lungs. In 1867, he obtained a habilitation in internal medicine. As a doctor, he participated in the Franco-German war (1870--1871) and was decorated with the Iron Cross Second Class. In 1872, he was awarded the title Extraordinary Professor of Medicinal Chemistry. From 1873 until his death, he was the first Ordinary Professor of Pharmacology at the University of Königsberg (present day Kaliningrad, Russia). After his promotion to director (1878) of the Laboratory for Medical Chemistry and Experimental Pharmacology (belonging to the pathology institute), he became a member of the Deutsche Akademie der Naturforscher Leopoldina in 1882. From 1910 onwards, this laboratory became an independent institution \[[@bib1]\].

His principal work consisted of the discovery of urobilin and urobilinogen in urine and their origin in bile. Besides studying indican and creatinine,liver insufficiency.

Folin and the Jaffe reaction
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At the end of the 19th century and at the beginning of the 20th century, creatinine was generally assayed using the Neubauer reaction (adding an alcoholic solution of zinc chloride to a creatinine-containing solution, yielding a complex with two molecules of creatinine and one molecule of zinc chloride). After weighing the precipitate and multiplying the result by 0.642, the amount of precipitated creatinine was found \[[@bib6]\].

In the spring of 1900, Otto Folin (1867--1934), one of the fathers of modern American clinical chemistry, was offered a position as research biochemist at the McLean Hospital in the suburbs of Boston. Folin, who had been trained in Sweden and Germany, decided to study the protein metabolism of normal versus mentally disturbed individuals by measuring as accurately