According to Wolfgang’s 1992 biography, Hesse was Walther’s “major supporter in many different projects,” creating drawings of microscopic samples for her husband’s published papers and aiding him in the lab. In the summer of 1881, Walther, who was attempting to study airborne microbes, grew frustrated with the gelatin used to coat his lab’s glass tubes. “One day, [he] asked Lina why her jellies and puddings stayed solid at these temperatures,” Wolfgang wrote. “She told him about agar-agar.” Stable at high temperatures, resistant to degradation, and easily sterilized and stored for lengthy periods of time, agar enabled long-term cultures, in which microbes can reproduce under controlled conditions, making them easier to analyze.
Walther sent a letter detailing the discovery to Koch, who was trying to determine the cause of tuberculosis, an infectious disease then killing roughly 1 in 7 infected people in Germany. On March 24, 1882, Koch held a highly praised presentation in which he proved that tuberculosis is caused by a bacterium, paving the way for better diagnosis and treatment of the disease. (The anniversary is commemorated annually as World Tuberculosis Day.) A few years later, in 1890, Koch wrote, “One could also indulge in the hope that in the not-too-distant future, the pathogens associated with all contagious diseases could be found.”
Popular accounts of microbiology history sometimes attribute the first use of agar in laboratory settings to Koch. The Nobel Prize website, for example, notes that the scientist “invented new methods … of cultivating pure cultures of bacteria on solid media such as potato, and on agar.” In his 1882 lecture, Koch mentioned agar’s role in discovering Mycobacterium tuberculosis but failed to acknowledge the Hesses’ contributions to his research. The couple themselves never wrote a report about agar, which might explain why their names are virtually unknown today.
Though Koch publicized agar’s applications, he didn’t immediately recognize its superiority as a microbial growth medium. For years, scientists (Walther included) continued to debate the merits of gelatin versus agar. At a time when women had no place in the lab (and almost nowhere beyond the kitchen), Hesse’s achievement was unassuming, everlasting and—as is often the case in scientific disciplines—gradual.
“In the Hesse family, this contribution to bacteriology was hardly ever mentioned,” Wolfgang wrote. “Lina never spoke about it, probably because she was a very unassuming person.”