376 PHYSIOLOGY CHAP. 



collection of experimental facts, showing how much of the progress 

 of our science is due to this illustrious physiologist. Undeniably, 

 however, it lacks that concise method and critical elaboration 

 which it would have received had the author been able to complete 

 his own work. 



The subsequent researches of William Edwards (born in 

 Jamaica, 1776; died Versailles, 1842) were on the lines of 

 Spallanzani's most important experiments. On bringing frogs, 

 whose lungs had been emptied by compression of the flanks, under 

 a bell-jar of hydrogen immersed in mercury, Edwards observed 

 that the .animal in the space of a few hours developed an amount 

 of carbonic acid almost equal to the volume of its body. Similar 

 results were obtained from experiments on fish, which breathe 

 through their gills. In order to prove that the same fact holds 

 for mammals, which die as soon as they are deprived of oxygen, he 

 took newborn animals, which have a longer resistance to asphyxia, 

 and showed that when immersed in an atmosphere of hydrogen, 

 they continue to exhale carbonic acid. These facts are only the 

 confirmation and generalisation of those enunciated twenty- five 

 years earlier by Spallanzani ; but Edwards deduced from them 

 more clearly and explicitly the erroneous nature of Lavoisier's 

 theory of pulmonary combustion, and the proof of Lagrange's 

 theory of pulmonary gas exchanges. Carbonic acid (as he 

 approximately concluded) is exhaled from the body independent of 

 the entrance of oxygen into the lungs and its absorption by the 

 blood. It is probably derived from the tissues, and may be 

 already formed and dissolved in the venous blood, from which it is 

 exhaled on circulating through the pulmonary vessels. 



Collard de Martigny (1830), Johannes Miiller (1835), Bischoff 

 (1837), Marchand (1844), with improved and varied methods of 

 experiment, obtained the same results as Spallanzani and 

 Edwards. 



IV. The theory of external respiration as a gaseous exchange 

 between the air contained in the pulmonary alveoli and the blood 

 gases circulating in the pulmonary capillaries, and the theory of 

 internal respiration in the sense of a gaseous exchange between 

 the blood gases circulating in the aortic capillaries and those 

 produced by the living elements of all the tissues, received a solid 

 experimental basis from the researches on the quality and quantity 

 of the gases contained in the blood, and the inter-comparison of 

 the gases extracted from arterial and those extracted from venous 

 or asphyxial blood. 



When in 1824 Edwards published his essay, The Influence of 

 Physical Agents on Life, in which the theory of the respiratory 

 gas exchanges was clearly formulated, some scanty data existed in 

 support of the hypothesis that the blood was the vehicle of these 

 exchanges, and held in solution or loose combination both the 



