Félix d'Herelle (April 25, 1873 – February 22, 1949), British-Canadian microbiologist, one of the discoverers of bacteriophages (small viruses that only attack and kill bacteria), and inventor of phage therapy.

D'Herelle was born in Montreal, Quebec, the son of French emigrants. His father, 30 years older than his wife, died when Félix was 6 years old. Félix, his mother and his younger brother Daniel, moved back to Paris. When sixteen years old, he started to travel through western Europe on bike. When 17, after finishing school, he travelled through South America. Afterwards, he continued his travels through Europe, including Turkey, where he met his wife, Marie Caire.

At age 24, now father of a daughter, he and his family moved back to Canada. He built a home laboratory and studied microbiology from books and his own experiments. He earned money by working for the Canadian government, studying the fermentation and distillation of maple syrup to schnapps. He also worked as a medic for a geological expedition, even though he had no medical degree or real experience. Together with his brother, he invested almost all his money in a chocolate factory, which soon went bankrupt.

With his money almost gone and his second daughter born, he took a contract with the government of Guatemala as a bacteriologist at the hospital in Guatemala City. As a side job, he was asked to find a way to make whiskey from bananas. Life in the rough and dangerous environment of the country was hard on his family, but d'Herelle, always adventurer at heart, rather enjoyed working close to "real life", compared to the sterile environments of a "civilized" clinic. He later stated that his scientific path began on this occasion.

In 1907, he took an offer from the Mexican government to continue his studies on fermentation. He and his family moved to a sisal plantation near Mérida, Yucatán. Disease struck at him and his family, but in 1909, he had successfully established a method to produce sisal schnapps. Machines for mass production were ordered in Paris, where he oversaw the machines' construction. Meanwhile, he worked in a laboratory at the Pasteur Institute in his spare time for free. He was offered the job of running the new Mexican plant, but declined, considering it "too boring". He did, however, take the time to attempt stopping a locust plague at the plantation using their own diseases. He extracted bacteria harmful for locusts from their guts.

D'Herelle and his family finally moved to Paris in early 1911, where he worked again as an unpaid assistant in a lab at the Pasteur Institute. He got attention in the scientific community the same year, when the results of his successful attempt to counter the Mexican locust plague with Coccobacillus were published. At the end of the year, restless d'Herelle was again on the road, this time in Argentina, where he was offered a chance to test these results on a much larger scale. Thus, in 1912 and 1913, he fought the Argentinian locust plagues with coccobacillus experiments. Even though Argentinia claimed his success was inconsistent, he himself declared it a full success, and was subsequently invited to other countries to demonstrate the method.

During World War I, d'Herelle and assistants (his wife and daughters among them) produced over 12 million doses of medication for the allied military. At this point in history, medical treatments were primitive, compared to today's standards. The smallpox vaccine, developed by Edward Jenner, was one of the few vaccines available. The primary antibiotic was the arsenic-based salvarsan against syphilis, with severe side effects. Common treatments were based mercury, strychnine, and cocaine. As a result, in 1900, the average life span was 45 years, and WWI did not change that to the better.

In 1915, British bacteriologist Frederick W. Twort discovered a small agent that infects and kills bacteria, but did not pursue the issue further. Independently, the discovery of "an invisible, antagonistic microbe of the dysentery bacillus" by d'Herelle was announced on September 3, 1917. The isolation of phages by d'Herelle works like this:

1. Nutritional medium is infected with bacteria; the medium turns opaque.
2. The bacteria are infected with phages and die, producing new phages; the medium clears up.
3. The medium is filtered through porcelain filter, holding back bacteria and larger objects; only the smaller phages pass through.

In early 1919, d'Herelle isolated phages from chicken feces, successfully treating a plague of chicken typhus with them. After this successful experiment, he felt ready for the first trial on humans. The first patient was healed of dysentery using phage therapy in August 1919. Many more followed.

At the time, none, not even d'Herelle, knew exactly what a phage is, not until the first phage was observed under an electron microscope by Helmut Ruska in 1939. D'Herelle claimed that it reproduces, somehow feeding off bacteria, which was confirmed much later. Others theorized that phages are inanimate objects, proteins for example, that are already present in bacteria, and only trigger the release of similar proteins, killing the bacteria in the process. Due to this uncertainty, and d'Herelle using phages without much hesitation on humans, his work was under constant attack from many other scientists.

In 1920, d'Herelle travelled to Indochina, pursuing studies of cholera and the plague, from where he returns at the end of the year. D'Herelle, officially still an unpaid assistant, finds himself out of a lab; d'Herelle later claims this was a result of a quarrel with the assistant director of the Pasteur Institute, Albert Calmette. The biologist Edouard Pozerski has mercy with d'Herelle and borrows him a stool (literally) in his laboratory. In 1921, he manages to publish a book about his works as an official Institute publication, by tricking Calmette. During the next year, doctors and scientists across western Europe take an heightened interest in phage therapy, successfully testing against a variety of diseases. Since, on rare occasions, bacteria become resistant against a single phage, d'Herelle suggest "phage cocktails" containing different phage strains.

Phage therapy soon becomes a boom, and a great hope in medicine. In 1925, d'Herelle receives the honorary doctorate of the University of Leiden, as well as the Leeuwenhoek medal, which is only awarded once every ten years. The latter was especially important to him, as his idol Louis Pasteur received the same medal (in 1895). The next year, he was nominated eight times for the Nobel prize, though he never was awarded one.

After a temporary position at the University of Leiden, d'Herelle got a position with the Conseil Sanitaire, Maritime et Quarantenaire d'Egypte in Alexandria. The Conseil was put in place to prevent plague and cholera spreading to Europe, with special emphasis on the sanitary concerns about muslim pilgrim groups returning from Mecca and Medina. D'Herelle uses phages he collected from plague-infected rats during his 1920 visit to Indochina on human plague patients, with success. The British Empire intiates a vast campaign against plague based on his results. 1927, d'Herelle himself changes his focus to new targets: India and cholera.

He isolated phages from cholera victims. As usual, d'Herelle did not choose a hospital run by European standards, but rather sought out a medical tent in a slum. According to his theory, one had to leave the sterile hospitals and study and defeat illness in its "natural" environment. His team then dropped phage solution in the wells of villages with cholera patients, reducing the death toll from 60 to 8 percent. The whole India enterprise took less than seven month. D'Herelle refused next year's request by the British government to work in India, as he had been offered a professorship at Yale university.

Meanwhile, European and US pharma companies had taken up the production of own phage medicine, and were promising impossible effects. To counteract this, d'Herelle agreed to co-found a French phage-producing company, piping the money back into phage research. But all companies suffered from production problems; results from commercial phage medicine were erratic, most likely due to the attempt to mass-produce something that was barely understood, leading to damaged phages in the product, or to insufficient amounts thereof. Also, wrong disagnoses often lead to the use of the wrong type of phages, which are quite specific in the choice of their "victims". Furthermore, many studies about the healing effects of phages were badly conducted. All this led to important parts of the scientific community turning against d'Herelle, who, known for his temper, made not a few enemies.

But he was already on the move again. This time, he went to Tbilisi (Georgia), at the time under the iron fist of Joseph Stalin. Though d'Herelle was known to critizize capitalism, he was not particularly fond of communism or of Stalin either. Nevertheless, he was welcomed like a hero, bringing the knowledge of salvation from diseases ravaging the eastern states all the way to Russia. Stalin's "cleansings" started while d'Herelle was taking a trip to France, and he was not allowed to return to Tbilisi. Then, World War II began.

Phage therapy boomed, despite all problems, driven by the military on both sides in an effort to keep the troops safe, at least from infections. Phage pioneer d'Herelle could not really enjoy this development; he was kept under house arrest by the Wehrmacht in Vichy, France. He used the time to write his book "The Value of Experiment", as well as his memoires, the latter counting 800 pages. After D-day, the new antibiotic drug penicillin became public knowledge and found its way into the hospitals in the west. As it was more reliable and easier to use than phage therapy, it soon became the method of choice, despite its side effects and problems with resistant bacteria. Phage therapy remained a common treatment in the states of the USSR, though, until its deconstruction following the cold war.

After the war, d'Herelle was seen in a more favourable light by the scientific community. In 1948, he was awarded the Prix Petit d'Ormoy of the French Academy of Science. During his life, he was nominated thirty times for the Nobel Prize.

D'Herelle died in Paris of pancreas cancer in 1949 and was burried in Saint-Mards-en-Othe (Aube).