John Mayow

Tractatus Quinque Medico-Physici (1674)

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The fifteen-year-old John Mayow came up to Wadham from Cornwall during the last full year of Dr John Wilkins' Wardenship, 1658. Although passing no formal medical qualifications (although he took a Doctorate in Civil Laws, D.C.L., when a Fellow of All Souls, Oxford, in 1670) he was one of the most brilliant experimental scientists of the age, who also, as an Oxford Master of Arts, M.A., would have had no trouble in researching, and openly practising medicine in Oxford and in Bath.

In the 17th-century, the only medical "Schools" in the proper sense, as places where one trained in clinical practice, were to be found in Paris, Padua, Montpellier, Bologna, and Leiden (Edinburgh came in the late 18th century). Generally speaking, in England, Scotland and most European countries, a medical training and a degree were based primarily on reading the Latin and Greek medical writers, such as Hippocrates, Celsus, and Galen. It was essentially an education in medical literature, supplemented by varying degrees of practical "hands on" training, obtained by accompanying established practitioners on their rounds, walking the wards of a major hospital - really St Bartholomew's and St Thomas's in London for English students - or travelling abroad. To formally obtain his Bachelor's or Doctor's degree in Oxford, the student would be verbally examined - by the Regius Professor of Medicine and a few colleagues - in the works of the prescribed Greek and Latin authors, usually often submitting a "thesis", which might well be a Latin medical poem. Considering the apparent informality of the qualifiying procedure, it is hardly surprising that many men went through the classical reading and bedside attending process and never bothered to request formal examination for a D.M. [Doctor of Medicine of Oxford University], especially if, like Mayow, they were already Doctors of Civil Law, or in other cases, of Divinity. And as the degree of M.A. was the internationally recognised badge of a university teacher, few patients would have had many qualms about being treated by an Oxford, or Cambridge, M.A. who had read deeply into classical and modern medicine and walked the wards of a hospital. In fact, numerous Anglican clergymen with M.A. degrees openly practised medicine acress the length and breadth of the country as did Mayow's Christ Church [College] Oxford contemporary, the Revd. John Ward, M.A., Vicar of Stratford-upon-Avon.

Mayow was inspired by Thomas Willis, Robert Boyle, and especially Robert Hooke, whose protégé in many ways he became. His life, tragically, was cut short, probably because of tuberculosis, when he died in 1679, aged 38.

The five treatises cover the following research areas:

On the vital forces in the air, characterised as a "nitro-aerial" spirit - which facilitated combustion
On respiration, and the chemical role of air therein
On the respiration of the foetus, in the uterus, and also the respiration of eggs
The source of muscular action
On the bone-deforming disease, Rickets

Central to the Tractatus was the chemistry of the air and its effect upon all manner of things, for many 17th-century scientists (and especially the Oxford group around Dr Wilkins at Wadham College) had come to abandon the classical Greek view that Air was an unchanging fundamental element (along with Earth, Water and Fire). Instead, they were coming to see it as a mechanically "elastic" medium which, in varying states of attenuation or compression, exhibited different chemical and physiological properties - a view developed in the wake of Robert Boyle's and Robert Hooke's ground-breaking experiments with a new air pump after 1658.

Hooke's experiments on charcoal (Micrographia, London 1665, observation no.16) and attempts to burn wood chips in a confined air space had led Hooke to believe that air contained a "nitrous", or combustive, part - from the known explosive agent in gunpowder, salt-petre, or nitre (modern potassium nitrate, formula KNO₃, with its triple Oxygen bond) - along with a more inert or unreactive component. Mayow, who had probably learned his laboratory techniques from Hooke in London, developed these investigations.

The idea of "aerial nitre", or a combustion-enhancing component in the air, derived no doubt from the well-known theories of Michael Sendivogius, the Polish alchemist who, in 1604, argued that thunder and lightning were occasioned by the "nitrous" or explosive part of the atmosphere encountering the "sulphurous", combustive or fiery particles, resulting in flashes and bangs in the air. The familiar sulphur-like smell in the air of what we now know derives from post-lightning Ozone, no doubt gave substantiation to this idea. Consequently, many 17th-century chemical, physical, and mechanical scientists began to devise "nitro-aerial" theories for spontaneous heat- or light-related natural phenomena. Dr Thomas Willis - A Christ Church [College] friend of Wilkins (see Cerebri Anatome essay) - devised an aerial-nitre-related theory of fermentation, an explanation for the spontaeous heat of fever patients, and also for muscle action; all ideas later developed by Mayow in the Tractatus. And while we now know that they were wrong scientifically, they were wrong for the "right reason", in so far as these speculative models were based upon the best experimental and observational evidence of the age, and were not mere flights of fancy.

Of brilliant originality were Mayow's attempts to determine the relative mechanical, or volumetric, parts of the air which supported either combustion or animal respiration: the "nitro-aerial" part. In Tractate no.1, chapter 7, Mayow describes - and illustrates with engravings - his experiments to combust material inside a sealed glass flask over a water trough. He found that once a candle in the apparatus had gone out, he could neither re-light it, nor fire a piece of campher also placed inside the flask, by focussing the sun's rays through a powerful burning glass, although when the flask was full of normal, non-combusted air, the burning glass could easily ignite the contents. After the sealed-in candle had gone out, however, it seemed that some vital component necessary for combustion had been exhausted from the remaining air. From the water that had risen up from the trough to occupy the now exhausted space within the flask, Mayow concluded that this vital "nitro-aerial" part of the air constituted about 1/30th part of the volume. And when a living mouse was sealed up in a similar apparatus, it was found to die after 1/14th of the air volume had been exhausted.

Of course this does not make Mayow (or Hooke) proto-discoverers of oxygen, for neither diplayed any concept of thinking in terms of chemically specific gases, as opposed to what they believed were the changing mechanical volumes caused by pressure differences. What was of monumental significance, however, was the resulting realisation that (a) both combustion and respiration seem to be chemically related to the atmosphere, and (b) not all of the atmosphere is involved in burning and breathing, but only a small, specific, volumetric part of it.

Mayow also conducted research experiments into the formation of what we now call metal oxides (chemical compounds which we, today, know are formed when atmospheric oxygen reacts with a pure metallic element). Mayow concluded that the "nitrous" part of the air was responsible for oxide formation.

Tractate no.5 contains Mayow's studies into the infant bone-deforming disease Rickets. In some ways here, he was guided by, and acknowledged, Dr Francis Glisson, F.R.S. and his treatise De Rachitide (1650) [On Rickets], although Mayow added important clinical observations of his own, so that Glisson and Mayow are generally seen as pioneers in the study of what they - mistakenly - believed to be the "new disease" of rickets.

In addition to being a research chemist of genius, John Mayow was also a meticulous and an original clinician, in his ability to see a diseased part of the body in context with the whole, and note parallel syndromes and features which seemed to accompany the disease. Of course, as happened so many items in previous centuries, a brilliant and perceptive description of a disease syndrome would yield no immediate therapeutic benefit, for not until the 20th century discovery that rickets is occasioned by a vitamin D deficiency in childhood could the disease be prevented or cured - if diagnosed early. Yet without the accumulation of a vast and growing body of accurate scientific descriptions, it would have been impossible for later generations to devise rational, safe, and reliable cures - for rickets and for countless other diseases as well.

Mayow's Tractatus Quinque, therefore, was a major, pioneering piece of original research which cast new light on several branches of experimental chemistry and medicine.

Text kindly provided, especially for this exhibition, by Allan Chapman