Introduction:

Pathophysiology (a.k.a. physiopathology) – a convergence of pathology with physiology – is the study of the disordered physiological processes that cause, result from, or are otherwise associated with a disease or injury. Pathology is the medical discipline that describes conditions typically observed during a disease state, whereas physiology is the biological discipline that describes processes or mechanisms operating within an organism. Pathology describes the abnormal or undesired condition, whereas pathophysiology seeks to explain the functional changes that are occurring within an individual due to a disease or pathologic state.

Nineteenth Century:

In Germany in the 1830s, Johannes Müller led the establishment of physiology research autonomous from medical research. In 1843, the Berlin Physical Society was founded in part to purge biology and medicine of vitalism, and in 1847 Hermann von Helmholtz, who joined the Society in 1845, published the paper "On the conservation of energy", highly influential to reduce physiology's research foundation to physical sciences. In the late 1850s, German anatomical pathologist Rudolf Virchow, a former student of Müller, directed focus to the cell, establishing cytology as the focus of physiological research, while Julius Cohnheim pioneered experimental pathology in medical schools' scientific laboratories.

Germ Theory:

By 1863, motivated by Louis Pasteur's report on fermentation to butyric acid, fellow Frenchman Casimir Davaine identified a microorganism as the crucial causal agent of the cattle disease anthrax, but its routinely vanishing from blood left other scientists inferring it a mere byproduct of putrefaction. In 1876, upon Ferdinand Cohn's report of a tiny spore stage of a bacterial species, the fellow German Robert Koch isolated Davaine's bacterides in pure culture —a pivotal step that would establish bacteriology as a distinct discipline— identified a spore stage, applied Jakob Henle's postulates, and confirmed Davaine's conclusion, a major feat for experimental pathology. Pasteur and colleagues followed up with ecological investigations confirming its role in the natural environment via spores in soil.

Scientific Medicine:

The American physician William Welch trained in German pathology from 1876 to 1878, including under Cohnheim, and opened America's first scientific laboratory —a pathology laboratory— at Bellevue Hospital in New York City in 1878. Welch's course drew enrollment from students at other medical schools, which responded by opening their own pathology laboratories. Once appointed by Daniel Coit Gilman, upon advice by John Shaw Billings, as founding dean of the medical school of the newly forming Johns Hopkins University that Gilman, as its first president, was planning, Welch traveled again to Germany for training in Koch's bacteriology in 1883. Welch returned to America but moved to Baltimore, eager to overhaul American medicine, while blending Vichow's anatomical pathology, Cohnheim's experimental pathology, and Koch's bacteriology. Hopkins medical school, led by the "Four Horsemen" —Welch, William Osler, Howard Kelly, and William Halsted— opened at last in 1893 as America's first medical school devoted to teaching German scientific medicine, so called.

Twentieth Century:

The first biomedical institutes, Pasteur Institute and Berlin Institute for Infectious Diseases, whose first directors were Pasteur and Koch, were founded in 1888 and 1891, respectively. America's first biomedical institute, The Rockefeller Institute for Medical Research, was founded in 1901 with Welch, nicknamed "dean of American medicine", as its scientific director, who appointed his former Hopkins student Simon Flexner as director of pathology and bacteriology laboratories. By way of World War I and World War II, Rockefeller Institute became the globe's leader in biomedical research.