Slide showing a chart illustrating 'potassium, magnesium and calcium contents of sea water and of various bloods'. Slide shows a chart illustrating 'potassium, magnesium and calcium contents of sea water and of various bloods'. 'X' axis shows contents of the three minerals, and the 'Y' axis shows the various bloods and sea water. There are 20 items on the 'Y' axis. Title below image reads: 'Fig. 76. - Potassium, magnesium and calcium contents of sea water and of various bloods (sera). The figures are based on a chlorine content taken as 100. In the case of the sea-urchin Echinus, values are given both for the coelomic fluid (Coel.) and for the ambulacral fluid (Amb.). (Bethe and Berger)'. Late 19th to early 20th century