420 



NA TURE 



[August 29, 1901 



burned it increases considerably in weight. "'Now we 

 can hardly conceive that the increase of weight of the 

 antimonium arises from anything else than from the igneo- 

 aereal particles inserted into it during the calcination.' " 



Mayow fully identified burning and breathing. He 

 found that either a lighted candle or an animal in an 

 enclosed space e,\hausts a certain proportion of the 

 air. "'We may infer,'" he says, "'that animals and 

 fire deprive the air of particles of the same kind.' " " ' It is 

 clear,' " he adds elsewhere, " ' that even the very plants 

 seem to have some need of breathing, some need of 

 drawing air into themselves.'" "In his tract, 'On 

 Respiration,' he gives an e.xposition of the mechanics of 

 breathing which might almost find its place in a text- 

 book of the present day." He further supposed that the 

 heat of the body is kept up by union of tiny nitro- 

 aereal particles with salino-sulphureous [i.e. combustible) 

 particles of the blood — a " sound theory," says Foster, 

 " of animal heat," although now superseded, as will be 

 subsequently seen, by one which places the union in the 

 tissues themselves. 



But the " great truth '' which had been reached by the 

 labours of these English physicists and physiologists died 

 out with Mayow. 



" The world had to wait for more than a hundred 

 years till Mayow's thought arose again, as it were, 

 from the grave in a new dress, and with a new 

 name ; and that which in the first years of the latter half 

 of the seventeenth century as igneo-aereal particles shone 

 out in a tiash and then died away again in darkness, in 

 the last years of the eighteenth century, as o,\ygen, lit a 

 light which has burned, and which has lighted the vi-orld 

 with increasing steadiness up to the present day." 



The rise of the modern doctrines of combustion and 

 respiration, the work of Black, Priestley and Lavoisier, 

 is dealt with in the ninth lecture of the series, the eighth 

 being devoted to the researches of Reaumur, Spallanzani, 

 Stevens and John Hunter on gastric digestion. Although 

 van Helmont had shown the stomach to be a great 

 digestive organ and the acid character of its secretion 

 its essential feature, subsequent authorities had ignored 

 or denied its agency in digestion. It was regarded as 

 having mainly a mechanical function. But Reaumur, who 

 was eminent in other sciences besides physiology, 

 showed clearly, by causing a kite to swallow small metal 

 tubes closed at each end by a grating and filled with 

 food, that without any trituration and with no semblance 

 of putrefaction both meat and bone became dissolved 

 whereas vegetable grains were little altered. He even 

 obtained gastric juice from pieces of sponge included in 

 the tubes, and found it to be acid. Spallanzani, who was 

 born in 1729 and the centenary of whose death was cele- 

 brated two years ago, was successively professor of logic 

 at Reggio and of natural history at Modena and at Pavia. 

 He wrote on many subjects of natural history, but in 

 physiology chiefly upon respiration and digestion — 

 experimenting by Reaumur's methods upon all kinds of 

 animals and even upon himself He obtained gastric 

 juice as Reaumur had done, but was successful in show- 

 ing its activity in Tztro, in which Reaumur had not 

 succeeded ; he failed, however, to detect its acid character. 

 Similar experiments to those of Spallanzani were made 

 independently by Stevens, of Edinburgh, who announced 

 NO. 1 66 I, VOL. 64] 



his results in an inaugural thesis in 1777, the same year 

 as the publication of Spallanzani's first paper on the 

 subject. Stevens also obtained " pure gastric fluid " from 

 the stomach of a dog killed during fasting, and found 

 that at the body temperature it readily dissolved meat, 

 and he made besides numerous e.xperiments by Reaumur's 

 method on digestion in vivo. John Hunter, in 1772, 

 " constantly found that there was an acid, though not a 

 strong one," in the gastric juice, but later on he is led to 

 regard this as not essential. The acidity which van 

 Helmont had insisted upon at the beginning of the 

 seventeenth century was not accepted until the 

 nineteenth. 



Stephen Hales (1677-1761) was a Fellow of Corpus 

 Christ! College, Cambridge, and became perpetual curate 

 of Teddington in Middlesex. " He was devoted to 

 science ; he had begun to experiment while at Cam- 

 bridge in the ' elaboratory ' of Trinity College," where 

 Bentley was then master; "and he continued his 

 researches amid his parish duties at Teddington." 

 He was the first to determine by experiment upon the 

 living animal (horse) the pressure of the blood in the 

 arteries, and he dealt also with the flow of sap in plants. 

 " His writings contain the first clear enunciation of the 

 existence of gases in a free and in a combined condition." 



It is the merit of Joseph Black (1728-1799), who was 

 professor of chemistry successively in Glasgow and Editi- 

 burgh, to have rediscovered the " gas " of van Helmont : 

 to this he gave the name of " fixed air.'' He proved that 

 it is given off in combustion, in fermentation and in 

 respiration ; that it is irrespirable ; and he at first thought 

 that it formed the irrespirable portion of the atmosphere. 

 But Rutherford, of Edinburgh, in his inaugural thesis in 

 1772, showed that after the "fixed air" (caused by com- 

 bustion) had been removed by caustic alkali, " a very large 

 proportion of air remains which extinguishes life and 

 flame in an instant." This was nothing else than the 

 discovery of nitrogen, although its connection with nitre 

 was first shown later by Cavendish. 



Just as Black rediscovered the gas sylvesfre of van 

 Helmont, so Priestley (1733-1804) and Lavoisier (1743- 

 1794) rediscovered the gas which Mayow had termed the 

 igneo-aereal spirit and which was ultimately named by 

 Lavoisier oxygen. Priestley was a Unitarian minister — 

 "a man of letters as well as man of science, prolific theo- 

 logian and ardent politician." He was the first to discover 

 that the something in the air which is removed by the 

 burning of a candle or by the respiration of an animal 

 is restored by vegetation. He obtained from mercuric 

 oxide {inercurius calcinatus per se), by heating it with a 

 burning glass, a quantity of "air." "' Having got about 

 three or four times as much as the bulk of my materials, 

 I admitted water to it, and found that it was not imbibed 

 by it. But what surprised me more than I can well 

 express was that a candle burned in this air with a 

 remarkably vigorous flame . . . and a piece of red-hot 

 wood sparkled in it.' " 



" He obtained the same gas from red precipitate 

 and from minium ; he found that a mouse lived well in it 



. . that it was four or five times as good as common 

 air." 



Imbued with the phlogistic theory, he regarded it as 

 common air which was freed from phlogiston, " dephlo- 



