Sect. II.] Physiology. 291 



was a principle of this theory, that the blood ab- 

 ^sorbs no air in the lungs; but that it di.sciiarges 

 hydrogen and carbon, which, combining with the 

 oxygen of the air inspired, form water and carl)onic 

 acid. This theory was adopted by la Place, Craw- 

 ford, Gren, and Girtanner, with some small modi- 

 fications, which it is unnecessary here to particu- 

 larise. Upon close inspection, it appears that this 

 theory of Lavoisier does not materially dilfer from 

 the original hypothesis of Dr. Priestley, viz. that 

 the object of respiration is to free the blood of 

 phlogiston. The diilerence consists chiefly in terms 

 and in detail. For if carbon and hydrogen be sub- 

 stituted for phlogiston, which is often necessary in 

 reconciling the statement of facts delivered by the 

 phlogistians and antiphlogistians, the two theories 

 will be found entirely to agree. M. Lavoisier did 

 little to establish his theory by proof. He only 

 attempted to prove that the amount of oxygen 

 absorbed in respiration exactly corresponds with 

 the quantity of it contained in the carbonic acid 

 and the w^ater emitted. But as this coincidence of 

 quantities cannot be proved, his theory is unsup- 

 ported, so far as the establishment of it depends 

 upon such coincidence. 



Afterwards, when a greater number of facts and 

 illustrations of this sulject had been collected, a 

 different theory was offered by la Grange. Ac- 

 cording to him, the oxygen which disappears in 

 respiration combines with the blood in its passage 

 through the lungs, and at the moment of this com- 

 bination there is set loose from the blood a quan- 

 tity of carbonic acid gas and water in the form of 

 vapour, which are thrown out with the air es- 



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