Chapter XVIII
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HYGIENE OF THE CIRCULATION
*Care of the Heart.*--The heart, consisting largely of muscle, is subject to the laws of muscular exercise. It may be injured by over-exertion, but is strengthened by a moderate increase in its usual work.(23) It may even be subjected to great exertion without danger, if it be trained by gradually increasing its work. Such training, by giving the heart time to gain in size and strength, prepares it for tasks that could not at first be accomplished.
In taking up a new exercise requiring considerable exertion, precautions should be observed to prevent an overstrain of the heart. The heart of the amateur athlete, bicyclist, or mountain climber is frequently injured by attempting more than the previous training warrants. The new work should be taken up gradually, and feats requiring a large outlay of physical energy should be attempted only after long periods of training.
Since the heart is controlled by the nervous system, it frequently becomes irregular in its action through conditions that exhaust the nervous energy. Palpitations of the heart, the missing of beats, and pains in the heart region frequently arise from this cause. It is through their effect upon the nervous system that worry, overstudy, undue excitement, and dissipation cause disturbances of the heart. In all such cases the remedy lies in the removal of the cause. The nervous system should also be "toned up" through rest, plenty of sleep, and moderate exercise in the open air.
*Effect of Drugs.*--A number of substances classed as drugs, mainly by their action on the nervous system, produce undesirable effects upon the organs of circulation. Unfortunately some of these are extensively used, alcohol being one of them. If taken in any but small quantities, alcohol is a disturbing factor in the circulation. It increases the rate of the heart beat and dilates the capillaries. Its effect upon the capillaries is shown by the "bloodshot" eye and the "red nose" of the hard drinker. Another bad effect from the use of much alcohol is the weakening of the heart through the accumulation of fat around this organ and within the heart muscle. The use of alcohol also leads in many cases to a hardening of the walls of the arteries, such as occurs in old age. This effect makes the use of alcohol especially dangerous for those in advanced years.
Tobacco contains a drug, called nicotine, which has a bad effect upon the heart in at least two ways: 1. When the use of tobacco is begun in early life, it interferes with the growth of the heart, leading to its weakness in the adult. 2. When used in considerable quantity, by young or old, it causes a nervous condition both distressing and dangerous, known as "tobacco heart."
Tea and coffee contain a drug, called caffeine, which acts upon the nervous system and which may, on this account, interfere with the proper control of the heart. In some individuals the taking of a very small amount of either tea or coffee is sufficient to cause irregularities in the action of the heart. Tea is considered the milder of the two liquids and the one less liable to injure.
*Effect of Rheumatism.*--The disease which affects the heart more frequently than any other is rheumatism. This attacks the lining membrane, or endocardium, and causes, not infrequently, a shrinkage of the heart valves. The heart is thus rendered defective and, to perform its function in the body, must work harder than if it were in a normal condition. Rheumatic attacks of the heart do most harm when they occur in early life--the period when the valves are the most easily affected. Any tendency toward rheumatism in children has, therefore, a serious significance and should receive the attention of the physician. Any one having a defective heart should avoid all forms of exercise that demand great exertion.
*Strengthening of the Blood Vessels.*--Disturbances of the circulation, causing too much blood to be sent to certain parts of the body and an insufficient amount to others, when resulting from slight causes, are usually due to weakness of the walls of the blood vessels, particularly of the muscular coat. Such weakness is frequently indicated by extreme sensitiveness to heat or cold and by a tendency to "catch cold." From a health standpoint the preservation of the normal muscular "tone" of the blood vessels is a problem of great importance. Though the muscles of the blood vessels cannot be exercised in the same manner as the voluntary muscles, they may be called actively into play through all the conditions that induce changes in the blood supply to different parts of the body. The usual forms of physical exercise necessitate such changes and indirectly exercise the muscular coat. The exposure of the body to cold for short intervals, because of the changes in the circulation which this induces, also serves the same purpose. A cold bath taken with proper precautions is beneficial to the circulation of many and so also is a brisk walk on a frosty morning. Both indirectly exercise and strengthen the muscular coat of the blood vessels. On the other hand, too much time spent indoors, especially in overheated rooms, leads to a weakening of the muscular coat and should be avoided.
*Checking of Flow of Blood from Wounds.*--The loss of any considerable quantity of blood is such a serious matter that every one should know the simpler methods of checking its flow from wounds. In small wounds the flow is easily checked by binding cotton or linen fiber over the place. The absorbent cotton, sold in small packages at drug stores, is excellent for this purpose and should be kept in every home. A simple method of checking "nosebleed" is that of drawing air through the bleeding nostril, while the other nostril is compressed with the finger.(24) Another method is to "press with the finger (or insert a small roll of paper) under the lip against the base of the nose." (25) Where the bleeding is persistent, the nostril should be plugged with a small roll of clean cotton or paper. When this is done, the plug should not be removed too soon because of the likelihood of starting the flow afresh.
In dealing with large wounds the services of a physician are indispensable. But in waiting for the physician to arrive temporary aid must be rendered. The one who gives such aid should first decide whether an artery or a vein has been injured. This is easily determined by the nature of the blood stream, which is in jets, or spurts, from an artery, but flows steadily from a vein. If an artery is injured, the limb should be tightly bandaged on the side of the wound nearest the heart; if a vein, on the side farthest from the heart. In addition to this, the edges of the wound should be closed and covered with cotton fiber and the limb should be placed on a support above the level of the rest of the body. A large handkerchief makes a convenient bandage if properly applied. This should be folded diagonally and a knot tied in the middle. Opposite ends are then tied, making a loose-fitting loop around the limb. The knot is placed directly over the blood vessel to be compressed and a short stick inserted in the loop. The necessary pressure is then applied by twisting the handkerchief with the stick. Time must not be lost, however, in the preparation of a suitable bandage. The blood vessel should be compressed with the fingers while the bandage is being prepared.
*Summary.*--The blood, to serve as a transporting agent, must be kept continually moving through all parts of the body. The blood vessels hold the blood, supply the channels and force necessary for its circulation, and provide conditions which enable materials both to enter and to leave the blood stream. The heart is the chief factor in propelling the blood, although the muscles and the elastic tissue in the walls of the arteries and the valves in the veins are necessary aids in the process. In the capillaries the blood takes on and gives off materials, while the arteries and veins serve chiefly as tubes for conveying the blood from one system of capillaries to another.
*Exercises.*--1. Of what special value in the study of the body was the discovery of the circulation of the blood?
2. State the necessity for a circulating liquid in the body.
3. Show by a drawing the general plan of the heart, locating and naming the essential parts. Show also the connection of the large blood vessels with the cavities of the heart.
4. Compare the purpose served by the chordae tendineae to that served by doorstops (the strips against which the door strikes in closing).
5. Explain how the heart propels the blood. To what class of pumps does it belong? What special work is performed by each of its divisions?
6. Define a valve. Of what use are the valves in the heart? In the veins?
7. By what means is pressure from contracting muscles in different parts of the body made to assist in the circulation?
8. Of what advantage is the elasticity of the arteries?
9. How is blood forced from the capillaries back to the heart?
10. Why should there be a difference in structure between the two sides of the heart?
11. Following Fig. 23, trace the blood through a complete circulation, naming all the divisions of the system in the order of the flow of the blood.
12. If the period of rest following the period of contraction of the heart be as long as the period of contraction, how many hours is the heart able to rest out of every twenty-four?
13. State the functions of the capillaries. Show how their structure adapts them to their work.
14. What kind of physical exercise tends to strengthen the heart? What forms of exercise tend to injure it? State the effects of alcohol and tobacco on the heart.
15. How may rheumatism injure the heart?
16. Give directions for checking the flow of blood from small and from large blood vessels.
PRACTICAL WORK
In showing the relations of the different parts of the heart, a large dissectible model is of great service (Fig. 24). Indeed, where the time of the class is limited, the practical work may be confined to the study of the heart model, diagrams of the heart and the circulation, and a few simple experiments. However, where the course is more extended, the dissection of the heart of some animal as described below is strongly advised.
*Observations on the Heart.*--Procure, by the assistance of a butcher, the heart of a sheep, calf, or hog. To insure the specimen against mutilation, the lungs and the diaphragm must be left attached to the heart. In studying the different parts, good results will be obtained by observing the following order:
1. Observe the connection of the heart to the lungs, diaphragm, and large blood vessels. Inflate the lungs and observe the position of the heart with reference to them.
2. Examine the sac surrounding the heart, called the _pericardium_. Pierce its lower portion and collect the pericardial fluid. Increase the opening thus made until it is large enough to slip the heart out through it. Then slide back the pericardium until its connection with the large blood vessels above the heart is found. Observe that a thin layer of it continues down from this attachment, forming the outer covering of the heart.
3. Trace out for a short distance and study the veins and arteries connected with the heart. The arteries are to be distinguished by their thick walls. The heart may now be severed from the lungs by cutting the large blood vessels, care being taken to leave a considerable length of each one attached to the heart.
[Fig. 24]
Fig. 24--Model for demonstrating the heart.
4. Observe the outside of the heart. The thick, lower portion contains the cavities called _ventricles_; the thin, upper, ear-shaped portions are the _auricles_. The thicker and denser side lies toward the left of the animal's body and is called the _left_ side of the heart; the other is the _right_ side. Locate the right auricle and the right ventricle; the left auricle and the left ventricle.
5. Lay the heart on the table with the front side up and the apex pointing from the operator. This places the left side of the heart to his left and the right side to his right. Notice the groove between the ventricles, called the inter-ventricular groove. Make an incision half an inch to the right of this groove and cut toward the base of the heart until the pulmonary artery is laid open. Then, following within half an inch of the groove, cut down and around the right side of the heart. The wall of the right ventricle may now be raised and the cavity exposed. Observe the extent of the cavity, its shape, its lining, its columns of muscles, its half columns of muscles, its tendons (chordae tendineae), the tricuspid valve from the under side, etc. Also notice the valve at the beginning of the pulmonary artery (the right semilunar) and the sinuses, or depressions, in the artery immediately behind its divisions.
6. Now cut through the middle of the loosened ventricular wall from the apex to the middle of the right auricle, laying it open for observation. Observe the openings into the auricle, there being one each for the vena cava superior, the vena cava inferior, and the coronary vein. Compare the walls, lining, shape, size, etc., with the ventricle below.
7. Cut off the end of the left ventricle about an inch above the apex. This will show the extension of the cavity to the apex; it will also show the thickness of the walls and the shape of the cavity. Split up the ventricular wall far enough to examine the mitral valve and the chordae tendineae from the lower side.
8. Make an incision in the left auricle. Examine its inner surface and find the places of entrance of the pulmonary veins. Examine the mitral valve from above. Compare the two sides of the heart, part for part.
9. Separate the aorta from the other blood vessels and cut it entirely free from the heart, care being taken to leave enough of the heart attached to the artery to insure the semilunar valve's being left in good condition. After tying or plugging up the holes in the sides of the artery, pour water into the small end and observe the closing of the semilunar valve. Repeat the experiment until the action of the valve is understood. Sketch the artery, showing the valve in a closed condition.
*To illustrate the Action of a Ventricle.*--Procure a syringe bulb with an opening at each end. Connect a rubber tube with each opening, letting the tubes reach into two tumblers containing water. By alternately compressing and releasing the bulb, water is pumped from one vessel into the other. The bulb may be taken to represent one of the ventricles. What action of the ventricle is represented by compressing the bulb? By releasing the pressure? Show by a sectional drawing the arrangement of the valves in the syringe bulb.
[Fig. 25]
Fig. 25--Illustrating elasticity of arteries.
*To show the Advantage of the Elasticity of Arteries.*--Connect the syringe bulb used in the last experiment with a rubber tube three or four feet in length and having rather thin walls. In the opposite end of the rubber tube insert a short glass tube which has been drawn (by heating) to a fine point (Fig. 25). Pump water into the rubber tube, observing:
1. The swelling of the tube (pulse) as the water is forced into it. (This is best observed by placing the fingers on the tube.)
2. The forcing of water from the pointed tubs during the interval when no pressure is being applied from the bulb. Compare with the action of the arteries when blood is forced into them from the ventricles.
Repeat the experiment, using a long glass tube terminating in a point instead of the rubber tube. (In fitting the glass tube to the bulb use a very short rubber tube.) Observe and account for the differences in the flow of water through the inelastic tube.
*To show the Advantage of Valves in the Veins.*--Attach an open glass tube one foot in length to each end of the rubber tube used in the preceding experiment and fill with water (by sucking) to within about six inches of the end. Lay on the table with the glass tubes secured in an upright position (Fig. 26). Now compress the tube with the hand, noting that the water rises in both tubes, being pushed in both directions. This effect is similar to that produced on the blood when a vein having no valves is compressed.
[Fig. 26]
Fig. 26.--*Simple apparatus* for showing advantage of valves in veins.
Now imitate the action of a valve by clamping the tube at one point, or by closing it by pressure from the finger, and then compressing with the hand some portion of the tube on the table. Observe in this instance that the water is *all* pushed in the same direction. The movement of the water is now like the effect produced on the blood in veins having valves when the veins are compressed.
*To show the Position of the Valves in the Veins.*--Exercise the arm and hand for a moment to increase the blood supply. Expose the forearm and examine the veins on its surface. With a finger, stroke one of the veins toward the heart, noting that, as the blood is pushed along on one side of the finger the blood follows on the other side. Now stroke the vein toward the hand. Places are found beyond which the blood does not follow the finger. These mark the positions of valves.
*To show Effect of Exercise upon the Circulation.*--1. With a finger on the "pulse" at the wrist or temple, count the number of heart beats during a period of one minute under the following conditions: (_a_) when sitting; (_b_) when standing; (_c_) after active exercise, as running. What relation, if any, do these observations indicate between the general
## activity of the body and the work of the heart?
2. Compare the size of the veins on the backs of the hands when they are placed side by side on a table. Then exercise briskly the right hand and arm, clenching and unclenching the fist and flexing the arm at the elbow. Place the hands again side by side and, after waiting a minute, observe the increase in the size of the veins in the hand exercised. How is this accounted for?
*To Show the Effect of Gravity on the Circulation.*--Hold one hand high above the head, at the same time letting the other hand hang loosely by the side. Observe the difference in the color of the hands and the degree to which the large veins are filled. Repeat the experiment, reversing the position of the hands. What results are observed? In what parts of the body does gravity aid in the return of the blood to the heart? In what parts does it hinder? Where fainting is caused by lack of blood in the brain (the usual cause), is it better to let the patient lie down flat or to force him into a sitting posture?
*To study the Circulation in a Frog's Foot* (Optional).--A compound microscope is needed in this study and for extended examination it is best to destroy the frog's brain. This is done by inserting some blunt-pointed instrument into the skull cavity from the neck and moving it about. A small frog, on account of the thinness of its webs, gives the best results. It should be attached to a thin board which has an opening in one end over which the web of the foot may be stretched. Threads should extend from two of the toes to pins driven into the board to secure the necessary tension of the web, and the foot and lower leg should be kept moist. Using a two-thirds-inch objective, observe the branching of the small arteries into the capillaries and the union of the capillaries to form the small veins. The appearance is truly wonderful, but allowance must be made for the fact that the _motion_ of the blood is magnified, as well as the different structures, and that it appears to move much faster than it really does. With a still higher power, the movements of the corpuscles through the capillaries may be studied.
NOTE.--To perform this experiment without destroying the brain, the frog is first carefully wrapped with strips of wet cloth and securely tied to the board. The wrapping, while preventing movements of the frog, must not interfere with the circulation.
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