Physiology

• 1. Introduction

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  Physiology is the scientific study of functions and mechanisms in a living system. Galen, working around 130 to 200 AD, cut into bodies to ask not what the parts looked like but what they did. He believed the body ran on four substances, that emotions rode along with black bile and blood, and that a brain governed thought while a liver fed growth. He was wrong about a great deal. Yet his way of probing the living body held its grip on medicine for the next fourteen centuries. How did a science built on earth, water, air and fire become the study of cells dividing and capillaries opening? And why do some researchers now argue, with real heat, about whether physiology is dead or alive?

• 2. From Humors To Machines

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  Hippocrates, working in the late fifth century BC, framed the body around four basic substances: earth, water, air and fire. Each carried a matching humor, black bile, phlegm, blood and yellow bile, and Hippocrates already sensed that emotions clung to them. The study of human physiology as a medical field begins here, in classical Greece, though early forms of physiology or anatomy can be reconstructed at around the same time in China, India and elsewhere.

  Aristotle pressed on the link between structure and function, and his critical thinking marked the true beginning of physiology in Ancient Greece. He kept the humoral theory but recast it as four primary qualities of life: hot, cold, wet and dry. Where Hippocrates described, Aristotle reasoned about why a part took the form it did.

  Galen turned argument into experiment and became the founder of experimental physiology. He insisted that humoral imbalances could be pinned to specific organs rather than floating through the whole body. He sorted people into temperaments, sanguine with blood, phlegmatic with phlegm, choleric with yellow bile, melancholy with black bile. His map of three connected systems, brain and nerves, heart and arteries, liver and veins, would shape medical thinking until a French physician finally gave the field its name.

• 3. Naming A Science

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  Jean Fernel, a French physician who lived from 1497 to 1558, introduced the term "physiology" itself. The word arrived as a wave of discoveries began to reshape what the body was understood to do. Galen, Ibn al-Nafis, Michael Servetus, Realdo Colombo, Amato Lusitano and William Harvey are all credited with important discoveries in the circulation of the blood.

  Santorio Santorio, in the 1610s, built instruments to make function measurable. He used a device called the pulsilogium to measure the pulse rate, and a thermoscope to measure temperature. Counting and timing the living body had become possible.

  Luigi Galvani, in 1791, described the role of electricity in the nerves of dissected frogs, opening a door onto how signals travel through tissue. In 1811, Cesar Julien Jean Legallois studied respiration through animal dissection and lesions, and located the center of respiration in the medulla oblongata. That same year, Charles Bell finished work on what became the Bell-Magendie law, comparing functional differences between the dorsal and ventral roots of the spinal cord. Francois Magendie described the sensory roots in 1824 and produced the first evidence of the cerebellum's role in equilibration, completing the law that now carries both their names.

• 4. The Body As Factory

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  Henri Milne-Edwards, a French physiologist working in the 1820s, introduced the notion of physiological division of labor. It let researchers, in his words, "compare and study living things as if they were machines created by the industry of man." The metaphor was deliberate and industrial.

  Inspired by the work of Adam Smith, Milne-Edwards wrote that the "body of all living beings, whether animal or plant, resembles a factory... where the organs, comparable to workers, work incessantly to produce the phenomena that constitute the life of the individual." In more differentiated organisms, the functional labor could be divided among different systems, which he called appareils.

  Joseph Lister, in 1858, studied the blood coagulation and inflammation that followed injuries and surgical wounds. He went on to discover and put antiseptics to work in the operating room. The death rate from surgery dropped by a substantial amount, a rare case where a physiological insight saved lives on the table. The factory, it turned out, could be kept from rotting.

• 5. The Steady State

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  Matthias Schleiden and Theodor Schwann, with the 1838 appearance of cell theory, made a radical claim: organisms are built from units called cells. From that point physiological knowledge began to accumulate at a rapid rate. The cell became the place where function was located.

  Claude Bernard, who lived from 1813 to 1878, arrived at the concept of the milieu interieur, the internal environment that the body works to hold steady. The American physiologist Walter B. Cannon took up that idea and championed it under a new name in 1929. By homeostasis, Cannon meant "the maintenance of steady states in the body and the physiological processes through which they are regulated."

  Ivan Pavlov, in 1891, ran research on "conditional responses" using dogs whose saliva flowed in answer to a bell and to visual stimuli. William Beaumont was the first American to put physiology to practical use. Michael Foster, Max Verworn and Alfred Binet, drawing on Haeckel's ideas, built what they called "general physiology," a unified science of life grounded in the actions of cells, later renamed in the twentieth century as cell biology.

• 6. What The Field Became

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  August Krogh won the Nobel Prize in 1920 for discovering how blood flow is regulated in the capillaries, the smallest vessels where exchange with tissue happens. The prize signaled that the fine mechanics of the body had become world-class science.

  Andrew Huxley and Hugh Huxley, with their research team, discovered the sliding filaments in skeletal muscle in 1954. The finding is known today as the sliding filament theory, and it explains how muscle actually contracts. In the twentieth century, biologists grew curious about how organisms other than humans function, which gave rise to comparative physiology and ecophysiology. Knut Schmidt-Nielsen and George Bartholomew were major figures in that work, and evolutionary physiology has more recently become a distinct subdiscipline.

  The debates about whether physiology is dead or alive turn on a strange kind of success. If physiology is less visible now than during its golden age in the nineteenth century, it is largely because the field gave birth to some of the most active domains in biology today, neuroscience, endocrinology and immunology among them. It is still seen as an integrative discipline, one that can pull data from many domains into a single coherent framework.

• 7. Women In Physiology

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  Ida Hyde was elected the first female member of the American Physiological Society in 1902, fifteen years after the society was founded in 1887 with only men in its ranks. Hyde, a representative of the American Association of University Women, worked to promote gender equality across science and medicine.

  J.S. Haldane proposed in 1913 that women be allowed to formally join The Physiological Society, which had been founded in London in 1876 as a dining club. On the 3rd of July 1915, six women were officially admitted: Florence Buchanan, Winifred Cullis, Ruth Skelton, Sarah C. M. Sowton, Constance Leetham Terry and Enid M. Tribe. The centenary of that election was marked in 2015 with the book "Women Physiologists: Centenary Celebrations And Beyond For The Physiological Society."

  Gerty Cori, with her husband Carl Cori, received the Nobel Prize in Physiology or Medicine in 1947 for their discovery of glycogen, the phosphate-containing form of glucose, and for the Cori cycle that describes how muscle converts glycogen into lactic acid. Barbara McClintock won the 1983 prize for the discovery of genetic transposition, and she remains the only female recipient of an unshared Nobel Prize. Bodil Schmidt-Nielsen became the first woman president of the American Physiological Society in 1975. Later laureates carried the line forward: Gertrude Elion in 1988 for drugs treating leukemia, gout, malaria and other diseases, Linda B. Buck in 2004 for odorant receptors, Francoise Barre-Sinoussi in 2008 for identifying HIV, and Elizabeth Blackburn in 2009 for the work on telomeres and the enzyme telomerase.