Edwin Klebs's Grundversuche.

In 1876, discussions of the role of microorganisms in disease causation focused on anthrax and wound infections, and even in respect to these diseases there was controversy. In a series of papers on the pathologicality of bacteria, Edwin Klebs identified four "Grundversuche" (fundamental tests) that provided a basis for his own research strategy. The Grundversuche can be read as the following hypotheses: first, all bacteria are pathological; second, bacteria never occur spontaneously; third, every disease is caused only by bacteria; and fourth, the bacteria that cause distinguishable disease are distinguishable. Although some of these hypotheses are literally false, together they constitute part of a rational basis for a bacterial theory of disease, and, as such, they mark a true revolution in etiological thought.