For her doctoral dissertation, Shorb had developed an antigen that turned out to be a worthwhile treatment for pneumonia. In fact, for a while before the development of
sulfa drugs in the late 1930s, her antigen was widely used for such treatments. So she had already proven her abilities to improve human health. Shorb knew that the same liver extract required to culture LLD was also the only effective treatment for
pernicious anemia. That disease earned the designation "pernicious" because it was almost invariably fatal, prior to the discovery of the raw liver treatment method in 1926. Even then, advanced cases might not respond. In fact, Mary's father-in-law had died from the disease. As with the yogurt culture media, no one knew what component of liver extract was the active ingredient. By the time Shorb took an interest, other researchers had only managed to separate the extract into active an inactive fractions. In theory, if you followed the prescribed procedure, the result would contain the active ingredient. That still did not tell you how much of the unknown substance you had. That could be determined only by treating a patient and observing how he or she responded. Shorb deduced that the LLD growth rate could be refined as an assay method for the active ingredient. Out of a job, she did manage to find some laboratory space at the University of Maryland. However, with few professional credentials, Shorb would need some luck to obtain funding for further research. Fortunately, a pernicious anemia researcher from Merck & Company, Dr.
Karl August Folkers, visited the university to talk about collaborative projects. He saw merit in her idea and persuaded his management to fund a trial. Despite the paltry level of the initial grant – $400 – Shorb proved the efficacy of her bioassay method. Merck was so impressed that they kept sending funds "for the rest of Mary's professional life." With the assay breakthrough, Folkers and his Merck team isolated crystals of the active ingredient –
Vitamin B12 – from multiple sources within about three months. With the discovery and isolation of vitamin B12, pernicious anemia ceased to be the scourge that had persisted for centuries. In 1949, the University of Maryland made Shorb a full research professor. Standing less than five feet tall, Shorb did not like to lecture, although she apparently possessed considerable charisma on a person-to-person level. She chose to work on problems that required a multidisciplinary approach long before that was "fashionable" or common. Thus, she drew graduate students to work in her lab from a number of departments at the university. Before her retirement in 1972, Shorb and various co-authors published 58 papers in refereed journals as well as "numerous" popular articles. She and her students also presented papers at many, many professional society meetings and symposia. ==Later life==