Walther Hesse (27 December 1846 – 19 July 1911) is best known for his work in microbiology, specifically his work in developing Agar as a medium for culturing microorganisms.
Born in Bischofswerda, Lusatia, as one of 12 children in the family of a medical practitioner, Hesse attended the Kreuzschule in Dresden and studied medicine at the University of Leipzig with Ernst Leberecht Wagner from 1866 till 1870, when he received his doctorate in pathology. Afterwards he participated in the Franco-Prussian War, and therein in the Battle of Gravelotte.
As a ship's doctor on the New York Line 1872/73 he examined seasickness – his works were classified by Prof. Gavingel of Le Havre as the first scientific study on this topic at all. In New York, Hesse met his later wife Angelina Fannie Eilshemius. The Eilshemius family were immigrants of Dutch-German origin – Angelina's brother Louis Eilshemius is known as an important painter, Swiss painter Louis Léopold Robert was their common grandfather. Walther and Angelina married 1874 in Geneva, together with Angelina's sister and a nephew of Louis Agassiz.
After some years as a medical practitioner in Pirna and Zittau, Hesse went 1877 to Schwarzenberg, Saxony. His investigations in Schneeberger Bergkrankheit, responsible for the commonly early death of miners in the Ore Mountains, are credited as the first unveiling of working conditions as cause of an interior disease (lung cancer). Within his time in Schwarzenberg, he took a year with Max Joseph von Pettenkofer at Munich to deepen his knowledge in occupational hygiene.
Hesse joined Robert Koch's laboratory (effectively in a post-doctoral position) in 1881 to study air quality. He was convinced that microorganisms were present everywhere, even in water and in the air. He used a series of filters, made mainly from wadding, in attempts to capture and observe microorganisms. When culturing the organisms he trapped with his filter, he used a gelatin-containing medium capable of solidifying. Frustratingly, the medium had a tendency to melt during the summer months, thus ruining the experiments. Additionally, many of the organisms he cultured were capable of degrading the gelatin medium, also ruining his experiments.
Legend has it that Hesse went on a picnic with his wife Angelina Fannie and noticed that the jellies and puddings that she had brought along did not melt in the hot summer weather. When asked why this was so, Lina (as she was called) replied that they contained Agar, and that she had been shown the trick by a Dutch neighbor (recently emigrated from Java (Indonesia)) when she was growing up. Further development of agar showed that it would not easily melt (though would remain molten at lower temperatures once it did), was not easily degraded by microorganisms and was a flexible medium.
In later years, Hesse was district physician in Dresden. He continued his scientific works, experimented with Petri dishes and investigated the microbiological foundations of typhus, cholera and diphtheria. He operated a laboratory at the Technical College Dresden together with Walther Hempel. Hesse introduced pasteurization of milk in Pfund's dairy. The family's tomb at the cemetery of Serkowitz was created by Arnold Kramer.