THE ELIMINATION OF WASTE SUBSTANCES.
The expenditures of the human body, or the waste products which
arise from the activity of the master tissues, are thrown off by
the excretory tissues, as the lungs, the skin, the kidneys, and the
terminal part of the intestines.
The lungs are hollow organs, and we may consider them as really two
bags containing air, each of which communicates by a separate orifice
with a common air tube, through the upper part of which, the larynx,
they freely communicate with the external atmosphere. The orifice of
the larynx is guarded by muscles, and can be opened or closed at will.
Each lung is partially subdivided into separate portions called
lobes. The right lung has three lobes, and the left lung has two. Each
of these lobes, again, is composed of a large number of minute parts,
called lobules. Each pulmonary lobule may be considered a lung in
miniature, consisting as it does of a branch of a bronchial tube,
air-cells, blood-vessels, nerves, and lymphatics, with a sparing
amount of areolar tissue.
The terminal portion of each lobule is composed of a group of
pouches or air-cells, which communicate with the intercellular air
passages. These cells are of various forms, according to the mutual
pressure to which they are subject. Their cell walls are nearly in
contact, and they vary from 1/50 to 1/90 of an inch in diameter.
Outside the cells a network of pulmonary capillaries is spread out
so densely that the interspaces or meshes are even narrower than the
vessels, which are on an average 1/3000 of an inch in diameter.
Between the atmospheric air in the cells and the blood in the
vessels nothing intervenes but the thin membrane of the cells and the
capillaries, and the delicate epithelium lining the former. And the
exposure of the blood to the air is the more complete because the folds
of membrane between contiguous cells, and often the spaces between
the walls of the same, contain only a single layer of capillaries,
both sides of which are thus at once exposed to the air.
The enlargement of the capacity of the chest in inspiration is a
muscular act; the muscles concerned in producing the effect being
chiefly the diaphragm, the external intercostal muscles, etc.
From the enlargement produced in inspiration, the chest and lungs
return in ordinary tranquil expiration by their elasticity; the
force employed by the inspiratory muscles in distending the chest and
overcoming the elastic resistance of the lungs and chest wall being
returned as an expiratory effort when the muscles are relaxed.
The acts of expansion and of contraction of the chest take up, under
ordinary circumstances, a nearly equal time, and can scarcely be said
to be separated from each other by an intervening pause. The quantity
of air that is changed in the lungs in each act of ordinary tranquil
breathing is variable, but probably 30 to 35 cubic inches are a fair
average in the case of healthy young and middle-aged men. The total
quantity of air which passes into and out of the lungs of an adult,
at rest, in 24 hours, has been estimated to be about 686,000 cubic
inches. This quantity is largely increased by exertion; and it has
been computed that the average amount for a hard-working laborer in
the same time is 1,568,390.
Breathing air is the quantity of air which is habitually and almost
uniformly changed in each act of breathing.
Complemental air is the quantity of air over and above this which a
man can draw into the lungs in the deepest inspiration.
After ordinary expiration, such as that which expels the breathing
air, a certain quantity of air remains in the lungs which may be
expelled by a forcible and deeper expiration; this is termed reserve
air. But even after the most violent expiratory effort, the lungs are
not completely emptied; a certain quantity of air remains in them,
over which there is no voluntary control, which may be called residual
air. Its amount depends, in great measure, on the absolute size of the
chest, and has been variously estimated at from 40 to 200 cubic inches.
Power of Inspiratory Power of Expiratory
Muscles. Muscles.
1.5 inches. weak 2.0 inches.
2.0 ,, ordinary 2.5 ,,
2.5 ,, strong 3.5 ,,
3.5 ,, very strong 4.5 ,,
4.5 ,, remarkable 5.8 ,,
5.5 ,, very remarkable 7.0 ,,
6.0 ,, extraordinary 8.5 ,,
7.0 ,, very extraordinary 10.0 ,,
The blood as it moves through the respiratory organs is exposed
to the air that alternately moves into and out of the air-cells
and minute bronchial tubes. The blood is propelled from the right
ventricle through the pulmonary capillaries in steady streams, and
slowly enough to permit every minute portion of it to be for a few
seconds exposed to the air, with only the thin walls of the capillary
vessels and air-cells intervening.
The atmosphere we breathe has in every situation in which it has been
examined in its natural state a nearly uniform composition. It is a
mixture of oxygen and nitrogen, carbonic acid, and watery vapor, with
traces of other gases, as ammonia, sulphuretta, hydrogen, etc. Of
every 100 volumes of pure atmospheric air, 79 volumes consist of
nitrogen and 21 of oxygen, about. The proportion of carbonic acid
is extremely small: 10,000 volumes of atmospheric air contains only
about 4 or 5 of carbonic acid. The average quantity of watery vapor
in the atmosphere in this country is about 1.40 per cent.
The changes produced by respiration on the atmosphere are that:
1. It is warmed; 2. Its carbonic acid is increased; 3. Its oxygen is
diminished; 4. Its watery vapor is increased; 5. A minute amount of
organic matter and of free ammonia is added to it.
1. The expired air is hotter than the inspired air. The temperature
varies from 97° to 99 1/2°.
2. Carbonic acid in respired air is always increased; but the
quantity exhaled in a given time is subject to change from various
circumstances. From every volume of air inspired about 4 1/2 per cent
of oxygen is abstracted; while rather a smaller quantity of carbonic
acid is added in its place. Under ordinary circumstances, the quantity
of carbonic acid exhaled into the air breathed by a healthy adult
man amounts to 1,346 inches, or about 636 grains, per hour. It is
estimated that the weight of carbon excreted from the lungs is about
173 grains per hour, or rather more than 8 ounces in 24 hours.
Of course the influence of age, sex, respiratory movements,
external temperature, season of the year, purity of the respired air,
hygrometric state of the atmosphere, period of day, food and drink,
exercise and sleep, have to be taken in consideration.
The oxygen of respired air is always less than in the same air before
respiration, and its diminution is generally proportionate to the
increase of the carbonic acid. It has been shown that for every volume
of carbonic acid exhaled into the air 1.17421 volumes of oxygen are
absorbed from it; and that when the average quantity of carbonic acid,
i.e., 1,346 cubic inches, or 636 grains, is exhaled in the hour, the
quantity of oxygen absorbed in the same time is 1,584 cubic inches,
or 542 grains.
The nitrogen in the atmosphere, in relation to the respiratory process
is supposed to serve only mechanically, by diluting the oxygen,
and moderating the action upon the system.
The most obvious change which the blood undergoes in its passage
through the lungs is that of color, the dark venous blood being
exchanged for the bright scarlet arterial blood. It gains oxygen,
loses carbonic acid, becomes 1° to 2° F. warmer; it coagulates sooner
and more firmly, and contains more fibrine.
The venous blood as it issues from the right ventricle is loaded with
carbonic acid. The oxygen present is insufficient to the whole of the
hæmoglobin of the red corpuscles; much reduced hæmoglobin is present,
hence the purple color of venous blood. As the blood-vessels pass
through the capillaries of the lungs, this reduced hæmoglobin takes
from the pulmonary air its complement of oxygen, all or nearly all
the hæmoglobin of the red corpuscles becomes oxy-hæmoglobin, and the
purple color forthwith shifts into scarlet. The hæmoglobin of arterial
blood is saturated or nearly saturated with oxygen. Passing from
the left ventricle to the capillaries, some of the oxy-hæmoglobin
gives up its oxygen to the tissues, becomes reduced hæmoglobin,
and the blood in consequence becomes once more venous, with a
purple hue. Thus the red corpuscles by virtue of their hæmoglobin
are emphatically oxygen-carriers. Undergoing no intrinsic change in
itself, the hæmoglobin combines in the lungs with oxygen, which it
carries to the tissues; these, more greedy of the oxygen than itself,
rob it of its charge, and the reduced hæmoglobin hurries back to the
lung in venous blood for another portion. Hæmoglobin combines loosely
with carbonic oxide just as it does with oxygen, but the affinity
with the former is greater than with the latter. While carbonic oxide
readily turns out oxygen, oxygen cannot so readily turn out carbonic
acid. This property of carbonic oxide explains its poisonous nature.
Respiratory changes in the tissues. Arterial blood passing through the
several tissues, becomes once more venous. A considerable quantity
of the oxy-hæmoglobin becomes reduced, and a quantity of carbonic
acid passes from the tissue into the blood. The blood which comes
from a contracting muscle, is not only richer in carbonic acid,
but also, though not to a corresponding amount, poorer in oxygen,
than the blood which flows from a muscle at rest.
A muscle is always producing carbonic acid, and when it contracts there
is a sudden and extensive increase of the normal production. Oxygen
is necessary for the life of the muscle. When venous blood instead
of arterial blood is sent through the blood-vessel of a muscle,
the irritability speedily disappears, and unless fresh oxygen be
administered the muscle soon dies.
Our knowledge of the respiratory changes in muscle is more complete
than in the case of any other tissue; but we have no reason to
suppose the phenomena of muscle are exceptional. On the contrary,
all the available evidence goes to show that in all the tissues
the oxidation takes place in the tissues and not in the adjoining
blood. It is a remarkable fact, that lymph, serous fluid, bile, urine,
and the other secretions contain no free or loosely combined oxygen,
while the tension of carbonic acid in peritoneal fluid is as high as
six per cent, and in bile and urine is still higher, etc.
All these facts point to the conclusion, that it is the tissues,
and not the blood, which become primarily loaded with carbonic acid,
the latter simply receiving the gas from the former by diffusion;
and that the oxygen which passes from the blood into the tissues is
at once taken up in the same combinations, so that it is no longer
removable by diminished tension.
The production of carbonic acid in the muscle is not directly dependent
on the consumption of oxygen. The muscles produce carbonic acid in
an atmosphere of hydrogen. What is true of muscle is true also of
other tissues and of the body at large.
Oxygen helps to wind up the vital clock; but once wound up, the clock
will go on for a period without further winding (Pflüger).
To sum up, then, the result of respiration in its chemical aspect. As
the blood passes through the lungs, the low oxygen tension of the
venous blood permits the entrance of oxygen from the air of the
pulmonary alveolus, through the thin alveolar wall, through the thin
capillary sheath, through the thin layer of blood plasma, to the red
corpuscles, and the reduced hæmoglobin of the venous blood becomes
wholly, or all but wholly, oxy-hæmoglobin. Hurried to the tissues,
the oxygen, at a comparatively high tension in the arterial blood,
passes largely into the tissues, in which the oxygen tension is always
kept at an exceedingly low pitch, by the fact that the tissues, in
some way at present unknown to us, pack away, at every moment, into
some stable combination each molecule of oxygen which they receive
from the blood. With much, but not all, of its oxy-hæmoglobin reduced,
the blood passes on as venous blood. How much hæmoglobin is reduced
will depend on the activity of the tissue itself. The quantity of
hæmoglobin in the blood is the measure of limit of the oxidizing power
of the body at large; but within that limit the amount of oxidation
is determined by the tissue, and by the tissue alone.
The skin is an excretory tissue, and consists principally of two
layers, an external covering of epithelium, termed the cuticle or
epidermis, and a layer of vascular tissue, named the corium derma or
cutis vera. The integument serves (1) for the protection of deeper
tissues, (2) as a sensitive organ in the exercise of touch, (3) as an
excretory organ, (4) as an absorbing organ, (5) for regulating the
temperature of the body. Within and beneath the corium are imbedded
several organs with special functions, namely, sudoriferous or sweat
glands, sebaceous or fat glands, and hair follicles; and on its
surface are sensitive papillæ. The so-called appendages of the skin,
the hair and nails, are modifications of the epidermis.
Sudoriferous glands: In the middle of each of the transverse furrows
between the papillæ, and irregularly scattered between the bases
of the papillæ in those parts of the surface of the body in which
there are no furrows between them, are the orifices or ducts of the
sudoriferous, or sweat glands, by which it is probable that a large
portion of the aqueous and gaseous materials excreted by the skin are
separated. Each of these glands consists of a small lobular mass,
which appears formed of a coil of tubular gland-duct surrounded by
blood-vessels and imbedded in the subcutaneous adipose tissue. From
this mass the duct ascends, for a short distance, in a spiral manner
through the deeper parts of the cutis, then passing straight, and
then sometimes again becoming spiral, it runs through the cuticle and
opens by an oblique, valve-like apparatus. The sudoriferous glands
are abundantly distributed over the whole surface of the body; but are
especially numerous, as well as very large, in the skin of the palm of
the hand. They are estimated from 2,738 to 3,528 in each superficial
square inch. They are almost equally abundant and large in the skin
of the sole. The glands by which the peculiar odorous matter of the
axilla is secreted form a nearly complete layer under the cutis, and
are like the ordinary sudoriferous glands, except in being larger
and having very short ducts. In the neck and back, where they are
least numerous, the glands amount to 417 on the square inch. The
total number is estimated, at 2,381,248; and supposing the orifice
of each gland to present a surface of 1/54 of a line in diameter (and
regarding a line as equal to 1/10 of an inch) the whole of the glands
would present an evaporating surface of about eight square inches.
Sebaceous glands secrete a peculiar fatty matter. Like the sudoriferous
glands, they are abundantly distributed over most parts of the body.
The quantity of matter which leaves the human body by way of the skin
is very considerable. It is estimated that while 7 grains pass through
the lungs per minute, as much as 11 escape through the skin. The
amount varies extremely. It is calculated that the total amount of
perspiration excreted from the whole body in 24 hours might range
from 2 to 20 kilos.
The total amount of perspiration is affected not only by the condition
of the atmosphere, but also by the nature and quantity of food taken,
the amount of fluid drunk, and the amount of exercise taken. It is
also influenced by the mental condition, by medicines and poisons, by
disease, and by the relative activity of the other excreting organs,
more particularly the kidneys.
The fluid perspiration or sweat, when collected, is found to be a
clear colorless fluid, with a strong and distinctive odor varying
according to the part of the body from which it is taken. Besides
accidental epidermic scales, it contains no structural elements. Its
reaction is generally acid, but in cases of excessive secretion may
become alkaline. The average amount of solids is about 1.81 per cent,
of which about two-thirds consists of organic substances. The chief
normal constituents are (1) sodium chloride (common salt), with small
quantities of other inorganic salts; (2) various acids of the fatty
series, such as fermic, acetic, butyric acid, with probably other
acids--CH2O2-C2H4O2--C4H8O2; (3) neutral fats and cholestrine; (4)
ammonia (NH3) (urea), and possibly other nitrogenous substances.
The average loss by cutaneous and pulmonary exhalation in a minute
is from 17 to 18 grains; the minimum, 11 grains; the maximum, 32
grains; of the average 18 grains 11 pass by the skin and 7 by the
lungs. The maximum loss by exhalation, cutaneous and pulmonary, in
twenty-four hours is about 3 3/4 pounds; the minimum, about 1 1/2
pounds. Valentine found the whole quantity lost by exhalation from
the respiratory and cutaneous surfaces of a healthy man who consumed
daily 40,000 grains of food and drink to be 19,000 grains, or 2 1/2
pounds. Subtracting from this, for the pulmonary exhalation, 5,000
grains, and for the excess of the weight of the exhaled carbonic acid
over that of the equal volume of the inspired oxygen, 2,256 grains,
the remainder, 11,744 grains, or nearly 1 5/7 pounds, may represent
an average amount of cutaneous exhalation in a day.
The Kidneys, two in number, are excretory organs. They are deeply
seated in the lumbar region, one on each side of the vertebral column,
at the back of the abdominal cavity, and behind the peritoneum. The
kidneys measure about 4 inches in length, 2 1/2 inches in breadth,
and 1 1/2 inches in thickness. The left is usually longer and narrower
than the right one. The weight of the kidney is usually stated to be
about 4 1/2 ounces in the male and somewhat less in the female.
The excretory apparatus consists of fine tubules (the tubuli
urineferi), malpighian bodies, blood-vessels, nerves, and lymphatics,
etc.
The kidneys are highly vascular, and receive their blood from the
renal arteries, which are very large in proportion to the organ they
supply. Each artery breaks up into four or five branches, these
again subdivide and break up into capillaries in the substance of
the kidney. The veins arise by numerous venous radicals from the
capillary network of the kidney, as seen near the surface of the
gland, and collect the blood from the capillary plexus around the
convoluted tubules which mainly compose this part, the smaller veins
joining together and ultimately forming a single vein and ending in
the inferior vena cava.
The kidneys are so arranged by their anatomical structure--that of
the cortical and medullary substance, the tubuli urineferi, pyramids,
malpighian bodies, etc.--that they separate from the blood the solids
in a state of solution. The secretion takes place by the agency of
the gland cells, and equally in all the parts of the urine tubes. The
protoplasmic cells which line at least a large portion of the tubuli
urineferi elaborate from the blood certain substances, and discharge
them into the channels of the tubules. All parts of the tubular
system of the kidney take part in the secretion of urine as a whole,
but there is another provision of vessels for a more simple draining
off of the water from the blood when required.
The large size of the renal arteries and veins permits so rapid
a transit of the blood through the kidneys that the whole of the
blood is purified by them. The secretion of urine is rapid in
comparison with other secretions, and as each portion is secreted,
it propels that which is already in the tubes onwards into the pelvis
of the kidney. Thence, through the ureter, the urine passes into the
bladder, into which its rate and mode of entrance has been watched. The
urine does not enter the bladder at any regular rate, nor is there a
synchronism in its movement through the two ureters. In a recumbent
posture the urine collects for a little time in the ureters, then flows
gently, and if the body is raised, runs from them in a stream till they
are empty. Its flow is increased in deep inspiration, or straining,
and in active exercise, and in fifteen or twenty minutes after meals.
Substances taken into the stomach pass very rapidly through the
circulation. It does not take longer than one minute for ferrocyanide
of potassium to pass through. Vegetable substances pass in from
sixteen to thirty-five. Neutral alkaline salts with vegetable acids,
which were generally decomposed in transitu, made the urine alkaline
in twenty-eight to forty-seven minutes. But the time of passage varied
much; and the transit was always slow when the substances were taken
during digestion.
There are really two distinct parts in the kidney--the actively
secreting part, the epithelium of the secreting tubules; and what
maybe called a filtering part, the malpighian bodies.
The specific gravity of urine is 1020--that is, the average human
urine. Urine varies--in the morning before breakfast it is darker,
urina sanguinis; urine secreted shortly after the introduction
of any considerable quantity of fluid into the body, urina potus;
and the urine evacuated immediately succeeding a solid meal of food,
urina cibi. The last kind contains a larger quantity of solid matter
than either of the others, the first and second being largely diluted
with water.
Specific gravity: The morning urine is best calculated for
analysis. The average healthy range may be stated at 1015 in the
winter to 1025 in the summer, and variations of diet and exercise may
make a great difference. In disease, the variations may be greater;
sometimes descending in albuminaria to 1004, and frequently ascending
in diabetes, when the urine is loaded with sugar, to 1050, or even
to 1060.
The whole quantity of urine secreted in twenty-four hours is subject to
variations according to the amount of fluid drunk, and the proportion
of the latter passing off from skin, lungs, and alimentary canal. The
average quantity voided in twenty-four hours by healthy male adults
from twenty to forty years of age amounts to 52 1/2 fluid ounces.
The chemical composition of urine. The average quantity of each
constituent of the urine in 1,000 parts is:
Water (O H2), 967
Urea (C O N2 H4), 14.239
Uric acid (C5 N4 H4 O3), .468
Coloring matter, mucus, and animal
extractive matter, 10.107
{ Sulphates (soda, potash), } 8.185
Salts. { Bisulphates (lime, soda, }
{ magnesia, ammonia), }
{ Chlorides (sodium, potassium), }
Silica, etc., Traces.
---------
1,000.000
Urea is the principal solid constituent of the urine, forming nearly
one-half of the whole quantity of solid matter. It is also the most
important ingredient, since it is the chief substance by which the
nitrogen of decomposed tissue and superfluous food is excreted from
the body.
The salts excreted by the kidneys in 24 hours are:
Urea (C N2 H4 O), 512 grains.
Chloride of sodium (Na Cl), 177 ,,
Phosphoric acid (H3 P O4), 48 ,,
Sulphuric acid (H2 S O4), 31.11 ,,
Uric acid (C5 N4 H4 O3), 8.53 ,,
The substances excreted consist mainly of carbonic acid gas (C O2),
which is expired by the lungs, and urea (C N2 H4 O), which is expelled
by the urine.
These excretions, or expenditures, or waste products of the human
body, present the carbohydrates--starch, sugars, and fats--and the
proteids--meats and albumen--taken into the system as food.
The daily average loss by the expenditure or waste products of the
body is estimated to be about:
Carbon, 4,500 grains.
Nitrogen, 3 to 500 grains.
Besides salts and water.
Of all the elements of the income and outcome, the nitrogen, the
carbon, and the free oxygen of respiration, are by far the most
important. Since water is of use to the body for merely mechanical
purposes, and not as food in the strict sense of the word, the
hydrogen element becomes a dubious one; the sulphur of the proteids,
and phosphorus of the fats, are insignificant in amount; while the
saline matters stand on a wholly different footing from the other
parts of the food, inasmuch as they are not sources of energy, and
pass through the body with comparatively little change.
The correct income will consist of so much nitrogen, carbon, hydrogen,
oxygen, sulphur, phosphorus, saline matters, and water, contained
in the proteids, fats, carbohydrates, salts, and water of the food,
together with the oxygen absorbed by the lungs, skin, and alimentary
canal.
The outcome will consist of: 1. The respiratory products of the lungs,
skin, and alimentary canal, consisting chiefly of carbonic acid and
water, with small quantities of hydrogen and carburetted hydrogen,
these two latter coming exclusively from the alimentary canal;
2. Perspiration, consisting chiefly of water and salts, with urea by
the skin, and other organic constituents of sweat amounting to very
little; 3. The urine, which contains practically all the nitrogen
really excreted by the body, as well as a large quantity of saline
matter and water.
HEAT AND TEMPERATURE.
The average temperature of the human body in those internal parts which
are more accessible, as the mouth and rectum, is from 98.5° to 99.5° F.
The chief circumstances by which the temperature of the healthy body
is influenced are the following:
Age. The average temperature of the new-born babe is only about 1°
F. above that proper to the adult. In old age the temperature rises
again, and approaches that of infancy.
Sex. In the female slightly higher than in the male.
Exercise. Active exercise raises the temperature of the body, through
muscular contraction, etc.
Climate and season. In passing from a temperate to a hot climate,
the temperature of the human body rises slightly, rarely more than 2°
to 3° F. In summer the temperature of the body is a little higher
than in winter, 1/5° to 1/3° F.
Cold alcoholic drinks depress the temperature 1/2° to 1°F.
Warm alcoholic drinks, as well as warm tea and coffee, raise the
temperature about 1/2° F.
In disease, as in pneumonia and typhus, it occasionally rises as high
as 106° or 107° F.
In Asiatic cholera a thermometer placed in the mouth sometimes rises
only to 77° or 79° F.
The temperature maintained by mammalia of an active state of life
averages 101° F. In birds, the average is as high as 107° F., the
highest temperature, 111.25°, being in the species of the linnets, etc.
The sources and distribution of heat. Wherever metabolism of protoplasm
is going on, heat is being generated. All over the body heat is being
set free; more abundantly in the more active tissues, and most of
all in those tissues the metabolism of which leads to little or no
external work. The metabolism of the tissues (including the blood)
and of the food within the alimentary canal is the source of the heat
of the body. But heat, being continually produced, is as continually
being lost, as we have seen, by the skin, urine, and feces. The blood
passing from one part of the body to another, and carrying warmth from
the tissues where heat is being actively generated, to the tissues or
organs where heat is being lost by conduction or evaporation, tends
to equalize the temperature of the various parts and thus maintain
a constant bodily temperature.
Taking the body as a whole, under normal conditions, the chief sources
of the production of heat are the muscles, and the abdominal viscera,
more especially the liver; and of these the liver deserves attention,
inasmuch as it is always at work, whereas the heat produced by the
muscles is at least largely dependent on their contracting, and they
may remain at rest for a considerable period. The brain, too, may be
regarded as a source of heat, since its temperature is higher than
that of the arterial blood with which it is supplied.
Heat is lost by the skin, respiration, feces, etc. The great regulator,
however, is undoubtedly the skin. The more blood passes through the
skin the greater will be the loss of heat by conduction, radiation,
and evaporation. The working of this heat-regulating mechanism is
well seen in the case of exercise. Since every muscular contraction
gives rise to heat, exercise must increase for the time being the
production of heat; yet the bodily temperature rarely rises as much
as a degree C., if at all. By exercise the respiration is quickened
and the loss of heat by the lungs increased. The circulation of blood
is also quickened, and the cutaneous vascular areas becoming dilated,
a large amount of blood passes through the skin. The expenditure of
heat may be tabulated thus:
By the skin, in conducting, radiating, and
evaporating, 77.5 per cent.
Warming expired air, 5.2 ,,
Evaporating the water of respiration, 14.5 ,,
In warming urine, etc., 2.6 ,,
THE CIRCULATION.
The heart is a hollow muscular organ divided by a longitudinal septum
into a right and a left half, each of which is again subdivided by
a transverse constriction into two compartments communicating with
each other, and named auricle and ventricle.
The heart is inclosed in the pericardium and placed behind the
sternum and costal cartilages on the border end or base, by which it
is attached, being directed upwards, backwards, and to the right,
and extending from the level of the fourth to that of the eighth
dorsal vertebra, the apex downwards, forwards, and to the left.
In size, it is about five inches long, three and a half in its
greatest width, and two in its extreme thickness from the anterior
to the posterior surface. The weight is from nine to ten ounces.
The circulation of the blood.--
The body is divided into two chief cavities, the chest or thorax,
and abdomen, by a curved muscular partition called the diaphragm or
midriff. The chest is almost entirely filled with lungs and heart,
the latter being fitted in, so to speak, between the two lungs, nearer
to the front than the back of the chest, and partly overlapped by them.
In the living body the heart and lungs are in constant rhythmic
movement, the result of which is an unceasing stream of air through
the trachea alternately into and out of the lungs, and an unceasing
stream of blood into and out of the heart.
The blood is conveyed away from the heart by the arteries and returned
to it by the veins; the arteries and veins being continuous with each
other, at one end by means of the heart, and at the other by a fine
network of vessels called capillaries. The blood, therefore, in its
passage from the heart passes first into the arteries, then into the
capillaries, and lastly into the veins, by which it is conveyed back
again to the heart--thus completing a revolution, or circulation.
There are two circulations by which all the blood must pass--the one a
shorter circuit from the heart to the lungs and back again, which is
called the pulmonic; the other the larger circuit, from the heart to
all parts of the body and back again, which is called the systemic;
and a subordinate stream of blood, that has been collected by the
blood-vessels of the intestines, passes by means of the portal vein
through the liver, and is called the portal circulation.
The principal force provided for constantly moving the blood on
this course, is that of the muscular substance of the heart; other
assistant forces are (2) those of the elastic walls of the arteries,
(3) the pressure of the muscles among which some of the veins run,
(4) the movements of the walls of the chest in respiration, and (5)
probably to some extent the interchange of relations between the
blood and the tissues which ensues in the capillary system during
the nutritive processes. The right direction of the blood's course
is determined and maintained by the valves of the heart.
The heart is divided into two chief chambers or cavities--right
and left. Each of these chambers is again divided into an upper and
lower portion called respectively auricle and ventricle, which freely
communicate with each other.
The right auricle communicates on the one hand with the veins of the
general system and on the other with the right ventricle. The valvular
curtain between the right auricle and the right ventricle is named
the tricuspid; by it the auricle is guarded from the ventricle. The
ventricle leads directly into the pulmonary artery and this in turn
into the lungs. The pulmonary artery is guarded by three semilunar
valves. The left auricle again communicates on the one hand with the
pulmonary vein and on the other with the left ventricle, which is
guarded by the mitral or bicuspid valve. The left ventricle leads
directly into the aorta, which is also guarded by three semilunar
valves. The aorta is a large artery which conveys the blood to the
general system.
The arrangement of the heart's valves is such that the blood can pass
only in one definite direction, and this is--from the right auricle the
blood passes into the right ventricle, and thence into the pulmonary
artery, by which it is conveyed to the capillaries of the lungs. From
the lungs, the blood, which is now purified and altered in color, is
gathered by the pulmonary veins and taken to the left auricle. From
the left auricle it passes into the left ventricle, and thence into
the aorta, by which it is distributed to the capillaries in every
portion of the body.
The Heart's action. The heart's action in propelling the blood
consists in the successive alternate contractions and dilatations of
the muscular walls of the two auricles and ventricles. The auricles
contract simultaneously; so do the ventricles; their dilatations also
are severally simultaneous; and the contractions of the one pair of
cavities are synchronous with the dilatations of the other.
Valves--Bi and Tricuspid. During auricular contraction the force of the
blood propelled into the ventricle is transmitted in all directions,
but being insufficient to raise the semilunar valves, it is expended
in distending the ventricle and in raising and gradually closing the
auriculo-ventricular valves (tricuspid and bicuspid valves). These
when the ventricle is full form a complete septum (partition) between
it and the auricle.
The arterial or semilunar valves are brought into action by the
pressure of the arterial blood forced back towards the ventricles, when
the elastic walls of the arteries recoil after being dilated by the
blood propelled into them in the previous contraction of the ventricle.
The sounds. When the ear is placed over the region of the heart two
sounds may be heard at every beat of the heart, which follow in quick
succession, and are succeeded by a pause or a period of silence. The
first sound is dull and prolonged; its commencement coincides with the
impulse of the heart and just precedes the pulse at the wrist. The
second is a shorter and sharper sound, with a somewhat flapping
character, and follows close after the arterial pulse.
First sound. The chief cause of the first sound of the heart appears
to be the vibration of the auriculo-ventricular valve, and also,
but to a less extent, of the ventricular walls, and the coats of the
aorta and pulmonary artery, all of which parts are suddenly put into
a state of tension at the moment of ventricular contraction.
The second sound is more complete than that of the first. It is
probably due entirely to the sudden closure and consequent vibration
of the semilunar valves when they are pressed down across the orifice
of the aorta and pulmonary artery.
Pulse. The heart of a healthy adult man in the middle period of life
acts from seventy to seventy-five times per minute. The frequency of
the heart's action gradually diminishes from the commencement to near
the end of life.
In persons of sanguine temperament, the heart acts somewhat more
frequently than in those of the phlegmatic; and in the female sex
more frequently than in the male; in children, more frequently still.
Capacity. The capacity of the two ventricles is probably exactly the
same. From the mean of various estimates taken, it may be inferred
that each ventricle is able to contain on an average about three
ounces of blood, the whole of which is impelled into the respective
arteries at each contraction.
Every time the ventricles contract three ounces of blood are pumped
out of the heart into the lungs and heart respectively.
Calculating seventy pulses per minute, the quantity of blood passing
through the heart would be about 211 ounces, or 14 1/4 pints per
minute; or 895 pints per hour, or 21,480 pints in 24 hours.
Velocity. The velocity of the stream of blood is greater in the
arteries than in any other part of the circulatory system, and in
them it is greatest in the neighborhood of the heart and during
the ventricular systole; the rate of movement diminishes during the
diastole of the ventricles, and in the parts of the arterial system
most distant from the heart. The rate is calculated to be about from
10 to 12 inches per second in the large arteries near the heart.
THE BLOOD.
Blood is a tissue of which the red corpuscles are the essential and
active elements, while the plasma is the liquid matrix. There are
two kinds of corpuscles, the white and the red. The protoplasm of the
white corpuscles is native indifferentiated protoplasm, in no respect
fitted for any special duty, as far as we know at present. The white
corpuscles are in reality embryonic structures, concerned chiefly in
the production of other forms, such as red corpuscles, and it may be
under certain conditions various elements of the other tissues. The red
corpuscles have a definite respiratory function. But these form a part
only of the blood. The largest portion of the blood, the whole mass
of the plasma, is an unorganized fluid with no proper physiological
(vital) properties of its own. Its function is to serve as the great
medium of exchange between all the tissues of the body. Just as the
whole organism lives on the things around it, its air and its food,
so the several tissues live on the complex fluid by which they are
all bathed and which is to them their immediate air and food.
Blood within the living vessel is a fluid; but when shed, or after
the death of the vessels, becomes solid by the process known as
coagulation. The average specific gravity of human blood is 1056,
varying from 1045 to 1075 within the limits of health. It has an
alkaline reaction, which in shed blood rapidly diminishes up to the
onset of coagulation.
Blood may, in general terms, be considered as consisting by weight of
more than one-third and less than one-half of corpuscles, the rest
being plasma, the corpuscles being supposed to retain the amount of
water proper to them. Human blood: corpuscles 513, plasma 487. The
average quantity of fibrine in the human blood is said to be two
per cent.
Composition of serum: In 100 parts there are in round numbers:
Water, 90 parts.
Proteid substance, 8 to 9 ,,
Fat extractives and saline matter, 2 to 1 ,,
Of the proteid substances the great mass consists of the so-called
serum-albumen.
Composition of red corpuscles: The red corpuscles contain less water
than the serum. In 100 parts of red corpuscle there are:
Water, 56.5
Solid, 43.5
The solids are almost entirely organic matter, the inorganic salts
in the corpuscles amounting to less than 4 per cent. In 100 parts of
dried organic matter of the corpuscles of human blood there are:
Hæmoglobin, 90.54
Proteid substance, 8.67
Lecithin, .54
Cholestrin, .25
The blood is distributed as follows in round numbers:
In the heart, lungs, large arteries and veins, About one-fourth.
In the liver, ,, ,,
In the skeletal muscles, ,, ,,
In the other organs, ,, ,,
The average proportion of the principal constituents of the blood in
1,000 parts is:
Water, 784
Red corpuscles (solid residue), 130
Albumen serum, 70
Saline matter, 6.03
Extractive fatty matter, 7.77
Fibrine, 2.20
The chemical composition of hæmoglobin is:
Carb. Hyd. Iron. Nit. Oxy. Sulph.
54.2 7.2 0.42 16.0 21.5 6.7
Mucine, 52.2 7.0 12.6 28.2
Proteids, 51.5 6.9 15.2 20.9 0.
to 54.5 to 7.3 to 17.0 to 23.5 to 2.0
THE ORGANS OF RESPIRATION.
The principal organs of respiration consist of larynx, trachea,
bronchi, lungs.
The larynx is affixed to the upper end of the windpipe, and is not
only the entrance for air into the respiratory organs from the pharynx,
but also the organ of voice.
The trachea measures from four inches to four inches and a half in
length, and from three-quarters of an inch to one inch in width; but
its length and width are liable to continual variations, according
to the position of the larynx and the direction of the neck.
The trachea divides into two branches, called bronchi, right and
left. The right bronchus, wider and shorter than the left, measuring
about an inch in length, passes outwards almost horizontally into the
root of the right lung on a level with the fourth dorsal vertebra. The
left bronchus, smaller in diameter but longer than the right, being
nearly two inches in length, inclines downwards and outwards to reach
the root of the right lung, which it enters on a level with the fifth
dorsal vertebra--that is, about an inch lower than the right bronchus.
The lungs, placed one on the right and the other on the left of the
heart and large vessels, occupy by far the larger part of the cavity
of the chest, and during life are always in accurate contact with the
internal surface of its walls. Each lung is attached at a comparatively
small part of its flattened inner or median surface by a part named
the root and by a thin membranous fold, which is continued downwards
from it.
The pleuræ are serous membranes forming two shut sacs, quite distinct
from each other, which line the right and left side of the thorax,
forming by their approximation in the middle line the mediastinal
partition, and are reflected each upon the root and over the entire
free surface of the corresponding lung.
The lungs. Each lung is irregularly pyramidal or conical, with its
base downwards, and one side (the inner) much flattened. The broad
concave base is of a semi-lunar form, and rests upon the arch of the
diaphragm. The apex is blunt, and reaches into the root of the neck,
above the first rib, where it is separated from the first portion of
the subclavian artery by the pleural membrane.
The lungs vary much in size and weight, according to the quantity of
blood and mucous or serous fluid they may happen to contain, which
is greatly influenced by the circumstances immediately preceding
death, as well as other causes. The weight of both lungs together,
as generally stated, ranges from 30 to 48 ounces, the more prevalent
weights being found between 36 and 42 ounces. The proportion borne
by the right lung to the left is nearly 22 ounces to 20, taking
the combined weight of the two at 42 ounces. The lungs are not only
absolutely heavier in the male than in the female, but appear to be
heavier in proportion to the weight of the body. The general ratio
between the weight of the lungs and body in the adult fluctuates
between one to thirty-five and one to fifty.
The average weight in twenty-nine cases, male and female:
Male. Female.
Right lung, 24 ounces. 17 ounces.
Left lung, 21 ,, 15 ,,
--------- ---------
45 ounces. 32 ounces.
The proportionate weight of the lungs to the body is:
Male. Female.
1 to 37 1 to 34
The substance of the lungs is of a light porous spongy texture, and
when healthy is buoyant in water. Specific gravity, 0.126; deprived
of air, 1.056.
When pressed between the fingers, the lungs impart a crepitant
sensation, which is accompanied by a peculiar noise, both effects
being caused by the air contained in the tissue. On cutting the lung
the same crepitation is heard.
The pulmonary tissues are endowed with great elasticity, in consequence
of which the lungs collapse to about one-third of their bulk when
the thorax is opened.
The root of each lung consists of bronchi, arteries, and veins,
together with the nerves, lymphatic vessels, and glands, connected
by areolar tissue, and inclosed in a sheath of the pleura.
Respiration consists of an expiration and an inspiration. The air
passes in through the nose or mouth, through the larynx, trachea,
bronchi, into the lungs.
Inspiration: By the contraction of certain muscles, the cavity of the
thorax is enlarged; in consequence the pressure of the air within the
lungs becomes less than that of the air outside the body, and this
difference of pressure causes a rush of air through the trachea into
the lungs until an equilibrium of pressure is established between the
air inside and that outside the lungs. This constitutes inspiration.
Expiration: Upon the relaxation of the inspiratory muscles (the
muscles whose contraction has brought about the thoracic expansion),
the elasticity of the chest walls and lungs, aided by the contraction
of certain muscles and other circumstances, causes the chest to return
to its original size, or even become smaller. In consequence of this
the pressure within the lungs now becomes greater than that outside,
and thus air rushes out of the trachea, until equilibrium is once
more established. This constitutes expiration.
The inspiratory and expiratory act together form a respiration.
The fresh air introduced into the upper part of the pulmonary passages
by the inspiratory movement contains more oxygen and less carbonic
acid than the old air previously present in the lungs. By diffusion the
new or tidal air, as it is frequently called, gives up the oxygen to,
and takes carbonic acid from, the old or stationary air, and thus
when it leaves the chest in expiration has been the means both of
introducing oxygen into and of removing carbonic acid from it. By
this ebb and flow of the tidal air and the diffusion between it and
the stationary air, the air in the lungs is being continually renewed,
through the alternate expansion and contraction of the chest. In what
may be considered normal breathing, the respiratory act is repeated
about seventeen times a minute; and the duration of the inspiration
as compared with that of the expiration and such pause as exists,
is about as ten to twelve.
When the ordinary respiratory movements prove insufficient to effect
the necessary changes in the blood, their rhythm and character become
changed. Normal respiration gives place to labored respiration, and
this in turn to dyspnoea, which unless some restorative event occurs
terminates in asphyxia.
Changes of the air in respiration:
1. The temperature of the expired air is variable, but under ordinary
circumstances is higher than that of the inspired air.
2. The expired air is loaded with aqueous vapor.
3. The expired air contains about 4 to 6 per cent less oxygen and about
4 per cent more carbonic acid than the inspired air, the quantity of
nitrogen suffering but little change. Thus:
Oxygen. Nitrogen. Carbon.
Inspired air contains 20.81 79.15 .04
Expired ,, ,, 16.033 79.557 4.380
While the air in passing in and out of the lungs is thus robbed of a
portion of its oxygen, and loaded with a certain quantity of carbonic
acid, the blood as it streams along the pulmonary capillaries undergoes
important correlative changes. As it leaves the right ventricle it
is venous blood of a dark purple or maroon color; when the blood
has passed through the lungs and falls into the left auricle, it
is arterial blood of a bright scarlet hue. In passing through the
capillaries of the body from the left to the right side of the heart,
it is again changed from the arterial to the venous condition.
The average composition of this gas in the two kinds of blood is as
follows. From 100 volumes may be obtained:
Oxygen. Carbonic Acid. Nitrogen.
Of arterial blood, 20 (16) vol. 39 (30) vol. 1 to 2 vol.
Of venous blood, 8-12 (6 to 10) 46 (35) vol. 1 to 2 vol.
Oxygen plays a most important role on this terrestrial globe. Life,
health, and food depend on it. This element penetrates, pervades,
everything and everywhere, unites and disunites with all other
elements, preserves and destroys. While its absence from a living
being, whether plant or animal, is death.
When a liquid such as water is exposed to an atmosphere containing a
gas such as oxygen, some of the oxygen will be dissolved in the water,
that is to say will be absorbed from the atmosphere. The quantity which
is so absorbed will depend on the quantity of oxygen which is in the
atmosphere above; that is to say, on the pressure of the oxygen; the
greater the pressure of the oxygen, the larger the amount which will
be absorbed. If, on the other hand, water containing a good deal of
oxygen dissolved in it be exposed to an atmosphere containing little or
no oxygen, the oxygen will escape from the water into the atmosphere.