Physiology and Hygiene for Secondary Schools

by Francis M. Walters

Fig. 12—A balanced change in water. The level remains constant although the water is continually changing; suggestive of the changes in the blood.

Changes in the Blood.—In performing its functions in the body the blood must of necessity undergo rapid and continuous change. The red corpuscles, whose changes have already been noted, appear to be the most enduring constituents of the blood. The plasma is the portion that changes most rapidly. Yet in spite of these changes the quantity and character of the blood remain practically constant.[14] This is because there is a balancing of the forces that bring about the changes. The addition of various materials to the blood just equals the withdrawal of the same materials from the blood. Somewhat as a vessel of water (Fig. 12) having an inflow and an outflow which are 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.