The germ theory of disease is a bit like a puzzle with lots of pieces making up a central idea. Each piece of the Trivial Pursuit pie could be seen as a part of the theory. One could be the germs that are the infectious part of any communicable disease. Another piece would be the infection caused by those germs. The next piece would be the course of the disease (how the disease manifests itself), followed by a piece for the symptoms that the disease causes. Another piece of the pie would be the treatment for the disease, whether antibiotics or vaccinations. The holder for these pieces would be Pasteur; he was the unifying element that brought all these pieces of the pie together. The steps needed to bring this idea together is described above; it is just the abstract idea of making a pie piece a concept in the germ theory.