Medicine has evolved enormously since ancient times, but it would never have been possible without the hard work of these men and women.

Hippocrates (c. 460–377 BCE)

Known as the father of medicine, Hippocrates wrote the oath that bears his name. Although it has been modified over the years, this text, considered a pillar of medical ethics, is still recited by medical graduates around the world.

During his lifetime, the Greek physician highlighted the importance of observing clinical signs before making a diagnosis. According to Hippocrates, diseases did not have a divine cause—instead, they were caused by a set of factors, including a patient’s age.

Galen (131–201)

Galen, author of nearly 500 treatises on medicine, philosophy, and ethics, the majority of which have unfortunately been lost, is one of the greatest physicians of ancient times. Through the dissection of animals and other experiments, Galen made significant discoveries, such as the fact that arteries carry blood, not air. He also identified seven pairs of cranial nerves.

Avicenna (980–1037)

Avicenna, a Persian philosopher and physician known in Muslim countries as Ibn Sīnā, wrote The Canon of Medicine, a five-volume medical encyclopedia that has influenced Western medicine for centuries. This large work focuses on the infectious nature of tuberculosis and other diseases.

Ambroise Paré (1510–1590)

The father of modern surgery, Ambroise Paré was an army surgeon and a surgeon to several kings of France, including Henry II and Henry III. During his career, Paré invented several surgical instruments and introduced the implantation of artificial limbs made of gold and silver. His most significant discovery was undoubtedly the ligation of arteries, a process much less painful than cauterization with a hot iron, still widely used in the 16th century.

A humanist, Paré is famous for saying: “I don’t care if you’re Catholic or Protestant, rich or poor. I only care what ails you.”

Andreas Vesalius (1514–1564)

Considered the father of modern anatomy, Flemish anatomist and surgeon Andreas Vesalius wrote and illustrated De humani corporis fabrica libri septem in 1543, the first comprehensive textbook on anatomy. Through the dissection of corpses, Vesalius provided medicine with a better understanding of human anatomy and corrected certain misconceptions dating to ancient times.

Antonie van Leeuwenhoek (1632–1723)

Antonie van Leeuwenhoek was passionate about small things. This Dutch microscopist used his homemade microscopes to become the first scientist to observe a bacterium and protozoan. His research also led to the discovery of spermatozoa.

Edward Jenner (1749–1823)

English surgeon Edward Jenner invented vaccination. When he noticed that farmers who had gotten cowpox, a relatively harmless disease contracted from cattle, were immune to smallpox, a widespread disease in Jenner’s day, he inoculated an eight-year-old boy with cowpox. After attempting to infect the boy with smallpox, Jenner found that the child was immune.

The process known as vaccination quickly spread across Europe. Smallpox was finally eradicated in 1980, a feat that likely would not have been possible without Jenner’s work.

John Dalton (1766-1844)

Daltonism (now known as colour blindness), which affects eight per cent of men and one per cent of women, was discovered by John Dalton, an English chemist who had the eye disease. Through his studies, Dalton concluded that colour blinded was genetic (his brother also suffered from it), caused by an abnormality in the vitreous humour.

René-Théophile-Hyacinthe Laënnec (1781-1826)

Without René-Théophile-Hyacinthe Laënnec’s discovery in 1816, the stethoscope as we know it today might not exist. Considered the father of clinical auscultation, the French physician also classified several pulmonary conditions, such as pneumonia, emphysema, and pneumothorax, from the sounds he heard with his invention.

Ignaz Philipp Semmelweis (1818–1865)

It’s hard to believe that surgeons didn’t always wash their hands before operating on patients. Yet, before a discovery by the Hungarian obstetrician Ignaz Philipp Semmelweis, this practice, now firmly instilled in all health professionals, was not widespread.

The physician made the discovery by comparing the number of deaths in the two maternity wards at the Vienna General Hospital. In the first ward, where the mortality rate was low, midwives delivered the babies. In the second ward, where the number of deaths was higher, deliveries were performed by medical interns. Semmelweis discovered that the students did not wash their hands after performing autopsies in the dissection room, unlike the midwives. As a result, they were unknowingly transmitting diseases to their patients who then contracted infections.

Louis Pasteur (1822-1895)

Louis Pasteur is one of the greatest scientists of all time. In addition to inventing pasteurization, this French chemist also invented vaccines against anthrax and rabies. Pasteur also discovered the bacteria and microbes responsible for infections such as Staphylococcus aureus, Streptococcus, and Streptococcus pneumoniae.

Jean-Martin Charcot (1825-1893)

Dubbed the father of neurology and the Napoleon of neuroses, physician Jean-Martin Charcot is considered the founder of modern neurology. A believer in hypnosis, Charcot used the science to gain a better understanding of hysteria and distinguish it from other conditions, such as epilepsy.

This scientist also studied other illnesses like multiple sclerosis and Parkinson’s disease.

Sir Joseph Lister (1827-1912)

Father of antiseptic surgery, Sir Joseph Lister forever changed the face of modern surgery. This British surgeon used antisepsis (carbolic acid) to dramatically decrease the number of post-operative deaths. Poor sterilization practices of the day caused roughly 35 per cent of amputees to die of infections soon after surgery.

While antiseptic procedures have evolved since then, Lister’s principle, that bacteria must never gain entry to an operation wound, still holds true to this day.

Robert Koch (1843-1910)

During his career, German physician Robert Koch made several major scientific breakthroughs. In 1876, he discovered the anthrax disease cycle; in 1882, the bacteria responsible for tuberculosis; and, in 1883, the origin and mode of transmission of cholera.

Koch received the Nobel Prize for Physiology or Medicine in 1905 and is the author of Koch’s postulates, a four-step method for identifying the specific organism responsible for a particular disease.

Wilhelm Röntgen (1845-1923)

Winner of the first Nobel Prize for Physics (1901), German physicist Wilhelm Röntgen invented radiography. After discovering X-rays, Röntgen performed the first radiograph on December 22, 1895, on a hand. The guinea pig was none other than his wife!

Thanks to Röntgen’s invention, physicians are better able to detect health problems such as bone fractures, lung tumours, and kidney stones.

Sir William Osler (1849-1919)

Originally from Canada, physician and professor of medicine Sir William Osler had a major impact on the education of future doctors. At the time, medical students had little contact with patients during their training (they learned in laboratories). Dr. Osler changed the game by encouraging his students to devote more time to patients.

His book, The Principles and Practice of Medicine, is one of the most important texts in modern medicine.

Sigmund Freud (1856-1939)

Founder of psychoanalysis, a form of therapy that focuses on an individual’s unconscious and the release of repressed emotions to deal with psychological issues, Sigmund Freud had a major impact on the practice of medicine and psychology. The name of the Austrian neurologist is associated with concepts still studied today in psychology and philosophy, such as the Oedipus complex, and the id, ego, and superego.

Aloïs Alzheimer (1864-1915)

We might not have the same knowledge of Alzheimer’s disease today if it wasn’t for the contribution of Alois Alzheimer (1864-1915), a German psychiatrist and neuropathologist who first described the disease in 1906.

After Alzheimer performed an autopsy on his patient Auguste Deter, he discovered the two main attributes of the disease: senile plaques and neurofibrillary degeneration.

Karl Landsteiner (1868-1943)

Without the help of Karl Landsteiner, blood transfusions might not be possible today. This Austrian-American immunologist and pathologist's discovery of ABO blood groups around 1901 earned him the Nobel Prize in Physiology or Medicine in 1930.

In addition to showing that it was possible to receive blood from a donor of the same blood group, the scientist published, in collaboration with colleagues, major works on syphilis, polio, and typhus.

Alexander Fleming (1881-1955)

In 1928, Scottish bacteriologist Alexander Fleming accidentally discovered one of the world’s most widely used antibiotics: penicillin. Fleming’s discovery, which has since saved millions of people from bacterial infections, earned him the Nobel Prize in Physiology or Medicine in 1945, together with Ernst Boris Chain and Howard Walter Florey.

Gregory Pincus (1903-1967)

At the behest of birth control activist Margaret Sanger, endocrinologist-biologist Gregory Pincus, in collaboration with gynecologist-obstetrician John Charles Rock, developed the first contraceptive pill in the late 1950s. In the United States, the pill was marketed in 1960 to married women only.

Virginia Apgar (1909-1974)

Virginia Apgar was a true pioneer. She was the first woman to become a certified anesthesiologist, the first professor of anesthesiology at the College of Physicians and Surgeons, and the first female physician to become a full professor at the university.

Her greatest contribution to medicine was the Apgar Score System, a simple set of observations still used today in maternity hospitals to quickly assess the health of newly delivered infants and determine their subsequent care.

Rosalind Franklin (1920-1958)

Known as the “Dark Lady of DNA” because her scientific contributions weren’t recognized during her lifetime, Rosalind Franklin is behind one of the greatest discoveries of the 20th century: the double-helical structure of DNA.

During her career, Franklin also studied the structure of viruses, becoming a pioneer in structural virology.

Christiaan Barnard (1922-2001)

Christiaan Barnard, a South African surgeon, made history on December 3, 1967, when he led a team of surgeons in performing the first human heart transplant in history. Although the patient died 18 days later, Barnard’s later transplant operations were increasingly successful. By the late 1970s, some of his heart transplant patients had survived for several years.

Today, 85 per cent of adult heart transplant patients worldwide have a survival rate of one year and 69 per cent have a survival rate of five years, a result that would likely be impossible without Dr. Barnard’s contributions.

Françoise Barré-Sinoussi (1947-)

In 2008, Françoise Barré-Sinoussi won the Nobel Prize in Physiology or Medicine for her joint discovery with Luc Montagnier of the human immunodeficiency virus (HIV) in 1983. The virologist now heads the committee for analysis of research and expertise responsible for advising the French government on treatments for COVID‑19.