Those who still mistakenly subscribe to the White-Draper hypothesis of a war of religion against science, and these days it is mostly gnu atheists and their ilk, invariably produce lists of the martyrs of science, those considered to have fallen in the war. Almost without fail those lists include the sixteenth century Spanish mathematicus and physicus Michael Servetus (Span. Miguel Serveto) who was born 29th September 1511 and was burnt at the stake as a heretic in Geneva 27th October 1553, for once by the Calvinists and not the Catholics. Servetus was an active Protestant theologian who amongst other radical theses denied the holy trinity, which led to his being imprisoned by the Inquisition in Vienne in France. He managed to escape and fled to Geneva where he was again incarcerated, tried for heresy on the basis of his most recent publication, Christianismi Restitutio, found guilty and sentenced to death, being as I stated above burnt at the stake. This is a very clear case of religious persecution and has nothing to do with science so why is he frequently listed as a science martyr? This is because the Restitutio as well as being a book on theology also contained an important medical discovery.
Servetus had led a fairly normal scholarly existence for the Renaissance, wandering around Europe studying bits of this and bits of that at various centres of learning until he ended up studying medicine in Paris in the 1530s. Paris was one of the leading centres for medical studies at the time and Servetus studied under the same set of excellent teachers as his contemporary Andreas Vesalius. He was an excellent student but became embroiled in a dispute involving his activities as an astrologer and was forced to leave Paris, settling in Vienne as a medical practitioner. It was here in 1553 that he ran foul of the Inquisition.
Servetus’ original contribution to medicine was the discovery of the small or pulmonary blood circulation. In antiquity Galen, the leading medical authority, had thought that blood flowed from the right ventricle to the left ventricle through microscopic holes in the septum or central wall in the heart. This theory was still accepted as gospel in the 16th century and Servetus hypothesised instead that the blood flows out of the right ventricle through the lungs and back into the left ventricle, pulmonary circulation. This was of course a very important step towards understanding blood circulation in general. However it is important to note that Servetus’ discovery remained without influence because nobody knew about it. Condemned as heretical, by Catholics, Calvinists and Lutheran Protestants alike, his Restitutio was like its author committed to the flames with only three copies surviving the immolation and remaining hidden and unread. Although his work had no direct influence on the history of medicine his fate is a good example of two important frequent occurrences in the history of science, firstly discoveries get lost and secondly discoveries are very often made independently by more than one person.
The discovery of pulmonary circulation actually got lost at least twice and Servetus was not its first discoverer. Pulmonary circulation had already been discovered in the thirteenth century by Ala-al-din abu Al-Hassan Ali ibn Abi-Hazm al-Qarshi al-Dimashqi, known as Ibn al-Nafis, and published in his Commentary on the Anatomy of Canon of Avicenna a text that simply disappeared and was first re-discovered in the twentieth century. Somehow this was a discovery that didn’t want to be made. However pulmonary circulation was discovered independently for a third time, and this time demonstrated empirically, by Realdo Colombo, Vesalius’ successor as professor of anatomy in Padua, in 1559 and this time it remained discovered.