It is universally acknowledged that George Gabriel Stokes (1819-1903) was a polymath who made major contributions to the fields of mathematics, chemistry, physics, fluidics and optics. However, his contributions to biology have received far less attention and this brief communication examines two of Stokes' major biological contributions, namely his description of the phenomenon of fluorescence and his studies on the changes in the colour of blood following oxidation and reduction. The paper on fluorescence is discussed because in it, Stokes demonstrates his wide-ranging biological knowledge and because the use of fluorescence is an invaluable experimental tool in biology. It was by developing the experimental approaches and equipment used to investigate fluorescence that Stokes then applied these to other investigations, including that of blood. From what we now know, what Stokes was describing in his paper on blood were the changes in the configuration of the haemoglobin molecule upon the acquisition and release of oxygen. This article is part of the theme issue 'Stokes at 200 (part 2)'.
Keywords: biology; blood; flow cytometry; fluorescence; haemoglobin.