HISTORICAL ACCOUNT. 693 
he strangled a pullet until it showed no signs of life, and then restored it by 
blowing air into its lungs. 
Boyle, 1 in 1666, showed by numerous experiments with the air-pump that 
a supply of fresh air was essential to life, both animal and vegetable, and he 
was of the opinion "that the depuration of the blood was one of the ordinary 
and principal uses of respiration." 
Mayow - (1668-1674) was the first to discover the real function of respira- 
tion ; he showed that air was a mixture, and that one of its constituents, which 
he named the nitro-aerial gas, was necessary for the support of a flame, that it 
combined with sulphur and other substances with the production of acids, 
that during calcination metals also combined with it and thus increased in 
weight. The nitro-aerial gas (oxygen) was necessary for all forms of life, and 
the respiration of an embryo was analogous to that of the adult. Mayow saw 
the analogy of respiration to combustion, and held that the function of respira- 
tion was to absorb the nitro-aerial gas and to remove the vapours arising from 
the blood. 
Stephen Hales, 3 about the year 1726, showed that animals in a closed 
vessel absorb air, and that a similar change is effected by a burning candle. 
He also observed, by experiments upon himself, that air is absorbed during 
respiration, and that " noxious vapours " are produced by repeatedly breathing 
air in a bladder ; these noxious substances, he found, could be removed by 
potash, and the air rendered fit for breathing. Hales suggested the use of a 
bladder of air and such an absorbent in the foul air of coal mines. He believed 
that during respiration the air cooled the blood and removed aqueous vaponr 
and noxious substances, but he rejected the view of Mayow that the blood 
combined with the nitro-aerial gas. 
About the year 1757, Black 4 discovered that a quantity of "fixed air" 
(carbon dioxide) was given off from the lungs, and that the expired air chiefly 
differed from the inspired by the addition of that gas. He observed that 
animals placed in carbon dioxide gas died of suffocation. 
In 1772, Priestley 5 published his " Observations on Different Kinds of Air," 
in which he showed that growing plants restored the property of supporting 
animal life to air which had been vitiated by the respiration of animals or by 
the burning of a candle. He also found that carbon dioxide was produced by 
putrefaction and by plants during the night-time. Priestley isolated oxygen 
and nitrogen, and showed that the change of colour in venous blood on 
exposure to the air was due to the action of oxygen, and that blood changed 
colour and gave off "phlogiston" even when it was separated from the air by 
a moist membrane and by the walls of the blood vessels in the lungs. He 
concluded that respiration deprived the air of a portion of its oxygen and 
imparted to it a quantity of aqueous vapour and " phlogiston." 
Lavoisier 6 (1777) extended and explained the discoveries of Mayow, Black, 
and Priestley; he overthrew the old theory of "phlogiston," and pointed out a 
distinction between the various so-called phlogistic processes. The calcination 
of metals he showed, as Mayow had observed a hundred years before, to be a 
combination with oxygen, whereby the metals gained in weight ; in respira- 
tion, on the other hand, oxygen was not only absorbed, but combined with 
carbon to form carbon dioxide. 
Lavoisier and Laplace showed experimentally that animal heat arose from 
a process of combustion, oxygen combining, as they thought, with carbon in 
the blood ; as regards the seat of this combustion, Lavoisier held that it was 
1 Phil. Trans., London, 1666, p. 424 ; 1670, pp. 2011, 2035. 
2 Ibid., 1668, p. 833 ; "Tractatus quincpie," Oxon. 1674. 
3 "Statical Essays," 2nd edition, 1731, vol. i. p. 236 et seq. 
4 "Lectures on Chemistry," ed. Robison, Edinburgh, 1803. 
5 Phil. Trans., London, 1772, vol. lxii., p. 147. 
6 Hist. Acad. roy. d. sc, Paris, 1775, 1777, 17S0, 1789, and 1790. 
