Fig. 2.
Spectrophotometric devices from the 1930s–1950s developed by Glenn Allan Millikan to measure blood oxygenation. (a) Picture of G. A. Millikan. Reprinted from Millikan,81 with permission from the publisher. (b, c) Principle of operation of the invented photoelectric colorimeter for oximetry of blood samples described in a publication in 1933.82 (d) Wavelengths used by the colorimeter. (b)–(d) Reprinted and modified from Millikan,82 with permission from the publisher. (e) A spectrophotometric oximeter developed by Millikan to perform muscle measurements on living animals.83 Reprinted from Millikan,83 with permission from the publisher. (f) Circuitry and picture of a spectrophotometric earlobe oximeter developed by Millikan and described in a publication in 1942.84 Circuitry visualization reprinted and modified from Millikan,84 with permission from the publisher. Picture of the Millikan’s oximeter (right) taken from Wood,85 with permission from the publisher.