xi RESPIRATORY EXCHANGES 377 



oxygen and the carbonic acid. The blood gases were first extracted 

 with the vacuum pump by Boyle and Mayow ; Humphry Davy 

 (1803) was the first to extract them by the method of warming, 

 and to recognise that arterial blood contains little carbonic acid 

 and much oxygen. 



Priestley (1776), Fontana (1804), Nasse (1816), Brande (1818), 

 Vauquelin (1820) and others were able either by the method of 

 simple diffusion, by bringing the blood into contact with indifferent 

 gases such as hydrogen and nitrogen, or by agitating the blood with 

 the said gases .or passing them through it, to determine the fact that 

 it holds both oxygen and carbonic ? 4 cid in solution. These results, 

 obtained with somewhat loose methods, were, however, contested 

 by other distinguished physiologists, so that John Davy, Johannes 

 Miiller, Gmelin, Tiedemann and others agreed in denying the 

 presence of free gases in the blood, while Yogel, Nasse, Scudamore, 

 Th. Bischof, Collard de Martigny, and van Enschut maintained 

 that carbonic acid was not found in the blood in a state of 

 solution. 



It was Magnus (1837), Professor of Physics at Berlin, who put 

 an end to this uncertainty, and performed his experiments on the 

 gases of the blood with the scientific method that was indispensable 

 to make his results convincing. He extracted the gases of the 

 blood by means of the Torricellian vacuum, with an ingenious 

 apparatus which as it were combined the mercury pump and the 

 pneumatic machine. As the result of his analysis, he stated that 

 both arterial and venous blood contain not only carbonic acid, but 

 oxygen and nitrogen as well, and that carbonic acid preponderates 

 in venous, oxygen in arterial blood. He was the first who attempted 

 to account for the mechanism of the pulmonary gas exchanges, 

 considered as an effect of simple diffusion, according to the physical 

 law formulated by J. Dalton in 1805. 



In 1857, however, Lothar Meyer demonstrated that the amount 

 of oxygen liberated from the blood does not increase proportionally 

 with the lowering of pressure, as it should according to Dalton's 

 law, and that it is only when the pressure acting on the blood is 

 reduced to -fa that the oxygen of the blood begins to dissociate. 

 On combining the vacuum method of extracting the blood gases 

 with the method of heating to 40 0. blood that had been 

 extracted and diluted with a quantity of water previously boiled 

 and deprived of its gases, he completed and partially rectified the 

 conclusions of Magnus. 



While approximately true, Meyer's data were not yet entirely 

 accurate, as was shown by the succeeding work of Hoppe-Seyler 

 (1854), Ludwig (1858), and Pfliiger (1865). They introduced in- 

 teresting improvements in technique, with the object of obtaining 

 the maximal quantity of gases that can be extracted from a given 

 quantity of arterial, venous, or asphyxial blood. In order, as 



