Science without LawsPhysicists regularly invoke universal laws, such as those of motion and electromagnetism, to explain events. Biological and medical scientists have no such laws. How then do they acquire a reliable body of knowledge about biological organisms and human disease? One way is by repeatedly returning to, manipulating, observing, interpreting, and reinterpreting certain subjectssuch as flies, mice, worms, or microbesor, as they are known in biology, model