handwashing and extreme cleanliness during surgery. In 1867, to further decrease the incidence of postsurgical wound
infections, Lister began using carbolic acid (phenol) spray disinfectant/antiseptic during surgery. His extremely
successful efforts to reduce postsurgical infection caused his techniques to become a standard medical practice.
Afewyearslater,Robert Kochproposedaseries ofpostulates (Koch’spostulates) basedontheideathatthecause ofa
specific disease could beattributed toaspecific microbe. Usingthese postulates, Kochandhiscolleagues were able to
definitively identify the causative pathogens of specific diseases, including anthrax, tuberculosis, and cholera. Koch’s
“one microbe, one disease” concept was the culmination of the 19th century’s paradigm shift away from miasma
theory and toward the germ theory of disease. Koch’s postulates are discussed more thoroughly inHow Pathogens
Cause Disease (http://cnx.org/content/m58867/latest/).
Figure 3.9 (a) Joseph Lister developed procedures for the proper care of surgical wounds and the sterilization of
surgical equipment. (b) Robert Koch established a protocol to determine the cause of infectious disease. Both
scientists contributed significantly to the acceptance of the germ theory of disease.
Part 2
After suffering a fever, congestion, cough, and increasing aches and pains for several days, Barbara suspects
that she has a case of the flu. She decides to visit the health center at her university. The PA tells Barbara that
her symptoms could be due to a range of diseases, such as influenza, bronchitis, pneumonia, or tuberculosis.
During her physical examination, the PA notes that Barbara’s heart rate is slightly elevated. Using a pulse
oximeter, a small device that clips on her finger, he finds that Barbara has hypoxemia—a lower-than-normal
level of oxygen in the blood. Using a stethoscope, the PA listens for abnormal sounds made by Barbara’s heart,
lungs, and digestive system. As Barbara breathes, the PA hears a crackling sound and notes a slight shortness
of breath. He collects a sputum sample, noting the greenish color of the mucus, and orders a chest radiograph,
which shows a “shadow” in the left lung. All of these signs are suggestive of pneumonia, a condition in which
the lungs fill with mucus (Figure 3.10).Clinical Focus
90 Chapter 3 | The Cell
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