They may be present in such masses as to form a dense wall around the bacteria, thus acting as a physical bar to their further extension.

The other form of amoeboid cell, which Metschnikoff calls the macrophage, has more feeble phagocytic action towards bacteria, and these are rarely found enclosed within them.

It is chiefly by means of their activity that other sorts of substances are removed.

They often contain dead cells or cell fragments, and when haemorrhage takes place in a tissue they enclose and remove the granules of blood pigment which result.

They often join together, forming connected masses, and surround such a foreign body as a hair, or a thread which the surgeon places in a wound to close it.