RESPIRATION.
_The Objects of Respiration--The Lungs--The Air-Passages--The Movements
of Respiration--Expiration and Inspiration--The Frequency of
Respiration--Capacity of the Lungs--The Air we breathe--Changes in the
Air from Respiration--Changes in the Blood--Interchange of Gases in the
Lungs--Comparison between Arterial and Venous Blood--Respiratory
Labor--Impurities of the Air--Dust--Carbonic Acid--Effects of Impure
Air--Nature's Provision for Purifying the Air--Ventilation--Animal
Heat--Spontaneous Combustion._
[Sidenote: 1. Difference between the two sets of capillaries? Change
effected by respiration or breathing?]
1. THE OBJECT OF RESPIRATION.--In one set of capillaries, or hair-like
vessels, the blood is impoverished for the support of the different members
and organs of the body. In another capillary system the blood is refreshed
and again made fit to sustain life. The former belongs to the greater or
_systemic_ circulation; the latter to the lesser or _pulmonary_, so called
from _pulmo_, the lungs, in which organs it is situated. The blood, as sent
from the right side of the heart to the lungs, is venous, dark, impure, and
of a nature unfit to circulate again through the tissues. But, when the
blood returns from the lungs to the left side of the heart, it has become
arterial, bright, pure, and no longer hurtful to the tissues. This
marvellous purifying change is effected by means of the very familiar act
of respiration, or breathing.
[Sidenote: 2. What are the lungs? How many lungs are there? Lung-substance?
Its properties? The pleura?]
2. THE LUNGS.--The lungs are the special organs of respiration. There are
two of them, one on each side of the chest, which cavity they, with the
heart, almost wholly occupy. The lung-substance is soft, elastic, and
sponge-like. Under pressure of the finger, it _crepitates_, or crackles,
and floats when thrown into water; these properties being {124} due to the
presence of air in the minute air-cells of the lungs. To facilitate the
movements necessary to these organs, each of them is provided with a double
covering of an exceedingly smooth and delicate membrane, called the
_pleura_. One layer of the pleura is attached to the walls of the chest,
and the other to the lungs; and they glide, one upon the other, with utmost
freedom. Like the membrane which envelops the heart, the pleura secretes
its own lubricating fluid, in quantities sufficient to keep it always
moist.
[Illustration: FIG. 34.--ORGANS OF THE CHEST.
A, Lungs. B, Heart. D, Pulmonary Artery. E, Trachea.]
{125}
[Illustration: FIG. 35.--LARYNX, TRACHEA, AND BRONCHIAL TUBES.]
[Illustration: FIG. 36.--DIAGRAM AND SECTION OF THE AIR-CELLS.]
[Sidenote: 3. Communication of the lungs with the external air? Bronchial
tubes?]
3. THE AIR-PASSAGES. --The lungs communicate with the external air by means
of certain air-tubes, the longest of which, the _trachea_, or windpipe,
runs along the front of the neck (Fig. 34, E, and 35). Within the chest
this tube divides into two branches, one entering each lung; these in turn
give rise to numerous branches, or bronchial tubes, as they are called,
which gradually diminish in size until they are about one-twenty-fifth of
an inch in diameter. Each of these terminates in a cluster of little
pouches, or "air-cells," having very thin walls, and covered with a
capillary network, the most intricate in the body (Fig. 36).
[Sidenote: 4. Office of the bronchial tubes? What further can you state of
them?]
4. These tubes are somewhat flexible, sufficiently so to bend when the
parts move in which they are situated; but they are greatly strengthened by
bands or rings of cartilage which keep the passages always open; otherwise
there would be a constantly-recurring tendency to collapse after every
breath. The lung-substance essentially consists of these bronchial tubes
and terminal air-cells, with the blood-vessels ramifying about them (Fig.
37). At the top of the trachea is the larynx, a sort of {126} box of
cartilage, across which are stretched the vocal cords. Here the voice is
produced chiefly by the passage of the respired air over these cords,
causing them to vibrate.
[Illustration: FIG. 37.--SECTION OF THE LUNGS.]
[Sidenote: 5. The epiglottis? When it does not close in time, what is the
consequence?]
5. Over the opening of the larynx is found the _epiglottis_, which fits
like the lid of a box at the entrance to the lungs, and closes during the
act of swallowing, so that food and drink shall pass backward to the
oesophagus, or gullet (Fig. 38). Occasionally it does not close in time,
and some substance intrudes within the larynx, when we at once discover, by
a choking sensation, that "something has gone the wrong way," and, by
coughing, we attempt to expel the unwelcome intruder. The epiglottis is one
of the many safeguards furnished by nature for our security and {127}
comfort, and is planned and put in place long before these organs are
brought into actual use in breathing and in taking food.
[Illustration: FIG. 38.--SECTION OF MOUTH AND THROAT.
A, The Tongue. B, The Uvula C, Vocal Cord. E, Epiglottis. L, Larynx.
N, Trachea. O, Oesophagus.]
[Sidenote: 6. Lining of the air-passages? Ciliated cells? Their uses? The
three diseases of the lungs?]
{128}
[Illustration: FIG. 39.--CILIATED CELLS.]
6. The air-passages are lined through nearly their whole extent with mucous
membrane, which maintains these parts in a constantly moist condition. This
membrane has a peculiar kind of cells upon its outer surface. If examined
under a powerful microscope, we may see, even for a considerable time after
their removal from the body, that these cells have minute hair-like
processes in motion, which wave like a field of grain under the influence
of a breeze (Fig. 39). This is a truly beautiful sight; and since it is
found that these little _cilia_, as they are called, always produce
currents in one direction, from within outward, it is probable that they
serve a useful purpose in catching and carrying away from the lungs dust
and other small particles drawn in with the breath (Fig. 39). The three
diseases which more commonly affect the lungs, as the result of exposure,
are pneumonia, or inflammation of the lungs, implicating principally the
air-cells; bronchitis, an inflammation of the large bronchial tubes; and
pleurisy, an inflammation of the investing membrane of the lungs, or
pleura. Among the young, an affection of the trachea takes place, known as
croup.
[Sidenote: 7. The act of breathing? Extension of the chest by breathing?]
7. THE MOVEMENTS OF RESPIRATION.--The act of breathing has two parts--(1),
_inspiration_, or drawing air into the lungs, and (2), _expiration_, or
expelling it from the lungs again. In inspiration, the chest extends in its
length, breadth, and height, or width. We can prove that this is the case
as regards the two latter, by observing the effect of a deep breath. The
ribs are elevated by means of numerous muscles, some of which occupy the
entire spaces between those bones. But the increase in length, or
vertically, is not so apparent, as it is caused by a muscle within the body
called the _diaphragm_, it being the thin partition which separates the
chest from the abdomen, rising like a dome within the chest. (Fig. 16).
{129}
[Sidenote: 8. Contraction of the diaphragm? Power of the diaphragm? Effects
of extending the walls of the chest? The habit of taking frequent and deep
inspirations?]
8. With every inspiration, the diaphragm contracts, and in so doing,
approaches more nearly a plane, or horizontal, surface, and thus enlarges
the capacity of the chest. Laughing, sobbing, hiccoughing, and sneezing are
caused by the spasmodic or sudden contraction of the diaphragm. The special
power of this muscle is important in securing endurance, or "long wind," as
it is commonly expressed; which may be obtained mainly by practice. It is
possessed in a marked degree by the mountaineer, the oarsman, and the
trained singer. As the walls of the chest extend, the lungs expand, and the
air rushes in to fill them. This constitutes an inspiration. The habit of
taking frequent and deep inspirations, in the erect position, with the
shoulders thrown back, tends greatly to increase the capacity and power of
the organs of respiration.
[Sidenote: 9. Expiration? The mechanism of expiration?]
9. EXPIRATION is a less powerful act than inspiration. The diaphragm
relaxes its contraction, and ascends in the form of a dome; the ribs
descend and contract the chest; while the lungs themselves, being elastic,
assist to drive out the air. The latter passes out through the same
channels by which it entered. At the end of each expiration there is a
pause, or period of repose, lasting about as long as the period of action.
[Sidenote: 10. Frequency of respiration? Effect of hurried action of the
heart?]
10. FREQUENCY OF RESPIRATION.--It is usually estimated that we breathe once
during every four beats of the heart, or about eighteen times in a minute.
There is, of course, a close relation between the heart and lungs, and
whatever modifies the pulse, in like manner affects the breathing. When the
action of the heart is hurried, a larger amount of blood is sent to the
lungs, and, as the consequence, they must act more rapidly. Occasionally,
the heart beats so very forcibly that the lungs cannot keep pace with it,
and then we experience a peculiar sense of {130} distress from the want of
air. This takes place when we run until we are "out of breath." At the end
of every fifth or sixth breath, the inspiration is generally longer than
usual, the effect being to change more completely the air of the lungs.
[Sidenote: 11. Respiration controlled by the will? Advantage of the
knowledge to us?]
11. Although, as a general rule, the work of respiration goes on
unconsciously and without exertion on our part, it is nevertheless under
the control of the will. We can increase or diminish the frequency of its
acts at pleasure, and we can "hold the breath," or arrest it altogether for
a short time. From twenty to thirty seconds is ordinarily the longest
period in which the breath can be held; but if we first expel all the
impure air from the lungs, by taking several very deep inspirations, the
time may be extended to one and a half or even two minutes. This should be
remembered, and acted upon, before passing through a burning building, or
any place where the air is very foul. The arrest of the respiration may be
still further prolonged by training and habit; thus it is said, the
pearl-fishers of India can remain three or four minutes under water without
being compelled to breathe.
[Sidenote: 12. Capacity of the lungs? Time required to renovate the air in
the lungs? In tranquil respiration? Importance of the provision?]
12. CAPACITY OF THE LUNGS.--The lungs are not filled and emptied by each
respiration. For while their full capacity, in the adult, is three hundred
and twenty cubic inches, or more than a gallon, the ordinary breathing air
is only one-sixteenth part of that volume, or twenty cubic inches, being
two-thirds of a pint. Accordingly, a complete renovation, or rotation, of
the air of the lungs does not take place more frequently than about once in
a minute; and by the gradual introduction of the external air, its
temperature is considerably elevated before it reaches the delicate
pulmonary capillaries. In tranquil respiration, less than two-thirds of the
breathing power is {131} called into exercise, leaving a reserve capacity
of about one hundred and twenty cubic inches, equivalent to three and one
half pints. This provision is indispensable to the continuation of life;
otherwise, a slight embarrassment of respiration, by an ordinary cold, for
instance, would suffice to cut off the necessary air, and the spark of life
would be speedily extinguished.
[Sidenote: 13. The atmosphere? How high or deep? How essential to life?
Marine life in perfectly pure water and air?]
13. THE AIR WE BREATHE.--The earth is enveloped on all sides by an
invisible fluid, called the atmosphere. It forms a vast and shoreless ocean
of air, forty-five miles deep, encircling and pervading all objects on the
earth's surface, which is absolutely essential for the preservation of all
vegetable and animal life,--in the sea, as well as on the land and in the
air. At the bottom, or in the lower strata of this aerial ocean, we move
and have our being. Perfectly pure water will not support marine life, for
a fish may be drowned in water from which the air has been exhausted, just
as certainly as a mouse, or any other land animal, will perish if put
deeply into the water for a length of time. The cause is the same in both
cases: the animal is deprived of the requisite amount of air. It is also
stated, that if the water-supply of the plant be deprived of air, its vital
processes are at once checked.
[Sidenote: 14. Composition of the air? Properties of the two gases?]
14. The air is not a simple element, as the ancients supposed, but is
formed by the mingling of two gases, known to the chemist as oxygen and
nitrogen, in the proportion of one part of the former to four parts of the
latter. These gases are very unlike, being almost opposite in their
properties: nitrogen is weak, inert, and cannot support life; while oxygen
is powerful, and incessantly active; and is the essential element which
gives to the atmosphere its power to support life and combustion. The
discovery of this fact was made by the French chemist, Lavoisier, in 1778.
{132}
[Sidenote: 15. Air once breathed? An animal in it? A candle? Analysis of
expired air? Change in volume?]
15. CHANGES IN THE AIR FROM RESPIRATION.--Air that has been once breathed
is no longer fit for respiration. An animal confined within it will sooner
or later die; so too, a lighted candle placed in it will be at once
extinguished. If we collect a quantity of expired air and analyze it, we
shall find that its composition is not the same as that of the inspired
air. When the air entered the lungs it was rich in oxygen; now it contains
twenty-five per cent. less of that gas. Its volume, however, remains nearly
the same; its loss being replaced by another and very different gas, which
the lungs exhaled, called _carbonic acid_, or, as the chemist terms it,
_carbon dioxide_.
[Sidenote: 16. What else has the expired air gained? When and where
noticed?]
16. The expired air has also gained moisture. This is noticed when we
breathe upon a mirror, or the window-pane, the surface being tarnished by
the condensation of the watery vapor exhaled by the lungs. In cold weather,
this causes the fine cloud which is seen issuing from the nostrils or mouth
with each expiration, and contributes in forming the feathery crystals of
ice which decorate our window-panes on a winter's morning.
[Sidenote: 17. Nature of the watery vapor? Its effects upon animals?]
17. This watery vapor contains a variable quantity of animal matter, the
exact nature of which is unknown; but when collected it speedily putrefies
and becomes highly offensive. From the effects, upon small animals, of
confinement in their own exhalations, having at the same time an abundant
supply of fresh air, it is believed that the organic matters thrown off by
the lungs and skin are direct and active poisons; and that to such
emanations from the body, more than to any other cause, are due the
depressing and even fatal results which follow the crowding of large
numbers of persons into places of limited capacity. {133}
[Sidenote: 18. Give some of the instances furnished by history.]
18. History furnishes many painful instances of the ill effects of
overcrowding. In 1756, of one hundred and forty-six Englishmen imprisoned
in the Black Hole of Calcutta, only twenty-three, at the end of eight
hours, survived. After the battle of Austerlitz, three hundred prisoners
were crowded into a cavern, where, in a few hours, two-thirds of their
number died. On board a steam-ship, during a stormy night, one hundred and
fifty passengers were confined in a small cabin, but when morning came,
only eighty remained alive.
[Sidenote: 19. Change in the blood from blue to red. Upon what does the
change depend? How shown?]
19. CHANGES IN THE BLOOD FROM RESPIRATION.--The most striking change which
the blood undergoes by its passage through the lungs, is the change of
color from a dark blue to bright red. That this change is dependent upon
respiration has been fully proved by experiment. If the trachea, or
windpipe, of a living animal be so compressed as to exclude the air from
the lungs, the blood in the arteries will gradually grow darker, until its
color is the same as that of the venous blood. When the pressure is removed
the blood speedily resumes its bright hue. Again, if the animal be made to
breathe an atmosphere containing more oxygen than atmospheric air, the
color changes from scarlet to vermilion, and becomes even brighter than
arterial blood. This change of color is not of itself a very important
matter, but it indicates a most important change of composition.
[Sidenote: 20. What does the air lose and gain by respiration? What, the
blood? Air as food?]
20. The air, as we have seen, by respiration loses oxygen and gains
carbonic acid: the blood, on the contrary, gains oxygen and loses carbonic
acid. The oxygen is the food of the blood corpuscles; while the articles we
eat and drink belong more particularly to the plasma of the blood. The air,
then, it is plain, is a sort of food, and we should {134} undoubtedly so
regard it, if it were not for the fact that we require it constantly,
instead of taking it at stated intervals, as is the case with our articles
of diet. Again, as the demand of the system for food is expressed by the
sensation of hunger, so the demand for air is marked by a painful sensation
called suffocation.
[Sidenote: 21. Moist animal membranes? How shown with the bladder?]
21. INTERCHANGE OF GASES IN THE LUNGS.--As the air and the blood are not in
contact, they being separated from each other by the walls of the air-cells
and of the blood-vessels, how can the two gases, oxygen and carbonic acid,
exchange places? Moist animal membranes have a property which enables them
to transmit gases through their substance, although they are impervious to
liquids. This may be beautifully shown by suspending a bladder containing
dark blood in a jar of oxygen. At the end of a few hours the oxygen will
have disappeared, the blood will be brighter in color, and carbonic acid
will be found in the jar.
[Sidenote: 22. Gaseous diffusion? If oxygen be not received? If carbonic
acid be retained?]
22. If this interchange takes place outside of the body, how much more
perfectly must it take place within, where it is favored by many additional
circumstances! The walls of the vessels and the air-cells offer no obstacle
to this process, which is known as gaseous diffusion. Both parts of the
process are alike of vital importance. If oxygen be not received, the
organs cease to act; and if carbonic acid be retained in the blood, its
action is that of a poison; unconsciousness, convulsions, and death
following.
[Sidenote: 23. Difference in the appearance and composition of the blood?
Temperature of the blood? The blood while passing through the lungs? The
consequence?]
23. DIFFERENCE BETWEEN ARTERIAL AND VENOUS BLOOD.--The following table
presents the essential points of difference in the appearance and
composition of the blood, before and after its passage through the lungs:--
{135}
_Venous Blood._ _Arterial Blood._
Color, Dark blue, Scarlet.
Oxygen, 8 per cent., 18 per cent.
Carbonic Acid, 15 to 20 per cent., 6 per cent., or less.
Water, More, Less.
The temperature of the blood varies considerably; but the arterial stream
is generally warmer than the venous. The blood imparts heat to the air
while passing through the lungs, and consequently the contents of the right
side of the heart has a higher temperature than the contents on the left
side.
[Sidenote: 24. What do we learn by means of the spectroscope? "Carriers of
oxygen?" Blue blood in the system?]
24. By means of the spectroscope, we learn that the change of color in the
blood has its seat in the corpuscles; and that, according as they retain
oxygen, or release it, they present the spectrum of arterial or venous
blood. There evidently exists, on the part of these little bodies, an
affinity for this gas, and hence they have been called "carriers of
oxygen." It was long ago thought that blue blood was a trait peculiar to
persons of princely and royal descent, and boastful allusions to the "_sang
azure_" of kings and nobles are quite often met with. Physiology, however,
informs us that blue blood flows in the veins of the low as well as the
high, and that so far from its presence indicating a mark of purity, it, in
reality, represents the waste and decay of the system.
[Sidenote: 25. The amount of air that passes in and out of the lungs?]
25. AMOUNT OF RESPIRATORY LABOR.--During ordinary calm respiration, we
breathe eighteen times in a minute; and twenty cubic inches of air pass in
and out of the lungs with every breath. This is equivalent to the use of
three hundred and sixty cubic inches, or more than ten pints of air each
minute. From this we calculate that the quantity of air which hourly
traverses the lungs is about thirteen cubic feet, or seventy-eight gallons;
and daily, not {136} less than three hundred cubic feet, an amount nearly
equal to the contents of sixty barrels.
[Sidenote: 26. Air absorbed in its transit through the lungs? The loss?
Carbonic acid exhaled? Effect of excitement or exertion? What estimate?]
26. Of this large volume of air five per cent. is absorbed in its transit
through the lungs. The loss thus sustained is almost wholly of oxygen, and
amounts to fifteen cubic feet daily. The quantity of carbonic acid exhaled
by the lungs during the day is somewhat less, being twelve cubic feet.
Under the influence of excitement or exertion, the breathing becomes more
frequent and more profound; and then the internal respiratory work
increases proportionately, and may even be double that of the above
estimate. It has been estimated that in drawing a full breath, a man exerts
a muscular force equal to raising two hundred pounds placed upon the chest.
[Sidenote: 27. Importance of the oxygen in the atmosphere? Injurious
character of gases?]
27. IMPURITIES OF THE AIR.--The oxygen in the atmosphere is of such prime
importance, and its proportion is so nicely adjusted to the wants of man,
that any gas or volatile substance which supplants it must be regarded as a
hurtful impurity. All gases, however, are not alike injurious. Some, if
inhaled, are necessarily fatal; _arsenuretted hydrogen_ being one of these,
a single bubble of which destroyed the life of its discoverer, Gehlen.
Others are not directly dangerous, but by taking the place of oxygen, and
excluding it from the lungs, they become so. Into this latter class we
place carbonic acid.
[Sidenote: 28. Pungency of gases? The inference? Our safeguard?]
28. Most of the actively poisonous gases have a pungent or offensive odor;
and, as may be inferred, most repugnant odors indicate the presence of
substances unfit for respiration. Accordingly, as we cannot see or taste
these impurities, the sense of smell is our principal safeguard against
them; and we recognize the design which has planted this sense, like a
sentinel at the proper entrance of the {137} air-passages, the nostrils, to
give us warning of approaching harm. Take, as an example, the ordinary
illuminating gas of cities, from which so many accidents happen. How many
more deaths would it cause if, when a leak occurs, we were not able to
discover the escape of the gas by means of its disagreeable odor.
[Sidenote: 29. The air of rooms in which fever-sick persons are confined?]
29. Organic matters exist in increased measure in the expired breath of
sick persons, and impart to it, at times, a putrid odor. This is especially
true in diseases which, like typhus and scarlet fever, are referable to a
blood poison. In such cases the breath is one of the means by which nature
seeks to expel the offending material from the system. Hence, those who
visit or administer to fever-sick persons should obey the oft-repeated
direction, "not to take the breath of the sick." At such times, if ever,
fresh air is demanded, not alone for the sick, but as well for those who
are in attendance.
[Sidenote: 30. Animalcula in the water? Dust in the air?]
30. DUST IN THE AIR.--Attention has lately been directed to the dust, or
haze, that marks the ray of sunshine across a shaded room. Just as, many
years ago, it was discovered that myriads of animalcula infested much of
the water we drank, so now the microscope reveals "the gay motes that dance
along a sunbeam" to be, in part, composed of multitudes of animal and
vegetable forms of a very low grade, the germs of fermentation and
putrefaction, and the probable sources of disease.
[Sidenote: 31. The best air filter? The remarks of Prof. Tyndall?]
31. It is found that the best filter by which to separate this floating
dust from the air is cotton wool, although a handkerchief will imperfectly
answer the same purpose. In a lecture on this subject by Prof. Tyndall, he
remarks that, "by breathing through a cotton wool respirator, the noxious
air of the sick room is restored to practical purity. Thus filtered,
attendants may breathe the air unharmed. {138} In all probability, the
protection of the lungs will be the protection of the whole system. For it
is exceedingly probable that the germs which lodge in the air-passages are
those which sow epidemic disease in the body. If this be so, then disease
can certainly be warded off by filters of cotton wool. By this means, so
far as the germs are concerned, the air of the highest Alps may be brought
into the chamber of the invalid."
[Sidenote: 32. Carbonic acid in volcanic regions? In Java? At Lake Avernus?
In mines?]
32. CARBONIC ACID IN THE AIR.--We have already spoken of this gas as an
exhalation from the lungs, and a source of impurity; but it exists
naturally in the atmosphere in the proportion of one half part per
thousand. In volcanic regions it is poured forth in enormous quantities
from fissures in the earth's surface. Being heavier than air, it sometimes
settles into caves and depressions in the surface. It is stated that in the
island of Java, there is a place called the "Valley of Poison," where the
ground is covered with the bones of birds, tigers, and other wild animals,
which were suffocated by carbonic acid while passing. The Lake Avernus, the
fabled entrance to the infernal regions, was, as its name implies,
bird-less, because the birds, while flying over it, were poisoned by the
gas and fell dead into its waters. In mines, carbonic acid forms the
dreaded _choke-damp_, while carburetted hydrogen is the _fire-damp_.
[Sidenote: 33. In the open air? Amount of carbonic acid exhaled by a man? A
gas-burner? A room fire? From furnaces?]
33. In the open air, men seldom suffer from carbonic acid, for, as we shall
see presently, nature provides for its rapid distribution, and even turns
it to profitable use. But its ill effects are painfully evident in the
abodes of men, in which it is liable to collect as the waste product of
respiration and of that combustion which is necessary for lighting and
warming our homes. A man exhales, during repose, not less than one-half
cubic foot of carbonic acid per hour. One gas-burner liberates five cubic
feet in the {139} same time, and spoils about as much air as ten men. A
fire burning in a grate or stove emits some gaseous impurity, and at the
same time abstracts from the air as much oxygen as twelve men would consume
in the same period, thus increasing the relative amount of carbonic acid in
the air. From furnaces, as ordinarily constructed, this gas, with other
products of combustion, is constantly leaking and vitiating the air of
tightly-closed apartments.
[Sidenote: 34. Effects of inhaling carbonic acid alone? In small
quantities?]
34. EFFECTS OF IMPURE AIR.--Carbonic acid, in its pure form, is
irrespirable, causing rapid death by suffocation. Air containing forty
parts per thousand of this gas (the composition of the expired breath)
extinguishes a lighted candle, and is fatal to birds; when containing one
hundred parts, it no longer yields oxygen to man and other warm-blooded
animals; and is of course at once fatal to them. In smaller quantities,
this gas causes headache, labored respiration, palpitation,
unconsciousness, and convulsions.
[Sidenote: 35. Effects of the air in crowded and badly ventilated rooms?]
35. In crowded and badly ventilated apartments, where the atmosphere
relatively contains from six to ten times the natural amount of carbonic
acid, the contaminated air causes dulness, drowsiness, and faintness; the
dark, impure blood circulating through the brain, oppressing that organ and
causing it to act like a blunted tool. This is a condition not uncommon in
our schools, churches, court-rooms, and the like, the places of all others
where it is desirable that the mind should be alert and free to act; but,
unhappily, an unseen physiological cause is at work, dispensing weariness
and stupor over juries, audience, and pupils.
[Sidenote: 36. A cause of consumption? How was the fact illustrated?]
36. Another unmistakable result of living in and breathing foul air is
found in certain diseases of the lungs, especially consumption. For many
years the barracks of {140} the British army were constructed without any
regard to ventilation; and during those years the statistics showed that
consumption was the cause of a very large proportion of deaths. At last the
government began to improve the condition of the buildings, giving larger
space and air-supply; and as a consequence, the mortality from consumption
has diminished more than one-third.
[Sidenote: 37. How, in the case of the lower animals? Tendency of certain
occupations?]
37. The lower animals confined in the impure atmosphere of menageries,
contract the same diseases as man. Those brought from a tropical climate,
and requiring artificial warmth, generally die of consumption. In the
Zoological gardens of Paris, this disease affected nearly all monkeys,
until care was taken to introduce fresh air by ventilation; and then it
almost wholly disappeared. The tendency of certain occupations to shorten
life is well known; disease being occasioned by the fumes and dust which
arise from the material employed, in addition to the unhealthful condition
of the workshop or factory where many hours are passed daily.
[Sidenote: 38. Give the fact as set forth in the table.]
38. The following table shows the comparative amount of carbonic acid in
the air under different conditions and the effects sometimes produced:--
PROPORTION OF CARBONIC ACID. In 1000 parts of Air.
Air of country. .4
" " city. .5
In hospital, well ventilated. .6
In school, church, etc., fairly ventilated. 1.2 to 2.5
In court-house, factory, etc., without ventilation. 4. to 40.
In bedroom, before being aired. 4.5
In bedroom, after being aired. 1.5
Constantly breathed, causing ill health. 2.
Occasionally breathed, causing discomfort. 3.
Occasionally breathed, causing distress. 10.
Expired air. 40.
Air no longer yielding oxygen 100.
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[Sidenote: 39. What can you state of the diffusive power of gases? The
added influence of the winds?]
39. NATURE'S PROVISION FOR PURIFYING THE AIR.--We have seen that carbonic
acid is heavier than air, and is poisonous. Why, then, does it not sink
upon and overwhelm mankind with a silent, invisible wave of death? Among
the gases there is a more potent force than gravity, which forever
precludes such a tragedy. It is known as the diffusive power of gases. It
acts according to a definite law, and with a resistless energy compelling
these gases, when in contact, to mingle until they are thoroughly diffused.
The added influence of the winds is useful, by insuring more rapid changes
in the air; air in motion being perfectly wholesome. The rains also wash
the air.
[Sidenote: 40. How is the constant purity of the air secured? Explain the
process?]
40. We have seen that the whole animal creation is constantly abstracting
oxygen from the atmosphere, and as constantly adding to it vast volumes of
a gas injurious alike to all, even in small quantities. How, then, does the
air retain, unchanged, its life-giving properties? The constant purity of
the air is secured by means of the vegetable creation. Carbonic acid is the
food of the plants, and oxygen is its waste product. The leaves are its
lungs, and under the stimulus of sunlight a vegetable respiration is set in
motion, the effects of which are just the reverse of the function we have
been considering. Thus nature purifies the air, and at the same time builds
up beautiful and useful forms of life from elements of decay.
[Sidenote: 41. What process occurs in the sea? How is the fact
illustrated?]
41. In the sea, as in the air, the same circle of changes is observed.
Marine animals consume oxygen and give off carbonic acid; while marine
plants consume carbonic acid and liberate oxygen. Taking advantage of this
fact, we may so arrange aquaria with fishes and sea-plants, in their proper
combinations, so that each supplies the needs of the other, and the water
requires seldom to be renewed. This {142} affords us, on a small scale, an
illustration of the mutual dependence of the two great kingdoms of nature;
as well as of those compensating changes which are taking place on such a
grand scale in the world about us.
[Sidenote: 42. Character of the external air? Of the air in our dwellings?
What becomes imperative? Imperfect ventilation of our dwellings?]
42. VENTILATION.--Since the external atmosphere, as provided by nature, is
always pure, and since the air in our dwellings and other buildings is
almost always impure, it becomes imperative that there should be a free
communication from the one to the other. This we aim to accomplish by
ventilation. As our houses are ordinarily constructed, the theory of
ventilation, "to make the internal as pure as the external air," is seldom
carried out. Doors, windows, and flues, the natural means of replenishing
the air, are too often closed, almost hermetically, against the precious
element. Special means, or special attention, must therefore be used to
secure even a fair supply of fresh air. This is still more true of those
places of public resort, where many persons are crowded together.
[Sidenote: 43. What hints are given for the ventilation of our dwellings?]
43. If there are two openings in a room, one as a vent for foul air, and
the other an inlet for atmospheric air, and if the openings be large, in
proportion to the number of air consumers, the principal object will be
attained. Thus, a door and window, each opening into the outer air, will
ordinarily ventilate a small apartment; or a window alone will answer, if
it be open both above and below, and the open space at each end be not less
than one inch for each occupant of the room, when the window is about a
yard wide. The direction of the current is generally from below upward,
since the foul, heated air tends to rise; but this is not essential. Its
rate need not be rapid; a "draught," or perceptible current, is never
necessary to good ventilation. The temperature of the air admitted may be
warm or cold. It is thought by many that if the {143} air is cold, it is
pure; but this is an error, since cold air will receive and retain the same
impurities as warm air.
[Sidenote: 44. State what Florence Nightingale says about inhaling night
air?]
44. Shall we open our bedrooms to the night air? Florence Nightingale says,
in effect, that night air is the only air that we can then breathe. "The
choice is between pure air without and impure air within. Most people
prefer the latter,--an unaccountable choice. An open window, most nights in
the year, can hurt no one. In great cities, night air is the best and
purest to be had in twenty-four hours. I could better understand, in towns,
shutting the windows during the day than during the night."
[Sidenote: 45. Warmth of the bird as compared with that of the air? Of the
fish and the water? Heat in animals and plants? How illustrated with the
thermometer?]
45. ANIMAL HEAT.--Intimately connected with respiration is the production
of animal heat, or the power of maintaining the temperature of the body
above that of the medium in which the creature moves; thus, the bird is
warmer than the air, and the fish than the water. This elevation of
temperature is a result of the various chemical changes which are
constantly taking place in the system. Although common to all animals, in a
greater or less degree, heat is not peculiar to them; since plants also
generate it, especially at the time of sprouting and flowering. If a
thermometer be placed in a cluster of geranium flowers, it will indicate a
temperature several degrees above that of the surrounding air.
[Sidenote: 46. Amount of heat in animals, how apportioned? As regards the
birds? Frogs, and other sluggish animals? Arrangement made by zoologists?]
46. Among animals great differences are noticed in this respect, but the
degree of heat produced is always proportional to the activity of
respiration and the amount of oxygen consumed. Accordingly, the birds,
whose habits are extremely active, and whose breathing capacity is the
greatest, have uniformly the highest temperature. Sluggish animals, on the
contrary, as frogs, lizards, and snakes, have little need for oxygen, and
have incompletely {144} developed lungs; these animals are cold to the
touch, that is, they have relatively a lower temperature than man, and
their positive temperature is but little above that of the external air.
Accordingly, zoologists have so arranged the animal kingdom that
_warm-blooded_ animals, including man, the birds, and the quadrupeds, are
classified together; while the _cold-blooded_ animals, such as the fish,
tortoise, frog, and all that have no vertebral column, are classed by
themselves.
[Sidenote: 47. State what is said respecting the temperature of the human
body.]
47. The temperature of the human body is about 100° Fahrenheit, and remains
about the same through winter and summer, in the tropics as well as in the
frozen regions of the north. It may change temporarily within the range of
about twelve degrees; but any considerable, or long-continued elevation or
diminution of the bodily heat is certain to result disastrously.
[Sidenote: 48. Ability of man to adapt himself to different climates? In
what does the power to resist cold consist? What is said about warm
clothing?]
48. Man is able to adapt himself to all extremes of climate; and, in fact,
by means of clothing, shelter, and food, is able to create for himself an
artificial climate where-ever he choses to reside. The power to resist cold
consists chiefly in preventing the heat which is generated by the vital
processes of the body from being lost by radiation. Warm clothing, such as
we wear in winter, has, in reality, the same temperature as that which is
worn in summer; but, by reason of being thick and porous, it is a bad
conductor of heat, and thus prevents the escape of that produced by the
body. If woollen fabrics were intrinsically warm, no one would wrap a piece
of flannel, or blanket, around a block of ice to prevent its melting in
summer.
[Sidenote: 49. Men in an atmosphere above the boiling-point? In foundries
and glass works?]
49. The faculty of generating heat explains how it is that we are enabled
to resist the effects of cold; but how does the body withstand a
temperature higher than its {145} own? Men have been known to remain
several minutes in an atmosphere heated above the boiling-point of water,
and yet the temperature of their own bodies was not greatly elevated. Those
who labor in foundries and glass-works are habitually subjected to very
high degrees of temperature, but they do not suffer in health more than
those engaged in many other occupations.
[Sidenote: 50. The regulation of the temperature of the body. Give the
explanation.]
50. The regulation of the temperature of the body is effected by means of
perspiration, and by its evaporation. So long as the skin acts freely and
the air freely absorbs the moisture, the heat of the body does not
increase, for whenever evaporation takes place, it is attended by the
abstraction of heat--that is, the part becomes relatively colder. This may
be tested by moistening some part of the surface with cologne, ether, or
other volatile liquid, and then causing it to evaporate rapidly by fanning.
The principle that evaporation produces cold has been ingeniously and
practically employed, in the manufacture of ice, by means of freezing
machines.
[Sidenote: 51, 52. State what is said of spontaneous combustion.]
51. SPONTANEOUS COMBUSTION.--Is it possible that the temperature of the
living body can be so increased, that its tissues will burn spontaneously?
From time to time, cases have been reported in which, by some mysterious
means, considerable portions of the human body have been consumed,
apparently by fire, the victim being found dead, or incapable of explaining
the occurrence. Hence, the theory has been current that, under certain
conditions, the tissues of the body might become self-ignited; and the fact
that this so-called _spontaneous combustion_ has ordinarily taken place in
those who had been addicted to the use of alcoholic drinks, has given a
color of probability to the opinion. It has been supposed that the flesh of
these unfortunate persons becoming saturated with the inflammable
properties of the alcohol thus taken into the {146} system, took fire upon
being exposed to a flame, as of a lighted candle, or, indeed, without any
external cause. But, whether this be possible or not, one thing is certain,
this strange kind of combustion has never been actually witnessed by any
one competent to give a satisfactory account of it.
52. The results that have been observed may be satisfactorily explained by
the accidental ignition of the clothes, or other articles near the body,
and by the supposition that the individual was at the time too much
stupefied by intoxication, to notice the source of danger, and provide for
his safety. The highest temperature that has been observed in the body,
about 112° Fahrenheit, is too low to ignite the vapor of alcohol; much less
will it cause the burning of animal tissues. It is undoubtedly true that
when the tissues are filled with alcohol, combustion will more easily take
place than when the body is in a normal state; but, under any condition,
the combustion of the body requires a higher degree of heat than can be
generated by the body itself, or the mere _proximity_ of a lighted candle,
or any cause of a similar character. {147}
QUESTIONS FOR TOPICAL REVIEW.
PAGE
1. What is the object of respiration? 123
2. What are the special organs of respiration? 123
3. In what organs does a change in the blood take place? 123
4. What is the nature of the change? 123, 133
5. Where are the lungs situated, and what is the character of the
substance of which they are composed? 123, 125
6. Describe the facilities provided for the lung movements. 124
7. Describe the trachea, or windpipe. 124, 125, 127, 128
8. Describe the bronchial tubes, and their uses. 125, 126
9. What can you state in relation to the epiglottis? 126, 127
10. What are the cilia and what use do they probably serve? 128
11. How may the lungs be affected by not being properly protected? 128
12. Describe the movements necessary to the act of perfect
respiration. 128, 129
13. What is the diaphragm, and what is its office? 128, 129
14. How may the organs of respiration be so improved as to
increase their capacity and power? 129, 137
15. What is stated in relation to the frequency of respiration? 129, 130
16. To what extent may the act of respiration be subjected to
our wills? 130
17. What may be said to be the capacity of the lungs? 130, 131
18. How long does it take every particle of air in the lungs to
be expelled and new air to take its place? 130
19. What would be the consequences, if the entire capacity of
the lungs were constantly used? 130, 131
20. What would be the consequences to a fish put into water from
which the air had been completely exhausted? Why? 131
21. What is the air, and what are its parts? 131, 136, 138
22. What is the character of the air that has been just breathed? 132
23. Why is it that such air is not fit for respiration? 132, 139
24. What are the effects, as recorded in notable cases, of confinement
in places the air of which has been breathed "over and over?" 133
25. What can you state of changes in the blood from respiration? 133
26. What of the air, as an article of food? 133, 134
27. What, on the subject of interchange of gases in the lungs? 134
28. Explain the difference between arterial and venous blood. 134, 135
29. Explain, if you can, the cause of the difference. 135
30. State what you can in relation to blue blood. 135
31. In relation to the amount of labor exerted in respiration. 135, 136
32. In relation to the deleterious properties of different
gases. 136, 137
33. In relation to the dust that floats in the air. 137, 138
34. What are the properties of carbonic acid gas? 132, 138, 141
35. In what places is carbonic acid gas commonly found? 132, 138, 139
36. Describe the effects of carbonic acid gas. 132, 138, 139, 141
37. What are the general effects of breathing any impure
atmosphere? 139, 140
38. What are Nature's provisions for purifying the air? 141, 142
39. What hints and directions are given on the subject of
ventilation? 142, 143
40. How does the temperature of the body compare with the medium
in which it lives? 143
41. How is temperature of the body regulated and sustained? 143, 144, 145
42. State what you can on the subject of spontaneous combustion. 145, 146
* * * * *
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