518 THE RESPIRATORY EXCHANGE 



dictory nature of the results of different observers so impressed the 

 celebrated physiologist Johannes Miiller that he felt obliged to 

 make experiments himself, before he expressed an opinion upon 

 the question. The results of his experiments were unfortunate, 

 for he, the leading physiologist of his time, confirmed the negative 

 results of other observers. He found that amphibia could produce 

 carbon dioxide in an atmosphere free from oxygen ; blood shaken 

 up with air would yield carbon dioxide, but venous blood itself 

 contained no carbon dioxide. So great were the difficulties to 

 explain, that Miiller considered that no satisfactory theory of 

 respiration could be advanced ; the carbon dioxide might be 

 secreted from the lungs and skin, but the puzzle remained, and 

 was only to be solved by further experiments. Such was the 

 position when the second edition of Miiller's Handbuch der 

 Physiologic was published in 1835. Two years later Magnus 

 showed that, with improved methods for the extraction of gas, 

 carbon dioxide, oxygen, and nitrogen could be obtained from 

 blood. j- -5j 



The perfection of the gas-pump was necessary, and great 

 advances were made when Ludwig and Setschenow, Pfliiger, and 

 Helmholtz constructed their mercurial gas-pumps, based upon the 

 principle of the Torricellian vacuum. Such gas-pumps, or modi- 

 fications of the same, are now used for the extraction of the gases 

 of the blood ; their construction and use will not be described 

 here, only the principles involved need be mentioned. The libera- 

 tion of the gases present in the blood in a state of simple solution 

 and the dissociation of those which are in loose chemical combina- 

 tion can be best effected by exposure to a vacuum, by warming 

 and shaking the blood ; the liberation of the carbon dioxide can 

 be facilitated by the addition of a weak acid. Three other methods 

 require mention here, for the reactions involved will be shown 

 later to be of great importance in connection with the nature of 

 the combinations in which the gases exist in the blood. Fernet 

 found that the gases in blood can be extracted by the passage of 

 a stream of hydrogen and the aid of a vacuum ; Claude Bernard 

 discovered that, when blood is shaken with double its volume of 

 carbon monoxide, the oxygen is driven out from its combination 

 with haemoglobin, owing to the stronger affinity and the mass 

 influence of the carbon monoxide ; and Haldane ( 1( ) has introduced 

 the ferricyanide method, whereby a rapid and accurate deter- 



