The adaptation of microbiological techniques to the study of the etiological agents of infectious disease. Some of the most significant scientific advances during the latter half of the nineteenth century and the first few decades of the twentieth century were in medical bacteriology. From the work of Louis Pasteur, Robert Koch, Theobald Smith, and others, it was shown that bacteria were responsible for many diseases of humans. During the early part of the twentieth century, the technology for the growth of bacteria was advanced to the extent that pure cultures of bacteria could be studied from defined environments. Not only did bacteria become models for the study of their own biochemical characteristics, but the same technology enabled bacteriologists to isolate and identify bacteria from patients with infectious disease. This spurred the discovery of most of the bacterial diseases that are currently known.