Page 58 - The Miracle of the Immune System
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THE MIRACLE OF THE IMMUNE SYSTEM
Phagocytosis in progress. The macrophage (yellow) while digesting the bac-
teria (blue).
are situated in the gaps in various tissues. They perform phagocytosis on
the micro-organisms from where they are, without moving.
If the invader antigens (foreign micro-organisms) are few enough for
the present eater cells to deal with, they are destroyed with no extra alarm
being given. But if the invader microbes are too great in number, the eat-
er cells may fail to get them under control. Unable to digest all of them,
they expand in size. When distended by the antigens, the cells burst, caus-
ing a liquid substance (pus) to overflow. This does not mean that the war
is lost. So far, the eater cells have just met the microbes, which have still
many tougher barriers to pass. The formation of pus activates the lym-
phocytes, which have been delivered from the bone marrow, the lymph
nodes, and above all, the thymus. In a second wave of defence, the new-
ly arriving defence cells attack everything they find around, including cell
