Theodor Wilhelm Engelmann

Theodor Wilhelm Engelmann (14 November 1843 to 20 May 1909) was a German botanist, physiologist, microbiologist, university professor and musician whose 1882 experiment measured the effects of different colors of light on photosynthetic activity and showed that the conversion of light energy to chemical energy took place in the chloroplast. He studied natural science and medicine at Jena, Heidelberg, Göttingen and Leipzig, received a doctorate in medicine at Leipzig in 1867, taught physiology at the University of Utrecht from 1870, became a professor there in 1877, and in 1897 began teaching physiology at the University of Berlin, where he also became editor of the Archiv für Anatomie und Physiologie. He retired in 1908 but remained editor until his death, and was a foreign member of the Royal Netherlands Academy of Arts and Sciences from 1870 and a regular member from 1897. From 1873 to 1897 he studied the contractions of striated muscle, and in 1875 he showed with dissected frogs that heart contractions come from the heart muscle itself rather than from an external nerve stimulus. In 1881 he observed bacteria moving toward the chloroplasts of Spirogyra, one of the first documented observations of positive aerotaxis, and in 1882 he used a micro-spectroscope built by Carl Zeiss to show that red and violet light drive the most photosynthesis.