Different microscopic organisms cause different diseases. When a dangerous microscopic organism is transferred from one person to many people, the disease it carries will spread. Why is this considered a theory instead of a hypothesis or a law?

In the human adult, the bone marrow produces all of the red blood cells, 60–70 percent of the white cells (i.e., the granulocytes), and all of the platelets. The lymphatic tissues, particularly the thymus, the spleen, and the lymph nodes, produce the lymphocytes (comprising 20–30 percent of the white cells).