THEORIES OF RESPIRATION In the history of physiological discovery the growth of knowledge as to the physiology of breathing was comparatively late. Before the middle of the Seventeenth Century hardly anything was known about breathing except its muscular mechanism and the facts that if the breathing of a man or higher animal is interrupted for more than a very short time death ensues, and that the breathing is increased by exertion and by some diseases. The discovery by Harvey of the circulation threw no positive light on the physiology of breathing, and it was still generally believed that the main function of respiration is to cool the blood. Robert BOYLE (1627-1692), prime mover in the founding of the Royal Society of London, published his The Spring and Weight of the Air in 1660, with a record of experiments he had carried out with a vacuum pump. He proved that the air had weight, and that the film of this gas normally surrounding the earth would support a column of 29 in. of mercury. In the same work he tells of many interesting experiments on animals in which he had found that if a candle were inserted along with a mouse in his exhaustion chamber, the mouse died and the candle went out almost simultaneously as the air was gradually withdrawn. BOYLE also was the first to study blood gases. His The Skeptical Chymist (1661) is a landmark in chemistry. Robert HOOKE (1635-1703), Boyle's assistant, showed that an animal could be kept alive by artificial respiration, and put forth the first ra­ tional theory of combustion. Joseph PRIESTLEY (1733-1804) Joseph PRIESTLEY, dissenting theologian and man of science, was born in 1733 in a small village in Yorkshire, lived in Birmingham, Leeds, Liverpool, and London, emigrated to New York in 1794, and died in Pennsylvania in 1804 ( he was a friend of George Washington and Thomas Jefferson). An acquaintance with Benjamin Franklin in 1766 turned Priestley's attention to the study of electricity, and he published his History of Electricity in 1767. PRIESTLEY's chemical experiments are mostly contained.in his Experiments and Observations on Different Kinds of Air (3 vols, 1774-7 ). He says that although the elementary nature of air was a philosophical maxim, he was in the course of his experiments "soon satisfied that atmospherical air is not an unalterable thing". On August 1, 1774, he obtained oxygen by heating red oxide of mercury, showing that the result­ ing gas supported the combustion of a candle in a dazzling manner. PRIESTLEY reasoned that the new gas must contain little or no phlogiston, and hence he called it ''dephlogisticated air". In 1775 PRIESTLEY found that a mouse lived twice as long in the new air as in the same confined volume of common air, and revived after­ wards when taken out. He breathed it himself, and fancied that his "breast felt peculiarly light and easy for some time afterwards 11 - hence he recommended its use in medicine. "Who can tell but that, in time, this pure air may become a fashionable article in luxury. Hitherto only two mice and myself have had the privilege of breathing it. 11 He says, however, that "the air which Nature has provided for us is as good as we deserve. 11 Carl Wilhelm SCHEELE, a Swedish apothecary, discovered oxygen in the same year as PRIESTLEY; his paper was not published until 1777. Sources: F. W. Gibbs, Joseph Priestley (1965) J. R. Partington, Short History of Chemistry (1960) W.R. Ackroyd, Three Philosophers- Lavoisier, Priestley, and Cavendish (1935) Antoine LAVOISIER (1743-1 794) Antoine Laurent LAVOISIER was born in Paris in 1743, the son of a wealthy lawyer. He was educated at the Coll~ge Mazarin, where he studied astronomy, botany, geology, and chemistry. He became a member of the prestigious Academy of Science in 1768, at the age of I r 25. A few weeks later he became a member of the Ferme Generale which collected taxes for the Crown under contract, and spent the rest of his life alternating between the laboratory and the counting house. For the Academy, LAVOISIER investigated the principles of street lighting, improving the water supply of Paris, conducting surveys for prison reform. On commission from Louis XVI, he headed a committee to investigate the claims of Franz MESMER. He was a member of the commission for the establishment of the metric system, and in 1 791 served as Secretary of the Treasury. Along with other members of his tax-collecting company, he was imprisoned in November 1793, and guillotined on May 8, 1794, just eleven .weeks before the end of the Reign of Terror. LAVOISIER was essentially a theorist; he completed the work of BLACK, CAVENDISH, and PRIESTLEY, and gave a correct explanation of their experiments; all of his work was characterized by its systematically quantitative methods. He proved that air consists of oxygen (so named by him in 1778) and "azote" (nitrogen). He overthrew the phlogiston theory of the process of combustion. With LAPLACE, he found that during muscular work oxygen is consumed in increasing amounts, and that carbon dioxide output, though raised, is not elevated proportionally. (LAVOISIER also held that the process of combustion took place in the lungs.) He defined a chemical element as "the last point which analysis is capable of reaching", and drew up a new list of chemi:cal nomenclature, which he adopted in his Traite' elementaire de Chemie (1789), the first textbook of chemistry intelligible to a modern reader unacquainted with the history of chemistry. Epilogue: SPALLANZANI in 1803 suggested that oxygen was absorbed through the lungs into the blood and carried by the circulation to nourish the various tissues of the body. MAGNUS carried out the first quantitative analysis of the blood gases (1837), and elucidated the principles of tissue respiration. In 1862 HOPPE-SEYLER attributed the oxygen-carrying function to the pigment hemoglobin. Sources: J.B.S. Haldane, Respiration(l922) J. F. Fulton, Physiology (Clio Medica, 1931) J. R. Partington, Short History of Chemistry (1960) W.R. Ackroyd, Three Philosophers Lavoisier, Priestley, and Cavendish (1935) Joseph BLACK (1 728-1 799) succeeded Wm. Cullen as professor of anatomy and lecturer in chemistry at the University of Edinburgh in 1756. In the same year he published his Experiments upon Magnesia alba, Quicklime, and some other Alcaline Substances. BLACK showed that when magnesia alba (basic carbonate) is heated a gas is evolved, which he called "fixed air" (carbon dioxide). He showed that fixed air is also present in expired air (making lime-water go turbid by bubbling expired air though it). He identified fixed ail- as being the same as the "wild gas 11 produced during fermentation, the same as the volatile in­ gredient of acidulous spring waters, the same as produced in the combustion of charcoal. Henry CAVENDISH (1731-1810), wealth)/ , gifted, eccentric, and psychotic, published his first chemical paper On Factitious Airs in 1766. "By factitious air, I mean in general any kind of air which is contained in other bodies in an unelastic state, and is produced from thence by art. 11 He exper­ imented with Black's fixed air; he discovered that "inflammable air" (hydrogen) was released by the action of dilute acids on metals, which he explained by saying that the "phlogiston of the metals flies off, without having its nature changed by the acid, and forms the inflammable air". He found that the inflammable air was eleven times lighter than common air. He also found that by firing a mixture of inflammable air in dephlogisticated air, he could form water. John MAYOW (1645-1679), working at 8xford, was the first to suggest that it is only a special fraction of the air that is of use in respiration. He concluded that a "nitro-aerial spirit" is present in limited proportion in air, and is absorbed from the air in the lungs by the blood, whence it is carried to the brain, and thence down the nerves to the muscles, where it unites with "sulphur" and produces muscular contraction. George Ernest STAHL (1660-1734) and his doctrine of " phlogiston" set back the clock. Phlogiston, he said, "is the matter and principle of fire, not fire itself." Phlogiston was material, sometimes the matter of fire, sometimes a dry earthy substance, sometimes a fatty principle, and sometimes invisible particles emitted by a burning candle. STAHL inverted the true theory of combustion; adding phlogiston was really removing oxygen, and removing phlogiston was adding oxygen. Thus phlogistication was almost equivalent to reduction, and dephlogistication to oxidation. - Adapted from J. B.S. Haldane, Respiration (1922) J. F. Fulton, Physiol~ I Clio Medica, 1931) J.R. Partington, Short History of Chemist!:_Y_ (1960) .