Physiology and Hygiene for Secondary Schools. Francis M. Walters
equal in amount may keep always at the same level, the balancing of the intake and outgo of the blood keeps its composition about the same from time to time.
Hygiene of the Blood.—The blood, being a changeable liquid, is easily affected through our habits of living. Since it may be affected for ill as well as for good, one[pg 035] should cultivate those habits that are beneficial and avoid those that are harmful in their effects. Most of the hygiene of the blood, however, is properly included in the hygiene of the organs that act upon the blood—a fact which makes it unnecessary to treat this subject fully at this time.
From a health standpoint, the most important constituents of the blood are, perhaps, the corpuscles. These are usually sufficient in number and vigor in the blood of those who take plenty of physical exercise, accustom themselves to outdoor air and sunlight, sleep sufficiently, and avoid the use of injurious drugs. On the other hand, they are deficient in quantity and inferior in quality in the bodies of those who pursue an opposite course. Impurities not infrequently find their way into the blood through the digestive organs. One should eat wholesome, well-cooked food, drink freely of pure water, and limit the quantity of food to what can be properly digested. The natural purifiers of the blood are the organs of excretion. The skin is one of these and its power to throw off impurities depends upon its being clean and active.
Effect of Drugs.—Certain drugs and medicines, including alcohol and quinine,15 have recently been shown to destroy the white corpuscles. The effect of such substances, if introduced in considerable amount in the body, is to render one less able to withstand attacks of disease. Many patent medicines are widely advertised for purifying the blood. While these may possibly do good in particular cases, the habit of doctoring one's self with them is open to serious objection. Instead of taking drugs and patent medicines for purifying the blood, one should study to live more hygienically. We may safely rely upon[pg 036] wholesome food, pure water, outdoor exercise and sunlight, plenty of sleep, and a clean skin for keeping the blood in good condition. If these natural remedies fail, a physician should be consulted.
Summary.—The blood is the carrying or transporting agent of the body. It consists in part of constituents, such as the red corpuscles, that enable it to carry different substances; and in part of the materials that are being carried. The latter, which include food and oxygen for the cells and wastes from the cells, may be classed as freight. Certain constituents in the blood destroy disease germs, and other constituents, by coagulating, close small leaks in the blood vessels. Although subject to rapid and continuous change, the blood is able—by reason of the balancing of materials added to and withdrawn from it—to remain about the same in quantity and composition.
Exercises.—1. Compare blood and water with reference to weight, density, color, odor, and complexity of composition.
2. Show by an outline the different constituents of the blood.
3. Compare the red and white corpuscles with reference to size, shape, number, origin, and function.
4. Name some use or purpose for each constituent of the blood.
5. What constituents of the blood may be regarded as freight and what as agents for carrying this freight?
6. After coagulation, what portions of the blood are found in the clot? What portions are found in the serum?
7. What purposes are served by water in the blood?
8. Show how the blood, though constantly changing, is kept about the same in quantity, density, and composition.
9. In the lungs the blood changes from a dark to a bright red color and in the tissues it changes back to dark red. What is the cause of these changes?
10. If the oxygen and hemoglobin formed a strong instead of a weak chemical union, could the hemoglobin then act as an oxygen carrier? Why?
[pg 037]11. What habits of living favor the development of corpuscles in the blood?
12. Why will keeping the skin clean and active improve the quality of one's blood?
PRACTICAL WORK
To demonstrate the Physical Properties of Blood (Optional).—Since blood is needed in considerable quantity in the following experiments, it is best obtained from the butcher. To be sure of securing the blood in the manner desired, take to the butcher three good-sized bottles bearing labels as follows:
1 Fill two thirds full. While the blood is cooling, stir rapidly with the hand or a bunch of switches to remove the clot.
2 Fill two thirds full and set aside without shaking or stirring.
3 Fill two thirds full and thoroughly mix with the liquid in the bottle.
Label 3 must be pasted on a bottle, having a tight-fitting stopper, which is filled one fifth full of a saturated solution of Epsom salts. The purpose of the salts is to prevent coagulation until the blood is diluted with water as in the experiments which follow.
Experiments.—1. Let some of the defibrinated blood (bottle 1) flow (not fall) on the surface of water in a glass vessel. Does it remain on the surface or sink to the bottom? What does the experiment show with reference to the relative weight of blood and water?
2. Fill a large test tube or a small bottle one fourth full of the defibrinated blood and thin it by adding an equal amount of water. Then place the hand over the mouth and shake until the blood is thoroughly mixed with the air. Compare with a portion of the blood not mixed with the air, noting any difference in color. What substance in the air has acted on the blood to change its color?
3. Fill three tumblers each two thirds full of water and set them in a warm place. Pour into one of the tumblers, and thoroughly mix with the water, two tablespoonfuls of the blood containing the Epsom salts. After an interval of half an hour add blood to the second tumbler in the[pg 038] same manner, and after another half hour add blood to the third. The water dilutes the salts so that coagulation is no longer prevented. Jar the vessel occasionally as coagulation proceeds; and if the clot is slow in forming, add a trace of some salt of calcium (calcium chloride). After the blood has been added to the last tumbler make a comparative study of all. Note that coagulation begins in all parts of the liquid at the same time and that, as the process goes on, the clot shrinks and is drawn toward the center.
4. Place a clot from one of the tumblers in experiment 3 in a large vessel of water. Thoroughly wash, adding fresh water, until a white, stringy solid remains. This substance is fibrin.
5. Examine the coagulated blood obtained from the butcher (bottle 2). Observe the dark central mass (the clot) surrounded by a clear liquid (the serum). Sketch the vessel and its contents, showing and naming the parts into which the blood separates by coagulation.
To examine the Red Corpuscles.—Blood for this purpose is easily obtained from the finger. With a handkerchief, wrap one of the fingers of the left hand from the knuckle down to the first joint. Bend this joint and give it a sharp prick with the point of a sterilized 'needle just above the root of the nail. Pressure applied to the under side of the finger will force plenty of blood through a very small opening. (To prevent any possibility of blood poisoning the needle should be sterilized. This may be done by dipping it in alcohol or by holding it for an instant in a hot flame. It is well also to wash the finger with soap and water, or with alcohol, before the operation.) Place a small drop of the blood in the middle of a glass slide, protect the same with a cover glass, and examine with a compound microscope. At least two specimens should be examined, one of which should be diluted with a little saliva or a physiological salt solution.16 In the diluted specimen the red corpuscles appear as amber-colored, circular, disk-shaped bodies. In the undiluted specimen they show a decided tendency to arrange themselves in rows, resembling rows of coins. (Singly, the corpuscles do not appear red when highly magnified.)
A few white corpuscles may generally be found among the red ones in the undiluted specimen. These become separated by the formation[pg 039] of the red corpuscles into rows. They