More than nine-tenths of the blood consists of red corpuscles. They are so small that a large drop of blood contains more than 250 million of them.
They are discshaped and concave on each side. These corpuscles contain a substance called haemoglobin, which is a compound of iron. Hemoglobin can contain very well with oxygen from the air in the lungs. It is the task of the red corpuscles to carry oxygen to cells in all parts of the body, and upon reaching these cells, to give up the oxygen to them.
When hemoglobin combines with oxygen, it turns bright red. That is why blood running out of a cut is always red - the hemoglobin is combining with the oxygen of the air.
Red blood corpuscles live only about fifty to seventy days and thus they must be replaced continuously. New red cells are formed within the marrow of the bones.
If a person lacks sufficient red corpuscles, he is said to have the disease anaemia. He is usually listless and thin, because his cells do not receive enough oxygen. Some types of anaemia may be cured by adding sufficient iron to an anaemic person's diet.
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