Georges Canguilhem repeatedly characterized the history of medicine during the nineteenth century as a history of shifts: the laboratory replaced the clinic, the active agent with its chemical structural formula replaced prepared medication, and the experimental animal replaced the sick person. In describing laboratory medicine as a further shift in nineteenth-century medicine, Georges Canguilhem places medical bacteriology within the tradition of pathological-anatomical dissection that emerged from the late eighteenth century onwards. The decisive achievement of the bacteriological laboratory was its ability to both observe a disease without recourse to the diseased person and replace clinical symptomology with reproduction of disease won through animal experiment. Evidence that specific microorganisms present in association with the pathological changes they caused became the measure of disease. It is worth noting that this act of measuring was, by and large, devoid of quantifying measurement, mathematics and statistics.