1. There are two types of giant cells discriminated by their method of formation; one is derived from a single monocyte or epithelioid cell and the other by the fusion of cells.
2. The epithelioid giant cell is formed by amitotic nuclear division; it tends to be small, simple, and relatively uniform in structure; its essential structure is a rosette of fine vacuoles which in the living state are stainable with neutral red.
3. The foreign body types show extreme variation in size and structure, according to the nature and the number of the cells out of which they are made. They lack any constant cytoplasmic pattern.
4. Both of these types of giant cells are probably formed in response to the need for phagocytosis of foreign material.
5. In tuberculosis it is probably only certain specific portions of the lipoids that induce the production of mono- and multinucleated epithelioid cells.
6. The stimuli for the formation of giant cells of the foreign body type are much more varied than those which produce epithelioid giant cells.