The examination of patients with deficiencies in their immune systems provides important clues to our understanding of the body's natural resistance to disease. According to immunologist Robert Good,(12) the discovery of agammaglobulinemia in 1952, a rare condition in which there is no gamma-globulin in the blood, leaving patients susceptible to infection because they are unable to form antibodies, "provided a new and clear cut opportunity to gain insight into the nature and significance of the immune response in man." Good referred to his studies as "experiments of nature."
Tomographic Brain Scans: These images enable researchers to build an accurate picture of disease processes as they occur in the human patient. Scan A depicts a normal scan while scan B shows brain damage after a stroke.
Human physiological studies are not restricted to cases of illness. The same scanning techniques which permit the investigation of disease in living subjects, are also being applied to physiological studies of healthy volunteers. For instance, nuclear magnetic resonance spectroscopy is being used to study muscle physiology.13 There are also new ways of investigating brain functions: the techniques involve electrical or magnetic stimulation of nerve cells through the intact skull of healthy subjects.(11) In the past, such studies were performed by inserting small electrodes into the brains of patients during therapeutic neurosurgery.
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