ix] Doctrines of Respiration. 245 



air. The metal when it was burnt into the oxide did not 

 give up phlogiston to the air, it took something from the air. 

 The metallic oxide in becoming metal, instead of gaining lost 

 in weight. The metal in becoming metallic oxide, instead of 

 losing gained in weight. Objections to the phlogiston theory 

 based on questions of weight had been urged before, but the 

 theory had swept them away. Now they were put in such a 

 way that they swept away the theory. Smitten with these 

 experiments the scientific Dagon, the image before which men 

 had bowed their knees for a hundred years, fell crumbling to 

 the ground. 



Men will tell you tales of how Priestley on a visit to Paris 

 in the late autumn or winter of 1774, chatted freely to his 

 scientific brethren about the experiment which he had just made 

 with his mercuric oxide and his burning-glass; and they will 

 assert that Lavoisier was thus led to his pregnant result. 

 Whether this be true or no does not seem to me to be of vital 

 importance ; whether Lavoisier got at his result wholly of 

 himself or no, he and he alone, not Priestley in any way, got at 

 the true meaning of the result. He and he alone really 

 discovered oxygen. 



Two years later, in 1777, the year of Haller's death, in a 

 paper entitled 'General Considerations concerning the Nature of 

 Acids and on the Principles of which they are composed/ he 

 brought forward abundant proofs that the principle which 

 combines with metals when they are calcined, the dephlogisti- 

 cated air of Priestley, is the constitutive principle of acidity. 



"I shall therefore designate dephlogisticated air, air emi- 

 " nently respirable, when in a state of combination or fixedness 

 " by the name of ' acidifying principle,' or, if one prefers the same 

 <l meaning in a Greek dress, by that of ' oxygine ' principle." 



In the same year 1777. he attacked the problem of animal 

 respiration in a paper, " Experiments on the Respiration of 

 " Animals and on the Changes which the Air undergoes in 

 "passing through the lungs." 



Upon the discovery of oxygen and of the true nature of 

 oxidation Priestley's image of the respiratory process forthwith 

 inverted itself. It was seen at once that respiration was 

 oxidation, that air which had been respired resembled air in 



