Plague bacteria
The infectious bacterium Yersinia pestis is the cause of plague. The bacteria (yellow), shown in a digitally colorized scanning electron microscopic image, infect the proventricular spines (purple) lining the digestive tract of an Oriental rat flea (Xenopsylla cheopis), which plays a critical role in the transmission of plague from rodents to humans.
germ theory
medicine
germ theory, in medicine, is the scientific principle that infectious diseases are caused by specific microorganisms (pathogens) that invade and reproduce within the body, disrupting normal physiological functions. These microorganisms include bacteria, viruses, fungi, and protozoa, which are too small to be seen except through a microscope. Germ theory serves a central role in explaining how diseases are transmitted, including through direct contact, contaminated surfaces, airborne particles, and vectors. Understanding these transmission pathways allows for...
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