Blood

the red liquid of the body. From one-tenth to one-thirteenth of a healthy person's body consists of blood. The blood of a horse equals one-eighteenth of the body-weight; that of an ox is about one twenty-third.

Blood is about eight-tenths water. This water keeps the organs of the body moist and flexible, but its chief office is to carry nutrients to the tissues and waste away from them. Although not the first to understand the circulation of the blood, Dr. Harvey of London was the first to announce distinctly that the blood is forced by the contraction of the heart through tubes or arteries to all parts, including the utmost extremities of the body, and that it is collected again by tiny drainage tubes which unite into larger and larger veins until they pour the blood back into the heart again. To complete its circuit, the blood is forced by a similar system of outgoing arteries and incoming veins through the lungs. It is then ready for another trip through the body. A round trip occupies from fifteen to thirty seconds. The blood of a horse circulates in thirty-one seconds.

As stated, the water of the blood is a carrier. The lungs and the digestive system pour gases, oxygen, hydrogen, nitrogen, sugars, salts and fats, lime, iron, and all kinds of food into the blood, which whirls the molecules along in its current and deposits them where they are needed to build up bone, muscle, sinew, and fat. Material no longer needed by the body is dumped into the veins and drained away, to be taken care of and expelled through the lungs, the kidneys, the skin, or the alimentary canal. Of course, the blood carries whatever is poured into it. If one's food is unwholesome, the blood carries poor building material. If the water one drinks, the air one breathes, or the food one eats contains germs, the microbes of disease, the blood carries them promptly to the tissues. Malaria, for instance, is nothing more or less than the presence of countless numbers of microscopic animals introduced into one's blood in the first instance by the bill of a certain mosquito.

Although the blood cannot refuse to carry germs of disease, nature has made a wonderful provision to render them harmless. The blood is full, literally swarming, with white, spherical corpuscles or cells that feed on bacteria. If one is in health and well nourished the chances are that these white cells will take care of all harmful animals and bacteria. In famine-stricken districts where the people have thin blood, lacking in vigorous white cells, contagious disease is most likely to get a footing and become an epidemic.

The color of the blood is due to still more numerous red cells or corpuscles, in the proportion of ninety-nine red cells to one white cell. They are so numerous as to be beyond comprehension--5,000,000 to a cubic millimeter. They are flat disks pressed inward on each face. They run through the fine capillaries, face to face, like a roll of coin. In most animals the red cells are circular, but in the camel and in reptiles they are oval. The red cells of the various animals differ greatly in size. Those of a frog are very large. Those of a sheep are small. Human corpuscles may be identified, therefore, under a microscope. More than one bloodstained knife and many a blood-stained garment has been examined to ascertain whether the telltale spots were caused by human blood. It is literally true that blood cries out against a murderer.

Millions of red corpuscles break down in the body during every second of time. New ones are supplied by the red marrow of the bones, where they are produced and sent into the circulation. The number of red corpuscles varies with conditions. They increase in high latitudes. They often decrease during disease of the body, producing a condition called anaemia.

The red corpuscles are the carriers of oxygen. Arterial blood, or blood going outward, has a bright red color, due to oxygen freshly obtained from the lungs. Venous blood, or blood returning through the veins, is dark, not only lacking oxygen, but laden with waste matter. The blood of animals is warm or cold according to the amount of oxygen it carries. Cold-blooded animals do not require to breathe so freely as the warm-blooded animals.

The proper temperature of the human body is about 98 degree F. The circulation of the blood equalizes the temperature of the body. Cold-blooded animals have the temperature of their surroundings. The blood does not supply enough oxygen to keep them warm. Warm-blooded animals are supplied with oxygen from the blood. Their bodies possess a temperature in a degree, at least, independent of their surroundings. The power of the blood to keep up the temperature of the body is indispensable to animal life in cold countries. The Eskimo, and, in fact, all people living in wintry climes would be frozen solid, were it not that the blood carries oxygen to all parts of the body and keeps the temperature very nearly constant at 98 degree.

Blood possesses a peculiar quality of clotting on exposure to air. Blood is composed of clear liquid and of blood cells or corpuscles. The liquid is called plasma. If plasma is exposed to the air, threads known as fibrin are formed. These fibrin threads entangle and inclose the corpuscles, forming what is known as a clot. This quality of clotting or coagulating closes wounds, if not too serious, and prevents bleeding. Physiologists are satisfied that clotting is not due to the fact that blood has ceased to be in motion, nor is it due to exposure to the air. They do not know why blood clots, neither do they know why it does not clot while it is within a healthy blood vessel.

See Malaria