Fig. 3.

Spectrophotometric devices and measurements from the 1930s developed and performed by Ludwig Nicolai, Kurt Kramer, and Karl Matthes. (a) Experimental setup developed by Nicolai to measure Hb oxygenation non-invasively on the hand.⁸⁹ The light path is marked in red. (b) Changes in ${\mathrm{O}}_2\mathrm{Hb}$ after arterial occlusion on the arm. Figures (a) and (b) reprinted and modified from Nicolai,⁸⁹ with permission from the publisher. (c) Picture of Kurt Kramer. Reprinted from the professor catalog of the University of Leipzig, with permission from the University of Leipzig, Germany. (d) Changes of ${\mathrm{O}}_2$ saturation in the flowing blood of the carotid aorta of a dog were measured with the method of Kramer.⁹⁰ Reprinted and modified from Kramer,⁹⁰ with permission from the publisher. (e) Picture of Kurt Matthes. Reprinted from von Kress,⁹¹ with permission from the publisher. (f) Example of spectrophotometric measurements of Matthes and Gross on a dog.⁹² Reprinted and modified from Matthes and Gross,⁹² with permission from the publisher.