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 hemoglobin,which is a compound of iron. Hemoglobin can combine 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 cells, to give up the oxygen to them.
When haemoglobin combines with oxygen, it turns bright red. That is why blood running out of a cut is always red - the haemoglobin is combining with the oxygwn of the air.
Red blood corpuscles live only about fifty to seventy days, and thus, they must be replaced continuously. New redcellsareformedwithinthe marrow of the bones.
If a person lacks sufficient red corpuscies, he is said to have the disease anaemia. He is usually Iistless and thin, be cause 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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