The Utero‐placental Circulation: Historiae Fides. II

THE mid-seventeenth century was alive with ideas on the elements of Air. John Mayow (1643-1679) was acquainted with ‘nitro-aerial particles’. Robert Boyle, in 1660, had seen animals die when the flame ceased to burn in his air pump. Robert Hooke, in 1667, considered air to contain two gaseous parts, one supporting combustion and the other not. Two years later (1669) Richard Lower found that dark venous blood could be changed to a bright red colour by taking up the ‘igneoaerial particles’ or ‘nitro-aerial spirit’ of air. Oxygen was thus discovered except by name. Combustion was becoming associated with respiration. Although J. B. van Helmont (1577-1644) had remarked upon a gas sylvestre (carbonic acid), the modern theory of respiration reached its near-completion in the 18th century by the discovery of the common gases in the atmosphere: carbon dioxide by Joseph Black (1757), hydrogen by Henry Cavendish (1766), nitrogen by Daniel Rutherford (1772), oxygen by Joseph Priestley, Carl W. Scheele and A.-L. Lavoisier. However, Priestley in 1772 and Lavoisier in 1778 sealed the true nature of the common gases in the air-oxygen was isolated and the fundamental basis of respiration demonstrated. Gastar Magnus, in 1837, showed that all tissues respire by assimilating oxygen and giving up carbon dioxide. Thus, nearly 200 years covers the time from Wm. Harvey’s observation that ‘if you deprive it (the newborn) from air it dies at once’, to the conclusion of the oxygen story. Felix Hoppe-Seyler (18251895) obtained crystalline haemoglobin and proved the spectrum of oxyhaemoglobin in 1862; shortly afterwards he showed that oxygen is loosely combined with haemoglobin and that gaseous interchanges between oxygen and carbon dioxide can occur in relation to haemoglobin. A function of the utero-placental circulation now became fully apparent. John Mayow had been right-‘they (the “nitroaerial particles”) were essential for the chemical changes on which life depends, and they were carried by the blood to the tissues and in the tissues they were the pivot, the essential factor, of the chemical changes by which the vital activities of this or that tissue is manifested’-and, ‘in the foetus, the blood conveyed by the umbilical arteries to the placenta brings not only nutritious juice but also a portion of nitro-aerial particles through the umbilical vessels, so that these should be regarded as rather a uterine lung’. Without