mentally in the following year by Lower (De Corde, 1669). The blood carries the nitroaerian constituent to the muscles, and their motion results from the chemical reaction (fermentation) in the muscle with the combustible matter contained therein. The heart, like any other muscle, ceases to act when the nitroaerian particles are no longer supplied to it.
In the ‘Tractatus quinque’ the subject of the earlier work is developed and treated from a higher point of view, and carefully tested in many details. The chemistry of burning is studied separately before being applied to physiology. The treatise ‘On Saltpetre and the Nitroaerian Spirit’ develops a theory of combustion on lines closely resembling those followed by Lavoisier in the next century. Saltpetre is recognised as containing a base and an acid, and the acid part is formed from one of the constituents of the air, its nitroaerian particles, the air being composed of these and of another gas, left after combustion and respiration. To produce combustion sulphureous, i.e. inflammable, matter must come into contact with the nitroaerian particles. When antimony is calcined its increase in weight is due to the fixation of these particles; the rusting of metals and the conversion of iron pyrites into a vitriol are due to the same cause. It is too much to say, as some have done, that Mayow proves his case fully. The best evidence of his mental calibre is that he himself distinguishes everywhere between his facts and the hypothesis which he seeks to establish. But the logical consequences of his hypothesis he developes with the greatest acuteness. He is, it is true, misled by the desire to explain everything mechanically (which has dominated physical science since Descartes) into long and useless speculations with regard to the elasticity of the air and of solid bodies, the nature of light and of the sun, &c. But whenever he sees a way of submitting his ideas to the test of experiment, he does so. He proves that a candle burning and a mouse breathing in a closed space act in precisely the same way on the air contained, and diminish its volume and alter its properties. The failure to grasp the notion of compound gases is his true stumbling-block. Yet he recognises the fact that different gases (e.g. air and nitric oxide) exist, and carefully shows that they all follow Boyle's law.
The older tract, ‘De Respiratione,’ revised, follows ‘De Sal-Nitro,’ and Mayow next extends his explanation of respiration to the fœtus and the egg. The maternal blood supplies the fœtus not only with nutrition, but with oxygen. The egg, he thinks, contains sufficient air for itself, and probably this air is itself ‘pure or vital air,’ and not ordinary air. Moreover, as the egg is kept warm and the chick does little work, it needs little respiration. In the tract on ‘Muscular Motion and Animal Spirits’ he comes to the conclusion that the nitroaerian particles must be identified with the animal spirits of his contemporaries, and that they are separated from the blood in the brain, and thence travel along the nerves to the muscles, where they combine with the combustible matter and cause the muscle to contract by the vehement motion set up in the fibres; an important modification of Descartes's theory. The animal spirits, he declared, must not be confounded with the universal sensitive soul. In the course of the five treatises the most various points are touched on, including the theory of the relation of the saltpetre in the soil with plants (De Sal-Nitro, p. 52); the remarkably lucid theory of chemical affinity (idem, p. 242); and the mechanical explanation of the act of jumping (De Motu Musculari, p. 100).
Mayow stands immeasurably above such men as Willis and Sylvius, with their medley of half-digested Cartesianism and iatrochemistry. He must be classed with Hooke and Boyle, possessing the scientific imagination of the one, the tenacity of the other, and succeeding where Boyle failed. He had the genius to perceive exactly the problems which must be solved before any great advance in chemistry or physiology could be made, to guess at and partly to discover their solutions; and he showed a critical faculty in theory and experiment that is not to be met with in these two sciences until we come to Lavoisier. His premature death retarded the advent of modern chemistry for more than a century (Hoffer, Hist. de la Chimie, ii. 262).
By his chief contemporaries, save possibly Lower, Mayow's work met with little understanding; several, like Pechlin, borrow his language, but neither grasp his ideas nor even mention his name. The anatomical discovery with regard to the ribs was alone definitely adopted by the text-books (S. Collins, Systeme of Anatomy, 1685, pp 826, 833, 837). It is noteworthy that Stephen Hales [q. v.] repeated some of Mayow's experiments on combustion (Vegetable Staticks, 1727, i. 230 et seq.). As soon as Priestley had discovered oxygen, Mayow's works were disinterred. Blumenbach gives them high praise (Institutiones Physiologicæ, 1786, p. 114), and he was followed by Yeats, Beddoes, Fourcroy, J. A. Scherer, and A. N. Scherer, who are as a rule more enthusiastic than critical. The
