases of bleeding. [Footnote: In
the case of the lower animals, which have no means of stopping hemorrhages
as we have, the coagulation is generally still more rapid. In some species
of birds it takes place almost instantaneously.] When a wound is made, and
bleeding commences, the fibrin forms a temporary plug, as it were, which
is absorbed when the healing process is finished. Thus we see how a Divine
foresight has provided not only for the ordinary wants of the body, but
also for the accidents to which it is liable. [Footnote: The fibrin is not
an essential ingredient of the blood. All the functions of life are
regularly performed in people whose blood lacks fibrin; and, in cases of
transfusion, where blood deprived of its fibrin was used, the vivifying
influence seemed to be the same. Its office, therefore, must mainly be to
stanch any hemorrhage which may occur.--FLINT.]

FIG. 37.

[Illustration: _The Heart._ A, _the right ventricle;_ B, _the
left ventricle;_ C, _the right auricle;_ D, _the left auricle._]

THE HEART is the engine which propels the blood. It is a hollow, pear-
shaped muscle, about the size of the fist. It hangs, point downward, just
to the left of the center of the chest. (See Fig. 31.) It is inclosed in a
loose sac of serous membrane, [Footnote: The mucous membrane lines the
open cavities of the body; the serous, the closed. The pericardium is a
sac composed of two layers--a fibrous membrane on the outside, and a
serous one on the inside. The latter covers the external surface of the
heart, and is reflected back upon itself in order to form, like all the
membranes of this nature, a sac without an opening. The heart is thus
covered by the pericardial sac, but not contained inside its cavity. A
correct idea may be formed of the disposition of the pericardium around
the heart by recalling a very common and very convenient, though now
discarded headdress, the cotton nightcap. The pericardium incloses the
heart exactly as this cap covered the heads of our forefathers.--
_Wonders of the Human Body_.] called the pericardium (_peri_,
about; and _kardia_, the heart). This secretes a lubricating fluid,
and is smooth as satin.

THE MOVEMENTS OF THE HEART consist of an alternate contraction and
expansion. The former is called the _sys'-to-le_, and the latter the
_di-as'-to-le_. During the diastole, the blood flows into the heart,
to be expelled by the systole. The alternation of these movements
constitutes the beating of the heart which we hear so distinctly between
the fifth and sixth ribs. [Footnote: Two sounds are heard if we put our
ear over the heart,--the first and longer as the blood is leading the
organ, the second as it falls into the pockets of the two arteries, and
the valves then striking together cause it. The first sound is mainly the
noise made by the muscular tissue. During the first, the two ventricles
contract; during the second the two auricles do so. The hand may feel the
heart striking the ribs as it contracts,--a feeling called the impulse,
or, if quicker and stronger than usual, palpitation. This is not always a
sign of disease, but in hypochondriacs is often an effect of the mind on
the nerves of the heart.--MAPOTHER]

FIG. 38.

[Illustration: _Chambers of the Heart_ A, _right ventricle;_ B,
_left ventricle,_ C, _right auricle,_ D, _left auricle,_ E,
_tricuspid valve,_ F, _bicuspid valve;_ G, _semilunar valves,_ H,
_valve of the aorta;_ I, _inferior vena cava,_ K, _superior vena
cava,_ L, L, _pulmonary veins._]

THE AURICLES AND VENTRICLES--The heart is divided into four chambers. In
an adult, each holds about a wineglassful. The upper ones, from appendages
on the outside resembling the ears of a dog, are called _auricles
(aures_, ears). are termed _ventricles_. The auricle and ventricle
on each side communicate with each other, but the right and left halves of
the heart are entirely distinct, and perform different offices. The left
side propels the red blood; and the right, the dark. The auricles are
merely reservoirs to receive the blood (the left auricle, as it filters in
bright and pure from the lungs; the right, as it returns dark and foul
from the tour of the body), and to furnish it to the ventricles as they
need. Their work being so light, their walls are comparatively thin and
weak. On the other hand, the ventricles force the blood (the left, to all
parts of the body; the right, to the lungs), and are, therefore, made very
strong. As the left ventricle drives the blood so much farther than the
right, it is correspondingly thicker and stronger.

NEED OF VALVES IN THE HEART.--As the auricles do not need to contract with
much force simply to empty their contents into the ventricles below them,
there is no demand for any special contrivance to prevent the blood from
setting back the wrong way. Indeed, it would naturally run down into the
ventricle, which is at that moment open to receive it. But, when the
strong ventricles contract, especially the left one, which must drive the
blood to the extremities, some arrangement is necessary to prevent it from
returning into the auricle. Besides, when they expand, the "suction power"
would tend to draw back again from the arteries all the blood just forced
out. This difficulty is obviated by means of little doors, or valves,
which will not let it go the wrong way. [Footnote: The heart of an ox or a
sheep may be used to show the chambers and valves. The aorta should be cut
as far as possible from the heart, and then by pumping in water the
perfection of these valves will be finely exhibited. Cutting the heart
across near the middle will show the greater thickness of the left
ventricle.]

THE TRICUSPID AND BICUSPID VALVES.--At the opening into the right
ventricle, is a valve consisting of three folds or flaps of membrane,
whence it is called the _tricuspid_ valve (_tri_, three; and
_cuspides_, points), and in the left ventricle, one containing two
flaps, and named the _bicuspid_ valve. These hang so loosely as to
oppose no resistance to the passage of the blood into the ventricles; but,
if any attempts to go the other way, it gets between the flaps and the
walls of the heart, and, driving them outward, closes the orifice.

FIG. 39.

[Illustration: _Diagram showing the peculiar Fibrous Structure of the
Heart and the Shape of the Valves._ A, _tricuspid valve,_ B,
_bicuspid valve;_ C, _semilunar valves of the aorta;_ D,
_semilunar valves of the pulmonary artery._]

THESE FLAPS ARE STRENGTHENED like sails by slender cords, which prevent
their being pressed back through the opening. If the cords were attached
directly to the walls of the heart, they would be loosened in the systole,
and so become useless when most needed. They are, therefore, fastened to
little muscular pillars projecting from the sides of the ventricle; when
that contracts, the pillars contract also, and thus the cords are held
tight.

THE SEMILUNAR VALVES.--In the passages outward from the ventricles, are
valves, called from their peculiar half-moon shape _semilunar_ valves
(_semi_, half; _Luna_, Moon). Each consists of three little
pocket-shaped folds of membrane, with their openings in the direction
which the blood is to take. When it sets back, they fill, and, swelling
out, close the passage (Fig. 40).

THE ARTERIES [Footnote: _Aer,_ air; and _tereo,_ I contain--so
named because after death they contain air only, and hence the ancients
supposed them to be air tubes leading through the body.] are the tube-like
canals which convey the blood _from_ the heart. They carry the red
blood (see note, p. 119). They are composed of an elastic tissue, which
yields at every throb of the heart, and then slowly contracting again,
keeps up the motion of the blood until the next systole. The elasticity of
the arteries acts like the air chamber of a fire engine, which converts
the intermittent jerks of the brakes or pump into the steady stream of the
hose nozzle.

The arteries sometimes communicate by means of branches or by meshes of
loops, so that if the blood be blocked in one, it can pass round through
another, and so get by the obstacle. [Footnote: This occurs especially
about the joints, where it serves to maintain the circulation during the
bending of a limb, or when the main artery is obstructed by disease or
injury, or has been tied by the surgeon. In the last case, the small
adjacent arteries gradually enlarge, and form what is called a collateral
circulation.] When an artery penetrates a muscle, it is often protected by
a sheath or by fibrous rings, which prevent its being pulled out of place
or compressed by the play of the muscles.

The arteries are generally located as far as possible beneath the surface,
out of harm's way, and hence are found closely hugging the bones or
creeping through safe passages provided for them. They are generally
nearly straight, and take the shortest routes to the parts which they are
to supply with blood.

THE ARTERIAL SYSTEM starts from the left ventricle by a single trunk--the
_aorta_--which, after giving off branches to the head, sweeps back of
the chest with a bold curve--the _arch of the aorta_ (_c_, Fig.
34)--and thence runs downward (_f_), dividing and subdividing, like a
tree, into numberless branches, which, at last, penetrate every nook and
corner of the body.

THE PULSE.--At the wrist (_k_, radial artery) and on the temple
(temporal artery) we can feel the expansion of the artery by each little
wave of blood set in motion by the contraction of the heart. In health,
there are about seventy-two [Footnote: This number varies much with age,
sex, and individuals. Napoleon's pulse is said to have been only forty,
while it is not infrequent to find a healthy pulse at one hundred or over.
In general, the pulse is quicker in children and in old people than in the
middle-aged; in short persons than in tall; in women than in men. Shame
makes the heart send more blood to the blushing cheek, and fear almost
stops it. The will can not check the heart. There is said, however, to
have been a notable exception to this in the case of one Colonel Townsend,
of Dublin, who, after having succeeded several times in stopping the
pulsation, at last lost his life in the act.] pulsations per minute. They
increase with excitement or inflammation, weaken with loss of vigor, and
are modified by nearly every disease. The physician, therefore, finds the
pulse a good index of the state of the system and the character of the
disorder. (See p. 314.)

THE VEINS are the tube-like canals which convey the blood _to_ the
heart. [Footnote: There is one exception to the general course of the
veins. The _portal_ vein carries the blood from the digestive organs
to the liver, where it is acted upon, thence poured into the ascending
vena cava, and goes back to the heart.] They carry the dark or venous
blood (note, p. 119). As they do not receive the direct impulse of the
heart, their walls are made much thinner and less elastic than those of
the arteries. At first small, they increase in size and diminish in number
as they gradually pour into one another, like tiny rills collecting to
form two rivers, the vena cava ascending and the vena cava descending
(_l, m_, Fig. 34), which empty into the right auricle.

Some of the veins creep along under the skin, where they can be seen, as
in the back of the hand; while others accompany the arteries, some of
which have two or more of these companions.

VALVES similar in construction to those already described (the semilunar
valves of the heart, page 114) are placed at convenient intervals, in
order to guide the blood in its course, and prevent its setting backward.
[Footnote: Too much standing, or tight elastics, often cause the veins in
the leg to swell, so that the valves can not work; the veins then become
_varicose_, or permanently enlarged, and, if they burst, the bleeding
may be profuse and even dangerous. Raising the leg and pressing the finger
on the bleeding spot will stay it. Walking does not encourage this
disease, for the active muscles force on the venous blood. Clerks who are
subject to varicose veins should have seats behind the counters where they
may rest when not actually employed. A deep breath helps the flow in the
veins, and a wound may suck in air with fatal effect. A maimed horse is
most mercifully killed by blowing a bubble of air into the veins of his
neck. As the deep-sea pressure would burst valves, the whale has none;
hence a small wound by the harpoon causes him to bleed to death.--
MAPOTHER.] We can easily examine the working of these valves. On baring
the arm, blue veins may be seen running along the arm toward the hand.
Their diameter is tolerably even, and they gradually decrease in size. If
now the finger be pressed on the upper part of one of these veins, and
then passed downward so as to drive its blood backward, swellings like
little knots will make their appearance. Each of these marks the location
of a valve, which is closed by the blood we push before our finger. Remove
the pressure, and the valve will swing open, the blood set forward, and
the vein collapse to its former size.

FIG. 40.

[Illustration: _Valves of the Veins._]

THE CAPILLARIES (_capillus,_ a hair) form a fine network of tubes,
connecting the ends of the arteries with the veins. They blend, however,
with the extremities of these two systems, so that it is not easy to tell
just where an artery ends and a vein begins. So closely are they placed,
that we can not prick the flesh with a needle without injuring, perhaps,
hundreds of them. The air cells of the blood deposit there their oxygen,
and receive carbonic acid, while in the delicate capillaries of the lungs
[Footnote: The capillary tubes are there so fine that the disks of the
blood have to go one by one, and are sadly squeezed at that. However,
their elasticity enables them to resume their old shape as soon as they
have escaped from this labyrinth.] they give up their load of carbonic
acid in exchange for oxygen.

FIG. 41.

[Illustration: _Circulation of the Blood in the Web of a Frog's Foot,
highly magnified._ A, _an artery;_ B, _capillaries crowded with
disks, owing to a rupture just above, where the disks are jammed into an
adjacent mesh;_ C, _a deeper vein; the black spots are pigment
cells._]

If, by means of a microscope, we examine the transparent web of a frog's
foot, we can trace the route of the blood. [Footnote: With small splints
and twine, a frog's foot can be easily stretched and tied so that the
transparent web can be placed on the table of the microscope.] It is an
experiment of wonderful interest. The crimson stream, propelled by the
heart, rushes through the arteries, until it reaches the intricate meshes
of the capillaries. Here it breaks into a thousand tiny rills. We can see
the disks winding in single file through the devious passages, darting
hither and thither, now pausing, swaying to and fro with an uncertain
motion, and anon dashing ahead, until, at last, gathered in the veins, the
blood sets steadily back on its return to the heart.

THE CIRCULATION [Footnote: The circulation of the blood was discovered by
Harvey in 1619. For several years, he did not dare to publish his belief.
When it became known, he was bitterly persecuted, and his practice as a
physician greatly decreased in consequence. He lived, however, to see his
theory universally adopted, and his name honored. Harvey is said to have
declared that no man over forty years of age accepted his views.] consists
of two parts--the _lesser_, and the _greater_.

FIG. 42.

[Illustration: _Diagram illustrating the Circulation of the Blood._--
MARSHALL. A, _vena cava descending (superior);_ Z, _vena cava
ascending (inferior);_ C, _right auricle;_ D, _right ventricle;_ E,
_pulmonary artery;_ F P, _lungs and pulmonary veins;_ G, _left auricle;_
H, _left ventricle;_ I, K, _aorta._]

1. _The Lesser Circulation_.--The dark blood from the veins collects
in the right auricle, and, going through the tricuspid valve, empties into
the right ventricle. Thence it is driven past the semilunar valves,
through the pulmonary artery, to the lungs. After circulating through the
fine capillaries of the air cells contained in the lungs, it is returned,
bright and red, through the four pulmonary veins, [Footnote: It is
noticeable that the pulmonary set of veins circulates red blood, and the
pulmonary set of arteries circulates dark blood. Both are connected with
the lungs.] to the left auricle.

2. _The Greater Circulation_.--From the left auricle, the blood is
forced past the bicuspid valve to the left ventricle; thence it is driven
through the semilunar valves into the great aorta, the main trunk of the
arterial system. Passing through the arteries, capillaries, and veins, it
returns through the venæ cavæ, ascending and descending, gathers again in
the right auricle, and so completes the "grand round" of the body. Both
these circulations are going on constantly, as the two auricles contract,
and the two ventricles expand simultaneously, and _vice versa_.

THE VELOCITY OF THE BLOOD varies so much in different parts of the body,
and is influenced by so many circumstances, that it can not be calculated
with any degree of accuracy. It has been estimated that a portion of the
blood will make the tour of the body in about twenty-three seconds
(FLINT), and that the entire mass passes through the heart in from one to
two minutes. [Footnote: The total amount of blood in an adult of average
weight is about eighteen pounds. Dividing this by five ounces, the
quantity discharged by the left ventricle at each systole, gives fifty-
eight pulsations as the number necessary to transmit all the blood in the
body. This, however, is an extremely unreliable basis of calculation, as
the rapidity of the blood is itself so variable. Chauvreau has shown by
experiments with his instrument that, corresponding to the first dilation
of the vessels, the blood moves with immense rapidity; following this, the
current suddenly becomes nearly arrested; this is succeeded by a second
acceleration in the current, not quite so rapid as the first; and after
this there is a gradual decline in the rapidity to the time of the next
pulsation.] (See p. 314.)

DISTRIBUTION AND REGULATION OF THE HEAT OF THE BODY.--1.
_Distribution_.--The natural temperature is not far from 98°.
[Footnote: The average temperature is, however, easily departed from.
Through some trivial cause the cooling agencies may be interfered with,
and then, the heating processes getting the superiority, a high
temperature or fever comes on. Or the reverse may ensue. In Asiatic
cholera, the constitution of the blood is so changed that its disks can no
longer carry oxygen into the system, the heat-making processes are put a
stop to, and, the temperature declining, the body becomes of a marble
coldness, characteristic of that terrible disease.--DRAPER.] This is
maintained, as we have already seen, by the action of the oxygen within
us. Each capillary tube is a tiny stove, where oxygen is combining with
the tissues of the body (see note, p. 107). Every contraction of a muscle
develops heat, the latent heat being set free by the breaking up of the
tissue. The warmth so produced is distributed by the circulation of the
blood. Thus the arteries, veins, and capillaries form a series of hot-
water pipes, through which the heated liquid is forced by a pump--the
heart--while the heat is kept up, not by a central furnace and boiler, but
by a multitude of little fires placed here and there along its course.

2. _Regulation_.--The temperature of the body is regulated by means
of the pores of the skin and the mucous membrane in the air passages. When
the system becomes too warm, the blood vessels on the surface expand, the
blood fills them, the fluid exudes into the perspiratory glands, pours out
upon the exterior, and by evaporation cools the body. [Footnote: Just as
water sprinkled on the floor cools a room.--_Popular Physics_, p.
255.] When the temperature of the body is too low, the vessels contract,
less blood goes to the surface, the perspiration decreases, and the loss
of heat by evaporation diminishes. [Footnote: Thus one is enabled to go
into an oven where bread is baking, or into the arctic regions where the
mountains are snow and the rivers ice. Even by these extremes the
temperature of the blood will be but slightly affected. In the one case,
the flood gates of perspiration will be opened and the superfluous heat
expended in turning the water to vapor; and, in the other, they will be
tightly closed and all the heat retained.]

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