Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] THE BLOOD 345 sues where the food is oxidized, the plasma brings back with it to the lungs the carbon dioxide liberated from the tissues of the body where oxidation has taken place. Blood returning from the tissues of the body has from 45 to 50 cubic centimeters of carbon dioxide to every 100 cubic centimeters. (See Respiration, page 380.) Some waste products, to be spoken of later, are also found in the plasma. Demonstration. — Get
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] THE BLOOD 345 sues where the food is oxidized, the plasma brings back with it to the lungs the carbon dioxide liberated from the tissues of the body where oxidation has taken place. Blood returning from the tissues of the body has from 45 to 50 cubic centimeters of carbon dioxide to every 100 cubic centimeters. (See Respiration, page 380.) Some waste products, to be spoken of later, are also found in the plasma. Demonstration. — Get some fresh beef blood. Let it stand overnight in a jar. In the morning it will be found to have separated into two parts, a dark red clot and a thin straw-colored liquid, called serum. Serum is found to be made up of about 90 per cent water, 8 to 9 per cent proteid, and from 1 to 2 per cent sugars, fats, and mineral matter. In these respects it rather closely resembles the fluid food that is absorbed from the intestines. Clotting of Blood. — Pour another jar of fresh beef blood into a pan and briskly whip it with a bundle of little rods (or with an egg beater). A stringy substance will be found to stick to the rods. This, if washed care- fully, is seen to be almost colorless. Test with nitric acid and ammonia. Note the deep orange color. It is a proteid substance called fibrin. Blood plasma, then, is made up of serum, a fluid portion, and fibrin, which, although in a fluid state in the blood vessels within the body, coagulates when removed from the body. It is this coagulation which aids in the formation of a blood clot. A clot is simply a mass of fibrin with a large number of corpuscles tangled within. The clotting of blood is of great physi- ological importance, for otherwise we might bleed to death from the smallest wound. In blood within the circulatory system of the body the fibrin is held in a fluid state called fibrinogen. It is believed that an enzyme, acting upon
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