THE STORY OF NINETEENTH-CENTURY SCIENCE 



be a simple element, serving a mere mechanical purpose 

 in the economy of the earth. 



But the discovery of oxygen gave the clew, and very 

 soon all the chemists were testing the air that came 

 from the lungs Dr. Priestley, as usual, being in the 

 van. His initial experiments were made in 1777, and 

 from the outset the problem was as good as solved. 

 Other experimenters confirmed his results in all their 

 essentials notably Scheeleand Lavoisier and Spallanzani 

 and Davy. It was clearly established that there is chem- 

 ical action in the contact of the air with the tissue of the 

 lungs ; that some of the oxygen of the air disappears, 

 and that carbonic acid gas is added to the inspired air. 

 It was shown, too, that the blood, having come in con- 

 tact with the air, is changed from black to red in color. 

 These essentials were not in dispute from the first. But 

 as to just what chemical changes caused these results 

 was the subject of controversy. "Whether, for example, 

 oxygen is actually absorbed into the blood, or whether 

 it merely unites with carbon given off from the blood, 

 was long in dispute. 



Each of the main disputants was biassed by his own 

 particular views as to the moot points of chemistry^ 

 Lavoisier, for example, believed oxygen gas to be com- 

 posed of a metal oxygen combined with the alleged ele- 

 ment heat; Dr. Priestley thought it a compound of pos- 

 itive electricity and phlogiston ; and Humphry Davy, 

 when he entered the lists, a little later, supposed it to be 

 a compound of oxygen and light. Such mistaken no- 

 tions naturally complicated matters, and delayed a com- 

 plete understanding of the chemical processes of respi- 

 ration. It was some time, too, before the idea gained 

 acceptance that the most important chemical changes 



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