Paradigm Shifts in the History of Medicine
Medical theory and practice have undergone many waves of change over the centuries, with many changes to come. Here, I explore paradigm shifts in microbiology as a part of medicine.
The history of medical advancement is marked by bursts of revolutionary changes in how humans have changed their perceptions of the natural world. In many cases, these changes were noted with the emergence of new theories and the annulment of others. Everything from disease causation to therapeutic strategies were points of debate and change. Were disease symptoms due to spiritual afflictions, a failure to appease the gods or even the result of being targeted by evil magic? Or were they due to imbalances in the bodily humors, injury, or of some natural causation? Were certain foods, exercise, prayers, or rest the best therapies? These are some of the questions people have asked over the centuries and in some cases, continue to ask today. The cultural framework of the medical domain greatly influences these perspectives, and it is no wonder that strong opinions and perspectives on science and medicine have varied across cultures and time. No field of medicine quite illustrates this point as well as that of infectious disease.
Germ Theory
Although we currently live in an era of broad acceptance of the germ theory of disease—the concept that microorganisms can invade other microorganisms and cause disease—this was actually a revolutionary concept that took centuries of experiments and observations until it was accepted. For example, while people could observe food spoilage in the home environment, there was little understanding of the process. This is most evident in the theory of spontaneous generation—the idea that living things (such as microbes and worms) arose from nonliving things (such as a cut of meat).
Firmly held belief in spontaneous generation hampered advancement in the understanding of the transmission of infectious disease for centuries, and this is despite the efforts of several talented scientists who worked to disprove it. For example, in the late 17th Century, the Italian physician Francesco Redi tested this idea with an experiment in which pieces of meat were placed in jars either left open, covered in gauze, or closed with a cork. Flies laid eggs on the meat in the open jar resulting in maggots on the meat, but not maggots were observed in the meat from the closed cork jar or the gauze-covered jar. This simple yet elegant experiment should have put the argument to rest. Still, additional tests went on until the 19th Century by Louis Pasteur and John Tyndall, whose experiments with sterile broth exposed to air eventually resolved the matter.
However, evidence of careful observations regarding disease transmissibility does appear much earlier than this period. For example, Biblical laws regarding basic sanitation and the necessity of burying solid waste (fecal materials) have been in place at least since the time of Moses (circa 13th Century BCE). The Hippocratic Corpus (c400 BCE) describes several sanitary and surgical procedures that indicate an understanding that disease could transfer from person to person through inanimate objects, such as clothing. Varro (116-27 BCE), the great Roman scholar and polymath, proposed that tiny animals entered the body through the mouth and nose to cause disease—a revolutionary concept at the time.
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