Florence Siebert

Florence Siebert hunted the deadly lung infection tuberculosis (TB) for 10 years. By purifying the substance tuberculin, which causes a skin reaction in TB carriers, she created a better way to diagnose TB in the 1930s that is still in use today.

About Her Life

Florence B. Siebert (1898–1991) was born in Easton, Pennsylvania. When she was three years old, she contracted polio. The disease left her partially disabled, and she had difficulty walking for the rest of her life. As a child she learned to play the violin, and as a teenager she became interested in science, reading biographies of famous scientists for pleasure.

After high school Siebert attended Goucher College in Baltimore, Maryland. She studied science hoping to be a doctor; going to the Johns Hopkins School of Medicine was her dream. But when she graduated from college in 1918, she took a temporary job in a chemistry lab at a paper mill in New Jersey, just to earn money for medical school. In those days women usually faced discrimination when hunting for scientific jobs, but World War I had taken many male scientists away to the battlefields, opening a window of opportunity for women scientists like Siebert. In addition, one of her professors, Jessie Minor, had become a director of research at the mill and helped her get the job.

Siebert soon decided she liked chemical research more than medicine, partly because the duties of a chemist did not require her to be on her feet as much as the duties of a doctor. (Even hospitals were not necessarily handicapped accessible in those days.) She went on to earn a Ph.D. in biochemistry from Yale University in 1923 and did postdoctoral research at the University of Chicago. While she was in Chicago, she learned to drive a car with hand controls for the accelerator, clutch, and brakes. Siebert found freedom and independence in her hand-controlled car, which she called "a new pair of legs."

Next she went to work at the Sprague Institute, also in Chicago. Here she made one of her first major discoveries, which was funded by the Christmas Seals program of the National Tuberculosis Association (now the American Lung Association). In those days patients often came down with short but intense fevers after receiving distilled water intravenously. Siebert discovered that although distilling the water killed bacteria and other microbes in the water, it often did not destroy the toxins that the bacteria had produced before they were killed. Sometimes spray from the water boiling in the distillation flask carried the toxins into the receiving flask, contaminating the distilled water. These toxins were causing the severe fevers. Siebert invented a new spray trap for the still that kept the toxins from contaminating the distilled water. The fevers became a thing of the past, and Siebert received the University of Chicago's Howard Taylor Ricketts Prize for her invention.

Siebert had been working at Sprague with an older scientist named Esmond R. Long, who was doing studies on tuberculosis (TB). Tuberculosis is a disease caused by a type of bacteria called Mycobacterium tuberculosis. The bacteria usually attack the lungs, but TB bacteria can attack any part of the body. If not treated properly, it can be fatal. TB was once the leading cause of death in the United States and is still a deadly killer around the world.* A person may be infected with the TB bacteria yet not actually develop the disease tuberculosis. This is called a latent or inactive infection, as opposed to an active infection.

In 1932 Long took a new job at the University of Pennsylvania. Realizing that Seibert was a talented scientist, he invited her to come with him to Philadelphia, and Siebert became an assistant professor at the University of Pennsylvania. Siebert's role in her collaborative research with Long was to improve an existing test for diagnosing tuberculosis called the tuberculin skin test. In the test a small amount of a substance called tuberculin, which is made by the TB bacteria, is injected underneath a patient's skin. Tuberculin was discovered back in the 1890s. It is an antigen, which is a substance that will trigger an immune response by the body in the form of what are called antibodies. If a person has been exposed to and infected by the TB bacteria, he or she will already have developed an immune response and formed TB antibodies. When the body is injected with the antigen tuberculin, these antibodies rush to the spot of the injection to attack the tuberculin, and within a few days they form a hard red bump. That red bump is how we can tell that someone has been infected by the TB bacteria. If the person doesn’t form a red bump on the skin, then he or she has not been infected with the TB bacteria and antibodies have never been formed.

The test as it existed in the early 1930s, however, was unreliable owing to impurities in the tuberculin. Siebert set to work on ways to purify tuberculin after it was harvested from the bacteria. Siebert and Long had earlier discovered that the active agent in tuberculin was a protein. So Siebert needed to separate the protein from the other substances in the tuberculin and purify it. It took almost a decade of work to develop the purification process. Finally, she developed a technique that used filters made from porous clay and cotton that had been treated with nitric acid. The purified tuberculin protein that Siebert developed is now known as purified protein derivative, or PPD, and is still used in TB skin tests today.

Siebert spent most of the rest of her career at the University of Pennsylvania. Despite her scientific achievements she remained at the rank of associate professor for nearly 20 years before being named a full professor. She became a specialist in the field of protein separation. As in the case of tuberculin, sometimes proteins need to be separated from each other or from other substances in order to study them individually. Siebert was one of the first U.S. scientists to master two important protein-separation techniques, ultracentrifugation and electrophoresis.

Siebert was a very small person, standing 4 feet 9 inches tall and weighing less than 100 pounds. She enjoyed playing the violin her whole life. Siebert died in 1991 at the age of 93.

*(Source: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for HIV, STD, and TB Prevention, Division of Tuberculosis Elimination http://www.cdc.gov/nchstp/tb/faqs/qa_introduction.htm#Intro1).