A Civic Biology Part 35

"The immediate stimulation to the heart's action soon pa.s.ses away and, like other muscles, the muscles of the heart lose power and contract with less force after having been excited by alcohol."--MACY, _Physiology_.

Alcohol, when brought to act directly on heart muscle, lessens the force of the beat. It may even cause changes in the tissues, which eventually result in the breaking of the walls of a blood vessel or the plugging of a vessel with a blood clot. This condition may cause the disease known as _apoplexy_.

Effects of Tobacco upon the Circulation.--"The frequent use of cigars or cigarettes by the young seriously affects the quality of the blood.

The red blood corpuscles are not fully developed and charged with their normal supply of life-giving oxygen. This causes paleness of the skin, often noticed in the face of the young smoker. Palpitation of the heart is also a common result, followed by permanent weakness, so that the whole system is enfeebled, and mental vigor is impaired as well as physical strength."--MACY, _Physiology_.

XXII. RESPIRATION AND EXCRETION

_Problems.--A study of respiration to find out:-- (a) What changes in blood and air take place within the lungs.

(b) The mechanics of respiration.

A study of ventilation to discover:-- (a) The reason for ventilation.

(b) The best method of ventilation.

A study of the organs of excretion._

LABORATORY SUGGESTIONS

_Demonstration._--Comparison of lungs of frog with those of bird or mammal.

_Experiment._--The changes of blood within the lungs.

_Experiment._--Changes taking place in air in the lungs.

_Experiment._--The use of the ribs in respiration.

_Demonstration experiment._--What causes the filling of air sacs of the lungs?

_Demonstration experiment._--What are the best methods of ventilating a room?

_Demonstration._--Best methods of dusting and cleaning.

_Demonstration._--Beef or sheep's kidney to show areas.

Necessity for Respiration.--We have seen that plants and animals need oxygen in order that the life processes may go on. Food is oxidized to release energy, just as coal is burned to give heat to run an engine. As a draft of air is required to make fire under the boiler, so, in the human body, oxygen must be given so that food in tissues may be oxidized to release energy used in work. This oxidation takes place in the cells of the body, be they part of a muscle, a gland, or the brain. _Blood, in its circulation to all parts of the body, is the medium which conveys the oxygen to that place in the body where it will be used._

[Ill.u.s.tration: Air pa.s.sages in the human lungs. _a_, larynx; _b_, trachea (or windpipe); _c_, _d_, bronchi; _e_, bronchial tubes; _f_, cl.u.s.ter of air cells.]

The Organs of Respiration in Man.--We have alluded to the fact that the lungs are the organs which give oxygen to the blood and take from it carbon dioxide. The course of the air pa.s.sing to the lungs in man is much the same as in the frog. Air pa.s.ses through the nose, and into the windpipe. This cartilaginous tube, the top of which may easily be felt as the Adam's apple of the throat, divides into two _bronchi_. The bronchi within the lungs break up into a great number of smaller tubes, the _bronchial tubes_, which divide somewhat like the small branches of a tree. The bronchial tubes, indeed all the air pa.s.sages, are lined with ciliated cells. The cilia of these cells are constantly in motion, beating with a quick stroke toward the outer end of the tube, that is, toward the mouth. Hence any foreign material will be raised from the throat first by the action of the cilia and then by coughing or "clearing the throat." The bronchi end in very minute air sacs, little pouches having elastic walls, into which air is taken when we inspire, or take a deep breath. In the walls of these pouches are numerous capillaries, the ends of arteries which pa.s.s from the heart into the lung. _It is through the very thin walls of the air sacs that an interchange of gases takes place which results in the blood giving up part of its load of carbon dioxide, and taking up oxygen in its place._ This exchange appears to be aided by the presence of an enzyme in the lung tissues. This is another example of the various kinds of work done by the enzymes of the body.

[Ill.u.s.tration: Diagram to show what the blood loses and gains in one of the air sacs of the lungs.]

Changes in the Blood within the Lungs.--Blood, after leaving the lungs, is much brighter red than just before entering them. The change in color is due to a taking up of oxygen by the _haemoglobin_ of the red corpuscles.

Changes taking place in blood are obviously the reverse of those which take place in air in the lungs. Every hundred cubic centimeters of blood going into the lungs contains 8 to 12 c.c. of oxygen, 45 to 50 c.c. of carbon dioxide, and 1 to 2 c.c. of nitrogen. The same amount of blood pa.s.sing out of the lungs contains 20 c.c. of oxygen, 38 c.c. of carbon dioxide, and 1 to 2 c.c. of nitrogen. The water, of which about half a pint is given off daily, is mostly lost from the blood.

Changes in Air in the Lungs.--Air is much warmer after leaving the lungs than before it enters them. Breathe on the bulb of a thermometer to prove this. Expired air contains a considerable amount of moisture, as may be proved by breathing on a cold polished surface. This it has taken up in the air sacs of the lungs. The presence of carbon dioxide in expired air may easily be detected by the limewater test. Air such as we breathe out of doors contains, by volume:--

Nitrogen 76.95 Oxygen 20.61 Carbon dioxide .03 Argon 1.00 Water vapor (average) 1.40

Air expired from the lungs contains:--

Nitrogen 76.95 Oxygen 15.67 Carbon dioxide 4.38 Water vapor 2 Argon 1

In other words, there is a loss between 4 and 5 per cent oxygen, and nearly a corresponding gain in carbon dioxide, in expired air. There are also some other organic substances present.

[Ill.u.s.tration: The respiration of cells.]

Cell Respiration.--It has been shown, in the case of very simple animals, such as the _amoeba_, that when oxidation takes place in a cell, work results from this oxidation. The oxygen taken into the lungs is not used there, but is carried by the blood to such parts of the body as need oxygen to oxidize food materials in the cells. Since work is done in the cells of the body, food and oxygen are therefore required. The quant.i.ty of oxygen used by the body is nearly dependent on the amount of work performed.

Oxygen is constantly taken from the blood by tissues in a state of rest and is used up when the body is at work. This is suggested by the fact that in a given time a man, when working, gives off more oxygen (in carbon dioxide) than he takes in during that time.

While work is being done certain wastes are formed in the cell. Carbon dioxide is given off when carbon is burned. But when proteins are burned, another waste product containing nitrogen is formed. This must be pa.s.sed off from the cells, as it is a poison. Here again the lymph and blood, the common carriers, take the waste material to points where it may be _excreted_ or pa.s.sed out of the body.

The Mechanics of Respiration. The Pleura.--The lungs are covered with a thin elastic membrane, the _pleura_. This forms a bag in which the lungs are hung. Between the walls of the bag and the lungs is a s.p.a.ce filled with lymph. By this means the lungs are prevented from rubbing against the walls of the chest.

[Ill.u.s.tration: The chest cavity (_a_) at the time of a full breath; (_b_), after an expiration. Explain how the cavity for lungs is made larger.]

Breathing.--In every full breath there are two distinct movements, inspiration (taking air in) and expiration (forcing air out). In man an inspiration is produced by the contraction of the muscles between the ribs, together with the contraction of the diaphragm, the muscular wall just below the heart and lungs; this results in pulling down the diaphragm and pulling upward and outward of the ribs, thus making the s.p.a.ce within the chest cavity larger. The lungs, which lie within this cavity, are filled by the air rushing into the larger s.p.a.ce thus made. That this cavity is larger than it was at first may be demonstrated by a glance at the accompanying figure. An expiration is simpler than an inspiration, for it requires no muscular effort; the muscles relax, the breastbone and ribs sink into place, while the diaphragm returns to its original position.

[Ill.u.s.tration: Apparatus to show the mechanics of breathing.]

A piece of apparatus which ill.u.s.trates to a degree the mechanics of breathing may be made as follows: Attach a string to the middle of a piece of sheet rubber. Tie the rubber over the large end of a bell jar. Pa.s.s a gla.s.s Y-tube through a rubber stopper. Fasten two small toy balloons to the branches of the tube. Close the small end of the jar with the stopper.

Adjust the tube so that the balloons shall hang free in the jar. If now the rubber sheet is pulled down by means of the string, the air pressure in the jar is reduced and the toy balloons within expand, owing to the air pressure down the tube. When the rubber is allowed to go back to its former position, the balloons collapse.

[Ill.u.s.tration: Diagram showing the relative amounts of tidal, complemental, reserve, and residual air. The brace shows the average lung capacity for the adult man.]

Rate of Breathing and Amount of Air Breathed.--During quiet breathing, the rate of inspiration is from fifteen to eighteen times per minute; this rate largely depends on the amount of physical work performed. About 30 cubic inches of air are taken in and expelled during the ordinary quiet respiration. The air so breathed is called _tidal air_. In a "long" breath, we take in about 100 cubic inches in addition to the tidal air. This is called _complemental air_. By means of a forced expiration, it is possible to expel from 75 to 100 cubic inches more than tidal air; this air is called _reserve air_. What remains in the lungs, amounting to about 100 cubic inches, is called the _residual air_. The value of deep breathing is seen by a glance at the diagram. It is only by this means that we clear the lungs of the reserve air with its accompanying load of carbon dioxide.

Respiration under Nervous Control.--The muscular movements which cause an inspiration are partly under the control of the will, but in part the movement is beyond our control. The nerve centers which govern inspiration are part of the sympathetic nervous system. Anything of an irritating nature in the trachea or larynx will cause a sudden expiration or cough.

When a boy runs, the quickened respiration is due to the fact that oxygen is used up rapidly and a larger quant.i.ty of carbon dioxide is formed. The carbon dioxide in the blood stimulates the nervous center which has control of respiration to greater activity, and quickened inspiration follows.

Need of Ventilation.--During the course of a day the lungs lose to the surrounding air nearly two pounds of carbon dioxide. This means that about three fifths of a cubic foot is given off by each person during an hour.

When we are confined for some time in a room, it becomes necessary to get rid of this carbon dioxide. This can be done only by means of proper ventilation. A considerable amount of moisture is given off from the body, and this moisture in a crowded room is responsible for much of the discomfort. The air becomes humid and uncomfortable. It has been found that by keeping the air in motion in such a room (as through the use of electric fans) much of this discomfort is obviated.

The presence of impurities in the air of a room may easily be determined by its odor. The odor of a poorly ventilated room is due to organic impurities given off with the carbon dioxide. This, fortunately, gives us an index of the amount of waste material in the air. Among the factors which take oxygen from the air in a closed room and produce carbon dioxide are burning gas or oil lamps and stoves, and the presence of a number of people.

[Ill.u.s.tration: Three ways of ventilating a room. _i_, inlet for air; _o_, outlet for air. Which is the best method of ventilation? Explain.]

Proper Ventilation.--Ventilation consists in the removal of air that has been used, and the introduction of a fresh supply to take its place. Heated air rises, carrying with it much of the carbon dioxide and other impurities. A good method of ventilation for the home is to place a board two or three inches high between the lower sash and the frame of a window or to have the window open an inch or so at the top and the bottom. An open fireplace in a room aids in ventilation because of the constant draft up the flue.

Sweeping and Dusting.--It is very easy to demonstrate the amount of dust in the air by following the course of a beam of light in a darkened room. We have already proved that spores of mold and yeast exist in the air. That bacteria are also present can be proved by exposing a sterilized gelatin plate to the air in a schoolroom for a few moments.[47]

Footnote 47: Expose two sterilized dishes containing culture media; one in a room being swept with a damp broom, and the other in a room which is being swept in the usual manner.

Note the formation of colonies of bacteria in each dish. In which dish does the more abundant growth take place?

Many of the bacteria present in the air are active in causing diseases of the respiratory tract, such as diphtheria, membranous croup, and tuberculosis. Other diseases, as colds, bronchitis (inflammation of the bronchial tubes), and pneumonia (inflammation of the tiny air sacs of the lungs), are also caused by bacteria.

[Ill.u.s.tration: Plate culture exposed for five minutes in a school hall where pupils were pa.s.sing to recitations. Each spot is a colony of bacteria or mold.]

Dust, with its load of bacteria, will settle on any horizontal surface in a room not used for three or four hours. Dusting and sweeping should always be done with a damp cloth or broom, otherwise the bacteria are simply stirred up and sent into the air again. The proper watering of streets before they are swept is also an important factor in health. Much dust is composed largely of dried excreta of animals. Soft-coal smoke does its share to add to the impurities of the air, while sewer gas and illuminating gas are frequently found in sufficient quant.i.ties to poison people. Pure air is, as can be seen, almost an impossibility in a great city.

[Ill.u.s.tration: A sleeping porch, an ideal way to get fresh air at night.]

How to get Fresh Air.--As we know, green plants give off in the sunlight considerable more oxygen than they use, and they use up carbon dioxide. The air in the country is naturally purer than in the city, as smoke and bacteria are not so prevalent there, and the plants in abundance give off oxygen. In the city the night air is purer than day air, because the factories have stopped work, the dust has settled, and fewer people are on the streets. The old myth of "night air" being injurious has long since been exploded, and thousands of people of delicate health, especially those who have weak throat or lungs, are regaining health by sleeping out of doors or with the windows wide open. The only essential in sleeping out of doors or in a room with a low temperature is that the body be kept warm and the head be protected from strong drafts by a nightcap or hood. Proper ventilation at _all_ times is one of the greatest factors in good health.