From 1888 he lectured in physiology and pathology at the National Veterinary School, also in Utrecht. In 1896, he invented the crystalloid solution known as Hamburger's solution or normal saline. Based on plant-based experiments by botanist Hugo de Vries, he developed a salt solution that was thought to have the same osmolality as human blood and therefore did not cause haemolysis of red blood cells. It is uncertain whether the saline was ever originally intended for intravenous administration.[3]
In 1901, he joined the University of Groningen as professor of physiology.[2] In 1911 he was instrumental in opening a dedicated physiological institute, and two years later chaired the 25th International Physiological Congress in Groningen.[1][2] Between 1902 and 1904 he published Osmotischer Druck und Ionenlehre in den medecinischen Wissenschaften ("Osmotic pressure and ion science in the medical sciences").[2][4][5][6] Work on these books had started while still in Utrecht.[1] Hamburger was serving as rector magnificus of the university when in 1914 it celebrated its 300th anniversary.[1] Throughout his academic career he emphasised the importance of physical chemistry in health science, and he actively opposed vitalism (i.e. the view that living organisms are somehow governed by different principles from inanimate substances).[1]
In 1918 he described the chloride shift (often called "Hamburger shift"), the process by which red blood cells exchange bicarbonate for chloride.[7][8] This was initially thought to be a passive phenomenon, but was later linked to active transport by the band 3 exchanger (SLC4A1).[8] He also conducted experiments on phagocytosis.[1] He was the first to quantify the process of phagocytosis by incubating neutrophil granulocytes (white blood cells capable of phagocytosis) with carbon particles, and measuring the uptake.[9]
^Pul, Refik; Chittappen, Kandiyil Prajeeth; Stangel, Martin (2013). "14: Quantification of Microglial Phagocytosis by a Flow Cytometer-Based Assay". In Joseph, Bertrand; Venero, José Luis (eds.). Microglia: Methods and Protocols V. Humana Press Inc. pp. 121–127. ISBN978-1-62703-519-4.