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.