How does the blood fight disease?

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Disease is caused by too much of harmful bacteria whithin the body, and it is the function of the white corpuscles to destroy bacteria. Most white corpuscles are larger and fewer than red ones.
For approximately every 1000 red cells there is only one white cell. White corpuscles have no definite shape, and they move about by changing their shape.
To destroy a bacteria a white cell moves over to the bacterium and then engulfs it. Once the bacterium is inside the white cell, it is digested.
When large number of harmful bacteria invade the blood, the body automatically increases the number of white corpuscles produced by the bone marrow. Then the body has sufficient white cells to destroy most of the invading bacteria.