Paul Ehrlich (German: [ˈpaʊl ˈeːɐ̯lɪç]; 14 March 1854 – 20 August 1915) was a German doctor and scientist who studied blood diseases, the body’s defense system, and treatments for infections. He shared the 1908 Nobel Prize in Physiology or Medicine with Élie Metchnikoff for their research on how the body fights disease. His major accomplishments include discovering a cure for syphilis in 1909 and improving a method to color bacteria so they can be seen under a microscope. The techniques he developed helped scientists identify different types of blood cells, which made it possible to diagnose many blood disorders.

His laboratory discovered arsphenamine (Salvarsan), the first drug to treat syphilis and the first effective medicine for infections caused by microbes. This discovery started the idea of using medicines to treat diseases, which became known as chemotherapy. Ehrlich introduced the idea of a "magic bullet," a treatment that targets a disease without harming the body. He also helped develop a treatment to fight diphtheria and created a way to ensure serums used in medicine were safe and effective. He founded and led the Paul Ehrlich Institute, a German research and regulatory organization named after him in 1947. This institute is responsible for testing vaccines and medicines in the country. A group of bacteria called Ehrlichia is named after him.

Ehrlich is known as the "father of immunology."

Life and career

Paul Ehrlich was born on March 14, 1854, in Strehlen, a town in the Prussian Province of Silesia (now called Strzelin, Poland). He was the second child of Rosa (Weigert) and Ismar Ehrlich, who led the local Jewish community. His father worked as an innkeeper, a maker of alcoholic drinks, and collected money for the royal lottery in Strehlen, a town with about 5,000 people. His grandfather, Heymann Ehrlich, had previously been a successful maker of drinks and manager of a tavern. Ehrlich was the uncle of Fritz Weigert and the cousin of Karl Weigert.

After finishing elementary school, Paul attended the well-known secondary school Maria-Magdalenen-Gymnasium in Breslau, where he met Albert Neisser, who later became a colleague. As a student, he was inspired by his cousin Karl Weigert, who owned one of the first microtomes (tools used to cut very thin slices of tissue). This inspired Ehrlich to become interested in staining microscopic tissue substances. He kept this interest throughout his medical studies.

Ehrlich studied medicine in Breslau and Strasbourg from 1872, with a short time in Freiburg, and earned his doctorate in Leipzig in 1878. His doctoral advisor, Julius Cohnheim, had moved to Leipzig.

After receiving his doctorate, Ehrlich worked at the Charité in Berlin as an assistant medical director under Theodor Frerichs, the founder of experimental clinical medicine. His work focused on histology (the study of tissues), hematology (the study of blood), and color chemistry (the study of dyes).

In 1883, Ehrlich married Hedwig Pinkus (1864–1948) in the synagogue in Neustadt (now Prudnik, Poland). The couple had two daughters, Stephanie and Marianne. Hedwig was the sister of Max Pinkus, who owned a textile factory in Neustadt (later known as ZPB "Frotex"). Ehrlich lived in the villa of the Fränkel family on Wiesenerstrasse in Neustadt.

After completing his medical training and earning the right to teach at the Charité medical school and teaching hospital in Berlin in 1886, Ehrlich traveled to Egypt and other countries in 1888 and 1889, partly to recover from tuberculosis he had contracted in the laboratory. After returning, he started a private medical practice and small laboratory in Berlin-Steglitz. In 1891, Robert Koch invited Ehrlich to join the staff at his Berlin Institute of Infectious Diseases. In 1896, a new branch of the institute, the Institute for Serum Research and Testing (Institut für Serumforschung und Serumprüfung), was created for Ehrlich’s work. Ehrlich became its founding director.

In 1899, Ehrlich’s institute moved to Frankfurt am Main and was renamed the Institute of Experimental Therapy (Institut für experimentelle Therapie). One of his important collaborators there was Max Neisser. In 1904, Ehrlich was named an honorary professor at the University of Göttingen. In 1906, he became the director of the Georg Speyer House in Frankfurt, a private research foundation linked to his institute. At the Georg Speyer House, Ehrlich discovered in 1909 the first drug specifically designed to fight a particular disease: Salvarsan, a treatment for syphilis, which was a serious and highly contagious disease in Europe at the time. In 1914, Ehrlich received the Cameron Prize from the University of Edinburgh. Two Nobel Prize winners, Henry Hallett Dale and Paul Karrer, worked with Ehrlich at his institute. In 1947, the institute was renamed the Paul Ehrlich Institute in his honor.

In 1914, Ehrlich signed the Manifesto of the Ninety-Three, which supported Germany’s World War I policies and militarism. On August 17, 1915, Ehrlich suffered a heart attack and died on August 20 in the Hessian town of Bad Homburg. German Emperor Wilhelm II sent a telegram expressing sorrow, stating, “I, along with the entire civilized world, mourn the death of this meritorious researcher for his great service to medical science and suffering humanity; his life’s work ensures undying fame and the gratitude of both his contemporaries and posterity.”

Ehrlich was buried at the Old Jewish Cemetery in Frankfurt (Block 114 N).

Research

In the early 1870s, Ehrlich’s cousin Karl Weigert was the first person to use dyes to color bacteria and to use aniline pigments for studying tissues and diagnosing diseases. While studying under the anatomist Heinrich Wilhelm Waldeyer in Strassburg, Ehrlich continued his cousin’s research on dyes and staining tissues for microscopic study. During his eighth semester at university in Freiburg im Breisgau, Ehrlich studied a red dye called dahlia (monophenylrosanilin), which led to his first published work.

In 1878, Ehrlich followed his dissertation advisor, Julius Friedrich Cohnheim, to Leipzig, where he earned a doctorate with a dissertation titled "Contributions to the Theory and Practice of Histological Staining" (Beiträge zur Theorie und Praxis der histologischen Färbung).

One major result of his research was the discovery of a new type of cell. Ehrlich found granules in the protoplasm of what were thought to be plasma cells. These granules could be seen using an alkaline dye. He believed the granules showed good nourishment and named the cells "mast cells," from the German word for animal feed. This focus on chemistry was unusual for a medical dissertation. Ehrlich described all known staining methods and the chemistry of the dyes used. At the Charité, he developed a technique to differentiate white blood cells based on their granules. He created a method to fix blood cells on glass slides by heating them over a Bunsen burner. Using both acidic and alkaline dyes, he also made new "neutral" dyes. This allowed him to distinguish lymphocytes from other white blood cells, such as eosinophil granulocytes and mast cells.

Starting in 1880, Ehrlich studied red blood cells. He showed that some red blood cells have nuclei and divided them into types: normoblasts, megaloblasts, microblasts, and poikiloblasts. These were the precursors of red blood cells. His work laid the foundation for understanding anemias and classifying leukemias.

At the Charité, Ehrlich analyzed blood and urine samples. In 1881, he published a new urine test to distinguish typhoid from diarrhea. The intensity of staining helped predict disease outcomes. The dye solution he used became known as Ehrlich’s reagent. His work bridging chemistry, biology, and medicine was groundbreaking but not widely accepted by the medical community, which lacked chemical knowledge. This made it difficult for him to find a suitable academic position.

As a student in Breslau, Ehrlich worked with pathologist Julius Friedrich Cohnheim and met Robert Koch, a district physician in Posen. Koch had studied the life cycle of the anthrax pathogen and shared his findings with Ferdinand Cohn, who introduced Koch to colleagues in Breslau. Ehrlich attended Koch’s presentation in Breslau in 1876.

On 24 March 1882, Ehrlich was present when Koch, working at the Imperial Public Health Office in Berlin, announced the discovery of the tuberculosis pathogen. Ehrlich later called this event his "greatest scientific experience." The next day, Ehrlich improved Koch’s staining method, which Koch praised. From then on, the two remained close friends.

In 1887, Ehrlich became a lecturer in internal medicine at Berlin University. In 1890, Koch asked him to manage the tuberculosis station at a Berlin hospital. There, researchers studied tuberculin, a potential treatment for tuberculosis. Ehrlich even tested it on himself. During the tuberculin controversy, Ehrlich supported Koch and emphasized tuberculin’s value for diagnosis. In 1891, Koch invited Ehrlich to join the newly created Institute for Infectious Diseases in Berlin. Though no salary was offered, Ehrlich was given access to laboratory staff, patients, chemicals, and animals, which he greatly appreciated.

Ehrlich began his first immunization experiments in his private lab. He exposed mice to poisons like ricin and abrin. After giving them small, increasing doses of ricin, he found they became immune to it. He called this immunization and observed that immunity lasted for months. However, mice immune to ricin were still vulnerable to abrin.

Ehrlich studied whether acquired immunity could be passed to offspring. He found that offspring of mice immune to abrin were not immune themselves, suggesting immunity was passed through antibodies from the mother’s bloodstream. He also showed that nursing mice raised by immune mothers were protected from poison, proving antibodies can be passed through milk.

Ehrlich researched autoimmunity but rejected the idea that the immune system could attack the body’s own tissues, calling it "horror autotoxicus." His student, Ernest Witebsky, later proved that autoimmunity can cause disease. In 1906, Ehrlich proposed that the body has mechanisms to prevent immune reactions from harming itself.

Emil Behring had developed an antiserum for diphtheria and tetanus at the Berlin Institute of Infectious Diseases until 1893, with mixed results. Koch suggested Behring and Ehrlich collaborate. Their work improved immunity in lab animals, and clinical tests with diphtheria serum in 1894 were successful. The chemical company Hoechst began selling Behring’s "Diphtheria Remedy" in August 1894. Ehrlich and Behring originally agreed to share profits after Hoechst’s costs were subtracted, but their agreement was changed multiple times, and Ehrlich eventually gave up some of his share.

Legacy

In 1910, a street in Frankfurt-Sachsenhausen was named after Paul Ehrlich. During Nazi Germany, Ehrlich’s achievements were not recognized, and the street was renamed to honor Emil Adolf von Behring, who was portrayed as the ideal Aryan scientist. After World War II ended, the street was renamed back to Paul-Ehrlich-Strasse. Since then, many German cities have named streets after Ehrlich.

In 1954, West Germany released a postage stamp to celebrate the 100th anniversary of Ehrlich’s and Emil von Behring’s birth. The 200 Deutsche Mark banknote, used until 2001, included an image of Ehrlich.

The German Paul Ehrlich Institute, which continues the work of the Steglitz Institute for Serum Research and the Frankfurt Royal Institute for Experimental Therapy, was named after Ehrlich in 1947. Ehrlich’s name is also used for many schools, pharmacies, the Paul-Ehrlich-Gesellschaft für Chemotherapie e. V. in Frankfurt am Main, and the Paul Ehrlich Clinic in Bad Homburg vor der Höhe. The Paul Ehrlich and Ludwig Darmstaedter Prize is the most important German award for biomedical research. A European network for PhD studies in Medicinal Chemistry is also named after him (Paul Ehrlich MedChem Euro PhD Network).

The Anti-Defamation League gives a prize named after Ehrlich and Günther K. Schwerin for human rights. A moon crater was named after Ehrlich in 1970.

A 1940 U.S. film titled Dr. Ehrlich’s Magic Bullet, starring Edward G. Robinson, highlighted Ehrlich’s discovery of Salvarsan, a treatment for syphilis. The Nazi government opposed this tribute to a Jewish scientist, so efforts were made to hide the film in Germany. The film was nominated for an Academy Award for Best Original Screenplay.

• 1882: Received the title of Professor
• 1890: Appointed Extraordinary Professor at the Friedrich-Wilhelms-Universität (now Humboldt University)
• 1896: Received the special Prussian title of Medical Councillor (Geheimer Medizinalrat)
• 1903: Awarded Prussia’s highest science honor, the Great Golden Medal of Science (previously given only to Rudolf Virchow)
• 1904: Honorary professorship in Göttingen; honorary doctorate from the University of Chicago
• 1907: Received the rare title Senior Medical Councillor (Geheimer Obermedizinalrat); honorary doctorate from Oxford University
• 1908: Awarded the Nobel Prize in Physiology or Medicine for his research on immunity
• 1911: Received Prussia’s highest civilian award, Privy Councillor (Wirklicher Geheimer Rat with the title "Excellency")
• 1912: Made an honorary citizen of Frankfurt a.M. and his birthplace, Strehlen
• 1914: Awarded the Cameron Prize for Therapeutics by the University of Edinburgh; appointed full Professor of Pharmacology at the newly established Frankfurt University.