Over ninety years ago, on November 8, 1845, Michael Faraday investigated the magnetic properties of dried blood and made a note “Must try recent

Over ninety years ago, on November 8, 1845, Michael Faraday investigated the magnetic properties of dried blood and made a note “Must try recent fluid blood.” If he had determined the magnetic susceptibilities of arterial and venous blood, he would have found them to differ by a large amount (as much as twenty per cent for completely oxygenated and completely deoxygenated blood); this discovery without doubt would have excited much interest and would have influenced appreciably the course of research on blood and hemoglobin.1
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