Microbiology, 2021

84 3 • The Cell
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.
CHECK YOUR UNDERSTANDING
• Compare and contrast the miasma theory of disease with the germ theory of disease.
• How did Joseph Lister’s work contribute to the debate between the miasma theory and germ theory and
how did this increase the success of medical procedures?
Clinical Focus
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-thannormal
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).
Figure 3.10 This is a chest radiograph typical of pneumonia. Because X-ray images are negative images, a “shadow” is seen as a
white area within the lung that should otherwise be black. In this case, the left lung shows a shadow as a result of pockets in the lung
that have become filled with fluid. (credit left: modification of work by “Christaras A”/Wikimedia Commons)
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